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LOBSTER Annual progress report (3rd year) Reporting Period: 01/01/2002 –30/04/2003

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INFORMATION SOCIETY TECHNOLOGIES (IST) PROGRAMME

Shared-cost RTD LOBSTER

Annual Progress Report (3rd year) Reporting period: 01/01/2002 - 30/04/2003

Project acronym: LOBSTER Project number: IST-1999-13322 Project full title: Large Optical Bandwidth by Amplifier Systems Based on

Tellurite Fibres Doped with Rare Earths Contract Start: 01/01/2000 Contract Termination: 30/04/2003 CEC Deliverable Number: IST-1999-13322/LOBSTER_D19 Contractual Date of Delivery to the CEC: 30/04/03 Actual Date of Delivery to the CEC: 25/07/03 Title of Deliverable: Annual progress report (3rd year) Reporting Period: 01/01/2002 –30/04/2003 Deliverable Type: (P/R/L/I)* P Workpackage contributing to the Deliverable: All Nature of the Deliverable: (P/R/S/T/O)** R Abstract: The Annual Progress Report provides a comprehensive account of the progress made on the project during the 3rd year and gives information about technical progress, specific results and resources employed.

Partner Code

Partner Name Short Name

P01 Telecom Italia Lab TILab P02 Optoelectronics Research Center (Southampton University) ORC P03 Otto Schott Institut (Jena University) OSI P04 Consorzio Nazionale Interuniversitario per le Telecomunicazioni CNIT P05 Turin Technology Centre (Agilent Technologies Italia) TTC


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Annual Progress Report (3rd year) Reporting period: 01/01/2002 - 30/04/2003 LOBSTER (IST-1999-13322): Large Optical Bandwidth by amplifier Systems based on Tellurite fibres doped with Rare earths Key Action : KA IV Action line : 1.1.2.-4.8.4 ABSTRACT The Annual Progress Report provides a comprehensive account of the progress made on the project during the 3rd year and gives information about technical progress, specific results and resources employed


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Contents Part 1 Project overview

Introduction 1.1) Executive summary, structure of report 5 1.2) Objectives, overall 5 1.3) Objectives, 3rd year 5 1.4) Project structure 6 1.5) Partners and consortium 7

Part 2 Project achievements in current audited period (01/01/2002 - 30/04/2003)

Description of the achievements 2.1) Work progress 2.1.1) WP1, Project Management 8 2.1.2) WP2, Specification and validation 9 2.1.3) WP3, Erbium doped fibre amplifier 15 2.1.4) WP4, Thulium doped fibre amplifier 21 2.1.5) WP5, Amplifier design and modelling 34 2.2) Cost Breakdown 2.2.1) Deliverables, plan/actual/status 41

2.3) Deliverable abstracts 42

2.4) Publications and patents 45


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PART 1: PROJECT OVERVIEW 1. Introduction 1.1) Executive summary, structure of report

This document (Annual Report 3rd year, D19) reports on the results of the work realised by the LOBSTER consortium in the third year of the project. Due to the project extension for 4 months, the referring period starts from the 1st of January 2002 and lasts to the 30th of April 2003.

It contains the description of the work performed on the glass materials, on the fiber fabrication and optimisation, on the Er-doped and the Tm-doped fiber amplifiers modelling and assembly.

System characterisation of the ultra-large amplifier –i.e. the features of the two devices seen from an “engineered” point of view-, are described in the Deliverable 18 and in the Final report (Deliverable 20).

The description of the work performed in the project during the third year is organised by Work-packages, and the achievements are reported according to this structure. 1.2) Objectives, overall

The main objective was to realise wideband optical fibre amplifiers for future DWDM networks, spanning approximately the 1.45-1.62 micron spectral range, and to demonstrate and evaluate their application in a high capacity photonic network. Hence, by starting from raw materials purified, various glass fabrication methods aiming at thermally stable and flawless preforms and special drawing techniques aiming at easy fiberization of low melting tellurite glass has been carried out.

Splicing methods between fibres of different glass types (tellurite and silica) have been investigated and their reliability addressed.

Different amplifier architectures (hybrid, single or double stage, etc.) and pumping configurations using single-mode tellurite fibres doped with selected Rare Earths have been designed consistent with an amplifier model program and the amplifiers assembled.

Amplifier performances have been validated in a WDM test-bed addressing transmission issues and the full compatibility with existing optical networking functions. 1.3) Objectives : third year

Whilst the main objective of the first year of the project was the selection of suitable glass compositions -from several points of view: e.g. thermal, mechanical, rheological and spectroscopic-, and that of the second dealt with the fibre fabrication –concentrating on the geometrical and optical properties-, during the third year the LOBSTER consortium worked hard on the amplifiers modelling, fabrication and their full characterisation.

Apart from the effort on the main topics, the feed-back coming from the amplifiers activity gave us suggestions of improvement on glass synthesis and mostly for the fabrication of new fibres, that could better cope with the specs of the project.


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1.4) Project structure Workplan and overall Methodology

*The names ofr CSELT and OTC have been changed to TILAB and TTC, respectively Workpackages and workpackage activities

Workpackage Workpackage activity

WP1 Project management 1.1 Internal technical project management 1.2 Internal financial project management 1.3 Assessment and evaluation 1.4 Dissemination and implementation

WP2 Specifications and validation 2.1 Specifications and design study 2.2 Test-bed arrangement 2.3 Validation tests

WP3 EDTF amplifier 3.1 Core/clad glass formulations and preform realisation 3.2 Spectroscopy 3.3 Fibre drawing and characterisation 3.4 Amplifier assembly and device performance

WP4 TDTF amplifier 4.1 Core/clad glass formulations and preform realisation 4.2 Spectroscopy 4.3 Fibre drawing and characterisation 4.4 Amplifier assembly and device performance

WP5 Amplifier design and modelling


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Interrelationship of Workpackages The following diagram represents the workpackages organisation in relation to

overall workplan. For the seek of clarity, WP 1, which is non-technical and whose function consists in the co-ordination and evaluation of the WPs 2-5, was omitted in Figure 1.2.

Glass formulations, characterisation and preform fabrication

EDTF(Er-doped Tellurite Fibre )

TDTF(Tm-doped Tellurite Fibre )

EDTF AmplifierFabrication and Modelling

TDTF AmplifierFabrication and Modelling

Large optical bandwidthby amplifiers combined

Test-bed trials

WP4: TDTF Amplifier4.1 Core/clad glass formulations and preform realisation4.2 Spectroscopy4.3 Fibre drawing and characterisation4.4 Amplifier assembly and device performance

WP3: EDTF Amplifier3.1 Core/clad glass formulations and preform realisation3.2 Spectroscopy3.3 Fibre drawing and characterisation3.4 Amplifier assembly and device performance

WP2: Specifications and validation

2.1 Specifications and design study2.2 Test-bed arrangement2.3 Validation tests

WP5: Amplifier design and modelling

4.1

4.3

4.4

3.2

3.3

3.4

2.2

2.12.3

4.23.1

1st y

2nd y

3rd y

Fig. 1.2. Interrelationship of WPs

1.5) Partners and Consortium

The consortium is composed of 5 partners: the research centre of the main Italian telecommunication operator group, an Italian optical components manufacturer, part of an important international company, and three research institutes from universities of UK, Italy and Germany: • Telecom Italia Lab (Italy), Financial coordinator

• Optoelectronics Research Centre, University of Southampton, ORC (United Kingdom), full partner • Centro Nazionale Interuniversitario per le Telecomunicazioni, CNIT (Italy), full partner • Otto-Schott-Institute, Friedrich-Schiller-University of Jena, OSI (Germany), full partner • Turin Technology Centre, Agilent Technologies Italia (Italy), Scientific coordinator


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PART 2: Project achievements in current audited period (01/01/2002 - 30/04/2003)

2) Description of the achievements

2.1) Work progress 2.1.1) WP1, Project Management

The main objective of the WP1 during the third year of the project has been to exploit the large theoretical and experimental knowledge developed during the first two years, which gave excellent results in terms of suitable glasses and good fibres, towards the final target, i.e. the fabrication of the Ultralarge Bandwidth Optical Amplifiers. Such an objective has been made easier because of the structure of the project, which assigned since the very beginning clear responsibilities to each partner, and to a flexible approach that all of them have constantly maintained, along the project. In fact, when some technical difficulties arose, there was full availability and open-mindedness to exchange information, experience, samples, instruments and people (especially students), who have spent some time in the laboratories of the other consortium partners. The conclusion of this fruitful collaboration within the consortium was the achievement of the demonstrator fabrication and of most of the specs, which had been established by the project itself. During the third year, three plenary meetings have been organised : in Pisa (I), host CNIT, Apr. ’02 ; in Southampton (UK), host ORC, Sept. ’02 ; and in Torino (I), host Agilent TTC, Jan. ’03. Moreover, a meeting devoted to the modelling of Tm and Er amplifiers was held in Parma (CNIT), Nov. ’02, in order to coordinate the work done by the partners on this issue. Two meetings organised by the horizontal initiative OPTIMIST have been attended, both in Torino: « Trends of Technologies for Photonics Networks », 6th Feb. ’02 ; and « Intelligent High-Capacity Optical Networks : Opportunities and Challenges », 15-16 Oct. ’02. Finally, in order to concretize the efforts to establish contacts with other IST projects, a new deliverable has been added to the list agreed at the beginning: the Deliverable22, “Applicability of ultra-wide fibre amplification to intelligent optical transport networks”, was written by people of TILab working in LOBSTER and in LION, and is devoted to the potential applications of the device developed within LOBSTER. Participation to the most important International and National Conferences has been performed by the partners, even with original contribution for disseminating knowledge gained within the project (see the list of papers and conference contributions in the last paragraph).


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2.1.2) WP2, Specification and validation The consortium formulated general specifications for the amplifiers to be realized

within LOBSTER activities [2.1]. These requirements were checked during amplifier characterization [2.10, 2.11] and transmission tests [2.12, 2.13].

2.1.2.1) Specifications Specifications originated from a general discussion of optical amplifier application

requirements. Aspects demanding for a wide amplification band have been stressed in [2.1]. At the same time, the need for a flat spectral gain distribution was remarked. Moreover, amplifiers with low noise figure are attractive since they can be used to make longer amplifier chains, in order to design more extended and branched networks. Also, high output powers are required to cope with longer transmission spans and/or higher insertion and branching losses related to more complex network topologies and to permit the insertion of components, such as dispersion compensating fiber modules, grating equalizing filters, variable optical attenuators and add-drop capabilities, without constraining the link power budget. The total output power enhancement in optical fiber amplifiers, together with glass nonlinearities, causes adverse non-linear effects such as four-wave mixing and cross-phase modulation. In order to suppress these impairments within the device, it is effective to adopt high doping levels and to modify the active fibre design [2.2, 2.3]. Eventually, it was remarked that the amplifiers must also have a low polarization-mode dispersion impact. This latter issue becomes extremely important if these devices are to be used at bit-rates above 10 Gbit/s and/or with polarisation-based formats or multi/demultiplexing schemes [2.4].

Taking all considerations into account, the conclusion was that two- or three-stage amplifiers should be adopted, because of their flexibility to combine counteracting design requirements such as high power and low noise figure characteristics. Single-stage amplifiers could be used as booster units in certain applications. Since the LOBSTER objective is the realization of one prototype amplifier, it has been necessary to formulate a set of specifications for a single-stage device, with a sufficient flexibility to cope with all aspects discussed above. This was accomplished as follows [2.1].

Specifications for the triple-band optical amplifier have been stated separately for the two split-band components, namely the Erbium-Doped Tellurite Fiber Amplifier (EDTFA) and the Thulium-Doped Tellurite Fiber Amplifier (TDTFA). While design issues (such as geometry, doping level, cut-off, refractive-index step, background loss, fibre length, …) were considered in [2.5] at the very start of the project, at the end of the second year, start of the third year the emphasis was put on WDM applications, limiting the discussion of geometrical and physical parameters to those particular cases requiring a specific receipt to improve the amplifier design [2.6]. Minimum performance requirements, common to both EDTFA and TDTFA, were given as follows:

(a) small-signal gain: > 25 dB; (b) noise figure: < 7 dB, (c) maximum output power: > 15 dBm; (d) PMD: average DGD values not exceeding 1 ps.

This set of device parameters is rather demanding. Based on the technical literature, it assures a wide use of the optical amplifiers in advanced dense wavelength-division


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multiplexed applications [2.7, 2.8]. It has been a major goal of the LOBSTER consortium to demonstrate the feasibility of such requirements. To further clarify the role of such issues, some considerations were added.

First, band flattening of the amplifier is beyond the scope of LOBSTER objectives. However, if the amplifier to be delivered provides a high non-flattened gain spectrum over a consistent wavelength range, conventional gain equalizing filters will give a satisfactory flat-gain bandwidth [2.9]. So, the definite procedure has been that of assessing the amplifier bandwidth in terms of the band B1 over which the optical gain is larger than 20 dB [2.1, 2.5]. Advanced experiments require a 50÷80 nm flat gain bandwidth [2.7, 2.8] to allocate a sufficient number of transmission channels (e.g., 64 ch @ 100 GHz spacing and 188 ch @ 50 GHz spacing, respectively, all at 40 Gbit/s). A value B1 = 70 nm has been considered adequate for a single-stage EDTFA device, to meet the needs of such applications. Typical pumping configurations require 120-150 mW pump power at 1480 nm (for each amplifier stage). Three-level pumping requires careful detuning from the 980 nm peak and has not been considered in the project. For the TDTFA, a value of B1 ~ 50 nm is reasonable to allow two-stage structures for providing a flat gain in excess of 20 dB over ~40 nm in the long-wavelength region of the S-band (sometimes called the S+-band) and to meet the requirements of advanced-WDM experiments [2.8]. These latter consider a flat gain bandwidth of 30 nm to allocate 85 channels (40 Gbit/s) at 50 GHz spacing, with noise figure lower than 7 dB over the 1475-1510 nm wavelength range.

2.1.2.2) Validation The EDTFA prototype characteristics have been detailed in [2.10]. They matched

all specifications. First of all, the NT93 fibre characterization gave a differential group delay due to PMD effects below 0.2 ps, showing that this kind of active fibre has a very small impact on line PMD. With the NT93 erbium-doped tellurite active fibre fabricated in the consoirtium, a small-signal gain in excess of 27.5 dB was obtained around the gain peak, achieving a second important amplifier specification. The requirements on noise figure, output power and bandwidth were not accomplished with the NT93 single-stage structure alone. The minimum noise figure level was 7.9 dB, against 7 dB required and the maximum output power 10.2 dBm, against 15 dBm as given in the specifications. As far as the gain bandwidth is concerned, we demonstrated with the NT93 alone a ~70 nm-wide, 8 dB gain level, against a 70 nm-wide, 20 dB gain level: this latter was the main discrepancy with respect to the given functional requirements.

A set of countermeasures was investigated at TILAB, to satisfy all device specifications by means of multi-stage (still single-stage EDTF) hybrid configurations for the (C+L)-band. With a C-band preamplifier upstream the EDTFA, a minimum noise figure of 3.7 dB for the compound device was obtained, thus matching also the specifications on this parameter. Moreover, a noise figure lower than 7 dB over the wavelength range 1545-1590 nm and below 8 dB on a 60 nm range was also demonstrated. Furthermore, using a C-band booster as a power amplifier downstream the EDTFA, a peak gain of 39.8 dB was reached, and a gain distribution over the L-band gain ranging from 11.8 to 18.8 dB was got: this means a 65 nm bandwidth at ~12 dB gain value. The insertion of the C-band booster downstream has negligible effects on the global channel


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noise figure and the device chain formed by the EDTFA and the C-band booster has a maximum output power of 20.7 dBm. Out of this level, 12.8 dBm are emitted over the L-band. Eventually, the three-stage (still single-stage EDTF) configuration given by C-band preamplifier, EDTFA and C-band booster all together, has even better cheracteristics: gain peak around 40 dB, noise figure not exceeding 7 dB in the wavelength range 1540 nm -1605 nm, maximum total output level of 21.1 dBm. Around 14 dBm are emitted over the L-band alone.

In conclusion, using a hybrid two- or three-stage configuration based over the consortium EDTFA prototype, also the specifications relevant to noise figure and output power have been satisfied. Finally, using proper pre-emphasis, it has been shown a beneficial effect over the bandwidth at 20 dB gain (in excess of 65 nm). With this latter achievement, all specifications have been practically met.

The EDTFA performance was tested through span transmission and non linear effect investigation. For the span tests, the G.655 fibre of the Free-light type has been considered as the reference choice for high-bit-rate, high capacity, long distance applications. It was decided to measure the BER performance with the single-stage device given by the NT93 active fiber alone, since this test characterizes the minimum performance obtainable with the consortium prototype; two- and three-stage configurations discussed above have larger span budgets because of (i) reduced noise figure and (ii) higher overall gain. Transmission tests were performed on G.655 carrier (two spans of Free-light fiber, 50 km each) at 2.5 Gbit/s1. A very small 0.5 dB penalty was obtained with respect to back-to-back condition. These conclusions have been extrapolated to the bit-rate of 10 Gbit/s, considering (i) the receiver sensitivity degradation and (ii) possible penalties due to chromatic dispersion. No appreciable chromatic dispersion contribution from the EDTFA itself is expected, because of the very short active fiber (0.8 m). In conclusion, in the case of a total G.655 span length of 100 km at 10 Gbit/s, the penalty at the receiver is expected to be ~1 dB with respect to back-to-back conditions. G.655 fiber spans in excess of 200 km need chromatic dispersion compensation to maintain the penalties below 1 dB, at STM-64 rates. In the case of G.652 fibres, chromatic dispersion impairments are higher and span lengths exceeding 40 km already require chromatic dispersion compensation, at 10 Gbit/s. Of course, these are not limitations of the EDTFA prototype, but are general constraints on high bit-rate transmission. G.653 fibres have not been considered. For still higher bit-rates (40 Gbit/s) OSNR values around 30 dB at the receiver are needed. These levels are still within the reach of LOBSTER prototype, considering that the improvement in noise figure obtained with the EDFA C-band preamplifier is nearly 5 dB with respect to the NT93 single-stage alone.

The robustness to non-linear effects, mainly four-wave mixing and cross-phase modulation [2.3], has been investigated with a set of closely spaced channels. Three signals spaced 25 GHz apart around the wavelength of 1552 nm, were input to the EDTFA in order to test non linear effects inside the device. Input and output spectra have been measured with a high resolution optical spectrum analyser and no evidence of non-linear interactions was found at output power levels of +5 dBm/ch.

1 The 10 Gbit/s BER tester set abruptly went out of order and it is still under repair.


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The TDTFA characterisation is reported in [2.11]. Small signal gain of 10 dB, noise figure of 8 dB and output power of 8 dBm have been achieved in a multi-channel set-up. Taking into account the saturation characteristics recorded elsewhere [2.14], this means the peak gain is expected to be ~13 dB around 1475 nm in small signal conditions. At present, the band over which gain is positive extends from 1467 to 1520 nm, and is limited by availability to the consortium of suitable signal sources. It is reasonable to foresee a net gain bandwidth of more than 80 nm, because the fluorescence spectrum of Thulium ions is quite symmetrical with respect to the peak [2.15, 2.16]. Hence the LOBSTER Consortium has succeeded in demonstrating experimentally net gain from a Thulium-Doped Tellurite Fibre Amplifier, for the first time in the scientific community. Though this result does not match amplifier specifications [2.1] directly, it should be reminded that those requirements were top level and rather tough for a brand new device, the active fibre and the mechanical joints of which are not optimised yet. Anyhow, the results obtained so far show that, reducing coupling losses to best levels reported in the literature and improving the fiber background loss, peak gain values of ~18 dB can be reasonably envisaged. Accordingly, minimum noise figures of ~5 dB are technically feasible, improving the input coupling joints and output powers of ~15 dBm are easily foreseen.

In conclusion, though TDTFA specifications have not been completely met, net gain has been experimentally demonstrated for a brand new optical amplifier. At the epilogue of LOBSTER activities, it is thought that the experimental material gathered in glass spectroscopy, fibre drawing, amplifier design and assembling and device modelling are sufficient evidence to the technical feasibility of required specifications. Because of the relatively low gain of the TDTFA, the transmission test has been limited to compare back-to-back performance with line performance in the presence of the amplifier. A 2.5 dB penalty is obtained at 1210 BER, which is due to the high noise figure of the prototype (8-11 dB). Also in this case the bit-rate is 2.5 Gbit/s. According to dispersion characteristics of the physical carrier in the S-band, a tolerable residual dispersion for 10 Gbit/s operation would correspond to ~100 km of G.655 fibre and to ~50 km of G.653 and G.652 fibre. Longer spans require chromatic dispersion compensation. Also the validation of span tests would have required a device gain higher than available. However, as stressed above, no technological limits are involved, since improving the fibre background loss and I/O coupling losses, a gain of at least ~18 dB would be at hand, with the glass technology developed so far in LOBSTER. At the same time, an improvement of the noise figure is also technically possible, so that no constraints are foreseen for in line application of the TDTFA. Indeed, the BER results demonstrate the absence of whatsoever BER floor and the possibility of reaching a sufficiently neat transmission quality for advanced optical network applications. The relatively low gain levels attained over the S-band have not motivated any tests on non linear effects within the TDTFA. However, since the glass host is the same as that of the EDTFA, the results obtained with it can be extended to the S-band amplifier.

As the final test, the global transmission capability of the integrated triple band amplifier has been carried out in the small-signal regime. The test referred to a signal spectral allocation over a ~130 nm band. The channel OSNR values are fully compatible with 10 Gbit/s applications and reasonably in line also with 40 Gbit/s applications. The total power variation is lower than 12 dB over the (S+C+L)-band.


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According to the availability of signal sources, the integrated triple-band amplifier has a net gain band that covers a spectral range from 1465 nm to 1520 nm in the S-band and a wavelength region from 1540 nm to 1610 nm in the (C+L)-band: that is, a net gain bandwidth of some 125 nm. Beyond the actual source availability, the Thulium lineshape symmetry suggests that the net gain band should start somewhere around 1430 nm. On the other side, the EDTFA net gain should theoretically extend up to 1634 nm. It is therefore reasonable that the band of the integrated amplifier is approximately 200 nm, minus the blind region due to band coupling. As discussed on several occasions, the net gain device band is only one basic feature of the device. The operating spectral characteristic is the flat bandwidth, the extension of which depends on the required gain level. In the LOBSTER framework, leaving aside equalisation issues, we decided referring to the band over which the signal is higher than 20 dB. The activity of the Consortium on the EDTFA prototype shows that it extends over nearly 70 nm (1530-1600 nm) in the (C+L) region. We didn’t succeed in reaching the 20 dB level with the TDTFA, but have shown this goal is not outside of technological reach. In summary, the characterisation results on the EDTFA consortium prototype have shown that it has matched all relevant specifications given previously. The transmission tests also had a positive result, confirming the applicability of the prototype to in line applications. The modular approach to the final EDTFA also can envisage preamplification (noise figure lower than 8 dB over ~60 nm band) and power amplification applications (output power higher than 21 dB, 14 dB of which over the L-band alone). The characterisation results for the TDTFA have been more modest, but obtained on a brand new technological object. Though amplifier specifications have not been met directly for the S-band amplifier, the result obtained so far (on-off gains in excess of 35 dB) and the clear evidence for further improvements seem quite satisfying in demonstrating the feasibility of all specifications with the current glass technology developed within the consortium. The results obtained so far with the TDTFA has been accepted for oral presentation at next ECOC/IOOC, in September 2003. References for WP2 [2.1] R. Caponi, A. Percelsi, M. Potenza, “Amplifier specifications and design study (II)”, CEC Deliverable IST-1999-13322/TILAB/LOBSTER_D10, 11 October 2001. [2.2] K. Aiso et al., “Erbium Lanthanum co-doped fiber for L-band amplifier with high efficiency, low non-linearity and low NF”, in OFC ‘2001, Anaheim (CA), March 17-22, 2001; Proc., paper TuA6. [2.3] T. Sakamoto et al., “Suppression of Nonlinear Effects in Tellurite-based EDFAs by Fiber Parameter Modification”, in OFC ‘2001, Anaheim (CA), March 17-22, 2001; Proc., paper TuI6. [2.4] K. Fukuchi et al. , “10.92-Tb/s (273 × 40-Gb/s) triple-band/ultra-dense WDM optical-repeatered transmission experiment”, in OFC ‘2001, Anaheim (CA), March 17-22, 2001; Proc., postdeadline paper PD24. [2.5] M. Potenza, M. Artiglia, “Amplifier Specifications and Design Study (I)”, CEC Deliverable. IST-1999-13322/CSELT/LOBSTER_D1, 11 April 2000. [2.6] A. Bogoni, A. Cucinotta, L. Potì, and S. Selleri, “Modelling of Er3+ and Tm3+-doped tellurite fibre amplifiers”, CEC Deliverable IST-1999-13322/CNIT/LOBSTER_D9, 31 July 2001.


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[2.7] S. Kinoshita, “Broadband fiber optic amplifiers”, in OFC ‘2001, Anaheim (CA), March 17-22, 2001; Proc., paper TuA1. [2.8] K. Fukuchi et al. , “10.92-Tb/s (273 × 40-Gb/s) triple-band/ultra-dense WDM optical-repeatered transmission experiment”, in OFC ‘2001, Anaheim (CA), March 17-22, 2001; Proc., postdeadline paper PD24. [2.9] M. Yamada et al., “Broadband and gain-flattened Er3+-doped tellurite fibre amplifier constructed using a gain equaliser”, Electron. Lett. Vol. 34, No. 4, 19th February 1998. [2.10] R. Caponi, A. Pagano, A. Percelsi, M. Potenza and B. Sordo, “EDTF-amplifier assembly”, CEC Deliverable IST-1999-13322/TILAB/LOBSTER_D14, 13 June 2003. [2.11] E. M. Taylor, L. N. Ng, J. Nilsson, R. Caponi, A. Pagano, M. Potenza, B. Sordo (Telecom Italia Lab), “Thulim-doped Tellurite amplifier assembly”, CEC Deliverable IST-1999-13322/ORC-TILAB/LOBSTER_D15, 25 July 2003. [2.12] R. Caponi, A. Pagano, A. Percelsi, M. Potenza and B. Sordo, “Test-bed arrangement and validation tests”, CEC Deliverable IST-1999-13322/TILAB/LOBSTER_D16, 31 December 2002. [2.13] R. Caponi, A. Pagano, M. Potenza and B. Sordo, “Device performance”, CEC Deliverable IST-1999-13322/TILAB/LOBSTER_D18, 15 July 2003. [2.14] R. Caponi, A. Pagano, M. Potenza, B. Sordo. B.M. Taylor, L. N. Ng, J. Nilsson, F. Poli, “Nearly 10 dB net gain from a Thulium-Doped Tellurite Fibre Amplifier over the S-band”, accepted for oral presentation at ECOC 2003. [2.15] LOBSTER Consortium, “Fibre drawing and characterisation of the Tm3+-doped tellurite fibre”, CEC Deliverable IST-1999-13322/ORC/LOBSTER_D13. [2.16] E. R. Taylor, L. Ng, H. Buerger, I. Gugov, N. Sessions, W. S. Brocklesby, “Spectroscopy of Tm3+-doped Tellurite Glasses for 1470 nm Fibre Amplifier”, CEC Deliverable IST-1999-13322/ORC/LOBSTER_D5, 12 January 2001.


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2.1.3) WP3, Erbium doped fibre amplifier

As pointed out in deliverable D12 «Fibre drawing and characterisation of the Er3+-doped tellurite fibre», the fibre fabrication method was seen to be most critical for achieving a fibre with gain and suitable for use in the amplifier. The method, which eventually worked best was a combination of melt casting and rod-in-tube pulling as depicted in Figure 3.1.

Fig. 3.1: The method used for single-mode EDT-fibre fabrication The method starts with the preparation of the inner clad tube by rotational

casting (A). Next, the core glass is poured into the tube leading to a multi-mode preform with a diameter of around 10 mm (B). Steps A and B are mandatory. If carried out properly, the bubble content both in the centre axis and on the interface can be kept at lowest levels. Any other preform preparation based on drilling or rod-in-tube assembling did not lead to light-guiding fibres. Then, the as-obtained preform was stretched on the drawing tower down to a diameter of around 1 mm (C). The furnace temperature should be kept as low as possible to avoid excessive crystal nucleation in the preform. The best part of the stretched preform was then taken, and fitted into an overclad tube (E), which was obtained by drilling a small bore (∅ ~ 1 mm) along the centre axis of a clad rod of 10 mm of diameter (D). Subsequent continuous drawing (F) of such a preform jacketed and sealed yielded in the single-mode (SM) fibre NT93, which performed successfully in the EDTF-amplifier (deliverable D14 «EDTF-amplifier assembly»). To guarantee fibre handleability during amplifier assembly and improve the lifetime of the amplifier, the tellurite fibre was overcoated during pulling with a UV-curable polymeric acrylate resin.


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Generally, the tellurite glasses for the preforms were made from high-grade commercial powders of purity higher than 99.99%. In the case of the NT93 fibre, the core glass was of TZN composition and co-doped with 5000 ppmw of Er3+ and 10000 ppmw of Ce3+, respectively. Since tellurite fibres strongly suffer from gain-reducing green up-conversion, Ce3+ ions were added in the hope to suppress this deleterious effect as already seen in other cases. The composition of clad and overclad was TZNB.

Even if the TZN/TZNB couple was far from being stable against nucleation and crystal growth and behaved poorly in comparison with improved compositions where Nb2O5 were added (deliverable D7 «Core/clad glass formulations and preform realisation for the Er3+-doped tellurite amplifier»), it was the best overall couple in terms of ease of high-quality glass preparation, surface cleaning by chemical etching, and fibre drawing. The NT93 fibre pulled from such a glass couple had a core diameter of 4.5 µm, a clad diameter of 125 µm, and a numerical aperture, NA, of 0.25, respectively, which gives a theoretical cut-off wavelength of 1470 nm.

Figure 3.2: Fibre NT93 under pumping conditions

Figure 3.3 : Background loss of SM fibre NT72 at 1280 nm

y = 0.038x + 0.3957R2 = 0.9883

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Linear (Att [dB])


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Whether the Ce3+ ions added had improved the gain efficiency of the fibre or not, could not be clarified unequivocally, since the smoothness of the core-clad interface was seen to play a key-role as well (deliverable D12 «Fibre drawing and characterisation of the Er3+-doped tellurite fibre»). As a matter of fact, green up-conversion was still present on pumping the fibre (Figure 3.2).

The fibre loss of NT93 was not measured explicitly, but another SM fibre of TZN/TZNB composition (NT72) fabricated earlier by the same method had a background loss of 3.8 dB/m at 1280 nm using the cut-back method (Figure 3.3). In addition, preliminary loss measurements on a single core rod of TZNW composition showed that a value of around 1 dB/m was within reach.

The activity of amplifier assembling and characterization went on with a multi-channel test using an amplifier set-up in dual-pumping configuration as depicted in Fig. 3.4.

Input signal, in (λ = 1535 ÷1605 nm)

Output (amplified) signal

Erbium-doped tellurite fibre

Isolator WDM coupler

Co-propagating pump laser(λ = 1480 nm; Ptypical ~ 100 mW)

Counter-propagating pump laser (λ = 1480 nm; Ptypical ~ 100 mW)

WDM coupler Isolator

Figure 3.4: Amplifier set-up

Sixteen laser transmitters were selected over the C- and L-bands. The set of transmission channels contained eight channels in the conventional C-band (wavelengths from 1539.77 nm to 1569.98 nm) and eight L-band channels (wavelengths from 1580.35 nm to 1604.03 nm). All sixteen transmission channels were input to the amplifier by means of a 16→1 multiplexer, the insertion loss of which was around 12 dB.

The basic configuration chosen for the NT93 fibre was a rather short sample, 80 cm long, in dual-pumping configuration. Such an active fibre length was expected to be sub-optimal, but longer specimens did not give better results, because the background loss was not negligible anymore.

During amplifier construction, the Achilles heel of the EDTFA engineering cropped up, i.e. how to make stable fibre joints between the active and passive fibres. Even if this problem has been addressed right from the beginning of the project, its extent could not be foreseen. Making polished angled splices on NT93 fibre turned out to be no big issue. But all the attempts to fix the tellurite fibre in a ferrule without breaking the fibre by using UV-


18

curable resin failed. This was surprising because previously the ferrule-based method worked well with fluoride fibres, which were even more fragile.

Hence, the only possibility left, was butt-coupling with index matching oil. The best index matching oil found to reduce reflections at the tellurite fibre faces had a refractive index of 1.7 (the optimum value to weaken Fresnel losses at the contact layer between n~1.46 and n~2 glass cores). This solution has made possible a substantial improvement of all channel gains, with a consistent increase of the C-band amplification performance. Moreover, this fluid suppressed lasing instabilities at the gain peak (around 1558 nm) that were observed preliminarily.

Fibre and amplifier assembled were characterised in terms of PMD, gain, noise figure, and output power of channels, respectively. The corresponding spectra are shown in Figures 3.5 to 3.8. Input power levels used were +2, -3, -8, -13 and –18 dBm.

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

1520 1530 1540 1550 1560 1570 1580 1590

Wavelength [nm]

DG

D [p

s]

Figure 3.5: NT93 fibre PMD measurement


19

-10

-5

0

5

10

15

20

25

30

1530 1540 1550 1560 1570 1580 1590 1600 1610

Wavelength (nm)

Gai

n (d

B)

2

-3

-8

-13

-18

Figure 3.6: Channel gain for the EDTFA amplifier

3.0

5.0

7.0

9.0

11.0

13.0

15.0

17.0

1530 1540 1550 1560 1570 1580 1590 1600 1610

Wavelength (nm)

Noi

se F

igur

e (d

B)

2

-3

-8

-13

-18

Figure 3.7: Channel noise figure for the EDTFA amplifier


20

-25

-20

-15

-10

-5

0

5

1530 1540 1550 1560 1570 1580 1590 1600 1610

Wavelength (nm)

Out

put P

ower

(dB

m)

2-3-8-13-18

Pmax = 10.2 dBm

Figure 3.8: Channel output power for the EDTFA amplifier

Whilst PMD characterisation and small-signal gain met the specifications established right away, i.e. a differential group delay due to PMD of below 0.2 ps (Fig. 3.5) and a small-signal gain in excess of 27.5 dB (Fig. 3.6), countermeasures had to be taken by TILAB to drop the minimum noise figure level of 7.9 dB (Fig. 3.7) further down than 7 dB (required), and boost the maximum output power of 10.2 dBm (Fig. 3.8) to 15 dBm (required) or beyond. Details on how this was accomplished can be found in deliverable D14 « EDTF-amplifier assembly ».


21

2.1.4) WP4 – Thulium doped fibre amplifier

Tellurite glasses are batched from high grade commercial powder of purity higher than 99.99%. The clad and core glasses are derived from a ternary composition in mole % of (95-x)TeO2:xLi2O:5TiO2. The glass will be referred to in the text as LTT. To fabricate a fibre the glass must be stable. The DTA is shown in figure 4.1 and shows no apparent crystallisation peak when heated at 10 oC/min. The viscosity diagram is also shown in the figure. The temperatures are defined accordingly: glass transition Tg, extrusion temperature TE, glass softening temperature Ts, fibre pulling range TF, and glass melting temperature Tm. The range of composition tried to use as core and clad is shown in figure 4.2. The glass has a refractive index of 2.0 and an associated Fresnel reflection of 11%.

0

4

8

12

16

20

240 280 320 360 400 440 480 520 560 600Temperature (Celsius)

Vis

cosi

ty (

log(

pois

e))

3

4

5

6

7

8

9

Cha

nge

in T

empa

ratu

reTg

TS

TE

TF

Tg

Tm

Figure 4.1

LTT glass - xLiO2+5TiO2+(95-x)TeO2

1,95

2,05

2,15

2,25

14 16 18 20 22 24 26mole% Li2O

refra

ctiv

e in

dex

(at 6

43.8

4nm

)

Figure 4.2


22

Glass melting takes place under oxygen atmosphere at a temperature of 850ºC for an hour before casting. Preforms and glass tubes are fabricated by extrusion, which is carried out at a temperature between Tg and Ts. The fibre is doped with 4000 ppm of Tm3+.

Several fabrication techniques were investigated: rod-in-tube, rotational casting, built-in-casting and extrusion. The extrusion technique gave the best results in terms of loss and reproducibility of process. A schematic of the process is shown in figures 4.3 and 4.4. Preforms with core to clad ratio between 0.3 and 0.5 are extruded from layered discs. A 4 mm rod primary preform gives a uniform region compared to 10 mm extruded rod preform. The cladding tubes used to sleeve the preform have an outer diameter of 10 mm and an inner diameter of 1 mm and 4 mm. The sleeving process uses the rod-in-tube technique twice to obtain the fibre dimensions. A photo of the extruded tube to accept the 1 mm rod is shown in figures 4.5 and 4.6. The conditions for extrusion are shown in Table 1. The disc is nominally 29 mm in diameter, the disc thickness is ~30mm, the extrusion temperature for all processes is 300°C. The pressure is preset (from several previous experimental trials) to give an extrusion rate of ~0.20 mm/min. There is evidence of die swell, more obvious in the larger than the smaller outer diameter. A cross-section of a fibre drawn from this assembly is shown in figure 4.7. The first extruded core/clad is represented by areas 1 and 2. The tube 1 by area 3. The fibre drawn from this (fibre-92) gave a loss of 1 dB/m at 1000nm. Fibre canes of approximately 1mm were obtained and inserted in tube 2. A fibre with core and clad compositions giving an NA of 0.4 was fabricated. A fibre (fibre-98) with cutoff at 1380nm, diameter of 2.6 micron, was fabricated and used for amplifier measurements.

0

2

4

6

8

10

12

0 20 40 60

extruded length (cm)

diam

eter

(m

m)

20

4

11

3

AB

Figure 4.3 Figure 4.4

Core = 3 mmClad =11 mm

Extrusion Die= 4 mm

Rod = 4.15 mm

29 mm

Core = 3 mmClad =11 mm

Extrusion Die= 4 mm

Rod = 4.15 mm

29 mm


23

Table 4.1: Extrusion parameters

Geometry Disc thickness (mm)

Temperature(°C)

Pressure (bar)

Extrusion rate(mm/min)

OD= 3.4–3.7 mm core/clad= 0.7-0.8

18mm 300 18 0.18

Tube 1: OD = 10.5mm, ID = 3.8mm

30mm 300 6 0.22

Tube 2: OD =10.3mm, ID = 0.85mm

30mm 300 9.85 0.15

Figure 4.6 Figure 4.7

Figure 4.8 – Fibre cross-section

Clad = 30mm

Extrusion DieTube

Tube by extrusionID = ~4.3 mmOD=~10 mm

Clad = 30mm

Extrusion DieTube

Tube by extrusionID = ~4.3 mmOD=~10 mm

Fibre 92 Fibre 93

NA=0.4 LTT tellurite fibre

Core = 3.0 micronCutoff = 1546 nm.

Principal Cane = 0.55 core/cladParent cane = .17 core/cladParent fibre loss = 1 dB/m (core~22 micron)

12

3


24

Using a white light source launched into the LTT fibre via a 20x microscope objective and collecting the output through a fibre feed to the optical spectrum analyzer (OSA), a cutback method was employed to obtain the fibre loss. The fibre length (fibre-98) was about 4.5 m with a single fibre loop of 20 cm diameter. The colour of the light at the end of the fibre was yellow. The attenuation curve is shown in figure 4.9 for a cutback of 1 m. The fibre loss is 3.4 dB/m. This reproduced for successive cutbacks up until the loop. In the absence of the loop and a cutback of 1 m, the attenuation averaged 5 dB/m. No detected light was apparent from the core as there was no evidence of the Tm3+ ground-state-absorptions. As the core diameter is small, most of the light is probably launched into the cladding, which guides against air, or the core is very lossy.

To get an idea of the loss at the core, another fibre using the original rod and tube 1 but fabricated earlier with a lossy tube 2 (greenish because of incomplete oxidation of TiO2), was measured. The fibre NA is the same as fibre-98 but the core diameter was 3 micron. A length of ~0.5 m was needed to get significant signals in the OSA. The attenuation curve for the core is shown in figure 4.10. The top curve shows the transmission data and the GSA of Tm3+. The lower curve is the attenuation curve and shows an attenuation of ~20dB/m.

Fibre 98 LTT

2

2,5

3

3,5

4

4,5

700 900 1100 1300 1500 1700

wavelength, nm

atte

nuat

ion

(dB

/m)

cladding loss=3.4dB/m

Figure 4.9

It was difficult to ascertain how well the light was being launched in the core, thus the loss using 1047nm pump was investigated. Using this pump wavelength, up-conversion results in blue fluorescence, hence it was easy to find the core. The 1047nm source from a Nd:YLF laser is fibre pigtailed and fusion spliced to a standard telecom fibre which was in turn butt-spliced to the LTT fibre.


25

Figure 4.10

The power before and after the LTT fibre was measured using a power meter. Light was launched both in the clad only (no blue fluorescence) and in the core (with blue fluorescence) with successive cutbacks to get an idea of the attenuation in the clad and core respectively. Table 2 summarises the results.

P0 is the incident power measured before the LTT fibre. A plot of log (Pout) versus length for different incident powers and a linear regression fitting gave the experimental P0, P0(meas) from the intercept and the attenuation (dB/m) from the slope.

Table 4.2: Attenuation results at 1047nm

Source: Nd:YLF. Single Mode silica to LTT butt-coupled linear fit to log(Pout) vs length (total 70cm)

P0(mW) incident

P0(meas) clad Attn clad (dB/m) P0(meas) core Attn core (dB/m)

528 378 9.6 302 .57 17.8 385 327 11.3 239 .62 18.8 258 185 9.7 154 .59 18.4

P0(meas)/P0=0.75 Ave=10.6 P0(meas)/P0=0.59 Ave=18.3

0.11 FR

P0

0.11 FR

delivery LTTP0(expted)= 0.89*(0.89P0)

To clad

0.11 FR

P0

0.11 FR


0.31 mismatch

To core

0.11 FR

P0

0.11 FR


To clad0.11 FR

P0

0.11 FR


0.11 FR

P0

0.11 FR


0.11 FR

P0

0.11 FR


0.11 FR

P0

0.11 FR


To clad

0.11 FR

P0

0.11 FR


0.31 mismatch

To core0.11 FR

P0

0.11 FR


0.31 mismatch0.11 FR

P0

0.11 FR


0.11 FR

P0

0.11 FR


0.11 FR

P0

0.11 FR


0.11 FR

P0

0.11 FR


0.31 mismatch

To core

-90

-85

-80

-75

-70

-65

500 700 900 1100 1300 1500 1700

-2 0

-1 0

0

1 0

2 0

3 0

4 0

5 0 0 7 0 0 9 0 0 1 1 0 0 1 3 0 0 1 5 0 0 1 7 0 0

Sign

al (d

Bm

)Lo

ss (d

B/m

)


26

Allowing for Fresnel reflection (11%), the expected transmitted intensity without attenuation in the clad is P0(expected)/P0=0.79. Allowing for Fresnel reflection and modal mismatch (-5 dB), then the expected coupling efficiency to the core is 0.51. The coupling efficiencies measured are reasonable

The loss in the clad, 10.6dB/m, is higher than the 3.4dB/m from the white light cut-back measurement. The reason for this is unclear. The loss in the core is high, 18.3 dB/m, and reflects the attenuation of light launched in the cladding since the single-mode fibre diameter is larger than LTT and ground-state absorption (GSA) plus any residual upconversion absorption at 1047nm. Care was taken to ensure that the cutback was performed after the blue fluorescence from upconversion was well attenuated, so that GSA was dominant.

Fibre-98 was setup for amplifier measurements. A 980/1550 WDM coupler was used to launch the 1047nm pump and 1492 nm signal source. The output of the WDM was spliced to a DSF and this in turn to a high NA fibre with cutoff at 1000nm. This gave a good modal field match at the signal wavelength for the LTT fibre. This input arm gave an attenuation of –2.9 dB for the 1047 nm pump. The signal arm gave an attenuation of –6.3 dB, half the loss is at the connection between the laser diode and the 1492 branch of the WDM. The fibre pigtail of the laser diode is angled polished to avoid back reflections into the laser. The output arm consists of the high NA fibre spliced to the DSF spliced to telecom single-mode fibre and fed to an OSA. With a –10dBm of 1492 nm at the end of the input arm, the loss of the output arm is 4 dB, that is the system signal to the optical spectrum analyser (OSA) is –14dBm. A 0.7m length of coated LTT fibre was inserted and the measured signal dropped to –34.4 dBm, hence an insertion loss ~20 dB. The on/off gain signal using 400mW of 1047nm (from a Nd:YLF laser) incident on the LTT fibre was 10dB. A Raman source at 1450 nm (-10dBm) was also used as a signal, with an on/off gain of 7dB.

The insertion loss of 0.7m of LTT fibre is ~20dB at 1492nm. To understand the origin of this loss, the attenuation at 980nm (representing a wavelength with no GSA) was measured using the cutback method in a setup not too dissimilar from the amplifier setup above. The launch for both used an old fusion splicer but in the 1492nm experiment, the output launch used a micro-positioner assembly which appeared very sensitive so that in the 980nm experiment, another old fusion splicer was used as the output launch pad. The system signal at 980nm measured at the OSA end was 8.9 dBm without the fibre and –11 dBm with the fibre of length 1.63m, i.e. an insertion loss of 20 dB. A cutback of 0.44 m increased the signal to –5dBm, hence a propagation loss of 13.6 dB/m. With a cutback of 0.33m the signal only increased at best to -4.1 dBm. It was observed that due to the constraint in space, the fibre after the 0.33m cutback had a tight bend before detection which would have introduced loss. The remaining fibre of final length 0.858 m gave an insertion loss of 12.3 dB. From the insertion loss, the propagation loss results ~10dB/m, and the coupling loss is 3.7 dB. This is a higher limit estimate of coupling loss on one side of the launch. From the cutback, the propagation loss is 13.6 dB/m. The 13.6 dB/m loss clearly includes the fibre background loss and light launched into the cladding because the coating (of lower index) does not strip the cladding modes. There is no GSA at 980 nm.


27

Returning to the measured loss at 1492nm then since the GSA at 1492nm is ~4 dB/m*0.7=2.8 and the propagation loss of the fibre is 13.6 dB/m * 0.7= 9.5 dB and a coupling loss of ~3.7 dB, altogether giving an expected insertion loss of ~16dB. Modal coupling loss and end-face reflections from both fibre ends will contribute ~1.5 dB to 3.7 dB coupling loss but there is also transverse mismatch and the quality of the butt-splice which depends on the integrity of the end faces to considered. From these results, splice losses from each end can be ~3 dB. The splice loss using the micro-positioners is higher than using a fusion splicer launch pad. A SEM picture of fibre is shown in figure 4.11, the density difference between the core and clad is not enough to distinguish the core from the clad but the cleave does seem smooth across the core (near the center).

Figure 4.11 Experiments using 980nm, 1047nm and 1492nm attenuation measurements are consistent. The fibre loss is higher than measured using a white light source but appears to be dominated by the quality of the launch.

The same fibre (No. 98) was used to assemble and characterise the Thulium-Doped Tellurite Fibre Amplifier (TDTFA) at TILAB. The scheme of this setup is shown in Fig. 4.12.

S - band amplifier scheme

Isolator Circulator

1047 nm pump

1047 nm pump

980/1550 nm WDM

IN OUTTm-doped fibre

1047 nm pump

1047 nm pump

1605 nm pump

1605 nm pump

980/1550 nm WDM

Figure 4.12 – Optical scheme adopted in TILAB for TDTFA assembly and characterisation

In the layout of Fig. 4.12, the fundamental pump wavelength is at 1047 nm, for both co-


28

propagating and counter-propagating directions, while an additional pump radiation at 1605 nm is used, to improve the ground state absorption. All the pump sources involved are equipped with good isolators (from manufacturers’ specifications), while the signal sources upstream are shielded by an isolator at the input end and by an analogous output device, which is an optical circulator. Such component, besides providing isolation from downstream connections, allows coupling the second counter-propagating pump radiation – an EDFA with an input signal at 1605 nm wavelength – with more selectivity than in the scheme used at ORC, where only WDM couplers are employed (see previous description). The other two pump radiations of Fig. 4.12, both at 1047 nm, are generated by Nd:YLF lasers.

Estimated pump power levels into the Tellurite fibre are as follows: (1) ~ 200 mW for the co-propagating wave at 1047 nm; (2) ~ 150 mW for the counter-propagating pump at 1047 nm; (3) ~20 mW for the idle radiation at 1605 nm. The active fibre is about 0.8 m long.

The major experimental problems occurred in the TDTFA assembly phase are related to the coupling of the active fibre to the silica pigtails of the input/output passive sections (Fig. 4.12). This difficulty originates from the impossibility of using current arc splicing techniques, due to the too high difference of the fusion temperatures (1000°C at least) that characterise the Tellurite and the silica glasses. Thus, the only feasible methods are based on the realisation of mechanical joints. In particular, due to lack of time and to various technical difficulties hindering the adoption of more stable solutions (on these aspect, see deliverable D15 « Thulium-doped Tellurite fibre amplifier assembly »), all joints between Tellurite (TeO2) and silica (SiO2) fibres have been simply realised through butt coupling in air. Such procedure is critically dependent the following two aspects of the fibres involved:

1) the mismatch of their geometries, which directly impacts on the modal mismatch;

2) the really high refractive index gap (from n ~ 1.5 for SiO2 to n ~ 2 of TeO2 matrixes).

Problem #1 has been successfully solved by gradually bridging the modal gap between the standard silica pigtails and the active Tellurite fibre, i.e. by splicing to the input/output fibre a modal adapter (also called “optical funnel”), which is formed by a cascade of three different fibre types: a conventional Single-Mode transmission Fibre (SMF), a Dispersion Compensating Fibre (DCF) and a high Numerical Aperture (NA) fibre. The fundamental characteristics of all the fibres used in the TDTFA setup – including the Tellurite – are reported in Tab. 4.3, together with the values of relevant coupling losses, estimated (in the bottom line) for each fibre with respect to the next one in the corresponding right column.

Type of fibre SMF DCF High NA f. TeO2 fibre Numerical Aperture (NA) 0.12 0.21 0.32 0.4 Cut-off wavelength (nm) 1200 1460 1000 1360

Modal diameter at 1480 nm (µm) 9.93 5.90 3.80 3.04 Calculated loss (dB) 1.13 0.81 0.21 –

Table 4.3 – Properties of all fibres used in the TDTFA setup

The second question (the refractive index gap between the two fibres under consideration) impacts not particularly on coupling loss – which is limited to only ~ 0.7 dB for the coupling of the two glasses through air – but increases much more seriously joints reflectance, with


29

consequent lighting up of laser effects (which limit the gain available to amplification).

In this case, the practical solution adopted (for lack of time, as before) has been the interposition of an index matching drop between the two fibre facets to be connected. For this purpose, a commercial liquid has been used, having n ~ 1.7, which can be considered close enough to the optimum value of n ~ 1.73. Thus, significant gain levels have been obtained from the TeO2 fibre (as illustrated in the following) without any lasing action.

To estimate the quality of the coupling procedures used – based on the combination of the index matching fluid with the described “optical funnels” – it is convenient to introduce the total insertion loss (i.e. the coupling loss) of the input and output amplifier’s sections alone, as measured in a configuration with no active fibre interposed. This parameter, ranging to about 6 dB (3 dB on each delivery arm), is ~ 0.8 dB more than expected from the theoretical estimate indicated in the last line of Table 4.3. Such difference seems fully acceptable, if all experimental difficulties and uncertainties are taken into account (viz., the suboptimal index matching used, the low repeatability of the manual scribing and pulling technique to cut Tellurite fibres, as well as of the alignment procedure for butt-coupling, etc.). For comparison, it must be considered, on the other hand, that a direct joint between the active Tellurite and the silica fibres would have implied an insertion loss of about 5 dB.

When the active fibre is inserted into the set-up of Fig. 4.12, the total insertion loss (measured at 1480 nm) of the TDTFA with all pumps off is as high as 24.5 dB, because of: 1) resonant GSA between the ground 6

3H and the 43F levels,

2) fibre background loss, 3) mechanical butt-coupling of the Te to the Si fibre (including transverse misalignment). The first characterisation of the TeO2 amplifier has been single channel. The typical set-up used in these cases consists of a tunable laser and an Optical Spectrum Analyser (OSA). For the testing of the TDTFA, the wavelength scanning of the source has covered the range from 1467 to 1523 nm (1465 to 1525 nm being the operating interval of the laser). The output power spectrum, obtained with an input level of -10 dBm and registered with the “max hold” option of the OSA, is shown in Fig. 4.13. The red line superimposed to experimental data indicates the ASE spectrum level, while the blue line is obtained from a three-point average of peak values. The spectral behaviour is nearly flat over about 30 nm.

Table 4.4 – Peak emission wavelength and frequency of the S-band transmitters

Channel Wavelength [nm] Frequency [THz] 1 1490.02 201.2 2 1500.46 199.8 3 1510.29 198.5 4 1520.25 197.2


30

-60

-50

-40

-30

-20

-10

0

1465 1469 1473 1477 1481 1485 1489 1493 1497 1501 1505 1509 1513 1517 1521 1525

WAVELENGTH (nm)

POW

ER (d

Bm

)

Figure 4.13 – TDTFA testing with the single-channel method (input power: -10 dBm)

Figure 4.14 – Single-channel measurement of the peak net gain, ranging to ~ 11 dB

(input power: -10 dBm)

From the output power curve of Fig. 4.13 both the on-off and the net gain of the TDTFA have been evaluated. A peak net value of 11 dB (corresponding to ~ 36 dB on-off) has been found close to 1480 nm. This result, representing the maximum gain level achieved with the TDTFA, is evidenced through a single shot in Fig. 4.14. The strong improvement of the on-off gain, with respect to the 10 dB previously reported (with reference to the same fibre) can be attributed to the pump coupling increase due to “optical funnels”. Moreover, a multi-wavelength characterisation has been undertaken, using four commercial WDM lasers as test sources. Their nominal emission wavelengths and optical frequencies (conformal to the ITU-T grid with 100 GHz spacing) are shown in Tab. 4.4. The output spectrum of these transmitters is shown in Fig. 4.15, while their practical packaging for standard rack mounting, as assembled in TILAB, is shown in Fig. 4.16.


31

-80

-70

-60

-50

-40

-30

-20

-10

0

10

1480 1490 1500 1510 1520 1530Wavelength [nm]

Out

put l

evel

[dB

m

WDM input1490 nm1500 nm15101520

Figure 4.15 – Output spectra of the S-band transmitters and of the global WDM signal

The measurements done with the described multi-wavelength set-up provide the TDTFA functional parameters. Corresponding results are shown in the following three diagrams.

Fig. 4.17 shows the spectral gain measured with different input power levels: -20, -10 and 0 dBm/channel. For total input power levels below -4 dBm, the TDTFA supplies net optical gain for all the λ’s. The corresponding small-signal on-off gain ranges from 26.5 to 32 dB.

Figure 4.16 – Four-channel S-band transmitter module assembled at TILAB

By combining these results with the previous ones from the single channel characterisation – where the measurement range has been limited on the short wavelength side by the source characteristics (see Figs. 4.13 and 4.14) – it can be concluded that the overall net gain bandwidth potentially available to the LOBSTER prototype TDTFA exceeds 80 nm.

In Fig. 4.18 the spectral noise figures of the channels for the same input conditions as before are shown. Taking into account the 3 dB input coupling loss, noise figures could be reduced down to ~ 5.5 dB, an interesting value in view of further improvements of the TDTFA setup. Fig. 4.19 shows the output power spectrum for the same input conditions.


32

-4

-2

0

2

4

6

8

1 4 8 5 1 4 9 0 1 4 9 5 1 5 0 0 1 5 0 5 1 5 1 0 1 5 1 5 1 5 2 0 1 5 2 5W av e le n g th [n m ]

Gai

n [d

B]

0 -1 0 -2 0

Figure 4.17 – Multiple-channel measurement of the Tellurite amplifier’s spectral gain

8

9

10

11

12

13

14

14 85 1490 1495 15 00 1505 1510 1 515 1520 152 5W av elen g th [n m ]

Noi

se F

igur

e [d

B]

0 -10 -20

Figure 4.18 – Multiple-channel measurement of the Tellurite amplifier’s noise figure

-20

-15

-10

-5

0

5

1485 1490 1495 1500 1505 1510 1515 1520 1525Wavelength [nm]

P_ou

t [dB

m]

0 -10 -20

Figure 4.19 – Multiple-channel measurement of the Tellurite amplifier’s output power

In this configuration, a total output signal power of 8 dBm has been obtained under


33

saturation conditions over all λ’s, which are 20 to 50 nm apart from the gain peak. By considering the possibility of reducing total coupling losses to ~ 1.5 dB and decreasing the fibre non resonant loss of ~ 6 dB, a saturation power larger than 15 dBm can be foreseen. On the basis on the above results, it can be concluded that the LOBSTER Project has demonstrated the first practical operation of a TDTFA for the S-band. The measured peak level of net gain around 11 dB (close to 1480 nm wavelength) and further expected improvements of the active Tellurite fibre structure and of the overall amplifier’s set-up show the possibility of reaching net gain values up to 20 dB, with a net gain bandwidth of more than 80 nm, noise figures limited to 6 dB and saturation powers in excess of 15 dBm.

There are essentially four things to improve on the amplifier setup: (1) reduce the attenuation of the fibre; (2) remove light launched in the clad by using a higher index outer cladding or coating; (3) improve the integrity of the butt-splice by improving the launch, and (4) improving the quality of the fibre surface by polishing the faces. All fibre attenuation measurements previously described show the uncertainties from items (2) through (4).


34

2.1.5) WP5, Amplifier design and modelling The models for Thulium-Doped Tellurite Fiber Amplifiers (TDTFAs) and Erbium-Doped Tellurite Fiber Amplifiers (EDTFAs) have been improved in order to provide our partners with significant information on amplifier design. In particular, both forward and backward pumping schemes at multiple wavelengths have been implemented. Thus the models have been applied in order to identify the best pumping scheme in accordance with the available signal and pump laser sources. Finally modelling results have been compared with experimental ones giving a good agreement. TDTFA Model The energy level diagram of Tm3+ in tellurite glasses is reported in fig. 5.1 along with the simplified three-level model used for the simulations.

Figure 5.1 Thulium energy level diagram in tellurite glasses (left), three-level model for TDTFAs (right).

In the implemented model the first level is 3H6, that is the ground-state level. 3H5 and 3F4 are considered as only one level, such as the second one, because their energy difference is negligible. For the same reason the third level is formed by 3H4, 3F3 and 3F2. The Tm3+ ions can be excited from the ground-state level to the second level or to the third one. The ground-state absorption (GSA) is around 800 nm from the 3H6 level to the 3H4, while the transition from the first to the second level involves the wavelengths around 1050 nm and 1470 nm. In these two bands, excited-state absorption (ESA) from the second to the third level must be considered too. Around 1470 nm, such as in the signal S-band, there is stimulated emission between the levels 3H4 and 3F4, i.e. between the third and the second level (fig. 5.1). The stimulated emission around 800 nm, which regards the transition 3H4 → 3H6 (fig. 5.1), has been introduced in the model for the first time. The second level lifetime, 3 ms, is larger than the third level one, 0.3 ms. As it will be seen in the following, this characteristic has a negative influence on obtaining population inversion among levels 2 and 3, and rather complex pumping configurations are needed. The spontaneous emission from the third level (fig. 5.1) concerns the transitions 3H4 → 3H6 around 800 nm, 3H4 → 3F4 around 1470 nm and 3H4 → 3H5 around 2300 nm. The branching-ratio is 0.89, 0.08 and 0.03, respectively, so the last spontaneous transition has been neglected. In the TDTFA model the amplified spontaneous emission (ASE) is considered in the wavelength range between 1400 nm and 1550 nm. The GSA and stimulated emission cross-section values for the thulium-doped fibre have been experimentally measured by ORC. These measurements are quite critical to perform and sometimes only estimates can be obtained. There are still some uncertainties about the entity of the excited-state absorption (ESA), which is particularly difficult to measure.


35

TDTFA pumping schemes Single pumping at 1050 nm and at 795 nm have low efficiency due to the low value of the GSA cross-section around 1050 nm and the short lifetime of the 3H4 level, respectively.

Figure 5.2 Dual-pumping schemes for TDTFAs: 1047 nm + 1550 nm (left), 795 nm + 1064 nm (centre) and

795 nm + 1400 nm (right). Higher efficiencies can be obtained with dual-wavelength pumping-schemes, because one pump can be responsible for populating the upper level and the other for depopulating the long-lived lower level. A ground-state pump at 1550 nm can be added to the up-conversion one at 1047 nm or 1064 nm, in order to increase the number of excited Tm3+ ions from the 3H6 level to the 3F4 (fig. 5.2, left). As demonstrated for thulium-doped fluoride fibres [5.1,5.2], by increasing the 1550 nm pump power launched in the doped-fibre, the population inversion of the amplifying transition can be decreased and a shift of the gain spectrum toward longer wavelengths is obtained. A 795 nm ground-state pump can be used, instead of the 1550 nm one, to increase the efficiency of the up-conversion pump (fig. 5.2, centre) [5.3]. There is a positive interaction between the two pumps: while the 795 nm directly increases the 3H4 level population, the 1064 nm helps primarily in depopulating the 3F4 level by strong excited-state absorption to the 3F2 level, simultaneously populating the 3H4 level. Up-conversion pumping around 1050 nm suffers from excited-state absorption on the 3H4 level to the 1G4 upper one [5.1]. A new pump at 1400 nm can be more efficient than the up-conversion one if added to the ground-state pump at 795 nm (fig. 5.2, right) [5.4]: in fact, it causes the transition 3F4 → 3H4, in order to excite Tm3+ ions to the upper level. In order to understand which is the best dual-pumping scheme for TDTFAs, several simulations have been performed. To study the dual-pumping scheme at 1047 nm + 1550 nm (fig. 5.2, left), 200 mW pump power at 1047 nm, both co- and counter-propagating with respect to the signal, have been considered. The pump power at 1550 nm has been changed between 0 mW and 80 mW. It is possible to notice that the TDTFA behaviour improves if a low pump power at 1550 nm is added. In fact, with only the up-conversion pump at 1047 nm, the gain is 17.7 dB, while it reaches 26.2 dB adding 40 mW at 1550 nm. If the pump power at 1550 nm increases beyond 40 mW, the signal gain decreases. This is due to the negative influence of the emission cross-section at 1550 nm which must be considered in tellurite glasses, as the emission spectra is broader than in fluoride ones. As regards the second dual-pumping scheme at 795 nm + 1064 nm (fig. 5.2, centre), the ground-state pump at 795 nm is used instead of the 1550 nm one to improve the efficiency of the up-conversion process [5.5]. It is interesting to notice that a gain of 29.2 dB is obtained at 1480 nm with 100 mW pump power both at 795 nm and 1064 nm, while a maximum gain of 25.6 dB is achievable with 400 mW total power at 1047 nm and 40 mW at 1550 nm, as previously demonstrated. It


36

seems that the ground-state pump at 795 nm can more efficiently enhance the signal gain, since it increases the population inversion between the levels 3H4 and 3F4, but it does not take part in the amplifying process. As regards the noise figure, the dual-pumping scheme at 795 nm + 1064 nm has been proved better than the one at 1047 nm + 1550 nm: in fact, a noise figure lower than 3.5 dB has been calculated for all the signals between 1460 nm and 1530 nm. However, the efficiency of the up-conversion pump at 1064 nm is degraded by the excited-state absorption from the 3H4 level to the 1G4 level. In order to avoid this negative effect, the up-conversion pump at 1064 nm can be substituted by a new pump at 1400 nm (fig. 5.2, right). Simulations have been performed with the dual-pumping scheme at 795 nm + 1400 nm. The pump power is 100 mW at both 795 nm and 1400 nm, as in the previous case. The highest gain, 23 dB, is still reached at 1480 nm, but is 6 dB lower than the one calculated with the previous pumping scheme at 795 nm + 1064 nm. Also the noise performances of the TDTFA are worse if the second pump is at 1400 nm and not at 1064 nm. This low efficiency is due to the emission cross-section at the pump wavelength, which is about 40% of the ESA one at 1400 nm, while it is negligible around 1050 nm. A possible solution is represented by a lower pump wavelength, such as 1370 nm, because the absorption cross-section values are almost the same, while the emission cross-section is only 20% of the ESA one [5.6]. Experimental validation of numerical results Many simulations have been performed in order to compare model results with the experimental gain measurements. Experimental results obtained by ORC for a single-mode fiber with numerical aperture equal to 0.2 and core diameter 5 µm have been compared with the simulated ones. Background losses for the doped-fiber and coupling losses for both pump and signal have been considered to reproduce the experimental setup. As regard the 795 nm + 1064 nm dual pumping scheme, the pump power was 250 mW at 795 nm and 60 mW at 1064 nm, both pumps were co-propagating with the signal to amplify. Simulations have been made using the two ESA spectra in order to understand how the ESA cross-section values influence the TDTFA gain performances. The measured on-off gain values are lower than the calculated ones with both ESA spectra. The gain difference is not constant in the considered wavelength range and it is a little higher if one ESA set is used instead of the other. The not perfect matching of theoretical and experimental results is probably due to the coupling losses, which can be underestimated, and/or to the background losses, which are considered constant in all the wavelength range studied, even if they have been measured only at 1400 nm. Moreover, the ESA cross-section value for the up-conversion pump at 1064 nm was not measured, but calculated, so its role can be questionable. A second up-conversion counter-propagating pump at 1047 nm was added to the ones used in the previous dual-pumping scheme. The power values considered for the simulations were 3 dB lower than the ones used for the experimental measurements, since coupling losses were taken into account. 250 mW pump power at 1047 nm is added to 150 mW at 795 nm and 60 mW at 1064 nm. The doped-fibre and signal characteristics were the same as in the previous case. The on-off gain values experimentally measured with this three pumping scheme were a little higher than those obtained with the dual-pumping scheme, in fact the maximum value was about 7.5 dB at 1485 nm.


37

It seems it was better to use a higher pump power at 795 nm and a lower one at 1047 nm or 1064 nm: in fact, almost the same on-off gain was obtained with 250 mW at 795 nm and 60 mW at 1064 nm, as well as with 150 mW at 795 nm and 310 mW total up-conversion pump power, at both 1047 nm and 1064 nm. The simulated on-off gain spectra were calculated with ESA 1 and ESA 2 and they are reported in fig. 5.3. In this case the results are not significantly influenced by the ESA cross-section values, because the difference is low, about 1 dB, at 1460 nm and decreases for higher signal wavelengths. The theoretical on-off gain values were higher than the measured ones, but the agreement was better than in the previous dual-pumping scheme: in particular, in this case the gain was overestimated at higher signal wavelengths.

Figure 5.3. On-off gain spectra obtained with ESA 1 and ESA 2

with three pumps at 795 nm, 1047 nm and 1064 nm. Also a single-mode fiber with high numerical aperture, that is 0.4, has been realized by ORC. Simulations have been performed for this doped-fiber with the pumping scheme at 795 nm + 1047 nm + 1064 nm. Results have shown that higher on-off gain values can be obtained with a higher NA tellurite Tm3+-ions doped fiber in agreement with experimental results. EDTFA Model A completely new EDTFA model has been implemented in order to describe a new pumping scheme at 980 nm with an auxiliary signal at 850 nm. The 1480 nm pump model has been usefully compared with experimental results. In order to model the experimentally observed green emission, an effective pump power has been introduced. Pumping scheme at 980 nm

A new pumping scheme was suggested by TTC in order to study if it was possible to reduce the experimentally observed green emission. The pump was at 980 nm and an auxiliary signal at 850 nm was used. A fibre with the following characteristics was simulated: NA 0.21, core radius 2.3 µm, doped area radius 2.3 µm, Er3+concentration 9.67 1025 ions/m3, fiber length 0.4 m. The 980 nm forward pump power was 100 mW. The GSA and ESA cross-sections at 980 nm


38

were 4.48 10-25 m2 and 6.8 10-25 m2, respectively. The 850-nm auxiliary signal power was -10 dBm. Only one signal at 1550 nm with –30 dBm power was considered in order to test the usefulness of the present pumping scheme. Model results allowed to conclude that this new pumping scheme was not efficient in order to eliminate green emission since the auxiliary signal was absorbed instead of amplified, causing an increase of the population of the green emission responsible level. Comparison between numerical and experimental results

In order to compare experimental results obtained by TILAB with numerical ones, a model with forward and backward pumping scheme was used. The pumping wavelength is 1480 nm, so that the three level model described in the deliverable LOBSTER_D9 was applied. Notice that the model takes into account both signal ESA and background losses. The calculated gain is about 7 dB higher than the measured one. This difference could be ascribed to the green emission, which was experimentally noticed but not considered in the model. In order to take into account of the green emission in the model two solutions have been followed. The first solution implies to reduce the 1480 nm pump power effectively used by the amplifier. The second one is quite more complex. It requires to suppose the existence of ESA phenomena at 1480 nm. This effect is described in the model by means of an ESA cross-section σESA at 1480 nm. In particular the σESA (@1480 nm) can be used as a fit parameter. As regards the first solution, it was found that the pump power value, which gives the better agreement with experimental results, was 42 mW. The corresponding gain spectra for different channel powers are reported in fig. 5.4. Numerical results are in good agreement with experimental ones, but there are still some differences in the gain spectra. For example, by considering the – 20 dBm/ch curve, the calculated gain of the channel number 1 (1539.77 nm) is 15.6 dB while the experimental one is about 14 dB. On the other hand, if one considers the channels at 1558.03 nm and 1604.03 nm, the simulation results are 25 dB and 7.2 dB, while the experimental values are 23 dB and 8 dB respectively. In conclusion, the difference between experimental and numerical results is greater for the peak channel and it is lower for the first and last channels. Similar remarks hold for all the other curves obtained with others signal channel powers. As regards the second solution suggested in order to describe the green emission, the gain spectra in function of the ESA cross section σESA (@1480 nm) is reported in fig. 5.5. The input channel power is –20 dBm/ch. As expected by raising the σESA (@1480 nm) value, the gain reduces. Moreover the σESA (@1480 nm) strongly affects the gain spectrum. In particular the gain of the first three channels is too high respect to experimental results. By considering the peak gain value as reference, the σESA (@1480 nm) value equal to 2 10 -26 m2 seems to best fit the experimental results. The gain differences ∆G between numerical and experimental results are reported in Table 5.1. Conclusions Several models for TDTFAs and EDTFAs have been developed. The models have been applied in order to identify the better pumping scheme, in accordance with the available signal and pump laser sources, and the optimum fiber length.


39

Finally, the model results have been compared with the experimental ones. The agreement between numerical and experimental values is quite good, some minor discrepancies are probably due to the losses, which can be underestimated.

-5

0

5

10

15

20

25

30

35

1520 1540 1560 1580 1600 1620

Wavelength (nm)

Gai

n (d

B)

-10 dBm/ c h

-15 dBm/ c h

-20 dBm/ c h

-25 dBm/ c h

-30 dBm/ c h

Figure 5.4 Gain spectra obtained with 42 mW forward and backward pump power.

-5

0

5

10

15

20

25

30

35

40

1530 1540 1550 1560 1570 1580 1590 1600 1610

Wavelength (nm)

Gai

n (d

B)

0 m^2

1.30E-26 m^2

2.0E-26 m^2

2.5E-26 m^2

Figure 5.5 Different gain spectra in function of the 1480 nm ESA cross section �ESA . The value 2·10 -26 m2

best fits the experimental results.

Table 5.1 Differences between calculated gain and experimental measured gain (from TILAB). The ESA cross section σESA(@1480nm) was 2.0·10 -26 m2.

Channel λ (nm) Calculated gain (dB)

Exp. gain (dB)

∆G (dB)

1 1539.77 22.2 14 8.2 2 1542.94 20.9 16 4.9 3 1546.12 19.1 16.2 2.9 4 1549.31 18.7 17 1.7 5 1552.52 20.6 19 1.6 6 1555.75 22.2 22 0.2 7 1558.03 21.7 23 -1.3

10 1583.69 5.2 9.3 -4.1 12 1590.41 4.2 9 -4.8 14 1597.19 3.5 8.3 -4.8 16 1604.03 2.2 8 -5.8


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References [5.1] F. Roy, D. Bayart, A. Le Sauze and P. Baniel, ``Noise and Gain Band Management of Thulium- Doped Fiber Amplifier with Dual-Wavelength Pumping Scheme'', IEEE Phot. Tech. Lett. 13, 788-790 (2001). [5.2] F. Roy, ``Recent advances in thulium-doped fiber amplifiers'', in Tech. Dig. OFC'02, paper ThZ1 (2002). [5.3] A.S.L. Gomes, M.T. Carvalho, M.L. Sundheimer, C.J.A. Bastos-Filho, J.F. Martins-Filho, M.B. Costa e Silva, J.P. von der Weid and W. Margulis, ``Characterization of Efficient Dual-Wavelength (1050 + 800 nm) Pumping Scheme for Thulium-Doped Fiber Amplifiers'', IEEE Phot. Tech. Lett. 15, 200-202 (2003). [5.4] F. Roy, A. Le Sauze, P. Baniel, D. Bayart, ``0.8-µm+1.4-µm pumping for gain-shifted TDFA with power conversion efficiency exceeding 50%'', in Tech. Dig. OAA'01, 24-26 (2001). [5.5] A. Cucinotta, F. Poli, S. Selleri, “Gain characteristics of thulium-doped tellurite fiber amplifiers by dual-wavelength (800nm + 1064 nm) pumping”, in Tech. Dig. OFC2003, FB1, [5.6] A. Cucinotta, F. Poli, S. Selleri, “Dual-pumping schemes for efficient Thulium-doped tellurite fiber amplifiers”, ECOC2003


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2.2) Cost Breakdown 2.2.1) Deliverables, plan/actual/status Del. no.

Deliverable name WP no.

Lead participant

Deliverable type // Security

Delivery (planned month)

Delivery (actual month)

D1 Amplifier specifications and design study (I)

2 TILab Report // IST 3 4

D2 Project presentation 1 OTC Report // Pub. 6 7

D3 Dissemination and Use 1 OTC Report // Pub. 6 9

D4 Spectroscopy of Er3+ in tellurite glasses 3 OTC Report // IST 12 13

D5 Spectroscopy of Tm3+ in tellurite glasses 4 ORC Report // IST 12 13

D6 Annual progress report (1st year) 1 OTC Report // FP5 12 14

D7 Core/clad glass formulations and preform realisation for the Er3+-doped tellurite amplifier

3 OSI Demonstration & Report // Int.

18 20

D8 Core/clad glass formulations and preform realisation for the Tm3+-doped tellurite amplifier

4 OSI Demonstration & Report // Int.

18 20

D9 Modelling of Er3+ and Tm3+-doped tellurite fibre amplifiers

5 CNIT Report // IST 18 20

D10 Amplifier specifications and design study (II)


D11 Annual progress report (2nd year) 1 TTC Report // FP5 24 28

D12 Fibre drawing and characterisation of the Er3+-doped tellurite fibre

3 TTC Demonstration & Report // Int.

27 32

D13 Fibre drawing and characterisation of the Tm3+-doped tellurite fibre

4 ORC Demonstration & Report // Int.

27 32

D14 EDTF-amplifier assembly 3 TILab Demonstration & Report

36 40

D15 TDTF-amplifier assembly 4 ORC Demonstration & Report // Int.

36 40

D16 Test-bed arrangement and validation tests


D17 Validation modelling through theoretical/ experimental comparison

5 CNIT Report // IST 38 38

D18 Device performance 2 TILab Demonstration & Report

40 40

D19 Annual progress report (3rd year) 1 TTC Report // Pub. 40 40

D20 Final report 1 TTC Report // Pub. 40 40

D21 Technology Implementation Plan 1 TTC Report // Pub. 40 40

D22 Applicability of ultra-wide fibre amplification to intelligent optical transport networks

2 TILab Report // Pub. 40 40

Due deliverables of the second year are highlighted by bold characters.


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2.3) Deliverable abstracts D12 Fibre drawing and characterisation of the Er3+-doped tellurite fibre, Abstract: Two methods are presented by which Er3+-doped tellurite single-mode fibres (EDTF) have been fabricated. By one of the methods, a combination of melt casting/ rod-in-tube drawing, preliminary gain measurements on EDTF provide a maximum net gain of 13 dB @ λ=1555 nm. The fibres are also discussed in terms of their geometry and mechanical strength. D13 Fabrication of Tm3+-doped tellurite fiber for 1470 nm Fibre Amplifier Abstract: Fiber fabrication and loss measurements are presented for thulium-doped tellurite fibers. Lowest background loss achieved ~1dB/m by improved built-in-casting method with a tilted mould arrangement. Results agree with that obtained from rotational casting and also that of TZC. Although rotational casting can produce rods with no air bubbles, the improved built-in-casting method is preferred due to low cost and is easy to make. The loss is reduced by a factor of 5 from 5dB/m to 1dB/m. Another method of casting, which we have investigated is extrusion which has shown considerable improvement by using a slower extrusion rate to reduce the loss down from 23dB/m to 3dB/m. D14 EDTF-amplifier assembly Abstract: The activities relevant for the Erbium-Doped Tellurite Fibre Amplifier assembly are discussed in detail. Several schemes for the amplifier set-up have been considered. Starting from the NT93 active fibre issued within the Consortium, an amplifier module has been built and its characterisation accomplished. Further investigations have been conducted, to realise a device based over this module, able to meet all specifications originally required. D15 TDTF-amplifier assembly Abstract::The report describes the test-bed deployment and the set of validation tests envisaged to assess the performance of the LOBSTER triple-band amplifier, in a multi-wavelength scenery, including 4 transmitters in the S-band, 8 transmitters in the C-band and 8 transmitters in the L-band. Each transmitter can be modulated up to 10 Gbit/s. A long-haul link is realised using two spans of single-mode fibres of different types and tuneable optical receivers, in order to test the amplifier in a realistic DWDM environment by means of BER measurements at bit rates up to 10 Gbit/s. To evaluate the impact of non-linear effects in the amplifier, a tuneable laser will be added to the DWDM comb at very narrow spacing, down to 20 GHz.


43

D16 Test-bed arrangement and validation tests Abstract: The report describes the test-bed deployment and the set of validation tests envisaged to assess the performance of the LOBSTER triple-band amplifier, in a multi-wavelength scenery, including 4 transmitters in the S-band, 8 transmitters in the C-band and 8 transmitters in the L-band. Each transmitter can be modulated up to 10 Gbit/s. A long-haul link is realised using two spans of single-mode fibres of different types and tuneable optical receivers, in order to test the amplifier in a realistic DWDM environment by means of BER measurements at bit rates up to 10 Gbit/s. To evaluate the impact of non-linear effects in the amplifier, a tuneable laser will be added to the DWDM comb at very narrow spacing, down to 20 GHz. D17 Validation Modelling – Theory and Experiments Abstract: Several models for Thulium-Doped Tellurite Fiber Amplifiers (TDTFAs) and Erbium-Doped Tellurite Fiber Amplifiers have been developed. In particular both forward and backward pumping schemes have been implemented. The models have been applied in order to identify the best pumping scheme in accordance with the available signal and pump laser sources. The model results have been compared with the experimental ones. D18 Device performance Abstract: The report describes the results of the validation tests envisaged to assess the performance of the LOBSTER triple-band amplifier in a multi-wavelength scenery. The test-bed has been presented in deliverable IST-1999-13322/TILAB/LOBSTER_D16. This document represents the technical conclusion of LOBSTER Project activity. It has been made possible by the convergence of a set of skills and expertise: from scientific and technological competence in the identification and realisation of bulk glass samples, to the process and technology expertise in preparing preforms and drawing active fibres, to skills in the design, modelling and integration of optical amplifiers for advanced network applications, to experience in analysing, considering and foreseeing applications for next generation intelligent optical networks. The Consortium thought is that the challenging program started three years ago, has been managed and carried out efficiently, and has been led to a satisfying conclusion. D19 Annual Progress Report (3rd year). Reporting period: 01/01/2002 - 30/04/2003 Abstract: The Annual Progress Reports provides a comprehensive account of the progress made on the project during the reporting period and gives information about technical progress, specific results and resources employed. D20 Final Report


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D21 Technology Implementation Plan D22 Applicability of ultra-wide fibre amplification to intelligent optical transport networks Abstract : The purpose of the present deliverable is to identify potential links between the technologically oriented activity of the IST LOBSTER Project and network-oriented investigations, like the work done in the frame of the IST LION Project. In the following, the impact of ultra-wide bandwidth optical amplifiers on the transport networks of the next generation (i.e. Automatically Switched Optical Networks / Generalised Multi-Protocol Label Switching, or, in short: ASON/GMPLS) will be analysed. These networks make use of a control plane and a set of protocols (e.g.: RSVP-TE, OSPF-TE, LMP, etc.) to provision automatically label-switched paths (e.g.: light-paths), in response to client requests. Particular attention will be devoted to the influence of ultra-wide band optical amplifiers, with respect to band availability, gain dynamics and spectral uniformity, power and noise levels, non-linear effects and transmission constraints, on ASON/GMPLS schemes and performance.


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2.4) Publications and patents Papers 795 NM AND 1064 NM DUAL PUMP THULIUM-DOPED TELLURITE FIBRE FOR S-BAND AMPLIFICATION L.N.Ng, E.R.Taylor, J.Nilsson Electronics Letters 2002 Vol.38(21) pp.1246-7 SPECTROSCOPY OF TM3+-DOPED TELLURITE GLASSES FOR 1470 NM FIBRE AMPLIFIER E.R.Taylor, L..N.Ng, N.P.Sessions, H.Buerger Journal of Applied Physics 2002 Vol.92 pp.112-17 National Conferences FIBRE TELLURATE PER AMPLIFICATORI OTTICI A BANDA ULTRA - ESTESA: REALIZZAZIONE DELL’AMPLIFICATORE IN BANDA C + L R. Caponi, A. Pagano, A. Percelsi, M. Potenza, B. Sordo (TILAB), J. Kraus, C. Bruschi, E. Chierici, L. Cognolato, E. Emelli, R. Maggio (Agilent TTC) Proc. Fotonica'03 Conference, Riva del Garda (Italy), 7-9 Apr. 2003, p.119 AMPLIFICATORI OTTICI IN FIBRA DROGATA CON TULIO PER AMPLIFICAZIONE IN BANDA S A. Cucinotta, M. Fuochi, F. Poli, S. Selleri Proc. Fotonica'03 Conference, Riva del Garda (Italy), 7-9 Apr. 2003, p.115 AMPLIFICATORI OTTICI IN FIBRA DROGATA CON TULIO A. Cucinotta, M. Fuochi, N. Tosi, S. Selleri, XIV Riunione Nazionale di Elettromagnetismo, 16-19 Sept. 2002, Ancona. TM3+ DOPED TELLURITE GLASS FOR S BAND AMPLIFIERS L.N.Ng, N.P.Sessions, J.Nilsson, W.S.Brocklesby, E.R.Taylor Rank Prize Symposium Grasmere 18-21 Jun 2001 International conferences BONDING STRENGTH AND FRACTOGRAPHIC ANALYSIS OF ZINC TELLURITE GLASS MODIFIED OPTICAL FIBRES, J. Kraus, C. Bruschi, E. Chierici, H. Buerger, I. Gugov Photonics West 2002, S. José, USA, Jan. 2002; Proc. SPIE Vol 4639 2002) p. 30 THULIUM-DOPED TELLURITE FIBER FOR S-BAND AMPLIFICATION L.N.Ng, E.R.Taylor, N.P.Sessions, R.C.Moore ECOC 2002 Copenhagen 8-12 Sep 2002; Paper 2.2.3 GAIN CHARACTERISTICS OF THULIUM-DOPED TELLURITE FIBER BY DUAL-WAVELENGTH (800 nm + 1064 nm) PUMPING A. Cucinotta, F. Poli, S. Selleri, Optical Fiber Communications Conference - OFC2003, Paper FB1, 23-28 March 2003, Atlanta, Georgia. NEARLY 10 dB NET GAIN FROM A THULIUM-DOPED TELLURITE FIBRE AMPLIFIER OVER THE S-BAND R. Caponi, A. Pagano, M. Potenza, B. Sordo (Telecom Italia Lab, Telecom Italia), E. M. Taylor, L. N. Ng, J. Nilsson (Optoelectronics Research Centre, University of Southampton), F. Poli (Dipartimento di Ingegneria dell'Informazione, Università di Parma); Paper accepted for oral presentation to ECOC/IOOC 2003, Rimini, September 21 - 25, 2003.


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DUAL-PUMPING SCHEMES FOR EFFICIENT THULIUM-DOPED TELLURITE FIBER AMPLIFIERS A. Cucinotta, F. Poli, S. Selleri, Paper accepted at ECOC2003, 21-25 Sepember 2003, Rimini, Italy. Patent application: US Patent Application No 10/172,375 “Tellurite glass and applications thereof” Inventors: E R Taylor, L N Ng, N Sessions, R Moore

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