Application and study of Multifunctional Semiconductor Optical Amplifier in

SubCarrier Multiplexed Optical Networks

PhD Thesis

Gerhátné Udvary Eszter

Supervisor: Prof. Berceli Tibor

Budapest University of Technology and Economics

Department of Broadband Infocommunications and Electromagnetic Theory 2009, Budapest

Introduction

Design and build of compound optical circuit consisting of several functionalities are difficult and complex. It is made to be simpler applying multifunctional devices, when device replaces numerous special elements. Multifunctionality in optical communication systems will decrease complexity, reduce fabrication, installation and maintenance cost, minimize the size, enhance the reliability and allow systems to work simultaneously with tolerable parameters. However we have to make a compromise, the specialized devices have higher level operation parameters than multifunctional device. The degradation of characteristic has to be minimized; hence the study of potential multifunctional devices is very important. The semiconductor optical amplifiers (SOAs) are very attractive sources for optical communication systems for their capability to be multifunctional devices. The SOAs have demonstrated their multifunctional capability by combining amplification with either modulation, gating, intensity detection, dispersion compensation, wavelength conversion, optical regeneration, etc. It demands more advanced system and device working state planning. It is a complex problem, because there is no one parameter, which guarantees the best trade-off between the different competitive aspects.

Research goals

The aim of this dissertation is to present my research results in the field of optical communication system applying multifunctional SOAs. The motivation of this work was the detailed investigation on extra function of SOAs. I summarized my results in three thesis groups. The first point covers studies what kind of extra functions can be realized by SOA in Subcarrier Multiplexed systems. I investigated in details the most important functions of multifunctional SOAs. So, the second and third thesis groups are concerned with the modulation function and detection function, respectively. I submitted a “black box” and a rate equation model, examined the efficiency, noise and linearity behavior.

Tentative and analysis method used in the dissertation

• Investigation on linear and nonlinear circuits • Optical device modeling, computer aided optical network analysis • Optical system modeling, design and evaluation. • Literature exploration in library, electrical database (IEEE Explore, Google

Scholar, Scopus, etc.) • computer aided measurement control, data processing and visualization • low and high frequency electrical and optical measurement techniques

New results

Thesis group1.: Optical networks applying multifunctional SOAs

The transmission of optical signals in an optical communication system using standard single mode optical fiber near 1550nm may be limited by optical effects. This bandwidth limitation mainly is caused by the radio-frequency (RF) carrier suppression effect due to dispersion-induced sideband cancellations at certain combinations of microwave frequencies and propagation distances. I made theoretical and experimental investigations of dispersion in optical systems. Based on these results I suggested a SOA based dispersion compensator. Measurements of SOA chirp parameter (LEF) can are found in the literature and have shown that LEF is not a mere constant factor, but it is for instance a function of bias current, wavelength and input optical power. During the calculation I took into account that LEF is negative for saturated SOAs. When the input power becomes larger than the saturation value, the chirp parameter rapidly falls to a negative value. The negative chirp affects both sidebands and then causes the asymmetrical optical power between sidebands and the RF carrier suppression effect is reduced. The optical amplification causes RF signal gain, but the SOA adds significant noise to the system. I have investigated with simulation and measurement how SOA dispersion compensator affects the level of harmonics.

T I/1 Thesis: I have explaind the frequency transfer function between the intensity modulations at the input and output. Based on my calculation I realized the frequency notches caused by the dispersion-induced carrier suppression effect may be sharply alleviated and the performance of the transmitted digital signal can be improved. Using SOA the link length or RF bandwidth is improved. I validated the theoretical result by optical simulation and measurements. Measurement results show, that parameter optimisation can be realised by optical power and bias current, too. [S-7][S-11][S-13]

I confirmed by simulation and measurement, that the SOA modifies the harmonic generation, too. The frequencies of second order harmonic rejections are shifted. The rejections of third order harmonic are eliminated. [S-8][S-9][S-21][S-41]

Investigation of SOA based dispersion compensator and novel network topology applying SOA-detector and/or SOA-modulator

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Szálhossz=50kmHullámhossz=1550nm Referencia szálhossz=4m

In the second part of the chapter I demonstrate novel optical system and topology using multifunctional SOA (SOA-modulator and/or detector). I have explained in detail the systems with high requirements concerning the electrical bandwidth, modulation or detection efficiency, noise, linearity. Two methods have been proposed and are currently under investigation for coding the optical label; the serial label (SL) and the optical subcarrier multiplexed label (SCML) techniques. In the SCM approach, a baseband digital label is modulated onto a RF subcarrier and then multiplexed (electronically or optically) with the packet on the same wavelength. It has the advantage that subcarrier labels allow for simplified label detection and processing, it can be removed and replaced more asynchronously than in the serial case. Furthermore, the subcarrier label can be directly extracted in the optical domain by the use of optical filtering techniques keeping the data payload intact. Three key functions are required in the nodes: label swapping, wavelength conversion and all-optical regeneration. I analyzed how the three functions can be achieved by SOA.

Radio-over-Fibre (RoF) technology provides a solution to the demands for a wireless connection to the costumer („last or first mile problem“). It entails the use of optical fibre links to distribute RF signals from a central location to Remote Antenna Units (RAUs). It combines the wireless and optical communications. It has low and frequency independent attenuation loss, large bandwidth, immunity to radio frequency interference, easy installation and maintenance, multi-operator and multi-service operation, and dynamic resource allocation. It can be applied in cellular system, satellite communication, video distribution approaches, etc. RoF applies SCM technique. I investigated the branching function in pure SCM systems.

T.I/2.Thesis: I developed optical subcarrier multiplexed label swapping/reinsertion utilizing SOA-modulator associated to the cross-phase modulation (XPM) performed in an active Mach-Zehnder interferometer wavelength converter block in packet switched all optical networks. I have profed by simulations that the SOA in the branches of the wavelength converter can add the label with same properties. Namely, the added subcarrier has same properties and after label detection the eye diagram and the bit error ration (BER) of the label will be same in case of the two different modulation places. The same modulation in both branches is not effective because of the interferometer operation. However the push-pull electrode concept is possible and it has the same advantages such as in MZ modulators. [S-3][S-19][S-20]

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The RoF can be combined with WDM techniques when every RAU uses own optical carrier. It provides large capacity, enhanced network security, protocol transparency and upgradeability. Hence it may be used in the future wide bandwidth access networks. However the WDM components have relative high cost. The future metro and access networks demand high capacity, therefore wavelength division multiplexed passive optical networks (WDM-PON) may be applied, where every subscriber has own wavelengths. It is made to be simpler applying same wavelength for uplink and downlink. The separation can be performed by time domain or frequency domain multiplexing. The subcarrier multiplexing (or combined baseband and subcarrier multiplexing) provides duplex communication. However it requires microwave (or millimeterwave) oscillator in every user unit, and the capacity is limited by the chromatic dispersion. The system concept is similar to the RoF system, but the information is used in the baseband, therefore it has to be downconvert from the subcarrier. The multifunctional SOA is well used in WDM-PON, it eliminates the additional expensive optical devices (external modulator, EDFA, etc.).

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T I/3 Thesis: I proved that the multifunctional device is well used for add/drop function in pure SCM system. The device amplifies the incomming weak optical signal, add a new channel as a modulator and drop the required channel. It realises small size, compact, low cost radio repeater. This application demand high level requirements from the SOA (signal-to-noise ratio, electrical bandwidth, linearity) [S-18][S-22][S-30][S-32]

In case of high input optical power the SOA works in saturated region, as a result the difference between the two output power levels is considerably reduced in the SOA output. Hence the downstream information is erased, the same optical carrier is reused for upstream. The system concept is complicate and relatively expensive. The data rewriter is composed of a linear optical amplifier, deeply saturated SOA, optical couplers, detector, and external modulator. I have suggested simplified structures. The same time I modulate the lightwave by modulating the SOA injection current with the upstream. However the saturated SOA has low modulation efficiency, it can’t be applied in SCM system, but it is powerful in baseband concept.

T I/4 Thesis: I recognized and certified, that the SOA is well used as a compact, low cost transceiver in RoF or WDM-PON approaches. The concept is similar to the application of EAT. The SOA detects the downstream information from the first optical carrier. It add the upstream to the second (continous wave) optical carrier provided by the central station. It is made to be simpler applying same wavelength for uplink and downlink. In this case the SOA add a new, modulated subcarrier to the common optical carrier. [S-18][S-25][S-26][S-44]

Thesis group 2. SOA-modulator

Compared with the Mach-Zehnder modulator, the SOA-modulator is a semiconductor based, lossless, fast, small size, low cost device, which requires low modulation power. However the SOA has remarkable optical noise and it demands more advanced amplifier-modulator working state planning. The main problem, that the datasheet does not inform us about the extra functions of the SOA. The description of operation desires more details. Accordingly, I have developed a model, which can calculate the expected characteristics of the multifunctional SOA, based on the datasheet parameters. The detected electrical power (Pdet) and the modulation depth can be calculated.

SOA

detmod

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det Z

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s

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∆⋅=

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R: Responsivity, a: optical loss between the SOA-modulator and the detector, sd: slope of optical gain curve, Pmod: modulation electrical power, Zdet and ZSOA: microwave impedance of detector and SOA, G0: optical gain, ∆I and ∆G: the modulation amplitude of current and gain I have take into account that the optical gain and the slope of optical gain curve depend on system and device parameters (temperature, wavelength, bias current, saturation, etc.). Additionally, I calculated with the effect of amplified spontaneous emission modulation in case of low optical power and large optical bandwidth.

However the “black box” model can’t describe every effect. I have developed a rate equation model. I have to take into account the longitudinal variation of the parameters. To solve that case I divided the active region into a large number of short sections. It means a quasi ideal situation: constant carrier density along the active region of the section. I have solved the differential equations and the photon density, the carrier density, the optical power, the gain and the modulation can be calculated one after the other. Based on this calculation I realized the summarized modulation content.

T II/1 Thesis: Considering small signal modulation, based on datasheet information I have developed the „black box” model of the modulation function. The modell calculates the realized modulation depth and the detected electrical power (detection by PIN). I validated the calculation with experimental work, and I showed the temperature dependence by measurement. [S-3][S-14][S-20][S-32][S-44][S-45]

Theoretical (two models) and experimental investigation of SOA-modulator (modulation efficiency, signal, noise, speed, linearity, chirp).

The modulation bandwidth depends on the device length, the mismatch between the velocity of microwave and optical signal, the applied electrode type, etc. In the experimental work I established, that the bandwidth is limited by the electrical parasitics. The optical output from an optical amplifier is composed of an amplified optical signal and an amplified spontaneous emission (ASE) with broad spectral width. Moreover interference is created between ASE components and light signal. So several types of noises (the shot noise belonging to signal and spontaneous emissions, beat noise between signal and spontaneous emissions, beat noise between spontaneous emission components, thermal noise of the receiver and excess noise belonging to incoherence of the input signal) can be observed, when the output photons are detected by a photodetector. I realized that the different noise components depend on the system and device parameters with different aspect. The signal is inverse proportional with the square of optical loss. In case of low loss one of the beat noises will dominate, which is square proportional with optical power, hence the SNR is constant. Increasing the optical loss, one of the shot noises has the highest level, it is proportional with the optical power, and the SNR decreases. Finally the constant thermal noise limit the system, the SNR rapidly decreases. I observed similar results in case of constant input optical power as a function of the SOA’s operation point, when the different noise components depend on the optical gain with different method. In the first range the constant thermal noise has highest level. As the gain operation starts and the optical power increases, the shot noise overcomes the thermal noise limit. In the third range the beat noises give the dominating contribution.

I investigated the nonlinear behavior of SOA-modulator. Cascading several linear SOAs a new problem arises, an increase in the distortion due to cross-modulation of the different channels. The variation of the bias current of the SOA-modulators results in the variation of the gain and that means a

T II/2 Thesis: I investigated the effect of wide band optical noise in the electrical regime and I compared with the noise of other external modulators. I have declared three diferent dominant noise ranges as a function of optical loss and optical gain by calculation. [S-17][S-31][S-34]

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multiplication function generating new modulation products which present distortion. The difference and sum frequency components are eliminated by filtering because they are out of the transmission band. The third order components are multiplied by the 3 modulation indices. The modulation indices are usually less than 0.1, these components are at least two orders of magnitude smaller than the useful modulation product. The rate equation model can take into account the detailed nonlinear carrier recombination rate. Based on this model I explained the level of harmonics, the optimal operation point and the frequency dependence. I considered the saturation effect, which affects the optical gain curve.

Based on my calculation results I concluded that the mismatch between the velocity of the traveling microwave signal and optical signal leads to dips in the modulation response and reduces the modulation bandwidth. I studied by experimentally the linearity versus bias point, optical reflection, temperature. Increasing the bias current, first the gain of the device increases, hence the IP3 and the SFDR improve. In the second part the optical gain doesn’t change significantly but the noise level rises, hence the SFDR decreases. Finally, the intermodulation products also start rise and the degradation of the SFDR is faster. The noise effect and the nonlinear distortion products are more significant in case of strong optical reflection level, i.e. without optical isolators. Based on my results I concluded that the SOA-modulator ensures efficient SFDR for the SCM optical communications.

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T II/3 Thesis: I have proofed by simulation that the SOA-modulator has higher linearity when the saturation is occurred. In the saturated regime the modulation efficiency decreases, but the operation is more linear. [S-15][S-16][S-17]

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When the pump current of the laser amplifier is modulated, the optical gain is affected in both magnitude and phase via the modulation of the complex refractive index caused by the electron density. Consequently, in SOA the optical signal becomes amplitude modulated (AM) and phase modulated (PM) caused by carrier density change. It can be modeled using the linewidth Enhancement Factor (LEF=Henry factor=α factor) approximation. Measurements of LEF can are found in the literature and have shown that LEF is not a mere constant factor, but it is for instance a function of bias current, wavelength and input optical power. The chirping parameter which is positive for light sources and unsaturated optical amplifiers is negative for saturated amplifiers. Based on these results I developed that the modulation of the laser amplifier can also be made in such a way that, the PM response is suppressed. Beside frequency modulation, however, this method does also reduce the amplitude of intensity modulation of the SOA. Thus, near-pure AM can be obtained.

T II/4 Thesis: I have determined and valiated by experimental work, that the system will be more instable in case of strong optical reflection, and larger SFDR degradation can be observed. The change of the SFDR is caused by two different effects. First the noise level of the device increases as a function of the bias point, the degradation is more significant without optical isolator. On the other hand the level of the nonlinear product will fluctuate in case of strong optical reflection. [S-2][S-6][S-15][S-42]

Thesis group 3. SOA-detector

The optical detector is characterized by the responsivity, the sensitivity, the noise, the frequency response (the bandwidth), the wavelength dependence, the linearity, the size, the required electrical power, etc. I have developed a model, which can calculate the expected detection characteristics of the multifunctional SOA, based on the datasheet parameters. I have estimated the static characteristics and responsivity from the unsaturated optical gain and input optical power, supposing the adequate bias current and temperature. I have investigated the responsivity dependence on temperature, optical power (saturation effect), bias current. Considering small signal modulation I expressed the detected electrical power versus system and device parameters.

Z2

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in

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DCSOAdet

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PDC: optical power, ain: optical loss before the SOA-detector, IDC: bias current, ∆IdetSOA: amplitude of the detected cosinusoidal signal, Z: microwave impedance of the SOA, R: Responsivity of SOA-detector, m: modulation depth. The detected electrical power depends on the microwave impedance of SOA, it is square proportional with the modulation depth, the input optical power and the responsivity. I considered by experimental work that the responsivity depends on the temperature, the bias current, the optical gain, and the optical reflections. The result of the detection experiment over input optical power is divided into two sections. In the unsaturated regime the detected electrical signal is square proportional to the optical power, but in the saturation regime the responsivity start to decrease and the relation goes to linear proportionality. Above transparency, when the bias current increases, i.e. the population inversion and the gain are higher the detected power increases. The diagram follows the shape of the optical gain curve. The decrease of the responsivity for high currents is mainly due to leakage effects since the voltage transfer function from the active region to the output electrode reduces for increasing total detector current because of the lowering of the dynamic impedance of the parallel leakage diode.

Theoretical (two models) and experimental investigation of SOA-detector (responsivity, noise, signal, speed, linearity).

T III/1 Thesis: Considering small signal modulation, based on datasheet information I have developed the „black box” model of detection function. The modell calculates the detected electrical power. I validated the calculation with experimental work, and I showed the temperature dependence and the leakage effect by measurement. [S-22][S-25][S-32][S-32][S-44]

However the “black box” model can’t describe every effect. I have developed a rate equation model, where I have to take into account the longitudinal variation of the parameters. I divided the active region into a large number of short sections calculating with constant carrier density along the active region of the section. I have solved the differential equations and the photon density, the carrier density. By means of the model the calculation of the responsivity, bandwidth and length effect was facilitated. In the unsaturated regime the transmitted optical signal and the detected electrical power rise along the device. The optical gain is constant, the detected current is proportional with the input optical power. However in the saturated regime the gain coefficient decreases along the device, and the detected electrical signal has lower level. The trait of the detected electrical signal follows the optical power curve. It is of interest to determine the magnitude of each contribution to the total noise in order to see which component dominates at different system parameters. The noise generated by a SOA acting as a detector is different from the noise generated by a SOA acting as an amplifier or modulator. There are several similar contributions to the total noise power at electrical connection of SOA-detector. However interference between ASE components and light signal is created inside the SOA device. So the noise components originating from the light amplification depend on input parameters as wavelength, input power or driving current with different aspect, than in case of other applications. The different noise components depend on the optical signal level with different aspect. The thermal noise, the spontaneous shot noise and the spontaneous beat noise are independent in the unsaturated regime, the signal shot noise and signal- spontaneous beat noise have linear relation with the input optical power. In case of small input optical power one of the constant noises dominates. Then signal shot noise or signal- spontaneous beat noise overcomes this limit. I calculated with measured SOA parameters and took into account the gain saturation effect. Hence the spontaneous shot noise and the spontaneous beat noise start to decrease as the optical gain decreases.

I observed similar results in case of constant input optical power as a function of the SOA gain. For low gain values thermal noise and shot noise dominate and for larger gain the beat noises give the dominating contribution. So the SNR increases up to a certain gain, reaches a maximum, finally it decreases. There exists an optimum amplifier bias point corresponding to maximum SNR of the SOA-detector.

I compared the linear behavior of traditionally used PIN and SOA-detector. During the experimental work the level of the intermodulation products did not depend on the device parameters. I concluded, that linearity is limited by the Mach-Zehnder modulator (it has a cosine type characteristic) and SOA can be treated as a linear detector. I validated my experimental results with simulation, where every element was treated as an ideal device expecting the PIN and SOA-detector. The simulation results show, that the spurious suppressions are in the same range with the two detector type and there are no essential differences between the two devices from the point of applications. However the SOA detector generates higher noise, than the PIN detector. Hence the SOA-detector provides lower SFDR, which is the figure of merit investigating the linearity together with the noise.

Exploitation of results

I was participated in a number of international cooperation. The subject of my PhD was motivated by my work in COST267 action. The results were published in international technical reports (Nefertiti NoE: IST-2001-32786, ISIS NoE: EU IST FP6 026592, OTKA T026557 and T034520). The results of the dissertation were published in Hungarian and international journals, conference proceedings and technical reports. I have got several independent citations. Some of these results were already moved and will be move into educational material.

T III/2 Thesis: I investigated the noises at the output of SOA-detector and compared with the noise of traditionally used PIN diode. Based on my calculation I realized three regions as a function of the avarage input optical power (optical loss between the transmitter and SOA-detector) where different noise component dominates. I expressed the noise components versus bias current and optical gain. I separeted different dominate noise components sections and I determined the signal to noise ratio. [S-1][S-4][S-10][S-31][S-34]

T III/3 Thesis: Based on my simulation and experimantel results I concluded the spurious suppressions are in the same range with the two detector type. However the SOA detector generate higher noise, than the PIN detector. Hence the SOA-detector provides lower SFDR, but the device ensures sufficient SFDR for SCM systems. [S-1][S-10]

Own publications

International journal papers [S-1] Udvary Eszter, Berceli Tibor: Semiconductor Optical Amplifier for

Detection Function in Radio over Fiber Systems, IEEE Journal of Lightwave Technology, Special Issue on MWP, Vol. 26, No. 08, Augusztus 2008, pp.2563-2570. L R IF2.824

[S-2] Udvary Eszter, Berceli Tibor: Linearity and chirp investigations on SOA as an external modulator in SCM systems, Proceedings of the European Microwave Association EUMA, Special Issue on Microwave Photonics, vol.3, September 2007, pp.217-222, R L

[S-3] Udvary Eszter, Berceli Tibor: Optical Subcarrier Label Swapping by Semiconductor Optical Amplifiers, IEEE Journal of Lightwave Technology, Vol. 21, No. 12, December 2003, pp. 3221 - 3225. L R IF1.983 H3 G3 S2

[S-4] Udvary Eszter, Marozsák Tamás: Distortion and Noise Problems of Subcarrier Multiplexed Optical Systems, Journal of Telecommunications and Information Technology, pp.60-64, 4/2001, Poland R

[S-5] Berceli Tibor, Járó Gábor, Marozsák Tamás, Mihály Sándor, Udvary Eszter, Varga Zoltán, Zólomy Attila: An Optical Carrier Generation Approach for Cellular Millimeter Wave Radio Systems, Journal on Fiber and Integrated Optics, Vol. 19, Number 2, 2000, pp.119-137 R L IF0.3

Foreign language journal papers published in Hungary [S-6] Udvary Eszter: Linearity and Chirp Investigations on Semiconductor

Optical Amplifier as an External Optical Modulator, Híradástechnika, Selected Papers, vol. LXII, 2007/7, pp.46-51. L R

Papers published through international conference proceedings [S-7] Udvary Eszter, Berceli Tibor, Marek Chacinski, Richard Schatz, Pierre-

Yves Fonjallaz: Reduction of Dispersion Induced Distortions in Radio over Fibre links, EuMC 2008, pp.1086-1089, Amsterdam 27-31 October, 2008, R

[S-8] Udvary Eszter, Hilt Attila, Berceli Tibor: Dispersion Elimination and Harmonic Behavior in Optical Networks, Networks2008, pp.1-17, Budapest, Magyarország, 2008. szeptember 28.-október 2. R

[S-9] Berceli Tibor, Udvary Eszter, Hilt Attila: A New Equalization Method for Dispersion Effects in Optical Links, Meghívott előadás, ICTON 2008, Volume 4, pp.98-101, Athens, Greece, June 22 - 26, 2008, R L

[S-10] Udvary Eszter, Berceli Tibor: Semiconductor Optical Amplifier for Detection Function in SubCarrier Multiplexed Systems, ICTON 2008, Vol.4, pp.170-173, Athens, Greece, June 22 - 26, 2008 R L

[S-11] Udvary Eszter, Berceli Tibor, Marek Chacinski, Richard Schatz, Pierre-Yves Fonjallaz: Improvements in Transmission over Optical Backbones of

Mobile Networks, CD-ROM, paper number: P42, ICT Mobile Summit, Stockholm, Sweden, 10-12 June 2008 R

[S-12] Udvary Eszter, Berceli Tibor: Linearity investigations on SOA as external modulator in SCM systems, FTTH, Wireless Communications and their interaction, 6th Workshop organized by the Network of Excellence ISIS, CD-ROM, paper number: P1, June 2-3, 2008, Stockholm, Sweden

[S-13] Udvary Eszter, Bartoss Viktória, Marek Chacinski, Richard Schatz, Berceli Tibor, Pierre-Yves Fonjallaz: Reduction of Dispersion Induced Distortions by Semiconductor Optical Amplifiers, MIKON-2008, Vol.1, pp.75-78, Wroclaw, Poland, May 19-21, 2008 R L

[S-14] Berceli Tibor, Udvary Eszter: Indoor Communications Applying an Optical Backbone, ICTON 2007, IEEE, Volume 3, pp. 277-280, Rome, Italy, 1-5 July, 2007 R L

[S-15] Udvary Eszter, Berceli Tibor: Linearity Investigations on SOA as External Modulator in SCM Systems, 12th Microcoll Colloquium on Microwave Communications, pp.65-68, Budapest, Hungary, 14-16 May 2007 R L

[S-16] Berceli Tibor, Udvary Eszter: Transmission Challenges of Cascaded Semiconductor Optical Amplifiers, MWP2005, IEEE, pp.129-132, Seoul, Korea, 12-14 October 2005 L R

[S-17] Udvary Eszter, Berceli Tibor: Noise and Linearity Investigation on SOA Modulators in SCM Systems, Topical Meeting on Optical Amplifiers and Their Applications CD-ROM (The Optical Society of America, Washington, DC, 2005), presentation number: TuC4, Budapest, Hungary, 7-10 August 2005 R

[S-18] Udvary Eszter, Berceli Tibor: Multifunctional SOAs in Fiber Radio Systems, PWCom 2005 12th Nefertiti Workshop “Photonics in Wireless Communication: Cost-Effective Solutions and Future Technologies”, CD-ROM, Session Fr-1, Säröhus, Göteborg, Sweden 1-3 June, 2005.

[S-19] Kovács Gábor, Udvary Eszter, Berceli Tibor: Semiconductor optical amplifiers for all-optical wavelength conversion, ICTON, vol.2, pp.37-40, Wroclaw, Poland, 4-8 July 2004 L R H2 W1 S2 G2

[S-20] Udvary Eszter, Berceli Tibor: Optical Subcarrier Label Swapping by Semiconductor Optical Amplifiers in Cross Phase Modulation Wavelength Converter Block, MWP2003, IEEE, pp.85-88, Budapest, Hungary, September 10-12, 2003,. L R

[S-21] Hilt Attila, Udvary Eszter, Berceli Tibor: Harmonic Distortion in Dispersive Fiber–Optical Transmission of Microwave Signals, International Topical Meeting on Microwave Photonics MWP2003, IEEE, pp.151-154, Budapest, Hungary, September 10-12, 2003, L R

[S-22] Udvary Eszter, Berceli Tibor: Branching Function by Semiconductor Optical Amplifier (SOA) in Subcarrier Multiplexed (SCM) Optical Systems, 11th Microcoll, pp.51-54, Budapest, Hungary, September 10-11, 2003, R L

[S-23] Udvary Eszter, Berceli Tibor, Marozsák Tamás, Hilt Attila: Semiconductor Optical Amplifiers in Analog Optical Links, ICTON’2003, IEEE, pp.201–206, Warsaw, Poland, 29 June - 03 July, 2003 R L

[S-24] Marozsák Tamás, Kovács Attila, Udvary Eszter, Berceli Tibor: Direct Modulated Lasers in Radio over Fiber Applications, MWP2002, IEEE, pp.129 – 132, 5-8 Nov. 2002, Awaji, Japán L R H6 W2 S6 G3

[S-25] Udvary Eszter, Marozsák Tamás, Berceli Tibor: Application of SOAs in Fibre Radio Systems, EUMC’2002, IEEE, Vol.2, pp.693, 23-26 September 2002, Milan, Italy R

[S-26] Udvary Eszter: Semiconductor Optical Amplifiers in Fibre Radio Networks, URSI 2002, CD-ROM, paper number: 1848, Maastricht, Netherlands, August 14-17, 2002,

[S-27] Udvary Eszter, Csörnyei Márk, Gislaine Maury, Yannis Le Guennec: SOAs in Subcarrier Multiplexed Optical Networks, MIKON-2002, IEEE, Vol. 3, pp.874-877, Gdansk, Poland, May 20-22, 2002, L R

[S-28] Hilt Attila, Berceli Tibor, Frigyes István, Udvary Eszter, Marozsák Tamás: Fiber-dispersion Compensation Techniques in Optical/Wireless Systems, MIKON-2002 IEEE, Vol.1. pp.25-36, Gdansk, Poland, May 20-22, 2002, L R H1 G1

[S-29] Marozsák Tamás, Udvary Eszter: Vertical cavity surface emitting lasers in radio over fiber applications, MIKON-2002, IEEE, Vol.1. pp. 41-44, Gdansk, Poland, May 20-22, 2002, L R H1 G1

[S-30] Udvary Eszter: Branching of Subcarrier Multiplexed Optical Networks by SOAs, EUMC’2001, pp.1-4, London UK, 24-28 September 2001 R

[S-31] Udvary Eszter: Noise Performance of Semiconductor Optical Amplifiers, EUROCON’2001, Vol.1 pp.161–163, Szlovákia, Pozsony, 4-7 July, 2001 R

[S-32] Udvary Eszter: Add/Drop in Subcarrier Multiplexed Optical Networks, ICTON’2001, IEEE, pp. 342 –345, Cracow, Poland, 18-21 June, 2001 R L

[S-33] Marozsák Tamás, Udvary Eszter, Berceli Tibor: A combined optical-wireless broadband Internet access: transmission challenges, IMS2001, IEEE, Digest, Vol. 2. pp.997-1000, Phoenix, Arizona, 20-25 May 2001 R S1 G1

[S-34] Udvary Eszter, Bánky Tamás, Hilt Attila, Marozsák Tamás: Noise and Gain Properties of Semiconductor Optical Amplifiers, Optical/Wireless Workshop, European MOIKIT project, CD-ROM, Budapest, Hungary, 12 March 2001.

[S-35] Marozsák Tamás, Udvary Eszter, Berceli Tibor: Transmission Characteristics of All Semiconductor Fiber OpticLinks Carrying Microwave Channels, EUMC2000, IEEE, Vol. 2. pp.52-55, Paris, France, 3rd-5th October 2000 R H1

[S-36] Udvary Eszter, Marozsák Tamás: Distortion and Noise Problems of Subcarrier Multiplexed Optical Systems, MIKON’2000, IEEE, Vol. 2. pp.431-434, Wroclaw, Poland, May 22-24, 2000 L R

[S-37] Berceli Tibor, Járó Gábor, Marozsák Tamás, Mihály Sándor, Udvary Eszter, Varga Zoltán, Zólomy Attila: Optical Millimeter Wave Generation for Cellular Mobile Systems, MIKON’2000, IEEE, Vol.3., pp.110-119, Wroclaw, Poland, 22-24 May 2000. R H1

[S-38] Marozsák Tamás, Berceli Tibor, Járó Gábor, Zólomy Attila, Hilt Attila, Mihály Sándor, Udvary Eszter, Varga Zoltán: A New Optical Distribution Approach for Millimeter Wave Radio, IEEE MWP'98, pp.63-66, Princeton, USA, 12-14 October, 1998. R H1

[S-39] Udvary Eszter, Zólomy Attila, Hilt Attila, Járó Gábor, Mihály Sándor, Berceli Tibor: A Millimeter Wave PLL Oscillator for Optical Receivers, ECS’97, pp.205-208, Bratislava, Slovakia, September 1997. R H1 S1

[S-40] Hilt Attila, Zólomy Attila, Berceli Tibor, Járó Gábor, Udvary Eszter: Millimeter Wave Synthesizer Locked to an Optically Transmitted Reference Using Harmonic Mixing, IEEE MWP’97, pp.91-94, Duisburg, Germany, 3-5 September 1997. R H1 W1 S1 G1

Publications in Hungarian journals [S-41] Gerhátné Udvary Eszter, Berceli Tibor, Hilt Attila: “Diszperzió hatásának

és a harmonikusok viselkedésének vizsgálata optikai hálózatokban”, Híradástechnika folyóirat, 2008/6 Június, vol.LXIII. pp. 20-26, L R

[S-42] Gerhátné Udvary Eszter: Félvezetős optikai erősítő-modulátor linearitás és chirp vizsgálata, Híradástechnika 2007/6 Június, vol.LXII., pp.14-19. L R

Papers published through Hunagrian conference proceedings [S-43] Gerhátné Udvary Eszter: Fiber Radio rendszerek, 16. Távközlési és

Informatikai Hálózatok Szeminárium, HTE, pp.130-138, 2008. október 15-17, Zalakaros

[S-44] Gerhátné Udvary Eszter: Félvezető Optikai Erősítők alkalmazása Segédvivős Optikai Hálózatokban, PKI Tudományos Napok, pp.173-184, 2004. November 29-30. Budapest

[S-45] Gerhátné Udvary Eszter: Többfunkciós félvezetős optikai erősítők, Kvantumelektronika 2003, V. Szimpózium - A Hazai Kvantumelektronikai Kutatások Eredményeiről, CD-ROM, 2003 október 21., Budapest.

Number of publications: 45 Number of lectured publications: 24 Number of refered publications: 37 Number of references to own publications (including self references): 35 Other author’s publications refering to own publications: 22 Number of references according to Web of Science (including self references): 11 Number of references according to Web of Science: 4 Number of references according to Scopus (including self references): 29 Number of references according to Scopus: 14 Number of references according to google scholar (including self references): 26 Number of references according to google scholar: 13

Foreign papers referring to own publications

first author: Udvary Eszter, Berceli Tibor: Optical Subcarrier Label Swapping by Semiconductor Optical Amplifiers, IEEE Journal of Lightwave Technology, Vol.21, No.12, December 2003, pp.3221-3225. • C. Díaz Giménez, I. Tafur Monroy, J.J. Vegas Olmos, S. Sales, A.M.J. Koonen: Performance

evaluation of a DPSK/SCM combined modulation scheme for optical label switching, NOC, 5-7 July 2005, London, UK, pp. 415-422. G

• Ni Yan, Idelfonso Tafur Monroy, Ton Koonen: All-Optical Label Swapping Node Architectures and Contention Resolution, ONDM, 7-9 July 2005, Milan, Italy, pp.1-9. GS

• Ryo Takahashi: „Recent Progress in Optical Packet Processing Technologies for Optical Packet-switched Networks”, NTT Technical Review July 2004, Vol2, No7 pp.12-22, GS

• B. S. G. Pillai: „Novel all-optical signal processing schemes and their applications in packet switching in core networks”, PhD thesis, The University of Melbourne, Australia, March, 2007 G

Udvary Eszter, Zólomy Attila, Hilt Attila, Járó Gábor, Mihály Sándor, Berceli Tibor: A Millimeter Wave PLL Oscillator for Optical Receivers, Proceedings of the first Electronic Circuits and Systems Conference, ECS’97, pp.205-208, Bratislava, Slovakia, September 1997. • Molchanov, P., Checkotun, V., Mulyar, P., Linnyk, O.: Microwave processing of optical signals

with the negative resistance circuits, Proceedings of SPIE - The International Society for Optical Engineering, Vol.4425, 2001, pp.46-52 S

Second author : Kovács Gábor, Udvary Eszter, Berceli Tibor: Semiconductor optical amplifiers for all-optical wavelength conversion, ICTON 2004, vol. 2 , pp. 37- 40, Wroclaw, Poland , 4-8 July 2004 • Z.G.Lu, P.Bock, J.R.Liu, M.Florjanczyk, T.Hall: “Ultrabroad tunable wavelength conversion in a

semiconductor optical amplifier”, Microwave and Optical Technology Letters Vol.48, No.11, November 2006, pp.2139-2142 WSG

• Andrzej Jajszczyk: „Optical networks – the electro-optic reality”, Optical Switching and Networking, Volume 1, Issue 1 , January 2005, Pages 3-18. G

• Lu, Z.G., Lin, P., Sun, F.G., Bock, P., Zhou, S., Zhang, X.P., Hall, T.: Ultrabroad tunable wavelength conversion with uniform efficiency and signal-to-noise ratio, 2005 Proceedings of SPIE - The International Society for Optical Engineering, Photonic Applications in Nonlinear Optics, Nanophotonics, and Microwave Photonics, 5971 GS

Marozsák Tamás, Udvary Eszter: Vertical cavity surface emitting lasers in radio over fiber applications, MIKON-2002, Gdansk, Poland, May 20-22, 2002, Vol.1. pp. 41-44. • Lukas Chrostowski: „Optical Injection Locking of Vertical Cavity Surface Emitting Lasers, PhD

thesis, University of California, Berkeley, 2003 G Marozsák Tamás, Udvary Eszter, Berceli Tibor: A combined optical-wireless broadband Internet access: transmission challenges, IMS2001, IEEE, Vol. 2. pp.997-1000, Phoenix, Arizona, 20-25 May 2001 • Chia, M.Y.W. Luo, B. Yee, M.L. Hao, J.Z.: Hybrid radio over fiber wireless LANs and Ethernet

networks, Optical Fiber Communication Conference, 2004. OFC 2004, 23-27 Feb. 2004, Los Angeles, USA, GS

Marozsák Tamás, Udvary Eszter, Berceli Tibor: Transmission Characteristics of All Semiconductor Fiber OpticLinks Carrying Microwave Channels, EuMC, Vol. 2. pp.52-55, Paris, France, 3rd-5th October 2000 • Boula-Picard, R.; Bibey, M.; Vodjdani, N.: „Semiconductor optical amplifiers for microwave

photonics links„ International Topical Meeting on Microwave Photonics, 2001. MWP '01. 2001, pp. 137 -140. 7-9. January, 2002, Renaissance Long Beach. Hotel. Long Beach, California

Third author: Hilt Attila, Berceli Tibor, Udvary Eszter.: Microwave Network Analysis Extended to Optical Systems, 13th Conference on Microwave Techniques (COMITE 2005), pp. 320-323, Prague, Czech Republic, September 2005 • Bódi Tamás, Szekeres Péter: "Félvezető eszközök és áramkörök optikai vezérlése", Híradástechnika

folyóirat, LXI évfolyam, 27.-34. old., 2006-2. (in Hungarian) Marozsák Tamás, Kovács Attila, Udvary Eszter, Berceli Tibor: Direct modulated lasers in radio over fiber applications, International Topical Meeting on Microwave Photonics (MWP2002), 5-8 Nov. 2002, pp.129 – 132, Awaji, Japán • Wen-Piao Lin: „A robust fiber-radio architecture for wavelength-division-multiplexing ring-access

networks”, IEEE JLT, Vol.23, Issue9, Sept. 2005, pp. 2610- 2620 WGS • Wen-Piao Lin, Wei-Ren Peng, Sien Chi: „Dynamic Wavelength Allocation in Wavelength Division

Multiplexing Radio-over-Fiber Access Network „ Japanese Journal of Applied Physics, Vol. 44, No. 3, 2005, pp. 1282-1286 W

• Wen-Piao Lin and Yu-Fang Hsu: “Dynamic Wavelength Allocation in WDM Fiber-Radio Access Networks”, ICTON 2005, Proceedings of 7th International Conference of Transparent Optical Networks, 3-7 July 2005, Vol.2, pp. 157-160, Barcelona, Catalonia, Spain SG

• Wen-Piao Lin, Wei-Ren Peng and Sien Chi : “A robust architecture for WDM radio-over-fiber access networks”, Optical Fiber Communication Conference, 2004. OFC 2004 Volume 2, FG3, 23-27, Feb. 2004 GS

• Bo, Z., Yinghua, L., Jinling, Z., Biao, Y: Nonlinear effect of OFDM in radio-over-fiber transmission, 2007 International Conference on Microwave and Millimeter Wave Technology, ICMMT '07, art. no. 4266134, 8-21 April 2007, pp.1–3, Guilin, China S

• Zhang, B., Lu, Y., Zhang, J : Effects of a microcavity on harmonic and intermodulation distortions of a vertical cavity surface emitting laser, Pan Tao Ti Hsueh Pao/Chinese Journal of Semiconductors Volume 27, Issue 9, September 2006, pp. 1625-1629 S

• Sim, C.K., Yee, M.L., Luo, B., Ong, L.C., Chia, M.Y.W.: Performance evaluation for wireless LAN, ethernet and UWB Co-existence on hybrid radio-over-fiber picocell, Conference on Optical Fiber Communication, Volume 3, 2005, Article number 1501388, pp.591-593 S

Co-author: Hilt Attila, Berceli Tibor, Frigyes István, Udvary Eszter, Marozsák Tamás: Fiber-dispersion compensation techniques in optical/wireless systems, MIKON-2002 14th International Conference on Microwaves, Radar and Wireless Communications, Gdansk, Poland, May 20-22, 2002, Vol.1. pp. 25-36. • Hashmi, S.; Mouftah, H.T.: „Integrated optical/wireless networking”, Canadian Conference on

Electrical and Computer Engineering, 2-5 May 2004, pp.2095 - 2098 Vol.4 SG Marozsák Tamás, Berceli Tibor, Járó Gábor, Zólomy Attila, Hilt Attila, Mihály Sándor, Udvary Eszter, Varga Zoltán: A New Optical Distribution Approach for Millimeter Wave Radio, IEEE MTT Microwave Photonics, MWP'98, pp.63-66, Princeton, New Jersey, USA, 12-14 October, 1998. • Masahiro Kiyokawa, J.Claude Bélisle, Pierre Tardif: "Millimeter-wave Fiber Radio Using

Subharmonic Local-Oscillator Distribution", Proc. of the IEEE MTT Topical Meeting on Microwave Photonics, MWP'2001, pp.57-60, 2001.

Hilt Attila, Zólomy Attila, Berceli Tibor, Járó Gábor, Udvary Eszter: Millimeter Wave Synthesizer Locked to an Optically Transmitted Reference Using Harmonic Mixing, IEEE Topical Meeting on Microwave Photonics, MWP’97, pp.91-94, Duisburg, Germany, 3-5 September 1997. • Ichiro Seto, Hiroki Shoki, Shigeru Ohshima: “Optical Subcarrier Multiplexing Transmission for

Base Station With Adaptive Array Antenna”, IEEE Transactions on Microwave Theory and Techniques, Vol. 49, No. 10, Pp.2036-2041, October 2001. WG S