optical active er doped waveguide...

POSTER 2017, PRAGUE MAY 23

Abstract – In the paper are presented the results of the gain

transmission characteristics measurement for the ion exchange

Ag-Na optical active planar waveguides realized on a glass

substrates. The attenuation measurements were performed by

the time impulse selective wavelength method using pulse

generator as well as broadband spectral measurement method

using supercontinuum optical source in the wavelength

domain. Both methods were compared and the results were

evaluated. It has been demonstrated, that pulse method can

very accurately measurement of the attenuation characteristics

in dependence on the pumping power, but only for one

wavelength. The minimum attenuation wavelength bandwidth

of the active waveguide can be determined by the broadband

spectral characteristic measurement.

I. INTRODUCTION

The active optical waveguides are currently the subject of

the intensive research. The active optical waveguides on

glass dotted by Er3+

– Yb3+

are known for the low losses,

optical transparency in the NIR spectrum, low weight and

excellent stability of the operating parameters. The simple

and cheap fabrication by two-stage ion exchange and an

easy setting of the optical attenuation parameters and focus

on the fiber determines the use of active optical waveguides

in many areas of information technology devices such as

optical amplifiers, active optical splitters, optical switches

and many others. This paper summarizes measurement

results of the spectral transmission characteristics of the

active optical planar waveguides, which were created using

the Ag-Na ion exchange on a glass substrate. The

measurement was realized using two methods - the pulse

method in the time area, and the broadband spectral

measurement method in the wavelength area. Both methods

were compared and the results were discussed. In the case of

the pulse method, it is possible to determine, quite precisely,

the transmission characteristics dependent on the pumping

power, but only for one wavelength. In the case of the

spectral characteristics measurements, it was possible to

determine the area, where the maximum amplification of the

active waveguide takes place. The spectral characteristics of

pumped and non-pumped waveguides were compared.

Optically active material makes use of the activator ions,

most commonly rare earth elements, specifically those that

are optically active in the area of the second (1300 – 1350

nm) or third (1530 – 1560 nm) optical attenuation windows

of silica waveguides. The used rare earth elements are

trivalent ions from the lanthanide group. The ability of ions

to generate optical radiation (photoluminescence) while

optically pumping is hidden in the insufficiently occupied 4f

subshell, which is localized inside the activation atoms. The

fully occupied subshells 5s a 5p work as a shield of the 4f

subshell from the external field perturbations (e.g., thermal)

from the atoms of the base material.

The three-orbital system of energy levels, where the Yb3+

ions are pumped to the 2F 5/2 level is shown in Fig. 1.

After a certain time, the electors pass through non-radiative

transition to a lower orbital 4I 13/2, and via radiation-

transition with stimulated emissions of photons 1550 nm to

the base state (4I 15/2).

Fig. 1. Energy levels of transitions in a complex of Er3+ - Yb3+ ions [ 4 ].

In regards to the optical amplifiers for the 1550 nm

wavelength, the most frequently used activators are Er3+

ions, which use electron transition in the 4f subshell. There

are eleven electrons for amplification, and three of the

valences electrons are unoccupied and therefore usable for

excitation. A part of the erbium ions is very frequently

replaced by Yb3+

, which can increase the optical activity

(intensity of luminescence) than the erbium itself. The

absorption cross-section of Yb3+

ions is larger by orders of

magnitude than Er3+

.itselves. The optimal activator

concentration finding is one of the most crucial tasks in the

research of optically active structure technology. The higher

concentration of activators causes the quenching of the

luminescence radiation. The activator atoms are clustering,

the energy migration or the cross-relaxation take place. As

an example, we present a planar configuration of a planar

optical amplifier (POA) depicted in Fig.2.

Fig. 2. The planar configuration of the optical amplifier [1].WDM - wavelength division multiplexer, AMP - amplifying waveguide, SPL –

splitter 1x4

Optical Active Er doped waveguide structures

Jiří Šmejcký

Faculty of Electrical Engineering, Technical University in Prague

[email protected]


w

h ns+n

nc

ns

The POA use the aluminum oxide waveguide doped with

Er3+

ions for the 1540 nm operation with the 1480 nm

pumping. The POA utilizes a planar interference WDM

filter at the input, which combines the pumping radiation

with the signal one. The mixed radiation is amplified in the

active planar waveguide. At the end of the waveguide is

wavelength divider, which splits the pumping and the signal

radiation. The signal part of the radiation is taken to an

interference splitter, and the pumping part is taken to a ring

resonator, which is tuned to the pump wavelength. The ring

resonator absorbs the energy of the pumping radiation.

II. TECHNOLOGY

A key part of an OPA used in our measurements was

samples of the diffused optical planar waveguide dotted by

Er3+

and Yb3+

realized in the glass.

Fig. 3. The planar diffused optical waveguide [2].

The planar diffused optical waveguide with ZnO precursor

after a first-degree ion exchange is depicted in Fig. 3. We

can see a gradient waveguide, in which the refractive index

changes continuously exponentially from the center to the

edge, according to the diffusion. The picture shows the first

Measurement procedure

The measurement of the samples was done by both the by

the time impulse selective wavelength method and the

spectral method with the aid of a broadband signal.

Fig. 4. The absorption characteristics waveguide dotted by Er,Yb [3].

Fig. 5. The luminescence characteristics of the waveguide dotted by

Er,Yb [3].

The comparison of the absorption and luminescence

spectrum the planar diffused optical waveguide with ZnO

precursor is shown in Fig. 4. It is clear that influence of the

ZnO concentration on the process of absorption (980 nm)

does not affect the absorption spectrum, where the

absorption takes place from the ytterbium ions. In opposite

to the luminescence spectrum, which arises from erbium

ions, where the increase of ZnO correlates to an increased

luminescence activity. This point to the fact that as the

concentration of ZnO increases so does the separation of

erbium ions, which prevents the clustering, so that more

energy is radiated (Fig.5).

III. MEASUREMENT AND RESULTS

The measurement of the samples was done by both the by

the time impulse selective wavelength method and the

spectral method with the aid of a broadband signal.

The measurement of transmission characteristics

at = 10 log (Ps,out/Ps,in) in dependence on the pumping power

Pp is shown in Fig. 6. In order to separate the spontaneous

emission a pulse modulation of the signal radiation was

used. The optical signal attenuation radiation component

was determined from the amplitude of the modulated

electrical signal at the output.

Fig. 6. The measurement of transmission characteristics

at = 10log Ps,out / Ps,in in dependence on the pumping power Pp.


Fig. 7. The modulated electrical signa at the oscilloscope. DC signal

component ASE represents the size of the amplified spontaneous emission.

at [dB] Ppumpid[mW]

Fig. 8. The transmission characteristics of samples M1 – 02 –C4 – K7 ,

M1 – 02 – C2 – K7 (type of glass-slice-chip-channel).

The measurement proved optical activity in samples M1 –

02 – C4 – K7 and M1 – 02 – C2 –K7 that also represent the

smallest attenuation. Time measurements of the M1 – 02 –

C4 – K7 and M1 – 02 – C2 – K7 samples reveal a static

attenuation of 1.27, for the maximum pumping of 20 dBm

and a differential gain of 18.55 W/mW of the pumping

power. The value of the differential gain does not depend on

the attenuation of the optical coupling to the waveguide and

the attenuation of the waveguide itself, so the real optical

activity of the sample can be considered. Saturation of this

parameter with pumping up to the power of 20dBm was not

observed during the measurements. The resulting

attenuation values of these samples, using this method, a

wavelength of 1550 nm, input power of – 1 dBm and zero

pumping are:

1. M1 – 02 – C4 – K7 ………… - 4,4 dB

2. M1 – 02 – C2 – K7 ………… - 4,8 dB

3. 2223 – C2 – K5 ………… - 9,5 dB

4. Y2 – 02 – C2 – K5 ………… - 17,2 dB

5. Y2 – 02 – C2 – K ………… - 16,8 dB

Measurements were done by the broadband method. The

sources of the measuring signal is a supercontinuum emitter.

Fig .9. Block scheme of measurement spectral characteristic.

Fig. 10. The spectral characteristic of wideband input signal

(supercontinuum)

The signal is broadband; its run is shown in Fig. 10. An

optical measuring IDIL amplifier (Safibra) was used as a

comparison in addition to the samples mentioned above

(Fig. 11). This method particularly allows searching for

those wavelengths that amplify the given sample. The

measurement proved an optical activity in samples M1 – 02

– C4 – K7 and M1 – 02 - C2 – K7 with the smallest

attenuation. The activity was not detected in other samples.

The following graphs show the spectral characteristics of the

input signal (green curve), spectral characteristics of the

measured sample without pumping and the spectral

characteristics of the measured sample with the wavelength

of 980 nm. The area where sample activity is specified is

marked by an ellipse. The areas of optical activity for the

individual samples are:

1. M1 – 02 – C4 – K7 ………… 1530 -1560 nm

2. M1 – 02 – C2 – K7 ………… 1540 -1590 nm

3. 2223 – C2 – K5 ………… non-measurable

4. Y2 – 02 – C2 – K5 ………… non-measurable

5. Y2 – 02 – C2 – K6 ………… non-measurable

y = 0,0102x - 4,6465

-5

-4,8

-4,6

-4,4

-4,2

-4

-3,8

0 20 40 60 80 100

izolator

Fianium

Example

SP. AQ6370c

Supercontinum

Input 980 nm

mux

Ps,in

-65

-55

-45

-35

-25

-15

800 1000 1200 1400 1600

Ps,in

[d

Bm

]

λ[nm]


Fig. 11. The spectral characteristic of an optical measuring IDIL amplifier.

In areas about the wavelength of 1550 nm happens at off

source pumping high inhibition, that is of incurred

absorption energy on erbium ions. At source pumping (laser

at 980 nm) then happens to expressive thickness signal 25

dB.

Fig.12. The spectral characteristic sample M1 – 02 – C2 – K7.

Fig. 13. The spectral characteristic sample M1 – 02 – C4 – K7.

A high attenuation, caused by the absorption of energy of

erbium ions, takes place around the 1550 nm wavelength

when the pumping source is turned off. A marked

strengthening of the signal (about 25dB) takes place with a

pumping source (laser at 980 nm).

IV MEASUREMENT EVALUATION AND

CONCLUTION

The time measurement method makes it possible to

determine attenuation and differential gain gd with very high

precision but only at one wavelength, in this case, the

wavelength of 1550 nm ( gd = Δ𝑎𝑡,𝑝𝑢𝑚𝑝𝑒𝑑

Δ𝑎𝑡,𝑢𝑛𝑝𝑢𝑚𝑝𝑒𝑑).

The spectral method enables to look up areas where the

samples attenuation strength (are optically active) and, with

lower exactness, also determine attenuation or gain.

Considering the measuring results using both the spectral

and the time method at the wavelength of λ = 1550 nm, the

samples with the lowest insertion loss have the biggest

differential gain. Insufficient pumping occurs at those

samples that have high insertion loss and thus signal

amplification is not achieved. According to our opinion, the

substantial attenuation is not caused by the composition of

the samples but the quality of the optical coupling. The need

for improvement of the optical coupling is indicated by an

evaluation of the results. There is a further need, based on

the extrapolation of the attenuation characteristic of the

active samples, to increase the power of the pumping define

to at least 320 mW to acquire an absolute positive gain

under the condition that saturation does not occur. This

hypothesis was not tested since a source of this power

output was not available. Another possibility of increasing

the gain is the lengthening of the active length of the

sample. Under the current parameters, it is necessary to

increase the active length of the sample to at least 10 cm to

get a positive gain.

ACKNOWLEDGMENT

Our research is supported by the Student Grant Competition

of the Czech Technical University in Prague under grant

number SGS16/162/OHK3/2T/13.

REFERENCES

[1] C.E.Chyssou,F.Di Pascale,C.W. Pitt:Improved gain performance

in𝑌𝑏3+ - sensitized 𝐸𝑟3+- doped aluminia (𝐴𝑙2𝑂3) channel optical

waveguide amplifiers.J. of Lightwave Technology,19,2001,

[2] O.Barkman,V.Prajzler,P.Nekvindova:Design and modeling of the

single mode optical Glass waveguides for passive photonics

structures, Optické komunikace 2011, Praha, 2011, p.101 – 104.

[3] P.G.KiK and A.Polman : Erbium-Doped Optical-Waveguide

Amplifiers on Silicon (MRS Bulletin/April 1998

[4] V.Prajzler, I. Hüttel, O. Lyutakov, J.Spirkova, J.Oswald, V. Jerabek:

Optical Properties of PMMA Polymer Doped with 𝐸𝑟3+ and

𝐸𝑟3+/𝑌𝑏3+ Ions, Journal of Physics, Conference Series 100, 2008,

p.1-4

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optical active er doped waveguide...

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