Nonlinear Polarization Rotation Characteristic Phenomenon in a Bulk Semiconductor Optical Amplifier

doi:10.4236/opj.2013.32B045

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Optics and Photonics Journal, 2013, 3, 187-191

doi:10.4236/opj.2013.32B045 Published Online June 2013 (http://www.scirp.org/journal/opj)

Nonlinear Polarization Rotation Characteristic

Phenomenon in a Bulk Semiconductor Optical Amplifier

Xanghua Feng1, Jiarong Ji2, Guomin Zhang1

1College of Science,Informa t ion E ng ineeri ng Univer si ty, Zhengzhou, China

2College of Opto electronic Science and Engineering National University of Defense Technology, Changsha, China

Email: [email protected]

Received 2013

ABSTRACT

The phenomena of polarization rotation induced by self-modulation in se miconducto r optical amplifier (SOA) are ana-

lyzed theoretically. The relationship between polarization parameters and gain as well as phase is obtained by the cor-

relation parameter of ellipse polarization and SOA nonlinearity polarization rotation theory. The experiment employs

polarizer drive by walking electromotor and power meter, the light power of 360 degree is measured. The transforma-

tion law of output polarization power components is found for obvious polarization rotation in the selected coordinate

axes based on connection of polarization state in difference axes. U sing this law make the manipulation easily on get-

ting ideal polarization state. It can offer a fine method to realize all-optical switch and other logic elements in experi-

ment. This work is of great significance for the applications of SOA nonlinear polarization rotation at high-speed

all-optical signal processing and all-optical logic gate.

Keywords: Strai ned Bulk S OA; Nonlinear Polariz a tion Rotation; Phase Difference; Polar izatio n Azimuth

1. Introduction

H.Soto and D.Erasme [1] first raised a concept of cross-

polariza tio n-modulatio n (X PolM) in 1999. They investi-

gate the transformation law of SOA birefraction with

Jone–matrix. The nonlinear polarization rotation induced

by SOA birefraction was used on all-optical wavelength

conve rsion, switch, l ogic gate in the paper [2,3].

From 2003, Dorren [4,5] et al. researched all-logic ele-

ments and all-optical switch base on XP o lM in theory

and experiment, and raised a theory model for polariza-

tion depende nt gai n saturation in te nsile strai n bulk SO A.

L.Q.Guo et al. set a 2.5 Gbit/s all-optical AND gate base

on XPolM [6-8]. They proved extinction ratio increased

8dB contrast all-optical AND gate base on cross-gain-

modulation. Due to the polarization rotation can induce

the variety of output power, the polarization rota tion co m-

bining other non-linearity effect can use in all-optical

nonlinear regeneration [9] and all-optical sampling [10]

and optical buffer [11] and optical data comparator [12].

Recently, with investigate deeply, the applications of SOA

nonlinear polarization rotation at high-speed all-optical

signal processing and all-optical logic are more and more

widespread along with research deeply [13,14].

2. Theory Model and Simulations

The tensile strain bulk SOA is used for experime nt. Based

on Dorren’s theory, The polarized optical field are de-

composed into a transverse electric (TE) and trans- verse

magnetic (TM) component. TE and TM mode propagate

“independently” through the SOA, although they have

indirect interaction with each other via the gain satura-

tion. Because of different confinement factor and effec-

tive refractive indexes experienced by TE and TM modes,

it results in a phase shift TE and TM modes of the light

upon leaving the SOA. When a light transit SOA, the out

powers for each polarization can be expressed as:

int

( )( )exp()

TE TETE

TE TE

out in

PP v

ττ α

= −

(1)

int

( )( )exp()

TM TMTM

TM TM

out in

PP v

ττ α

= −

(2)

where Pin is input power, Pout is output power, Γ is the

confinement factor, g is the gain, L is the length of the

SOA.

By relation of gain and phase, output phase through L

can be expressed as

TE TE TE

TE TE

φφ

= −

(3)

TM TMTM

TM TM

φφ

= −

(4)

where α is phase modulation coefficients, it express the

X. H. FENG ET AL.

188

coupling rel atio n of gain and refractive index in SOA.

Through L, the phase difference between TE and TM

modes can be computed from (3) and (4)

TMTE

φφφ

−=∆

(5)

In the most simple approach, one would choose

TM TE

αα

. By(1)-(5), we can get:

(lnln )

TM TM

out in

TE TE TE

out in

φφ

∆ =−+∆

(6)

(6) express the relation of phase difference and input/

output power. Due to the change of TE and TM output

powers, the phase difference between TE and TM modes

change.

out

is more and the phase difference is mo r e,

as Figure 1. Three curves represent the phase difference

range of 800(curve1), 1000 (curve3) and 1200 (curve2).

The calculation parameters of this paper use parameters

of literature [4 ] .

It is get different rotation degree by same input phase

difference and different TE/TM input powers. It is also

get different rotation degree by differe nt input phase dif-

ference and same TE/TM input powers. As Figure 2, the

rotation degree of curve1 is more. More rotation degree

can be obtained by chose right input phase difference.

Definition extinction ratio

10log( )

long axis

short axis

The output extinction ratio change with input polariza-

tion state. The linear output can be obtained by adjusting

input phase difference at arbitrarily input powers, as Fig-

ure 3. Curve 1 express when input power is -1dBm,

Curve 2 express when input power is -5.9dBm, output

light is linearly polarized light.

The experiment employs polarizer driving by walking

electromotor and power meter. If the polarizer axis(x, y

axis) is different to SOA perpendicular axis (TE, TM

-10-8 -6 -4-20 2 46

100

120

140

160

180

In put Power(dBm)

Phase Difference(deg)

curve 1

curve 2

curve 3

Figure 1. P hase dif fere nce va riations d epen d on diff erent TE

mode and the TM mode output po wer.

-10 -8 -6 -4 -2 0246

-30

-20

-10

In put P ower (dB m )

Pol arizat ion A zim uth

curve1

curve2

curve3

Figure 2. Polarization Azimuth variations depend on different

phase difference of TE mode and the TM mode.

-10 -8 -6 -4 -2 0246

In put Power (dB m )

Ext inction Ratio(dB )

curve1

curve2

Figure 3. Extinction ratio variations depend on different phase

difference of TE mode and the TM mode

axis), the power satisfy:

cossinsin 2cos

xTETMTE TM

P PPPP

ϕ ϕϕφ

=+− ∆

(7)

sincossin 2cos

yTETMTE TM

P PPPP

ϕ ϕϕφ

=++ ∆

(8)

where

is angle between x axis and T E axi s. Px and Py

are affected by

∆

obviously. The phase difference

cosine law appear on x y axis from Figure 4. We can

speculate cosine changing is more obvious, polarization

state changing is more. The biggest difference between

Px and Py is more, output light is more close to linearly

polarized light. It means SOA output polarization state

variety with input power is known by polarizer. So expe-

riment operation become easily. So long as adjusting

suitable input polarization state, we can get expect pola-

rization state at ar bitrarily input power.

X. H. FENG ET AL.

189

3. Experimental Results

Experimental setup is used to measure SOA nonlinear

polarization rotation as Figure 5. A commercial polari-

zation-independent SOA is employed. Its saturation power

is 10dBm. A walking electromotor controlled by com-

puter drive a polarizer, so the light power of every orient-

tation is measured. The walking electromotor rotate cir-

cuit, sampling point is 400. The distribution of power is

displayed on computer.

In this paper, two input pump polarization states(A and

B) are selected as contra st. Figure 6 is an input and output

polarization light power of A polarization state corre-

sponding with 360 degree.

-10 -8-6-4-20 2 4 6

-2

In put Power (dB m )

Output P ower(dBm)

x axes

y axes

Figure 4. SOA output power o n xy perpendic ular a xes.

Laser

EDFA

SOA

ATT

Figure 5. Experimental setup is used to measure SOA polariza-

tion power. EDFA: erbium-doped fiber amplifier, ATT:

Attenuat or, PC: Polarizati on co ntroller, PL: Polarizer, PM :

Power meter.

0.5

1.5

210

240

270

120

300

150

330

180 0

210

240

270

120

300

150

330

180 0

(a) (b)

Figure 6. Input and output polarization light power of A

polarizatio n state co rres pond w it h 36 0 degree. (a) Input; (b)

output.

Figure 7 is an input and output polarization light power

of A polarization state corresponding with 360 degree.

In Figures 6 or 7, long axis power

, short axis

power

, angle

of x axis and long axis, x axis

power

, y axis power

, 450 power

are easy to

find out. According to transform relation of different

axis,

cossinsin 2cos

44 2

x yxy

P PPPP

ππ π

= +−∆

(9)

get:

( )/2

cos

PP P

+−

∆=

(10)

For arbitrary orthogonal axis, phase difference betwee n

perpendicular components can be getting at this coordi-

nate.

Figure 8 is output probe power

correspond-

ing A and B.

Figure 9 is polarization Azimuth variatio n curves cor-

respond to A and B. Because polarization state drift and

systemic vibration make power measurement error, po-

larization azimuth extinction ratio will produce error.

Figure 10 is extinction ratio variation curves correspond

to A and B. Figure 11 is phase difference of x and y var-

iation curves correspond to A and B.

4. Conclusions

From ahead experimental resul t, we can get the conclusion.

Polarization state rotation always occurs through SOA,

rotation degree is different follow different input power

and input po lariza tion sta te. Two d iffere nt i nput polar iza-

tion states lead to output power and gain obvious differ-

ence of x and y axis. Their phase difference, polarization

Azimuth and extinction ratio are difference obviously.

Due to x and y axis do not coincide TE and TM axis,

obvious cosine variation curve is observed at Figure 8(a).

It implies input polarization state of Figure 6(a) arise

phase difference of TE and TM modes bigger change,

and it arise rotation bigger degree and extinction ratio

0.5

1.5

210

240

270

120

300

150

330

180 0

210

240

270

120

300

150

330

180 0

(a) (b)

Figure 7. Input and output polarization light power of B

polarizati o n state corres p ond w ith 36 0 degree. (a) Input; ( b)

output

X. H. FENG ET AL.

190

-10 -8-6-4-20 2 46

Input P ower(dB m )

Out put Power(dBm)

x axes

y axes

(a)

-10 -8 -6 -4 -2 0246

Input P ower(dB m )

Out put Power(dBm)

x axes

y axes

(b)

Figure 8. Output polarization light power. (a) Correspond

to A polarization state; (b) correspond to B polarization state.

-10 -8-6-4-20 2 46

-40

-30

-20

-10

Input Power(dBm )

Polarizat ion Azi m uth(deg)

(a)

-10 -8 -6 -4 -202 4 6

100

105

110

115

Input P ower(dB m )

Polarizat ion Azi m uth(deg)

(b)

Figure 9. Polarization azimuth variation curve. (a) Correspond

to A polarization state; (b) correspond to B polari zati on state.

-10 -8 -6 -4 -2 0246

Input P ower(dBm )

Extincti on Ratio( dB )

(a)

-10 -8-6-4 -20 2 46

Input P ower( dBm )

Extincti on Ratio( dB )

(b)

Figure 10. Extinction ratio variation curve. (a) Correspond to

A polarization state; (b) correspond to B polarization state.

-10-8 -6 -4 -20 2 4 6

100

110

120

130

140

150

160

Input P ower(dB m )

Phase Di fference( de g)

(a)

-10 -8-6-4-20 2 4 6

100

105

110

115

120

125

Input Power(dBm )

Phase Di ff erece(dBm)

(b)

Figure 11. Phase difference variation curve. (a) Correspond

to A polarization state; (b) correspond to B polarization s tate .

X. H. FENG ET AL.

191

bigger change. Cosine variation curve is not observed at

Figure 8 (b). It implies input p olarization state of Figure

7(a) do not arise phase difference of TE and TM modes

bigger change, and it not arise rotation and extinction

ratio bigger change. Thus it can be seen, if input polari-

zation state arise phase difference of TE and TM modes

bigger change, output powers at x axis or y axis appear

cosine variation. It proves in theory and experiment, ar-

bitrary output probe polarization states can be obtained

through adjusting input pump polarization states. In ex-

periment, the adjusting of polarization states can mani-

pulate easily base on transform relation of different coor-

dinate syste m.

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