PGNET2006M.F, Chiang

M. F. Chiang, Z. Ghassemlooy, Wai Pang Ng,

H. Le Minh, and V. Nwanafio

Optical Communication Research Group

Northumbria University, United Kingdom

http://soe.unn.ac.uk/ocr/

Crosstalk Investigation of an All-Optical Serial-to-Parallel Converter Based on the

SMZ

PGNET2006M.F, Chiang

Contents

Introduction Semiconductor Optical Amplifier Symmetric Mach-Zehnder (SMZ) Gain Profiles and Switching Window Serial-to-Parallel Converter Crosstalk Results Conclusions

PGNET2006M.F, Chiang

Introduction

There is a growing demand for all optical switches and router at very high speed, to avoid the bottelneck imposed by the electronic switches.

In all-optical packet-switched networks, a Serial-to-Parallel Converter (SPC) is an important element in the header processing unit for address recognition.

SPC based on non-linear all-optical devices, e.g. SOAs, have have non-ideal switching window, thus experiencing residual channel crosstalk.

Here we investiagte a SPC at 80Gb/s investigating its crosstalk characteristics.

PGNET2006M.F, Chiang

Input signals (light)

Carrier density &

SOA gain (XGM)

SOA refractive index &

Induced phase (XPM)

Input signals

P

N

Injection current

SOA

Semiconductor Optical Amplifier (SOA)

PGNET2006M.F, Chiang

0 00 0

( )( )( )

i s

m

Ig N L

g N N Lg L eLwdG e e e

SOA Gain Profile

gm: the material gain, : the optical loss, g0: the gain coefficient, I: the injection current, N: the carrier density at the operating current I, N0: the carrier density at transparency, i: the current injection efficiency, s: the spontaneous recombination lifetime of the carriers, e: the electronic charge, L, w, and d: the length, width, and thickness of the active region of the SOA.

PGNET2006M.F, Chiang

S’(t+π/2)

S’(t)

S’’(t)

S’’’(t)

S’’’(t+π/2)

Pout,1(t)=S’’’(t)+S’’’(t+π/2+π/2)

Pout,2(t)=S’’’(t+π/2)+S’’’(t+π/2)

Pin(t)=S(t)

Signals emerge from output2

S’(t+π/2)

S’(t)

S’’(t)

S’’(t+π/2)

S’’’(t+ π)

S’’’(t+π/2)

Pout,1(t)=S’’’(t + π)+S’’’(t+π/2+π/2)

Pout,2(t)=S’’’(t+π/2 + π)+S’’’(t+π/2)

Pin(t)=S(t)

Signals emerge form output1CP1

π

Case 1: Without CP (SMZ is balanced)

Case 2: With CP1 only (SMZ unbalanced) Case 3: With both CP1&CP2

(SMZ is balanced again)

CP2π

Pout,2(t)=S’’’(t+π/2 + π)+S’’’(t+π/2 + π)

Pout,1(t)=S’’’(t + π)+S’’’(t+π/2+π/2 + π)

Signals emerge from output2 again

S’’’(t+π/2+ π )

Symmetric Mach-Zehnder (SMZ)Case 1: Without CP (SMZ is balanced)

Case 2: With CP1 only (SMZ unbalanced)

PC2

Output2

Output1

Coupler4

Coupler3

Coupler2

Coupler1

SOA2

SOA1 PBS

PC1

PBSS’’(t+π/2)

PC2

Output2

Output1

Coupler4

Coupler3

Coupler2

Coupler1

SOA2

SOA1 PBS

PC1

PBS

PC 3-dB coupler PBS

PGNET2006M.F, Chiang

out,1 in 1 2 1 2

1( ) ( ) ( ) ( ) 2 ( ) ( ) cos( )

8P t P t G t G t G t G t LEF 1 20.5 ln /G G

Gain Profiles of SOA1&SOA2 and SMZ Switching Window (SW)

Pout,1(t): The power at output1 of SMZ, Pin(t): the power of the input signal, : the phase difference of the input signals between the upper and lower arms of the SMZ,

and LEF: the linewidth enhancement factor.

;

PGNET2006M.F, Chiang

Bit 3 Bit 2 Bit 1 Bit 0

1 x 4 Splitter

3Tb

2Tb

Tb

Bit 0

Bit 1

Bit 2

Bit 3

Tsw

CP1

CP2

Serial-to-Parallel Converter (SPC) - 1

PGNET2006M.F, Chiang

.. .1.. 1.. 0.. 1

Outputparallel

bits

MSB LSB

SOA2

SOA1

CP2

CP1

Tb

2 Tb

3 Tb

1x4 Spliter

0

3

2

1

PC 3-dB couplerFDL

SMZ1

PBS

Inputserialbits

Serial-to-Parallel Converter (SPC) - 2

PGNET2006M.F, Chiang

10 nt t10log /CXT P P

Crosstalk (CXT)

Pnt: sum of the output signal power of all non-target channels and Pt: the output signal power of the target channel.

Switching window

No-target channels

PGNET2006M.F, Chiang

VPI Simulation ParametersSOA

ParametersDefault Values

SOA ParametersDefault Values

Injection current

0.15 ACarrier density at

transparency1.4 x 1024 m-3

Length 500 x 10-6 mLinewidth

enhancement factor4

Width 3 x 10-6 mRecombine constant

A1.43 x 108 s-1

Height 80 x 10-9 mRecombine constant

B1 x 10-16 m3 s-1

Confinement factor

0.15Recombine constant

C3 x 10-41 m6 s-1

Internal losses 40 x 102 m-1 Initial carrier density 3 x 1024 m-3

Differential gain 2.78 x 10-20 m2

System Parameters Default Values

Signal power 1 mW

Control power 20 mW

Tsw 10 ps

FWHM of signal & control pulses 2 ps

Emission wavelength of signal & control pulses

1552.52 nm

Operation bit rate 80 Gb/s

PGNET2006M.F, Chiang

Simulation Results – 1

-21

-20

-19

-18

-17

-16

-15

-14

0 20 40 60 80 100 120 140 160 180 200 220

Control Power (mW)

CX

T R

atio

(d

B)

SP=0.5mW

SP=1mW

SP=2mW

SP=4mW

-19.8

-19.6

-19.4

-19.2

-19

-18.8

-18.6

-18.4

0 0.5 1 1.5 2 2.5 3 3.5

FWHM of CP&SP (ps)

CX

T R

atio

(d

B)

PGNET2006M.F, Chiang

Simulation Results – 2

-29

-27

-25

-23

-21

-19

-17

-15

0 2 4 6 8 10 12 14 16

Tsw (ps)

CX

T R

atio

(d

B)

-20

-19.5

-19

-18.5

-18

-17.5

-17

-16.5

-16

-15.5

0 2 4 6 8 10Linewidth Enhancement Factor

CX

T R

atio

(d

B)

PGNET2006M.F, Chiang

Simulation Results – 3

-22

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0 0.1 0.2 0.3 0.4 0.5 0.6

Inject Current (mA); Confinement Factor

CX

T R

atio

(dB

)

Inject Current

ConfinementFactor

-21

-20

-19

-18

-17

-16

0 200 400 600 800 1000 1200

SOA Length (um)

CX

T R

atio

(d

B)

PGNET2006M.F, Chiang

Simulation Results – 4

SOA Parameters

Optimum Values

System ParametersOptimum

Values

Injection current 0.15 A Signal power 0.5 mW

Length 1000 x 10-6 m Control power 20 mW Confinement

factor0.15 Tsw 3 ps

Linewidth enhancement

factor 0.5

FWHM of signal &

control pulses 1 ps

Operation bit rate SPC Output power CXT

80 Gb/s 2.80 mW – 33.27 dB

160 Gb/s 1.40 mW – 28.20 dB

320 Gb/s 0.47 mW – 22.78 dB

PGNET2006M.F, Chiang

Conclusions

In the SPC,CXT is highly dependent on the gain of the SMZ switching window and the difference in the gain profiles of the SOAs in the gain recovery region.

There is a trade-off between the amount of CXT and the power level of the output signal.

By carefully selecting the SOA parameters the CXT level of the SPC could be further controlled to ensure the optimum performance.

PGNET2006M.F, Chiang

Thank You !

Question, please ?