M. F. Chiang1, Z. Ghassemlooy1, W. P. Ng1, and H. Le Minh2

1. Optical Communications Research Group

School of Computing, Engineering and Information Sciences

Northumbria University, Newcastle upon Tyne, UK2. Department of Engineering Science, University of Oxford, UK

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

Simulation of an All-Optical 12 SMZ Switch with a High Contrast Ratio

Contents

Introduction

Symmetric Mach-Zehnder (SMZ)

Optical inverter based on SMZ

All-Optical 12 SMZ Switch with a High Contrast Ratio

Simulation Results

Conclusions

Introduction- Research Aim

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

All-optical switches, such as SMZs are the key components adopted for switching and routing due to their ultrafast switching time (pico- to sub-picoseconds). However, SMZs have low inter-output CR (< 10 dB).

It is essential to have a high inter-output CR switch for lower value of output crosstalk (CXT).

Ref: www.iqe.ethz.ch/photonics

SMZ SMZ

UNIUNI TOAD TOAD

Ref: (Princeton)

Ref: (Japan)

Introduction All-Optical Switches

Symmetric Mach-Zehnder (SMZ)

Semiconductor Optical Amplifier (SOA)

Input signals (light)

Carrier density &

SOA gain (XGM)

SOA refractive index &

Induced phase (XPM)

Input signals

P

N

Injection current

SOA

Advantages: 1. narrow and square switching window2. compact size3. thermal stability and low power operation

Drawback: 1. low inter-output CR (< 10 dB) due to the problem of maintaining the same

phase shift.

Undesired signal

Symmetric Mach-Zehnder (SMZ)

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

Inter-output Contrast Ratio (CR) of a 12 Switch

The inter-output CR of a 1×2 switch is defined as the power

ratio between the switched and non-switched signals at

outputsij

where i, j = 1 or 2.

Typically the value of inter-output CR observed at the SMZ

output 2 (CR21) is less than 10 dB.

Here we propose a 1×2 switch utilizing an optical inverter

that offers improved CR21.

All-Optical 12 SMZ Switch with a High Contrast Ratio

SMZ1

SMZ2

inverter CP

CP

CP

Output1 (SMZ1_op1) Input packets

CLK CEM

SMZ1_op2

Output2 (SMZ2_op1)

CEM: clock extraction module

low inter-output CR (< 10 dB)

Improved CR (> 32 dB)

All-optical Inverter Based on SMZ

A A bar

1 0

0 1

SOA

SOA

Input (CLK)

CP 1 (CLK)

CP 2 (A)

Output (A bar)

Simulation Results-Simulation Parameter

Simulation Tool: Virtual Photonic Inc. (VPI)

Parameter and description Value

Inject current 0.15 A

Length 500 x 10-6 m

Width 3 x 10-6 m

Height 80 x 10-9 m

Confinement factor 0.15

Differential gain 2.78 x 10-20 m2

Carrier density at transparency 1.4 x 1024 m-3

Initial carrier density 3 x 1024 m-3

Linewidth enhancement factor 5

Recombine constant A 1.43 x 108 s-1

Recombine constant B 1 x 10-16 m3s-1

Recombine constant C 3 x 10-41 m6s-1

TABLE ISOA SIMULATION PARAMETER

TABLE IISIGNAL AND CONTROL PULSES

DEFAULT PARAMETERS

Parameter and description Value

Data packet bit rate – 1/Tb 160 Gb/s

Packet payload length 1 bytes (8 bits)

Packet guard time 1.5 ns

Wavelength of data packet 1554 nm

Data & control pulse widths – FWHM 2 ps

Bit duration Tb 6.25 ps

Control signal (CP) power 40 mW

Simulation Results-Time Waveforms

Output waveforms observed at the proposed 12 switch

Input packets

Control pulse

Output1

Output2

Simulation Results-Time Waveforms

Output CR ratio observed at the proposed 12 switch

CR (< 10 dB)

The improvedCR (> 30 dB)

Simulation Results-The contrast ratio (CR) against the

input packet power

0

5

10

15

20

25

30

35

40

45

50

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Input packet pow er (dBm)

CR

(dB

) CR of CP

CR at output1

CR at output2

CP

Simulation Results-The contrast ratio (CR) against the

control pulse power

7

12

17

22

27

32

37

42

47

13 14 15 16 17 18 19

Control pulse power (dBm)

CR

(dB

) CR of abar

CR at output1

CR at output2

CP

Conclusion

The advantages and drawbacks of SMZs were introduced.

The principle of the proposed all-optical 12 SMZ switch with a high contrast ratio was explained.

By carefully selecting the power of the control pulses, inter-output CR of > 32 dB was achieved over a wide range of input packet power (12 dB).

The proposed 12 switch offered an improvement in the inter-output CR of ~ 25 dB in comparison with a single SMZ switch. The proposed switch could potentially be adopted for high-speed signal processing and packet routing in all-optical networks.

Special ThanksSpecial Thanks for

Prof. Z. Ghassemlooy

Dr. Wai Pang Ng

Dr. Hoa Le Minh

All colleagues in NCRLab

&

Your Attention

Questions/Suggestions/Comments, pleaseQuestions/Suggestions/Comments, please

Thank you for your kind attention.Thank you for your kind attention.