Presentation Outline

Introduction All-optical packet switching All-optical router Mach-Zehnder Interformeter(MZI)

SOA structure ProblemProposedOur proposal

Presentation Outline

Segmentisation modelUniform biasingNon-uniform biasing

Triangular bias current Sawtooth bias current

Comparison between uniform and non-uniform biasing techniques

Conclusions

All-optical packet switching

Edge Router (Ingress/Egress) with 4-bit address XXXX

Core Router

1011

1010 0110

0111

Client Network

Client Network

1001

XXXX

Low-speed packet

Low-speed packet

High-speed packet

Core Network

Buffer

Input

Output

Main modules Optional modules

Packet

Delay unit

Clock Extraction

Header Extraction

Header Recognition

Look-up Routing Table

Reconfiguration

Optical Switching Unit

Controlling Contention

Signal Processing (2R, 3R, equalization)

Splitter

All-optical router

Mach-Zehnder Interformeter (MZI)

CP1

SOA1

SOA2 CP2

Input Output 1

Output 2

Symmetric Mach-Zehnder (SMZ)

Mach-Zehnder Interformeter (MZI)

Advantages of SMZ Narrow and square switching window Compact size Thermal stability and low power operation High integration potential Strong nonlinearity characteristics

Mach-Zehnder Interformeter (MZI)

Injection current (I)

L

Input facet of active region Input signals

Output signals

Output facet

H

w

SOA structure

Energy gap

E2 (conduction band)

E1 (valence band)

Stimulated absorption

Stimulated emission

Spontaneous emission

Hole Electron (carrier)

Photon Inducing photon

Stimulated photon

Input optical signal (photon)

Output amplified optical signal

SOA structure

Problem

For high-speed applications, the SOA must have a fast gain recovery time to avoid system penalties arising from bit pattern dependencies. The gain recovery of the conventional SOAs is limited by the long carrier-recovery time.

Proposed

The slow gain recovery can be improved by increasing the injected bias current, the device length or by changing the pulse width (input energy) of the input signal [5]. Several research groups have reported theoretical and experimental results on externally injected SOAs (assist light or holding beam ) [6,7].

Our proposal

Novel non-uniform bias current techniques are injected to the SOA in order to achieve a linear output gain compared to the uniform biasing for ultra-high speed routers.

segment1

segment2

………….. …………….

segment5

t=0 t=l/vgg

t=L/vg

input signal

output signal

Ni

N(1)

N(5)

Segmentisation model of the SOA

• Normalized SOA gain response to single (doted) and multiple (solid) input pulses.

0 1 2 3 4 5 6

x 10-9

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Time, t (s)

Nor

mal

ized

SO

A g

ain,

G

multiple input pulses

single input pulse

Uniform Biasing

• Normalized output gain achieved by successive input pulses.

2.8 3 3.2 3.4 3.6 3.8 4 4.2

x 10-9

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Time, t (s)

Norm

aliz

ed o

utpu

t gai

nUniform Biasing

• Sawtooth (doted) and triangular (solid) bias currents.

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

x 10-9

0

0.05

0.1

0.15

0.2

0.25

0.3

Time, t (s)

Bias

cur

rent

, I (A

)

sawtooth

triangular

Non-uniform Biasing

• Normalized SOA gain response to multiple of input pulses using triangular bias current.

0 1 2 3 4 5 6

x 10-9

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Time, t (s)

Norm

alize

d SO

A ga

in, G

Triangular bias current

• Normalized output gain achieved by successive input pulses using triangular bias current as a ratio of uniform bias current.

2.8 3 3.2 3.4 3.6 3.8 4 4.2

x 10-9

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Time, t (s)

Norm

aliz

ed o

utpu

t gai

nTriangular bias current

• Normalized SOA gain response to multiple of input pulses using sawtooth bias current.

0 1 2 3 4 5 6

x 10-9

0

0.5

1

1.5

2

2.5

3

3.5

Time, t (s)

Norm

alize

d SO

A ga

in, G

Sawtooth bias current

• Normalized output gain achieved by successive input pulses using sawtooth bias current as a ratio of uniform bias current.

2.8 3 3.2 3.4 3.6 3.8 4 4.2

x 10-9

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Time, t (s)

Norm

aliz

ed o

utpu

t gai

nSawtooth bias current

0 0.5 1 1.5 2 2.5 3 3.5 4

x 10-15

12

14

16

18

20

22

24

26

28

30

Energy, E (J)

Gain

stan

dard

dev

iation

,

(dB)

uniform (40Gbps)sawtooth (40Gbps)

triangular (40Gbps)

uniform (20Gbps)

sawtooth (20Gbps)triangular (20Gbps)

uniform (10Gbps)

sawtooth (10Gbps)triangular (10Gbps)

40 Gbps 20 Gbps

10 Gbps

Comparing uniform and non-uniform biasing

• Gain standard deviation against the input signal energy for uniform (dot-dashed), sawtooth (doted) and triangular (solid) biasing for a range of data rates.

0 0.5 1 1.5 2 2.5 3 3.5 4

x 10-15

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Energy, E (J)

Gain

stan

dard

dev

iatin

diffe

renc

e (d

B)

sawtooth (40Gbps)sawtooth (20Gbps)

sawtooth (10Gbps)

triangular (40Gbps)

triangular (20Gbps)triangular (10Gbps)

10 Gbps

40 Gbps

20 Gbps

Comparing uniform and non-uniform biasing

Improvement of the gain standard deviation upon uniform biasing

•For sawtooth bias current:• at 10 Gbps 3.25 dB• at 20 Gbps 0.51 dB• at 40 Gbps min improvement

•For triangular bias current:• at 10 Gbps 2.4 dB• at 20 Gbps 0.4 dB• at 40 Gbps min improvement

• Gain standard deviation against the average sawtooth bias current for 1 fJ input signal energy.

0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

5

10

15

20

25

30

Average bias current, I (A)

Gain

stan

dard

dev

iation

,

(dB)

We have proposed novel techniques to bias the SOA.The total gain response of a segmentized SOA model is simulated.We have investigated applying triangular and sawtooth biasing shapes in order to optimize the gain standard deviation for data rates of 10, 20 and 40 Gbps. Results showed an enhancement to the gain uniformity achieved using non-uniform biasing, especially sawtooth biasing.The impact of the input pulse energy on the gain standard deviation and the output gain for all biasing techniques are investigated. The impact of the average bias current used on the gain uniformity is presented.