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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.