1. Sheffield Hallam University
Simulation of an All Optical T
ime
Division M
ultiplexing Router E
mploying
T
OADs
Razali Ngah and Z Ghassemlooy
Optical Communications Research Group
School of Engineering

2. Contents
1.
2.
3.
4.
5.
6.
7.
8.
Introduction
OTDM Communication System
OTDM Packet Format
All optical switching
OTDM Router Using TOADs
Simulation Results and Discussions
Conclusions
Further works
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3. Introduction
Why Optical domain?
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Cont.
3

4. Introduction
Multiplexing Techniques
- to extend a transmission capacity
- OTDM vs. WDM
OTDM
WDM
Single wavelength
Multiple wavelength
High bit rate (up to 640Gb/s)
Lower bit rate (2.5 – 100Gb/s)
Immature technology
Reaching an advanced stage of
development
Chromatic dispersion & timing jitter
FWM, SRS & XPM
OTDM can provide users with better throughput delay
performance, faster single-channel access times for high-datarate end users

5. OTDM Communication System
- 10 Gbps is commercially available
- There are two types:
-Bit Interleaved TDM
-Slotted (packet) TDM

6. OTDM Packet Format
Clock
(Frame Sync.)
Address
Payload
Format of OTDM packet
Multiplexing of Clock Pulse
- Space Division Multiplexing
- Wavelength Division Multiplexing
- Orthogonal Polarization
- Intensity Division Multiplexing
- Time Division Multiplexing
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Cont.

7. OTDM Packet Format
- Space division multiplexing
-The clock is carried on by a separate transmission fibre
from the data packets
-Problems: (i) time varying differential delay between the
clock and data, and (ii) the cost of installing a separate
clock fibre for each network node in new installation is
not practical for wide area networks
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Cont.

8. OTDM Packet Format
- Wavelength division multiplexing
-Different wavelengths are allocated to clock and payload
-Problems: Only practical for predetermined path lengths
between nodes in single hop networks.
The relative delay between the clock and data will be random
in asynchronous packet-switched since the optical path length
through which a packet travels is non-deterministic
Orthogonal Polarization
-An orthogonally polarized clock pulse is used
-Problem: Difficult to maintain the correct polarization
throughout the system
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Cont.

9. OTDM Packet Format
- Intensity Division Multiplexing
-Higher intensity for the optical clock pulse is used to
differentiate it from the data
-Problem: The clock pulse amplitude and its position
become difficult to maintain in long distance transmission
- Time Division Multiplexing
-Self-synchronization approach, the clock is located at the
start of the packet
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Cont.

10. All Optical Switching
a). Asymmetric Terahertz Optical Demultiplexer
(TOAD)
b). Mach-Zehnders interferometer (MZI)
c). Ultrafast nonlinear interferometer (UNI)
- Optical control pulse is used to change SOA’s gain
and refractive index
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11. Asymmetric Terahertz Optical Demultiplexer
(TOAD)
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12. All Optical Router Using TOADs
Clock
Data packet
Data Packet
TOAD1
(Clock
extra.)
Data Packet
TOAD2
(read
address)
Clock
Port 1
TOAD3
(route
payload)
Address
Payload
Port 2
Block Diagram of 1x2 OTDM Router
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Cont.
5

13. All Optical Router Using TOADs
SOA
Fibre
loop
PBS1
SOA
PBS2
PC
Reflected clock pulse
Clock + data packet in
50:50
Data packet out
Reflected Port
(Port 1)
Transmitted Port
(Port 2)
Clock recover module
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Clock
out

14. Simulation Results and Discussion
- The model was simulated using Virtual Photonics (VPI)
simulation package
- Simulation parameters:
Parameters
Data bit rate (per channel)
Clock pulse FWHM width
Address bit FWHM width
Injection current of SOA
SOA length
SOA active areas
SOA confinement factor
SOA Differential gain
SOA carrier density transparency
SOA Linewidth enhancement factor
SOA recombination coefficient A
SOA recombination coefficient B
SOA recombination coefficient C
SOA Initial carrier density
Values
2.5 Gbps
1 ns
0.5ns
0.15A
0.5 mm
3x10-13 m2
0.15
2.78x10-20 m2
1.4x1024 m-3
5
1.43x108 1/s
1.0x10-16 m3/s
3.0x10-41 m6/s
3.0x1024 m-3
Cont.

15. Simulation Results and Discussion
- OTDM packet
Cont.

16. Simulation Results and Discussion
Extracted Clock Signal
Transmitted Output of TOAD1
Cont.

17. Simulation Results and Discussion
Reflected Output TOAD2
(Address bit)
Transmitted output of TOAD2
(Payload)
Cont.

18. Simulation Results and Discussion
Payload at Port 2 of TOAD3

19. Conclusions
-A node model for an OTDM router (1X2) for asynchronous packet
routing is presented
-The switching devices employed for clock recovery and payload
routing are carried out in optical domain using TOADs
-Simulation results demonstrate that clock recovery, address
recognition and payload routing has been achieved successfully
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20. Further works
- To simulate multiple input and output networks
- Crosstalk and noise analysis for multiple input and output
networks
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21. Thank you