1. Razali Ngah and Z Ghassemlooy Optical Communications Research Group
Sheffield Hallam University
Simulation of an All Optical Time Division Multiplexing Router Employing
TOADs
Razali Ngah and Z Ghassemlooy
Optical Communications Research Group
School of Engineering

2. Contents 1. Introduction 2. OTDM Communication System
3. OTDM Packet Format
4. All optical switching
5. OTDM Router Using TOADs
6. Simulation Results and Discussions
Conclusions
8. Further works
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3. Introduction
Why Optical domain?
Cont.
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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-data-rate 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 Format of OTDM packet Multiplexing of Clock Pulse
(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
Cont.
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7. Space division multiplexing
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
Cont.
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8. -Different wavelengths are allocated to clock and payload
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
Cont.
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9. Intensity Division Multiplexing
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
Cont.
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10. a). Asymmetric Terahertz Optical Demultiplexer (TOAD)
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
Cont.
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13. All Optical Router Using TOADs
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14. Simulation Results and Discussion
The model was simulated using Virtual Photonics (VPI) simulation package
Simulation parameters:
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