optical time division multiplexing

basics of otdm including multiplexing and demultiplexing metods for more details refer G.P Agrawal.

1. Optical TDM system Submitted by Amandeep kaur 1243844 D4 ECE

2. Optical communication Multiplexing and why Types of multiplexing Basic requirement WHAT IS ??

3. Types of Multiplexing Wavelength division multiplexing(WDM) Optical time division multiplexing(OTDM) Hybrid WDM-OTDM

4. PROBLEMS WITH OTDM Nonlinearity associated with fibre , eg . Stimulated Raman Scattering results in SNR degradation as the number of channel increases Four wave mixing: limits the channel spacing Cross phase modulation: limits the number of channels High gain flat amplifiers Packet switched service by means of light paths: an extremely inefficient way of utilizing network resources

5. OTDM – What does it offer ? Flexible bandwidth on demand at burst rates of 100 Gb/s per wavelength (in the longer term). The total capacity of single-channel network = DWDM , but OTDM provide: potential improvements in network performance in terms of user access time, delay and throughput, depending on the user rates and statistics . Less complex end node equipment (single-channel Vs. multichannels )

6. Can operate at both: 1500 nm (like WDM) due to EDFA 1300 Offers both broadcast and switched based network.

7. Key Components for OTDM 1 . Transmitter • Ultra short optical pulse generation • Modulation format (OOK, DQPSK, DPSK, M-ARY QAM) 2. Transmission channel • Dispersion-managed fiber for ultra-short pulse propagation 3. Receiver 8 • Optical clock extraction • OTDM demultiplexing

8. Higher bit rate multiplexed data streams

9. System Composition light emitting part , transmission receiving part.

10. Transmitting Part consists of ultra-narrow pulse light source high repetition frequency ultra-short optical pulse source species includes erbium doped fiber ring laser, active modelocking Semiconductor laser, semiconductor ultra-short pulse source, ultrashort optical pulse sources. the optical time division multiplexer

11. The Receiving Part Includes demultiplexer , optical clock extraction low-speed optical receiver.

12. D emultiplexer Optical demultiplexer includes optical Kerr switch , optical modulator switch, four wave mixing (FWM) switch, nonlinear optical loop mirror (NOLM), cross phase modulation (XPM) switching etc

13. Demultiplexing schemes for OTDM signals based on (a) cascaded LiNbO3 modulators, (b) XPM in a nonlinear optical-loop mirror, and (c) FWM in a nonlinear medium.

14. cascaded LiNbO3 modulators

15. modulator halves the bit rate by rejecting alternate bits in the incoming signal . Different channels can be selected by changing the phase of the clock signal . Advantage- uses commercially available components . Disadvantages- limited by the speed of modulators. The electro-optic technique also requires a large number of expensive components, some of which need high drive voltage.

16. nonlinear optical-loop mirror (NOLM)

17. constructed using a fiber loop whose ends are connected to the two output ports of a 3-dB fiber coupler Sagnac interferometer mirror because it reflects its input entirely when the counterpropagating waves experience the same phase shift over one round trip.

18. FWM in a nonlinear medium

19. OTDM signal is launched together with the clock signal (at a different wavelength) into a nonlinear medium. the pulse train at this new wavelength is an exact replica of the channel that needs to be demultiplexed . A polarization-preserving fiber is often used as the nonlinear medium for FWM