Performance limitations of a terahertz optical TDM transmission link due to fiber dispersion and demultiplexer crosstalk

Abstract

Performance analysis of high bit rate optical time division multiplexed system affected by fiber dispersion and impairments due to nonlinear optical loop mirror (NOLM) which is used as ademultiplexeris presented in this thesis. Optical time division multiplexing (OTDM) technique is a process of optically combining number of lower speed signals. It offers transmitting high bit rate signal within a single wavelength of light. Thus it ensures utilization of full optical bandwidth. But complex synchronization process and switching circuitry limits the choice of OTDM system. As the dispersion index is a function of bit rate the high bit rate signal gets highly affected by the fiber dispersion. It is found from the analysis that the effect of fiber dispersion becomes significant for the value of dispersion index is higher than 0.30.

The performance of NOLM demultiplexer is broadly affected by channel crosstalk and relative intensity noise of the NOLM. Channel crosstalk in the demultiplexed signal is introduced by the intrinsic crosstalk and switching window profile of the control signal. The system suffers higher power penalty as the intrinsic crosstalk increases. Such penalty becomes significant when intrinsic crosstalk is higher than -25 dB. As the intrinsic crosstalk is a function of coupling ratio, to maintain the intrinsic crosstalk within -25 dB level the coupling ratio must be within the range of 0.47 to 0.53. The system also gets affected by the switching window profileof the control pulse for which channel crosstalk occurs. The system suffers higher power penalty as the number of demultiplexing channel increases. At the same time the system suffers more power penalty with the increment of the amount of pulse walk-off between signal and control pulse.Apart from channel crosstalk the system performance is also affected by the intensity fluctuation of the demultiplexed signal which is called relative intensity noise. The system suffers more power penalty as the relative intensity noise of the NOLM increases and the penalty becomes significant for the value of such noise higher than 〖10〗^(-5).The thesis indicates some parameters by optimizing of which the system performance can be improved. That is how the outcome of this research is expected to open a new horizon in the arena of high speed optical time division multiplexing data transmission system through fiber optic communication link in future.