Using Low-Density Parity-Check Codes to Reduce the Effect of Laser Line width For Optical Communication

The performance of coherent optical communication systems is degraded significantly by the phase noise of the semiconductor lasers. The phase noise is induced by spontaneous emission in the laser cavity and yields broadening in the laser linewidth. This paper addresses the application of the Low-Density Parity-Check (LDPC) codes as Forward Error Correcting (FEC) codes to relax the laser linewidth requirement. These codes are applied to three types of heterodyne optical receivers (BPSK, DPSK and QPSK) operating with finite laser linewidth

Performance Evaluation of Multimode Fiber-Based Optical OFDM Communication System

The most significant limitation of data transmission in Multimode Fibers (MMFs) is intermodal dispersion due to the propagation velocity of each of the guided mode is different. This paper addresses this problem by adopting optical Orthogonal Frequency Division Multiplexing (OFDM) scheme to compensate intermodal dispersion and to enhance the bandwidth-distance product of MMF. The optical OFDM scheme adopted here is based on treating the signal fading due to intermodal dispersion in MMFs in a similar manner to that caused by multipath effect in wireless channels. A MATLAB simulink model is developed for the optical OFDM system. Simulation results are reported for 1Gbps link operating with different digital subcarrier modulation schemes to assess the impact of various parameters on system performance. The results indicate clearly that a Bit Error RateBER) of 10-5 can be achieved for a 1Gbps, 1km (10ns-dispersion) link operating with 1550nm, -23.6dBm laser and 16- Quadrature Amplitude Modulation (QAM) subcarrier modulation scheme

Investigation of Raman Amplification In Photonic Crystal Fibers

In this paper, Raman amplification characteristics in photonic crystal fibers (PCFs) are investigated in details. Performance comparsion between PCF-based Raman amplifier and other conventional fiber-based counterparts is presented. The simulated results reported here can be used as a guide line to design PCF-based Raman amplifier that outperforms the conventional fiber amplifiers. Raman gain as high as 33 dB can be obtained with a well designed PCF even at low pump power of 300 mW