FWM

Fiber optic communication has revolutionized telecommunication systems. The need for large transmission capacity has driven the rapid development of fiber optic communication. Nonlinear fiber optics plays the important role in the design of such high-capacity lightwave systems. Nonlinear optics deals with the behavior of light in nonlinear media. Nonlinear effects in the optical fiber occurring due to nonlinear refractive index are Self-Phase Modulation (SPM), Cross-Phase Modulation (XPM), Four-Wave Mixing (FWM). Nonlinear effects are useful for designing lasers, amplifiers, switches, multiplexers, demultiplexers, logic devices etc. But they can limit performances of optical fibers. Nonlinear effects are reviewed using OptiSystem simulation results in this paper.

The development of all optical super fast arithmetic logic unit (ALU) is one of the most important requirement for construction of super fast all optical processor. All optical half-adder and half-subtractor have performed most of the essential functions of the arithmetic logic unit. Here in this paper the author has proposed a scheme of single module for phase encoded simultaneous operation of half-addition and halfsubtraction for the same input bits using four wave mixing (FWM) in semiconductor optical amplifier (SOA). This type of single module for simultaneous operations using phase encoding based on the difference of phase with the reference signal one through FWM in SOA will gives fast response to accomplish the demand of super fast all optical processing.

In this paper, electro-optic phase modulator (EOPM) is used to reduce the effect of four-wave mixing (FWM), which is placed after 64 DWDM-channels multiplexer. It was found that the FWM is very sensitive to the phase deviation of the EOPM, and it can be reduced by introducing a phase shift between pulses. The simulation results confirmed the ability of the EOPM in improving the system performanceas indicated by the bit error rates. In term of comparison, the system of 64 channels based intensity modulated/ direct detection (IM/DD) transmission achieved bit error rate of 10-26 over 30 km and 70km without and with EOPM, respectively. Keyword: DSF DWDM EOPM FWM SMF 1. INTRODUCTION Optical fiber offers huge bandwidth utilized by dense wavelength division multiplexing (DWDM) network [1], [2]. Nonlinear effects have a huge impact on the performance of DWDM; mainly four-wave mixing (FWM) phenomena. The FWM mainly occurs due to the interaction between two or more wavelengths, in which new wavelengths are generated due to the variations in the refractive index of the fiber [2]. Thus, the newly generated wavelengths may coincide with the original wavelengths resulted in introducing server source of impairments. The phase of the signal in On-Off keying modulation (OOK) is an extra degree of freedom since the data is carried by signal's intensity and the inter and intra-channel FWM consider as the major source of impairments in high data rate OOK system. Hence, by using alternate-phase return-to-zero (APRZ) modulation, the phase of an RZ signal is modulated at half the bit rate in order to give a phase shift to neighboring bits which causes the intra-channel FWM contributions to interfere destructively [3]. Although such approach has been shown to be able to reduce the intra-channel FWM effects, however, it has been tested only for a single channel. In [4]; asynchronous phase modulation (APM) proposed and resulted in increasing the power tolerance of NRZ-OOK over a long distance. Similarly, in [5] an optical phase conjugation (OPC) firstly proposed for suppression the FWM effect. Unfortunately, the OPC possess several limitations as it is very complex, possess extra loss, and it cost too much. Recent studies in [6-9] used different modulation formats in DWDM system to increase the nonlinear tolerance such as the return to zero (RZ), carrier suppression return to zero (CSRZ), Differential phase shift keying (DPSK), Differential Quadrature Phase Shift Keying (DQPSK), optical duo-binary (ODB) and duo-binary return-to-zero (DRZ). The results of these studies revealed that CSRZ and DRZ modulations have better performance and are