The Application of SOA in All-optical Wavelength Conversion and ROF System

Wavelength conversion has been suggested as one of the key functions for wavelengthdivision-multiplexing (WDM) optical networks and photonic switch blocks. Several methods, such as a self-phase modulation (SPM), a cross-gain modulation (XGM), and crossphase modulation (XPM), can be used to realize all optical wavelength conversion (AOWC) [1-29]. However, four-wave mixing (FWM) based on nonlinear media, such as optical fiber and semiconductor optical amplifier (SOA), is considered to be the most promising scheme because it is fully transparent to the signal bit rate and modulation format. AOWC in SOA has many advantages such as easily compatible and highly covert efficiency. AOWC based on FWM in SOA for regular signal such as ON/OFF keying (OOK) signal has already investigated maturely but not for OFDM signals. This chapter discusses the performance for OFDM signal in AOWC based on FWM in an SOA. We found the result for OFDM signal is the same as that of OOK signal. Multiple frequency mm-wave generation is one of the key techniques in radio over fiber (ROF) system. Many methods can generate multiple frequency mm-wave such as using optical carrier suppression (OCS), suppression of odd-order sidebands, multi-cascaded external modulators and so on. Some references have proposed that multiple frequency mm-wave can be generated by using SOA based on FWM effect and discuss polarization insensitive in SOA. This chapter also introduces this method to generate mm-wave and discusses the polarization insensitive all-optical up-conversion for ROF system based on FWM in a SOA. We have proposed and experimentally investigated polarization insensitive all-optical upconversion for ROF system based on FWM in a SOA. One method is that a parallel pump is generated based on odd-order optical sidebands and carrier suppression using an external intensity modulator and a cascaded optical filter. Therefore, the two pumps are always parallel and phase locked, which makes the system polarization insensitive. This scheme has some unique advantages such as polarization insensitive, high wavelength stability, and low-frequency bandwidth requirement for RF signal and optical components. The other method is where co-polarized pump light-waves are generated by OCS modulation to keep the same polarization direction and phase locking between two pumps. This scheme also has excellent advantages such as small size, high-gain, polarization insensitivity, and lowfrequency bandwidth requirement for RF signal and optical components, and high