This work presents a comprehensive study of the four wave mixing (FWM) effect in the highly nonlinear fibre (HNLF) and semiconductor optical amplifier (SOA); and their applications. The nonlinearity parameters such as zero-dispersion wavelength (ZDW), chromatic dispersion (CD) and nonlinear coefficient of HNLF has successfully investigated by using several FWM techniques. Results from all techniques have been achieved approximately similar to the manufacturer specification. This technique is then employed for the measurement of the FWM power and FWM efficiency in a SOA, in addition to the...