Effects of Fiber Propagation on Microwave Signals Generated by Laser Dynamics

Recent research on the nonlinear dynamics of semiconductor laser demonstrated the generation of microwave oscillation beyond the modulation bandwidth. It utilizes the dynamics of an optically injected laser diode, which emits an optical carrier with microwave subcarrier sidebands. It is a promising source for radio-over-fibre (RoF) systems in wireless networks. However, the important effects of optical fibre dispersion and nonlinearity have not been sufficiently investigated in relation to the signal generated. Dispersion not only causes data distortion, but also affects the phases between the subcarrier sidebands. The phase changes can cause microwave power penalty and degrade the quality of the signal. Thus the light source should be optimized to mitigate the problem. Furthermore, fibre nonlinearity is an important problem for high-power transmission. Brillouin scattering reflects light above a threshold and limits the RoF signal strength. A solution should be sought using the optical injection system.