Optical Injection Instabilities of Semiconductor Lasers for Radio-over-fiber Applications

Description

Wireless communication is ubiquitous in modern societies. Large area coverage to wireless customers is enabled by the deployment of many basestations. The basestations are then connected to and coordinated by a central office. The connection from the central office to the basestations can be conveniently provided by the radio-over-fiber (RoF) technology. Optical fibers are used to transmit optical carrier signals that carry microwave modulations as subcarriers, which are in turn modulated with data. A simplified basestation requires only a photodetector to extract the microwave and an antenna to radiate the signal. This allows the centralization of electronics and the deployment of a large number of basestations. This research concerns with the generation and the data modulation of the photonic microwave at the central office for the downlink. Semiconductor lasers are compact, rugged, and high-speed devices suitable for RoF. In the past, direct current modulation was often used for RoF. However, as the required RoF subcarrier frequency increases over the years, the laser modulation bandwidth has become insufficient. This hurdle has been circumvented recently through the research on the nonlinear dynamics of optically injected semiconductor lasers. The dynamical instabilities of an injected laser can be harnessed to generate high frequency microwave signals beyond the usual modulation bandwidth limit. Building on these results, the goal of this research is to investigate the different aspects of modulating the subcarrier for data transmission. Based on the optical injection system, three configurations for data modulation are investigated: modulated microwave injection, modulated optical injection, and direct data modulation. These methods also incorporate frequency division multiplexing (FDM) as in most practical RoF networks. The transmission performances, such as the bit-error rate (BER) and the allowed data rate, will be examined under the effects of intermodulation distortion, dispersion-induced power penalty, and cross-talk. The three configurations will be compared in parallel to characterize their respective advantages. The success of the research will extend our understanding about the data modulation properties of the optical injection system. The results will be useful for future RoF designs using semiconductor lasers.