High-Gain, Narrow-Band Optical Amplification for Photonic Microwave Applications Using Stably Injection-Locked Semiconductor Lasers

Narrow-band optical amplification is required in many applications, such as optical communications, optical signal processing, and radio-over-fiber systems. To achieve selective optical amplification using conventional wideband optical amplifiers, the useful optical signals need to be optically filtered before and after optical amplification to ensure only the desired signals are extracted and the excess optical noise caused by the amplifiers is minimized. However, the quality of the extracted low-power optical signals would be affected due to the deterioration of optical signal-to-noise ratio [1–3]. In this paper, we propose a scheme that provides high-gain and high-quality narrow-band optical amplification based on a simple optical injection structure. For the proof of concept, we apply the proposed scheme to amplify an optical signal that carries closely spaced frequency components for photonic microwave down-conversion in a radio-over-fiber system. The schematic diagram of the proposed optical amplification scheme, which consists of two typical single-mode distributed-feedback semiconductor lasers, is presented in Fig. 1.