Optical-Domain Wideband Microwave Amplification System

摘要

An optical-domain wideband microwave amplification system which takes advantage of the large bandwidth capacity of optical devices to amplify optically carried microwave signals is proposed. A comprehensive theoretical model of the system including link gain, noise and spur-free dynamic range (SFDR) is established, with which all kinds of performance of the system can be analyzed conveniently for given system parameters. Based on the theoretical model, an experiment platform for the microwave amplification system is established. The source microwave signal is modulated up to the optical domain by carrier-suppressed modulation in a Mach-Zehnder intensity modulator (MZM) whose DC bias voltage is controlled by an automatic-bias-voltage-control (ABVC) module. The output optical signal from the MZM is amplified by a commercial erbium-doped-fiber-amplifier (EDFA) and then passes an optical band-pass filter (OBPF) to filter out out-band amplified spontaneous emission (ASE) noise. Finally the optical signal is fed into a photo-detector (PD) and the amplified microwave signal is obtained at the output of it. Owning to the wide gain spectrum and the large small-signal gain of the EDFA, wideband microwave gain which is larger than 17 dB is obtained over 12GHz-bandwidth. The microwave gain is quite stable while the input microwave power varies from -60 dBm to -15 dBm and the input microwave frequency is tuned from 100 MHz to 12 GHz. The noise floor is approximately -137 dBm /Hz, which is mainly caused by the ASE noise brought in by the EDFA. The SFDR of the system is third-order inter-modulation dominated and is measured to be 113.1dB·Hz~(2/3).