Microwave signal processing using photonic techniques.

Abstract

Microwave signal processing using photonic technologies is a technique to process microwave or radio frequency (RF) signals with the help of photonic devices or subsystems. Processing of RF signals conveyed by an optical carrier directly in the optical domain offers great flexibility in selecting the radio frequency of operation, RF bandwidth, and the filter response. This technique can overcome the limitations of conventional electrical signal processors such as limited bandwidth and electromagnetic interference. It also has the advantages of high rate-distance product, low loss, and tunable and adaptive functions. The major parts of the thesis are devoted to the development of the microwave signal processing techniques such as microwave photonic filter (MPF) and microwave signal instantaneous frequency measurement (IFM) using photonic techniques.

In order to realize microwave photonic filter (MPF), various schemes of division, delay and summing of a modulated optical signal have been proposed in the literature. The coherent summing of optical signals is sensitive to polarization fluctuation caused by environmental perturbation. Therefore the incoherent approach is more attractive in practice for stable operation. To satisfy the requirement of incoherent summing, either the laser coherence time is needed to be shorter than the optical delay time, or the state of polarization (SOP) of the optical signals after division needs to be orthogonal.

Tunability is an important feature of microwave photonic filters. Based on the working principles of microwave photonic filters, tunability can be realized through changing the number of taps, tap weights, and time delay between taps.