Microwave Frequency Measurement Using Fiber Bragg Grating as V-shape Filter

Broadband, low loss and cost-effective transmission capability of optical fiber links has led to a widespread applications in almost every field. Instantaneous microwave frequency measurement is one of the fields facilitated by optical communication. In this paper, a new optical technique for microwave frequency measurement, which was based on an optical V-shape fiber Bragg grating (FBG) filter and RF power monitoring, is proposed theoretically and experimentally. The microwave signal was modulated onto an optical carrier using a Mach-Zehnder modulator (MZM) which was biased at quadrature point, and divided into two identical parts afterwards by an optical coupler. One part of the light was reflected by an FBG, and the other served as a reference signal. Both the reflected and reference signals are compared to get a monotone frequency dependent power ratio function (PRF). Through a table looking up process from the PRF, the frequency of an unknown microwave signal can be obtained.