Instantaneous frequency measurement by optical filters based on vernier effect

An instantaneous frequency measurement system is proposed based on two optical filter response functions that are utilized to making coarse and fine measurement of unknown RF frequency. The latter response is periodic, which plays a role like a vernier, and the filter is made of FBG. This system employs one intensity modulator, three optical filters and power meters, and powers of single-side signals in three channels are measured. In experiment, 16-GHz range and less than 100-MHz error are successfully achieved for -6-dBm power of RF input.