Multiple frequencies analysis in FBG based instantaneous frequency measurements

摘要

This article describes the design principles of instantaneous frequency measurement system of microwave signals based on the use of amplitude-phase modulation conversion of single optical carrier into symmetrical dual-frequency ones for additional frequency separation according its wavelength range, and same its modulation by unknown frequency and subsequent “frequency-amplitude” measurement conversion in fiber Bragg grating with Gaussian reflection profile. Distinction and measurement of the instantaneous frequencies made depending on the amplitudes, modulation indexes and form of the signals on the difference frequency envelope of unknown frequency components, received at the photodetector in two separated ranges 0,25-12,5 GHz and 12,5-25 GHz. Such approach increases the SNR and allows measuring of several unknown frequencies simultaneously vs classical IM-DD approach in FBG based systems of given type. From another side this method realization have to use expensive wideband photoreceiver. The main purpose of article is to show how to decrease bandwidth of system photoreceiver in two times.