Beat frequency measurement system for multiple dual polarization fiber DFB lasers

This paper describes the design and testing of an electronic system intended to record the beat frequency signal from up to eight serially multiplexed dual polarization fiber distributed feedback lasers. The beat frequency from each laser is first mixed down to around 70 MHz and then measured using a PC based counter system. The gate frequency and, hence, the sampling rate, is designed to be around 1 kHz, and the frequency resolution of the system is found to be equal to the gate frequency. The system has been used to measure the beat frequency variation of fiber lasers due to either rapidly varying temperature or flexing motion. Measurements made with multiple fiber laser sensors show that the crosstalk between different sensors is very low.