Development Of Dual-path Fiber Laser Balanced Heterodyne Detection Circuit Based On FPG

In the field of distributed and high-precision optical fiber sensor measurement,laser heterodyne beat detection has become the key technology of weak signal amplification and high-precision signal extraction.How to reduce the cost of detection system and realize the accuracy and miniaturization of laser beat measurement is an urgent problem in the actual test.In this paper,based on the detailed analysis of the development process and principle of optical heterodyne detection technology at home and abroad,combined with experiments,it has been verified that in the field of optical heterodyne detection,compared with the traditional single ended detection,the balanced detection technology can improve the signal-to-noise ratio of the output signal.Therefore,this paper takes FPGA as the core to develop a dual channel optical fiber laser balanced heterodyne detection circuit.Two laser passes through 2×2 coupler incident to the balance detector to realize the photoelectric beat frequency conversion.The beat frequency signal in the radio frequency domain has been down converted into intermediate frequency signal through the mixing circuit.The demodulation circuit of beat frequency signal controlled by FPGA has been designed to collect intermediate frequency signal.The digital signal processing has been carried out in FPGA.The time-frequency conversion has been completed through FFT transformation,and the frequency difference information of the two-way laser signal has been analyzed,The measurement information has been transmitted to the upper computer interface of Matlab GUI through Gigabit Network for storage and display.The simulation and experiment results show that the circuit can realize the real-time detection of two-way laser beat signal in the wide frequency range of0.41～3.45 GHz,and the frequency resolution is 7.6k Hz,which lays the foundation for the transmission and induction of the two-way fiber laser balanced heterodyne detection circuit with miniaturization,low cost,high resolution and good real-time performance.