Driving And Modulation Of Semiconductor Light Source Based On FPG

Light sources and their modulation performance determine the detection limit and application range of sensing systems,but the high cost of external modulators limits their practicality.In this paper,we aim to build a low-cost modulable light source,and deeply study the driving and modulation technology of semiconductor light source to realize the relevant sensing test.The main research is as follows:(1)The OPA690-based laser diode constant-current driver circuit module is designed and an avalanche photodiode based detection platform is built.Through testing,the linearity between the control voltage and output current of the driver module reaches0.995,the maximum variation in the range of 0～43.7 m A is less than 0.06 m A,and the current stability is better than 0.57%,the nonlinear error in the range of 0～2 V is less than 3.2%.Further,the effect of bias current on the spectral output characteristics of the laser diode was investigated.As the bias current(11～33 m A)increased,the wavelength tuning range was 0.34 nm,the extinction ratio increased significantly to a maximum value of 33.10 d B,and the linewidth decreased significantly to a minimum value of0.050 nm.(2)Based on the direct frequency synthesis technique,a signal source that can be used for modulation of semiconductor lasers is designed using a field-programmable gate array(FPGA).Experimental test results show good output characteristics for a variety of modulated signal states.The accuracy is better than 99.33% in the frequency range of 0～30 MHz,and the amplitude can still reach 8.32 V at the output signal frequency of 10 MHz.In addition,the signal phase is continuously adjustable in the range of 0～2π,and the maximum error rate is less than 1%.Further,the effect of the modulation signal on the spectral output characteristics of the laser diode was investigated.As the modulation signal frequency increased from 5 k Hz to 10 k Hz and the amplitude increased from 0.6 V to 2.2 V,the linewidths showed different degrees of broadening,0.039 nm and 0.05 nm,respectively.(3)Based on the transmission differences of orthogonal polarization modes in the polarization-preserving fiber,a Sagnac ring interferometer based on the polarization-preserving fiber was constructed and the corresponding temperature sensing experiments were carried out.The experimental results showed that the designed laser light source obtained a temperature response enhancement of about 10%with a sensitivity of-2.18 d B/°C compared with a commercial broadband light source.Further,an intensity demodulation based temperature detection system was constructed,and the absolute intensity sensitivity measured was-0.979 μW/°C,corresponding to a detection limit of 0.01°C.