Fig. 1. Schematic diagram of temperature control of 980 nm semiconductor laser based on FPGA

Fig. 2. Schematic diagram of interface circuit of ADC128S022

Fig. 3. Amplification circuit of input voltage

Fig. 4. Principle of semiconductor refrigeration

Fig. 5. Flow diagram of FPGA control module

Fig. 6. Interface diagrams.(a) ADC driving module; (b) state machine switching module

Fig. 7. Flowchart of switching of state machine

Fig. 8. Interface diagrams. (a) DAC driving module; (b) PWM module

Fig. 9. Experimental device diagram

Fig. 10. PI curves of 980 nm laser.(a) PI curves without setting temperature control module; (b) PI curves of setting temperature control module

Fig. 11. Temperature variation of laser

Fig. 12. Output pulse spectrum of EDFA without temperature control module.(a) Output spectrum of EDFA; (b) center wavelength change

Fig. 13. Output pulse spectrum of EDFA when temperature control module is installed.(a) Output spectrum of EDFA; (b) center wavelength change