Design Of Tunable High Precision Laser Driving System

With the demand for large-capacity,long-distance,high-performance communication,coherent optical communication has become the most important communication method in the 21 st century.Semiconductor lasers have been widely used as signal sources and local oscillator of coherent optical demodulation in coherent optical communication systems due to their small size,easy tuning and direct modulation.The direct factors affecting the quality of coherent optical communication—the stability of the signal sources and the coherence of the optical carrier extracted by the local oscillator source—have become the focus of research.The semiconductor laser drive circuit directly affects the stability of the signal sources,and also affects the coherence of the optical carrier extracted by the local oscillator source.Therefore,it is of great significance for the research of the semiconductor laser drive circuit.Based on the analysis of the principle of semiconductor laser drive circuit,this paper analyzes the factors affecting current and temperature stability and proposes improvement measures.A new constant current source drive circuit and temperature control circuit are designed and tested by semiconductor laser.The specific content and results are as follows:(1)Analyze the classical constant current source drive circuit and point out the factors affecting the current stability,and propose an improved scheme and test the semiconductor laser.By selecting the P-type FET as the constant current source circuit steady current device,the current stability in the circuit is improved;by improving the circuit structure and increasing the PID control circuit,the steady-state error in the constant current source circuit is eliminated;through the multi-operator amplifier control circuit,The current fluctuation is reduced while achieving more effective protection of the semiconductor laser.The theoretical analysis of the factors affecting current stability in the newly designed constant current source drive circuit is carried out.Finally,by constructing the physical circuit structure and testing the semiconductor laser,the experimental results show that the driving current fluctuation is less than 3?A.(2)For the principle analysis of temperature measuring device and temperature control device in the temperature control system of semiconductor laser,two different types of temperature control schemes are designed and the temperature control circuit is built to test the temperature of the semiconductor laser.A bridge type temperature measuring circuit,a PID control circuit,and a power amplifier part OPA569 are used to drive the TEC circuit,and the semiconductor laser is tested.The test result indicates that the temperature fluctuation range of the semiconductor laser is less than 0.008°C;the integrated temperature control is built.The chip MAX1978 peripheral bridge temperature measuring circuit,PID control circuit and PWM filter circuit and test the semiconductor laser,the test results show that the semiconductor laser temperature fluctuation range is less than 0.003°C.(3)Measure the current in constant current source circuit and temperature in temperature control circuit.The 12-bit analog-to-digital chip ADC7895 is combined with the high-precision operational amplifier OPA2227 to measure the current signal in the constant current source circuit and the temperature signal in the temperature control circuit.Through the amplifier circuit to amplify the weak signal in the circuit and compare with the reference voltage of the analog-to-digital converter ADC7895,the change of the current signal in the constant current source circuit and the temperature signal in the temperature control circuit is measured.