Design,Realization And Optimization Of Highly Stable Laser Source

The highly stable laser source is widely used in optical fiber communication systems,optical fiber sensing,and optical fiber attenuation measurement.The semiconductor laser diode has many advantages,such as high conversion efficiency,small size,lightweight,high reliability,directly modulated and strong integration with other semiconductor devices.In this paper,the 1550 nm butterfly encapsulated semiconductor laser is the best choice for making a highly stable laser source.With the theoretical analysis of the basic characteristics of the semiconductor laser,it is understood that the semiconductor laser is not only a threshold device,but also a temperature-sensitive device,the stability of its output optical power is closely related to the driving current and operating temperature.Therefore,to make the output optical power of semiconductor laser stable,it is necessary to keep the driving current and operating temperature stable.The core of this design is to design the constant current source circuit and temperature control circuit for the semiconductor laser.In the design of the constant current source circuit,it is effective to amplify the tiny reference current source to get the drive current that we need.What's more,temperature compensation for the circuit can reduce the sensitivity of the drive current to temperature,further ensuring the stability of the drive current.After experimental verification and analysis of the experimental data,it is found that the drive current fluctuation in 30 minutes can be kept within ±18 ppm.In the design of the temperature control circuit,we realize the PID control network in the form of an analog circuit for temperature control.Through the analysis of the PID control network,it is found that the PID parameters of the PID control network cannot adapt to the change of the external environment,resulting in the PID control effect can only reach the local optimal and not control the temperature well.Therefore,the adaptive control theory is introduced to achieve self-tuning PID temperature control,so that the PID parameters can be updated with the external environment changing.According to the experimental verification and analysis of the experimental data,it is found that the temperature control effect is improved significantly,and the operating temperature fluctuation of the semiconductor laser can be controlled within ±0.00115? with the ambient temperature fluctuating between 20?and 40?.In the design of temperature control circuit,firstly,an analog PID control circuit is designed for temperature control,and it is found that the temperature control network based on the analog PID cannot adapt to the influence of the change of the external environment on the controlled system,resulting in the PID control effect can only reach the local optimal.Aiming at the shortcomings of the analog PID control and according to the adaptive control theory,the mathematical model of the controlled system is estimated in real-time and the self-tuning control is designed based on the mathematical model of the controlled system.Therefore,the PID parameters can be modified online in real time according to the influence of the change of external environment on the controlled system,and the PID control can achieve the real-time optimal or sub-optimal control effect.The self-tuning control is proved to be effective,when the ambient temperature fluctuates between 20? and 40?,the operating temperature fluctuation of the semiconductor laser can be controlled within±0.00115?.Besides,to solve the problem that the preheating time of the stable laser source is too long,the temperature control process is divided into pre-heating and constant temperature control of two phases.So the stability of laser source preheating time shortened to 20 minutes,and the use efficiency of the stable laser source is improved significantly.Finally,according to the analysis of experimental data,it is found that the short-term(15 minutes)stability of the output power of the stable laser source is±0.00065 dB,and the long-term(8 hours)stability is up to ±0.00115 dB,and the wavelength fluctuation of the output laser is less 3 pm over 8 hours.