Design Of High Precision Temperature Controller For Narrow Line Width Laser Diodes

Because of its wide wavelength,a long service life and a high conversion efficiency,a semiconductor laser plays an irreplaceable role in many fields.But the semiconductor laser is a sensitive device,as for 780 nm Distributed Feedback Laser,its line width usually down to 1 MHz,the temperature changes by 1 mK and the frequency changes by 30 MHz.Apart from a well-engineered optomechanical design and the low noise current driver,the most important part of the diode laser system is its temperature control,which is responsible for getting the most out of a laser system.Though laser temperature controllers developed through research by foreign countries deliver excellent performance,with their one-hour stability being about1 mK,they feature very high price,long purchase cycle,large volume and unsuitability for integration.Yet the research in this field in our country is relatively backward,and temperature control products of related companies can only realize one-hour temperature control stability of about 10 mK.Therefore,it is of great realistic significance to develop a high-precision temperature control system with one-hour stability lower than 1 mK.In this paper,the overall scheme was firstly determined according to the design indicator,based on which the specific design requirements for each module were figured out.Then,the principle diagram was designed,the component models were selected,and the performance of each module was verified one by one to ensure that the hardware won't affect the final temperature control results.Though low-temperature drift and low-noise components were used,some modules still failed to satisfy the noise requirement of the system.So a corresponding algorithm was added to the software to reduce the influences of hardware noises.After the entire design of principle diagram was completed,detailed PCB single board design was carried out,including model selection of passive devices,layout and wiring design,thermal design,EMC/ESD design,etc.Then modules of the single board were tested one by one,and the test results were basically consistent with the theoretical analysis values.The temperaturecontroller was used to a set of DBR semiconductor laser,and the PI parameter was adjusted to a suitable value to test the temperature control stability.According to the test result,the one-hour temperature control stability was 1 mK.Finally,a simple constant flow source was self-made to supply power to DBR for its free operation;and the beat frequency of a freely rotating DBR and a frequency-locked DBR were tested to determine the change of the output frequency precisely and further to get the actual effect of temperature control,hence increasing the data persuasiveness.