Software Design Of Swept-Frequency Light Source

LiNbO₃ modulator has been widely used in high-speed optical modulation field because of its low loss,high efficiency and low cost,thus has become one of the important optical devices in the optical field.However,due to the influence of lithium niobate crystal characteristics,when the external temperature,current,pressure and other factors change,the bias operating point of the modulator will change slowly eventually leading to the deterioration of signal quality,and affecting the research work.This paper mainly completes two parts of proj ects.The first part is the design of sweep signal generator,which is mainly generated by CPU controls frequency generator.The other is the automatic control of the modulator's bias point.The low frequency disturbance signal control method is used to ensure the stability of the LiNbO₃ modulator's working point.By introducing sinusoidal signal and bias voltage to modulate input,and analyzing and processing the fundamental and second harmonic components of the output signal,the drift of the bias point is judged and a closed-loop control is formed.This paper focuses on the software design of the whole sweep light source system where the lithium niobate chip is located.The aim is to ensure the stability of the lithium niobate modulator through the control of the algorithm.Specifically,it includes the software flow design of the whole system.The whole system uses multi-threads to work concurrently.The receiving threads are responsible for the instruction interaction between the CPU and the host computer.On the one hand,the instructions of the host computer are transmitted to other threads for execution,On the other hand,the fault instructions of the system are reported to the main control system.At the same time,RP thread is responsible for the generation of sweep signal source,including the design and implementation of SPI module.The lithium niobate module is controlled by two threads.The PWM module and the DA module are responsible for the generation of low frequency signals and bias voltage,and the AD module is responsible for the sampling and analysis of the output signal of the modulator.The stability of bias point of lithium niobate modulator is guaranteed by the action of each driving modules.