摘要
半导体激光器由于波长覆盖范围大、易调谐、体积小、重量轻、结构简单、功耗低、寿命长等优势,在量子信息、精密测量、光学传感等领域均有广泛应用.由于自由运转的半导体激光器输出频率起伏较大,在应用中需要对其频率进行反馈控制.然而传统反馈控制系统存在结构复杂、体积庞大、稳定性差等缺点,因此我们搭建了一套基于FPGA的外腔半导体激光器稳频系统.该系统以铯原子饱和跃迁线为参考频率,以FPGA电路模块代替信号发生器、锁相放大器、PID、示波器等器件,对激光器工作电流施加反馈,成功将激光器的输出频率分别稳定到|62S1/2,F=4〉→|62P3/2,F=4,5〉交叉峰和|62S1/2,F=4〉→|62P3/2,F=5〉跃迁线对应的频率.80 s内激光器输出频率起伏为3.0(0.3)MHz.该系统简单易用,集成度高,可用于多种锁定系统.
Abstract
Semiconductor lasers have been widely used in quantum information,precision measurement,optical sensing and other fields due to the advantages of large wavelength coverage,easy tuning,small size,light weight,simple structure,low power con-sumption and long working lifetime.Since the output frequency of free-running semiconductor laser fluctuates widely,it is neces-sary to stabilize its frequency by feedback control.However,the traditional feedback control system has some disadvantages,such as complex structure,large size and poor stability,so we construct a stabilization system of external cavity diode laser based on a Field Programmable Gate Array(FPGA)module.In this paper we use PyRPL,an open-source software package,to provide an arbitrary signal generator,a lock-in amplifier,a Proportional-Integral-Differential(PID)controller and an oscilloscope based on STEM125-14.And the saturated absorption spec-trum of cesium atoms is used as the reference frequency for the stabilization system to lock a semiconductor laser.The arbitrary signal generator is used to generate sawtooth signal to scan the external cavity length of the semiconductor laser,thus realizing the tuning of the laser frequency.The lock-in amplifier module is used to generate sinusoidal signal to modulate laser current and to demodulate the modulated signal of the saturated absorption spectrum,and then error signal through filtering is generated.The PID module is used to employ the feedback signal to control the laser current,which makes the laser frequency be stabilized to the atomic transition lines.Using the FPGA module as a core circuit device,the frequency of laser is stabilized to the frequency of crossover line of|62S1/2,F=4〉→|62P3/2,F=4,5〉and the transition line of|62S1/2,F=4〉→|62P3/2,F=5〉.The frequency fluctuation of the locking laser within 80 s is 3.0(0.3)MHz.The Allan deviation and frequency spectra of the error signal when the laser is locked and unlocked are compared and the results show that frequency fluctuation can be suppressed effectively when the feedback is applied.The system with advantages of high integration,compact and easy to use,can be used in a variety of locking systems.
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