可调谐激光器激光波长宽范围自动偏频锁定

针对激光多波长干涉绝对测距中构建多级合成波长的需求,提出了一种锁至飞秒光频梳的可调谐激光器(External CavityDiode Laser,ECDL)输出激光波长的宽范围自动偏频锁定方法。首先,设计了光栅+双凸透镜梳齿滤波的拍频信号探测单元,实现了宽范围ECDL激光波长与目标梳齿的拍频探测。接着,采用锁相放大原理对拍频信号进行鉴频鉴相,具备捕获带宽大、鉴相范围宽和鉴相精度高的优点。然后,利用多重闭环控制实现了ECDL输出激光波长宽范围的自动调节及偏频锁定。实验结果表明,本方法实现了10 nm波长范围内ECDL至光频梳的自动锁定,拍频信号信噪比的平均值约为35.9 dB;在4h内,ECDL激光频率的标准差为1.49 kHz,1s平均时间的相对阿伦方差为4.76×10^-12,满足精密干涉测量中宽范围波长调节和高精度稳频的要求。

Automatic offset-frequency locking of external cavity diode laser in wide wavelength range

To construct different synthetic wavelengths for multi-wavelength interferometric absolute distance measurements,an automatic offset-frequency locking method was proposed to lock the frequency of a tunable external cavity diode laser(ECDL)to a femtosecond optical frequency comb(OFC)in a wide wavelength range.First,based on the grating and double convex lens comb filtering,a beat signal detection unit was designed.In addition,the beat signal detection between the ECDL and target comb modes in a wide wavelength range was realized.A phase-frequency detector was then designed based on the principle of a lock-in amplifier;phase-locking with a large capture range,wide monotonic phase range,and high accuracy was achieved.Finally,multiple closed-loop controls were adopted to realize automatic adjustment and offset-frequency locking of the ECDL over a wide wavelength range.Experimental results show that the proposed method can automatically lock the ECDL to OFC in the range of 10 nm,and the average signal-to-noise ratio of the beat signal is approximately 35.9 dB.Over 4 h,the standard deviation of the ECDL laser frequency is approximately 1.49 kHz,and the relative Allan deviation is approximately 4.76 × 10^-12 at 1 s.The proposed automatic offset-frequency locking method can satisfy the requirements of widerange wavelength adjustment and high-precision frequency stabilization in precision interferometry.