A High-Precision Offset Frequency Locking Technique With Delay Line Reference and AOM-Based Compensation

Abstract

We demonstrate a high-precision, high robustness frequency offset locking method,which made the frequency offset between mode-locked laser and continuous-wave laser below less than 3 Hz.The coarse frequency lock control is realized by the feedback control of PZT with electrical delay line as the reference. The fine frequency compensation is realized by feedforward control of an acousto-optic modulator. The fractional frequency instability was 7.4 × 10 −10 for an averaging time of 1 s, 3.3 × 10 −8 for an averaging time of 10,000 s when the narrow linewidth laser is free-running. In this experiment, the fractional frequency instability can be achieved at 1.1 × 10 −15 for an averaging time of 1 s, at 3.6 × 10 −18 for an averaging time of 10,000 s when the system is fine frequency locked. Compared with the unlocked laser, the fractional frequency instability can be improved about 5∼6 orders of magnitude. This work lays the foundation for simple structure, high robustness and high precision laser frequency control situation, such as quantum precision measurement and optical lattice clocks.