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 feed-forward control of an acousto-optic modulator. The fractional frequency instability was 7.4×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> for an averaging time of 1 s, 3.3×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-15</sup> for an averaging time of 1 s, at 3.6×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-18</sup> 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.
Highlights
We evaluated the instability of the frequency offset between narrow linewidth laser (NLL) and mode-locked laser (MLL)
We demonstrate a novel frequency-locking method for the high robustness, high-precision frequency offset locking between MLL and NLL
We use an electrical delay-line as a frequency reference to improve the fractional frequency instability to 2.6 × 10−12 for an averaging time of 1 s, and use acousto-optic modulator (AOM) to improve the fractional frequency instability to 1.1 × 10−15 for an averaging time of 1 s
Summary
F REQUENCY-stabilized lasers are applied in precision metrology fields [1]–[3] and in advanced spectroscopy laboratories [4], astronomy [5], [6] and very long baseline interferometry [7]–[9], telecommunications industries [10], measurement of basic physical parameters [11]–[14], gravitational wave detection [15], low-noise microwave signal generation [16]–[18] and optical clock comparison [19]–[21]. The frequency offset locking between two 1550 nm lasers, including mode-locked laser (MLL) and narrow linewidth laser (NLL), is realized by electrical delay line and acousto-optic modulator (AOM). The frequency offset locking between two 1550 nm lasers has a relative frequency instability of 1.1 × 10−15 at an averaging time of 1 s (corresponding to an absolute frequency less than 3 Hz) and 3.6 × 10−18 at an averaging time of 10 000 s. This laser could be employed as a pump laser for wavelength conversion in long-distance quantum communication. This work has a strong attraction for quantum measurement and precision frequency metrology
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