How to get a stable optical frequency comb?

Optical Frequency Combs: The Ultimate Light Ruler

An optical frequency comb is like a ruler of light with incredibly precise markings. While typical instruments measure in millimeters or milliseconds, an optical frequency comb surpasses nanometer accuracy in length measurements and exceeds femtosecond, even reaching attosecond, precision in time.

Frequency combs provide a 'wavelength ruler' that enables unprecedentedly precise frequency and time-domain calibration across a wide range of wavelengths. Research into frequency combs is a breakthrough point for next-generation atomic clocks, astronomical observations, attosecond optical physics, precision spectroscopy, and high-speed data transmission.

The emergence of stable optical frequency combs has made ultra-precise measurements possible. Therefore, the generation of stable optical frequency combs has become a hot research topic for experts and scholars both domestically and internationally.

A crucial step in constructing an optical frequency comb is stabilizing the comb tooth spacing. Dr. Shu-wei Huang, a senior researcher at the University of California, used the Vescent D2-125 Reconfigurable Servo to stabilize the comb tooth spacing of their optical frequency comb, which is based on a microcavity laser.

Dr. Shu-wei Huang used a narrow-linewidth continuous-wave laser to pump a Kerr microresonator to generate the optical frequency comb. This microresonator is designed to output a free spectral range of 17.9 GHz around a 1600 nm pump wavelength. The two degrees of freedom of the frequency comb—the comb tooth spacing and the carrier-envelope phase shift—are independently phase-locked to two microwave synthesizers. The microresonator's thermal capacity is only $2\times 10^{-15}{\text{ m}}^3$, making the comb tooth spacing extremely susceptible to technical noise such as pump power perturbations, temperature changes, and optical alignment drift. Therefore, a servo loop with a bandwidth of over 500 kHz is critical for stabilizing the comb tooth spacing of microresonator frequency combs. Dr. Shu-wei Huang provided a detailed explanation of how they implemented the frequency comb tooth spacing servo loop using the Vescent D2-125 Reconfigurable Servo.