Optical frequency reference based on a cryogenic silicon resonator.

Area of Science:

• Physics
• Metrology
• Optical Engineering

Background:

• Optical atomic clocks require highly stable laser sources.
• Cryogenic operation of optical resonators can reduce thermal noise and improve stability.
• Vibrations and temperature fluctuations are key challenges in achieving high-performance optical references.

Purpose of the Study:

• To develop and characterize a 1.5 μm laser stabilized to a cryogenic silicon optical resonator.
• To investigate the frequency instability and drift of the cryogenic optical reference.
• To identify sources of noise and limitations in the current system.

Main Methods:

• Stabilization of a 1.5 μm laser to a silicon optical resonator.
• Operation of the resonator within a closed-cycle cryostat at 1.7 K with passive vibration isolation.
• Frequency instability measurements over various integration times (1 s to 6000 s).

Main Results:

• Achieved frequency instability of 2 × 10⁻¹⁴ at 1 s integration time, limited by residual vibrations.
• Demonstrated frequency instability of 6.2 × 10⁻¹⁵ at 100 s and 3.5 × 10⁻¹⁶ at 6000 s.
• Measured a mean fractional frequency drift rate of -3.7 × 10⁻²⁰/s over 190 days.

Conclusions:

• The cryogenic optical reference shows promising performance for high-accuracy optical frequency dissemination.
• Residual vibrations and laboratory temperature variations significantly impact short-to-medium term stability.
• Further mitigation of environmental factors could enable reaching the thermal-noise-limited performance of the resonator.