High precision optical cavity length and width measurements using double modulation

Area of Science:

• Optics
• Precision Measurement
• Resonator Technology

Background:

• Optical resonators are crucial components in various scientific applications.
• Accurate measurement of resonator length and linewidth is essential for performance optimization.
• Existing methods may face limitations in precision or susceptibility to errors.

Purpose of the Study:

• To develop a high-precision technique for measuring optical resonator length and linewidth.
• To demonstrate the effectiveness of doubly phase modulated light for these measurements.
• To analyze systematic errors and identify areas for improvement.

Main Methods:

• Utilizing doubly phase modulated light with radio frequency (RF) and audio frequency modulations.
• Demodulating transmitted or reflected light while sweeping RF frequency across optical resonance.
• Deriving expressions for demodulated power and identifying zero crossings for linewidth measurement.

Main Results:

• Achieved absolute length accuracy as low as 70 parts per billion (ppb) for cavities up to 4 km.
• Determined the cavity width of a 16 m cavity with an accuracy of approximately 6000 ppm.
• Identified systematic errors indicating potential for substantial accuracy improvement.

Conclusions:

• The developed technique offers high precision for optical resonator length metrology.
• The method provides a reliable way to measure cavity linewidth.
• Further reduction of technical uncertainties can significantly enhance measurement accuracy.