Tunable locking of calcite narrow frequency filters through modulation switching

Area of Science:

• Physics
• Optical Engineering
• Metrology

Background:

• Generating Raman beams for gravimetry using fiber phase modulators is convenient but produces unwanted frequencies.
• Existing frequency filtering methods involve birefringent calcite crystals and polarizers, which require precise tuning.

Purpose of the Study:

• To present a novel method for tuning frequency filters used in gravimetry.
• To enable continuous monitoring and adjustment of the filter position without disrupting the gravimetric sequence.

Main Methods:

• A tunable frequency filter was developed using a birefringent calcite crystal and a polarizer.
• A feedback signal for tuning was generated by comparing light transmission with and without phase modulation from the fiber modulator.
• The fiber phase modulator, already part of the gravimetry system, was utilized for both modulation and filter monitoring.

Main Results:

• The proposed method allows for precise and continuous tuning of the frequency filter.
• The system can seamlessly switch between filter monitoring and other operational uses, such as phase modulation.
• This adaptability is crucial for the efficient execution of complete gravimetric sequences.

Conclusions:

• The developed tunable filter and feedback method offer a practical solution for managing unwanted frequencies in Raman beam gravimetry.
• This technique enhances the operational flexibility and reliability of gravimetric systems utilizing fiber phase modulators.