A fiber-optic interferometer with subpicometer resolution for dc and low-frequency displacement measurement

Area of Science:

• Optics and Photonics
• Metrology
• Instrumentation

Background:

• Accurate displacement sensing is crucial for various scientific and industrial applications.
• Traditional interferometers often face limitations in low-frequency noise and robustness.
• Developing high-resolution, stable interferometric systems remains an active area of research.

Purpose of the Study:

• To design and construct a fiber-optic interferometer optimized for low-frequency (dc to 1 kHz) displacement measurements.
• To achieve high resolution and linearity over a specified dynamic range.
• To demonstrate a robust homodyne interferometer system with improved noise performance.

Main Methods:

• Utilized a tunable infrared laser source (1550 nm) with enhanced stability and coherence control.
• Employed "bend-insensitive" fiber and all-spliced construction for system robustness.
• Implemented a homodyne detection scheme without requiring differential detection.

Main Results:

• Achieved displacement linearity of 1% over a +/- 25 nm range.
• Demonstrated noise-limited resolution of 2 pm, with 40 fm Hz(-1/2) resolution above 20 Hz.
• Approached the shot-noise limit of 20 fm Hz(-1/2) at 1 kHz with 10 microW optical power.

Conclusions:

• The developed fiber-optic interferometer provides a robust and high-resolution solution for low-frequency displacement sensing.
• The system's performance is attributed to the stable laser source, specialized fiber, and optimized construction.
• This interferometer design offers a pathway to achieving near-shot-noise-limited measurements in practical applications.