Fiber optic Fourier transform spectrometer with a coherent interferogram averaging scheme.

Area of Science:

• Optics and Photonics
• Spectroscopy
• Interferometry

Background:

• Fiber optic Fourier transform spectrometers are crucial for various analytical applications.
• Coherent interferogram averaging can significantly improve signal-to-noise ratio (SNR) but is challenging to implement with fiber optics due to environmental perturbations.

Purpose of the Study:

• To construct and demonstrate a fiber optic Fourier transform spectrometer capable of coherent interferogram averaging.
• To overcome the limitations of nonlinear mirror movement and independent fiber arm perturbations in achieving uniform interferogram sampling.

Main Methods:

• A fiber optic interferometer was designed with one arm periodically stretched to generate modulation.
• Simultaneous detection of fundamental and second harmonics of the modulation frequency in the photocurrent output.
• An external clock for sampling was generated from phase quadrature outputs, enabling uniform sampling despite nonlinear movement and perturbations.

Main Results:

• The developed spectrometer successfully achieved coherent interferogram averaging.
• Uniform sampling of the interferogram was maintained even with nonlinear mirror translation and random fiber perturbations.
• Sampling start position variation was limited to within 100 nm over 100 scans.
• A ~10-fold increase in SNR was achieved with 100 coherent averages without spectral deformation.

Conclusions:

• The novel fiber optic Fourier transform spectrometer enables robust coherent interferogram averaging.
• The external clock generation method effectively compensates for environmental noise and mechanical instabilities.
• This technology offers improved performance for spectroscopic analysis in challenging environments.