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Closed-loop phase stabilizing and phase stepping methods for fiber-optic projected-fringe digital interferometry.

Zhang Chao1, Duan Fa-Jie

  • 1State Key Lab of Precision Measuring Technology and Instruments, Tianjin University, Tianjin 300072, China. chao_zhangchao@163.com

The Review of Scientific Instruments
|December 2, 2011
PubMed
Summary
This summary is machine-generated.

Active homodyne control stabilizes interferometers against phase fluctuations. This study introduces two phase tracking methods (PTAC and PTDC) to maintain quadrature, achieving high phase step accuracy for fiber-optic digital interferometry.

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Area of Science:

  • Optics and Photonics
  • Interferometry
  • Control Systems

Background:

  • Interferometers are sensitive to environmental fluctuations like temperature gradients, affecting phase stability.
  • Stabilizing phase steps is crucial for accurate measurements in full-field interferometry.

Purpose of the Study:

  • To introduce closed-loop active homodyne control for stabilizing a fiber-optic interferometer.
  • To develop and compare two phase tracking methods (PTAC and PTDC) for maintaining quadrature.
  • To assess the accuracy of π/2-rad phase steps using a novel harmonic ratio method.

Main Methods:

  • Implementation of closed-loop active homodyne control in a fiber-optic Michelson interferometer setup.
  • Development of AC phase tracking (PTAC) and DC phase tracking (PTDC) feedback control loops.
  • Utilizing a harmonic ratio method to estimate phase step accuracy.

Main Results:

  • PTAC achieved a root-mean-square (RMS) phase stability of 1.5 mrad and phase step accuracy of 2.6 mrad.
  • PTDC resulted in an RMS phase stability of 2 mrad and phase step accuracy of 13.8 mrad.
  • The system demonstrated stable operation for over two hours without integrator resetting.

Conclusions:

  • Closed-loop active homodyne control effectively stabilizes fiber-optic interferometers.
  • PTAC offers superior phase step accuracy and stability compared to PTDC for projected-fringe digital interferometry.
  • The proposed harmonic ratio method provides a reliable means for estimating phase step accuracy.