PHASE DETECTION WITH SUB-NANOMETER SENSITIVITY USING POLARIZATION QUADRATURE ENCODING METHOD IN OPTICAL COHERENCE TOMOGRAPHY

This paper presents a phase-resolved optical coherence tomography (OCT) system that uses the polarization quadrature encoding method in a two-channel Mach-Zehnder interferometer. OCT is a powerful optical signal acquisition method that can capture depth-resolved micrometer-resolution images. In our method, a complex signal is optically generated, and its real and imaginary components are encoded in the orthogonal polarization states of one sample beam; absolute phase information can then be acquired instantaneously. Neither phase modulation nor numerical Fourier or Hilbert transformation to extract phase information is required, thereby decreasing data acquisition rates and processing time. We conducted signal post-processing to select data from the instabilities of reference scanning delay lines; the measured phase sensitivity was as low as 0.23°, and the corresponding path-difference resolution was 265 pm. A localized surface profile measurement of a chromium-coated layer deposited on a commercial resolution target surface was conducted. The results confirmed that successful images can be obtained even with very small optical path differences using the proposed method.