Polarization sensitive spectral domain OCT using an interference signal modulated at a constant frequency and a two-path reference arm with a single reference mirror
Embodiments include apparatuses and methods for spectral domain polarization sensitive optical coherence tomography including a reference assembly for detection of the polarization sensitive spectral interferograms formed by vertically and horizontally polarized beam components. Interference signals between the reference and sample beams may be modulated at a constant frequency.
1. An apparatus comprising:
a first light path of a spectral domain optical coherence tomography (OCT) system reference arm through which a horizontally-polarized light beam passes;
a second light path of the spectral domain OCT system reference arm through which a vertically-polarized light beam passes;
a mobile reference mirror to reflect the horizontally-polarized light beam and the vertically-polarized light beam to form a joined beam with an optical pathlength difference between the horizontally-polarized light beam and the vertically-polarized light beam; and
a signal modulation device that moves the mobile reference mirror at a constant velocity across a B scan to modulate, at a constant modulation frequency, an interference signal formed by the horizontally- and vertically-polarized light beams.
2. The apparatus of claim 1 , further comprising a beam splitter to receive a source light beam and split the source light beam into a first reference light beam and a second reference light beam.
3. The apparatus of claim 2 , wherein the beam splitter receives a vertically-polarized and/or a horizontally-polarized source light beam.
4. The apparatus of claim 1 , wherein the first light path and the second light path have different path lengths to form the horizontally-polarized light beam and the vertically-polarized light beam with the optical pathlength difference, and wherein the optical pathlength difference is fixed.
5. The apparatus of claim 1 , wherein the first light path includes a quarter wave plate.
6. The apparatus of claim 5 , wherein the quarter wave plate includes a fast axis oriented at about 45°.
7. The apparatus of claim 1 , wherein the signal modulation device is a linear moving stage and the reference mirror is affixed to the linear moving stage.
8. The apparatus of claim 7 , wherein the interference signal formed by the horizontally- and vertically-polarized light beams is a spectral interferogram.
9. The apparatus of claim 1 , wherein the first light path and/or the second light path includes a neutral density filter.
10. The apparatus of claim 1 , further comprising:
a light source to provide a first and a second reference light beams;
a sampling assembly to provide light from the light source to a sample to obtain a sample light beam; and
a spectrometer configured to detect a spectral interferogram formed by the horizontally-polarized light beam, the vertically-polarized light beam, and the sample light beam.
11. An apparatus comprising:
a first light path of a spectral domain optical coherence tomography (OCT) system reference arm through which passes a horizontally-polarized light beam;
a second light path of the spectral domain OCT system reference arm through which passes a vertically-polarized light beam;
a reference mirror to reflect the horizontally-polarized light beam and the vertically-polarized light beam to form a joined beam with an optical pathlength difference between the horizontally-polarized light beam and the vertically-polarized light beam; and
a signal modulation device that sweeps a sample light beam across a sample to introduce a constant modulation frequency for spatial varying spectral interferograms formed by the reflected horizontally- and vertically-polarized light beams.