Methods and systems for polarization-sensitive optical coherence tomography
A system for polarization-sensitive optical coherence tomography (PS-OCT) of a sample comprises an interferometric arrangement comprising a reference arm and a sample arm, the sample arm being arranged to emit optical radiation towards the sample; a phase modulation system arranged at an input to the sample arm; and a detector arranged to detect a signal generated by interference between a reference beam from the reference arm and a sample beam from the sample arm. The phase modulation system comprises: an electro-optic modulator; a polarizer arranged at a rotation angle relative to the fast axis of the electro-optic modulator; and a signal generator for delivering a driving voltage to the electro-optic modulator; wherein the rotation angle and the driving voltage are selected such that the phase modulation system generates three mutually orthogonal polarization states.
1. A system for polarization-sensitive optical coherence tomography (PS-OCT) of a sample, comprising:
an interferometric arrangement comprising a reference arm and a sample arm, the sample arm being arranged to emit optical radiation towards the sample;
a phase modulation system arranged at an input to the sample arm; and
a detector arranged to detect a signal generated by interference between a reference beam from the reference arm and a sample beam from the sample arm;
wherein the phase modulation system comprises:
an electro-optic modulator;
a polarizer arranged at a rotation angle relative to the fast axis of the electro-optic modulator; and
a signal generator for delivering a driving voltage to the electro-optic modulator;
wherein the rotation angle and the driving voltage are selected such that the phase modulation system generates three mutually orthogonal polarization states.
2. A system according to claim 1 , wherein the rotation angle is between about 17.6 degrees and about 38.1 degrees.
3. A system according to claim 2 , wherein the rotation angle is 27.3678 degrees.
4. A system according to claim 1 , wherein the driving voltage has a sawtooth waveform.
5. A system according to claim 4 , wherein the sawtooth waveform is a 3-point step driving waveform, the steps corresponding to modulation depths of −120 degrees, 0 degrees, and 120 degrees.
6. A system according to claim 1 , comprising at least one processor that is configured to determine the Mueller matrix of the sample from the signal detected by the detector.
7. A system according to claim 6 , wherein the at least one processor is configured to determine birefringence of the sample based on the Mueller matrix.
8. A system according to claim 7 , wherein the at least one processor is configured to apply a constraint to the determination of the birefringence of the sample based on a priori knowledge of one or more structural parameters of the sample.
9. A phase modulation system for polarization-sensitive optical coherence tomography (PS-OCT) of a sample, the phase modulation system being positionable at an input of a sample arm that is arranged to emit optical radiation towards the sample, the phase modulation system comprising:
an electro-optic modulator;
a polarizer arranged at a non-zero rotation angle relative to the fast axis of the electro-optic modulator; and
a signal generator for delivering a driving voltage to the electro-optic modulator;
wherein the rotation angle and the driving voltage are selected such that the phase modulation system generates three mutually orthogonal polarization states.
10. A phase modulation system according to claim 9 , wherein the rotation angle is between about 17.6 degrees and about 38.1 degrees.
11. A phase modulation system according to claim 10 , wherein the rotation angle is 27.3678 degrees.
12. A method of polarization-sensitive optical coherence tomography (PS-OCT) of a sample, comprising:
generating, by sample arm optics, a sample beam for illuminating the sample; and
detecting an interference signal generated by interference of the sample beam with a reference beam;
wherein the sample arm optics have a phase modulation system arranged at an input thereof, the phase modulation system being configured to:
transmit an input beam through a polarizer arranged at a rotation angle relative to the fast axis of an electro-optic modulator; and
deliver a driving voltage to the electro-optic modulator;
wherein the rotation angle and the driving voltage are selected such that the phase modulation system generates three mutually orthogonal polarization states.
13. A method according to claim 12 , wherein the rotation angle is between about 17.6 degrees and about 38.1 degrees.
14. A method according to claim 13 , wherein the rotation angle is 27.3678 degrees.
15. A method according to claim 12 , wherein the driving voltage has a sawtooth waveform.
16. A method according to claim 15 , wherein the sawtooth waveform is a 3-point step driving waveform, the steps corresponding to modulation depths of −120 degrees, 0 degrees, and 120 degrees.
17. A method according to claim 12 , comprising determining the Mueller matrix of the sample based on the interference signal.
18. A method according to claim 17 , comprising determining birefringence of the sample based on the Mueller matrix.
19. A method according to claim 18 , comprising applying a constraint to the determination of the birefringence of the sample based on a priori knowledge of one or more structural parameters of the sample.
20. A method according to claim 19 , wherein the sample is an eye, and wherein the method further comprises generating a fiber anisotropy image and/or a fiber orientation image of the sclera of the eye.
21. A method according to claim 20 , wherein the constraint is that the fiber collagen is circumferential around the optical nerve head on the sclera.