Fiber-based optical low coherence tomography
First Claim
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1. A fiber-based optical low-coherence reflectometer comprising:
- a polarization-maintaining source path;
a polarization-maintaining reference path;
a polarization-maintaining sample path optically aligned with a collimating lens, a variable wave retarder, and a focusing lens, wherein the focusing lens is disposed to focus light on a sample; and
a polarization-maintaining detection path, wherein the polarization-maintaining source path, reference path, sample path and detection path are each connected to a polarization-maintaining path coupler.
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Abstract
Generally, and in one form of the present invention, is a polarization-maintaining fiber-based polarization sensitive optical low coherence reflectometer for depth resolved birefringence measurement. With the present invention, linear birefringence of a sample may be measured from data recorded in a single A-Scan. In addition, the present invention provides for the simultaneous measurement of retardation and orientation of birefringent axes, wherein measured retardation is insensitive to sample rotation in the plane perpendicular to ranging.
233 Citations
36 Claims
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1. A fiber-based optical low-coherence reflectometer comprising:
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a polarization-maintaining source path;
a polarization-maintaining reference path;
a polarization-maintaining sample path optically aligned with a collimating lens, a variable wave retarder, and a focusing lens, wherein the focusing lens is disposed to focus light on a sample; and
a polarization-maintaining detection path, wherein the polarization-maintaining source path, reference path, sample path and detection path are each connected to a polarization-maintaining path coupler. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A method for characterizing birefringence of a sample comprising the steps of:
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creating a polarization-maintaining optical source path using a broadband light source;
creating a polarization-maintaining optical reference path that is optically coupled to a first collimator directed to an optical delay line with dispersion control;
creating a polarization-maintaining optical sample path that is optically coupled to a second collimator, a variable wave retarder, and a focusing lens, wherein the focusing lens focuses light on the sample;
creating a polarization-maintaining optical detection path optically coupled to a third collimator and a polarizing beam splitter, wherein the polarizing beam splitter is optically coupled to a first and second photodetectors that produce a first and second output signal, respectively;
connecting the polarization-maintaining source path, reference path, sample path and the detection path to a polarization-maintaining path coupler;
converting the first and second output signals from the polarization-maintaining optical detection path with an analog-to-digital converter; and
connecting a processor to the analog-to-digital converter for collection of birefringent data about the sample. - View Dependent Claims (23, 24, 25)
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- 26. A polarization-maintaining optical fiber sample path optically aligned with a collimating lens, a variable wave retarder, and a focusing lens, wherein the focusing lens is disposed to focus light on a sample to characterize birefringence about the sample with rotation insensitivity of the measured retardation of the birefringent sample.
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27. A polarization-maintaining optical fiber sample path optically aligned with a collimating lens, a quarter wave retarder, and a focusing lens, wherein the focusing lens is disposed to focus light on a sample and light back scattered from the birefringent sample after traversing through the quarter wave retarder is elliptically polarized.
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30. A method of optically analyzing a sample comprising the steps of:
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placing a sample in front of a polarization-maintaining optical sample path that is optically coupled to a first collimator, a variable wave retarder, and a focusing lens, wherein the focusing lens is disposed to focus light on the sample;
creating a polarization-maintaining optical source path to introduce light;
creating a polarization-maintaining optical reference path that is optically coupled to a second collimator, wherein the collimator is directed into a rapid scanning delay line to be used as a reference; and
detecting light changes on the sample using a polarization-maintaining optical detection path optically coupled to a third collimator and a polarizing beam splitter, wherein the polarizing beam splitter is optically coupled to a first and second photodetectors that produce a first and second output signals, respectively, wherein the first and second output signals are filtered and converted with an analog-digital converter to digital data about the sample;
wherein the polarization-maintaining optical source path, reference path, sample path and detection path are connected to a polarization-maintaining path coupler.
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31. A system of characterizing birefringence of a sample comprising:
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a broad bandwidth optical light source;
a polarization-maintaining optical source path incorporating a polarizing element and correlates optical signals in fast and slow fiber polarization channels and optically connects both channels to a polarization-maintaining path coupler;
a polarization-maintaining path coupler that separates light into polarization-maintaining optical sample and reference paths while maintaining energy separation of optical signals in the fast and slow fiber polarization channels;
a polarization-maintaining optical reference path optically connected to the polarization-maintaining path coupler and optically coupled to an optical delay line;
a polarization-maintaining optical sample path optically connected to the polarization-maintaining path coupler, wherein the polarization-maintaining optical sample path comprises a quarter wave retarder and a focusing lens, wherein the focusing lens is disposed to focus light on the sample;
said sample placed in front of the polarization-maintaining optical sample path from which birefringence is characterized;
a polarization-maintaining optical detection path optically connected to the polarization-maintaining path coupler and a polarizing beam splitter that is optically coupled to a first and second photodetectors that produce first and second output signals, respectively, wherein the first and second output signals are filtered and amplified;
an analog-to-digital converter connected to the filter-amplifier; and
a processor connected to the analog-to-digital converter.
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32. A method for determining depth-resolved phase retardation of a sample birefringence comprising the steps of:
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initially estimating pseudo fast axis orientation [φ
f(i=0), θ
f(i=0)] and cone apex-angle [θ
o(i=0)], wherein the fast axis orientation is F (φ
f, θ
f) and the cone apex-angle is θ
o;
determining F and θ
o using a Levenberg-Marquardt method; and
computing the least square determination of depth-resolved phase retardation [δ
(z, Δ
z)].
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33. A method for determining depth-resolved phase retardation [δ
- (z, Δ
z)] of a sample comprising the step of;
computing δ
(z,Δ
z)=Npm, wherein Np is the number of data points about a sample recorded over optical depth Δ
z.
- (z, Δ
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34. A method for determining an unbiased estimate of [F (φ
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f, θ
f), θ
o] comprising the steps of;
minimizing a residual function, wherein the residual function is wherein ε
i is the shortest distance between an i'"'"'th data point (Si) and an arc on a Poincaré
sphere specified by [of, φ
f, θ
f, θ
o]. - View Dependent Claims (35)
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f, θ
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36. A fiber-based optical low-coherence reflectometer comprising:
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a path coupler that separates light into sample and reference paths while maintaining energy separation of optical signals into fast and slow fiber polarization channels;
a source path comprising a first polarization-maintaining optical fiber having a first end and a second end, wherein the first end of the first optical fiber is coupled to a light source and the second end is connected to a polarizer that splits the light source into a first and second polarization channels with independent phase components; and
a second polarization-maintaining optical fiber having a first end and a second end, the first end connected to the polarizer and the second end connected to the path coupler;
a reference path comprising a third and fourth polarization-maintaining optical fiber, the third polarization-maintaining optical fiber having a first end and a second end, the first end connected to the path coupler, the second end connected to a phase modulator; and
a fourth polarization-maintaining optical fiber having a first end and a second end, the first end connected to the phase modulator, the second end to a connector and optically aligned with a first collimator that collimates light emitting from the second end of the fourth polarization-maintaining optical fiber into an optical delay line;
a sample path comprising a fifth polarization-maintaining optical fiber having a first and a second end, the first end connected to the path coupler, the second end to a connector and optically aligned with a second collimator that collimates light emitting from the second end of the fifth polarization-maintaining optical fiber to a variable wave retarder and a focusing lens, wherein the focusing lens is aligned to focus light on a sample; and
a detection path comprising a sixth polarization-maintaining optical fiber having a first end and a second end, the first end connected to the path coupler, the second end aligned with a third collimator that collimates light emitting from the sixth polarization-maintaining optical fiber onto a polarizing beam splitter, wherein the polarizing beam splitter splits the light from the sixth polarization-maintaining optical fiber into a first beam and a second beam that are mutually orthogonal and capable of producing a first and second output signal about the sample.
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Specification