Method and apparatus for performing optical measurements
First Claim
1. A system for performing selected optical measurements on a sample comprising:
- a short coherence length optical radiation source at a wavelength λ
;
a reference optical reflector;
a first optical path leading to said reflector;
a second optical path leading to said sample;
means for applying optical radiation from said source through the first optical path to said reflector and through the second optical path to the sample;
means for altering the relative lengths of said optical paths in accordance with a predetermined velocity profile, said profile providing for continuous alteration in said relative length at an instantaneous velocity V for each point on the profile in at least the region of said profile where said measurements are to be performed;
means for combining reflections from the reflector received through the first optical path and reflections from the sample received through the second optical path, the resulting combined optical output having interference fringes at length matched points on the two paths and having an instantaneous modulating frequency including a Doppler shift frequency at a frequency fD= 2V/λ
;
means for demodulating said output; and
means for processing the demodulated output to obtain information concerning said selected measurements.
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Abstract
A method and apparatus for performing various optical measurements is provided utilizing an optical coherence domain refrectometer (OCDR). A short coherence optical radiation source applies optical radiation through like optical paths to a sample and an optical reflector. The optical reflector is movable in accordance with a predetermined velocity profile to permit interferometric scanning of the sample, the resulting output having a Doppler shift frequency modulation. This output may be demodulated and detected to obtain desired measurements and other information. Additional information may be obtained by applying radiation from two or more sources at different wavelengths to the sample and reflector and by separately demodulating the resulting outputs before processing. Birefringent information may be obtained by polarizing the optical radiation used, by suitably modifying the polarization in the sample and reference paths and by dividing the output into orthogonal polarization outputs which are separately demodulated before processing.
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Citations
51 Claims
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1. A system for performing selected optical measurements on a sample comprising:
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a short coherence length optical radiation source at a wavelength λ
;a reference optical reflector; a first optical path leading to said reflector; a second optical path leading to said sample; means for applying optical radiation from said source through the first optical path to said reflector and through the second optical path to the sample; means for altering the relative lengths of said optical paths in accordance with a predetermined velocity profile, said profile providing for continuous alteration in said relative length at an instantaneous velocity V for each point on the profile in at least the region of said profile where said measurements are to be performed; means for combining reflections from the reflector received through the first optical path and reflections from the sample received through the second optical path, the resulting combined optical output having interference fringes at length matched points on the two paths and having an instantaneous modulating frequency including a Doppler shift frequency at a frequency fD= 2V/λ
;means for demodulating said output; and means for processing the demodulated output to obtain information concerning said selected measurements. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30)
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31. A method for performing selected optical measurements on a sample comprising the steps of:
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causing short coherence length optical radiation of a wavelength λ
to impinge on a reference reflector and on the sample through first and second optical paths, respectively;altering the relative lengths of said paths in accordance with a predetermined velocity profile, said profile providing for continuous alteration in said relative length at an instantaneous velocity V for each point on the profile in at least the region of said profile where said measurements are to be performed; combining reflections from the reflector received through the first optical path and reflections from the sample received through the second optical path, the resulting combined optical output having interference fringes at length matched points on the two paths and having an instantaneous modulating frequency including a Doppler shift frequency at a frequency fD= 2V/λ
;demodulating said output; and processing the demodulated output to obtain information concerning said selected measurements. - View Dependent Claims (32)
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33. A system for performing selected optical measurements on a sample having at least one birefringent layer comprising:
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a short coherence length optical radiation source at a wavelength λ
, said radiation being polarized in a first state;means for defining a reference optical path and a sample optical path through which radiation from said source may bidirectionally pass; means for altering the polarization of the radiation passing through at least one of said paths in a manner such that radiation from said source in said paths have different polarization states, reflected radiation from said sample having a polarization in a state which varies as a function of the birefringence of said layer; means for interferometrically combining reflected radiation from said optical paths; means for providing a controlled variation in the relative path lengths for interferometrically combined radiation; means for splitting and detecting the interferometrically combined output as two outputs having orthogonal polarization states; means for separately processing the two outputs to obtain separate interferometric signals; and means for combining said interferometric signals to provide a selected indication of birefringence profile. - View Dependent Claims (34, 35, 36)
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37. A system for performing selected optical measurements on a sample comprising:
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means for providing short coherence length optical radiation at at least two different wavelengths λ
1 and λ
2, at least one spectral characteristic of the sample being different between wavelengths λ
1 and λ
2 ;means for defining a reference optical path and a sample optical path through which said radiation at different wavelengths may bidirectionally pass; means for interferometrically combining reflected radiation from said optical paths, said means for combining having at least a first combined optical output modulated at a frequency f1 and a second combined optical output modulated at a frequency f2 ; means for providing a controlled variation in the relative path lengths for interferometrically combined radiation; means for separately demodulating said first and said second combined optical outputs; and means for processing the two outputs to obtain information concerning said selected measurements. - View Dependent Claims (38, 39)
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40. A method for optically measuring a microstructural feature of selected biological tissue comprising the steps of:
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generating a short coherence length optical signal at a selected wavelength; passing said signal through a reference optical path and through a sample optical path terminating at said biological tissue, said paths being bidirectional to also pass reflected radiation; interferometrically combining reflected optical signals from said optical paths; providing a controlled variation in the relative path lengths of the interferometrically combined beams; detecting the results of said interferometrically combining step; and processing the result of the detecting step to obtain information concerning said microstructural feature. - View Dependent Claims (41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51)
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Specification