Method and apparatus for performing optical measurements

A method for performing selected optical measurements on a sample comprising the steps of:

• causing short coherence length optical radiation of a wavelength .lambda. 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 f.sub.D= 2V/.lambda.;
• demodulating said output;
• and
• processing the demodulated output to obtain information concerning said selected measurements.

A system for performing selected optical measurements on a sample having at least one birefringent layer comprising:

• a short coherence length optical radiation source at a wavelength .lambda., 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.

A system for performing selected optical measurements on a sample comprising:

• means for providing short coherence length optical radiation at at least two different wavelengths .lambda..sub.1 and .lambda..sub.2, at least one spectral characteristic of the sample being different between wavelengths .lambda..sub.1 and .lambda..sub.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 f.sub.1 and a second combined optical output modulated at a frequency f.sub.2 ;
• 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.

A method for optically measuring a microstructural feature of selected biological tissue comprising the steps of:

• 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.