Optical measurements of properties in substances using propagation modes of light

Abstract

This application describes designs, implementations, and techniques for controlling propagation mode or modes of light in a common optical path, which may include one or more waveguides, to sense a sample.

1 . A device for optically measuring a sample, comprising:
 a light source to produce an input beam for optically probing a sample;   a waveguide having a proximal end to receive the input beam from the light source and a distal end towards which the received input beam is guided by the waveguide;   a probe head coupled to the distal end of the waveguide to receive the input beam and to reflect a first portion of the input beam back to the waveguide and direct a second portion of the input beam to the sample, the probe head configured to overlap reflection of the second portion from the sample with the first portion and to export to the waveguide the reflection as a reflected second portion;   a differential delay modulator in optical communication with the proximate end of the waveguide to receive light in the first portion and the reflected second portion from the proximate end of the waveguide, the differential delay modulator operable to split the received light into a first beam and a second beam and to produce variable relative phase delays between the first beam and the second beam; and   a detection module to detect light that combines the first beam and the second beam and is output by the differential delay modulator, the detection module operable to extract information of the sample carried by the reflected second portion at different depths in the sample based the variable relative phase delays produced by the differential delay modulator.