Patent ID: 7745777

Claim:
An apparatus for detecting a beam of light reflected from a region of interest, comprising: a light source that produces a light beam having a first polarization state; a first polarization beam splitter that directs the light beam along a first optical path, and allows light having a second polarization state, orthogonal to the first polarization state, to pass; an optical polarization modulator, located along the first optical path, that applies a net rotation of ninety degrees to the polarization of light passing through the optical polarization modulator in a first direction and applies a net rotation of zero degrees to the polarization of light passing through the optical polarization modulator in a second direction, the first polarization beam splitter directing the light beam through the optical polarization modulator to the region of interest; a second polarization beam splitter, positioned along the first optical path such that the optical polarization modulator is between the first polarization beam splitter and the second polarization beam splitter, that allows a first portion of the beam of light that is reflected from the region of interest having the second polarization state to pass to the optical polarization modulator and directs a second portion of the beam of light that is reflected from the region of interest having the first polarization state along a second optical path; and a third polarization beam splitter configured to allow light having the second polarization state to pass and reflect light having the first polarization state, the third polarization beam splitter being positioned as to combine light from the first optical path and light from the second optical path and direct the combined light onto a sensor.