Rotating polarizer angle sensing system

Claim 1

A system for measuring angular determination of aircraft structure, including wing twist in flight and position of actuated control surfaces, said system comprising: a linearly polarized light source consisting of linearly polarized continuous wave laser: a 1/4 wave retardation plate disposed at the output beam of said linearly polarized light source for providing a beam of circularly polarized light; a rotating linear polarizer rotating at a constant speed for converting said circularly polarized light beam into a modulated beam of linearly polarized light which has a plane of polarization rotating at twice the speed of said rotating linear polarizer; a negative lens inserted into said modulated beam for providing the first element of a telescope utilized for focussing said modulated beam on a target; a beam splitter for dividing said modulated beam into a reference beam and a test beam; a linear polarizer for demodulating said reference beam and establishing a reference optical signal of known phase angle determined by the polarization plane of said rotating linear polarizer; a photo-voltaic cell for converting said reference optical signal to an electric reference signal; an object lens utilized in combination with said negative lens to focus said modulated beam on said target; said target consisting of a retro-reflector and a linear polarizer, whereby said modulated beam becomes a reflected beam of linearly polarized light; a lens system including a positive lens for collecting said reflected light from said target; a first surface mirror for redirection of said reflected light to a photo-voltaic cell receiver; a lens for focussing said reflected light on said receiver; a filter for controlling the intensity of said reflected light to the linear range of said receiver; said receiver converting said reflected light to an electric test signal; and, a phase detection circuit for measuring phase angle between said reference signal and said test signal.

Claim 2

A system for measuring angular determination of aircraft structure, including wing twist in flight and position of actuated control surfaces, said system comprising: a linearly polarized light source consisting of linearly polarized continuous wave laser: a 1/4 wave retardation plate disposed at the output beam of said linearly polarized light source for providing a beam of circularly polarized light; a rotating linear polarizer rotating at a constant speed for converting said circularly polarized light beam into a modulated beam of linearly polarized light which has a plane of polarization rotating at twice the speed of said rotating linear polarizer; a negative lens inserted into said modulated beam for providing the first element of a telescope utilized for focussing said modulated beam on a target; a beam splitter for dividing said modulated beam into a reference beam and a test beam; a linear polarizer for demodulating said reference beam and establishing a reference optical signal of known phase angle determined by the polarization plane of said rotating linear polarizer; a photo-voltaic cell for converting said reference optical signal to an electric reference signal; an object lens utilized in combination with said negative lens to focus said modulated beam on said target; said target consisting of a retro-reflector and a linear polarizer, whereby said modulated beam becomes a reflected beam of linearly polarized light; a lens system including a positive lens for collecting said reflected light from said target; a first surface mirror for redirection of said reflected light to a photo-voltaic cell receiver; a lens for focussing said reflected light on said receiver; a filter for controlling the intensity of said reflected light to the linear range of said receiver; said receiver converting said reflected light to an electric test signal; and, a phase detection circuit for measuring phase angle between said reference signal and said test signal.