Patent ID: 7110121

Claim:
A measuring apparatus, comprising: a light source for producing light beams for at least two optical channels, wherein said light source includes a modulator to produce said light beams including a modulation characteristic; said optical channels each including: an interferometer for receiving one said light beam and providing therefrom a reference beam and a measurement beam; a reflective target for receiving and redirecting said measurement beam; a beam splitter for receiving the redirected said measurement beam and providing therefrom a first portion and a second portion; a detector for sensing said first portion and producing a detector signal based thereon; said interferometer further for receiving said second portion of said measurement beam and combining said second portion with said reference beam to form a result beam; and a receiver for sensing said result beam and producing a receiver signal based thereon; and a processing system for processing said detector signals and said receiver signals into position data suitable for communication to an external system, wherein said processing system includes a demodulator to process at least one of said detector signals and said receiver signals with phase sensitive detection.