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US 9,518,816 B2Granted
Dual beam splitter interferometer measuring 3 degrees of freedom, system and method of use
AssigneesUniversity of Rochester, Delft University of Technology
InventorsJonathan D. Ellis, Josephus Wilhelmus Spronck
Life of this patent
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Abstract
A compact, balanced, up to three degrees of freedom measuring interferometer having dual beam splitters rotated ninety degrees with respect to each other and a measurement detector including a quadrant detector or multi-core fiber with four detectors which enables fiber delivery of an optical source without periodic error, an interferometer system, and method for using is disclosed.
Claims19
An interferometer comprising:
- a first beam splitter capable of splitting a first light beam having a first frequency;
- a second beam splitter rotated ninety degrees with respect to the first beam splitter and capable of splitting a second light beam having a second frequency;
- a reference mirror;
- a reference detector;
- and
- a measurement detector comprising a quadrant detector or a multi-core fiber with four detectors;
- wherein the first beam splitter is capable of a) transmitting a portion of the first light beam to the reference mirror and reflecting bad to the first beam splitter where a portion of the reflected first light beam is split and transmitted to the reference detector and a portion of the reflected first light beam is split and transmitted upstream in the first light beam and b) splitting a portion of the first light beam to the second beam splitter where a portion of the first light beam is split and transmitted to the measurement detector and a portion of the first light beam is split and transmitted upstream in the second light beam, and wherein the second beam splitter is capable of a) transmitting a portion of the second light beam to a measurement mirror and reflecting back to the second beam splitter where a portion of the reflected second light beam is split and transmitted to the measurement detector and a portion of the reflected second light beam is split and transmitted upstream in the second light beam and b) splitting a portion of the second light beam to the first beam splitter/here a portion of the second light beam is split and transmitted to the reference detector and a portion of the second light beam is split and transmitted upstream in the first light beam;
- and wherein the first light beam is spatially separated from the second light beam, the first and second frequencies having a different frequency, and the path of the first light beam through the first beam splitter is the same length as the path of the second light beam through the second beam splitter;
- and wherein the path of the first light beam transmitted from the first beam splitter to the reference detector and the path of the second light beam transmitted from the second beam splitter to the reference detector generate a reference interference signal that is detected at the reference detector and the path of the second light beam transmitted from the second beam splitter to the measurement detector and the path of the first light beam transmitted from the first beam splitter to the measurement detector generate a measurement interference signal that is detected at the measurement detector.
6 more elements
A method of using an interferometer to measure a target moved from a first position to a second position, comprising:
- directing a first light beam having a first frequency to a first beam splitter where a) a portion of the first light beam is transmitted to and reflects off a reference mirror back to the first beam splitter along the same path;
- and where a portion of the reflected first light beam is split and transmitted to a reference detector and a portion of the reflected first light beam is split and transmitted upstream in the first light beam and b) a portion of the first light beam is split and transmitted to a second beam splitter rotated ninety degrees with respect to the first beam splitter, where a portion of the split first light beam is split and transmitted to a measurement detector comprising a quadrant detector or a multi-core fiber with four detectors and a portion of the split first light beam is transmitted upstream in a second light beam;
- directing the second light beam having a second frequency to the second beam splitter where a) a portion of the second light beam is transmitted through the second beam splitter to a measurement mirror of a target in a first position and reflecting back to the second beam splitter where a portion of the reflected second light beam is split and transmitted to the measurement detector and a portion of the reflected second light beam is split and transmitted upstream in the second light beam and b) a portion of the second light beam is split and transmitted to the first beam splitter where a portion of the split second light beam is split and transmitted to the reference detector and a portion of the split second light beam is transmitted upstream in the first light beam, wherein the first light beam is spatially separated from the second light beam, the first and second light beams have a different frequency, the path of the first light beam through the first beam splitter is the same length as the path of the second light beam through the second beam splitter, the path of the first light beam transmitted from the first beam splitter to the reference detector and the path of the second light beam transmitted from the second beam splitter to the reference detector creating a reference interference signal, and the path of the second light beam transmitted from the second beam splitter to the measurement detector and the path of the first light beam transmitted from the first beam splitter to the measurement detector creating a measurement interference signal;
- detecting the reference interference signal at the reference detector and the measurement interference signal at the measurement detector for the target in the first position;
- moving the target to a second position,
- detecting the reference interference signal at the reference detector and the measurement interference signal at the measurement detector for the target in the second position, and
- calculating the difference in at least one of the tilt, tip and displacement values of the target from the first and second positions.
4 more elements
Dependencies are inferred from the claim text.