Back to results
US 7,030,994 B2Granted
Method and apparatus to measure fiber optic pickup errors in interferometry systems
AssigneeZygo Corporation
InventorHenry A. Hill
Life of this patent
Estimating the term…
Abstract
Methods and apparatus for characterizing and compensating non-cyclic errors in fiber optic pickups in interferometry systems are disclosed.
Claims39
A method comprising:
- using a fiber optic pickup comprising an input coupler and a fiber to couple two input beams derived from a common source into the fiber to produce an output beam, wherein the output beam comprises information about an optical path length difference between the two input beams,
- wherein imperfections in the fiber optic pickup cause a measurable interferometric test phase derived from the output beam to deviate from the expression Φ=pknL, where p is an integer, k is the wavenumber of the output beam, and nL corresponds to the optical path length difference, wherein the deviation comprises a non-cyclic error term that varies as a function of a separation of one or both of the input beams from an axis of the input coupler;
- measuring the test phase while varying the separation of at least one of the input beams from the axis;
- comparing the measured test phase to a reference phase indicative of the optical path difference;
- and
- determining a representation indicative of the non-cyclic error term for the fiber optic pickup based on the comparison.
3 more elements
An apparatus comprising:
- a fiber optic pickup including an input coupler and a fiber configured to couple two input beams derived from a common source into the fiber to produce an output beam, wherein the output beam comprises information about an optical path length difference between the two input beams,
- wherein imperfections in the fiber optic pickup cause a measurable interferometric phase derived from the output beam to deviate from the expression Φ=pknL, where p is an integer, k is the wavenumber of the output beam, and nL corresponds to an optical path length difference between the two input beams, wherein the deviation comprises a non-cyclic error term that varies depending on a separation of one or both of the two input beams from an axis of the input coupler;
- and
- an electronic storage medium providing a representation indicative of the non-cyclic error term for the fiber optic pickup.
1 more element
A method comprising:
- positioning an interferometer relative to a measurement object, wherein during operation of the interferometer directs two beams along different paths and then combines them to produce an output beam, wherein at least one of the beams contacts the measurement object and the output beam comprises information about an optical path length difference between the two beams;
- transporting the output beam with a fiber optic pickup to a detector positioned at a location remote from the interferometer,
- wherein imperfections in the fiber optic pickup cause a measurable interferometric phase derived from the output beam to deviate from the expression Φ=pknL, where p is an integer, k is the wavenumber of the output beam, and nL corresponds to the optical path length difference, wherein the deviation comprises a non-cyclic error term that depends on the separation of the output beam components from an axis of the fiber optic pickup;
- correcting the measured phase based on a representation indicative of the non-cyclic error term for the fiber optic pickup;
- and
- monitoring the position of the measurement object based on the corrected phase.
3 more elements
Dependencies are inferred from the claim text.