Zygo Corporation

Hewlett-packard Company

Alan H Field

Henry Allen Hill

Carl A Zanoni

Frank C Demarest

Joseph Bakach

Scott M Detro

An interference signal S(t) is provided from interference between two beams directed along different paths. The signal S(t) is indicative of changes in an optical path difference n{tilde over (L)}(t) between the different paths, where n is an average refractive index along the different paths, {tilde over (L)}(t) is a total physical path difference between the different paths, and t is time. An error signal is provided to reduce errors in an estimate of {tilde over (L)}(t). The error signal is derived at least in part based on one or more collective properties of a distribution of multi-dimensional values. At least one of the multi-dimensional values in the distribution is generated from a plurality of samples of the signal S(t) (e.g., samples of the signal captured at different times).

Cyclic error compensation in interferometry systems

A pair of orthogonally polarized optical beams that differ in frequency by a constant oscillator-generated reference frequency are directed through and traverse respective fixed and variable length paths of a heterodyne interferometer, following which the beams are mixed and directed to a detector that generates an electrical measurement signal having a phase that varies with changes in the variable path length. Changes in the measurement signal phase are determined by counting cycle-to-cycle phase changes of the reference frequency signal between sampling instants defined by time-spaced occurrences of a known phase of the measurement signal. The resulting count is simultaneously used to determine both changes in length of the variable length path and the elapsed time interval between the sampling instants. Each of the change in path length and and elapsed time interval determinations are accumulated over an extended plurality of sampling instant pairs to provide the current path length and the time of the final measurement of path length change.

Method and apparatus for determining the position of a moving body and

A dual high stability interferometer system capable of measuring linear and angular displacement simultaneously of a movable plane mirror (90) comprises a frequency stabilized laser input beam (10) which is divided into two parallel spatially displaced beams by a beamsplitter (14). An optical system (20) is disposed to produce a first output beam having two orthogonally polarized components in which the phase difference between the two components of the third output beam is related to four times the linear displacement of the movable plane mirror (90) at a first position. A polarizer (93) mixes the orthogonal components of the third output beam with the interference between the two polarization components being detected by a photodetector (94) which produces an electrical signal (96) from which a phase meter/accumulator (99) extracts the phase change, with this phase change being related to four times the linear displacement of the movable mirror (90) at the first position. The optical system (20) also produce a second output beam whose orthogonally polarized components have a phase difference related to four times the linear displacement of the movable mirror (90) at a second position. Another polarizer (95) mixes these orthogonal components and a photoelectric detector (194) and another phase meter/accumulator (109) cooperate to provide a second measured phase which is related to four times the linear displacement of the movable mirror (90) at the second position.

Dual high stability interferometer

A wavelength tracking compensator for a laser interferometer measurement system comprises a stable physical standard optical cavity and a double path, differential interferometer mounted on a baseplate. The interferometer monitors the apparent changes in the cavity's length caused by actual changes in the index of refraction of the surrounding air. The cavity is supported with a temperature compensated mount that utilizes the principle of differential thermal expansion of two different metals to create a mount which exactly matches the coefficient of expansion of the cavity material. A semi-kinematic mount supports the double path, differential interferometer and allows the interferometer to be accurately aligned to the cavity with three rotational degrees of freedom to prevent any cosine error in the cavity's optical path length measurement, to prevent polarization leakage, and to maximize optical power at the receiver. A phase measurement system interpolates between interference fringes to extend measurement resolution and provides absolute phase information relative to the fringes so that the measurement system can prevent measurement uncertainty caused by a beam interruption and recover from an interruption without re-initialization.

Growing community of inventors

San Jose, CA, United States of America

Alan H Field