Optics: measuring and testing – By light interference – Spectroscopy
Reexamination Certificate
1999-10-15
2001-12-18
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
Spectroscopy
C356S452000, C356S454000
Reexamination Certificate
active
06331892
ABSTRACT:
COPYRIGHT NOTICE
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to wavelength monitoring devices for measurement, control, or locking of optical signal generators and related components.
2. Description of the Related Art
Optical wavelength monitors are needed in a wide range of applications ranging from telecommunications to test and measurement. Optical wavelength monitors perform a wide range of functions. In the laboratory or during assembly of optical components they may include both measurement and display capability. In telecommunications applications they may be part of a closed loop control circuit for locking or tuning an optical signal source and related components. Typically such systems are expensive, and may additionally have a large form factor. Their accuracy may be affected by power fluctuations and noise levels in the optical beam.
What is needed is an optical wavelength monitor with small form factor, low cost, and tolerance for the power fluctuations and noise levels typically associated with optical signal generators.
SUMMARY OF THE INVENTION
Interference elements are disclosed for measurement of wavelength in optical devices. They may be used for display, monitoring, control or locking of optical signal sources. They may be used to determine relative and absolute wavelength variations in an optical beam.
In an embodiment of the invention an apparatus for monitoring wavelength in an optical beam generated by an optical source is disclosed. The optical source includes: an interference element, detectors, and logic. The interference element is positioned in the path of the optical beam to generate a periodic fringe pattern. The detectors are located within the generally periodic fringe pattern to generate signals corresponding to the intensities of the fringe pattern at a plurality of locations. The logic is coupled to the detectors for [iteratively] sampling two selected pairs of the signals generated by the detectors, for determining a ratio of the differences of the two selected pairs of the signals, and for comparing a current ratio with a prior ratio to detect a variation in the wavelength of the optical beam generated by the optical source.
In an embodiment of the invention the apparatus for monitoring wavelength includes: an interference element, detectors and logic. The interference element is positioned in tie path of the optical beam to generate a generally periodic fringe patter. The detectors are located within the generally periodic fringe pattern to generate signals corresponding to the intensities of the fringe pattern at a plurality of locations. The logic is coupled to the detectors for sampling two selected pairs of the signals generated by the detectors, for determining a ratio of the differences of the two selected pairs of the signals, and for calculating the wavelength of the optical beam based on parameters which correlate the ratio with wavelength.
In an embodiment of the invention the apparatus for monitoring wavelength in an optical beam comprises: a beam splitter, a stationary reflector; a movable reflector; a detector; and logic. The beam splitter is positioned in the path of the optical beam to split the optical beam into a first and a second beam. The stationary reflector is positioned in an optical path of the second beam. The movable reflector oscillates over a known distance along an optical path of the first beam to vary an optical path length of the first beam. The detector detects interference fringes generated by a combination of a portion of the first beam reflected by the movable reflector and a portion of the second beam reflected by the stationary reflector, and generates an AC signal corresponding thereto. The logic samples the AC signal and determines at least one of a relative wavelength and an absolute wavelength of the optical beam based on the AC signal and the known distance of the reflector.
In another embodiment of the invention the apparatus for measuring wavelength in an optical beam comprises:
means for generating a generally periodic fringe pattern of the optical beam;
means for generating signals corresponding to intensities of the generally periodic fringe pattern at a plurality of locations; and
logic coupled to the means for generating for sampling two selected pairs of the signals, for determining a ratio of the differences of the two selected pairs of the signals, and for comparing a current ratio with a prior ratio to detect a variation in the wavelength of the optical beam generated by the optical source.
In still another embodiment of the invention the apparatus for monitoring wavelength in an optical beam includes:
means for splitting optical beam into a first and a second beam;
means for reflecting the second beam;
means for varying an optical path length of the first beam by a known distance;
means for detecting interference fringes generated by a combination of a portion of the first beam reflected by the means for varying and a portion of the second beam reflected by the means for reflecting, and to generate an AC signal corresponding thereto; and
means for sampling the AC signal and determining at least one of a relative wavelength and an absolute wavelength of the optical beam based on the AC signal and the known distance of the means for varying the optical path length.
In another embodiment of the invention a method for monitoring a wavelength in an optical beam is disclosed. The method comprises the acts of;
generating a generally periodic fringe pattern of the optical beam;
generate signals corresponding to the intensities of the fringe pattern at a plurality of locations;
sampling two selected pairs of the signals generated in the act of generating signals;
determining a ratio of the differences of the two selected pairs of the signals;
comparing a current ratio with a prior ratio to detect a variation in the wavelength of the optical beam generated by the optical source.
In another embodiment of the invention the method for monitoring comprises the acts of:
splitting optical beam into a first and a second beam;
varying an optical path length of the first beam by a known distance;
detecting interference fringes generated by a combination of a portion of the first beam and the second beam;
generating an AC signal corresponding to a level of the interference fringes detected in the act of detecting;
sampling the AC signal; and
determining at least one of a relative wavelength and an absolute wavelength of the optical beam based on the sampling of the AC signal in the sampling act and the known distance of the optical path length in the varying act.
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Bozicevic Field & Francis LLP
Hall Robert C.
New Focus Inc.
Turner Samuel A.
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