Optics: measuring and testing – Standard
Reexamination Certificate
1999-10-29
2001-06-19
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Standard
C356S437000, C356S432000
Reexamination Certificate
active
06249343
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to calibration references for use with optical wavelength measuring devices such as Optical Spectrum Analyzers. In particular it pertains to calibration references using broad band light sources coupled to gas cells providing absorption lines at known wavelengths, and methods for using them.
2. Art Background
Optical wavelength measuring devices such as Optical Spectrum Analyzers are complex eletromechanical systems. Periodic calibration is required to maintain the accuracy of such systems. To perform such calibration, references are used. A reference may be emissive, providing energy at a known wavelength or frequency, or group of wavelengths or frequencies, or it may be absorptive, coupled to a broadband source and providing absorption lines at known wavelengths or frequencies. It is understood that wavelength and frequency are reciprocals, and may be interchanged.
To be suitable as a reference, the device in question should provide a stable output in varying environmental conditions, such as temperature, humidity, and atmospheric pressure. The device must also provide a stable reference over long periods of time. The other requirement for a reference is that it cover the frequency or wavelength range of interest. References based on mechanical properties can be manufactured, but they are typically bulky, and require initial calibration and periodic recalibration, typically at the factory.
Modern optical communications systems have extended from wavelengths in the 1.5 micrometer region to the 1.6 micrometer region. What is needed is a reference which covers both the 1.5 and 1.6 micrometer regions, and one which remains stable over time.
SUMMARY OF THE INVENTION
A stable reference for calibrating optical systems is provided by filtering the light emitted from a broadband source through two gasses, providing stable absorption lines in both the 1.3 and 1.5 micrometer regions of the spectrum. The gasses may be provided in two separate cells or mixed in one cell. Calibration using the reference is performed by making a plurality of measurements at known wavelengths of the gasses, deriving a correction model from the measurements.
REFERENCES:
patent: Re. 35355 (1996-10-01), Ryan et al.
patent: 5818598 (1998-10-01), Kebabian
Technical Digest—Symposium on Optical Fiber Measurements, 1992; Digest of a symposium sponsored by the National Institute of Standards and Technology in cooperation with the IEEE Lasers and Electro-Optics Society and the Optical Society of America; Sep. 15-17, 1992; pp. 191-194.
2010WR Series—Wavelength Reference Standard—Preliminary; Newport, pp. 2-18 and 2-19.
Egerton Peter
Wang Gary
Wildnauer Kenneth R.
Agilent Technologie,s Inc.
Font Frank G.
Martin Robert T.
Punnoose Roy M.
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