Optics: measuring and testing – By shade or color – With color transmitting filter
Patent
1997-01-21
1998-01-06
McGraw, Vincent P.
Optics: measuring and testing
By shade or color
With color transmitting filter
356419, G01J 351
Patent
active
057060924
ABSTRACT:
A differential spectrometry system detects very narrow-band spectral features, while providing much higher optical transmittance and signal-to-noise ratios than prior optical-filter-based spectrometer systems. A plurality of light detectors (10a, 10b) detect light that falls within respective wide wavebands. The wide wavebands have overlapping and non-overlapping portions, one of which is the desired narrow waveband. The detector outputs are operated upon to produce an output signal (22) which includes substantially only the desired narrow waveband. In the preferred embodiment, the light detectors (10a, 10b) are implemented with a pair of optical detectors (30a, 30b) and respective optical interference filters (24a, 24b). The filters have substantially identical cut-off wavelengths (.lambda..sub.2) and cut-on wavelengths that are shifted by .DELTA..lambda. with respect to each other (.lambda..sub.1 and (.lambda..sub.1 +.DELTA..lambda.), respectively). The detector outputs are differenced with an operational amplifier (33), so that detector signals resulting from spectral features common to both detectors (30a, 30b) are canceled. The remaining signal (36) varies according to the amount of (.lambda..sub.1 +.DELTA..lambda.)!. A preferred method of fabricating the optical interference filters (24a, 24b) is also provided.
REFERENCES:
patent: 4896965 (1990-01-01), Goff et al.
Peterson Cathy M.
Stannard John E.
Walter Geoffrey A.
West Roger A.
Denson-Low W. K.
McGraw Vincent P.
Santa Barbara Research Center
Schubert W. C.
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