Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Patent
1997-03-10
1998-09-22
McGraw, Vincent P.
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
356334, 250372, G01J 318, G01N 2133
Patent
active
058122621
DESCRIPTION:
BRIEF SUMMARY
This invention relates to radiation detectors, and relates more especially to a robust device which is small enough to be hand held.
One application for a robust yet accurate spectrographic hand-held device is in the measurement of ultraviolet radiation from the sun. There are currently concerns in many countries about the effect on living organisms, and especially on human health, of UV radiation from the sun. Currently available detectors however are either insufficiently accurate or are too large and heavy to be made widely available, e.g. for use on an individual basis as a personal portable device.
A known arrangement for providing a robust radiation detector is to provide all, or substantially all, of the components attached to a radiation-transparent body, the radiation path within the detector lying substantially within the body.
Such an arrangement is disclosed in U.S. Pat. No. 5,159,404, Carl-Zeiss-Stiftung, in which a diode-array spectrometer comprises a biconvex lens having a concave grating mounted on one convex surface, and a diode array spaced a small distance from the other convex surface. The device relies on the small air gap to allow tilting of the diode array to correct for tolerance variations of the carrier body. The device uses a curved diffraction grating which is not easy to manufacture, or to apply to the convex surface.
Another arrangement is described in PCT patent application, publication number: WO 92/11517, The Boeing Company, in which a demultiplexor/detector for a wavelength division multiplexing system comprises a planar waveguide having a variable line-spacing diffraction grating formed on a curved edge and a planar detector array attached to a straight edge. Such a device is robust in that there is no air gap, but is complex to manufacture.
Various configurations for demultiplexer units and a convex mirror are disclosed in the Journal of Lightwave Technology vol. LT-2, no.5, October 1984, New York US pages 731-734; Y. Fujii et al. `Optical Demultiplexer Utilizing an Ebert Mounting Silicon Grating`. These units include an input fibre, a mirror, a flat diffraction grating, and an output fibre. The radiation entering the demultiplexer from the input fibre reflects off the mirror, onto the diffraction grating, then back onto the mirror and then onto the output fibre. The configurations shown all suffer to a greater or lesser degree from reflection loss reduction of the radiation and aberration.
It is an object of the invention to provide a radiation detector which is relatively simple to manufacture, and which provides both spectral and intensity measurement of a light source.
According to the invention, a radiation detection system comprising a radiation-transparent wave guide (10) having on one face entrance aperture means (18) to receive radiation, a first planar face (23) having associated radiation detector means (24), a curved reflective face (20, 22) positioned to receive radiation (36) from the entrance aperture means (18), and a second planar face (26) positioned to receive radiation (38) from the curved reflective face (20, 22) and having a planar diffraction grating (28) associated therewith, the arrangement being such that the curved reflective face (20, 22) and the planar diffraction grating (28) focus radiation (36, 38) diverging from the entrance aperture means (18) characterised in that the radiation detector means (24) is mounted on a different face from diffraction grating (28), radiation (36, 38) is diffracted by the diffraction grating (28) directly onto radiation detection means (24), and that a required spectral band and spectral order is focused on the radiation detector means (24).
Preferably the curved reflective face directs radiation onto the planar diffraction grating as a converging beam.
Preferably the central ray of the converging beam is incident on the planar diffraction grating at a small angle to the normal to the grating.
Preferably a first order spectrum is focussed onto the radiation detector means, and preferably this spectrum lies on t
REFERENCES:
patent: 4375919 (1983-03-01), Busch
patent: 4935631 (1990-06-01), Mosley et al.
patent: 5026160 (1991-06-01), Dorain et al.
Fujii et al, "Optical Demultiplexer Utilizing an Ebert Mounting Silicon Grating" Journal of Lightwave Technology, vol. LT-2, No. 5 Oct. 1984, pp. 731-734.
Beranek et al. "Physical Design & Fabrication . . . . Multimode Fiber-Optic WDM Systems" IEEE Transactions on Components, Hybrids & Manufacturing Technology Aug. 1993, pp. 511-516.
Patent Abstracts of Japan, vol. 005, No. 173, (P-087) 12 Aug. 1981, 56100323 (Ritsuo).
Ridyard Andrew
Shrewsbury David
4D Controls Limited
McGraw Vincent P.
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