Integrated-optic spectrometer and method

Details Integrated-optic spectrometer and method Integrated-optic spectrometer and method

1999-05-05

2001-05-01

Font, Frank G. (Department: 2877)

Optics: measuring and testing

By dispersed light spectroscopy

For spectrographic investigation

C356S300000, C356S303000, C356S435000

Reexamination Certificate

active

06226083

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to a system for analyzing light. More specifically, the invention is related to an integrated-optic spectrometer and method for guiding an inputted light source and diffracting discrete wavelengths from the guided light for composition analysis, by use of successive diffraction gratings.
BACKGROUND OF THE INVENTION
A spectrometer is generally any device that produces a spectrum by the dispersion of light and is calibrated to measure transmitted energy or radiant intensities with respect to wavelengths of radiation. Said in a different way, a spectrometer is a photometer for measuring the relative intensities of light in different parts of a spectrum.
Spectrometers are used in numerous different industries. Examples of such industries include the automotive industry, for identifying certain paint or pigment compositions, thereby making possible the application of a matching paint; the textile industry, for ensuring the consistency of color from one dye lot to the next; and the cosmetic industry, for identifying the facial properties of a consumer, thereby allowing the identification of cosmetics which will enhance these facial properties.
Spectrometers utilized for these and other purposes typically utilize a diffraction grating which may be either curved or flat, to disperse the light into a spectrum. The diffracted light intensity at each wavelength is then measured by a suitable detector, such as a photodiode detector array or a photomultiplier tube.
While current spectrometers are effective in analyzing the optical properties of certain samples, they are generally costly, bulky, and heavy. Therefore, there is a need in
SUMMARY OF THE INVENTION
In the context of this document, “integrated-optic” refers to a device or devices, fabricated on or in an optical waveguide by any process or method for producing micromachined or micro-level structures, including, but not limited to, disposition techniques (e.g., sputtering, evaporation, screen printing, etc.), microlithography, holegraphy, or thin-film fabrication techniques.
Briefly described, the invention is an integrated-optic spectrometer which utilizes the combination of a waveguide, fabricated onto an oxidized substrate, which has an array of diffraction gratings and a detector array, capable of analyzing discrete wavelengths, which is mounted on the waveguide so as to receive the light of different wavelengths diffracted by the grating array. The diffraction gratings each comprise a series of grating lines and are constructed to provide for optimal transmission of wavelengths not diffracted by the diffraction grating. Therefore, the inputted light is guided through the waveguide and discrete wavelengths are diffracted by the diffraction gratings onto the photodiode detector array which in turn measures the intensity of the light at the discrete wavelengths for determining composition, while optimally transmitting non-diffracted wavelengths through the waveguide.
In general, the architecture of a first embodiment of the invention comprises a single layer waveguide. The surface layer of a substrate is first oxidized, creating a buffer layer. This buffer layer is then either etched by a technique such as holographic or microlithographic techniques, or otherwise fabricated upon, thereby creating diffraction gratings. A waveguide is then fabricated onto the buffer layer creating a path through which the light to be analyzed may travel. A clad layer is then fabricated to encompass the waveguide and gratings, thereby providing protection to the waveguide and hampering interference from outside elements. Finally, a suitable detector array is mounted on the clad layer so as to measure the intensity of the wavelengths diffracted by each grating in the array. Depending on the desired field of application, the diffraction gratings may be designed to diffract the selected wavelength of light either within the plane of the waveguide, but in a different direction from the inputted light, or out of plane of the waveguide.
A second embodiment of the present invention utilizes a bi-layer waveguide. This embodiment comprises a first layer of waveguide fabricated onto the oxidized surface layer of a substrate, or buffer layer, a second buffer layer fabricated onto the top of the first waveguide layer, a grating structure etched or otherwise fabricated onto the second buffer layer, thereby fabricating the grating structure, a second waveguide layer fabricated onto the top of the second buffer layer, and a clad layer fabricated on top of the second waveguide layer. A suitable detector array is then mounted either on top of the clad or along its side, as described previously. Fabricating the diffraction gratings on, or in, the second buffer layer of this embodiment maximizes the intensity of the diffracted light due to the location of the diffraction gratings between the first and second waveguide layers. Because the second buffer layer in quite thin, as compared to the two waveguide layers, this multi-layer system functions as a single thick waveguide with gratings embedded in or near its center.
Optionally, the integrated-optic spectrometer may be equipped with numerous diffraction gratings constructed in succession. Both of the above-mentioned embodiments utilize diffraction gratings which are constructed to provide for optimal transmission of wavelengths to successive diffraction gratings, after the diffraction of discrete wavelengths by preceding diffraction gratings. Therefore, successive diffraction gratings are provided for while providing an accurate analysis of the diffracted light by the detector array.
The invention has numerous advantages, a few of which are delineated hereafter, as examples. Note that the embodiments of the invention that are described herein possess one or more, but not necessarily all, of the advantages set out hereafter.
One advantage of the invention is that it may be utilized in a multitude of industries due to its low weight, and small size.
Another advantage of the invention is that it may be implemented on a single chip, thereby decreasing cost and making possible the fabrication of hand-held battery powered devices, incorporating the invention.
Another advantage of the invention is that it allows for multiple diffraction gratings to be utilized in succession while preventing each successive diffraction grating from distorting non-diffracted wavelengths which pass through the waveguide.
Another advantage is that the second embodiment provides for a thicker waveguide since two waveguide layers are used. Therefore, a larger reflected light source may be analyzed, and the inputted light may be more easily coupled into the waveguide.
Another advantage provided by the second embodiment is that it provides diffraction gratings at the peak of the guided mode intensities, insuring strong interaction with the gratings.
Other objects, features, and advantages of the present invention will become apparent to one with reasonable skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional objects, features, and advantages be included herein within the scope of the present invention, as defined by the claims.


REFERENCES:
patent: 4684252 (1987-08-01), Makiguchi et al.
patent: 4790669 (1988-12-01), Christensen
P. St. J. Russell, “Novel Thick-Grating Beam-Squeezing Device in ta2O5Corrugated Planar Waveguide,” Electronics Letters, vol. 20, No. 2, Jan. 19, 1984, pp. 72-73.
G. Notni and R. Kowarschik, “Diffraction Analysis if Three-Dimensional Volume Grating With Arbitrary Boundaries,” J. Opt. Soc. Am. A, vol.6, No. 11, Nov. 1989, pp. 1682-1691.
Dietrich Marcuse, “Theory of Dielectric Optical Waveguides,” Academic Press, New York, 1974.
L. A. Weller-Brophy and D. G. Hall, “Local Norman Mode Analysisw of Guided Mode Interaction With Waveguide Grating,” IEEE, Journal of Lightwave Technology, vol. 6, No. 6, Jun. 1988, pp. 1069-1082.
Herwig Kogelnik, “Coupled Wave Theory for Thick Hologram Grating,” The

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