Optics: measuring and testing – Inspection of flaws or impurities – Transparent or translucent material
Patent
1995-10-20
1997-08-12
Font, Frank G.
Optics: measuring and testing
Inspection of flaws or impurities
Transparent or translucent material
315135, 315138, 315136, G01N 2100
Patent
active
056571178
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The object of the invention is a device for examining optical waveguides, which comprises a prism to be positioned on an optical waveguide under investigation, a point at which incoming light enters the device, as well as control means for altering the angle of light directed to the prism from the entering point of incoming light.
BACKGROUND OF THE INVENTION
Prism coupling is one of the most common methods to test integrated optical circuits and structures. It is used in connection with methods to determine the effective refractive indices and thicknesses of the waveguides, by means of the structure of the propagating modes of light within the waveguide. This technique is described in the publication by Tien, P. K., Ulrich, R., and Martin, R. J.: Modes of propagating light waves in thin deposited semiconductor films, Applied Physics Letters 14 (1969) 9, pp. 291-294. Prism coupling is also required in measuring distributions of propagating modes and attenuation in the structures.
The device by which the testing is to be performed comprises a source of light, such as a laser, a prism having an unbeveled corner to which the incoming ray of light is directed at a desired angle, as well as measuring devices such as a light detector and a CCD-camera situated perpendicularly to the waveguide. The light must be directed to the prism at a characteristic angle pertaining to one of the propagating modes in the waveguide. This requires that the source of light be turned with respect to the prism, e. g. by means of a goniometer. Since the source of light is often relatively large, its precise positioning places great demands on the fine mechanism of the device and at the least makes the whole device large and inflexible to varied geometries.
SUMMARY OF THE INVENTION
The purpose of this invention is to remove the drawbacks of the prior art and present a device, by means of which the positioning can be simplified and where the interchange of light sources can be easily performed. In order to realize this purpose, it is in general characteristic of the invention that the control devices include a mirror, whereby the projection of the reflective surface of the mirror in the plane of altering the angle is in the form of an ellipse, a rotatable mirror is placed at the focal point of the ellipse and the unbeveled corner of the prism is situated at the second focal point of the same ellipse. The point at which the light from the light source is directed to the waveguide under investigation by means of the mirrors, can then be constant within the device, and the angle at which the light enters the prism can then be altered by turning the rotatable mirror in the focal point of the ellipse, around an axis perpendicular to the plane in which the angle is varied. Since the point of the rotatable mirror at which light is projected is situated at the focal point of the ellipse, the ray of light impinging on the elliptic mirror will always be reflected precisely to the other focal point of the same ellipse, where the coupling corner of the prism in the prism coupler is located. The three-dimensional form of the mirror will also have options described further in the text.
Since the optics of the device are mostly reflecting, the device is also independent of the wavelength of light, and different light sources can then be used without adjustments.
According to one preferred embodiment, the device can be connected with the light source by means of an Optical fiber. The connecting point can then be made precise with respect to the mirror permanently, and no adjustment of the light source in the prism coupling device need be performed prior to measurements.
According to one further embodiment, the device will have manipulators, such as a micrometer screw, a linear DC motor, a stepping motor, or a piezoelectric manipulator, arranged to move the waveguide and the prism placed upon it, perpendicularly with respect to the direction of the light beam entering the device, so that the angle of the prism will stay at
REFERENCES:
patent: 3873209 (1975-03-01), Schinke et al.
patent: 3918818 (1975-11-01), Giles
patent: 4692024 (1987-09-01), Bloss
patent: 4779978 (1988-10-01), Hatton et al.
patent: 5125740 (1992-06-01), Sato et al.
Derwent's abstract, No. 83-838217/49, week 8349, Abstract of SU 998894 (Legnd Kalinin Poly), 23 Feb. 1983.
Font Frank G.
Ratliff Reginald A.
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