Optics: measuring and testing – By configuration comparison – With photosensitive film or plate
Reexamination Certificate
1999-10-16
2001-06-26
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
By configuration comparison
With photosensitive film or plate
C356S073100
Reexamination Certificate
active
06252660
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and a device for measuring or determining the length of a light guide.
Light guides are increasingly used in communications technology for signal and data transmission. A growing field of application is the use of light guides in motor vehicles because they require less space than a conventional wire harness. The quality control of the light guides is usually carried out such that the attenuation of the light passing through the light guide is measured. This attenuation, however, only provides a reliable result with respect to the quality of the light guide when the length of the light guide is known. However, this length, when the light guide is already mounted in its proper location of use, can no longer be measured with simple measuring means.
It is therefore an object of the present invention to provide a method and a device for determining or measuring the length of a light guide in a simple manner.
SUMMARY OF THE INVENTION
The method of the invention for determining the length of a light guide is characterized by the steps of passing light of two different wavelengths or wavelength ranges through a light guide whose length is to be measured, determining a ratio of incident light intensity to exit light intensity for each one of the wavelengths or wavelength ranges passing through the light guide, calculating the length of the light guide based on wavelength-dependent attenuation coefficients of the light guide and the ratios of incident light intensity to exit light intensity for each one of the wavelengths or wavelength ranges of the light.
A further method of the invention for determining the length of a light guide is characterized by the steps of guiding a light, emitted by at least one light source and having two different wavelengths or wavelength ranges, into a reference light guide of a known length and into a specimen light guide whose length is to be determined, determining a ratio of exit light intensity of the reference light guide for the different wavelengths or the different wavelength ranges and a ratio of exit light intensity of the specimen light guide for the different wavelengths or the wavelength ranges, calculating a ratio of incident light intensity of the different wavelengths or the two different wavelength ranges for the reference light guide based on the ratio of exit light intensity of the reference light guide, the known length, and the attenuation coefficient of the reference light guide, and calculating the length of the specimen light guide based on the ratio of incident light intensity of the two different wavelengths or the two different wavelength ranges, the ratio of exit light intensity of the specimen light guide, and an attenuation coefficient of the specimen light guide.
The device of the invention for determining a length of a specimen light guide has a light source emitting a light beam, a device for introducing the light beam emitted by the light source into a light window of the specimen light guide, a first measuring device for determining a ratio of incident light intensity of the light beam at the light window for two different wavelengths or two different wavelength ranges, a second measuring device for determining a ratio of exit light intensity for the two different wavelengths or the two different wavelength ranges of light exiting from an exit window of the specimen light guide
The invention takes advantage of the fact that the attenuation coefficient of a light guide essentially depends on the wavelength. When the attenuation for two different wavelengths or wavelength ranges is measured, it is possible to determine the length of the light guide from the measured results and the attenuation coefficient of the material of the light guide.
The methods and device present invention provide a simple and reliable quality control for a light guide.
REFERENCES:
patent: 4176954 (1979-12-01), Bouillie et al.
patent: 5534994 (1996-07-01), Hanson et al.
patent: 5541730 (1996-07-01), Chaney
patent: 5737067 (1998-04-01), Sansone
patent: 6011615 (2000-01-01), Mamyshev et al.
Braumandl Walter
Frisch Ernst Georg
Pham Hoa Q.
Robert W. Becker & Associates
Sensor Instruments GmbH
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