Optical proximity detector

Details Optical proximity detector Optical proximity detector

2000-06-09

2002-12-24

Epps, Georgia (Department: 2873)

Optics: measuring and testing

Position or displacement

C250S227170, C324S244100

Reexamination Certificate

active

06498654

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a device for detecting the proximity of a magnetic target, and more specifically to an optical proximity detector which employs the Faraday effect to so detect the proximity of a magnetic target thereto.
BACKGROUND OF THE INVENTION
When a beam of polarized light passes through an optical material known as a “Faraday material”, which is exposed to a magnetic field, the Faraday effect causes the material to shift the plane of polarization of the light beam by an angle which is proportional to the strength of the magnetic field. Typically, the magnetic target which is placed in the lines of a magnetic field may take the form of a mechanical device such as a rotating shaft or a door. The change in position of the mechanical device relative to the optical sensor can be detected by the Faraday effect associated with the variation of the magnetic field strength as a result of the magnetic target's change in position within the magnetic field. Various instrument configurations have been developed to exploit the Faraday effect of a selected material in order to detect the position of such a mechanical device, and the detection of a mechanical device's position with optical transducers which measure variations in the intensity of a magnetic field modulated by a magnetic target is well-known. However, although the prior art is highly developed, a number of deficiencies still exist.
U.S. Pat. No. 4,947,035 to Zook discloses a fiber-optic transducer having a 2×1 bidirectional coupler, a fiber, a graded index, or GRIN, lens which collimates light and supplies it to a polarizer, and a permanent magnet radially spaced from the sensor axis. The transducer measures modulation of a magnetic field caused by the mechanical motion of a target device.
U.S. Pat. Nos. 5,149,962; 5,214,377; 5,334,831 and 5,399,853 to Maurice disclose a proximity detector having a pair of fibers with an input polarizer and a second polarizer acting as an analyzer entering into a second optical fiber.
U.S. Pat. No. 5,192,862 to Rudd discloses a polarizer-less optic sensor having a magneto-optical material which exhibits the Faraday effect to provide a phase grating, wherein the intensity of the input light's center beam and diffracted orders change with the magnitude of a magnetic field.
All of these prior art references suffer from a number of disadvantages. One such disadvantage of many of the configurations disclosed in the prior art is that they typically require a polarizing beam splitter component which serves to pass a component of the input light to a particular polarization state as it passes through multiple ports. This is typically done to track optical intensity or polarization states in order to provide-increased sensitivity for the detector.
Another disadvantage of the prior art optical proximity detectors is that they often require a reference path to track the optical intensity or polarization states from the input light source. This, in turn, may disadvantageously require a single mode fiber or more than one fiber to connect a transceiver and sensor. Requiring a reference path may also disadvantageously necessitate the use of more than one optical source and detector.
Yet another disadvantage of the prior art optical proximity sensors is that light typically passes through a sensor with an entrance and exit fiber, where light entering the sensor is directed down a different fiber than the one that delivered it. Such a configuration also disadvantageously requires more than one linear polarizer.
Still another disadvantage of prior designs for optical proximity sensors has been that, when used with certain Faraday materials, they require that the sensor have a permanent magnet radially positioned in order to achieve the proper sensitivity, and that the light source and optical fiber be precisely configured and selected to correspond with the sensor. Such a design limits the applications for which the sensor can be used and increases its manufacturing costs, as relative position and alignment of the components become more critical.
What is desired therefore is an optical proximity detector which does not require a polarizing beam splitter component which serves to pass a component of the input light to a particular polarization state as it passes through multiple ports, which does not require a reference path to track the optical intensity or polarization states from the input light source, which is configured such that light entering the sensor is not directed down a different fiber than the one that delivered it, and which does not require that the sensor have a permanent magnet radially positioned in order to achieve the proper sensitivity, and that the light source and optical fiber be precisely configured and selected to correspond with the sensor.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to provide an optical proximity detector which employs a fiber optic beam splitter having a multimode fiber with a matched optical source.
Another object of the invention is to provide an optical proximity detector which employs a single optic fiber connecting a transceiver and a sensor wherein no reference path is required to track optical intensity or polarization states.
A further object of the invention is to provide an optical proximity detector which is reflective and not transmissive, and wherein substantially all of the light entering a sensor is redirected back down the same optical fiber which delivers it.
Yet another object of invention is to provide optical proximity detector which employs a single optical source and a single optical detector.
Another object of the invention is to provide in optical proximity detector which is arranged such that the proximity of a target directly correlates with the intensity of the light collected at the detector and is not calculated by processing of a reference channel and a probe channel.
Still another object of invention is to provide optical proximity detector which can resolve the position of the target as well as report a binary position status.
Other objects of the invention will be obvious and may in part appear hereinafter.
These and other objects of the present invention are achieved by provision of a proximity detector for detecting the position of a magnetic target having a transceiver module with a light emitting source, an optical detector, and a 2×2 optical coupler joining the light emitting source and optical detector. A sensor having an outer case houses a collimating lens, a polarizer, a Faraday material, and a mirror. A multi-mode optical fiber connects the transceiver module to the sensor. Preferably, the proximity detector detects the position of the magnetic target, which is substantially axially spaced from the sensor, using a single polarizer aligned with a single Faraday material. Most preferably, the Faraday material comprises a Bismuth-Iron-Garnet material.
In another aspect, the proximity detector comprises a transceiver module having a light emitting source aligned with a band pass filter, a first optical detector, a second optical detector, a first 2×1 optical coupler, and a second 2×1 optical coupler. The first 2×1 optical coupler joins the first optical detector and the light emitting source. A sensor having a single polarizer is aligned with a single Faraday material, and a single multi-mode optical fiber connects the transceiver module to the sensor. The second optical detector verifies operation of the sensor with the light emitting source, and the second 2×1 optical coupler joins the second optical detector and the light emitting source with the first 2×1 optical coupler.
The invention and its particular features will become more apparent from the following detailed description considered with reference to the accompanying drawings.


REFERENCES:
patent: 4516073 (1985-05-01), Doriath et al.
patent: 4560932 (1985-12-01), Mitsui et al.
patent: 4843232 (1989-06-01), Emo et al.
patent: 4863270 (1989-09-01), S

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