Optics: measuring and testing – By polarized light examination – With birefringent element
Patent
1991-09-09
1993-07-20
Rosenberger, Richard A.
Optics: measuring and testing
By polarized light examination
With birefringent element
356150, 250225, G01J 404
Patent
active
052298345
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a sensor for detecting and measuring the angle of rotation of a plane of light polarization, the sensor including a polarizing optical component which is subjected to an external influence that causes the plane of polarization delivered by said component to be rotated.
Sensors for detecting and measuring physical magnitudes such as temperature or a displacement and which are of the type that uses light spectrum modulation encoding are already known. Essentially they comprise a polarizer, a birefringent crystal subjected to the physical magnitude to be measured, and an analyzer, with such sensors being connected by optical fibers firstly to a source of incoherent light and secondly to light spectrum analysis apparatus, generally comprising a demodulator interferometer. In such sensors, the light spectrum delivered by the optical fiber is modulated periodically at a frequency which is a function of the path length difference within the birefringent crystal, said path length difference itself being a function of the physical magnitude to be measured.
Such sensors may be used in locations that are not easily accessible and/or in a dangerous environment and/or situated at relatively long distances from the light source and the light analyzing apparatus.
An essential object of the invention is to provide a sensor for detecting and measuring the angle of the rotation of a plane of light polarization that provides the same advantages as prior sensors of the light spectrum modulation type.
To this end, the present invention provides a sensor for detecting and measuring the angle of rotation of a plane of light polarization, the sensor comprising a source of incoherent light, an optical fiber connecting the source to a polarizing optical system subjected to an external influence that causes a rotation in the plane of polarization of the light delivered by the system, the sensor being characterized in that said system is associated with a light spectrum modulator device essentially comprising a birefringent crystal and an analyzer, and with an achromatic quarterwave plate placed before or after the birefringent crystal.
The sensor of the invention provides light flux whose spectrum is modulated at a frequency which is a function firstly of the path length difference in the birefringent crystal and secondly of the angle rotation of the plane of light polarization delivered by the above-mentioned optical system.
Demodulating this light flux thus makes it possible to retrieve this angle of rotation, given that the path length difference in the birefringent crystal is known.
The sensor of the invention may operate in transmission, in which case it is connected at its end facing away from the light source to a demodulator interferometer.
Alternatively it may operate in reflection, with its end facing away from the light source including optical reflection means, and preferably of the retroreflecting type, the above-mentioned analyzer being placed between the birefringent crystal and said optical reflection means.
In one embodiment of this sensor, the above-mentioned optical system is a polarizer associated with a magneto-optical component subjected to a magnetic field.
In this case, the magnetic field may be determined by measuring the angle of rotation of the plane of polarization of the light delivered by the magneto-optical component. It is thus possible to measure an electrical current that is producing the magnetic field.
In a variant, the above-mentioned system may be a single polarizer mounted to rotate about the optical axis of the sensor. In this case, it is possible to measure the angular position of the polarizer or its speed of rotation.
In another variant, and when the sensor operates in transmission, the above-mentioned optical system includes a polarizer and an active element of the rotatory polarization type, such as a cholesteric crystal, for example, having relatively high rotatory power which is a function of temperature.
When the external phenomenon is of the alternating variat
REFERENCES:
patent: 3520617 (1970-07-01), Webb
patent: 4709145 (1987-11-01), Spillman
patent: 4749854 (1988-06-01), Martens
patent: 4883952 (1989-11-01), Jones
Bertin & Cie
Rosenberger Richard A.
LandOfFree
Sensor for detecting and measuring the angle of rotation of a pl does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sensor for detecting and measuring the angle of rotation of a pl, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sensor for detecting and measuring the angle of rotation of a pl will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1764572