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Lensless Magneto-optic speed sensor

United States Patent

5,719,497
February 17, 1998
View the Complete Patent at the US Patent & Trademark Office
Los Alamos National Laboratory - Visit the Technology Transfer Division Website
Lensless magneto-optic speed sensor. The construction of a viable Faraday sensor has been achieved. Multimode fiber bundles are used to collect the light. If coupled directly into a 100 or 200 .mu.m core fiber, light from a light emitting diode (LED) is sufficient to operate the sensor. In addition, LEDs ensure that no birefringence effects in the input fiber are possible, as the output from such light sources have random polarization. No lens is required since the large diameter optical fibers and thin crystals of materials having high Verdet constants (such as iron garnets) employed permit the collection of a substantial quantity of light. No coupler is required. The maximum amount of light which could reach a detector using a coupler is 25%, while the measured throughput of the fiber-optic bundle without a coupler is about 42%. All of the elements employed in the present sensor are planar, and no particular orientation of these elements is required. The present sensor operates over a wide range of distances from magnetic field sources, and observed signals are large. When a tone wheel is utilized, the signals are independent of wheel speed, and the modulation is observed to be about 75%. No sensitivity to bends in the input or output optical fiber leads was observed. Reliable operation was achieved down to zero frequency, or no wheel rotation.
Veeser; Lynn R. (Los Alamos, NM), Forman; Peter R. (Los Alamos, NM), Rodriguez; Patrick J. (Santa Fe, NM)
The Regents of the University of California (Los Alamos, NM)
08/ 647,364
May 9, 1996
The invention was made with government support under Contract No. W-7405-ENG-36 awarded to The Regents of the University of California by the U.S. Department of Energy. The government has certain rights in this invention.