| 摘要 |
An optical speed sensor includes a laser diode 10 that provides a broadband source light 12 to a coupler 18 which provides a source light 22 to a fiber Bragg grating 26 which reflects a first reflection wavelength of light 28 and passes the remainder as a light 30. The light 30 is incident on another fiber Bragg grating 32 which reflects a second reflection wavelength of light 34. The power of an output signal 40 is indicative of the reflected light beams 34,28, and is measured by a photodetector 46. The gratings 26,32 are mounted on a magnetostrictive material 60 which is connected to a permanent magnet 62 which is connected to a material 70 which conducts magnetic fields. The material 60 expands and contracts in response to the strength of magnetic fields therein. The reflection wavelengths for both gratings 26,32 are the same when the tooth 100 is not nearby, thereby causing the output signal 40 to be primarily equal to the reflected light 28. However, when the tooth 100 is nearby, the material 60 and the grating 32 expands causing the reflection wavelengths to separate, thereby causing the power of the output signal 40 to increase. Because both gratings 26,32 are on the same material thermal expansions will have no effect on the sensor measurement. Alternatively, one of the gratings 26,32 may be mounted to the material 70 or the magnet 62. The detection may performed in either reflection or transmission mode.
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