High sensitivity position sensor and method

Details High sensitivity position sensor and method High sensitivity position sensor and method

1989-05-16

1991-05-21

Willis, Davis L.

Optics: measuring and testing

By particle light scattering

With photocell detection

356358, G01B 902

Patent

active

050170104

ABSTRACT:
A highly sensitive apparatus for sensing the position of a movable member comprises an optical directional coupler providing four external ports. Light from a short coherence length diode laser is injected into the first port. The coupler serves as a beam splitter to direct one portion of the injected light to the member via the second port and a single mode optical fiber. Part of this one portion is reflected concurrently from the member and from the adjacent polished coating at the end face of said fiber back into said fiber and optically coupled via the third port to a photodetector to provide a signal whose amplitude is indicative of the position of the member, based upon the relative phase of said concurrent reflections.
The other portion of the injected light is optically coupled to and via the fourth port to another photodetector for providing, as a reference, a signal proportional to the intensity of the injected light. These two signals are supplied to a subtractive circuit for providing an output in which power fluctuations of the laser are minimized.

REFERENCES:
patent: 4572670 (1986-02-01), Fredrickson
patent: 4652744 (1987-03-01), Bowers et al.
patent: 4724318 (1988-02-01), Binnig
G. Meyer & N. M. Amer, "Novel Optical Approach to Atomic Force Microscopy", Appl. Phys. Lett. 53 (12), Sep. 19, 1988, pp. 1045-1047.
A. D. Drake & D. C. Leiner, "Fiber-Optic Interferometer for Remote Subangstrom Vibration Measurement", Rev. Sci. Instrum. 55(2) Feb. 1984, pp. 162-165.
Rugar, Mamin, Erlandsson, Stern, Terris, "Force Microscope Using a Fiber-Optic Displacement Sensor", Rev. Sci. Instrum. 59 (11), Nov. 1988, pp. 2337-2340.
H. Hattori & T. Takeo, "Optical Fiber Position Sensor Using a Frequency Modulated Semiconductor Laser", SPIE, vol. 838 Fiber Optic & Laser Sensors V (1987) pp. 288-291.
A. Lew, C. Depeursinge, "Single-Mode Fiber Evanescent Wave Spectroscopy", SPIE, vol. 514 (Sep. 1986) 2nd Int'l Conf. on Optical Fiber Sensors, pp. 71-74.

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