Optical sensing devices

• US 4,522,495 A
• Filed: 06/13/1983
• Issued: 06/11/1985
• Est. Priority Date: 06/13/1983
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Shajenko, Peter
• Primary Examiner(s): Willis, Davis L.
• Assistant Examiner(s): Koren, Matthew W.
• Application Number:
  US06/503,913
• Time in Patent Office: 729 Days
• Field of Search: 356/345, 356/361, 250/227
• US Class Current: 356/517
• CPC Class Codes: G01D 5/266 by interferometric means G01D5/353 takes precedence
• CPC Class Codes: G01K 5/52 with electrical conversion means for final indication
• CPC Class Codes: G01N 21/45 using interferometric methods; using Schlieren methods
• CPC Class Codes: G01R 15/245 using magneto-optical modulators, e.g. based on the Faraday or Cotton-Mouton effect
• CPC Class Codes: G01R 15/248 using a constant light source and electro-mechanically driven deflectors

Abstract

Optical sensing devices comprising dual chamber apparatii which use signal and reference light beams together with interferometric methods for detection of physical quantities of interest. The signal part of the chamber experiences the effects of a particular physical quantity to be measured which produces variations in the optical length of the light beam by movement of a mirror, thereby modulating that beam in proportion thereto. Concurrently, the reference beam, of equal pathlength, is passed through an adjacent chamber, isolated from such effects. The modulated signal beam and unmodulated reference beam are then combined to form a fringe pattern, the zero and first order fringes which are superimposed on apertures of an optical fibers, which carry the resultant light beams to a photodetectors for converting the optical signals to proportional electrical signals.

Claims

1. An optical fiber sensing system, for very accurate measurement of the effects of a physical phenomena, comprising:

a light source means for producing a light beam;

a first multimode optical fiber, connected to said light source means, for receiving and transmitting said light beam;

beam splitting means, connected to said first fiber, for receiving said light beam and dividing said light beam into a signal light beam and a reference light beam, each of said signal and reference beams being of equal phase and amplitude;

sensing means for receiving said signal beam and said reference beam from said beam splitting means, said sensing means being divided into a signal chamber and a reference chamber such that said signal beam and said reference beam experience all environmental effects equally, said signal chamber being further arranged so as to further expose only said signal beam to said physical effect to be measured thereby modulating said signal beam in proportion thereto;

path length adjusting means, for receiving said reference beam from the reference chamber of said sensing means and changing the pathlength of said reference light beam to equal the path length of said signal light beam, thus assuring temporal coherence therebetween;

beam recombining means for receiving said signal beam from the signal chamber of said sensing means and said reference beam from said path length adjusting means, said recombining means combining said signal beam and said reference beam in such a way as to form a fringe pattern having at least a center fringe and a fringe in quadrature relationship with the center fringe;

non-transparent plate means, fixedly attached to said recombining means for receiving center fringe and the fringe in quadrature relationship therewith and separating all the light energy of said center fringe from all the light energy of the fringe in quadrature relationship with said center fringe in such a way that 90°

phase quadrature is maintained between said signal and reference light beams;

a zero order, multimode optical fiber, attached to said plate means, for receiving and transmitting therethrough said center fringe light energy from said plate means;

a first order, multimode optical fiber, attached to said plate means, for receiving and transmitting therethrough the fringe in quadrature relationship with said center fringe light energy from said plate means;

a first photodetector means, connected to said zero order fiber, for receiving said center fringe light energy and converting said light energy to a proportional zero order electrical signal;

a second photodetector means, connected to said first order fiber, for receiving the fringe in quadrature relationship with said center fringe light energy and converting said light energy to a proportional first order electrical signal; and

data processor means, connected to said first and said second photodetectors for receiving said zero order and said first order electrical signals, and processing said signals in such a way as to extract said physical effect measurement therefrom.

2. A sensing system according to claim 1 wherein said light source means further comprises an incandescent bulb.

3. A sensing system according to claim 2 wherein said sensing means further comprises:

a movably mounted signal mirror for modulating said signal beam by varying the optical path length thereof; and

a fixedly mounted reference mirror for receiving and reflecting said reference beam.

4. The sensing system of claim 3 wherein said non-transparent plate means includes a central circular aperture for allowing therethrough the light intensity of said center fringe and an annular aperture surrounding the central aperture for allowing therethrough the light intensity of the fringe in quadrature relationship with said center fringe.

5. The sensing system of claim 1 which further includes magnetic materials for responding to changes in the magnetic field to cause modulation of the signal light beam.

6. The sensing system of claim 1 which further includes means to cause modulation of the signal light beam in response to changes in electric currents.

7. The sensing system of claim 1 which includes means for modulating the signal light beam to detect variations in voltage of a system.

8. The sensing system of claim 1 which further includes means for modulating the signal light beam in response to temperature variations in a system.

9. The sensing system of claim 1 which also includes means for modulating the signal light beam in response to vibrations in a system.

10. The sensing system of claim 1 which further includes means for modulating the signal light beam in response to the changes in the applied forces in a system.

11. The sensing system of claim 1 which also includes means for modulating signal light beams to detect changes in the refractive index of a fluid in response to the temperature variation thereof.