Multi-lever miniature fiber optic transducer

• US 4,599,711 A
• Filed: 10/29/1984
• Issued: 07/08/1986
• Est. Priority Date: 10/29/1984
• 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: Cuomo, Frank W.
• Primary Examiner(s): Jordan, Charles T.
• Assistant Examiner(s): Eldred, John W.
• Application Number:
  US06/665,464
• Time in Patent Office: 617 Days
• Field of Search: 367/141, 367/169, 367/149, 73/655, 73/705, 332/7.51, 350/96.15, 350/96.29, 350/96.18, 250/227
• US Class Current: 367/141
• CPC Class Codes: H04R 23/008 using optical signals for detecting or generating sound

Abstract

An improved bifurcated multi-lever fiber optic transducer comprising one ht transmitting fiber and two receive fibers having different core diameters separated at one end and combined at the common distal end in the vicinity of a reflective surface parallel to the fiber end plane which is sensitive to axial motion caused by minute pressure changes, either in air or water, such that any displacement of the reflector from equilibrium will increase or decrease the illuminated areas of the two receive fibers which can be used to generate a processed output signal proportional to this motion. The resulting probe is of minimal diameter, has significantly improved sensitivity and produces an output independent of power variations at the input.

Claims

1. A multi-lever hydrophone system, for receiving acoustic signals from a remote sound source, comprising:

a light source, for providing a light beam;

a transmit optical fiber having a first preselected cross sectional area and numerical aperture, the proximal end of said fiber being attached to said light source, for transmitting said light beam therethrough to the distal end thereof, said light beam then exiting therefrom;

miniature reflector means, positioned a preselected distance from and aligned parallel to the end plane of said transmit fiber distal end so as to form a fiber-reflector gap therebetween, for providing an axially responsive reflective surface upon which the light beam exiting said transmit fiber distal end may impinge, said reflector means moveably responding to said acoustic signals in proportion thereto;

a bead of optically clear potting material, filling the gap between said reflector means and said transmit fiber end plane, for moveably bonding said reflector means to said transmit fiber such that the light beam exiting from said transmit fiber propagates in a conically expanding manner therethrough to said reflector means, reflects therefrom, and further expands conically while propagating back through said potting material to said transmit fiber end plane, the reflected circular illuminated area being greater than that of the transmit fiber;

at least one receive optical fiber pair further comprising a first receiving fiber having a second preselected cross sectional area and numerical aperture and a second receive fiber having a third cross sectional area and numerical aperture, said receive fiber pair being juxtaposed alongside said transmit fiber distal end such that the transmit fiber and the receive fiber pair distal ends are aligned to form a common end plane, said at least one receive fiber pair distal ends also being moveably bonded to said bead of optically clear potting material, for receiving said reflected circular illuminated area of said light beam from said reflector means, the areal portion of said circular illuminated area which impinges on said first receive fiber being designated area `A` and the areal portion of said circular illuminated area which impinges on said second receive fiber being designated area `B`, and transmitting light energy proportional to said illuminated areas A and B;

a first photodetector means, attached to the proximal end of said first receive fiber, for receiving the light energy transmitted therethrough and converting said transmitted light energy to a proportional electrical signal A;

a second photodetector means, attached to the proximal end of said second receive fiber, for receiving the light energy transmitted therethrough and converting said transmitted light energy to a proportional electrical signal B; and

signal processing means, attached to said first and second photodetector means, for receiving said A and B electrical signals therefrom and outputing a combined electrical signal modulated in proportion to said acoustic signals from said sound source, said signal processing means further comprising a first output generating means, attached to said first and second photodetector means, for receiving said A and B electrical signals and producing a signal representing the ratio A/B therefrom, and a second output generating means, attached to said first and second photodetector means, for receiving said A and B electrical signals and producing a signal representing the ratio A-B/A+B therefrom.

2. A system according to claim 1 wherein said A-B/A+B ratio generating means further comprising:

an adder, for producing an A+B signal;

a subtractor, for producing an A-B signal; and

a divider, for receiving said A-B output from said subtractor and said A+B output from said adder, and producing the quotient A-B/A+B therefrom.

3. A system according to claim 2 wherein said transmit fiber and said first receive fiber have equal cross sectional areas and the same numerical apertures, and said second receive fiber as a smaller cross sectional area than said first receive fiber.

4. A system according to claim 3 wherein said transmit fiber and said first and second receive fibers have cladding about the cores thereof.

5. A system according to claim 3 wherein said transmit fiber and said first and second receive fibers are unclad cores.