Temperature compensated optical fiber interferometric magnetometer

• US 4,609,871 A
• Filed: 07/02/1984
• Issued: 09/02/1986
• Est. Priority Date: 07/02/1984
• 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: Bobb, Lloyd C.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US06/627,306
• Time in Patent Office: 792 Days
• Field of Search: 324/96, 324/225, 324/244, 324/260, 250/227, 250/231 R, 350/96.1, 350/96.29, 350/374-376
• US Class Current: 324/244.1
• CPC Class Codes: G01R 33/0327 with application of magnetostriction
• CPC Class Codes: G02B 6/4457 Bobbins; Reels

Abstract

Temperature compensation of an optical fiber interferometer is achieved by wrapping and bonding one fiber arm transversely about the length of a magnetostrictive rod which is sensitive only to the magnetic field component along its length. The other fiber arm is wrapped and bonded about two generally semicircular caps, attached to either end of the rod, in a direction along the longitudinal axis of the rod.

Claims

1. An interferometric device for measuring the strength of a magnetic field independent of variations in ambient temperature, comprising:

a source of coherent light signals;

means, optically coupled to said source, for splitting the light signals therefrom into two subsignals of equal amplitude, frequency, and phase;

a magnetostrictive rod adapted to be sensitive to variations only in the magnetic field component along its length;

a first optical fiber coiled and bonded contiguously and transversely about said rod, and optically coupled at one end to receive one subsignal from said splitting means;

two convex caps, each attached to the ends of said rod;

a second optical fiber coiled and bonded contiguously about said caps in a direction along the longitudinal axis of said rod, and optically coupled at one end to receive the second subsignal from said splitting means;

means, optically coupled to the other end of said first and second fiber, for recombining the subsignals therefrom into a signal the intensity of which varies in proportion to the magnetic field of interest;

photodetector means, optically coupled to said recombining means, for receiving the recombined signal and converting it into a substantially equivalent electrical signal; and

processing means, connected to said photodetector means, for determining the strength of the magnetic field.

2. An interferometric device according to claim 1, further comprising feedback means, coupled between the output of said photodetector means and said first fiber, for actively maintaining phase quadrature.

3. An interferometric device according to claim 2, wherein said feedback means comprises:

a phase compensator; and

piezoelectric means, contiguously attached to said first fiber, for adjusting the phase of the subsignal therein.

4. An interferometric device according to claim 1, wherein said source is a single-mode laser.

5. An interferometric device according to claim 4, wherein said rod is sensitized through exposure to an axial bias field.

6. An interferometric device according to claim 5, wherein said splitting means is a beam-splitting coupler having one input port and two output ports.

7. An interferometric device according to claim 6, wherein said recombining means is a coupler having two input ports and one output port.