USA As Represented by Secretary of the Navy

The United States of America

Alan B Tveten

Anthony Dandridge

Sandeep T Vohra

Bruce A Danver

Kee P Koo

Aileen M Yurek

Nicholas J Frigo

Thomas G Giallorenzi

Frank Bucholtz

George H Sigel, Jr

Ronald O Miles

This invention pertains to a sensor comprising of glass optical fiber, a cellular pressure release material surrounding the fiber, and means for determining responsivity of the sensor, the sensor having responsivity of at least about &minus;160 dB re rad/m-&mgr;/Pa, which corresponds to sensitivity of about 50 times better than prior art. The sensor can be made part of an optical interferometer which is characterized by splitting of an entering light beam and measurement of an optical phase shift caused by light traversing different paths. The sensor can form a part of a fiber Bragg grating geometry characterized by a fiber Bragg grating in the glass fiber covered by the cellular pressure release material wherein shift of the Bragg wavelength induced by strain on to the cellular pressure release material is measured.

Coated fiber pressure sensors utilizing pressure release coating material

The interferometric fiber optic accelerometer is viewed as a mass-spring transducer housed in a sensor case. The sensor case is attached to a moving part whose motion is inferred from the relative motion between the mass and the sensor case. A flexural disk is housed in a sensor case which is accelerated in a direction normal to the plate surface. The plate undergoes displacement resulting in strains on the plate surface. A coil of optical fiber, made to be part of an optical interferometer, is attached to the flexural disk, the strain from the disk is transferred to the fiber thus changing the path length of the fiber interferometer. The interferometer output in demodulated providing the acceleration response. The design of the accelerometer housing is such that it is highly immune to extraneous signals, i.e., dynamic and hydrostatic pressure. Fabrication of the optical fiber coils is accomplished by winding the optical fiber, with a specially designed chuck to form reference and sensing fiber coils which are then bonded to the flexural disk to form the accelerometer.

Fiber optic accelerometer sensor and a method of constructing same

The interferometric fiber optic accelerometer is viewed as a mass-spring nsducer housed in a sensor case. The sensor case is attached to a moving part whose motion is inferred from the relative motion between the mass and the sensor case. A flexural disk is housed in a sensor case which is accelerated in a direction normal to the plate surface. The plate undergoes displacement resulting in strains on the plate surface. A coil of optical fiber, made to be part of an optical interferometer, is attached to the flexural disk, the strain from the disk is transferred to the fiber thus changing the path length of the fiber interferometer. The interferometer output in demodulated providing the acceleration response. The design of the accelerometer housing is such that it is highly immune to extraneous signals, i.e., dynamic and hydrostatic pressure. Fabrication of the optical fiber coils is accomplished by winding the optical fiber, with a specially designed chuck to form reference and sensing fiber coils which are then bonded to the flexural disk to form the accelerometer.

Apparatus for winding optic fiber coils

A hydrophone group for shallow towed applications in less than 50 feet of ter. The hydrophone group has a series of hydrophones connected by relatively insensitive fiber optic interconnects. The individual hydrophones are sufficiently sensitive such that the interconnecting optical fiber does not introduce excessive noise. Each hydrophone is basically a sensing fiber wrapped around an air-backed mandrel. Each air-backed mandrel is formed of an extended solid frame substantially non-compliant along a longitudinal axis. The extended solid frame is provided with a channel around the periphery thereof. The channel extends substantially the entire length of the extended solid frame. A flexible outer covering surrounds the extended solid frame. The flexible outer covering is highly compliant in a radial direction extending from the longitudinal axis. The air-backed mandrel has a high frequency mechanical resonance. Each hydrophone is connected in a chain by a plurality of interconnects having a substantially lower sensitivity than each hydrophone.

Hydrophone group design for shallow towed applications

A sensing portion for an interferometric planar hydrophone is disclosed which comprises: a support assembly; a plurality of hollow compliant mandrels mounted to the support assembly in a fixed planar relationship with respect to each other to form a planar configuration; a sensing optical fiber sequentially wound around each of the plurality of mandrels to form a single, serial, optical sensing arm or path between an input position on a first one of the plurality of mandrels and an output position on a last one of the plurality of mandrels; and an acoustically transparent material encapsulating the sensing portion to form a sealed compliant planar hydrophone. In an operational system, an interferometric planar hydrophone is disclosed which comprises: the sensing portion in which the sensing arm is operative to measure a predetermined measurand in a preselected environment and which sensing portion further includes a reference optical fiber environmentally isolated from the predetermined measurand; a light source for transmitting coherent light to both of the sensing and reference optical fibers; and circuitry responsive to light received from the sensing and reference optical fibers for developing an output signal indicative of phase shift differences between the sensing and reference optical fibers to determine the predetermined measurand.

Hydrophone transduction mechanism

Improved passive and laser-conditioned magnetic field sensor of compact and integrated construction for enabling the detection of a magnetic field as well as an improved method of manufacture for assembling and selectively pretensioning a subassembly in order to provide an enhanced formation of the subassembly prior to use. The sensor is generally made up of a magnetic field sensing device, first and second fiber-optic elements, first and second couplers, a laser source and a combined detector and analysis means. The first and second couplers interconnect the first and second fiber-optic elements. The magnetic field sensing device is advantageously connected to one of the fiber-optic elements and is generally made up of a magneto-strictive material (MSM) of ribbon-like shape, a nonmagnetic substrate and a sensing element of optic fiber construction. This element is of predetermined and selective multistrand design between its ends and of generally serpentine shape. The sensing device is advantageously formed such that the MSM and the sensing element are uniformly and selectively pretensioned. As the result of this pretensioning, the MSM elongates when a magnetic field is detected thereby decreasing the elongation of the sensing element. Despite this decrease, the sensing element remains tensioned because of sufficient pretensioning and the phase shift in the laser as it is conducted through the optic fiber is detectable by the combined means.

Magnetic field sensor and method of manufacture for a subassembly thereof

A passive device for reducing polarization fading in interferometers with significantly degrading the signal-to-noise ratio. In one embodiment, light from an interferometer output is passed through a lens to a polarization mask. The polarization mask comprises at least three distinct polarizers which pass distinct states of polarization. After passing through the polarizers each independently polarized signal is detected, demodulated and passed to a means for signal extraction.

Method for reduction of polarization fading in interferometers

A fiber optic magnetometer for detecting DC magnetic fields includes a first optical fiber having a magnetostrictive jacket thereon which defines a sensing arm, and a second fiber defining a reference arm. An AC magnetic field of frequency .omega..sub.o and constant amplitude is imposed on the magnetostrictive jacket so as to cause a time varying optical path length change, having an .omega..sub.o component, in the sensing arm fiber. This induces a corresponding time varying phase shift, also having an .omega..sub.o component, in light transmitted through the sensing arm fiber which is detected by a phase detector. The phase detector produces a signal proportional to the phase shift, this signal being passed to a lock-in amplifier set to amplify at .omega..sub.o. The lock-in amplifier produces an output signal proportional to the amplitude of the .omega..sub.o component, wherein this amplitude is proportional to any DC magnetic fields to which the device is exposed.

Fiber optic magnetometer for detecting DC magnetic fields

A sensor for sensing conditions such as acoustic waves, temperature changes, acceleration current and magnetic fields. The sensor employs a diode laser having its cavity contained between end facets defined by partially reflective mirrors, supplemented by an external cavity formed between one of the end facets of the laser and a translatable external reflector. The reflector is position-responsive to a condition to be sensed. A change in the reflector's positions causes laser output light to be fed back through the mirror into the laser cavity with varying phase such that an increase or decrease in laser emission is created. A change of detector voltage or change in laser current provides an indication of environmental condition being sensed.

Growing community of inventors

Fort Washington, MD, United States of America

Alan B Tveten