Andrew Corporation

Kvh Industries, Inc.

Richard B Dyott

Sidney M Bennett

Eric L Brooker

John D Myhre

Thomas D Monte

Reinhard Ulrich

John D Meyer

Steven R Emge

Sid Bennett

Yung-Yien Huang

A method is described for reducing the effect of linear birefringence in an optical fiber, in particular a circular-cored single-mode fiber. The invention may also be directed to an optical fiber having a reduced linear birefringence. A length of the optical fiber may be subdivided into a plurality of sections and a twist having a predetermined sense of rotation and a twist angle may be introduced between the sections. Fibers of this type may find applications, for example, in fiber-optic current and magnetic field sensors.

Reduction of linear birefringence in circular-cored single-mode fiber

A method and device for measuring the current in a conductor are presented. They utilize the Faraday effect on counter-propagating circularly polarized beams of light in a fiber optic coil. The light beams are transformed to and from circular polarization by a polarization transformer comprised of a birefringent fiber with a twist through an appropriate angle at an appropriate distance from one end.

Current sensor

A method for incorporating an optical material into an optical fiber and optical devices utilizing the method are disclosed. Fiber material may be removed from the optical fiber to expose the fiber core and the core may then be at least partially removed. The optical material may then be incorporated into the core area to replace the removed core. Cladding material may then be deposited over the optical material and an electrode may be fixed to the cladding over the optical material to form an optical device.

Method of incorporating optical material into an optical fiber

The invention is directed to a Faraday-type current sensor which is less susceptive to effects caused by rotation, acceleration and vibration of the sensor coil. The sensor coil of the invention includes a first coil section which forms the current sensing coil and a second coil section which is optically connected to the first coil section and forms a compensation or &ldquo;bucking&rdquo; coil. The optical fiber of the first coil section preferably has an almost zero birefringence and is connected in series with the optical fiber of the second coil section which preferably has a large birefringence. The illuminating radiation propagates through the sensor coil in such a way, as viewed along the coil axis, that the propagation direction of the radiation in the first coil section with respect to the coil axis is opposite from the propagation direction in the second coil section.

Faraday-effect current sensor with improved vibration response

A system and a method for controlling the scale factor of a fiber optic sensor are disclosed. The scale factor may be maintained at a constant level by controlling the power level of the light source based on the amplitude of a modulation superimposed on the modulator drive signal. Alternatively, scale factor may be maintained at a constant level by setting the detected signal at twice the modulator drive frequency to zero.

Method for controlling fiber optic sensor scale factor using amplitude modulation

A reduced minimum configuration (RMC) fiber optic current sensor (FOCS) is proposed which includes a sensing coil or sensing region, a light source and an optical path arranged between the front output of the light source and the fiber optic sensing coil/region. At least one quarter wave plate is disposed between the optical path and the sensing coil/region for converting linearly polarized light beams into circularly polarized light beams propagating through the sensing coil/region. The circularly polarized light beams propagating though the sensing region experience a differential phase shift caused by a magnetic field or current flowing in a conductor proximate to the sensing coil. A light detector is located at the back output of the light source and produces an output signal in response to return light intensity transmitted through the light source. The return light intensity is a measure of the magnetic field in the sensor coil/region. The magnetic field may be produced by an electric current flowing through a wire, wherein the sensor coil can be wound around the wire. Electronics is described which minimizes effects caused by changes in the environmental conditions.

Reduced minimum configuration fiber optic current sensor

A method for fabricating a transformer of linearly polarized light to elliptically polarized light is presented. The method involves twisting a birefringent fiber through angles that depend on the polarization desired. This technique obviates the need to splice fibers, as in common approaches. In the final step of the method, the polarization can be fine tuned by heating the fiber to cause the core of the fiber to diffuse into the cladding. Also, methods and systems are presented to transform substantially polarized light to substantially randomly polarized light.

Polarization transformer

The invention is directed to a system and a method for controllably broadening the spectral characteristics, such as the emission linewidth, of a semiconductor laser by discharging an electric pulse, for example, a charged transmission line, across the laser terminals. The linewidth-broadened lasers find application in fiber optic sensors, such as fiber optic gyroscopes and current sensors, which have a relatively short de-coherence length.

Broadening the linewidth of a semiconductor laser

A fiber optic sensor with a digital signal processing system and a method of using a digital signal processing system with a fiber optic sensor is disclosed. The system digitally samples the output signal of the fiber optic sensor at a frequency which is an integer multiple of the modulator drive frequency and multiplies the sampled output signal with predetermined sine and cosine coefficients corresponding to the (fundamental) modulator drive frequency and at most the second, third and fourth harmonic thereof. This simple system can maintain a constant modulation depth and modulator phase shift and provide sensor output data over a wide operating range of the fiber optic sensor. The fiber optic sensor can be employed, for example, for rotation rate and magnetic field measurements.

DSP signal processing for open loop fiber optic sensors

A phase modulator is provided with supports attached to the resonating element. The supports have a length which is an odd number of quarter wavelengths of a longitudinal acoustic wave excited in the supports by the resonating element. As such, a longitudinal acoustic wave excited at the resonating element end of the support travels along the support, is reflected at the other end of the support, and returns in opposite phase to that of the excited wave, thereby causing a null in longitudinal amplitude of the wave and reducing the damping of the resonating element.

Support system for resonating element of phase modulator

A microwave antenna comprises a single moded metal waveguide tapering inwardly to a cutoff dimension near the distal end thereof. The antenna also comprises a first solid dielectric waveguide mounted coaxially within the distal end portion of the metal waveguide and tapering outwardly toward the inwardly tapering portion of the metal waveguide. The first dielectric waveguide extends beyond the distal end of the metal waveguide in the axial direction. The antenna also comprises a second dielectric waveguide surrounding the first dielectric waveguide beyond the distal end of the metal waveguide and having a dielectric constant lower than the dielectric constant of the first dielectric waveguide. A distal end portion of the first dielectric waveguide tapers inwardly toward the axis thereof, to launch signals propagating toward the distal end of the first dielectric waveguide into the second dielectric waveguide.

Microwave transition using dielectric waveguides

A fiber-optic gyro includes a source of light and a coil of optical fiber with multiple turns. The coil is rotatable about an axis of sensitivity and optically couples light from the source to the coil to create counter-propagating light beams within the coil. The counter-propagated light beams produce an output signal indicative of the coil rotation rate, which is fed to a photodetector. The multiple turns of the coil vary in size on both sides of the mid-point of the fiber that forms the coil, and these multiple turns are collapsed in the direction of the axis of the coil.

Fiber optic rotation sensor or gyroscope with improved sensing coil

The sensing coil of a fiber optic gyroscope is wholly or partially surrounded by a gel. The components attached to the coil, such as the directional coupler(s) and polarizer, may also be wholly or partially submerged in the gel. The gel is contained by a rigid housing, in which the inner walls of the housing form a cavity for the coil and the gel. The cavity is filled with the gel, and the gel may be bonded to the inner walls of the housing. The gel remains stiff enough to maintain the coil in a fixed position relative to the housing, and soft enough to avoid any significant effect on the h of the coil over the operating temperature range. Furthermore, the gel can be loaded with particles to adjust the specific gravity of the gel, to modify the thermal properties of the gel and to increase the viscosity of the gel for improved vibration damping. In a modified form, the optical-fiber sensing coil is positioned on a mounting surface and otherwise surrounded by the gel. Alternatively, the optical fiber sensing coil is wound around a form that has a layer of gel on the coil-supporting surface.

Coil mounting arrangement for fiber optic gyroscope using a gel loaded

The sensing coil of a fiber optic gyroscope is mounted by submerging the coil in a gel which surrounds and supports the coil. The components attached to the coil, such as the directional coupler(s) and polarizer, may also be submerged in the gel. The gel is contained by a rigid housing, in which the walls of the housing are spaced away from the coil. The intervening space between the coil and the innermost walls of the housing are filled with the gel, and the gel may be bonded to those innermost walls. The gel remains stiff enough to maintain the coil in a fixed position relative to the housing, and soft enough to avoid any significant effect on the h of the coil over the operating temperature range. In a modified form, the optical-fiber sensing coil is wound around a bobbin that has a layer of gel on the coil-supporting surface. A coating of adhesive is applied to the outside surfaces of the coil to hold the coil windings together in a stable configuration around the layer of gel.

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Oak Lawn, IL, United States of America

Richard B Dyott