Abstract: 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 “bucking” 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.

Abstract: 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.

Abstract: 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.

Abstract: The invention is directed to an apparatus and a method for reducing noise, in particular RIN noise, in optical sensors, in particular fiber-optic sensors. The optical sensor produces a sensor output signal representing a physical quantity to be measured and also contains a first noise component, which is detected by a first detector. A separate detector detects an input light noise component of the input light source of the optical sensor and produces a second noise component. The second noise component is electronically processed and time-delayed or phase shifted by a time delay which substantially correspond to the time delay experienced by the sensor input light traversing the optical sensor. The time-delayed processed signal is then subtracted from the sensor output signal to produce a reduced noise optical sensor signal corresponding to the measured physical quantity.

Abstract: 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.

Abstract: 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.

Abstract: The invention is directed to an apparatus and a method for reducing noise, in particular RIN noise, in optical sensors, in particular fiber-optic sensors. The optical sensor produces a sensor output signal representing a physical quantity to be measured and also contains a first noise component, which is detected by a first detector. A separate detector detects an input light noise component of the input light source of the optical sensor and produces a second noise component. The second noise component is electronically processed and time-delayed or phase shifted by a time delay which substantially correspond to the time delay experienced by the sensor input light traversing the optical sensor. The time-delayed processed signal is then subtracted from the sensor output signal to produce a reduced noise optical sensor signal corresponding to the measured physical quantity.

Abstract: 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.

Abstract: A system and a method for determining a satellite antenna attitude are disclosed. Radio signals from a satellite, such as a GPS satellite, are received by a plurality of coupled antenna elements forming an antenna array. Local attitude values of the antenna array and/or the antenna elements with respect to a reference plane are determined using a shaft encoder or gyro, whereas a carrier-phase antenna attitude is determined from the received radio signals. The array and/or array elements are rotated over a predetermined angle and a correction value of the antenna attitude is determined from a time-averaged difference between the local attitude values and the carrier-phase attitude values.

Abstract: 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.

Abstract: The invention is directed to an apparatus and a method for reducing noise, in particular RIN noise, in optical sensors, in particular fiber-optic sensors. The optical sensor produces a sensor output signal representing a physical quantity to be measured and also contains a first noise component, which is detected by a first detector. A separate detector detects an input light noise component of the input light source of the optical sensor and produces a second noise component. The second noise component is electronically processed and time-delayed or phase shifted by a time delay which substantially correspond to the time delay experienced by the sensor input light traversing the optical sensor. The time-delayed processed signal is then subtracted from the sensor output signal to produce a reduced noise optical sensor signal corresponding to the measured physical quantity.

Abstract: An apparatus and method for sensing angular displacement of a rotating object. A reference object is provided that maintains an independent angular reference. An angular displacement of the rotating object may be measured with respect to the reference object. The apparatus may include a turn sensor for measuring directional changes in the heading of the object, an angular compensator, and a servomotor for maintaining the turn sensor in a same angular position. The object may be a vehicle such as a boat, car, train, airplane or any other vehicle. The turn sensor is coupled to the servomotor that may be attached to a platform of the vehicle. As the vehicle rotates, the heading of the vehicle changes. The servomotor rotates the turn sensor housing to keep the sensor at the same angular position. The heading may be determined by measuring an angular difference between the position of the turn sensor in relation to the moving object.

Abstract: An interferometric fiber optic gyroscope (IFOG) system includes a fiber sensing coil and a semiconductor or rare-earth doped fiber light source emitting light with an associated light source intensity. The source has a front output and back output. An optical coupler is attached to the front output for receiving said light from said light source and the coupler creates two substantially equal intensity light beams for simultaneous transmission into the sensing coil said coupler attached to the coil. The fiber sensing coil supplies return light to the coupler from said equal intensity light beams and the coupler combines and interferes the return light into a combined light beam. An optical phase modulator has a phase modulation amplitude, and the modulator coupled to the coil. An oscillator is coupled to the modulator and produces a periodic voltage which controls the phase modulation amplitude.

Abstract: 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. Using this transformer of polarized light, a current sensor is presented that exploits the Faraday Effect in a Sagnac interferometer.

Abstract: An optical fiber which modifies the optical signals propagated through the fiber and has refractive properties which change in response to electromagnetic energy. The outer surface of the fiber forms at least one groove extending along a selected length of the fiber for receiving an electrode, which would apply an electrical voltage to the fiber resulting in a change of the refractive properties of the fiber.

Abstract: An apparatus and method for sensing angular displacement of a rotating object. A reference object is provided that maintains an independent angular reference. An angular displacement of the rotating object may be measured with respect to the reference object. The apparatus may include a turn sensor for measuring directional changes in the heading of the object, an angular compensator, and a servomotor for maintaining the turn sensor in a same angular position. The object may be a vehicle such as a boat, car, train, airplane or any other vehicle. The turn sensor is coupled to the servomotor that may be attached to a platform of the vehicle. As the vehicle rotates, the heading of the vehicle changes. The servomotor rotates the turn sensor housing to keep the sensor at the same angular position. The heading may be determined by measuring an angular difference between the position of the turn sensor in relation to the moving object.

Abstract: An optical fiber which modifies the optical signals propagated through the fiber and has refractive properties which change in response to electromagnetic energy. The outer surface of the fiber forms at least one groove extending along a selected length of the fiber for receiving an electrode, which would apply an electrical voltage to the fiber resulting in a change of the refractive properties of the fiber.

Abstract: A mobile satellite communication system includes an antenna assembly mountable on a vehicle and a satellite tracking assembly. The antenna assembly includes an antenna device for receiving first satellite signals from a first satellite in a first frequency band and for transmitting and receiving second satellite signals to and from a second satellite in a second frequency band, and a drive subassembly for rotating the antenna device relative to the vehicle in response to a control signal. The satellite tracking assembly maintains the antenna device pointed at the first and second satellites as the vehicle moves. The system further includes a receiver coupled to the antenna device for receiving the first satellite signals and a transceiver coupled to the antenna device for transmitting and receiving the second satellite signals. The first satellite signals may be video and imagery data signals transmitted in the Ku band by a direct broadcast satellite.

Abstract: An optical fiber which modifies the optical signals propagated through the fiber and has refractive properties which change in response to electromagnetic energy. The outer surface of the fiber forms at least one groove extending along a selected length of the fiber for receiving an electrode, which would apply an electrical voltage to the fiber resulting in a change of the refractive properties of the fiber.

Abstract: 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.