Abstract: A combination fiber optic current and voltage sensor having a common source and other components. One other common component for certain configurations is the detector. Voltage sources are necessarily designed to avoid coherence and intensity problems when sharing a broadband source with a current sensor. An embodiment of a combination voltage/current sensor shares a birefringence modulator, polarizer, source, detector and electronics. A multitude of fiber optic current sensors and another multitude of fiber optic voltage sensors can share a common fiber light source.

Abstract: A voltage sensor utilizing a non-reciprocal phase shift induced by a time variation of an electric field of the voltage to be measured. A light source provides broadband light to a polarizer. The polarized light is distributed to two linear polarizations. The two polarizations of light are provided with a dynamic or static phase shift relative to each other before or after being birefrigently modulated with an electro-optic sensor in accordance with the electric field of a voltage to be measured. The modulated light goes through a delay line that is terminated with a quarter-wave plate and mirror. The quarterwave plate may be an optical fiber. The portion of light entering the quarter-wave device in a first polarization is reflected in a second polarization and the portion of light entering the quarter-wave device in the second polarization is reflected in the first polarization. The electro-optic sensor again birefringently modulates the light.

Abstract: An interferometric fiber optic gyroscope having compensation electronics to virtually eliminate rotation rate sensing errors caused by Kerr effect in the IFOG due to differing intensities of the counter-propagating beams relative to each other. Compensation accounts for varying intensities of the beams due to all or some changes of: the light beam splitter ratio relative to temperature; fiber coil loss due to temperature and longevity; and the intensity of the light source because of age.

Abstract: A fiber optic interferometric sensor (10, 70) includes a sensing fiber (32, 92) which forms a closed optical path around a current-carrying conductor (44, 94). The sensing fiber (32, 92) has a predetermined number of twists which causes a predetermined amount, T, of circular rotation of the polarization state of the light waves traveling on the optical path, thereby reducing a scale factor error introduced by linear birefringence in the sensing fiber.

Abstract: The fiber optics sensor includes a polarization maintaining optic fiber forming an optical loop, and a sensing medium coupled to the optic fiber and disposed generally midway in the optical loop. First and second quarter waveplates, coupled to the optic fiber and oriented at approximately 45.degree. with one another in close proximity to the sensing medium, convert two counter-propagating linearly polarized light waves traveling in the optical loop into two counter-propagating circularly polarized light waves prior to passing through the sensing medium. The first and second quarter waveplates further convert the counter-propagating circularly polarized light waves into two linearly polarized light waves after exiting the sensing medium. The counter-propagating circularly polarized light waves passing through the sensing medium experience a differential phase shift caused by a magnetic field or current flowing in a conductor proximate to the sensing medium.

Abstract: A signal processing circuit (10) for a fiber optic sensor (12) includes a d.c. block (14) coupled to the fiber optic sensor (12) for removing d.c. components from the fiber optic sensor output signal, and a low pass filter (16) coupled to the d.c. block (14) for reducing noise in the fiber optic sensor output signal and generate a filtered signal. A comparator (18) is coupled to the low pass filter (16) and generates a squared signal indicative of zero crossings in the filtered signal. A lock-in amplifier or synchronous demodulator (20) is coupled to the comparator (18) and generates an output signal indicative of a phase shift in the two light waves propagating in the fiber optic sensor (12).

Abstract: A fiber optics sensor (10) and method for attaining accurate measurement are provided. A polarization maintaining optic fiber (22) forms a linear optical path. An optical element (24) is used to convert linearly polarized light waves to circularly polarized light waves which propagate along the optical path and pass through a sensing medium (24). Because of external stresses and disturbances, the optical element (24) introduces light of the wrong state of polarization into the optical path. The result is a scale factor error in the measurement and an extra incoherent D.C. light detected at the detector (36). The presence and magnitude of the extra incoherent D.C. light is used to provide a normalizing factor to compensate for the scale factor error.

Abstract: A number of optical interferometric sensor configurations are provided. The interferometric sensors include a polarization maintaining optic fiber forming either a loop or linear optical path. Circularly polarized light propagate along the optical path and pass through a field-sensitive sensing medium. A differential phase shift induced in the light waves by a magnetic field is then detected by a photodetector and associated signal processing electronics.

Abstract: A fiber optic gyro utilizing a multimode mode high power laser diode source with the partly reflective mirror to reflect back some light to the source to cause coherence collapse and broaden the line width and employing a long depolarizer connected to the fiber optic coil to reduce the effects of mode partition noise in the light.

Abstract: A noise reducer for reducing the results in the system output signal of optical noise introduced into an optical subsystem therein, having a phase modulator, by a source through obtaining a noise representation signal used to offset the noise components in the signal obtained from the output of the optical subsystem. This noise representation signal is not delayed in the obtaining thereof by any more than half the delays of the waves emitted from the source in reaching the optical subsystem output. The noise reducer may incorporate a device for adjusting the amplitude of the noise representation signal. It may also include another device for adjusting the phase of the noise representation signal, which may be used to affect the amplitude of the noise representation signal. These adjustments can result in an optimization of the noise representation signal so as to better effectively cancel the optical noise signal at the output of the fiber optic gyro having the noise reducer.

Abstract: A spectrum stabilizer for stabilizing the wavelength of light emitted by a source for use in an optical system where the source can have that wavelength altered by varying one or more source parameters, such as source current, temperature and/or alignment of the output end of the source with an optical fiber of the optical system, and wherein light from a selected point in the optical system is coupled to a double mode waveguide for wavelength sensing.

Abstract: An optical fiber rotation sensor having an ordinary single mode fiber coil with a depolarizer in series therewith configured with component optical path lengths therein and birefringent axes relationships therein chosen with respect to the source autocorrelation. Amplitude related phase errors due to polarization mode coupling can be eliminated or reduced economically, and signal fading can be substantially prevented.

Abstract: An optical fiber rotation sensor having configurations thereof chosen with respect to the source autocorrelation. Both amplitude related and intensity related phase errors due to polarization mode coupling can be eliminated or reduced economically.

Abstract: An error control arrangement for an optical fiber rotation sensor having electromagnetic waves propagating in opposite directions passing through a bias optical phase modulator operated by a phase modulation generator both of which can contribute second harmonic distortion resulting in errors in the sensor output signal which are controlled. Control of the bias optical phase modulator contribution for a modulator having a piezoelectric body wrapped with an optical fiber portion is accomplished by mounting the body utilizing layers having nonlinear stiffness.

Abstract: An optical fiber is subjected to a series of traveling flexural waves propagating along a length of the fiber. At least a portion of an optical signal propagating within the optical fiber in a first propagation mode is coupled to a second propagation mode. The optical signal in the second propagation mode has a frequency which is equal to either the sum of or the difference between the frequency of the optical signal in the first propagation mode and the frequency of the traveling flexural waves.

Abstract: An apparatus utilizes a two-mode optical waveguide with a non-circular core to provide stable spatial intensity patterns in both propagation modes for light propagating therein. The light has a wavelength, and the non-circular core has cross-sectional dimensions selected such that (1) the waveguide propagates light at that wavelength in a fundamental mode and a higher order mode, and (2) substantially all of the light in the higher order mode propagates in only a single, stable intensity pattern. Embodiments of the invention include, for example, modal couplers, frequency shifters, mode selectors and interferometers. One of the interferometer embodiments may be used as a strain gauge.

Abstract: An optical fiber is subjected to a series of traveling flexural waves propagating along a length of the fiber. At least a portion of an optical signal propagating within the optical fiber in a first propagation mode is coupled to a second propagation mode. The optical signal in the second propagation mode has a frequency which is equal to either the sum of or the difference between the frequency of the optical signal in the first propagation mode and the frequency of the traveling flexural waves.