Abstract: A system for sensing subterranean acoustic waves emitted from an acoustic source includes a plurality of laser sources, a plurality of subterranean optical sensors, at least one optical detector, and electronics. The laser sources each emit light at a different frequency. The subterranean optical sensors receive the light and alter the light in response to the acoustic waves. The optical detector receives the altered light and outputs an electrical signal. The electronics receives the electrical signal and converts it into seismic data format. The hydrophone for sensing the acoustic signals is able to operate at pressures of at least 5,000 psi and temperatures of at least 130 degrees Celsius. A hydrophone may be housed in a cable having a diameter of less than about 1.5 inches. The hydrophone's sensor preferably includes a reference mandrel, two sensing mandrels, and a telemetry can, all of which are aligned in a coaxial, end-to-end configuration to reduce the profile of the hydrophone.

Abstract: An optical geophone or hydrophone for detecting seismic vibrational energy comprising a laser material, which generates a lasing frequency signal, the frequency of which varies in accordance with vibrational energy incident upon the laser material, a light source occurring at an excitation frequency for providing excitation energy incident upon the laser material, so that the laser material emits light at the lasing frequency modulated by the vibrational energy and a fiber optic cable for transmitting the excitation frequency light to the laser material and receiving the frequency modulated lasing frequency for transmission to a receiver. The laser material comprises a first face and a second face, the first face being parallel to the second face. The first face is coated so that it passes substantially all of the lasing frequency light and reflects substantially all of the excitation frequency light.

Abstract: A folded Sagnac fiber optic sensor array uses a common delay path to reduce distributed pickup in downlead fibers. The sensor array is used to detect perturbations (e.g., acoustic waves in water). By basing the folded Sagnac sensor array on operating principles similar to the Sagnac interferometer the sensor array has a stable bias point, has reduced phase noise, and allows a broadband signal source to be used rather than requiring a more expensive narrowline laser. A large number of sensors can be multiplexed into the architecture of the sensor array. In one particularly preferred embodiment, the sensor array is configured with couplers and amplifiers selected to direct substantially equal portions of an input light signal to each sensor in the array. In another particularly preferred embodiment, first and second delay paths are provided for light at first and second wavelengths to increase the dynamic range of the sensors.

Abstract: A folded Sagnac fiber optic sensor array uses a common delay path to reduce distributed pickup in downlead fibers. The sensor array is used to detect perturbations (e.g., acoustic waves in water). By basing the folded Sagnac sensor array on operating principles similar to the Sagnac interferometer the sensor array has a stable bias point, has reduced phase noise, and allows a broadband signal source to be used rather than requiring a more expensive narrowline laser. A large number of sensors can be multiplexed into the architecture of the sensor array. In one particularly preferred embodiment, the sensor array is configured with couplers and amplifiers selected to direct substantially equal portions of an input light signal to each sensor in the array. In another particularly preferred embodiment, first and second delay paths are provided for light at first and second wavelengths to increase the dynamic range of the sensors.

Abstract: An optical hydrophone described herein includes a housing defining a chamber. The housing is acoustically transparent to acoustic waves at a frequency of interest. An optically transparent material fills the chamber and has air-filled voids defined therein that resonate within the material when an incoming acoustic wave impinges on the material. Light introduced into the material and passed therethrough is affected by the air-filled voids resonating within the material. Light is transmitted to and from the material by optical fibers which are coupled to the material on either side thereof. A plurality of these optical hydrophones can be configured in a linear array through which light is passed. Such linear arrays can be used to measure incoming acoustic signals.

Abstract: An optical hydrophone described herein includes a housing defining a chamber. The housing is acoustically transparent to acoustic waves at a frequency of interest. An optically transparent material fills the chamber and has air-filled voids defined therein that resonate within the material when an incoming acoustic wave impinges on the material. Light introduced into the material and passed therethrough is affected by the air-filled voids resonating within the material. Light is transmitted to and from the material by optical fibers which are coupled to the material on either side thereof. A plurality of these optical hydrophones can be configured in a linear array through which light is passed. Such linear arrays can be used to measure incoming acoustic signals.

Abstract: A support structure for piezoelectric elements in a marine seismic cable is provided. The support structure comprises upper and lower cylindrical halves, each with channels formed therein. Two axial channels are adapted to retain three piezoelectric elements each. A third axial channel, positioned between the sensor element channels, is adapted to retain a flexible circuit. Transverse channels between the sensor element channels and the circuit channels accommodate extension from the flexible circuit. The piezoelectric elements are mounted within their respective channels with a resilient pad with adhesive on both sides. The piezoelectric elements are graded so that any group of three piezoelectric elements exhibits approximately the same sensitivity as any of the other three groups of piezoelectric elements on the support structure.

Abstract: An apparatus for determining the velocity of sound waves which includes a liquid medium having a plurality of gas bubbles. In the liquid medium, a laser transmits a light pulse to interact with the bubbles excited by the sound wave. Backscattered light from the interaction of the light pulse is received. A processor is then responsive to the detector to provide detection of the acoustic wave through the fluid medium.

Abstract: A system for digitally demodulating optical hydrophone signals is provided. The system includes an optical hydrophone connected to an analog-to-digital converter and further connected to a digital signal processor. Within the digital signal processor, a demodulator is calibrated by a preferred automatic calibration circuit such that mixer frequencies are coherently mixed with the incoming acoustic signals received by the hydrophone. The automatic calibration circuit preferably determines an extreme case of phase offset by following a programmable routine including a series of tests. After the extreme case is detected, the precise phase calibration is known and provided to the demodulator mixer tables. The automatic calibration circuit can be utilized for automatic calibrations of multisensor systems containing large numbers of hydrophones.

Abstract: An apparatus for determining the velocity of sound waves which includes a liquid medium having a plurality of gas bubbles. In the liquid medium, a laser transmits a light pulse to interact with the bubbles excited by the sound wave. Backscattered light from the interaction of the light pulse is received. A processor is then responsive to the detector to provide detection of the acoustic wave through the fluid medium.

Abstract: There is provided a fiber-optic hydrophone having a compliant sensing mandrel coaxial with and adjacent to a rigid reference mandrel. A first optical fiber is wound around the compliant sensing mandrel and a second optical fiber is wound around the reference mandrel. The first and second optical fibers comprise different arms of an interferometer. Flexible sealing members, such as O-rings, seal the compliant sensing mandrel to the hydrophone. One O-ring is disposed near each end of the sensing mandrel. A cylindrical support member is disposed inside the sensing mandrel. At least a portion of the support member is spaced from the sensing mandrel so as to provide a sealed cavity between the sensing mandrel and the support member. The sealed cavity is filled with air or similar compliant substance.

Abstract: A system for digitally demodulating optical hydrophone signals is provided. The system includes an optical hydrophone connected to an analog-to-digital converter and further connected to a digital signal processor. Within the digital signal processor, a demodulator is calibrated by a preferred automatic calibration circuit such that mixer frequencies are coherently mixed with the incoming acoustic signals received by the hydrophone. The automatic calibration circuit preferably determines an extreme case of phase offset by following a programmable routine including a series of tests. After the extreme case is detected, the precise phase calibration is known and provided to the demodulator mixer tables. The automatic calibration circuit can be utilized for automatic calibrations of multisensor systems containing large numbers of hydrophones.

Abstract: A folded Sagnac fiber optic sensor array uses a common delay path to reduce distributed pickup in downlead fibers. The sensor array is used to detect perturbations (e.g., acoustic waves in water). By basing the folded Sagnac sensor array on operating principles similar to the Sagnac interferometer the sensor array has a stable bias point, has reduced phase noise, and allows a broadband signal source to be used rather than requiring a more expensive narrowline laser. A large number of sensors can be multiplexed into the architecture of the sensor array. In one particularly preferred embodiment, the sensor array is configured with couplers and amplifiers selected to direct substantially equal portions of an input light signal to each sensor in the array. In another particularly preferred embodiment, first and second delay paths are provided for light at first and second wavelengths to increase the dynamic range of the sensors.

Abstract: A folded Sagnac fiber optic sensor array uses a common delay path to reduce distributed pickup in downlead fibers. The sensor array is used to detect perturbations (e.g., acoustic waves in water). By basing the folded Sagnac sensor array on operating principles similar to the Sagnac interferometer the sensor array has a stable bias point, has reduced phase noise, and allows a broadband signal source to be used rather than requiring a more expensive narrowline laser. A large number of sensors can be multiplexed into the architecture of the sensor array. In one particularly preferred embodiment, the sensor array is configured with couplers and amplifiers selected to direct substantially equal portions of an input light signal to each sensor in the array. In another particularly preferred embodiment, first and second delay paths are provided for light at first and second wavelengths to increase the dynamic range of the sensors.

Abstract: A folded Sagnac fiber optic acoustic sensor array operates in a manner similar to a Sagnac interferometer but uses a common delay path to reduce distributed pickup in downlead fibers. The fiber optic acoustic sensor array is used to detect acoustic waves in water. By basing the folded Sagnac sensor array on operating principles similar to the Sagnac interferometer rather than basing the array on a Mach-Zehnder interferometer, the sensor array has a stable bias point, has reduced phase noise, and allows a broadband signal source to be used rather than requiring a more expensive narrowline laser. A large number of acoustic sensors can be multiplexed into the architecture of the folded Sagnac fiber optic acoustic array.

Abstract: There is provided a fiber-optic hydrophone having a compliant sensing mandrel coaxial with and adjacent to a rigid reference mandrel. A first optical fiber is wound around the compliant sensing mandrel and a second optical fiber is wound around the reference mandrel. The first and second optical fibers comprise different arms of an interferometer. Flexible sealing members, such as O-rings, seal the compliant sensing mandrel to the hydrophone. One O-ring is disposed near each end of the sensing mandrel. A cylindrical support member is disposed inside the sensing mandrel. At least a portion of the support member is spaced from the sensing mandrel so as to provide a sealed cavity between the sensing mandrel and the support member. The sealed cavity is filled with air or similar compliant substance.

Abstract: An array through a first to a second side of a three-sided junction, accessed remotely by a single mode fiber transmits a light pulse sequence to the array and receives sound modulated return light signals via the second to a third side of the junction. Within each hydrophone, butt coupled fiber joints form a continuous structure, encapsulated within a compressible plastic tube for mechanical stability. Tube volume expands and contracts linearly with variations in acoustic pressure thereby proportionally modulating the optical path therethrough. Each joint is a partial reflector reflects part of the incident light beam back via the second to third side of the junction to a posthydrophone compensating interferometer which compensates for path difference between equally spaced array joints; From the third side of the junction the reflections from the butt coupled fiber joints pass through a light detector and signal processor.

Abstract: A system is disclosed that provides. a sonar operator with the most likely range to a target of interest. The system generates and displays a contour based on ship's parameters, target parameters, environmental data, and operator parameters. The sonar operator can vary many of the parameters in “what if” scenarios so as to generate groups of contours for preselected probabilities of detection. Contours can be used to show the actions that should be taken to ensure a favorable outcome.

Abstract: The invention provides a small optical microphone/sensor (2) for measuring distances to, and/or physical properties of, a reflective surface, comprising a source of light (4) coupled to a light waveguide (6) for transmitting a light beam through the waveguide; the waveguide (6) having at one of its ends a pointed face (12) with an angle determined by Snell's Law of Refraction sin ⁢   ⁢ α 1 sin ⁢   ⁢ α 2 = n 2 n 1 wherein &agr;1 is the angle of travel of the light beam through the waveguide media; &agr;2 is the angle of travel of the light beam in a second media when exiting from the pointed face, and n1 and n2 are the light indices of the light waveguide media and the second media; the reflect

Abstract: A folded Sagnac fiber optic acoustic sensor array operates in a manner similar to a Sagnac interferometer but uses a common delay path to reduce distributed pickup in downlead fibers. The fiber optic acoustic sensor array is used to detect acoustic waves in water. By basing the folded Sagnac sensor array on operating principles similar to the Sagnac interferometer rather than basing the array on a Mach-Zehnder interferometer, the sensor array has a stable bias point, has reduced phase noise, and allows a broadband signal source to be used rather than requiring a more expensive narrowline laser. A large number of acoustic sensors can be multiplexed into the architecture of the folded Sagnac fiber optic acoustic array.

Abstract: A digital vibration transducer for producing a digital signal representative of a vibration of a vibrating member is provided. The transducer includes a laser source producing a light beam that is focused on a detection area. The light beam is reflected towards this detection area by a reflector, at an angle with the optical axis of the light beam and pivotable about a pivot axis. A linkage assembly connects the vibrating member to the reflector to convert the vibrating of the vibration member into a pivoting of the reflector, thereby sweeping the reflected light beam across the detection area. A sensing and encoding assembly is provided in the detection area and produces the digital signal representative of the vibration of the vibrating member relatively to the sweeping of the light beam.

Abstract: An apparatus for phase angle demodulation. The apparatus functions as a highly-linear angle-modulation demodulator and is particularly useful for seismic streamers comprising very-large arrays of optical hydrophones. The apparatus includes a demodulator and a processor in which the demodulator contains a signal input and a reference input. The apparatus is configured such that a phase modulated signal having a carrier frequency is connected to the signal input, and a reference signal is connected to the reference input. A difference frequency is defined as the non-zero difference in frequency between the reference signal frequency and the carrier frequency. The processor filters the output from the demodulator in order to separate the phase demodulated signal from the difference frequency.

Abstract: A submarine bow dome acoustic sensor assembly comprises an outer hull bow portion, an inner pressure hull wall extending athwartships and in conjunction with the outer hull bow portion defining a free-flood compartment, and an acoustic bow panel disposed in the compartment and connected to the pressure hull wall by acoustically isolating supports. A laser scanner is disposed in the compartment and is oriented so as to project a laser beam onto a surface of the acoustic bow panel, and a sensor is disposed in the compartment and oriented so as to receive reflections of the laser beam off the acoustic panel and to transmit data from which a position of a sound generating source can be determined.

Abstract: A system and method are provided for converting an electrical signal to an optical signal for a fiber optic system. The electrical signal produced by a sensor (10) based upon a parameter being measured is connected across a material (12, 34, 40) that changes dimension responsive to an applied electrical signal. An optical fiber (14, 30, 38) is coupled to the material (12, 34, 40) where dimension changes of the material (12, 34, 40) produce strain in the optical fiber (14, 30, 38). This strain is operable to affect light traveling through the optical fiber (14, 30, 38) to produce an optical signal for a fiber optic system. In one embodiment, the sensor (10) can be a geophone sensor that produces an electrical signal proportional to motion of the geophone sensor. In another embodiment, the sensor (10) can be a hydrophone sensor that produces an electrical signal proportional to acoustic pressure incident on the hydrophone sensor.

Abstract: A pressure sensitive optical fiber is enclosed within a pressure chamber. A mass is positioned so as to vary the pressure in the pressure chamber in response to a seismic signal. Variations in the chamber pressure are directly detected by the pressure sensitive fiber.

Abstract: A continuous liquid level measurement system is disclosed which is based upon a differential pressure measurement. The pressure of the liquid level to be measured is calibrated with a second pressure measurement of the pressure above the liquid in order to get a more accurate pressure measurement which is related in a predetermined manner to the level of the liquid. For instances in which the liquid to be measured is in a harsh environment, the invention provides for a means for mounting the sensitive pressure measurement devices remotely from the liquid.

Abstract: An internal device for use in an underwater cable may comprise a body having an outer periphery, body being mountable inside the cable with the cable surrounding the outer periphery of the body. The body may include a cutaway portion, a slot, or a dovetail joint. An underwater cable arrangement may comprise an underwater cable and an internal device disposed in the cable with the cable surrounding the device. The underwater cable may include a stress member connected to the internal device by an interference fit or the internal device may include a slot for receiving the stress member. A method of connecting a stress member of an under water cable to an internal device includes forming an interference fit between a region of increased diameter of the stress member and the internal device.

Abstract: A system for sensing subterranean acoustic waves emitted from an acoustic source includes a plurality of laser sources, a plurality of subterranean optical sensors, at least one optical detector, and electronics. The laser sources each emit light at a different frequency. The subterranean optical sensors receive the light and alter the light in response to the acoustic waves. The optical detector receives the altered light and outputs an electrical signal. The electronics receives the electrical signal and converts it into seismic data format. Preferably, the light emitted from the optical sources is modulated at a plurality of modulation frequencies. The electronics can be used to demodulate the signal. The electronics may demodulate the electrical signal by mixing the signal with periodic waveforms having frequencies corresponding to the modulation frequencies and twice the modulation frequencies.

Abstract: A folded Sagnac fiber optic acoustic sensor array operates in a manner similar to a Sagnac interferometer but uses a common delay path to reduce distributed pickup in downlead fibers. The fiber optic acoustic sensor array is used to detect acoustic waves in water. By basing the folded Sagnac sensor array on operating principles similar to the Sagnac interferometer rather than basing the array on a Mach-Zehnder interferometer, the sensor array has a stable bias point, has reduced phase noise, and allows a broadband signal source to be used rather than requiring a more expensive narrowline laser. A large number of acoustic sensors can be multiplexed into the architecture of the folded Sagnac fiber optic acoustic array.

Abstract: A seismic sensor array includes a means for passive electrical to optical energy transformation and transmission. This transformation is used remotely with traditional sensor arrays, which may include hydrophones, geophones, or a combination of them. The transformation means is used to develop an optical signal in a fiber which then conveys the seismic signals to a recording center or data accumulator.

Abstract: The invention is directed to a fiber-optic sensor for measuring acoustic signals originating from a single point remote from the sensor.

Abstract: The present invention relates to a Sagnac interferometric sensor array for acoustic sensing and method of sensing acoustic signal that is able to observe acoustic signals coming from several sources simultaneously. The acoustic sensor of the present invention is a Sagnac interferometric sensor array employing a depolarizer. Unlike a single Sagnac interferometric sensor, two light signals traveling in the opposite directions from each other pass through the off-center position of the loop at different times in the Sagnac loop when they are pulses, and thus, it is possible for the light pulses to be maintained at a constant phase difference by giving arbitrarily a certain amount of phase to them. By using the fact, the interferometer is constructed in such a way that the interference light output coincides with the applied acoustic signals in waveform. This invention suggests a way of fabricating an array of fiber-optic acoustic sensors that is easy to be made and is highly sensitive at some frequency band.

Abstract: A seismic sensor array includes a means for passive electrical to optical energy transformation and transmission. This transformation is used remotely with traditional sensor arrays, which may include hydrophones, geophones, or a combination of them. The transformation means is used to develop an optical signal in a fiber which then conveys the seismic signals to a recording center or data accumulator. The transformation means preferably comprises a stack of piezoelectric elements capped on each end by a rounded crown to accommodate an optical fiber wound around the stack and the crowns.

Abstract: In accordance with the present invention, a photon transducer system is provided for obtaining information on acoustic signals within a fluid environment. The photon transducer system uses a laser-based Doppler interferometer located within a pressure release surface. The pressure release surface is formed by generating a gas pocket in the fluid, creating a boundary layer between the laser light source and the surrounding fluid. Laser light is reflected from the boundary and is detected by the interferometer to obtain the Doppler velocity of the pressure release surface. The pressure incident on the boundary can be determined from the measured velocity, providing information on the incident acoustic pressure.

Abstract: An element that is sensitive to a pressure or acceleration signal comprises an optical element capable of changing its index of refraction and/or path length in response to a time varying pressure or in response to acceleration and a pliant mounting member supporting the optical element. The mounting member changes its geometrical configuration in response to the time varying pressure or acceleration. Some embodiments of the invention use a mechanical amplifier to achieve the needed sensitivity.

Abstract: The present invention relates to a removable air mandrel for use in manufuring towed sonar arrays. The removable air mandrel is used to position hydrophone mandrels and has an inflatable tubular structure which includes expansion limiters. The expansion limiters are preferably fibers incorporated into the tubular structure. A process for using the removable air mandrel to assemble a towed sonar array is also disclosed.

Abstract: A system for digitally demodulating optical hydrophone signals is provided. The system includes an optical hydrophone connected to an analog-to-digl converter and further connected to a digital signal processor. Within the digital signal processor, a basic demodulator has a first and second mixing tables, the first table operating at a modulating frequency, .omega., injected into reference legs of the hydrophone, and a second table operating at 2.omega.. The mixer frequencies are coherently mixed with the incoming acoustic signals received by the hydrophone. An automatic calibration circuit which adjusts the phase of the mixers is connected to the basic demodulator.

Abstract: An assembly module provides well-organized optical fiber component attachment features and convenient fiber routing areas for assembling and containing a fiber optic device such a telemetry module. The module comprises a first substrate having a first side and a second side. The first side includes a plurality of sidewalls and a recessed floor surface bounded by the sidewalls. Some of the sidewalls have a cavities formed therein. A plurality of channels extend from the ends of the cavities. A plurality of projections extend from the sidewalls over selected portions of the floor surface such that a lower edge of each projection is spaced apart from the floor surface. Optical fiber components (couplers, splices, etc.) may be mounted in the cavities, and optical fibers are routed to and from the optical fiber components on regions between the sidewalls and through the channels.

Abstract: Device (20) for measuring pressure waves in a liquid medium (E), comprising; one or more sensor elements (23) permeable to optical radiation; one or more support members (22) on which a sensor element (23) is arranged in each case and which is at least slightly flexible; a chamber (25) at least partly enclosed by a support member (22) and filled with the liquid medium; and a second compensation chamber (27) which is actively coupled to the first compensation chamber via an at least partially flexible wall (26), wherein the second compensation chamber is filled with gas; and detection means for detecting changes in the length of the sensor element.

Abstract: A system for measuring changes in an environmental parameter such as displacement, velocity, acceleration, or pressure, includes a laser for providing a pulsed, coherent light signal, and an interferometer having a first and second optical legs of unequal optical path lengths. The signal is split into first and second beams that are directed into the first and second optical legs. Either a fixed mirror disposed on a frame or a moving mirror on one side of the proof mass reflects the first beam received at the end of the first optical leg. The frame also suspends a proof mass at opposite ends. An optical pick-off embodied in a movable mirror formed on the proof mass reflects the second beam received from the end of the second optical leg. The proof mass with mirror moves in response to changes in the value of the parameter to be measured.

Abstract: A fiber optic hydrophone structure comprises a casing around which is wound an optical fiber. The casing includes complementary top and bottom diaphragm members that mesh together and which are separated by a spacer ring. The spacer ring is tapered to knife edges which abut the inside surfaces of the top and bottom diaphragm members. The spacer thus acts as a fulcrum when a seismic signal causes motion of the diaphragms.

Abstract: The investigation, development and application of a laser-based ultrasonic inspection system to the problems of evaluating polymer/graphite composite materials has been realized. The use of lasers to generate and detect ultrasonic waveforms in materials provides a means to detect material properties remotely. The study consisted of three main aspects: 1) A confocal Fabry-Perot (CFP) based system has been devolved which uses light reflected from the CFP interferometer to derive the ultrasonic signal. This allows higher frequency components of the detected waveforms to be discerned when compared to a CFP-based system using light transmitted through the CFP interferometer. 2) Thermoelastic and ablative laser generation of acoustic pulses in polymer/graphite composite materials has been investigated. Thermoelastic generation of ultrasound occurs when thermal energy deposited by a pulsed laser creates a localized expansion in the material.

Abstract: Method and apparatus for detecting conditions in the atmosphere which are hazardous to flying aircraft and providing early warning to pilots or ground personnel. The method includes using a laser beam and a coherent optical receiver to optically sense sound waves produced by those hazardous conditions and measuring the effect of those sound waves on the transmitted and received optical beams.

Abstract: A folded Sagnac fiber optic acoustic sensor array operates in a manner similar to a Sagnac interferometer but uses a common delay path to reduce distributed pickup in downlead fibers. The fiber optic acoustic sensor array is used to detect acoustic waves in water. By basing the folded Sagnac sensor array on operating principles similar to the Sagnac interferometer rather than basing the array on a Mach-Zehnder interferometer, the sensor array has a stable bias point, has reduced phase noise, and allows a broadband signal source to be used rather than requiring a more expensive narrowline laser. A large number of acoustic sensors can be multiplexed into the architecture of the folded Sagnac fiber optic acoustic array.

Abstract: A portable tracking array to be used in a system for determining the track nd/or the range of a target vehicle. The array includes a fiber optic hydrophone for acquiring acoustic signals from the target vehicle. The fiber optic hydrophone is encapsulated within a plastic material such as polyurethane. The array further includes a fiber optic cable for transmitting signals to and for receiving signals from the fiber optic hydrophone, which fiber optic cable has an end encapsulated within a termination coupling, and a length of perforated material extending between the terminal coupling and the plastic material encapsulating the fiber optic hydrophone to allow water entry and to substantially eliminate air cavities which interfere with acoustic performance.

Abstract: A noise attenuation system for use with sound receiving devices, including first and second relatively small optical microphone devices having at least one sound responsive membrane operative to produce an output signal in accordance with sound waves picked up by the optical microphone devices, at least one pair of light guides affixed to the first or second optical microphone devices, the pair of light guides each having an input end portion and an output end portion, the input end portion of a first light guide is connectable to a source of light and the output end portion of the second light guide is connectable to a light intensity detecting means. Each of the output portion of the first light guide and input end portion of the second light guide has an axis and a rim and is oriented with respect to each other to include an angle between the axes, and each of the light guide rims is cut at an angle with respect to the axis of its light guide.

Abstract: A system for measuring changes in an environmental parameter, such as velocity or pressure, includes an optical signal source for providing a pulsed, coherent light signal, and an interferometer having a first and second optical legs of unequal optical path lengths. The signal is split into first and second beams that are respectively directed into the first and second optical legs of the interferometer. A fixed mirror reflects the first beam received at the end of the first optical leg. An optical pick-off includes a movable mirror, positioned to reflect the second beam received from the end of the second optical leg. The movable mirror is movable in response to changes in the value of the parameter to be measured. An optical coupler combines the first and second beams after they have been reflected back into their respective optical legs, producing an interference signal, which is detected by an optical detector.

Abstract: A fiber optic hydrophone array is provided in which a plurality of tubes, g., fiber optic hydrophones, are to be secured about an elongate elastomeric member having a diameter that hinders each tube from being slid thereover. Each time a tube is to be positioned and secured, longitudinal tension is applied to the elongate elastomeric member to form a reduced cross section along its length in order to facilitate the sliding of each tube therealong. Adhesive is applied about the elongate elastomeric member at a desired position along its length while longitudinal tension is being applied. Then, one tube is slid along the length of reduced cross section to the desired position. The longitudinal tension in the elongate elastomeric member is then relaxed. The reduced cross section expands radially outward thereby forming a void free layer of adhesive between the tube and the elongate elastomeric member.

Abstract: A method and apparatus for discriminating digital data received from a plurality of spatially distinct acoustic sensing nodes of a distributed undersea optical surveillance system. The present invention advantageously employs Code Division Multiplexing (CDM), which is a synchronous variation of Code Division Multiple Access (CDMA), to communicate a plurality of digital data bit-streams from the nodes to a common location remote therefrom. The inventive system generates at the remote location a pseudo-random reference signal that functions as a carrier for communicating sensed acoustic data from the nodes to the remote location. Using the known spatial relationship between the nodes and the remote location and the pseudo-random reference signal, the present invention operatively synchronizes correlators at the remote location to receive and differentiate data from the various individual nodes.

Abstract: New apparatus comprise a comprises an optical fiber based RF signal train generator for storing transient RF pulses and regenerating the identical replicas for analysis. The apparatus further comprise comprises an RF receivers receiver to process one stored pulse with a reference to other another stored pulse. The present invention drastically increases our abilities to investigate acoustical, electromagnetic, and optical transient phenomena.