Abstract: Methods and apparatus for cable termination and sensor integration at a sensor station within an ocean bottom seismic (OBS) cable array are disclosed. The sensor stations include a housing for various sensor components. Additionally, the sensor stations can accommodate an excess length of any data transmission members which may not be cut at the sensor station while enabling connection of one or more cut data transmission members with the sensor components. The sensor stations further manage any strength elements of the cable array.

Abstract: Seismic sensor systems and sensor station topologies, as well as corresponding cable and sensor station components, manufacturing and deployment techniques are provided. For some embodiments, networks of optical ocean bottom seismic (OBS) stations are provided, in which sensor stations are efficiently deployed in a modular fashion as series of array cable modules deployed along a multi-fiber cable.

Abstract: Methods and apparatus for cable termination and sensor integration at a sensor station within an ocean bottom seismic (OBS) cable array are disclosed. The sensor stations include a housing for various sensor components. Additionally, the sensor stations can accommodate an excess length of any data transmission members which may not be cut at the sensor station while enabling connection of one or more cut data transmission members with the sensor components. The sensor stations further manage any strength elements of the cable array.

Abstract: Seismic sensor systems and sensor station topologies, as well as corresponding cable and sensor station components, manufacturing and deployment techniques are provided. For some embodiments, networks of optical ocean bottom seismic (OBS) stations are provided, in which sensor stations are efficiently deployed in a modular fashion as series of array cable modules deployed along a multi-fiber cable.

Abstract: A seismic sensor station includes a housing containing a fiber optic hydrophone and a fiber optic accelerometer that can both be made from a single length of optical fiber arranged inside the housing. The fiber optic accelerometer is arranged in a liquid/oil filled compartment of the housing for dampening of mechanical resonances in the accelerometer due to mechanical disturbances and pressure fluctuations.

Abstract: Seismic sensor systems and sensor station topologies, as well as corresponding cable and sensor station components, manufacturing and deployment techniques are provided. For some embodiments, networks of optical ocean bottom seismic (OBS) stations are provided, in which sensor stations are efficiently deployed in a modular fashion as series of array cable modules deployed along a multi-fiber cable.

Abstract: Storage and installation systems used in storage, deployment or retrieval of a seismic cable array include one or more baskets adapted for being stacked. Each basket is dimensioned to allocate, in an ordered arrangement, a number of seismic stations interconnected by sections of seismic cable. Corresponding methods of storing a seismic cable and deploying/retrieving a seismic cable are based on the use of baskets having an ordered arrangement of seismic stations.

Abstract: A method for interrogating time-multiplexed interferometric sensors using multiple interrogation pulses so as to increases the allowable interrogation pulse duty-cycle and improve the signal-to-noise ratio. In each TDM repetition period a sequence of multiple interrogation pulses are generated. The pulses in the sequence are separated by a time that is equal to the sensor imbalance. The phase from pulse to pulse in each TDM time-slot is modulated at a different, linear rate such that the pulse in time-slot m will have an optical frequency that is shifted by m??, where ?? is the sub-carrier frequency. Because multiple reflections do not need to fade out the inventive method can enhance the signal-to-noise ratio of interferometric sensors such as inline Fabry-Perot sensors.

Abstract: Unwanted signal components in time-division multiplexed (TDM) systems may lead to crosstalk and noise if these pulses overlap with signal pulses from an interrogated sensor. The crosstalk and noise are dominated by interference between the signal pulses from the interrogated sensor and the unwanted signal components and can be greatly reduced by suppressing this interference signal. The unwanted signal components may include overlapping pulses originating from different sets of interrogation pulses (repetition periods). Modulating the phase or frequency between the repetition periods so that the unwanted interference signal does not appear at frequencies from which the phase of the interrogated sensor is demodulated suppresses this interference. Other unwanted signal components include leakage light during dark periods of the duty cycle of an interrogation signal.

Abstract: A bend stiffener includes a first elongate member having a longitudinal conduit and a second elongate member also having a longitudinal conduit connected to an end of the first member thereby effectively extending the length of the bend stiffener. The first member has a resilience to bend when the bend stiffener is subject to a certain load, i.e. at a large tension and small angle, while the second member is designed to have less resilience than the first member, whereby the second member starts bending earlier than the first member when the bend stiffener is subjected to a smaller load, i.e. at a low tension and/or a large angle. The first and second members may provide one or more channels from the second member to the hydrophone. The channel surfaces may have a nonmetallic material. The second member has a resilience to transfer incident pressure waves into the channel therein.

Abstract: Methods and apparatus reduce coherence of an optical signal that is used to interrogate optical interferometric sensors. The optical field phasor of the interrogation source is modulated in a controlled manner to produce a broadened optical source power spectrum at the output of the source unit. The output from the source unit is launched into an optical sensor network, comprising a multiple of optical pathways from its input to the detection unit, where pairs of optical pathways form sensor interferometers. A compensating interferometer with delay difference similar to the sensor delay difference may be arranged in a serially coupled manner with the optical sensor network, either before or after the network. The coherence modulation may be performed through direct modulation of the source or through external modulation of the light with piezoelectric ring modulator, a Lithium niobate phase or intensity modulator, or an acoustooptic modulator.

Abstract: Seismic sensor systems and sensor station topologies, as well as corresponding cable and sensor station components, manufacturing and deployment techniques are provided. For some embodiments, networks of optical ocean bottom seismic (OBS) stations are provided, in which sensor stations are efficiently deployed in a modular fashion as series of array cable modules deployed along a multi-fiber cable.

Abstract: A method and apparatus that uses specific source modulation and detectors to detect a response that carries information about a system response matrix associated with each sensor in a interferometric sensor array and extracting a sensor response in a manner that eliminates polarization-induced signal fading and that is insensitive to lead fiber birefringence fluctuations.

Abstract: Unwanted signal components in time-division multiplexed (TDM) systems may lead to crosstalk and noise if these pulses overlap with signal pulses from an interrogated sensor. The crosstalk and noise are dominated by interference between the signal pulses from the interrogated sensor and the unwanted signal components and can be greatly reduced by suppressing this interference signal. The unwanted signal components may include overlapping pulses originating from different sets of interrogation pulses (repetition periods). Modulating the phase or frequency between the repetition periods so that the unwanted interference signal does not appear at frequencies from which the phase of the interrogated sensor is demodulated suppresses this interference. Other unwanted signal components include leakage light during dark periods of the duty cycle of an interrogation signal.

Abstract: Devices and methods of accurately determining optical wavelengths, such as the Bragg wavelengths of an FBG sensor array. Wavelength-swept light having a characteristic spectrum is swept over a bandwidth and is applied to an interference filter. The interference filter produces an optical spectrum having one or more reference peaks that are identifiable because of the characteristic spectrum. The optical spectrum is converted into electrical signals having at least one electrical signal that is identifiable because of the characteristic spectrum. The identifiable electrical signal is used by a signal processor as an absolute, high accuracy wavelength reference. Temperature compensation or temperature stabilization can compensate the characteristic wavelength. Fiber Bragg sensor systems can use the wavelength reference to determine the Bragg wavelength of FBG elements. The characteristic spectrum can be imparted by the light source or an optical element such as a transmission line filter.

Abstract: Accelerometers for determining acceleration and methods of fabricating an accelerometer are disclosed. In one embodiment, the accelerometer includes a frame, a mass movably suspended on the frame, a fixed element having a rounded surface that does not move with respect to the frame, a movable element having a rounded surface that moves with the mass, and a sensing coil of optical waveguide wrapped around the rounded surfaces to detect movement of the mass in response to acceleration based on interferometric sensing of a change in length of the sensing coil. A method of fabricating the accelerometer includes suspending the mass in the frame and wrapping the optical waveguide around the rounded surfaces. Sensitivity and low fabrication cost of the accelerometers enables their use for integration within an ocean bottom seismic cable. Further, the accelerometer may be an in-line or a cross-line accelerometer depending on the arrangement within the frame.

Abstract: Embodiments of the present invention generally provide methods, apparatus, and systems for compensating for frequency fluctuations in source light used to interrogate an optical sensor. The optical sensor may be interrogated to generate a sensor signal. A reference device co-located with the optical sensor may also be interrogated to generate a reference signal. Optical parameters extracted from the reference signal may be used to correct parameters extracted from a sensor signal.

Abstract: A method and apparatus for reducing crosstalk between sensors in an inline Fabry-Perot (FP) sensor array. The inline FP sensor array comprises a plurality of fiber Bragg gratings arranged periodically along an optical fiber. The sensors are formed between each of the Bragg gratings. A light source provides multiplexed pulses as interrogation pulses for the array. The light pulses are applied to one end of the sensor array and a light detector detects reflected pulses. The detected pulses comprise a composite of reflections from all the Bragg gratings along the fiber. The apparatus processes the detected signals using an inverse scattering algorithm to detect an accurate phase response from each of the Bragg sensors while reducing crosstalk from other Bragg sensors within the array. One form of inverse scattering algorithm is a layer-peeling algorithm.

Abstract: Methods for coating an optical fiber with optical fiber Bragg grating (FBG) with a hermetic coating, particularly a coating of carbon, are employed to avoid ingress of gases, vapors or fluids in the ambient environment. This ingress can be from water or hydrogen, which can diffuse in the fiber glass and cause deviation/drift in the measured Bragg measurements. Bragg gratings that maintain the grating strength at temperatures in excess of 1000° C. are used and can be formed by heating the fiber above 1000° C. in a chamber with a reactive gas that produces deposition of carbon.

Abstract: An optical wavelength readout system for application in optical sensing systems is disclosed. The system includes a Master unit including a wavelength swept optical source for launching light into a string of optical sensors, and a detection and processing unit for detecting and processing the light emitted by the source. The system also includes a Slave unit including a light coupling device for coupling light from the light source into the string of sensors and for coupling light reflected from the string of sensors to a detection and processing unit arranged to detect and process the reflected light. The Master unit includes a wavelength reference unit adapted to make a reference signal available to other parts of the sensing system. The reference signal represents a generally exact relation between the wavelength of the light emitted from the source and time.