Abstract: An improved technique for acoustic sensing involves, in one embodiment, launching into a medium, a plurality of groups of pulse-modulated electromagnetic-waves. The frequency of electromagnetic waves in a pulse within a group differs from the frequency of the electromagnetic waves in another pulse within the group. The energy scattered by the medium is detected and, in one embodiment, the beat signal may be used to determine a characteristic of the environment of the medium. For example, if the medium is a buried optical fiber into which light pulses have been launched in accordance with the invention, the presence of acoustic waves within the region of the buried fiber can be detected.

Abstract: An improved technique for acoustic sensing involves, in one embodiment, launching into a medium, a plurality of groups of pulse-modulated electromagnetic-waves. The frequency of electromagnetic waves in a pulse within a group differs from the frequency of the electromagnetic waves in another pulse within the group. The energy scattered by the medium is detected and, in one embodiment, may be used to determine a characteristic of the environment of the medium. For example, if the medium is a buried optical fiber into which light pulses have been launched in accordance with the invention, the presence of acoustic waves within the region of the buried fiber can be detected.

Abstract: A photonic integrated circuit (PIC) with embedded optical temperature sensing includes an optical interferometer containing a first arm and a second arm, and one or more optical waveguide sections configured to measure an internal temperature of the PIC. The one or more optical waveguide sections are implemented as one or more sections of the first arm and the second arm. The first arm and the second arm have a first optical path length (OPL) and a second OPL and are made of a first material and a second material, respectively.

Abstract: A lightweight miniature interferometric device for interferometric inspection of circular multi-channel fiber optic connectors that includes the interferometric microscope, holding fixture, multi-axis motion mechanism and computing device. The system performs an interferometric inspection of multi-channel fiber optic connector. The method of interferometric inspection provides automatic scan of the multi-channel fiber optic connector, reconstructing 3D surfaces of fiber optic termini of the connector and analyzing its parameters. The system connects to the connector by holding fixture and performs an interferometric inspection of each fiber optic terminus of the connector by means of multi-axis motion mechanism.

Abstract: One or more fiber optic rotary joints (FORJ), free space beam combiners, OCT, SEE and/or fluorescence devices and systems for use therewith, methods of manufacturing same and storage mediums are provided. One or more embodiments of FORJs may be used with numerous applications in the optical field, including, but not limited to, OCT and fluorescence applications. Examples of such applications include imaging, evaluating and diagnosing biological objects, such as, but not limited to, for Gastro-intestinal, cardio and/or ophthalmic applications, and being obtained via one or more optical instruments.

Abstract: An ophthalmic apparatus that includes a light source of wavelength sweeping type; a measurement optical system; a reference optical system; a light receiving element that receives interference light; a sample clock signal generator that generates a sample clock signal from the light from the light source, the sample clock signal cyclically changing at equal frequency intervals; a signal processor that samples an interference signal based on the sample clock signal, the interference signal being outputted from the light receiving element when the light receiving element receives the interference light. The ophthalmic apparatus generates period data based on the sample clock signal, the period data indicating a relationship between a period of the sample clock signal and time; and determines a processing duration of the interference signal sampled at the signal processor based on the period data.

Abstract: The invention provides an Optical Coherence Tomography (OCT) system capable of acquiring two orthogonally polarized depth scans from a target such as the fingerprint region of a finger. In the preferred embodiment the birefringence of tissue components and, optionally, other aspects of the target are measured in order determine a characteristic of the target, such as whether it is real of fake finger.

Abstract: A device may use a camera to capture an image of an end face of an optical fiber in a field of view of the camera. The device may monitor a focus metric associated with the image while the image is manually focused using an opto-mechanical assembly. The device may automatically initiate a test to inspect the image of the end face of the optical fiber for compliance with a set of criteria related to cleanliness and damage based on the focus metric satisfying a condition. The device may output a result from the test indicating whether the end face of the optical fiber satisfies the set of criteria related to cleanliness and damage.

Abstract: A sensor assembly for passive detections of downhole well features. Embodiments include a casing collar locator assembly that utilizes fiber optics in combination with a magneto-responsive sensor to detect casing collars and provide real-time location information in a well. The sensor may be configured to work with a poled monolithic structure that is dimensionally responsive to voltage in a way that substantially eliminates noise during detections. Additionally, the sensor may be intentionally imbalanced, utilizing multiple fibers of different lengths and multiple wavelength monitoring so as to provide enhanced directional information as well as allow operators to decipher and address circumstances of polarization fade.

Abstract: Example embodiments add an optical amplifier to an multi-channel, continuously swept OFDR measurement system, adjust amplified swept laser output power between rising and falling laser sweeps, and/or utilize portions of a laser sweep in which OFDR measurements are not typically performed to enhance the integrity of the OFDR measurement system, improve the performance and quality of OFDR measurements, and perform additional measurements and tests.

Abstract: A differential signature detection system is provided. The system comprises: a target sensor, wherein the target sensor is configured to measure acoustical signals within a first narrow band around a target frequency; an offset sensor, wherein the offset sensor is configured to measure acoustical signals within a second narrow band around an offset frequency; and a controller coupled to the target sensor and the offset sensor, wherein the controller is configured to: compare a signal output of the target sensor with an output of the signal output of the offset sensor to calculate a differential measurement that comprises a difference in signal peak intensity; compare the differential measurement to a reference signal, wherein the reference signal comprises a threshold indicative of a presence of a characteristic signature peak associated with a target object; and produce an output based on the comparison between the differential measurement and the reference signal.

Abstract: A low coherence interferometry imaging system comprising a common-path interferometer that is at least partially integrated as part of a planar lightwave circuit is disclosed. Imaging systems in accordance with the present invention are implemented in integrated optics without the inclusion of highly wavelength-sensitive components. As a result, they exhibit less wavelength dependence than PLC-based interferometers of the prior art. Further, the common-path interferometer arrangement of the present invention avoids polarization and wavelength dispersion effects that plague prior-art PLC-based interferometers. Still further, an integrated common-path interferometer is smaller and less complex than other integrated interferometers, which makes it possible to integrate multiple interferometers on a single chip, thereby enabling multi-signal systems, such as plane-wave parallel OCT systems.

Abstract: Optical switches and methods of switching include a first hybrid coupler configured to accept an input and to provide two branches. A phase tuner on a first branch includes a Mach-Zehnder phase shifter configured to shift a signal on the first branch by a selected phase. A loss compensator on a second branch is configured to match a loss incurred on the first branch. A second hybrid coupler is configured to recombine the two branches such that the phase shift generated by the phase tuner determines which output of the second hybrid coupler is used.

Abstract: A fiber optical sensor and methods for sensing a physical quantity such as rotation using the same. The sensor has an optical fiber supporting propagation of light that is configured as an interferometer. One or more segments of the optical fiber, where the segments may be non-contiguous, are poled in such a manner that a phase shift in light propagating through the fiber is created in response to application of a voltage to an electrode thereby inducing an electric field across a poled segment of the fiber. A phase modulator comprising multiple poled segments is additionally described. Applying phase-shifting effects differentially across poled segments of optical fibers of an array of optical fibers may also allow for steering an optical beam.

Abstract: A prefabricated mat-like structure having lengths of fiber mounted thereon or therein in a predetermined deployment pattern that provides a high spatial density of fiber to give increased spatial sensing resolution is described. The prefabricated mat-like structures may be very easily deployed by being placed against and/or wrapped around an object to be monitored, typically being fastened in place by clamps or the like. In addition, easy removal from the object is also obtained, by simply unfastening the mat-like structure, which may then be redeployed elsewhere. The prefabricated mat-like structure having the fiber already mounted thereon or therein therefore provides a very convenient and easily installable and removable solution.

Abstract: The disclosure provides for an optical communication device that includes a photodetector, an optical fiber, a first lens, and a second lens. The optical fiber may be configured to relay light. The first lens may include a first surface and a second surface and has an image plane. The first lens may be configured to receive the light output from the optical fiber, where the received light has a first cross-sectional area at the first surface. The second lens may include a third surface positioned at the image plane of the first lens and a fourth surface positioned adjacent to the photodetector. The second lens may be configured to receive the light output from the first lens and to output light having a second cross-sectional area at the fourth surface that is smaller than the first cross-sectional area.

Abstract: The invention relates to a system (20) for full-field interference microscopy imaging of a three-dimensional diffusing sample (206).

Abstract: An image capture device includes, in part, N optical transmit antennas forming a first array, N phase modulators each associated with and adapted to control a phase of a different one of the transmit antennas, M optical receive antennas forming a second array, M phase modulators each associated with and adapted to control a phase of a different one of the receive antennas, and a controller adapted to control phases of the first and second plurality of phase modulators to capture an image of an object. The first and second arrays may be one-dimensional arrays positioned substantially orthogonal to one another. Optionally, the first array is a circular array of transmitters, and the second array is a one-dimensional array of receivers positioned in the same plane as that in which the circular array of the transmitters is disposed.

Abstract: The invention relates to a device for measuring fluid parameters, comprising a Coriolis flow meter. The meter comprises a flow tube and an actuator forcing the flow tube into vibration and/or rotation. Further, the meter comprises a displacement sensor for sensing a displacement of the flow tube. The displacement sensor is arranged for measuring an optical fiber length change.

Abstract: A modular assembly for an imaging system can allow precision alignment to occur in isolated manufacturing stages, with the separate components being assembled together in later stages. An exemplary system includes a support structure, multiple imaging modules exchangeably coupled to the support structure and each including lenslets and a photonic integrated circuit (PIC) device arranged to receive light from the lenslets, multiple fiber arrays each connected to corresponding one of the multiple imaging modules, and a camera system connected to the fiber arrays. The lenslets the PIC device can be integrally coupled prior to assembly with the support structure, so that precise alignment of the lenslets with respect to the PIC device is performed in isolation.

Abstract: Systems and methods for interrogating sensing systems utilising bursts of samples. Bursts of samples correspond to optical pulses returning from optical sensors, where pulses are spaced at a period significantly longer than the pulse width, giving irregular sample spacing. The interrogation system and method processes the irregular busts of samples to recover phase information from received signals.

Abstract: Microelectromechanical systems (MEMS)-based devices capable of measuring wall shear stress vectors in three-dimensional aerodynamic flow fields are provided. A device can include a sensor that senses wall shear stress vectors in two in-plane axes and an interface circuit including a modulation section and a demodulation section. The device can be capable of making direct, real-time wall shear stress measurements without any need for using secondary measurements and/or models for validation.

Abstract: An optical fiber includes primary optical core(s) having a first set of properties and secondary optical core(s) having a second set of properties. The primary set of properties includes a first temperature response, and the secondary set of properties includes a second temperature response sufficiently different from the first temperature response to allow a sensing apparatus when coupled to the optical fiber to distinguish between temperature and strain on the optical fiber. A method and apparatus interrogate an optical fiber having one or more primary optical cores with a first temperature response and one or more secondary optical cores with a second temperature response. Interferometric measurement data associated with each primary and secondary optical core are detected when the optical fiber is placed into a sensing position.

Abstract: An image processing apparatus includes a memory that stores instructions, and at least one processor that executes the instructions to acquire measurement signals including information on a tomography of a subject in a depth direction obtained by performing optical coherence tomography on the subject, to acquire a base signal based on the measurement signals, and to calculate phase shifts between the measurement signals and the base signal. The processor further executes the instructions to smooth the phase shifts, to adjust phases of the measurement signals corresponding to the smoothed phase shifts based on the smoothed phase shifts, and to generate a background signal corresponding to a noise component based on the phase-adjusted measurement signals. In addition, the processor subtracts the background signal from the phase-adjusted measurement signals, and generates a tomographic image of the subject based on the phase-adjusted measurement signals from which the background signal is subtracted.

Abstract: A method for controlling the splitting ratio of an input optical signal to one or more output ports is described. The splitting ratio of a fiber-coupled signal in the communications band is controlled using cross phase modulation from a pump signal in the 980-1090 nm band. This design allows the nonlinear fiber in which the cross phase modulation occurs to be standard single mode fiber having a zero dispersion wavelength between 1250 and 1350 nm, such as SMF-28e fiber, which helps to maintain the lowest possible loss and a low cost while still allowing for power efficient interactions with signal wavelengths in the technologically important 1520-1610 nm band. The design is compatible with low insertion loss, narrow switching windows, and low added noise. The location of the pump pulse can be controlled allowing for the location of an input pulse to be determined.

Abstract: Methods and apparatuses are provided that greatly expand the utility of conventional hollow waveguide-based sensors via either straight, substrate-integrated channels or via meandering (e.g., circuitous, curved or folded optical paths) waveguide sensor designs. Full- or hybrid-integration of the meandering hollow waveguide with light source, detector, and light-guiding optics facilitates compact yet high-performance gas/vapor and/or liquid sensors of the substrate-integrated hollow waveguide sensor.

Abstract: The present invention involves a method of controlling at least one first element (22) for heating a multi-resonant optical device (10), automatically alternating between at least a first mode and a second mode, wherein, in the first mode, the first heating element is controlled by a first feedback loop (20) to lead the optical device to operate at a first resonance peak and wherein, at least during part of the second mode, the first feedback loop is made diverging to lead the optical device to operate at a second resonance peak.

Abstract: Disclosed herein are adapters configured to be optically coupled to a plurality of microscopes, said adapter comprising: a) a first microscope interface configured to optically couple a first microscope to an optical element in optical communication with an optical probe; b) a second microscope interface configured to optically couple a second microscope to the optical element in optical communication with the optical probe; and c) an optical arrangement configured to direct light collected from a sample with aid of the optical probe to (1) the first microscope and second microscope simultaneously, or (2) the first microscope or second microscope selectively.

Abstract: The present invention is related to a method for determining distributed temperature variation of a few mode optical fiber comprising the steps of:—providing a few mode optical fiber;—enlighting a first end of said few mode optical fiber by means of a coherent light source;—determining the interference pattern of coherent light at a second end of the optical fiber;—selecting one maximum of intensity at the second end of the optical fiber by spatially filtering the enlighting at the first end of the optical fiber;—determining the path length of the trajectory of the selected maximum of intensity;—based upon the determined path length of the trajectory of the selected maximum of intensity, determining the temperature variation of the few mode optical fiber.

Abstract: Using hDVS techniques to detect a disturbance in a coherent Rayleigh backscatter caused by the presence of another optical signal in the fiber. The interaction can be caused by a pump pulse travelling shortly after a probe pulse and at a frequency close to that of the probe plus or minus a Brillouin frequency shift. This results in gain or attenuation of the backscatter signal. The Brillouin shift is a function of temperature and strain.

Abstract: A device. The device includes a substrate a substrate, a first optical waveguide disposed on the substrate and a second optical waveguide disposed on the substrate. The device further includes a coupling element disposed on the substrate, the coupling element configured to couple an optical signal in the first optical waveguide to the second optical waveguide, and couple an optical signal in the second optical waveguide to the first optical waveguide. A first reflective element is disposed at an end of the first optical waveguide configured to reflect optical signals in the first optical waveguide. A second reflective element disposed at an end of the second optical waveguide configured to reflect signals in the second optical waveguide.

Abstract: Optics for apodizing an optical imaging probe beam, and methods for fabricating optics for apodizing an optical imaging probe beam are provided. In some embodiments, optics for apodizing an electrical comprises: an optical fiber; a focusing element coaxially aligned with the optical fiber; an element having a cylindrical bore and an angled reflective surface, wherein a first portion of a beam focused by the focusing element enters the cylindrical bore and a second portion of the beam is reflected at an angle to produce a beam with a generally annular-shaped profile.

Abstract: In order to measure the contrast of interference in an interference-based, closed-loop, phase-modulating optical sensor device, the gain of the feedback loop in a feedback controller is evaluated. This gain is found to be a measure for the contrast. The contrast evaluated in this way can e.g. be used for period-disambiguation when determining the measurand of the sensor device. The sensor device can e.g. be a high-voltage sensor or a current sensor.

Abstract: Methods and systems for encoding multi-level pulse amplitude modulated signals using integrated optoelectronics are disclosed and may include generating a multi-level, amplitude-modulated optical signal utilizing an optical modulator driven by first and second electrical input signals, where the optical modulator may configure levels in the multi-level amplitude modulated optical signal, drivers are coupled to the optical modulator; and the first and second electrical input signals may be synchronized before being communicated to the drivers. The optical modulator may include optical modulator elements coupled in series and configured into groups. The number of optical modular elements and groups may configure the number of levels in the multi-level amplitude modulated optical signal. Unit drivers may be coupled to each of the groups. The electrical input signals may be synchronized before communicating them to the unit drivers utilizing flip-flops.

Abstract: A semiconductor device may include a semiconductor wafer, and a reference circuit carried by the semiconductor wafer. The reference circuit may include optical DUTs, a first set of photodetectors coupled to outputs of the optical DUTs, an optical splitter coupled to inputs of the optical DUTs, and a second set of photodetectors coupled to the optical splitter. The optical splitter is to be coupled to an optical source and configured to transmit a reference optical signal to the first set of photodetectors via the optical DUTs and the second set of photodetectors.

Abstract: Embodiments of the present disclosure disclose a modulator, including: a first modulation module, configured to: receive first to-be-modulated data, and output a first transmission curve according to the first to-be-modulated data; a second modulation module, configured to: receive second to-be-modulated data, and output a second transmission curve according to the second to-be-modulated data, where a period of the second transmission curve is half of a period of the first transmission curve; and a combination module, configured to perform phase superposition on the first transmission curve and the second transmission curve, to obtain a combined linear result. In addition, this solution further provides a modulation system and a method for implementing higher order modulation, so that a linear result that can be modulated can be obtained by controlling a superposition ratio between transmission curves, to implement linear curve transmission.

Abstract: A method and an apparatus for measuring and displaying dental plaque are provided, and the method includes the steps of dividing near infrared light output from a light source into measurement light and reference light, applying the measurement light toward a tooth in an oral cavity and scanning the tooth with the measurement light, producing interference light from reflected light and back-scattered light from the tooth and the reference light, generating an optical coherence tomographic image based on a scattering intensity value of the interference light, extracting a dental plaque region having a specific scattering intensity value from the optical coherence tomographic image, and quantifying the dental plaque. A method and an apparatus for measuring and displaying gingiva and/or alveolar bone are further provided. A method and an apparatus for quantifying dental plaque, digitizing the dental plaque, and generating an image of the dental plaque in a noncontact, noninvasive manner are thereby provided.

Abstract: An apparatus, methods and a system for cuffless blood pressure monitoring are provided. The system includes an optical BCG sensor, a PPG sensor, a transceiver and a signal processing device. The BCG sensor optically couples to the subject, acquires BCG signals from the subject, and optically transmits the subject's BCG signals. The PPG sensor optically couples to the subject for acquiring PPG signals from the subject and optically transmits the acquired subject's PPG signals. The transceiver is coupled to the BCG sensor and the PPG sensor for receiving the BCG signals and the PPG signals and generating a BCG electronic signal from the subject's BCG signals and a PPG electronic signal from the subject's PPG signals.

Abstract: A sensor head of a test and measurement instrument can include an input configured to receive an input signal from a device under test (DUT), an optical voltage sensor having signal input electrodes and control electrodes or one set of electrodes, wherein the input is connected to the signal input electrodes, and a bias control unit connected to the control electrodes and configured to reduce an error signal or the input signal bias control signal are electrically combined and applied to a single set of electrodes.

Abstract: An optofluidic flow meter to determine a rate of fluid flow in a flow member includes: the flow member; a primary fluid conduit disposed in the flow member and that receives a fluid; a secondary fluid conduit disposed in the flow member; and a fiber optic comprising a fiber Bragg grating interposed between a first flow region of the primary fluid conduit and a second flow region of the secondary fluid conduit and that: physically distorts relative to a pressure differential between the primary fluid conduit and the secondary fluid conduit; and produces a shift in a Bragg wavelength in response to a physical distortion due to the pressure differential.

Abstract: Systems, methods and devices are provided for calibrating a flexible implement that employs fiber Bragg gratings (FBGs) for shape sensing. In some embodiments, methods and devices are provided for determining the longitudinal location of a FBG within an optical fiber that is employed for shape sensing. In other embodiments, methods and devices are employed for the determination of calibration parameters that relate the measured wavelength shift of a set of FBGs to the curvature at the location within the flexible implement where the set of FBGs resides. Various calibration devices are disclosed that employ guiding features for bending the flexible portion of the flexible implement along known curved profiles. In some embodiments, keyed features are incorporated into the flexible implement and the calibration device, such that the flexible implement is inserted into the device in a known orientation. In some embodiments, the flexible implement may incorporate a strain isolation mechanism.

Abstract: A laser treatment head guides a laser beam to a target area within a body cavity and includes a laser output element having a deflection element. The laser output element with deflection element is rotatable relative to a guide element about an axis. First and second thread elements mutually engage to cause the deflection element to perform a combined axial and rotational movement relative to the guide element. A control unit and the laser treatment head are configured such that the target area is irradiated by individual pulses (p) in a helical pattern of irradiation spots over a section of the circumference of the body cavity. The control unit is further configured such that reference locations (X) on the target area are irradiated by an individual pulse number (N) of subsequent pulses (p), thereby heating the mucosa tissue within the target area to a predetermined temperature.

Abstract: In view of the active vision model based on structured light, a hardware structure of a depth perception device (a chip or an IP core) for high-precision images is disclosed. Simultaneously, the module is not only capable of serving as an independent chip, but also an embedded IP core in application. Main principle of the module is as follows. Speckle image sequence (obtained from an external image sensor and unknown depth information) is processed by adaptive and uniform pre-processing sub-module, then is inputted to the module to be compared with the standard speckle image (known depth information), then motion-vector information of the inputted speckle image is obtained by pattern matching of image blocks (similarity calculation) by the block-matching motion estimation sub-module, then depth image is obtained by depth calculation, and finally high-resolution sequence of depth image is outputted by post-processing the depth image.

Abstract: An interferometric measurement method aims at calculating end face surface angle of multi-fiber connector or ferrule taking into account parallelism deviation angles of the connector or ferrule guide holes. The parallelism deviation angles are measured by scanning the side surfaces of guide pins inserted into the guide holes, which is done simultaneously with the end face scanning. Interferometric data from connector or ferrule end face and side surfaces of the guide pins is gathered during one scanning session—either one simultaneous scan or several scans without moving or re-inserting the connector or ferrule.

Abstract: Optoelectronic oscillator systems and an optoelectronic oscillator noise reduction method. One example of an optoelectronic oscillator system includes an optical source positioned at a first end of a fiber-optic path, the optical source being configured to transmit an optical signal along the fiber-optic path, an optical modulator positioned to receive and modulate the optical signal based on at least a reference signal, a retro-reflector positioned at a second end of the fiber-optic path, the retro-reflector being configured to receive and retro-reflect the optical signal, the retro-reflected optical signal having at least a frequency range of inherent fiber noise canceled, and an optical circulator positioned along the fiber-optic path between the optical modulator and the retro-reflector, the optical circulator being configured to direct the optical signal to the retro-reflector and direct the retro-reflected optical signal along a feedback path to a first photodetector to generate the reference signal.

Abstract: An example system for inspecting fiber optic cables includes: a fixture including a body configured to hold a plurality of fiber optic cables, the fixture including a front portion defining a plurality of apertures positioned adjacent to ends of the fiber optic cables; and an adapter including two or more pin members extending therefrom, the two or more pin members being configured to be positioned in two or more of the plurality of apertures in the fixture to hold the fixture relative to the adapter.

Abstract: An optical interrogation system, e.g., an OFDR-based system, measures local changes, of index of refraction of a sensing light guide subjected to a time-varying disturbance. Interferometric measurement signals detected for a length of the sensing light guide are transformed into the spectral domain. A time varying signal is determined from the transformed interferometric measurement data set. A compensating signal is determined from the time varying signal which is used to compensate the interferometric measurement data set for the time-varying disturbance. Further robustness is achieved using averaging and strain compensation. The compensation technique may be applied along the length of the light guide.

Abstract: An imaging apparatus configured to image an object to be examined is provided. The apparatus includes a splitting unit configured to split light obtained by combining the returned light and the reference light into a plurality of lights having different polarization components; and a detecting unit configured to detect the plurality of lights. The apparatus further includes a correcting unit configured to correct a phase difference between different polarization components generated by an optical member provided on an optical path of the measurement light or an optical path of the reference light.

Abstract: An optical IQ modulator (IQM) including two parallel Mach-Zehnder modulators (MZM1, MZM2) generates single sideband data signals. A control unit (18) generates additional optical single sideband pilot signals (PS1, PS2) positioned in a lower and a higher sideband respectively, and also further pilot signals (PS3, PS4) in both sidebands. A IQ modulator output signal (MOS) converted into electrical monitoring signals (MOS) and monitored. A control unit (18) selects control signals (CS12, CS3, CS4) and controls the IQ modulator via its bias ports (6, 7, 8) till the power transfer functions (PTF) of the Mach-Zehnder modulators (MZM1, MZM2) and the phase difference (??) between their output signals is optimized.

Abstract: Fiber optic cable structures suitable for distributed acoustic sensing that are capable of discriminating between stimuli acting on the cable in different directions, the cable structure including a core structure (202, 203, 204) with an optical fiber wound around the periphery of the core structure, the core further including a mass (203) which is movable in a preferred direction within the cable such that movement of said mass in said preferred direction causes a change in length of the fiber wound around the periphery of the core.