Abstract: A bond separation inspection method using an optical fiber sensor. The method includes a step of embedding a sensor part of an optical fiber sensor in an adhesive joining a plurality of members together. The sensor part is embedded in the adhesive in such a way that the sensor part undergoes a compressive strain. Separation of the bond is detected on the basis of an optical characteristic of the sensor part when light from a light source is directed into the optical fiber sensor.

Abstract: Resonant sensor with optical excitation and monitoring device using this sensor. This sensor comprises a doped silicon resonator (4) to absorb radiation (Re) with wavelength longer than 1100 nm and may be used for example to monitor the pressure in an oil well.

Abstract: A micro piezo-optic composite transducer comprises: dielectric material; electrodes situated over opposing surfaces of the dielectric material; an optical fiber embedded in the dielectric material, the optical fiber configured to have a wavelength response as a function of material strain; and piezoelectric fibers embedded in the dielectric material and situated on opposing sides of the optical fiber.

Abstract: A highly sensitive accelerometer for determining the acceleration of a structure includes a mass within a housing suspended by opposing support members. The support members are alternately wound around a pair of fixed mandrels and the mass in a push pull arrangement. At least a portion of one of the support members comprises a transducer capable measuring the displacement of the mass within the housing. An embodiment of the invention employs optical fiber coils as the support members for use in interferometric sensing processes. Arrays of such interferometer based accelerometers may be multiplexed using known techniques.

Abstract: A method and apparatus for sensing temperature using optical fiber is provided. In one embodiment, a method for sensing temperature using optical fiber includes launching a polarized optical signal having sufficient intensity to produce Brillouin scattering of the signal into a polarization maintaining optical fiber, receiving a first signal reflected from the launched signal, receiving a second signal reflected from the launched signal; and resolving a metric indicative of temperature from the first and second received signals. The method is particularly useful for sensing temperature in hazardous locations such as down hole gas and oil field applications or other applications where minimization of strain effects to signal transmission is desired.

Abstract: This invention relates to a new technique of interrogating fiber grating sensors employed for measuring physical quantities such as temperature and force. The technique involves the edge filtering of transmitted light that occurs when a narrow bandwidth light of suitable wavelength from a laser source is passed through a Long Period Fiber Grating (LPFG). When the characteristics attenuation spectrum of the LPFG is shifting, an energy modulation effect will be achieved when one measures the intensity of the transmitted narrow bandwidth light. The narrow bandwidth strong light is best obtained by the reflection of a broad band light from a fiber Bragg gratings (FBGs).

Abstract: A system for detecting dispersion in an incoming optical signal centered about a channel center frequency. The system includes a splitter unit for separating the incoming signal into first and second groups of signals. The system further includes a first compensation region adapted to apply a desired positive dispersion characteristic to a signal in the first group and a second compensation region adapted to apply a desired negative dispersion characteristics to a signal in the second group. The splitter also includes a receiver unit connected to the first and second compensation regions, and adapted to compare the received signals and to detect the dispersion in the incoming optical signal on the basis of the comparison. The system can be selectively balanced at different optical frequencies by varying the amount of dispersion applied by the first and second compensation regions.

Abstract: Disclosed herein is an accelerometer and/or displacement device that uses a mass coupled to a rhomboidal flexure to provide compression to an optical sensing element preferably having a fiber Bragg grating (FBG). The transducer includes a precompressed optical sensor disposed along a first axis between sides of the flexure. The top portion of the flexure connects to the mass which intersects the flexure along a second axis perpendicular to the first axis. When the mass experiences a force due to acceleration or displacement, the flexure will expand or contract along the second axis, which respectively compresses or relieves the compression of the FBG in the optical sensing element along the first axis. Perturbing the force presented to the FBG changes its Bragg reflection wavelength, which is interrogated to quantify the dynamic or constant force.

Abstract: High-resolution measurement of a parameter is provided at multiple different locations simultaneously along an optic fiber. Light within a predefined range of wavelengths is transmitted into an optic fiber that contains multiple birefringent fiber optic pressure transducers, each including a Fiber Bragg Grating. Each grating defines a spatially modulated index of refraction and a wavelength that is unique within the system. A sweeping comb filter is used to apply optical comb filtering to light reflected from the transducers so as to pass filtered light having multiple spectral portions, each spectral portion associated with one transducer. The free spectral range of the sweeping comb filter is set to be approximately equal to the spectral range of a single spectral portion. Wavelength division multiplexing is applied to the filtered light so as to separate the spectral portions.

Abstract: A sensor embedded in a high temperature metal is incorporated into a sensing system for measuring temperature, strain, or other properties of a metal structure. An optical system transmits light to and receives output signals from the sensor for analysis. With rotating structures, an optical fiber lead transmits light between the sensor and external surface of the structure along its rotational axis, allowing the lead to remain fixed with respect to the optical system as the structure rotates at high speeds.

Abstract: Fiber-optic-based systems and methods for monitoring physical parameters using a remotely deployed circulator are disclosed. In a preferred embodiment the circulator is remotely deployed with respect to an optical source/detector and coupled thereto by two dedicated fiber optical cables: a forward line for passing light from the source through the circulator to fiber-optic-based sensors, and a return line for passing light reflected from the sensors through the circulator back to the detector. By using separate forward and return lines in conjunction with the circulator, backscattering phenomenon experienced on the forward line will not interfere with the reflected light signals coming from the sensors. The circulator, and hence the sensors, may therefore be remotely deployed from the source/detector present at a monitoring station, greatly expanding distances which optical sensing systems can span.

Abstract: A method and apparatus for sensing temperature using optical fiber is provided. In one embodiment, a method for sensing temperature using optical fiber includes launching a polarized optical signal having sufficient intensity to produce Brillouin scattering of the signal into a polarization maintaining optical fiber, receiving a first signal reflected from the launched signal, receiving a second signal reflected from the launched signal; and resolving a metric indicative of temperature from the first and second received signals. The method is particularly useful for sensing temperature in hazardous locations such as down hole gas and oil field applications or other applications where minimization of strain effects to signal transmission is desired.

Abstract: An optical medium having a cavity that defines a variable gap is provided. The optical medium is used in an optical sensor, laser, and variable frequency resonator, by way of example. The cavity is physically altered in response to changes in a measurable parameter like pressure, temperature, force, flow rate, and material composition. The optical medium is characterized in some embodiments by having a cavity disposed near or within a high Q optical resonator. The optical resonator can be formed by various structures of which Bragg reflector cavities, ring resonators, microdiscs, and microspheres are examples. The optical resonator is preferably coupled to a laser source. The altering of the cavity affects the resonance condition within the optical resonator and thereby the laser signal of the system. If the laser source is a mode locked laser, the repetition rate of the pulse train changes in response to changes in the measurable parameter.

Abstract: An integrated optical chip device for molecular diagnostics comprising a tunable laser cavity sensor chip using heterodyned detection at the juncture of a sensor laser and a reference laser, and including a microfluid chip to which the sensor chip is flip-chip bonded to form a sample chamber that includes exposed evanescent field material of the tunable laser cavity to which fluid to be diagnosed is directed.

Abstract: A multiple mode pre-loadable fiber optic pressure and temperature sensor includes a generally cylindrical structure having at least one compression element, a fiber optic having a Bragg grating in contact with one side of the compression element, a diaphragm in contact with the other side of the compression element, and a fluid port in fluid communication with the diaphragm. According to preferred aspects of the, a groove is provided in at least one compression element for receiving the fiber optic. The sensor is pre-loaded by straining the diaphragm over the adjacent compression element when the cover is attached. The compression element in contact with the diaphragm preferably has a contoured surface contacting the diaphragm and the diaphragm is stretched to match that contour. By varying the contour of the compression element and the thickness of the diaphragm, the dynamic range of the sensor can be changed. The preferred diaphragm has a variable thickness and is made as an integral part of the structure.

Abstract: A source and/or method of generating quantum-correlated and/or entangled photon pairs using parametric fluorescence in a fiber Sagnac loop. The photon pairs are generated in the 1550 nm fiber-optic communication band and detected by a detection system including InGaAs/InP avalanche photodiodes operating in a gated Geiger mode. A generation rate>103 pairs/s is observed, a rate limited only by available detection electronics. The nonclassical nature of the photon correlations in the pairs is demonstrated. This source, given its spectral properties and robustness, is well suited for use in fiber-optic quantum communication and cryptography networks. The detection system also provides high rate of photon counting with negligible after pulsing and associated high quantum efficiency and also low dark count rate.

Abstract: A fiber optic sensor comprises two independent fibers having Bragg gratings which are coupled to commutating broadband optical sources through splitters and wavelength discriminators. The ratio of detected optical energy in each of two detectors examining the wave intensity returned to a wavelength discriminator coupled with the characteristic of the wavelength discriminator determines the wavelength returned by the grating. In another embodiment, tunable filters are utilized to detect minimum returned wave energy to extract a sensor wavelength Reference to the original grating wavelength indicates the application of either temperature or strain to the grating. In another embodiment, a plurality of Bragg grating sensor elements is coupled to sources and controllers wherein a dimensional change in a fiber having a Bragg grating is detected using a measurement system comprising broad-band sources, optical power splitters, a high-sensitivity wavelength discriminator, optical detectors, and a controller.

Abstract: A differential measurement system using pairs of Bragg gratings including at least one optical sensor having two Bragg gratings in two optical waveguides and having sensitivities adjusted so that respective spectra of the two gratings have a relative spectral shift dependent on a parameter or parameters to be measured. The system also includes an optical source to supply light to the two optical waveguides to interrogate them, a mechanism enabling light to pass successively through the two Bragg gratings of the same sensor, photodetectors to measure the power level of light having passed only through one of the two optical waveguides and the power level of light having passed successively through the two optical waveguides, and a processor to process the power levels and supply values of the parameter or parameters measured. The system is applicable in particular to measurements of temperatures, stresses, and pressures.

Abstract: An optical fiber sensor system comprising of an optical fiber including plurality of sensitive elements, each sensitive element has characteristic spectral band which in normal undisturbed condition lies in a first wavelength range and, under an influence of some specified condition to be detected, shifts to a second wavelength range; first and second wavelength ranges do not overlap. Means for probing an optical transmission or reflection of the fiber operate within second wavelength range to monitor the changes of the transparency or reflectivity of the fiber caused by the shift of characteristic spectral band into the second wavelength range. The invention provides means for distributed monitoring of equipment or construction structures and detection of specified conditions and can provide alarm signal when the specified conditions become effective.

Abstract: Systems for detection and compensation of modal dispersion in an optical fiber system including a multisegment photodetector coupled to an end of an optical fiber for detecting optical signals exiting the optical fiber and for converting the optical signals to an electrical output are provided. A representative multisegment photodetector includes a plurality of photodetector regions configured such that each of the plurality of photodetectors detects a portion of the plurality of optical signals exiting the end of the optical fiber and modifies the signal to reduce the affects of modal dispersion. Other systems are also provided.

Abstract: The fast switching multifunction antenna of the present invention is a variable length antenna that may be switched to provide the equivalent function of a broadband antenna. The variable length antenna quasi-continuously transmits or receives signals at a plurality of frequencies by changing the effective length of the antenna using a variety of switching mechanisms. The present invention may comprise a plurality of antenna segments, a plurality of selectively actuable switches for interconnecting the antenna segments, and a switching mechanism operably coupled to the plurality of selectively actuable switches for switching them at a switching rate that is greater than twice the highest frequency to be transmitted or received. The switching rate will be fast enough to allow the antenna to sample the highest frequency and all of the required lower frequencies within the desired frequency range without the loss of information at any frequency.

Abstract: In the present invention an optical waveguide grating sensing device for a dual-parameter optical waveguide grating sensor includes a first optical waveguide grating of a first resonant wavelength provided in a first section of an optical waveguide and a second optical waveguide grating of a second resonant wavelength provided in a second of an optical waveguide. The first and second gratings have different coefficients of rate of change of wavelength as a function of temperature and have substantially the same coefficient of rate of change of wavelength as a function of stain.

Abstract: An apparatus and method for determining a physical parameter affecting an optical sensor or a number of sensors in a network. The apparatus uses a narrow linewidth source at an emission wavelength &lgr;e and an arrangement for varying the emission wavelength &lgr;e of the radiation. An analysis module with curve fitting is used to generate a fit to the response signal obtained from the optical sensor. The physical parameter is determined form the fit rather than from the response signal. The apparatus can be employed with Bragg gratings, etalons, Fabry Perot elements or other optical sensors.

Abstract: An optical reading system is described herein which can be used to detect the presence of a biological substance (e.g., cell, drug, chemical compound) on a surface of a grating-based waveguide sensor. In one embodiment, the reading system includes a light source (e.g., laser, diode) for directing a light beam into the grating-based waveguide sensor and a detector (e.g., spectrometer, CCD imaging device) for receiving a reflected light beam from the grating-based waveguide sensor and analyzing the reflected light beam so as to detect a resonant wavelength/angle which corresponds to a predetermined refractive index that indicates whether a biological substance is located on the surface of the grating-based waveguide sensor.

Abstract: A reflected light from a Bragg grating in an electrical transformer or other apparatus at which temperature is to be measured, is positioned by an optocoupler through a second fiber provided with a second Bragg grating whose reflection wavelength is different from that of the first grating. The nonreflected light intensity is measured by a photodetector and is used to signal the temperature measurement.

Abstract: An optical spectrum analyzer (10), receiving a multi-channel optical signal (12). The optical signal (12) is passed through an optical isolator (14) and a fiber coupler (16) to a tunable optical filter. The tunable optical filter comprises one or more fiber Bragg gratings (18) inscribed in a length of optical fiber. The optical fiber is mounted on a means operable to apply a variable strain to the fiber, to they tune the peak wavelength of the Bragg grating (18) over a desired wavelength range, the tunable optical filter thereby reflecting each channel of the input signal (12) in turn. The detector (20) therefore detects a signal only if the input signal (12) contains wavelengths corresponding to the reflection wavelength of a grating (18).

Abstract: This system comprises at least one optical sensor (C1, C2, C3) comprising two Bragg gratings (B11, B12; B21, B22; B31, B32) written in two optical waveguides and having sensitivities adjusted so that the respective spectra of the two gratings have a relative spectral shift which depends on the parameter or parameters to be measured. The system also comprises an optical source (6) provided in order to supply light to the two optical waveguides so as to interrogate the latter, means enabling the light to pass successively through the two Bragg gratings of the same sensor, photodetectors in order to measure, on the one hand, the power level of light (R1) having passed only through one of the two optical waveguides and, on the other hand, the power level of light (R′1) having passed successively through the two optical waveguides, and means to process these power levels and supply the values of the parameter or parameters measured.

Abstract: The Bragg grating device for measuring an acceleration, has at least two optical Bragg gratings (11, 12), each formed in elastic material, for supplying optical radiation (S) and at least one deflectable mass (M) connected to both gratings for generating an inertial force that is dependent on the acceleration which acts upon the device, in order to produce elastic extension of one of the two gratings and simultaneous elastic contraction of the other grating. The device is also suitable for vibration frequency measurement.

Abstract: A highly sensitive accelerometer for determining the acceleration of a structure includes a mass within a housing suspended by opposing support members. The support members are alternately wound around a pair of fixed mandrels and the mass in a push pull arrangement. At least a portion of one of the support members comprises a transducer capable measuring the displacement of the mass within the housing. An embodiment of the invention employs optical fiber coils as the support members for use in interferometric sensing processes. Arrays of such interferometer based accelerometers may be multiplexed using known techniques.

Abstract: A fiber optic sensor comprises two independent fibers having Bragg gratings which are coupled to commutating broadband optical sources through splitters and wavelength discriminators. The ratio of detected optical energy in each of two detectors examining the wave intensity returned to a wavelength discriminator coupled with the characteristic of the wavelength discriminator determines the wavelength returned by the grating. In another embodiment, tunable filters are utilized to detect minimum returned wave energy to extract a sensor wavelength Reference to the original grating wavelength indicates the application of either temperature or strain to the grating. In another embodiment, a plurality of Bragg grating sensor elements is coupled to sources and controllers wherein a dimensional change in a fiber having a Bragg grating is detected using a measurement system comprising broad-band sources, optical power splitters, a high-sensitivity wavelength discriminator, optical detectors, and a controller.

Abstract: An apparatus for measuring pressure in a medium comprises a laser for emitting light; a dichroic beam splitter that reflects the light from the laser; a first lens that receives and focuses the light from the beam splitter; a first optical fiber for receiving the light from the first lens; a crystal having fluorescence properties and having a hemispherical shape, the crystal being attached to an end of the first optical fiber; a second lens that receives and focuses fluorescence generated by the crystal and reflected by the dichroic beam splitter; a second optical fiber for receiving the fluorescence from the second lens; a spectrometer that receives the fluorescence from the second optical fiber; a streak camera connected to the spectrometer; a charge-coupled device connected to the spectrometer; and a delay generator connected to the charge-coupled device, the streak camera and the laser.

Abstract: A sensor system comprises first and second fibre bragg gratings (FBGs). The two fibre bragg gratings receive light from a common light source and produce respective measurement signals having a spectrum dependent on a measurement signals having a spectrum dependent on a measurand, and a common reference signal. The two measurement signals pass through respective edge filters to respective detectors and a third detector monitors the reference intensity. A processor produces a value for the measurand from the received and detected signals. The system can be used in a temperature compensated strain gauge.

Abstract: A fiber optic sensor comprises two independent fibers having Bragg gratings which are coupled to commutating broadband optical sources through splitters and wavelength discriminators. The ratio of detected optical energy in each of two detectors examining the wave intensity returned to a wavelength discriminator coupled with the characteristic of the wavelength discriminator determines the wavelength returned by the grating. In another embodiment, tunable filters are utilized to detect minimum returned wave energy to extract a sensor wavelength Reference to the original grating wavelength indicates the application of either temperature or strain to the grating. In another embodiment, a plurality of Bragg grating sensor elements is coupled to sources and controllers wherein a dimensional change in a fiber having a Bragg grating is detected using a measurement system comprising broad-band sources, optical power splitters, a high-sensitivity wavelength discriminator, optical detectors, and a controller.

Abstract: To provide an optical fiber strain sensor device and a strain detection method, for measuring precisely AE and for detecting effectively a rapid strain change due to a shock load, an optical fiber strain sensor device includes an FBG sensor mounted on an object to be measured, a broadband light source for directing a broadband wavelength light ray to the FBG sensor, and an FBG filter that reflects or transmits a light ray reflected from the FBG sensor, and, using the FBG filter, the optical fiber strain sensor device processes and detects a change in the center wavelength of the light ray that has been incident from the broadband light source and then has been reflected from the FBG sensor.

Abstract: An ac technique for cavity ringdown spectroscopy permits 1×10−10 absorption sensitivity with microwatt light power. Two cavity modes are provided temporally out of phase such that when one mode is decaying, the other mode is rising. When one of the modes probes intra-cavity absorption of a sample gas, heterodyne detection between the two modes reveals dynamic time constants associated with the cavity and the cavity plus intra-cavity absorption. The system and method provides a quick comparison between on-resonance and off-resonance modes and enables sensitivities that approach the shot-noise limit.

Abstract: A chemical sensing system and method. The system (10) includes a transmitter having a laser for providing a collimated beam of electromagnetic energy at a first frequency and a Q switch in optical alignment with the beam. The system further includes a crystal for shifting the frequency of the beam from the first frequency to a second frequency. A mechanism is included for shifting the beam from the second frequency to a third frequency in the range of 8-12 microns. The system includes a mechanism for switching the polarization state of the second beam and providing third and fourth beams therefrom. The third beam has a first polarization and the fourth beam has a second polarization. The second polarization is orthogonal relative to the first polarization. The frequency shifted third and fourth beams are combined to provide an output beam in the range of 8-12 microns. The output beam is transmitted and a return signal is detected by a receiver in the illustrative chemical sensing application.

Abstract: An ac technique for cavity ringdown spectroscopy permits 1×10−10 absorption sensitivity with microwatt light power. Two cavity modes are provided temporally out of phase such that when one mode is decaying, the other mode is rising. When one of the modes probes intra-cavity absorption of a sample gas, heterodyne detection between the two modes reveals dynamic time constants associated with the cavity and the cavity plus intra-cavity absorption. The system and method provides a quick comparison between on-resonance and off-resonance modes and enables sensitivities that approach the shot-noise limit.

Abstract: An optical fiber sensor system comprising of an optical fiber including plurality of sensitive elements, each sensitive element has characteristic spectral band which in normal undisturbed condition lies in a first wavelength range and, under an influence of some specified condition to be detected, shifts to a second wavelength range; first and second wavelength ranges do not overlap. Means for probing an optical transmission or reflection of the fiber operate within second wavelength range to monitor the changes of the transparency or reflectivity of the fiber caused by the shift of characteristic spectral band into the second wavelength range.

Abstract: A composite structure contains crystalline and/or polycrystalline triboluminescent elements distributed therein externally and/or internally, totally and/or regionally. The structure is instrumented with at least one optical fiber which is coupled therewith penetratingly and/or superficially/tangentially. Each optical fiber is exteriorly light transparent/translucent along at least a longitudinal portion thereof which is situate in the vicinity of at least one triboluminescent element. Concomitant with the occurrence of damage in and/or on the structure is the occurrence of mechanical action with respect to at least one triboluminescent element, a consequence of which is the occurrence of triboluminescence which, to at least some degree, passes radially into at least one optical fiber so as to reach the optical fiber's transmissive axial core and thereby be transmitted to remotely located photosensitive equipment. The triboluminescent elements can exist wholely and/or partly in various capacities, e.g.

Abstract: An apparatus is provided in which multiple devices are connected in series forming a signal path through which a signal propagates. Each device may have one or more operating frequencies and each operating frequency may generate a corresponding intensity modulation with respect to the signal. For one embodiment, the apparatus includes multiple delay lines through which the signal travels. The length of each delay line is configured to reduce the intensity modulation generated by each device based upon one or more factors including the one or more operating frequencies associated with each device and multiple null orders corresponding to different lengths of the delay lines.

Abstract: The present invention concerns an apparatus for coupling light (1) of at least one wavelength of a laser light source (2) into an optical assemblage (3), preferably into a confocal scanning microscope, having an optically active component (4) that serves in particular to select the wavelength and to set the power of the coupled-in light (5). To ensure that changes in the power and/or wavelength of the laser light source do not affect the power of the light (5) coupled into the optical assemblage, the apparatus according to the present invention is characterized in that in order to influence the coupled-in light (5), the component (4) serves as the adjusting element of a control system (11).

Abstract: One problem that arises in the context of controlling tunable filters, and more specifically, Fabry-Perot tunable filters concerns the control algorithms for these MOEMS devices. An optical filter system comprises a tunable optical filter that scans a pass band across a signal band to generate a filtered signal. A filter tuning voltage generator generates a tuning voltage to the optical tunable filter. A photodetector generates an electrical signal in response to the filtered signal. Finally, a controller, that is responsive to the photodetector, triggers the filter tuning voltage generator. To increase the ease at which the results of a scan of the signal band of a WDM signal can be analyzed and improve spectral resolution, the change in the pass band of the tunable filter as a function of time is linearized in frequency or wavelength. This is achieved through the use of essentially an arbitrary waveform generator as the filter tuning voltage generator.

Abstract: An automatically adjustable arrangement for tuning the accumulated chromatic dispersion present in an optical communication system uses a dispersion variation-based measuring arrangement to determine both the magnitude and sign of the accumulated dispersion. A relatively small portion of a received optical signal including an unknown amount of chromatic dispersion is tapped off at an optical receiver and a small amount of additional dispersion is added to the tapped-off signal so that nonlinear detection can be used to determine both the magnitude and sign of the dispersion present in the transmission signal. This information is then fed back to a tunable dispersion compensator to provide the real-time, automatic correction to the dispersion present in the system.

Abstract: A dispersion discriminator and method for determining the amount of dispersion in an optical signal. The discriminator includes first and second dispersion arms for causing first and second additional amounts of dispersion to be added in first and second portions of the optical signal, respectively. The first and second additional amounts are of opposite polarities and preferably of substantially equal magnitude. The discriminator includes a detector capable of receiving the first and second portions of the optical signal from the arms; detecting, for each of a plurality of frequencies, a difference in a characteristic of the first and second portions; determining a particular frequency at which the difference falls outside a predetermined range; and mapping the particular frequency and the difference at that frequency to a magnitude of dispersion in the optical signal.

Abstract: A optical fiber sensor for measuring temperature and/or pressure employs temporally created long period gratings. The gratings may be produced by a periodic change in the refractive index of the fiber along the fiber longitudinal axis caused by periodically spaced compressive and/or expansive forces or by spaced-apart unbalanced forces that cause periodic fiber micro-bending. Pressure and temperature are determined by measuring changes in both the wavelength at which light is coupled from a mode guided by a core to a different mode and an amount of such coupling. The gratings are created intrinsically and extrinsically. Single and multiple core fibers are used.

Abstract: The invention relates to a frequency-coded fiber laser pressure sensor (1) which is especially suitable for measuring isotropic pressures in oil wells. The sensor principle provided for in the invention is based on the fact that in a fiber laser (2) doped with Er3+ a monomode or bimodal sensor fiber (5, 5a, 5b) is positioned whose pressure-related birefraction results in a frequency shift and beat frequencies between the orthogonal linear polarisation modes x, y or the spatial modes LP01 and LP11straight line. The beat frequencies are easily measured using a frequency counter (19). Temperature-related variations in birefraction are compensated in a differential arrangement of two sensor fiber segments (5a, 5b). Fiber-integrated Bragg gratings (4a, 4b) with low bandwidths (0.2 nm) are especially suitable as laser end reflectors.

Abstract: A fiber optic sensor comprises two independent fibers having Bragg gratings which are coupled to commutating broadband optical sources through splitters and wavelength discriminators. The ratio of detected optical energy in each of two detectors examining the wave intensity returned to a wavelength discriminator coupled with the characteristic of the wavelength discriminator determines the wavelength returned by the grating. In another embodiment, tunable filters are utilized to detect minimum returned wave energy to extract a sensor wavelength. Reference to the original grating wavelength indicates the application of either temperature or strain to the grating. In another embodiment, a plurality of Bragg grating sensor elements is coupled to sources and controllers wherein a dimensional change in a fiber having a Bragg grating is detected using a measurement system comprising broad-band sources, optical power splitters, a high-sensitivity wavelength discriminator, optical detectors, and a controller.

Abstract: A fiber optic acoustic sensor system including an optical conductor having low reflectivity mirrors is provided. Optical sensors are provided by sections of the optical conductor bounded by pairs of the low reflectivity mirrors. Pulses of light are injected into the optical conductor and reflected by the low reflectivity mirrors. The reflected pulses of light are processed using a compensating interferometer to generate interference patterns representative of the environmental conditions acting upon the optical conductor.

Abstract: A chromatic dispersion discriminator for determining the amount of chromatic dispersion in optical signals used by optical transmission systems is described. The discriminator provides a means of detecting the polarity and magnitude of dispersion in optical signals received over a dispersive optical link, thereby allowing the correct amount of dispersion compensation to be applied to each optical signal.

Abstract: Disclosed is an apparatus for monitoring wavelength division multiplexed optical signal performance transmitted onto a main optical path.