Abstract: A fiber optic sensor includes two reflective elements in series. The first reflective element is formed as a partially mirrored surface on the end of a single-mode optical fiber lead which is bonded into a ferrule. A sleeve is used to join the ferrule to a second ferrule which is turn is bonded to a length of single-mode optical fiber. The second reflective element is a partially mirrored surface on the cleaved end of the second fiber. The second fiber may be affixed to or embedded in a structure to be monitored and changes its optical path length in response to a condition of the structure. Light introduced into the sensor is reflected from the first or second reflective element and thus follows two optical paths. The path length difference between the two optical paths is twice the optical path length of the second fiber.

Abstract: Multi-stage, all-pass optical filters used to make low-loss, multi-channel dispersion compensation modules are disclosed. The all-pass optical filters can be ring resonators in waveguides, Gires-Tournois Interferometers (GTIs) in free space form, and the like. The coupling constants and circulating path lengths may also be distinctively varied in each of the series of GTIs, tuning the net dispersion spectrum of the GTI set, such that the sum of the dispersions from the series of GTI's can provide a system with greater bandwidth than the same number of identical GTIs. The local dispersion slope can also be tuned in this manner. Multi-cavity GTIs can also be formed with similar performance enhancing properties.

Abstract: An all-optical switch, an all-optical signal waveform reshaping element and an all-optical asymmetric demultiplexer are formed of an optical interferometer having a compact and simple structure. Nonlinear gain media are provided at positions different from each other in two arms of a Mach-Zehnder optical interferometer. Then, an optical cavity is formed by mounting a mirror on an optical input-output port in each of a first and a second multi-mode optical interferometers connected with the two arms. Furthermore, when a saturable absorption medium is placed on the mirror of one of the multi-mode optical interferometers, a mode-locked laser oscillation is induced.

Abstract: Method and assembly for sustained elimination or reduction of polarization induced signal fading in optical interferometer networks comprising at least two optical paths from an input port to an output port, the transmission delays of the paths differing by ?, an interrogation arrangement interrogating the optical phase differences between the paths, containing at least one optical source launching optical power into a port, a detector arrangement converting the optical power from an output port into electrical detector signals, and a control and signal processing unit capable of processing detector signals to determine the phase difference. The method comprising the steps of: altering the input polarization state produced by the source with a modulation frequency that is comparable to or higher than 1/(4?) receiving the optical signals at the detector arrangement providing a detector signal; processing the detector signal determining the phase difference between the optical signals.

Abstract: A fiber-optic gauge having at least one sensor mounted onto a side of an optical fiber. In one embodiment, the sensor is optically coupled to the fiber using a thin-film filter inserted into the fiber and preferably oriented at about 45 degrees with respect to the fiber axis. The sensor may be one of a plurality of sensors similarly mounted on and optically coupled to a single optical fiber. Each sensor is designed to change its reflectivity in response to a change in an external physical parameter, e.g., pressure, and is preferably adapted for interrogation with monochromatic light. The interrogating light has a plurality of wavelength components, each corresponding to a different sensor. Light reflected from the sensors is de-multiplexed and analyzed to measure the reflectivity of each sensor and to derive the corresponding value of the physical parameter, thereby providing a parameter measurement at each sensor location.

Abstract: An electromagnetic resonant sensor has a dielectric sensor body through which electromagnetic wave energy is propagated. The sensor body has a cavity, with surfaces facing one another to define a gap that varies as a function of a parameter to be measured. The resonant frequency of an electromagnetic standing wave in the body and the variable gap changes as a function of the gap dimension.

Abstract: A linear interferometric sensor system in which the light output from the interferometric sensor is optically bandpass filtered before conversion to an electrical signal by an adjustable band-pass filtering device and the center wavelength of the adjustable band-pass filtering device is controlled by a feedback circuit responsive to the steady state component of the electrical signal corresponding to the filtered sensor return. In a preferred embodiment, the adjustable band-pass filtering device is an electrically tunable optical filter. The invention is particularly useful in self calibrating interferometric/intensity-based sensor configuration, but can be used with other linear interferometric sensor configurations.

Abstract: An optical fiber pressure sensor having a base layer 20 with an optical fiber hole, a fiber stop layer 28 and, optionally, an etch stop layer 24. The fiber stop layer optionally has a fiber stop hole 33 that is smaller than the optical fiber 22. A diaphragm cap layer 32 is bonded to the fiber stop layer 28. The diaphragm cap layer 32 has a diaphragm 34 spaced apart from the optical fiber. The optical fiber and diaphragm form an Etalon that changes cavity length with applied pressure. Optionally, the device is made almost entirely of silicon, and so has reduced mechanical stress problems caused by thermal expansion mismatches. This allows the present sensor to be used in high temperature environments such as internal combustion engines.

Abstract: Thin film filters have been a basic building block of many wavelength division multiplexed (WDM) systems providing the means by which a signal, defined by a center wavelength, can be separated from a group of WDM signals. In an effort to maintain the same performance over a range of operating temperatures, thin film filters have been coated onto specially designed substrates, which expand and contract with the change in temperature to counteract the effects that the temperature change has on the thin film filters. Unfortunately, only very few materials provide the necessary thermal expansion characteristics to counteract the shift in center wavelength. Moreover, the application of a force onto only one side of the filter causes the thin film filter to bend or curve. Accordingly, the present invention solves the aforementioned problems by providing a thin film filter sandwiched between a substrate and a superstrate, which apply equal forces to each side of the filter.

Abstract: A transmission-type extrinsic Fabry-Perot interferometric optical fiber sensor and a method used for integrity monitoring of structures and measuring strain and temperature are provided. The transmission-type extrinsic Fabry-Perot interferometric optical fiber sensor includes first single-mode optical fiber and second single-mode optical fiber, laser device, and optical detector. The first single-mode optical fiber is inserted into an end of a capillary quartz-glass tube and the second single-mode optical fiber is inserted into the other end of the capillary quartz-glass tube. Air gap is formed between the first single-mode optical fiber and the second single-mode optical fiber in the capillary quartz-glass tube. Gap length of the air gap changes in response to magnitude and direction of transformation of the capillary quartz-glass tube. The laser device launches light into an end of the first single-mode optical fiber.

Abstract: A miniaturized chemical sensor features an optical microcavity coated with a surface layer, and a waveguide that evanescently couples light into the microcavity. The surface layer is adapted to chemically interact with one or more molecule species in a chemical vapor surrounding the microcavity, so as to alter the evanescent light coupling between the optical microcavity and the waveguide. The chemical interaction causes a change in the index of refraction of the microcavity, resulting in a measurable phase difference readout. The refractive index sensitivity is substantially increased, because of the high Q-value of the optical microcavity.

Abstract: The invention provides a dispersion compensation system and method formed by cascading a series of GT cavities with three setting parameters, reflectivity, resonant wavelength, and free-spectral-range. In one aspect of the invention, the GT cavities can synthesize any shape of combined dispersion compensation, including positive, negative, slope dispersion compensation. In another aspect of the invention, the GT cavities are tunable or dynamic to accommodate various types of dispersion compensation. Advantageously, the present invention provides an effective cost solution for a more precise dispersion compensation tuning.

Abstract: A miniature, fiber-coupled Fabry-Perot interferometer has a piezoelectric transducer coupled to first and second collimating lenses. The collimating lenses collimate and interfere light energy within a gap formed between the lenses as part of the interferometer. Preferably, the lenses are matched mode gradient index lenses. Light energy coupled to the collimating lens is thus collimated and interfered within the gap. The piezoelectric transducer expands or contracts to adjust the gap, thereby adjusting the free spectral range of the interferometer. An input fiber provides input to the interferometer; an output fiber carries processed light energy of the selected free spectral range to external devices and optical systems. Metal coatings may be used to provide a capacitive feedback of lens position to calibrate the gap and, thus, the free spectral range.

Abstract: One aspect of the invention relates to an optical signal processing device including a Mach-Zehnder interferometer which includes a reference arm comprising a first Fabry Perot interferometer and a sample arm comprising a second Fabry Perot interferometer including at least two mirrors forming a Fabry-Perot cavity therebetween, and an adsorbing material disposed within the cavity. The Fabry-Perot interferometer in the sample arm permits a first portion of an input signal to pass multiple times through the sample while a second portion of the input signal passes through the reference arm, and the first and second signal portions are combined at an output to result in constructive or destructive interference between the signal portions.

Abstract: An optical sensor is provided. The sensor includes an optical fiber having a free extremity on which a polymer layer is deposited normal to the longitudinal axis. A light source injects a analytical light beam in the fiber, which is reflected by the polymer layer. The reflected beam is analyzed by a spectrum analyzer, which determines the thickness of the polymer layer based on the Fabry-Perot effect. This thickness is related to a substance to be detected. An optical nose made from a plurality of such sensors is also provided, and may be used to detected a variety of substances.

Abstract: An all-optical switch, an all-optical signal waveform reshaping element and an all-optical asymmetric demultiplexer are formed of an optical interferometer having a compact and simple structure. Nonlinear gain media are provided at positions different from each other in two arms of a Mach-Zehnder optical interferometer. Then, an optical cavity is formed by mounting a mirror on an optical input-output port in each of a first and a second multi-mode optical interferometers connected with the two arms. Furthermore, when a saturable absorption medium is placed on the mirror of one of the multi-mode optical interferometers, a mode-locked laser oscillation is induced.

Abstract: A pressure sensor is formed on a substrate, the surface of the substrate having a p-n junction and a shell with a beam inside the shell over the p-n junction. The beam and the shell and the p-n junction surface form optical Fabry-Pérot cavities. An optical fiber is positioned in a hole formed in the underside of the substrate below the p-n junction. Light from the fiber charges the p-n junction and drives it into vibration mode. Pressure changes change the tension in the diaphram to vary the frequency with changes in pressure, so that pressure can be detected.

Abstract: A chemical sensing probe comprises an optical fiber or may be mounted on an optical fiber. The probe has a chemically sensitive measuring material which exhibits a change in volume and/or a change in refractive index in the presence of a given chemical. The change in volume and/or refractive index gives a change in an optical path length through the probe which can be measured interferometrically.

Abstract: To form an optical element (20), in particular an interferometric sensor, an optical fiber (1) is placed tangent to a cylindrical supporting element (2); a straight portion (1a) of the optical fiber and the supporting element are surface fused; and a cavity (26) is formed in the optical fiber (1), the cavity being defined by facing surfaces (27,28) of the straight portion (1a) substantially perpendicular to the axis of the straight portion (1a). The optical fiber (1) and supporting element (2) may be subjected to traction during surface fusion, to form a small cross-section portion close to the cavity, and which, when light is conducted by the optical element, provides for reducing the amount of light dispersed in the cavity.

Abstract: An optical pressure sensor includes an optical fiber having a well defined end part and a casing having a cylindrically shaped cavity with an inner diameter that is essentially the same as the outer diameter of fiber. The end of the optical fiber is positioned at a chosen axial position inside the cavity, thereby closing one end of the cavity. A body is positioned in the cavity and has a first, at least partially, reflective surface. The partially reflective surface, fiber, and casing define a chamber. The chamber contains a compressible fluid. At least one of the body and the optical fiber is movably connected to the casing in the axial direction thus to provide a pressure coupling between the chamber and the environment.

Abstract: The invention relates to Fabry-Perot interferometers (FFPI) that are thermally or electromechanically tunable. These interferometers are particularly useful as components of optical filters which can be tuned by coordinated tuning of the component filters. The tunble FFPI of this invention can be made by fiber bonding or fusion techniques and as a result, are relatively low cost devices.

Abstract: A dynamic change detecting apparatus permits selection of a combination condition of various detection sensitivities and dynamic ranges.

Abstract: A tunable optical cavity constructed from a fixed mirror and a movable mirror is disclosed. A circuit applies an electrical potential between first and second electrically conducting surfaces thereby adjusting the distance between the fixed and movable mirrors. The fixed mirror and the moveable mirror are positioned such that the mirrors form the opposite ends of the optical cavity. The distance between the fixed mirror and the moveable mirror is a function of the applied electrical potential. The thermally induced vibrations are reduced by utilizing an electrical feedback circuit that measures the distance between the mirrors. The feedback circuit dynamically changes the potential between the substrate and the support member so as to reduce fluctuations in the cavity resonance frequency.

Abstract: A method for calibrating tunable optical filters, calibrated tunable filters and devices employing such filters. The method is of particular use with fiber Fabry-Perot tunable filters and more particularly for filters which employ piezoelectric transducers as tuning elements. Sets of calibration coefficients are generated which span the wavelength region and operating temperature range of the filter. Calibrated tunable filters are combined with a means for storing the sets of calibration coefficients and means for correcting wavelength measurements using the sets of coefficients in devices which measure wavelengths of light. The sets of calibration coefficients can also be used to tune the filter to pass a selected wavelength of interest.

Abstract: A sensitive refractive index based detector comprises a first laser cavity (7) and a second laser cavity (7′) each for generating a respective laser light beam. Each laser cavity is defined in a planar waveguide. The surface of the waveguide of the first laser (7) receives a sample to be detected. Light from the two lasers is mixed using a coupling grating (3) and a beat frequency between the lasers dependent upon the refractive index of the substance is measured at a detector (4). Extremely sensitive measurement of small quantities of substance are made possible.

Abstract: Swept-wavelength lasers with accurately calibrated wavelength output which can be very rapidly scanned or swept over a selected wavelength band. The invention provides lasers that generate wavelengths in the 1550 nm range that can be swept over about 50 nm. These swept-wavelength lasers are generally useful as accurately calibrated high power light sources. Calibration is achieved by use of a calibrated reference system. Swept-wavelength lasers are particularly useful as components of sensor interrogator systems which determine wavelengths reflected (or transmitted) by Fiber Bragg Gratings (FBG) in sensor arrays. Swept wavelength lasers of this invention are also generally useful for testing of WDM systems, particularly for their applications to current communication systems. the invention provides lasers, interrogator systems and systems for testing WDM components employing the lasers as a calibrated light source.

Abstract: A method for measuring the wavelength of light, particularly short pulses of light, with improved accuracy comprises passing the light down a backscatter medium such as an optical fiber and detecting and measuring the wavelength of the backscattered light which will have a pulse length of potentially far greater length than that of the initial pulse. The use of interferometers in conjunction with a reference light of known wavelength enables very accurate measurements to be made.

Abstract: A light beam from a laser source is divided into two light beams at a half mirror, and the plane of polarization of one of the two divided light beams is rotated by 90 degrees at a half-wave plate so as to be orthogonal to that of the other of the two divided light beams. The two divided light beams are superimposed and introduced into a sample to be measured in anisotropy. After passing through the sample, the superimposed light beam is split at a polarized light beam splitter into the above two light beams, and the plane of polarization of the other of the two light beam is rotated by 90 degrees at a half-wave plate so as to correspond to that of the one of the two light beams. Then, the two light beams is superimposed again at a half mirror, and an interference pattern of the superimposed light beam is projected on a screen.

Abstract: An interferometer is integrated on an optical chip. The optical chip is formed on a layer of silicon separated from a substrate by a layer of insulating material. The optical chip includes an integrated fiber connector for connecting the optical chip to one or more optical fibers. The fiber connector includes a groove formed in the substrate for receiving an optical fiber and a waveguide for transmitting light to or from the fiber connector. The waveguide includes rib waveguides formed in the layer of silicon and at least one phase modulator for altering the phase of light traveling along one of the rib waveguides. This arrangement forms an interferometer in which light transmitted along different optical paths can be combined and the effective path length of at least one of the optical paths can be altered by the phase modulator.

Abstract: A method and circuit is disclosed wherein two waveguides coupled to an optical resonator are further coupled such that beams propagating therein interfere with one another to provide a desired output response. In one embodiment, multiplexed channels of light can be demultiplexed by the device described heretofore, or alternatively, the phase relationship between these two beams can be altered prior to their being combined to provide, for example, a linearized output response useful in applications such as wavelength locking.

Abstract: A multi-wavelength reference for use in identifying and measuring wavelengths of radiation from an optical device. The invention provides an interferometer to generate a comb of accurately spaced peaks spanning a selected wavelength range combined with a fiber Bragg grating (FBG) of known Bragg wavelength to generate a peak or notch of known wavelength for use in identifying or marking a peak of the comb. The combination provides an accurate multi-wavelength reference useful in particular with high resolution wavelength scanners, such as tunable FFPI. The invention further provides systems for controlling, and/or compensating for, relative shifts in the wavelengths of the interferometer and the FBG as a function of changing temperature.

Abstract: A dynamic change detecting apparatus permits selection of a combination condition of various detection sensitivities and dynamic ranges.

Abstract: A method and circuit is disclosed wherein two waveguides coupled to an optical resonant ring resonator are further coupled such that beams propagating therein interfere with one another to provide a desired output response. In one embodiment, multiplexed channels of light can be demultiplexed by the device described heretofore, or alternatively, the phase relationship between these two beams can be altered prior to their being combined to provide, for example, a linearized output response useful in applications such as wavelength locking. By varying the reflectivity of the FSR and the coupling ratios and/or by varying the phase relationship between the two beams, a variety of desired output responses can be realized.

Abstract: A fiber optic acoustic emission (FOAE) sensor particularly suitable for vibration sensing in a hostile environment has a pair of optical fibers each having an end face. In one embodiment, a hollow tube or core having opposite open ends receives the end faces of the optical fibers. Means are provided for fixing the optical fibers in the hollow core with the end faces facing each other and spaced by a distance from each other in the core. A signal processing unit is connected to the optical fibers for supplying light to, and for receiving light from, the optical fibers and for measuring variations in optical phase which result in changes in the light intensity due to vibrations of the hollow core. The hollow core is fixed in a resonant cylinder, and the resonant cylinder is fixed in a housing to complete the sensor.

Abstract: A method and circuit is disclosed wherein two waveguides coupled to an optical resonant ring resonator are further coupled such that beams propagating therein interfere with one another to provide a desired output response. In one embodiment, multiplexed channels of light can be demultiplexed by the device described heretofore, or alternatively, the phase relationship between these two beams can be altered prior to their being combined to provide, for example, a linearized output response useful in applications such as wavelength locking. By varying the reflectivity of the FSR and the coupling ratios and/or by varying the phase relationship between the two beams, a variety of desired output responses can be realized.

Abstract: A fiber optic fiber Fabry-Perot interferometer diaphragm sensor and method of measurement is provided. A fiber Fabry-Perot interferometer diaphragm sensor (12a, 12b, 12c) includes a base (54a, 54b, 54c) and a diaphragm (52a, 52b, 52c) with an optic fiber (30) coupled under tension between the base (54a, 54b, 54c) and the diaphragm (52a, 52b, 52c). A fiber Fabry-Perot interferometer element (40) is contained within the optic fiber (30) and operates to sense movement of the diaphragm (52a, 52b, 52c). In a particular embodiment, the diaphragm (52a) moves in response to a pressure (P) applied to the diaphragm (52a). In another embodiment, a proof mass (72) is coupled to the diaphragm (52b) such that the diaphragm (52b) moves in response to an acceleration (A). In yet another embodiment, a magnetic body (80) is coupled to the diaphragm (52c) such that the diaphragm (52c) moves in response to a magnetic field (M).

Abstract: An apparatus for interferometric sensing comprises a first broadband switched optical source, a first matched interferometer, a plurality of first sensing interferometers, and a detector. The first matched interferometer contains a first phase modulator. The optical path length difference in each of the first sensing interferometers is approximately equal to the optical path length difference in the first matched interferometer Each of the first sensing interferometers returns an optical interference signal to the detector at a substantially different wavelength The first broadband switched optical source is switched so as to emit optical radiation at wavelengths corresponding to each of the first sensing interferometers at different times.

Abstract: An integrated wavelength monitor and a method for obtaining such a device are disclosed. The device suitable for integration into a laser semiconductor laser module for fiber optic communication can be made in the following way: An interference filter is created directly onto a position sensitive photo detector by depositing a number of layers of different optical transparent materials forming an optical filter. The interference filter may also be created separately and subsequently mounted directly on top of the detector. The integrated position sensitive device (13) is mounted with an angle behind a laser in the same position as a normal power monitor detector. The electrically derived lateral position of light hitting the Position Sensitive Device provided with the interference filter will be dependent of the wavelength of the incident light and this derived position is used for the wavelength monitoring.

Abstract: An interferometric sensor includes a broadband optical source, a depolarizer for depolarizing optical radiation emitted by the broadband optical source, a matched interferometer, a sensing interferometer, and a detector. The matched interferometer contains a phase modulator. The sensor is configured so that the optical path length difference in the sensing interferometer is approximately equal to the optical path length difference in the matched interferometer.