Showing papers on "Fiber Bragg grating published in 1993"
TL;DR: In this paper, a photolithographic method is described for fabricating refractive index Bragg gratings in photosensitive optical fiber by using a special phase mask grating made of silica glass.
Abstract: A photolithographic method is described for fabricating refractive index Bragg gratings in photosensitive optical fiber by using a special phase mask grating made of silica glass. A KrF excimer laser beam (249 nm) at normal incidence is modulated spatially by the phase mask grating. The diffracted light, which forms a periodic, high‐contrast intensity pattern with half the phase mask grating pitch, photoimprints a refractive index modulation into the core of photosensitive fiber placed behind, in proximity, and parallel, to the mask; the phase mask grating striations are oriented normal to the fiber axis. This method of fabricating in‐fiber Bragg gratings is flexible, simple to use, results in reduced mechanical sensitivity of the grating writing apparatus and is functional even with low spatial and temporal coherence laser sources.
953 citations
TL;DR: The use of a fiber Fabry–Perot filter for detecting the wavelength shift of a Fiber Bragg grating sensor or network of sensor elements along a common fiber path is described.
Abstract: The use of a fiber Fabry–Perot filter for detecting the wavelength shift of a fiber Bragg grating sensor or network of sensor elements along a commonfiber path is described. Results obtained by using a system with four sensor elements are presented.
798 citations
TL;DR: This system is shown to be capable of resolving sub-microstrain changes in the quasi-static strain applied to a grating and has a resolution of ~6 x 10(-3) microstrain/ radicalHz at a strain perturbation frequency of 1 Hz.
Abstract: The operation of a fiber Bragg grating strain sensor system that uses interferometric determination of strain-induced wavelength shifts and incorporates a reference channel to compensate for random thermal-induced drift in the output is described. This system is shown to be capable of resolving sub-microstrain changes in the quasi-static strain applied to a grating and has a resolution of ~6 x 10(-3) microstrain/ radicalHz at a strain perturbation frequency of 1 Hz.
235 citations
TL;DR: In this article, Boron codoped germanosilcate fibres are shown to be highly photosensitive and a UV written 1.53 μm Bragg grating with 95% reflectivity and a 1.1nm bandwidth is formed with a UV intensity as low as 1W/cm2 in only 10 min.
Abstract: Boron codoped germanosilcate fibres are shown to be highly photosensitive. A UV written 1.53 μm Bragg grating with 95% reflectivity and a 1.1nm bandwidth is formed with a UV intensity as low as 1W/cm2 in only 10 min.
220 citations
Patent•
02 Nov 1993TL;DR: In this article, the authors described a novel optical fiber devices (amplifiers and lasers) consisting of one or more optical "cavities", depending on the type of device.
Abstract: Novel optical fiber devices (amplifiers and lasers) are disclosed. The devices comprise one or more optical "cavities", depending on the type of device. The cavities typically are formed by means of in-line refractive index gratings in a length of silica-based optical fiber. The gratings typically have peak reflectivity of at least 98%. Use of such cavities enables CW pumping of the devices, making the devices suitable for use in optical fiber communication systems. In an exemplary embodiment the device is a Raman amplifier for 1.3 μm signal radiation, and in another exemplary embodiment the device is a Raman laser having an output suitable for pumping an Er-doped fiber amplifier. An exemplary pump radiation source is a laser diode-pumped CW Nd:YAG laser.
201 citations
TL;DR: In this paper, a transmission phase grating was used to write a 94% reflectivity in-fibre index grating in a photosensitive optical fiber with a single UV laser beam at 242 nm.
Abstract: A transmission phase grating was used to write a 94% reflectivity in-fibre index grating in a photosensitive optical fibre with a single UV laser beam at 242 nm. This method offers the possibility of high-volume production of in-fibre gratings.
190 citations
TL;DR: In this paper, a tunable erbium doped fiber laser which utilizes a broadband mirror and an intracore Bragg grating reflector in side-pump configuration is described.
Abstract: The development of a fiber laser sensor system which permits efficient interrogation of Bragg grating sensors is reported. A tunable erbium doped fiber laser which utilizes a broadband mirror and an intracore Bragg grating reflector in side-pump configuration is described. The wavelength of the laser oscillation is determined by the Bragg grating, which is remotely located and used as a strain sensor. This arrangement is used in conjunction with a passive wavelength demodulation system (WDS) to form a self-contained fiber laser strain sensor system, allowing efficient interrogation of the Bragg sensor. This device provides interrupt-immune sensing of static and dynamic strains with a bandwidth of 13.0 kHz. >
170 citations
TL;DR: In this paper, a unified theory that relates optical phase changes to applied strain and temperature fields in structurally embedded interferometric optical fiber sensors of all types, as applied to Mach-Zehnder, Michelson, intrinsic and extrinsic Fabry-Perot, polarimetric, dual-mode, and Bragg grating sensors, with resistance strain gauge concepts and the theory of elasticity solutions, is theoretically explored.
Abstract: Using the unified theory that relates optical phase changes to applied strain and temperature fields in structurally embedded interferometric optical fiber sensors of all types, as applied to Mach-Zehnder, Michelson, intrinsic and extrinsic Fabry-Perot, polarimetric, dual-mode, and Bragg grating sensors, with resistance strain gauge concepts and the theory of elasticity solutions, the response of optical fiber sensors that are embedded in transversely isotropic composite materials is theoretically explored. The concepts of transverse strain sensitivity and thermal apparent strain are carefully defined for embedded optical fiber sensors, and it is found that errors resulting from these effects completely dominate the desired sensor response for all sensors except the extrinsic Fabry-Perot. Conditions that minimize these errors are presented. The theory of elasticity solutions used in this analysis encompasses six different thermomechanical loading conditions. Comparisons to Buffer and Hocker's model are also presented.
157 citations
TL;DR: In this article, an erbium fiber amplifier with a highly flattened gain spectrum was demonstrated using an all-fibre photosensitive Bragg grating, achieving an ASE spectrum flattened to within ± 0.5 dB over a bandwidth of 35 nm in the 1550 nm window.
Abstract: An erbium fibre amplifier with a highly flattened gain spectrum is demonstrated for the first time using an all fibre photosensitive Bragg grating. An ASE spectrum flattened to within ±0.5 dB over a bandwidth of 35 nm in the 1550 nm window is achieved with a 3 mm long radiation coupling Bragg fibre grating.
155 citations
TL;DR: In this paper, a single pulse of high power 249 nm excimer laser light was used to photoinduce point-by-point each individual index element forming the grating.
Abstract: Optical fibre Bragg reflectors have been fabricated using a single pulse of high power 249 nm excimer laser light to photoinduce point-by-point each individual index element forming the grating. Bragg reflectors with a length of 360 μm and reflectivity of 70% have been made.
153 citations
TL;DR: A fiber-optic strain gauge system for use in structural monitoring and smart-structure applications is described, which permits the measurement of both static and dynamic strains with a noise-limited resolution.
Abstract: A fiber-optic strain gauge system for use in structural monitoring and smart-structure applications is described. The strain gauge uses a fiber-optic Bragg grating sensor to measure strain and a passive, wavelength demodulation system to determine the wavelength of the narrow-band, backreflected spectrum from the grating sensor. The fiber-optic strain gauge system permits the measurement of both static and dynamic strains with a noise-limited resolution of 0.44 microstrain/√Hz, a measurement dynamic range of 27.8 dB, and a bandwidth of 250 Hz.
Patent•
27 Sep 1993
TL;DR: A measurement system for fiber sensors includes a broadband light source providing continuous light which is launched into a fiber 20 having a plurality (or string) of Bragg grating sensors 24, 28, 34.
Abstract: A measurement system for fiber sensors includes a broadband light source 11 providing continuous light which is launched into a fiber 20 having a plurality (or string) of Bragg grating sensors 24, 28, 34. Each sensor has a predetermined central reflection wavelength which shifts as a function of applied strain. Reflected light 40 from the sensors 24, 28, 34 are fed to a plurality of optical bandbass filters 50, 64, 78, each having a monotonic region in a passband corresponding to one of the sensors. Each monotonic region transmits the reflected wavelength from a corresponding sensor. Light 52, 66, 80 is passed from the filters 50, 64, 78 to optical detectors 54, 68, 82 each providing an electrical signal having a magnitude related to transmission of the filter at the reflection wavelength of the sensor. Optional demodulators 58, 72, 86 are connected to each of the detectors 54, 68, 82 if the light source 10 is modulated. Such modulation provides noise immunity and allows demultiplexing of several strings of sensors.
TL;DR: In this paper, the integrated operation of a 16*1 WDM source with distributed Bragg reflector (DBR) lasers and electroabsorption modulators has been demonstrated by using repeated holographic exposures and wet chemical etching, 16 different wavelengths from 1.544 to 1.553 mu m with an average channel spacing of 6 AA.
Abstract: The integrated operation of a 16*1 wavelength-division-multiplexed (WDM) source with distributed Bragg reflector (DBR) lasers and electroabsorption modulators has been demonstrated. By using repeated holographic exposures and wet chemical etching, 16 different wavelengths from 1.544 to 1.553 mu m with an average channel spacing of 6 AA are obtained. A high-performance combiner is used to obtain a very uniform coupling into the single-output waveguide, and with the integration of an optical amplifier an average optical power of -8 dBm per channel is coupled into a single-mode fiber. >
Patent•
27 Dec 1993
TL;DR: In this article, an endoscopic light delivery system for delivering light to tissue includes a laser source for generating light, and fiber optics encased in a plastic buffer for conveying the light generated by the laser source.
Abstract: An endoscopic light delivery system for delivering light to tissue includes a laser source for generating light. Fiber optics encased in a plastic buffer are optically coupled to the laser source for conveying the light generated by the laser source. A tip member secured to the fiber optics positions a mirror adjacent to the light delivery end of the fiber optics. The mirror redirects light conveyed by the fiber optics in a direction lateral to the fiber optics. A heat resistant ring encircling the fiber optics near the light delivery end shields the fiber optics from heat to prevent the plastic buffer near the light delivery end from melting. A lateral extension of the tip member spaces the mirror and fiber optics away from tissue. A band with a circumferential groove encircles the light receiving end of the fiber optics. A connector having a bore is capable of receiving the light receiving end of the fiber optics in the bore and locking the band within the bore by engaging the groove with a locking device.
TL;DR: In this article, a new technique for the interrogation of in-fibre Bragg grating sensors using an acousto-optic tunable filter (AOTF) is demonstrated.
Abstract: A new technique for the interrogation of in-fibre Bragg grating sensors using an acousto-optic tunable filter (AOTF) is demonstrated. The scheme involves frequency shift keying (FSK) of the RF drive to the AOTF to track the wavelength shifts of a Bragg grating. Experimental results are presented for temperature measurement. This technique provides a frequency-agile system, capable of rapid, random access and very wide tuning range.
TL;DR: In this article, a technique for the detection of wavelength shifts in wavelength-encoded fiber Bragg sensors, which is capable of interrogating several sensors on a common fibre path using a mode-locked laser principle, is described.
Abstract: A technique for the detection of wavelength shifts in wavelength-encoded fibre Bragg grating sensors, which is capable of interrogating several sensors on a common fibre path using a mode-locked laser principle, is described. Preliminary results obtained using two sensor elements are presented.
TL;DR: The photoinduced periodic refractive-index perturbations have been observed directly with an optical microscope and are shown to have the same period as the phase mask and to be highly localized on one side, the irradiated side of the fiber core-cladding boundary.
Abstract: Optical fiber Bragg reflectors have been written by irradiating the fiber from the side through a phase mask with a single pulse of high-power 249-nm excimer-laser light. Efficient tapping of light to the radiation modes has been achieved for light at wavelengths shorter than the Bragg wavelength. The photoinduced periodic refractive-index perturbations have been observed directly with an optical microscope and are shown to have the same period as the phase mask and to be highly localized on one side, the irradiated side of the fiber core–cladding boundary.
TL;DR: In this article, the authors report the fabrication of low loss (<0.2 dB) fiber Bragg gratings of 10 nm reflection bandwidth, and of 19 nm bandwidth lossy gratings.
Abstract: We report the fabrication of low loss (<0.2 dB) fiber Bragg gratings of 10 nm reflection bandwidth, and of 19 nm bandwidth lossy gratings. With this technology we also demonstrate the direct writing of channel waveguides in commercial germania‐doped wafers without the use of photoresist and etching.
Patent•
AT&T1
TL;DR: In this article, a method for making Bragg gratings in glass optical fibers, or other glass optical waveguides, which is relatively insensitive to perturbations in the actinic light used for processing, is described.
Abstract: The invention involves a method for making Bragg gratings in glass optical fibers, or other glass optical waveguides (10), which is relatively insensitive to perturbations in the actinic light used for processing. This method is suitable for mass production and lends itself well to the manufacturing environment. The inventive method involves first providing an optical phase grating (20). An interference pattern is generated by impinging a single light beam (30) on the grating. The optical waveguide to be processed is exposed to this interference pattern, leading to the formation of a Bragg grating in the waveguide.
TL;DR: In this paper, the operation of single and multipoint active fiber sensors for both strain and temperature measurements is reported, where the primary advantage of an active sensor over a passive sensor is a significant increase in signal-to-noise ratio.
Abstract: The operation of single- and multipoint active fiber sensors for both strain and temperature measurements is reported. An active fiber source consists of a pair of wavelength-matched Bragg gratings formed in a rare earth doped fibre, and when, optically pumped, lase in a narrow bandwidth around the Bragg wavelength. The primary advantage of an active sensor over a passive sensor is a significant increase in signal-to-noise ratio. >
TL;DR: In this article, the authors used real time measurements of the spectral transmission, of the fwhm bandwidth and of the resonance wavelength of the Bragg gratings to estimate the refractive index change photoinduced in the core of the fiber.
Patent•
01 Feb 1993
TL;DR: In this paper, a tunable optical waveguide laser arrangement is described, where two end reflectors are situated in the waveguide, each at one of the axially spaced ends thereof and extending normal to the axis to delimit a laser cavity, constituted by a Bragg grating consisting of a multitude of axially consecutive grating elements constituted by periodic refractive index perturbations with a given periodicity.
Abstract: A tunable optical waveguide laser arrangement includes a solid optical waveguide capable of guiding light along an axis between axially spaced ends thereof and being at least in part of an excitable material that emits light in response to stimulation by light. Stimulating light is launched into the waveguide for axial propagation therein and attendant emission of light by the excitable material. Two end reflectors are situated in the waveguide, each at one of the axially spaced ends thereof and extending normal to the axis to delimit a laser cavity. Each of the reflectors is constituted by a Bragg grating consisting of a multitude of axially consecutive grating elements constituted by periodic refractive index perturbations with a given periodicity. The length of the cavity, the peak reflectivity of the Bragg gratings and the gain of the excitable material are so coordinated with one another as to enable lasing in only a single longitudinal mode. The length of that portion of the optical waveguide that incorporates the two Bragg gratings and an intervening region of the optical waveguide is uniformly controlledly varied with attendant continuous tuning of the laser output wavelength without longitudinal mode hopping.
TL;DR: An active, single-frequency, polarimetric, Bragg-grating fiber-laser strain sensor that yields a single beat frequency that varied at a rate of -4.1 MHz/mstrain for linear strain and -0.37 MHz/(deg/cm) for torsional strain is reported.
Abstract: We report the operation of an active, single-frequency, polarimetric, Bragg-grating fiber-laser strain sensor. The short Bragg-grating fiber-laser design limited lasing to two orthogonal polarization modes that, when optically mixed, yielded a single beat frequency that varied at a rate of -4.1 MHz/mstrain for linear strain and -0.37 MHz/(deg/cm) for torsional strain.
TL;DR: Optical low-coherence reflectometry is used for the first time to investigate distributed feedback structures within a single-mode fiber as discussed by the authors, which allows the location, the length, and the coupling coefficient of the grating to be determined precisely.
Abstract: Optical low-coherence reflectometry is used for the first time to investigate distributed-feedback structures within a single-mode fiber. This nondestructive method allows the location, the length, and the coupling coefficient of the grating to be determined precisely. >
TL;DR: The observed dependence of index modulation on time and intensity does not agree with the predictions of a model based on depletion of a defect population by one-photon absorption.
Abstract: We have written Bragg gratings of as much as 94% reflectance in germanium-doped optical fiber by two-beam interference of 244-nm continuous-wave UV light. We measured grating reflectance as a function of exposure time for UV light intensities ranging from 1.5 to 47 W/cm2. The observed dependence of index modulation on time and intensity does not agree with the predictions of a model based on depletion of a defect population by one-photon absorption.
Patent•
26 Apr 1993TL;DR: In this paper, the authors defined the optical resonant cavity of an optical communication system, which is at least partially defined by a distributed Bragg reflector (10, 20) formed in a portion of the core.
Abstract: An article, such as an optical communication system, which includes a laser formed in an optical waveguide or optical fiber having a rare-earth-doped core or core portion. In one embodiment, the optical resonant cavity of the laser is at least partially defined by a distributed Bragg reflector (10, 20) formed in a portion of the core. In contrast to the prior art, the length of the optical resonant cavity is about 5 cm or less.
TL;DR: In this paper, a technique for multiplexing Bragg gratings in a fiber laser arrangement is described, which has successfully been used to multiplex two and three Bragg grating gratings with very little crosstalk.
Abstract: A technique for multiplexing Bragg gratings in a fiber laser arrangement is described. This technique has successfully been used to multiplex two and three Bragg gratings with very little crosstalk. The Bragg grating laser sensors were used to measure both strain and temperature. Independent strain and temperature tuning of the gratings shows no crosstalk. >
30 Dec 1993
TL;DR: In this article, the detection of wavelength shifts of fiber Bragg sensors based on the use of a tunable bandpass filter, interferometric detection, and active laser configurations is described.
Abstract: Techniques for the detection of wavelength shifts of fiber Bragg grating sensors based on the use of a tunable bandpass filter, interferometric detection, and active laser configurations are described. The methods used to multiplex several sensors along a single fiber using these approaches are also discussed, and results presented.
Patent•
AT&T1
TL;DR: In this article, an optical filter is adapted for selectively transmitting electromagnetic radiation within a wavelength passband bounded by a pair of stop bands of relatively low transmissivity, and the filter includes at least one Bragg grating formed in a waveguiding optical medium.
Abstract: An optical filter is adapted for selectively transmitting electromagnetic radiation within a wavelength passband bounded by a pair of stop bands of relatively low transmissivity. The filter includes at least one Bragg grating formed in a waveguiding optical medium. The Bragg grating has at least one wavelength band of relatively low transmissivity. This low-transmissivity band corresponds to at least a portion of one of the stop bands of the filter.