Showing papers on "Fiber Bragg grating published in 1999"

Fiber Bragg Gratings

Abstract: * Provides an overview of Fiber Bragg Gratings (FBGs), from fundamentals to applications* Evaluates the advantages and disadvantages of particular applications, methods and techniques* Contains new chapters on sensing, femtosecond laser writing of FBGs and poling of glass and optical fibers* Includes a special version of the photonic simulator PicWave(tm), allowing the reader to make live simulations of many of the example devices presented in the book This fully revised, updated and expanded second edition covers the substantial advances in the manufacture and use of FBGs in the years since the publication of the pioneering first edition It presents a comprehensive treatise on FBGs and addresses issues such as the merits of one solution over another; why particular fabrication methods are preferred; and what advantages a user may gain from certain techniques Beginning with the principles of FBGs, the book progresses to discuss photosensitization of optical fibers, Bragg grating fabrication and theory, properties of gratings, specific applications, sensing technology, glass poling, advances in femtosecond laser writing of Bragg gratings and FBG measurement techniques In addition to material on telecommunications usage of FBGs, application areas such as fiber lasers and sensors are addressed in greater detail This special version of Picwave is limited to modelling only the passive fibre devices covered in this book However the full PicWave package is capable of modelling other non-linear and active devices such as laser diodes and SOAs as discussed in Chapter 8 More information about PicWave can be found at wwwphotondcom/products/picwavehtm In addition to researchers, scientists, and graduate students, this book will be of interest to industrial practitioners in the field of fabrication of fiber optic materials and devices Raman Kashyap, Canada Research Chair holder on Future Photonics Systems, and Professor at cole Polytechnique, University of Montr al since 2003, has researched optical fibers and devices for over 30 years He pioneered the fabrication of FBGs and applications in telecommunications and photonics * Provides an overview of Fiber Bragg Gratings (FBGs), from fundamentals to applications* Evaluates the advantages and disadvantages of particular applications, methods and techniques* Contains new chapters on sensing, femtosecond laser writing of FBGs and poling of glass and optical fibers* Includes a special version of the photonic simulator PicWave(tm), allowing the reader to make live simulations of many of the example devices presented in the book

Fiber Bragg gratings

Abstract: Since the discovery of photosensitivity in optical fibers there has been great interest in the fabrication of Bragg gratings within the core of a fiber. The ability to inscribe intracore Bragg gratings in these photosensitive fibers has revolutionized the field of telecommunications and optical fiber based sensor technology. Over the last few years, the number of researchers investigating fundamental, as well as application aspects of these gratings has increased dramatically. This article reviews the technology of Bragg gratings in optical fibers. It introduces the phenomenon of photosensitivity in optical fibers, examines the properties of Bragg gratings, and presents some of the important developments in devices and applications. The most common fabrication techniques (interferometric, phase mask, and point by point) are examined in detail with reference to the advantages and the disadvantages in utilizing them for inscribing Bragg gratings. Reflectivity, bandwidth, temperature, and strain sensitivity of the Bragg reflectors are examined and novel and special Bragg grating structures such as chirped gratings, blazed gratings, phase-shifted gratings, and superimposed multiple gratings are discussed. A formalism for calculating the spectral response of Bragg grating structures is described. Finally, devices and applications for telecommunication and fiber-optic sensors are described, and the impact of this technology on the future of the above areas is discussed.

Applications of long-period gratings to single and multi-parameter sensing.

Abstract: Photoinduced long-period gratings are shown as versatile sensors for temperature, axial strain and index of refraction measurements. The principle of operation of such devices is discussed and the application to simultaneous temperature and strain is demonstrated.

Fabrication of long-period fiber gratings by focused irradiation of infrared femtosecond laser pulses

Abstract: We have fabricated long-period fiber gratings by use of a novel technique using focused irradiation of infrared femtosecond laser pulses. We investigate the thermal stability of the fabricated fiber gratings. The values of the loss peak wavelength and the transmittance of the fiber gratings after heat treatment below 500°C are the same as initial values before heat treatment. The fiber gratings that were fabricated by this technique have a high resistance to thermal decay. We propose that this technique mill be useful for fabrication of fiber gratings with a superior aging characteristic.

An efficient inverse scattering algorithm for the design of nonuniform fiber Bragg gratings

Abstract: Presents an efficient method for the design of complex fiber Bragg gratings. The method relies on the synthesis of the impulse response of the grating by means of a differential layer-peeling algorithm. The algorithm developed takes into account all the multiple reflections inside the grating, giving an exact solution to the inverse scattering problem. Its low algorithmic complexity enables the synthesis of long fiber gratings. The method is illustrated by designing several filters with interest for optical fiber communication systems: dispersionless bandpass filters and second- and third order dispersion compensators.

Highly tunable Bragg gratings in single-mode polymer optical fibers

Abstract: A Bragg grating in a single-mode polymer optical fiber (POF) has been created. The novel grating has a length of 1 cm with a reflectivity of 80% and a linewidth of about 0.5 nm. The wavelength tunability of the POF grating by stretching was investigated and a wavelength tunable range of 20 nm has been achieved. Based on the properties of the polymer, we believe that this kind of grating has a wavelength tuning potential of more than 100 nm.

Optical Fiber Sensor Technology

Abstract: List of contributors. Preface. 1. Overview of fiber sensor developments D.A. Jackson. 2. Foundations of optical fiber technology V. Handerek. 3. Sources for optical fiber sensors K.T.V. Grattan. 4. Optical detectors and receivers J.D.C. Jones. 5. Multimode optical fiber sensors G.R. Jones, R.E. Jones, R. Jones. 6. Multimode optical fiber chemical sensors J.O.W. Norris. 7. Single mode optical fiber sensors V. Handerek. 8. Optical fiber modulation techniques for single mode fiber sensors R.P. Tatam. 9. Fiber optic white-light interferometric sensors B.T. Meggitt. 10. Nonlinear effects in optical fibers A.J. Rogers. 11. Distributed fiber optic sensors A.H. Hartog. 12. Schemes for referencing of intensity-modulated optical sensor systems G. Murtaza, J.M. Senior. 13A. Hybrid optical fiber sensors R.C. Spooncer, G.S. Philp. 13B. Optical fiber current measurement A.J. Rogers. 13C. Fiber optic techniques for temperature measurement K.T.V. Grattan. 14. Advanced external fiber optic sensors D.A. Jackson. Index.

Grating resonances in air-silica microstructured optical fibers.

Abstract: We report what is believed to be the first demonstration of optical fiber gratings written in photonic crystal fibers. The fiber consists of a germanium-doped photosensitive core surrounded by a hexagonal periodic air-hole lattice in a silica matrix. The spectra of these gratings allow for a detailed characterization of the fiber. In particular, the gratings facilitate coupling to higher-order leaky modes. We show that the spatial distribution and the effective index of these modes are determined largely by the design of the lattice and that the grating spectra are unaffected by the refractive index surrounding the fiber. We describe these measurements and corresponding simulations and discuss their implications for the understanding of such air-hole structures.

Pd-coated elastooptic fiber optic Bragg grating sensors for multiplexed hydrogen sensing

Abstract: We report a new type of optical hydrogen sensor with a fiber optic Bragg grating (FBG) coated with palladium thin film. The sensing mechanism in this device is based on mechanical stress that is induced in the palladium coating when it absorbs hydrogen. The stress in the palladium coating stretches and shifts the Bragg wavelength of the FBG. Using FBGs with different wavelengths many such hydrogen sensors can be multiplexed on a single optical fiber. Here multiplexing two sensors is demonstrated. Moreover, hydrogen and thermal sensitivities of the sensors were calculated using a simple elastic model. Additionally, to quantify the amount of stress in the palladium film as a function of hydrogen concentration, a novel and very sensitive method was devised and used to detect deflections in a Pd-coated cantilever using an evanescent microwave probe. This stress was in the range of 5.26–8.59×10−7 Pa for H2 concentrations of 0.5–1.4% at room temperature, which is about three times larger than that found in the bulk palladium for the same range of H2 concentrations.

Polarization mode dispersion compensation

Abstract: Polarization mode dispersion in an optical signal transmitted through a waveguide of a communications system is compensated by separating the dispersed signal into components corresponding to principal polarization states. The components are delayed by respective delays differing by a delay increment which is controlled to correspond to the dispersion delay and the delayed components are recombined to provide a dispersion compensated optical output signal. Each of the delays is provided by an chirped Bragg reflector forming part of a delay line, the Bragg reflectors comprising optical fibres with chirped intracore index gratings. Transducers or temperature controllers acting on one of the fibres allows dimensional control of the grating periodicity such that the position of Bragg reflection is variable. Wavelength division multiplexed optical signals are compensated using sampled gratings which allow a common Bragg reflection position for each wavelength.

New and flexible fiber-optic delay-line filters using chirped Bragg gratings and laser arrays

Abstract: We propose a novel kind of radio-frequency filters that are composed by a linearly chirped fiber grating and a laser array. These structures are capable of providing full transfer-function reconfiguration and resonance tunability. A thorough theoretical modeling and operation features are provided along with the experimental demonstration of the proposed features.

Passively Q-switched 0.1-mJ fiber laser system at 1.53 mum.

Abstract: We demonstrate a passively Q-switched fiber laser system generating pulses with as much as 0.1 mJ pulse energy at 1.53µm and > 1kHz repetition rate. This was achieved with a simple MOPA (master oscillator, power amplifier) scheme with a single pump source, realized with large mode area fiber and multiple reflections on a semiconductor saturable absorber mirror (SESAM).

Dependence of fringe spacing on the grating separation in a long-period fiber grating pair.

Abstract: The spectral spacing of the interference fringes formed by a pair of long-period fiber gratings was investigated. The variation of the fringe spacing was measured while the separation between the gratings was changed from 22 to 500 mm. When the grating separation was much longer than the length of the individual grating, the inverse of the fringe spacing became linearly proportional to the grating separation and to the differential effective group index of the fiber. In the third stop band of the grating pair, made along a dispersion-shifted fiber centered at 1.55 µm, the differential effective group index was calculated to be ∼6.4 × 10-3, which is approximately twice the differential effective index of the fiber. The discrepancy between the two indices was observed to decrease with the band order, a phenomenon that is explained by the first-order dispersion of the fiber. The measured interference fringes were not regularly spaced in the frequency domain, but regular spacing is required in wavelength-division multiplexing communication systems. Analysis of the second-order dispersion of the fiber and the grating-induced nonlinear phase shift within grating regions as the factors that induce chirping on the fringe spacing is presented.

Long-period fiber gratings based on periodic microbends.

Abstract: We demonstrate a new type of high-performance long-period fiber grating based on arc-induced periodic microbends. The fabrication method is simple and does not require special fibers. Flexibility in controlling the filter parameters makes it possible to produce arbitrary filter profiles by use of a simple apodization technique, which is difficult to do with conventional long-period gratings.

Fiber Bragg grating cavity sensor for simultaneous measurement of strain and temperature

Abstract: A novel and short (5 mm long) fiber grating based sensor with a fiber grating Fabry-Perot cavity (GFPC) structure was fabricated and tested for simultaneous measurement of strain and temperature. The sensor exhibits unique properties that it possesses two spectral peaks within its main reflection band and the normalized peak power difference, in addition to its peak wavelength shift, changes linearly with strain or temperature. The accuracy of this particular sensor in measuring strain and temperature are estimated to be /spl plusmn/30 /spl mu/s in a range from 0 to 3000 /spl mu/s and /spl plusmn/0.4/spl deg/C from 20/spl deg/C to 60/spl deg/C, respectively.

Bragg grating fast tunable filter for wavelength division multiplexing

Abstract: A Bragg grating fast tunable filter prototype working over a linear tuning range of 45 nm with a maximum tuning speed of 21 nm/ms has been realized. The tunable filter system is based on two piezoelectric stack actuators moving a mechanical device thus compressing an apodized fiber Bragg grating. The filter allows both traction and compression and can work in transmission and in reflection. It is designed to work with a channel spacing of 100 GHz according to the ITU specifications for wavelength division multiplexing systems.

Electrically tunable power efficient dispersion compensating fiber Bragg grating

Abstract: Novel devices only offer reasonable telecommunication solutions when they can be packaged and manufactured efficiently and at low cost. We demonstrate such a compact and power efficient tunable dispersion compensating fiber Bragg grating (FBG) device. The device relies on a distributed on-fiber thin-film heater deposited onto the outer surface of an unchirped FBG. Current flowing though the thin film generates resistive heating that is governed by the thickness profile of the metal film. A chirp in the grating is obtained by using a coating whose thickness varies with position along the length of the grating in a prescribed manner; the chirp rate is adjusted by varying the applied current. Using an electrical power of less than 1 W in a packaged device, we demonstrate a linearly chirped Bragg grating in which the dispersion is continuously tuned from -300 to -1350 ps/nm, with an average deviation from linearity of approximately 10 ps.

Fiber Bragg Grating Temperature Sensor with Controllable Sensitivity

Abstract: We demonstrate a fiber Bragg grating (FBG) sensor with controllable sensitivity by connecting two metal strips that have different temperature-expansion coefficients. By changing the lengths of the metal strips we successfully controlled and improved the temperature sensitivity to 3.3 times of that of bare FBG.

A fiber optic sensor for transverse strain measurement

Abstract: A fiber optic sensor capable of measuring two independent components of transverse strain is described. The sensor consists of a single Bragg grating written into high-birefringent, polarization-maintaining optical fiber. When light from a broadband source is used to illuminate the sensor, the spectra of light reflected from the Bragg grating contain two peaks corresponding to the two orthogonal polarization modes of the fiber. Two independent components of transverse strain in the core of the fiber can be computed from the changes in wavelength of the two peaks if axial strain and temperature changes in the fiber are zero or known. Experiments were performed to determine the response of the sensor by loading an uncoated sensor in diametral compression over a range of fiber orientations relative to the loading. The results of these experiments were used with a finite element model to determine a calibration matrix relating the transverse strain in the sensor to the wavelength shifts of the Bragg peaks. The performance of the sensor was then verified by measuring the transverse strains produced by loading the fiber in a V-groove fixture.

Bragg grating pressure sensor

Abstract: A fiber grating pressure sensor includes an optical sensing element (20, 600) which includes an optical fiber (10) having a Bragg grating (12) impressed therein which is encased within and fused to at least a portion of a glass capillary tube (20) and/or a large diameter waveguide grating (600) having a core and a wide cladding and which has an outer transverse dimension of at least 0.3 mm. Light (14) is incident on the grating (12) and light (16) is reflected from the grating (12) at a reflection wavelength μ1. The sensing element (20, 600) may be used by itself as a sensor or located within a housing (48, 60, 90, 270, 300). When external pressure P increases, the grating (12) is compressed and the reflection wavelength μ1 changes.

Bragg solitons in the nonlinear Schrödinger limit: experiment and theory

Abstract: We present a detailed experimental and theoretical study of nonlinear pulse propagation in an apodized fiber Bragg grating. In particular, we consider the generation and the propagation of Bragg solitons with a frequency content just outside the grating’s photonic bandgap, where, thanks to the apodization, the transmissivity of the grating is high and the strong grating dispersion dominates. We demonstrate the efficient launching of Bragg solitons with velocities as low as 50% of that in untreated fiber. The experimental results agree well with numerical simulations obtained by solving the full nonlinear coupled-mode equations that govern the experimental geometry. We also show that, for most parameters, the experimental results are in very good agreement with a nonlinear-Schrodinger-equation model. Thus many of the results known for the nonlinear Schrodinger equation can be brought to bear on our results.

Sampled fiber grating based-dispersion slope compensator

Abstract: We propose a novel design for a compact dispersion slope compensator based on sampled fiber Bragg gratings. By chirping the sample function in a sampled grating, we show that the dispersion slope can be controlled to match that of current transmission fibers. Interleaving several sampled gratings provides an effective technique to reduce UV-induced refractive index requirements to readily achievable levels.

Fiber laser hydrophone array

Abstract: In recent years growing interest has surrounded the development of fiber laser sensors (FLS). This is due to their ultra high sensitivity to temperature and strain as well as their ability to be multiplexed along a single fiber using WDM techniques. It is their extreme sensitivity that has led to them being considered as acoustic pressure sensors rather than standard fiber Bragg gratings. The work presented here describes the development of an array of FLS configured as hydrophones. We discuss the design of the single mode fiber laser used throughout our system; comparing examples based upon distributed Bragg reflectors (DBR) and distributed feedback (DFB). In addition we discuss both the theoretical and experimental acoustic sensitivity enhancements obtained by the application of an elasto-plastic coating to the FLS. The array configuration is described, as is the heterodyne interrogation scheme using an unbalanced Mach-Zehnder interferometer with WDM channel selection. Results from the measurement of the minimal detectable acoustic signal of a bare fiber laser are shown to be -69 dB re.Pa/(root)Hz at 1 kHz when using a 200 m path imbalanced readout interferometer. Further gains in the sensitivity due to the application of various coatings are reported, as is a full characterization of an array of fiber laser hydrophones. Finally we discuss the future research of the FLS, and the areas in which the technology is particularly applicable.

Compression-tuned Bragg grating and laser

Abstract: A compression-tuned Bragg grating includes a tunable optical element 20, 600 which includes either an optical fiber (10) having at least one Bragg grating (12) impressed therein encased within and fused to at least a portion of a glass capillary tube (20) or a large diameter waveguide grating (600) having a core and a wide cladding. Light (14) is incident on the grating (12) and light (16) is reflected at a reflection wavelength .lambda. 1. The tunable element 20, 600 is axially compressed which causes a shift in the reflection wavelength of the grating (12) without buckling the element. The shape of the element may be other geometries (e.g., a "dogbone" shape) and/or more than one grating or pair of gratings may be used and more than one fiber (10) or core (612) may be used. At least a portion of the element may be doped between a pair of gratings (150, 152), to form a compression-tuned laser or the grating (12) or gratings (150, 152) may be constructed as a tunable DFB laser. Also, the element (20) may have an inner tapered region (22) or tapered (or fluted) sections (27). The compression may be done by a PZT, stepper motor or other actuator or fluid pressure.

Simultaneous measurement of strain and temperature by use of a single-fiber Bragg grating and an erbium-doped fiber amplifier

Abstract: We propose and demonstrate a novel sensor by using a single-fiber Bragg grating that can simultaneously measure strain and temperature with the aid of an erbium-doped fiber amplifier. By using a linear variation in the amplified spontaneous emission power of the erbium-doped fiber amplifier with temperature, we determine the temperature. By subtracting the temperature effect from the fiber Bragg grating Bragg wavelength shift, we determine the strain. Experiments show rms deviations of 18.2 µe and 0.7 °C for strain and temperature, respectively.

Static fiber-Bragg grating strain sensing using frequency-locked lasers

Abstract: Novel and highly sensitive static strain interrogation technique is demonstrated, where the sensing element is a fiber-Bragg grating (FBG) and the light source is a frequency-locked diode laser. Locking the laser frequency to the center of an absorption line (atomic line of potassium in our experiment) eliminates the slow frequency drift of the laser. The stabilized laser source is used to measure low frequency ("static") strain, with a sensitivity of 1.2 nanostrain//spl radic/Hz rms at 1.5 Hz.

Dynamic dispersion compensation in a 10-Gb/s optical system using a novel voltage tuned nonlinearly chirped fiber Bragg grating

Abstract: We experimentally demonstrate dynamic dispersion compensation using a novel nonlinearly chirped fiber Bragg grating in a 10-Gb/s system. A single piezoelectric transducer continuously tunes the induced dispersion from 300 to 1000 ps/nm. The system achieves a bit-error rate=10/sup -9/ after both 50 and 104 km of single-mode fiber by dynamically tuning the dispersion of the grating between 500 and 1000 ps/nm, respectively. The power penalty after 104 km is reduced from 3.5 to <1 dB.