Showing papers on "Fiber Bragg grating published in 1998"

Analysis of the response of long period fiber gratings to external index of refraction

Abstract: This paper demonstrates that the change in wavelength of a long period fiber grating attenuation band with changes in external index of refraction can be enhanced by proper selection of the grating period. We calculate and experimentally verify that the wavelength shift caused by changing the external index from n=1 to n=1.44 of the attenuation band which appears in the 1400-1600 nm region in a 200-/spl mu/m period grating is four times that in a 350-/spl mu/m period grating. Changes in the spectrum over a wavelength range from 1100 to 1600 nm and 1

High-spatial-resolution distributed strain measurement in optical fiber with rayleigh scatter.

Abstract: A method of measuring strain over 30-cm intervals to an accuracy of10 microstrain in unaltered low-loss communications-grade single-modeoptical fiber is presented. The method uses a tunable external cavity diode laser to measure the reflected intensity of a reflector-fiber system as a function of wavelength. This measurement is performed with no strain applied to the fiber to produce a reference and then again after a strain has been induced. Cross correlation of the Rayleigh scatter spectra from a selected section of fiber in the strained and unstrained states determines the spectral shift resulting from the applied strain.

Interrogation of fiber grating sensor arrays with a wavelength-swept fiber laser

Abstract: We demonstrate a novel application of a wavelength-swept fiber laser to fiber Bragg grating sensor-array interrogation. The laser provides high signal powers of >3 mW with <0.1-nm spectral resolution over a 28-nm wavelength span. Using time-interval counting, we demonstrate static-dynamic strain measurements with a resolution of 0.47mu? rms at a sampling rate of 250 Hz.

Sinc-sampled fiber Bragg gratings for identical multiple wavelength operation

Abstract: Through a periodic sine modulation of the refractive index-profile in fiber Bragg gratings (FBGs), we demonstrate gratings with multiple equally spaced and identical wavelength channels. We show 10-cm-long gratings with 4, 8, and 16 identical uniform wavelength channels separated by the ITU spacing of 100 GHz and a 22.5-cm-long grating with four identical dispersion compensating channels with a 200-GHz separation designed to dispersion compensate 80-km data transmission through standard fiber at 1.55 /spl mu/m.

Switchable optical components

Abstract: This invention relates to a number of components, devices and networks involving integrated optics and/or half coupler technology, all of which involve the use of electronically switchable Bragg grating devices and device geometries realized using holographic polymer/dispersed liquid crystal materials. Most of the components and devices are particularly adapted for use in wavelength division multiplexing (WDM) systems and in particular for use in switchable add/drop filtering (SADF) and wavelength selective crossconnect. Attenuators, outcouplers and a variety of other devices are also provided.

Optical all-pass filters for phase response design with applications for dispersion compensation

Abstract: Lossless all-pass optical filters are introduced, which can approximate any desired phase response while maintaining a constant, unity amplitude response. Architectures using cascade and lattice structures based on ring resonators and cavities defined by reflectors are discussed. Two applications are presented: 1) for fiber dispersion compensation and 2) for compensation of the nonlinear phase response of narrow bandpass optical filters such as thin-film or Bragg grating filters. All orders of dispersion can be compensated in principle, and the filters are periodic so multiple channels can be compensated with a single device. The architectures are very compact compared to alternatives such as chirped Bragg gratings.

Gain characteristics of tellurite-based erbium-doped fiber amplifiers for 1.5-µm broadband amplification

Abstract: The signal-gain characteristics of tellurite-based erbium-doped fiber amplifiers are clarified based on spectroscopic properties and signal-gain measurements. The potential of tellurite-based erbium-doped fiber for use as a broadband light source is also described.

Tunable optical filters for dense WDM networks

Abstract: WDM is currently taking over as the leading technology in point-to-point transmission links. For optical implementation of WDM networks, logical functionalities such as wavelength (channel) selection should be carried out in the wavelength domain; thus, the development of dynamic optical devices is required. One key device is a tunable optical filter. Important features of such a filter include low insertion loss, narrow bandwidth, high sidelobe suppression, large dynamic range, fast tuning speed, a simple control mechanism, small size, and cost effectiveness. Here, an extensive overview of the different technologies used to produce tunable optical filters is presented. Among them, fiber filters such as fiber Bragg gratings and fiber Fabry Perot are the most commercialized, yet inherently limited in their dynamic speeds. For high demanding dynamics, micro-machined and acousto-optic filters can offer a good solution for microsecond tuning speeds. Faster tunable devices, in nanosecond tuning speeds, might emerge out of microresonators, electrooptic filters, and active DBR filters.

Flexural beam-based fiber Bragg grating accelerometers

Abstract: A flexural beam is utilized as the primary transduction mechanism for demonstrating a series of fiber Bragg grating (FBG) accelerometers. The fully packaged FBG accelerometers reported in this work have many desirable features including good acceleration sensitivity (212.5 /spl mu//spl epsiv//g), high resonant frequencies (on the order of 1 kHz), very low cross-axis sensitivity (<1% of the primary axial responsivity), and low noise (/spl sim/1 mg//spl radic/(Hz) near 1 Hz). Arrays of such devices can be utilized in a variety of applications, including structural monitoring. Closed-form analytical formulas describing the resonant frequency and responsivity of the FBG accelerometer are provided which may be utilized to tailor the sensor performance to specific applications.

Fiber Bragg Gratingを用いた水中音波の検出

Abstract: A fiber Bragg grating (FBG), which is formed in a fiber core by introducing a periodic variation of the refractive index reflects selectively a particular wavelength of light due to the Bragg reflection. The reflected optical power is modulated if sound pressure is applied to the FBG. Using the FBG which has such a feature we made the fundamental experiments on the detection of underwater sound. Good linearity is obtained under various conditions with the insertion of optical isolators that avoid the fluctuation of detected output due to the Fabry-Perot interference effect between the FBG and the various facets. The sensitivity of detection is maximized if the slope of the curve in the transmittance-wavelength characteristics is steepest at the operating wavelength. Simultaneous multiplex detection is made possible by wavelength division multiplexing with two FBGs in series connection.

Ring-doped cladding-pumped single-mode three-level fiber laser

Abstract: We propose and theoretically analyze three-level cladding-pumped fiber lasers in which the laser-active dopant is placed in a ring around a single-mode core. A ring-doped laser can work efficiently at wavelengths with strong small-signal absorption. This is otherwise difficult in a cladding-pumped fiber. Moreover, ring doping makes the laser less sensitive to quenching of the laser-active dopant and to excited-state absorption of the lasing field. In simulations of a Yb3+-doped fiber laser, ring doping increased the slope efficiency to 62%, up from 13% for a conventional core-doped fiber.

Method and apparatus for determining the shape of a flexible body

Abstract: A fiber optic measurement system capable of greatly improving the cost, complexity, and efficiency with which flexible body shape estimates are made. The fiber optic shape measurement system uses Bragg grating sensor technology and time, spatial, and wavelength division multiplexing, to produce a plurality of strain measurements along one fiber path. Using a plurality of fibers, shape determination of the body and the tow cable can be made with minimal ambiguity. Also disclosed is a method to resolve the body shape based on strain-to-shape structural analysis. Possible applications include, but are not limited to, sensing the shape and position of flexible bodies, aid in improving the efficiency of existing acoustic surveying processing techniques, and related applications in geophysical prospecting.

High-power diode-cladding-pumped Tm-doped silica fiber laser

Abstract: The operation of a diode-pumped Tm-doped silica fiber laser that uses the cladding-pumping arrangement to produce high-power cw output at wavelengths near 2 µm is reported. We obtained a maximum output power of 5.4 W at a slope efficiency of 31% with respect to the launched pump power at a total optical-to-optical efficiency of 22%. The fiber-laser output wavelength was tuned between 1.880 and 2.033 µm by adjustment of the fiber length, with >4 W of power obtainable from 1.94 to 2.01 µm. Self-pulsations detected in the output from the double-clad fiber laser may indicate the presence of ion-clustering effects.

A genetic algorithm for the inverse problem in synthesis of fiber gratings

Abstract: A new method for synthesis of fiber gratings with advanced characteristics is proposed. By combining the Runge-Kutta method for calculating the reflection spectrum of a fiber grating and a genetic algorithm, we obtain a promising method for the synthesis. Compared to other methods, the proposed method facilitates the task of weighting the different requirements to the filter spectrum. In addition, the method is general, and would thus be useful for other inverse problems.

Optimization of apodized linearly chirped fiber gratings for optical communications

Abstract: The dispersion characteristics of apodized, linearly chirped fiber Bragg gratings and their potential as dispersion compensators have been studied systematically. It is shown that the positive hyperbolic-tangent profile results in an overall superior performance, as it provides highly linearized time-delay characteristics with minimum reduction in the linear dispersion. To compensate for the linear dispersion of 100 km of standard telecom fiber over certain bandwidth (in nanometers), the required grating length is 19.24 cm/nm.

WDM optical communication systems with wavelength stabilized optical selectors

Abstract: The present invention provides a wavelength division multiplexed optical communication system with dynamically stabilized wavelength selectors. To accurately correlate the wavelength of a wavelength selector to the wavelength emitted by an optical transmission source, the present invention uses an optical detector and feedback loop to optimize the wavelength of an optical selection element in accordance with a wavelength of an incident optical channel. In one embodiment, the optical selection element is a Bragg grating associated with a grating wavelength controller, such as a temperature regulator or strain tuning system, to adjust the wavelength band of maximum reflectivity of the grating. The feedback loop communicates with the optical detector and the wavelength controller to modify the grating's reflection wavelength band in accordance with the wavelength of an incident optical channel.

Distributed measurement of static strain in an optical fiber with multiple bragg gratings at nominally equal wavelengths.

Abstract: The Fourier transform relationship between the reflected light froma Bragg grating and the complex spatial modulation of the Bragg grating is used to produce a distributed strain sensing system A tunable external cavity diode laser along with a reference reflector in anoptical fiber are used to produce a measurement of the phase and amplitude of the reflected light from the modulated Bragg grating as a function of wavelength The system is demonstrated with 22 Bragg gratings in a single fiber on a cantilever beam and compared with foil strain gauge readings

Multiparameter fiber optic sensor for use in harsh environments

Abstract: A sensor capable of measuring a number of physical parameters in a harsh environment includes a plurality of intrinsic fiber optic sensor elements formed within a core of an optical fiber, the optical fiber being disposed within a capillary tube made of a high strength, corrosion resistant material. The sensor is located at a distal end of the capillary tube, and the capillary tube is mounted in a monitoring location, such as mounted to the casing of an electrically submersible pump (ESP), such that the sensor can be utilized to measure physical parameters, including static and dynamic pressure, temperature, acceleration and acoustic signals, at the monitoring location. Each sensor is constructed such that a reference element, such as a rigid element, isolates a reference location in the optical fiber from mechanically induced strain. A Bragg grating sensing element is positioned with respect to the reference element, and responsive to an optical signal and to a strain associated with a respective measurand field for providing an optical sensing signal related to a magnitude of the respective measurand field.

Continuous arbitrary strain profile measurements with fiber Bragg gratings

Abstract: A new distributed strain sensing technique using a fiber optic Bragg grating has been developed and tested. This is the first `true' distributed strain sensor, to the authors' knowledge, with a high spatial resolution of about 1 mm. Since gratings can be made with a length of tens of centimeters, this new fiber optic measurement technique could have broad applications to smart materials and structures where monitoring of a continuous strain profile over a length of millimeters to tens of centimeters is needed. In this paper three different demodulation approaches are reviewed indicating a trade-off between a relatively simple measurement process for selected types of strain profile and a more complete measurement process that is suitable for any strain profile. Experimental results with different approaches are presented.

Highly sensitive dynamic strain measurements by locking lasers to fiber Bragg gratings

Abstract: A novel, sensitive, simple, and robust strain interrogation technique is analyzed and experimentally tested. By locking a laser wavelength to the midreflection wavelength of a standard fiber Bragg grating and measuring the error signal, we achieve high dynamic strain sensitivity of 45 picostrain/Hz rms at 3 kHz, where the dominant noise in the experiment is the laser frequency noise.

Tunable nonlinearly chirped grating

Abstract: A nonlinearly chirped fiber grating (100) for achieving tunable dispersion compensation, chirp reduction in directly modulated diode lasers (102), and optical pulse manipulation. A dynamical dispersion compensation mechanism can be implemented in a fiber communication system based on such a nonlinearly chirped fiber grating (100).

Single-longitudinal-mode fiber laser with a passive multiple-ring cavity and its application for video transmission.

Abstract: A single-longitudinal-mode erbium-doped fiber laser with a passive multiple-ring cavity (MRC) is proposed for the first time to the authors' knowledge. The laser is fundamentally structured by insertion of three different short ring cavities, which serve as mode filters, into the main cavity. When it is combined with a mode-restricting intracavity fiber Bragg grating, the MRC resonator ensures single-longitundinal-mode laser oscillation. The laser can successfully suppress side-mode frequencies of as much as 1 GHz and provide an output power of 23 mW with a side-mode suppression ratio of 51 dB at 1533 nm. The short-term linewidth of the laser output measured is ~2 kHz . The ability of this fiber laser to act as an AM transmitter source is also demonstrated.

Generalized expression for the growth of long period gratings

Abstract: Experimental results have shown that the peak loss wavelength of long period gratings can shift in the direction of either shorter or longer wavelengths as the induced index change of the grating increases. An expression, which the authors believe to be novel, is derived and verified experimentally, to explain this phenomena. It is shown that the waveguide dispersion characteristics of the core and clad effective indices play a key role in the evolution of the transmission characteristics of the grating.

Nonlinear self-switching and multiple gap-soliton formation in a fiber Bragg grating.

Abstract: We report, for the first time to our knowledge, the experimental observation of quasi-cw nonlinear switching and multiple gap-soliton formation within the bandgap of a fiber Bragg grating. As many as five gap solitons with 100-500-ps durations were generated from a 2-ns pulse at a launched peak intensity of approximately 27 GW/cm(2). A corresponding increase in the grating transmission from 3% to 40% of the incident pulse energy was observed.

Enhanced Q switching in double-clad fiber lasers.

Abstract: A novel cladding pumped Nd3+ fiber laser operating in an enhanced Q-switched regime with a stable repetition rate is described. By exploiting fiber nonlinearities in the laser cavity, we demonstrated a peak power of 3.7??kW enhanced by an order of magnitude greater than that of conventional Q-switched fiber devices. Pulse durations as short as 2??ns have been achieved.

Influence of nonideal chirped fiber grating characteristics on dispersion cancellation

Abstract: The effect of nonideal dispersion and reflection characteristics of chirped fiber gratings on the performance of 10-Gb/s nonreturn-to-zero-transmission systems operating over standard fiber is investigated. The system penalty for different amplitude and period ripples are quantified. Analyses of an experimental grating confirm that current fabrication technology can meet the requirements for <1-dB-penalty operation.

All-fiber zero-insertion-loss add-drop filter for wavelength-division multiplexing.

Abstract: We developed and fabricated an all-fiber add–drop filter by recording a Bragg grating in the waist of an asymmetric mode converter–coupler formed by adiabatic tapering and fusing of two locally dissimilar, single-mode optical fibers. The insertion loss of the device was ~0.1 dB. A narrow spectral bandwidth ( 90%) were also demonstrated. In addition, the filter was polarization independent.

Fiber optical Bragg grating refractometer

Abstract: We have demonstrated an evanescent field refractive index fiber sensor comprising a 42-mm Bragg grating in an etched fiber together with a tunable Distributed Bragg Reflector (DBR) laser. Characterization of different aqueous sucrose solutions resulted in a resolution of roughly 10 mM sucrose. The sensor in the presented form has a theoretical sensitivity of higher than 10 -5 refractive index unit (riu) in a refractive index region close to the cladding index of the fiber. However, the technique allows for an even higher sensitivity than 10 -6 riu with a proper signal processing scheme.

Analysis of phase-shifted long-period fiber gratings

Abstract: Phase-shifted long-period fiber gratings (LPFG's) are analyzed by the coupled-mode theory together with the fundamental-matrix method. The effects of introducing multiple phase shifts at various locations along a LPFG are highlighted. The results compare well with published experimental data.

Dispersion tuning of a linearly chirped fiber Bragg grating without a center wavelength shift by applying a strain gradient

Abstract: We propose a new method for controlling the chirp of a linearly chirped fiber Bragg grating (FBG) without a center wavelength shift by using beam bending. The beam consists of a plastic sleeve enclosing a 10-cm-long chirped FBG and a metal rod. The grating pitch could be varied to give positive or negative chirp as well as zero chirp (i.e. uniform pitch) as applying displacement to one end of the beam without rotation. The dispersion at the two extremes of mechanical displacement were -791 ps/nm and +932 ps/nm. The center wavelength shift of the FBG was as small as 0.09 nm over the dispersion tuning range.