Showing papers on "Single-mode optical fiber published in 1998"

Large mode area photonic crystal fibre

Abstract: The authors report the realisation of a new design for a large mode area monomode optical fibre. This photonic crystal fibre will guide only a single mode, no matter how large the fibre diameter, provided the shape is kept constant. This is demonstrated with a fibre which has a core diameter equal to approximately 50 free-space wavelengths.

Group-velocity dispersion in photonic crystal fibers.

Abstract: The dispersion properties of photonic crystal fibers are calculated by expression of the modal field as a sum of localized orthogonal functions. Even simple designs of these fibers can yield zero dispersion at wavelengths shorter than 1.27 µm when the fibers are single mode, or a large normal dispersion that is suitable for dispersion compensation at 1.55 µm.

Single-mode excitation of multimode fibers with ultrashort pulses.

Abstract: Single-mode excitation of step-index multimode fibers with light sources with short temporal coherence lengths is demonstrated. Multimode fiber designs with reduced microbending-induced mode coupling are described that allow the propagation of the fundamental mode over long lengths with negligible mode coupling even in the presence of tight fiber bends. At a wavelength of 1.56microm a fiber with a core diameter of 45microm can preserve the fundamental mode for a propagation length of ~20m . Such fibers allow coiling with a coil diameter as small as 7cm.

Multicore optical fibre

Abstract: An optical fiber for transmitting radiation comprising two or more core regions, two or more core regions, each core region comprising a substantially transparent core material and having a core refractive index, a core length, and a core diameter, wherein said core regions are arranged within a cladding region, said cladding region comprising a length of first substantially transparent cladding material, having a first refractive index, wherein said first substantially transparent cladding material has an array of lengths of a second cladding material embedded along its length, wherein the second cladding material has a second refractive index which is less than said first refractive index, such that radiation input to said fiber propagates along at least one of said core regions. The cladding region and the core regions may be arranged such that radiation input to said optical fiber propagates along one or more said lengths of said core regions in a single mode of propagation. The optical fiber may be used as a bend sensor, a spectral filter or a directional coupler. The invention also relates to a method of manufacturing a multicore optical fiber.

Optical imaging apparatus which radiates a low coherence light beam onto a test object, receives optical information from light scattered by the object, and constructs therefrom a cross-sectional image of the object

Abstract: A low coherence beam emitted by a low coherence light source is split into two portions. One portion is transmitted from the outward end of a first single mode fiber via a detachable connector to a beam scanning probe, and then to a biological tissue; and the other is transmitted from an optical coupler placed midway along the light path via a second single mode fiber to a light path modifier. The light path modifier includes a galvanometer mirror to modify the light path length in accordance with a scan range, and a uniaxial stage to adjust the light path length to absorb the variation in lengths of different beam scanning probes. The light path is adjusted by the uniaxial stage such that the beam interference is detected for the scan range, to ensure stable acquisition of tomographic images.

Multiscale pulse dynamics in communication systems with strong dispersion management.

Abstract: The evolution of an optical pulse in a strongly dispersion-managed fiber-optic communication system is studied. The pulse is decomposed into a fast phase and a slowly evolving amplitude. The fast phase is calculated exactly, and a nonlocal equation for the evolution of the amplitude is derived. In the limit of weak dispersion management the equation reduces to the nonlinear Schrodinger equation. A class of stationary solutions of this equation is obtained; they represent pulses with a Gaussian-like core and exponentially decaying oscillatory tails, and they agree with direct numerical solutions of the full system.

Automatic compensation of first order polarization mode dispersion in a 10 Gb/s transmission system

Abstract: We demonstrate a novel, adaptive optical polarization mode dispersion equalizer in a 10-Gb/s transmission experiment. The equalizer comprises a fast electrooptic polarization transformer an adjustable differential polarization delay line, and a simple electric distortion analyzer for automatic feedback control.

Low attenuation optical waveguide

Abstract: Disclosed is a single mode optical waveguide fiber having a core refractive index profile in which the profile parameters are selected to providean attenuation minimum. A set of profiles having the same general shape and dimensions is shown to have a group of profiles contained in a sub-set which exhibit a minimum of attenuation as compared to the remaining members of the set. The members of the sub-set have been found to have the lowest effective group index, n geff, and the lowest change in .beta.2 under waveguide fiber bending.

Sol-gel glass waveguide and grating on silicon

Abstract: This paper reports on the fabrication and characterization of hybrid organic-inorganic glass sol-gel slab and channel waveguides by ultraviolet light imprinting in thin films deposited by a one-step dip-coating process. The adjustment of chemical composition of the materials provides precise selection of refractive index from 1.48 to 1.52 at the wavelength of 632.8 mn. The refractive index of the waveguides at 1.55 /spl mu/m is similar to that of optical fiber, thus reducing the reflection loss between the two to less than 0.01 dB. The effect of ultraviolet light exposure and heat treatment on waveguide refractive index is studied. Fabrication parameters to produce ridge waveguides are optimized to achieve very smooth side walls. Propagation losses in these waveguides are /spl sim/0.1 dB/cm. Single mode buried waveguides, at 1.55 /spl mu/m wavelength, with circular mode profile are demonstrated.

Local birefringence measurements in single-mode fibers with coherent optical frequency-domain reflectometry

Abstract: Measurements of intrinsic and induced birefringence of optical fibers are performed at 1550 nm using the optical frequency-domain reflectometry technique. The experiment confirms the theoretical analysis, which predicts the appearance of oscillations on the detected Rayleigh backscattering intensity, with periods equal to the polarization beat length L/sub b/ and to L/sub b//2. Polarization mode-coupling length values are obtained from local birefringence and polarization mode dispersion measurements.

PMD second-order effects on pulse propagation in single-mode optical fibers

Abstract: The time-space varying birefringence in single-mode optical fibers causes the polarization mode dispersion (PMD) to be a serious problem in high bit-rate transmissions. The PMD first- and second-order statistics are well known in the literature, but second-order PMD-induced pulse distortions have still to be clarified for sequences of pulses of arbitrary shape. We give, for the first time, the exact PMD time impulse response, up to second order. We show, both numerically and experimentally, that the effect of the rotation of the principal states of polarization (PSP) is to generate power overshoots on the "1" and "0" bit sequences.

Polarization mode dispersion induced pulse broadening in optical fibers.

Abstract: A simple and exact analytical expression is derived for the amount of broadening that a pulse suffers when it is subjected to the combined actions of polarization mode dispersion, chromatic dispersion, and chirping. The theory is then applied to various manifestations of second-order polarization mode dispersions.

Effects of Random Perturbations in Plastic Optical Fibers

Abstract: REVIEW The most important feature of an optical fiber waveguide is its bandwidth, which defines its information-carrying capacity. A major limitation on the bandwidth of multimode glass and plastic optical fibers is modal dispersion, in which different optical modes propagate at different velocities and the dispersion grows linearly with length. However, in plastic optical fibers, experimental and theoretical results indicate that the modes are not independent but are highly coupled, which leads to a characteristic square-root length dependence and an unanticipated large enhancement of the bandwidth to gigahertz levels. The ever increasing demands for low-cost, high-bandwidth communications media for voice, video, and data transmission in short- and medium-distance applications are generating a new assessment of multimode optical fibers to serve as high-speed fiber links.

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.

Dispersion-free fiber transmission for femtosecond pulses by use of a dispersion-compensating fiber and a programmable pulse shaper.

Abstract: We demonstrate nearly distortionless 2.5-km fiber transmission of sub-500-fs pulses, using a combination of standard single-mode fiber, dispersion-compensating fiber, and a programmable pulse shaper for simultaneous quadratic and cubic dispersion compensation. The dispersion-compensating fiber corrects the bulk of the quadratic and the cubic phases for the single-mode fiber, and the fiber-pigtailed programmable pulse shaper exactly compensates the residual dispersion terms. Together these elements permit complete recompression of pulses, which first broaden by ?400 times in the single-mode fiber.

Fiber spin-profile designs for producing fibers with low polarization mode dispersion.

Abstract: Using coupled-mode theory, we develop a theoretical model to analyze the effects of fiber spin profiles on polarization mode dispersion (PMD). Constant, sinusoidal, and frequency-modulated spin profiles are examined, and phase-matching conditions are analyzed. Our analysis shows that PMD can be reduced effectively by use of frequency-modulated spin profiles.

Free-space optical signal switch arrangement

Abstract: A free-space N by M where N and M > 1 optical signal switch (OXC) requires only transmitter beam steering for controlling to which receiver an optical signal from a transmitter is directed. In a preferred embodiment the transmitters handle single mode optical signals and the receivers handle multimode optical signals. The OXC may optionally include a fixed optical unit implemented using either a single fixed shared lens or a plurality of M optical elements for further directing each of the M optical signals to their respective receivers.

Polarization mode dispersion characterization of single-mode optical fiber using backscattering technique

Abstract: This paper presents a completely new method able to characterize polarization mode dispersion (PMD) properties of randomly birefringent single-mode fibers, using polarization sensitive backscattering technique. We show analytical relationships between evolution of polarization state of backscattered signal with respect to state of polarization of forward one. Our technique allows one to measure differential group delay, beat length, and correlation length at the same time over long single-mode fibers using only one fiber end. Experimental data fit very well with numerical results, confirming the capability of our technique for fast routine characterization of PMD during cabling, before and after installation.

Generation of ultra-broad-band supercontinuum by dispersion-flattened and decreasing fiber

Abstract: It has been made clear through model simulations that dispersion-flattened and decreasing fiber (DFDF) is one of the most suitable fibers for broad-band supercontinuum (SC) generation. SC generation In a bandwidth of 280 nm with intensity fluctuation less than 15 dB has been experimentally observed by using the DFDF designed and manufactured with an optimized dispersion profile.

Discrete wavelength liquid crystal tuned external cavity diode laser

Abstract: The invention comprises a liquid crystal Fabry-Perot interferometer tuned external cavity semiconductor laser. The laser oscillates single mode at a discrete set of wavelengths defined by the transmission of an intracavity static Fabry-Perot etalon. The liquid crystal Fabry-Perot interferometer has a free spectral range larger than the gain bandwidth of the laser amplifier so that it selects only one transmission wavelength. Its resolution bandwidth is much greater than the free spectral range of the external cavity. The static intracavity etalon's free spectral range is greater than the resolution bandwidth of the liquid crystal Fabry-Perot interferometer. The static etalon maintains a single mode oscillation by providing a filter narrow enough to select only one external cavity mode.

All-fiber bandpass filter with adjustable transmission using cladding-mode coupling

Abstract: We demonstrate an all-fiber bandpass filter with 2-nm bandwidth and more than 25 dB of nonresonant light suppression (ignoring sidelobes) in a 60-nm-wide spectral range around its central wavelength. This novel device uses a pair of long-period gratings to couple resonant light from the fiber core into the cladding and then back into the core. The amplitude transmission through the filter is dynamically adjustable over a 20-dB range.

Analysis of intensity interference caused by cross-phase modulation in dispersive optical fibers

Abstract: Under a set of broadly justified simplifying assumptions, an analytical approach to the problem of cross phase modulation in optical fibers is presented. Simple analytical expressions describing intensity interference caused by cross-phase modulation (XPM) are derived. It turns out that within a physically realizable range of parameters the power penalties induced by XPM have a linear dependence on the power of the interfering signal. Examples of specific systems are presented and discussed.

Improved array topologies for implementing serial fiber bragg grating interferometer arrays

Abstract: An interferometer array includes a plurality of interferometer sub-arrays, each sub-array including a plurality of interferometers. Each interferometer in a sub-array is implemented with a respective pair of fiber Bragg gratings and a sensing length of optical fiber positioned between the respective pair of fiber Bragg gratings. The fiber Bragg gratings in each respective pair of fiber Bragg gratings have the same characteristic wavelength that is different from the characteristic wavelength of every other pair of fiber Bragg gratings in the sub-array. The sub-arrays are interconnected to minimize the common-wavelength crosstalk between the sensors in the overall interferometer array. In one embodiment, the sub-arrays are connected in series along a common length of optical fiber such that the maximum common-wavelength crosstalk is limited by the number of sub-arrays connected in series. In a second embodiment of the invention, branches are interconnected to a common input/output optical fiber via optical couplers, and each branch has one or more sub-arrays connected in series. The common-wavelength crosstalk is limited by the number of arrays in each sub-array. In a third embodiment of the invention, branches are interconnected between an input optical fiber and an output optical fiber via optical couplers, and each branch has one or more sub-arrays connected in series. Optical signal delay elements are positioned in the input optical fiber to incrementally increase the delay experienced by an input optical signal before it reaches each successive branch connected to the input optical fiber. Therefore, the return optical signals from each sub-array in a branch are separated in time from the return optical signals from the sub-arrays in the other branches.

Embedded Fiber Bragg Grating Sensors for Industrial Composite Cure Monitoring

Abstract: An embedded Fiber Bragg Grating (FBG) strain sensor and an FBG temperature sensor have been shown to be able to accurately monitor the industrial composite cure process of a glass/ epoxy plate devoted to aeronautical applications. The internal absolute strain level in the plate was determined, free of temperature effect thanks to a differential method. After curing, a residual compression strain of about -0.22% was observed, which represents a short part of the range in compression for a single mode fiber. Later on, the embedded FBG strain sensor could be used as a smart sensor for the health monitoring of composite structures, e.g. for impact or layer delamination detection.

Characterization and optimization of a laser-scanning microscope in the femtosecond regime

Abstract: We report on a detailed characterization and opti- mization of a commercial laser-scanning microscope in the femtosecond (fs) regime for two-photon microscopy. This in- cludes, to our knowledge for the first time, the measurement of the second-order dispersion of the whole microscope and a comparison with the value derived from material constants of the single optical components. It is also shown that by using an appropriate prism stretcher the temporal broadening of the fs pulse can be compensated for. Even if a 2-m-long single mode fiber is used to couple the fs laser to the mi- croscope an observed temporal broadening of a factor of 30 has been compensated by a simple grating compressor for the first time. With the optimized system two-photon cross sec- tions of several relevant biological dyes have been determined and the feasability of exciting special UV fluorochromes by two-photon absorption was successfully demonstrated. No photo-bleaching was detectable. In addition, the lateral and axial resolutions of the optimized system were measured and compared with typical values obtained for a confocal micro- scope.

Fiber optic intrusion sensor with the configuration of an optical time-domain reflectometer using coherent interference of Rayleigh backscattering

Abstract: The optical fiber intrusion sensor is investigated in the configuration of an optical time domain reflectometer using coherent interference of Rayleigh backscattering in a single mode fiber. When the modulation pulse width was 4 usec, the spatial resolution of this intrusion sensor was about 400m, the signal to noise ratio was about 3.3 and the bandwidth was about 30.5Hz.

Elimination of birefringence induced scale factor errors in the in-line Sagnac interferometer current sensor

Abstract: This paper presents theoretical and experimental results showing the effects of linear and circular birefringence on the sensing coil of an in-line Sagnac interferometer current sensor. Linear birefringence induces local scale factor variations along the length of the sensing coil which can be suppressed with circular birefringence. We show that by winding the sensing coil with tension in a helix configuration, these variations may be effectively reduced to zero for ordinary single mode fiber. In our opinion, this method of implementation overcomes the need to use annealed fiber in the sensing coil.