Showing papers on "Photonic-crystal fiber published in 1995"

Laser-guided atoms in hollow-core optical fibers.

Abstract: We have used optical forces to guide atoms through hollow-core optical fibers. Laser light is launched into the hollow region of a glass capillary fiber and guided by grazing-incidence reflection from the walls. When the laser is detuned 1--30 GHz red of the Rb D2 resonance lines, dipole forces attract atoms to the high-intensity region along the axis and guide them through the fiber. We show that atoms may be guided around bends in the fiber and that in initial experiments the atoms experience up to 18 reflections from the potential walls with minimal loss.

Excitation of resonances of microspheres on an optical fiber.

Abstract: Morphology-dependent resonances (MDR's) of solid microspheres are excited by using an optical fiber coupler The narrowest measured MDR linewidths are limited by the excitation laser linewidth (<0025 nm) Only MDR's, with an on-resonance to off-resonance intensity ratio of 10(4), contribute to scattering The intensity of various resonance orders is understood by the localization principle and the recently developed generalized Lorentz-Mie theory The microsphere fiber system has potential for becoming a building block in dispersive microphotonics The basic physics underlying our approach may be considered a harbinger for the coupling of active photonic microstructures such as microdisk lasers

Long-period fiber gratings as band-rejection filters

Abstract: Optical fiber communication systems that use optical amplifiers are increasingly seeking high-performance devices that function as spectrally-selective band-rejection filters. For example, ASE filters that improve erbium amplifier performance and band-rejection filters in Raman lasers/amplifiers1 must have low insertion losses and low back-reflections. In addition, they must be relatively inexpensive to mass-produce and should be compact after packaging. While bulk-optic filters and short-period Bragg gratings2,3 can be used for some of the applications, all the aforementioned requirements are rarely met. In this paper, we present a novel class of photoinduced, long-period fiber gratings that function as highly-efficient band-rejection filters.

Eroded monomode optical fiber for whispering-gallery mode excitation in fused-silica microspheres.

Abstract: We demonstrate the efficient excitation of high-Q whispering-gallery modes in near-spherical fused-silica microparticles in the size range 60–450 μm by the use of an eroded monomode optical fiber. When the sphere is placed in the evanescent field of the guided fiber mode, light is resonantly coupled from the fiber into the microparticle. We report a broadening of resonance modes and a shift of the resonance central frequency as the coupling strength is increased by reduction of the gap between the sphere and the fiber.

Intermodal dispersion in two-core optical fibers.

Abstract: The switching characteristics of a two-core optical fiber can be described by the beating of the even and odd modes of the composite two-core structure. It is shown that the group-delay difference between these two modes can be as large as 10 ps/m. This intermodal dispersion sets a limit on the shortest duration of the optical pulse that can be switched effectively in devices that use long lengths of two-core fibers, such as wavelength-division multiplexers, polarization splitters, and nonlinear directional couplers.

Measurement of the nonlinear refractive index in optical fiber by the cross-phase-modulation method with depolarized pump light.

Abstract: Depolarized pump light is used in measurements of the nonlinear refractive index, n2, in optical fiber by the cross-phase-modulation method. High measurement repeatability within ±1% is obtained by this method. The nonlinear refractive index is determined for dispersion-shifted fiber, standard single-mode fiber, pure silica-core single-mode fiber, and dispersion-compensating fiber as 3.35 × 10−20, 2.96 × 10−20, 2.79 × 10−20, and 4.44 × 10−20 m2/W, respectively, at 1.55 μm. This shows that the nonlinear refractive indices of the optical fibers differ greatly according to glass composition.

Elliptical fiber waveguides

Abstract: Part 1 Introduction: historical introduction nomenclature of modes dielectric waveguides. Part 2 The dielectric slab waveguide: the dielectric slab waveguide modal cut-off propagation constants group velocity power distribution far-field radiation pattern. Part 3 Circular dielectric waveguide: circular dielectric waveguide modal cut-off group velocity power distribution far-field radiation pattern. Part 4 Elliptical dielectric waveguides: elliptical dielectric waveguides modes transcendental equations birefringence power distribution a perturbation approach far-field radiation pattern. Part 5 Higher order modes in elliptical dielectric waveguides: elliptical waveguides with conducting walls cut-off in elliptical dielectric waveguide propagation constants of the higher order modes the LP 11 modes birefringence in the over-moded region difference in group velocity between the fundamental and first higher order modes. Part 6 Elliptically cored fiber construction and measurements: design requirements fiber design fiber attenuation measurement the refractive indices of germania- and fluorine-doped silica the effect of temperature on the propagation constant measurement of fiber birefringence the effect of temperature on birefringence measurement of group velocity polarization mode dispersion measurement of the mode coupling/polarization crosstalk factor h measurement of higher mode cut-off determination of the axes of birefringence and the axes of the core ellipse. Part 7 The D fiber: the D fiber fiber manufacture measurements etching the fiber coupling between fibers the D fiber directional coupler loop mirror indium-coated D fiber polarizer diffraction gratings on D fiber optoelectronic devices on D fiber. Part 8 Applications of elliptical core fiber: applications of elliptical fiber fiber-optic gyroscope sensors using the higher order modes in elliptical core fiber Bragg gratings in E fibers coupling of modes using acoustic waves use of the optical Kerr effect the elliptical core fiber as a current sensor correction of dispersion using over-moded fiber. Part 9 Rare-earth-doped elliptically cored fiber: background fabrication fiber characteristics loop mirror reflectors fiber lasers with elliptical cores differential reflection coefficient applications. Appendices: Maxwell's equations physical interpretation of Maxwell's equations electromagnetic waves in free space harmonic fields classification of solutions to the wave equations uniform TEM plane wave velocity of wave.

Fiber lasers and their applications

Abstract: The use of optical fiber amplifiers in optical telecommunication systems has opened up many new possibilities with the amplifier's large gain and wide spectral bandwidth. They include ultra-long distance signal transmission without repeaters, and multi channel optical frequency division multiplexing. Very short optical pulses, optical soliton pulses, and wavelength tunable laser sources with extremely narrow linewidth are also of great interest as light source for broadband optical communication. More recently, new applications of the optical fiber amplifiers to sensors have been intr~duced. '-~ They are in forms of various types of fiber lasers whose output optical frequencies or temporal properties are determined by the optical pathlengths of laser cavities. The magnitude of external pertubations that change the optical pathlength of the cavity can be measured by monitoring the output characteristics of the laser. To achieve good performance from the fiber laser sensors, the longitudinal mode and polarization properties of the fiber laser have to be understood in detail. One of the good exam les is a polarimetric fiber laser sensor','where the frequency difference between two eigen polarization components of the laser output has a linear dependence on the net birefringence of the fiber laser cavity. External perturbations such as longitudinal strain, lateral stress, and temperature change can easily be measured with such a fiber laser sensor. Since the sensor has a frequency readout with an inherently linear scale factor, complicated electronic signal processing can be avoided. This is an important feature for practical sensors that has been pursued since the early stage of sensor development. Another example utilizes mode locked operation with short optical pulse output? The timing of the pulses is determined by the phase difference in a fiber interferometer that is part of the laser cavity. Therefore, the output is in time interval that can be conveniently measured. Rotation rate sensing can be accomplished with this approach. Other examples include fiber ring laser sensors using either rare-earth doped fiber amplifiers4 or stimulated Brillouin scattering amplifier? The operating principles and applications of several fiber laser sensors will be described. Some of the recent activities including new results obtained with a fast semiconductor amplifier instead of a slow fiber amplifier in a fiber laser cavity will be pres,ented. The properties of fiber laser output as a function of linear and circular birefringence in the cavity will also be briefly discussed.

Confinement and bistability in a tapered hemispherically lensed optical fiber trap

Abstract: We describe the operation and performance of a dual fiber optical trap created using tapered lensed optical fibers pigtailed to 1300 nm laser diodes. Single‐mode fibers, having mode field diameters of ∼9.5 μm, and separated by up to 350 μm, are used to demonstrate dielectric particle confinement over two orders of magnitude in fiber trapping power ratio. Axial and transverse trap efficiencies, as well as the existence of bistable trapping positions, are predicted and experimentally confirmed. The use of fiber lenses results in the creation of an optical trap that provides strong transverse optical confinement and which is nearly insensitive to the fiber polarization state.

Compression-tuned single-frequency Bragg-grating fiber laser

Abstract: Wideband continuously tunable single-frequency lasers are required in a wide range of spectroscopic, communications, and sensor applications. To date, tensile stress has been used to achieve continuous tuning in Bragg-grating fiber lasers.1 Strain tuning yields a Bragg-wavelength change of approximately 1.2 nm/millistrain in the 1.55-µm regime and is limited by the fiber strength. Young's modulus for SiO2 is 1.02×107 psi (5.27×108 Torr). For fiber proof tested at 100 kpsi (5.17 M Torr), a maximum strain of roughly 1% can be applied without degrading the fiber strength and eventually breaking the fiber. This limits tensile strain tuning to the 10-nm regime. Fiber strength limitations associated with tensile stress are relieved with compressive stress is implemented because silica is 23 times as strong under compression as it is under tension.2 A single-frequency erbium-doped, Bragg-grating fiber laser that uses uniform compression to continuously tune over a 32-nm range while maintaining uniform power is described.

Dispersion compensation for optical fiber systems

Abstract: Much of the currently embedded optical fiber was originally designed for light with a wavelength of 1.3 microns. If this fiber is to be used with tomorrow's optically amplified, high-speed, long span-length lightwave system operating at 1.5 microns, the chromatic dispersion in the fiber must be compensated. Dispersion compensation will be required in long-haul l0 Gb/s systems using conventional fiber. Many compensation techniques have been demonstrated and they exhibit a variety of different and often complimentary properties. Transmitter compensation techniques are the most easily implemented but provide a limited amount of compensation. The most commercially advanced technique is negative dispersion fiber. Chirped Bragg gratings are advancing rapidly, but will always be hampered by their narrow bandwidth. The adoption of any particular technique for use in a high-speed network will depend on the constraints imposed by the, as yet, undefined network architecture. >

Instrumentation for interrogating many-element fiber Bragg grating arrays

Abstract: Fiber Bragg grating (FBG) arrays have provided the Smart Structures community with a powerful means for real-time and absolute point measurements of strain throughout extended structures. The mechanical properties of these optical fiber sensors uniquely suit them for unobtrusive and reliable incorporation into composite materials, while wavelength encoding of the measurand enables independent interrogation of many devices distributed along a single fiber. In view of recent progress towards practical and economical FBG array fabrication via the computer-controlled in-line writing process during fiber draw, there is a complementary need for economical instrumentation which makes efficient use of the reflected signals. This is an important issue, especially since the reflectivity of narrow-line, type I gratings produced during fiber draw is typically less than 5%.

Collection of scintillation light from small BGO crystals

Abstract: We propose to develop a high resolution positron emission tomography (PET) detector designed for animal imaging. The detector consists of a 2-D array of small bismuth germanate (BGO) crystals coupled via optical fibers to a multi-channel photomultiplier tube (MC-PMT). Though this approach offers several advantages over the conventional BGO block design, it does require that a sufficient number of scintillation photons be transported from the crystal, down the fiber and into the PMT. In this study we use simulations and experimental data to determine how to maximize the signal reaching the PMT. This involves investigating factors such as crystal geometry, crystal surface treatment, the use of reflectors, choice of optical fiber, coupling of crystal to the optical fiber and optical fiber properties. Our results indicate that using 2/spl times/2/spl times/10 mm BGO crystals coupled to 30 cm of clad optical fiber, roughly 50 photoelectrons are produced at the PMT photocathode for a 511 keV interaction. This is sufficient to clearly visualize the photopeak and provide adequate timing resolution for PET. Based on these encouraging results, a prototype detector will now be constructed. >

Estimation of nonlinear refractive index in various silica-based glasses for optical fibers

Abstract: The dependence of the nonlinear refractive index n2 on glass compositions for optical fibers is clarified. The relation between n2 and germanium- or fluorine-doped SiO2 is calculated on the basis of the measurement of n2 at 1.55 μm with the improved cross-phase-modulation method, taking into account the radial distribution of the optical power in the fibers.

Enhanced photosensitivity in tin-codoped germanosilicate optical fibers

Abstract: Enhanced photosensitivity is found in tin-codoped germanosilicate optical fibers. A photo-induced refractive index change (/spl sim/1.4/spl times/10/sup -3/) 3 times larger than that observed in pure germanosilicate fibers has been demonstrated. Unlike the technique of using boron-codoping to enhance the photosensitivity of germanosilicate fibers, tin-doping does not have a significant effect on fiber loss at the important telecommunication window of 1.55 /spl mu/m. High temperature stability of the gratings in tin-codoped germanosilicate fibers is also much over boron-codoped fibers. >

Compression-tuned fiber laser

Abstract: A fiber laser (26) including a rare-earth doped fiber laser cavity (32) delimited by a pair of reflective elements (28, 30), such as Bragg gratings, is tuned by compressing the cavity (32) and the gratings (28, 30). Because an optical fiber is much stronger under compression than in tension, the laser (26) is tunable over a much broader range than conventional tension/stretching techniques.

Birefringence dispersion measurement in optical fibers by wavelength scanning

Abstract: We describe a method for measuring modal birefringence in optical fibers. It combines an interferometric technique with wavelength scanning and permits a precise nondestructive measurement of the birefringence along different sections of a long optical fiber. The experimental results for high-birefringence fibers, 10 and 100 m long, are presented. An accuracy of approximately 0.1% is achieved in the spectral range of 600–850 nm.

Multiparameter sensor system using a multiple grating fiber optic birefringent fiber

Abstract: Spectrally separated fiber gratings are written in substantially the same location of a birefringent optical fiber to form a multiparameter environmental sensor. This sensor is particularly useful for the measurement of three axes of strain and temperature at a single location in composite material. This is possible due to the splitting of each of the dual overwritten fiber gratings via the birefringence of the optical fiber resulting in four spectral outputs and four equations that may be solved to determine the two transverse strains, the longitudinal strain and the temperature. This invention also describes systems that may be used to demodulate the multiparameter fiber gratings.

Upconversion fiber laser

Abstract: An upconversion fiber laser uses a pump source which may be another fiber laser, such as a high power, diode-laser-pumped, fiber laser. The upconversion fiber laser includes an optical fiber whose core region is doped with an active lasing ionic species capable when optically pumped of undergoing upconversion excitation, such as certain rare earth ionic species, and which is embedded in a cladding of the optical fiber. Use of a fiber pump laser can improve coupling of pump light into the optical fiber, thereby achieving higher pump intensities in the core region and improved upconversion efficiency. The upconversion fiber laser's resonant laser cavity is defined by feedback means which can include at least one reflective grating formed in the optical fiber, as well as a reflective end face of the optical fiber. Any portion of the optical fiber that lies outside of the resonant laser cavity, such as any portion beyond the integral reflective grating, may act as an optical power amplifier for the upconverted laser output. The disclosure includes other embodiments in which pump brightness can be further increased with multiple pump sources.

High-power optical fiber amplifier or laser device

Abstract: A high-power optical fiber device comprising a pump source of light-emitting facets (110), optical means (102) for collimating an d converging the array, an optical beam rotator (130) for transforming the array by rotating individual light emissions, and an optical fiber structure (170) having a core (174) surrounded by an inner cladding (172) for transferring pump energy into the core, the inner cladding having a cross-sectional shape in the form of a convex polygon.

Highly sensitive optical fiber cavity coating removal detection

Abstract: A highly sensitive optical fiber cavity coating removal detector employs an optical fiber (18) having a pair of Bragg gratings (20, 30) embedded therein and separated by a section of fiber making up an optical cavity (26). The optical path length of the cavity (26) is sized with the central reflection wavelength of the fiber gratings (20, 30) so as to create an optical resonator. The cavity (26) is coated with a material (40) which corrodes or is otherwise removable, such as aluminum. The coating (40) exerts forces (46) radially inward on the cavity (26) so as to cause the refractive index of the cavity and thus its optical path length to change, thereby causing the resonator to come out of resonance. The forces (46) on the cavity (26) are reduced when the coating (40) corrodes, thereby causing the resonator to re-enter resonance. Additionally, the coating causes optical losses to exist due to non-uniform variations in refractive index caused by non-uniform forces from coating irregularities.

Photoinduced Bragg gratings in As(2)S(3) optical fibers.

Abstract: Bragg gratings have been fabricated in As2S3 optical fibers through the photoinduced refractive-index change process. Bragg filters in the fiber show a more-ideal response than those fabricated in the corresponding bulk material. Some features characteristic of chalcogenide fibers and Ge-doped oxide fibers are discussed comparatively.

High-power soliton fiber laser based on pulse width control with chirped fiber Bragg gratings.

Abstract: Chirped fiber Bragg gratings control the pulse width and energy in Kerr mode-locked erbium fiber soliton lasers. We create high-energy pulses by providing large amounts of excessive negative dispersion, which increases the pulse width while keeping the nonlinearity of the cavity constant. With a chirped fiber grating of 3.4-ps(2) dispersion, 3-ps pulses with an energy content higher than 1 nJ are generated at a repetition rate of 27 MHz. By controlling the polarization state in the cavity, we obtain a tuning range from 1.550 to 1.562 mu;m.

Development of a terbium-lithium glass for slow neutron detection

Abstract: We have developed a new terbium-doped, lithium-loaded scintillating glass for slow neutron detection. This glass has the advantages of an emission spectrum with a maximum at 550 nm and of being drawn easily into optical fibers for the fabrication of scintillating optical fiber plates.

Strong photosensitive gratings in tin-doped phosphosilicate optical fibers.

Abstract: Strong photosensitive gratings of both type I and II have been demonstrated in germanium-free tin-doped phosphosilicate fibers. An index change of ~1.2 × 10−3 has been achieved in 40 s of exposure. The fibers have strong absorption (~0.8 dB/μm) at the writing wavelength of ~248 nm because of tin doping. This is the first time to our knowledge that such strong gratings have been written in a phosphorous-containing silica fiber without low-temperature hydrogenation and that type II gratings have been written in a germanium-free fiber. The tin-doping technique can be used to write gratings in rare-earth-doped phosphosilicate fibers and to produce low-N.A. fibers for mass production of strong single-pulse type II gratings during fiber pulling.

Highly nonlinear optical fiber for all optical processing applications

Abstract: We have designed and fabricated highly nonlinear dispersion-shifted germania-doped silica fibers for use in the EDFA gain window, and measured a 9-fold increase in the fiber nonlinearity, compared to conventional dispersion-shifted fiber. We have also measured the contribution of the germania index-raising dopant to the effective fiber nonlinearity. We believe that our new fiber design will afford a significant reduction in the required fiber length for nonlinear switching, leading to a broader wavelength switching window, and allowing compact device packaging. >

Linearly polarized fiber-optic laser

Abstract: A fiber-optic laser comprising a birefringent optic fiber possessing a Bragg grating at each of its ends,. A light source emits a light beam having two modes of polarization in the fiber. The birefringence of the fiber makes it possible to keep the two polarization modes separate. The two Bragg gratings are photo-recorded in the fiber and are made in such a way that their resonance wavelength is matched for one polarization. The wave emitted by the fiber is then polarized linearly along P1. Applications to linearly polarized lasers for optical transmission, instrumentation, spectroscopy, medicine, the detection of chemical species and telemetry.

Fiber with multiple overlapping gratings

Abstract: Two or more overlapping fiber gratings are formed in a section of optical fiber to sense environmental effects that can vary the spacing between the lines of the grating to vary the center frequency of the spectral envelope, either reflected or passed thereby. The fiber gratings if properly oriented can respond to strain applied thereto in x, y, and z directions and temperature so that a three axis sensor can be formed at a short length of optical fiber and be calibrated for temperature. The multiple optical gratings are formed by sensitizing an optical fiber to light and then using two or more light interference patterns to form the gratings.

Sensing apparatus and method for detecting strain between fiber bragg grating sensors inscribed into an optical fiber

Abstract: A sensing apparatus and related method for sensing strain between fiber Bragg grating sensors inscribed in an optical fiber. The fiber is inscribed with a first fiber Bragg grating sensor and a second fiber Bragg grating sensor. A strain detection unit detects strain between the first fiber Bragg grating sensor and the second fiber Bragg grating sensor based on the optical propagation time of light projected into the fiber and reflected by the first fiber Bragg grating sensor and the optical propagation time of light projected into the fiber and reflected by the second fiber Bragg grating sensor. More specifically, light projected into the fiber is modulated with an RF signal. A phase change of the RF signal is determined from the light projected into the fiber and reflected by the first fiber Bragg grating sensor and from the light projected into the fiber and reflected by the second fiber Bragg grating sensor. The phase change of the RF signal is related to the optical propagation time of light projected into the fiber and reflected by the first and second fiber Bragg grating sensors. The strain between the first and second fiber Bragg grating sensors is then determined from the detected phase changes.