Showing papers on "Single-mode optical fiber published in 1995"

Fundamentals of optical fibers

Abstract: Preface.Introduction.Chapter 1. Selected Topics in Electromagnetic Wave Propagation.1.1. Maxwell's Equations and the Fundamental Fields.1.2. Electromagnetic Wave Propagation in Sourceless Media.1.3. Power Transmission.1.4. Group Velocity.1.5. Reflection and Transmission of Waves at Plane Interfaces.1.6. Material Resonances and Their Effects on Wave Propagation.Problems.References.Chapter 2. Symmetric Dielectric Slab Waveguides.2.1. Ray Analysis of the Slab Waveguides.2.2. Field Analysis of the Slab Waveguides.2.3. Solutions of the Eigenvalue Equations.2.4. Power Transmission and Confinement.2.5. Leaky Waves.2.6. Radiation Modes.2.7. Wave Propagation in Curved Slab Waveguides.Problems.References.Chapter 3. Weakly-Guiding Fibers with Step Index Profiles.3.1. Rays and Fields in the Step Index Fiber.3.2. Field Analysis of the Weakly-Guiding Fiber.3.3. Eigenvalue Equation for LP Modes.3.4. LP Mode Characteristics.3.5. Single Mode Fiber Parameters.3.6. Derivation of the General Step Index Fiber Modes.Problems.References.Chapter 4. Loss Mechanisms in Silica Fiber.4.1. Basic Loss Effects in Transmission.4.2. Fabrication of Silica Fibers.4.3. Intrinsic Loss.4.4. Extrinsic Loss.4.5. Bending Loss.4.6. Source-to-Fiber Coupling.Problems.References.Chapter 5. Dispersion.5.1. Pulse Propagation in Media Possessing Quadratic Dispersion.5.2. Material Dispersion.5.3. Dispersion in Optical Fiber.5.4. Chromatic Dispersion Compensation.5.5. Polarization Dispersion.5.6. System Considerations and Dispersion Measurement.Problems.References.Chapter 6. Special Purpose Index Profiles.6.1. Multimode Graded Index Fiber.6.2. Special Index Profile Optimization.Problems.References.Chapter 7. Nonlinear Effects in Fibers I: Non-Resonant Processes.7.1. Nonlinear Optics Fundamentals.7.2. Nonlinear Phase Modulation on Pulses.7.3. The Nonlinear Schrodinger Equation.7.4. Additional Non-Resonant Processes.Problems.References.Chapter 8. Nonlinear Effects in Fibers II: Resonant Processes and Amplification.8.1. Raman Scattering.8.2. Stimulated Brillouin Scattering.8.3. Rare-Earth-Doped Fiber Amplifiers.Problems.References.Appendix A: Properties of Bessel Functions.Appendix B: Notation.Index.

Continuous wave operation of a vertical transition quantum cascade laser above T=80 K

Abstract: Continuous wave operation of a quantum cascade laser at λ=4.6 μm is reported above liquid nitrogen temperature. Optical powers of 15 mW at 50 K and 2 mW at 85 K are reported. The single mode spectrum is temperature tunable over 1.8 cm −1. These devices also operated in pulse mode with 20 mW peak power at 200 K. Gain measurements show evidence for ultralow linewidth enhancement factor α<0.1.

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.

Reduced bandwidth optical digital intensity modulation with improved chromatic dispersion tolerance

Abstract: A simple optical modulation scheme using a lithium niobate Mach-Zehnder modulator driven by a three level drive waveform is proposed. The two-level intensity modulated (IM) optical signal obtained possesses a smaller optical bandwidth and thus greater chromatic dispersion tolerance compared with existing two-level IM methods used for high data rate transmission (e.g. 10 Gbit/s).

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.

In-line fiber etalon (ILFE) fiber-optic strain sensors

Abstract: This paper describes an optical fiber interferometer that uses a short segment of silica hollow-core fiber spliced between two sections of single-mode fiber to form a mechanically robust in-line optical cavity. The hollow-core fiber is specifically manufactured to have an outer diameter that is equal to the outer diameter of the single mode lead fibers, thereby combining the best qualities of existing intrinsic and extrinsic Fabry-Perot sensors. Uniaxial tension and pure bending strength tests are used to show that the new configuration does not diminish the axial strength of bare fiber and reduces the bending strength by 17% at most. Similar tests confirm that the fiber sensor has 1.96% strain to failure. Axisymmetric finite element analysis is used to investigate the reliability of the in-line etalon when it is embedded in a typical thermoset composite, and parametric studies are performed to determine the mechanically optimal cavity length. The fiber optic sensor is tested using low coherence interferometry with pseudo-heterodyne demodulation under strain and temperature fields. The strain response compares well with resistance strain gages, and the temperature tests confirm the low thermal apparent strain of this sensor. >

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 devices and sensors based on multimode fiber Bragg gratings

Abstract: New sensing and diagnostic methods are implemented with multimode fiber Bragg gratings (MMFBG) and methods for sensor addressing and multiplexing are described. Real time structural strain and vibration monitoring using optical time domain reflectometry (OTDR) is discussed. The first all-mode, wave optics calculations of the reflectivity of Bragg gratings in highly multimode optical fibers are presented, including the effects of individual mode power changes due to microbending transducer loss upstream from the grating. Two categories of multimode fiber gratings are possible, independent mode and mode coupling, and the fabrication differences between these types of gratings are described. The reflectivity properties of independent mode multimode fiber gratings are examined and compared to single mode fiber gratings. In particular, multimode fiber gratings offer added flexibility in grating design and performance characteristics compared to single mode fiber gratings, because the reflectivity response may be tuned by the spatial periodicity, length, core size, numerical aperture, and mode coupling characteristics of the grating.

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. >

All solid state laser source for tunable blue and ultraviolet radiation

Abstract: Tunable blue and ultraviolet single mode laser light has been generated by frequency quadrupling the output of a semiconductor laser with two successive frequency doubling stages. The laser source is based on a commercial high power semiconductor laser near 972 nm which combines a low power single mode master oscillator with a high power amplifier. The doubling stages consist of nonlinear crystals which are placed inside compact optical buildup resonators. Up to 156 mW tunable blue radiation near 486 nm and 2.1 mW ultraviolet light near 243 nm have been produced.

Modal analysis of a small surface emitting laser with a selectively oxidized waveguide

Abstract: We describe studies of an index‐guided ∼4×3 μm2 vertical cavity surface emitting laser with a cw, room temperature 133 μA threshold current and 53% slope efficiency fabricated using selective wet thermal oxidation to provide optical and electrical confinement. While the device operates strictly single mode, a large number of transverse modes are evident in the subthreshold luminescence observed in both vertical and lateral directions. Despite the lumped nature of the index region, the transverse mode wavelengths agree very well with those predicted for a conventional distributed waveguide structure. Waveguide dimensions and an effective index step of 2% between the active and cladding region are determined by fitting the modal data.

Modulational instability in lossy optical fibers

Abstract: The modulational instability in an optical fiber, with loss taken into account, is analytically investigated. It is demonstrated how the linearized equation for perturbation can be solved exactly in terms of Bessel functions, and qualitative differences from previous analytic approaches are pointed out. Finally, the limits imposed by this instability on optical communication systems are discussed. The use of this theory in system design is examined.

Anamorphic microlens for laser diode to single-mode fiber coupling

Abstract: An anamorphic fiber microlens is evaluated for coupling between laser diodes and single-mode fibers. A theoretical model, based on scalar diffraction and Gaussian mode shapes for the laser and fiber fields, is developed to predict the coupling performance of this microlens. Experimentally, the average coupling efficiency of this lens is measured to be 78%. The lateral sensitivity is also measured and compared with the values predicted by the model. >

Single longitudinal mode ridge waveguide 1.3µm Fabry-Perot laser by modal perturbation

Abstract: The authors introduce a cost effective technique which converts the multi-longitudinal mode output of a 1.3 /spl mu/m ridge waveguide Fabry-Perot laser into a single mode by creating modal perturbations along the length of the ridge. Up to 25 dB side mode supression is measured on their first lasers.

150 mW unsaturated output power at 3 µm from a single-mode-fiber erbium cascade laser

Abstract: We report on an erbium cascade laser in a fluorozirconate fiber. Lasing on the transition 4I11/2 -> 4I13/2 at 2.71 µm is supported by colasing on the transition 4S3/2 -> 4I9/2 at 1.72 µm. This recycles the excitation that is lost via excited-state absorption and avoids the saturation of the output power. Threshold at 2.71 µm is 33 mW launched pump power at 791 nm. The measured slope efficiency of 22.6% is relatively close to the 29.1% stokes-efficiency limit. An output power of 158 mW is obtained, limited only by the 1.43 W power available from the Ti:sapphire pump laser. Output power is 15 and slope efficiency 2.5 times higher than reported in previous publications.

Subcarrier multiplexing with dispersion reduction and direct detection

Abstract: An SCM system for simultaneously reducing the concomitant problems of receiver complexity and dispersion penalty and without requiring the use of an expensive, high-bandwidth optical detector. The system provides both a dispersion reduction and a direct detection to the receiver, with microwave mixers and lithium niobate external modulators that produce sidebands that are only separated by a few gigahertz from a principal laser optical carrier. Digital data streams are independently impressed upon these sidebands for transmission over an ordinary single-mode fiber. Independent high-speed data streams are upconverted to microwave frequencies. These subcarriers are then combined with a microwave power combiner and amplified with a microwave amplifier. A solid-state 1550-nm laser carrier is modulated by the microwave subcarriers. An erbium-doped fiber amplifier (EDFA) is used just prior to long-distance transmission over ordinary single-mode fiber. The transmitted optical signal may then traverse multiple EDFAs to compensate for long-haul optical fiber losses prior to detection. At a receiving end, the optical signal is split into multiple paths. The subcarrier channels are optically pre-selected using a narrowband optical filter, such as a fiber Fabry-Perot (FFP) filter. An optical detector converts the selected optical signal into a baseband electrical data stream.

Single mode optical fiber

Abstract: This invention relates to a dispersion-shifted fiber containing silica glass as the major component and in which the zero-dispersion wavelength is set to fall within a range of 1,560 nm to 1,580 nm and the mode field diameter with respect to light having a predetermined wavelength is set to 8 μor more This dispersion-shifted fiber is a single-mode optical fiber capable of decreasing the influence of nonlinear optical effect and having a structure for suppressing an increase in bending loss of the optical fiber, and includes a core region constituted by the first core portion and the second core portion, and a cladding portion In particular, an outer diameter a of the first core portion and an outer diameter b of the second core portion satisfy at least a relationship 010≦a/b ≦029

Fundamentals of multiaccess optical fiber networks

Abstract: Semiconductor light sources single mode optical fibers optical receivers optical amplifiers passive devices and network topologies wavelength division multiaccess networks time division multiaccess networks code division multiaccess networks

A surface mount type single-mode laser module using passive alignment

Abstract: A novel single-mode laser module has been developed using a surface mounting technique. A simple receptacle structure for the module output port is also designed. This module offers high coupling efficiency and optical coupling using the passive alignment technique. A module size of 7.6 mm/spl times/12 mm/spl times/3 mm is achieved, which is very friendly for the automatic assembly line as well as the module mounting process on circuit boards. A laser diode (LD) is passively positioned by utilizing a pair of alignment marks, each of which located on the LD and Si substrate, a single-mode fiber with a microhemispherical lens on the fiber facet is self-aligned on a Si-V groove. The LD to single-mode fiber coupling loss and standard deviation are found to be 5 dB and 1.5 db, respectively. The simple receptacle structure enables one to use this module in the same way as conventional surface mount electrical components. The module assembly process is simplified by successively mounting subassembly parts.

Single-mode, passive antiguide vertical cavity surface emitting laser

Abstract: We report the characteristics of a single-mode, low threshold, passive antiguide region (PAR) vertical cavity surface emitting laser (VCSEL) using both organometallic chemical vapor deposition (OMCVD) and molecular beam epitaxy (MBE) for the regrowth of the PAR structure. The novel passive antiguide region surrounding the active region is demonstrated to be a highly effective transverse mode and polarization mode selection mechanism. A stable single fundamental mode at high currents has been achieved experimentally for laser aperture as large as 16 /spl mu/m diameter, In addition, very low threshold current of 0.8 mA and current density of 490 A/cm/sup 2/ are achieved with 8 and 32 /spl mu/m diameter VCSEL's, respectively. A detailed numerical two- and three-dimensionaI analysis was performed using the beam propagation method. The modal losses were calculated as a function of the cladding refractive index and the laser size. Quantitative results leading to approximate formulae have been achieved. The high mode selectivity obtained from the numerical analysis is in good agreement with the experimental results we have achieved. >

Theoretical analysis of birefringence and form‐induced polarization mode dispersion in birefringent optical fibers: A full‐vectorial approach

Abstract: A new numerical method for analyzing birefringence and dispersion characteristics of birefringent optical fibers is presented. A major advantage of the method, based on the solution of full‐vectorial Maxwell equations, is its high accuracy no matter how great the geometrical anisotropy of the optical fiber. To verify the reliability of our numerical procedure, the modal birefringence and the form‐induced polarization mode dispersion in elliptical core fibers with different eccentricities are investigated and their values compared with some theoretical and experimental results.

A fiber lens with a long working distance for integrated coupling between laser diodes and single-mode fibers

Abstract: A new scheme is proposed for lensed fibers with a long working distance, as used in the coupling between laser diodes and single-mode fibers. The scheme consists of the combination of a hemispherically-ended coreless-fiber tip and an expanded-core fiber. The working distance is measured as 169 /spl mu/m with a relatively low coupling-loss of 4.2 dB at a wavelength of 1.49 /spl mu/m. Tolerances for a 1-dB loss increment for axial-, lateral-, and angular-misalignment are 35, 2.6 /spl mu/m, and 0.8 degrees, respectively. The new configuration is suitable for alignment-free coupling between arrayed laser diodes and an array of single-mode fibers. >

Polarization properties of the flint glass fiber

Abstract: To realize stable characteristics of a current sensor using the Faraday effect in an optical fiber, it is necessary to prevent the influence of birefringent effect on light passing the fiber, which is caused by photo-elastic effect and/or lack of axial symmetry of its structure. The flint glass fiber manufactured from flint glass with very small photo-elastic constant, which has circular core and satisfies the single ode condition,has been developed to solve this problem. This paper reports results of a study to clarify polarization properties of the fiber and to consider a method for highly stabilizing the polarization. From experiments to investigate the relationship between state of polarization of light inserted to the fiber and that emitted from another end, it was confirmed that the birefringence due to the photo-elastic effect and the lack of symmetry are negligibly small. It also became known that the azimuth angle of polarization of the emitted light depends on the shape of the curve of the fiber. Namely, a rotation of the polarization plane is equal to the amount of line integral of the torsional rate along the curve. A countermeasure is necessary for this phenomenon, because characteristics of the current sensor may be influenced if the flint glass fiber coil is deformed by environmental factors. From a consideration of the mechanism of the phenomenon, it is inferred that the problem can be solved by reciprocating light in the fiber to stabilize the polarization. The effect of this method is confirmed experimentally. >

Circular groove guide for short millimeter and submillimeter waves

Abstract: A new type of groove guide, circular groove guide, has been designed for use as a low losses, high power handling, low dispersion and single mode transmission medium in the short millimetric and submillimetric waves ranges. The characteristic equations of TE modes and TM modes have been developed and the propagation characteristics of the fundamental mode have been discussed. Experimental measurements are in good agreement with theoretical results. >

Cladding-pumped MOPA structure

Abstract: A master oscillator and power amplifier configuration for a high power cladding-pumped laser structure, and a method of making same, is disclosed. The laser structure comprises a single mode core having at least one oscillator defined therein, and a first and second cladding layer for waveguiding and radiation retention. The core is doped with refractive-index modifying dopants, in addition to ionized rare earth elements. The refractive-index modifying dopants facilitate writing one or more spaced pairs of index gratings in the core, each pair defining an oscillator. Oscillator cavity length is determined by the desired mode spacing and is less than one-half of the single mode core length. The index gratings are formed via a ultraviolet light-induced refractive index change in the core, which index change varies periodically along the core. The periodic variation is created by projecting an interference pattern on the core.

Chaotic synchronization and modulation of nonlinear time-delayed feedback optical systems

Abstract: We present a special chaos synchronization system based on coupled time-delayed feedback optical systems. As far as we know, this paper reports for the first time simulations of synchronization in such optical circuits. The unsolved problem of the channel in communication applications of chaos synchronization for electronic systems make the optical systems very attractive. The quasi-infinite bandwidth, very low attenuation and practically noiseless characteristic of single mode fiber, used as information transmission medium, are the three main advantages of our system. We show by simulations that synchronization is effective, use a chaos shift keying modulation/demodulation scheme for binary information transmission and present some estimation of the bit rate in a such system. >

Coherent optical frequency domain reflectometry for a long single-mode optical fiber using a coherent lightwave source and an external phase modulator

Abstract: Coherent optical frequency domain reflectometry (C-OFDR) is demonstrated for a long single-mode optical fiber at a wavelength of 1.55 /spl mu/m by using a highly coherent lightwave source and an electrooptical (EO) external phase modulator. Rayleigh backscattering and Fresnel reflection from a 16.4-km optical fiber are observed when the modulation frequency is swept from 4 GHz to 8 GHz for 40 ms. The insertion of an optical fiber delay line in a probe lightwave path makes it possible to distinguish the Rayleigh backscattering profile due to the first-order modulation sideband in the phase-modulated lightwave from those due to the higher order sidebands. A spatial resolution of better than 100 m is achieved for two neighboring Fresnel reflectors located near the far end of the test fiber. >

Dispersion characteristics of a helically cladded step-index optical fiber: an analytical study

Abstract: A new type of step-index optical fiber, the helically cladded fiber (HCF), in which a conducting sheath helix is introduced at the core–cladding interface boundary, is proposed. By application of the appropriate sheath-helix boundary condition at the core–cladding interface, the modal characteristic equation is determined. The dispersion curves are also obtained. Analysis of the modal characteristic equation and dispersion curves reveals that only hybrid modes are supported, and the lowest-order mode is HE01. The pitch angle of the helix has no effect on the cutoff condition. Its effect is more pronounced in the case of the first odd modes. One retrieves the modal characteristics of the step-index fiber by setting the pitch angle equal to zero. Further, a fact of technical importance emerges: that the HCF behaves as a monomode guide for a comparatively large core radius.

Method of producing an optical fiber preform from a plurality of tubes having different thermal conductivities

Abstract: Disclosed is an optical fiber capable of preventing an increase in an optical loss from occurring during fabrication and extraction of a single mode fiber preform and enhancement of an optical transmission efficiency, a method of producing the same comprising the steps of forming a first quartz robe having a first thermal conductivity, said first quartz tube being used as a clad; depositing a core layer and a clad layer inside the first quartz robe to form a preliminary perform by heating of the fist quartz robe; forming a second quartz tube having a second thermal conductivity lower than the first thermal conductivity; and depositing the second quartz tube to said preliminary preform by heating to produce the optical fiber preform. On embodiment, uses N overclad layers having thermal conductivites Kx such that K0 >K1 >K2 . . . >KN and coefficients of viscosity μ0 <μ1 <μ2 . . . <μN.