Showing papers on "Dispersion-shifted fiber published in 1975"

Phase-matched-stimulated four-photon mixing in silica-fiber waveguides

Abstract: Stimulated four-photon mixing has been observed in silica-fiber waveguides. Phase matching is achieved by using the dispersion of the waveguide modes to compensate for bulk dispersion. The coherence lengths can be greater than 10 m and the gains more than double the usual Raman gain.

Perturbation theory of a doubly clad optical fiber with a low-index inner cladding

Abstract: A doubly clad optical fiber which is composed of the core, inner cladding, and outer cladding is called a W -type fiber when the core has the largest index of refraction of the three and the inner cladding has the lowest. A W -type fiber is known to have several advantages over a conventional singly clad (SC) fiber. This paper presents simple, closed form approximations of a W -type fiber with respect to cutoff, the attenuation constant in the leaky wave region and a rapid change of the group velocity near cutoff, etc. In the approach to be described, a W -type fiber is thought of as a combined system of an SC fiber and an outer perturbing medium.

Mode coupling in a multimode optical fiber with microbends

Abstract: Experimental observations of the radiation pattern of a short multimode fiber with different induced deformations are reported here. Theoretical calculations are also made, based on the assumption of strong coupling between two particular modes of the fiber, and are in good agreement with experiment. We obtain numerical evaluations of the coupling coefficients and excess loss as a function of the amplitude of the deformation, and indications on the requirements to be met in cabling the fibers are derived from the experimental results.

Excitation of parabolic-index fibers with incoherent sources

Abstract: We study the excitation of a parabolic-index fiber by an incoherent source. The theory is based on approximating the fiber modes by Laguerregaussian functions. The dependence of the total light power injected into the fiber core on the separation between source and fiber, and on the transverse displacement of the source, is shown in graphic form. Also shown are far-field radiation patterns, which indicate the distribution of power versus mode number, for several launching conditions and plots of power versus azimuthal mode number for given values of the compound mode number. The study of launching efficiency versus source radius leads to prescriptions for optimizing the ratio of source to fiber core radius without a matching lens. Use of a lens for matching the image of a small source to the size of the fiber core increases the launching efficiency relative to the power consumption of the light-emitting-source diode.

Shuttle pulse measurements of pulse spreading in an optical fiber.

Abstract: Partially transparent mirrors were pressed against fiber ends so that the length dependence of pulse spreading could be determined without cutting the fiber into pieces. Measurements were made by comparing the widths of laser pulses (λ = 0.9 μm) through the output end mirror, which returned from 9½ successive round trips (2014-m extrapolated length) along a 106-m multimode fiber. Mode mixing was significant in this fiber (fabricated by Corning Glass Works), and a square root of length pulse width dependence was observed. However, some of the mode-mixing effects on pulse width were caused by the way in which the fiber was wound on a drum.

New Slitless Optical Fiber Laser-Raman Spectrometer

Abstract: A new slitless optical fiber laser-Raman spectrometer has been developed in which long, thin, low loss optical fibers, either liquid filled or solid core, act simultaneously as the sample and entrance aperature. The fiber end is placed at the focus of the collimator lens, and the resultant parallel radiation is dispersed by three large triangular Steinheil prisms in series. The dispersed radiation is then focussed by the camera lens to a series of points in the focal plane. The Raman points are detected photoelectrically by scanning with either an exit pinhole or slit, and a photomultiplier whose photocathode surface can be as small as the fiber end. Because of the long fiber lengths employed and of the high transmission efficiency of the spectrometer, very large Raman signals result. For example, the extremely weak Raman intensity maximum from fused silica at Δν- ≈ 2165 cm−1 is readily detected visually in the focal plane using a fiber length of 85 m and a few hundred milliwatts of 476.5 nm excitation. The new spectrometer will be of considerable use in Raman studies of pure and doped glasses in fiber form, and of a wide range of liquids and mixtures where small sample amounts are involved. It may also be possible eventually to extend this slitless method to studies of water, aqueous solutions, and gases by employing straight dielectric waveguide techniques.

Excitation of the fundamental and low-order modes of optical fiber waveguides with gaussian beams. 2: offset beams.

Abstract: The excitation efficiencies of the dominant and low-order modes in an optical fiber are theoretically determined for an incident Gaussian beam that is offset with respect to the fiber axis. The excitation efficiencies are shown to be strongly influenced by both the numerical aperture of the fiber and the wavefront curvature of the incident beam.

Transmission properties of a low−loss near−parabolic−index fiber

Abstract: Pulse dispersion, refractive−index profile, and loss measurements were made on a low−loss graded−index optical fiber fabricated by a chemical vapor deposition technique. The transmission loss spectra had a minimum value of 3.8 dB/km at 1.06−μm wavelength. The core refractive index had a power−law profile with an exponential coefficient of 2.2±0.1. Mode−mixing effects and the near−parabolic−index profile in a 5.6−km extrapolated fiber length (actual length =1.12 km) reduces modal dispersion by a factor of 17 from the result expected for an ungraded step−index fiber.

Light scattering from unclad fibers: ray theory

Abstract: Information contained in the position of the peaks of backscattered light intensity from an unclad fiber, with laser light incident at right angles to the fiber axis, is utilized to determine the parameter b/λ (b = fiber radius, λ free space wavelength). For known laser wavelength the fiber diameter can thus be determined. The theory is based on an approximate ray analysis and is compared with the results of the exact wave theory. Good agreement is obtained. The accuracy of this procedure may vary between 1% and 10%.

Mode coupling in an optical fiber with core distortions

Abstract: The variations in the geometry of a step-index optical fiber are determined as functions of position along the axis of the fiber by an analysis of the backscattered light produced when a beam from a cw laser is incident perpendicular to the fiber axis. The power spectrum computed from this distortion function is then utilized with coupled-mode theory to predict the mode coupling, the reduction in pulse dispersion, and the accompanying increased radiation loss of the fiber. The theoretical calculations support experimental observations and account for a partial reduction in the multimode pulse dispersion.

Higher-order mode fiber optics t-coupler

Abstract: A higher order mode, simplex, fiber optics T-coupler is based on using only the higher order lossy modes of single fiber optics whether the cable is single fiber or a fiber bundle. This allows for T-couplers that discriminate on modes.

Length dependence of pulse dispersion in a long multimode optical fiber.

Abstract: Shuttle pulse measurements performed on a 1280-m long multimode optical fiber were used to determine pulse dispersion along a 6400-m extrapolated length. The fiber's steady-state mode coupling length was determined without breaking the fiber. The impulse responses for one, three, and five trips through the fiber were recorded and Fourier transformed to yield the corresponding baseband frequency responses. It was concluded that the coupling length was approximately 840 m, and that the impulse response became increasingly more symmetrical for fiber lengths beyond this coupling length. This agrees with theory.

Focusing Effects in Interferometric Analysis of Graded-Index Optical Fibers

Abstract: The effects of ray bending due to graded refractive-index profiles have been studied in relation to the measurement of optical-fiber refractive-index profiles by microscopic interferometric techniques. In particular, the wavefront curvature produced by a simple parabolic profile has been calculated analytically. It is concluded that profile measurements by currently used methods require samples for which the fiber thickness (length) is much less than the effective focal length of the fiber. For parabolic profile fibers with diameter d greater, similar 100 microm, this poses no problem; however, for small-core versions of this fiber, sample thicknesses of 10-15 microm may be required and an alternate measurement technique is described. Interferograms made on a Leitz transmitted-light interference microscope are included in illustrations.

Shuttle pulse measurements of pulse spreading in a low loss graded-index fiber.

Abstract: Shuttle pulse measurements in a multimode optical fiber were used to determine pulse dispersion, at λ = 0.9-μm wavelength, in eight increments from 148-m to a 2516-m extrapolated length. There was relatively little mode mixing in this low loss fiber (minimum loss = 1.7 dB/km at λ = 1.04 μm), and the observed pulse width was primarily due to the grading of the refractive-index profile.

Measurement of very short optical delays in multimode fibers

Abstract: We describe a new method for measuring group‐delay differences between the modes of an optical fiber of the order of 1 psec. This is accomplished by Fourier analyzing the intensity output of the fiber, which is fed with a quasimonochromatic signal whose frequency is linearly modulated in time. We present the results of an experiment, in which time delays of the order of 10 psec have been measured. This confirms the potential of the method for measuring dispersion in optical fibers.

Dispersion-Optimized Optical Single-Mode Glass Fiber Waveguides

Abstract: The optical dispersion in singly clad dielectric monomode waveguides is calculated by taking into account the frequency dependence of the refractive indices of the core and the cladding materials. The total dispersion is composed of the material dispersion and the dispersion of the waveguide structure. Fibers can be optimized in such a way that these two portions have opposite signs. The portion due to material dispersion, however, is about 2 orders of magnitude greater than that due to waveguide structure dispersion (considering typical glasses at wavelengths of 0.9 μm and 1.06 μm). Thus, complete compensation of these portions is impossible, and the fibers cannot be made dispersion-free at these wavelengths. The total dispersion at 1.06 μm, however, is smaller than at 0.9 μm by a factor of ⅔.

Optical transmission path coupler

Abstract: PURPOSE:In order to improve the transmission characteristics of optical fiber, by means of making the taper angle of shaft-core taper hole smaller on its insertionside, in an optical transmission coupler which reciprocally joins paired fiber holder which contains the front-edge of optical fiber being naked in the shaftcore taper hole.

Radius of uncladded optical fiber from back-scattered radiation pattern*

Abstract: The back-scattered pattern produced by a plane-polarized beam incident normally on a large uncladded optical fiber can be used to determine the refractive index and the radius of the fiber. The geometric-optics method is used to analyze the pattern. A new procedure to find the radius of the fiber is proposed. The procedure can make use of nearly the whole of the back-scattered pattern, without need to measure exactly the positions of all of the individual fringes. Special attention is given to the limits of accuracy.

A 120-MHz Bandwidth Linear Signal Transmission System Using Fiber Optics

Abstract: A complete linear fiber-optic-signal transmission system with an upper frequency limit greater than 150 MHz is described. The transmitter accepts signals in the range of 1 to 15 mV and amplitude modulates an LED. The emitted light signal is carried via fiber optics to a receiver employing a silicon avalanche detector and an amplifier which increases the signal level to the hundreds of millivolts range. Sine-wave bandwidth is 30 kHz-120 MHz (voltage response down to 70 percent), and phase distortion is low, thus preserving pulseshapes. For a transmission path consisting of 15 m of low-cost fiber cable, the dynamic range is 30 dB with harmonic content 30 dB below signal.

Low order mode propagation photo fiber

Abstract: PURPOSE:Holding group delay time difference between modes small, allowing wide band characteristic, and making core diameter larger than that of single mode fiber.

Launching efficiencies of the HE(1m) modes in a selffocusing optical fiber waveguide.

Abstract: The launching efficiencies of the HE1m modes and the over-all launching efficiency are calculated for the cases in which a self-focusing optical fiber is excited axially by a TEM0n beam mode or by a beam consisting of several beam modes. It is shown that, when the fiber is excited by a TEM00 mode whose spot size s is very large compared with the characteristic spot size so of the fiber, the HE1m modes are almost equally excited and that, if s is matched to so, the over-all launching efficiency is nearly 100%. The over-all launching efficiency as well as the launching efficiencies of the HE1m modes decrease considerably when the fiber is excited by a beam containing the TEM01 mode that is out of phase with the TEM00 mode. The effect of the off-axis excitation by a TEM00 mode on the over-all launching efficiency is also examined.

Optimized parabolic-index optical fiber communication system with incoherent light source

Abstract: The disclosed optical fiber communication system employs a fiber with a core having an index of refraction graded in an approximately parabolic fashion and a light-emitting diode joined directly to the fiber to serve as the light source for the system. It has been found that the overall electrical efficiency of the system, at least with respect to drive power for the diode, is maximized when the ratio of the diode radius to the radius of the fiber core is about 0.2. More broadly, the ratio of radii is found advantageously to lie in the range between about 0.1 and about 0.8, not only for efficiency reasons but also to maximize the amount of light injected into the fiber.

Plastic optical fiber displacement sensor for study of the dynamic response of a solid exposed to an intense pulsed electron beam

Abstract: The principle of the branched fiber bundle sensor has been known for many years. The apparatus which is described in this paper is distinguished by simple fabrication, low cost, high sensitivity, and a fast response time. It is used for measuring the velocity of the back surface of an irradiated aluminum target. In spite of intense consecutive bremsstrahlung, the plastic fiber probe gives good results, whereas with glass fiber a large scintillation impulse appears which covers the signal.

Optical transmission fiber

Abstract: PURPOSE:By establishing a given connection with distance from the center of a fiber to the maximum refractive index section of an O ring, the thickness of the O ring section and the refractive index distribution of the ring section, an optical transmission fiber of which signal distortion is few shall be obtained.

Frequency speciality compensation method of the light fiber

Abstract: PURPOSE:To make improve the transmission content and the frequency speciality of the light fiber substancally, by adding the simple operation on the way of propagating to the low degree mode and the high degree mode propagated of the light fiber.

Coherence of laser radiation traveling along an optical fiber

Abstract: The degree of coherence of the laser radiation transmitted by a single optical fiber was determined by the Young interference method. It was found that the modulus of the complex degree of coherence decreased with increasing fiber length and also with decreasing diameter (in the case of large diameters). However, for fibers up to 10 cm long this modulus did not fall below ~0.7. The results obtained were explained by a difference between the paths of different rays of the laser beam which appeared during the passage through the fiber; the imperfections in the fiber also played an important role. The main factors responsible for the path difference were considered and their relative importance was estimated.

Transmission Properties Of Optical Fiber Waveguides

Abstract: Guided optical communications using glass optical fiber waveguides is a rapidly growing field In this paper a discussion of the transmission characteristics of the optical fiber will be given This will include first a description of rays and modes in the waveguide Attenuation, long the benchmark for judging fibers has its sources broadly grouped into two categories, absorption and scattering These will be further subdivided into their contributing factors and discussed, giving a summary of the current status of attenuation reduction The information carrying capacity is potentially limited by two things, differing group velocity for each mode and finite spectral width of the transmitted light These will be discussed, showing the effect that material properties and the radial index gradient have on information bandwidth In the multimode waveguide energy may be transferred between modes during transmission This can be beneficial by causing the information capacity to decrease only as the (fiber length)12 rather than directly as the fiber length as in the case of no mode coupling It can also be detrimental since there is an additional attenuation associated with mode coupling This effect will have an impact on fiber parameters as well as on fiber packaging and will be discussed© (1975) COPYRIGHT SPIE--The International Society for Optical Engineering Downloading of the abstract is permitted for personal use only

Spectral transmission characteristics and chromatic dispersion of uv optical fibers.

Abstract: Schott's uv fiber optics with special organic cladding are supposed to increase the spectral transmission response at lower wavelengths. However, it was observed that chromatic dispersion occurred when certain geometrical arrangements of the fiber were made. Spectral transmission characteristics were analyzed in detail for both coherent and incoherent radiation sources. The cause of this chromatic dispersion is presently unknown.