Showing papers on "Optical fiber published in 1978"

Photosensitivity in optical fiber waveguides: Application to reflection filter fabrication

Abstract: The observation of photosensitivity in Ge‐doped core optical fibers is reported. The photosensitivity is manifested by light‐induced refractive‐index changes in the core of the waveguide. Narrowband reflectors in a guide structure have been fabricated using this photosensitivity and the resulting DFB reflectors employed as laser mirrors in a cw gas laser in the visible.

Light propagation in graded-index optical fibers

Abstract: An accurate numerical method is described for solving the Helmholtz equation for a general class of optical fibers. The method yields detailed information about the spatial and angular properties of the propagating beam as well as the modal propagation constants for the fiber. The method is applied to a practical graded-index fiber under the assumptions of both coherent and incoherent illumination. A spectral analysis of the calculated field shows that leaky modes are lost and steady-state propagating conditions are established over a propagation distance of a fraction of a meter.

Theory of Bragg fiber

Abstract: The possibility of using Bragg reflection in a cylindrical fiber to obtain lossless confined propagation in a core with a lower refractive index than that of the cladding medium is proposed and analyzed.

Self-phase-modulation in silica optical fibers

Abstract: We report measurements of frequency broadening due to self-phase-modulation (SPM) in optical fibers. The use of single-mode silica-core fibers and mode-locked argon-laser pulses leads to the simplest and cleanest measurements yet made of SPM. The qualitative features of the frequency spectrum are in good agreement with theoretical expectations. The experiment provides an independent measurement of ${n}_{2}$, the self-focusing coefficient. The results also point to some simple and useful techniques based on fibers for the measurement and analysis of mode-locked laser pulses.

Fiber optics strain gauge.

Abstract: We have demonstrated a fiber optics strain gauge measuring strains of <0.4 × 10. It utilizes the change in optical pathlength caused by strain in a fiber. Strain is measured as motion of fringes in an optical interference pattern. Optical phase shifts per unit strain per unit fiber length of about 1.2 × 10 m 1 are predicted by theory and observed in experiments. If light from a laser having sufficient coherence length is launched into two single-mode fibers of approximately the same length, the light issuing from the other ends can be made to interfere and produce visible fringes. If the optical pathlength through one fiber is changed with respect to the optical path through the other, the fringes will shift; the amount of fringe shift is proportional to the relative change in optical paths. Thus, by observing the motion of the fringes, we can determine the optical pathlength changes that occur. Introducing different strains in the two fibers causes a difference in optical pathlengths and, hence, motion of the fringes. This phenomenon serves as a sensitive fiber-optic strain gauge. If one or both fibers are attached to a structure which is then strained under load, the strain in that structure can be determined from the motion of the optical interference fringes. To calculate the expected fringe shift due to longitudinal strain, let the section of single-mode fiber to be strained be of length L with its axis in the x direction. The propagation constant of the mode in the fiber is designated by β, its freespace propagation constant is k0, the fiber core index is n, the core diameter is D, and Poisson's ratio for the fiber material is μ. The phase of the light wave after going through this fiber section is  = βL. Straining the fiber in the axial direction by an amount ε changes this phase by an amount

cw three-wave mixing in single-mode optical fibers

Abstract: Strong continuous three‐wave mixing of 514.5‐nm argon laser light in a single‐mode fiber is reported. The effect, due to the third‐order nonlinearity of silica, has been observed for light whose frequency spectrum consists of either a few discrete monochromatic frequency components separated by ∼1 GHz or a quasicontinuous distribution of frequencies having a spectral envelope ∼4 GHz wide. We show that the effect provides a simple and effective method for measuring the nonlinearity of silica. In the first manifestation of the effect, the nonlinearity mixes the frequency components to produce new frequencies. In the second, multiple mixing occurs that broadens the quasicontinuous spectrum. This manifestation of the effect is large; broadening by a factor of 4 has been observed with lower intensity levels than are required to produce stimulated Brillouin scattering in the same fiber. A theoretical model is presented to describe spectral broadening by three‐wave mixing for the case of small broadening. The effect of three‐wave mixing on the operation of continuous stimulated Brillouin and Raman oscillators is also discussed. Finally, it is noted that the presence of this effect may constrain the design of long‐haul single‐mode fiber optical communication trunks.

Polarization and magnetooptic properties of single-mode optical fiber

Abstract: The polarization and magnetooptic properties of a sample of single-mode optical fiber have been investigated. The fiber acts as a linear retarder, and the degree of retardation is dependent on the external pressure applied to the fiber. The stress optic coefficient is found to be 8.72 x 10(-10) N(-1) m(2). The direction of linear polarization is rotated when a longitudinal magnetic field is applied to the fiber (Faraday effect). The Verdet constant is 1.56 x 10(-2) min A(-1). The intrinsic specific linear retardation of the fiber is found to be less than 0.44 rad m(-1) from the magnetooptic measurements. The fiber has been used in an experimental current measurement device.

Narrow-band Bragg reflectors in optical fibers.

Abstract: The formation and characterization of narrow-band-waveguide reflection filters in Ge-doped silica optical fibers is described. The filters can have complex response profiles and are tunable in frequency by mechanical strain.

Fiber optic light delivery apparatus and medical instrument utilizing same

Abstract: Disclosed is a fiber optic fiber transmission line which transmits light a distance from its source and is terminated, at its light delivery end, by a second fiber optic fiber of a larger diameter than the first fiber. An interlocking connector keeps the first and second fiber in positive contact in an efficient light energy transmission relationship. A plurality of second fibers form a set of tips for use in causing light convergence or divergence at the transmission line output.

Optical sensing apparatus and method

Abstract: A sensor for measuring stress, temperature, pressure, sound, etc. comprising an optical waveguide, preferably an optical fiber waveguide, a light source which injects light into one end of the waveguide, a deformer contacting and deforming the waveguide to cause light to couple from originally excited modes to other modes, and an optical detector to detect the change in light coupling caused by deformation of the waveguide.

Spontaneous and stimulated Raman scattering in long low loss fibers

Abstract: This paper considers the problem of forward Raman scattering process in a single transverse mode fiber. Both pump wave depletion and spontaneous scattering are considered in the analysis. Analytic solutions of the governing differential equations are obtained. We examine the conditions under which a nondepleted pump approximation is valid. Expressions are derived for the maximum fiber loss and the minimum fiber length which allow significant pump to Stokes wave conversion. It is shown that for a given fiber length there is an optimal pumping power, or at a given pump power there is an optimal fiber length that yields maximum first-order Stokes power output. Good agreement with published experimental results in the threshold power prediction is obtained.

Polycrystalline fiber optical waveguides for infrared transmission

Abstract: A new type of fiber optical waveguide utilizing TlBr and KRS‐5 has been prepared; its infrared transparency extends to wavelengths well beyond those transmitted by known glassy materials.

Linear polarization in birefringent single‐mode fibers

Abstract: Single‐mode fibers which maintain linear polarization are described. The fibers are birefringent and linear polarization is maintained along either of the two principal axes. The birefringence arises from the deliberate enhancement of anisotropic strains.

A universal fiber-optic (UFO) measurement system based on a near-IR fiber Raman laser

Abstract: A universal fiber-optic measurement system, which is useful for measuring loss and dispersion in the 1.06-1.6 \mu m wavelength region, is described. The source is a silica fiber Raman laser pumped by a mode-locked and Q -switched Nd:YAG laser at 1.06 μm. Subnanosecond multiple-Stokes pulses in the 1.1-1.6 \mu m wavelength region are generated in a low-loss single-mode silica fiber. The use of this near-infrared fiber Raman laser for characterizing various transmission properties of single and multimode test fibers is demonstrated. Loss spectra, intramodal dispersion, and intermodal dispersion data are obtained in the wavelength region of minimum loss and minimum material dispersion for silica fibers.

Physical behavior of the neck-down region during furnace drawing of silica fibers

Abstract: During the drawing of optical fibers, the maintenance of a uniform fiber diameter is a difficult task. Parameters affecting the diameter variations are the temperature and viscosity distributions within the neck‐down region, the neck‐down shape, and the fiber drawing tension. A physical model is presented that predicts the neck shape and temperature distribution within the neck‐down region during the drawing of a high silica rod into a fiber. The model is formulated by an iterative technique to obtain solutions from the coupled equations of momentum and energy for given fiber‐drawing conditions. It is demonstrated that the predicted values of the viscosity, neck shape, and drawing tension agree well with those of measured values.

ZnCl2 glass: A potential ultralow‐loss optical fiber material

Abstract: Zinc chloride glass is a potentially useful medium for ultralow‐loss (∼1 dB/103 km) optical fibers for wavelengths in the 3.5–4‐μm region. In this region, intrinsic absorption, scatter, and material dispersion are all expected to be small, and the common fully oxidized transition metal impurities and H2O should exhibit extremely weak absorption as well.

Optical channel waveguide switch and coupler using total internal reflection

Abstract: Light beam switching and coupling in a four-port channel waveguide-horn structure has been accomplished using electrooptic modulation of the critical angle of a refractive index interface in a Y -cut LiNbO 3 substrate. The resulting double-pole double-throw switch/coupler is potentially capable of simultaneously providing a combination of desirable characteristics.

Polarization characteristics of noncircular core single-mode fibers

Abstract: It is well known that geometrical or dielectric imperfections in conventional graded-index single-mode fibers depolarize light after a few centimeters. A slight improvement in the polarization performance of these fibers is achieved by introducing noncircularity in the core shape. This is evident from the measurements on borosilicate fibers with dumbbell shaped cores. This result is correlated with Marcatili’s analysis, which shows that changing the core geometry, from square to rectangular, does not appreciably alter the difference in the propagation constants of the two fundamental modes with orthogonal polarizations. Thus, the noncircular geometry and the associated increase in stress-induced birefringence introduced during the manufacturing process alone are not sufficient to improve the polarization performance, and the enhancement of the anisotropic birefringence is necessary to achieve single-polarization fibers.

Packaged fiber optic modules

Abstract: A module for a fiber optic data transmission system which will accommodate either a suitable light source or a photoelectric detector. The module incorporates an integrated electronic assembly, such as a hybrid microelectronic assembly. The assembly has provision for a photoelectric transducer which preferably has a cylindrical mount disposed in a cylindrical recess of the electronic assembly. The entire assembly may be surrounded by a cylindrical can having a transparent window. The transducer is provided with a collimating lens which permits it to receive or emit a collimated light beam. Between the fiber optic bundle and the transducer, there is preferably disposed a focusing lens. The focusing lens receives or emits the collimated light beam and focuses it on the fiber optic bundle. A housing surrounds the entire module. Means, such as a retainer ring, are provided for holding the electronic assembly within the housing. Similar means are provided for maintaining the focusing lens within the housing. The distance between the focusing lens and the optical bundle is established by means of a ferrule which in turn is urged toward the housing by a nut and threaded sleeve portion.

Fiber optic temperature sensor

Abstract: An inexpensive, lightweight fiber optic micro-sensor that is suitable for applications which may require remote temperature sensing. The disclosed temperature sensor includes a phosphor material that, after receiving incident light stimulation, is adapted to emit phosphorescent radiation output signals, the amplitude decay rate and wavelength of which are functions of the sensed temperature.

Viabilities of the Wavelength-Division-Multiplexing Transmission System Over an Optical Fiber Cable

Abstract: This paper describes the feasibility and the applicability of the Wavelength-Division-Multiplexing (WDM) system with two types of preliminary WDM transmission experiments. Through this study, it has become clear that WDM technologies play a major role in optical fiber systems and have the possibilities of realizing the various optical fiber transmission systems.

Fusion splices for single-mode optical fibers

Abstract: A practical low loss splicing method based on the discharge fusion for single-mode fibers was developed. Average splice losses of 0.4, 0.2, and 0.1 dB for fibers with 5.2, 7, and 10 μm core diameters, respectively, are obtained by a simple apparatus utilizing the self-alignment effect due to the surface tension of melted fiber ends. The surface tension effect is analyzed both experimentally and theoretically. Experimental splice losses, both after and during heating, coincide with the theoretical estimated values. It was found that the optimum heating temperature for low loss splices is near 2000°C at 8.5 W electric discharge power. Splicing loss causes are examined. The main cause of the practical splice loss is the residual core axis misalignment caused by an insufficient surface tension effect and core eccentricity with respect to cladding.

Optical fibre terminations and connectors

Abstract: A termination for an optical fibre is formed with an integral lens for producing an expanded parallel light beam. A pair of terminations provide an optical coupler for connecting between a corresponding pair of optical fibres.

Fiber-optic acoustic sensor

Abstract: An optical fiber acoustical sensor for detecting sound waves in a fluid mum. An optical fiber coil through which a light beam is transmitted is placed in a fluid medium. A sound wave propagating through the fluid medium and incident on the optical fiber coil changes the index of refraction and the length of the optical fiber at the area of incidence. These changes cause a shift in the transmitted light which is detectable to denote the presence of the sound wave.

Electroluminescent diode and optical fiber assembly

Abstract: An optical fiber and an electroluminescent semiconductor diode are each secured to separate mounting blocks which in turn are secured to each other, either directly or through an additional block, with the optical fiber aligned with the output of the diode. The mounting blocks are secured together by a thin layer of a bonding material which is preferably fast setting so as to prevent or limit relative movement between the mounting blocks which could cause misalignment of the optical fiber and the diode. The bonding material is preferably of the type which is cured when subjected to ultraviolet light, and at least one of the mounting blocks is preferably transparent to the ultraviolet light.

Single polarization optical fibers: Exposed cladding technique

Abstract: A simple method is described for fabricating fibers with large strain birefringence starting with standard MCVD preforms. The method is illustrated using borosilicate fibers. The birefringence and polarization properties are measured in a long fiber and the birefringence is also measured using a fiber slice and polarizing microscope.

Nd : Y2O3 single‐crystal fiber laser: Room‐temperature cw operation at 1.07‐ and 1.35‐μm wavelength

Abstract: Single‐crystal fibers have been grown from high‐purity 1.5 wt% Nd2O3 : Y2O3 powder mixtures, and short lengths of the fiber in dielectric mirror resonators have been evaluated as lasers at both 1.07‐ and 1.35‐μm wavelength. The laser transition cross sections were approximately equal at the two wavelengths, and they were about two‐thirds the cross section of Nd : YAG at 1.31 μm. The fluorescence lifetime of the laser samples was 340 μsec. Loss in the material was approximately 3% per cm. The absorption spectrum from 0.7 to 1.0 μm and fluorescence spectra for the 4F3/2→4I9/2, 4F3/2→4I11/2, and 4F3/2→4I13/2 manifolds of Nd3+ in Y2O3, taken with fiber samples, are reproduced in detail. The resultant energy levels are given. With a Kr laser operating at 0.7525 μm as the end pump, minimum observed laser threshold was 0.57 mW absorbed pump power for a 100‐μm‐diam 2.5‐mm‐long fiber operating cw in room‐temperature air at 1.07 μm. The lasers operated in one or two transverse modes and had active linewidths of app...

Differential mode attenuation measurements in graded-index fibers

Abstract: An automated apparatus is described for measuring mode-dependent scattering and total attenuation in graded-index waveguides. Measurements are reported for two low-loss waveguides and several high-loss waveguides. The results illustrate the ability of this technique to identify different types of loss mechanisms.

Wideband near-i.r. continuum (0.7-2.1 μm) generated in low-loss optical fibres

Abstract: A wideband near-infrared continuum is obtained by nonlinear optical interactions in low-loss single-mode and multimode silica fibres pumped by pulses from a Q-switched Nd:y.a.g. laser. With 50 kW pump power coupled into a 315 m long 33 μm core-diameter low-loss multimode fibre, a continuum spanning the spectral range 0.7–2.1 μm with a total power of 12 kW is generated. In single-mode and low-mode-number fibres a similar continuum of lower power has been obtained. Such continuum sources are useful for measurement of fibre properties as well as for spectroscopic study of other optical materials.