Showing papers on "Photonic-crystal fiber published in 1975"

Mode Coupling Effects in Graded-index Optical Fibers

Abstract: Mode coupling theory is applied to the study of multimode optical fibers with graded-index cores. For coupling caused by random bends in the waveguide axis, the results predict the dependence of the induced losses on the fiber's characteristics. The impulse response is determined for fibers with random bends having several different power spectra. The results are used to predict the transmitted power, the delay time, and the rms pulse width in fibers with graded-index cores.

Microbending loss in optical fibers

Abstract: The loss induced in optical fibers by random bends in the fiber axis is studied by winding fibers under constant tension onto a drum surface that is not perfectly smooth. The tension forces the fibers to conform to slight surface irregularities, which can result in an increase in the optical loss on the order of 100 dB/km. This microbending loss may be a significant design consideration in system applications of low-loss optical fibers. Data are presented on the reduction of the effect by means of coatings and increased numerical aperture.

Single-crystal fiber optical devices: A Nd:YAG fiber laser

Abstract: Single−crystal fibers of Nd:YAG have been grown in diameters as small as, but not limited to, 50 μm by a pedestal growth (modified zone melting) technique. Room−temperature cw laser operation has been achieved with 0.5−1−cm−long samples. The method is directly applicable to the growth of single−crystal fibers of various materials for devices covering a wide range of applications, especially for optical communications.

Optical transmission fiber

Abstract: An optical transmission fiber which is formed by applying and baking a liquid resin composition or a solution or a dispersion prepared by dissolving or dispersing in a solvent a liquid or solid resin composition onto a glass fiber for optical transmission and, further, coating thereover by melt extrusion a thermoplastic resin composition.

Formation of a Spherical Lens at Optical Fiber Ends with a CO(2) Laser.

Abstract: A study was made of the use of a CO(2) laser for producing a hemispherical lens at the end of a fiber. When the fiber end is heated to the softening points of the material, it tends to become spherical in shape due to surface tension. A one-dimensional heat conduction model for the fiber can reasonably predict the required laser power for a given pulse length to produce lenses on fibers made of various kinds of materials. A He-Ne laser beam was coupled into a fiber to investigate the properties of the spherical lens. We also observed that such lens can couple light from a source into the fiber, can be used for imaging, and can focus enough laser intensity for machining various materials.

Polarization optics of index-gradient optical waveguide fibers.

Abstract: An investigation of the polarization optical properties of index-gradient glass fibers confirmed the applicability of the linear birefringent model to fibers of this type. The phase retardation (delta(s) = 58 degrees /cm) is homogeneously distributed along the whole length of the fiber. The depolarization occurring when the incident polarization angle coincides with the fast (or slow) axis of the fiber is negligibly small. The measuring technique employed allows the phase retardation between the wave components in the privileged directions within the fiber to be determined as a function of the temperature (Deltadelta(s)/DeltaT = 0.09 degrees /K cm). As the fiber is twisted the polarization vector rotates synchronously with the twisted endface of the fiber.

Method of making optical waveguides from glass fibers

Abstract: A procedure is described for drawing glass fibers which are particularly suitable for use in optical waveguides. A laser is used as a souce of heat and an optical system is provided for focusing an annular beam around a glass preform from which the glass fiber is drawn. Particular attention is devoted to the optical focusing system to provide highly uniform distribution of heat and insure very precise short and long term fiber diameter control and precise control of the optical properties (freedom from scattering centers, profile of optical properties across the diameter) of the fiber. Precise diameter control of glass fibers for optical waveguides is highly desirable because it minimizes optical losses and facilitates low-loss splicing of individual glass fibers.

The coupling of light‐emitting diodes to optical fibers using sphere lenses

Abstract: The use of a truncated sphere of high‐refractive‐index material is proposed as a lens designed to improve the coupling efficiency between a light‐emitting‐diode source and an optical fiber. A method of calculating the coupling efficiency for such lens systems is described. Numerical results for the variation of efficiency with lens parameters are presented and discussed for coupling to a fiber bundle with a numerical aperture of 0.14. Improvements of two orders of magnitude in the coupling efficiency over that attainable with the close coupling geometry are predicted.

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.

Double optical fiber waveguide ring laser gyroscope

Abstract: A laser gyroscope for determining rotation of an area circumscribed by two closely adjacent optical fiber waveguides which serve as double laser cavities. Laser oscillation is restricted to one direction only in each optical fiber waveguide with the direction of oscillation in each waveguide being opposite to that in the adjacent optical fiber waveguide. Fractional parts of the laser radiation from the laser oscillation in each optical fiber waveguide are superimposed to develop a beat frequency therebetween which is proportional to the angular rotation of the area circumscribed by the two optical fiber waveguides.

Low-Loss FEP-Clad Silica Fibers

Abstract: Easy-to-fabricate, low-loss optical fibers are described that consist of a pure fused silica core surrounded with a loosely fitting, extruded, FEP cladding tube. Because of their large numerical aperture (NA), these fibers are particularly well suited for the transmission of the incoherent light emitted by light-emitting diodes. Whereas the losses approached those of the core material for small angle excitation (i.e., 7.6 dB/km at 0.8 μm for a Suprasil 2 fiber of 230-m length), they increased to 14 dB/km for a steady-state NA of 0.3. The measured pulse dispersion of up to 30 nsec agrees well with the expected 24 nsec for a step-index fiber with an NA of 0.3.

Angle selective coupler for optical fibers

Abstract: There is disclosed an angle selective coupler for coupling optical energy into and/or out of optical fibers. The coupler consists of a section of the optical fiber modified in such a way as to allow optical excitation of a plurality of higher order modes of optical transmission, each mode being defined by a given angle of propagation relative to the fiber axis. In one embodiment the coupling section comprises a single strand of glass fiber waveguide which is tapered along its length. The existence of the tapered section allows coupling of radiation from an external source into a given propagation angle in the fiber. In another embodiment no taper is used, but the fiber cladding is etched down to a thin layer and higher index material is deposited over the thin layer. This allows coherent coupling of radiation into one or more higher order modes in the optical fiber as determined by the angle of the incident light beam with respect to the cladding of the fiber. In either embodiment the device uses total internal reflection to function as an angle selective input or output connector for efficient coupling of optical energy into a given propagation angle within the fiber waveguide. The existence of a plurality of such angles permits the coupler to be used in a modal multiplexing duplexer.

Material structure of germanium-doped optical fibers and preforms

Abstract: The structural characteristics of preforms and optical fibers fabricated by modified chemical vapor deposition were studied by optical, interference, and scanning electron microscopy. It was observed that the structural features resulting from the deposition process are preserved through subsequent processing and appear in the fiber with the exception of a region at the center of the fiber. Here, selective evaporation of dopant material from the inner surface of the deposit results in a refractive index depression on the axis of the optical waveguide.

Low dispersion optical fiber wave guiding structures with periodically deformed waveguide axis

Abstract: The disclosure is directed to optical fiber waveguiding structures, and techniques for fabricating the same, which are designed to have reduced modal dispersion as a result of the deliberate enhancement of mode coupling in the fibers. The mode coupling is achieved in each of the structures by means of an enveloping outer jacket, typically of plastic, which is selectively deformed so as to modify the straightness of the fiber axes in a spatially periodic manner. Several alternative techniques are presented for properly deforming the outer jacket either before or after it is combined with the fibers. Since, with these structures and techniques, the outer jacket provides the desired fiber perturbations, the fibers themselves can be fabricated using standard techniques without the need for any special procedures for modifying their parameters.

Modes in fiber optical waveguides with ring index profiles

Abstract: Calculations have been made of mode properties of optical fibers with ring index profiles. Three idealized profiles with regions of depressed index on axis were chosen for study. The quantities of interest are the propagation constant for various modes, the group delay, and the near and far field mode patterns. Near and far field patterns are compared with Gaussian TEM laser modes. The results are particularly relevant to studies of nonlinear interactions in fiber waveguides.

Glass Fibers for Optical Communications

Abstract: Glass fiber optics have been used for many years for flexible light distribution bundles, faceplates for cathode-ray tubes, medical endoscopes, and similar purposes. Only recently (1) has serious research been directed toward the use of glass fiber as a long distance communication medium (2, 3). Such a communication system requires three main components: a transmitter, a receiver, and a transmission medium. The transmitter will most likely consist of a GaAIAs laser or light emitting diode (LED) driven with a digital signal. Such transmitters can operate at a wavelength of 800-900 nm at data rates up to hundreds of megabits per second. Another possible transmitter is based on an externally modulated Nd: YAG laser operating at 1060 nm. The receiver of an optical communication system will probably be a semiconductor photodetector that can be part of an integrated circuit chip used for processing the signal. Silicon avalanche diodes and silicon PIN diodes are sensitive at the GaAIAs wavelengths, and they have been built with bandwidths of at least a few hundred megacycles. Using lasers and avalanche photodiodes, losses of about 75 dB can be tolerated between repeaters operating at 1 megabit/sec, but only 45 dB loss is tolerable at 1000 megabits/sec. An excellent review of 'transmission and receiving devices has been published by Miller, Marcatili & Li (2). The transmission medium will be an optical fiber waveguide, consisting of a core of relatively high refractive index surrounded by a cladding of relatively low refractive index, The maximum tolerable loss per kilometer is governed by the distance over which transmission must take place. Losses as high as 100 dB/km may be acceptable for very short systems, as on airplanes or ships, whereas losses as low as 4 dB/km or less may be required for long distance systems where expensive repeaters must be spaced many kilometers apart. In addition to loss, another important characteristic of glass fiber waveguides

Optical aging characteristics of borosilicate clad fused silica core fiber optical waveguides

Abstract: Very low transmission loss fiber optical waveguides have been developed during the past two years which have pure fused silica cores surrounded by borosilicate glass claddings. A recent study of the binary borosilicate glass system revealed that the low refractive index values which can be achieved with this glass and which are essential for the fiber cladding application occur only when the glass is quenched. Annealing causes the refractive index to increase to a less acceptable value. Although fibers are naturally quenched during drawing, there is a legitimate concern that the cladding might spontaneously anneal at its operating temperature in an unacceptably short time. The details of the annealing time−temperature relationship are determined in the present work and effective lifetimes for borosilicate clad fibers are predicted. It is concluded that lifetimes in excess of 100 years should be expected if the fiber operating temperature does not exceed 60 °C.

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.

Optical Fiber-Stripline-Coupler

Abstract: A device for coupling a glass fiber to a stripline of an integrated optical device is described. The adjustment is sufficiently precise to connect single-mode waveguides. In the case of single-mode fiber-fiber-connections, coupling efficiencies between 85%h and 95% were measured.

A Semi-Transparent Mirror-Type Directional Coupler for Optical Fiber Applications (Letters)

Abstract: A directional coupler for optical fiber applications is constructed of two pieces of optical fibers cut obliquely and a thin dielectric film. Coupling coefficient -20 dB to -10 dB depending on the refractive index of the dielectric film, insertion loss 1 dB, and directivity -20 dB are measured. They agree with the analytical results.

Quasi-ray analysis of crosstalk between multimode optical fibers

Abstract: A model based on frustrated total reflection of waves in a multilayered medium has been developed to analyze the crosstalk between multimode optical fibers. Kappa (κ), the parameter indicating the power distribution among the modes of the fiber, and fiber cladding thickness play very important roles in determining the crosstalk isolation between fibers. Significant but less dominant effects on crosstalk are due to variations in fiber numerical aperture, length, and transmitting wavelength.

Advances in Communication through Light Fibers

Abstract: Publisher Summary This chapter focuses on the advances in communication through light fibers. Recent breakthrough in the purification of glass has made it possible to manufacture very low-loss optical fibers. The fibers provide almost all the attractive features of an ideal optical transmission line, such as, low cost, small size, lightweight, flexible, larger bandwidth, high tensile strength, no short circuiting issues, resistant to nuclear radiation, and heat resistance. These optical fibers are used as the communication media for transmitting optical signals. The bandwidth of a single-mode fiber is limited by the dispersion of the normal mode and by the material dispersion effects. One of the unique characteristics of a dielectric fiber waveguide is that below a certain frequency called the cut-off frequency of a particular mode, that mode simply no longer exists. A fiber of a given cross section will support a finite number of guided modes and a continuous spectrum of radiation modes. Any irregularity in the fiber because of diameter variation, bending, interface irregularities, or the presence of scattering centers will produce coupling of the energy of one mode to the others. Mode coupling within an optical fiber may produce the desirable effect of reducing the delay distortion that result from uncoupled multimode operation or may produce the undesirable effect of signal contamination.

Fiber-optic laser illumination

Abstract: Multiple-wavelength light from an ion laser was transmitted through a 85-µm optical fiber to provide illumination for viewing and color photography. Also adequate black-and-white TV display and photography were obtained using red light from an He-Ne laser transmitted through the same optical fiber.

An analysis of the effect of lossy coatings on the transmission energy in a multimode optical fiber

Abstract: Lossy plastic coatings are used as a means of providing mechanical protection for optical fibers during the optical-cable manufacturing process. A model utilizing a quasi-ray analysis has been developed in this paper to determine the effects of lossy coatings on the transmission energy in a multimoded step-index optical fiber. Cladding thickness is the dominant fiber parameter that plays a critical role in preventing transmission loss due to a lossy coating. Other parameters that significantly affect transmission loss are transmitting wavelength, the real and imaginary part of the refractive index of the lossy coating, and the fiber core diameter.

Woven fiber optics.

Abstract: In this paper we describe how the art of weaving can be applied to fiber optics in order to produce precisely controlled reproducible image guides and image dissectors. As examples of the types of device for which woven fiber optics are applicable, we describe a 3:1 interleaver for use with a cathode-ray tube to produce color images, and a high speed alpha numeric output device. The techniques of weaving fiber optics are discussed in sufficient detail in order to allow for further work. Although, in principle, one might be able to weave glass optical fibers, all the work described here made use of plastic optical fibers 0.25 mm in diameter.

Optical Waveguide Technology for Modern Urban Communications

Abstract: The technology of optical waveguide systems has developed rapidly over the past few years, and they now appear to offer vast new capabilities in urban communications. A review and a status report of this technology is given; glass fiber waveguides are discussed in some detail because they show considerable promise for interactive networks. Optical sources, detectors, and integrated optical circuits are discussed.