Showing papers on "Dispersion-shifted fiber published in 1971"

Pulse distortion in fiber optic bundles.

Abstract: The achievement of very low attenuation values of about 20 dB/km (Ref. 1) in optical fibers has stimulated interest in long path guided optical communications using fiber optic transmission lines. The major emphasis has been on single-mode fibers due to their expected large bandwidth capability in the multiGHz range for kilometer lengths. Single-mode fibers have core diameters of a few microns. Light from a coherent laser source can be coupled into such a fiber efficiently by focusing the light to a small spot at the fiber end. The expense of a fiber optic communication system can be reduced considerably if inexpensive light emitting diodes are used as sources. Since LED's emit incoherent radation into a rather large cone from a relatively large source area, efficient coupling into a single-mode fiber is not possible. Radiation from an LED can, however, be efficiently coupled into a bundle of multimode fibers by simply close-coupling the two elements. Additional advantages of LED sources include reliability, low power requirements, small size, and simple pulse modulation. Pulse distortion effects in multimode fiber bundles are therefore of major interest. Pulse propagation measurements in single fibers have been carried out previously by Williams and Kao on a 27-m long multimode fiber and by Gambling et al. on a 33-m long multimode fiber. The first-mentioned workers observed no time delay difference for light pulses of 50-nsec duration entering the fiber at different angles of incidence but did observe a pulse broadening of 3 nsec for pulses at normal incidence. The latter group using about 1-nsec wide pulses from an He– Ne, mode-locked laser, looked for pulse broadening but could find none within the limits of detectability, i.e., about 0.5 nsec. We have made similar measurements on a bundle of multimode fibers about twice as long and have found both time delay differences for pulses launched at different angles as well as pulsebroadening effects for pulses launched at any angle of incidence. We now consider a geometrical optics model for describing the propagation of light down a clad fiber. Figure 1 shows a merid-

Fiber optics for spectroscopic illumination.

Abstract: Absolute and angular transmission measurements were made on a single sheathed fiber 0.15 mm in diameter and 2.1 m long, and an optical angular transfer function was defined and calculated. The effective transmission of the source brightness was calculated as a function of the f numbers of the entrance and output optics of the fiber, and these results were used to choose a suitable optical system for illumination of a spectrometer.

Wavelength Division Multiplexing in Light Interface Technology.

Abstract: : The report describes the investigation and fabrication of a five channel wavelength division multiplex (WDM) optical communication link. The transmitter consists of five different wavelength Ga(1-x)Al(x)As light emitting diodes (LEDs) and the receiver consists of five narrowband photodiodes (PDs). The light is conducted from the transmitter to the receiver by a fiber optic bundle. Various techniques (dichroic filters, furcated fiber bundle, and LED and PD plane arrays) of coupling the light into and out of the fiber bundle are investigated. Measurements of receiver sensitivity, optical efficiency, and optical cross-coupling between channels were made. A theoretical analysis of the link optical efficiency and expected cross-coupling is performed and design information for future WDM optical links is established. It is also determined that fiber bundles which are classified as incoherent are, in general, quasi-coherent. It was necessary to incorporate optical mixing cylinders at the entrance and exit of the bundle to uniformly distribute the light throughout the cross-section. (Author)

Light Interface Technology Improvement Investigation.

Abstract: : The report establishes a baseline model for an optical data link utilizing a single fiber bundle. This model is solely concerned with light interface technology (LIT) for digital signal transmission. Data link performance is characterized by the pulse amplitude, pulse rise and fall times, pulse delay, and signal-to-noise ratio of the photodiode output. The LIT link has been analyzed as an entirety considering four major areas; light emitting diodes, fiber optic light guide, fiber optic/diode interface, and photodiode. Fiber optic/diode interface has been investigated with regard to loss mechanisms of coupling light into and out of fiber bundles. Fiber optic light guides have been surveyed and evaluated. The three major types that have been given consideration are total internal reflection fibers, total internal refraction fibers and waveguide mode fibers. Space division multiplexing investigations considering Lambertian sources were completed for the TIR and SELFOC fiber types. Number of channels possible, optical cross coupling of fibers, and sampling effect are the main topics discussed. Analog properties of a typical link were investigated with respect to distortion. Experiments were completed using various wavelength LEDs and at various temperatures. (Author)