Showing papers on "Dispersion-shifted fiber published in 1972"

Total Optical Attenuation in Bulk Fused Silica

Abstract: A survey has been made of optical attenuation in a series of commercially available silica, SiO2, samples to determine the suitability of this material for fiber optical communications. The absorptive component of the attenuation was measured by a precision calorimetric technique, while the scattering component was determined by a new method based on spontaneous Brillouin spectroscopy. Both techniques set an upper limit on the loss and are precise to within a fraction of 1 dB/km. Of the samples tested, the best has a total attenuation of less than 3 dB/km at the 1.06‐μ wavelength of the YAlG : Nd laser.

Material dispersion in optical fiber waveguides.

Abstract: In weakly guiding dielectric (glass) fiber waveguides the factors governing the envelope delay distortion of optical signals can be separated conveniently into material and waveguide contributions. By making use of the fact that the normal dispersion of the index-of-refraction of glasses accurately fits a single oscillator Sellmeier equation, simple relations of general validity are obtained for the material contribution to the group delay and frequency dependence of the group delay in dielectric fiber waveguides. Using these results expressions are obtained for the material contribution to the information bandwidth of fiber optic waveguides excited by wideband sources (light emitting diodes) and narrow band sources (lasers). It is shown that in single mode guides the bandwidth limitation imposed by material dispersion is negligible, while in multimode guides the difference in group delay of higher order modes imposes the most severe bandwidth limitation.

Picosecond pulse distortion in optical fibers

Abstract: Low-loss glass fibers are a prospective transmission medium for optical communication systems. To study their dispersion characteristics, we investigated the propagation of short optical pulses in up to 10 m of cladded fiber. The pulses, 7 ps long and 6 THz in spectral width, were derived from a mode-locked Nd:glass laser by frequency doubling (0.53-μm wavelength). We measured the broadened pulses emerging from the fiber by a sampling technique that employed an optical Kerr shutter of 10 ps gating time. The fiber had a core diameter of 11 μm and an index difference of 1 percent between core and cladding. The loss was about 1.8 dB/m. Our measurements showed satisfactory agreement with a theory that takes material dispersion and mode dispersion into account and assumes strong attenuation of the high-order modes in the particular fiber tested. At the end of 10 m, the 7-ps pulse reached a width of 110 ps, haft of which can be accounted for by material dispersion. When we extrapolate these results to practical systems, we conclude that pulses from a light-emitting diode transmitted through a fiber with the above design would broaden by at least 2.6 ns/km (because of material dispersion), and possibly by as much as 33 ns/km, if all modes were excited and reached the detector with comparable attenuation and negligible coupling.

Method utilizing an optical fiber raman cell

Abstract: A long length of liquid-core optical fiber is employed as a Raman cell, wherein the fiber core contains the material whose Raman spectrum is to be analyzed. Spectral intensifications of from 102 to 103 times greater than that obtained by conventional means are realized, using very small sample volumes. Optimum fiber lengths are disclosed.

Mode detection and delay equalization in multimode optical fiber transmission systems

Abstract: This application describes a detector-equalizer circuit for equalizing the dispersion produced in a multimode optical fiber. The circuit comprises an array of photodetectors whose physical configurations conform to the radiation pattern at the end of the optical fiber. The photodetectors selectively respond to each of the modes or to groups of modes propagating along the fiber. The several output signals thus produced are delayed an appropriate amount relative to each other, and then combined in time coincidence in a common output circuit.

Fiber-dispersion measurements using a mode-locked krypton laser

Abstract: Mode delay and material dispersion limit the signal bandwidth of potential fiber communication systems. 200-ps pulses from a krypton laser, mode-locked at three different wavelengths, prove to be adequate for measuring both effects in relatively short fibers (33 m). The results are in good agreement with theory.