The sharp structure observed in the fundamental optical spectra of crystals, both vibrational and electronic, can be classified and interpreted by symmetry arguments based explicitly on the existence of long-range order. Indeed, this is one of the few properties of crystals which cannot be accounted for on the basis of short-range order alone: If the long-range order is destroyed, the sharp structural detail, which is typical for crystals, disappears. However, the broad features of the spectra are similar if the short-range order is similar.

Optical Properties of Amorphous Semiconductors

The presence of bound hydroxyl (SiOH) in silica is well known to produce an optical fundamental absorption band at about 2.7 μm. For optical fiber applications the influence of the corresponding overtones and combination modes on the absorption spectrum are of significant importance. A literature review is presented which reveals uncertainties regarding the correct absorption band intensities as well as their spectral positions. We present precise data on spectral position and relative intensities of OH absorption bands in state of the art synthetic silica. Our investigations cover the influence of different manufacturing techniques, OH content, and a comparison of bulk and fiber data. With the knowledge of the conversion factors between the intensities of different OH absorption bands it is possible to predict the entire OH related transmission performance of an optical component by measurement of a single absorption band, e.g., the fundamental mode at 2.7 μm or the 1.38 μm band in the low loss range of optical fibers.

Analysis of OH absorption bands in synthetic silica

Very-low-OH-content optical fibres consisting of borosilicate-cladding phosphosilicate-core have been produced by a chemical vapour deposition technique. One of the fibres, whose transmission loss was less than 1 dB/km between 0.95 and 1.37 μm, showed a minimum loss of 0.47 dB/km at 1.2 μm.

Spectral losses of low-OH-content optical fibres

A semiautomatic method is described for measuring, fast and accurately, the mode propagation losses of planar or channel waveguides for integrated optical circuits. It involves a video camera aided by a microcomputer, and the real-time measurement is feasible over a broad range from low loss (<1 dB/cm) to high loss (of the order of 102 dB/cm). We examined the propagation properties of several optical waveguides prepared by sputtering or ion migration.

Measuring mode propagation losses of integrated optical waveguides: a simple method.

The fabrication of an extremely‐low‐loss glass optical waveguide, having as little as 4 dB/km total attenuation, has allowed interpretation of the absorption spectrum to a much greater degree than previously possible It is shown that, beyond about 700 nm, intrinsic ultraviolet absorption will have no effect Between 700 and 1100 nm, all absorption can be accounted for on the basis of OH to within ±07 dB/km Marked reduction of the water content will leave the scattering as the major loss mechanism, thereby permitting total attenuations of about 2 dB/km

On the ultimate lower limit of attenuation in glass optical waveguides

The attainment of 20-dB/km attenuation in experimental single-mode glass optical waveguides has spurred interest in their use for optical communications. The primary wavelength region of interest is in the red or near-infrared region of the spectrum. In this work independent attenuation measurements from 600 nm to 1060 nm have been made on low-loss waveguides and bulk cladding glass, using both laser and scanning-prism monochromator sources. Three bands were observed in the waveguides, at 725 nm, 875 nm, and 950 nm, and identified as due to OH in the glass. Absorptions too small to be precisely measured in the bulk glass are seen to be exceedingly important in the waveguides and easily measured in them.

Spectral Response of Low-Loss Optical Waveguides

The construction, calibration, and use of an integrating cube scattering detector used to measure scattering losses in optical fibers is described. The detector consists of six 1-cm sq silicon solar cells, each sensitive surface of which comprises one interior surface of a cube 1 cm on edge. Small holes in the center of two opposite faces of the cube permit the optical fiber to pass through the detector so that all the scattered light falls on a photosensitive surface.

Integrating Cube Scattering Detector

A sensitive method for measuring small displacements of a light beam is described which does not require the use of light probes or multielement detectors. Instead, the light beam whose displacement is to be measured, as well as a comparison light beam, is passed alternately through a rotating light chopper and then both beams are made to overlap on the surface of a photodetector. If the intensity of the two beams is made equal and if the phase (relative to the light chopping sequence) is properly adjusted, the photodetector output will be constant. Any beam displacement perpendicular to the edge of the rotating light chopper will disrupt the established phase relationship and produce a signal component in quadrature (i.e., 90° out of phase) with that which would be produced if only the intensity of one beam were changed. Theory shows the relationship between the amplitude of the quadrature component and the beam displacement. Measurements as small as 5 × 10−6 cm have been made and another more sensitive configuration is suggested. By reinterpreting the transverse spatial dimensions as distances parallel to the light beam, theory shows that this technique should result in a very sensitive optical ranging device.

A. R. Tynes

Papers

Spectral Response of Low-Loss Optical Waveguides

Integrating Cube Scattering Detector

A novel method for the measurement of small displacements of a light beam and for optical ranging.