RESUMO
Changes in transverse refractive index induced by the photoelastic effect are calculated when an optical fiber is subjected to a uniformly applied diametral stress. For moderate values of the force per unit length applied to the fiber, we find that regions of comparable or higher refractive index than the core may be induced in the outer region of the fiber. Thus the stressed region is capable of acting as a mode converter that affects the transmission characteristics of the fiber and may enable coupling of energy in or out of the fiber.
RESUMO
An approximate treatment of solitons (nonlinear pulses) in inhomogeneous waveguides is presented. We find that, for slowly varying inhomogeneity, both bright and dark solitons are supported by waveguides. These solitons acquire a time-dependent velocity and acceleration but otherwise propagate through the waveguide without changing shape.
RESUMO
The topical meeting on Optical Phenomena in Infrared Materials, sponsored jointly by the Optical Society of America and the U.S. Air Force Office of Scientific Research, was held in December 1976. The meeting stressed research on optical effects in materials for modern IR applications such as laser windows, solar energy conversion, infrared detection and integrated optics. The November 1977 issue of Applied Optics publishes a representative selection of the papers given.
RESUMO
The sources of the residual absorption of ir materials in their transparent region between 2microm and 10microm are reviewed with emphasis upon recent developments. On the longer wavelength side of this spectral region, many insulating crystals are limited by intrinsic multiphonon absorption, and, on the shorter wavelength side, all insulating crystals are limited by extrinsic effects associated with impurities, defects, and surfaces. During the last few years, the general character of the intrinsic multiphonon absorption has become sufficiently well understood so that its frequency and temperature dependence can be accounted for in both ionic and covalent crystals. The nature of extrinsic absorption is more complicated as it arises from a number of sources. In some cases, the measured absorption coefficient can be attributed with some certainty to a specific origin. In others, especially for the ionic crystals at shorter wavelengths, the origin of the extrinsic residual absorption is not known and may be limited by the experimental measurement techniques, at least in some of the better crystals.
RESUMO
Experimental and theoretical investigations of multiphonon absorption in semiconducting solids are conducted. We find that structure persists at lower absorption levels (~10(-2) cm(-1)) and at high temperatures (up to ~550 K) in these materials, in agreement with theoretical predictions. The theoretical analysis indicates that the observed rate of decrease of the absorption with increasing frequency is consistent with available models for the interionic potential and electric moments in these materials. Moreover, the structure in the spectrum is found to be almost exclusively a result of density of states effects, as opposed to k-selection rules.
RESUMO
The temperature coefficient of the refractive index dn/dT of CaF(2), SrF(2), and BaF(2) single crystals is measured by a laser interferometric technique at a number of frequencies over temperatures ranging from 20 degrees C to 85 degrees C. Although dn/dT is found to display little dispersion between 0.6328 microm and 3.39 mum, its magnitude shows a slight increase with temperature. A possible origin of the latter effect is discussed.
RESUMO
The pressure derivative of the refractive index (dn/dP) and the elastooptic constants (P(ij)) in the transparent frequency regime of semiconducting and ionic crystals are investigated theoretically. The electronic contribution to dn/dP of semiconductors is obtained by carrying out pseudopotential calculations of the band structure as a function of hydrostatic pressure, and the results compared with experiment. The lattice contribution to dn/dP is obtained by relating dn/dP to changes in the effective ionic charge and the phonon spectrum as functions of pressure. As for the P(ij), we perform a detailed application of the theory of Humphreys and Maradudin to calculate these for a variety of cubic crystals as functions of frequency in the transparent regime. The parameters required in the calculation are determined from improved prescriptions, which relate various microscopic functions to experimental data on the pressure dependence of phonon frequencies. The theoretical results are checked employing a relatio between dn/dP and the P(ij). Overall, one finds that frequency dispersion is most important for the ionic materials and is generally negligible for the more highly covalent materials.
RESUMO
The vector Kirchhoff approach to thermal lensing in solids is investigated. The relation of the thermal rise in the sample to the optics of lensing is elucidated. Various analytical results and series representations for the transmitted intensity are derived for the case of Gaussian beams incident on circular samples, in various special limits. An expression for the time-dependent shift in the diffraction focus is obtained. Numerical computations illustrating lensing effects both at small times and in the steady state are presented. Effects of stress-induced birefringence, including the oscillation of the maximum intensity and diffraction focus as a function of time, are illustrated. Similar effects are also shown to occur when the incident power or sample thickness is varied, for solids characterized by large stress-induced contributions.
