RESUMO
In this paper we present a new method for estimating the bandwidth of multimode optical fibers based on the frequency correlation function of the speckle patterns generated by the interference of fiber modes. This technique, which does not require a pulse or signal generator, can be utilized to estimate the bandwidth of a multimode fiber using a relatively short length of fiber. By applying this method to a test fiber we obtained a bandwidth of approximately 36 MHz km which is in relatively good agreement with the approximately 44-MHz x km bandwidth measured by a conventional pulsed technique.
RESUMO
Modal noise in multimode optical fibers is usually analyzed by using the conventional statistical theory developed for speckle. We show that when little light is lost from the fiber to radiative modes, a constraint of constant total power is introduced that is not present in conventional speckle theory. Experimental results show a marked departure in the behavior of speckle signal-to-noise ratio from the predictions of conventional speckle theory. A suitable modification of this theory is introduced, bringing the theoretical and experimental results into agreement.
RESUMO
Coupling has been measured for dry-spliced fibers as a function of break angle. The angles were measured interferometrically to about 0.1 degrees accuracy. An analysis is performed, and the measurements are found to be within 1.0% RMS of the calculation.
RESUMO
The scattering from clad fiber optical waveguides that have cores whose surfaces are perturbed in various ways is calculated with the induced dipole method. Such scattering is of interest because it can couple the guided modes of a multimode waveguide, thereby reducing the temporal dispersion. The five surface deviations considered are a rectangular radial step, a sinusoidal perturbation of the radius, a sinusoidal meander of the core, a deviation where the core alternates periodically along the core axis between a y-extended elipse and a z-extended elipse (x is the core axis), and a helical meander of the core axis.
RESUMO
This paper reports the measurement of the angular distribution of light scattered from a low-loss fiber at 1.06 microm and 0.633 microm. In addition to Rayleigh scattering, a previously undetected, near-forward scattering peak was observed. The new peak is shown to be consistent with scattering by narrow dielectric filaments aligned with the axis. The total scattering loss rate at 0.633 microm is ~10 dB/km, about (1/4) of which is due to the near-forward peak. The total scattering loss rate at 1.06 microm is ~1 dB/km.
RESUMO
Cylindrical transparent media whose refractive index decreases with increasing cylinder radius have been investigated in connection with coherent light propagation in gas waveguides. Recently, graded index glass rods (trade named SELFOC rods) have been used as imaging devices. We report here on a geometrical optical study of graded index systems used for relaying images at unit magnification. We have found that two index distributions previously studied result in large image aberrations when the presence of skew rays is taken into account. We have derived an index distribution which is "ideal" for helical skew rays. Using ray tracing methods we have examined image aberrations for various index distributions and for various rod geometries. We find that (1) no one refractive index distribution can be "ideal" for both meridional and skew rays, (2) image resolution is generally low, reaching about 1000 spots per field, and (3) the optimal index distribution varies with the ratio of rod length to radius and the relative aperture and is intermediate between the helically ideal and the meridionally ideal distributions.
RESUMO
An application of varifocal mirror autostereoscopic imaging to 3-D computer-generated movies is described. A high speed movie projector and oscillating varifocal mirror project moving autostereoscopic images at 15 volumetric images per second. In order to distribute evenly the component images along the depth axis, linear time scans of the image volume are required. However, the image position is a nonlinear function of the mirror displacement, which, in turn, has a nonlinear frequency response to the mirror driving voltage. Analytical and experimental investigations are reported in which approximately linear scans for duty cycles approaching 90% were attained.
