New light-focusing fibers made by a continuous process

Magnetooptical current transformer. 2: Components

In this second part, the most important components of a magnetooptical current transformer are described and their suitability is discussed. Today He-Ne gas lasers and laser diodes seem to meet best the requirements of the light source. Single-mode optical fibers are capable of transmitting polarized light without depolarization. A fiber coil wound on a special coil former is used as a measuring sensor. Two P-I-N photodiodes, together with an analog electronic circuit, transform the optical into an electrical measuring signal.

Compound eyes: old and new optical mechanisms

Over the last twenty years classical views of how compound eyes work optically have undergone a series of overhauls. Exner's central concept of an optically inhomogeneous lens cylinder has survived, and such devices are now made commercially. He was wrong, however, about some crustacean eyes. They produce images by a mirror mechanism that was not discovered until 1975, and which now shows promise as an optical system capable of development.

Pulse dispersion measurements in conventional Selfoc fibers

Measurements of pulse dispersion in conventional Selfoc fibers have been carried out. The principal light source was a pulsed mode-locked ruby laser. Qualitative agreement has been found with theory, which predicts multimode operation and, hence, large pulse dispersion in such fibers under greatly mismatched launching conditions. Under such conditions, we have observed dispersion equivalent to ~20 nsec/km.

Visibility of interference fringes: effect of the optical guide length in coherent light

The visibility of the interference fringes produced by a wavefront of coherent light passing through an optical guide, divided, and recombined is studied. A cladding fiber and a light-focusing fiber are used as the optical guide. The relationship of the visibility of the interference fringes to the length of these fibers is determined. The visibility of the interference fringes produced through the light-focusing fiber and those produced through the cladding fiber are almost independent of the length of the fiber despite random internal reflection.

Light beam propagation along helical bands of parabolic index optical fibers

The present paper analyzes the propagation behavior of light beams along parabolic index optical fibers for the cases where the center axes of the fibers are deformed along helical bends, which are caused when several optical fibers are twisted into a bundle for the purpose of cabling. The analysis is based on geometrical optics and is limited to the case where the center axes of the fibers are bent along a double helix, which arises when two fibers are twisted into a bundle, and the two bundles thus obtained are entwisted once more into a cable. It is also assumed that the center axis of the cable thus established is curved in a circular bend with a constant curvature. Ray equations for this case are derived, and their solutions are studied in detail theoretically and numerically. As a result, conditions are obtained for the occurrence of the divergence phenomenon of the beam trajectory as well as for the matched incidence of light beams to minimize the undulation amplitude of beam trajectories. Moreover, it is clarified that whether the two helices composing the double helix are twisted in the same or opposite directions has somewhat different effects upon the conditions for the divergence phenomenon and the matched incidence as well as the propagation behavior of light beams. Some problems with the application of the present cabling technique to parabolic index optical fibers are also discussed.

Magnetooptical properties of index-gradient optical fibers

The magnetooptical Faraday rotation of a guided He-Ne laser beam in index-gradient fibers was measured. The proportionality between the rotation of the polarization vector and the length of the light path in an applied homogeneous longitudinal magnetic field is disturbed. The measuring results can be explained by means of a theoretical model combining the Faraday effect with birefringence.

Polarization optics of index-gradient optical waveguide fibers

An investigation of the polarization optical properties of index-gradient glass fibers confirmed the applicability of the linear birefringent model to fibers of this type. The phase retardation (delta(s) = 58 degrees /cm) is homogeneously distributed along the whole length of the fiber. The depolarization occurring when the incident polarization angle coincides with the fast (or slow) axis of the fiber is negligibly small. The measuring technique employed allows the phase retardation between the wave components in the privileged directions within the fiber to be determined as a function of the temperature (Deltadelta(s)/DeltaT = 0.09 degrees /K cm). As the fiber is twisted the polarization vector rotates synchronously with the twisted endface of the fiber.

Mode Coupling Effects in Graded-index Optical Fibers

Mode coupling theory is applied to the study of multimode optical fibers with graded-index cores. For coupling caused by random bends in the waveguide axis, the results predict the dependence of the induced losses on the fiber's characteristics. The impulse response is determined for fibers with random bends having several different power spectra. The results are used to predict the transmitted power, the delay time, and the rms pulse width in fibers with graded-index cores.

Optical fibers for communication

The transparency of glass fibers in the visible and near infrared-improved beyond all expectations by recent breakthroughs-seems now sufficient to transmit optical signals unprocessed over miles. No wonder that efforts have intensified all over the world to utilize fibers in future communication systems. Materials research and fabrication are the fields where present progress is most rapid. New ways of preform preparation by deposition, doping, or diffusion are being studied and found to offer improvements and versatility. As far as materials are concerned, fused silica has shown the lowest bulk losses and hence receives the most interest, but many glasses are being studied as well. As new processes become available and record lows in fiber loss are being reached, propagation theory is finding new challenges as well. On the one hand, multimode fibers seem desirable with respect to transmitter compatibility, splicing, and fabrication tolerances. On the other hand, the signal distortion caused by mode delay differences in multimode fibers can be considerable and requires equalization-inherent in the fiber or at the fiber end. Beyond that, the wavelength dependence of the refractive index produces dispersion effects serious enough to be of importance. Thinking ahead, one is confronted with the question of fiber handling, strength, and life. The technology of making cables and splices from a brittle material like glass is in its infancy, and we can only indicate the extent of these difficult problems ahead.