J. A. Arnaud
Bell System Technical Journal, The (Volume:53 , Issue: 8 ), pages 1643 – 1656, Oct. 1974
The theory of propagation in a new single-material, single-mode, optical fiber is given. The modes are of the whispering-gallery type, with the propagation taking place along helicoidal paths close to the boundary of a cylindrical dielectric rod. The beams are confined in the azimuthal direction in helicoidal ridges. It is shown that single-mode, low-loss operation is possible if the helix period is of the order of the rod cross-section area divided by the wavelength and the ridge area is of the order of 1 percent of the rod cross-section area for two channels. The rod is supported by helicoidal wings that play a role in the mode-selection mechanism.
LIEN VERS L’ARTICLE : THEORY OF THE SINGLE-MATERIAL, HELICOIDAL FIBER
J. A. Arnaud
Bell System Technical Journal, The (Volume:53 , Issue: 8 ), pages 1599 – 1618, Oct. 1974
A dielectric slab can keep optical beams confined transversely in its plane if it is tapered, with the slab thickness having a maximum along some straight line. When the square of the local wave number of the slab (k2) is a quadratic function of the transverse coordinate (y), the rays in the plane of the slab are sinusoids whose optical length is almost independent of the amplitude. For thin slabs (2d « λ) as well as for thick slabs (2d » λ), pulse spreading is large because the ratio of the local phase to group velocity is strongly dependent on the distance (y) from axis. We show that pulse spreading is almost negligible, however, if the thickness of the slab is properly chosen. For example, if the slab thickness on axis is 2.5 micrometers and the refractive index of the slab is 1 percent higher than that of the surrounding medium, pulse spreading is only 0.05 nanosecond per kilometer at a wavelength of 1 micrometer. Pulses in clad fibers having the same width (0.2 millimeter) and carrying the same number of modes (15) spread 50 times faster. Splicing and matching to injection lasers may be easier with planar fibers than with conventional fibers. Low-dispersion planar fibers are therefore attractive when used in conjunction with sources that are multimoded in one dimension. Closed-form expressions are given for square-law and linear-law profiles.
LIEN VERS L’ARTICLE : PULSE SPREADING IN MULTIMODE, PLANAR, OPTICAL FIBERS
J. A. Arnaud, A. A. M. Saleh
Applied Optics, vol 13, n°10, october 1974
A periodic sequence of layers with alternately high and low refractive indices can guide loosely bound surface waves parallel to the layers. Most of the power flows in free space, and, thus, the losses may be considerably smaller than the bulk losses of the dielectric materials used. Possible applications are briefly discussed.
LIEN VERS L’ARTICLE : GUIDANCE OF SURFACE WAVES BY MULTILAYER COATINGS