We demonstrate experimentally for what is to our knowledge the first time that air–silica microstructure optical fibers can exhibit anomalous dispersion at visible wavelengths. We exploit this feature to generate an optical continuum 550 THz in width, extending from the violet to the infrared, by propagating pulses of 100-fs duration and kilowatt peak powers through a microstructure fiber near the zero-dispersion wavelength.

Visible continuum generation in air–silica microstructure optical fibers with anomalous dispersion at 800 nm

Mode-matching and beam-propagation methods are used to analyze single-mode operation of optical GeSi-Si and Si-SiO/sub 2/ semiconductor rib waveguides. The waveguide dimensions that allow only the fundamental HE/sub 00/ or EH/sub 00/ mode to propagate have been determined. For both material systems, it is found that the rib can be several microns wide and several microns high, thus allowing efficient coupling to single-mode fibers. Numerical examples are given for monomode guiding group-IV materials, but the results apply to III-V rib waveguides. It is shown that single-mode rib guides with large cross sections are feasible as long as the waveguide is at least several millimeters long. >

Large single-mode rib waveguides in GeSi-Si and Si-on-SiO/sub 2/

Dielectric waveguides are the structures that are used to confine and guide the light in the guided-wave devices and circuits of integrated optics. This chapter is devoted to the theory of these waveguides. Other chapters of this book discuss their fabrication by such techniques as sputtering, diffusion, ion implantation or epitaxial growth. A well-known dielectric waveguide is, of course, the optical fiber which usually has a circular cross-section. In contrast, the guides of interest to integrated optics are usually planar structures such as planar films or strips. Our discussion will focus on these planar guides even though most of the fundamentals are applicable to all dielectric waveguide types.

Theory of Dielectric Waveguides

An efficient and powerful technique has been developed to treat the problem of wave propagation along arbitrarily shaped single-mode dielectric waveguides with inhomogeneous index variations in the cross-sectional plane. This technique is based on a modified finite-element method. Illustrative examples were given for the following guides: (a) the triangular fiber guide; (b) the elliptical fiber guide; (c) the single material fiber guide; (d) the rectangular fiber guide; (e) the embossed integrated optics guide; (f) the diffused channel guide; (g) the optical stripline guide.

Single-mode optical waveguides.

Low-loss single- and multimode optical fibers were fabricated solely from pure fused silica. Their spectral losses corresponded closely to those of unclad fibers drawn from the same material, provided the cores of the single-material fiber preform were redrawn under pure conditions. The lowest steady-state loss of about 3 dB/km at a wavelength of 1.1 μm was obtained with a fiber 130 meters long that had a Spectrosil WF core. Experimental numerical apertures agreed excellently with theoretical predictions.

Low-loss single-material fibers made from pure fused silica

The slab-coupled waveguide, consisting of a dielectric rod lying on a slab that in turn covers a substrate, is a multidielectric waveguide that includes such special cases as the single-material fiber, the rib waveguide, and the strip-loaded film guide. These guides have recently become known as potentially useful either for long-distance optical transmission or for integrated optics. Simple, closed-form, approximate solutions have been found to describe the following properties of the guide: number of modes, their field configurations and propagation constants, numerical aperture, requirements for single-mode operation, field penetration in the slab, tolerance to curvature of the guide axis, dispersion, and impulse response.

E. A. J. Marcatili

Papers

Slab-coupled waveguides