Showing papers by "Philip St. J. Russell published in 1995"

Full 2-D photonic bandgaps in silica/air structures

Abstract: Full 2-D photonic bandgaps are demonstrated for all polarisations in structures with refractive index contrast as small as that of silica and air. They occur for light propagating out of the transverse plane, with a longitudinal component of wave vector. A new type of optical fibre based on these structures is proposed.

Photonic Bloch waves and photonic band gaps

Abstract: Photonic band gap materials are dielectrics with a synthetic, three dimensional, multiply periodic microstructure (lattice constant of order the optical wavelength) whose distinguishing feature is a very large modulation depth of refractive index. When appropriately designed, these “photonic crystals” exhibit ranges of optical frequency where light cannot exist — the photonic band gaps 7. The current interest in these materials 1–22 has led us to re-appraise propagation in structures that, while not exhibiting a complete photonic band gap (PBG), nevertheless display anomalous and intriguing propagation effects in the vicinity of their Bragg conditions54–58. In most cases, around each Bragg condition appear incomplete momentum and energy gaps (i.e., ranges of, respectively, wavevector and frequency where propagation is forbidden) with widths that are given approximately by the product of the index difference with, respectively, the vacuum wavevector and h times the optical frequency. With the exception of the multi-layer dielectric stack, most conventional electromagnetic gratings, such as those encountered in holography 27, waveguides 45, distributed feedback lasers 35,37,38, acousto-optic 47 and x-ray 61 diffraction, consist of weak periodic perturbations about a mean refractive index. In these gratings, while strong spatial and temporal dispersion are present around each Bragg condition, the ranges of angles and frequencies over which this occurs are very narrow; and although PBG’s do appear, they are incomplete and mostly very weak.

All-fiber sliding-frequency Er 3 + /Yb 3 + soliton laser

Abstract: We report a simple all-fiber sliding-frequency soliton laser incorporating a recently developed low-insertion-loss acousto-optic fiber frequency shifter. The frequency shifter simultaneously provides the spectral filtering and polarizing properties required for pulsed operation to be obtained.

A method of forming electrets in optical fibres

Abstract: A method of forming electrets in optical fibres, which method comprises thermally poling the optical fibres in order to provide the optical fibres with a built-in electret, the method being such that the optical fibres are thermally poled in the absence of air. Optical fibres devices when produced by the method of the invention, include: frequency converters, linear electro-optic modulators, linear electro-optic switches, electric field sensors, second order non-linear mirrors, electrically controllable Bragg gratings, and transducers for exciting surface acoustic waves on glass substrates.

Procede de formation d'electrets dans des fibres optiques

Abstract: Un procede, qui permet de former des electrets dans des fibres optiques, consiste a etablir par voie thermqiue une polarisation inherente dans ces fibres, en l'absence d'air. Lorsqu'elles sont produites par ce procede, des fibres optiques peuvent entrer dans la fabrication de convertisseurs de frequences, modulateurs electro-optiques lineaires, commutateurs electro-optiques lineaires, capteurs de champs electriques, miroirs non lineaires de second ordre, reseaux des Bragg a commande electrique et transducteurs permettant de produire des ondes acoustiques de surface sur des substrats de verre.