Abrupt discontinuity in the broad band density of states in a photonic crystal near PBG and low group velocity can have practical impact in many exiting applications of photonic crystals, for example, optical transistor, tunable filters, chromatic dispersion compensators and pulse compression. However it is difficult to excite EM modes in the photonic crystal at frequency close to its PBG by external beam because of tremendous group index mismatch. To solve this problem we propose an idea of a transition interface with a smooth group index profile. Firstly, the idea has been investigated in general using a multi-layer stack as a “toy” model. Then, general trends have been verified for 2D photonic crystals with infinite thickness and slab photonic crystals with one-dimensional periodicity. It has been shown that if there is no interface, reflection/back-diffraction from the photonic crystal at the frequency in the transmission window near its edge is close to 100%. However in case of transition interfaces the transmission increases and abrupt edge of the broad band transmission spectrum takes place. The thicker transition interface - the more abrupt transmission spectrum. It has been shown that not only thickness, but also the group velocity profile in the transition interface is essential.
Scattering losses for fused silica were measured over a wide wavelength range (193-800 nm) using different laser sources. The data indicate that scattering centers are smaller than ~ 12 nm, and scattering is consistent with Rayleigh type even at 193 nm. Scattering losses scale with wavelength as 1/λ4, and scattering loss at 193 nm was found to be (0.65±0.08)x10-3/ cm absorption units or (0.15±0.02)% transmission per cm. CaF2 measurements were completed in the visible wavelength range. The experimental approach for DUV wavelength measurements for CaF2 is described. Estimated scattering losses at 193 nm are ~0.003% transmission per cm and ~0.006% transmission per cm at 157 nm. Data for CaF2 indicate deviation from Rayleigh-type scatter.
Planar photonic crystal structures are a new way to achieve the confinement and guiding of light in an optical circuit. Acceptably low levels of optical loss will be key to developing this technology into commercially viable devices. Meaningful measurement of the loss of these devices is complicated by their reduced size and their optical model structure. To date no satisfactory loss measurement of these waveguides has been made. We analyze the challenges to be reached that will lead to accurate and quantitative measurements.
Some theoretical problems which may be useful for investigations of glass-composite optical properties are studied. These problems are: estimations of the optical properties limiting values; the effective dielectric function calculations for disordered systems of absorbing particles; coherent Rayleigh-scattering calculations for systems of spherical shells; Mie theory calculations for semiconductor particles with quantum confinement of excitons; Mie-theory calculations of Faraday effect spectra.
The magnetic circular dichroism and optically detected EPR spectra of rareearth
ions Er3+, Tm3+, Yb3+ in clusters formed by these ions or by diamagnetic
ions Lu3+ or Y are obtained. Thus new paramagnetic states of Er3+,Tm3+ and Yb3'
ions in fluorites with nearly tetragonal symmetry of these ions in clusters and
coalescence of clusters into grains were established. It is concluded that in the
whole range of activator concentrations 0.1-40 mol% the clusters under investigation
are similiar in structure to the high symmetry Y6F37 clusters previously observed
by X-ray methods in natural mineral of tveitite. The noncentral F ions in
clusters are probably responsible for the existence of two-level systems also discovered
by our studies in activated fluorites.
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