Alexander V. Tishchenko

Highly-dispersive dielectric transmission gratings with 100% diffraction efficiency.

A new approach for the realization of highly dispersive dielectric transmission gratings is presented, which enables the suppression of any reflection losses and, thus, 100% diffraction efficiency. By applying a simple two-mode-model a comprehensible explanation as well as a theoretical design of such a reflection-free transmission grating is presented.

99% efficiency measured in the -1st order of a resonant grating

A resonant diffraction grating comprising a mirror, a dielectric layer and a high index corrugation at the layer-air interface is shown to exhibit off-Littrow the record diffraction efficiency of 99% in the -1st reflected order at 1064 nm wavelength thanks to the excitation of a leaky mode of the layer. Such high figure is obtained by a grating 5 to 10 times shallower than in current attempts to realize high efficiency all-dielectric gratings.

Coupling gratings as waveguide functional elements

Waveguide grating couplers allow the essential function of waveguide access to be integrated together with optical processing functions on a monolithic planar substrate. Grating coupling technology is topologically and, to a large extent, technologically compatible with the planar processes which define the optical processing waveguide circuit. Poor coupling efficiency, highly dispersive character, absence of user-friendly modelling tools and fabrication difficulties have long prevented this technology from being implemented into practical sensors and microsystems. This paper makes a review of the points where decisive technological progress has been made, illustrates some useful features of waveguide coupling gratings and underlines some of the difficulties which the designer may encounter.

Modal analysis and suppression of the Fourier modal method instabilities in highly conductive gratings

The Fourier modal method (FMM), often also referred to as rigorous coupled-wave analysis (RCWA), is known to suffer from numerical instabilities when applied to low-loss metallic gratings under TM incidence. This problem has so far been attributed to the imperfect conditioning of the matrices to be diagonalized. The present analysis based on a modal vision reveals that the so-called instabilities are true features of the solution of the mathematical problem of a binary metal grating dealt with by truncated Fourier representation of Maxwells equations. The extreme sensitivity of this solution to the optogeometrical parameters is the result of the excitation, propagation, coupling, interference, and resonance of a finite number of very slow propagating spurious modes. An astute management of these modes permits a complete and safe removal of the numerical instabilities at the price of an arbitrarily small and controllable reduction in accuracy as compared with the referenced true-mode method.

Narrowband, polarization-independent free-space wave notch filter

A two-dimensional-corrugated-slab-waveguide add/drop filter providing 100% resonant reflection at 1.55 microm wavelength for both TE and TM polarizations with identical FWHM is designed. The fabricated device exhibits a reflectivity spectrum of more than 95% peak reflection for both polarizations at 1.537 microm. The coupling scheme involves the TE0 guided mode only; it is made relatively tolerant by means of a double-sided crossed grating.

Identity of long-range surface plasmons along asymmetric structures and their potential for refractometric sensors

The field identity of the long-range surface plasmon (LRSP) mode in an asymmetric metal dielectric structure is elucidated and it is shown that it can be pictured as having a zero crossing of the longitudinal electric field at the middle of the metal film. A parametric dependence between the metal and the dielectric layer thicknesses leading to a LRSP mode in an asymmetric structure is given. The sensitivity of an asymmetric four layer structure supporting a grating excited LRSP mode regarding sensing objectives has been investigated. It is compared with the sensitivity of a usual plasmon mode propagating along a metal–dielectric interface. The existence of an anomalous increase of the reflection coefficient in the case of the LRSP is observed theoretically and experimentally. The comparative study is made on the basis of analytical expressions which reveal that the LRSP does not bring a decisive advantage over the standard plasmon for sensor application but its specific features can be advantageously use...

Analytical treatment of the thermal problem in axially pumped solid-state lasers

A complete analytical analysis of the temperature distribution in a laser rod in an axial pumping scheme is presented. The heat source distribution, as well as the front or side cooling means, have a circularly cylindrical symmetry. The longitudinal heat-source distribution is strongly inhomogeneous.

Modal method in deep metal-dielectric gratings: the decisive role of hidden modes

The modal method is well adapted for the modeling of deep-groove, high-contrast gratings of short period, possibly involving metal parts. Yet problems remain in the case of the TM polarization in the presence of metal parts in the corrugations: whereas most of the diffraction features are explained by the interplay of an astonishingly small number of true propagating and low-order evanescent modes, the exact solution of the diffraction problem requires the contribution of two types of evanescent modes that are usually overlooked. We investigate the nature and the role of these modes and show that metal gratings can be treated exactly by the modal method.

Anomalous light reflection at the surface of a corrugated thin metal film

The process of excitation of surface electromagnetic waves (SEWs) in corrugated thin metal film is investigated theoretically and experimentally. The existence of an anomalous increase of the reflection coefficient is demonstrated. The excitation of long-range plasmons in thin metal films opens new possibilities for sensor applications.

A monolithic optical phase-shift detector on silicon

A novel monolithically integrated device used as an optical phase-shift detector is presented. It consists of a diffraction grating etched at the surface of a p-n photodiode fabricated by a process compatible with a standard silicon CMOS technology. When two coherent light beams are collimated toward the surface of the device, the detected optical power generates a current depending on the relative phase between the two incident beams. The operating principle of this detector and the results obtained by finite-difference time-domain modeling are presented. The fabrication process of the first devices is described and the experimental validation of the concept is demonstrated.