Marcin Wielichowski

Optimization of 2D slab photonic crystal geometry for gas sensing

The two-dimensional (2D) slab photonic crystal (PhC) geometry is optimized for the application of the PhC as a near-infrared spectroscopic gas sensors active element. Sensor operation in the slow-light regime is assumed. The 2D theoretical model is based on the finite-difference time-domain (FDTD) propagation of the electromagnetic field. Linear-defect 2D photonic crystal structures are considered. Optimization is performed according to the following criteria: maximum light coupling efficiency, maximum light extraction efficiency, and maximum light-gas overlap. In the simulations, output signal collection is performed by means of either an output strip waveguide. Antireflection sections suited for individual PhC geometry types, are applied to prevent excessive reflections resulting from the high group velocity of light propagating in the slow-light regime within the PhC. Configurations with and without antireflection sections are compared. Triangular-lattice 2D PhC types are: line-defect crystals and line-defect crystals featuring an additional row of holes that improve the light-gas overlap.

Phase Shaping to Control the Performance of a Contra-Directional Grating-Assisted Coupler

We propose a method of improving the performance of a planar grating-assisted contra-directional coupler for use as a photonic switch. By means of a nonuniform Bragg grating, rapid phase jumps are introduced within the reflection spectra of coupler supermodes. This creates a reflection peak of steep slopes, flat top, and desired width. Sample numerical results are given for realistic material and device parameters. A discrete layer-peeling method is employed for the synthesis of the Bragg grating.

Design and analysis of photonic optical switches with improved wavelength selectivity

Efficient optical modulators and switches are the key elements of the future all-optical fiber networks. Aside from numerous advantages, the integrated optical devices suffer from excessive longitudinal dimensions. The dimensions may be significantly reduced with help of periodic structures, such as Bragg gratings, arrayed waveguides or multilayer structures. In this paper we describe methods of analysis and example of analytical results of a photonic switch with properties modified by the application of periodic change of effective refractive index. The switch is composed of a strip-waveguide directional coupler and a transversal Bragg grating.

Modelling of out-of-plane losses in a 2D photonic crystal waveguiding structure fabricated by interference lithography in slow light regime

The results of 3D FDTD calculations of out-of-plane radiation losses in slow light regime for a 2D Silicon-On-Insulator (SOI) Photonic Crystal (PhC) slab are presented. In a 2D PhC slab structure periodicity causes a scattering out of waveguiding modes to the radiating modes. Optical sensors based on 2D PhCs working in slow light regime call for long devices in order to make the path of light propagation longer. At the same time, slowing down the group velocity of light extends signal interaction time with the investigated surroundings. By using a 3D model of an SOI PhC slab we will present the influence of the hole depth and side walls slope of a 2D PhC on the out-of-plane scattering. The possibility of utilising an interference lithograph to fabricate the modelled structure is discussed as well.

Modeling and optimization of grating coupler for slab waveguide

In the following paper, designing, modeling and optimizing an optical coupler based on titanium dioxide TiO2 is described. A rectangular diffraction grating integrated with a TiO2 waveguide is modeled. The optimized parameter is the coupling efficiency. The following parameters are also considered: coupler length, grating period, and grating etching depth. Critical values of grating filling factor preventing the coupling of light into the structure are determined. Finally, parameters of a structure showing the best coupling efficiency are presented.

Design procedure for planar add-drop multiplexer based on contra-directional coupler and apodized Bragg grating

A wavelength selective add-drop multiplexer utilizing a directional coupler loaded with a first order Bragg grating can be realized both in fiber and planar technologies. Specifically for the planar case, we detail a systematic design procedure leading from general assumptions concerning the functional parameters of the device down to geometrical dimensions of the resulting planar microstructure. The functional parameters include: channel spectral width and channel isolation. The resulting dimensions are: waveguides etch depth, grating etch depth and lengths of apodized-grating trenches. Grating apodization profile of the form sin^n is assumed. Design curves are presented, enabling an optimal choice of the apodization profiles exponent n considering a tradeoff between the required channel isolation and the resulting grating length.

Application of discrete layer peeling algorithm for design of selective photonic devices obeying the constraints of the fabrication process

Results of the Discrete Layer Peeling (DLP) inverse scattering algorithm do not directly correspond to Bragg gratings technological parameters. We propose a method of transforming a stack of discrete complex reflectors resulting from DLP into physical and geometrical parameters of a Bragg grating suitable for fabrication in planar technology. Particularly, the method keeps lengths of grating sections (teeth and grooves) above a required technological minimum. While the stack of complex reflectors is a natural output DLP, it can also be computed from a space distribution of the complex coupling coefficient determined in other ways.

Modeling of all-optical photonic switch based on contra-directional grating-assisted coupler

We outline a method of calculating the spectral response of a contra-directional grating-assisted optical coupler. Interference of reflected / transmitted supermodes is taken into account. Sample numerical results for a planar device are presented. The results include spectral response of a sole grating-assisted coupler, changes introduced by an additional coupler without grating and changes introduced by refractive-index modulation induced by an additional control beam