Szymon Lis

Photonic crystal microcavity in GaN-on-sapphire slab waveguide for sensor applications

Gallium nitride is an important material for the contemporary optoelectronics. Large electric band gap, high temperature resistivity and environmental resistance make GaN interesting also for sensor applications. However, asymmetric structure of GaN-on-sapphire slab waveguide, grown as a conventional epitaxial heterostructure, poses a problem with achieving high quality (Q) factor resonators. In this paper, issues related to an asymmetric structure of a waveguide and theoretical possibilities to achieve high Q-factor resonator in the GaN planar structures are discussed. Three dimensional (3-D) finite-difference time-domain (FDTD) modeling tools were used. It is shown that the highest Q-factor value of ~ 23 000 is obtained for a symmetrical membrane in L9 (nine points-defect cavity) micro-cavity based on GaN planar waveguide. In reference to the simulation results, we also discuss the technological issues, i.e. fabrication of photonic crystal patterns in GaN layers. New approach presented here included deep RIE etching with use of only single masking layer and conductive polymer usage in e-beam pattering. Possible applications of the micro-resonators for sensor applications are discussed.

SiO2 - TiO2 Thin Film for Integrated Optics Fabricated by the Sol-Gel Technique

In this paper the fabrication process and optical measurements of sol-gel SiO2-TiO2 thin films are presented. The first part is devoted to the basics of sol-gel technique, where fabrication of silica-titania films is shortly described. Investigated layers were obtained from three different precursors: tetraethyl orthosilicate (TEOS), tetrabutoxytitanate (TNBT) and titanium isopropoxide (TIPO), mixed in various amounts in order to tailor the refractive index of a layer. Sol-gel films were coated by dip-coating method on silicon substrate with 1 mum SiO2 optical substrate in the first case, and on bare silicon substrate in the second case. Thickness and refractive index of deposited layers was measured at 632.8 nm wavelength by use of ellipsometry. Refractive index dependence of SiO2-TiO2 composition in sol-gel thin film is presented

Application of spectrophotometry and ellipsometry for determination of optical parameters of optical coating thin films

In the present work usefulness of spectrophotometry and ellipsometry for the determination of different parameters of optical thin films have been discussed. The principles of their operation and some exemplary results for TiO2 thin films deposited by magnetron sputtering are presented.

Excitation of Surface Plasmon Polaritons on sinusoidally corrugated metal-dielectric interface fabricated using interference lithography

Using Finite-difference time-domain (FDTD) method, the excitation of surface plasmon polaritons (SPP) at the sinusoidally corrugated metal-dielectric interface was simulated. The sample structure was made by creating onedimension sinusoidally corrugated dielectric layer on top of metal thin film deposited on dielectric substrate. The thickness of metal film was simulated in range from 10 to 200 nm. Sinusoidally corrugated grating was modelled with different pitch and height. Additionally influence of a dielectric layer between grating and metal layer was simulated. The optical response of the structure was obtained in the regime of wavelength and angle. All simulations were performed for gold (Au) thin films deposited on glass substrate. Then selected structures were fabricated and measured. The gold film was thermally evaporated on glass substrate then the one-dimension sinusoidally corrugated dielectric layer was made in a photoresist using interference lithography.

A silicon photonic quasi-crystal structure obtained by interference lithography

Photonic quasi-crystal structures have been prepared and investigated. Symmetrical patterns were fabricated by interference lithography in negative tone photoresist and transferred to silicon by reactive ion etching. Theoretical influences of pattern detail (radius of hole) on the photonic band gap have been studied. Three types of 2D photonic quasi-crystals have been prepared: 8-fold, 10-fold and 12-fold pattern. Finally, finite-difference time-domain method was used for theoretically prediction of transmission spectrum for fabricated 12-fold quasi-crystal.

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.

Characterization of two dimensional photonics structures using optical sccaterometry

The technology of photonics structures has being still developed. The main problem, which this technology copy with, is characterization of geometrical parameters in a nano regime. The best method should be quick, easy to use, cheep and precise. Two popular methods such as microscopy AFM or SEM are expansive to maintain and use. Moreover the time of a measurement is long and the inspected area are relatively small. Majority photonic structures are periodic due to optical methods look quite promising. One of them is optical scatterometry which is the angle-resolved measurement and characterization of light scattered from a structure. This technique is able to precisely measure geometrical parameters of structures in the sub-micron size. Additionally scatterometry is quick and non-invasive method. In previous paper has been presented results of using this method to obtain profile one dimensional photonic crystal. In this paper is described the method to measure two dimensional nano-structures and results characterization of two dimensional photonic crystal PhC in photoresist obtained by holographic lithography.

Quick and non-invasive method for characterisation of profiles of nano-photonics structures

Depth and profile information of one or two-dimensional photonic crystals can be obtained through measurements of reflective diffractive patters obtained from the structures and subsequent numerical analysis. The technique is known as a scatterometry. The method is non-invasive and fast, and competitive to the alternatives of AFM, SEM etc. In our paper we presented results of investigation 1D photonic crystal fabricated in GaN with period Λ = 400 nm, fill factor ff = 50% and depth d = 400 nm. Using computer algorithm of Rigorous Coupled Wave Analysis (RCWA) and measuring diffracted light we extracted the profile parameters of Λ = 420 nm, ff = 51%, d = 400 nm. Possibility of application of our method for analysis 2D photonic crystals is discussed also.