Milija Sarajlić

Light modulation utilizing photonic crystal-based photoelastic elements with dual built-in defect

In this paper we analyze optical modulation by stress-sensitive active elements based on photonic crystals utilizing photoelasticity effects. Our approach is to utilize thin film sensitive elements with photonic bandgap on micromachined silicon diaphragms. We propose two designs, one of them based on 1D Bragg-type dielectric stacks and shaped using conventional photolithography, and the other utilizing nanolithography (scanning probe lithography) to build a photonic bridge structure. In both cases the properties of a built-in defect are modified by stress, resulting in a proportional decrease of the corresponding localized mode peak height. Conventional optical fibers are used for signal readout in our stress-sensitive all-optical modulators.

Metal-dielectric photonic crystal for the enhancement of solar-blind ultraviolet silicon photodiodes

We report the fabrication of metal-dielectric photonic crystals as bandpass filter for the UV radiation with a sidelobe suppression in excess of 4 orders of magnitude. The metal-dielectrics were designed for the enhancement of the operation of UV photodiodes and for the use of Si PIN photodiodes as solar-blind devices. The bandpass filters were fabricated by RF sputtering of alternating SiO2 and silver layers.

Scanning Probe-Shaped Nanohole Arrays with Extraordinary Optical Transmission as Platform for Enhanced Surface Plasmon-Based Biosensing

We analyzed the use of subwavelength ordered nanohole patterns for detection of miniscule amounts of biological analytes. Owing to their surface plasmon resonance (SPR) operation, such structures show an extraordinarily high optical transmission in visible spectrum, at the same time concentrating the illumination to the very small area of the nanoholes and being much more sensitive to refractive index changes than the conventional SPR sensors. We applied an approximate analytical approach to design our V-shaped, nanometer-sized hole arrays. We utilized scanning-probe nanolithography to fabricate the designed nanoholes in silver substrate. We investigated the topography of the obtained patterns by atomic force microscopy. Compared to conventional SPR optical sensors, the nanohole array-based structures allow for the detection of smaller quantities of analytes, enhance nonlinear effects and ensure improved sensitivities to different analytes

A Consideration of Transparent Metal Structures for Subwavelength Diffraction Management

We considered theoretically and experimentally one-dimensional multilayered metallodielectric nanofilms with nanometric thickness for imaging below the diffraction limit. We investigated their behavior in the ultraviolet and visible spectrum from the point of view of near field optics, but also considered some of their properties in the far field. We designed our structures using the transfer matrix method and utilized RF sputtering to fabricate them. We consider some possible approaches to extract optical information from such multilayers

Gradient-index infrared metamaterials based on metal-dielectric submicrometer pillar arrays

This paper presents the design and microfabrication of a two-dimensional metal-dielectric metamaterial structure based on an array of pillars with submicrometer diameters and heights. The diameters of pillars periodically vary along one axis in a sawtooth fashion and are constant along the other. The electromagnetic field distribution within this graded metamaterial was considered utilizing an accurate analytical approach. The pillar arrays were fabricated in photoresist and subsequently covered with a sputter-deposited aluminum film. Structures were defined by direct laser writing in photoresist film. Controlled overexposure has been applied in order to make pillar features smaller than the nominal resolution of the equipment. The structures were characterized by optical and atomic force microscopy and by angle-dependent Fourier Transform infrared spectroscopy. The produced graded frequency-selective surfaces may be used e.g. in sensing.

Modeling of the conductivity alteration in the gold thin film-based mercury sensor using the fuchs theory

We report on the development and testing of the metallic mercury sensor. Sensor is based on the gold thin film layer where sensing is achieved by formation of the gold-mercury amalgam. Complete technological procedure and design is performed at IHTM-CMTM in Belgrade, Serbia. We test the sensor by exposing it to the various mercury concentrations and compare results to the Langmuir adsorption theory. We explain resistivity alteration during gold-mercury adsorption by the Fuchs theory of conductivity in thin films. This is the basis for the more detailed understanding of the sensor functionality.

Photoacoustic spectroscopy: investigation of sputter damage in Si surface by Ar plasma

The effect of Ar plasma etching on the surface of Si was investigated by photoacoustic spectroscopy. The surface of Si sample (p-tip, 10 k/spl Omega/cm, 420 /spl mu/m) was treated with Ar plasma from 2 min to 80 min. Amplitude and phase PA spectra were measured in the energy range from 0.75 to 1.55 eV. The amplitude ratio and phase difference of photoacoustic signals of Si samples Ar plasma etched and incoming Si samples indicate existence of two surface energy states (the generation-recombination centers) at 0.31 and 0.99 eV.

Method of microcantilever deflection measurement utilizing mechanochromic effect in photonic crystals

In this paper we present a method for microcantilever deflection measurement utilizing a stress-tunable photonic crystal (Photonic Bandgap, PBG) waveguide. The method uses the mechanochromic effect, i.e. the modulation of transmissive properties by applied force. A 2D photonic crystal-based channel waveguide with a 90/spl deg/ band is used as sensitive element. The structure is monolithically integrated with the basis of the microcantilever where deflection-induced stress is maximal. Applied stress simultaneously causes a shift of the photonic bandgap edge and photoelastic refractive index change and this is used for amplitude modulation of light signal. The approach may be used in deflection or stress sensing in various other MEMS sensors.