Generalized method of images and reflective color generation from ultra-thin multipole resonators

The multipole expansion has found limited applicability for optical dielectric resonators in inhomogeneous environment, such as on the surface of substrates. Here, we generalize the method of images to multipole analysis for light scattering by dielectric nanoparticles on conductive substrates. We present examples illustrating the physical insight provided by our method, including selection rules governing the excitation of the multipoles. We propose and experimentally demonstrate a new mechanism to generate high resolution surface color. The dielectric resonators employed are very thin (less than 50 nm), i.e. similar in thickness to the plasmonic resonators that are currently being investigated for structural color. The generalized method of images opens up new prospects for design and analysis of metasurfaces and optical dielectric resonators

Interference measurement of single living cells' refractive index

81 p.In recently years there has been a rapid increase of research interests to determine the physical parameters of singe living cells, such as size, shape, and refractive index (RI) as demanded in biological studies and cell-based drug screening. The RI measurement also provides an approach to label-free cell detection. In this project, an optofluidic system on chip has been developed for measuring the single living cell's parameters, such as effective RI, diameter, hence the volume, cell dry mass, cell water mass, cell water concentration and cell total mass, etc.Master of Science (Photonics

Optofluidic differential spectroscopy for absorbance detection of sub-nanolitre liquid samples

We present a novel optofluidic differential method for carrying out absorbance spectroscopy of subnanolitre volumes of liquid samples on a microfluidic chip. Due to the reduction of liquid volume, the absorbance detection in microfluidics is often hindered by either low sensitivity or complex fabrication. To address this issue, we introduced an optofluidic modulator which can be easily integrated into a PDMS (polydimethylsiloxane) based microfluidic chip. The modulator was controlled by the fluid pressure and the absorbance spectrum of the analyte was obtained by taking differential measurements between the analyte and reference medium. An advantage is that this method doesn't need a complicated fabrication step. It is compatible with conventional microfluidic chips and measurements can be carried out on a normal transmission microscope. The performance of the device was tested by measuring solutions containing methylene blue, with concentrations as low as 13 mu M

Optofluidic pressure sensor based on interferometric imaging

We present a chip-scale optofluidic interferometric sensor for measuring liquid pressure based on an imaging method. The chip was constructed with a polymer by multilayer soft lithography. It consists of a flexible air gap optical cavity, which, upon illumination by monochromatic light, generates interference patterns that depend on pressure. The pressure was measured by imaging and analyzing the interference patterns. We also employed a pattern recognition algorithm that significantly simplified the calculation and enhanced the measurement reliability. This pressure sensor was demonstrated with a working range of 0-22 psi and an accuracy of +/- 1.4% of full scale when temperature stabilized. (C) 2010 Optical Society of Americ

Imaging based interferometric pressure sensor

An imaging based interferometric pressure sensor apparatus compromise a fluid pressure sensor unit (1) and an optical monitor (2). The disposable pressure sensor part comprises a rigid transparent cover plate 3 and a flexible diaphragm (4), in between forming an air-gap cavity (8). By illuminating the air-gap cavity (8) with a light source (6), the air-gap cavity generates an interference pattern which is captured by the optical imaging device (7). The pressure of the fluid (5) to be sensing is applied to flexible diaphragm, causing the deformation of the diaphragm and the variation of the air-gap thickness. Hence the interference pattern varies with pressure of fluid. The optical monitor (2) includes light source 6 and optical image device (7) which records the interference pattern from the fluid pressure sensor unit (1). The pressure of the fluid is measured by processing the captured image

Pneumatically tunable optofluidic 2 x 2 switch for reconfigurable optical circuit

We presented a pneumatically tunable 2 x 2 optofluidic switch for on-chip light routing that was controlled by compressed air. The device was fabricated with an optically clear elastomer-polydimethylsiloxane ( PDMS)-by soft-lithography. The optical switching is realized with a tunable air-gap mirror by which the light is deflected due to total internal reflection in the bypass state. When the device is subjected to high pressure, the air gap collapses and hence the light will be switched to the crossover state. The device had a switching speed of more than 5 Hz and an extinction ratio of 8 dB. This switch can be readily integrated with other microfluidic circuits. We demonstrated a simple reconfigurable optical waveguide circuit for dual-channel microfluidic spectroscopy measurement on a chip

Novel tuning method for optofluidics

We introduce a novel tuning mechanism for optofluidic devices by embedding pressure driven actuator inside microfluidic chips. Multiple tunable optofluidic devices remotely controlled by the pressure of air or liquid were demonstrated