Jayshri Sabarinathan

Fluid detection with photonic crystal-based multichannel waveguides

A simple fluid detection scheme, based on light propagation through linear defect waveguides in photonic crystals, is demonstrated with isopropanol and xylene. The two-channel photonic crystal waveguide sensor is made from a GaAs-based heterostructure. The preferential channeling of light is controlled by the change in the refractive index of the corresponding waveguide branch due to the presence of the inserted fluid in the guide regions only.

Characteristics of a photonic bandgap single defect microcavity electroluminescent device

A microcavity surface-emitting coherent electroluminescent device operating at room temperature under pulsed current injection is described. The microcavity is formed by a single defect in the center of a 2-D photonic crystal consisting of a GaAs-based heterostructure. The gain region consists of two 70-/spl Aring/ compressively strained In/sub 0.15/Ga/sub 0.85/As quantum wells, which exhibit a spontaneous emission peak at 940 nm. The maximum measured output power from a single device is 14.4 /spl mu/W. The near-field image of the output resembles the calculated TE mode distribution in a single defect microcavity. The measured far-field pattern indicates the predicted directionality of a microcavity light source. The light-current characteristics of the device exhibit a gradual turn-on, or a soft threshold, typical of single- or few-mode microcavity devices. Analysis of the characteristics with the carrier and photon rate equations yields a spontaneous emission factor /spl beta//spl ap/0.06.

Submicron three-dimensional infrared GaAs/AlxOy-based photonic crystal using single-step epitaxial growth

A relatively simple technique is demonstrated to fabricate three-dimensional face-centered-cubic infrared photonic crystals with submicron feature sizes using GaAs-based technology, single-step epitaxial growth, and lateral wet oxidation. The photonic crystals were fabricated with feature sizes (a) of 1.5 and 0.5 μm. Transmission measurements reveal a stopband centered at 1.0 μm with a maximum attenuation of 10 dB for the submicron (a=0.5 μm) photonic crystal. This technique is scalable to small photonic crystal periodicity and hence to shorter wavelengths.

An electrically injected InAs/GaAs quantum-dot photonic crystal microcavity light-emitting diode

An electrically injected InAs/GaAs self-organized quantum-dot photonic crystal microcavity light-emitting diode operating at 1.04 μm is demonstrated. Light–current characteristics are obtained for devices with two- and five-defect period cavities with maximum light output of 0.17 μW measured in the surface-normal direction. Near-field images were also obtained for an injection current of 8.35 mA, showing light confinement within a few periods of the photonic crystal defect microcavity.

Near-infrared optical response of thin film pH-sensitive hydrogel coated on a gold nanocrescent array

A hydrogel-based chemiresponsive sensor for monitoring H(+) (pH) has been developed by coating the surface of a gold nanocrescent array structure with a thin film of a poly(2-hydroxylethyl methacrylate)-based (poly-HEMA) hydrogel. The transmission measurement results of the close-packed gold nanocrescent array fabricated via electron beam lithography demonstrate near-infrared localized surface plasmon resonance peaks with sensitivities up to 332 nm/RIU in detecting refractive index change. Measurements of the hydrogel under solutions of increasing pH show the plasmon peak blueshifts by 17 nm and the integrated transmission increases by 1.8 in the operating range of 4.5 - 6.4 pH, which is ideal for biochemical sensor applications.

3-D FDTD Analysis of Gold-Nanoparticle-Based Photonic Crystal on Slab Waveguide

In this paper, metallic photonic crystals (PC) based on 2-D periodic arrays of gold nanoparticles were investigated on indium tin oxide slab waveguides using 3-D finite-difference time domain simulations with nonuniform mesh techniques. The PC effects were studied by changing the lattice constants from 300 to 500 nm. The results obtained indicate that the waveguide-excited plasmon absorption peak of periodic array of gold nanoparticles is tunable from 672 to 707 nm due to the second grating order propagating backward at the grazing angle. The nanoparticle-induced extinction of the waveguide mode was also investigated by varying the slab thickness from 100 to 375 nm. The results show that the extinction peak shifts from 650 to 705 nm. The theoretical results predict that the interactions of the periodic array of gold nanoparticles are strongly affected by the dispersion of the waveguide.

Growth of high density self-organized (In,Ga)As quantum dots with ultranarrow photoluminescence linewidths using buried In(Ga,Al)As stressor dots

High density InAs and In0.4Ga0.6As dots were grown by molecular beam epitaxy on buried In0.4Al0.6As and In0.4Ga0.3Al0.3As stressor dots, respectively. Selective radiative recombination was achieved by engineering the band gap of the dots. Structural and luminescence measurements reveal increased size uniformity in the active region dots along with an increase in the dot density. A narrow photoluminescence linewidth of 19 meV was measured at T=17 K.

Quantum Dot Photonic Crystal Light Sources

The control and manipulation of light on a planar IC similar to that achieved for electrons in semiconductor chips on submicrometer and nanometerscales is an area of very active research today. While electronic device miniaturization is close to reaching its maximum possible potential, photonic devices have unique properties that have yet to be exploited. With increasing advances in nanofabrication techniques and the understanding of optical properties of semiconductors, several optical devices such as lasers, detectors, interferometers,and waveguides have been constantly shrinking in size. We have achieved very high speed integrated optical devices at 10-100-/spl mu/m length scales. However, there is a need to further reduce the size of devices to make them competitive in size and cost to existing electronic devices and to utilize their potential and unique properties in a wide range of applications ranging from communications, displays to sensors. Photonic crystals have emerged as one of the best potential candidates that can achieve the goal of compact miniaturized photonic chips. In this paper, we describe the current efforts and advances made in the photonic crystal microcavity light sources and their future prospects.

Protein Binding Detection Using On-Chip Silicon Gratings

We demonstrate a silicon gratings-based biosensor to detect functionalized protein binding on its surface. The designed silicon gratings have sensitivities up to 197 nm/RIU in detecting refractive index change and 1.61 nm per nanometer of thickness change of bio-material on the surface of silicon gratings. Functionalizing proteins on gratings surface by eliminating unspecific binding makes this device more selective and efficient. Streptavidin at a concentration of 0.016 μmol/mL was functionalized on silicon substrate and biotin of 12 μmol/mL concentration was used as a target molecule in our detection experiments. Normal transmission measurements of gratings are made in air at different stages of immobilization, bare silicon grating, after attaching streptavidin and after trapping biotin. Total shifts in resonant peak wavelength of ∼15 nm in normal transmission were observed after immobilizing biotin with ∼7 nm of shift in resonant peak wavelength after functionalizing streptavidin to silicon substrate.

Mechanical sensitivity enhancement of silicon based photonic crystal micro-pressure sensor

We describe here a sensor consisting of a line defect photonic crystal waveguide suspended over a silicon substrate. Under applied pressure, the photonic crystal waveguide is deflected toward the substrate, causing a decrease in optical transmission due to the coupling of the waveguide field to the silicon substrate. Bridge engineering can increase the mechanical sensitivity of the bridge: maintaining constant bridge footage, we are able to increase sensitivity by about 5.5 times.