Design of highly sensitive refractive index sensors in the visible region utilizing metal layer assisted guided modes.

We present a systematic comparison of the metal layer assisted guided mode resonance-based sensing structures with the traditional guided mode resonance-based sensing structures sharing identical design parameters for various two-dimensional square hole and pillar grating type lattice configurations. The surface and volume integrals of the electromagnetic field intensity profiles at resonance have been computed for all the considered structures to show that the waveguide-pillar-based structures offer the strongest interaction between the resonant modes and the sensing region, resulting in a superior sensitivity. Further insights into the nature of metal assisted guided mode resonance-based sensors and the ways to generate a strong resonant response are reported for the visible range of operation.

Investigation on bandgap, diffraction, interference, and refraction effects of photonic crystal structure in GaN/InGaN LEDs for light extraction.

In this paper, we have made a clear differentiation among bandgap, diffraction, interference, and refraction effects in photonic crystal structures (PhCs). For observing bandgap, diffraction, and refraction effects, PhCs are considered on the top p-GaN surface of light emitting diodes (LEDs), whereas for interference effect, hole type PhCs are considered to be embedded within n-GaN layer of LED. From analysis, it is observed that at a particular lattice periodicity, for which bandgap lies within the wavelength of interest shows a significant light extraction due to inhibition of guided mode.

Bragg gratings written in Sn-Er-Ge-codoped silica fiber: investigation of photosensitivity, thermal stability, and sensing potential.

Bragg gratings were fabricated in an Sn-Er-Ge-codoped silica fiber with a phase mask and ultraviolet radiation from a 248-nm KrF excimer laser. The photosensitivity of the fiber was examined by studying the initial growth rate of the gratings written into it. The thermal stability of the gratings was investigated and modeled in terms of both the refractive-index modulation and the effective refractive index of the fiber core.

Analysis of thermal decay and prediction of operational lifetime for a type I boron-germanium codoped fiber Bragg grating.

The thermal decay of a type I fiber Bragg grating written at 248 nm in boron-germanium codoped silica fiber was examined in terms of its reflectivity and Bragg wavelength change. In addition to the decay in reflectivity, which was observed, a shift in Bragg wavelength over the temperature range considered was seen. A mechanism for the decay in the reflectivity was developed and modeled according to a power law, and the results were compared with those from the aging curve approach.