Optical Waveguide Gratings Research Articles

66.3: Design of Color Backlight for High Efficiency Display using Optical Waveguide Gratings

AbstractWe report a novel backlight with waveguide gratings instead of using color filters to reduce power consumption. The waveguide gratings enable the red‐green‐blue (RGB) light propagate separately and be emitted toward the respective pixels unidirectionally. Selective emitting rate and direction is obtained by optimizing the grating geometry. This device shows potential for micro‐display.

Application of Optical Biosensors in Small-Molecule Screening Activities

The last two decades have seen remarkable progress and improvements in optical biosensor systems such that those are currently seen as an important and value-adding component of modern drug screening activities. In particular the introduction of microplate-based biosensor systems holds the promise to match the required throughput without compromising on data quality thus representing a sought-after complement to traditional fluidic systems. This article aims to highlight the application of the two most prominent optical biosensor technologies, namely surface plasmon resonance (SPR) and optical waveguide grating (OWG), in small-molecule screening and will present, review and discuss the advantages and disadvantages of different assay formats on these platforms. A particular focus will be on the specific advantages of the inhibition in solution assay (ISA) format in contrast to traditional direct binding assays (DBA). Furthermore we will discuss different application areas for both fluidic as well as plate-based biosensor systems by considering the individual strength of the platforms.

Calculation of optical-waveguide grating characteristics using Green’s functions and Dyson’s equation

We present a method for calculating the transmission spectra, dispersion, and time delay characteristics of optical-waveguide gratings based on Green's functions and Dyson's equation. Starting from the wave equation for transverse electric modes we show that the method can solve exactly both the problems of coupling of counterpropagating waves (Bragg gratings) and co-propagating waves (long-period gratings). In both cases the method applies for gratings with arbitrary dielectric modulation, including all kinds of chirp and apodization and possibly also imperfections in the dielectric modulation profile of the grating. Numerically, the method scales as O(N) where N is the number of points used to discretize the grating along the propagation axis. We consider optical fiber gratings although the method applies to all one-dimensional (1D) optical waveguide gratings including high-index contrast gratings and 1D photonic crystals.

Sub-micron period grating structures in Ta2O5 thin oxide films patterned using UV laser post-exposure chemically assisted selective etching

A high-resolution and low-damage method for patterning relief structures in thin Ta2O5 films by chemically assisted UV laser selective etching is presented. The method is based on the initial exposure of the Ta2O5 films to pulsed UV radiation (quadrupled Nd:YAG laser at 266 nm) at fluences below the ablation threshold, for the creation of volume damage in the exposed areas. Subsequent immersion of the exposed sample in a KOH solution results in selective etching of the UV-exposed areas, developing relief structures of high quality. Interferometric exposure was used for the patterning of such gratings with periods of the order of 500 nm in films with a thickness of 100 and 500 nm. The behaviour of the patterning process is studied using diffraction efficiency measurements and AFM scans. Diffraction efficiency increases by a factor of ≈63, compared to the undeveloped structure, were obtained for gratings exposed with 1000 pulses of 30 mJ/cm2 energy density, which were developed in a KOH solution. The etching method presented is being applied to the fabrication of gratings in optical waveguides.

Analysis of antiresonant reflecting optical waveguide gratings by use of the Method of Lines

The modal spectral response of an antiresonant reflecting optical waveguide (ARROW) with periodic corrugations or grating is calculated for both shallow and deep gratings with the Method of Lines. The effect of the ARROW layer thickness and the grating depth on the spectral response is studied. It is found that when the ARROW-layer thickness is close to resonance, the ripples in the reflection spectra become smooth and the peak reflectivity drops. This is attributed to the large increase in the leakage loss of the ARROW waveguide near resonance. The ARROW grating is characterized by modal reflectivity spectra, which exhibit a strong polarization discrimination property, in favor of the TE polarization.

Tunable microfluidic optical fiber gratings

We demonstrate periodic refractive index gratings in optical waveguides formed by microfluidic plugs that are infused into the airholes of a microstructured optical fibers. The periodic microfluidic plugs, created in the cladding, cause resonant coupling between copropagating optical fiber modes, which results in wavelength-dependent attenuation. We also demonstrate the ability to tune the resonant wavelength by compressing the microfluidic structure. These microfluidic resonant structures provide an alternative method for creating and tuning long-period gratings in optical fibers. This also represents an example of a resonant microfluidic structure and establishes potential strategies for enhanced tunable photonic crystal devices.

Radiation losses on discontinuities in integrated optical waveguides

A method to obtain the electromagnetic scattering properties of step discontinuities between integrated optical waveguides is presented. The method involves a new generalized scattering-matrix concept, together with the generalized telegraph-equation formalism and the modal matching technique. Our model encloses the optical waveguides with perfectly conducting walls. Reflection, transmission, and radiation coefficients can be obtained for step discontinuities in monomode or multimode optical waveguides with arbitrary refractive index profile functions. Furthermore, the method can be applied to any cascaded set of multiple discontinuities between planar or channel optical waveguides. In this way, segmented optical waveguides, optical waveguide gratings, transitions, and tapers can be analyzed by modelization as multiple abrupt discontinuities. Excellent convergence and accuracy were observed finding the optical waveguide modes. Results on convergence and accuracy for effective indices, as well as for radiation losses for step discontinuities, are given and compared with those presented by other authors.