Guided-mode resonant grating filter with an antireflective surface for the multiple channels

In this paper, a new type of guided-mode resonant grating (GMRG) filter with an antireflective surface called the 'moth-eye structure' for the multiple channels is presented by using rigorous coupled-wave analysis (RCWA) and the S-matrix method. Long range, low sidebands and multiple channels are found when the GMRG filters with antireflective surface are illuminated with incident polarization light. It is calculated that the multiple channel phenomenon can be shown when the depth of antireflective surface is increased. Moreover, the wavelengths of the multiple channels can be easily shifted by changing the depth of the homogenous layer which is under the antireflective surface, and the optical properties of GMRG filters such as low sideband reflection and narrow band are not badly spoiled when the depth is changed.

Novel method for design of surface relief guided-mode resonant gratings at normal incidence

We demonstrate that the surface relief guided-mode resonant gratings with specified central wavelength and FWHM in the visible wavelength range can be designed by analyzing the complex poles of Reflectance and transmission coefficient matrix algorithm (RTCM), a variant of S-matrix propagation algorithm proposed for calculation of multilayer gratings. In addition, FWHM is computed with couple-mode (CM) theory of resonant gratings which is firstly extended by Norton et al. in calculation of waveguide grating. Furthermore, the side band reflections of the filter can be reduced to less than 5% in the visible wavelength with the antireflection (AR) design technique widely used in the thin-film field. (C) 2008 Elsevier B.V. All rights reserved.

Compensation of reflectance response deviations of guided-mode resonant filters induced by overetching fabrication

Unless the fabrication error control is well treated, it easily causes overetched fabrication errors, which causes the resonant peak value deviation during the fabrication process of guided-mode resonant filters (GMRFs). Hence, the fabrication error control becomes a key point for improving the performance of GMRF. We find that, within the range of the groove depth from 93 to 105 nm, the relationship between the overetched error and the resonant peak value deviation is nearly linear, which means that we can compensate the reflectance response deviation and reduce the resonant peak value deviation by the method of covering the layer film on the GMRF. Simulation results show that the deviation is compensated perfectly by this way. (C) 2008 Optical Society of America

Electric field enhancement in guided-mode resonance filters

Electric fields inside guided-mode resonance filters (GMRFs) may be intensified by resonance effects. The electric field enhancement is investigated in two GMRFs: one is resonant at normal incidence, the other at oblique incidence. It is shown that the two GMRFs exhibit different behaviors in their electric enhancement. Differences between the electric field distributions of the two GMRFs arise because coupling between counter-propagating modes occurs in the first case. It is also shown that the order of the electric field of maximum amplitude can be controlled by modulation of the dielectric constant of the grating. (c) 2006 Optical Society of America.

Nonpolarizing guided-mode resonance filter

A normal-incidence nonpolarizing guided-mode resonance filter is designed. There are two waveguide layers and one grating layer in the filter. By adjusting the distance between the two waveguide layers, the same resonance wavelength for both TE and TM polarization can be achieved. An antireflection design method is also used to decrease the sideband reflection of the filter. The results show that the filter has high reflection, more than 99.9% at 500 nm, and the FW-HMs of TE- and TM-polarized light are 2.16 and 0.15 nm, respectively. (C) 2009 Optical Society of America

Model for quantum efficiency of guided mode plasmonic enhanced silicon Schottky detectors

Plasmonic enhanced Schottky detectors operating on the basis of the internal photoemission process are becoming an attractive choice for detecting photons with sub bandgap energy. Yet, the quantum efficiency of these detectors appears to be low compare to the more conventional detectors which are based on interband transitions in a semiconductor. Hereby we provide a theoretical model to predict the quantum efficiency of guided mode internal photoemission photodetector with focus on the platform of silicon plasmonics. The model is supported by numerical simulations and comparison to experimental results. Finally, we discuss approaches for further enhancement of the quantum efficiency.

鉴别用变方位角导模共振滤光片的设计

设计了在0°和90°方位角下都具有低旁带的鉴别用导模共振滤光片。利用严格的耦合波理论，分析了这种器件在不同入射角、不同光栅槽深和覆盖不同厚度SiO2层情况下的衍射特性。得到了满足鉴别要求的导模共振滤光片结构。在30°入射角情况下，对于TE模式偏振光，设计的滤光片在0°和90°方位角下都有形状对称的反射光谱、低的旁带、两个位置分开的共振峰和适当的半宽度。

Resonant transmission near nonrobust periodic slab modes.

We present a precise theoretical explanation and prediction of certain resonant peaks and dips in the electromagnetic transmission coefficient of periodically structured slabs in the presence of nonrobust guided slab modes. We also derive the leading asymptotic behavior of the related phenomenon of resonant enhancement near the guided mode. The theory applies to structures in which losses are negligible and to very general geometries of the unit cell. It is based on boundary-integral representations of the electromagnetic fields. These depend on the frequency and on the Bloch wave vector and provide a complex-analytic connection in these parameters between generalized scattering states and guided slab modes. The perturbation of three coincident zeros-those of the dispersion relation for slab modes, the reflection constant, and the transmission constant-is central to calculating transmission anomalies both for lossless dielectric materials and for perfect metals.

Design, fabrication and characterization of resonant waveguide grating based optical biosensors

The absence of rapid, low cost and highly sensitive biodetection platform has hindered the implementation of next generation cheap and early stage clinical or home based point-of-care diagnostics. Label-free optical biosensing with high sensitivity, throughput, compactness, and low cost, plays an important role to resolve these diagnostic challenges and pushes the detection limit down to single molecule. Optical nanostructures, specifically the resonant waveguide grating (RWG) and nano-ribbon cavity based biodetection are promising in this context. The main element of this dissertation is design, fabrication and characterization of RWG sensors for different spectral regions (e.g. visible, near infrared) for use in label-free optical biosensing and also to explore different RWG parameters to maximize sensitivity and increase detection accuracy. Design and fabrication of the waveguide embedded resonant nano-cavity are also studied. Multi-parametric analyses were done using customized optical simulator to understand the operational principle of these sensors and more important the relationship between the physical design parameters and sensor sensitivities. Silicon nitride (SixNy) is a useful waveguide material because of its wide transparency across the whole infrared, visible and part of UV spectrum, and comparatively higher refractive index than glass substrate. SixNy based RWGs on glass substrate are designed and fabricated applying both electron beam lithography and low cost nano-imprint lithography techniques. A Chromium hard mask aided nano-fabrication technique is developed for making very high aspect ratio optical nano-structure on glass substrate. An aspect ratio of 10 for very narrow (~60 nm wide) grating lines is achieved which is the highest presented so far. The fabricated RWG sensors are characterized for both bulk (183.3 nm/RIU) and surface sensitivity (0.21nm/nm-layer), and then used for successful detection of Immunoglobulin-G (IgG) antibodies and antigen (~1μg/ml) both in buffer and serum. Widely used optical biosensors like surface plasmon resonance and optical microcavities are limited in the separation of bulk response from the surface binding events which is crucial for ultralow biosensing application with thermal or other perturbations. A RWG based dual resonance approach is proposed and verified by controlled experiments for separating the response of bulk and surface sensitivity. The dual resonance approach gives sensitivity ratio of 9.4 whereas the competitive polarization based approach can offer only 2.5. The improved performance of the dual resonance approach would help reducing probability of false reading in precise bio-assay experiments where thermal variations are probable like portable diagnostics.

Quasi-self-imaging planar waveguide lasers with high-power single-mode output

We describe high-power planar waveguide laser which can achieve single-mode output from a multi-mode structure. The planar waveguide is constructed with incomplete self-imaging properties, by which the coupling loss of each guided mode can be discriminated. Thermal lens effects are evaluated for single-mode operation of such high-power diode-pumped solid-state lasers. (c) 2005 Elsevier B.V. All rights reserved.