Guided-mode Resonant Grating Filter Research Articles

Two-dimensional grating guided-mode resonance tunable filter.

A two-dimensional (2D) grating guided-mode resonance (GMR) tunable filter is experimentally demonstrated using a low-cost two-step nanoimprinting technology with a one-dimensional (1D) grating polydimethylsiloxane mold. For the first nanoimprinting, we precisely control the UV LED irradiation dosage and demold the device when the UV glue is partially cured and the 1D grating mold is then rotated by three different angles, 30°, 60°, and 90°, for the second nanoimprinting to obtain 2D grating structures with different crossing angles. A high-refractive-index film ZnO is then coated on the surface of the grating structure to form the GMR filter devices. The simulation and experimental results demonstrate that the passband central wavelength of the filter can be tuned by rotating the device to change azimuth angle of the incident light. We compare these three 2D GMR filters with differential crossing angles and find that the filter device with a crossing angle of 60° exhibits the best performance. The tunable range of its central wavelength is 668-742 nm when the azimuth angle varies from 30° to 90°.

Analysis of Guided-mode Resonant Grating Filters by Using a Rigorous Coupled-wave Method

Analysis of Guided-mode Resonant Grating Filters by Using a Rigorous Coupled-wave Method

Analysis of finite-sized guided-mode resonant gratings using the fast multipole boundary element method

Guided-mode resonant grating filters are dispersive devices that utilize resonance anomalies. When they are modeled as finite imperfect periodic structures, it is time-consuming to calculate their optical properties precisely, and huge computational memories are needed to accommodate the large analytical domain. This limits the numerical performance, and so existing reports, which use the conventional boundary element method, refer to structures with less than 100 periods. This paper shows that general optical properties and the impact of production error distributions can be calculated for guided-mode resonant grating filters with several hundred periods using the fast multipole boundary element method.

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.

Out-of-plane motion of 260-nm thick guided-mode resonant grating filter controlled by four micro-thermal actuators

We fabricate a wavelength-selective variable-reflection filter driven by four bimorph actuators to realize out-of-plane motion in parallel. The actuators are designed using a simple calculation model for controlling position of the filter anywhere within air gap fabricated in between the filter and silicon substrate. In order to keep a 260-nm thick filter flat, the filter and actuators are stabilized by torsion bars each with a width and length of 3 and 10 μm, respectively. Displacement, flatness and surface roughness of the fabricated filter are measured. As a result, 10.1 μm of the displacement is obtained at 24.7 mW input power using a 70-μm length actuator. Besides, the filter with a flat surface and roughness of 0.08 μm is obtained. Reflectivity of the filter consisting of 800-nm period grating is also measured.

Guided-Mode Resonant Grating Filter Fabricated on Silicon-on-Insulator Substrate

We propose a guided-mode resonant grating (GMRG) filter using silicon-on-insulator wafer. In the fabrication, electron beam lithography and fast atom beam etching are used. The periods of the three filters are 680, 700, and 720 nm, respectively. The reflectivity is measured to be nearly 100% at the wavelength of 1502 nm for the 700 nm period GMRG filter with a fill factor of 0.760. The optical properties of the filters are analyzed using a rigorous coupled-wave analysis (RCWA).

Dynamic guided-mode resonant grating filter with quadratic electro-optic effect

We propose a novel and simple concept of dynamic switching of guided-mode resonant grating filters with quadratic electro-optic effect within a waveguide layer modulated by external fields due to comb-shaped electrodes that also behave as a grating. As the device has subwavelength structure, the performance must be analyzed electromagnetically. We describe numerical simulation with the finite-difference time-domain method specially modified so that it can treat inhomogeneous anisotropic media such as lead lanthanum zirconate titanate.

Wave Localization of Doubly Periodic Guided-mode Resonant Grating Filters

It is known that a doubly periodic guided-mode resonant grating (GMRG) filter has a broad angular selectivity with a narrow spectral bandwidth. This means that the doubly periodic GMRG filter operates for small beam diameter and grating area. This report describes the wave localization in the doubly periodic GMRG filter. We investigated the spread area of light waves in the waveguide layer and the accumulation of field energy by numerical simulation using the finite differential time domain (FDTD) method. Simulation results showed that, in the case of a doubly periodic GMRG filter with a Q factor of 600, the field energy is spread over an area 5 um in width, which corresponds to the expected value from the angular tolerance. And the magnitude of the field energy in the waveguide layer was Q factor times greater than the incident energy. On the other hand, a singly periodic GMRG filter with the same Q factor spread the field energy over an area 72 urn in width. This filter does not work for a small size structure or a small diameter light beam.

Guided-mode resonant grating filter with an antireflection structured surface.

We describe a new structure of guided-mode resonant grating (GMRG) filters with low sideband reflectance. This GMRG filter consists of a high-index thin film on an antireflective structured surface called "moth-eye structure." Since the high-index film undulates along the surface structure, the film acts as a modulated optical waveguide. An incident light wave satisfying a resonant condition is reflected by the GMRG filter, and nonresonant light waves pass through the filter. This GMRG filter is valid for reducing reflection of nonresonant light waves in a wide spectral range. The resonant reflection of this new filter was investigated by numerical calculation based on an electromagnetic grating analysis. In the case of a triangular antireflective surface structure whose thickness is 2x greater than its period, the sideband reflectance for nonresonant light waves was lower than 0.5% for TM-polarized light in a wide range of wavelengths.

Nonpolarizing guided-mode resonant grating filter for oblique incidence.

A new type of guided-mode resonant grating filter is described. The filter is independent of polarization state for oblique incidence. The filter has a crossed grating structure, and the plane of incidence on the filter contains the symmetric axis of the grating structure. Theoretical considerations and numerical calculations using two-dimensional rigorous coupled-wave analysis show that a rhombic lattice structure is suitable to such filters. In this configuration an incident light wave is diffracted into the waveguide and is divided into two propagation modes whose directions are symmetric with respect to the plane of incidence. In particular, when the propagation directions of the two modes are perpendicular to each other, the fill factor of grating structure can be approximately 50%. The filter was designed for an incident angle of 45 degrees. Tolerances of setting errors and fabrication errors for this filter were estimated by numerical calculations.

Normal-incidence guided-mode resonant grating filters:?design and experimental demonstration

Guided-mode resonant grating filters have numerous applications. However, in weakly modulated gratings designed for use at normal incidence, the filtering resonance of these subwavelength-period devices splits for angles of incidence that are even slightly off normal incidence. Strongly modulated gratings are designed that essentially overcome this practical problem near normal incidence. In addition, these gratings can have, by design, either broad or narrow spectral characteristics. An experimental demonstration (1.5-2.0-mu m wavelength range) of such a normal-incidence guided-mode resonant silicon grating upon a sapphire substrate is presented. The measured reflection resonance had a FWHM of 67-100 nm for angles of incidence of 0-8 degrees and peak efficiency of ~80% .