Resonant Grating Filter Research Articles

Wavelength-stabilised external-cavity laser diode using cavity resonator integrated guided mode filter

The first wavelength-stabilised external-cavity laser diode using a new generation of resonant grating filters called the cavity resonator integrated guided mode filter (CRIGF) is reported. The CRIGF combines high reflectivity and spectral selectivity for tightly focused beams allowing the simplified `cat's eye' external cavity to be used. Output powers of more than 10 mW together with a side mode suppression ratio larger than 35 dB for a drive current of 50 mA are achieved. CRIGF-controlled operation at a wavelength spanning a 20 nm range is also demonstrated, with a linear relationship between the CRIGF period and output wavelength.

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.

Measurement and modeling of 2D hexagonal resonant-grating filter performance

We report the measurement of a polarization-independent guided-mode resonant filter with a Q factor of approximately 2200 functioning near normal incidence in the near infrared (850 nm). Besides this remarkable performance, we provide a detailed optical and structural characterization of the component, which points out the origins of the limitation of the experimental performance. We conclude that the defaults in question can be corrected by improving the lithography process, and we are confident that even greater performance will be obtained in future realizations.

Impact of electron-beam lithography irregularities across millimeter-scale resonant grating filter performances

We investigated the impact of electron-beam lithography writing imperfections on the performance of two-dimensional resonant grating notch filters. This large area photonic device provides an interesting benchmark to assess the acceptable limits of unavoidable fabrication errors. We found that field stitching errors up to 100 nm have no detrimental effect on the filter linewidth, whereas a 2.5 nm electron-beam writing resolution, responsible for digitization disorder, is tolerable only for high-index contrast filter designs. Such an electron-beam writing strategy could also be beneficial for photonic crystal guiding structures or any periodic nanopatterned device with which the optical mode interacts with a large number of periodic elementary units.

High performance bi-dimensional resonant grating filter at 850nm under high oblique incidence of ∼60°

We present an experimental demonstration of a polarization quasi-independent narrow-band (less than 0.8nm) filter operating under high oblique incidence. The structure is a resonant grating with a hexagonal lattice which has been carefully designed to ensure polarization quasi-independence of the narrow-band resonance peak over a wide angular range around 60° of incidence. A good agreement between experimental results and theoretical calculations is shown.

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.

Design of reflection resonant grating filters

Resonant grating filters based on grating abnormality have attracted much attention in recent years owing to their high peak reflectivity，low sideband reflection and controllable line width of central wavelength. Some special characteristics which are hard to be achieved by multilayer stack alternated with high and low refractive indices can be realized with guide-mode resonance of sub-wavelength gratings whose line width of central wavelength can be compressed to less than one nanometer under the condition of weak modulation of gratings. However，the sideband reflections near or far from the central wavelength are still somewhat high due to Fresnel reflection between air and material. According to the effective medium theory (EMT)，sub-wavelength waveguide gratings can be viewed as thin films. In this paper，the sideband reflections of resonant grating filters are effectively reduced through antireflection design based on thin film theory and narrow band resonant filters are attained in the range of visible wavelength with good characteristics.

Design and analysis of double layer resonant grating filters in the visible spectral region

Guide-mode resonances of double-layer gratings are analyzed with the Fourier modal method and the relationship between spectral characteristics of resonant gratings such as peak diffraction efficiency, linewidth and side-band reflectance and depth, period and fill ratio of grating are illustrated in detail. It is shown that the diffraction efficiency of resonant gratings will be higher than 99.5 percent when the groove depth tolerance is in the range of 15 percent, and mean while the relative error of line width will reach to 7 and 60 percent respectively for the negative and positive conditions. Compared with the position of resonant wavelength, the line width of resonant grating filters is relatively sensitive to the error of groove depth and residual thickness of waveguide layer when they deviate from designed values. Moveover, the resonant wavelength and width of spectrum do vary as a function of period and fill ratio.

Tunable Liquid Crystal-Resonant Grating Filter Fabricated by Nanoimprint Lithography

We demonstrate a tunable filter consisting of a subwavelength resonant grating filter cladded by a liquid crystal cell. The resonant wavelength of the grating filter is tuned by electrically varying the refractive index of the liquid crystal. A tuning range of around 20 nm has been achieved.

Control of resonance separation over a wide spectral range in multiwavelength resonant grating filters

The spectral separation of resonances within multiwavelength resonant grating filters is studied through the use of a grating layer with constant structural parameters in combination with single-layer, multimode waveguides and multilayer, multimode waveguides. The use of multilayer, multimode waveguides are shown to provide the ability to control resonance separations for multiwavelength filters from hundreds of nanometers to only a few nanometers.

Experimental demonstration of a narrowband, angular tolerant, polarization independent, doubly periodic resonant grating filter

Resonant grating filters are promising components for free-space narrowband filtering. Unfortunately, due to their weak angular tolerance, their performances are strongly deteriorated when they are illuminated with a standard collimated beam. Yet this problem can be overcome by resorting to a complex periodic pattern known as the doubly periodic grating [Lemarchand et al., Opt. Lett.23, 1149 (1998)]. We report what we believe to be the first experimental fabrication and characterization of a bidimensional doubly periodic grating filter. We obtained a 0.5 nm bandpass polarization independent reflection filter for telecom wavelengths (1520-1570 nm) that presents a transmittivity minimum of 18% with a standard incident collimated beam.

Tunable External Cavity Laser With a Liquid-Crystal Subwavelength Resonant Grating Filter as Wavelength-Selective Mirror

We demonstrate a tunable external cavity laser consisting of a voltage-tuned liquid-crystal cladded subwavelength resonant grating filter placed directly in front of a semiconductor laser gain chip. The filter acts as a tunable wavelength-selective mirror. As the applied voltage to the filter changes from 0 to 22 V, the laser wavelength demonstrates a tuning range of 7 nm, which may be further increased. As the laser has simple cavity design and no moving parts, it can be low cost and easy to fabricate and assemble.

Multiple wavelength resonant grating filters at oblique incidence with broad angular acceptance

Multilayer, multimode waveguides are utilized in resonant grating filters having a broadened angular acceptance bandwidth for multiple wavelengths at a single oblique angle of incidence. It is shown that the waveguide grating structure should support a few leaky modes in order to support a multiwavelength resonant filter at oblique incidence with broadened angle acceptance at each wavelength.

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).

Resonant grating filters as refractive index sensors for chemical and biological detections

A chemical and biological sensor based on a free-space waveguide resonant grating optical filter has been developed. Different from the conventional surface plasmon resonance sensors and the conventional waveguide mode sensors, which require either prism coupling or grating coupling, the proposed free-space optical sensor device does not require special separate coupling. The inherent 100% coupling efficiency at resonance can significantly boost probe efficiency. Both simulation and experimental results have demonstrated that the sensor could deliver a resolution of better than 0.001–0.0001 for refractive index sensing, which is enough for detecting various chemical and biological materials. More importantly, under an angular detection scheme, the proposed waveguide resonant grating sensor could be one order’s more sensitive than the conventional surface plasmon resonance sensor.

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.

Design and characterization of a tunable polarization-independent resonant grating filter

We present the design, analysis and characterization of a polarization-independent tunable resonant grating filter. Polarization independence is achieved by setting the plane of incidence parallel to the grating grooves and optimizing the fill factor to obtain a strong reflection peak for all incident polarization states. Experimental measurements show that approximate angular insensitivity to the input polarization orientation concurrent with tunability over a wavelength range of roughly 1530 nm to 1560 nm is achieved. Modulation of the reflectivity peak shape with variations in the orientation of the incidence plane are observed, and found to be in qualitative agreement with theoretical predictions.

Tunable, oblique incidence resonant grating filter for telecommunications.

We have designed a tunable, oblique-incidence resonant grating filter that covers the C band as an add-drop device for incident TE-polarized light. We tune the filter by tilting a microelectromechanical systems platform onto which the filter is attached. The fabrication tolerances as well as the role of finite incident-beam size and limited device size were addressed. The maximum achievable efficiency of a finite-area device as well as a scaling law that relates the resonance peak width and the minimum device size is derived. In good agreement with simulations, measurements indicate a negligible change in shape of the resonance peak from 1526 nm at a 45 degrees angle of incidence to 1573 nm at a 53 degrees angle with a full width at half-maximum of 0.4 nm. In this range the shift of the peak wavelength is linear with respect to changes in the angle of incidence.