Resonant Grating Research Articles

Divergence-tolerant resonant bandpass filters.

Bandpass filters based on subwavelength dielectric gratings are grounded in physical principles that are totally distinct from their thin-film counterparts. Ease in fabrication, design scalability, material sparsity, and on-chip integration compatibility makes them a promising alternative especially for long-wavelength applications. Here we demonstrate the interesting attribute of resonant bandpass filters of high angular stability for fully conical light incidence. Fashioning an experimental bandpass filter with a subwavelength silicon grating on a quartz substrate, we show that fully conical incidence provides an angular full width at half-maximum linewidth of ∼9.5° compared to a linewidth of ∼0.1° for classical incidence. Slow angular variation of the central wavelength with full conical incidence arises via a corresponding slow angular variation of the resonant second diffraction orders driving the pertinent leaky modes. Moreover, full conical incidence maintains a profile with a single passband as opposed to the formation of two passbands characteristic of resonant subwavelength gratings under classical incidence. Our experimental results demonstrate excellent stability in angle, spectral profile, linewidth, and efficiency.

Integrated label-free optical biochemical sensor with a large measurement range based on an angular grating-microring resonator.

We propose and design a photonic-integrated optical biochemical sensor, which comprises a microring resonator and angular gratings in a silicon-on-insulator waveguide. With the combination of the angular gratings, the measurement range of the angular grating-microring resonator-based sensor significantly increases without the restriction of a free spectral range. Optimization of the several key structural parameters is investigated to achieve favorable transmission properties. A high-quality factor of more than 1.03×105 can meet the requirements of high sensitivity and low detection limit. The simulation results on the biochemical bulk sensing show that a concentration sensitivity of more than 95.27 pm/% and detection limit of less than 0.329% can be obtained. A large measurement range of 50.2 nm is achieved by the combination of the angular gratings. The investigation on the combination of microring resonator and angular grating is a valuable exploration of the liquid and gas biomedical sensing for the ultra-large measurement range.

High-contrast grating resonators for label-free detection of disease biomarkers

A label-free optical biosensor is described that employs a silicon-based high-contrast grating (HCG) resonator with a spectral linewidth of ~500 pm that is sensitive to ligand-induced changes in surface properties. The device is used to generate thermodynamic and kinetic data on surface-attached antibodies with their respective antigens. The device can detect serum cardiac troponin I, a biomarker of cardiac disease to 100 pg/ml within 4 mins, which is faster, and as sensitive as current enzyme-linked immuno-assays for cTnI.

Unpolarized resonance grating reflectors with 44% fractional bandwidth.

There is immense scientific interest in the properties of resonant thin films embroidered with periodic nanoscale features. This device class possesses considerable innovation potential. Accordingly, we report unpolarized broadband reflectors enabled by a serial arrangement of a pair of polarized subwavelength gratings. Optimized with numerical methods, our elemental gratings consist of a partially etched crystalline-silicon film on a quartz substrate. The resulting reflectors exhibit extremely wide spectral reflection bands in one polarization. By arranging two such reflectors sequentially with orthogonal periodicities, there results an unpolarized spectral band that exceeds those of the individual polarized bands. In the experiments reported herein, we achieve zero-order reflectance exceeding 97% under unpolarized light incidence over a 500nm wide wavelength band. This wideband represents a ∼44% fractional band in the near infrared. Moreover, the resonant unpolarized broadband accommodates an ultra-high reflection band spanning ∼85 nm and exceeding 99.9% in efficiency. The elemental polarization-sensitive reflectors based on one-dimensional (1D) resonant gratings have a simple design and robust performance, and are straightforward to fabricate. Hence, this technology is a promising alternative to traditional multilayer thin-film reflectors, especially at longer wavelengths of light where multilayer deposition may be infeasible or impractical.

Compact spectrometer system based on a gradient grating period guided-mode resonance filter.

We demonstrate a compact spectrometer system by using a gradient grating period guided-mode resonance filter-mounted on a linear photodetector array-that exhibits spatially dependent resonance characteristics; a specific incident wavelength is reflected such that the underlying array pixels measure minimum intensity. A precalibrated transmission efficiency matrix is used to determine each pixel's transmission efficiency for specific wavelengths. Unknown spectral information can be calculated from the measured intensity. Grating periods of 250-388 nm in 2-nm increments are used in each 100-cycle period. Device length is 2.23 mm. Spectral range of 506-700 nm is measurable with 1-nm resolution.

Broadband on-chip near-infrared spectroscopy based on a plasmonic grating filter array.

We demonstrate an ultra-compact, broadband on-chip near-infrared (NIR) spectroscopy system based on a narrow-band plasmonic filter array. The entire filter array, consisting of 28 individual subwavelength metallic gratings, was monolithically integrated in a thin gold film on a quartz substrate, covering a 270 nm spectra from 1510 nm to 1780 nm. In order to achieve a high spectral resolution, extremely narrow slits are created for the gratings with a polymer waveguide layer on top, generating narrow-band guided-mode resonances through coupling with the surface-plasmon resonances of the metallic gratings. Experimental results show that the transmission bands of the filter array have full width at half-maximum of only 7 nm-13 nm, which is sufficient for NIR spectroscopy. The NIR absorption spectroscopy of xylene using the on-chip plasmonic filter array matches very well with the results from conventional Fourier transform infrared spectroscopy, which proves the great potential for NIR sensing applications.

Integrated coherent combining of angled-grating broad-area lasers

In this paper, we investigated coherent beam combining of angled-grating broad-area lasers in a completely integrated approach. We obtained the simultaneous coherent beam combining and single transverse mode operation on a single chip through the integrated coupling regions and the transverse Bragg resonance (TBR) gratings, respectively. The proposed combining method can be easily extended to a zigzag-like laser array. We analyzed the scalability of the zigzag-like combining structure and compared it with other coherent combining methods. Two and six angled-grating broad-area lasers are fabricated and coherently combined by use of the proposed method. The high contrast interference fringes within an overall single lobe envelope in the measured far field prove that the emitters in the array are indeed coherently combined. By p-side-down bonding, we obtained over 1 Woutput power with over 90% combining efficiency in the two coherently combined lasers.

Differentiating space–time optical signals using resonant nanophotonics structures

A theoretical description of the space–time transformations of an optical signal, which passes through resonant gratings and Bragg gratings with a defect, is proposed. The problem of differentiating a space–time optical signal using a resonant grating has been solved. The strict solution to the Maxwell equations using the Fourier modal method is involved to determine the parameters of the transfer function of the resonant diffraction structure and to carry out numerical modeling, which has confirmed the proposed theoretical description.

Sound transmission properties assisted by the phase resonances of composite acoustic gratings

We investigated composite gratings for their sound transmission properties induced by phase resonances. Each periodic unit of the composite grating consisted of a rectangular slit and a triangular slit. The triangular slit showed special properties in generating enhanced phase resonance and in restraining sound transmission. By adjusting the triangular slit's opening, we could regulate the frequency and sound transmission at phase resonance. These features of the composite grating can be used in designing acoustic filters for sound reduction.

Double Directions Nanoscale Range Finding Using Fano Resonance in Coupled Gratings

In this paper, a theoretical demonstration is given of nanoscale range finding by exciting Fano resonance in coupled gratings. Metallic ridges induce oscillation mode, whose interference with surface plasmon polartions generate narrow Fano resonance. The concept of hybridization is employed to understand the coupling effect of surface plasmon polartions and the oscillation due to metallic ridges. Fano behavior in this structure is captured by using the temporal coupled-mode theory. The gained fundamental understanding opens up new ways to control nanoscale spacing distances and tailor Fano resonance, thus facilitating rational design of nanosensors to improve the performance of nanomotion control systems.

Polymer Fiber Optic Sensors – A Mini Review of their Synthesis and Applications

Fiber optic sensors (FOSs) are optical fiber based sensing devices that have been widely used to detect physical, chemical and biological parameters. Polymer optical fibers (POFs), an important type of optical fibers, have been stifled their talents in the field of optical sensing due to the overwhelming popularity of glass optical fibers (GOFs). The unique physical and chemical properties of POFs start attracting interests to be utilized in the fabrication of high performance sensors in recent years. This article reviews the recent progress of POFs based FOSs. In particular, the article will focus on novel techniques implemented on the POF sensor fabrication, including monolayer graphene, evanescent wave absorption, localized surface plasmon resonance and fiber Bragg grating.

Linear variable filter based on a gradient grating period guided-mode resonance filter

In this letter, we fabricated and characterized a linear variable filter based on a guided-mode resonance filter (GMRF) with gradient grating periods. The GMRF was first fabricated through nanoreplica molding on a plastic substrate, which was followed by the deposition of a thin TiO2 film. The grating periods of the GMRF vary from 250 to 550 nm with a 2-nm increment in each period consisting of 100 cycles. The results show that a 6-mm-long GMRF has a filtering range of 506–915 nm.

基于导模共振效应的宽带宽透射型滤波器的设计与优化

基于导模共振效应的宽带宽透射型滤波器的设计与优化

Subwavelength Grating Structure with High Aspect Ratio and Tapered Sidewall Profiles

ABSTRACTCMOS-compatible fabrication and etching processes are often used in subwavelength grating structures manufacturing, it normally generates tapered sidewall profile of the gratings. In this work, we have studied the impacts on resonance mode characteristics of subwavelength grating structures due to the tapered sidewall profile, as well as grating with high aspect ratio. Our simulation results have revealed that both of these two factors play important roles on the resonance mode behavior of subwavelength grating devices. We also discussed the mechanism between the guided mode resonance and the grating cavity mode resonance. Our study will provide guidance for a series of integrated photonics devices applications, such as compact optical filter, photonics amplifier, and lasers, while the realistic subwavelength grating structure is considered.

Biosensor based on excessively tilted fiber grating in thin-cladding optical fiber for sensitive and selective detection of low glucose concentration.

We report a highly sensitive, high Q-factor, label free and selective glucose sensor by using excessively tilted fiber grating (Ex-TFG) inscribed in the thin-cladding optical fiber (TCOF). Glucose oxidase (GOD) was covalently immobilized on optical fiber surface and the effectiveness of GOD immobilization was investigated by the fluorescence microscopy and highly accurate spectral interrogation method. In contrast to the long period grating (LPG) and optical fiber (OF) surface Plasmon resonance (SPR) based glucose sensors, the Ex-TFG configuration has merits of nearly independent cross sensitivity of the environmental temperature, simple fabrication method (no noble metal deposition or cladding etching) and high detection accuracy (or Q-factor). Our experimental results have shown that Ex-TFG in TCOF based sensor has a reliable and fast detection for the glucose concentration as low as 0.1~2.5mg/ml and a high sensitivity of ~1.514 nm·(mg/ml)⁻¹, which the detection accuracy is ~0.2857 nm⁻¹ at pH 5.2, and the limit of detection (LOD) is 0.013~0.02 mg/ml at the pH range of 5.2~7.4 by using an optical spectrum analyzer with a resolution of 0.02 nm.

Periodicity Matters: Grating or lattice resonances in the scattering by sparse arrays of subwavelength strips and wires

This article reviews the nature and history of the discovery of high-quality natural modes existing on periodic arrays of many subwavelength scatterers; such arrays can be viewed as specific periodically structured open resonators. These grating modes (GMs), like any other natural modes, give rise to the associated resonances in electromagnetic-wave scattering and absorption. Their complex wavelengths are always located very close to (but not exactly at) the well-known Rayleigh anomalies (RAs), determined only by the period and the angle of incidence. This circumstance has long been a reason for their misinterpretation as RAs, especially in the measurements and simulations using low-resolution methods. In the frequency scans of the reflectance or transmittance, GM resonances usually develop as asymmetric Fano-shape spikes. In the optical range, if a grating is made of subwavelength-size noble-metal elements, then GMs exist together with better-known localized surface-plasmon (LSP) modes. Thanks to high tunability and considerably higher Q-factors, the GM resonances can potentially replace the LSP-mode resonances in the design of nanosensors, nanoantennas, and solar-cell nanoabsorbers.

Fano resonances of dielectric gratings: symmetries and broadband filtering.

The guided mode resonances (GMRs) of diffraction gratings surrounded by low index materials can be designed to produce broadband regions of near perfect reflection and near perfect transmission. These have many applications, including in optical isolators, in hybrid lasers cavities and in photovoltaics. The excitation of rapid GMRs occurs in a background of slowly varying Fabry-Perot oscillation, which produces Fano resonances. We demonstrate the critical role of the polarity of adjacent Fano resonances in the formation of the broadband features. We design gratings for photovoltaic applications that operate at wavelengths where material absorption must be considered and where light is incident at non-normal angles.

Surface-normal coupled four-wave mixing in a high contrast gratings resonator.

We demonstrate enhanced four-wave mixing using a silicon high contrast grating (HCG) resonator on a SOI (silicon-on-insulator) wafer directly coupled with free space Gaussian beam in surface-normal direction. The measured quality factor for HCG resonator is ~7330. Peak conversion efficiency of -19.5dB is achieved at low pumping power ~900µW. Surface-normal coupling allows for easily and robust alignment system. The very small footprint and high efficiency of our device provide an effective method for wavelength conversion in chip-scale integrated optics.

Spatiotemporal optical pulse transformation by a resonant diffraction grating

The diffraction of a spatiotemporal optical pulse by a resonant diffraction grating is considered. The pulse diffraction is described in terms of the signal (the spatiotemporal incident pulse envelope) passage through a linear system. An analytic approximation in the form of a rational function of two variables corresponding to the angular and spatial frequencies has been obtained for the transfer function of the system. A hyperbolic partial differential equation describing the general form of the incident pulse envelope transformation upon diffraction by a resonant diffraction grating has been derived from the transfer function. A solution of this equation has been obtained for the case of normal incidence of a pulse with a central frequency lying near the guided-mode resonance of a diffraction structure. The presented results of numerical simulations of pulse diffraction by a resonant grating show profound changes in the pulse envelope shape that closely correspond to the proposed theoretical description. The results of the paper can be applied in creating new devices for optical pulse shape transformation, in optical information processing problems, and analog optical computations.

Single-layer optical bandpass filter technology.

Resonant periodic surfaces and films enable new functionalities with wide applicability in practical optical systems. Their material sparsity, ease of fabrication, and minimal interface count provide environmental and thermal stability and robustness in applications. Here, we report an experimental bandpass filter fashioned in a single patterned silicon layer on a quartz substrate. Its performance corresponds to bandpass filters requiring 15 traditional Si/SiO(2) thin-film layers. The feasibility of sparse narrowband high-efficiency bandpass filters with extremely wide, flat, and low sidebands is thereby demonstrated. This class of devices is designed with rigorous solutions of Maxwell's equations while engaging the physical principles of resonant waveguide gratings. An experimental filter presented exhibits a transmittance of ∼72%, bandwidth of ∼0.5 nm, and low sidebands spanning ∼100 nm. The proposed technology is integration-friendly and opens doors for further development in various disciplines and spectral regions where thin-film solutions are traditionally applied.