Subwavelength Metallic Gratings Research Articles

Reflection-type spatial amplitude modulation of visible light based on a sub-wavelength plasmonic absorber.

We present a method for reflection-type spatial amplitude modulation using a sub-wavelength plasmonic absorber structure that can operate in the visible region. We utilize a pixelated array of absorbing elements based on a two-dimensional sub-wavelength metal grating, and the reflectance of each pixel is controlled by simple structural modification. For the purpose of validation, numerical simulations were performed on an amplitude modulation hologram fabricated using our method.

Giant and broadband circular asymmetric transmission based on two cascading polarization conversion cavities.

In this paper, a three-layered sandwiched metamaterial is proposed to achieve giant and broadband asymmetric transmission of circularly polarized waves at the near-infrared communication band. The metamaterial consists of two layers of identical 45° tilted chiral S-shaped metasurfaces sandwiched with a subwavelength metallic grating. Based on the delicate combination of broadband polarization conversion and a cavity-enhanced effect, the asymmetric parameter can reach a maximum value of 0.87 and over 0.6 in a wide range from 1.2 to 2.0 μm, which has not been found in previous reports. Furthermore, a perfect robustness to misalignments is obtained as the effect originated from function-independent cascading cavities, which effectively reduce the requirement of alignment precision in layer-by-layer photolithography processes. The proposed nanostructure has a great potential to be used as a circular polarization rotator or diode-like device in optical communication systems.

Surface Plasmon Interference Lithography Assisted by a Fabry–Perot Cavity Composed of Subwavelength Metal Grating and Thin Metal Film**Supported by the Natural Science Foundation of Hebei Province under Grant Nos A2013402069 and A2013402081.

A surface plasmon interference lithography assisted by a Fabry–Perot (F-P) cavity composed of subwavelength metal gratings and a thin metal film is proposed to fabricate high-quality nanopatterns. The calculated results indicate that uniform straight interference fringes with high contrast and high electric-field intensity are formed in the resist under the F-P cavity. The analyses of spatial frequency spectra illuminate the physical mechanism of the formation for the interference fringes. The influence of the F-P cavity spacing is discussed in detail. Moreover, the error analyses reveal that all parameters except the metal grating period in this scheme can bear large tolerances for the device fabrication.

Comprehensive analysis of diffraction efficiency of conical beam from sub-wavelength binary metallic grating using rigorous coupled-wave theory

Rigorous coupled-wave theory has been implemented to study comprehensively diffraction efficiency of binary metallic gratings. We have investigated diffraction efficiency for TE and TM polarizations and conical incident beam in more detail than the other reported studies. As a general case, we study diffraction efficiency with respect to incident angles and grating period. Calculated first-order diffraction efficiencies for one-dimensional binary metallic gratings have been shown to converge to the correct value with an effect of increasing number of space harmonics over a wide range of grating depth. More field number of space harmonics is shown to be required for the convergence of gratings with larger grating periods, deeper gratings, TE and TM polarization, and conical diffraction.

Electrically controlled infrared optical transmission and reflection through metallic grating using NEMS technology

The enhanced optical properties of metallic subwavelength gratings with very narrow slits have recently been extensively studied in the field of plasmonics. The optical transmission and reflection of such nanostructures, which act as nano-electro-mechanical systems (NEMS) actuators, can be electrically controlled by varying their geometrical parameters, giving them great flexibility for numerous applications in photonics, opto-electronics, and sensing. The previous challenges in controlling the optical properties were overcome by forming a metallic subwavelength grating with an NEMS actuator in mid-air, allowing the grating to be physically moved with the bias voltage. The device can shift the plasmon resonance wavelength with an electrical signal. The resonance wavelength for Wood’s anomaly at the infrared region is predicted through simulations to shift by approximately 150 nm. We discuss the effect of polarization on the optical properties and grating mechanism. The reported effect may be used to achieve active spectral tuning and switching in a wide range of applications.

Subwavelength Gold Grating as Polarizers Integrated with InP-Based InGaAs Sensors

There are currently growing needs for polarimetric imaging in infrared wavelengths for broad applications in bioscience, communications and agriculture, etc. Subwavelength metallic gratings are capable of separating transverse magnetic (TM) mode from transverse electric (TE) mode to form polarized light, offering a reliable approach for the detection in polarization way. This work aims to design and fabricate subwavelength gold gratings as polarizers for InP-based InGaAs sensors in 1.0-1.6 μm. The polarization capability of gold gratings on InP substrate with pitches in the range of 200-1200 nm (fixed duty cycle of 0.5) has been systematically studied by both theoretical modeling with a finite-difference time-domain (FDTD) simulator and spectral measurements. Gratings with 200 nm lines/space in 100-nm-thick gold have been fabricated by electron beam lithography (EBL). It was found that subwavelength gold gratings directly integrated on InP cannot be applied as good polarizers, because of the existence of SPP modes in the detection wavelengths. An effective solution has been found by sandwiching the Au/InP bilayer using a 200 nm SiO2 layer, leading to significant improvement in both TM transmission and extinction ratio. At 1.35 μm, the improvement factors are 8 and 10, respectively. Therefore, it is concluded that the Au/SiO2/InP trilayer should be a promising candidate of near-infrared polarizers for the InP-based InGaAs sensors.

Performance enhancement of photodetector using defect subwavelength metallic Grating

A defect subwavelength metallic grating is proposed to improve light transmittance and quantum efficiency, leading to better responsivity of photodetector at 1550nm wavelength. We mainly focus on the refractive index of rectangle defect influence on performance. With optimizing the parameter, responsivity can be increased 4.5 times, compared to the photodetector with uniform subwavelength metallic grating. In addition, response bandwidth of the structure can reach 76GHz.

Liquid crystal on subwavelength metal gratings

Optical and electrooptical properties of a system consisting of subwavelength metal gratings and nematic liquid crystal layer are studied. Aluminium gratings that also act as interdigitated electrodes are produced by focused ion beam lithography. It is found that a liquid crystal layer strongly influences both the resonance and light polarization properties characteristic of the gratings. Enhanced transmittance is observed not only for the TM-polarized light in the near infrared spectral range but also for the TE-polarized light in the visible range. Although the electrodes are separated by nanosized slits, and the electric field is strongly localized near the surface, a pronounced electrooptical effect is registered. The effect is explained in terms of local reorientation of liquid crystal molecules at the grating surface and propagation of the orientational deformation from the surface into the bulk of the liquid crystal layer.

Small divergence substrate emitting quantum cascade laser by subwavelength metallic grating.

Metallic periodic structure in subwavelength scale offers an exciting way to couple light into surface plasmons (SPs), thus manipulating the properties of near-field optics. We show that subwavelength metallic grating (SMG) defined on the substrate side of substrate emitting quantum cascade lasers enables far-field improvement in mid-infrared spectrum. The SMG is designed to tailor the interaction of SPs with single mode transverse magnetic light. The experiment results are in good agreement with the simulated model. A far-field full width at half maximum (FWHM) divergence angle of 3.9 ° in the direction perpendicular to the laser waveguide layers is obtained, improved by a factor of 8.5 compared with traditional surface emitting device.

Surface-normal plasmonic modulator using sub-wavelength metal grating on electro-optic polymer thin film

In this work, we present the design, fabrication, and characterization of a surface-normal plasmonic modulator using sub-wavelength metal grating. The device consists of a 1.77μm efficiently poled electro-optic polymer film, which is sandwiched between a plasmonic grating and an indium–tin oxide film. A strong Fano resonance with a sharp plasmonic bandgap at 1522nm wavelength was observed and electro-optical modulation was demonstrated based on the refractive index modulation of the polymer film. With future improvement in lowering the driving voltage and increasing the modulation depth, this hybrid organic/plasmonic modulator can readily expand into modulator arrays for three dimensional optical interconnects.

Polarization-independent and omnidirectional nearly perfect absorber with ultra-thin 2D subwavelength metal grating in the visible region.

A polarization-independent and omnidirectional nearly perfect absorber in the visible region has been proposed. The absorber is two-layer structure consisting of a subwavelength metal grating layer embedded in the high refractive index and lossless dielectric layer on the metal substrate. Extraordinary optical absorption with absorption peaks of over 99% can be achieved over the whole visible region for both TM and TE polarization. This absorption is attributed to cavity mode (CM) resonance caused by the coupled surface plasmon polaritons (SPP). Through adjusting the grating thickness, the absorption peak can be tuned linearly, which is highly advantageous to design various absorbers. Furthermore, the absorbance retains ultra-high over a wide angular range of incidence for both TM and TE polarization. This nearly perfect absorber offers great potential in the refractive index (RI) sensors, integrated photodetectors, solar cells and so on.

Resonant transmission and mode modulation of acoustic waves in H-shaped metallic gratings

In this work, we demonstrate that resonant full transmission of acoustic waves exists in subwavelength H-shaped metallic gratings, and transmission peaks can be efficiently tuned by adjusting the grating geometry. We investigate this phenomenon through both numerical simulations and theoretical calculations based on rigorous-coupled wave analysis. The transmission peaks are originated from Fabry-Perot resonances together with the couplings between the diffractive wave on the surface and the multiple guided modes in the slits. Moreover, the transmission modes can be efficiently tuned by adjusting the cavity geometry, without changing the grating thickness. The mechanism is analyzed based on an equivalent circuit model and verified by both the theoretical calculations and the numerical simulations. This research has potential application in acoustic-device miniaturization over a wide range of wavelengths.

Blocking-assisted infrared transmission of subwavelength metallic gratings by graphene

The transmittance of simple one-dimensional gratings and two-dimensional pillar arrays is usually broadband with poor selectivity in the infrared region. In this paper, it is demonstrated that covering graphene on top of a Ag grating will improve both the magnitude and coherence of the transmitted infrared radiation. The underlying mechanism of this anomalous blocking-assisted transmission is attributed to the excitation of localized magnetic resonances. Quantitative predictions of the resonance wavelength for different geometric parameters and graphene chemical potentials are provided based on the equivalent-circuit model. The enhancement is alignment-free and actively tunable. Such graphene-covered gratings may help improve the performance and robustness of optical devices, such as polarizers, color filters, lab-on-chip sensors, and transparent conductors.

Generation of terahertz vector beams with a concentric ring metal grating and photo-generated carriers.

A scheme for vector terahertz (THz) beam generation is proposed. A subwavelength metal grating is utilized to adjust the polarization of the THz radiation. The amplitude and phase distributions of the THz beam are dynamically regulated by a THz computer-generated hologram (CGH) pattern of the photo-generated carriers. A radially polarized THz beam and a vector THz vortex beam with a topological charge of 1 are generated to demonstrate the validity and the effectiveness of the proposed scheme. Experimental results correspond to the theoretical simulations well. Moreover, the proposed method is applicative for a broadband THz radiation. These results could be applied in the THz sensing, THz imaging, and THz communication in the future.

单层亚波长金属光栅偏振器透射机理研究

单层亚波长金属光栅偏振器透射机理研究

亚波长金属光栅的发展趋势

亚波长金属光栅的发展趋势

Electronically controlled wavelength‐tunable transmission filter based on metal grating incorporating polymer‐dispersed liquid crystal

A novel narrow-band tunable transmission filter based on a sub-wavelength metallic grating incorporating polymer-dispersed liquid crystal (PDLC) with a tunable range of 47.2 nm is demonstrated. The transmission peak wavelength can be tuned from 1524.9 to 1572.1 nm when the refractive index of the PDLC layer is varied by different applying voltages. More than 95% transmission efficiency can be achieved at the resonant wavelength, while the −3 dB bandwidth is about 1.6 nm. In addition, the resonant wavelength of the filter varies in a linear fashion with regard to the refractive index of the PDLC layer. Hence, a desired resonant wavelength can be selected easily by controlling the applied voltage.

Full Resonant Absorption of Light in Metallic Subwavelength Gratings with Asymmetric Binary Nanogrooves

Metallic subwavelength gratings with nanogrooves usually show weak optical absorption in low-order surface plasmon resonances in the grooves. Here, we show that, by introducing another asymmetric nanogroove in each period of the gratings, the absorption can be strongly enhanced up to a full level when difference of the binary groove depths is in a critical value; while the absorption is suppressed when the binary nanogrooves are symmetrically identical. It is further verified that the high absorption appears only for surface plasmon (SP) resonances in the deeper nanogrooves, under the assistance of the shallower ones. Meanwhile the fields are also further enhanced in the deeper nanogrooves. Interaction of resonances in the binary nanogrooves in this phenomenon is shown due to near-field multiple scattering of coupled surface plasmon waves at the metal surfaces and in the nanogrooves, instead of direct resonance coupling. This work provides a new dimension in designing optical properties of metallic nanostructures, which can be used in sensing, filtering, and field enhancement applications.

Nearly perfect absorption in a single-layer metallic grating with rectangular grooves on its front surface

A subwavelength metallic grating can support horizontal surface plasmons (HSPs) at its horizontal metallic boundaries and vertical cavity modes (CMs) inside its slits. It has been shown that the coupling between these two resonant modes can enhance the absorption of the transverse magnetic polarized wave with the maximum absorption up to 75 % (Roszkiewicz et al. in Opt Lett 37(18):3759–3761, 2012). In this work, we propose and analyze a modified grating structure and show that it is possible to raise the absorption to nearly 100 %. The modified structure is a freestanding metallic grating with rectangular grooves on its front surface which can change the distribution of the HSPs on the same side, while leave those on the other side unaffected. When the HSPs on the front surface are changed to some certain situations, all incident energy can be launched into the grating slits by the CMs resonance and then be prohibited from transmitting through the grating by the HSPs on the back surface. Therefore, in such a single-layer metallic grating structure, all of the incident energy is absorbed, i.e., nearly 100 % absorption is obtained.

Transmissive Color Switch Tapping Into a Polarization-Selective Spectral Filter

Electrically controlled transmissive color switches enabling high brightness were demonstrated, by tapping into a polarization-selective nanostructured spectral filter, which is stacked on a liquid crystal-based polarization switch. The spectral filters, based on one-dimensional subwavelength metallic gratings, function as a polarizer and color filter simultaneously. Three independently fabricated spectral filters provided high transmission beyond 80% at 465, 560, and 615 nm, respectively, for blue, green, and red colors. The proposed color switches incorporating the spectral filters were practically observed to exhibit a bright-color state, with a transmission beyond 63%, and an almost opaque dark state, exhibiting an extinction ratio of ~10 dB and a low insertion loss of ~2 dB for a drive voltage range of 2 V.