Search Results (9)

Quantum well infrared photodetectors (QWIPs) are popular due to their following advantages: low cost, maturity of manufacturing, high uniformity, ease of wavelength adjustment, resistance to heat, and resistance to ionizing radiation. However, their low absorption efficiency due to their unique anisotropic absorption properties and ohmic loss of the metal grating severely limit their further adoption. We cleverly used cascaded dielectric metasurfaces to replace the traditional single-layer metal grating, which increased the absorption efficiency to near the upper limit of 100%. By analyzing the near-field profile of the electric field of the miniaturized device, we found that the upper grating, QWIP, and lower grating formed a high-efficiency FP cavity with a strong photon localization capability, allowing the microdevice to effectively achieve 99.3% absorption. In addition, QWIPs with cascade gratings can be incorporated into a polarimeter, allowing for the comprehensive detection of linear polarization information at a wavelength of 14 $\mathsf{\mu }\mathrm{m}$ through rational rotations. Our proposed double-layer grating coupling method can be considered a technology that can effectively address the low-absorption problem associated with QWIPs. Full article

Surface lattice resonances (SLRs) with high-quality factors supported by metal nanoparticle arrays are useful for plasmonic nanolasers, biochemical sensors, and surface-enhanced Raman spectroscopy. Most nanoparticle arrays are fabricated on a substrate, and the refractive index mismatch between the substrate and superstrate suppresses the performance of SLRs. In this work, we propose unique SLRs excited in suspended, self-aligned symmetric double-layer gratings with index-matched environment. The self-aligned double-layer gratings are fabricated using a single-step electron beam lithography and exhibit a Fano-like spectra resulting from interference between out-of-plane plasmonic resonances and diffraction modes. By changing the incident angle and refractive index of the surrounding medium, the SLRs can be tuned from visible to near-infrared regions with a high-quality factor of 120. Full article

In this work, a broad dual-band bandpass filter is designed by applying double-layered spoof surface plasmon polaritons (DLSSPPs) as the main transmission line (MTL) and loading combined-stub dual-mode resonators (CSDMRs) onto the MTL with certain spaces. Each CSDMR consists of an open stub and a short stub that are connected in parallel. Efficient mode conversion between the quasi-transverse electromagnetic waves in the microstrip line and the spoof surface plasmon polaritons (SSPPs) on the double-layered surface plasmon waveguide is realized using gradient double-layered metal gratings and via the sector structure impedance matching technique. A parametric study of the CSDMR demonstrates that center frequencies and bandwidths can be controlled by varying the stub lengths and widths of the CSDMRs. A second-order dual-band filter is designed and fabricated, and simulated and experimental S-parameters agree well. A lower loss of the passband is achieved compared with the filters that apply single-layered SSPPs. The space between two CSDMRs is shortened because of the slow-wave effect of the DLSSPPs. The lowpass performance of the DLSSPPs exhibits good rejection from the cutoff frequency above. Full article

We propose a stacked dual-band quantum well infrared photodetector (QWIP) integrated with a double-layer gold disk. Two 10-period quantum wells (QW) operating at different wavelengths are stacked together, and gold nano-disks are integrated on their respective surfaces. Numerical calculations by finite difference time domain (FDTD) showed that the best enhancement can be achieved at 13.2 and 11.0 µm. By integrating two metal disks, two plasmon microcavity structures can be formed with the substrate to excite localized surface plasmons (LSP) so that the vertically incident infrared light can be converted into electric field components perpendicular to the growth direction of the quantum well (E_Z). The E_Z electric field component can be enhanced up to 20 times compared to the incident light, and it is four times that of the traditional two-dimensional hole array (2DHA) grating. We calculated the enhancement factor and coupling efficiency of the device in the active region of the quantum well. The enhancement factor of the active region of the quantum well on the top layer remains above 25 at the wavelength of 13.2 μm, and the enhancement factor can reach a maximum of 45. Under this condition, the coupling efficiency of the device reaches 2800%. At the wavelength of 11.0 μm, the enhancement factor of the active region of the quantum well at the bottom is maintained above 6, and the maximum can reach about 16, and the coupling efficiency of the device reaches 800%. We also optimized the structural parameters and explored the influence of structural changes on the coupling efficiency. When the radius (r₁, r₂) of the two metal disks increases, the maximum coupling efficiency will be red-shifted as the wavelength increases. The double-layer gold disk structure we designed greatly enhances the infrared coupling of the two quantum well layers working at different wavelengths in the dual-band quantum well infrared photodetector. The structure we designed can be used in stacked dual-band quantum well infrared photodetectors, and the active regions of quantum wells working at two wavelengths can enhance the photoelectric coupling, and the enhancement effect is significant. Compared with the traditional optical coupling structure, the structure we proposed is simpler in process and has a more significant enhancement effect, which can meet the requirements of working in complex environments such as firefighting, night vision, and medical treatment. Full article

Guided-mode resonance (GMR) sensors are widely used as biosensors with the advantages of simple structure, easy detection schemes, high efficiency, and narrow linewidth. However, their applications are limited by their relatively low sensitivity (<200 nm/RIU) and in turn low figure of merit (FOM, <100 1/RIU). Many efforts have been made to enhance the sensitivity or FOM, separately. To enhance the sensitivity and FOM simultaneously for more sensitive sensing, we proposed a metal layer-assisted double-grating (MADG) structure with the evanescent field extending to the sensing region enabled by the metal reflector layer underneath the double-grating. The influence of structural parameters was systematically investigated. Bulk sensitivity of 550.0 nm/RIU and FOM of 1571.4 1/RIU were obtained after numerical optimization. Compared with a single-grating structure, the surface sensitivity of the double-grating structure for protein adsorption increases by a factor of 2.4 times. The as-proposed MADG has a great potential to be a biosensor with high sensitivity and high accuracy. Full article

Nanoimprint technology is powerful for fabricating nanostructures in a large area. However, expensive equipment, high cost, and complex process conditions hinder the application of nano-imprinting technology. Therefore, double-layer self-priming nanoimprint technology was proposed to fabricate ordered metal nanostructures uniformly on 4-inch soft and hard substrates without the aid of expensive instruments. Different nanostructure (gratings, nanoholes and nanoparticles) and different materials (metal and MoS₂) were patterned, which shows wide application of double-layer self-priming nanoimprint technology. Moreover, by a double-layer system, the width and the height of metal can be adjusted through the photoresist thickness and developing condition, which provide a programmable way to fabricate different nanostructures using a single mold. The double-layer self-priming nanoimprint method can be applied in poor condition without equipment and be programmable in nanostructure parameters using a single mold, which reduces the cost of instruments and molds. Full article

The miniaturization and integration of photonic devices are new requirements in the fast-growing optics field. In this paper, we focus on a feature-rich sub-wavelength nanograting-coated single-layer metal film. The numerical results show that the reflection behaviors of this proposed structure can realize bidirectional dual-channel ultra-narrowband polarized filtering and bidirectional wavelength-modulated sensing in a wide refractive index (RI) range from 1.0 to 1.4 for incident angle of 10° with transverse-magnetic (TM) polarized illumination at wavelengths between 550 nm to 1500 nm. Moreover, the bidirectional properties of filtering and sensing are not obviously decreased when increasing incident angle from 10° to 30°, and decreasing incident angle from 10° to 0°. The calculated RI sensitivity can be up to 592 nm/RIU with a high figure of merit (FOM) of 179.4 RIU⁻¹. More to the point, this nanograting has a simple structure and is less sensitive to the height and shape of grating ridge, which provides great convenience for the fabrication of devices. The other thing that is going on is that this structure can also realize synchronously tunable color filtering, including green to red, with high color purity in the visible band by choosing the period. The underlying physical mechanism is analyzed in detail, and is primarily attributed to surface plasmon polariton (SPP) resonance and dipole resonance at double plasmon resonance wavelengths. This work has tremendous potential in developing multipurpose and high-performance integrated optical devices such as spectral filters, colored displays and plasmon biomedical sensors. Full article

Infrared (IR) polarimetric imaging has attracted attention as a promising technology in many fields. Generally, superpixels consisting of linear polarizer elements at different angles plus IR imaging array are used to obtain the polarized target signature by using the detected polarization-sensitive intensities. However, the spatial arrangement of superpixels across the imaging array may lead to an incorrect polarimetric signature of a target, due to the range of angles from which the incident radiation can be collected by the detector. In this article, we demonstrate the effect of the incident angle on the polarization performance of an alternative structure where a dielectric layer is inserted between the nanoimprinted subwavelength grating layers. The well-designed spacer creates the Fabry–Perot cavity resonance, and thereby, the intensity of transverse-magnetic I-polarized light transmitted through two metal grating layers is increased as compared with a single-layer metal grating, whereas transverse-electric (TE)-transmitted light intensity is decreased. TM-transmittance and polarization extinction ratio (PER) of normally incident light of wavelength 4.5 μm are obtained with 0.49 and 132, respectively, as the performance of the stacked subwavelength gratings. The relative change of the PERs for nanoimprint-lithographically fabricated double-layer grating samples that are less than 6% at an angle of incidence up to 25°, as compared to the normal incidence. Our work can pave the way for practical and efficient polarization-sensitive elements, which are useful for many IR polarimetric imaging applications. Full article

The paper is devoted to the structure and properties of the composite material based on multi-walled carbon nanotubes (MWCNTs) covered with pyrolytic iron and chromium. Fe/MWCNTs and Cr/MWCNTs nanocomposites have been prepared by the metal organic chemical vapor deposition (MOCVD) growth technique using iron pentacarbonyl and bis(arene)chromium compounds, respectively. Composites structures and morphologies preliminary study were performed using X-ray diffraction, scanning and transmission electron microscopy and Raman scattering. The atomic and chemical composition of the MWCNTs’ surface, Fe-coating and Cr-coating and interface—(MWCNTs surface)/(metal coating) were studied by total electron yield method in the region of near-edge X-ray absorption fine structure (NEXAFS) C1s, Fe2p and Cr2p absorption edges using synchrotron radiation of the Russian-German dipole beamline (RGBL) at BESSY-II and the X-ray photoelectron spectroscopy (XPS) method using the ESCALAB 250 Xi spectrometer and charge compensation system. The absorption cross sections in the NEXAFS C1s edge of the nanocomposites and MWCNTs were measured using the developed approach of suppressing and estimating the contributions of the non-monochromatic background and multiple reflection orders radiation from the diffraction grating. The efficiency of the method was demonstrated by the example of the Cr/MWCNT nanocomposite, since its Cr2p NEXAFS spectra contain additional C1s NEXAFS in the second diffraction order. The study has shown that the MWCNTs’ top layers in composite have no significant destruction; the MWCNTs’ metal coatings are continuous and consist of Fe₃O₄ and Cr₂O₃. It is shown that the interface between the MWCNTs and pyrolytic Fe and Cr coatings has a multilayer structure: a layer in which carbon atoms along with epoxy –C–O–C– bonds form bonds with oxygen and metal atoms from the coating layer is formed on the outer surface of the MWCNT, a monolayer of metal carbide above it and an oxide layer on top. The iron oxide and chromium oxide adhesion is provided by single, double and epoxy chemical binding formation between carbon atoms of the MWCNT top layer and the oxygen atoms of the coating, as well as the formation of bonds with metal atoms. Full article