High Refractive Index Dielectric Layer Research Articles

Side-polished photonic crystal fiber sensor with ultra-high figure of merit based on Bloch-like surface wave resonance

A Bloch surface wave (BSW) resonance configuration is introduced for biosensing with an ultra-high figure of merit (FOM). The BSW excitation is realized through the evanescent field of the core-guided fundamental mode of a side-polished photonic crystal fiber (PCF). By taking advantage of the air hole periodic microstructure of the PCF cladding, the BSW platform can be achieved with only a single high refractive index dielectric layer on its flat surface. The dielectric layer deposited on the polished surface of the PCF modifies the local effective refractive index, allowing direct manipulation of the BSWs, whereby the resonance wavelength of the surface wave can be adjusted by choosing the material and thickness of this layer. Here, we numerically investigate Bloch-like surface wave (BLSW) resonance conditions around telecom wavelengths for silicon, titanium dioxide, copper monoxide, and aluminum oxide termination layers. The BLSW excitation platform materials have low loss, which results in higher surface field enhancements and narrower resonances, which are advantageous properties for the sensors. The obtained results open new avenues for the application of optical surface waves in biosensing with high FOM. Furthermore, these results show a much higher figure of merit (FOM) than traditional approaches, allowing for increased sensitivity and accuracy.

The influence of single layer MoS2 flake on the propagated surface plasmons of silver nanowire

We demonstrate enhancing the excitation and transmission efficiency of the propagated surface plasmon (SP) of an Ag nanowire (Ag NW) in hybrid Ag–MoS2 structures by contrasting the SP propagation of the Ag NW on different substrates, including SiO2 and monolayer MoS2, or partially overlapping the Ag NW on MoS2 flakes. The simulation results show that the leaky radiation of the hybrid plasmonic modes H1 and H2 can be prominently suppressed due to the high refractive index dielectric layer of MoS2, which provides an optical barrier for blocking the leaky radiation, resulting in reduced propagation loss. This paper provides a feasible and effective method to improve the SP propagation length.

Transparent Colored Display Enabled by Flat Glass Waveguide and Nanoimprinted Multilayer Gratings

In this paper, a type of transparent colored static display consisting of a flat glass waveguide and embedded multilayer gratings is presented, by which multiple patterns and colors with a wide field of view (FOV) can be displayed. The embedded grating is achieved by nanoimprinting followed by deposition of a high refractive index dielectric layer. The process can be repeated to produce multilayer gratings, which are shaped into specific patterns to be displayed, and they are designed to have proper periods and orientations to independently extract light incident from different edges of the glass plate. Such transparent display offers the advantages of low cost, easy fabrication and wide FOV, and it is suitable for colored signage and decorative applications.

Bandwidth-enhanced carpet cloak by using a phase-gradient metasurface with a multilayer unit cell in terahertz range

The metasurfaces can effectively manipulate the phase, polarization and amplitude of electromagnetic waves. The development of metasurfaces provides a new choice for designing ultra-thin and arbitrary-shaped carpet cloak devices. Here, we firstly use the classical Snell’s law to derive the generalized Snell’s reflection law for reflective cloak devices, and explores the working principle and design method of metasurface reflection cloak. A multi-layer metasurface structure is proposed to design a broadband terahertz wave carpet cloak device with well cloak effect in the wide frequency range from 0.67 THz to 0.85 THz. Based on Snell’s law, we innovatively cover the metasurface structural unit with a high refractive index dielectric layer to achieve a wide-angle response of the metasurface. Based on the full-wave simulation analysis of the finite integral method, the results show that the designed cloak still has a good cloak effect under the wide angle from 35°to 55°.

Enhancement of bandwidth and angle response of metasurface cloaking through adding antireflective moth-eye-like microstructure.

Ultrathin metasurface provides a completely new path to realize cloaking devices on account of their fascinating ability to control electromagnetic wave. However, the conventional cloaking devices are limited by their narrow bandwidth. To overcome this challenge, we present the realization of ultrabroadband and wide angle metasurface cloaking through high refractive index dielectric layer and antireflective "moth-eye-like" microstructure in this work. Two options are proposed and demonstrated numerically in terahertz region. By using local phase compensation, the proposed carpet cloaks can suppress significantly the unexpected scattering and reconstruct wavefront. The cloaking effects of the proposed design are verified from 0.65THz to 0.9THz with a wide range of angles. Moreover, the proposed metasurface cloaking is probable to extend to the optical and microwave domains and can be applied in stealth, illusion optic, radar and antenna systems.

Surface plasmon resonance biosensor based on graphene and grating excitation.

A surface plasmon resonance biosensor based on a graphene-decorated grating excitation structure is proposed in this paper. The biosensor consists of a three-layer structure, including a graphene layer, a grating layer, and a high refractive index layer. The material of the grating layer is silica. The graphene is physically deposited on the grating ridges. An incident light with transverse magnetic polarization is used to excite surface plasmons in the mid-infrared spectral region, which is highly localized at both ends of the graphene layer. The property of the sensor is improved by the high refractive index dielectric layer, which enhances the absorption of incident light and increases the depth of the spectra. The finite-difference time-domain method is used to simulate the property of the sensor. The structure of the sensor could be optimized by changing the structural parameters and comparing the simulation results. The effective refractive index (RI) on the surface and the wavelength of the reflective resonance absorption peak will be changed when the surface of graphene adsorbs the surrounding analyte. The results show that the relationship between the analyte RI and the resonance wavelength is linear. The measurement range of analyte RI is 1-1.8, and the sensitivity is 2780nm/RIU.

Emission Enhancement of Surface Plasmon Coupled Blue LED With a Surface Al Nanoparticle

Emission enhancement of a radiating dipole at a desired emission wavelength in blue range coupling with a surface plasmon (SP) resonance mode induced on a nearby surface Al nanoparticle (NP) is demonstrated. Meanwhile, increasing the size of the NP and utilizing a high refractive index dielectric layer to cover the NP are effective approaches to a spectral red-shift of the SP resonance mode of Al, the location and direction of the radiating dipole also play important roles in the SP coupling effect. Such advantages make surface Al NP be an alternative low-cost and simple technique used in SP-coupled light-emitting diodes.

Broadband polarizing beam splitter based on two-layer metal grating with a high refractive index dielectric layer

A polarizing beam splitter (PBS) based on a two-layer metal grating operating in the near-infrared wavelength region is proposed. The PBS structure comprises a high refractive index dielectric layer and a subwavelength grating layer, which increases the transmittance and the extinction ratio of the grating. Using the rigorous coupled-wave analysis (RCWA) method, the parameters of the proposed polarizing beam splitter were simulated and optimized. The results show that transmission of more than 97% for the transverse-magnetic (TM) wave polarization and reflection of more than 98% for the transverse-electric (TE) wave polarization are achieved within the 1220–1690nm wavelength range. The corresponding maximum extinction ratios for the transmittance and reflectance are 33dB and 34dB, respectively. When compared with a single-layer PBS grating, the proposed two-layer structure shows greater design flexibility. The proposed PBS shows potential for application to devices such as routers and switches.

Electro-absorption Modulator with Dual Carrier Accumulation Layers Based on Epsilon-Near-Zero ITO

An electro-absorption modulator based on indium tin oxide is proposed by constructing a waveguide consisting of metal-dielectric-ITO-dielectric-Si stack. Applying a negative voltage bias on the ITO layer, carrier accumulation occurs at both dielectric-ITO interfaces, which dramatically changes the guided mode properties due to the epsilon-near-zero effect. By tuning the real part of the permittivity around zero, the guided plasmonic mode concentrates in either ITO or dielectric layers, resulting in a high propagation loss. These dual carrier accumulation layers significantly improve the extinction ratio of the modulator. A further improvement is obtained by using high refractive index dielectric thin layers, which provides a strong optical confinement in the carrier accumulation layers. The dual carrier accumulation layer device shows a 200 % increase of the modulation efficiency compared to a single accumulation layer design. A modulation depth of 9.9 dB/μm can be achieved by numerical simulation.

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.

OLED Light Outcoupling Enhancement by Extracting Surface Plasmon Polariton Energy

The extraction method of surface plasmon polariton (SPP) energy was investigated to assess its ability to improve the outcoupling efficiency of organic light-emitting diodes (OLEDs). A multi-cathode OLED (MC-OLED) structure was used; this structure was composed of a semitransparent cathode (Ag), a high refractive index dielectric layer (WO3), and a reflector (Ag). The dependence of the current efficiency of MC-OLEDs on the thicknesses of the Ag cathode and the WO3 dielectric was examined, and optimal thicknesses were identified. Current efficiency can be increased by 20% more than conventional OLEDs by using a 50-nm Ag cathode and a 100-nm WO3 dielectric.

Low resistive transparent and flexible ZnO/Ag/ZnO/Ag/WO3 electrode for organic light-emitting diodes

Transparent electrodes cannot easily be created with high transmittance and low sheet resistance simultaneously, although some optoelectronic devices, such as large organic light-emitting diode (OLED) displays and lightings, require very low resistive transparent electrodes. Here, we propose a very low resistive transparent electrode (∼1.6Ω/sq) with a high transmittance (∼75%) for OLED devices, the transmittance level of which represents the highest reported value to date given such a low sheet resistance level. It consists of a stacked silver (Ag)/zinc oxide (ZnO)/Ag multilayer covered by high refractive index dielectric layers. The proposed multilayer electrode with optimal layer thicknesses has a high and wide spectral transmittance peak due to interference. The low sheet resistance is a result of two Ag layers connected via the sandwiched ZnO layer. In addition to its low sheet resistance coupled with high transmittance, the proposed multilayer electrode has good flexibility. An OLED with an anode of the stacked Ag/ZnO/Ag multilayer shows performance comparable to that of an anode of indium tin oxide.

Long range surface plasmons on asymmetric suspended thin film structures for biosensing applications

We show that long-range surface plasmons (LRSPs) are supported in a physically asymmetric thin film structure, consisting of a low refractive index medium on a metal slab, supported by a high refractive index dielectric layer (membrane) over air, as a suspended waveguide. For design purposes, an analytic formulation is derived in 1D yielding a transcendental equation that ensures symmetry of the transverse fields of the LRSP within the metal slab by constraining its thicknesses and that of the membrane. Results from the formulation are in quantitative agreement with transfer matrix calculations for a candidate slab waveguide consisting of an H(2)O-Au-SiO(2)-air structure. Biosensor-relevant figures of merit are compared for the asymmetric and symmetric structures, and it is found that the asymmetric structure actually improves performance, despite higher losses. The finite difference method is also used to analyse metal stripes providing 2D confinement on the structure, and additional constraints for non-radiative LRSP guiding thereon are discussed. These results are promising for sensors that operate with an aqueous solution that would otherwise require a low refractive index-matched substrate for the LRSP.

Electromagnetic fields distribution in multilayer thin film structures and the origin of sensitivity enhancement in surface plasmon resonance sensors

The performance of surface plasmon resonance (SPR) sensors depends on the design parameters. An algorithm for calculating the electromagnetic fields distribution in multilayer structure is developed relying on Abeles matrices method for wave propagation in isotropic stratified media. The correlation between field enhancement and sensitivity enhancement is examined and found to agree with the overlap integral in the analyte region. This correlation was verified in the conventional SPR sensor based on Kretschmann configuration, and in the improved SPR sensor with high refractive index dielectric top layer for several cases, e.g. field enhancement due to resonance, the sensitivity dependence on the wavelength, the influence of prism refractive index on sensitivity, and the effect of the layers materials and thicknesses.

High Refractive Index Dielectric Prepared by Electron Beam Evaporation for Photonic Crystal Optical Biosensor Application

The fabricated photonic crystal biosensor device consists of SOG material and titanium dioxide (TiO2) thin films as low and high refractive indexes dielectric layers, respectively. Nano-Imprinting Lithography (NIL) process was used to duplicate periodic line as grating structure from Ni-master mold onto SOG/glass. High refractive index dielectric thin film layer was deposited by using electron beam evaporation system. The surface morphology and thickness of thin film are characterized by atomic force microscope (AFM) and field emission scanning electron microscope (FE-SEM), respectively. The optical measurement system is set up to observed the sensitivity of fabricated device. A shift of reflected peak wavelength observed from DI-water and IPA was tested. The morphology and the thickness of the prepared dielectric thin films are affected to the efficiency of fabricated device.

带有高折射率介质层的金属光栅偏振器特性的研究

带有高折射率介质层的金属光栅偏振器特性的研究

带有高折射率介质层的金属光栅偏振器特性的研究

带有高折射率介质层的金属光栅偏振器特性的研究

Subwavelength Silica-Based Optical Waveguide With a Multilayered Buffer for Sharp Bending

A subwavelength SiO2-based optical waveguide with an air cladding and a multilayered buffer is presented. This multilayered buffer includes alternating low and high refractive index dielectric layers. The thicknesses of these dielectric layers are chosen optimally by using genetic algorithm so that the theoretical leakage loss of the present optical waveguide is minimized (<0.001 dB/mm at the central wavelength, e.g., 1550 nm). The modal analysis with a full-vectorial finite-difference method shows that the present SiO2 optical waveguide has the ability of sharp bending with a very small bending radius (~ 10 mum).

Low-index-material-based nano-slot waveguide with quasi-Bragg-reflector buffer

A low-index-material-based nano-slot waveguide based on a quasi-Bragg-reflector buffer is presented. This quasi-Bragg-reflector buffer includes alternating low and high refractive index dielectric layers. The thicknesses of these dielectric layers are chosen optimally by using a genetic algorithm so that the leakage loss of the present optical waveguide is minimised. An SiO 2 -based slot-waveguide is designed as an example and the quasi-Bragg-reflector buffer is formed by using several Si/SiO 2 bilayers. The theoretical leakage loss for an SiO 2 -based slot-waveguide with three optimised Si/SiO 2 bilayers is about 0.01 dB/mm (at 1550 nm). The modal analysis with a full-vectorial finite-difference method shows that the present slot waveguide has an enhancement of the field distribution in the nano-slot region.

The Introduction of Alternative Process Gas Regimes during the Reactive Sputter Deposition of Titania Coatings

TiO2 films are widely used as high refractive index dielectric layers in multilayer optical devices and functional films. The optical properties of titania films, and their stability, are critically dependent on the film structure, which in turn, is dependent on the deposition conditions used. In this study, titania films were grown by reactive pulsed magnetron sputtering in a dual variable field strength planar magnetron system. The effect of deposition conditions, including the use of alternate process gas regimes incorporating nitrogen, on film properties was investigated. Studies showed that the hysteresis behaviour of the Ti/O2 system was progressively reduced as the proportion of nitrogen in the process gas was increased. RBS analysis determined, though, that even for process gas regimes with equal flow rates of nitrogen and oxygen, no nitrogen could be detected in the films. Improvements were also noted in the wear resistance of the coatings deposited under these conditions, without any detrimental effect on their optical properties. Thus, the alternative process gas regimes explored here offer the potential for enhanced process control and improved coating durability during the reactive sputter deposition of titania films.