High Refractive Index Of Silicon Research Articles

High-performance SiO2-SiNx distributed Bragg reflectors fabricated by ion-assisted reactive magnetron sputtering

With the rapid improvement of photonics, the demand for high-performance distributed Bragg reflectors (DBRs) is increasing. In this study, high-performance DBRs stacked by silica and high refractive index silicon nitride layers were designed and fabricated, which were deposited by ion-assisted reactive magnetron sputtering. TEM, EDX, and XPS were utilized to investigate the crystal properties, elemental composition, and bonding properties of the films. Additionally, AFM, SEM, and Raman spectra were used to analyze the morphology, roughness, and stress of DBRs. The result shows that the films prepared by ion-assisted reactive magnetron sputtering are mainly amorphous. DBRs have extremely smooth surfaces with a root mean square roughness (Rq) of approximately 0.5 nm. No obvious defects are found in their surface and cross-section. And the residual stresses of DBRs are relatively low. The reflectance results show that the maximum reflectance of 6-pair DBR on the silicon substrate is higher than 99.9%. The stopband bandwidth covers approximately 800–1150 nm. In this work, DBRs deposited by ion-assisted reactive magnetron sputtering feature high deposition quality, thinness, and broadband high reflection, which have great application potential in high-performance optical devices.

Fano Resonances in Metal Gratings with Sub-Wavelength Slits on High Refractive Index Silicon.

The enhancement of optical waves through perforated plates has received particular attention over the past two decades. This phenomenon can occur due to two distinct and independent mechanisms, namely, nanoscale enhanced optical transmission and micron-scale Fabry-Perot resonance. The aim of the present paper is to shed light on the coupling potential between two neighboring slots filled with two different materials with contrasting physical properties (air and silicon, for example). Using theoretical predictions and numerical simulations, we highlight the role of each constituent material; the low-index material (air) acts as a continuum, while the higher-index material (silicon) exhibits discrete states. This combination gives rise to the so-called Fano resonance, well known since the early 1960s. In particular, it has been demonstrated that optimized geometrical parameters can create sustainable and robust band gaps at will, which provides the scientific community with a further genuine alternative to control optical waves.

Inverse design of a Si-based high-performance vertical-emitting meta-grating coupler on a 220 nm silicon-on-insulator platform

Efficient extraction of light from a high refractive index silicon waveguide out of a chip is difficult to achieve. An inverse design approach was employed using the particle swarm optimization method to attain a vertical emitting meta-grating coupler with high coupling efficiency in a 220-nm-thick silicon-on-insulator platform. By carefully selecting the figure of merit and appropriately defining parameter space, unique L-shape and U-shape grating elements that boosted the out-of-plane radiation of light were obtained. In addition, a 65.7% (−1.82 dB) outcoupling efficiency and a 60.2% (−2.2 dB) fiber-to-chip vertical coupling efficiency with an 88 nm 3 dB bandwidth were demonstrated by numerical simulation. Considering fabrication constraints, the optimized complex meta-grating coupler was modified to correspond to two etching steps and was then fabricated with a complementary metal-oxide-semiconductor-compatible process. The modified meta-grating coupler exhibited a simulated coupling efficiency of 57.5% (−2.4 dB) with a 74 nm 3-dB bandwidth in the C-band and an experimentally measured coupling efficiency of 38% (−4.2 dB).

A Hydrogen-Containing Di-Phenyl Siloxane Cross-Linker for Ultra-High Hardness and High Refractive Index Silicone Resin and its Application in LED Encapsulation

A Hydrogen-Containing Di-Phenyl Siloxane Cross-Linker for Ultra-High Hardness and High Refractive Index Silicone Resin and its Application in LED Encapsulation

Silicon oxynitride platform for linear and nonlinear photonics at NIR wavelengths

The development of versatile and novel material platforms for integrated photonics is of prime importance in the perspective of future applications of photonic integrated circuits for quantum information and sensing. Here we present a low-loss material platform based on high-refractive index silicon oxynitride (SiON), which offers significant characteristics for linear and non-linear optics applications in a wide range of red/near-infrared wavelengths. The demonstrated propagation loss <1.5 dB/cm for visible wavelengths enables the realization of long and intricate circuitry for photon manipulations, as well as the realization of high quality factor resonators. In addition, the proposed SiON shows a high nonlinear index of 10−19 m2/W, improving the strength of nonlinear effects exploitable for on-chip photon generation schemes.

Synthesis of High Refractive Index Silicone LED Encapsulation with Ultra-High Hardness

Synthesis of High Refractive Index Silicone LED Encapsulation with Ultra-High Hardness

Angle-tolerant polarization controlled continuous color palette from all-dielectric nanograting in reflective mode

High-performance angle-tolerant polarization tunable reflective color filters with an adopted one-dimensional silicon grating structure are proposed. The polarization-tunable color filtering properties and incident angle-insensitive properties are thoroughly investigated to achieve the angle-tolerant polarization controlled continuous color palettes. Benefiting from high refractive index of silicon, the proposed color filters evidently provide a high angular tolerance of 30° in conjunction with a large polarization-tunable color range. Moreover, full and vivid colors covering the entire visible range can be produced by simply altering the grating thickness. The combination between the all-dielectric nanostructure with a high angular tolerance and the polarization-tunable filtering properties, described in this paper, can be applied in anti-counterfeiting, imaging and filtering technologies, and so forth.

Silicon-coated gold nanodiffraction grating structures as plasmonic absorbers for short-wavelength infrared light

As a plasmonic absorber for short-wavelength infrared hyperspectral imaging, a silicon-coated gold nanodiffraction grating structure is proposed. This plasmonic absorber leads to absorption peaks in short-wavelength infrared region by the high refractive index of silicon coating on gold grating. It is relatively easy to fabricate with smaller size than those of already known absorbers. By performing fabrication, simulation, and measurement, we demonstrate the sharp absorption peaks of short-wavelength infrared light using only 400–1000 nm grating interval. We believe this miniaturized absorber will be able to be applied to hyperspectral imaging without a spectroscope owing to its sharp absorption peak at a specific wavelength.

A High-Sensitivity SPR Sensor with Bimetal/Silicon/Two-Dimensional Material Structure: A Theoretical Analysis

In this paper, we reported a theoretical study of a novel Surface plasmon resonance (SPR) biosensor composed of BK7 prism, gold (Au)/silver (Ag) bimetallic layer, silicon and two-dimensional (2D) materials. The bimetallic layer combines the advantages of Au and Ag and the high refractive index silicon layer enhances the electric field on the surface of the sensor, so that the sensor has a better overall performance in terms of sensitivity and figure of merit (FOM). Compared with ordinary dielectrics, 2D materials have excellent photoelectric properties, such as larger specific surface area, higher carrier density and stronger adsorption capacity, which improve the detection ability of the sensor. The sensitivity of the optimized sensor achieves 297.2°/RIU, 274°/RIU and 246°/RIU when the silicon layer is covered with graphene, MXene (Ti3T2Cx) and MoS2, respectively. Compared with the traditional SPR sensor, the sensitivity of the structure has been significantly improved, and its excellent performance has broad application prospects in biosensing and other fields.

Study of waveguide background at visible wavelengths for on-chip nanoscopy.

On-chip super-resolution optical microscopy is an emerging field relying on waveguide excitation with visible light. Here, we investigate two commonly used high-refractive index waveguide platforms, tantalum pentoxide (Ta2O5) and silicon nitride (Si3N4), with respect to their background with excitation in the range 488-640 nm. The background strength from these waveguides were estimated by imaging fluorescent beads. The spectral dependence of the background from these waveguide platforms was also measured. For 640 nm wavelength excitation both the materials had a weak background, but the background increases progressively for shorter wavelengths for Si3N4. We further explored the effect of the waveguide background on localization precision of single molecule localization for direct stochastic optical reconstruction microscopy (dSTORM). An increase in background for Si3N4 at 488 nm is shown to reduce the localization precision and thus the resolution of the reconstructed images. The localization precision at 640nm was very similar for both the materials. Thus, for shorter wavelength applications Ta2O5 is preferable. Reducing the background from Si3N4 at shorter wavelengths via improved fabrication will be worth pursuing.

Large-area, low-cost near-infrared meta-surface reflector based on a pixelated two-dimensional silicon disk array.

All-dielectric meta-surfaces composed of dielectric meta-atoms with electric and magnetic multipole resonances provide a low loss alternative to plasmonic meta-surfaces in some optical research fields such as meta-lens and meta-surface holography. We utilize the digital holography lithography technique to obtain the large area meta-surface perfect reflector made of high refractive index and low loss silicon discs arrays, with the capability to delicately control the optical response in the near infrared spectrum. Three types of meta-surface reflectors (discs, truncated cones and diamond-shaped discs) were fabricated, which correspondingly exhibited nearly 1 peak reflectance and greater than 97% average reflectance in their respective perfect reflectance spectral regions. Digital holography lithography only takes 4 min to fabricate millions of photoresist disks over an area of 100 mm2, which is high processing efficiency and low cost. The fabrication strategy opens a new avenue for the production of large-area meta-surfaces in the optical field, especially in the mass production of optical communication devices, semiconductor lasers, etc.

All-dielectric metasurface for high-performance structural color

The achievement of structural color has shown advantages in large-gamut, high-saturation, high-brightness, and high-resolution. While a large number of plasmonic/dielectric nanostructures have been developed for structural color, the previous approaches fail to match all the above criterion simultaneously. Herein we utilize the Si metasurface to demonstrate an all-in-one solution for structural color. Due to the intrinsic material loss, the conventional Si metasurfaces only have a broadband reflection and a small gamut of 78% of sRGB. Once they are combined with a refractive index matching layer, the reflection bandwidth and the background reflection are both reduced, improving the brightness and the color purity significantly. Consequently, the experimentally demonstrated gamut has been increased to around 181.8% of sRGB, 135.6% of Adobe RGB, and 97.2% of Rec.2020. Meanwhile, high refractive index of silicon preserves the distinct color in a pixel with 2 × 2 array of nanodisks, giving a diffraction-limit resolution.

Edge Couplers in Silicon Photonic Integrated Circuits: A Review

Silicon photonics has drawn increasing attention in the past few decades and is a promising key technology for future daily applications due to its various merits including ultra-low cost, high integration density owing to the high refractive index of silicon, and compatibility with current semiconductor fabrication process. Optical interconnects is an important issue in silicon photonic integrated circuits for transmitting light, and fiber-to-chip optical interconnects is vital in application scenarios such as data centers and optical transmission systems. There are mainly two categories of fiber-to-chip optical coupling: off-plane coupling and in-plane coupling. Grating couplers work under the former category, while edge couplers function as in-plane coupling. In this paper, we mainly focus on edge couplers in silicon photonic integrated circuits. We deliver an introduction to the research background, operation mechanisms, and design principles of silicon photonic edge couplers. The state-of-the-art of edge couplers is reviewed according to the different structural configurations of the device, while identifying the performance, fabrication feasibility, and applications. In addition, a brief comparison between edge couplers and grating couplers is conducted. Packaging issues are also discussed, and several prospective techniques for further improvements of edge couplers are proposed.

Optimizing shape characteristics of high refractive index particles to improve forward scattering

High Refractive Index Dielectric nanoparticles have been proposed as an alternative to metallic ones due to their low losses and their directionality properties. In particular, at the Zero-Backward condition (near Zero-Forward condition), incident radiation is forward (backward) scattered being null (almost null) in the backward (forward) direction. Both Scattering Directionality Conditions have been evidenced experimentally for several geometries, including spherical nanoparticles. In this work, we numerically analyze the amount of scattered electromagnetic energy in the forward region under the Zero-Backward condition for different geometries of isolated High Refractive Index silicon nanoparticles. The study is focused on cylinders, ellipsoids and parallelepipeds, being the latter the most promising one. To establish comparisons, the volume of all of the geometries has been kept constant and equal to that of a spherical particle of radius 150 nm, for which Kerker conditions hold in the near-infrared. This research looks at those applications where high efficiency forward scattering is required, for instance, in photovoltaic devices.

Special Issue of Silicon Photonics [Scanning the Issue

Silicon, well established as an electronics platform, was first seriously explored as an optical waveguide platform in 1987 by Soref and Bennett. Light at fiber-optic communication wavelengths can pass through crystalline silicon with very high transmission. Silicon waveguides can be made by etching into the thin crystalline silicon layer on a silicon-on-insulator wafer. Because of the high refractive index of silicon compared to the surrounding oxide, these waveguides can bend with radii less than five micrometers and make compact splitters/combiners, filters, and polarization elements. High-speed optical modulators can be made by rapidly changing free electron and hole densities in the silicon in the optical path, and photodetectors can be made by epitaxially growing germanium on the silicon, both using electrically connected p-n junctions. The only element missing to complete an optical integration platform is an integrated light source, rendered very difficult because of the indirect bandgap of silicon and germanium. While to date, no practical electrically pumped light emitter has been deployed based on silicon itself, multiple hybrid and heterogeneous solutions have been reported.

Design and optimization of thin film polarizer at the wavelength of 1540 nm using differential evolution algorithm

In this paper, a thin film polarizer at the wavelength of 1540 nm in infrared region was designed and optimized using differential evolution method. It is shown how the algorithm’s parameters can change the output result to obtain the best consequence of optimization. This polarizer consists of a few pairs of high and low refractive index dielectric materials, titanium dioxide and silicon dioxide, respectively, with $$BK_{7}$$ glass substrate and the angle of incident light was supposed 56° that is the Brewster angle for $$BK_{7}$$ glass. Our final optimized polarizer has 91.20 and 0.336% transmittance for P and S polarization, respectively, and a 271 ratio of $$\frac{{T_{P} }}{{T_{S} }}$$ which has high significance for this polarizer. It consists of eight pairs of layers with low and high refractive index materials and 3369.1 nm physical thickness which is used to separate S and P polarized light for Q-switching process.

Broadband Electromagnetic Dipole Resonance by the Coupling Effect of Multiple Dielectric Nanocylinders

Broadband resonant scattering in a visible region that can be obtained by coupled multiple silicon nanocylinders. For a single high refractive index silicon nanocylinder, the electric dipole and magnetic dipole resonances can be observed. By constructing a silicon nanocylinder dimer, the interaction between the particles plays an important role in broadband scattering. Interestingly, due to magnetic-magnetic dipole interaction, a splitting phenomenon of magnetic resonance mode is revealed. A new magnetic resonant mode emerges at a longer wavelength in dimer and trimer by changing the diameter of one nanocylinder in dimer or trimer, and the gap size between nanocylinders. The scattering bandwidth can further increase with the effect of substrate, which is attributed to the extension of resonant mode into substrate. The broadband optical response can be revealed by the calculated scattering resonant spectra and the spatial electromagnetic field distributions. Furthermore, the transmission of periodic nanocylinder structure, including single nanocylinder and dimer, is demonstrated. By decreasing the gap between nanocylinders in dimer for periodic array structure, a new electric resonant mode occurs. These results can provide a guideline to realize broadband resonant optical elements.

Efficient Silicon Metasurfaces for Visible Light

Dielectric metasurfaces require high refractive index contrast materials for optimum performance. This requirement imposes a severe restraint; devices have either been demonstrated at wavelengths of 700nm and above using high-index semiconductors such as silicon, or they use lower index dielectric materials such as TiO$_{2}$ or Si$_{3}$N$_{4}$ and operate in the visible wavelength regime. Here, we show that the high refractive index of silicon can be exploited at wavelengths as short as 532 nm by demonstrating a silicon metasurface with a transmission efficiency of 47% at this wavelength. The metasurface consists of a graded array of silicon posts arranged in a square lattice on a quartz substrate. We show full 2{\pi} phase control and we experimentally demonstrate polarization-independent beam deflection at 532nm wavelength. The crystalline silicon is placed on a quartz substrate by a bespoke layer transfer technique and we note that an efficiency >70% may be achieved for a further optimized structure in the same material. Our results open a new way for realizing efficient metasurfaces based on silicon in the visible wavelength regime.

Design and fabrication of silicon-based linear polarizer with multilayer nanogratings operating in infrared region

We have proposed and experimentally demonstrated a silicon-based linear polarizer with multilayer nanogratings working in 3 to 5 μm of an infrared region. A dielectric grating is first fabricated in a low-refractive index thin layer on a Si-substrate and then double-layer metallic gratings are formed by evaporating a metallic film onto the dielectric grating. With the designed structure of multilayer nanogratings coupled with a low-refractive-index dielectric layer on the high-refractive index silicon substrate, both high transverse magnetic transmission (TMT) and high extinction ratio (ER) can be effectively achieved across 3- to 5-μm range in the infrared band without the complicated metallic ion etching process that is required in conventional nanowire grids. An ER of 40 dB and TMT of averagely higher than 80% were obtained experimentally from a linear polarizer with a multilayer grating of 280-nm period. The Si-based multilayer grating structure shows possibilities of implementing polarization in a fashion of relatively easy-fabrication, semiconductor process compatible, and high performance.

Bioinspired broadband midwavelength infrared antireflection coatings on silicon

Silicon has been extensively used in manufacturing refractive infrared optics due to its high refractive index and excellent transmission over a very broad range of infrared wavebands. However, the high refractive index of silicon leads to large reflection loss which greatly limits the performance of the final optoelectronic devices. Here, the authors report a simple and scalable templating nanofabrication technology for making subwavelength-structured, broadband antireflection coatings on crystalline silicon wafers, targeting the midwavelength infrared (MWIR) waveband (3–8 μm), which has important implications for various civilian and military purposes. Periodic arrays of silicon nanopillars with tapered shapes, which mimic the microstructured cornea of nocturnal moths, can be patterned on both surfaces of silicon wafers using self-assembled monolayer silica colloidal crystals as structural templates. The resultant moth-eye gratings can greatly enhance optical transmission for the entire MWIR region. Finite-difference time-domain simulations have also been performed and the theoretical predictions agree reasonably well with the experimental optical measurements.