Refractive Index Of Silicon Research Articles

All-dielectric transmissive narrow-band filters adjustable within wide spectral range

The challenge of obtaining transmission spectra with both a wider tunable spectral range and high resolution persists. In this paper, a novel all- dielectric transmissive grating structure based on Mie resonance is proposed. The structure excites the Mie resonance by embedding a high refractive index contrast grating in a KF-Si film system band-stop filter. The dipole resonance energy is confined within the high refractive index silicon grating material, expanding the cutoff bandwidth of the KF-Si film system to over 400 nm and achieving single-peak transmission in the visible range. And the continuous transmission spectrum has an adjustable range of 300 nm with the highest spectral resolution (FWHM) (∼20 nm) can be achieved by adjusting the grating period. To suppress the coupling energy excitation between the higher-order magnetic dipole and the substrate, a silicon-rich nitride (SRN) matching layer is introduced between the KF-Si film system and the substrate. This layer enhances the intensity of the resonance peaks while simultaneously suppressing the short-wavelength sidebands, thereby improving the saturation and purity of the spectrum. In addition, we obtained a large angular tolerance of up to 15° by stacking the silicon film system. This work is of great significance for the advancement of hyperspectral imaging and display technology.

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).

Widely tunable refractive index silicon nitride films deposited by ion-assisted pulsed DC reactive magnetron sputtering

Silicon nitride films were deposited by ion-assisted pulsed DC reactive magnetron sputtering, where the regulation of power on the refractive index was emphasized. The power of the ion source and target was found to affect the refractive index. Refractive indices ranged from 2.13 to 2.63 (@632 nm) at ion source powers of 150, 300, 450, and 600 W, and from 2.45 to 3.02 (@632 nm) at target powers of 800, 1000, and 1200 W. The refractive index range was further extended to 1.89–3.02 (@632 nm) by co-adjustment, and extinction coefficients remained low in the visible to near-infrared band. The composition of deposited amorphous silicon nitride films varies with power, covering nitride-rich to silicon-rich. With no obvious defects on the surface and cross-section, the roughness slightly decreased with power, and the minimum roughness recorded was only 0.12 nm. In this work, a method for depositing silicon nitride films with a widely tunable refractive index range was proposed, which is promising for the application of optical thin films and waveguides.

Highly Sensitive Integrated Photonic Sensor and Interrogator Using Cascaded Silicon Microring Resonators

Silicon photonic sensors have formed a favorable platform for various sensing applications due to the great advantages of high-performance, compactness, and large-scale integration capability. However, interrogation systems for reading out the encoded sensing information from an integrated sensor are still bulky and inflexible for various portable applications. In this paper, we propose a monolithic silicon refractive index sensor and interrogator by utilizing the cascaded microring resonators. A novel dithering and bias scan interrogation technique is designed for highly sensitive refractive index sensing with a broadband light source. The reflective index for aqueous solutions of ethanol with different concentrations are measured in the experiment, verifying that the sensitivity of the sensor is 125.1 nm/RIU and the detection accuracy of the whole system is 7.76<inline-formula><tex-math notation="LaTeX">$\boldsymbol{\times 10^{-6}}$</tex-math></inline-formula> RIU. This integrated photonic sensor and interrogator will be a promising solution for large-scale applications in biological and chemical sensing scenarios.

Improved silicon optical parameters at 25°C, 295 K and 300 K including temperature coefficients

AbstractAlthough the author's earlier tabulations of silicon's refractive index and absorption coefficient over a wide range of wavelengths have found wide use, recent luminescent measurements have shown that refinement is needed at wavelengths beyond 1200 nm. An updated dataset is described for lightly doped silicon tabulated over the 250‐ to 1450‐nm range in 10‐nm increments at three temperatures, 25°C, 295 K and 300 K, incorporating the most recent experimental results. Temperature coefficients are also included allowing reasonably accurate estimates of optical parameters over the much broader −24°C to 200°C range.

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.

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.

Exploring optical properties of solar cells by programming and modeling

One of the main factors influencing the efficiency of solar cells is their optical properties. So, most light is reflecting back and transmit through solar cell. This leads to a decrease in the efficiency. We know that the refractive index of silicon is 3-4 depending on the wavelength of light, and the refractive index of air is about 1. This causes to reflect 34 percentages of the incident light. To reduce the amount of reflected light, the surface of the solar cell should be covered with an anti-reflection layer. It is important to determine the conditions of the types and thicknesses of the material covering the surface of the solar cell. Semiconductor devices modeling has become very popular. Because the results obtained through modeling are very close to the experimental results. In this study, we also modeled the solar cell with and without an anti-reflective layer using the Sentaurus TCAD software package and presented the results obtained. A new program was developed using the C # programming language, and a library was developed to help new researchers study the optical properties of solar cells directly for that program, and a number of results were obtained.

Enhancement of transmission in 1D thermal tunable metallic photonic crystal filter with exponential gradation thickness

Using the transfer matrix method, the transmission of 1D thermal tunable metallic photonic crystal (PC) filter with symmetry exponential gradation of thickness has been examined in this article. For the purpose of making this structure, three different materials silicon, silica, and silver have been used. The refractive index of silver is considered as a function of temperature and wavelength. The dependence of the silicon refractive index on the wavelength is also considered in calculations. The effect of the variation of temperature and incident angle on the transmission peaks has been investigated. By increasing the temperature, the transmission peaks in the position of defect modes move toward the larger wavelength at a given incident angle. When the incident angle is increased, however, they shift toward the shorter wavelength in both polarizations. The height of transmission peaks decreases linearly by increasing the temperature. Results are compared with those obtained in our previous work. The position of the transmission peaks in the structure with the exponential gradation of thickness is higher than the non-graded and linear graded, and the transmission peaks are sharper in TE polarization.

Carbon-rich amorphous silicon carbide and silicon carbonitride films for silicon-based photoelectric devices and optical elements: Application from UV to mid-IR spectral range

In the work we demonstrated the possibility to apply amorphous non-stoichiometric silicon carbide (a-SixC1-x:H) and silicon carbonitride (a-SixC1-x-yNy:H) films for improvement of exploitation characteristics of silicon-based photoelectric devices and optical elements in very wide spectral range - from UV to mid-IR. The a-SixC1-x:H films possessing optical properties required for effective antireflection (AR) effects for silicon (refractive index (n) at λ = 632 nm from 1.86 to 1.98, optical bandgap (Eopt) from 2.7 to 3.1 eV, and extinction coefficient (k) is close to zero practically in all spectral range) were obtained by PE-CVD from methane, silane, hydrogen, and argon gas mixture. To deposit silicon carbonitride films some amount of nitrogen was added to the gas mixture. For the a-SixC1-x-yNy:H films the following optical parameters were obtained: n = 1.76–1.93, Eopt = 3.1–3.4 eV, k~0. It has been shown that the proposed films possess unique mechanical properties and ratio of the films hardness to their Young modulus is very high (H/E > 0.13). It is evidence of the films high wear resistance that is of great importance when the films are used for protection of silicon optical elements in IR spectral range. It is established that the films of both types are very suitable as excellent AR coatings for silicon in the spectral range of Si-based solar cell photosensitivity, telecommunication windows, and mid-IR. Deposition of even single layer AR film allowed us to reduce reflection losses significantly (reflection coefficient (R) at minimum of reflection becomes close to zero). As a result, efficiency of etched multicrystalline Si-based solar cell (SC) was significantly improved. Transmittance of Si-based optical elements with front and rear AR films reached practically 100% in the telecommunication windows spectral range.

Experimental evidence of photonic band gap in hybrid Si/SiNOCH multilayer structure at the infrared range

Hybrid one dimensional photonic crystal (1D PC) based on alternating layers of inorganic materials, the silicon (Si), grown by radiofrequency magnétron sputtering and organic compound, HMDSO mixed with nitrogen N2 (HMDSO+N2), deposited by radiofrequency Plasma Enhanced Chemical Vapor Deposition (RF-PECVD) for different N2/HMDSO flow rate at a fixed power of 200W. As the refractive index of silicon (Si) is n=3.4, to obtain a good contrast index between the inorganic and organic layers leading to appearance of large photonic band gap, we have varied the flow of the mixed gaz (HMDSO+N2) for having a lower refractive index 1.7 corresponding to a layer with the same chemical composition element of the SiNOCH material as confirmed by IR measurement. After optimization of the Si and SiNOCH thickness layers with respect to the Bragg low, we have measured the photonic band gap (PBG) of Si/SiNOCH photonic structure through transmission and reflection spectra. The PBG appears after 5 periods of alternating layers with a width of 740 nm in the near infrared (NIR) region centered at 1500 nm. Our experimental results are interpreted successfully by a theoretical model based on the transfer matrix method (TMM).

A Dynamically Modulated All‐Dielectric Metasurface Doublet for Directional Harmonic Generation and Manipulation in Transmission

AbstractIn this paper, an electrically tunable all‐dielectric metasurface doublet is proposed operating at mid‐infrared frequency regime with dynamic 2π phase span in transmission mode. Each layer of the metasurface consists of a periodic array of silicon nanobars configured into p‐i‐n junctions in which the double carrier injection into the intrinsic region under forward bias allows for tuning of the silicon refractive index. The physical mechanism is based on the spectral overlap of high quality factor guided mode resonances supported by each constituent layer establishing an extreme Huygens' operation regime of nearly reflectionless transmission with steep phase spectrum. The short response time of field‐driven carrier injection in p‐i‐n junctions allows for modulation of refractive index with radio‐frequency biasing signals, yielding a stable time‐modulated all‐dielectric metasurface with directional frequency conversion and harmonic generation in transmission. A systematic approach is adopted to control the output spectrum of generated frequency harmonics through engineering the temporally modulated phase of transmitted light via adjusting the modulation waveform. Specifically, pure frequency mixing and concurrent dual‐frequency generation in transmission mode are demonstrated. Unique applications of the time‐modulated all‐dielectric metasurface are presented including wavelength‐multiplexed metalens for dual‐polarity focusing/diffusing and frequency diverse transmitarray for ultrafast spatiotemporal beam‐scanning.

Empirical model for the temperature dependence of silicon refractive index from O to C band based on waveguide measurements.

An accurate model for the silicon refractive index including its temperature and wavelength dependence is critically important for many disciplines of science and technology. Currently, such a model for temperatures above 22°C in the optical communication bands is not available. The temperature dependence in the spectral response of integrated echelle grating filters made in silicon-on-insulator is solely determined by the optical properties of the slab waveguide, making it largely immune to dimensional uncertainties. This feature renders the echelle filters a reliable tool to evaluate the thermo-optic properties of silicon. Here we investigate the temperature dependence of silicon echelle filters for the wavelength range of both O and C bands, measured between 22°C to 80°C. We show that if a constant thermo-optic coefficient of silicon is assumed for each band, as is common in the literature, the predictions show an underestimate of up to 10% in the temperature-induced channel wavelength shift. We propose and assess a model of silicon refractive index that encompasses both the wavelength and temperature dependence of its thermo-optic coefficients. We start from literature data for bulk silicon and further refine the model using the echelle filter measurement results. This model is validated through accurate predictions of device channel wavelengths and their temperature dependence, including the quadratic term, over a wide wavelength and temperature range. This work also demonstrates a new high-precision method for characterizing the optical properties of a variety of materials.

All-solution-processed Si films with broadband and omnidirectional light absorption

Silicon photonic structures have attracted a great deal of attention due to their potential benefits of efficient light management in optoelectronic applications. In this paper, we demonstrate broadband optical absorption enhancement in solution-processed amorphous silicon (a-Si) by leveraging the advantages of silicon photonic structures. Graded refractive index silicon multi-layer structures are employed by modulating optical constants with simple process optimization, resulting in significantly improved reflectance over a broad range of visible wavelengths. In addition, nanopatterning flexibility of solution-processed silicon provides benefits for tailoring silicon optical properties. With the incorporation of the two-dimensional submicron pattern into silicon films, the absorptivity of silicon films improves considerably below the wavelength of the bandgap (λ ∼ 800 nm), and the limited bandwidth of absorptivity in silicon films can be extended to near-infrared wavelengths by coating with a thin gold layer. The methodology is generally applicable to a platform for improving the broadband optical absorption of photonic and optoelectronic devices.

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.

Wavelength dispersion phenomena observed for emitted optical radiation from a p+nn+ silicon avalanche mode light-emitting device in a radio frequency bipolar-integrated circuitry

A two-junction micro p+np+ silicon avalanche-mode light-emitting device (Si AMLED) is analyzed for its dispersion characteristics, which generally resulted in different wavelengths of light (colors) being emitted at different angles from the surface of the device. The SiAMLED is integrated into on-chip bipolar radio frequency-integrated circuitry at micron dimensions. LEDs have high-frequency modulation frequencies reaching into the GHz range. Such devices, which are of micron dimension, operate at 8 to 10 V, 1 μA to 2 mA. The emission wavelength is in the 450- to 850-nm range, emission spot sizes are about 1 μm2, and emission intensities are up to 200 nW . μm − 2. The observed geometrical-chromatic dispersion characteristics range from 0.01 deg / nm wavelength for green radiation at a 5 deg exit angle to the normal of the device to 0.16 deg / nm wavelength for blue radiation at a 60 deg exit angle to the normal of the surface of the device. The high dispersion characteristics of the emitted radiation are attributed to the positioning of the optical source ∼1 μm subsurface to the silicon–silicon oxide interface, as well as to the high-refractive index differences between silicon and the surrounding lower refractive index silicon oxide layers. It is believed that the identified dispersion characteristics will have interesting and futuristic on-chip electro-optic applications for on-chip micro-optical wavelength dispersers, futuristic optical communication demultiplexers, along with on-chip microgas and biosensor applications.

Comparative study of two thermal tunable filters with and without symmetrical linear gradation of thickness

By using transfer matrix method, a comparative analysis is made for two thermal tunable metallic photonic crystal graded and non-graded filters. The transmission spectra of these two structures are investigated. Three different materials form the structure, Silicon, Silica and Silver as a metallic layer. The dependence of the silicon refractive index on the wavelength is considered in our calculations. In addition, the complex refractive index of Silver is the function of temperature and wavelength simultaneously. The effect of temperature and incident angle on the transmission is considered in this work. The results show that, the transmission peaks (TPs) are tunable with temperature and incident angle. The TPs shift toward the larger wavelength by increasing the temperature. At a constant temperature, TPs shift toward the shorter wavelength by increasing the incident angle. The temperature dependence of TPs is linear in both structures. The effect of the temperature on the height of the TP is also investigated. As the results show, the height of the TPs is also tunable with temperature and decreases linearly by increasing temperature due to the temperature dependence of the Silver loss factor. In order to increase the height of the TPs, we apply the symmetry linear gradation of thickness to one of the constituent layers. The linear gradation of the thickness leads to increase the height of TPs compare with the non-graded structure. Furthermore, the wavelength of TPs in the graded structure is larger and more significant than the non-graded one.

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.