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The following study involved the utilization of dispersion polymerization to synthesize micron/nano-sized polystyrene (PS) spheres, which were then deposited onto a silicon substrate using the floating assembly method to form a long-range monolayer. Subsequently, dry etching techniques were utilized to create subwavelength structures. The adjustment of the stabilizer polyvinylpyrrolidone (PVP), together with changes in the monomer concentration, yielded PS spheres ranging from 500 nm to 5.6 μm in diameter. These PS spheres were suspended in a mixture of alcohol and deionized water before being arranged using the floating assembly method. The resulting tightly packed particle arrangement is attributed to van der Waals forces, Coulomb electrostatic forces between the PS spheres, and surface tension effects. The interplay of these forces was analyzed to comprehend the resulting structure. Dry etching, utilizing the PS spheres as masks, enabled the exploration of the effects of etching parameters on the resultant structures. Unlike traditional dry etching methods controlling RF power and etching gases, in the present study, we focused on adjusting the oxygen flow rate to achieve cylindrical, conical, and parabolic etched structures. [ABSTRACT FROM AUTHOR]

The development of renewable energy sources is nowadays of enormous importance, not only for the climate change fight but also for the security of the energy supply. The latest geopolitical unfortunate events in Europe have highlighted our energy dependency on foreign fossil fuels. In this context, solar technologies are already playing an essential role in shifting towards neutral carbon economies, ensuring a reliable energy supply. In this regard, dispatchability provided by CSP plants is key to pave the way towards energy transition. It is worth noting that the long-term durability and performance of solar components in arid regions are crucial to increase the reliability and performance of CSP plants while reducing O&M costs. In this work, an innovative approach based on nano-structuring the solar receiver tube glass is presented, which provides improved anti-reflective (AR) and anti-soiling (AS) properties, also showing good durability with respect to abrasion. Spectral transmittance improvement, soiling rate decrease, and durability measurements are presented for nano-structured glasses, comparing with current state of the art glass performance. The achieved experimental results suggest that the new structured glasses would be good candidates for CSP applications

The following study involved the utilization of dispersion polymerization to synthesize micron/nano-sized polystyrene (PS) spheres, which were then deposited onto a silicon substrate using the floating assembly method to form a long-range monolayer. Subsequently, dry etching techniques were utilized to create subwavelength structures. The adjustment of the stabilizer polyvinylpyrrolidone (PVP), together with changes in the monomer concentration, yielded PS spheres ranging from 500 nm to 5.6 μm in diameter. These PS spheres were suspended in a mixture of alcohol and deionized water before being arranged using the floating assembly method. The resulting tightly packed particle arrangement is attributed to van der Waals forces, Coulomb electrostatic forces between the PS spheres, and surface tension effects. The interplay of these forces was analyzed to comprehend the resulting structure. Dry etching, utilizing the PS spheres as masks, enabled the exploration of the effects of etching parameters on the resultant structures. Unlike traditional dry etching methods controlling RF power and etching gases, in the present study, we focused on adjusting the oxygen flow rate to achieve cylindrical, conical, and parabolic etched structures.

Polarization-dependent dual-band THz metamaterial using a modified Trishul structure is proposed in this paper. The absorber has three layers namely, a conducting ground plane, a dielectric substrate, and a structure top metallic patch. The top and bottom metallic is made up of gold material and the dielectric substrate is polyimide. The characteristics are obtained using the finite element method. The structure has obtained two resonant peaks at 0.78 THz(f1) and 1.65 THz(f2) for the X-polarized wave and at 0.81 THz(f3) and 1.53 THz(f4) for the Y-polarized wave respectively. The simulation result reveals that the absorber has obtained ultra-narrow band absorption with a full width half maximum(FWHM) of 4.8 GHz, 10 GHz, 5 GHz, and 10 GHz for f1, f2, f3, and f4 respectively. In addition, the underlying physical mechanism of the multi-band characteristics is analyzed using electric field and surface current distributions. The proposed absorber design has importance in the emerging THz system for polarization imaging and sensing applications. Also, flexible metamaterials could be useful for soft robotics applications also.

Optical vortices carrying orbital angular momentum (OAM) have recently attracted increasing interest for providing an additional degree of freedom for capacity scaling in optical communications. The optical vortex generator is an essential component to facilitate OAM-enabled optical communications. Traditional devices face challenges of limited compactness, narrow bandwidth, and first-order OAM modes. Here, using the direct-binary search (DBS) optimization algorithm, we design, fabricate, and demonstrate a digitized subwavelength surface structure on silicon platform for the generation of wavelength-/polarization-/charge-diverse optical vortices. It features an ultra-compact footprint (∼3.6 × 3.6 μm2) and ultra-wide bandwidth (1480–1630 nm), supporting two polarizations (x-pol., y-pol.) and high-order OAM modes (OAM+1, OAM−1, OAM+2, OAM−2) with high purity of larger than 84%. The mode crosstalk matrix is measured in the experiment with favorable performance. When generating x-pol. OAM+1, x-pol. OAM−1, y-pol. OAM+1, and y-pol. OAM−1 mode, the crosstalk of the worst case is less than −14 dB. When generating OAM+1, OAM−1, OAM+2, and OAM−2 mode, the crosstalk between any two OAM modes is less than −10 dB, and the lowest crosstalk is about −17 dB. In addition, we also show the possibility for generating much higher-order OAM modes (e.g. OAM+3, OAM−3, OAM+4, and OAM−4) with the digitized subwavelength surface structure. The wavelength-/polarization-/charge-diverse optical vortex generator enables the full access of multiple physical dimensions (wavelength, polarization, space) of lightwaves. The demonstrations may open up new perspectives for chip-scale solutions to multi-dimensional multiplexing optical communications.

We report on subwavelength reflective gratings for hyperspectral applications operating in a very large spectral band (340–1040 nm). Our study concerns a blazed-binary grating having a period of 30 μm and composed of 2D subwavelength structures with size from 120 nm to 350 nm. We demonstrate the manufacturing of the gratings on 3″ wafers by two lithography technologies (e-beam and nanoimprint) followed by classical dry etching process. Optical measurements show that the subwavelength grating approach enables a broadband efficiency, polarization behaviour and wavefront quality improvement with respect to the requirements for the next generation of spectro-imagers for Earth observation missions. An outlook towards spherical substrate based on nanoimprint lithography is also reported with the results of mixed features replication (holes and pillars in the range of 160–330 nm) on a 540 mm concave substrate which demonstrate uniformity and accuracy capabilities over 3″ surface. [ABSTRACT FROM AUTHOR]

Metalens has emerged as an important optical block in free-space optical systems, which shows excellent performance. Even the metalens based on gradient index (GRIN) profiles can be implemented for on-chip beam focusing behavior. However, for most previous schemes, the GRIN metalenses can only achieve on-chip beam focusing behavior in one dimension, which limits their applications in low-loss waveguide interconnecting or fiber-to-chip coupling. In this paper, an on-chip half Maxwell’s fisheye lens based on GRIN profiles with subwavelength features, integrated with silicon waveguides, is experimentally demonstrated. Benefitting from the index distribution and beam focusing characteristics of the half Maxwell’s fisheye lens, an on-chip beam transforming can be achieved for transverse electric (TE) fundamental mode in two waveguides with different heights and widths. The simulated 1 dB bandwidth can reach 1100 nm, which exhibits great prospects in integrated photonic circuits. The measured insertion loss of an on-chip 5.4 μm-length lens is less than 1 dB to connect a 220 nm-height, 8 μm-wide waveguide, and a 60 nm-height, 0.5 μm-wide waveguide in the wavelength range of 1280–1620 nm.

At nano-scale new phenomena have been discovered, allowing devices’ miniaturisation, energy harvesting, and power reduction. The Extraordinary Optical Transmission (EOT) phenomenon was reported in 1998 by Ebessen, who stated that the resonant peaks in the response of metallic nano antennas were more intense than predicted by classical diffraction theories. Years later, the main reason for this behaviour was attributed to the Surface Plasmon Polaritons (SPP), at least in ultraviolet and visible regions. In this article, a new method to model the radiation-matter interaction on a dielectric-metal interface is proposed, based on Maxwell’s equations and Fresnel Coefficients in absorbing media. Transmission percentage, angle and propagation length are obtained for a rigorous sweep on incident angle and wavelength. The results taken using some noble metals allow us to observe the presence of surface phenomena at expected SPP resonances. First, it is noticeable huge values of transmission in ultraviolet and visible regions, meaning that the metal does not reflect all the radiation. Also, the transmission angle tends to be higher, meaning huge surface components. Furthermore, the transmission length is on orders of 50-100 nm, meaning that phenomena as EOT only occurs at the nano-scale, since waves should arrive at another interface before being absorbed.

Multi-wavelength imaging ability is important for bio-imaging, to obtain multi-modal information of biological activities. We propose a multi-wavelength super-resolution imaging method, employing the Bloch surface waves (BSWs) supported by one-dimensional photonic crystal as subwavelength structured illumination fields. Here 488 nm (blue), 532 nm (green), and 632.8 nm (red) are chosen as the illumination wavelengths, and a two-dimensional equilateral triangular grating is designed to couple the incident plane waves to the BSWs in the all-dielectric photonic crystal. The triangular grating ensures a more uniform resolution improvement along with whole lateral directions and provides better imaging quality compared with lattice grating. In our demonstration, the resolution improvements are above 2.4 fold for the three wavelengths, and lateral resolutions are below 120 nm in the Rayleigh criterion. Moreover, as the illumination device is composed of a periodic planar structure, the larger field of view is achievable. The proposed method could achieve multi-wavelength wide-field super-resolution surface imaging while maintaining high speed, good imaging quality and bio-compatibility.

Grating couplers (GCs) are important for light to couple between optical fibers and photonic integrated circuits (PICs). The Bound State in Continuum (BIC) waveguides offer new functionalities for PIC. High-Q resonators, electro-optical modulator, and photodetectors can be built on it without etching steps. Due to the special waveguide geometry of BIC waveguides, a high efficiency GC is still missing. In this work, we demonstrated a subwavelength grating (SWG) GC for BIC waveguide with a coupling efficiency of 8 dB and a 1 dB bandwidth >70 nm. The device shows ultra-broadband behavior which is extremely useful for BIC-based PICs.

With the traditional multilayers coating, it is difficult to achieve broadband and wide-angle antireflection optical properties simultaneously. As one of the most promising candidates for omnidirectional and broadband antireflection coating, the moth-eye structure has gained considerable attention in the past several decades because of its excellent optical performance and self-cleaning function. The challenges in the use of this technology, namely, its manufacturing cost and mechanical structural stability, limit its popularization. In this paper, a moth-eye structure surface combined with a residual layer of an identical material is proposed; the proposed composite structure can be formed by a one-step process of half-etched technology. For the design and optimization of the composite moth-eye structure, composite structures were compared by performing effective medium approximation (EMA) and rigorous coupled– wave analysis (RCWA). The structural parameters of the micro–nano surface were optimized to increase the mechanical stability considerably. The results showed that the optimized composite moth-eye structure has high transmittance for incident angles from 0° to 80° in the infrared spectrum. Furthermore, the transmission diffraction at high orders was suppressed efficiently at super-wide incident angles.

We propose a 1310/1550 nm wavelength diplexer on a 220-nm silicon-on-insulator (SOI) platform. The device is based on a compact two-mode interference (TMI) coupler enabled by a subwavelength grating (SWG) slot. The ideal beat length ratio of 2:1 is achieved with the transverse magnetic (TM) mode by fine-tuning the SWG slot parameters, resulting in a TMI length of only 37 µm. We reveal that the key to high extinction ratio (ER) is the careful design of the tapers, and the device achieves high ERs of 28.05/42.54 dB at 1310/1550 nm with simulation. The measured bandwidths for ER $>$ 15 dB are 82 nm and 56 nm at O- and C-band. Moreover, the design guarantees large calculated 1-dB-insertion-loss (IL) bandwidths of 192/123 nm at 1310/1550 nm. To the best of our knowledge, this is the first experimental demonstration of a high-performance compact silicon 1310/1550 nm diplexer based on a TMI coupler.

We propose a graphene plasmonic structure by applying two graphene layers mingled with a thin gold layer in a silicon grating. By utilizing the finite-difference time-domain (FDTD) method, we investigate the optical response of the system, and observe that the design achieves dual tunable electromagnetically induced transparency (EIT)-like effect at terahertz frequencies. The EIT-like effect arises from the destructive interference between the grapheme-layer bright modes and the gold-layer dark mode. The EIT-like phenomenon can be adjusted by the Fermi level, which is related to the applied voltage. The results show that the group delay of the present structure reaches 0.62 ps in the terahertz band, the group refractive index exceeds 1200, the maximum delay-bandwidth product is 0.972, and the EIT-like peak frequency transmittance is up to 0.89. This indicates that the device has good slow light performance. The proposed structure might enable promising applications in slow-light devices. [ABSTRACT FROM AUTHOR]

We report an inverse-designed, high numerical aperture (∼0.44), extended depth of focus (EDOF) meta-optic, which exhibits a lens-like point spread function (PSF). The EDOF meta-optic maintains a focusing efficiency comparable to that of a hyperboloid metalens throughout its depth of focus. Exploiting the extended depth of focus and computational post processing, we demonstrate broadband imaging across the full visible spectrum using a 1 mm, f/1 meta-optic. Unlike other canonical EDOF meta-optics, characterized by phase masks such as a log-asphere or cubic function, our design exhibits a highly invariant PSF across ∼290 nm optical bandwidth, which leads to significantly improved image quality, as quantified by structural similarity metrics.

Grating couplers (GCs) are important for light to couple between optical fibers and photonic integrated circuits (PICs). The Bound State in Continuum (BIC) waveguides offer new functionalities for PIC. High-Q resonators, electro-optical modulator, and photodetectors can be built on it without etching steps. Due to the special waveguide geometry of BIC waveguides, a high efficiency GC is still missing. In this work, we demonstrated a subwavelength grating (SWG) GC for BIC waveguide with a coupling efficiency of 8 dB and a 1 dB bandwidth >70 nm. The device shows ultra-broadband behavior which is extremely useful for BIC-based PICs. [ABSTRACT FROM AUTHOR]

For example, in Ref. [[19]] the reported achromatic metalenses have a diameter of HT ht and an NA of HT ht . [Extracted from the article]

Structured illumination microscopy (SIM) is one of the most powerful and versatile super-resolution methods due to its live-cell imaging ability of subcellular structures with high speed. In this paper, we propose an alternative SIM assisted by Bloch surface wave (BSW). Through replacing the conventional laser interference fringes with sub-diffraction BSW counterparts with higher spatial frequency, the imaging resolution of SIM could be enhanced greatly and the super-resolution imaging capability down to 80 nm could be achieved. Compared with traditional wide-field fluorescence microscopy, this BSW SIM demonstrates 2.78 times enhancement in imaging resolution, which surpasses general SIM with only 2 times improvement. Moreover, the structured illumination intensity could be boosted drastically, which is beneficial to nonlinear super-resolution imaging techniques, such as saturated SIM. This BSW SIM would provide a super-resolution, wide field of view approach for surface super-resolution fluorescent imaging while maintaining high imaging speed and good bio-compatibility.

The applicability of resonant waveguide grating (RWG)-based structures as filters to control the spectral response in an optical communication system is investigated. A new physical model for the structure is established on the basis of the Fabry–Pérot (FP) etalon model and coupled leaky mode theory (CLMT). It is found that the flat-top spectral response of the filter is achieved by the combined effect of the guided-mode resonance of an RWG and its Fabry–Pérot resonance (FPR). The bandwidth-tunable spectral response of the filter can be varied according to the change in the eigenvalues of the RWG by changing the structural parameters such as strip width of the grating and incident angle. The flat-top and bandwidth-tunable RWG-based resonant filter is a promising application for high-performance optical communication systems.

We propose a coupled-tolerant subwavelength photonic racetrack resonator (PRR) on the silicon-on-insulator (SOI) platform, in which a subwavelength grating (SWG) PRR is coupled to a symmetrical SWG bus waveguide. The material equivalent refractive index can be manipulated by the SWG characteristic and thus an additional fabrication degree of freedom can be achieved. The resonant characteristics can be improved significantly by controlling the pillar size and increasing the interaction length between SWG racetrack and bus waveguide (RBW). The simulation results show that the PRR has a high-quality factor and large extinction ratio around 1550nm. Two groups of SWG and strip waveguide (SW) PRRs are fabricated. The fabrication tolerance is tested when fabrication error is changed from 0 to 20 nm and the quality factor is more than 7000 in de-ionized water. The testing results show that the tolerance in SWG-PRR has a 2.0-fold improvement than that in the SW-PRR. Then a fabricated SWG-PRR is employed to monitor different concentration glycerol injected on the chip. An optimal quality factor of 9500 around 1550 nm and bulk sensitivity of 412± 0.5 nm/RIU are achieved. Therefore, the structure is a potential candidate for label-free sensing in medical diagnosis and environmental monitoring.

An independently tunable dual-resonance hybrid structure incorporating graphene is proposed to achieve selective light trapping and response tuning in the visible and near-infrared band. The incident light with different wavelengths are intensely localized in two separated resonant cavities via the synergetic effect of the guided mode resonances (GMRs) and optical Tamm states (OTSs), which leads to the strong enhancement of the light-matter interaction of graphene in different parts of the structure. The dual-band perfect absorption associated with critical coupling is achieved, whereas the two resonant modes can be independently tuned by adjusting the corresponding structural parameters. Furthermore, by dynamically changing the permittivity of the resonant cavities or the chemical potential of graphene, the absorption wavelength can be continuously adjusted and the absorption efficiency can be regulated stepwise.

An independently tunable dual-resonance hybrid structure incorporating graphene is proposed to achieve selective light trapping and response tuning in the visible and near-infrared band. The incident light with different wavelengths are intensely localized in two separated resonant cavities via the synergetic effect of the guided mode resonances (GMRs) and optical Tamm states (OTSs), which leads to the strong enhancement of the light-matter interaction of graphene in different parts of the structure. The dual-band perfect absorption associated with critical coupling is achieved, whereas the two resonant modes can be independently tuned by adjusting the corresponding structural parameters. Furthermore, by dynamically changing the permittivity of the resonant cavities or the chemical potential of graphene, the absorption wavelength can be continuously adjusted and the absorption efficiency can be regulated stepwise. [ABSTRACT FROM AUTHOR]

Self-accelerating beams show considerable captivating phenomena and applications owing to their transverse acceleration, diffraction-free and self-healing properties in free space. Metasurfaces consisting of dielectric or metallic subwavelength structures attract enormous attention to acquire self-accelerating beams, owing to their extraordinary capabilities in the arbitrary control of electromagnetic waves. However, because the self-accelerating beam generator possesses a large phase gradient, traditional discrete metasurfaces suffer from insufficient phase sampling, leading to a low efficiency and narrow spectral band. To overcome this limitation, a versatile platform of catenary-inspired dielectric metasurfaces is proposed to endow arbitrary continuous wavefronts. A high diffraction efficiency approaching 100% is obtained in a wide spectral range from 9 to 13 μm. As a proof-of-concept demonstration, the broadband, high-efficiency and high-quality self-accelerating beam generation is experimentally verified in the infrared band. Furthermore, the chiral response of the proposed metasurfaces enables the spin-controlled beam acceleration. Considering these superior performances, this design methodology may find wide applications in particle manipulation, high-resolution imaging, optical vortex generation, and so forth.

Abstract The efficiency of optical power transferred between two bidimensional waveguides, continuous waveguide and periodic subwavelength waveguide has been designed and optimized by using a taper composed by variable length segments (0.03 − 0.27 µm). Waveguides with variable width (270 − 330 nm) have been considered and the number of segments on the taper region has been varied from 10 to 15. The optimized taper was efficiently designed using bio-inspired algorithms based on the genetic algorithms and the artificial immune system. The power coupled has been computed using the frequency domain finite element method. The best solution is 20% shorter than previously existent tapers with coupling light efficiency above 90% over a broadband interval of frequencies and it exhibits high fabrication error tolerances.

A mid-infrared (mid-IR) dual-band filter with ultra-high resolving power is designed and numerically investigated. It is composed of an Al2O3 layer between a gold grating and a CaF2 substrate. Each unit cell of the grating consists of two gold strips with different heights. The filter provides two high-extinction ultra-narrow stop bands. One is at a wavelength of ~3.8392 μm with a full-width at half-maximum (FWHM) of ~0.8 nm, and the other is at a wavelength of ~3.8435 μm with a FWHM of ~1.8 nm. The resolving power of the filter is >2100. The two stop bands result from the (+1) and (-1) waveguide modes, respectively. An interaction between the two resonance modes exists and affects the stop bands. We can control the interaction by adjusting the grating parameters, thus designing the FWHMs and lineshapes of the two stop bands flexibly.

This paper deals with the optimization of photonic structures, specifically waveguide couplers between a continuous waveguide (CWG) and a periodically segmented waveguide (PSW). For this purpose, a numerical technique called finite element method (FEM) is used in conjunction with an adapted optimization technique called Scatter Search (SS). In this work the possibilities of finding high coupling efficiencies are extended through the creation of adaptations to the Scatter Search algorithm and the enormous amount of solutions generated to be evaluated by such procedure. The results have showed that the adaptation of the technique is valid for optimization of tapers.

In recent years, with the development of photonic crystals, metamaterials, metasurfaces, and other related disciplines, the relationship between the structures and functionalities of artificial optical/electromagnetic materials and devices has become a research hotspot. This article reviews the optical/electromagnetic properties and performance of typical artificial micro/nanostructures. Based on the analogy of mechanics and optics/electromagnetism, the concept of “Electromagnetic Architectures” is proposed. In particular, we reviewed several typical methods for the study of optical/electromagnetic structural‐functional relationships, including semi‐classical analytical models, heuristic optimization methods, deep neural networks, topological optimization methods, etc. The viewpoint of this paper may push further researches on the structural‐functional relationship of artificially structured materials and devices, and find broad application prospects in imaging, communication, photonic chips, among many others.

We propose a graphene plasmonic structure by applying two graphene layers mingled with a thin gold layer in a silicon grating. By utilizing the finite-difference time-domain (FDTD) method, we investigate the optical response of the system, and observe that the design achieves dual tunable electromagnetically induced transparency (EIT)-like effect at terahertz frequencies. The EIT-like effect arises from the destructive interference between the grapheme-layer bright modes and the gold-layer dark mode. The EIT-like phenomenon can be adjusted by the Fermi level, which is related to the applied voltage. The results show that the group delay of the present structure reaches 0.62 ps in the terahertz band, the group refractive index exceeds 1200, the maximum delay-bandwidth product is 0.972, and the EIT-like peak frequency transmittance is up to 0.89. This indicates that the device has good slow light performance. The proposed structure might enable promising applications in slow-light devices.

Photovoltaic technology is currently at the heart of the energy transition in our pursuit to lean off fossil-fuel-based energy sources. Understanding the workings and trends of the technology is crucial, given the reality. With most conventional PV cells constrained by the Shockley–Queisser limit, new alternatives have been developed to surpass it. One of such variations are heterojunction cells, which, by combining different semiconductor materials, break free from the previous constraint, leveraging the advantages of both compounds. A subset of these cells are multi-junction cells, in their various configurations. These build upon the heterojunction concept, combining several junctions in a cell—a strategy that has placed them as the champions in terms of conversion efficiency. With the aim of modelling a multi-junction cell, several optic and optoelectronic models were developed using a Finite Element Tool. Following this, a study was conducted on the exciting and promising technology that are nanoantenna arrays, with the final goal of integrating both technologies. This research work aims to study the impact of the nanoantennas’ inclusion in an absorbing layer. It is concluded that, using nanoantennas, it is possible to concentrate electromagnetic radiation near their interfaces. The field’s profiles might be tuned using the nanoantennas’ geometrical parameters, which may lead to an increase in the obtained current.

The paper proposes a method for calculating the phase function of subwavelength diffractive optical elements. The method is based on diffraction gratings with a varying period for generating vector beams with arbitrary-order cylindrical polarization. Formulas for the phase function of the grating are obtained with due regard for the period variation for increasing the efficiency of the polarization conversion of the incident beam. The obtained phase functions are supposed to be used for creating polarization-conversion diffractive optical elements for noise-resistant optical communication systems.

We present the realization of a high-efficiency, compact, and thermally tunable unidirectional launcher of surface plasmon polaritons (SPPs) in a double-slit structure filled with phase change materials (PCMs). PCMs such as VO2 provide a feasible way for tailoring optical properties, particularly refractive index as a function of heat. By introducing a narrow hybrid dielectric layer beneath the slits, SPPs couple efficiently into waveguide mode and propagate within the slot waveguide with considerably high intensity. Our simulation results revealed up to 80% coupling efficiency into the slot waveguide with extinction ratio of 1:800 between the left and the right slots can be achieved at telecommunication wavelength for normally incident P-polarized light. By heating the coupler above the VO2 phase transition temperature, the coupling and consequently the crosstalk approaches zero. Propagation length and other properties of the structure are characterized to confirm the feasibility of the coupler. This approach of unidirectional coupling into slot waveguides may lead to the development of integrated plasmonic circuits and on-chip applications.

In this paper, we report a new and generic method for all-dielectric resonators operating at terahertz (THz) frequencies based on polymer/ceramic composite particles. In this method, the polymer solution is added into ceramic powders (strontium titanate) and prilling technology is employed to make them become polymer/ceramic composite micro particles. The prepared micro particles are then assembled as single-layer all-dielectric resonators. By using a THz time-domain spectrometer, we find that various Mie resonances can be induced in these all-dielectric resonators. It is also demonstrated that the permittivity of the composite particles can be improved by being sintered at proper temperatures, thereby provides a new way for ceramic all-dielectric resonators in THz range. This method, free from complex process, time-consuming, expensive equipment, and clean room, provides a generic method for high-throughput and low cost THz all-dielectric resonators, which is promising for developing potential applications in wide-bandwidth THz devices.

The applicability of resonant waveguide grating (RWG)-based structures as filters to control the spectral response in an optical communication system is investigated. A new physical model for the structure is established on the basis of the Fabry–Pérot (FP) etalon model and coupled leaky mode theory (CLMT). It is found that the flat-top spectral response of the filter is achieved by the combined effect of the guided-mode resonance of an RWG and its Fabry–Pérot resonance (FPR). The bandwidth-tunable spectral response of the filter can be varied according to the change in the eigenvalues of the RWG by changing the structural parameters such as strip width of the grating and incident angle. The flat-top and bandwidth-tunable RWG-based resonant filter is a promising application for high-performance optical communication systems. [ABSTRACT FROM AUTHOR]

Structured illumination microscopy (SIM) is one of the most powerful and versatile super-resolution methods due to its live-cell imaging ability of subcellular structures with high speed. In this paper, we propose an alternative SIM assisted by Bloch surface wave (BSW). Through replacing the conventional laser interference fringes with sub-diffraction BSW counterparts with higher spatial frequency, the imaging resolution of SIM could be enhanced greatly and the super-resolution imaging capability down to 80 nm could be achieved. Compared with traditional wide-field fluorescence microscopy, this BSW SIM demonstrates 2.78 times enhancement in imaging resolution, which surpasses general SIM with only 2 times improvement. Moreover, the structured illumination intensity could be boosted drastically, which is beneficial to nonlinear super-resolution imaging techniques, such as saturated SIM. This BSW SIM would provide a super-resolution, wide field of view approach for surface super-resolution fluorescent imaging while maintaining high imaging speed and good bio-compatibility. [ABSTRACT FROM AUTHOR]

In this work, we design a plasmonic metasurface as an optical refractive index sensor with high sensitivity and switching characteristics for the mid-infrared spectral region by employing organic material with reconfigurable attributes. This structure contains a cross element at the center which is surrounded by a frame with four similar rectangular parasitic elements at each corner. The parasitic elements as plasmonic absorbers are exploited for concentrating energy and reducing the reflection from the metasurface. This plasmonic absorber is utilized to improve the figure of merit (FOM) and sensitivity of the sensor because of the semi-Fano characteristic of the reflection response. Organic materials are being employed in this technique to design the absorber due to their distinct switching characteristics inside the gaps between the parasitic elements and cross frame which can be considered for controlling electric field distribution and reflection of the metasurface. The use of organic materials reduces the reflection of the metasurface about −11 dB in comparison to the primary model without organic material. In fact, the equivalent circuit and electric field can be highlighted to describe the features of this absorber and the DNA load effects. The switching ratio is obtained 42 times, and this absorber is modified for 110 THz with a reflection of −32 dB, and the FOM obtained for the sensor is 51 RIU−1, with linear variation and sensitivity of 2440 nm/RIU. [ABSTRACT FROM AUTHOR]

We analyze the theoretical and physical properties of a CMOS compatible optical leaky wave antenna (OLWA) integrated into a Fabry-Pérot resonator (FPR) at 193.4 THz (wavelength ?0 = 1550 nm). The presented OLWA design is composed of a silicon (Si) dielectric waveguide sandwiched between two silica glass (SiO2) domains, and it comprises periodic perturbations (cavities of vacuum). We first describe the radiation of the isolated OLWA whose radiation pattern is due to the excitation of a leaky wave, slowly decaying while traveling. The perturbations are indeed designed to obtain a leaky wave harmonic with very low attenuation and phase constants. Then, we integrate the same OLWA into a FPR where two leaky waves with the same wavenumber are travelling in opposite directions inside the resonator. We show that the radiation level at the broadside direction can be effectively controlled by modifying the optical properties of the Si waveguide through electron-hole excess carrier generation (found to be highly enhanced when it is integrated into a FPR). The design of the integrated OLWA is properly set to guarantee the constructive interference of the two radiated beams provided by the two leaky waves in the FPR. The modal propagation constant in the integrated OLWA can be then altered through excess carrier generation in Si, thus the antenna can be tuned in and out of the resonance thanks to the high FPR quality factor, and the LW modal dispersion relation. This allows for enhanced radiation level control at broadside, and preliminary results show up to 13 dB beam modulation. © 2012 SPIE.

We analyze the theoretical and physical properties of a CMOS compatible optical leaky wave antenna (OLWA) integrated into a Fabry-Pérot resonator (FPR) at 193.4 THz (wavelength ?0 = 1550 nm). The presented OLWA design is composed of a silicon (Si) dielectric waveguide sandwiched between two silica glass (SiO2) domains, and it comprises periodic perturbations (cavities of vacuum). We first describe the radiation of the isolated OLWA whose radiation pattern is due to the excitation of a leaky wave, slowly decaying while traveling. The perturbations are indeed designed to obtain a leaky wave harmonic with very low attenuation and phase constants. Then, we integrate the same OLWA into a FPR where two leaky waves with the same wavenumber are travelling in opposite directions inside the resonator. We show that the radiation level at the broadside direction can be effectively controlled by modifying the optical properties of the Si waveguide through electron-hole excess carrier generation (found to be highly enhanced when it is integrated into a FPR). The design of the integrated OLWA is properly set to guarantee the constructive interference of the two radiated beams provided by the two leaky waves in the FPR. The modal propagation constant in the integrated OLWA can be then altered through excess carrier generation in Si, thus the antenna can be tuned in and out of the resonance thanks to the high FPR quality factor, and the LW modal dispersion relation. This allows for enhanced radiation level control at broadside, and preliminary results show up to 13 dB beam modulation. © 2012 SPIE.