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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Optical Resonances in a 3D Superlattice of Photonic Band Gap Cavities
摘要： The confinement of light in three dimensions (3D) is an active research topic in Nanophotonics, since it allows for ultimate control over photons [1]. A powerful tool to this end is a 3D photonic band gap crystal with a tailored defect that acts as a cavity or even a waveguide [2]. When a one-dimensional array of cavities is coupled, an intricate waveguiding system appears, known as a CROW (coupled resonator optical waveguide) [3]. Remarkably, 3D superlattices of coupled cavities that resonate inside a 3D band gap have not been studied to date. Recently, theoretical work has predicted the occurrence of “Cartesian light”, wherein light propagates by hopping only in high symmetry directions in space [4]. This represents the optical analog of the Anderson model for spins or electrons that is relevant for neuromorphic computing and may lead to intricate lasing [5]. To experimentally study the propagation of light in a 3D superlattice of band gap cavities, we have fabricated 3D nanostructures from silicon by reactive ion etching (see Fig. 1). The photonic crystal has the cubic diamond-like inverse woodpile structure that is composed of two perpendicular sets of pores (in the X and Z directions) [6] and that reveals a broad 3D photonic band gap. By intentionally making two proximal perpendicular pores smaller, light is confined at their intersection, thus forming a cavity [7]. By fabricating two arrays of defect pores (see Fig. 1) we realize a 3D cavity superlattice. The challenge we address here is to experimentally identify resonances in this complex system. We measure reflectivity of the crystals with a large aperture (NA = 0.85) for both s and p-polarizations. With our setup we also record lateral scattered light, i.e., light that is input in the Z-direction, scattered, and detected in the X-direction. In presence of the intentional defects, we observe troughs in the stop band in reflectivity. The corresponding lateral scattering spectrum shows peaks in the stopband at the same frequencies as the reflectivity troughs, see Fig. 2. To distinguish cavity resonances from random speckle, we record several spectra at different locations on the crystal. Peaks reproducing at the same frequencies are attributed to light scattered from the cavity resonances. The appearance of the scattering peaks strongly depends on polarization in conformity with numerical calculations [7]. We now extend the numerical work to the range of pore sizes probed experimentally.
关键词： nanophotonics,Cartesian light,3D photonic band gap,cavity superlattice,coupled resonator optical waveguide
更新于2025-09-12 10:27:22
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[IEEE 2019 International Workshop on Fiber Optics in Access Networks (FOAN) - Sarajevo, Bosnia and Herzegovina (2019.9.2-2019.9.4)] 2019 International Workshop on Fiber Optics in Access Networks (FOAN) - Realization of sucrose sensor using photonic waveguide: An application to biophotonics
摘要： A photonic waveguide sensor is explored in the present paper for effective sensing of sucrose concentration in an aqueous solution at a wavelength of 1550 nm by employing a 1-D photonic waveguide structure. The proposed structure comprises three layers, out of which odd layers are considered to be an InAs compound semiconductor having thickness of 700nm each whereas an even layer is air having thickness of 300 nm. Additionally, the effect of concentration variation of sucrose is theoretically examined with reference to reflected intensity, diffraction loss and transmitted intensity at the aforementioned waveguide. Reflected intensity from the said structure is computed through band gap analysis by a manipulating finite difference time domain (FDTD) technique, whereas diffraction loss and transmitted intensity are computed through numerical formulations. Further, simulation for diffraction loss with respect to different sucrose concentration has been carried out and interestingly the upshots revealed logarithmic deviation of diffraction efficiency with reference to variation in sucrose concentration from 10 gm/100ml to 70 gm/100ml. Apart from this, it is also revealed that there exists noteworthy shifts in both reflected as well as transmitted intensity with rise in sucrose concentration. Additionally, it is affirmed that both reflected light intensity and transmitted light intensity can be nicely fitted linear relationship having R2=0.998 and with a precise R2=0.9919 respectively, which claim an accurate sensing of sucrose concentration by using the proposed semiconductor based photonic waveguide and find applications in biophotonics.
关键词： band gap,sucrose sensing,photonic waveguide,FDTD
更新于2025-09-12 10:27:22
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Synthesis and Photovoltaic Effect of Electron-Withdrawing Units for Low Band Gap Conjugated Polymers Bearing Bi(thienylenevinylene) Side Chains
摘要： A novel (E)-5-(2-(5-alkylthiothiophen-2-yl)vinyl)thien-2-yl (TVT)-comprising benzo[1,2-b:4,5-b’]dithiophene (BDT) derivative (BDT-TVT) was designed and synthetized to compose two donor-acceptor (D-A) typed copolymers (PBDT-TVT-ID and PBDT-TVT-DTNT) with the electron-withdrawing unit isoindigo (ID) and naphtho[1,2-c:5,6-c’]bis[1,2,5]thiadiazole (NT), respectively. PBDT-TVT-ID and PBDT-TVT-DTNT showed good thermal stability (360 °C), an absorption spectrum from 300 nm to 760 nm and a relatively low lying energy level of Highest Occupied Molecular Orbital (EHOMO) (?5.36 to –5.45 eV), which could obtain a large open-circuit voltage (Voc) from photovoltaic devices with PBDT-TVT-ID or PBDT-TVT-DTNT. The photovoltaic devices with ITO/PFN/polymers: PC71BM/MoO3/Ag structure were assembled and exhibited a good photovoltaic performance with a power conversion efficiency (PCE) of 4.09% (PBDT-TVT-ID) and 5.44% (PBDT-TVT-DTNT), respectively. The best PCE of a PBDT-TVT-DTNT/PC71BM-based device mainly originated from its wider absorption, higher hole mobility and favorable photoactive layer morphology.
关键词： polymer solar cells,photovoltaic property,benzo[1,2-b:4,5-b’]dithiophene,low band gap,bi(thienylenevinylene)
更新于2025-09-11 14:15:04
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[IEEE 2019 21st International Conference on Transparent Optical Networks (ICTON) - Angers, France (2019.7.9-2019.7.13)] 2019 21st International Conference on Transparent Optical Networks (ICTON) - Simulations of LED Patterned with IP-DIP Woodpile Structure
摘要： In this paper, we present simulations of three-dimensional (3D) photonic crystal structure (PhC) in IP-Dip polymer. We investigated woodpile structure and LED patterned by woodpile structure by various simulation methods. Structure was designed by the computer aided design (CAD) and optical properties were simulated by finite-difference time-domain (FDTD) and rigorous coupled-wave analyses (RCWA) simulation methods. We are focused on diffraction of optical radiation by woodpile structure and possibility of influencing extraction ratio and radiation patterns of LED with patterned woodpile structure. There is improving a significant percentage of transmittance of the radiation. It results in the influence of the radiation from the LED and it has positive impact on the LED parameters.
关键词： photonic crystal,simulations,3D woodpile structure,light extraction,photonic band gap,radiation pattern
更新于2025-09-11 14:15:04
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Quantitative Analysis of Photon Density of States for One-Dimensional Photonic Crystals in a Rectangular Waveguide
摘要： Light propagation in one-dimensional (1D) photonic crystals (PCs) enclosed in a rectangular waveguide is investigated in order to achieve a complete photonic band gap (PBG) while avoiding the difficulty in fabricating 3D PCs. This work complements our two previous articles (Phys. Rev. E) that quantitatively analyzed omnidirectional light propagation in 1D and 2D PCs, respectively, both showing that a complete PBG cannot exist if an evanescent wave propagation is involved. Here, we present a quantitative analysis of the transmission functions, the band structures, and the photon density of states (PDOS) for both the transverse electric (TE) and transverse magnetic (TM) polarization modes of the periodic multilayer heterostructure confined in a rectangular waveguide. The PDOS of the quasi-1D photonic crystal for both the TE and TM modes are obtained, respectively. It is demonstrated that a “complete PBG” can be obtained for some frequency ranges and categorized into three types: (1) below the cutoff frequency of the fundamental TE mode, (2) within the PBG of the fundamental TE mode but below the cutoff frequency of the next higher order mode, and (3) within an overlap of the PBGs of either TE modes, TM modes, or both. These results are of general importance and relevance to the dipole radiation or spontaneous emission by an atom in quasi-1D periodic structures and may have applications in future photonic quantum technologies.
关键词： TE,PDOS,photonic crystals,waveguide,photonic band gap,TM,complete PBG
更新于2025-09-11 14:15:04
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Optical and structural investigation of synthesis ZnO/Ag Nanoparticles prepared by laser ablation in liquid
摘要： ZnO/Ag nanoparticle was synthesis by using pulsed laser ablation in liquid with various Ag doped at a time of 1, 3, and 5 min. Characterization was carried out with UV–Vis (UV–Visible) Spectrometer, PL 325 (Photoluminescence 325) spectrometer, XRD (X-Ray di?raction), and TEM (transmission electron microscopy). The enhancement of dopant time, the band gap value decrease from 3,021 eV to 2,781 eV and the wavelength peak position was shifted to the red shift which can transform the structure of ZnO nanoparticles and can be applied as food packaging in the future.
关键词： TEM,ZnO/Ag nanoparticles,Laser ablation,Photoluminescence,Band gap
更新于2025-09-11 14:15:04
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Emergence of point defect states in a plasmonic crystal
摘要： Plasmonic crystals are well known to have band structure including a band gap, enabling the control of surface plasmon propagation and con?nement. The band dispersion relation of bulk crystals has been generally measured by momentum-resolved spectroscopy using far ?eld optical techniques while the defects introduced in the crystals have separately been investigated by near ?eld imaging techniques so far. Particularly, defect related energy levels introduced in the plasmonic band gap have not been observed experimentally. In order to investigate such a localized mode, we performed electron energy-loss spectroscopy (EELS) on a point defect introduced in a plasmonic crystal made up of ?at cylinders protruding out of a metal ?lm and arranged on a triangular lattice. The energy level of the defect mode was observed to lie within the full band-gap energy range. This was con?rmed by a momentum-resolved EELS measurement of the band gap performed on the same plasmonic crystal. Furthermore, we experimentally and theoretically investigated the emergence of the defect states by starting with a corral of ?at cylinders protrusions and adding sequentially additional shells of those in order to eventually form a plasmonic band-gap crystal encompassing a single point defect. It is demonstrated that a defectlike state already forms with a crystal made up of only two shells.
关键词： point defect,band gap,Plasmonic crystals,momentum-resolved spectroscopy,electron energy-loss spectroscopy
更新于2025-09-11 14:15:04
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Structural, optical and electrical studies of DC-RF magnetron co-sputtered Cu, In & Ag doped SnS thin films for photovoltaic applications
摘要： This work reports the tuning of optical and electrical properties of SnS through the incorporation of Cu, In and Ag atom without altering its chemical and crystal structural properties, using DC-RF magnetron co-sputtering technique with an in-situ substrate temperature of 400 °C. Doping is increased up to ~10% by varying the DC sputtering voltage as evident from EDAX analysis. Morphological studies show the variation in surface morphology, particle size and surface roughness due to the incorporation of dopant cation into SnS lattice sites. Film with optimized doping of ~5% resulted the substitutional doping of dopant cations (Cu2+, In3+ and Ag2+) into SnS lattice sites which resulted an improved absorption coefficient and hall carrier concentration with a decrease in band gap and electrical resistivity. Hall measurement studies of Cu 4.8% doped SnS film shows the p-type conductivity with lowest electrical resistivity of 90 Ω cm and improved carrier concentration of 1017 cm?3.
关键词： SnS thin films,Optical energy band gap,Co-sputtering,Electrical resistivity,Phase formation
更新于2025-09-11 14:15:04
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Photodetector based on heterostructure of two-dimensional WSe2/In2Se3
摘要： Heterojunctions formed by two-dimensional (2D) layered semiconducting materials have been studied extensively in the past several years. These van der Waals (vdW) structures have shown great potential in future electronic and optoelectronic devices. However, the optoelectronic performance of these devices is limited by the indirect band gap of the multilayer materials and low light absorption of single layer materials. Here, we fabricate photodetectors based on heterojunctions composed of n-type multilayer α-Indium Selenide (In2Se3) and p-type Tungsten Diselenide (WSe2) for the first time. The direct band gap of multilayer α-In2Se3 and type-II band alignment of the WSe2/In2Se3 heterojunction enable high optoelectronic performance of the devices at room temperature in the air. Without light illumination, the dark current is effectively suppressed to 10-13 A under -1 V bias and a high rectification ratio of 7.37×103 is observed. Upon laser illumination with the wavelength of 650 nm, the typical heterojunction device exhibits a photocurrent on/off ratio exceeding 1.24×105, a maximum photo responsivity of 26 mA/W and short photoresponse time of 2.22 ms. Moreover, the heterojunction photodetectors show obvious light response in the wavelength range from 650 nm to 900 nm. The present 2D vdW heterojunctions composed of direct band gap multilayer materials show great potential in future optoelectronic devices.
关键词： In2Se3,photodetector,two-dimensional materials,WSe2,direct band gap materials,heterojunction
更新于2025-09-11 14:15:04
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Wide band-gap Cu <sub/>2</sub> SrSnS <sub/>4</sub> solar cells from oxide precursors
摘要： Recent progress in the efficiency of Cu2ZnSnS4 (CZTS) solar cells has been relatively slow due to severe bulk band tailing issues that have proven difficult to resolve. Band tails in CZTS are caused by defect-related potential fluctuations, as diagnosed by the large shift between the CZTS band gap and its photoluminescence (PL) peak. In this work, we demonstrate that the PL-band gap shift can be decreased roughly by a factor of 5 when Zn is replaced by the heavier cation Sr. The resulting Cu2SrSnS4 compound is of considerable interest for photovoltaics due to its sharp band edges and suitable band gap (1.95-1.98 eV) for a top absorber in tandem cells. Trigonal CSTS thin films are synthesized in this work by sulfurization of strongly Cu-poor co-sputtered Cu2SrSnO4 precursors. The first functioning CSTS solar cells are demonstrated, even though the very high conduction band of CSTS implies that the typical CdS/ZnO electron contact of CZTS solar cells must be redesigned to avoid large voltage losses.
关键词： tail states,tandem solar cell,sputtering,wide band-gap absorber,Kesterite,cation substitution,potential fluctuations
更新于2025-09-11 14:15:04