This PDF file contains the front matter associated with SPIE Proceedings Volume 10720, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists, and Introduction (if applicable).

Nature holds situations in which sudden changes are caused by smooth alterations. The famous Airy and Pearcey beams represent diffraction patterns of corresponding fold and cusp bifurcations, respectively. When classified in a hierarchical order, they are subsequently followed by swallowtail and butterfly beams. These beams are generally characterized as cuspoid beams, accelerated on bent trajectories. They lead to various applications, among them the realization of curved waveguides. Their umbilic counterparts, however, characterized by even more complex diffraction patterns, have up to now only been characterized, but not yet been utilized as functional fabrication templates for applications in photonics. In this contribution, we present our results on embedding higher-order cuspoid and umbilic catastrophes in tailored light. These light structures show versatile curved strands of high intensity during propagation. The elliptic umbilic beam even morphs from a hexagonal transverse intensity pattern to a beam with a single central hot spot to become again the original hexagonal pattern. We thus exploit the dynamics of these caustics to optically induce corresponding photonic lattices in nonlinear media and demonstrate light propagation in elliptic umbilic lattices. Our approach enables fabricating continuously transforming lattices with varying band structure, paving the way for advanced topological photonics.

Selection of the correct crystalline phase in the NaYF₄:Er nanomaterial system is expected to increase the upconversion photoluminescence efficiency for potential solar cell applications in the near IR region. Further, several recent reports involve the use of the cubic phase for biomedical in situ pressure sensing applications. Thus, it is vital to understand the precise annealing conditions necessary for the rational design of the nanomaterial species. We report the initial studies on phase purity (cubic and hexagonal phase) of NaYF₄:Yb (18%), Er (2%) using thermal decomposition at 320°C. The as-synthesized (spherical and cubic) agglomerated nanoparticles were estimated to have a mean size of 200 nm from scanning electron microscopy (SEM), and present as aggregated particles in high-resolution transmission electron microscopy data (HRTEM). Powder X-ray diffraction (PXRD) measurements were carried out to infer the relative abundance of the two phases as a function of air annealing at different temperatures. Contrary to previously reported partial studies, we find that the initial mixed phase of 50:50 composition remains resistant to any change until 450°C, at which point the content of the hexagonal phase starts declining, resulting in a nearly pure cubic phase at 550°C. Thus, it is found that hexagonal phase does not dominate the product at any reasonably low processing temperature. Photoluminescence (PL) measurements on the unannealed material at 785 nm result in localized broadband emission in green (centered at 540 nm) and red (centered at 660 nm). This work establishes optimal annealing conditions for this important photonic nanomaterial for potential biomedical applications.

We demonstrate efficient and compact 1xN wavelength-demultiplexing by using objective-first inverse design algorithm. Ultra-high device performances were achieved for the certain designs of 1x2, 1x3, and 1x4 demultiplexers with very small footprints at the orders of a few microns. The presented 1x2, 1x3, and 1x4 devices operate at the wavelength sets of 1.31μm, 1.55 μm; 1.31 μm, 1.47 μm, 1.55 μm, and; 1.31 μm, 1.39 μm, 1.47 μm, 1.55 μm, respectively. The transmission efficiencies at the corresponding target wavelengths of each vertically or horizontally aligned channels were obtained mostly to be near-unity together with very small crosstalk ranges of around 0.01% - 1.2%. The inverse design approach allowing the implementation of more than four output channels together with the novel functionalities will pave the way for compact and manufacturable 1xN couplers, which is of ultimate significance for integrated photonics.

The theoretical and experimental study of porous silicon-based UV microcavities is discussed in this work. The obtaining of CMs in the Ultraviolet range expands the field of research of porous silicon photonic structures. The porous silicon microcavities (PSM) consisted of two Bragg reflectors (BRs) with a defect between them. It was fabricated by electrochemical etching. Microcavities (MCs) were subjected to dry oxidation process (DOP). In this way we obtained an oxidized porous silicon (OPS) that induces a shift of the response to the ultraviolet (UV) region on both, the minimum peak of the reflectance spectrum and the maximum peak of the transmittance spectrum; two UV microcavities showed maximum transparency in the UV of 67 %. The shift is explained as due to the formation of silicon dioxide (SiO₂); this wavelength shift shows a logarithm-like function of oxidation times. It was used a theoretical model to predict the refractive index of the MCs that contains two components (Si and air) and tree component (Si, SiO₂, and air). Moreover, a photonic model was used to obtain the photonic band gap structure and the defect modes of different MCs in the UV-Visible range. The theoretical results showed that the experimental peaks within the UV photonic bandgap are indeed defect modes. Characterization of MCs was performed by SEM, FTIR and UV-Vis-NIR spectroscopy before and after the DOP. These results open the possibility to create silicon-based photonic structures within the UV range where usually silicon or porous silicon either strongly absorb or scatter light.

The optical properties of ZnO has been widely investigated in detail. Typical photoluminescence (PL) of ZnO contains two parts of emission: near bandgap transition induced ultraviolet emission, and a relatively wide visible emission ranging from green to red, which is closely related to concentration of the structural defects. While the green luminescent has been reported to be associated with oxygen vacancies Vo. In this work, we report on an efficient technique namely desulfurization to increase the amount of oxygen vacancy in a ZnO nanowires array. In the case of the desulfurized sample the PL is increased by more than 1 order of magnitude as to compare with the sulfurized one and more than 2 orders of magnitude as to compare with the as grown sample. Structural analysis as well as morphological analysis confirm the origin of the green band emission enhancement in PL emission. Samples preparation as well an in-depth analysis including quantum efficiency will be presented and discussed within the frame of new rare-earth free phosphor material.

The emission properties of aluminum-doped zinc oxide are numerically investigated. A complete model for photoluminescence, based on the set of rate equations for electron-hole recombination, is used to study the influence of carrier concentration (10¹⁷-10²⁰ cm^-3 ) on the visible and ultraviolet (UV) emission. The set of coupled rate equations is solved numerically using the fourth order Runge-Kutta technique for various optical pump intensities and pulse durations. The results for low carrier concentration (~10¹⁷ cm^-3 ) show that at low pump intensity (0.01 mJ/cm² ) visible emission is dominant in the emission spectrum and, as the pump intensity increases (~1 mJ/cm² ), the UV emission becomes dominant. The study of ultrafast dynamics shows that for pump pulse durations of less than ~ 1 ns the intensity of the UV emission is an order of magnitude larger compared to the visible intensity for aluminum-doped ZnO samples with carrier concentration ~10¹⁸ cm^-3 .

Photonic Integrated Circuits (PICs) in the visible wavelength range have been extensively used for life science applications. Silicon Nitride has been the most widely used material, as it allows to fabricate low loss waveguides with the refractive index ranging from 1.9 to 2.1. For downscaling of PICs, many investigations into Titanium Oxide (TiO2) have been studied. The refractive index of TiO2 ranges from 2.3 to 2.6. Despite a high refractive index, TiO2 tends to crystallize at temperatures above 300ºC, limiting its potential for CMOS compatible fabrication. In addition, the presence of oxygen vacancies in TiO2 results into photon absorption in the visible range, leading to high propagation losses. We investigate Niobium Oxide (Nb2O5) as an alternative waveguide material, focusing on material and optical properties for light propagation in the visible wavelength range. Physical vapor deposition of the Nb target in Oxygen atmosphere results in stoichiometric Nb2O5. On a 200mm wafer, a 90nm Nb2O5 is deposited on 2.3µm bottom clad (SiO2). The extracted refractive index is above 2.3, while the extinction coefficient is 0 for visible wavelengths. From X-ray diffraction, the as-deposited layers were amorphous, while the surface roughness was below 0.3 nm. Waveguides were patterned using 193 nm lithography and etched using chlorine based chemistry. In the visible range, optical losses for un-cladded waveguides were below 5 dB/cm, comparable to our in-house SiN platform. There were no significant changes in optical losses after 400ºC anneal, signifying its potential for improved propagation after top-cladding deposition.

Due to the high surface to volume ratio, nanowire based components benefit from new properties typical of the nanoscale. ZnO nanowires have already proved their usefulness in the realization of multiple electronic components, such as FET transistors, gas detectors, photodetectors, LEDs or even solar cells. ZnO nanowires have also shown themselves to be very promising UV detectors thanks to their significant photoconductive gain, as high as G =10^8 [1]. This makes them suitable for single photon detection, or at least detection of very dim light. The main current drawback is the recovery time (minimum time between 2 detections) which we develop last hours. The device we developed is a good candidate for opto-electronic applications. Our device is a photodetector with ohmic contact and it behaves like a transistor. Our experiments stress out the importance of surface effect on the electrical by taking measurements in different atmospheres (oxygen, air, vacuum and argon). These surface states are the reason for the existence of a photoconductive gain, we obtain a maximum gain of G =6.10^6. In counterpart of this great gain, the persistence of the photocurrent (which can last up to several hours) prevents the device from operating at high frequency. We propose a method to reduce this time by applying a gate voltage. REFERENCES [1] C. Soci , A. Zhang, B. Xiang, S. A. Dayeh, D. P. R. Aplin, J. Park, X. Y. Bao, Y. H. Lo, and D. Wang, Nano Lett. 7, 1003 (2007).

The white quantum dots (WQDs), which have both the surface state and band edge emission, have been pay more attention due to their broad emission spectrum. However, the low quantum yield (QY) and poor stability limits their application in solid-state lighting. In order to solving above problems, the QDs were prepared by colloidal chemistry method and adding Zn to form CdSe:Znx QDs. The result shows that the QY of as-prepared and Zn doped CdSe QD is 42 and 52 %. Moreover, the second emission peak shows red-shifted at low Zn content, and blue-shifted at 10 % of Zn content. In addition, Zncontaining samples also have a broad emission peak, and consists of two particle sizes. The QY can be maintained for 10 at% -Zn samples after 120 days aging at room temperature, meaning that the sample have good stability

Commercial white LEDs (WLEDs) use yellow-emitting cerium-doped yttrium aluminum garnet phosphor, along with an InGaN-based blue LED. However, such phosphors suffer from the following disadvantages: (1) limited phosphor performance due to thermal degradation, (2) significant backscattering losses, and (3) poor absorption. Current commercial WLEDs have a luminous efficacy varying from 75~100 lm/W, with some showing higher values, but with a trade-off in the color rendering indices (CRIs). To work towards the US Department of Energy target of a luminaire of 200 lm/W, it is necessary to develop new designs for phosphors for WLEDs with high efficiency and better color rendering. Here, we propose and study theoretically core-shell (CS) and core-shell-shell (CSS) metal-semiconductor nanowires (NWs) as phosphor components in white LEDs, using a Mie formalism for absorption and a Green’s function approach for emission. Coupling of the plasmon resonance oscillations at the metal surface with the electric fields of the incident light enables an enhanced absorbance of CS NWs of 0.6-0.9 for blue light compared to the absorbance of 0.2-0.4 observed in the CS quantum dots. We have predicted that the External Quantum Efficiency (EQE) can be enhanced by almost 11 times for red phosphors, by 36 times for yellow phosphors and as high as four orders of magnitude for the green phosphors relative to the bare semiconductor nanowires, when carefully choosing the semiconductor and metal materials and dimensions. CSS NWs further improve values of the EQE by as much as 60% relative to the CS nanowires for red phosphors and 3 times for yellow phosphors, due to the addition of another enhanced electric field from the semiconductor core to the Purcell factor.

The steady advance of nanotechnology from investigation to application and to manufacturing is increasing the demands on nanoscale metrology and lithography. As dimensions shrink to the nano-scale, the available metrologies, necessary for any advanced manufacturing process, become limited. Optical metrology faces resolution limits associated with the large size of the photon relative to the nanostructure. Interference techniques offer sub-wavelength resolution, but at the expense of experimental and signal processing complexity. Electron and ion microscopies (SEM, TEM, FIB, etc.) offer resolution but require high vacuum and are generally unavailable for in-line manufacturing applications. Scanning probe techniques such as atomic force microscopy (AFM), scanning tunneling microscopy (STM), and near-field scanning optical microscopy (NSOM) are very attractive, yet, still unreliable to produce ideal results. For example, AFM, commercial tips are often pyramidal, resulting in significant artifacts requiring complex and uncertain deconvolution of the data. For STM and STL (scanning-tunneling lithography), amorphous/polycrystalline metal tips are the dominant commercial technology but are subject to erosion and wear. For NSOM, metal tips require a complex alignment - optical fibers offer an alternative but are difficult to combine with AFM and STM functionality. To overcome to the above-mentioned problems, we have developed a single nanowire probe systems, based on single crystal III-N semiconductors. Uniform GaN nanowire arrays, formed thought a combination of wet and dry etch of MOCVD GaN films, were achieved over a large area (>105 μm2) with an aspect ratio as large as 50, a radius as small as 17 nm, and atomic-scale sidewall roughness (<1 nm), allowing metrology of vertical structures with no artifact correction. Doping, during MOCVD film growth, controlled the conductivity of the GaN. Studies of the etching mechanism for different doping level are also reported. Optical emission properties of the 65 nm radius and 2 micron length GaN, mounted on an AFM tip shows a lasing at 365 nm with a line width of 0.15 nm and a Q-factor of 1139-2443. Our results show that fabrication of high-quality GaN nanowire arrays with adaptable aspect ratio and large-area uniformity is feasible through a top-down approach using interferometric lithography and is promising for fabrication of III-nitride-based nanophotonic devices (radial/axial) on the original substrate. Indeed we will also present the state of the art results of these nanowires in AFM and STM metrology as well in field emission and scanning tunneling lithography and NSOM and demonstrate as, such a single wide-bandgap tip technology offers the functionality and versatility of several incumbent technologies in one single, universal, system.

We developed an ion beam based processing scheme to synthesize Ag nanoparticles embedded within Si. Such embedded Ag nanostructures are expected to significantly enhance second harmonic generation thus the Pockel's effect in Si owing to the electric dipoles possessed by Ag nanostructures and the strong electric field effects associated with surface plasmon excitation of Ag nanostructures. Preliminary work in this direction has revealed an interesting correlation between the enhancement of second harmonic generation and the Ag nanostructure size/shape. Such nanosystems are capable of enhancing second harmonic generation from Si for on-chip silicon modulator fabrication.

Targeted, sequential deposition of metals using localized surface plasmon resonance (LSPR) is a promising fabrication route for solar fuel catalysts and sensors. This work examines liquid-phase, reductive photodeposition of platinum (Pt) nanoparticles onto the longitudinal ends of gold nanorods (AuNR) under surface plasmon excitation. Reductive Pt nucleation is initiated by plasmonic hot electrons at the Au-liquid interface, whose sites are governed by the plasmon polarity. In this work, in situ spectroscopic monitoring of the photodeposition process permitted real-time feedback into AuNR surface functionalization with the Pt precursor, Pt growth kinetics under monochromatic AuNR LSPR excitation, and their evolving light-matter interactions. Energy dispersive spectroscopy (EDS) mappings show Pt deposition was localized toward the AuNR ends. Coordinated X-ray photoelectron spectroscopy (XPS) measurements with density functional theory (DFT) calculations of the Pt-decorated AuNR density of states (DOS) elucidated optoelectronic behavior. Catalytic photodeposition using plasmonic hot electrons provide an economical path towards targeted, hierarchal assembly of multi-metallic nanoarchitectures at ambient conditions with specified optoelectronic activity.

Monolayer tungsten disulfide (WS2) has emerged as a material for optoelectronic applications because of its remarkable quantum yield of photoluminescence. However, the existing studies of defects in monolayer WS2 are insufficient to specifically discern Raman scattering properties caused by the defect. Here, we report that resonance tip-enhanced Raman spectroscopy imaging and correlation study with scanning tunneling microscopy can reveal defect-induced Raman modes denoted as D and D′ modes in monolayer WS2. Furthermore, our density functional theory calculations demonstrate that sulfur vacancies introduce not only the red-shifted A1g mode but also the D and D′ modes. The observed defect-related Raman modes can be utilized to evaluate the quality of monolayer WS2 and will be helpful to improve the performance of WS2 optoelectronic devices.

Titanium nitride is being studied as an alternative plasmonic material for its tunability and high durability. TiN can be grown with high quality and competitive optical properties, but the current magnetron sputtering method used to achieve this quality requires a high temperature. For low temperature or CMOS compatible design, Atomic Layer Deposition (ALD) is a promising method; ALD TiN films are conformal allowing ultrathin, few monolayer, thicknesses. However, TiN films deposited with ALD have struggled to reach the metallicity and quality of sputtered films. Here, we present a study on films produced via Plasma Enhanced Atomic Layer Deposition (PE-ALD) that approach the metallicity of sputtered films while remaining relatively low loss compared to similar films that are achieved with a CMOS compatible method. Several TiN films on sapphire and silicon of comparable thicknesses (~70nm) and varied temperature, 375 to 475 C, are studied by spectroscopic ellipsometry and x-ray diffraction to characterize optical properties and film quality. Peak optical properties occurred at a deposition temperature at 375 C which we attribute to the precursor, tetrakis(dimethlamino) titanium(IV), gas breakdown temperature ~425 C (lower deposition temperatures currently being explored). This film exhibits a figure of merit (-Re{ε}/Im{ε}) of 2 compared to other ALD films of 1.2 and sputtered films as high as 3.6. XRD results show epitaxial quality films with lattice constants that approach bulk as temperature is increased. These conflicting trends suggest that transitioning to a different precursor may allow for an optical property improvement of materials at a higher temperature deposition.

Plasmonic photocatalyst has attracted much attention since plasmonic nanostructures were demonstrated to increase the visible and/or infrared light activity of conventional semiconductor and further to improve the performance of the photoelectrochemical (PEC) water splitting. Here we utilized highly conductive reduced graphene oxide (RGO) nanosheets and gold nanotriangles (NTs) with remarkable localized surface plasmon resonance (LSPR) in the visible region to improve the photoresponse of TiO₂ branched nanorods (NRs), which were fabricated by a two-step hydrothermal grown method. Upon the concurrent addition of Au NTs and RGO, the photocurrent, which was measured by three-electrode PEC reactor under illumination of simulated solar light, showed a pronounced ~37% improvement compared to TiO₂ branched NRs and ~450 % enhancement compared to TO₂ NRs. It iss believed that not only the photon scattering effect and LSPR response in visible region (~675 and ~530 nm) of Au NTs but also the high conductivity and large surface area of RGO assisted in harvesting visible light, accelerated charge carrier transportation, and reduced the charge recombination rate to improve the PEC water splitting performance of TiO₂.

The geometric structures, energy and optical properties of intrinsic and Cu, Ti, Zr-doped graphenes were investigated using first-principles method. The results indicate that the doped graphenes can be prepared by experiment under certain conditions and stable. The absorption spectrums show that the absorption rates of doped systems are larger, and the amplitude ratios of them are smaller than that of intrinsic graphene in the range of visible light. The real parts of conductivity are larger and the fluctuations become smaller. Thus, it can be predicted that Cu, Ti, Zr-doped graphene can be used as visible light sensitive materials in sensors.

Isotropic sillenite crystals such as Bismuth Silicon Oxide (BSO) present highly interesting opto-electronics properties including electro-optic effect and photorefractivity. BSO is also a highly suitable candidate for sensitive temperature-independent electric field sensors [1]. Then the production of low cost BSO-based optical-waveguides is becoming a major challenge. However, BSO high density (> 7 g.cm3) and non-standard dimensions are a hurdle for standard fabrication approaches such as ion diffusion or exchange and standard clean-room technologies. Here we report for the first time the successful fabrication of low loss BSO ridge waveguides with high index contrast. The proposed technique is based on optical-grade dicing [2], which allows low cost and massive production of photonic devices in different types of material. Ridge waveguides are made in a 15-µm thick chemical mechanical polished thin layer of BSO bonded on a lithium-niobate wafer. Propagation losses, group velocity and modal birefringence of optical modes have been measured by Optical-Coherence-Tomography. The waveguides support both TE and TM guided modes at telecom wavelength (1.55 µm) and present propagation losses lower than 2 dB/cm. This approach promises to be powerful for shaping single crystal thin films even in exotic formats. We expect low loss optical-waveguide in BSO will pave the way toward compact and highly sensitive electric-field sensors, scintillators, LED and laser applications. [1] I. Saniour et al, NMR in Biomedicine,31, (2018). [2] N. Courjal et al, Journal of Physics D: Applied Physics, 305101,(2011).

Manuscript presents the results of study the anomalous light absorption by a system: graphene monolayer on the water surface. Properties of single-layer graphene-water complex were investigated with the help of powerful laser beam. According to the investigation, an increase in light absorption by the sample was observed. Two possible causes of such anomalous absorption were considered: the doping process of single-layer graphene by the water molecules, and the scattering of optical radiation by microbubbles formed as a result of heating process of the monolayer.

We report Purcell factor enhancement in Silicon dimer in the visible region. Dimer of Silicon spheres having diameter 130 nm has the electric field enhancement at the wavelength of 620 nm. Point electric dipole has been placed between the Silicon dimer to calculate the Purcell factor. Purcell factor or spontaneous emission rate depends on quality factor Q and mode volume V by the relation Q/V. For high Purcell factor, quality factor should be high and mode volume should be small. But high quality factor has the disadvantage that light matter interaction takes place over a very narrow bandwidth. So that coupling of emitters with cavities is very weak. Another way of increasing Purcell factor is to decrease mode volume. In our design, quality factor is 50 which is not so high but mode volume is very small of the order of 10^-4 μm3 , which results in very high Purcell factor of 2400. Enhancement of Purcell factor takes place due to high local density of states. In this type of dielectric nanoparticles, electric field enhancement takes place due to Mie resonance. In single dielectric nanoparticle, electric and magnetic field confine in the nanoparticle at the wavelengths of resonance. But, in the dielectric dimer, electric field confinement between the two nanoparticles results in high Purcell factor. High Purcell factor in dielectric nanoparticles leads to many applications in nanoantennas and lasers.

We observed plasmon resonance peaks at two different wavelengths by combining plasmon wave from aluminum (Al) and gold (Au) nano-particles (NP). We model the absorption characteristics of two nano particles placed with nano meter scale gap using RF module of COMSOL 5.3 modeling program. The coupled plasmon layer has two peaks at 525 and 640 nm, which are different from the constituent individual metal plasmon layers of Al and Au NPs with peak at 450 nm and 700 nm respectively. Good agreement exits between modeling data with experimental results.