This PDF file contains the front matter associated with SPIE Proceedings Volume 10914, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Persistent luminescence (PersL) imaging without real-time external excitation has been regarded as the next generation of autofluorescence-free and heating effect-free optical imaging technique. However, in order to acquire improved spatial resolution and deep penetration depth, developing new near-infrared (NIR) persistent phosphors with intense and long duration PersL over 1000 nm is still a challenging task. Herein, by utilizing the persistent energy transfer from Ce³⁺ to Er³⁺, we have successfully developed a series of garnet persistent phosphors of Gd₃Al_5-xGa_xO₁₂ (x=2.0, 2.5, 3.0, 3.5) doped with Ce³⁺, Cr³⁺ and Er³⁺ ions (GAGG:Ce-Cr-Er), which exhibit long yellow PersL ranging from 480 nm to 780 nm mainly due to the 5d-4f parity-allowed transition of Ce³⁺, and NIR PersL in the broad range from 1450 nm to 1670 nm due to the typical Er³⁺: ⁴I_13/2→⁴I_15/2 transition in garnets. Spectroscopic results of photoluminescence (PL), PersL, thermoluminescence (TL) and fluorescence/PersL decay curves of obtained garnet solid-solutions are discussed in detail, which suggest that GAGG:Ce-Cr-Er ganets with multi-wavelength PersL bands can be a potential candidate for longterm in-vivo optical imaging in the third biological window. Moreover, taking advantage of the Gd³⁺ host ion with seven unpaired electrons in its 4f shell, enhanced positive contrast for magnetic resonance imaging (MRI) also can be expected using this material as a T1-weighted agent. Thus, the GAGG:Ce-Cr-Er persistent phosphor in the form of nano-particles possesses the possibility as a dual-mode medical diagnosis platform featuring both the deep tissue penetration for in vivo bio-imaging and the high spatial resolution for MRI.

In this contribution the influence of fabrication technique (solution doping, gas-phase doping) and the choice of suitable material systems (Al, P, Yb:SiO₂ and Al, F, Yb:SiO₂) for high power fiber laser materials on their optical properties is analyzed. The materials under analysis contain low amounts of codopants (Yb < 0.15 mol%, other <1.2 mol%). The effects on refractive index, attenuation, absorption and emission cross section as well as on photodarkening are addressed. The main part concerns with the analysis of photodarkening, in fact the evolution of individual defect centers are spectrally and temporally investigated by means of 2D curve fitting. It is suggested that this spectro-temporal fitting procedure can lead to new insights in the development of photodarkening on a level of the defects themselves.

A pure Ce-doped silica fiber is fabricated using modified chemical vapor deposition (MCVD) technique. Fluorescence characteristics of a Ce-doped silica fiber are experimentally investigated with continuous wave pumping from 440 nm to 405 nm. Best pump absorption and broad fluorescence spectrum is observed for ~ 405 nm laser. Next, the detailed analysis of spectral response as a function of pump power and fiber length is performed. It is observed that a -10dB spectral width of ~ 280 mn can be easily achieved with different combinations of the fiber length and pump power. Lastly, we present, for the first time to the best of our knowledge, a broadband fluorescence spectrum with -10dB spectral width of 301 nm, spanning from ~ 517.36 nm to ~ 818 nm, from such fibers with non-UV pump lasers.

Metasurfaces that can refract and focus light in unique ways provide the opportunity for advanced light manipulation and development of novel applications. Due to the flat nature of metasurfaces (typical thickness < 100nm), conventional three-dimensional optical elements such as prisms or lenses could be replaced by flat, low-profile, and low-cost versions. In addition, the optical response of near-zero refractive index metasurface systems, i.e., vanishing permittivity and permeability values, have been shown to exhibit unique optical properties. Those features can be exploited in various optical applications such as wavefront engineering, radiation pattern tailoring, non-reciprocal magneto-optical effects, nonlinear ultrafast optical switching, and broadband perfect absorption. However, most of the studies on epsilon-near-zero (ENZ) optical properties are limited to the excitation of ENZ mode in the planar structures or meta-surfaces with short interaction length, restricting the excitation platform for novel optical device applications. In this talk, I will report a novel optical waveguide design of a hollow step index fiber modified with a thin layer of conducting oxide epsilon-near-zero materials. We show an excitation of highly confined waveguide mode in the proposed fiber near the wavelength where permittivity of conducting oxide material approaches zero [1]. I will present our study on “meta”-optical fiber by integrating metasurfaces with optical fibers to develop novel and ultracompact in-fiber optical devices such as an optical fiber metalens and color filter [2,3]. These advanced “meta”/ENZ-optical fibers open the path to revolutionary in-fiber optical imaging and communication devices. 1. K. Minn, A. Anopchenko, J. Yang, H. W. Lee, “Excitation of epsilon-near-zero resonance in ultra-thin indium tin oxide shell embedded nanostructured optical fiber,” Nature Scientific Reports 8, 2342 (2018). 2. J. Yang, I Ghirmire, P. C. Wu, S. Gurung, C. Arndt, D. P. Tsai, H. W. Lee, “Photonic crystal fiber metalens”, submitted (2018). 3. Indra Ghimire, Jingyi Yang, Sudip Gurung, Satyendra K. Mishra and Ho Wai Howard Lee,” Polarization dependent photonic crystal fiber color filter using asymmetric metasurfaces,” Submitted (2018)

Despite the significant advances made in the field of metamaterials and metasurfaces in recent years, many applications of such devices are hampered by the lack of active refractive index tuning. Here, we report on a new class of tunable quantum materials based on 3D topological Dirac semimetals with extremely high electrical and thermal refractive index tuning. Realized optical reflectivity data, performed on thin films of Cd3As2 over a broad range of frequencies demonstrate larger than traditional thermo-optic shifts in III-V semiconductors. Dynamic Fermi level tuning, instigated from the Pauli blocking in the linear Dirac cone, offers large and tunable absorption peak in the mid-infrared region. In contrast to recent efforts in 3D Dirac semimetals which are mostly focused on single crystal Cd3As2, our data based on MBE-grown Cd3As2 can galvanize newfound applications in the field of meta-optics and can enable several applications such as ultra-thin programmable optical devices, photodetectors, and on-chip directional antennas.

We present methods to realize nanoimprinted nanocomposite membrane-type metamaterials with tuned refractive index. Here, the idea is separation of the cured UV-curable resist from top and bottom stamps to make freestanding patterned membranes with controlled thickness. Manipulating the refractive index of the resist material is implemented by changing the volume fraction of nanoparticles in the host polymer. These patterned membrane devices are applied in guided-mode resonance devices exhibiting effective spectral signatures in subwavelength periodic media. We present numerous simulated and fabricated nanomembranes with excellent resonance characteristics.

Arsenic triselenide (As₂Se₃) is of interest for use in dielectric metasurfaces for several reasons: It has a high linear refractive index, n=2.8, enabling high index contrast with its surrounding medium; it has an exceptionally high optical nonlinearity (n₂ < 900 × that of silica) making it a good candidate for nonlinear metasurfaces; and its band gap of 1.8 eV and wide transmission window, spanning from approximately 1.5-14 μm, make it useful for applications in the shortwave infrared into the long-wave infrared. We discuss recent results in which we showed that unpassivated As₂Se₃ films degrade significantly under ambient conditions in the presence of light. We discuss the mechanism of this degradation and show that deposition of a thin (~10 nm) Al₂O₃ passivation layer, deposited via atomic layer deposition, together with preventing exposure to below-band gap light inhibits degradation. Finally, we fabricate initial As₂Se₃-based dielectric metasurfaces by writing features via a laser direct write system. For mid-wave to long-wave infrared applications, features with relevant sizes can be written using this technique. We measure resonances for these structures and compare to theoretical results.

This paper explains and demonstrates the unique properties of micron-size silicon-on-insulator (SOI) waveguides. It gives an overview of the silicon photonics research at VTT, as well as latest R&D highlights. The benefits of high mode confinement in rib and strip waveguides are described, reaching from low losses and small footprint to polarization independent operation and ultra-wide wavelength range from 1.2 to over 4 μm. Most of the results are from photonic integrated circuits (PICs) on 3 μm SOI, while a 25 Gbps link with a transceiver on 12 μm SOI is also reported. Wavelength multiplexing and filtering is demonstrated with some breakthrough performance in both echelle gratings and arrayed waveguide gratings. Lowest losses are below 1 dB and lowest cross-talk is below -35 dB. Progress towards monolithically integrated, broadband isolators is described, involving polarization splitters, reciprocal polarization rotators and nonreciprocal Faraday rotation in 3 μm SOI waveguide spirals. Quick update is presented about switches, modulators and Ge photodiodes up to 15 GHz bandwidth. Hybrid integration of lasers, modulators and photodiodes is also reported. The added value of trimmed SOI wafers and cavity-SOI wafers in Si photonics processing is addressed. Latest results also include up-reflecting mirrors with <0.5 dB loss, which support wafer-level testing and packaging.

Antireflective coatings (ARC) are a necessary element of solar cells and infrared (IR) optical applications. Current state-of-the-art coatings consist of materials such as TiO2 and Si3N4 deposited on silicon via chemical vapor deposition (CVD). This method of coating is undesirable due to the costly, tedious, and time intensive nature of the process. Herein, we have developed a novel antireflective coating (ARC) that is facile in nature. Through the implementation of high sulfur content polymers, with ultrahigh refractive index, and near to mid infrared (IR) transparency, we have been able to demonstrate high-quality films via spin/dip coating. This polymer was produced via inverse vulcanization of elemental sulfur, a byproduct of petroleum refining, and the organic monomer 1,3-diisopropenylbenzene (DIB) to yield poly(sulfur-r-(1,3-diisopropenylbenzene)) (poly(s-r-DIB)). The reaction product (poly(s-r-DIB)) was taken up into solution and deposited directly onto a silicon substrate. To verify the performance of a quarter wave antireflection coating, the spectra of the coated silicon wafer was taken. In this we found we could create a high performance, single layer, antireflection coating. Due to the unique nature of the polymer (poly(s-r-DIB)) used in this system we were able to fine tune the thickness of the coating, and therefore the target wavelength in which desired performance could be observed. Further investigation of the system is underway, as the polymer’s index can be tuned to fit a variety of substrates, making this system ideal for a multitude of antireflective applications.

Mid-Infrared (Mid-IR) techniques have gained considerable attention because of their inherent molecular selectivity and their potential for rapid label-free detection in applications such as water quality and environmental monitoring, security, food safety, and point-of-care diagnostics. Waveguide evanescent-field-based Mid-IR spectroscopy can detect analytes at very low concentrations using molecular absorption fingerprints, potentially offering high sensitivity and selectivity over a wide range of compounds. Moreover, significant footprint reduction compared to ATR-based FTIR measurements can be achieved with optical waveguide-based Mid-IR sensing through integration of various optoelectronic and microfluidic components realizing fully packaged lab-on-a-chip systems. Recently we have developed low-loss chalcogenide optical waveguides and demonstrated waveguiding in the mid-wave and long-wave infrared spectral bands. High contrast GeTe4 and ZnSe channel waveguides were fabricated on bulk substrates and on silicon wafers (with suitable optical isolation layers) using lift-off and dry etching techniques after photolithographically patterning the thin films. These waveguides were exhibiting optical losses as low as 0.6 dB/cm in the mid-wave IR band and were validated for the Mid-IR evanescent wave spectroscopy with water and IPA. We have also demonstrated the effectiveness of simple paper-based fluidics with our waveguides. In addition, we investigate a new family of free-standing Ta2O5 rib waveguides for trace gas detection with evanescent field overlap with the surrounding medium (air) up to about 70%. The waveguides are being fabricated and the fabrication and characterization results will be presented.

Applications that require awareness of the structure, environment or objects are growing, and include augmented and virtual reality applications, gesture recognition and facial recognition for consumer, industrial and entertainment applications. This is creating a demand for 3D data capture and the use of depth sensors. Structured Light Illumination (SLI) is one of the leading depth sensor technologies. It is an indirect measurement of distance through observed distortion of a projected light pattern. To miniaturize these sensors for consumer applications, custom optics are required for the projector including diffractive optical elements (DOE). SLI is currently preferred due to its small form factor, high resolution and low power consumption. It can deliver high spatial resolution while working in low light conditions. To use SLI for high accuracy applications, the stability of the pattern under various environmental conditions and temperature ranges is required. We show simulations of the impact of the DOE substrate CTE on the generated dot patterns, and ultimately the depth accuracy and distortion of the 3D image. Measurements of commercially available consumer structured light sensors support the simulations.

Optical frequency domain reflectometry (OFDR) has been investigated for two decades as a way to replace the sensing based on fibre Bragg gratings (FBG) currently used in most industries for those applications, using the intrinsic Rayleigh scatter of fibres instead. [1] OFDR allows completely distributed strain and temperature measurements along a fibre. The increase of backscatter using UV laser exposition was recently reported, and was found to increase the sensitivity in both temperature and strain sensing. [2] We present a technique allowing to increase by over 50 dB the backscattered signal amplitude, based on the writing of a Random Optical Grating by Ultraviolet or ultrafast laser Exposure, i.e. a very weak, random grating over the entire length of the fibre. This improvement is, to the authors’ knowledge, over 25 dB higher than what was previously reported for UV exposure for the same exposition power. [2] This ROGUE is generated by inducing phase noise during the continuous writing of a FBG using a Talbot interferometer. This leads to a grating with a very broad bandwidth regardless of the exposure length and greatly increases the signal without limiting the scanning bandwidth, resulting in no loss in resolution. Using these enhanced fibres, we obtained a noise level over an order of magnitude lower than using regular unexposed fibres, allowing measurements of smaller temperature variations. Fibres where such ROGUEs are inscribed also allow the use of a much smaller scanning bandwidth with similar accuracy, resulting in faster acquisition speed. REFERENCES [1] M. Froggatt and J. Moore, "High-spatial-resolution distributed strain measurement in optical fiber with rayleigh scatter," Appl Opt, vol. 37, no. 10, pp. 1735-40, Apr 1 1998. [2] S. Loranger, M. Gagne, V. Lambin-Iezzi, and R. Kashyap, "Rayleigh scatter based order of magnitude increase in distributed temperature and strain sensing by simple UV exposure of optical fibre," Sci Rep, vol. 5, p. 11177, Jun 16 2015.

Driven by the increasing demands of ultra-broad bandwidth transmission in telecommunications as well as in large-scale scientific experiments, interests in developing on-chip DWDM networks based on silicon photonics is increasing rapidly. With compact structures, low loss and robust fabrication, Echelle grating (EG) (de-)multiplexers become one of the key components. Two competitive design methods are the Rowland circle (RC) and the two stigmatic points (TSP) method, with the latter one offering remarkable advantages on optical aberrations and degrees of freedom. We demonstrate a self-developed design kit for both methods involving MATLAB calculation, COMSOL Multiphysics simulation and GDSII layout. In our kit, several parameters are reserved to optimize the geometry in terms of device footprint, reflector configurations etc.. By making rigorous simulation on an HPC cluster, we obtained well-performing, robust and compact EG (de-)multiplexers based on the two stigmatic points method. For the 7-channel, 9th diffraction order and 800 GHz channel spacing device, we get a simulated average optical loss of 2.3 dB and a crosstalk of less than -20 dB with an on-chip footprint of 400×690 μm². Our silicon-photonic devices were fabricated on a 250 nm silicon-on-insulator (SOI) platform using e-beam lithography and dry etching. The comparison between measurement results of fabricated devices and simulation results was carried out, as well as a comparison between designs based on both design methods. Additionally, the experimental result of a 25- channel (de-)multiplexer with 200 GHz channel spacing in the C-band is presented to study the performance of the TSP method for a narrow channel spacing and large footprint design.

The study of Bloch surface waves (BSWs) in dielectric multilayers has been useful in many applications in the fields of optics, photonics, and bio-sensing. BSW mode excitation can be achieved by the addition of a grating on the top of dielectric multilayer which provides phase matching between incident light and BSWs. However, grating coupling only provides coupling over a narrow angular range for incident monochromatic radiation. This paper reports work on realizing broadband coupling using maximum length sequence (MLS) grating structures. An MLS grating contains all possible combinations of a binary sequence save one; thus a grating with an MLS profile contains a superposition of a broad range of periods. We hypothesize that such a surface structure will permit coupling of a broad angular range of monochromatic light or a wide spectral range of collimated light into Bloch surface wave on a multilayer. We investigate the comparative spectral characteristics of MLS grating coupling with other single period counterparts. We believe our investigation provides a method to achieve efficient coupling of a higher fraction of incident light into BSWs than a single period grating or by using prism coupling.

We report for the first time successful inscription of high reflectivity Bragg grating in nanostructured core active fiber. Nanostructurization of the fiber core allows to separate the active and photosensitive areas and to distribute them all over the core. As a result unfavorable clustering between germanium and ytterbium particles is avoided. The distribution of discrete glass areas with feature size smaller than λ/5 results in effectively continuous refractive index profile of the fiber core. We present a single-mode fiber with built-in Bragg grating for laser application with the core composed of ytterbium and germanium doped silica rods. The core structure is arranged as a regular lattice of 1320 doped with ytterbium and 439 doped with germanium silica glass rods. The average germanium doping level within the core of only 1.1% mol allowed efficient inscription of Bragg grating. The nanostructured core was 8.6 μm and the internal cladding was 112 μm in diameter coated with low index polymer to achieve the double-clad structure. In the first proof-of-concept in the laser setup we achieved 35 % of slope efficiency in relation to launched power for the fiber length of 18 m. The output was single-mode with spectrum width below 1 nm. The maximum output power limited by pumping diode was 2.3 W. The nanostructurization opens new opportunities for development of fibers with a core composed of two or more types of glasses. It allows to control simultaneously the refractive index distribution, the active dopants distribution and photosensitivity distribution in the fiber core.

With success of silicon photonics having mature to foundry-readiness, the intrinsic limitations of the weak electro-optic effects in Silicon limit further device development. To overcome this, heterogeneous integration of emerging electrooptic materials into Si or SiN platforms are a promising path to deliver <1fJ/bit device-level efficiency, 50+Ghz fast switching, and <10's um^2 compact footprints. Graphene's Pauli blocking enables intriguing opportunities for device performance to include broadband absorption, unity-strong index modulation, low contact resistance. Similarly, ITO has shown ENZ behavior, and tunability for EOMs or EAMs. Here we review recent modulator advances all heterogeneously integrated on Si or SiN such as a) a DBR-enabled photonic 60 GHz graphene EAM, b) a hybrid plasmon graphene EAM of 100aJ/bit efficiency, d) the first ITO-based MZI showing a VpL = 0.52 V-mm, and e) a plasmonic ITO MZI with a record low VpL = 11 V-um. We conclude by discussing modulator scaling laws for a roadmap to achieve 10's aJ/bit devices.

Active photonic devices such as high speed optical modulators are required in various applications such as fiber optic communications, frequency shifting and also in fiber optic gyroscopes for space systems. Bulk lithium niobate have primarily been used due to the lack of method of creating low loss, high index waveguides. Thin film single crystal lithium niobate-on-insulator is a promising platform for advancing optical modulators due to the availability of strong electro-optic effect and high index contrast for wave guiding. We have achieved low-loss waveguides (< 3 dB/cm) in this material system based on our fabrication techniques. With this fabrication technique, we fabricated and characterized optical modulators based on Mach-Zehnder design. We have carried out simulation of the top-bottom electrode configuration and have shown higher electric field compared to side electrode placement which then reduces the required Vπ L hence reducing required length of the active region. Furthermore the arrangement of the electrodes allows a more uniform and directional field to applied across the lithium niobate. Lower drive voltage achieved will enable advances of use of lithium niobate-on-insulator in optical modulators which will be useful in future applications.

Hollow-core anti-resonant fiber (HAF) shows promising applications. Nevertheless, there has been a persistent problem when it comes to all-fiber integration due to lack of HAF based fiber components. Interconnecting a solid core based fiber component with HAFs remains limited solutions. As a result, most of the HAF based optical systems rely on free space optical components that make the system cumbersome and increases the complexity of the system. In response to this remained challenge, we investigate a reliable, versatile, and efficient method to convert a HAF into a fiber filter. By locally heating a HAF with a CO2 laser, the fiber structure gets deformed and cladding capillaries shrink to produce a thicker wall. This process is analogous to "writing" a new fiber with a thicker wall on the original fiber, resulting in creating new high loss regions (resonant wavelengths) in the original transmission bands. Thus, construction of a fiber filter is realized by “writing” a new fiber on the original fiber. Feasibility of this method is confirmed through experiments, adopting both one and two-layer HAF. The HAF based fiber filters are found to have transmission spectra consistent with simulation prediction. Both band pass and band reject fiber filters with more than 20 dB extinction ratio are obtainable without extra loss. Thus, an in-fiber HAF filter is demonstrated by CO2 writing process. Its versatile approach promises controlled band selection, and would find interesting applications to be discussed.

The study of amorphous phase-separated Dielectric Nano-Particles (DNPs) smaller than 10 nm is a great challenge for the materials community. In conjunction with Transmission Electron Microscopy (TEM) and Electron-Probe Micro-Analysis (EPMA), we took advantage of a recent technology, Tri-Dimensional (3D) Atom Probe Tomography (APT) to investigate the variations of the chemical composition in sub-20-nm oxide nanoparticles, grown in silicate glass through heat treatments, at their early stages of nucleation. More precisely, we are investigating the core of an optical fiber drawn from a preform prepared according to the Modified Chemical Vapor Deposition (MCVD) process. We provide here a comprehensive set of experimental data obtained from direct measurements of the concentration for P, Mg, Ge and Er within amorphous dielectric nanoparticles (DNP) of radii ranging from 1 nm to 10 nm. We report on an increase of the concentration of Mg and P with the size of the DNPs. Most importantly, we also demonstrate that erbium ions are partitioned in these small DNPs and their environment changes with the size of the nanoparticles. Molecular dynamics simulations were also implemented to discuss the structural modifications of the Er environment. This presentation highlights the trade off on the size of the DNPs: smaller to reduce light scattering vs bigger to modify luminescence properties.

In the presented work, we investigated the optical and thermal stability of upconversion nanoparticles based on the three widely used matrices (NaYF₄, Y₂O₃, LaF₃). Analysis of the upconversion emission as a function of pump power density in a wide range revealed a multi-stage functional dependence. The stages of linear growing, saturation and degradation with both reversible and irreversible characters were discovered. For matrices of nanoparticles with low-temperature stability (NaYF₄), the dependence proves to be irreversible that could cause by a change in the structure and chemical composition of the matrix. Reversible dependence occurs in matrices with high-temperature stability (Y₂O₃ and LaF₃) and is caused by multiphonon nonradiative relaxation, which can be temperature-stimulated because of self-heating and low air-cooling of the crystal matrixes with low thermal conductivity.

Transparent oxyfluoride glass-ceramics obtained by the adequate heat treatment of Nd³⁺-doped glass with composition 70SiO₂–7Al₂O₃–16K₂O–7LaF₃ (mol%) are investigated. Site-selective laser spectroscopy demonstrates that depending on the Nd³⁺ concentration, cubic (α-phase) and hexagonal (β-phase) KLaF₄ nanocrystals precipitate from the starting glass. The presence of both crystalline phases are unambiguously identified from the emission and excitation spectra and lifetime measurements of the ⁴F_3/2 state of Nd³⁺ ions. The spectroscopic results are in agreement with those obtained with XRD and HR-TEM techniques: α-KLaF₄ nanocrystals are found to be present for all NdF3 concentrations whereas β-KLaF₄ nanocrystals are predominant in the GC samples doped with 0.5 mol%.

A detailed investigation of the dependence of the real time luminescence of Eu³⁺-doped tin dioxide nanopowders on rare earth site symmetry and host defects is given. Ultrafast spectroscopy shows that host-rare earth energy transfer occurs at a transfer rate of about 1.5×10⁶ s^-1, whereas the intrinsic broad band SnO₂ emission has a very short build up time, of the order of 60 ps, and a lifetime of hundreds of picoseconds. These results validate the hypothesis that both host and matrix-excited RE emissions are decoupled due to the different origins of the involved physical mechanisms.

Light scattering by all-dielectric nanoparticles attract significant attention of photonics community. Single nanoparticles can be used both as nanoantennas and as building blocks to construct 2D and 3D meta-structures. In this work we study scattering effect when silicon nanoparticles are embedded in different media. To analyze the evolution of multipole moments and their contributions to the scattering cross-sections of the nanoparticles in media, we use semi-analytical multipole decomposition approach. Explicitly, we investigate the behavior of electric and magnetic multipoles, up to third order, while dielectric nanoparticle made of silicon is embedded in a media. We found that electric and magnetic multipoles experience different red shift as refractive index increases. Due to this behavior separated high-order multipole resonances overlap with each other; thereby, scattering cross section peaks, which could be observed when a particles are in air, merge to the joint scattering cross section peaks. Such resonances overlap also affect both far-field radiation diagrams and field distribution inside the nanoparticle. Importantly, we noticed that when index of a surrounding media increases, the cubical nanoparticles provide spectral broadening of forward scattering effect. Our results provide fundamental information for understanding the scattering effect in all-dielectric nanoantennas or metasurfaces embedded in different dielectric media and operating in wide spectral range. For practical utilization, explored here dielectric nanoparticles could be used in broad range of applications such as in-vitro and in-vivo biomedical devices for sensing and drug delivering, sub-wavelength nano-amplifiers, and many other emerging applications.

The refractive index, Abbe number and transmittance are the most important properties of optical glass. Nevertheless, in many applications the spatial refractive index variation - called homogeneity – is of highest priority. The index homogeneity of optical glass is a key property in industrial metrology devices and professional movie cameras for example. These applications often use small to medium sized lenses produced from cold cuts or hot pressings. On the other side of the range, scientific instruments of large astronomical telescopes require optical glasses with excellent index homogeneities on large apertures of several 100 mm up to even meter sized lenses e.g. for atmospheric dispersion correction. The challenge of enabling highest refractive index homogeneities in small and large dimensions requires tight control of all production steps from melting to hot forming and fine annealing. This paper gives an insight overview on the process of generating high quality glass part from small glass pressings to meter sized glass blanks. It gives suitable help for the interpretation of refractive index homogeneity of optical glass in relation to their dimensions. Latest results added to this overview reflect the current state of this topic at the optical glass manufacturer SCHOTT.

In the last twenty years the field of chalcogenide glasses has seen increasing interest, due to their broad transparency window in the mid-IR. Furthermore, chalcogenides are showing one of the highest nonlinear refractive indices among glasses. Due to these reasons, the development of chalcogenide microstructured optical fibers with low optical losses can allow for new breakthroughs in various research fields, e.g. new mid-IR laser sources, mid-IR spectroscopy, sensing and applications based on nonlinear effects, like supercontinuum generation. In this framework, chalcogenide glasses with the lowest possible amount of impurities are needed to minimize absorption losses. This study is focused on the attempt of eliminating the pollutants usually giving rise to absorption peaks inside the transparency windows: oxygen, hydrogen, carbon and water. Samples were prepared using a double distillation method: getters that can react with the impurities during the synthesis were added to the initial charge, and the reaction byproducts were eliminated by a two-steps distillation process. Ge₁₀As₂₂Se₆₈ was chosen as the system to study because of its nonlinear, optical and thermomechanical properties. Different combinations of chlorides (for the elimination of hydrogen and carbon) and metals (for the elimination of oxygen) were used, and the attenuation spectra of the resulting glasses were compared. The chosen chlorides are TeCl₄, SeCl₄, SbCl₃, GaCl₃; the metals are Mg, Al, Zr, Ni. A holey fiber has been realized by casting method using the best sample, showing that the method is suitable for this composition and that the attenuation before and after the casting are comparable.

This paper presents an innovative one-step doping approach for the preparation of Al-Yb co-doped silica glasses for fiber preforms. Today, fiber-lasers are of great interest in industry due to highest precision and flexibility in system design combined with high power output and excellent beam quality. Industrially established processes such as modified chemical vapor deposition (MCVD), outside vapor deposition (OVD) and reactive powder sintering technology (REPUSIL) are used to fabricate co-doped silica glasses for laser fibers. However, none of these processes is able to simultaneously incorporate laser active dopants increasing the refractive index (rare earth elements, RE), glass matrix modifiers (e.g. aluminum, Al₂O₃) and dopants reducing the refractive index (e.g. fluorine, F). Instead, the incorporation of the individual refractive index changing dopants, into a silica glass matrix, has to be carried out in subsequent and separate steps. The novel approach pursues to overcome this limit by application of atmospheric-pressure microwave plasma with oxygen used as reactive gas in combination with a powder sintering process, targeting the preparation of tailored rareearth doped preforms for high power fiber-laser applications. As a proof of principle, silica powders doped with Al³⁺ and Yb³⁺ have been synthesized successfully. These have been proven to perfectly suit the subsequent processing via the powder sintering process. The plasma generated Al₂O₃ doped SiO₂ particles have an averaged particle size of 30 nm a specific surface area of about 55 m²/g, at an Al₂O₃ concentration of up to 3 mol%. In a second set of experiments, microwave atmospheric pressure plasma-based co-doping of SiO₂ with Al and Yb species has been successfully demonstrated for the first time.

Sapphire optical fiber is an excellent candidate for harsh environment sensing due to its high melting point, small size, and chemical resistance. Various optical sensors in sapphire fiber have been explored for decades. However, there is still lack of accurate data on sapphire fiber optical properties at elevated temperatures, which impedes the development of sapphire fiber sensors. In this paper, we fabricate single crystal sapphire fiber via a laser heated pedestal growth system and measure the optical properties of our fiber from room temperature to 1500 ℃ in ambient air and in different gas environments.

Amorphous photonic materials offer an alternative to photonic crystals as a building block for photonic integrated circuits due to their shared short-range order. By using the inherent disorder of amorphous photonic materials, it is possible to design flexible-shaped waveguides that are free from restrictions of photonic crystals at various symmetry axes. Effects of disorder on photonic crystal waveguide boundaries have examined before, and it is shown that flexible waveguides with high transmission are possible by forming a wall of equidistant scatterers around the defect created inside amorphous material configuration. Based on this principle, waveguides with various flexible shapes are designed and fabricated for planar circuit applications. A silicon-on-insulator (SOI) slab with random configuration of air hole scatterers is used. The amorphous configuration is generated through realistic Monte Carlo simulations mimicking crystalline-to-amorphous transition of semiconductor crystals via an assigned Yukawa potential to individual particles. The design parameters such as average hole distance, slab thickness and hole radius are adjusted so that the waveguide is utilizable around 1550 nm telecommunications wavelength. Such waveguides on slab structures are characterized here and the level of randomness and band gap properties of amorphous configurations are analyzed in detail. These efforts have the potential to lead easier design of a wide range of components including but not limited to on-chip Mach-Zehnder interferometers, splitters, and Y-branches.

Looking at the literature of the last years is evident that glass-based rare-earth-activated optical structures represent the technological pillar of a huge of photonic applications covering Health and Biology, Structural Engineering, Environment Monitoring Systems and Quantum Technologies. Among different glass-based systems, a strategic place is assigned to transparent glass-ceramics, nanocomposite materials, which offer specific characteristics of capital importance in photonics. These two-phase materials are constituted by nanocrystals or nanoparticles dispersed in a glassy matrix. The respective composition and volume fractions of crystalline and amorphous phase determine the properties of the glass-ceramics. The key to make the spectroscopic properties of the glass-ceramics very attractive for photonic applications is to activate the nanocrystals by luminescent species as rare earth ions. From a spectroscopic point of view the more appealing feature of glass-ceramic systems is that the presence of the crystalline environment for the rare earth ions allows high absorption and emission cross sections, reduction of the non-radiative relaxation thanks to the lower phonon cut-off energy and tailoring of the ion-ion interaction by the control of the rare earth ion partition. Although the systems have been investigated since several years, chemical and physical effects, mainly related to the synthesis and to the ions interactions, which are detrimental for the efficiency of active devices, are subject of several scientific and technological investigations. Here we focus on fabrication and assessment of glass-ceramic photonic systems based on rare earth activated SiO₂-SnO₂ glasses produced by sol-gel route.

An optical isolator using Tb³⁺-rich magneto-optical glass was demonstrated. We successfully developed a glass having a large Faraday effect, whose Verdet constant was 60 rad/T m at 1064 nm, ~1.6 times that of Tb₃Ga₅O₁₂ crystal (TGG). The glass was also highly transparent in the visible―near-IR region. An optical isolator operating at a wavelength of 1064 nm was developed using the glass, whose isolation was over 33 dB and insertion loss was under 0.2 dB. The size of the magnet could be reduced, and consequently, a small (51 × 40 × 40 mm³) optical isolator was realized.

The development of compact eye-safe optical amplifiers has been recently triggered by the need of airborne LIght Detection And Ranging systems (LIDARs) for environmental monitoring and surveillance. Among potential candidate materials, phosphate glasses can incorporate high amounts of rare earth ions, thus allowing for high optical gain per unit length which would result in few-cm long optical amplifier sections. Another advantage guaranteed by a short length optical amplifier is the possibility to reduce the unwanted non-linear effects, e.g. Stimulated Brillouin Scattering, which cause distortion in the beam profile and affect the performance of the device. We report on the design and fabrication of Yb/Er-doped phosphate glasses to be used as active materials for the core of a waveguide amplifier. The prepared glasses were characterized in their physical and optical properties and the best composition selected for the fabrication of the amplifier. Suitable cladding compositions were explored, and the final core/cladding glass pair was processed by melt-quenching the glasses into the desired shapes: core rods were obtained by casting the glass into preheated cylindrical glass molds, while the cladding glass tubes were fabricated by extrusion using an in-house developed equipment. The optical waveguide was then obtained using a custom induction heated optical fiber drawing tower. Preliminary results of optical amplification are presented for the single stage Master Oscillator Power Amplifier (MOPA), using a CW source as seed laser. The reported activity was carried out in the framework of the NATO Science for Peace and Security project “Caliber”, grant no. SPS G5248.

A comprehensive study of photoresponse linearity characteristics, for high performance short wavelength infrared (SWIR) photodiodes of various materials, is performed. These photovoltaic (PV) detectors were manufactured at Teledyne Judson Technologies (TJT) as standard products, with the state-of-the-art technologies. A broad range of detectors made from several IR materials were selected for linearity tests, including InGaAs (cutoff wavelength from lattice matched 1.7μm to extended wavelength of 1.9-2.6μm), SWIR PV HgCdTe (2.5-2.8μm cutoff), Ge (1.8μm cutoff), and InAs (3.5μm cutoff). Comprehensive linearity test data are presented for each detector material. Characterization of linearity dependence on detector size, operating temperature, reverse bias, and light spot size is studied. Detector size ranges from <0.25mm dia. up to 10mm dia., detector operating temperature from room temperature to thermoelectric cooled (TEC) temperatures, detector bias from 0V up to 10V reverse bias for some materials, and light spot size from 10μm up to 1mm. This work focuses on photocurrent saturation in the high optical power (or photon flux) range. Two saturation mechanisms are investigated, including series resistance effect and Auger recombination effect.

The fabrication and characterization of InAs/GaSb type-II superlattice long-wavelength infrared (LWIR) photodetectors for high operating temperature (HOT) are assessed regarding possible device yield. We investigate laterally-operated photoconductors with a detector cutoff wavelength in the LWIR at an operating temperature accessible with 3-stage thermoelectric cooling, realized by suitably tailoring the layer composition. Type-II superlattices with a layer composition of 14 monolayers InAs and 7 monolayers GaSb are grown on semi-insulating 3-inch GaAs substrates. We report on the growth of three different buffer layer variants that serve as growth templates for GaSb-based layers on GaAs substrates. The characterization of 75 nominally equal single element detectors per sample evidences the reliability of device processing. The electro-optical evaluation of a randomly chosen subset indicates a high uniformity of responsivity and noise of LWIR InAs/GaSb HOT photoconductors. At 210 K, the devices operate at a cutoff wavelength of 10.5 μm and achieve a mean peak spectral detectivity of 3.3 × 10⁸ Jones.

We report on the fabrication and characterisation of an all-epitaxial Germanium-on-Insulator (GOI) Metal- Semiconductor-Metal (MSM) photodetector. The MSM photodetector is fabricated on a (111)-oriented epitaxial Ge layer, grown on an epitaxial Gd₂O₃/Si(111) substrate, by molecular beam epitaxy (MBE). The first step is the growth of the 15-nm thick Gd₂O₃ epitaxial layer over CMOS-grade silicon, atop which an epitaxial layer of Ge is grown. Near infrared (NIR) MSM photodetectors have been fabricated over the Ge epitaxial layer with an inter-digitated (IDT) contact structure, with an active area of 100 μm x 124 μm. For the particular IDT dimensions, the dark current has been measured to be 475 μA. A responsivity of ~ 2 mA/W is observed at a -5V bias, when excited at 1550 nm.

Methylammonium lead halide perovskites have received substantial attention in photoelectric research communities, because of excellent optoelectronic properties, including long electron-hole diffusion distance, large absorption coefficients in the UV–Vis spectral region, low-cost, solution-based processing and low binding energy of exciton. Many records, such as efficiencies have been kept by these perovskite solar cells. However, other excellent properties, such as ultrafast properties have not been studies intensively. Here vertical field effect phototransistors (VFE_pTs) based on methylammonium lead halide perovskites were design and fabricated. VFE_pTs exhibit high performances including an ultrafast photoresponse time (less than 20 ns) and a high photoresponsivity (~ 10 mAW⁻¹). The methylammonium lead halide perovskite vertical phototransistors open path on ultrafast devices with low cost solution fabrication process, but high level performances.

All-inorganic cesium lead halide perovskite quantum dots (PQDs) have been applied in optoelectronic fields owing to their unique properties including high carrier mobility, air stabilities and highly efficient photoluminescence. To overcome existing limitations in photodetection for light with particular wavelength and cost of state-of-the-art systems, new-style device structures and composite material systems are needed with low-cost fabrication and high performances. Here we synthesized the CsPbX₃ (X = Cl, Br, and I) PQDs by changing the composition at room temperature and fabricated vertical field effect phototransistors (VFEpTs) with Au/Ag nanowires as the transparent source electrode and composition-dependent CsPbX₃ (X = Cl, Br, and I) PQDs as active materials. It dominates to obtain photoresponse for specific wavelength in the visible spectrum and high performances. Particularly, VFEpTs based on CsPbCl_1.5Br_1.5 CsPbBr₃, and CsPbBr_1.5I_1.5 PQDs are sensitive for blue, green, and red lights, respectively. It is worth mentioning that the device exhibits quantitative characterization for the contents of white light. Furthermore, CsPbX₃ VFEpTs exhibit high performances including a short photoresponse time (less than 6 ms) and a high photoresponsivity (<9 × 10⁴ AW⁻¹). Allinorganic PQDs open up opportunities to integrate inorganic semiconductors, into high performances and flexible devices by using low cost, room temperature, large area, and solution based methods.

In this work, metal-semiconductor-metal photodetectors (MSM PDs) on a GeSn-on-insulator (GeSnOI) platform were demonstrated. This platform was realized by direct wafer bonding (DWB) and layer transfer methods using 9% Sn composition of GeSn film epitaxial-grown on Si. The compressive strain in the GeSn film was observed as ~0.23%, which indicates a significant reduction of the strain compared to the ~5.5% lattice mismatch at an interface of the Ge_0.91Sn_0.09/Si. GeSn MSM PDs demonstrated on a GeSnOI platform displayed a low dark current of 4nA at a 1V of bias voltage due to the insertion of a thin aluminum oxide (Al₂O₃) layer in an interface of metal/GeSn for an alleviation of Fermi-level pinning. The responsivity was 0.5 and 0.29 A/W at the wavelength of 1,600 and 2,033nm at 2V, respectively. This work paves the way for GeSnOI photonics as the next promising platform along with Si-on-insulator (SOI) and Ge-on-insulator (GOI) platforms for mid-infrared (MIR) communication and sensing applications.

Refractive lenses that offer color correction over a wide spectral range often rely on a complex design with multiple elements to reduce chromatic aberration. In this work we demonstrate a two-element lens design with achromaticity spanning the visible to the mid-infrared. The air-spaced doublet designed from commercially available materials show significant reduction in spot size and chromatic shift compared to single lens alternatives. The lenses were tested on a beam-scanning sum-frequency generation (SFG) microscope to validate the improved optical performance. Though standard practice is to use reflective components for ultra-broadband applications, limitations in performance, particularly at off-axis field angles, provide merit for the use of broadband refractive focusing optics.

Elastomeric mirror is one of the main components of systems that require tunable optical characteristics, and is being applied in various devices such as optical zoom camera, electrostatic actuator, and augmented/virtual reality (AR/VR) display. Generally, to fabricate an elastomeric mirror, a metal layer is deposited on an elastomer substrate by vacuum process such as thermal evaporation, e-beam evaporation, and sputtering. However, these processes can damage the elastomeric substrate, thereby degrading the quality of the mirror surface. The metal layer formed on the elastomeric substrate is also vulnerable to small deformation, which limits applications of elastomeric mirror. In this work, we report all-solution-processed elastomeric mirror film whose constituent layers were deposited sequentially by spin coating and dip coating method. The film consists of polydimethylsiloxane (PDMS) base, aluminum (Al) mirror, and PDMS encapsulation layer. As a material of mirror layer, we selected a ‘mirror ink’, which composed of Al powder, organic solvent, adhesive and mainly used for screen printing. We adjusted the dilution concentration of mirror ink to make it suitable for the solution process and controlling the roughness of the coated mirror layer. In addition, there was no damage to the mirror layer against deformation due to the presence of encapsulation layer, so it can be attachable well to the curved surface. As an example of application, we demonstrated a seamless display system by placing the elastomeric mirror between two curved panels. We expect that our elastomeric mirror will be applicable to various tunable optical systems.

Injection moulding is key to fast mass production for smart devices, mobility and medical products, like micro-optics, covers and lab-on-a-discs respectively. For optics, several million if not billions of small lenses are merged into objectives. One characteristic type of objective holder is the lens barrel. The successful assembly of lenses with diameters of just a couple of millimetres into a lens barrel is an error-prone task antagonized with mass production and an optical inspection at the end of the assembly. Before the assembly and after the manufacture of the individual optics, the sprue separation takes place. This is a critical moment because even optics whose dimensions are within the target tolerance after manufacturing can be damaged by improper action. Common methods here are the separation by means of a blade, hot wire, laser or saw blade. Each of these methods has its advantages and disadvantages, but all have in common the introduction of stress and/or heat into the component. The Fraunhofer IPT investigates a much more elegant way removing the sprue from injection-moulded optics in an automated environment. Based on the ultrasound technology developed by IPT back in the 1980s, we use a high frequency generator to get an AC voltage and piezo crystal for the inverse piezoelectric effect. The crystal oscillates with a high frequency and low amplitude. Next, the λ/2 to λ/4 sonotrode amplifies the amplitude. The sonotrode is designed with a CAD model, simulated in ANSYS and the complete experimental verified on real lenses afterwards.

DOC is a coating technology that combines a CVD diamond-like carbon (DLC) film and a physical vapor deposition (PVD) coating in a custom coating chamber. DOC coatings combine the best attributes of DLC and PVD, while minimizing their disadvantages. Traditional PVD IR coatings on windows, lenses and mirrors have good optical properties, but are relatively soft, making them easily scratched during cleaning and handling. DLC coatings are extremely durable but have limited optical performance, bandwidth and higher absorption losses. DOC is not quite as hard or durable as DLC, because it is relatively thin. However, DOC is harder and more durable than standard PVD films. The advantage of DOC is that it is able to be integrated into the optical coating design. This allows coatings to be designed with similar performance to a traditional PVD film, but with much improved durability. Many demanding applications from aerospace to 3D printing have found DOC to be a good solution. In this paper various applications that incorporate DLC or PVD coated optics will be compared with DOC coating alternatives, providing insight for possible solutions using this new technology.

A few different Sodium borate glasses were made by the melt quenching technique. A sodium borate glass embedded with Dy³⁺ revealed white color when excited by a diode laser. A chromaticity diagram was developed which revealed color coordinates to be x=0.403 and y=0.426 for 375 nm diode laser excitation. A glass that was embedded with Dy³⁺, and Sm³⁺ revealed warm white light under diode laser excitation. However, another glass embedded with Dy³⁺, Sm³⁺, and Tb³⁺ revealed warm white light whose color coordinates are x=0.375 and y=0.455 and the coordinated color temperature is 5173 K.

The ternary chalcogenides LiGaS₂ (LGS) and LiGaSe₂ (LGSe) are well known semiconductors and widely used for laser induced damage thresholds (LIDT), optical parametric amplification (OPA) and other nonlinear optical (NLO) devices in infra-red region. The first-principle calculations with local density approximation (LDA) are performed to calculate the Debye temperature of LiGaS₂ and LiGaSe₂ semiconductors. The values of longitudinal, transverse and average sound velocities and Debye temperature are studied at 0, 10 and 20 GPa pressures and await for experimental verification. The values of bulk modulus (B) and shear modulus (G) have also been calculated. The present study shows that LiGaS₂ and LiGaSe₂ both are stable upto 20 GPa pressure and become unstable afterwards. The estimated values of all parameters are in good agreement with the available known values at 0 GPa pressure.

We performed numerical analysis of the propagation characteristics of transversely disordered optical fibers with random hexagonal As₂Se₃ and AsSe₂ rods for infrared light in the wavelength of 1-10 μm using beam propagation method and finite element method. Local confinement by random refractive index distribution was observed in both methods. It was revealed that the beam diameter is minimal around a hexagonal rod pitch of 0.8 times of the wavelength.

Grating is an important optical element widely used in high power laser system which is required for higher diffraction efficiency and high laser damage threshold. Compared with the traditional grating materials, diamond has excellent optical transmission properties, high anti-damage threshold, high thermal conductivity etc. Diamond grating has wide application prospect in high power laser system. Based on rigorous couple wave analysis method (RCWA) diffraction characteristics of diamond gratings with different structures were simulated and optimized; Also the diffraction characteristics of between diamond gratings and fused silica gratings were compared and analyzed. The studies showed that the optimized diamond grating could obtain high diffraction efficiency more than 94% in wider bandwidth and the bulk of diamond grating would be much smaller than that of fused silica gratings.

A KTa_1-xNb_xO₃ (KTN) varifocal lens achieves a fast response of microseconds, a large aperture of 3 mm, a random change of focusing length and a high transmission exceeding 99%. However, the variable lens power is smaller than that of other varifocal lenses. We successfully revealed the best way to obtain a variable lens power of 5 m^-1 with a KTN varifocal lens. We simulated the relationships between the length of a KTN lens and both wave aberration and variable lens power. The wave aberration increased with increases in variable lens power. We employed the ratio of the wave aberration to the variable lens power to evaluate the scanning resolution, which improved as the ratio decreased. The best length for a KTN lens was 5.3 mm for an octagonal structure whose aperture size, thickness, and electrode angle were 3 mm, 4 mm and 26.5 degrees, respectively. Our experimental results agreed with the simulation. A wave aberration of less than λ/ 10 (λ=1064 nm) and a variable lens power of 0-2.5 m^-1 were obtained. We concluded that combining a pair of optimized structures was the best way to obtain a variable lens power of 0-5 m^-1, which is comparable to that of varifocal lenses using other principles.

We have studied polluting gases in tobacco smoke by investigating the phenomenon of capturing and photocatalysis effects of ZnO nanowire array (NWA). Capturing and photocatalysis reactions were continuously tracked by FTIR spectroscopy. The presence of ZnO improves the capture rate at room temperature, while the photocatalytic reactions can lead to a further reduction of the pollutants. MEMS-FTIR spectrometer operating in the Mid-Infra-Red appeared as a very promising tool for the online monitoring of air purification process.

Neodymium (Nd)-doped fibers are potential candidates for optical fiber amplifiers operating near the 1.3-μm spectral region due to the ⁴F_3/2→⁴I_13/2 transition of Nd³⁺ ions. But, there is an amplified spontaneous emission at 1.06 μm due to the ⁴F_3/2→⁴I_11/2 transition whose branching ratio is about 5 times larger than that at 1.3 μm. In order to suppress the transmission of the 1.06-μm emission, we propose a new tellurite all-solid photonic bandgap fiber (ASPBF) with a single line of high index rods and double cladding layers. Tellurite glasses of TeO₂-Li₂O-WO₃-MoO₃-Nb₂O₅ (TLWMN), TeO₂- ZnO-Na₂O-La₂O₃ (TZNL) and TeO₂-ZnO-Li₂O-K₂O-Al₂O₃-P₂O₅ (TZLKAP) are developed. High-index rods of TLWMN and an Nd-doped TZNL rod are arranged symmetrically and horizontally in the x-axis of a hexagonal TZNL cladding. The outer cladding is made of the TZLKAP glass. The finite element method is used to calculate the mode distribution and the bandgap properties. The fiber transmission spectra are numerically investigated with the effects of rod diameter and filling factor variation. When the core diameter is 3.0 μm, rod diameter is 2.3 μm and filling factor is from 0.7 to 0.8, the 1.06-μm emission which is caused by the ⁴F_3/2→⁴I_11/2 transition can be suppressed as compared with the 1.33-μm emission which is caused by the ⁴F_3/2→⁴I_13/2 transition.

Single-mode Er-Yb fibers based on phosphorosilicate glass matrix highly doped with fluorine have been fabricated using modified all-gas phase MCVD technology. Fibers have core doped by 6.5 mol.% of P₂O₅, 0.9 wt.% of F and different concentration of Er and Yb. The core NA was about 0.07-0.08 relative to the pure silica level. Slope efficiency of more than 19% was achieved using amplifier scheme with co-propagating pump at 976 nm and signal at 1555 nm (input signal power was about 0.6W). Slope efficiency in the laser configuration has reached 34% relative to the input pump power.

Mold free and additive embedding of quasi-spatial filter (QSF) for simple optical detection was proposed. With a concept of “silicone optical technology (SOT)” we proposed, fully flexible and digitally fabrication of compact optical module for flow-injection analysis (FIA) was demonstrated. It was attained by combining silicone 3D printed rough-frame and injecting and coating method for embedding SOT-QSF that can trap unexpected light signal as tilted incidence. SOT-QSF’s coaxial cylindrical structure of PDMS core and carbon-dispersed-PDMS clad was fabricated by injecting and coating method. The coating properties and optical trapping performance was evaluated. These embedding techniques and method developments will be useful for on-site applications with general FIA researches and for rapid on-demand-fabrication based on researcher’s idea.

The optical properties of hydrogenated graphene have been studied at different occupancies of hydrogen atoms using first-principle density functional theory (DFT) calculations. The optical parameters such as dielectric function ε(ω), refractive index n(ω), absorption spectrum α(ω) and electron energy loss function L(ω) have been studied at 25%, 50%, 75% and 100% occupancies of hydrogen on pristine graphene for the first time. The calculated values for 100% occupancy agree well with the values reported in our earlier publication. However, for other occupancies await for the experimental verification. The present study gives the information about the variation of above parameters at different occupancies, which is of great importance for selecting the materials for substrate in IC design and designing the various linear and nonlinear optoelectronic devices.

We have proposed the systematic measurement of coating geometry for specialty fibers based on dark field illumination technique. The measured dark-field projection image shows clear interfaces between different refractive index materials. Using own developed image processing tool, the interfaces automatically detected and analyzed. Every degree of measurements provides circularity of each layer and then shows the center point of individual layer. Using this technique, coating diameter, coating non-circularity and coating ellipticity for double clad fiber were successfully measured and high resolution camera also detected some of existing coating defect and delamination.

In this work we demonstrate the advantages of investigating diffractive optical elements in the phase domain. In this regime we can detect features that are not restrained by the diffraction limit and relate them to the geometrical and optical properties of the sample under test. To accomplish that, we use the custom made spectral high resolution interference microscope. Phase map recordings allow for easier and more precise localization of the positions, where phase changes happen. We show the localization capabilities by detecting phase singularities created by a trench. We also apply the concept to abrupt phase jumps of a phase diffractive component and determine the achievable resolution.

In this paper, a novel design of circular photonic crystal fiber (C-PCF) gas sensor is presented and analyzed by full vectorial finite element method. The suggested design has a spiral porous core region to achieve high sensitivity. The geometrical parameters of the proposed sensor are studied to achieve high sensor sensitivity. The introduced C-PCF offers high sensitivity of 72.04 % at the wavelength of 1.33 μm. The reported sensor also offers a compact, accurate and useful tool for detecting harmful gases over a wide transmission band from wavelength of 1 μm to 1.8 μm.

We propose and design long-range hybrid plasmonic waveguides (HPW) consisting of a combination of plasmonic thin film and nano-scale structures of a high refractive index material (such as silicon), with a low refractive index material (such as silica) surrounding the nano-scale structures and the plasmonic thin film. The effective refractive index and the corresponding propagation length obtained for these plasmonic waveguides, obtained using a full-vector finite difference eigen mode (FDE) solver, demonstrates the viability of these hybrid plasmonic waveguides in applications that demands long propagation range with reasonable field confinement. These waveguides not only have high propagation lengths ⎯ even greater than 1 mm for certain geometrical parameters of the plasmonic waveguides ⎯ but can also have tight mode confinement (low effective mode area). Moreover, the proposed hybrid plasmonic waveguides can also be easily fabricated using the conventional nanolithography processes. Moreover, we study the effect of the variation of different waveguide parameters on the propagation length and effective mode area.

Rare earth-doped fiber lasers are interesting in the field of optical fiber lasing and sensing. One of the interesting topics is the tunable/switched multi-wavelength lasers. However, due to the homogeneous broadening gain, it is difficult to generate multiple wavelengths in the fiber lasers based on erbium-doped fibers. Here, we propose a tunable multiwavelength erbium-doped fiber ring laser based on an optical fiber tip Fabry-Perot (FP) interferometer, which acts a wavelength filter and a reflector of the fiber ring laser. With the purpose to propose a method for switch multiwavelength spectra, the strain and thermal variations around the modal interferometers are investigated. The spectra are symmetric with a maximal power difference about 25 dB between the lasing modes and the average of the side mode suppression ratio, which is tuned into the C-band with a resolution of 0.02 nm. This laser offers low wavelength drift, good signal to noise ratio and high-power stability, and can therefore be used for sensing applications.

The ability of a lens assembly to withstand extreme environmental conditions is a common problem for engineers. Once the optical engineer has a design that matches the required optical specifications, the opto-mechanical engineer is tasked with developing mechanics that can withstand the environmental specification. Using FEA and theoretical analysis, a StingRay GhostSight VisSwir lens was put through varying levels of common environmental stresses experienced within the field, including high shock and vibration as well as extreme temperature and pressure variations. The GhostSight was then mechanically modified in subtle ways to improve performance against these stresses. These same modifications can be implemented in other lens assembly designs to provide similar high performance capabilities in extreme settings.

High efficiency, Ge-on-Si single-photon avalanche diode (SPAD) detectors operating in the short-wave infrared region (1310 nm - 1550 nm) at near room temperature have the potential to be used for numerous emerging applications, including quantum communications, quantum imaging and eye-safe LIDAR applications. In this work, planar geometry Ge-on-Si SPAD designs demonstrate a significant decrease in the dark count rate compared to previous generations of Ge-on-Si detectors. 100 μm diameter microfabricated SPADs demonstrate record low NEPs of 2.2×10^-16 WHz^-1/2, and single-photon detection efficiencies of 18% for 1310 nm at 78 K. The devices demonstrate single-photon detection at temperatures up to 175 K.

This paper presents a technique for temperature cross-sensitivity compensation in liquid level sensor based on an in-fiber Mach-Zehnder interferometer. By using a commercial splicing machine and three different fibers, it is possible to construct a liquid level sensor with range of 120 mm and submillimeter resolution (0.88 mm). The sensor arrange is anchorage into a glass pipette, where the liquid level can be easily supervised. A broadband source is used to illuminate the sensor and the transmitted spectrum is monitored with an optical spectrum analyzer with 30 pm resolution. The interference pattern, created by the interferometer, is analyzed with either the traditional method of tracking peaks and dips or the overall spectrum envelope. These interferometers are sensitive to temperature variations, leading measurements errors on the liquid level estimation. Thus, an analysis of the temperature effect in the sensor response is performed. The result shows that the proposed technique reduces the sensor temperature cross-sensitivity by more than an order of magnitude. With traditional method (using peaks and dips), the value achieved was ~9.595 mm/°C, whereas the proposed approach based on the spectrum envelope leads to a temperature cross-sensitivity of about 0.562 mm/°C. The proposed sensor arrange is suitable for industrial applications such as chemical processing, fuel storage and transportation systems, oil tanks/reservoirs, and treatment plants, where there is simultaneous variations of temperature and level.

Publisher’s Note: This paper, originally published on 27 February 2019, was replaced with a corrected/revised version on 28 December 2020. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.

Publisher’s Note: This paper, originally published on 27 February 2019, was replaced with a corrected/revised version on 16 November 2021. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.