This PDF file contains the front matter associated with SPIE Proceedings Volume 12417, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

In recent years, a growing interest has settled for optical materials and fibers for the mid infrared (mid-IR) region. This interest originates from societal needs for health and environment for instance, and also from demand for defence applications. Indeed, the mid-IR spectral region contains the atmospheric transparent windows (3-5 μm) and (8-12 μm) where thermal imaging (military and civilian) can take place. The elaboration of chalcogenide microstructured optical fibers (MOFs) permits to combine the mid infrared transmission of chalcogenide glasses up to 18 μm to the unique optical properties of MOFs thanks to the high degree of freedom in the design of their geometrical structure. In this context, additive manufacturing of glass materials appears as an attractive technique to achieve more elaborate designs that can hardly be obtain using more common methods such as the stack-and-draw or molding. Taking advantages of the specific physical properties of chalcogenide glasses such as low Tg and extrusion temperature, we have shown that chalcogenide preforms can be rapidly obtained by fused deposition modeling (FDM) using a customized RepRap-style 3D printed fed with chalcogenide glass rods. Such as-prepared preforms can be drawn into chalcogenide optical fibers. Those early-stage results open a new way for the elaboration of chalcogenide MOFs.

All material types are being considered, from crystals to ceramics and glasses, with focus on those RE3+ hosts with low maximum energy. In this work, a comparative study was performed on the mid-IR (3-5 um) spectroscopic properties of erbium doped in low-phonon fluoride (BaF2) and chloride (CsCdCl3) crystals as well as sulphide (Ga2Ge5S13) glasses. Among the studied materials, Er3+:CsCdCl3 showed the longest 4I9/2 emission lifetime of ~11 ms whereas the ~ 46 us observed from Er3+:BaF2 was the shortest 4I9/2 lifetime. These results reflect the reduced nonradiative rates through multiphonon relaxation in chloride crystals. Spectroscopic results and data modeling including the temperature dependent emission and decay dynamics, Judd-Ofelt analysis, and transition cross-sections will be presented.

We report the results of the effect of prolonged low-Earth orbit exposure on phase-change materials (PCMs) and PCM-based metasurfaces. During a 6-month exposure as part of the Materials on the International Space Station Experiment (MISSE-14) test campaign led by NASA Langley Research Center, Ge2Sb2Te5 (GST) and GST-based metasurface spectral filters were monitored for their response to extreme temperature cycles, UV and ionizing radiation fluences, and atomic oxygen fluences. Upon return to Earth, the samples were characterized and compared to their pre-flight condition to glean insight into the effects of the space environment on metasurface performance and PCM optical and structural properties.

We present a femtosecond laser written, apodized chirped fiber Bragg grating (acFBG) used for dispersion control inside picosecond all-fiber lasers. A fiber fixation setup enables a plane-by-plane (pbp) written acFBG in a standard, polarization-maintaining fiber by applying a beam-slit configuration. The spectral specifications of the acFBG are examined in detail, and the grating is validated inside a mode-locked fiber laser oscillator. This letter provides a route to the fast prototyping of acFBGs with customized parameters for use as dispersion compensating elements inside ultrafast all-fiber lasers.

We report on the systematic investigation of a polymer-optical fiber Bragg grating (POFBG) sensor for shape deformation with regard to its temperature and humidity sensitivity under various bending conditions and additionally with regard to strain and torsion, which are all relevant effects in the designated application in a novel 3D shape detection sensor system. The concept relies on the fast and simple inscription of Bragg gratings in graded-index multimode cyclic transparent optical polymer (CYTOP) fibers with the phase mask method and a krypton-fluoride excimer laser in the UV. When the fibers undergo deformation such as strain, torsion or bending or are affected by environmental effects, the lattice constant of the FBGs as well as the optical components can change and the spectral position of the Bragg peak shifts accordingly into the red or blue wavelength region. While the cross-sensitivity to humidity is relatively small over the full range from 10% to 98% relative humidity and, therefore, negligible, the cross-sensitivity to temperature is relevant and lies in the range from 17.2 pm/K (straight position) to 45.6 pm/K (upward bending position). The effect of strain on the sensor can be observed by the shift of the Bragg peak to the red wavelength region. Also, the impact from torsion on the sensor is clearly observable, even after multiple turns of the fiber, and the functionality of the sensor is preserved when plastic deformation occurs. The presented results offer the potential to use the sensor in everyday applications and specifically to track the motion of human hands. For example, sensor gloves can be used to detect early stage of motion impairment of focal dystonia patients in medical diagnostics or for augmented and virtual reality devices.

Femtosecond laser point-by-point writing is a commonly used method for fabrication of Fiber Bragg Grating sensors dedicated to harsh environments, such as high temperature or irradiation. In addition, a femtosecond laser platform allows for inscription of compact fiber optic diffraction gratings that consist of micro-voids or filaments formed into the fiber core and cladding by focusing laser pulses using microscope objectives. Light propagating in the fiber is coupled to radiation modes due to Mie scattering, thus providing wavelength dispersion in free space. Chirping the grating period further allows focusing of the outcoupled light in a given plane. Such an all-fiber focusing grating forms a compact photonic device permitting its use for FBG sensor interrogation. In this paper, fabrication of such spectrometers operating at 850 and 1550 nanometers is described. A characterization setup allowing measurements of spectra of FBGs at those wavelength bands is presented, and results corresponding to various focusing distances, grating lengths and chosen microscope objectives are exposed. Azimuthal distribution of scattered light is discussed, as well as focusing distance versus grating period chirp and spectrometer resolution versus grating length. Finally, spectra reflected by pointby- point FBG sensors are presented, thus demonstrating the great potential interest of such gratings for FBG interrogation.

Conventional UV-inscribed fiber Bragg gratings (FBGs) start to lose their reflectivity (‘bleach’) at temperatures above 200°C [1]; at 380°C, they bleach completely. Using a focused fs IR-laser it is possible to generate extremely stable gratings in any optically transparent materials, independently from the fiber material and doping. These type II gratings are known to be reflective at temperatures up to 1000°C [2]. UV-inscribed FBGs require stripping and re-coating of the polymeric coating due to the high absorption of UV light by the typical coating materials. This can allow moisture to be trapped, which weakens the glass. Femtosecond FBGs can be written through many different coatings, including polyimide, which retains its integrity at temperatures up to 300°C. In order to take full advantage of the capabilities of a Femtosecond FBG, it would be beneficial to have a coating that can withstand higher temperatures. Metal-coated fibers are capable of withstanding temperatures up to 500°C and beyond – but Femtosecond lasers are unable to write gratings through the metal coating. In this paper we will demonstrate the first gold-coated Femtosecond FBGs and their performance as a highly sensitive temperature sensor up to 500°C. The spectra of the FBGs are to be compared before and after the gold coating is applied to show that the coating does not have an impact on FBG performance. Data will be presented comparing FBG measured temperature to that measured by high-sensitivity thermocouple.

Rare-earth-doped fibers with single-crystal cores have the potential for 10x higher TMI threshold than their glass counterparts and are a promising candidate for use as gain media in high-power laser systems. Their utility has been limited by parasitic optical losses and difficulty in fabrication. This paper explores methods to reduce the losses in these fibers in the core, in the cladding and at the core-cladding interface. Fabrication methods are also discussed.

Persistent luminescence (PersL) property offers great potential for anti-counterfeiting applications, by taking advantage of the possibility of making observations under background-free conditions. However, some challenges still persist, mainly due to the low security when working in the visible range. Thus, to overcome those difficulties, materials with near-infrared (NIR) emissions are highly required. In this work, we propose the use of Zn_1.3Ga_1.4Sn_0.3O₄ nanoparticles (ZGSO NPs, with size around 140 nm) doped with Cr³⁺,Ni²⁺,Er³⁺ which have a strong PersL at 700 nm (NIR-I) and at 1300 nm (NIR-II) by optimising the doping ratio of Ni²⁺ and Er³⁺ ions. Such ZGSO PersL NPs have been evaluated for multilevel anti-counterfeiting technology in dual-windows.

We investigated a growth technique for ultra-low-density self-assembled InAs QDs using Bi surfactant-assisted interdiffusion epitaxy (IDE). The samples were grown using a solid-source molecular beam epitaxy system. InP(311)B substrates were used to grow InAs QDs. After growing the InP buffer layer, a 100 nm-thick InGaAlAs barrier layer and a 1 nm-thick InP were used for the IDE process, and self-assembled InAs QD were formed. The density of QDs was very low, approximately 3.2×107/cm2, which is three orders of magnitude smaller than that of the conventional QD. Moreover, sharp photoluminescence was observed from a single QD at 1522 nm.

Three types of halide-perovskite-based fast-acting fluorescent materials have been demonstrated for high-speed visible light communication. All-inorganic metal-halide perovskite CsPbI₃ was utilized to generate red color at 685 nm, and twodimensional (2D) hybrid organic-inorganic halide perovskite nanosheets, (PEA)₂PbI₄ and (PEA)₂PbBr₄ (PEA= C₈H₉NH₃), with peak photoluminescence (PL) wavelengths of 525 nm and 408 nm, were respectively used for green- and blue-light emission. The materials were then embedded in the polymethyl methacrylate (PMMA) to improve their durability and flexibility in practical applications. Pumped by a 405-nm violet laser, the red and green phosphors exhibit –3-dB modulation bandwidths of 14 MHz and 193 MHz, respectively. For the blue phosphor, a 124-MHz –3-dB bandwidth was obtained by using a 375-nm UVA laser diode. Benefitting from either the short PL lifetime or high PL quantum yield, aggregate Gb/s data transmission was achieved in the communication link. Direct current biased optical orthogonal frequency-division multiplexing (DCO-OFDM) modulation scheme was implemented with an adaptive quadrature amplitude modulation (QAM) signal. The transmission net data rates of RGB phosphors are 0.51 Gb/s, 0.93 Gb/s, and 0.43 Gb/s, respectively. The corresponding average bit error ratios are 3.5×10^-3, 3.6×10^-3, and 3.6×10^-3, which are below the 7%-overhead forward error correction (FEC) criterion. Taking advantage of the tunability of the halide perovskite materials covering the whole visible range could further fulfill high-speed color-pure wavelength-division multiplexing by using a single source with multiple luminescent materials emitting light at different wavelengths. Besides, combining luminescent materials with specific colors, simultaneous white-light illumination, and high-speed communication can also be realized.

Knowledge of the optical constants of particulate samples is critical in order to accurately model their optical behavior. For example, the dispersion and attenuation of a silicate sand are required to model scattering through a dust cloud. Most methods of measuring these quantities, however, require a polished solid sample and are therefore not suited to particulates. We present a novel method of measurement based on spectroscopic ellipsometry that can be applied to any particulate material. First, an adhesive compound is prepared and polished, and its optical constants are extracted. Then, a mixture of the adhesive and a particulate sample is prepared, and, treating the mixture as a Bruggeman effective medium, the optical constants of the particulate material are determined. We test the method’s effectiveness using pure silica powder, demonstrating that the results match literature values. The method is then applied to real sand samples. We present data for several types of sand and show that it is possible to accurately determine their optical properties and to observe the Christiansen effect in these samples.

On-chip silicon photonic filters acting as spectral shapers for the input spectrum are important in various applications including optical communication, computing, and spectroscopy sensing. We used the photonics inverse design framework, aided by the Particle Swarm Optimization (PSO) algorithm, to obtain miniature and efficient filtering structures in the Silicon on Insulator (SOI) platform. These optical filters are less than 10 μm, or just a few wavelengths, in size along any dimension. The investigated structures demonstrate good light filtering characteristic, with various filter types and wavelength ranges. The performance of designed filters is comparable to widely-used mm-long Bragg grating filters, while being a tiny fraction of their size. We also study a class of filters to directly resolve the issue of removing back reflected light without using a circulator or adding a third port (as is generally done) using the optimization process. Our structures are expected to have a much wider range of applications than grating-type filters, primarily due to their miniature footprint, independence from external devices like circulators for back-reflection control, and greater tolerance to thermal effects. Our work also highlights the possibility of designing and fabricating photonic components as a next step, by inversely designing components that best match a given set of requirements instead of depending on general conventional devices.

The theoretical transmittance spectra of a highly optimized interference coating design for a tristimulus filter can mimic a target spectrum with near-zero spectral mismatch. But to make such a filter in practice requires a tightly controlled deposition process that employs broadband in situ spectral monitoring which provides continuous feedback and allows subsequent layer correction. We demonstrate spectral matching (using the integral parameter f1') <1.5% and model the effects of spectral mismatch on color measurement accuracy. Optical modeling showing the sensitivity of the filter response to variations in angle of incidence and for determining how to deal with stray light are also demonstrated.

Random antireflection nano-structured surfaces (ARS) have been studied for their broadband antireflection (AR) properties and polarization insensitivity. ARS are designed and modeled using effective medium approximations (EMA) as thin layers of the desired effective permittivity through a global density average, independent of surface feature distributions. To study the AR efficiency of varying transverse feature distributions of ARS on optical surfaces, we methodically simulated and analyzed the performance of pseudo-random deterministic Dammann gratings, acting as a quarter-wave-thickness AR overcoating on a functional binary 50% duty cycle test grating, using rigorous coupled wave analysis. We chose a fused silica dielectric substrate, numerically simulated at normal incidence conditions for both polarizations at 633nm wavelength. The study parameters consisted of Dammann gratings of different orders for evanescent diffraction control, chosen to have effective permittivities comparable to predicted EMA requirements to match AR efficiency, varying periodic scales, and distinct surface distribution autocorrelation scales to control the structure factor. The goal is to elucidate the transition of evanescent coupling orders from the Dammann ARS to the functional test grating, without perturbing the original diffractive performance, while it enhances transmitted overall power efficiency. The simulated results exhibit variations in the performance of candidate designs, signifying the importance of surface feature distributions on the overall efficiency of ARS as an effective antireflection treatment for diffractive components. Not only subwavelength periodicity scales, but nearwavelength scales as well show high transmission efficiency without presence of parasitic orders from the base binary test grating, in contrast to EMA design guidelines.

Organic electro-optic (EO) polymers are promising candidates for high performance modulator. An EO polymer modulator has excellent optical properties such as low driven voltage and high-speed operation. We successfully developed an EO polymer to demonstrate modulator for visible wavelength. A modulator was demonstrated and evaluated using developed EO polymer at wavelength 640nm. As results of applying a voltage to the fabricated modulator, the voltage-length product 0.52 Vcm was obtained. This is much more efficient than the conventional modulator for near-infrared wavelength.

Existing UV sensors often use vacuum photo-multiplying tubes (PMTs). Solid state photodetectors are either blind to UV (use silicon) or have low sensitivity (use wide bandgap semiconductors). We report on our efforts to develop polymer nanocomposites made of the nanoparticles (NPs) of perovskites CsPbX₃ (X stands for Cl, Br, and I) and lanthanide doped compounds that captured UV photons and efficiently converted their energy into visible and near-infrared (NIR) photons. The wavelength of these low-energy photons matches the spectral response of silicon avalanche photo diodes (APDs) with an electronic gain of < 10⁶. For instance, NPs of perovskite CsPbBr₃ with a diameter of 16 nm produced strong visible radiation at 512 nm being excited with a 372-nm UV laser while the NPs of La₂O₃: Eu³⁺ demonstrated strong photoluminescence in red region (between 600 and 650 nm) with a quantum yield of 60%. The nanocomposites were integrated with silicon APDs. The proposed combination worked as a UV detection system with two orders of magnitude improved sensitivity. Such a photodetector is particularly useful for the non-line-of-sight (NLOS) free space optical communication (FSO) in the solar-blind spectral region 100-280 nm where the background noise from solar UV radiation is eliminated due to absorption by ozone layer in the upper atmosphere.

Avalanche photodiodes (APD) can improve the signal to noise ratio in applications such as LIDAR, range finding and optical time domain reflectometry. However, APDs operating at eye-safe wavelengths around 1550 nm currently limit the sensitivity because the APDs’ impact ionization coefficients in the avalanche layers are too similar, leading to poor excess noise performance. The material AlGaAsSb has highly dissimilar impact ionization coefficients (with electrons dominating the avalanche gain) so is an excellent avalanche material for 1550 nm wavelength APDs. We previously reported a 1550 nm wavelength AlGaAsSb SAM APD with extremely low excess noise factors, 1.93 at a gain of 10 and 2.94 at a gain of 20. Using a more optimized design, we have now realized an AlGaAsSb SAM APD with a lower dark current (7 nA at a gain of 10 from a 230 μm diameter APD), a higher responsivity (0.97 A/W) and a lower excess noise (1.9 at a gain of 40), compared to our previous SAM APD. Noise-equivalent-power (NEP) measurements of our APD with a simple transimpedance amplifier circuit produced an NEP 12 times lower than a state-of-the-art APD under identical test conditions, confirming the advantage of low-noise AlGaAsSb SAM APDs.

Plasmonic metasurfaces composed of arrays of rectangular metallic bars are well known for their strong optical response in the infrared spectral range. In this study, we explore the polarization sensitivity of plasmonic metasurfaces for encoding information. The polarization-sensitive optical response depends strongly on the orientation of the metallic bars allowing the encoding of information into the metasurface. Here we demonstrate that a 2-dimensional polarization encoded metasurface can be obtained by using mask-less two-photon polymerization techniques. This novel approach for the fabrication of plasmonic metasurfaces enables the rapid prototyping and adaptation of polarization sensitive metasurfaces for the encoding of multiplexed images.

Developing single photon avalanche diodes (SPADs) at short-wave infrared (SWIR) wavelengths beyond 1000 nm has attracted interest lately. Numerous quantum technology applications such as light detection and ranging (LIDAR), imaging through obscurants and quantum communications require sensitivity in this region. In quantum communications, operation at the telecoms wavelengths of 1310 nm and 1550 nm is essential. Ge-on-Si SPADs offer potential for lower afterpulsing and higher single photon detection efficiencies in the SWIR in comparison with InGaAs/InP SPADs, at a lower cost due to Si foundry compatibility. In this study, Ge-on-Si devices are fabricated on silicon-on-insulator (SOI) substrates, with a separate absorption, charge and multiplication layer (SACM) geometry and a lateral Si multiplication region. This Si foundry compatible process will allow for future integration with Si waveguides and optical fibres. The Ge is selectively grown inside sub-μm wide SiO₂ trenches, reducing the threading dislocation in comparison with bulk Ge; a typical process for integrated Ge detectors. Here we deliberately exposed Ge sidewalls with an etch-back technique, to allow a passivation comparison not normally carried out in selectively grown devices planarised by chemical-mechanical polishing. Reduced dark currents are demonstrated using thermal GeO₂ passivation in comparison to plasma-enhanced chemical-vapourdeposition SiO₂. The improved passivation performance of GeO₂ is verified by activation energy extraction and density of interface trap (D_it) calculations obtained from temperature-dependent capacitance-voltage (CV) and conductance-voltage (GV) measurements. This highlights the benefit of optimal surface passivation on sub-μm wide selectively grown Ge-on-SOI photodetector devices, potentially critical for waveguide integrated SPADs.

As part of the laser development process, NASA’s Goddard Space Flight Center (GSFC) requested support from the NASA Engineering and Safety Center (NESC) to independently assess the Technology Readiness Level (TRL) of the LISA Laser System (LS). The independent assessment included the following tasks: (a) assess the design for weaknesses and suggest improvements to mitigate risks, (b) assess the laser reliability plan for weaknesses and suggest improvements to mitigate risks and improve effectiveness, and (c) assess the current redundancy plan on laser subsystems for weaknesses and suggest improvements to mitigate risks and improve effectiveness. The presentation will focus on the assessment findings and the current development progress of the LISA laser to meet the mission requirements with a delivery of a form, fit, and functional TRL6 laser to the LISA mission by late 2023.

This work presents an accurate experimental comparison among the spectro-temporal performances of near infrared and visible emitting solid state random lasers under ultrafast pumping. The near infrared random lasers are based on stoichiometric Nd crystal powders whereas the visible random laser is a ground powder of a hybrid compound based on Rhodamine B incorporated into a di-ureasil host. We demonstrate that despite the different nature of the base materials, the spectro-temporal dynamics of both kind of systems can be described by a rate-equations model based on the photon paths in an amplifying medium with an exponential probability distribution.

Tuning color output and enhancing upconversion emission of Er³⁺ ions in transparent sodium lutetium fluoride glassceramics in bulk and optical fibers, by adjusting the Yb³⁺ doping level and the excitation power, has been demonstrated. The addition of Yb³⁺ enhances the UC emission and tunes the color from green to yellow due to an increase of the red-to-green intensity ratio. Moreover, the relative emission intensities of blue, green, and red emissions can be changed by controlling the excitation power which tunes the color from yellow to green.

There is strong medical demand for continuous CO2 partial pressure (pCO2) monitoring. While there has been significant progress in the development of CO2 sensors, their implementation with optical wearable device remains under-explored. We have developed highly sensitive, rapidly responding, humidity insensitive and photostable CO2 sensing materials that can be used with optical wireless wearable device for real-time monitoring pCO2. The preliminary results reveal the prototype device is able to reliably detect reversible CO2 changes within physiological ranges.

We report on the development, test and comparison of a prototype sensor glove for 3D shape detection of the human hand. The prototype is based on polymer optical fibers with eccentrically inscribed Bragg gratings, which are mantled with a simple jacket woven into a textile fabric glove. All of these elements are lightweight and flexible, taking away the drawback of motion handicaps, that sensor gloves usually come with due to material stiffness. The sensor glove is tested with a set of approximately 15 different and simply defined hand gestures, which incorporate iconic and everyday gestures like grasping a cylindrical shape or showing numbers with fingers, assisted with 3D printed models. Hence a set of gestures is defined, subsequently we compared two commercial systems based on optical sensors from 5DT (Data Glove 5/ 14 Ultra) with the prototype. The prototype is not capable to measure motion accurately yet, due to its long integration times as of now, it is, however, advanced in the measurement accuracy, especially regarding the direction of the shape deformation, which is rendered possible by the structure of the FBG sensor. In the next steps, the integration time of the sensor, as well as its illumination and the evaluation will be improved. For that step, the light source, the optical spectrum analyzer and the computer will be replaced by integrated devices like LEDs, photodiodes and single-board microcontrollers. In the future, the gloves, as well as the used technology of the sensor, offer the potential for application in logistics, virtual and augmented reality as well as medical diagnostics and general observation.

The state-of-the-art quantum infrared photodetectors have high performance, but obtaining high sensitivity in mid- and long-wavelength infrared (MWIR and LWIR) requires cooling and exotic materials. Whereas thermal detectors offer lower cost without the need for cooling but are typically slower and less sensitive than cooled quantum infrared detectors. Nanothermoelectrics and nanomembranes offer opportunities for enhancing the performance of uncooled MWIR and LWIR imaging and sensing. Similar to thermoelectric detectors, the infrared sensitive signal in those is generated by the thermoelectric effect, providing advantages over resistive bolometers, i.e. less noise sources and zero power consumption in the detector itself. We have recently demonstrated that nano-thermoelectrics provides a route towards high-sensitivity and cost-effective LWIR detection. When the thickness of the thermoelectric polysilicon membrane is reduced, increased phonon scattering leads to reduced thermal conductivity. This gives rise to the high thermoelectric figures of merit determining the detector sensitivity. The speed stems from the low-thermal-mass device design with an integrated metal nanomembrane absorber and the lack of separate support structures. We report integrated circuit concept for the readout of these detectors, and study how the absorber grid geometry determines the device performance. The fabricated devices have thermal time constants, responsivities and specific detectivities D* in the ranges of 190 – 208 μs, 334 – 494 V/W, and (7.9 – 8.7)·10⁷ cmHz^1/2/W, respectively. The differences in the device performance originate from the differences in the thermal mass, total resistance, and impedance matching of the absorber grid. By optimization, we expect that D* = 8.3·10⁸ cmHz^1/2/W can be reached.

In this work, we demonstrate a compact pn junction ring modulator with very large extinction ratio and high quality factor. The modulator consists of a 5-μm radius ring and a single-bus straight waveguide. Both the ring and straight waveguides have a width of 480 nm and heigh of 220 nm. The waveguides are rib-structured and the rib thickness is 110 nm with a slab thickness of 110 nm from a 300mm wafer with 220-nm silicon-on-insulator (SOI) thickness. A 100-nm gap is designed between the rib ring and the bus waveguides. The modulator has three nominal doping levels with concentrations of 10¹⁸, 10¹⁹, and 10²⁰ cm^-3 for the core, slab, and the contact areas, respectively. The device is fabricated using the American Institute for Manufacturing integrated Photonics (AIM Photonics) Multi-Project Wafer (MPW) service. It is tested using the AIM Photonics inline vertical gratting coupled automated tool with a tunable light source that has wavelengths ranging from 1485 nm to 1590 nm and a wavelength resolution of 60 pm. The fabricated 5-μm radius ring modulator exhibits high quality output with a very large extinction ratio of 29 dB over a broad wavelength spectrum of about 100 nm. The device has a very wide free spectral range (FSR) of about 19 nm.

We propose a novel modular photonic integrated Wavelength Selective Switch (WSS) based on a reconfigurable optical multiplexer architecture, capable to operate over the S+C+L bands and scalable. The densely integrated solution takes advantage of an input stage with grating assisted contra-directional couplers to separate channels in the three considered communication bands, followed by a cascade of two-stage ladder ring resonators, to separating each transmitted channel. A final switching stage routes the signal to the desired output fiber, with a cascade of thermally controlled Mach-Zehnder interferometers. The transmission penalty of the proposed solution has been evaluated in a coherent transmission scenario.

We successfully fabricated 150 mm diameter Ytterbium doped Yttrium Aluminum Garnet (Y₃Al₅O₁₂, YAG) transparent ceramics with high optical quality by the solid-state reaction method. In-line transmittance of Yb:YAG ceramics at 1030 nm was found to be equal to that of single crystal Yb:YAG. We confirmed that there is a good correlation between Yb³⁺ dopant concentrations (0.35-10.0 at. %) and absorption spectra. We also confirmed that our Yb:YAG transparent ceramics have good uniformity of Yb³⁺ concentration and excellent optical properties. Our Yb:YAG transparent ceramics show promise as a laser gain medium for high-power laser applications.

Optical fibers are commonly used for data transmission and sensing in industrial, geophysical, and aerospace markets, where they may be employed in high vacuum and cryogenic environments. The performance and integrity of optical fibers and their coatings is well understood over temperatures of ≈40 to 300 °C and pressures up to 100 atm, but their characteristics at cryogenic temperatures under high vacuum remain relatively unexplored. This study investigates the optical and mechanical reliability of selected fibers operating at cryogenic temperatures. The fiber samples under investigation were prepared with either an acrylate or polyimide coating. Several properties of the fibers were assessed, including optical loss, mechanical strength, and coating integrity. Optical loss was monitored continuously over a single temperature cycle from 300K to 4K and back. Additional samples were subjected to either one or three temperature cycles and held at 4K for extended periods. Mechanical strength of the thermally cycled fibers was determined via a 2-point bend method, and the coating material was characterized using Fourier transform infrared spectroscopy and thermogravimetric analysis.

Oxide and hydroxide minerals are a class of inorganic materials commonly associated with metals and are used in a wide variety of applications ranging from pigments and environmental cleanup to battery cells and catalysts. This work presents initial characterization of synthetic crystals of goethite, hematite, and cryptomelane subjected to shock compression experiments using transmission electron microscopy (TEM) and confocal Raman spectroscopy (CRS). Given the high adsorption property of these minerals, doping with rare-earth elements has the potential to result in novel optical properties and applications.

This paper presented a sensitivity analysis of petrol adulteration. The benzene and xylene are mainly used as adulterants in petrol because of their low cost and easy miscibility. In comparison to traditional methods, the proposed etched fiber Bragg grating (eFBG) sensor is able to detect up to low-level adulteration efficiently when coated with a TiO₂ layer. Adulteration in benzene-petrol and xylene-petrol is detected using concentration mixing with 10% increments in each case. The experimental outcomes of sensitivity and Bragg wavelength shifting were studied. TiO₂-coated eFBG sensors achieved the sensitivities of 6.2 nm/RIU and 5.6 nm/RIU, which is 7% and 5% enhanced as compared to bare eFBG sensors in the case of benzene-petrol and xylene-petrol, respectively. This type of sensor is well-suited for on-road use in real-time.

This conference poster presentation was prepared for the Photonics West OPTO 2023 Symposium.

Black silicon induced junction photodiodes have nearly ideal responsivity across a wide range of wavelengths between 175-1100 nm, with external quantum efficiency over 99 % at visible wavelengths, when a single spot is measured using light beam between 1 to 2mm in diameter. The spatial uniformity of responsivity is also an important characteristic of a high-quality photodiode, when considering its usage as a reference in photometry. We study here the spatial uniformity of responsivity of large area (8mmx8mm) black silicon photodiodes at 405 nm wavelength. Our results show that the spatial non-uniformity is less than 0.5 % over 90 % of the surface area, and thus the photodiodes meet the thigh criteria typically set for reference standards and are hence suitable for such application.

Recently, the development of IoT technologies such as for autonomous driving and factory automation has been thriving. Both imaging devices and sensing devices that use optics are the most important devices among IoT technologies. When developing these devices, controlled light source is one of most important parts. There are not many reports of the development of single illumination optics with a super-wide-angle light distribution compared to camera lenses. Single illumination optics with super-wide-angle light distribution is desired for cost reduction and space saving of IoT device. However, it was difficult to make it with high efficiency and high uniformity due to severe requirement of geometrical tolerance and an increase of Fresnel reflection in large angle region. We report development and manufacturing of micro lens array diffuser with super-wide-angle distribution and high efficiency. Our optical design including an antireflection coating for super-wide-angle region could make the curvature of the lenslet low and enable us to manufacture this optics. In our design, it is achieved a super-wide-angle light distribution of about 170 degrees and high efficiency of about 80% using a micro-lens-array diffuser consisting of about 100-micron lenslet. And, we have realized a mass-produced product with high similarity between the micro lens array and the mold by using the technology to transfer the mold shape to the resin with high precision.

In this work, chalcogenide all-solid hybrid microstructured optical fibers (Ch-ASHMOF) using As₂Se₃, As₂S₅ and AsSe2 glasses are proposed. The polarization-maintaining properties are induced by breaking the symmetry of the rod arrangement and the core shape. The fibers have all-normal chromatic dispersion profiles which are flattened about -10 ps/km/nm over a wavelength range from 5 to 10 m and the birefringence values are up to 4.5x10^-4 at 10 μm. By pumping the fiber with a 200-fs-pulse laser source at 5.3 μm, a broad supercontinuum generation from 2 to 10 μm in the mid-infrared window is experimentally demonstrated.

For interferometric measurement methods such as optical white light interferometry, the coherence length of the implemented broadband light source is of central importance in order to realize a high axial resolution as well as a large dynamic range of the measurement system. In the case the broadband light sources are spectrally resolved by a spectral dispersive element, the spatial coherence and emission duration define primarily the coherence of the light source when no stimulated emission occurs. Broadband light sources with a high brilliance, such as supercontinuum and laser-driven plasma light sources, are particularly interesting for interferometric measurement methods because of their high spectral width and beam quality with enormous spectral power density. Especially for interferometric measurements, the coherence of the light source is essential. In the scope of the investigations, the coherence length and spectral power density of highpower supercontinuum light source based on a Yb-doped photonic crystal fiber in a nonlinear fiber amplifier setup and a commercially available laser-driven plasma light source were comparatively investigated with conventional white light sources. It was shown that the investigated high-power supercontinuum light source can be used very well for interferometric investigations. Furthermore, the achieved spectral pulse peak power densities exceed the laser-driven plasma light sources by a factor of one million.

The growing requirements for ultrafast communication speeds are constantly pushing the need to explore new devices and materials to reduce bottlenecks in optical communication networks. One such device is a phase only spatial light modulator implemented using liquid crystal on silicon. Achieving this requires polarization independent and fast-switching optical materials. Blue-phase liquid crystal is one such candidate. Popular opinion is that blue-phase liquid crystal is polarization-independent. In this study using microscopic and polarimetric methods, we demonstrate that in the off-state of blue-phase, the alignment layers affect the optical polarization behavior.

We propose a numerical study of the three-layered Tungston-MgF2-Gold-based ultrawideband metamaterial absorber for the infrared wavelength spectrum. The behaviour of the metamaterial absorber is investigated for the infrared wavelength range of 0.25 to 3 μm. The absorber's behaviour is examined under various physical conditions to determine the best possible outcomes and structural dimensions. This structure may trap more than 98% of the near-infrared and visible light spectrums. Far-infrared and THz spectral absorption are both well-served by the proposed structure. This proposed infrared absorber design can be used for designing a high-efficiency solar cell.

This conference poster presentation was prepared for the Photonics West OPTO 2023 Symposium.

LiDAR (Light Detection and Ranging) is thought to be one of the necessary sensors for automatic driving systems and advanced driver assistance systems. Recently, the LiDAR of the automotive vehicle is installed in the grille or near the headlights. These installed positions are very weak for a variety of pollutions. One of the measures to keep the LiDAR window surface clean is the use of anti-fingerprint coating. In this study, the hybrid optical coating for automotive LiDAR window (BK7 glass) which have the multifunction of UV-VIS absorption, NIR transmission, mechanical hardness and easy cleanability was developed. The surface hardness of the whole front coating and performance of anti-fingerprint coating were measured. The several reliability tests were performed. The coated window passed all tests.