The Large Binocular Telescope Interferometer (LBTI)'s Nulling-Optimized Mid-Infrared Camera (NOMIC) is among the most capable thermal-infrared imaging systems available for high-contrast, high-angular-resolution astronomical observations. Here we describe two in-progress upgrades to LBTI/NOMIC: (1) the design, fabrication, and installation of a quadruple annular groove phase mask (Q-AGPM) coronagraph, and (2) the installation of a 13 micron-cutoff Teledyne GeoSnap array. The Q-AGPM is the first coronagraph to be installed within NOMIC and one of the first optimized for N-band ( 11 micron) observations. It places four annular groove phase masks on a single diamond substrate so that, in the LBTI dual-aperture imaging mode, each of the two telescope beams can be chopped between a pair of masks without loss of observing efficiency. The GeoSnap array will replace NOMIC's original AQUARIUS array, delivering higher quantum efficiency, larger well depth, faster and more linear readout, and freedom from the excess low-frequency noise that requires aggressive chopping. Together these upgrades substantially improve the achievable contrast and sensitivity at small angular separations. We also present a high-contrast Fizeau imaging sequence obtained with LBTI's new FFTCam fringe tracker, which confirms the interferometric gain over a single aperture through injection/recovery tests: relative to an equal-time single aperture exposure, the S/N = 3 contrast is a factor of 2-4 deeper across 0.2-1 arcsec, spanning the contrast- and background-limited regimes. Finally, we describe the role of the upgraded LBTI/NOMIC instrument within the Breakthrough Watch program at the University of Arizona, which aims to perform the deepest observations yet of the habitable zones of the nearest single Sun-like stars.

Polymeric materials for photonic integrated circuits have attracted much interest over the past decades due to their unique properties, including a simple and low-cost fabrication process, low absorption, a broad wavelength range, and a large selection of materials. Polymer-based microring resonators (MRRs) have been widely designed for many applications, from optical communication to medical diagnostics. In medical diagnostics, polymer waveguide MRRs excel as compact and highly sensitive ultrasonic detectors in photoacoustic imaging. In this work, we address the relation of the fabrication parameters to the optical properties of MRRs exhibiting a high quality factor (Q-factor). We use nanoimprint lithography and the UV-curable organic-inorganic material OrmoCore as the waveguide layer. We report our results on loss and coupling characteristics related to structural parameters such as the ring diameter and the residual layer thickness. We achieve low waveguide propagation losses of <0.38 dB/cm and Q-factors of >10(6).

In this article, second‐ and third‐harmonic generation (SHG and THG) microscopy is used to investigate the nonlinear optical response of GaAs nanocavities embedded in a gold film and compare them to bare GaAs nanocavities. The results reveal that the surrounding metallic environment significantly modifies both the intensity and spatial distribution of the nonlinear signals. When the harmonic wavelength is spectrally detuned from the nanocavity resonance the effects due to metallic environment start suppressing the SHG contrast. Numerical simulations confirm that at a 1060 nm pump wavelength, the SHG produced at 530 nm is suppressed due to the dominant plasmonic response of gold. Meanwhile the THG produced at 353 nm, which coincides with the nanocavity resonance enables high‐contrast imaging. Furthermore, by shifting the pump to 710 nm and aligning SHG at 356 nm with the nanocavity resonance, a strong SHG contrast is recovered, demonstrating a pathway to enhanced imaging of metal–semiconductor heterostructures.

Polymeric materials are one option to realize photonic integrated circuits (PICs). Pure and hybrid polymer materials have garnered significant interest due to their distinctive properties, such as a simple, efficient, and scalable fabrication process as well as refractive index tuning [1]–[3]. Microring resonators (MRRs) fabricated in polymer waveguides have demonstrated groundbreaking applications in biosensing, medical diagnostics, food analysis, and environmental monitoring [1]–[4]. Additionally, they are emerging as miniaturized ultrasonic detectors for photoacoustic imaging [5], [6]. However, polymers face challenges in achieving both low and high refractive indices, which are crucial for versatile applications. This limitation highlights the need to improve the refractive index contrast between the core and cladding in various applications. Recent advancements in virtual - and augmented reality (VR/AR) devices have expanded the range of available polymer solutions. For example, low-refractive-index polymers have been used for lower cladding layers [7], while UV-curable hybrid organic-inorganic materials have been employed as waveguide materials.

The laser-induced damage threshold of a grating waveguide output coupler (GWOC) exposed to laser radiation at a wavelength of 1030 nm and with a pulse duration of 500 fs was investigated. The GWOC is a combination of a sub-wavelength circular grating and a partial reflector based on a Nb2O5 and SiO2 multilayer sequence. It was designed to be used as an output coupler of a thin-disk laser cavity for the generation of beams with radial polarization. The results revealed a laser-induced damage threshold (LIDT) fluence of 0.36 J/cm² for single-pulse tests and 0.26 J/cm² for multiple-pulse conditions with up to 1000 shots. These threshold values are comparable to those of an unstructured output coupler with Nb2O5 and SiO2 coating layers, highlighting the minor influence of the grating on the LIDT.

On-chip emitters that generate single and entangled photons are essential for photonic quantum information processing technologies. Semiconductor quantum dots (QDs) are attractive candidates that emit high-quality quantum states of light, however at a rate limited by their spontaneous radiative lifetime. In this study, we utilize the Purcell effect to demonstrate up to a 38-fold enhancement in the emission rate of InAs QDs by coupling them to metal-clad GaAs nanopillars. These cavities, featuring a sub-wavelength mode volume of 4.5x10-4 (λ/n)3 and quality factor of 62, enable Purcell-enhanced single-photon emission across a large bandwidth of 15 nm with a multi-photon emission probability as low as 0.5 eliminates the need for implementing tuning mechanisms typically required to achieve QD-cavity resonance, thus relaxing fabrication constraints. Ultimately, this QD-cavity architecture represents a significant stride towards developing solid-state quantum emitters generating near-ideal single-photon states at GHz-level repetition rates.

This article presents the design, fabrication, and characterization of edge-coupled 1D optical phased arrays (OPAs) combined with collimating lenses. Our concept was tested with two OPAs having different collimation ranges. Both OPA designs have 3-mu m waveguide spacing and the maximum beam steering range is about 30 degrees based on wavelength tuning around 1550 nm. The first generation had 37 channels with 108 mu m of waveguide array width and the second generation had 512 channels with 1.5 mm array width. As the array outputs are edge coupled, suitable lenses are required to collimate the beam vertically. We report the comparison between a commercially available straight cylindrical lens and custom 3D printed curved cylindrical lenses. In the experiments, we demonstrate 1D beam steering of the light outcoupled from the waveguide facets and collimated by these lenses and analyzed parameters such as Rayleigh range and beam divergence. These parameters are estimated to be 9.9 mm and 7.0 mrad (0.4 degrees), respectively, for the commercial lens, whereas 40.1 mm and 3.5 mrad (0.2 degrees) for the dedicated 3D printed lens, showing a clear improvement.

We report on an all-dielectric compound anapole metasurface featuring metaatoms based on concentric disks and rings arranged in a square lattice. In this free-standing metasurface, the radiating multipole components cancel each other out in the far field, regardless of the angle of incidence and the polarization of incoming radiation. To demonstrate experimentally a broadband transparency in the terahertz range, we fabricated a silicon metasurface with a total thickness of 60 mu m using electron beam lithography and plasma deep etching techniques. Terahertz time-domain spectroscopy experiments revealed that the transmittance spectra measured at various incident angles and polarization states agree well with the respective modeling data. The proposed compound anapole approach has strong application potential for broadband terahertz photonics and sensing devices.

In this article we demonstrate rapid manufacturing of an illumination quality double-sided centimeter-scale optics without any post-processing. Two methods are presented: additive manufacturing (AM) using an optically transparent material with a water-soluble support material (support method), and alternatively, using only the optically transparent material but flipping the optics mid-process (flipping method). The main advantage of the flipping method is that only one material is needed. However, the use of support material is more straightforward, allows better alignment between the two sides of the lens and enables more complex lenses manufactured in the future. Both methods result in sufficient surface quality, i.e. surface roughness R q = 11.48 ±3.32 nm and form accuracy of ±10 μ m, for the purposes of illumination optics.

Tunability of properties is one of the most important features of 2D materials, among which graphene is attracting the most attention due to wide variety of its possible applications. Here, we demonstrated that the carrier concentration in graphene can be efficiently tuned by the material of the dielectric substrate on which it resides. To this end, we fabricated samples of CVD-grown graphene transferred onto silicon wafers covered with alumina, titanium dioxide, and silicon dioxide. We measured the transmission spectra of these samples using a time-domain terahertz spectrometer and extracted the Drude frequency-dependent graphene conductivity. We found that the sheet resistance of graphene is strongly affected by the underlying dielectric material, while the carrier scattering time remains the same. The carrier concentration value was found to range from 7×1011/cm2 in the case of alumina and 4.5×1012/cm2 in the case of titanium dioxide. These estimations are consistent with what can be extracted from the position of the G-peak in the Raman spectra of graphene. Our results show a way to control the graphene doping level in applications where it does not have to be adjusted.

Direct observation of exoplanets and proto-planetary disks with the METIS instrument at the Extremely Large Telescope will provide new insights into the processes of planet formation and exoplanet atmospheres. This will be possible thanks to a powerful vector vortex coronagraph that can suppress the starlight to reveal faint signals around it. Here we present the process of making the phase masks at the heart of the coronagraph. These annular groove phase masks consist of deep sub-wavelength gratings in diamond that are etched using inductively coupled oxygen plasma with a strong bias. The METIS instrument requires a wider bandwidth than such components have previously been demonstrated for, leading to a grating design with higher aspect ratio and more vertical walls. To achieve this, the etch mask used for diamond etching was changed from aluminium to silicon and the plasma power was increased. We also improved on our method for reducing the grating depth of finished components to fine-tune them. Together with improved optical testing, this allowed us to produce the best vortex phase masks so far demonstrated for the astronomical N-band.

Epsilon-near-zero (ENZ) materials have gained recent interest due to their exotic optical properties, but their potential is limited by intrinsic material losses. Enhanced epsilon-near-zero (eENZ) materials are periodically stratified media consisting of alternating ENZ and dielectric layers. In this study, we demonstrate the fabrication and optical characterization of 15-layer ENZ-dielectric thin film stack, wherein indium tin oxide functions as the ENZ material and titanium dioxide as the dielectric. We experimentally show the enhanced optical transmission of the structure over a bare ENZ film with similar thickness. Further, we display the giant polarization dependent optical response of the material, which is characterized by the narrowing from 56° to 14° in half-width at half-maximum of the transmission cone. These properties are physically attributed to guided-waves, Fabry–Pérot resonances, and Ferrell–Berreman plasmons within the film stack. The experimental realization of our material paves the way for devices utilizing eENZ-materials, such as coherence switchable lasers and light sources with directional emission.

Semiconductor quantum dots (QDs) have recently caused a stir as a promising and powerful lighting material applied in real-time fluorescence detection, display, and imaging. Photonic nanostructures are well suited for enhancing photoluminescence (PL) due to their ability to tailor the electromagnetic field, which raises both radiative and nonradiative decay rate of QDs nearby. However, several proposed structures with a complicated manufacturing process or low PL enhancement hinder their application and commercialization. Here, we present two kinds of dual-resonance gratings to effectively improve PL enhancement and propose a facile fabrication method based on holographic lithography. A maximum of 220-fold PL enhancement from CdSe/CdS/ZnS QDs are realized on 1D Al-coated photoresist (PR) gratings, where dual resonance bands are excited to simultaneously overlap the absorption and emission bands of QDs, much larger than those of some reported structures. Giant PL enhancement realized by cost-effective method further suggests the potential of better developing the nanostructure to QD-based optical and optoelectronic devices. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Spectral scatterometry is a technique that allows rapid measurements of diffraction efficiencies of diffractive optical elements (DOEs). The analysis of such diffraction efficiencies has traditionally been laborious and time consuming. However, machine learning can be employed to aid in the analysis of measured diffraction efficiencies. In this paper we describe a novel system for providing measurements of multiple measurands rapidly and concurrently using a spectral scatterometer and an artificial neural network (ANN) which is trained utilising transfer learning. The ANN provides values for the pitch, height, and line widths of the DOEs. In addition, an uncertainty evaluation was performed. In the majority of the studied cases, the discrepancies between the values obtained using a scanning electron microscope (SEM) and artificial neural network assisted spectral scatterometer (ANNASS) for the grating parameters were below 5 nm. Furthermore, independent reference samples were used to perform a metrological validation. An expanded uncertainty (k = 2) of 5.3 nm was obtained from the uncertainty evaluation for the measurand height. The height value measurements performed employing ANNASS and SEM are demonstrated to be in agreement within this uncertainty.

Stability and precision of atomic devices are closely tied to the quality and stability of the internal atmosphere of the atomic vapor cells on which they rely. Such atmosphere can be stabilized by building the cell with low permeation materials such as sapphire, or aluminosilicate glass in microfabricated devices. Recently, we showed that permeation barriers made of Al$_{2}$O$_{3}$ thin-film coatings deposited on standard borosilicate glass could be an alternative for buffer gas pressure stabilization. In this study, we hence investigate how helium permeation is influenced by the thickness, ranging from 5 to 40 nm, of such Al$_{2}$O$_{3}$ thin-films coated by atomic layer deposition. Permeation rates are derived from long-term measurements of the pressure-shifted transition frequency of a coherent population trapping (CPT) atomic clock. From thicknesses of 20 nm onward, a significant enhancement of the cell hermeticity is experienced, corresponding to two orders of magnitude lower helium permeation rate. In addition, we test cesium vapor cells filled with neon as a buffer gas and whose windows are coated with 20 nm of Al$_{2}$O$_{3}$. As for helium, the permeation rate of neon is significantly reduced thanks to alumina coatings, leading to a fractional frequency stability of 4x10$^{-12}$ at 1 day when the cell is used in a CPT clock. These features outperform the typical performances of uncoated Cs-Ne borosilicate cells and highlight the significance of Al$_{2}$O$_{3}$ coatings for buffer gas pressure stabilization.

Quantification of pattern distortion in nanoimprint lithography (NIL) is required when applying it to specific applications, especially those with tight tolerances. We present a systematic study on full wafer NIL distortion using soft stamps made of different carrier foils and UV-curable polymer structure layers. These errors are evaluated by overlay patterning using NIL and optical lithography on 4-in. wafers over a distance of 80 mm. Potential causes for pattern distortion and possible correction methods are discussed in terms of stamp composition and environmental impact. Pattern distortion along axes causing dimensional change is stamp dependent, and stiffer stamps show less pattern dimensional change than the softer ones. In the best case, the minimum variation is 4 parts per million (ppm), and in the worst case, 252 ppm with a softer stamp. Stamp flatness and uniform contact during imprinting are important in reducing high-order pattern distortion. A maximum dimensional variation of 32 ppm in a batch run demonstrates good pattern repeatability. Long-term dimensional stability can be affected by relative humidity, with variations on the order of 100 ppm.

We present for the first time the experimental demonstration of resonant waveguide grating (RWG) employing a dual duty-cycle profile for the stabilization of a 50 W laser diode emitting in the near-infrared spectral range.

We demonstrate that a type of guided-mode resonance with near-zero dispersion can be excited in a silicon nitride square-lattice grating, and the modal dispersion can be engineered by varying the polarization angle of incoming light.

Semiconductor quantum dots (QDs) have been extensively researched and have attracted a lot of attention for their ability to deterministically generate single and entangled photons. Such solid-state non-classical light sources are implemented, for example, in quantum key distribution protocols and in on-chip linear optical quantum computing. One of the key practical requirements from these sources is for them to emit at a high repetition rate and a common solution is to embed the QDs in a photonic cavity that enhances the spontaneous emission rate of quantum emitters via the Purcell effect $\mathrm{F}_{\mathrm{p}}\sim \mathrm{Q}/\mathrm{V}$ , where Q is the cavity quality factor and V the mode volume. Typically, moderate/high-Q cavities are used for enabling Purcell enhancement of the QD emission. [1–3]