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We have developed a fiber coupled demultiplexed local oscillator (LO) source for cryogenic applications based on a distributed feedback quantum cascade laser (QCL) at an operating wavelength of 10.6 μm. The coupling scheme relies on the combination of a phase grating generating multiple LO beams and a polycrystalline fiber delivering the demultiplexed LO signal to a superconducting mixer at 4 K in a closed-cycle cryostat. This scheme eases the use of a beam splitter in front of the mixer. Reflection phase grating generating 2 × 2 beams has been achieved with a total power efficiency of 64% based on a gold covered etched silicon nanostructure. The diffraction beam has been readily coupled into a 2 m long polycrystalline fiber, where a single-lobe circular beam has been delivered at the fiber output. By aligning the fiber core position to the center of a superconducting hot electron bolometer mixer at the rear side, we demonstrate the application of a fiber coupled demultiplexed QCL source for pumping the superconducting mixer with adequate LO power. [ABSTRACT FROM AUTHOR]

Fiber-based devices with advanced functionalities are emerging as promising solutions for various applications in flexible electronics and bioengineering. Multimaterial thermal drawing, in particular, has attracted strong interest for its ability to generate fibers with complex architectures. Thus far, however, the understanding of its fluid dynamics has only been applied to single material preforms for which higher order effects, such as the radial dependency of the axial velocity, could be neglected. With complex multimaterial preforms, such effects must be taken into account, as they can affect the architecture and the functional properties of the resulting fiber device. Here, we propose a versatile model of the thermal drawing of fibers, which takes into account a radially varying axial velocity. Unlike the commonly used cross section averaged approach, our model is capable of predicting radial variations of functional properties caused by the deformation during drawing. This is demonstrated for two effects observed, namely, by unraveling the deformation of initially straight, transversal lines in the preform and the dependence on the draw ratio and radial position of the in-fiber electrical conductivity of polymer nanocomposites, an important class of materials for emerging fiber devices. This work sets a thus far missing theoretical and practical understanding of multimaterial fiber processing to better engineer advanced fibers and textiles for sensing, health care, robotics, or bioengineering applications. [ABSTRACT FROM AUTHOR]

Orbital angular momentum (OAM) modes in fibers process great potentials in providing, from a higher dimension, extra communication channels to meet the ever-growing bandwidth requirement for modern information infrastructures. Long period fiber gratings are commonly used to generate these modes in fibers by coupling fundamental modes to degenerate higher order modes. In order for the generation process to be selective for a certain OAM mode, careful control of the state of polarization (SOP) is required for input fundamental modes. Here, we propose a non-conventional long period fiber grating with not only longitudinal index modulation but also azimuthal parity-time symmetry index modulation, and by placing this grating system at the parity-time exceptional point, an OAM mode with its topological charge matched to the parity-time modulation could be exclusively excited by using any fundamental modes with an arbitrary SOP except for the particular SOP with exactly opposite helicity. Our concept demonstrated here to generate OAM modes in fibers may open up promising applications in parity-time OAM-fiber optics. [ABSTRACT FROM AUTHOR]

We demonstrate a monolithic waveguide sensor integrated with a detector on-chip for mid-infrared absorption spectroscopic sensing. The optical sensing element comprises a chalcogenide glass spiral waveguide, and the detector is a PbTe photoconductor integrated directly with the chalcogenide waveguide. The limit of detection of the sensor for methane gas was experimentally assessed to be 1% by volume. Further optimization of the fabrication process and normalization of the laser power fluctuations should result in a maximum sensitivity of 330 ppmv. [ABSTRACT FROM AUTHOR]

We propose an on-chip mid-infrared (MIR) photonic spectroscopy platform for aerosol characterization to obtain highly discriminatory information on the chemistry of aerosol particles. Sensing of aerosols is crucial for various environmental, climatic, warfare threat detection, and pulmonary healthcare applications. Currently, chemical characterization of aerosols is performed using FTIR spectroscopy, yielding chemical fingerprinting because most of the vibrational and rotational transitions of chemical molecules fall in the IR range, and Raman spectroscopy. Both techniques use free space bench-top geometries. Here, we propose miniaturized on-chip MIR photonics-based aerosol spectroscopy consisting of a broadband spiral-waveguide sensor that significantly enhances the particle-light interaction to improve sensitivity. The spiral waveguides are made of a chalcogenide glass material (Ge23Sb7S70) which shows a broad transparency over the IR range (1–10 μm). We demonstrate the sensing of N-methyl aniline-based aerosol particles with the device. We anticipate that the sensor will readily complement existing photonic resonator-based particle sizing and counting techniques to develop a unified framework for on-chip integrated photonic aerosol spectroscopy. [ABSTRACT FROM AUTHOR]

A chlorine plasma etching-based method for the fabrication of high-performance chalcogenide-based integrated photonics on silicon substrates is presented. By optimizing the etching conditions, chlorine plasma is employed to produce extremely low-roughness etched sidewalls on waveguides with minimal penalty to propagation loss. Using this fabrication method, microring resonators with record-high intrinsic Q-factors as high as 450000 and a corresponding propagation loss as low as 0.42dB/cm are demonstrated in submicron chalcogenide waveguides. Furthermore, the developed chlorine plasma etching process is utilized to demonstrate fiber-to-waveguide grating couplers in chalcogenide photonics with high power coupling efficiency of 37% for transverse-electric polarized modes. [ABSTRACT FROM AUTHOR]

Over the past century, whispering gallery mode optical cavities have enabled numerous advances in science and engineering, such as discoveries in quantum mechanics and non-linear optics, as well as the development of optical gyroscopes and add drop filters. One reason for their widespread appeal is their ability to confine light for long periods of time, resulting in high circulating intensities. However, when sufficiently large amounts of optical power are coupled into these cavities, they begin to experience optothermal or photothermal behavior, in which the optical energy is converted into heat. Above the optothermal threshold, the resonance behavior is no longer solely defined by electromagnetics. Previous work has primarily focused on the role of the optothermal coefficient of the material in this instability. However, the physics of this optothermal behavior is significantly more complex. In the present work, we develop a predictive theory based on a generalizable analytical expression in combination with a geometry-specific COMSOL Multiphysics finite element method model. The simulation couples the optical and thermal physics components, accounting for geometry variations as well as the temporal and spatial profile of the optical field. To experimentally verify our theoretical model, the optothermal thresholds of a series of silica toroidal resonant cavities are characterized at different wavelengths (visible through near-infrared) and using different device geometries. The silica toroid offers a particularly rigorous case study for the developed optothermal model because of its complex geometrical structure which provides multiple thermal transport paths. [ABSTRACT FROM AUTHOR]

Shows that the leakage current through a metal-semiconductor-metal-photodetector can be reduced by placing a thin interfacial silicon dioxide layer between the Schottky metal and the silicon substrate. Factor reduction in leakage-current density.

We report on the fabrication of all-in-fiber capacitors with poly(vinylidene fluoride) (PVDF) as the dielectric material. Electrodes made of conductive polymer are separated by a PVDF thin film within a polycarbonate casing that is thermally drawn into multiple meters of light-weight, readily functional fiber. Capacitive response up to 20 kHz is measured and losses at higher-frequencies are accounted for in a materials-based model. A multilayered architecture in which a folded PVDF film separates interdigitated electrodes over an increased area is fabricated. This structure greatly enhances the capacitance, which scales linearly with the fiber length and is unaffected by fiber dimension fluctuations. [ABSTRACT FROM AUTHOR]

We report on an all-in-fiber liquid crystal (LC) structure designed for the modulation of light incident transverse to the fiber axis. A hollow cavity flanked by viscous conductors is introduced into a polymer matrix, and the structure is thermally drawn into meters of fiber containing the geometrically scaled microfluidic channel and electrodes. The channel is filled with LCs, whose director orientation is modulated by an electric field generated between the built-in electrodes. Light transmission through the LC-channel at a particular location can be tuned by the driving frequency of the applied field, which directly controls the potential profile along the fiber. [ABSTRACT FROM AUTHOR]