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  • Volume 56, Issue 05

    • Volume 56, Issue 05

    Optics

    Waveguides can be laser-written into silicon carbide for photonic circuits

    John Wallace
    May 19, 2020
    Using a femtosecond laser, waveguides have been written into the bulk of SiC; modal properties can be tailored by altering the writing parameters.
    FIGURE 1. A single shot of the terahertz time-domain waveform is shown with a 120 ps time window (a). The inset magnifies the time trace indicating a signal-to-noise ratio (SNR) of >100 with a root-mean-squared (RMS) noise value of 0.013 at 100 µs measurement time without averaging. The Fourier transform of the terahertz time-domain waveform (b) shows >30 dB dynamic range in spectral power.
    Detectors & Imaging

    Kilohertz pixel scanning rates meet terahertz spectroscopic imaging

    May 19, 2020
    Efficient terahertz generation and high-speed asynchronous optical sampling enable 10,000 pixel-per-second spectroscopic imaging with >100 signal-to-noise ratio.
    (Image credit: Bar-Ilan University)
    The cladding-mode fiber-optic sensor is demonstrated, in which the strength of coupling between core and cladding mode is shown as a function of position along 2 m of a bare standard fiber and fine-tuning of the optical frequency of a readout probe wave (a). Most of the fiber is kept in air; the frequency of strongest coupling at that point is noted as zero for convenience. Two short sections of fiber, each 8 cm long, are immersed in ethanol and water (see legend at the top of the panel); the two sections stand out. The frequencies of core-cladding coupling are offset by 3 GHz and 2 GHz, respectively, in agreement with calculations. The (b) image is the same as (a), but with the ethanol allowed to evaporate. The frequency of coupling at that point returns to its baseline value of the fiber in air. Measured (red) and calculated (blue) discrete spectra of coupling from the core mode to a series of different cladding modes (c).
    Fiber Optics

    Dynamic reconfigurable gratings create new cladding-based fiber sensor

    Gail Overton
    May 19, 2020
    Instead of depending on fixed-position fiber Bragg gratings, core-launched laser light can couple to the cladding modes of standard fiber through Brillouin dynamic gratings and...
    FIGURE 1. Concept of the tapered double-clad fiber (T-DCF) laser amplifier.
    Lasers & Sources

    Tapered double-clad fiber: The future of ultrafast high-power laser processing

    May 19, 2020
    New fiber technology is poised to deliver multikilowatt power, ultrashort pulse durations, repetition rates up to 1 GHz, and high beam quality in a small package.
    FIGURE 1. Spectra of sodium benzoate in a white polyethylene bottle in the standard Raman configuration (a), defocused laser excitation covering a larger-area, deeper into the sample (b), and with the reflective cavity of STRaman technology with much-enhanced signal over the larger area and depth beneath the surface (c).
    Spectroscopy

    Portable Raman spectroscopy system identifies samples through opaque packaging

    May 19, 2020
    Collinear laser excitation and Raman scattering collection enables measurement of samples inside of packaging to increase field safety.

    More content from Volume 56, Issue 05

    (Image credit: Technical University of Darmstadt)
    The experimental setup (a) for the ghost communication demonstration exploits polarization correlations of unpolarized thermal light from an EDFA; unpolarized light is visualized by the Poincaré sphere with the dynamics of the instantaneous Stokes vector (b, red dots). The realized proof-of-principle communication between Bob and Alice is depicted by an encoding table for the “0” and “1” bits (c).
    Fiber Optics

    Correlated unpolarized photons enable camouflaged secure communication

    John Wallace
    May 19, 2020
    Exploiting the infinite number of polarization states of unpolarized thermal light and their correlation properties leads to a new approach for secure data communications.
    FIGURE 1. This image shows a poorly lit scene (a) and a zoomed-in region showing the effect of Gaussian noise (b).
    Software

    Filtering techniques eliminate Gaussian image noise

    Ayush Dogra
    May 19, 2020
    Block-matching, 3D filters, nonlinear means filtering, and Shearlet transform techniques show success in denoising images.
    FIGURE 1. SS-OCT at megahertz speed is not as futuristic as it may seem: The OCTA 12 × 12 mm FOV scan (a) was captured in less than 2.5 s (at 1.7 million A-scans/second) and delivers the same quality as the image in (b), which took 25 s to scan using a 100 kHz system.
    Detectors & Imaging

    New directions in biomedical OCT

    Barbara Gefvert
    May 19, 2020
    An industry session at BiOS 2020 reveals where new developments are taking OCT.
    (Image credit: NASA)
    FIGURE 1. OSLO, by Lambda Research Corporation, was used in the design and analysis of the James Webb Space Telescope (JWST).
    Optics

    Lens-design software enables modern precision optics

    John Wallace
    May 19, 2020
    Having grown in capabilities over decades of development, modern optical-design software models, optimizes, and tolerances complex optical systems with ease.
    (Image credit: J. Chhablani and G. Barteselli; Creative Commons Attribution-Share Alike 3.0 Unported license)
    OCT images, such as this one displaying signs of chorioretinopathy, contain anatomical insights into abnormal conditions; artificial intelligence (AI) can help mine clinical images to assist in diagnosis.
    Detectors & Imaging

    Deep learning for OCT image analysis

    Richard Gaughan
    May 19, 2020
    Deep learning is used to segment ophthalmic OCT images in order to recognize the tear meniscus of the human eye.
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    Lasers & Sources

    Hourglass-shaped laser-diode cavity forms a parallel ultrafast random-bit generator

    John Wallace
    May 19, 2020
    Due to its many spatiotemporally interfering lasing modes, the “entropy-creating” laser diode produces random bits at a speed on the order of 100 Tbit/s.
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    Commentary

    Make the most of this time

    John Lewis
    May 19, 2020
    Tapered double-clad fiber, lens-design software, spectroscopic imaging, seeing through opaque packaging, filtering techniques for denoising images, and OCT are featured in the...
    Arianna M. Charbon, Kazuhiro Morimoto, Edoardo Charbon
    A megapixel photon-counting camera is based on single-photon avalanche diode (SPAD) image sensors. The new camera can capture images in faint light at unprecedented speeds.
    Detectors & Imaging

    Photon-counting camera has megapixel SPAD array for single-photon TOF and other imaging

    John Wallace
    April 16, 2020
    The megapixel SPAD array has max photon detection probability of 27% and a median dark-count rate of 2 counts/s.
    (Image credit: SIOM)
    Schematic of a spatiotemporal plasma-lens filter.
    Lasers & Sources

    Plasma-lens filter improves temporal contrast of ultrafast laser pulses

    John Wallace
    April 16, 2020
    A plasma-lens filter (STPLF) passes the highest-intensity temporal pulse portions and scatters the lower-intensity prepulse while providing spatial filtering.
    Conard Holton2
    Commentary

    COVID-19 crisis management for photonics businesses

    Conard Holton
    April 14, 2020
    Innovation and leadership will be the keys to successful short- and long-term responses to the pandemic.
    HZDR / Juniks
    A new photodetector is based on layers of metal-organic frameworks.
    Detectors & Imaging

    Metal-organic semiconductor photodetector has 400 to 1575 nm spectral detection range

    John Wallace
    April 12, 2020
    An iron-based metal-organic semiconductor in thin-film form detects visible through near-IR radiation.
    (Image credit: Macquarie University)
    This diamond Raman laser produced by researchers at Macquarie University is pumped with light at 1018 nm to produce a 1178 nm output, which is then frequency-doubled to the 589 nm yellow sodium line. Used to produce guide stars in the upper atmosphere for adaptive optical systems in large ground-based telescopes, such a laser can do so at higher efficiency than existing lasers.
    Lasers & Sources

    Diamond Raman laser could have higher power and efficiency for telescope adaptive optics

    John Wallace
    April 3, 2020
    Emitting at the yellow sodium line, a diamond Raman laser could also enable more point-like guide stars to be generated through AO systems.
    (Image credit: Chung-Ang University)
    A novel algorithm for orienting a vehicle-mounted camera with respect to the outside environment consists of feature projection and line-structure detection (part 1, center), determining the vanishing point along the direction of driving, and determining the two other perpendicular vanishing points (part 2, bottom).
    Test & Measurement

    Novel camera calibration algorithm aims at making autonomous vehicles safer

    John Wallace
    March 2, 2020
    A fast camera-orientation estimation algorithm that pinpoints vanishing points could make self-driving cars safer.