Browse research summaries from:

Research Summaries are produced by Springer Nature and are licensed under the Creative Commons Attribution-NonCommercial-No Derivative Works 3.0 Unported License. For more details see the Author Benefits page.


Research summaries for 2017

Microwave photonics: few-mode communication

The use of few-mode, large-core optical fibres can dramatically enhance the performance of microwave photonics communications. Fibre-optic microwave photonic links have become a basic building block for microwave photonics, but their performance is currently limited by the power-handling capability of optical fibres. Now, Guifang Li at the University of Central Florida in the USA and co-workers reduced nonlinear crosstalk in a wavelength-division multiplexed communications link by 30 decibels through employing a 20-kilometre-long few-mode fibre. Using a few-mode fibre allowed them to overcome the optical nonlinearity problems that tend to plague single-mode fibres when large optical signal powers are used. Experiments using single-wavelength channels also showed improved transmission. Future research will explore using few-mode fibres to perform functions such as tunable delay and wavelength-independent lossless signal combination.

Light Sci Appl. Research Summary. Published online 11 August 2017

Organic optoelectronics: flexible, ultrasensitive phototransistors

High-gain phototransistors that operate from the ultraviolet to the near infrared could enable sensitive, broadband light detection. The excellent optoelectronic properties of organolead halide perovskites make them promising for various optoelectronic devices. Now, FY and co-workers from The Hong Kong Polytechnic University have fabricated low-voltage, high-gain phototransistors based on a vertical heterojunction consisting of a perovskite (CH3NH3PbI3-xClx) and an organic-semiconductor (PEDOT:PSS). Their high sensitivity is attributed mainly to the strong light absorption and long charge carrier lifetimes of the perovskite. The phototransistors can be fabricated on plastic substrates by solution processing, making them both flexible and compatible with cost-effective mass-production. Tests with light-emitting diodes that emit light at wavelengths of 370, 598 and 895 nanometers and a monochromator confirmed the broadband operation of the phototransistors.

Light Sci Appl. Research Summary. Published online 11 August 2017

Metasurfaces: improved multitasking

Nanoantennas that alter the phase of optical signals using geometric parameters bring multiple light-shaping capabilities to a single device. Erez Hasman from the Technion — Israel Institute of Technology and co-workers patterned silicon surfaces into a two-dimensional array of interspersed nanorods to promote both geometric phase modulation and sharing of nanoantenna aperture space. While this approach enables control over photonic spin and wavefront generation, it also creates speckle noise that can affect performance. The team used Wigner distributions, a quantum-based signal analysis method, to determine the ultimate information capacities of channels within geometric phase metasurfaces. Their evaluations propose ways to combine data-carrying optical angular momentum (OAM) beams with swirling light vortices into a device that could simultaneously determine the frequency, polarization, and OAM of light at different wavelengths.

Light Sci Appl. Research Summary. Published online 11 August 2017

Remote sensing: random light's spiral code

The angular properties of natural sources of light, such as sunlight, could lead to robust technologies for remote sensing and imaging. In the past few years, photons entangled through the orbital angular momentum (OAM) degree of freedom have been utilized to probe specimens noninvasively in a technique known as digital spiral imaging. A team of researchers led by Omar S Magaña-Loaiza, Gui-Lu Long and Robert W Boyd demonstrates that fluctuations in OAM intensity seen in natural light can achieve similar imaging correlations at any illumination level. The team found signatures of Fourier components, which can be used to recover the specimen’s spatial or phase information. Despite the lack of perfect correlations, these spiral spectra are detectable in a fraction of the time required for quantum entanglement and are immune to environmental noise.

Light Sci Appl. Research Summary. Published online 28 July 2017

Plasmonic metasurfaces: beam switching and lensing realized

Plasmonic metasurfaces employing a phase-change material have yielded highly compact devices for switching and focusing light beams. Such devices are promising for realizing nanophotonic components for applications in scanning, imaging and holography. Xinghui Yin at the University of Stuttgart, Germany, and co-workers fabricated gold patterned nanostructures on a layer of the phase-change material germanium−antimony−tellurium (GeSbTe; GST). Since the amorphous and crystalline phases of the GST layer have very different optical dielectric constants, thermally triggering a phase change in the layer allowed a 3.1 μm wavelength light beam to be steered in different directions. A different design of the gold nanopattern realized a cylindrical bifocal lens that had different focal lengths for the amorphous and crystalline GST phases. This demonstration opens the way for a wide range of active optical elements based on plasmonic metasurfaces.

Light Sci Appl. Research Summary. Published online 28 July 2017

Metasurfaces: different colours, different directions

Reflective silver nanostructures with asymmetric resonance properties can separate and transport light according to its colour components. Recent progress in metasurfaces has shown that arrays of tiny metallic antennas are efficient light harvesters and can bend incident light into directional beams thanks to resonance enhancements from surface plasmons. Olivier Martin and co-workers from the Swiss Federal Institute of Technology report a way to filter these beams into colours using ‘dolem’-shaped antennas in which two parallel nanorods are perpendicular to a third. In this arrangement, a scattering phenomenon known as the Fano resonance creates anomalous reflections that limit the channel bandwidth to less than 100 nanometres. Geometric tuning of the Fano-assisted resonances enabled the team to produce a plasmonic device that splits broadband light into two different wavelengths travelling in opposite directions.

Light Sci Appl. Research Summary. Published online 28 July 2017

Freeform optics: shrinking spectrometer size

Imaging spectrometers that use optics with freeform shapes will be more compact and have enhanced performance, predicts a theoretical study. Jacob Reimers and colleagues from the University of Rochester, USA, studied the benefits of using freeform optics in a visible–infrared spectrometer with the Offner–Chrisp geometry, which features a slit and three concentric mirrors with a diffraction grating on the convex surface of the secondary mirror. Introducing freeform surfaces into the optical design can enable reducing the spectrometer size by a factor of five, tripling the spectral bandwidth, or doubling the slit length relative to similar designs that have conventional spherical or aspherical surfaces. Furthermore, the freeform design was predicted to simultaneously correct for blurring aberrations and distortion. Simulations indicated that the spectrometer’s performance was diffraction limited across its wavelength band of operation.

Light Sci Appl. Research Summary. Published online 28 July 2017

Nanoscale vibrational spectroscopy of chemical and biological samples in their native aqueous environments is now possible. The sensitivity of current vibrational nanospectroscopies deteriorates drastically for samples immersed water. Mingzhou Jin, Feng Lu and Mikhail Belkin at the University of Texas at Austin, USA, have developed a nanospectroscopy technique that retains high sensitivity and nanoscale spatial resolution even when the sample is immersed in water. It operates by detecting oscillations in the tip of an atomic force microscope driven by rapid thermal expansion when the sample absorbs mid-infrared laser light under resonant conditions. The sample is placed on top of a semiconductor germanium prism and covered with a layer of water and a cover slide. It is then illuminated with a train of light pulses from a quantum cascade laser to induce the photoexpansion.

Light Sci Appl. Research Summary. Published online 28 July 2017

Optical vortices: ordinary polymers get the spiral touch

Helical microstructures can be directly polymerized into standard photoresists using beams derived from interfering holograms. Recent studies have shown that optical vortices can pattern polymer surfaces with the same left- or right-handed chirality of the spinning light beam, but only if the material’s structure has a built-in asymmetry. Dong Wu and co-workers from the University of Science and Technology of China report that optical vortices generated by liquid-crystal devices called spatial light modulators (SLMs) are stable enough to engrave chiral microstructures into more-common isotropic polymers. Directing femtosecond laser pulses onto an SLM produced holograms and plane waves that interfered and co-propagated into helices without the phase sensitivity of typical split-beam setups. This approach enabled controllable fabrication of spiral patterns with different lobes and orientations over large areas with a 100-nanometer-scale precision.

Light Sci Appl. Research Summary. Published online 14 July 2017

Plasmonic metasurfaces: breaking the diffraction limit on a budget

Surfaces with ‘nanoscatterers’ that manipulate light for colour generation and spectroscopy can now be fabricated using low-cost polymers. Producing nanoscale metallic materials with robust surface plasmons normally requires meticulous lithographic procedures. Silvia Vignolini from the University of Cambridge in the UK and colleagues have developed a simple, bottom-up approach to make aluminum nanoscatterers by exploiting the phase separation forces within a polystyrene/poly(methyl methacrylate) blend. Spin coating this mixture in a humid environment produced a film with circular nanostructures that were etched away to yield random distributions of nanoholes. Evaporating aluminium onto the perforated polymer provided the right light scattering for fade-resistant structural colours, tunable across the visible spectrum via the initial polymer blend. By tweaking the aluminum thickness, the optical response of the nanohole film could be tailored for broadband enhancement of Raman spectroscopy.

Light Sci Appl. Research Summary. Published online 14 July 2017

View all Research Summaries for 2017