Spiral twisting offers additional opportunities for controlling the loss, dispersion, and polarization state of light in optical fibers with noncircular guiding cores. Here, we report an effect that ...appears in continuously twisted photonic crystal fiber. Guided by the helical lattice of hollow channels, cladding light is forced to follow a spiral path. This diverts a fraction of the axial momentum flow into the azimuthal direction, leading to the formation of discrete orbital angular momentum states at wavelengths that scale linearly with the twist rate. Core-guided light phase-matches topologically to these leaky states, causing a series of dips in the transmitted spectrum. Twisted photonic crystal fiber has potential applications in, for example, band-rejection filters and dispersion control.
In the past few decades, novel syntheses of a wide range of nanoparticles (NPs) with well‐defined chemical composition and structure have opened tremendous opportunities in areas ranging from optical ...and electronic devices to biomedical markers. Controlling the assembly of such well‐defined NPs is important to effectively harness their unique properties. The assembly of NPs at liquid–liquid interfaces is becoming a central topic both in surface and colloid science. Hierarchical structures, including 2D films, 3D capsules, and structured liquids, have been generating significant interest and are showing promise for physical, chemical, and biological applications. Here, a brief overview of the development of the self‐assembly of NPs at liquid–liquid interfaces is provided, from theory to experiment, from synthetic NPs to bio‐nanoparticles, from water–oil to water–water, and from “liquid‐like” to “solid‐like” assemblies.
Self‐assembly of nanoparticles (NPs) at liquid–liquid interfaces opens new pathways for nanotechnology through the controlled fabrication of nanoscopic materials with unique optical, magnetic, and electronic properties. A brief overview of recent developments in this field is provided, from theory to experiment, from synthetic NPs to bio‐nanoparticles, from water–oil to water–water, and from “liquid‐like” to “solid‐like” assemblies.
Helically twisted photonic crystal fibres Russell, P. St.J.; Beravat, R.; Wong, G. K. L.
Philosophical transactions - Royal Society. Mathematical, Physical and engineering sciences/Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences,
02/2017, Letnik:
375, Številka:
2087
Journal Article
Recenzirano
Odprti dostop
Recent theoretical and experimental work on helically twisted photonic crystal fibres (PCFs) is reviewed. Helical Bloch theory is introduced, including a new formalism based on the tight-binding ...approximation. It is used to explore and explain a variety of unusual effects that appear in a range of different twisted PCFs, including fibres with a single core and fibres with N cores arranged in a ring around the fibre axis. We discuss a new kind of birefringence that causes the propagation constants of left- and right-spinning optical vortices to be non-degenerate for the same order of orbital angular momentum (OAM). Topological effects, arising from the twisted periodic 'space', cause light to spiral around the fibre axis, with fascinating consequences, including the appearance of dips in the transmission spectrum and low loss guidance in coreless PCF. Discussing twisted fibres with a single off-axis core, we report that optical activity in a PCF is opposite in sign to that seen in a step-index fibre. Fabrication techniques are briefly described and emerging applications reviewed. The analytical results of helical Bloch theory are verified by an extensive series of 'numerical experiments' based on finite-element solutions of Maxwell's equations in a helicoidal frame.
This article is part of the themed issue ‘Optical orbital angular momentum’.
Over the past 30 years, atomic force microscopy (AFM) has played an important role in elucidating the structure and properties of polymer surfaces. AFM-based techniques have enabled the quantitative ...determination of the physicochemical properties of polymer surfaces with high spatial resolution and under a wide variety of conditions. Coupled with the improvements in spatial and temporal resolution, multiparametric and multifunctional characterization has revealed the delicate interplay between structure, dynamics, and properties at the surfaces of complex systems. Here we summarize some of the significant advances that have been made in synthetic polymeric materials, most in the past 10 years, where AFM has been crucial, and we provide our perspective on where AFM will be insightful in future and instrumental in advancing emerging areas.
Gas-filled hollow-core photonic crystal fibre is being used to generate ever wider supercontinuum spectra, in particular via dispersive wave emission in the deep and vacuum ultraviolet, with a ...multitude of applications. Dispersive waves are the result of nonlinear transfer of energy from a self-compressed soliton, a process that relies crucially on phase-matching. It was recently predicted that, in the strong-field regime, the additional transient anomalous dispersion introduced by gas ionization would allow phase-matched dispersive wave generation in the mid-infrared-something that is forbidden in the absence of free electrons. Here we report the experimental observation of such mid-infrared dispersive waves, embedded in a 4.7-octave-wide supercontinuum that uniquely reaches simultaneously to the vacuum ultraviolet, with up to 1.7 W of total average power.Dispersive wave emission in gas-filled hollow-core photonic crystal fibres has been possible in the visible and ultraviolet via the optical Kerr effect. Here, Köttig et al. demonstrate dispersive waves generated by an additional transient anomalous dispersion from gas ionization in the mid-infrared.
Unlike the capillaries conventionally used for gas-based spectral broadening of ultrashort (<100 fs) multi-millijoule pulses, which produce only normal dispersion at usable pressure levels, ...hollow-core photonic crystal fibres provide pressure-adjustable normal or anomalous dispersion. They also permit low-loss guidance in a hollow channel that is about ten times narrower and has a 100-fold-higher effective nonlinearity than capillary-based systems. This has led to several dramatic results, including soliton compression to few-cycle pulses, widely tunable deep-ultraviolet light sources, novel soliton-plasma interactions and multi-octave Raman frequency combs. A new generation of versatile and efficient gas-based light sources, which are tunable from the vacuum ultraviolet to the near infrared, and of versatile and efficient pulse compression devices is emerging.
Magnetic nanostructures are being developed for use in many aspects of our daily life, spanning areas such as data storage, sensing and biomedicine. Whereas patterned nanomagnets are traditionally ...two-dimensional planar structures, recent work is expanding nanomagnetism into three dimensions; a move triggered by the advance of unconventional synthesis methods and the discovery of new magnetic effects. In three-dimensional nanomagnets more complex magnetic configurations become possible, many with unprecedented properties. Here we review the creation of these structures and their implications for the emergence of new physics, the development of instrumentation and computational methods, and exploitation in numerous applications.
Over the past years, ultrafast lasers with average powers in the 100 W range have become a mature technology, with a multitude of applications in science and technology. Nonlinear temporal ...compression of these lasers to few- or even single-cycle duration is often essential, yet still hard to achieve, in particular at high repetition rates. Here we report a two-stage system for compressing pulses from a 1030 nm ytterbium fiber laser to single-cycle durations with 5 µJ output pulse energy at 9.6 MHz repetition rate. In the first stage, the laser pulses are compressed from 340 to 25 fs by spectral broadening in a krypton-filled single-ring photonic crystal fiber (SR-PCF), subsequent phase compensation being achieved with chirped mirrors. In the second stage, the pulses are further compressed to single-cycle duration by soliton-effect self-compression in a neon-filled SR-PCF. We estimate a pulse duration of ∼3.4 fs at the fiber output by numerically back-propagating the measured pulses. Finally, we directly measured a pulse duration of 3.8 fs (1.25 optical cycles) after compensating (using chirped mirrors) the dispersion introduced by the optical elements after the fiber, more than 50% of the total pulse energy being in the main peak. The system can produce compressed pulses with peak powers >0.6 GW and a total transmission exceeding 66%.
Soliton fibre lasers mode-locked at a high harmonic of their round-trip frequency have many potential applications, from telecommunications to data storage. Control of multiple pulses in passively ...mode-locked fibre lasers has, however, proved very difficult to achieve. This has recently changed with the advent of fibre lasers mode-locked by intense optomechanical interactions in a short length of photonic crystal fibre. Optomechanical coupling between cavity modes gives rise to highly stable, optomechanically bound, laser soliton states. The repetition rate of these states corresponds to the mechanical resonant frequency in the photonic crystal fibre core, which can be a few gigahertz. Here we show that this system can be successfully used for programmable generation and storage of gigahertz-rate soliton sequences over many hours.
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