Researchers demonstrate the ability to multiplex and transfer data between twisted beams of light with different amounts of orbital angular momentum — a development that provides new opportunities for increasing the data capacity of free-space optical communications links.

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Terabit free-space data transmission employing orbital angular momentum multiplexing

A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

Supercontinuum generation in photonic crystal fiber

This Review summarizes the simultaneous transmission of several independent spatial channels of light along optical fibres to expand the data-carrying capacity of optical communications. Recent results achieved in both multicore and multimode optical fibres are documented.

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Space-division multiplexing in optical fibres

Metamaterials, artificial electromagnetic media that are structured on the subwavelength scale, were initially suggested for the negative-index 'superlens'. Later metamaterials became a paradigm for engineering electromagnetic space and controlling propagation of waves: the field of transformation optics was born. The research agenda is now shifting towards achieving tunable, switchable, nonlinear and sensing functionalities. It is therefore timely to discuss the emerging field of metadevices where we define the devices as having unique and useful functionalities that are realized by structuring of functional matter on the subwavelength scale. In this Review we summarize research on photonic, terahertz and microwave electromagnetic metamaterials and metadevices with functionalities attained through the exploitation of phase-change media, semiconductors, graphene, carbon nanotubes and liquid crystals. The Review also encompasses microelectromechanical metadevices, metadevices engaging the nonlinear and quantum response of superconductors, electrostatic and optomechanical forces and nonlinear metadevices incorporating lumped nonlinear components.

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From metamaterials to metadevices.

The rise in output power from rare-earth-doped fiber sources over the past decade, via the use of cladding-pumped fiber architectures, has been dramatic, leading to a range of fiber-based devices with outstanding performance in terms of output power, beam quality, overall efficiency, and flexibility with regard to operating wavelength and radiation format. This success in the high-power arena is largely due to the fiber’s geometry, which provides considerable resilience to the effects of heat generation in the core, and facilitates efficient conversion from relatively low-brightness diode pump radiation to high-brightness laser output. In this paper we review the current state of the art in terms of continuous-wave and pulsed performance of ytterbium-doped fiber lasers, the current fiber gain medium of choice, and by far the most developed in terms of high-power performance. We then review the current status and challenges of extending the technology to other rare-earth dopants and associated wavelengths of operation. Throughout we identify the key factors currently limiting fiber laser performance in different operating regimes—in particular thermal management, optical nonlinearity, and damage. Finally, we speculate as to the likely developments in pump laser technology, fiber design and fabrication, architectural approaches, and functionality that lie ahead in the coming decade and the implications they have on fiber laser performance and industrial/scientific adoption.

High power fiber lasers: current status and future perspectives [Invited]

Dispersion-less square filter fibre Bragg gratings for 25GHz DWDM-channel separations are demonstrated. The filters show a useful bandwidth of 75% and reflectivity in excess of 99.9%. We test the gratings at 10Gbit/s and demonstrate that they at no point in the stop-band are limited by dispersion-induced distortion.

High reflectivity linear-phase fibre Bragg gratings for dispersion-free filtering in DWDM systems

We have fabricated an ytterbium doped holey fibre with an effective area of just 2.5µm2 at the laser wavelength (1.03µm) as shown in Fig.1(a). The fibres display huge birefringence at 1.55µm (beat length 0.3mm) owing to the high index contrast between the core and the cladding, the small dimensions, and the elliptical core shape. Using this fibre, we have demonstrated a low threshold and environmentally stable mode-locked laser using frequency feedback technique (see Fig.1 (b)). Furthermore, the fibre exhibits anomalous dispersion at the laser wavelength. Using this feature along with the high nonlinearity, we have also demonstrated broadly and continuously tunable Raman soliton generation by seeding with only pico-joule femtosecond pulses into the fibre. In a single pulse regime, the tuning range covers from 1.06 to 1.33µm, a region that is difficult to access using conventional solid state laser technology. In a multiple pulse regime, we have obtained femtosecond pulses as long as 1.58µm as shown in Fig.1(c).

Development and applications of ytterbium-doped highly nonlinear holey optical fibres

A study of the dynamics of temporal optical Fourier transforms is presented in the interest of improving transform quality. Experimental verification of how a complete Fourier transform can be obtained in both domains is demonstrated.

Complete temporal optical Fourier transformations using dark parabolic pulses

Bragg gratings in optical fibre waveguides have now been around for nearly 25years and they were soon after being realised identified as one of the most significant fibre-optic inventions with potentials in a wide variety of areas among telecommunications equivalent to that of the erbium doped fibre amplifier. The highlight of some of the most recent advances in Bragg grating devices and applications in advanced components are discussed.

Advance Bragg Grating Devices and Where They Are Going

We experimentally demonstrate a novel optical packet compression scheme based on temporal imaging of TDM packets through time lensing in fibres, while maintaining the pulse width by virtue of soliton propagation during the compression stage. In particular, 4-bit packets at 10 Gbit/s were compressed into 4-bit packets at 40 Gbit/s. The time lens effect is based on switching the original 10 Gbit/s 4-bit packet with a suitably chirped square pulse and on compressing the chirped packet by propagating it in a standard single mode fibre.

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Periklis Petropoulos

Papers

High reflectivity linear-phase fibre Bragg gratings for dispersion-free filtering in DWDM systems

Development and applications of ytterbium-doped highly nonlinear holey optical fibres

Complete temporal optical Fourier transformations using dark parabolic pulses

Advance Bragg Grating Devices and Where They Are Going

Optical packet compression in fibres based on time lens and solitonic effects