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]

We experimentally demonstrate a novel optical packet compression scheme based on linearly chirping the packets followed by dispersive compression and multiwavelength conversion back onto a single wavelength. In particular, four-bit packets at 10 Gb/s were compressed into four-bit packets at 40 Gb/s. Error-free performance was achieved for the final compressed packet.

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All-optical packet compression based on time-to-wavelength conversion

Fibre Bragg gratings with reduced/eliminated in-band dispersion are presented. When tested in add-drop configurations at 10 Gbit/s both 25 GHz and 50 GHz bandwidth gratings are shown to exhibit superior performance with no dispersion-induced penalties in the stopband. Furthermore, the demonstrated linear-phase Bragg gratings have >70% channel filling factor values and reflectivities in excess of 99.9%.

Dispersion-free fibre Bragg gratings

This paper investigates the nonlinear generation of ultra-flat broadband spectra suited to communication applications. The technique is based on the inclusion of a linear pulse shaping element prior to a nonlinear fiber, where highly controllable spectral broadening is enabled. An adaptive pulse shaping system exploiting optimization algorithms (evolution strategy-ES) allows for automatic convergence to the desired spectrum. Using this technique, a spectrum exhibiting a 3-dB bandwidth of ~12 nm and a 0.5-dB bandwidth of ~8 nm is reported. The technique can be used to generate even broader spectra or indeed spectra exhibiting more exotic shapes.

/pdf/nonlinear-generation-of-ultra-flat-broadened-spectrum-based-3radfzau3t.pdf

Nonlinear Generation of Ultra-Flat Broadened Spectrum Based on Adaptive Pulse Shaping

We report on the fabrication of the first bismuth-oxide-based glass holey fiber. We measured high nonlinearity of /spl gamma/=460 W/sup -1/ km/sup -1/ at 1550 nm. Simulations predict anomalous dispersion at 1550 nm.

Highly nonlinear bismuth-oxide-based glass holey fiber

A stable optical beat-signal with frequency >; 160 GHz is produced by injection-locking two narrow-linewidth semiconductor lasers emitting at frequencies spaced by the beat-frequency to a low-jitter 10-GHz optical comb. The generated beat-signal with broadband noise suppression of >; 75 dB is temporally compressed by factors of up to four in a high stimulated Brillouin scattering threshold aluminosilicate highly nonlinear fiber. The generated subpicosecond pulses have a root mean square (rms) timing jitter below 150 fs measured over 1 s.

Periklis Petropoulos

Papers

All-optical packet compression based on time-to-wavelength conversion

Dispersion-free fibre Bragg gratings

Nonlinear Generation of Ultra-Flat Broadened Spectrum Based on Adaptive Pulse Shaping

Highly nonlinear bismuth-oxide-based glass holey fiber

Stable and Efficient Generation of High Repetition Rate ( $>$ 160 GHz) Subpicosecond Optical Pulses