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

Internet data traffic capacity is rapidly reaching limits imposed by optical fiber nonlinear effects Having almost exhausted available degrees of freedom to orthogonally multiplex data, the possibility is now being explored of using spatial modes of fibers to enhance data capacity We demonstrate the viability of using the orbital angular momentum (OAM) of light to create orthogonal, spatially distinct streams of data-transmitting channels that are multiplexed in a single fiber Over 11 kilometers of a specially designed optical fiber that minimizes mode coupling, we achieved 400-gigabits-per-second data transmission using four angular momentum modes at a single wavelength, and 16 terabits per second using two OAM modes over 10 wavelengths These demonstrations suggest that OAM could provide an additional degree of freedom for data multiplexing in future fiber networks

http://science.sciencemag.org/content/sci/340/6140/1545.full.pdf

Terabit-Scale Orbital Angular Momentum Mode Division Multiplexing in Fibers

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 report simultaneous transmission of six spatial and polarization modes, each carrying 40 Gb/s quadrature-phase-shift-keyed channels over 96 km of a low-differential group delay few-mode fiber. The channels are successfully recovered by offline DSP based on coherent detection and multiple-input multiple-output processing. A penalty of ;28 dB.

Mode-Division Multiplexing Over 96 km of Few-Mode Fiber Using Coherent 6 $\,\times\,$ 6 MIMO Processing

High-power fibre lasers are in demand for industrial, defence and scientific applications. This review provides an overview of the present state of the art in the field and discusses present challenges and the future outlook.

High-power fibre lasers

Multiple higher-order-modes propagating simultaneously in large-mode-area optical fibers are measured and their relative power levels quantified using spatially and spectrally resolved imaging.

Measuring the modes of optical fibers using S 2 imaging

It is demonstrated that the lateral resolution of a non-linear scanning multi-photon microscope can be improved significantly by using the light from an LP{in02} mode instead of a Gaussian-like beam.

Enhanced resolution in nonlinear microscopy using the LP0 2 mode of an optical fiber

Resonant couplers, such as long-period fiber-gratings (LPG) induce coupling between two copropagating modes in a fiber by phase-matching the relevant modes. While this process enables arbitrarily strong coupling and can even be the spectra are highly wavelength dependent, since phase is a wavelength dependent quantity. In this paper, we report the demonstration of microbend-induced LPGs in a specially designed few-mode fiber, with record 3 d B bandwidths of 565 nm. The coupling is spectrally flat over a bandwidth of 110 nm. This is enabled by a unique fiber design that allows simultaneously matching the phase, group delay, dispersion as well as the dispersion slope of two modes. This feature is utilised to demonstrate broadband, spectrally flat VOAs, with continuous tunability from 0-10 dB. The spectral characteristics of LPGs that couple the LPol and LPll modes can be described by a detuning parameter 8

Record bandwidth microbend gratings for spectrally flat variable optical attenuators

The nonlinear properties of a nanosecond pulse in a higher-order-mode, Er-doped-fiber amplifier with 2440µm2 effective area are compared to a conventional 880 µm2 area fiber. Both 1480nm pump and 1554nm signal propagate in the LP09 mode.

Nanosecond pulse amplification in a higher-order mode erbium-doped fiber amplifier

We demonstrate that ionic self-assembled multilayers (ISAM) adsorbed on long period gratings (LPG) function effectively as biosensors. Theoretical simulations and experimental measurements confirm that ISAM-coated-LPGs provide a thermally-stable, reusable platform for building efficient optical sensors.

Samir Ghalmi

Papers

Measuring the modes of optical fibers using S 2 imaging

Enhanced resolution in nonlinear microscopy using the LP0 2 mode of an optical fiber

Record bandwidth microbend gratings for spectrally flat variable optical attenuators

Nanosecond pulse amplification in a higher-order mode erbium-doped fiber amplifier

Ionic self-assembled multilayers adsorbed on long period fiber gratings for use as biosensors