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

It is now shown that coupled optical microcavities bear all the hallmarks of parity–time symmetry; that is, the system’s dynamics are unchanged by both time-reversal and mirror transformations. The resonant nature of microcavities results in unusual effects not seen in previous photonic analogues of parity–time-symmetric systems: for example, light travelling in one direction is resonantly enhanced but there are no resonance peaks going the other way.

Parity–time-symmetric whispering-gallery microcavities

Orbital angular momentum (OAM), which describes the “phase twist” (helical phase pattern) of light beams, has recently gained interest due to its potential applications in many diverse areas. Particularly promising is the use of OAM for optical communications since: (i) coaxially propagating OAM beams with different azimuthal OAM states are mutually orthogonal, (ii) inter-beam crosstalk can be minimized, and (iii) the beams can be efficiently multiplexed and demultiplexed. As a result, multiple OAM states could be used as different carriers for multiplexing and transmitting multiple data streams, thereby potentially increasing the system capacity. In this paper, we review recent progress in OAM beam generation/detection, multiplexing/demultiplexing, and its potential applications in different scenarios including free-space optical communications, fiber-optic communications, and RF communications. Technical challenges and perspectives of OAM beams are also discussed.

Optical communications using orbital angular momentum beams

Photonic crystal fibers are a new class of optical fibers. Their artificial crystal-like microstructure results in a number of unusual properties. They can guide light not only through a well-known total internal reflection mechanism but using also photonic bandgap effect. In this paper different properties possible to obtain in photonic crystal fibers are reviewed. Fabrication and modeling methods are also discussed.

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Photonic Crystal Fibers

We present a photonic-plasmonic mode converter using modecoupling-based polarization rotation for connecting a silicon wire and hybrid plasmonic waveguides on a metal-inserted silicon platform. By using the polarization rotator based on defect-introduced silicon wire waveguide, the proposed mode converter can convert the photonic TE mode into the hybrid plasmonic TM mode. At the beginning, to identify a cross-sectional structure for polarization conversion, we investigate the hybrid parameters that determine the degree of mode rotation using the two-dimensional vector finite element method. Next, using the three-dimensional vector finite element method, we investigate the conversion characteristics of the whole device including input and output ports. Numerical results show that the extinction ratio of 46 dB and the insertion loss of 0.36 dB are achieved. The tolerance of the defect is also numerically evaluated. Our proposed mode converter can reduce insertion losses compared to conventional mode converters based on a taper-introduced butt joint structure.

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A photonic-plasmonic mode converter using mode-coupling-based polarization rotation for metal-inserted silicon platform

In this paper, we investigate the ultimate low loss property for several realistic core shapes in triangular-type air-guiding photonic bandgap fibers (PBGFs) through a full-vector modal solver based on the finite element method. We show that the surface mode free condition is expressed as a normalized silica-ring thickness T = 0.5 for any core size and the cladding structural parameters, regardless the core radius of the silica-ring is one of the main factors of dominating the surface mode's condition, and the wavelength range of the PBG changes on varying the structural parameters of the cladding. Moreover, we propose a novel type of PBGF without surface mode, which exhibits lower scattering losses caused by surface roughness of the silica-ring in comparison to 19 cell-core PBGFs and suppresses the mode coupling between fundamental-like and higher order modes when compared to 37 cell-core PBGFs.

Structural optimization of air-guiding photonic bandgap fibers for realizing ultimate low-loss waveguides

We theoretically address the thermo-optical response of multi-core photonic crystal fiber (PCF) couplers infiltrated with nematic liquid crystals (LCs). The enhanced thermo-optical properties of LC-based PCF couplers are highly attractive for photo-thermal sensing applications.

Tunable Photonic Crystal Fiber Couplers Infiltrated with Highly-Thermo-Responsive Liquid Crystal Substances

A tunable TE 0 -TE 1 mode divider based on wavelength-insensitive-coupler is experimentally demonstrated for the first time. Arbitrary branching ratios can be realized by using thermo-optic heaters. The proposed device is useful for gain-equalization in MDM networks.

A Tunable Mode Divider Based on Wavelength Insensitive Coupler using Thermo-Optic Effect for Gain-Equalization in MDM Network

We experimentally demonstrated all-solid photonic bandgap fibers with ~50μm core diameters and excellent higher order mode suppression, which can be used for high power fiber lasers to overcome the limits of fiber nonlinearities.

Kunimasa Saitoh

Papers

A photonic-plasmonic mode converter using mode-coupling-based polarization rotation for metal-inserted silicon platform

Structural optimization of air-guiding photonic bandgap fibers for realizing ultimate low-loss waveguides

Tunable Photonic Crystal Fiber Couplers Infiltrated with Highly-Thermo-Responsive Liquid Crystal Substances

A Tunable Mode Divider Based on Wavelength Insensitive Coupler using Thermo-Optic Effect for Gain-Equalization in MDM Network

All-solid photonic bandgap fiber with record mode area