Nicolas Y. Joly

Supercontinuum and four-wave mixing with Q-switched pulses in endlessly single-mode photonic crystal fibres.

Photonic crystal fibres exhibiting endlessly single-mode operation and dispersion zero in the range 1040 to 1100 nm are demonstrated. A sub-ns pump source at 1064 nm generates a parametric output at 732 nm with an efficiency of 35%, or parametric gain of 55 dB at 1315 nm. A broad, flat supercontinuum extending from 500 nm to beyond 1750 nm is also demonstrated using the same pump source.

Ultrafast nonlinear optics in gas-filled hollow-core photonic crystal fibers [Invited]

We review the use of hollow-core photonic crystal fibers (PCFs) in the field of ultrafast gas-based nonlinear optics, including recent experiments, numerical modeling, and a discussion of future prospects. Concentrating on broadband guiding kagome-style hollow-core PCF, we describe its potential for moving conventional nonlinear fiber optics both into extreme regimes—such as few-cycle pulse compression and efficient deep ultraviolet wavelength generation—and into regimes hitherto inaccessible, such as single-mode guidance in a photoionized plasma and high-harmonic generation in fiber.

Splice-free interfacing of photonic crystal fibers.

We report a new method for making low-loss interfaces between conventional single-mode fibers and photonic crystal fibers (PCFs). Adapted from the fabrication of PCF preforms from stacked tubes and rods, this method avoids the need for splicing and is versatile enough to interface to virtually any type of index-guiding silica PCF. We illustrate the method by forming interfaces to two problematic types of PCF, highly nonlinear and multicore. In particular, we believe this to be the first method capable of individually coupling light into and out of all the cores of a fiber with multiple closely spaced cores, without input or output cross talk.

Pressure-assisted melt-filling and optical characterization of Au nano-wires in microstructured fibers

We report a novel splicing-based pressure-assisted melt-filling technique for creating metallic nanowires in hollow channels in microstructured silica fibers. Wires with diameters as small as 120 nm (typical aspect ration 50:1) could be realized at a filling pressure of 300 bar. As an example we investigate a conventional single-mode step-index fiber with a parallel gold nanowire (wire diameter 510 nm) running next to the core. Optical transmission spectra show dips at wavelengths where guided surface plasmon modes on the nanowire phase match to the glass core mode. By monitoring the side-scattered light at narrow breaks in the nanowire, the loss could be estimated. Values as low as 0.7 dB/mm were measured at resonance, corresponding to those of an ultra-long-range eigenmode of the glass-core/nanowire system. By thermal treatment the hollow channel could be collapsed controllably, permitting creation of a conical gold nanowire, the optical properties of which could be monitored by side-scattering. The reproducibility of the technique and the high optical quality of the wires suggest applications in fields such as nonlinear plasmonics, near-field scanning optical microscope tips, cylindrical polarizers, optical sensing and telecommunications.

Plasmon resonances on gold nanowires directly drawn in a step-index fiber

High quality metallic wires (diameters down to 260nm) are fabricated using direct fiber drawing from a gold-filled cane. Measurements show coupling of light from the glass-core to plasmonic resonances on the wire, causing dips in the transmission at specific wavelengths.

Raman-like light scattering from acoustic phonons in photonic crystal fiber

Raman and Brillouin scattering are normally quite distinct processes that take place when light is resonantly scattered by, respectively, optical and acoustic phonons. We show how few-GHz acoustic phonons acquire many of the same characteristics as optical phonons when they are tightly trapped, transversely and close to modal cut-off, inside the wavelength-scale core of an air-glass photonic crystal fiber (PCF). The result is an optical scattering effect that closely resembles Raman scattering, though at much lower frequencies. We use photoacoustic techniques to probe the effect experimentally and finite element modelling to explain the results. We also show by numerical modelling that the cladding structure supports two phononic band gaps that contribute to the confinement of sound in the core.

Time-spectrally-resolved ultrafast nonlinear dynamics in small-core photonic crystal fibers: Experiment and modelling

Nonlinear dynamics of ultrashort optical pulses in the vicinity of the second zero-dispersion point of a small-core photonic crystal fiber is visualized and studied using cross-correlation frequency-resolved optical gating. New spectral features observed in the experiments match well with recent theoretical predictions of the generation of new frequencies via mixing of solitons and dispersive waves. Power- as well as length-dependent dynamics is obtained showing strong interaction between solitons and dispersive waves, soliton-soliton interaction, soliton stabilization against Raman self-frequency shift and Cherenkov continuum generation.

Intermediate asymptotic evolution and photonic bandgap fiber compression of optical similaritons around 1550 nm.

In this paper, we report the first complete characterization of the self-similar generation of optical similaritons, using high dynamic range ultrashort pulse metrology to study the intermediate asymptotic evolution towards the parabolic pulse profile, and to optimize additional propagation in highly-nonlinear fiber and compression to the sub-100 fs regime in hollow-core bandgap-guiding photonic crystal fiber (PCF). Our similariton amplifier used normally dispersive (Dap-40 ps/nm-km) Er3+ fiber with a 140 mW 1480 nm pump and 80 pJ, 1.1 ps sech2 input pulses at 1550 nm

Tunable vacuum-UV to visible ultrafast pulse source based on gas-filled Kagome-PCF.

An efficient and tunable 176-550 nm source based on the emission of resonant dispersive radiation from ultrafast solitons at 800 nm is demonstrated in a gas-filled hollow-core photonic crystal fiber (PCF). By careful optimization and appropriate choice of gas, informed by detailed numerical simulations, we show that bright, high quality, localized bands of UV light (relative widths of a few percent) can be generated at all wavelengths across this range. Pulse energies of more than 75 nJ in the deep-UV, with relative bandwidths of ~3%, are generated from pump pulses of a few μJ. Excellent agreement is obtained between numerical and experimental results. The effects of positive and negative axial pressure gradients are also experimentally studied, and the coherence of the deep-UV dispersive wave radiation numerically investigated.

Optofluidic refractive-index sensor in step-index fiber with parallel hollow micro-channel.

We present a simple refractive index sensor based on a step-index fiber with a hollow micro-channel running parallel to its core. This channel becomes waveguiding when filled with a liquid of index greater than silica, causing sharp dips to appear in the transmission spectrum at wavelengths where the glass-core mode phase-matches to a mode of the liquid-core. The sensitivity of the dip-wavelengths to changes in liquid refractive index is quantified and the results used to study the dynamic flow characteristics of fluids in narrow channels. Potential applications of this fiber microstructure include measuring the optical properties of liquids, refractive index sensing, biophotonics and studies of fluid dynamics on the nanoscale.