Third harmonic generation in silica microfibres

We theoretically and experimentally study third harmonic generation in silica microfibres. Phase matching at critical diameters was achieved by intermodal-coupling with higher order third harmonic modes, which were successfully generated using 4ns 1.55µm pump pulses

Exome-chip association analysis of intracranial aneurysms

Objective: To investigate to what extent low-frequency genetic variants (with minor allele frequencies <5%) affect the risk of intracranial aneurysms (IAs). Methods: One thousand fifty-six patients with IA and 2,097 population-based controls from the Netherlands were genotyped with the Illumina HumanExome BeadChip. After quality control (QC) of samples and single nucleotide variants (SNVs), we conducted a single variant analysis using the Fisher exact test. We also performed the variable threshold (VT) test and the sequence kernel association test (SKAT) at different minor allele count (MAC) thresholds of >5 and >0 to test the hypothesis that multiple variants within the same gene are associated with IA risk. Significant results were tested in a replication cohort of 425 patients with IA and 311 controls, and results of the 2 cohorts were combined in a meta-analysis. Results: After QC, 995 patients with IA and 2,080 controls remained for further analysis. The single variant analysis comprising 46,534 SNVs did not identify significant loci at the genome-wide level. The gene-based tests showed a statistically significant association for fibulin 2 (FBLN2) (best p = 1 × 10-6 for the VT test, MAC >5). Associations were not statistically significant in the independent but smaller replication cohort (p > 0.57) but became slightly stronger in a meta-analysis of the 2 cohorts (best p = 4.8 × 10-7 for the SKAT, MAC ≥1). Conclusion: Gene-based tests indicated an association for FBLN2, a gene encoding an extracellular matrix protein implicated in vascular wall remodeling, but independent validation in larger cohorts is warranted. We did not identify any significant associations for single low-frequency genetic variants

Photonic band gap fibres: the new way of guiding light

Photonic Bandgap Fibres (PBGFs) are a radically new class of optical fibres whose guiding properties rely on the existence of photonic bandgaps. These fibres can guide light within an air-core thanks to a periodic array of micrometer-size holes running along the fibre length [1], see Fig 1a,b. PBGF have opened up numerous possibilities in photonics, largely through their ability to overcome the limitations of conventional optical fibres, for example by permitting guidance of light at wavelengths where silica fibres present high loss. They offer great prospects for communications due to the potential for low loss that results from the light being guided in air. In addition, these features make them ideal for sensors since there can be a large overlap between the light and gases, liquids, or nanoparticles introduced into the central hole. Such fibres could then be used wherever high sensitivity detectors are needed such as in the bio-medical field, or even for homeland security applications

Photonic bandgap fibres for broadband transmission of SWIR wavelengths

Hollow core photonic bandgap fibres can achieve light guidance in air, which offers a number of potential benefits for applications relevant to electro-magnetic remote sensing, including higher nonlinear and damage thresholds for high power beam delivery and operation at wavelengths that are not feasible using conventional fibres. Because they rely on coherent scattering from a highly ordered lattice of air holes as the mechanism of light guidance, bandgap fibres can only operate over a finite range of wavelengths. This paper investigates the parameters affecting the bandwidth of transmission in PBGFs and identifies realistic PBGF structures for wide-bandwidth operation in the SWIR wavelength region

Parabolic pulse formation in tapered microstructured optical fibres

In this paper we present simulations of pulse shaping in a microstructured optical fibre (MOF) taper. The MOF has been modelled in the normal dispersion regime and taper parameters proposed. We show results of parabolic pulse generation in the linearly tapered optical fibre, for Gaussian input pulses of different widths and powers

Designing hollow-core photonic bandgap fibres free of surface modes

Hollow-core photonic bandgap fibres (PBGFs) confine light within an air-core due to photonic bandgap effects. Such fibres allow for a very weak overlap between the guided mode and the fibre structure, which paves the way for novel and technologically enabling properties, such as low nonlinearity, high damage thresholds and transmission beyond silica's own transparency window [1]. Mid-IR transmission, not feasible in conventional fibres due to the very high absorption of silica beyond 2µm, has been recently demonstrated in silica PBGFs [2]. However, these fibres had a narrow low-loss operational bandwidth of less than 100nm, due the presence of surface modes (SMs) at their core-cladding interfaces [3]. By systematically studying feasible silica PBGFs core structures we identify new designs regimes that robustly eliminate the presence of surface modes. Optimal fibre designs with a wide transmission spectrum of ~ 350nm centred at ~ 2 µm are proposed. at the boundary with the cladding as shown in Fig.1. A systematic investigation of the effect of the ring thickness on the fibre's transmission properties was carried out. The normalized boundary thickness (T) was varied in the range 0.175 &lt; T &lt; 3.5 and for each fibre we solved for the modes within the bandgap. In order to assess the performance of the fibres we calculated the normalized interface field intensity of the fundamental air-guided mode, factor F [4]. This factor suffices to identify designs with broad transmission spectra as its value critically depends on whether or not the fibre supports surface modes

Observation of simultaneous generation of multiple harmonics in hexagonally poled lithium niobate

We present temperature-tuning measurements for 3rd harmonic and 4th harmonic generated by type I and type II processes in a hexagonally poled lithium niobate crystal. We also determine the quasi-phase-matching reciprocal lattice vectors involved and discuss improvements in the efficiencies

Advances and limitations in the modelling of fabricated photonic bandgap fibers

We model fabricated silica photonic bandgap fibers and achieve good agreement between simulated and measured properties. We identify the size of the SEM bitmap image as the ultimate limit to the accurate calculation of surfaces modes within the bandgap

Design of highly nonlinear bismuth-oxide holey fibres with zero dispersion and enhanced Brillouin suppression

We demonstrate that Bi-based holey fibres can achieve the same nonlinear performance as their all solid counterparts, but with greatly improved dispersion control. Longitudinally tapering the structural parameters allows at least a further 13.5 times improvement in the Kerr-to-Brillouin figure-of-merit

2D hexagonal poling for nonlinear photonic crystals and quasicrystals in LiNbO₃

We report on the fabrication of bidimensional arrays of hexagonal domains with strictly periodic and quasi-periodic patterns for the implementation of nonlinear photonic crystals and quasi-crystals in z-cut congruent LiNbO3