Zero-group-velocity modes in chalcogenide holey photonic-crystal fibers

Complete two-dimensional photonic bandgap in refractive-index ratio 2.1 photonic crystals due to high-order bands

We find that in a suitably designed photonic crystal (PC) certain high-order photonic bands are less affected by the refractive-index ratio (RIR) than low-order bands, enabling the realization of a robust and complete two-dimensional (2D) photonic bandgap in a moderate refractive-index-ratio PC. A detailed theoretical investigation of low- and high-order bandgaps in a series of PCs with different configurations is performed that shows that high-order bands may favor substantial complete photonic bandgaps (CPBGs) for systems with a moderate RIR. Furthermore, the importance of the geometry and structural parameters on achieving a high-order CPBG is found. Specifically, a hexagonal lattice PC of annular-hole-peripheral connecting rods is proposed, which can support a CPBG with a refractive-index ratio (RIR) as low as n_high:n_low=2.1; to the best of our knowledge, this is the lowest RIR used to obtain a 2D CPBG in a PC.

Point-Defect-Localized Bound States in the Continuum in Photonic Crystals and Structured Fibers

We show that point defects in two-dimensional photonic crystals can support bound states in the continuum (BICs). The mechanism of confinement is a symmetry mismatch between the defect mode and the Bloch modes of the photonic crystal. These BICs occur in the absence of band gaps and therefore provide an alternative mechanism to confine light. Furthermore, we show that such BICs can propagate in a fiber geometry and exhibit arbitrarily small group velocity which could serve as a platform for enhancing nonlinear effects and light-matter interactions in structured fibers.

Guiding light in a water core all-solid cladding photonic band gap fiber - an innovative platform for fiber-based optofluidics

We present a single-channel photonic band gap fiber design allowing for guiding light inside a water core, which is surrounded by solid microstructured cladding, consisting of an array of high refractive index strands in silica. We address all relevant properties and show that the microstructure substantially reduces loss. We also introduce a ray reflection model, matching numerical modelling and allowing for time-effective large-scale parameter sweeps. Our single channel fiber concept is particularly valuable for applications demanding fast and reliable injection of liquids into the core, with potential impact in fields such as optofluidics, spectroscopy or bioanalytics.

Combining ε-Near-Zero Behavior and Stopped Light Energy Bands for Ultra-Low Reflection and Reduced Dispersion of Slow Light

We investigate media which exhibits epsilon-near-zero (ENZ) behavior while simultaneously sustaining stopped light energy bands which contain multiple points of zero group velocity (ZGV). This allows the merging of state-of-the-art phenomena that was hitherto attainable in media that demonstrated these traits separately. Specifically, we demonstrate the existence of Ferrell-Berreman (FB) modes within frequency bands bounded by points of ZGV with the goal to improve the coupling efficiency and localization of light in the media. The FB mode is formed within a double layer, thin-film stack where at subwavelength thicknesses the structure exhibits a very low reflection due to ENZ behavior. In addition, the structure is engineered to promote a flattened frequency dispersion with a negative permittivity able to induce multiple points of ZGV. For proof-of-concept, we propose an oxide-semiconductor-oxide-insulator stack and discuss the useful optical properties that arise from combining both phenomena. A transfer matrix (TM) treatment is used to derive the reflectivity profile and dispersion curves. Results show the ability to reduce reflection below 0.05% in accordance with recent experimental data while simultaneously exciting a polariton mode exhibiting both reduced group velocity and group velocity dispersion (GVD).

High index contrast semiconductor ARROW and hybrid ARROW fibers

We investigate the guidance properties of two photonic crystal fibers that have been fabricated by filling the holes of a silica template with hydrogenated amorphous silicon inclusions. The first is an all-solid fiber that guides light via an antiresonant reflecting optical waveguiding mechanism and the second is only partially filled so that it guides light by a hybrid of modified total internal reflection and antiresonant reflecting optical waveguiding. It will be shown that, by selectively filling the silica template to leave an unfilled internal ring of holes, the fiber's confinement loss can be reduced significantly. This novel fiber design in which the light guided in the silica core can be modified by the semiconductor cladding provides a route to integrating functional semiconductor fibers with existing silica fiber infrastructures.

Slow-light enhanced absorption in a hollow-core fiber

Light traversing a hollow-core photonic band-gap fiber may experience multiple reflections and thereby a slow-down and enhanced optical path length. This offers a technologically interesting way of increasing the optical absorption of an otherwise weakly absorbing material which can infiltrate the fibre. However, in contrast to structures with a refractive index that varies along the propagation direction, like Bragg stacks, the translationally invariant structures studied here feature an intrinsic trade-off between light slow-down and filling fraction that limits the net absorption enhancement. We quantify the degree of absorption enhancement that can be achieved and its dependence on key material parameters. By treating the absorption and index on equal footing, we demonstrate the existence of an absorption-induced saturation of the group index that itself limits the maximum absorption enhancement that can be achieved.