Impact of structural distortions on the performance of hollow-core photonic bandgap fibers

Orders of magnitude loss reduction in photonic bandgap fibers by engineering the core surround

We demonstrate how to reduce the loss in photonic bandgap fibers by orders of magnitude by varying the radius of the corner strands in the core surround. As a fundamental working principle we find that changing the corner strand radius can lead to backscattering of light into the fiber core. Selecting an optimal corner strand radius can thus reduce the loss of the fundamental core mode in a specific wavelength range by almost two orders of magnitude when compared to an unmodified cladding structure. Using the optimal corner radius for each transmission window, we observe the low-loss behavior for the first and second bandgaps, with the losses in the second bandgap being even lower than that of the first one. Our approach of reducing the confinement loss is conceptually applicable to all kinds of photonic bandgap fibers including hollow core and all-glass fibers as well as on-chip light cages. Therefore, our concept paves the way to low-loss light guidance in such systems with substantially reduced fabrication complexity.

7-cell hollow-core photonic bandgap fiber with broad spectral bandwidth and low loss

The limited spectral bandwidth achieved in state-of-the-art hollow-core photonic bandgap fibers (HC-PBGF) has hindered its implementation in a wide range of applications. Here we demonstrate that broad spectral bandwidth and low loss can be simultaneously achieved in 7-cell HC-PBGF. Several 7-cell HC-PBGFs operating at 1550 nm telecom band and 1 μm laser band are present. One of the fibers exhibits a minimum loss of 6.5 dB/km at 1633 nm and a 3 dB bandwidth of 458 nm, approaching a bandwidth to central wavelength ratio of 26%. This is to our knowledge the broadest bandwidth achieved in triangular lattice HC-PBGF and the lowest transmission loss in 7-cell HC-PBGF.

Combining Hollow Core Photonic Crystal Fibers with Multimode, Solid Core Fiber Couplers through Arc Fusion Splicing for the Miniaturization of Nonlinear Spectroscopy Sensing Devices

The presence of fiber optic devices, such as couplers or wavelength division multiplexers, based on hollow-core fibers (HCFs) is still rather uncommon, while such devices can be imagined to greatly increase the potential of HCFs for different applications, such as sensing, nonlinear optics, etc. In this paper, we present a combination of a standard, multimode fiber (MMF) optic coupler with a hollow core photonic bandgap fiber through arc fusion splicing and its application for the purpose of multiphoton spectroscopy. The presented splicing method is of high affordability due to the low cost of arc fusion splicers, and the measured splicing loss (SL) of the HCF-MMF splice is as low as (0.32 ± 0.1) dB, while the splice itself is durable enough to withstand a bending radius (rbend) of 1.8 cm. This resulted in a hybrid between the hollow core photonic bandgap fiber (HCPBF) and MMF coupler, delivering 20 mW of average power and 250-fs short laser pulses to the sample, which was good enough to test the proposed sensor setup in a simple, proof-of-concept multiphoton fluorescence excitation-detection experiment, allowing the successful measurement of the fluorescence emission spectrum of 10−5 M fluorescein solution. In our opinion, the presented results indicate the possibility of creating multi-purpose HCF setups, which would excel in various types of sensing applications.

Nondestructive determination of the core size of a hollow-core photonic bandgap fiber using Fabry-Perot interference

In this Letter, we propose a simple and nondestructive method for the determination of the core size of a hollow-core photonic bandgap fiber (HC-PBF) and its axial uniformity based on a Fabry-Perot cavity induced by a pair of opposite silica-air interfaces within the hollow core. The experimental results indicate that the core size test of the HC-PBF has a nanometer-level precision, and its axial uniformity test has an ultimate spatial resolution of tens of microns. The method provides an effective and precise tool for the investigation of the hollow-core size and its longitudinal evolution.

Studying the limits of production rate and yield for the volume manufacturing of hollow core photonic band gap fibers

Hollow core photonic band gap fibers have great potential in low latency data transmission and power delivery applications, but they are currently only fabricated in research scale fabrication facilities, with km-scale lengths. To drive cost reduction and volume manufacturing it is essential to be able to upscale the preform size, but before embarking on costly experimental attempts it is useful to apply fluid dynamics models to study how the fiber drawing dynamics would be affected by such a change. In this work we use a fluid dynamics model to virtually draw increasingly longer lengths of the same fiber from preforms of identical length but different diameters. Taking advantage of our fast numerical model we explore the physical dynamics of the draw process. We discover that the draw tension is the key thermodynamic parameter and that an upper length limit exists beyond which undesirable distortions in the microstructure become difficult to control. These mechanisms are identified and possible mitigation methods described which could allow the fabrication of over 200 km fiber from a single preform.

Accurate modelling of fabricated hollow-core photonic bandgap fibers

We report a novel approach to reconstruct the cross-sectional profile of fabricated hollow-core photonic bandgap fibers from scanning electron microscope images. Finite element simulations on the reconstructed geometries achieve a remarkable match with the measured transmission window, surface mode position and attenuation. The agreement between estimated scattering loss from surface roughness and measured loss values indicates that structural distortions, in particular the uneven distribution of glass across the thin silica struts on the core boundary, have a strong impact on the loss. This provides insight into the differences between idealized models and fabricated fibers, which could be key to further fiber loss reduction.

MicroStructure Element Method (MSEM): viscous flow model for the virtual draw of microstructured optical fibers

We propose a new method to accurately model the structural evolution of a microstructured fiber (MOF) during its drawing process, given its initial preform structure and draw conditions. The method, applicable to a broad range of MOFs with high air-filling fraction and thin glass membranes, is an extension of the Discrete Element Method; it determines forces on the nodes in the microstructure to progressively update their position along the neck-down region, until the fiber reaches a final frozen state. The model is validated through simulation of 6 Hollow Core Photonic Band Gap Fibers (HC-PBGFs) and is shown to predict accurately the final fiber dimensions and cross-sectional distortions. The model is vastly more capable than other state of the art models and allows fast exploration of wide drawing parameter spaces, eliminating the need for expensive and time-consuming empirical parameter scans.