Bending-induced mode non-degeneracy and coupling in chalcogenide negative curvature fibers

Optimization method for low-loss single-mode bending negative curvature anti-resonant hollow-core fiber designed by mode modification

A method of designing negative curvature anti-resonant hollow-core fibers (NC-AR-HCFs) with bending resistance is proposed, by which the fundamental mode (FM) and higher-order mode (HOM) can be adjusted. An asymmetric double-ring negative curvature hollow-core fiber (ADR-NC-HCF) is proposed to verify the method. The ADR-NC-HCF achieves the FM loss of 0.8 dB/km at 1550 nm under the bending radius of 20 mm. The coupling relation between the modes in ADR-NC-HCFs is analyzed revealing the physical principle of the design method. Based on the principle, the fiber can be directionally optimized to achieve a lower loss of the FM or higher-order mode extinction ratio.

Understanding bending-induced loss and bending-enhanced higher-order mode suppression in negative curvature fibers

We present a numerical analysis on bending-induced loss and bending-enhanced higher-order mode suppression in negative curvature fibers. We provide underlying mechanisms on how geometrical parameters affect the bending properties. We find that fiber parameters influence the bending performance by altering the resonant coupling conditions, as well as light leakage through inter-tube gaps. We identify regions in the parameter space that exhibit excellent bending properties and offer general guidelines for designing negative curvature fibers that are less sensitive to bending. Moreover, we explore the possibility of enhancing higher-order core mode suppression through mechanical bending. We find that up to nine-fold increase in the higher-order mode extinction ratio can be achieved by bending the fiber.

Geometry of Chalcogenide Negative Curvature Fibers for CO2 Laser Transmission

We study the impact of geometry on leakage loss in negative curvature fibers made with As 2 Se 3 chalcogenide and As 2 S 3 chalcogenide glasses for carbon dioxide (CO 2 ) laser transmission. The minimum leakage loss decreases when the core diameter increases both for fibers with six and for fibers with eight cladding tubes. The optimum gap corresponding to the minimum loss increases when the core diameter increases for negative curvature fibers with six cladding tubes. For negative curvature fibers with eight cladding tubes, the optimum gap is always less than 20 μ m when the core diameter ranges from 300 μ m to 500 μ m. The influence of material loss on fiber loss is also studied. When material loss exceeds 10 2 dB/m, it dominates the fiber leakage loss for negative curvature fiber at a wavelength of 10.6 μ m.

Polarization-filtering and polarization-maintaining low-loss negative curvature fibers

We propose a polarization-filtering and polarization-maintaining negative curvature fiber in which two nested resonant tubes are added to a standard negative curvature fiber with one ring of tubes. The coupling between the glass modes in the nested resonant tubes and the fundamental core modes is used to increase the birefringence and differential loss for the fundamental core modes in the two polarizations. We show computationally that the birefringence and the loss ratio between the modes in the two polarizations can reach 10^-5 and 850, respectively. Meanwhile, the low-loss mode has a loss that is lower than 0.02 dB/m. The relatively simple design of this polarization-maintaining negative curvature fiber will be useful in hollow-core fiber devices that are sensitive to polarization effects, such as fiber lasers, fiber interferometers, and fiber sensors.

Measurement of resonant bend loss in anti-resonant hollow core optical fiber

We present the results of measurements of resonant spectral bend loss using a novel apparatus in a series of hollow core anti-resonant optical fibers, important for their applications in the delivery of industrial power ultra-short laser pulses. The measured bend losses exhibit clear wavelength-bend diameter resonances. We demonstrate, in good agreement with theoretical analysis, that the sensitivity to bend diameter (in terms of minimum bend radii) is dependent on the ratio between cladding and core structure size. By decreasing the cladding capillary diameter: core diameter ratio from 0.70 to 0.43 the minimum bend diameter is decreased from >160 mm to ~15 mm at a wavelength of 800 nm. Furthermore it is demonstrated that the exact position of the loss bands is highly dependent on the orientation of the fiber structure with the bend plane.

Photochemistry in a soft-glass single-ring hollow-core photonic crystal fibre

A single-ring hollow-core photonic crystal fibre (HC-PCF), guided by anti-resonant reflection, is investigated as a highly efficient and versatile microreactor for liquid-phase photochemistry and catalysis.