Abstract
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.
Highlights
Since 2011 a variety of anti-resonant hollow core fibers (AR-HCFs) have been reported with leakage losses reduced from several dB/m to tens of dB/km or less [1,2,3]
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
In good agreement with theoretical analysis, that the sensitivity to bend diameter is dependent on the ratio between cladding and core structure size
Summary
Since 2011 a variety of anti-resonant hollow core fibers (AR-HCFs) have been reported with leakage losses reduced from several dB/m to tens of dB/km or less [1,2,3]. Due to the leaky nature of the guidance mechanism in AR-HCFs, bend losses increase as bend diameters are decreased due to the reduced reflectivity from the cladding [8]. This form of leakage is inevitable and will occur anywhere the fiber is bent. In comparison to the six-cell design, seven-cell AR-HCF has been numerically verified as providing the optimum combination of leakage loss, bend loss and single mode performance required for high power laser delivery applications [20]. The resonant bend loss of seven cell AR-HCF is systematically measured and compared with the predictions of the analytical model
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