Ultrathin Lensed Photonic Crystal Fibers with Wide Bandwidth and Long Working Distances

We have demonstrated an effective approach to fabricating ultrathin lensed photonic crystal fibers (PCFs) with long working distances. The analytic function of the maximum working distance of lensed PCF has been first revealed, agreeing well with the numerical solutions. Our specific lensed PCF can be experimentally optimized in terms of the collapsed PCF length and fiber tip curvature by use of a graphite filament furnace. A maximum collimating working distance up to 4.84 mm for a lensed PCF with the diameter of 125 μm is demonstrated, which is more than four times as long as previous lensed PCFs. The ultrawide working bandwidth over 770 nm is also demonstrated. The significantly enhanced features in terms of key performance parameters such as working distances and bandwidth will accelerate a variety of applications using such ultrathin lensed PCFs.