Fabrication method for ultra-long optical micro/nano-fibers

Nonlinear optical interactions can be enhanced dramatically by tight light-confinement and long interaction-length. Optical fiber tapers with micro/nano-thickness waists considerably increase light-matter interactions in or near their waists. Here, we propose and demonstrate a novel tapering method of fabricating uniform, low-loss, and ultra-long micro/nano fibers. The technique comprises three steps for conventional flame-brushing and pulling, recalibration, and one-directional pulling. Using the proposed method, two strands of tapered fibers are fabricated, having 0.82-μm/1.6-μm diameters, 220-mm/500-mm uniform lengths with <55-nm/66-nm diameter variances, and high transmittances of 90.2%/91.5%. A figure of merit indicating the nonlinear-optic efficiency is defined and used to compare the results obtained in this study with those for tapered fibers in references. The proposed tapering method will be very useful for the fabrication of tapered fiber devices exploiting nonlinear optic effects, including Brillouin scattering, Raman amplification, and other third-order nonlinearities for supercontinuum generation.