On-fiber 3D printing of photonic crystal fiber tapers for mode field diameter conversion

Summary form only given. The large mismatch between the Mode Field Diameter (MFD) of conventional single-mode fibers (SMFs) and the MFD of highly nonlinear Photonic Crystal Fibers (PCFs), that can be down to 1.5 μm, or Large Mode Area PCF, that can be up to 25 μm, would require a substantial fiber mode size rescaling in order to allow an efficient direct coupling between PCFs and SMFs. Over the years different solutions have been proposed, as fiber splicing of SMF to PCF. However these procedures are not straightforward, as they involve developing special splicing recipes, and can affect PCF optical properties at the splice interface [1].Here we propose on-fiber Two-Photon Lithography (TPL) [2,3] fabrication of polymer PCF-based waveguiding structures to create ultra-compact and fiber-integrated beam shaping devices. In particular, we apply this approach to the fabrication of a PCF taper for optical fiber MFD conversion [4]. Thanks to the versatility of TPL, 3D structures with arbitrary geometry can be fabricated, and by considering the reciprocity principle, tapers for adiabatic up-scale and down-scale mode size converters can be designed.