Very low-loss passive fiber-to-chip coupling with tapered fibers

A novel passive fiber-to-chip coupling based on the use of fiber tapers embedded in a guiding structure is proposed. By beam-propagation calculations it is verified that this new coupling method exhibits a very low insertion loss. Major advantages of the proposed method compared with butt coupling are demonstrated by simulation results: first, tolerance requirements for the fibers, e.g., diameter variations and core eccentricity, and for fabrication of the alignment structure are reduced by at least 1 order of magnitude. Second, coupling to waveguides of nearly arbitrary dimensions and refractive indices seems to be possible. Experimental results on thermal drawing of fiber tapers are presented and used as input data for the simulations. A concept for fabrication of the new coupling method with the Lithographic Galvanik Abformung (LIGA) technique is presented.