Wide-Band Optical Mode Converters for Coupling Between Fibers and Silicon Photonic Wires With Large Misalignment Tolerance

A wideband optical mode converter is presented for coupling between fibers and sub-wavelength silicon photonic wires with large misalignment tolerance. This converter consists of a three-dimensional (3-D) SU-8 taper and silicon inverted nanotapers, which are cascaded and show coupling losses of 2.8 dB and 4.1 dB for the TE- and TM-polarized waves launched from a cleaved single mode fiber. The fiber misalignment tolerance for 3-dB transmittance drop is estimated to be $\pm {3}~\mu{\hbox {m}}$ .