Near-infrared self-written waveguide spot size converter for single- and multichannel fiber-to-chip self-coupling

Near-infrared (NIR) light-induced self-written (LISW) optical waveguide technology provides passive alignment between telecommunications and silicon photonic devices and offers high-throughput and self-alignment advantages. Although fiber-to-chip self-coupling based on the NIR LISW technique has been reported, the loss assessment of NIR LISW optical self-coupling between a spot-size converter (SSC) and standard single-mode fiber (SSMF) has not been investigated. Therefore, in this study, we demonstrated that an NIR LISW optical waveguide enables low-loss, single- and multichannel fiber-to-chip self-coupling. The achieved high-numerical-aperture-SMF–SSMF and single-channel-SSC–SSMF self-couplings demonstrated insertion-loss improvements of 6.2 and 7.2 dB, respectively. Simultaneous multichannel fiber-to-chip self-coupling of NIR LISW optical waveguides between a 1 × 4 silicon waveguide coupler and four-channel single-mode-fiber array was successfully achieved using our technique, yielding a maximum loss improvement of 7.0 dB. The results demonstrate the potential of the NIR LISW optical waveguide technique for addressing the cost and takt time challenges associated with the manufacturing of silicon photonic devices.