Mode Conversion\nTrimming in Asymmetric Directional\nCouplers Enabled by Silicon Ion Implantation

An on-chip asymmetric directional coupler (DC) can convert\nfundamental\nmodes to higher-order modes and is one of the core components of mode-division\nmultiplexing (MDM) technology. In this study, we propose that waveguides\nof the asymmetric DC can be trimmed by silicon ion implantation to\ntune the effective refractive index and facilitate mode conversion\ninto higher-order modes. Through this method of tuning, transmission\nchanges of up to 18 dB have been realized with one ion implantation\nstep. In addition, adjusting the position of the ion implantation\non the waveguide can provide a further degree of control over the\ntransmission into the resulting mode. The results of this work present\na promising new route for the development of high-efficiency, low-loss\nmode converters for integrated photonic platforms, and aim to facilitate\nthe application of MDM technology in emerging photonic neuromorphic\ncomputing.