Grating Coupler And High Speed Electroabsorption Modulator Based On Silicon-on-Insulator Wafer

Nowadays, silicon platform is emerging to be the best candidate of photonic integrated circuits (PICs) due to not only the dominant status of silicon in microelectronics but also the great benefits brought to the photonics. Regarding the recent breakthroughs concerning active devices on silicon substrate, the question left is no longer the feasibility of silicon PIC but the competitiveness of its solution compared with its counterpart.Firstly, along with the down scaling of the silicon waveguide's cross section, the cou-pling between the silicon PIC and the external fiber becomes a troublesome issue due to the mismatch of the mode and the polarization. One of the promising solution is to use the grating coupler as the input/output interface for the silicon PIC. We have attempted to improve the performance of the grating coupler from two aspects:improve its coupling efficiency and make it being versatile. For the former, a nonuniform grating coupler based on the lag effect in the dry etching process has been developed with a coupling efficiency of 64%, nearly a double of a standard one. For the latter, a polarization beam splitter (PBS) based on a one-dimensional grating coupler has been proposed and experimentally demon-strated. An extinction ratio of around-20 dB, as well as a maximum coupling efficiency of over 50% for both polarizations, is achieved by such a PBS with a bottom Bragg reflector underneath.Secondly, silicon-compatible techniques make it possible to achieve active function on silicon platform, but more devotion is required in order to catch up with its counterpart. Hybrid silicon platform, where theâ…¢/â…¤material is transplanted to the silicon on insulator wafer, is attractive to realize high performance silicon active devices. We have developed several high speed electroabsorption modulators (EAMs) on the hybrid silicon platform, using a general approach based on the transmission line analysis. A record bandwidth of 43 GHz, as well as a dynamic extinction ratio of 8.8 dB at 50 Gb/s with a 2 V driving voltage swing applied, has been achieved for a hybrid silicon traveling-wave EAM, proving that it is the fastest silicon modulator so far. We have also proposed an efficient hybrid EAM based on a microring. It is able to have an enhanced extinction ratio, a relaxed sensitivity and an improved optical bandwidth.