Passive technologies for future large-scale photonic integrated circuits on silicon: polarization handling, light non-reciprocity and loss reduction

Silicon-based large-scale photonic integrated circuits are becoming important,due to the need for higher complexity and lower cost for optical transmitters,receivers and optical buffers.In this paper,passive technologies for large-scale photonic integrated circuits are described,including polarization handling,light non-reciprocity and loss reduction.The design rule for polarization beam splitters based on asymmetrical directional couplers is summarized and several novel designs for ultra-short polarization beam splitters are reviewed.A novel concept for realizing a polarization splitter–rotator is presented with a very simple fabrication process.Realization of silicon-based light non-reciprocity devices(e.g.,optical isolator),which is very important for transmitters to avoid sensitivity to reflections,is also demonstrated with the help of magneto-optical material by the bonding technology.Low-loss waveguides are another important technology for large-scale photonic integrated circuits.Ultra-low loss optical waveguides are achieved by designing a Si3N4 core with a very high aspect ratio.The loss is reduced further to,0.1 dB m21 with an improved fabrication process incorporating a high-quality thermal oxide upper cladding by means of wafer bonding.With the developed ultra-low loss Si3N4 optical waveguides,some devices are also demonstrated,including ultra-high-Q ring resonators,low-loss arrayed-waveguide grating(de)multiplexers,and high-extinction-ratio polarizers.