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

Abstract

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 m−1 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. Newly developed photonic components could allow large-scale photonic integrated circuits to be built on silicon substrates. Daoxin Dai from Zhejiang University, China, alongside co-workers from the University of California, USA, have proposed several new optical technologies for use in photonic integrated circuits, which substitute or work alongside electrical circuits in optical devices. The researchers have designed new ultrashort polarization-handling devices that split high-intensity beams of light, and a ring optical isolator that reduces reflections. The team have also created a new waveguide based on silicon nitride that can guide optical waves with a minimal loss of energy. These new technologies will allow scientists to construct higher performance, more compact optical devices.