NOVEL WAVEGUIDE CONCEPT FOR NONRECIPROCAL LIGHT PROPAGATION

Silicon photonics has received significant attention in the recent years as a technology, which could enable high-speed performance at low cost and power requirements. The technology is expected to bring significant performance gains in areas such as communication, high-performance computing, and photovoltaics. However, to make this technology feasible for market adoption, it is crucial to ensure that photonic components can be fabricated at low cost, and also ensure that they use processes compatible with CMOS (complimentary metal oxide semiconductor) equipment. Currently, there are numerous academic and industry initiatives focusing on producing different building blocks of optical interconnects. The goal is to achieve a single all-silicon circuit, which integrates both electronic and photonic components, and also achieve high-volume manufacturing at low costs.
As a result of a cooperative research conducted at the California Institute of Technology and the University of California, San Diego, a new method has been proposed for radically limiting the back-reflection of light signals at silicon chip-integrated waveguides. This new optical isolator enables nonreciprocal light propagation on a silicon photonic chip without the need for integrating conventional methods based on magnetic field or nonlinear optical materials. The team has fabricated the silicon waveguide with metal spots along the sides, which interacts with the propagating light wave differently depending on its propagation direction. The metallic-silicon pattern enables light to travel freely in one direction, but dissipates it when it travels in the opposite direction. In this regard, the structure resembles an electrical diode, which in conventional electronics systems enables the signal to travel in only one direction. The waveguide, which is 0.8-micrometers-wide, has been incorporated into a prototype device, and tested using at a 0.55 micrometer-wavelength. The advantage of the proposed concept is that while it offers breakthrough performance, the device can be manufactured using standard CMOS processing, which ensures ease of integration into existing production flow.
The significance of the proposed optical isolator is that in holds promise for improving the performance of silicon photonics chips by limiting the interference of reflected light beams with optical components, such as light sources. This feature is critical to enable the integration of multiple photonic components on the single chip, and as a result bring photonic chips closer to commercial reality. The proposed optical isolator is still in the experimental stage. However, future work will be focused on integrating this technology into a fully operational integrated circuit.