Introduction to the Special Issue on Ultralow Loss Planar Waveguides and Their Applications

The fifteen papers in this special issue focus on ultra low loss planar waveguides and the applications. Ultra-low loss optical planar waveguide technology is a critical research area driven by the need to improve energy efficiency and advance the power handling capability, performance, function and complexity of photonic integrated circuits and systems-on-chip. An increasing number of applications require lower planar waveguides losses and advances in materials, waveguide design, processing techniques and monolithic and heterogeneous integration. Low loss operation from the visible to the infrared and passive and active waveguide structures as well as linear and non-linear optical devices are needed. Examples of applications driving these advancements include data-communications, bio-sensing, positioning and navigation, low noise microwave synthesizers, spectroscopy, RF signal processing, quantum communication, and atomic clocks. The special issue comes at an important stage in low loss waveguides and photonic integration and the purpose is to demonstrate the current state-of-the-art in the area of this technology and highlight recent progress and trends to lower waveguide loss, as the key element to realize new functions and their potential applications.