Toward 3D Integration of Highly See-Through Photonic Circuits in Glass

Embedding naked-eye-invisible electronic and optical elements in transparent panels is at the heart of enabling mobile transparent accessories by making see-through smart screens. Here, a novel invisible photonic element, highly see-through (HST) waveguide, is reported, which is written by femtosecond laser in glass. A general synergistic control of the thermodynamic and dynamic behavior over the matter fluid in the laser irradiated confined region to tune the cross-section of waveguides and suppress the generation of scattering centers in the waveguides is established. An effective reduction of light leakage (covering red, green, and blue coupled light) by an order of magnitude compared to conventional waveguides is achieved, making it highly see-through at bright illumination of >100 lux. A general dynamical model based on a frozen-in shock wave diffusion process is proposed, which is applicable to various glasses regardless of their compositions. Ultra-wide tuning of HST waveguide mode diameters from 4.9 to 26.5 mu m is demonstrated, making it versatile for functionalizing various transparent screens by mode-matching with fiber sources and integrated planar waveguides of different working wavelengths.