Laser-written high-contrast waveguides in glass

Abstract

Laser writing of waveguides in bulk glasses opens the opportunity for creating three-dimensional photonic devices. In order to become practical, the numerical aperture (NA) of these waveguides should be significantly higher than currently achievable of 0.1 – 0.15. One reason is that with higher NAs one can decrease the bending radii of the embedded photonic devices without significant loss penalty and make them compact. Thus, femtosecond-laser-written waveguides in glasses do not allow bending radii smaller than 15 - 20 mm. In order to overcome this limitation, we propose to fabricate waveguides in phase-separable and leachable glass where the index contrast is determined by the difference between the refractive indices of the unprocessed glass and of the leached porous glass. We show that we can achieve the NA = 0.25 prior to optimization. Surface and sub-surface treatment with a nanosecond ultraviolet (UV) laser produces a similar effect with even higher NA = 0.35. Applications may include a range of tightly packed embedded and three-dimensional photonic devices in bulk glass like directional couplers, splitters, interferometers, etc.