Abstract

Femtosecond laser writing (FLW) enables mask-free three-dimensional photonic integration in transparent materials and offers a flexible route for prototyping glass-based photonic circuits. Here, we present a monolithic fabrication approach that combines femtosecond laser waveguide writing, femtosecond laser-induced chemical etching (FLICE), laser ablation, and metallization to realize reconfigurable photonic circuits in borosilicate glass. The process is implemented in a CAD-to-device workflow that allows optical, mechanical, and electrical structures to be co-designed and fabricated within the same substrate. A stress-assisted waveguide-writing regime is developed in borosilicate glass, enabling single-scan fabrication of optical waveguides, directional couplers, and Mach–Zehnder interferometers at writing speeds of 30 mm/s. The fabricated devices demonstrate stable guiding, directional coupling, and interferometric operation, providing a practical basis for implementing reconfigurable photonic building blocks in this material platform. FLICE is then used to fabricate suspended glass microbridges incorporating femtosecond-laser-written waveguides and integrated resistive microheaters. These structures act as thermally isolated thermo-optic phase shifters and enable a full 2π phase shift with an electrical power consumption of approximately 17 mW. The results demonstrate the feasibility of combining FLW and FLICE within a single borosilicate glass substrate to monolithically integrate passive photonic circuits with actively tunable thermo-optic phase shifters. This work establishes a laser-based fabrication route for reconfigurable three-dimensional photonic circuits in glass and provides a basis for future optimization toward larger programmable photonic systems.

IPC Classification

Keywords