Integrated photonic platforms based on femtosecond laser-inscribed S-bend and Y-branch waveguides in Nd3+-doped GeO₂–PbO glass

Abstract

This work reports the fabrication and characterization of active double-line waveguide structures produced by femtosecond laser irradiation in Nd³⁺-doped GeO₂–PbO glass embedded with silver nanoparticles. Straight, S-bend, and Y-branch configurations were investigated aiming at photonic applications in complex architectures. The waveguides were formed by four overlapping tracks arranged in a double-line geometry. Optical characterization included propagation loss, relative gain, and beam quality (M²) measurements. The straight waveguide presented the best beam symmetry and the highest internal gain, reaching 5.61 dB/cm. The S-bend structure, fabricated with a 40 mm bending radius, despite the additional bending losses achieved a positive internal gain of 3.84 dB/cm. The Y-branch waveguide, produced with a 5° opening angle, showed a power splitting ratio of 54/46 and gains superior to those of the S-bend configuration. For the first time, active S-bend and Y-branch waveguides were demonstrated in Nd³⁺-doped GeO₂–PbO glass containing silver nanoparticles. These results highlight the potential of this platform for advanced integrated photonic devices.