Towards Integrated Photonics: a review of femtosecond laser-written double-line waveguides in GeO2-PbO glasses

This review focuses on the fabrication and characterization of optical waveguides inscribed in GeO 2 –PbO glasses using femtosecond (fs) laser irradiation. Fs laser writing offers key advantages, such as three-dimensional structuring, high precision, and minimal thermal effects to the surrounding material, enabling the production of complex photonic devices within transparent substrates. The discussion covers different cases, each from a distinct sample and reported in separate works: a straight waveguide doped with Yb 3+ /Er 3+ , operating as an optical amplifier in the third telecommunications window, straight waveguides doped with Nd 3+ , with and without Ag nanoparticles and the role of the plasmonic effects on the optical properties at 1064 nm. The results of S-bend and Y-shaped configurations containing Ag nanoparticles are also reviewed due to their relevance for resonant ring and beam splitters, respectively. The role of larger radius is discussed as well as the best Y configuration with respect to the opening angle and separation between the arms. The quality factor (M 2 ) of the proposed architecture is used to evaluate the symmetry between the x and y axes that is relevant to indicate comparable light guidance. The review highlights different configurations as well as their optical properties and the potential applications for integrated photonics. • Review of recent advances in fs-laser-written dual-line waveguides in GeO 2 –PbO glasses • Fs-laser-written waveguides in GeO 2 –PbO glasses: a platform for integrated photonics • S-bend and Y-shaped architectures micromachined by fs laser in GeO 2 –PbO glasses • Waveguides with enhanced optical gain: the plasmonic effects of Ag nanoparticles