Direct writing with ultrashort laser pulses is considered to be a very efficient technique for fabricating 3D waveguide structures, such as s-curved waveguides, beam splitters or Y-type waveguides, because it allows for the fabrication of structures with arbitrary geometries in various transparent materials. Among them, Y-branch splitters represent basic elements for the development of integrated photonic devices of interest in various applications, including power dividers, interferometers, multiplexers or micro-fluidic devices.

In this work, we report on the realization of Y-branch beam splitters in 1.1-at.% Nd:YAG ceramics by picosecond-laser beam writing. Laser emission performances were investigated under the pump at 807 nm with fiber-coupled diode lasers. For quasi-continuous-wave pumping, laser emission at 1.06 mm was generated for all waveguides. The linear waveguide (NYAG-Y0; 150 mm width x 100 mm height) yielded laser pulses with an energy of E_p= 2.2 mJ for a pump energy of E_pump= 12.8 mJ at 807 nm (corresponding to an overall optical-to-optical efficiency, η_o, of 0.17); the slope efficiency was η_s= 0.21. The NYAG-Y1 waveguide (1° splitting angle; 75 mm width x 100 mm height) emitted laser pulses with a maximum energy of E_p= 1.32 mJ (η_o= 0.10 and η_s= 0.12). Furthermore, the NYAG-Y2 waveguide (2° splitting angle; 75 mm width x 100 mm height) yielded laser pulses with a lower energy of E_p= 1.20 mJ at an efficiency of η_o= 0.09 and with a slope of η_s= 0.11. The emission performances of these Y-branch waveguide beam splitters confirm that they are promising candidates for realizing the use of integrated devices of interest for various advanced photonics circuits.

Funding: This work was financed by the project PD 63/2022, PN-III-P1-1.1-PD-2021-0522, and partially supported by the program NUCLEU-LAPLAS VII 30N/2023, Ministry of Research, Innovation and Digitization, Romania. The support of the National Interest Infrastructure facility IOSIN - CETAL at INFLPR is acknowledged.