Laser-written β-BBO depressed cladding waveguides for TM and TE polarizations

β-Barium Borate (β-BBO) is crucial for generating UV light and advancing nonlinear optical processes. Transitioning from bulk crystals to waveguides enhances efficiency and capabilities. In this study, we present the first, to our knowledge, successful fabrication of laser-written depressed-cladding waveguides in β-BBO which demonstrate good confinement for both transverse magnetic (TM) and transverse electric (TE) polarizations. These waveguides were created using ultrashort laser pulses, forming a low-index cladding around the core. This significant breakthrough is particularly important for nonlinear optical processes like second harmonic and sum frequency generation, as frequency conversion in BBO is based on birefringent phase matching which requires light guidance for both polarizations. The ability to adjust the core size enhances their suitability for application specific waveguide geometries, indicating substantial potential for efficient frequency conversion and high-power photonic applications.