Laser-written depressed cladding waveguides in the z-cut of birefringent nonlinear optical crystals for efficient frequency conversion

Depressed cladding waveguides, capable of guiding both transverse magnetic (TM) and transverse electric (TE) polarizations, offer significant benefits for efficient frequency conversion and high power usage due to their large mode field diameter. However, strong birefringence in materials like LiNbO3 poses challenges for waveguide fabrication in the z-cut orientation. We report on the successful fabrication of these waveguides in birefringent nonlinear optical crystals using tightly focused ultrashort laser pulses. Experimental investigations reveal their potential in nonlinear optical processes such as second harmonic generation, with the flexibility to adjust the core size for specific applications.