Fabrication and polarization modulation of waveguides in 4H-SiC crystals by femtosecond laser direct writing

The dual-line waveguides, vertical-dual-line waveguides, and rectangular depressed-cladding waveguides have been fabricated in 4H-SiC crystals by femtosecond laser direct writing. Dual-line waveguides can only support guidance along ne polarization, vertical-dual-line waveguides can only support guidance along no polarization, and rectangular depressed-cladding waveguides can support guidance along both no and ne polarizations. These results indicate that, by altering spatial distribution of femtosecond-laser-modified areas, one could modulate the polarization sensitivity of 4H-SiC waveguides. Additionally, in consideration of the unique 2D-guidance feature, it can be predicted that rectangular depressed-cladding waveguide would play an important role in nonlinear frequency conversion. By collecting and analyzing micro-Raman spectra, it has been found that crystal network is almost undamaged in waveguide core. This work is not only significant to construct polarization-dependent devices, but also important to realize many photonic applications (e.g., frequency conversion) in nonlinear optics.