Guiding and magneto-optical properties of TGG waveguide by proton implantation combined with femtosecond laser ablation

Key words: 
• optical waveguide /
• ion implantation /
• terbium gallium garnet crystal (TGG) /
• magneto-optical effect /
• femtosecond laser ablation

Abstract: Integrating the magneto-optical effect into a waveguide-based photonic device becomes more and more interesting. In the work, the planar optical waveguide firstly was prepared in a terbium gallium garnet crystal (TGG) via the proton implantation with the energy of 4$\times10^{-1}$ MeV and the fluence of 6$\times 10^{8}$ ions/μm$^{2}$. Subsequently, a femtosecond laser with a central wavelength of 800 nm and a power of 3 mW was used to ablate the surface of the planar waveguide, forming the ridge optical waveguide. The dark-mode curve of the planar waveguide was measured by a prism coupling technique. The top-view morphology of the ridge waveguide was observed via a Nikon microscope. The mode field distributions of the planar and ridge waveguides were obtained by an end-face coupling system, and the propagation losses of the two waveguides were measured to be 2.26 dB/cm and 2.58 dB/cm, respectively. The Verdet constants were measured to be $-72.7 ^\circ$/T$\cdot$cm for the TGG substrate and $-60.7 ^\circ$/T$\cdot$cm for the ridge waveguide. The TGG waveguides have a potential in the fabrication of magneto-optical waveguide devices.