Fabrication and characterization of ion-exchanged optical waveguides in potassium lithium niobate crystal substrates

Optical waveguides have been successfully fabricated in KLN crystal substrates using the ion-exchange process for the first time. Only the TM mode can be guided in such waveguides. The refractive index profile of the waveguide can be approximately fitted by a complementary error function. To understand how the ion-exchanged waveguide is formed in the KLN substrate, an Rb+-K+ ion-exchange mechanism was proposed. After ion exchange, the structural alternation between substrate and ion-exchanged layer was investigated using the X-ray diffraction method. The waveguide transmission loss was measured.