Chemical etching and fabrication of ridge waveguides on Bi12GeO20 single crystals

Chemical etching of Bi12GeO20 was investigated, and the developed technology was applied to the fabrication of ridge waveguides by an easy and rapid chemical etching method. The etching solution was prepared by mixing concentrated HCl, concentrated H2O2, and 5M NH4Cl. Ridge waveguides (0.3 mm to a few microns in size) prepared on the (110) surface had a trapezoidal cross section, and for a higher volume ratio of HCl and a longer etching time the cross section was triangular. Rectangular ridge guides were also prepared on the (100) surface, but this application is limited to small-size (several microns) ridges because with deep etching the surface is covered with etch pits and becomes rough.