Rib waveguides, which are made of magnetic garnet films of composition (LuNdBi)3(FeAl)5O12 (LNB), fabricated by Ar sputter etching have large propagation loss in comparison with LNB slab waveguides. X-ray photoelectron spectroscopy (XPS) is used to investigate chemical states of constituent elements existing in the surface layer where a Ti mask has been deposited during the etching process. The analysis shows that Fe chemical shift due to Ar+ ion bombardment can cause increase in the optical absorption loss, and hence the propagation loss. It is effective for suppressing the loss increase to employ a SiO2 mask deposited onto LNB film instead of a Ti mask.
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