Fabrication of Y-Splitters and Mach–Zehnder Structures on (Yb,Nb):RbTiOPO<inline-formula><tex-math> $_{\bf 4}$</tex-math></inline-formula>/RbTiOPO<inline-formula><tex-math>$_{\bf 4}$</tex-math></inline-formula> Epitaxial Layers by Reactive Ion Etching

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Reactive ion etching of RbTiOPO4 (0 0 1) substrates and (Yb,Nb):RbTiOPO4/RbTiOPO4 (0 0 1) epitaxial layers has been performed using fluorine chemistry. A maximum etch rate of 8.7 nm/min was obtained, and the deepest etch achieved was 3.5 μm. The (Yb,Nb)-doped epitaxial layers showed a slower etching rate when compared with undoped material. Liquid phase epitaxial growth of cladding layers has also been performed, resulting in a high-quality interface growth without appreciable defects. 9-mm-long Mach–Zehnder interferometer and 9-mm-long Y-splitter structures were designed and patterned in RbTiOPO4 substrates and (Yb,Nb):RbTiOPO4/RbTiOPO4 (0 0 1) epitaxial layers. The structures fabricated in RbTiOPO4 substrates were filled with laser active (Yb,Nb):RbTiOPO4 higher refractive index core material, and finally an RbTiOPO4 cladding was grown on the samples. The refractive index difference between the (Yb,Nb):RbTiOPO4 layer and the RbTiOPO4 substrate at 1.5 μm has been measured and optical waveguiding at this wavelength has been demonstrated.