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

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.