Fabrication of Si-based waveguide splitters using photosensitive sol-gel method

In this paper, a photosensitive sol-gel method for 1 × 8 Y-branch optical splitter is reported. The poly (methyl methacrylate) (PMMA) cladding films with different thicknesses (above 10 μm) on Si substrates are prepared on Si substrates by dip-coating, the root-mean-square roughness (Rrms) of which is less than 0.7 nm. The UV photosensitive organic-inorganic composite SiO₂/ZrO₂/H core films are then coated on these PMMA cladding films using photosensitive sol-gel method. The refractive indexes of PMMA cladding films examined by spectroscopic ellipsometer are 1.4854, 1.4815 and 1.4806 at 0.85, 1.31 and 1.55 μm, while that of the SiO₂/ZrO₂/H gel films are 1.5569, 1.5489 and 1.5472 μm, respectively, which is larger than that of PMMA cladding films. Therefore, the composite structure of SiO₂/ZrO₂/H gel films on PMMA-on-Si substrates could be used to fabricate waveguide splitter. Based on the inherent photosensitivity of the SiO₂/ZrO₂/H gel film, 1 × 8 Y-branch optical power splitters with a thickness of 5 μm are fabricated by irradiating the gel film with UV light through a mask followed by dissolving the non-irradiated area in a suitable solvent. The line-width and output spacing of this splitter are 25 and 110 μm, respectively. The observed near-field pattern indicates that the light with a wavelength of 1.53-1.56 μm can be transmitted and split into eight branches in the optical splitter, which is fabricated by using the above technique.