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

Abstract

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 SiO 2/ZrO 2/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 SiO 2/ZrO 2/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 SiO 2/ZrO 2/H gel films on PMMA-on-Si substrates could be used to fabricate waveguide splitter. Based on the inherent photosensitivity of the SiO 2/ZrO 2/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.