Fabrication of an integrated optical filter using a large-core multimode waveguide vertically coupled to a single-mode waveguide.

We demonstrate the feasibility of the process for fabricating a single-mode waveguide and a large-core multimode waveguide aligned vertically on the same substrate. Using this process, we propose and demonstrate a filter that drops optical signal propagating in a single-mode waveguide to a multimode waveguide in the specific wavelength interval by a long-period grating. We use perfluorocyclobutane and benzocyclobutane for the cladding and core of the single-mode waveguide, respectively. The large core of the multimode waveguide is made of Norland Optical Adhesive 61. For the grating period of 315.9 um, the fabricated filter has the center wavelength of 1537.7 nm, at which the maximum attenuation is 17.8 dB.