We present a simple fabrication technique using a hydrophobic composite elastomer for patterning an SU-8-based rib waveguide Bragg grating filter via solvent-assisted microcontact molding (SAMIM). The proposed technique utilizes a two-layered composite stamp made of polydimethylsiloxane and hard polydimethylsiloxane, which enables both the rib waveguide and surface relief grating structure to be patterned simultaneously. The SAMIM method realizes patterning at ambient temperatures with the weight of the mold applying all the pressure necessary. By allowing the mold to absorb solvent when in contact with the polymer, the solvent dissolves or swells the polymer’s surface, creating the desired pattern. This composite mold successfully demonstrates the SAMIM creation of the SU-8 rib waveguide and gratings, paving the way for a facile and efficient reproduction of a polymeric rib waveguide grating filter. Based on experimental results, the stamp demonstrates an operational life span in excess of 10 successful replications, utilizing a Bragg grating test pattern with a grating period of , a depth of , and a total length of . The resulting waveguides show a band-rejection gain of at the center wavelength of and a bandwidth of .