A method for manufacturing an optical device having an optical block, through which a light is transmitted, is provided. The method includes steps of: forming a plurality of silicon oxide members, which is disposed on a silicon substrate, wherein the silicon oxide members are arranged in parallel each other by a predetermined clearance between two adjacent silicon oxide members; and pouring a super critical fluid into the clearance so that the clearance is filled with a product formed from a predetermined compound for forming the optical block, wherein the predetermined compound is dissolved in the super critical fluid.