Disclosed is a modified metal oxide sol that has a large hydrophilizing effect and antistatic effect, can be produced at low cost and is capable of being a coating. Accordingly, an improved assembling efficiency, stronger fastening force between waveguide units, and better air-tightness of the waveguide are obtained by using resin molding to fasten the pair of the waveguides. The second chip has a first chip surface and a second chip surface, which is opposite the first chip surface. 005 to 10 weight percent of a water miscible organic solvent, and water.