An optical waveguide is produced by using a polymer obtained by using a silsesquioxane derivative represented by the formula (1-0). In the formula (1-0), R0 independently represents hydrogen, alkyl having 1 to 40 carbon atoms in which optional hydrogen may be replaced by fluorine and optional —CH2— may optionally be replaced by —O—, —CH═CH—, cycloalkylene, or cycloalkenylene, aryl in which optional hydrogen may optionally be replaced by halogen, or with alkyl having 1 to 20 carbon atoms whereby optional hydrogen may be replaced by fluorine and optional —CH2— may be replaced by —O—, —CH═CH—, cycloalkylene, or phenylene, or arylalkyl in which optional hydrogen in the aryl may be replaced by halogen or alkyl having 1 to 20 carbon atoms, and hydrogen in the alkylene of the arylalkyl may be replaced by fluorine, and optional —CH2— in the alkylene of the arylalkyl may be replaced by —O—, —CH═CH—, or cycloalkylene, and Y is a group represented by the formula (a) or (b):