U.S. patent application publication No. US2013/0259423 discloses an optical assembly that provides alignment marks on an upper surface of a circuit board and performs centering of alignment holes in an optical module with respect to the alignment marks, thereby performing alignment between the module and the circuit board. Japanese patent application publication No. JP2014-137410 discloses aligning markers provided on the bottom surface of a lens array with markers on an electric board by using an imaging device, thereby achieving centering.