Semiconductor optical device

A semiconductor optical device comprising:

• a stem;
• a semiconductor optical element secured to the stem;
• a resin cap including
• a cylindrical body portion having an inside surface and an outside surface which extend along an entire length of the cylindrical body portion,
• a plate portion disposed at a first end of the cylindrical body portion, and
• an edge portion disposed at a second end of the cylindrical body portion, wherein the edge portion has a lower surface bonded to the stem so that the resin cap covers the semiconductor optical element;
• and
• a lens attached integrally to the plate portion of the cam, wherein
• the cylindrical body portion has at least one first portion and a plurality of second portions which are spaced apart from each other in a circumferential direction of the cylindrical body portion, and which project inwardly relative to the at least one first portion,
• each of the second portions has a first engagement feature, the stem has a plurality of second engagement features, and
• each second engagement feature vertically underlies and engages or contacts the first engagement feature of a respective one of the second portions.