Optical semiconductor module

An optical semiconductor module comprising:

• a housing;
• a temperature control element having a temperature control plane, the temperature control element being configured to cool or heat the temperature control plane;
• a first board mounted on the temperature control plane, the first board having a first side and a second side reverse to the first side, the first side having a surface contact with the temperature control plane, the first board having a first thermal conductivity;
• a semiconductor laser device mounted on the second side of the first board;
• and
• a second board mounted on the second side of the first board, the second board having a third side and a fourth side reverse to the third side, the third side being fixed to the second side of the first board, the fourth side including a wiring pattern, the wiring pattern being electrically connected with the housing via a first bonding wire and electrically connected to the semiconductor laser device via a second bonding wire, the second board having a second thermal conductivity smaller than the first thermal conductivity,
• wherein the housing is configured to accommodate the temperature control element, the first board, the second board, and the semiconductor laser device,
• wherein the second board is juxtaposed with the semiconductor laser device on the second side of the first board, and
• wherein the second board has a hollowed part, and the semiconductor laser device is disposed within the hollowed part in a plan view from a direction perpendicular to the fourth side.