Optical transmission module

An optical transmission module comprising:

• a stem having a plate shape and made of metal;
• a block fixed to the stem;
• a sub-mount fixed to a side surface of the block;
• a plurality of semiconductor lasers provided at the sub-mount;
• and
• a cap with a lens fixed thereto, the cap covering all members placed above the stem, wherein
• a plurality of lead pins whose number is the same as a number of the plurality of semiconductor lasers are provided so as to respectively penetrate through a plurality of holes formed in the stem,
• the plurality of lead pins and the plurality of semiconductor lasers are electrically connected to each other, respectively,
• single-phase electrical signals with the stem as a ground potential are respectively applied to the plurality of semiconductor lasers from an external power supply, through the plurality of lead pins, respectively, so as to cause modulation and oscillation of the plurality of semiconductor lasers,
• the number of the plurality of semiconductor lasers provided at the side surface of the block is two,
• arrangement from one of the lead pins to a corresponding one of the semiconductor lasers and arrangement from the other lead pin to the other corresponding semiconductor laser are line-symmetric as seen in a direction perpendicular to the side surface of the block, to reduce a difference between a value of an impedance from the one of the lead pins and a value of an impedance from the other lead pin,
• all oscillation wavelengths of the plurality of semiconductor lasers are the same, and
• the single-phase electrical signals at the same phase are respectively applied to the semiconductor lasers.