Semiconductor optical device, semiconductor optical integrated device, and semiconductor optical apparatus

A semiconductor optical device, comprising:

• a semiconductor multilayer including a first conductivity type semiconductor layer, an optical functional layer, and a second conductivity type semiconductor layer which are grown in the stated order in a stacking direction on a substrate;
• a first electrode including a first connection portion connected to the first conductivity type semiconductor layer;
• and
• a second electrode including a second connection portion connected to the second conductivity type semiconductor layer,
• wherein a mesa portion of the first conductivity type semiconductor layer, the optical functional layer, and the second conductivity type semiconductor layer form a mesa structure extending in an extending direction,
• wherein the first electrode is arranged on one side of the mesa structure in a width direction perpendicular to the stacking direction and the extending direction,
• wherein the first conductivity type semiconductor layer includes:
• the mesa portion;
• and
• a base portion which is continuous below the mesa portion, extends at least on the one side in the width direction, and is in contact with the first connection portion in a connected portion, and
• wherein the semiconductor optical device includes four or more semiconductor interfaces in a first region on the one side in the width direction of the connected portion of the base portion which is in contact with the first connection portion.