OPTICAL INTEGRATED DEVICE

PROBLEM TO BE SOLVED: To provide an optical integrated device capable of reducing reflection return light to a single mode LD, and preventing increase in oscillation line width of the single mode LD.SOLUTION: In an optical integrated device, an interference type optical amplification region having a branch waveguide is provided between a single mode LD and a reflection point for reflecting output light of the single mode LD. Light is amplified in the optical amplification region, and a phase difference is given to light passing through the branch waveguide. Thereby, because principle loss is added to the reflection return light in a Mach-Zehnder type waveguide configured as an optical interferometer, the light intensity of the reflection return light reflected at the reflection point and returned to the single mode LD can be reduced. As a result, influences given to a line width of the single mode LD by the reflection return light can be suppressed.