Abstract: The semiconductor optical device is mounted junction down on a mounting plate via the solder metal of the mounting plate. The electrode of the semiconductor optical device facing the mounting plate is partially coated with a dielectric film and the dielectric film is in contact with the solder metal on the mounting plate. The reaction between the semiconductor optical device and the solder metal of the mounting plate can be suppressed without deteriorating the thermal conductivity between the semiconductor optical device and the mounting plate. Therefore, it is possible to improve the reliability of the semiconductor optical device mounted in the junction down form since diffusion of the solder metal into the semiconductor can be prevented.

Abstract: A variable optical attenuator includes an optical fiber on an incident side and an optical fiber on an emission side; a polarization rotator element that includes a liquid crystal layer and a pair of substrates that are arranged in such a manner that the liquid crystal layer is sandwiched between the substrates; and a Savart plate that is arranged between the optical fibers and the polarization rotator element. In the polarization rotator element, rotation of a polarizing direction is controlled by controlling a birefringence characteristic of liquid crystal, which is controlled by controlling alignment of the liquid crystal layer.