Optical semiconductor device and control method of the same

An optical semiconductor device comprising:

• a wavelength tunable laser element;
• a beam splitter that splits an outgoing beam of the wavelength tunable laser element into a first light beam and a second light beam, and outputs the first light beam and the second light beam;
• and
• an etalon that transmits the first light beam and the second light beam, wherein
• the first light beam enters the etalon from a first direction, and forms a first optical path in the etalon,
• the second light beam enters the etalon from a second direction different from the first direction, and forms a second optical path in the etalon, and
• an optical path length of the first optical path is different from an optical path length of the second optical path.

An optical semiconductor device comprising:

• a wavelength tunable laser element;
• a beam splitter that splits an outgoing beam of the wavelength tunable laser element into a first light beam and a second light beam, and outputs the first light beam and the second light beam;
• a polarizer that makes a polarization state of one of the first light beam and the second light beam different from a polarization state of the other of the first light beam and the second light beam by changing a polarization state of at least one of the first light beam and the second light beam;
• and
• an etalon that transmits the first light beam and the second light beam that have passed through the polarizer, wherein
• the etalon is composed of a material that has a refractive index unique to a polarization state of a light beam entering the etalon.

A control method of an optical semiconductor device, the optical semiconductor device including a wavelength tunable laser element, a beam splitter that splits an outgoing beam of the wavelength tunable laser element into a first light beam and a second light beam parallel to each other and outputs the first light beam and the second light beam, an etalon that transmits the first light beam and the second light beam, a first detection unit that receives the first light beam that has passed through the etalon, a second detection unit that receives a second light beam that has passed through the etalon, and a third detection unit that receives another second light beam before passing through the etalon, wherein

• an optical path length to the first light beam of the etalon is different from an optical path length to the second light beam of the etalon, and
• the control method includes:
• a step of driving the wavelength tunable laser element in a driving condition corresponding to a target wavelength of the outgoing beam of the wavelength tunable laser element, and
• a step of selecting a target wavelength with use of a detection result of one of the first detection unit and the second detection unit and a detection result of the third detection unit.