Optical device

Patent Pending PROBLEM TO BE SOLVED: To provide an optical device suppressing changes in a drive current and an optical output over time. ; SOLUTION: An optical amplifying element 20 on a stem 10 is called transmissive SOA and is adapted to amplify short-wavelength light incoming into an incidence side end face 20A to emit light having larger luminance than the incident light from an injection side end face 20B.