A method for adjusting an optical source used for fabricating an optical receiver comprising a signal beam input port, a polarization beam splitter, and signal generation units, is disclosed. The optical source generates a reference beam by combining first and second beams having polarization directions orthogonal each other. The reference beam is introduced to the signal beam input port to measure a first size of an electric signal generated in one of the signal generation units. A half-wavelength plate is disposed in an optical path between the beam splitter and the one of the signal generation units. After that, the reference beam is introduced to the signal beam input port to measure a second size of an electric signal generated in the one of the generation units. At least one of the first and second beams is adjusted such that the first size and the second size become close to each other.