| 摘要 |
PURPOSE:To realize correct positioning through less adjusting manhour by positioning a quadripartite photodetector so that the difference of the sum signals of each two photodetectors at both sides separated by a parting line becomes zero. CONSTITUTION:A hologram optical element 35 has a third area and a fourth area different from a first area and a second area in their grating patterns, and third area and the fourth area have semicircular shapes which is a circular shape centering at an optical axis 41 after being separated by the same parting line as the parting line 40 to separate the first area and the second area. By making the hologram optical element into such a shape, the intensities of diffracted lights from a pair of the first area and the second area and the pair of the third area and the fourth area are made equal to each other. Thus, the position adjustment can be executed correctly and easily by a null-balance method through the appropriate calculation of the output of the photodetector. |
