| 摘要 |
PURPOSE:To decrease the number of necessary photodetecting elements fitted to a photodetector by providing light transmission plate bodies, a coupler which guides a laser beam into a slab type waveguide, etc. CONSTITUTION:The light transmission plate bodies 19 and 20 are provided on planes crossing laser beams L1 and L2 at a specific angle. The coupler 21 guides the beams L1 and L2 into the slab type waveguide A to propagate them only in one direction. Then, when a direction in which the beams are propagated by utilizing the total reflection of both top and reverse surfaces in the waveguide A corresponds to a nearly horizontal X axis, there is no shift in transmission position in the lengthwise direction of an end surface 22 in the waveguide A in a Y-axial direction even if the beam L1 incident on the coupler 21 is displaced in an X-axis corresponding direction. Therefore, only stable displacement in the Y-axial direction is detected by the photodetecting element 15 of a photodetector 12 facing the end surface 22 of the waveguide A. Displacement in the X-axial direction is the same. Thus, the elements 15 are arranged only in one direction where detection is performed and the number of the elements can be decreased. |
