| 摘要 |
The light beam emitted by the light source (2) is irradiated on the information storage medium (3) via the optical system (4,5,6). The reflected light beam is irradiated by the light guide path element (1). Then, by the grating serving as the input-coupler to the waveguide layer, a part of the light beam is input-coupled with the waveguide layer while the remaining part is transmitted and received by the light receiving portion below. At this time, according to the positional relationship between the information storage medium (3) and the optical system (6), an adjustment is made such that the coupling efficiency to the waveguide layer by the first grating pattern is maximized when the relative distance between the information storage medium (3) and the optical system (6) is increasing, and the coupling efficiency to the waveguide layer (16) by the second grating pattern is maximized when the relative distance between the information storage medium (3) and the optical system (6) is decreasing. In the light receiving portion (30) which is divided according to the respective grating patterns, the received light quantity becomes minimum when the respective coupling efficiencies are maximum. <IMAGE> |
