| 摘要 |
<p>A point where a first diffraction grating (13) and an incident optical axis (C) intersect is named as first intersection point (PG1), lengths from the first intersection point (PG1) to points where +/- primary-order diffracted lights by the first diffraction grating (13) intersect a light receiving plane are named as first-a(1a) optical path length, first-b(1b) optical path length, and an average thereof is named as first average optical path length (L1). A point where a second diffraction grating (14) and the incident optical axis (C) intersect is named as second intersection point (PG2), lengths from the second intersection point (PG2) to points where +/- primary-order diffracted lights by the second diffraction grating (14) intersect a light receiving plane are named as second-a(2a) optical path length, second-b(2b) optical path length, and an average thereof is names as second average optical path length (L2). At this time, the first diffraction grating (13), the second diffraction grating (14) and the light receiving device substrate (2) are disposed in such a way that a first curve in which the first average optical path length (L1) is constant and a second curve in which the second average optical path length (L2) is constant are in contact with each other at a single point. <IMAGE></p> |
