| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem that even when a back cut face is only inclined, the area of a lens surface decreases and consequently light collection efficiency of a Fresnel lens is lowered and, in addition, when the focal distance of the lens surface located on the periphery is shortened in order to obtain a fixed beam spot size, a lens loss increases and the light collection efficiency is lowered. SOLUTION: When a light receiving element 110 is disposed more on the side of the lens 100 than on the side of the focusing position of the lens 100 and the range of the angle at which light is received is defined as±α°, a back cut face group 112 is inclined within at least 2α°. This makes it possible to improve the light collection efficiency in which optical signals are coupled onto the light receiving element 110. COPYRIGHT: (C)2009,JPO&INPIT
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