光学传感器应用笔记：点源发射器

　　光学传感器应用笔记：点源发射器

　　LED（发光二极管），半导体光源，已经引进和发展了几十年。LED被应用在许多设备中，如指示器和一般照明产品，例如照明元件。作为一种绿色光源，LED可以为许多应用提供长寿命和高效率的光源。然而，对于一些特殊的应用，标准的LED并不总是完美的选择。点源排放（PSE）提供需要精确的光束，如编码器应用的一个不错的选择，机器视觉和医用纤维。

　　PSE是一种半导体二极管结构类似于一个标准的LED，但是，光是通过一个明确界定的圆形区域，通常是25μm - 200μm直径发射。产生的光是“光斑”，输出光产生非常窄的几乎平行的视角。与激光二极管相比，这两个特性非常适合于需要接近平行光源和更低功率的应用

　　Figure 1 shows side view structure of standard LED and PSE. The first difference in these two structures is emitting light direction. Standard LED output light is directed to the side. In order to refocus the light direction， standard LEDs normally need a reflective cavity to force the light from the side to the top. This can cause light output loss， power dissipation， and variations in final output light beam and viewing angle. However， PSEs emit light to the upper surface through an aperture / window on top of the structure. The second difference in these two structures is the position of the cathode contact. The cathode contact pad of a standard LED is typically located in the center of the structure， which can obstruct light output due to the top wire bond. SEs can easily solve this problem by locating the cathode contact wire bond to the side of the aperture window， eliminating any obstructions and dark spots （represented in Figure 2）。 The light emitted from the standard LED （left in Figure 2） has several dark spots due to the bonding pad， obstruction from the wire bond as well as the reflector cup （shown in Figure 3）。 A PSE （right in Figure 2） has a much more narrow， defined， and precise beam with no dark spots.