| Popis: |
The use of edge-emitting LEDs in short-distance single-mode transmission applications has recently generated interest due to cost and reliability advantages compared with conventional laser sources. However, a primary reason for the low cost of conventional packaged LEDs has been the relative' insensitivity of LED-to-multimode-fiber coupling. In this paper we will consider the impact of switching from a multimode to single-mode fiber on coupling efficiency and sensitivity. Experimental results for several different coupling schemes will be presented, including both direct coupling to single-mode fiber and indirect coupling to single-mode fiber through a multimode pigtail. We show that coupling sensitivity in the direction perpendicular to the junction plane is comparable to that for a laser, regardless of the coupling scheme used. However, in spite of increased sensitivity, some relaxation of alignment tolerances can be obtained by trading off coupling efficiency for decreased sensitivity. Simple expressions are derived which predict the coupling efficiency/sensitivity trade-offs. A discussion of these options and their impact on LED packaging will be included. |
