Background: High brightness light emitting diodes (LEDs) have become available that appear suitable to replace light sources currently used for illumination through thin light guides, e.g. in endoscopy. We investigated the essential characteristics of a series of commercial single LEDs relevant for direct coupling to a single optical multimode fiber. Methods: LED fiber coupling efficiency was assessed experimentally and theoretically by using a ray tracing software. Results: Surface emitting LEDs proved suitable to be coupled directly into plastic optical fibers (POFs). We have successfully applied a 1 mm core POF-fiber (outer diameter 1.01 mm) in contact with a OSTAR LED (Osram Opto Semiconductors, Regensburg, Germany) to achieve a coupling efficiency of 10-20%, which gave 42 mW, 23.7 mW and 27 mW for blue, green and red LED respectively. Ray tracing simulation revealed a considerable part of photons travelling "out of axis" in spirals along the core-clad interface (non-meridional beams). They account for approximately 30% of the transmitted power.

Date Published: 7 February 2008
PDF: 5 pages
Proc. SPIE 6852, Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications VIII, 68520X (7 February 2008); doi: 10.1117/12.763714

Published in SPIE Proceedings Vol. 6852:
Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications VIII
Israel Gannot, Editor(s)