I need to get the best optical coupling on a 5mm T1-3/4 RGB LED into some fiber, PMMA acrylic optical fibers. Actually, the coupling is not entirely as good as I'd hoped. I just hot-knifed the end. LOTS of light spilled out without going into the fiber.

I tried various things- heating the end of the fibers and jamming them onto the LED so it matched the dome shape, grinding down the LED's end until just above the bondwires so the beam doesn't spread laterally.

Well, they werent bad per se... I just would like to see if anyone has specific advice on the right way to do this.

I saw Carlco makes a Luxeon Rebel-to-fiber coupler, but its a BIG (~1 dia) coupler. I need this to stay on the order of like 5mm-8mm. dia.