GaInAsP/InP fast, high-radiance, 1.05-1.3-µm wavelength LED's with efficient lens coupling to small numerical aperture Silica optical fibers

Power levels up to 100 µW have been launched from GaInAsP LED's with 14-µm-diameter emitting regions into low-loss small numerical aperture (NA) silica fibers at a dc drive level of only 25 mA. A maximum launch power of 206 µW at 100-mA dc was obtained from slightly larger devices. The high coupling efficiency was achieved using truncated spheres of Ti
2
O
3
:SiO
2
glass as microlenses. Gains over the butt coupled case exceeded a factor of twelve for the small-area devices. The high operating current densities (2-20 kA/cm
²
) for the small-area devices resulted in modulation bandwidths extending to beyond 300 MHz (-3 dB optical). The surface-emitting LED's showed an enhanced performance over edge-emitting LED's fabricated from similar material. Linewidths of the devices, which were prepared by liquid-phase epitaxy with step followed by ramp cooling, were approximately 3 kT. Even with the relatively broad linewidth, material dispersion limits in silica fibers exceeding 1 GHz . km around 1.3 µm are predicted. These devices are suitable for long-haul, wide-bandwidth fiber links operating in the 1.3-µm window.