A new LED structure with a self-aligned sphere lens for efficient coupling to optical fibers

A practical new structure of the high radiance GaAs-GaAlAs LED with a self-aligned sphere lens has been developed for efficient coupling to low-less optical fibers as a light source for fiber optic communications. In this new configuration, the sphere lens is automatically settled into the center of the light-emitting surface by an etched hole containing clear epoxy resin. When applied to a low-loss optical fiber (
NA = 0.14
, core diameter: 80 µm), a coupling efficiency in excess of 9 percent has been reproducibly achieved for an LED structure with an emitting-area diameter of 35 µm and with a lens having a diameter of 100 µm and a refractive index of 2.0. Using an LED with a light-emitting-layer carrier concentration of 3 × 10
¹⁸
/cm
³
, an optical power of 150 to 200 µW coupled into the fiber and a cut-off frequency (optical power down to ½) of about 90 MHz have been reproducibly obtained.