Optimized Led for Single-Fiber Optical Links.

Abstract : The power coupled into an N.A. = 0.15, 90-micrometers core, multimode fiber from an edge-emitting, light-emitting diode has been significantly increased by the development of the narrow active region, double-heterojunction (DH) LED. As much as 0.8 mW has been coupled into a single fiber. The new diode structure results in a narrow (approx. 25 deg FWHM) emitted beam (in the direction perpendicular to the junction plane), and leads to optical coupling efficiencies 3 to 5 dB better than previously achieved. The radiance of the emitting facet is greatly increased, to over 1000 W/sq cm--sr, a factor of 10 greater than previously reported. The new structure also results in LEDs that can be modulated at high frequencies (150 MHz). Coupling from the narrow-active-region, DH diodes into the fiber is further enhanced, by about 3 dB, with the use of a microlens melted onto the fiber end. Overall coupling efficiencies of 9 to 11 dB are achieved. With the high modulation speed and coupled power of these diodes, material dispersion effects in the fiber, rather than signal power or diode speed, limit the usable distance-bandwidth product. (Author)