High-Speed Digital Lightwave Communication Using LEDs and PIN Photodiodes at 1.3 um

Optical-fiber communication systems that use L E D S as sources and PIN photodiodes as detectors offer the attractive features of reliability, simplicity, and low cost. Operation of such systems at high digital speeds is now made possible by the availability of InGaAsP L E D S and detectors, and of low-loss fibers that exhibit minimal material dispersion in the wavelength region near 1.3 /xm.1 The bandwidth-distance product at the wavelength of minimum dispersion is inversely proportional to the square of the spectral width of the source and, for germania-doped silica fibers, is 3.5 GHz · km or more if surface-emitting 1365 are used.2 Thus high-speed digital systems of a few hundred Mb/s can be operated over repeater spans of 5 to 10 km. An earlier paper 3 presented a discussion of material-dispersion-limited operation of fiber systems that use LEDS and reported an experiment that showed the effects of material dispersion on a 137-Mb/s data link operating at X = 0.89 or 1.20 jum. In the present paper, we discuss further the application of LEDS and PIN photodiodes in highspeed digital fiber systems and describe two optical repeater experiments (with bit rates of 44.7 and 274 Mb/s) at X = 1.3 jum using InGaAsP LEDS as transmitters and InGaAs PIN photodiodes followed by GaAsFET preamplifiers as receivers. Experimental results are compared with theory. LEDS II. SYSTEM CONSIDERATIONS