InGaAsP LEDs for 1.3-um Optical Transmission

The present generation of optical transmission systems employs GaAlAs laser emitters operating at 0.8 to 0.9 jum.1 In this wavelength range fiber attenuation (about 4 dB/km) and especially chromatic dispersion limit the usefulness of light-emitting diodes (LEDs) to short data links of few kilometers. By shifting the LED emission wavelength close to 1.3 /im two properties of the fused silica fiber permit much longer distances and higher data rates. First, the fiber loss is greatly reduced at longer wavelength, 2 with cabled fiber loss below 1 d B / k m possible. Second, pulse spreading owing to material dispersion is reduced as d2n/d2 of the refractive index approaches zero at 1.27 to 1.30 fim.'1 Thus, 1.3-ju.m LED-based transmission systems with high 1 data rates and repeater distances in excess of 10 km are feasible.4 Indeed, transmission experiments have demonstrated repeaterless LED-based operation over a distance of 24 km at the DS3 rate (44.7 Mb/s) and 7 km at rates as high as DS4 (274 Mb/s). 5 Such LED systems are attractive alternatives to laser systems since light-emitting diodes operate over a wide temperature range with unequalled reliability and their drive electronics is very simple. These advantages of longer wavelength operation can be realized for devices fabricated out of the quaternary alloy Ini-jGaxAs^Pi-^. 6 These alloys can be grown exactly lattice-matched to InP substrates (for y/x ~ 2.2) with compositions ranging from 1.1 [im to 1.65 jum.7 These quaternary LEDs are efficient, fast, and very reliable.