The performance of 1.55-pm optical communication systems can be considerably improved by use of semiconductor lasers oscillating predominantly in a single longitudinal mode. At very high bit rates (a few Gbit/s) the performance of such systems is limited by the frequency chirp that broadens the laser linewidth in the ≳ 20.1-nm range. This leads to a significant broadening of the laser pulse during its propagation inside the fiber because of a relatively large fiber dispersion (16-20) ps/nm/km). Clearly the performance of directly modulated semiconductor lasers can be improved if it is possible to reduce the chirp. The coupling of the laser to an external Bragg reflector (EBR) provides the possibility of considerable chirp reduction. Indeed, the chirp reduction by up to a factor of 15 at 1 Gbit/s has been reported by the use of silicon-chip Bragg reflectors.1 The question then arises as to what improvement in the bit rate of 1.55-μm lightwave systems can be expected by use of EBR lasers. To answer this question, we simulated the lightwave system numerically.2 This paper reports the results of such computer simulations.
© 1988 Optical Society of AmericaPDF Article