IMPROVED TRANSMISSION PERFORMANCE RESULTING FROM THE REDUCED CHIRP OF A SEMICONDUCTOR-LASER COUPLED TO AN EXTERNAL HIGH-Q RESONATOR

The coupling of a Fabry-Pcrot laser to an external high-Q resonator, whose resonance frequencies are not altered by changes in the carrier density, yields a dynamic single-longitudinal-mode laser with a significantly reduced transient frequency chirp. The improvement in the receiver sensitivity due to the reduced chirp is examined for NRZ and RZ intensity modulation, direct detection systems operating in the 1.55-µm wavelength region with conventional single-mode optical fiber. The methodology involves a) solving modified rate equations numerically for the optical power and phase of the external resonator laser in response to an injected current waveform, b) modeling the signal transmission properties of single-mode optical fibers by convolution and modulus squared operations, and c) using a truncated pulse train approximation to evaluate the probability of error in the presence of intersymbol interference, shot noise, APD multiplication noise, and preamplifier circuit noise. The numerical results indicate an almost three-fold improvement in the achievable transmission distance for a bit rate of 4.8 Gb/s with either encoding format. In addition, the pulse shaping caused by the nonlinear modulation response of the laser, the fiber dispersion, and the receiver filtering is examined by evaluating the dependence of the receiver sensitivity on the decision time and decision threshold. © 1990 IEEE