Improved transmission performance resulting from the reduced chirp of a semiconductor laser coupled to an external high-Q resonator

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- mu m 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, avalanche photodiode multiplication noise, and preamplifier circuit noise. The numerical results indicate an almost threefold improvement in the achievable transmission distance for a bit rate of 4.8 Gb/s.>