A simple method for the chirp reduction in single-frequency semiconductor lasers

The direct current modulation of single-longitudinal mode semiconductor lasers causes a dynamic shift of the peak emission wavelength (chirping) arising from gain-induced variations of the laser refractive index. This linewidth broadening results in data-dependent distortion in long-haul, high-bit-rate, direct detection optical communication systems due to interaction with the generally nonzero chromatic dispersion of monomode fibers. Here it is shown that the frequency chirping of 1.55 /spl mu/m DFB lasers and the bit error of the system can be greatly reduced by the use of a delta stub in the microstrip driving circuit of the laser.