The Reduction of the Frequency Chirp of Two Section Distributed Feedback laser without Suppressing Spatial Hole Burning

The spectral linewidth of a DFB laser increases significantly when directly modulated at a high frequency , a phenomenon known as frequency chirping . Means for reducing the frequency chirp have included the use of laser with a smaller linewidth enhancement factor of the active material and methods which reduce the spatial hole burning (SHB). The second approach involves fabrication of either complex laser structures which introduce gain coupling or quarter wavelength shift three section DFB lasers. We report here on the measurement of the frequency chirp of a two section DFB laser under large signal modulation . It was found that the frequency chirp of a two section laser can be minimized by simply adjusting the injection current distribution in the laser. The unique advantage for using two section DFB lasers is that frequency chirp can be reduced even when SHB is not suppressed.