Ultrashort Pulses from a Gain-Switched DFB Laser by Fiber Compensation of the Chirp and Thermal Tuning of the Cavity

Abstract

Ultrashort pulses of -3.5 ps were obtained for the first time from a gain-switched DFB laser at λ = 1.55 μm through passive compression in a negative dispersion fiber. The corresponding length was optimized for a precise compensation of the quadratic laser chirp using a parabolic law which describes the evolution of the second-order central moment of the pulse while propagating along the fiber. This formula, together with the one which relates the second-order central moment of the pulse autocorrelation versus the same moment of the pulse intensity, holds for any kind of pulse regardless of its profile. A further improvement of the pulse width and shape was obtained through the thermal tuning of the DFB cavity in the operation range of 17-26°C.