Abstract

We report on the generation of short (2 ps) pulses directly from a self-mode-locked semiconductor amplifier inserted in a ring cavity. The amplifier is in fact a superluminescent diode consisting of a 500 mm long double quantum-well InGaAlAs ridge waveguide with strained InGaAs active layers ; an angled stripe geometry provides a low coherence emission with a broad spectrum centered near 855 nm. The amplifier is placed in a ring cavity with three gold minors and a 83% transmission output coupler. Collimation of the laser output and careful alignment of the cavity mirrors allows laser emission with a threshold bias current I_th near 46 mA. Self-mode locking is achieved when the dc bias current is set at ~1.2 I_th, and when the cavity is slightly misaligned. Figures 1 and 2 show typical non-colinear autocorrelation traces and optical spectra of the pulses circulating in the clockwise (cw) and counterclockwise (ccw) directions. The counterpropagating pulses have similar temporal profiles with durations from 2 to 6 ps (after deconvolution) and characterized by a weak pedestal that falls to zero. Remarkably, the pulse respective optical spectra are different, as the spectrum of the ccw pulse has a 2.9 nm bandwidth peaked at 864 nm, whereas that of the cw pulse is peaked near 867 nm with a bandwidth of 0.9 nm. Both circulating pulses have a time-bandwidth product exceeding several times the Fourier-transformed limit, which suggests that they can be compressed to subpicosecond durations.

© 1998 IEEE