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We report on the optical gain and loss of waveguides containing lithographically defined quantum dots. Lasing action has previously been demonstrated in a nominally identical structure. Measurements are made by monitoring the transmission of a resonant pulse while varying the injection current. We measure a maximum modal gain of 1.8 cm \(^{{-1}}\) at the peak of the ground state emission for a two-layer structure. The peak gain is insufficient for ground state lasing to be achieved in a structure with as-cleaved facets, but the gain per dot is comparable with that demonstrated in self-assembled quantum dots.

We report lasing wavelength bistability with respect to applied bias on the saturable absorbers in two-section mode-locked quantum dot lasers. We show data from three different devices exhibiting wavelength bistability. All lasers display wavelength bistability. Only one lasing wavelength is present at a time, with all other wavelengths totally quenched. The switchable ranges (the wavelength difference between two bistable lasing branches) are different for all three lasers and in one device can be manipulated by changing the current injection. All lasers show the remarkable property of switching only in integer multiples of about 8 nm. The bistable operation can be explained by the interplay of the cross-saturation and self-saturation properties in gain and absorber, and the quantum-confined Stark effect in absorber. The measured switching time between bistable wavelengths is 150 ps.

We report a two-section mode-locked quantum-dot laser with an emission wavelength that is bistable with respect to applied bias on the saturable absorber region. The two stable lasing wavelengths for this device are about 1173 and 1166 nm with a power contrast ratio of over 30 dB. The largest switchable wavelength range is 7.7 nm. The optical power and pulsewidth (6.5ps) are almost identical in the two lasing modes under optimized conditions. The operation of this laser can be explained by the interplay of the spectral-hole burning and the quantum-confined Stark effect