CW and mode-locked integrated extended cavity lasers fabricated using impurity free vacancy disordering

A phosphorus-doped silica (P:SiO2) cap containing 5 wt% P has been demonstrated to inhibit the bandgap shifts of p-i-n and n-i-p GaAs-AlGaAs quantum-well laser structures during rapid thermal processing. Bandgap shift differences as large as 100 meV have been observed between samples capped with SiO2 and with P:SiO2. The technique has been used to fabricate GaAs-AlGaAs ridge lasers with integrated transparent waveguides. With a selective differential blue-shift of 30 nm in the absorption edge, devices with 400 mu m/2.73-mm-long active/passive sections exhibited an average threshold current of 9 mA in continuous-wave (CW) operation, only 2.2 mA higher than that of discrete lasers of the same active length and from the same chip. Extended cavity modelocked lasers were also investigated and compared to all active devices. For the extended cavity device, the threshold current is a factor of 3-5 lower, the pulsewidth is reduced from 10.3 to 3.5 ps and there is a decrease in the free-running jitter level from 15 ps (measurement bandwidth 10 kHz-10 MHz) to 6 ps. In addition, the extended cavity lasers do not exhibit any self-pulsing modulation of the mode-locked pulse train, unlike the all-active lasers, and the optical spectra indicate that the pulses are more linearly chirped.