An external-cavity laser with a quantum-dot (QD) gain medium is attractive because it combines the advantages of both
QDs and the external-cavity configuration. Investigations of external-cavity QD lasers have revealed that these lasers
demonstrate good performance with features such as a wide wavelength tuning range, stable lasing oscillation, and highspeed
transmission. In this study, we employed an 800-GHz etalon filter inserted into an external cavity and obtained a
four-channel oscillation spectrum that coincided with the local area network (LAN)-WDM grid. Each mode of the four
channels oscillated stably at the single longitudinal mode defined by the external-cavity length. We sliced the four
channels into a single channel using an inline band-pass filter. The filtered single channel has a high side-mode
suppression ratio (SMSR) of 43.9 dB and a low relative intensity noise (RIN) of -137.9 dB/Hz in the frequency range of
0.5–20 GHz. For comparison with a multi-quantum well (MQW) gain medium, we obtained the four-channel spectrum
using the same setup. However, each channel was multi-mode, and the four-channel simultaneous oscillation could not
be maintained for a few dozen minutes. Furthermore, when we sliced the four-channels into a single channel, the
spectrum intensity became changing; therefore, we could not measure the RIN. These results show that both the stable
single longitude modes and the low RIN spectrum of the filtered mode are inherent in the QD medium, indicating that
the external-cavity comb laser with the QD gain medium is promising as a light source for WDM transmission.
We present a general method that improves the emission efficiency of InAs quantum dots (QDs) fabricated by antimony
surfactant-mediated growth. Unlike conventional InAs/GaAs QDs, we show that the control of the interface properties of
the InAs/Sb:GaAs QDs is crucial. Our method consists in growing InAs QDs on an antimony-irradiated GaAs surface, in
order to exploit the surfactant properties of antimony, and then removing the excess segregated antimony by applying a
high arsenic pressure before capping. In such a way, one benefits from the advantages of the antimony-surfactant
mediated growth (high density QDs, no coalescence, no emission blueshift after annealing), without the detrimental
formation of antimony-induced non-radiative defects. We show that the lasing characteristics of InAs/Sb:GaAs QD
lasers grown by metal organic chemical vapor deposition in the 1.3 μm band are drastically improved, with a reduced
threshold current density and higher internal quantum efficiency. These studies advance the understanding of key
processes in antimony-mediated growth of InAs QDs and will allow full utilization of its advantages for integration in
opto-electronic devices.
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