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The InGaAs quantum dots (QDs) were grown with InGaAsP(λg=1.0–1.1μm) barrier, and the emission wavelength was controlled by the composition of InGaAs QD material in the range between 1.35 and 1.65μm. It is observed that the lateral size increases and the height of the QDs decreases with the increase in relative concentration of trimethylgallium to trimethylindium supplied during InGaAs QD growth. It is seen that the higher concentration of group III alkyl supply per unit time leads to higher QD areal density, indicating that the higher concentration causes more QDs to nucleate. By optimizing the growth conditions, the QDs emitting at around 1.55μm were grown with an areal density as high as 8×1010cm−2. The lasing action between the first excited subband states at the wavelength of 1.488μm has been observed from the ridge waveguide lasers with five QD stacks up to 260K. The threshold current density of 3.3kA∕cm2 at 200K and a characteristic temperature of 118K were measured.

The growth conditions for InGaAs∕InGaAsP∕InP quantum dots (QDs) have been optimized and QDs of high luminescence efficiency and the room temperature operation of QD lasers emitting at ∼1.5μm have been demonstrated. Lattice-matched InGaAsP (λg=1.0–1.1μm) was used as a barrier layer for the InGaAs QDs and the emission wavelength was controlled by the QD composition. High-density InGaAs QDs with an areal density as high as 1.13×1011cm−2 have been grown. The integrated and peak intensity of the photoluminescence (PL) spectra at room temperature are as high as 25% and 10% of those at 10K, respectively. The room temperature PL peak intensity is about 50% that of a high-quality InGaAs∕InP quantum well. Room temperature, pulsed operation at ∼1.5μm has been achieved from broad area lasers with a 1mm cavity length. Threshold current density per QD stack of ∼430A∕cm2 is measured for the five-, seven-, and ten-stack QD lasers.

The gain and phase dynamics of a high quality quantum dot semiconductor optical amplifier were measured at various wavelengths. In the ground state (GS), the amplitude of the slow component was negligible and the fast dominant gain recovery time was 0.7 ps. In the excited state (ES), the slow component was not negligible although small. The time required to recover from 90% to 10% was 2.0 ps in the GS but gradually increased to 31 ps in the ES. This finding predicts no pattern effects in the GS, but finite pattern effects in the ES.

Selective area growth was adopted to grow high-quality quantum dots (QDs) of different energy levels on the same plane at 1.5 μm. At room temperature, the photoluminescence (PL) peak of InAs/InGaAsP QDs on InP substrate was shifted from 1445 to 1570 nm for sample 1 (from 1385 to 1485 nm for sample 2) in a plane, with a PL intensity comparable to those of regular samples grown without dielectric patterns. The dot shape was a round dome, with the density reduced by 28% and the height increased by 17%. Time-resolved PL indicated that the selectively grown QDs behaved similarly to regular QDs. These results open up a practical method for in-plane integration of QD devices.

We experimentally investigate wavelength conversion in quantum dot and quantum well optical amplifiers via four-wave mixing. Our results show superior conversion efficiency in a quantum dot device compared to a quantum well device with identical gain. Furthermore, a small-signal modulation bandwidth >25GHz was measured with greater than 100% efficiency. Cross talk between two simultaneously input beams was found to be 20dB below the signal power demonstrating the possibility for high-speed, multichannel performance. Cross-gain modulation measurements were performed as well and show a much smaller bandwidth of 1GHz indicating that four-wave mixing is superior for high-speed signals.

The authors have fabricated ridge waveguide quantum dot (QD) semiconductor optical amplifiers (SOAs) on InP substrates that operate in the 1.5μm region. The active layer consists of InAs∕InGaAsP QD layers with a high dot density, but which still have good isolation between dots in the lateral and vertical directions, as confirmed by time-resolved photoluminescence measurements. One of these QD SOAs exhibited a fiber-to-fiber gain of 22.5dB and a chip gain of 37dB at 1.51μm. The spectral gain shape was found to be maintained for variations of the peak gain from 12to22dB, reflecting the zero-dimensional density of states at room temperature.

The carrier lifetime of an InAs/InGaAsP quantum dot (QD) on an InP substrate is measured to be twice that of an InAs/InAlGaAs QD on the same substrate, although the ground-state energy levels and barrier heights of these QDs are comparable. These differences are interpreted in terms of the smaller conduction band-offset in InAs/InGaAsP QDs compared to InAs/InAlGaAs QDs.

Nitridized quantum dots (QDs) were prepared by metal-organic chemical vapor deposition. These QDs all showed strong photoluminescence (PL) emission at 1.3μm at room temperature, narrow spectral widths of 30meV, and large separations of 98meV between the ground and first excited states. Interestingly, the PL peak positions of the nitridized QDs were all around 1.3μm, despite the QDs having been prepared using significantly different amounts of nitrogen. Time-resolved PL revealed no electronic coupling between the QDs. These properties could potentially make these nitridized QDs very useful candidates for the fabrication of devices emitting at 1.3μm.

We have unambiguously estimated the vertical and lateral electronic couplings between quantum dots (QDs) by comparing the carrier lifetimes at different energy positions inside the ground state band. InGaAs∕InGaAsP QDs on InP(100) substrate give photoluminescence around 1.55μm and have the dot density over 1011∕cm2. The measured carrier lifetimes are almost the same across the entire photoluminescence band, indicating negligible lateral electronic coupling between QDs at this high dot density. However, for a QD sample with the 15nm barrier spacing between QD layers the lifetime increases with increasing wavelength, clearly indicating the significant vertical electronic coupling between QDs.

Continuous-wave operation at room temperature from InGaAs∕InGaAsP∕InP quantum dot (QD) laser diodes (LD) has been achieved. A ridge waveguide QD LD with 7 QD-stacks in the active region lases at 1.503μm at 20°C and that with 5 QD-stacks lases at 1.445μm at room temperature. The shift in lasing wavelength is believed to be due to the difference in the quantized energy states involved in producing gain for lasing. With smaller number of QD stacks and shorter cavity length, the lasing wavelength shifts to shorter wavelength indicating that more of higher excited states are involved in producing gain. By increasing the number of QD stacks to 15, lasing at 1.56μm has been achieved under pulsed mode.