Effect of p-doping on the intensity noise of epitaxial quantum dot lasers on silicon

Ultra-high thermal stability InAs/GaAs quantum dot lasers grown on on-axis Si (001) with a record-high continuous-wave operating temperature of 150 °C

Direct epitaxial growth of group III-V light sources with excellently thermal performance on silicon photonics chips promises low-cost, low-power-consumption, high-performance photonic integrated circuits. Here, we report on the achievement of ultra-high thermal stability 1.3 µm InAs/GaAs quantum dot (QD) lasers directly grown on an on-axis Si (001) with a record-high continuous-wave (CW) operating temperature of 150 °C. A GaAs buffer layer with a low threading dislocation density (TDD) of 4.3 × 106 cm-2 was first deposited using an optimized three-step growth method by molecular beam epitaxy. Then, an eight-layer QD laser structure with p-type modulation doping to enhance the temperature stability of the device was subsequently grown on the low TDD Si-based GaAs buffer layer. It is shown that the QD laser exhibits the ultra-high temperature stability with a characteristic temperature T0=∞ and T1=∞ in the wide temperature range of 10-75 °C and 10-140 °C, respectively. Moreover, a maximum CW operating temperature of up to 150 °C and a pulsed operating temperature of up to 160 °C are achieved for the QD laser. In addition, the QD laser shows a high CW saturation power of 50 mW at 85 °C and 19 mW at 125 °C, respectively.

Optical noise characteristics of injection-locked epitaxial quantum dot lasers on silicon

This work theoretically investigates the relative intensity noise (RIN) and spectral linewidth characteristics of epitaxial quantum dot (QD) lasers on silicon subject to optical injection. The results show that the RIN of QD lasers can be reduced by optical injection, hence a reduction of 10 dB is achieved which leads to a RIN as low as -167.5 dB/Hz in the stable injection-locked area. Furthermore, the spectral linewidth of the QD laser can be greatly improved through the optical injection locked scheme. It is reduced from 556.5 kHz to 9 kHz with injection ratio of -60 dB and can be further reduced down to 1.5 Hz with injection ratio of 0 dB. This work provides an effective method for designing low intensity noise and ultra-narrow linewidth QD laser sources for photonics integrated circuits on silicon.

Significantly enhanced performance of InAs/GaAs quantum dot lasers on Si(001) via spatially separated co-doping

We report the significantly enhanced performance of InAs/GaAs quantum dot (QD) lasers on Si(001) by spatially separated co-doping, including n-doping in the QDs and p-doping in the barrier layers simultaneously. The QD lasers are a ridge waveguide of 6 × 1000 µm² containing five InAs QD layers. Compared with p-doped alone laser, the co-doped laser exhibits a large reduction in threshold current of 30.3% and an increase in maximum output power of 25.5% at room temperature. In the range of 15°C-115°C (under 1% pulse mode), the co-doped laser shows better temperature stability with higher characteristic temperatures of threshold current (T₀) and slope efficiency (T₁). Furthermore, the co-doped laser can maintain stable continuous-wave ground-state lasing up to a high temperature of 115°C. These results prove the great potential of co-doping technique for enhancing silicon-based QD laser performances towards lower power consumption, higher temperature stability, and higher operating temperature, to boost the development of high-performance silicon photonic chips.

Multimode Physics in the Mode Locking of Semiconductor Quantum Dot Lasers

Quantum dot lasers are an attractive option for light sources in silicon photonic integrated circuits. Thanks to the three-dimensional charge carrier confinement in quantum dots, high material gain, low noise and large temperature stability can be achieved. This paper discusses, both theoretically and experimentally, the advantages of silicon-based quantum dot lasers for passive mode-locking applications. Using a frequency domain approach, i.e., with the laser electric field described in terms of a superposition of passive cavity eigenmodes, a precise quantitative description of the conditions for frequency comb and pulse train formation is supported, along with a concise explanation of the progression to mode locking via Adler’s equation. The path to transform-limited performance is discussed and compared to the experimental beat-note spectrum and mode-locked pulse generation. A theory/experiment comparison is also used to extract the experimental group velocity dispersion, which is a key obstacle to transform-limited performance. Finally, the linewidth enhancement contribution to the group velocity dispersion is investigated. For passively mode-locked quantum dot lasers directly grown on silicon, our experimental and theoretical investigations provide a self-consistent accounting of the multimode interactions giving rise to the locking mechanism, gain saturation, mode competition and carrier-induced refractive index.

Uncovering recent progress in nanostructured light-emitters for information and communication technologies

Semiconductor nanostructures with low dimensionality like quantum dots and quantum dashes are one of the best attractive and heuristic solutions for achieving high performance photonic devices. When one or more spatial dimensions of the nanocrystal approach the de Broglie wavelength, nanoscale size effects create a spatial quantization of carriers leading to a complete discretization of energy levels along with additional quantum phenomena like entangled-photon generation or squeezed states of light among others. This article reviews our recent findings and prospects on nanostructure based light emitters where active region is made with quantum-dot and quantum-dash nanostructures. Many applications ranging from silicon-based integrated technologies to quantum information systems rely on the utilization of such laser sources. Here, we link the material and fundamental properties with the device physics. For this purpose, spectral linewidth, polarization anisotropy, optical nonlinearities as well as microwave, dynamic and nonlinear properties are closely examined. The paper focuses on photonic devices grown on native substrates (InP and GaAs) as well as those heterogeneously and epitaxially grown on silicon substrate. This research pipelines the most exciting recent innovation developed around light emitters using nanostructures as gain media and highlights the importance of nanotechnologies on industry and society especially for shaping the future information and communication society.

Quantum-dot semiconductor lasers with prominent relative intensity noise and spectral characteristics

Relative intensity noise (RIN) behavior of a quantum dot laser (QDL) at free running and under optical injection locking (OIL) has been reported in detail. Considering the mutual effects of the inhomogeneous and homogeneous broadenings, different and also non-routine RIN characteristics of a QDL at low, intermediate, and high homogeneous broadening regimes have been discussed. Results demonstrate that an injection-locked quantum dot laser exhibit enhanced characteristic over free-running operation along with low-frequency noise behavior in a wide range of homogeneous broadening values. RIN reduction of about 25, 55, and 7 dB/Hz have been achieved for low, intermediate, and high values of homogeneous broadening which implies the spontaneous emission noise suppression even at low injection power. The promising impact of the OIL on side-mode suppression for the intermediate homogeneous broadening regime has also been discussed. Our results guarantee the single-mode and low-noise operation of the OIL-QDL at any homogeneous broadening value.