Quantum dot lasers (QDLs) have emerged as a revolutionary technology for silicon photonics, addressing key challenges in integrating light sources into optoelectronic chips. QDLs exhibit excellent temperature insensitivity and defect tolerance, which significantly reduces the complexity of their fabrication. Unlike quantum well lasers, QDLs are less sensitive to temperature variations, which enhances their stability under uncooled conditions. Furthermore, their three-dimensional quantum confinement renders them less susceptible to defects arising from lattice mismatches during epitaxial growth, resulting in less performance degradation. This defect insensitivity simplifies the fabrication process, particularly for large-scale integration on silicon, and reduces the manufacturing challenges associated with dislocation defects. One of the most distinctive features of QDLs is their resistance to optical feedback, which is a critical attribute for the development of isolator-free silicon photonic integrated circuits. Conventional lasers suffer from performance degradation and operational instability when exposed to optical feedback and require bulky and expensive optical isolators. In contrast, QDLs maintain a stable performance even under strong feedback conditions, enabling more efficient chip designs and reducing manufacturing costs. This makes QDLs ideal for compact, efficient, and cost-effective on-chip light sources, which are in increasing demand to support high-performance technologies, such as next-generation communication, artificial intelligence, and cloud computing. Beyond feedback resistance, QDLs exhibit excellent four-wave mixing (FWM) efficiency, which is a key factor in dense wavelength division multiplexing (DWDM) systems. Efficient wavelength conversion is critical for maximizing the data transmission capacity, and QDLs surpass other laser technologies by enabling direct FWM in the light source, significantly enhancing the scalability and efficiency of integrated photonic systems. Moreover, QDLs are essential in mode-locked configurations to generate optical frequency combs, which are crucial for on-chip optical interconnects. These combs provide the stable, low-noise, broadband light sources necessary for high-capacity data transmission, making QDLs a key technology for future optical interconnects, particularly in data centers and high-performance computing environments.

optical feedback insensitivity, FWM, and mode locking. A major breakthrough is their ability to maintain stable operation under strong optical feedback, which typically causes instability in traditional lasers. Studies show that QDLs can remain stable even under feedback levels as high as -7.4 dB without exhibiting chaotic behavior (Fig. 2). This level of insensitivity eliminates the need for bulky and expensive optical isolators, thus reducing the system complexity and costs, making QDLs an ideal choice for isolator-free silicon photonic circuits. In high-speed data transmission, QDLs have demonstrated impressive performance, achieving modulation rates of up to 25 Gbit/s over 2 km without performance degradation even in the presence of feedback (Fig. 3), positioning them as crucial components in short-distance high-speed optical communication systems.

Another area of significant progress is the FWM capability of QDLs. FWM is a nonlinear optical process critical for DWDM systems that enables efficient wavelength conversion to maximize data transmission capacity. Owing to their broader gain spectrum and faster carrier dynamics, QDLs exhibit a much higher FWM conversion efficiency than that of quantum well lasers. P-doped QDLs, in particular, have demonstrated FWM efficiencies as high as -4 dB (Fig. 4), substantially enhancing the performance of DWDM systems by enabling more efficient on-chip wavelength routing. The direct integration of FWM-based wavelength converters onto silicon chips represents a significant advancement in silicon photonics, reducing power consumption and maximizing efficiency.

QDLs also excel in mode-locked configurations, which are crucial for generating optical frequency combs, a series of evenly spaced frequency components essential for high-capacity data transmission, precise metrology, and spectroscopy. Mode-locked QDLs have successfully generated optical frequency combs with bandwidths exceeding 36 nm, which can be further expanded by combining multiple sources (Fig. 5). These lasers exhibit high coherence and low relative intensity noise, making them suitable for a wide range of applications including on-chip optical interconnects and coherent optical communication systems. The ability to generate high-quality low-noise frequency combs with a broad bandwidth establishes QDLs as key drivers of next-generation optical networks.

In summary, QDLs are expected to become a foundational technology in silicon photonics, addressing critical challenges in the integration of photonic and electronic devices. Their unique properties, including low noise, high thermal stability, resistance to optical feedback, and efficient nonlinear optical processes such as FWM and mode-locked frequency comb generation, make them essential for future high-performance photonic integrated circuits. Ongoing research promises to further enhance their performances, paving the way for broader applications in isolator-free optical communication systems, quantum computing, and advanced sensing technologies. In addition to their technical advantages, QDLs offer scalability for on-chip systems, thereby presenting the potential for cost-effective mass production. As these lasers continue to evolve, they are expected to drive innovation not only in telecommunications and data centers but also in fields such as quantum cryptography, coherent communication, and precision metrology. Their role in next-generation photonic networks is critical for satisfying the growing demand for faster, more efficient, and secure optical communication technologies.