In recent years, standard CMOS microprocessors have approached their maximum power dissipation per unit area, effectively placing a limit on computational power. This highlights the urgent need to explore alternative technologies. One promising avenue is the use of superconductors, which demonstrate zero resistivity below a critical temperature. However, circuits based on superconductors necessitate the use of cryostats to maintain low temperatures, presenting challenges in data transfer with the room temperature environment. While coaxial cables are often employed for this purpose, they suffer from limited data transfer rates and contribute significantly to heat load. On the contrary, photonics integrated circuits (PICs) coupled with optical fibers present a viable solution. They enable scalable, cost-effective, and power-efficient optical interconnections capable of supporting high data transfer rates while minimizing heat transfer. In this presentation, We will discuss the latest advancements in cryogenic PICs, focusing on their application in interfacing with cryogenic computing systems such as single-flux-quantum logic circuits and superconducting qubits.
Microcombs are revolutionizing optoelectronics by providing parallel, mutually coherent wavelength channels for time-frequency metrology and information processing. To implement this essential function in integrated photonic systems, it is desirable to drive microcombs directly with an on-chip laser in a simple and flexible way. However, two major difficulties have prevented this goal: (1) generating mode-locked comb states usually requires a significant amount of pump power and (2) the requirement to align laser and resonator frequency significantly complicates operation and limits the tunability of the comb lines. Here, we address these problems by using microresonators on an AlGaAs on-insulator platform to generate dark-pulse microcombs. This highly nonlinear platform dramatically relaxes fabrication requirements and leads to a record-low pump power of <1 mW for coherent comb generation. Dark-pulse microcombs facilitated by thermally controlled avoided mode crossings are accessed by direct distributed feedback laser pumping. Without any feedback or control circuitries, the comb shows good coherence and stability. With around 150 mW on-chip power, this approach also leads to an unprecedentedly wide tuning range of over one free spectral range (97.5 GHz). Our work provides a route to realize power-efficient, simple, and reconfigurable microcombs that can be seamlessly integrated with a wide range of photonic systems.
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