3D integration enables ultralow-noise isolator-free lasers in silicon photonics
Photonic integrated circuits are widely used in applications such as telecommunications and data-centre interconnects1–5. However, in optical systems such as microwave synthesizers6, optical gyroscopes7 and atomic clocks8, photonic integrated circuits are still considered inferior solutions despite their advantages in size, weight, power consumption and cost. Such high-precision and highly coherent applications favour ultralow-noise laser sources to be integrated with other photonic components in a compact and robustly aligned format—that is, on a single chip—for photonic int...