Inverse design for ultra-compact integrated photonics

Ultra-compact photonic integration represents a transformative frontier in optical communication and computing systems, offering unprecedented potential for performance enhancement through extreme device miniaturization. However, balancing high performance with minimal device size remains a formidable challenge. Here, we have developed novel optimization algorithms that improve the design paradigm of compact photonic components, achieving record-breaking miniaturization while maintaining exceptional performance. One critical achievement is the realization of a 12–0.5 μm mode size converter with an extremely short length of 2.43 μm, delivering more than 90% transmission efficiency. Furthermore, we have pushed the boundaries of functional device integration by demonstrating micrometer-scale power splitters and wavelength demultiplexers with extraordinary capabilities. Notably, a particularly innovative device is the three-port circular wavelength demultiplexer, which measures mere 1.8 μm in length and enables versatile signal demultiplexing between any input–output port combinations. The strong integration capabilities of the proposed devices are demonstrated through a multichannel system incorporating an array of 14 functional devices within an effective length of only 15.81 μm, achieving a quite low loss and a wide operation bandwidth. These advancements highlight the superior performance of ultra-compact photonics, accelerating the development of high-density photonic circuits for optical communications.