A Single Ring Performs as a Photonic Molecule
A photonic molecule is a tiny optical-cavity structure that couples multiple resonant light modes. The coupling provides “an extra design handle”—says Harvard University’s Jinsheng Lu—for controlling the light response in devices such as lasers, filters, and sensors. Traditionally, photonic molecules have consisted of two or more light-confining rings or crystals, which are connected via evanescent fields. Such multicomponent structures are difficult to integrate into larger networks. Lu and colleagues have now built a more compact photonic molecule from a single resonant ring [1].
A single cavity confines photons at specific resonant frequencies, which depend on the cavity’s geometry. A photonic molecule combines different resonant systems, creating new modes whose properties depend on the coupling. By choosing the design of a photonic molecule, researchers can, for example, tune the resonant frequencies in a filtering application, or they can create an amplified response for a sensing device.
The photonic molecule of Lu and colleagues is a silicon ring with a radius of 80 µm. The researchers etched the sidewalls of the ring with a periodic pattern of a dozen or so shallow notches, with a spacing of about 6 µm. These notches produce an interference effect that shuffles energy from one mode to another. Light was fed into the ring through an adjacent waveguide, and the outgoing light was analyzed—with dips in the spectrum corresponding to resonant modes. In experiments with different rings, the researchers showed that they could control the resonant behavior by changing the spacing, the depth, and the number of notches.
–Michael Schirber
Michael Schirber is a Corresponding Editor for Physics Magazine based in Lyon, France.
References
- J. Lu et al., “Multimode single-ring photonic molecule,” Phys. Rev. Lett. 136, 103803 (2026).