Reversible orbital angular momentum photon–phonon conversion

Orbital angular momentum (OAM) has gained great interest due to its most attractive feature of high dimensionality, and several groundbreaking demonstrations in communication based on OAM multiplexing have been carried out. Accordingly, a rapid data-density growth from OAM multiplexing has posed a great challenge to the signal-processing layer. Meanwhile, in another area, optical signal-processing circuit based on photon–phonon conversion has received considerable attention and made rapid progress. Here, with the aim of finding the intersection between OAM multiplexing and photon–phonon conversion, we report on the observation of reversible OAM photon–phonon conversion. A specific OAM state can be flexibly and controllably interconverted between the photonic and phononic domains via Brillouin photon–phonon coupling within the decay time of the acoustic signal, in which OAM and spin angular momentum are independently conserved. Our result demonstrates the controllable OAM transfer between photons and phonons; shows the potential of using OAM multiplexing to extend the capacity of a photon–phonon conversion-based signal-processing scheme; and may trigger the development of an OAM-multiplexed photon–phonon circuit.