Compact acoustic monolayered metadecoder for efficient and flexible orbital angular momentum demultiplexing

Detecting the orders of an orbital angular momentum (OAM)-carrying beam is of fundamental interest and practical importance in wave physics. Yet accurate and fast demultiplexing of free-space OAM beams within physical space comparable to wavelength still remains challenging. Here, a passive monolayered metadecoder with compactness, high efficiency and flexibility is designed systematically and demonstrated experimentally for real-time demultiplexing of multiple OAM modes in free space. A simple yet effective mechanism of simultaneously untwisting and reshaping the synthesized vortex beams is presented to remarkably downsize the device and arbitrarily modulate the propagation path of output beam with amplified intensity and intact information, whose detection needs no sensor array or postprocessing. Consequently, the resulting device features the ultra-compact size, enhanced signal-to-noise ratio, high spectral and spatial selectivity, controllable detection locations, and furthermore, the compatibility to existing multiplexing methods. The effectiveness of proposed mechanism is demonstrated numerically and experimentally via parallel and real-time demultiplexing of a synthesized acoustic vortex using a planar metadecoder much more compact than existing devices in all three dimensions. The realization of metadecoder offers the possibility of high-capacity and miniaturized passive devices harnessing OAM and may promise important applications, including advances in high-speed underwater communication and optical on-chip signal process. Published under an exclusive license by AIP Publishing.