Optical routing via high-efficiency composite acoustic diffraction

Acousto-optical modulation (AOM) is a powerful and widely used technique for rapidly controlling the frequency, phase, intensity, and direction of light. Based on Bragg diffraction, AOMs typically exhibit moderate diffraction efficiency, often less than 90% even for collimated inputs. In this work, we demonstrate that this efficiency can be significantly improved using a composite (CP) setup comprising a pair of 4-F-linked AOMs, enabling beam splitting with fully tunable splitting amplitude and phase. The efficiency enhancement arises from two effects, termed ``momentum echo'' and ``high-order rephasing,'' which can be simultaneously optimized by adjusting the relative distance between the two AOMs. This method is resource efficient, does not require ultra-collimation, and maintains control bandwidth. Experimentally, we achieve a diffraction efficiency exceeding 99% (excluding insertion loss) and a 35-dB single-mode suppression of the zeroth-order beam, demonstrating a full-contrast optical router with a switching time of less than 100 ns. Theoretically, we formulate the dynamics of CP AOM in terms of multimode quantum control and discuss extensions beyond the $N=2$ configuration presented in this work. The substantially enhanced performance of CP AOMs, coupled with reduced acoustic amplitude requirements, may significantly advance our ability to accurately control light at high speeds with low-loss acousto-optics.