High‐Fidelity Self‐Imaging via Bloch Oscillations in Gradient‐Engineered Waveguide Arrays

Self‐imaging based on Bloch oscillations offers a promising approach for optical information transport and parallel signal processing. However, in conventional femtosecond laser‐written lattices, the achievable propagation‐constant gradient is limited by fabrication constraints, leading to long Bloch oscillation periods and reduced reconstruction fidelity. Here, we implement a gradient‐engineered platform based on femtosecond laser‐written composite waveguides, where each lattice site consists of coupled sub‐waveguides, enabling flexible control of the propagation constants. In addition, a sawtooth‐profile modulation is introduced to locally tailor the effective potential landscape. This combined design enables tunable Bloch oscillation dynamics with reduced oscillation periods and improved wavepacket confinement compared with conventional single‐waveguide lattices. Experimentally, point‐to‐point imaging with energy recovery exceeding 99% is demonstrated, with a compact oscillation period of 8 mm. This platform also enables parallel multi‐port transmission of binary‐encoded sequences and two‐dimensional images, with high reconstruction fidelity across a broad wavelength range from 633 to 852 nm. These results demonstrate a fabrication‐tolerant route toward compact self‐imaging for optical information processing.