Ultraviolet-visible bipolar photodetector for hardware-software collaborative encrypted information transmission

Secure optical communication increasingly demands encryption strategies that go beyond software-based algorithms and penetrate the physical layer. Here, we demonstrate an ultraviolet-visible bipolar photodetector that enables hardware-software collaborative encrypted information transmission by introducing signal polarity as an intrinsic physical key. The device is constructed using a vertical back-to-back N-I-P-I-N architecture based on a perovskite/organic hybrid heterojunction, where a thin p-type interlayer reconstructs the built-in electric field distribution and enables wavelength-dependent polarity reversal. As a result, the photodetector exhibits balanced bipolar responsivity with peak values of -0.16 and +0.13 A W^-1 in the ultraviolet and visible regions, respectively, microsecond-level response time, and a high specific detectivity exceeding 10¹² Jones. By combining polarity-encoded optical signals with software-based principal component analysis and spatial permutation, a multi-key image transmission system is realized. Image reconstruction requires simultaneous access to both the material-defined polarity key and the algorithmic key. The image reconstructed after decryption at the receiving end has high fidelity (PSNR > 30 dB). This work demonstrates how rational device architecture design can elevate photodetectors from passive receivers to active security primitives, opening a new avenue for physical-layer encryption in high-speed and covert optical communication.