image: Figure | The color image encryption system based on the PMH-SPD. Comparison of the decryption results between the commercial camera, PMH-SPD and Si-SPD in the presence of a scattering medium used Hadamard and Point-scan-like patterns for an encrypted color image projected by a projector. Correct information (“OK”) is hidden in the color image (mixed color consisting of red and blue, excluding green), and can be decrypted by the PMH-SPD, but not the commercial camera or the Si-SPD. DMD: digital micromirror device.
Credit: Shuang Zhang et al.
Traditional optical encryption systems rely on commercial array detectors like CCDs or CMOS for image capture. This creates a major vulnerability: since these are "generic" devices, an eavesdropper can use the same hardware to intercept the encrypted data. It's akin to installing a high-security lock on your front door, only to find that the key can be easily duplicated by anyone.
While single-pixel imaging technology offers a way to encrypt an object's spatial information into a one-dimensional signal, its conventional single-pixel detectors cannot distinguish multiple wavebands. This limitation hinders their application in color image encryption.
In a new paper published in Light: Science & Applications, a team of scientists, led by Prof. Hong-Chao Liu, Prof. Shuang-Peng Wang from University of Macau, and Prof. Shuang Zhang from University of Hong Kong, has developed an optically programmable dual-band perovskite single-pixel detector. This device acts not only as a detector but also as a decryption key. It can successfully decrypt hidden information under complex disturbances and effectively prevent eavesdropping by commercial cameras and silicon-based single-pixel detectors (Si-SPD), successfully establishing a high-security detector-dependent color image encryption scheme by integrating the imaging and decryption processes.
At the heart of this new encryption system is a unique perovskite detector (PMH-SPD) based on the MAPbBr3-MAPbBr3-xIx microwire heterostructure. Its core capability is optical programmability: short-wavelength light can "activate" and dramatically boost its response to long wavelengths. This creates a critical divergence in its output between different imaging modes, i.e. single-pixel imaging mode and point-scan imaging mode. In single-pixel imaging mode, the PMH-SPD detector uses global blue light illumination to modulate the red light response, thereby revealing the concealed information. In point-scanning mode, however, the red light information cannot be extracted. This very difference is the key to decryption. In contrast, for a commercial silicon detector (Si-SPD), the outputs from both imaging modes are identical, making it impossible to distinguish the hidden information.
Researchers leveraged this phenomenon to build a detector-dependent encryption scheme. Here, the PMH-SPD itself becomes the physical decryption key, seamlessly integrating imaging and decryption. In tests, it successfully extracted hidden information even through severe scattering, color shifts, and uneven lighting. Crucially, conventional detectors—even with filters—failed to decode the corrupted signal, proving the scheme's security and the PMH-SPD's uniqueness as a hardware key.
These scientists compared their work to other existing image encryption schemes:
“This new scheme rethinks optical encryption by making the detector itself the key. It surpasses conventional methods by using a compact, filter-free detector to directly decrypt color images, seamlessly merging imaging and decryption to eliminate data leaks. Unlike "in-sensor" techniques that encrypt grayscale images at capture, our method decrypts pre-encrypted color content, ensuring the transmitted light signal remains a secure, unreadable secret to all other detectors.”
They also envisioned future work:
“Our future research strategy is built on two pillars derived from this work. The first is to translate the inherent tunability of perovskites into customizable security. We plan to engineer narrowband PMH-SPDs with precisely defined detection wavelengths, effectively making the spectral response a unique, unforgeable hardware key. The second, more profound direction is to generalize our pioneering method. By demonstrating that a photoconductive semiconductor can serve as an optically programmable core, we have established a universal modulation strategy. This principle can be extended to diverse material systems and device architectures, opening a broad pathway for next-generation encryption hardware.”
Article Title
Optically programmable dual-band perovskite single-pixel detector for color image encryption