Bipolar Photodetectors for Physical-Layer Encrypted Optical Communication: Dual Modes Enabled by Self-Powered Operation and Low-Voltage Modulation

Bipolar photodetectors (BPDs) are critical for physical-layer encrypted optical communication, yet existing devices suffer from a trade-off: self-powered BPDs lack tunability, while voltage-modulated ones require high bias and consume excessive energy. To address this, we fabricated a heterojunction BPD with the structure glass/FTO/MoOx/CdSe/Sb2S3/Au, integrating self-powered operation and low-voltage modulation in one device. Under zero bias, it exhibits wavelength-dependent bipolar photoresponse: negative photocurrent for <685 nm light and positive for >685 nm light, enabling energy-autonomous spectral discrimination. With low-voltage modulation, forward bias (as low as 180 mV) enhances long-wavelength response, while reverse bias (−220 mV) amplifies short-wavelength detection. The device shows fast response (rise time ∼ 132–148 μs), long-term stability (>2000 s). We further proposed two encryption modes for secure communication: self-powered tristate encryption (enhancing security) and low-voltage direct valid signal extraction (enabling real-time transmission). This work provides a versatile platform for energy-efficient, secure optoelectronic systems.