Multiple quantum wells (MQWs) serve as the backbone of modern optoelectronic devices, yet their optical absorption is inherently limited by intersubband transition selection rules, rendering them nearly insensitive to normal-incidence light and thereby posing a significant challenge for normal-incidence light detection and system integration. Bound states in the continuum (BICs) offer a transformative approach to localize light in subwavelength structures, but their “perfect confinement” often prevents light from reaching the device active region for photoelectric conversion. To overcome these challenges, a joint research team has demonstrated a novel strategy to precisely tailor optical absorption in MQWs by controlling the asymmetry of rectangular BIC metasurfaces. A controlled “leaky mode” existed in quasi-BIC enables trapped light into MQWs. This innovative approach effectively bridges the gap between extreme light localization and high-efficiency optoelectronic response.
Building on this concept, the team fabricated a high-quality Al 0.28 Ga 0.72 As/GaAs superlattice MQW, topped with a meticulously patterned metasurface resonator array. The optical absorption within MQWs could be modulated by engineering the asymmetric parameters of rectangular metal resonator metasurface, enabling a tunable nonlinear photoresponse directly harnessed for on-chip image sensing and contrast-enhancement preprocessing. Additionally, a linear photoresponse modulated by incident angle and external bias voltage allows a hardware implementation of a neural network for a high-level processing of image recognition and edge detection respectively. The breakthrough lies in the multifunctional operation (both linear and nonlinear photoresponse) within the BIC-MQW system, demonstrating a proof-of-concept in-sensor machine vision system for low-energy consumption and high-density integration by avoiding the complex processing circuits.
The coexistence of enhanced absorption and broadened spectral response opens new doors for broadband spectroscopy and highly integrated multifunctional chips. Owing to the mature fabrication technology of MQW, the large-scale and high-yield manufacturing of BIC-MQW system is feasible on wafer level. The research team aims to scale the array size up to over 1,000 pixels and implement it with high-speed and pulse-coded optical computing schemes. The advancements could revolutionize real-time object tracking and optically encrypted communication.
Light: Science & Applications
Quasi-bound states in the continuum driven photoresponse in multiple quantum wells for machine vision