image: Figure 1: Schematic diagram of metasurface-based single-shot imaging system for complete characterization of arbitrary light field intensity, phase, and polarization
Credit: ©Science China Press
Light fields, as a form of electromagnetic waves, are characterized by fundamental parameters including intensity, phase, and polarization. Precise imaging of these three parameters is crucial for optical detection, communication, and biomedical diagnostics. Traditional methods for measuring light parameters primarily rely on complex optical systems that require multiple bulk optical elements such as polarizers, waveplates, and beam splitters. This not only increases system complexity and cost but also requires multiple measurements to obtain complete parameter distribution information, severely limiting its application in dynamic light field characterization. In recent years, metasurface-based imaging technology has provided a new technical approach to overcome the limitations of traditional optical systems. However, existing metasurface imaging techniques still have significant limitations: most methods can only obtain partial parameter information and have specific requirements for the parameter distribution of the light field under test, which seriously restricts their practical application range. Therefore, developing new imaging technology capable of simultaneous measurement of all parameters for arbitrary light fields has important scientific value and application prospects.
To address this issue, Professor Yanjun Bao and Professor Baojun Li's research team from Jinan University proposed a metasurface-based imaging technique that can simultaneously obtain complete information about intensity, phase, and polarization of arbitrary light field distributions through a single exposure. This technology precisely designs metasurface structural parameters through optimization algorithms, achieving controllable and efficient diffraction of orthogonal polarization components of the incident light field while generating the required reference light field. This innovative design enables the system to obtain all parameter information of the light field in a single exposure. This work greatly expands the application prospects of metasurfaces in the optical field, and the related findings were published in National Science Review (NSR) under the title "Single-shot simultaneous intensity, phase, and polarization imaging with metasurface."
The metasurface imaging system can diffract an incident light field with arbitrary intensity, phase, and polarization distribution into seven sub-images and image them on a CMOS sensor (Figure 1). Three of the sub-images are interference patterns between x-polarized images and uniform background light fields with 120-degree phase differences, used for phase information reconstruction; the other four sub-images are different phase interference patterns of x and y polarized images, used for intensity and polarization information extraction.
To optimize the multiple diffraction efficiencies and uniform background light field intensity, the research team employed a gradient descent algorithm for optimization. Compared to traditional forward design, the multi-level diffraction efficiency improved by approximately 5 times, and the uniform background light intensity increased by about 14 times.
The optimized metasurface Jones matrix has four degrees of freedom, which can be realized through pixel units composed of four nanorod structures (Figures 3a-b). The research team designed three different input light field distributions for verification. After processing through this imaging system and image calibration, they successfully reconstructed all parameter information of the input light field (Figure 3c), achieving complete characterization of intensity, phase, and polarization information for arbitrary light field distributions under single-exposure conditions.