Mid-wavelength infrared (MWIR) is a unique regime with various potential applications in fingerprint detections. It is also one of three atmospheric transmission windows that shows significant possibilities in low-light-level night vision and free-space communications. The accurate detection of unknown photons in this band plays an indispensable role in aeronautics and astronautics applications. However, with the conventional bulky measurement setup with many cascaded optical elements or metasurface based devices, they are limited by the restricted longitudinal dispersion and the lack of simultaneous resolving of wavelength and polarization state.

In a new paper published in Light: Science & Applications, a team of scientists, led by Dr. Guanhai Li from the state key laboratory of infrared physics, Shanghai Institute of Technical Physics, China, and co-workers have proposed a versatile photonic slide rule based on an all-silicon metasurface that enables the simultaneous reconstruction of incident photons’ frequency and polarization state. The metasurface leverages both achromatically focusing and azimuthally evolving phases with topological charges +1 and -1 to ensure the confocal annular intensity distributions in the far-field.

Inspired by conventional slide rules, which embed the computation rules into the inherent evolutions of physical parameters, the team presents the photonic slide rule and demonstrate the prototype to characterize incident photons’ frequency and polarization state. With an all-silicon metasurface design, different wavelengths and polarization states correspond to different phase profiles, thus resulting in the angle-resolved focusing spots in the far-field. Two distinct groups of meta-atoms are designed to have different vortex beam carriers and phase dispersions. The angle-resolved interference pattern in the far-field of two groups of meta-atoms provides an easy-to-access retrieval of the wavelength and the state of polarization. As an analog, they successfully migrate the arithmetic logic of dispersive phases to the inherent variation of photonic dimensions-frequency and polarization with the all-silicon metasurface.

The research team selected the meta-atoms with different polarization responses and arranged with spatial multiplexing to further construct the secondary mapping of the unknown photon polarization information in the focal plane. With this handling, they achieved the simultaneous resolving of the frequency and polarization state of the unknown incident photon. As shown in Figure 2, the rotation angles of the inner and outer rings resolve the frequency of the incident photon, while the polarization information of the incident photon can be straightforwardly obtained from the position of the focusing spots. The inner ring corresponds to the left-handed circular polarization state, and the outer ring is right-handed circular polarization state.

Finally, through theoretical analysis, numerical simulation and experimental measurement, the research team confirmed that the metasurface-based photonic slide rule can effectively overcome the limitation of traditional bulk material devices in the workspace, especially the axial distance, and realized a new scheme of ultra-compact and highly-integrated characterization of the unknown photons’ wavelength and polarization state. This work provides an analog of the conventional slide rule to flexibly characterize the photons in an ultra-compact and multifunctional way and may find applications in integrated optical circuits or pocketable devices.

Dr. Yu Feilong and Dr. Chen Jin are the co-first authors of this paper, and Dr. Li Guanhai is the corresponding author. Profs. Chen Xiaoshuang and Lu Wei provided significant instructions on this work.