June 5, 2023
The liquid crystal metasurface could enable multidimensional light field sensing

The liquid crystal metasurface could enable multidimensional light field sensing

Schematics of conventional spectropolarometry (a) and computational spectropolarometry with a tunable liquid crystal metasurface (b). Credit: Yibo Ni et al.

While conventional photodetectors can only measure light intensity, the light field contains much richer information. This information includes but is not limited to phase, polarization and spectrum.

Multidimensional light field information measurement can find its application in various fields. For example, polarization measurements can reveal the material composition and surface texture of objects. Spectral analysis can be crucial for chemical study and telecommunications based on wavelength division.

Conventional polarimeters and spectrometers are often bulky, which hinders their applications on miniature platforms. Amplitude-division polarimeters and spectrometers use polarization beam splitters and dispersive elements. These are designed to spatially separate and distinguish light of different polarization and wavelengths.

Alternatively, time-division polarimeters and spectrometers take advantage of tunable polarization and wavelength filters to sequentially measure the intensity of light with different polarization and spectral components. Through the multiplexing of polarization and spectrum sensing mechanisms, complex systems have been recently developed that can simultaneously measure the polarization and spectrum of light. However, multiplexing inevitably leads to a further increased system form factor and complexity.

In a new paper published in eLighta team of scientists, led by Professor Yuanmu Yang from the State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instruments, at Tsinghua University, developed a near-infrared spectropolarimeter based on an electrically tunable liquid crystal metasurface.

The paper, titled “Computational spectropolarometry with a tunable liquid crystal metasurface,” showed how simultaneous polarization and spectral measurements are achieved through a tunable metasurface with high-quality factor guided mode resonances in combination with a computational reconstruction algorithm.

The liquid crystal metasurface could enable multidimensional light field sensing

Shapes of the liquid crystal metasurface. b Simulated metasurface reflectance as a function of liquid crystal rotation angle for incident light polarized along the x axis. ce Spectropolometric reconstruction results for monochromatic (c), broadband (d) and narrowband (e) incident light. Credit: Yibo Ni et al.

Metasurface is an emerging class of planar diffractive optical elements. Its design flexibility has opened up new avenues for vector light field manipulation. Metasurface-based polarimeters and spectrometers have been developed in recent years. Computational polarimeters and spectrometers have also been demonstrated. These devices showed how the polarization or spectrum of incident light can be encoded using a tunable graphene-embedded metasurface or array of metasurfaces.

Simultaneous multiplexing and reconstruction of multidimensional light field information remains challenging. Metasurface-based spectropolometry has been demonstrated by spatially splitting incident light with different polarization components and wavelengths. However, such an approach requires an array of detectors for polarization and spectrum detection at a single spatial location. Prevents its use for spectropolarimetric imaging.

The liquid crystal metasurface could enable multidimensional light field sensing

Photograph and scanning electron microscopy image of the fabricated liquid crystal metasurface. b,c Experimental results of spectropolometric reconstruction for monochromatic (b) and broadband (c) incident light. Credit: Yibo Ni et al.

The researchers proposed and experimentally demonstrated a spectropolarimeter that simultaneously measures the polarization and spectrum of near-infrared light. The core material of the system is an electrically tunable silicon metasurface embedded in liquid crystals. The metasurface is tailored to support multiple high quality guided mode tunings.

The metasurface has rich and anisotropic spectral features that can be widely tuned by applying different bias voltages. The system can reconstruct the full parameters and Stokes spectrum of the incident light from the reflected light intensity recorded by a single-pixel photodetector. The liquid crystal metasurface fabrication is fully compatible with the complementary metal oxide semiconductor (CMOS) and liquid crystal on silicon (LCoS) manufacturing process. This means the system can be mass produced at low cost.

Demonstration of a tunable metasurface-based multidimensional light-field encoder enables simultaneous measurement of polarization and spectrum of near-infrared light. The metasurface encodes polarization and spectral information using the high-Q guided mode anisotropic resonances. Although the liquid crystal metasurface currently operates in the reflective mode, one can also design a transmissive liquid crystal metasurface to allow more compact integration with the photodetector.

When integrated with an appropriate detector array, the liquid crystal metasurface can be used for spectropolarimetric imaging without sacrificing spatial resolution. The proposed liquid crystal metasurface can be used in many applications that require polarization and spectral measurements, such as in biomedical imaging, remote sensing, and optical communication. Such a strategy can also be extended to build compact systems that can measure additional light-field information, such as the depth of a target scene or the wavefront of the incident light.

More information:
Yibo Ni et al, Computational Spectropolarometry with Tunable Liquid Crystal Metasurface, eLight (2022). DOI: 10.1186/s43593-022-00032-0

Provided by the Chinese Academy of Sciences

Reference: Liquid crystal metasurface could enable multidimensional light-field sensing (2022, November 4) retrieved November 4, 2022 from https://phys.org/news/2022-11-liquid-crystal-metasurface-enable-multi -dimensional.html

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