Research on On-Chip Full-Stokes Polarimeters Based on Optoelectronic Polarization Eigenvectors

Academic Background

The polarization state of light plays a significant role in optical communication, biomedical diagnostics, remote sensing, cosmology, and other fields. The Stokes vector, consisting of four parameters, is used to fully describe the polarization state of light, providing comprehensive information on light intensity and polarization. Conventional polarimeters usually rely on discrete optical components, such as prisms, lenses, filters, polarizers, and wave plates. However, their bulky size significantly limits miniaturization and broader application.

With advancements in nanophotonics and metasurface technology, researchers have begun exploring compact polarimeters based on metasurfaces. However, integrating existing metasurface-based polarimeters into the infrared spectral range remains challenging, with issues such as pixel alignment, optical crosstalk, and infrared absorption becoming key obstacles.

To address these challenges, this paper introduces an on-chip full-Stokes polarimeter based on the concept of optoelectronic polarization eigenvectors (OPEVs). By configuring four OPEVs, an optimized optoelectronic conversion matrix (OCM) was established, enabling high-precision full-Stokes polarization detection. The polarimeter comprises four subpixels that share the same few-layer molybdenum disulfide (MoS₂) as the detection material. Each subpixel integrates a plasmonic metasurface, corresponding to a distinct OPEV. By optimizing the geometric arrangement of the metasurfaces, the condition number of the OCM is minimized, achieving high-accuracy Stokes parameter reconstruction.

Paper Details

The paper, authored by Jie Deng, Mengdie Shi, Xingsi Liu, and other collaborators, was created by researchers from institutions such as the Shanghai Institute of Technical Physics of the Chinese Academy of Sciences, the National University of Singapore, Southeast University, and the University of Electronic Science and Technology of China. It was published in Nature Electronics in November 2024, under DOI https://doi.org/10.1038/s41928-024-01287-w.

Research Process

1. Concept and Design of the Optoelectronic Polarization Eigenvector (OPEV)

OPEV is a four-dimensional vector that describes the linear relationship between the incident Stokes vector and the photocurrent generated by the detector. By configuring four OPEVs, the research team constructed an optoelectronic conversion matrix (OCM) that maps the Stokes vector of the incident light to photocurrent. The photocurrent in each subpixel can be expressed as:

[ j_{ph} = \mu \cdot S ]

where (\mu) is the OPEV and (S) is the Stokes vector.

2. Design and Fabrication of the On-Chip Polarimeter

The on-chip polarimeter consists of four subpixels, each integrating a plasmonic metasurface. The geometric arrangement of these metasurfaces was optimized to ensure the minimum condition number for the OCM. Specifically, the metasurfaces in the four subpixels were geometrically configured in four distinct orientations: (y, +), (y, -), (x, +), and (x, -). This configuration allows the four OPEVs to form a regular tetrahedron, minimizing the condition number of the OCM.

3. Experiments and Results

Experimental validation confirmed that using the optimized OCM, combined with a machine learning algorithm (Gaussian process regression), resulted in full-Stokes reconstruction with root mean square errors (RMSEs) of less than 1% across the entire polarization state space. Specifically, the RMSEs for Stokes parameters (S_0), (S_1), (S_2), and (S_3) were 0.13%, 0.98%, 0.96%, and 0.58%, respectively, demonstrating extremely high precision in the near-infrared range.

4. Broadband Polarization Reconstruction

To ensure the OCM’s condition number remained consistently low across a wavelength range of 1200–1600 nm, the metasurface’s geometric parameters were adjusted. Experimental results showed that the reconstruction errors for Stokes parameters remained below 0.4% across this wavelength range, highlighting the wide applicability of the polarimeter in the near-infrared spectrum.

Main Results

1. High-Accuracy Stokes Reconstruction: By optimizing the OCM and integrating machine learning algorithms, the research achieved Stokes parameter reconstruction with RMSEs below 1%.
2. Broadband Polarization Reconstruction: The polarimeter demonstrated consistent accuracy across the 1200–1600 nm wavelength range, with reconstruction errors below 0.4%.
3. On-Chip Integration: The polarimeter’s compact design and on-chip integration make it highly suitable for various application scenarios.

Conclusions and Significance

This paper presents an on-chip full-Stokes polarimeter based on optoelectronic polarization eigenvectors, solving the challenges of miniaturization and high-precision detection. The results demonstrate high reconstruction accuracy in the near-infrared range, making the polarimeter a promising tool for applications such as optical communication, remote sensing, and biomedical diagnostics. Additionally, the study introduces a new methodological framework and guidelines for achieving compact, high-accuracy polarimetry.

Research Highlights

1. High Precision: Achieved RMSEs of less than 1% for the reconstruction of all Stokes parameters.
2. Broadband Applicability: Demonstrated accuracy across a wavelength range of 1200–1600 nm with errors below 0.4%.
3. Compact Form Factor: The on-chip polarimeter is significantly smaller than conventional commercial polarimeters.

Additional Insights

The research further validates the applicability of OPEVs to different photodetection mechanisms, including black phosphorus and InGaAs-based infrared detectors. The study also includes a metasurface design framework that can optimize photodetectors for various use cases, providing valuable reference points for future work.

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This study provides a new paradigm for polarization detection, particularly in the near-infrared range, with considerable advances in precision and miniaturization. By optimizing metasurface geometry and developing an efficient optoelectronic conversion matrix, the researchers successfully demonstrated a high-performance, on-chip full-Stokes polarimeter with significant potential for real-world applications.