Anapole-state-enhanced 2D chiral photodetector operating in the near-infrared second window

metasurface, as shown in Fig. 3e–j. For the SHG signal, the data can be fitted by the equation: ISHG?ðθÞ = ½ISHGmin 1=2sin2ðθ + φÞ + ISHGmax 1=2cos2ðθ + φÞ2 × cos23θ, ð1Þ where ISHG min, ISHG max reflect the minimum and maximum SHG intensity, θ is the angle between the polarization and the edge of TMDCs, and φ is the angle between the edge of TMDCs and the x- direction of the structure, which is equal to zero here. Similarly, for the photocurrent, the data can be fitted by the equation: IphcðθÞ = ½Iphc min 1=2sin2ðθ + φÞ + Iphc max 1=2cos2ðθ + φÞ2, ð2Þ where Iphc min, Iphc max reflect the minimum and maximum photo- current. For the SHG component parallel to the excitation light, the term cos23θ in Eq. (1) is replaced by sin23θ59,60, as shown in Supple- mentary Fig. 17. Then, the total SHG signal ISHG = ISHG ⊥+ ISHG ∥can be written the same as Eq. (2). Hence, the polar plots of SHG intensity and photocurrent mutually corroborate the device’s capability for polar- ization resolution. In the case of the MoS2/WSe2 heterostructure on the SiO2/Si substrate, Iphc min = Iphc max, and the polarization ratio (defined as Iphc max/Iphc min), PR = 1. A larger PR indicates a better ability for polarization resolution. At the wavelength of 1200 nm, as shown in Fig. 3g, h, the PR attains a value of up to 40, representing a notably high performance compared to other photodetectors based on 2D materials, which is attributed to the different performance between the optical mode excited by H- and V-polarized light in the metasurface. As mentioned above, there is a GPP mode at 1200 nm under H-polarization, as shown in Fig. 3a. While no resonance exists nearby under V-polarization, as shown in Fig. 3b. Similarly, the PRs of varying wavelength are depen- dent on the mode resonance under different polarizations. At the wavelength of 1060 nm, where no resonance exists under both polarizations, PR = 2. At the wavelength of 1550 nm, PR = 6 proves that the quasi-BIC under H-polarization exhibits greater enhancement than the GPP mode under V-polarization. In fact, the mode wavelength of the metasurface under V-polarization can be regulated independently by the length of the horizontal groove, as shown in Supplementary Fig. 18. Then, the PR of different wavelengths can be modulated manually, which expands the potential of our device for constructing linear-polarization-sensitive photodetectors. Design of chirality-resolved photodetector Beyond linear polarization control, we further extended the func- tionality to chiral light detection by breaking the mirror symmetry of the metasurface along the x-direction. To introduce in-plane chirality, the horizontal groove length (LH) was designed to be finite. To main- tain the target operational wavelength, the period was increased to P = 1200 nm, while all other parameters remained consistent with the structure in Fig. 1a. As shown in Fig. 4a, under circularly polarized excitation, the structure with Δx = 0 exhibits identical optical respon- ses for left- and right-handed circular polarizations (LCP and RCP), due to the preserved mirror symmetry. Two resonant modes are observed: one associated with the quasi-BIC (blue dashed line), excited pre- dominantly by the horizontal field component of the incident light, and another corresponding to the GPP mode (green dashed line) supported by the horizontal groove, driven by the vertical field com- ponent. The maximum circular polarization response occurs at the spectral overlap of these two modes. Introducing a lateral shift of Δx = 50 nm in the vertical groove (inset, Fig. 4b) breaks the mirror symmetry along the x-direction. Figure 4b shows the mapped reflec- tion spectra under LCP illumination for varying Δys. For Δy > 0, the hybridized behavior of the horizontal and vertical modes remains similar to the symmetric case. In contrast, when Δy < 0, the splitting occurs between the two modes, strongly suppressing the response to LCP light. Under RCP illumination, the mapped reflection spectra exhibit similar but mirror-symmetrical characteristics to that of LCP illumination, as shown in Fig. 4c. Consequently, this tailored asym- metry enables pronounced chirality-specific responses, allowing the device to distinguish between LCP and RCP without external optical elements. For the multipole decomposition after breaking the sym- metry along the x-direction, it does not destroy the anapole state but rather makes it chiral-dependent, as shown in Supplementary Fig. 23. Experimentally, structures with Δx = 50 nm and varying Δys are fabricated by FIB. Figure 4d, e show the measured reflection spectra under different circularly polarized light, with the SEM images by the side. Under the LCP illumination, the mode resonances demonstrate a combination of both horizontally and vertically polarized modes, marked by the orange line, as shown in Fig. 4d. While for the RCP light, the mode resonances predominantly exhibit characteristics corre- sponding to the horizontally polarized mode, marked by the blue line, as shown in Fig. 4e. And the vertically polarized mode marked by green line is covered up by the horizontally polarized one. When Δy = 250 nm, the electric field intensity distributions at the wavelength of 1550 nm are shown in Fig. 4f. It can be observed that the fields are distributed within both the vertical and horizontal grooves under the LCP illumination, corresponding to the horizontally polarized quasi- BIC mode and the vertically polarized GPP mode, respectively. The field intensity associated with the former is greater than that of the latter, attributable to the inherent characteristics of quasi-BICs. For RCP light, the field intensity mainly exists among the horizontal groove, corresponding to the vertically polarized GPP mode. Then, the performance of the metasurface for the LCP light is much better than that for