Introduction

Terahertz (THz) waves hold significant promise for applications in chemical analysis, biological sensing, medical diagnostics, and security screening due to their unique properties including strong penetrability, nonionizing photon energy, and rich spectral fingerprints spanning a wide range of molecular vibrations and resonances1,2,3,4. THz spectrometers and imaging systems are thus indispensable tools for spectral characterization and nondestructive inspection. While conventional THz time-domain spectrometers (THz-TDS) enable the direct acquisition of broadband spectra with phase information, these systems typically rely on coherent detection schemes (Fig. 1a), which necessitate bulky optical setups incorporating mechanical delay lines5,6,7,8. Moreover, spatial information must be acquired through raster scanning, especially when single-pixel detectors (SPDs) are used for imaging. As a result, the realization of compact, low-cost and portable THz spectrometers remains a longstanding challenge.

Fig. 1: Simplified THz computational spectrometer or single-pixel imaging (THz-CS/SPI) architecture compared with conventional THz-TDS.
Fig. 1: Simplified THz computational spectrometer or single-pixel imaging (THz-CS/SPI) architecture compared with conventional THz-TDS.
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a Conventional THz-TDS employs a mechanical delay line and coherent balanced detection (red dashed box). b THz-CS/SPI replaces the delay line and coherent detection with SLM-based encoding and an SPD that records intensity only; the spectral/spatial information is reconstructed computationally, enabling miniaturization (red dashed box). Some graphical elements are adapted from Ryo Mizuta Graphics.

A promising route to miniaturization involves replacing coherent detection with an incoherent SPD (Fig. 1b), sacrificing direct access to broadband phase-resolved spectral data. To compensate, computational techniques such as compressed sensing, regularization, and deep learning algorithms are employed to reconstruct spectral and spatial information from intensity-only measurements9,10,11. These methods rely on solving the inverse problem \({{{\bf{I}}}}={{{\mathbf{\Phi }}}}\cdot {{{\bf{X}}}}\), where Ф denotes the measurement matrix, X represents the object (spectral or spatial distribution), and I is the recorded intensity vector. Crucially, successful reconstruction depends on the measurement matrix comprising sufficiently uncorrelated spectral or spatial encoding patterns.

In this context, spatial or spectral light modulators (SLMs) play a central role by generating decorrelated modulation frames that define the measurement matrix12,13,14. The degree of frame-to-frame decorrelation directly affects reconstruction fidelity, alongside factors such as modulation speed and spectral bandwidth that determine overall performance. Both natural materials (e.g., quantum dot, liquid crystals, and perovskites) and artificial photonic materials (e.g., metasurfaces and photonic crystals) have been explored as candidates for encoding patterns, particularly in the visible and infrared spectral regimes15,16,17,18,19. However, the inherently weak interaction between THz radiation and most natural materials poses a substantial barrier to developing THz-compatible SLMs that combine low correlation coefficients, broad bandwidth, and high-speed modulation.

Metasurfaces have emerged as a powerful platform for enhancing light-matter interactions in THz SLMs20,21,22. As artificial materials, metasurfaces offer unparalleled flexibility in tailoring the spatial distributions and shaping spectral responses of electromagnetic fields, enabling local field confinement in the spatial domain and enhanced interaction in the temporal domain23,24,25. When integrated with functional natural materials, such as semiconductors or phase-change media, hybrid metasurfaces exhibit dynamic tunability and serve as versatile platforms for reconfigurable metadevices in molding wavefront and exploring physical phenomena26,27.

In conventional active metasurfaces, enhanced light-matter interactions are naturally associated with high quality factor resonances (Q), where Q ≈ f/Δf, with f denoting the central frequency and Δf the full width at half maximum (FWHM) linewidth, and thus possess a very narrow bandwidth. High-Q resonances are often leveraged to reduce modulation thresholds and amplify tunability. However, their narrow spectral width inherently limits the broadband spectral encoding needed for computational spectrometry. Furthermore, the modulation speed of traditional metasurface-based SLMs is constrained to the millisecond range by the intrinsic relaxation times of constituent materials, such as liquid crystals, phase-change materials, and micro-electromechanical systems (MEMS), as well as the RC time constants of drive circuitry28,29,30,31. All-optical modulation schemes provide an alternative route by eliminating complex electronics, thereby enabling ultrafast modulation on the picosecond timescale32,33. Nevertheless, the inherent trade-off between low spectral correlation (enabled by high-Q resonances) and broadband spectral coverage remains a fundamental limitation for broadband computational spectroscopy.

Recent advances in the physics of bound states in the continuum (BICs) offer a systematic framework for overcoming this trade-off34,35,36. BICs support theoretically infinite Q factors and allow for the engineering of radiation channels, dispersion relations, and modal profiles37,38,39. Pixelated BICs metasurfaces have been shown to maintain high-Q resonances while expanding the spectral coverage, proving beneficial for applications such as ultrasensitive hyperspectral imaging and molecular barcoding40,41. However, in such pixelated schemes with N spatial elements, each metasurface pixel interacts with only 1/N of the incident power at its resonant frequency, with the remaining (N−1)/N constituting background energy. This spatial multiplexing approach inevitably reduces the signal-to-noise ratio (SNR).

To address this limitation, we introduce a strategy that folds multiple BICs into a broadband spectral region, thereby preserving high Q-factors while enhancing light utilization without reducing SNR42. By breaking symmetry to convert BICs into quasi-BICs (q-BICs), a dense set of high-Q resonances can be excited across a wide frequency range. These resonances exhibit diverse mode profiles and enhanced sensitivity, enabling broadband spectral modulation with intrinsically low correlation coefficients.

Here, we experimentally demonstrate a broadband, low-correlation, and ultrafast SLM based on hybrid metasurfaces supporting multiple q-BICs, and show their applications in THz computational spectrometer (THz-CS) and THz single-pixel imaging (THz-SPI). As a proof-of-concept demonstration, the broadband spectral correlation is reduced by transferring three q-BICs to the interested spectral range (0.30-0.55 THz), and the metasurfaces are designed to modulate transmission spectra in an all-optical manner with nanosecond scale response time. Incorporated into a THz system with an incoherent SPD without spectral resolution capability, the active hybrid metasurfaces acting as an SLM enables ultrafast THz-CS with 0.03 THz spectral resolution covering 0.25 THz bandwidth and 1.9 ns reconstruction time. The all-optical hybrid metasurface architecture is readily extendable for ultrafast single-pixel imaging via pixelated metasurfaces.

Results

Our design employs metasurfaces composed of classical double-gap split-ring resonators (DSRRs), chosen for their well-understood electromagnetic behavior. When the symmetry of the unit cells is broken, Fano resonances emerge due to interference between q-BICs resonances and the broad radiative background. These Fano resonances, known for their sharp lineshapes and strong sensitivity, are particularly attractive for use in sensing and active modulation43,44. To achieve broadband operation with low spectral correlation, we excite multiple Fano resonances with distinct mode symmetries. This is accomplished by engineering the mode dispersion of DSRRs arranged in a square lattice. When the lattice periodicity is doubled, two guided modes at the Brillouin zone edge are folded to the Γ point (inset in Fig. 2a). Upon symmetry breaking, these modes become radiative, producing two additional q-BICs (labeled q-BIC I and q-BIC III) in the vicinity of the original Fano resonance (q-BIC II). These new resonances retain the BIC character, exhibiting an inverse quadratic dependence of Q on the in-plane wavevector45. Further details of the band-folding design and simulations are provided in Supporting Information S3.

Fig. 2: Broadband spectral modulation with multiple BICs in hybrid metasurfaces.
Fig. 2: Broadband spectral modulation with multiple BICs in hybrid metasurfaces.
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a Underlying physics of multiple BICs interpreted from reciprocal space and realized by period engineering in real space. b Mode pattern analysis with surface current and electric field distributions at three q-BIC resonances. The unit cell structure diagram of multi-BICs metasurfaces and key geometrical parameters: p = 94.5 μm, l = 78 μm, g = 4 μm, w = 10 μm, and a = 8 μm. c Two types of hybrid metasurfaces by integrating silicon patches at different positions of metallic resonators. External perturbation is introduced by pulse laser with wavelength at 800 nm whose photon energy is higher than bandgap of silicon to inject photocarriers, and thus induces intense modulation of all the three q-BICs. d Correlation coefficient evolution at different conductivities of silicon patches.

We introduce symmetry breaking by laterally displacing the capacitive gap in one of the two DSRRs along the x axis (d = 27 μm, Fig. 2a inset), which breaks both the C2 symmetry of resonator and lattice symmetry, converting all three BICs into radiative q-BICs. Experimentally, we observe three distinct resonances centered at 0.35 THz, 0.44 THz, and 0.48 THz, with Q-factors of 16.1, 10.5, and 22.5, respectively, in good agreement with simulations. The intrinsic ohmic losses of metallic resonators restrict the increase of Q-factors to a higher value comparable to dielectric metasurfaces. Specifically, the three resonances deliver around 60% relative bandwidth centered at 0.42 THz46. Mode profiles, visualized via surface current and local electric field distributions (Fig. 2b), reveal that q-BIC I and II correspond to antiphase and in-phase oscillating current loops in the neighboring two DSRRs, deemed as inductive-capacitive (LC) resonances (anti-LC and parallel-LC) with the localized electric field predominantly concentrated in the capacitive gaps. q-BIC III manifests as a dipole-like mode, with electric fields primarily concentrated at the metallic arm edges.

These distinct local field distributions underpin our design of hybrid metasurfaces for broadband low-correlation modulation. To achieve active modulation, we embed silicon patches at strategic locations within the resonators. Optical pumping of the silicon alters its conductivity with excess photocarrier accumulation, thereby modifying the equivalent inductance and capacitance on nanosecond timescales47,48, which significantly impacts the resonance conditions due to strong local field enhancement. Detailed influence on each q-BICs resonances due to perturbation of silicon conductivity is summarized in Supporting Information S4, and perturbation in capacitive gaps tunes q-BIC I and q-BIC II, while perturbation in resonator arms mainly contributes to the modulation of q-BIC III. Hybrid metallic split-ring resonators (SRRs) integrated with semiconductors have been studied for various applications in the THz regime49. Leveraging their well-established physics, we use band folding to broaden the modal spectrum and apply it to THz-CS/SPI. More importantly, our theoretical framework based on q-BICs and dispersion engineering is general and applies to a wide range of metallic or dielectric resonators, rather than being limited to DSRRs.

We investigate two hybrid metasurface types to assess their modulation correlation: frequency-shift type, where silicon patches are embedded in the capacitive gaps without electrically shorting them, thus preserving mode profiles while shifting resonance frequencies; and mode-change type, where gaps are fully filled in one resonator, leading to quenching of LC resonances upon conductivity increase. Spectral modulation characteristics are presented in Fig. 2c. In the frequency-shift design, all three q-BICs exhibit redshifts and reduced depths with increasing silicon conductivity. In contrast, the mode-change design suppresses the original resonances and induces new dipolar responses. Correlation coefficients between modulated and unmodulated spectra reveal that mode-change designs consistently produce lower values, indicative of greater spectral diversity and lower inter-frame redundancy (Fig. 2d).

Having addressed the trade-off between broadband spectral coverage and high-Q resonances to reduce modulation correlation coefficients, we next turn to the implementation of an ultrafast measurement matrix essential for high-speed computational reconstruction. To this end, we fabricated the metallic DSRRs and integrated them with a patterned silicon epilayer on a sapphire substrate. Optical micrographs of the fabricated hybrid metasurfaces are shown as insets in Fig. 3a and e (see “Methods” for detailed fabrication procedures). To probe ultrafast broadband spectral modulation, we employed an optical-pump THz-probe (OPTP) system using femtosecond optical pulses with a fluence of 0.52 mJ/cm2 offering external pump perturbation. Upon excitation, photocarriers are generated in the silicon patches, modulating the local conductivity and consequently altering the resonant behavior of the metasurface at specific frequencies. We recorded the electric field variation ΔE/E0 at the peak of the time-domain signal pulse, where E0 represents the reference field amplitude without pump measured under identical conditions, and \(\Delta E={E}_{pump}-{E}_{0}\). The subsequent excitation and relaxation dynamics of these nonequilibrium carriers were tracked using the delayed THz probe. The photocarrier density reaches its peak ~27 ps after the pump pulse (defined as τ  =  0 ps), and then gradually decays over ~1.9 ns via carrier recombination and trapping processes. From the measured differential transmission spectra, we estimate the time-dependent silicon conductivity to vary from ~4800 S/m after excitation, decaying to ~300 S/m over the 1.9 ns relaxation period (see Supporting Information S5).

Fig. 3: Ultrafast measurement matrix with two types of active hybrid metasurfaces under external perturbation.
Fig. 3: Ultrafast measurement matrix with two types of active hybrid metasurfaces under external perturbation.
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a, e Measured relaxation dynamics of active hybrid metasurfaces at a pump fluence of 0.52 mJ/cm2 with microscopic images of the fabricated hybrid metasurface samples. b, f Simulated and c, g experimental dynamic spectral evolution of the two types of hybrid metasurfaces. d, h Auto-correlation function in terms of frequency.

Although both types of hybrid metasurfaces (frequency-shift and mode-change) exhibit similar temporal carrier dynamics, governed primarily by the intrinsic properties of the silicon epilayer, their spectral evolution diverges significantly due to differences in silicon distribution and its interaction with the local electromagnetic fields. Figure 3b and c illustrate the spectral evolution of the frequency-shift metasurface based on both experimental data and numerical simulations. As photocarriers accumulate, all three q-BIC resonances undergo a redshift and exhibit reduced resonance depth, attributable to the modulation of equivalent inductance, capacitance, and resistance in the resonator circuit. These spectral features recover progressively to their steady-state positions over the 1.9 ns timescale. A persistent, unperturbed feature at ~0.41 THz, observed experimentally, is attributed to Fabry-Pérot interference within the sapphire substrate, which is relatively insensitive to free-carrier modulation. In contrast, the mode-change metasurface demonstrates a more complex spectral evolution (Fig. 3f and g). At τ  =  0 ps, a new resonance emerges at ~0.38 THz, replacing the original q-BIC I and q-BIC II resonances, suggesting a mode transition induced by gap quenching. The q-BIC III resonance, however, shows a redshift trend similar to that observed in the frequency-shift design. All three resonances gradually return to their unperturbed states over the course of 1.9 ns. This ultrafast and dynamic spectral evolution effectively forms a time-varying modulation mask as a measurement matrix enabling object encoding and spectral information reconstruction on a nanosecond timescale.

The presence of three distinct q-BICs resonances induces strong spectral undulations across the broadband range of 0.30 to 0.55 THz, providing a robust encoding basis for a THz-CS. Upon optical excitation, the hybrid metasurface generates a sequence of temporally varying spectral frames with high contrast, each exhibiting unique modulation patterns, within a nanosecond timescale. These dynamically evolving frames effectively constitute a measurement matrix for spectral reconstruction. To quantitatively evaluate the encoding quality of the measurement matrix formed by the hybrid metasurfaces, we calculate the spectral auto-correlation function50,51,52:

$$C(\Delta f)={\langle \frac{{\langle T(f,\tau )T(f+\Delta f,\tau )\rangle }_{f}}{{\langle T(f,\tau )\rangle }_{f}{\langle T(f+\Delta f,\tau )\rangle }_{f}}-1\rangle }_{\tau }$$
(1)

where T(f, τ) is the transmission amplitude at frequency f and at time τ, and <·>f/τ indicates averaging over frequency f or time τ. The auto-correlation function is normalized such that C(0) = 1. The resulting auto-correlation profiles, shown in Fig. 3d and h, characterize the degree of spectral diversity encoded across modulation frames.

The half-width at half-maximum (HWHM) of C(Δƒ), i.e., the frequency offset where the auto-correlation falls to C(Δƒ) = 0.5, defines the achievable spectral resolution when the active hybrid metasurface is used as an SLM in THz-CS. Based on 10 uniformly spaced temporal frames selected from the 1.9 ns carrier relaxation window, we extract spectral resolutions of 0.028 THz and 0.024 THz for the frequency-shift and mode-change metasurfaces, respectively (see Supporting Information S6). The improved resolution of the mode-change design is attributed to its greater spectral decorrelation across frames, and it is thus selected as the prototype for experimental validation of the THz-CS using an SPD in a simplified system configuration (More modulation strategies are provided in Supporting Information S7).

The proposed simplified THz-CS architecture is illustrated in Fig. 4a. A broadband THz pulse generated from an antenna is transmitted through the sample, forming an unknown spectral response S(f). Unlike conventional systems that rely on mechanical delay lines and coherent detection schemes, the proposed system leverages an active hybrid metasurface as an SLM in conjunction with an SPD, and divides partial femtosecond pulses from transmitter path to drive the SLM, thereby significantly reducing the complexity, size, and cost of the spectrometer.

Fig. 4: Demonstration of ultrafast THz-CS based on SLM of active hybrid metasurface.
Fig. 4: Demonstration of ultrafast THz-CS based on SLM of active hybrid metasurface.
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a Optical setup of THz-CS incorporating with an SLM of active hybrid metasurface. Some graphical elements are from Ryo Mizuta Graphics. b Computational spectral reconstruction performance for bandpass filters with a typical Lorentzian lineshape. c Peak frequency difference between reconstructed and original spectra (top) and frequency resolving power (bottom). d Computational spectral reconstruction performance for a more complex lineshape with broadband (top) and two coupled resonances (bottom). e Reconstruction quality evaluation based on PSNR depending on the number of measurement frames.

Spectral modulation frames are generated by photoexciting the hybrid metasurface with a pulsed optical pump, synchronized with the SPD to trigger the series of signal acquisition on a nanosecond timescale. The unknown spectrum is encoded by a measurement matrix T(f), determined by the metasurface’s dynamic response across modulation frames. The SPD records the resulting intensity vector I, from which the original broadband spectrum can be reconstructed computationally. The fidelity of the reconstruction both in spectral resolution and SNR is governed by the spectral resolution and inter-frame correlation of T(f), the number of modulation frames, algorithmic efficiency, and system stability (see Supporting Information S8 and S9). In addition, we analyze the impact of system repeatability and experimental uncertainties on the performance (see Supporting Information S11 and S12).

As a proof of concept, we evaluated the spectral reconstruction performance using a set of THz band-pass filters with different center frequencies and approximately Gaussian passbands. This choice reflects the intended application of our THz-CS, detecting absorption features of biomacromolecules, pharmaceuticals, and gases, whose line shapes are typically well approximated by Gaussian under practical conditions. The attempts to reconstruct rectangular and triangular waveforms can be found in Supporting Information S13. With only 10 modulation frames, the reconstructed spectra faithfully reproduce the filters’ original lineshapes and central frequencies, achieving a FWHM of ~0.03 THz (Fig. 4b), comparable to the resolution obtainable from conventional time-domain spectroscopy with a scan time of ~30 ps. The average peak frequency difference (Δƒ) between reconstructed and original spectra is 3.95 × 10-3 THz, with a minimum of 4 × 10-5 THz. The average frequency resolving power (\({R}_{f}=\frac{f}{\Delta f}\)) at the specified operating frequency is ~1193, which is comparable with previous reports (Fig. 4c)53,54. Spectral reconstruction with different features was carried out for a single-pass filter with a broader bandwidth and spectrum with two closely spaced Lorentzian peaks (~0.05 THz apart), and the reconstructed spectra reveal excellent quality via the proposed THz-CS system (Fig. 4d). We note that the reported 0.25 THz operational bandwidth refers to the frequency range over which the resonant low-spectral-correlation modulation is significant and the reconstructed spectra remain accurate. To achieve a broader operational bandwidth, the DSRR metasurface can be geometrically scaled to produce multiple modules, each providing a substantial frequency coverage in distinct spectral regions. By assembling these modules, the system can achieve an ultra-wide operational bandwidth while maintaining low spectral correlation.

The overall quality of the reconstructed spectrum is characterized by the peak signal-to-noise ratio (PSNR, \({{{\rm{PSNR}}}}=10\cdot {\log }_{10}(\frac{{{{{\rm{MAX}}}}}_{{{{\rm{I}}}}}^{2}}{{{{\rm{MSE}}}}})\) where MSE is mean squared error, MAXI is maximum possible pixel value of the spectrum), and a larger PSNR indicates a higher-quality reconstructed spectrum55. Based on the example of single-peak bandpass filter spectrum centered at 0.39 THz, we observe an improved PSNR with a larger number of measurements under both types of hybrid metasurface SLMs (Fig. 4e). The PSNR increases as the number of measurements rises from 5 to 15, but it saturates once the frame count exceeds ~20, indicating that additional frames contribute redundant information due to non-negligible correlation between adjacent modulation states. With 10 measurements, the mode-change SLM attains an excellent reconstruction PSNR of 30.1 dB, commonly regarded as the threshold for high-quality reconstruction15,56,57. The comparison between the two types of hybrid metasurface SLMs indicates an overall better performance of mode-change type with lower number of measurements. We also investigate the relationship between the PSNR of the reconstructed spectra and the spectral resolution (see Supporting Information S10).

In addition to spectral reconstruction by using the broadband, low-correlation ultrafast modulation, the hybrid metasurface can be spatially pixelated to encode spatial information, functioning as a high-speed SLM for THz-SPI. In a conventional THz-SPI system, a continuous-wave THz beam transmits through or reflects from the target object X, and is subsequently modulated by predefined spatial masks Φ before being detected by an SPD, forming an intensity vector I (Fig. 5a). However, the overall imaging speed is severely constrained by the slow modulation rate of conventional SLMs, which often rely on electronically driven spatial masks with complex peripheral circuitry. We present a circuit-free, all-optical solution based on our hybrid metasurface, which enables ultrafast spatial modulation by harnessing the rich spectral responses and mode distributions of band-folded q-BICs.

Fig. 5: Schematic diagram of ultrafast THz-SPI based on an SLM of multiple pixelated active hybrid metasurfaces.
Fig. 5: Schematic diagram of ultrafast THz-SPI based on an SLM of multiple pixelated active hybrid metasurfaces.
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a Schematic diagram of the THz-SPI setup based on the 3 × 3 hybrid metasurfaces forming an ultrafast SLM. Some graphical elements are from Ryo Mizuta Graphics. b Arrangement of 9 pixels metasurfaces with different scaling factors. c Contrasting modulation dynamics of each single pixel during the relaxation process after external perturbation forming a high-quality and ultrafast SLM for central frequency at 0.45 THz. Here ΔT(ω) indicates the transmission variation in frequency domain. d Spatial-resolved evolution of transmission intensity in the nine pixels over time. Seven frames were chosen for performance characterization with large spatial transmission intensity contrast in each frame as the dashed lines shown in (c). e Dependence of MSE as a function of compressive ratios to reconstruct the cross-shape pattern. f Comparison between the original object and the reconstructed image.

Operating at a central frequency of 0.45 THz, we design a 3 × 3 pixelated mode-change type metasurface array, where each pixel is scaled by a geometrical factor S (Fig. 5b) to induce distinct temporal transmission dynamics in response to a uniform optical pump. The pixels are selected to produce strongly contrasting transient responses during the relaxation process, as detailed in Supporting Information S15. Figure 5c illustrates the time-resolved transmission responses of the nine pixels over a 1.9 ns interval, revealing diverse and uncorrelated temporal modulation patterns. Unlike conventional SLMs, in which each pixel must be individually addressed, the proposed SLM scheme generates rich spatial modulation frames under a single uniform optical stimulus, significantly simplifying system complexity and improving stability.

To demonstrate imaging capability, we extract seven representative frames (Fig. 5c and d) from the transient modulation dynamics induced by a single uniform pump pulse to form a modulation matrix with high spatial randomness and orthogonality—key attributes for successful reconstructed images. Using these seven frames, we acquire the corresponding intensity vector I from the SPD and reconstruct binary images representing the target scene using regularization algorithm (see Supporting Information S14). The reconstructed images (Fig. 5f) clearly resolve the target patterns (“T”, “H”, and “Z”), with high fidelity quantified by a MSE that remains close to zero for compression ratios exceeding 66.7% (Fig. 5e). Robustness against system noise is also confirmed, and the reconstruction remains accurate for noise levels up to 0.50% (Supporting Information S16 and S17). This demonstration establishes the hybrid metasurface as a unified platform for ultrafast spectral and spatial modulation, providing a scalable, CMOS-compatible, and optically driven route toward next-generation THz imaging systems.

Discussion

Although our current proof-of-concept demonstrates a THz-CS operating in the 0.30-0.55 THz range, the bandwidth can be readily extended by folding additional guided modes into the desired frequency window via lattice engineering42. This not only increases bandwidth but also reduces spectral correlation, enhancing resolution. From a device physics perspective, the high efficiency and broadband modulation arise from dispersion engineering of BICs. Resonance Q-factors were engineered at appropriate values to balance bandwidth, local field enhancement and spectral diversity, prioritizing low-correlated modulation and computational reconstruction over extreme confinement.

In contrast to conventional SLMs, where each pixel is individually addressed by electrical signals to control local amplitude or phase, typically with modulation speeds limited to the kHz range, the all-optical SLM presented here operates at GHz speeds, free from RC delay constraints and without peripheral circuitry. The hybrid metasurface architecture, based on CMOS-compatible silicon patches and metallic resonators, enables scalable fabrication with high quality and throughput. The spatial resolution of the proposed scheme is theoretically limited by minimal pixel size of unit cells and a THz detector with higher sensitivity for larger-density modulation matrix readout. For the scenario of large-area object imaging, a hybridized scheme combined with raster scan is necessary, which provides a clear and immediately deployable pathway.

The proposed all-optical modulation scheme initiates a viable route toward ultrafast THz SLMs. Compared with conventional THz spectrometers and imaging systems (Supporting Information S18-S21), our THz-CS/SPI achieves markedly faster modulation, higher integration, and substantially lower cost. The total modulation time for generating the measurement matrix can be further reduced by either (i) utilizing the rising edge of the carrier dynamics, which occurs on the picosecond timescale, rather than the relaxation process, or (ii) replacing standard silicon with alternative fast-relaxing semiconductors, such as ion-implanted silicon or gallium arsenide, to further compress the modulation cycle into the picosecond regime. The achievable spatial resolution in single-pixel imaging can be improved by designing SLMs with more pixels and optimizing reconstruction algorithms58,59. Spectral resolutions also can be systematically improved through metasurface engineering and system-level optimization by enhancing modulation depth, designing low-correlation measurement matrices, and adopting advanced reconstruction algorithms.

In this work, we have developed an active hybrid metasurface platform that provides a dynamic, broadband, and low-correlation modulation basis, enabling both THz-CS and THz-SPI within a simplified architecture centered on an SPD. By embedding multiple q-BIC resonances into a single metasurface, we successfully overcome the conventional trade-off between spectral bandwidth and resonance Q factor. The integration of semiconductor patches in the hybrid metasurface enables all-optical modulation with nanosecond-scale response times and broadband spectral resolution down to 0.03 THz. Beyond spectral reconstruction, we further demonstrated spatial encoding by pixelating the metasurface into a 3 × 3 SLM, achieving high-fidelity single-pixel imaging reconstruction using temporally resolved modulation frames. This entirely optically driven approach eliminates the need for electronic addressing, peripheral circuitry, or mechanical scanning, offering substantial simplification of the system architecture. The platform’s CMOS compatibility and GHz-level modulation speed highlight its strong potential for integration into compact, ultrafast THz devices. Looking forward, further advancements could be achieved by expanding operational bandwidth through higher-order band folding, enhancing spatial resolution via finer pixelation, and reducing modulation latency using alternative semiconductor materials with faster carrier dynamics. Collectively, this work establishes a versatile, scalable, and high-speed solution for integrated THz spectroscopy and imaging, laying the groundwork for future generations of ultrafast optoelectronic systems.

Methods

Fabrications

Additional fabrication details are provided in Supporting Information S1. The sample substrate consisted of silicon-on-sapphire (SOS), featuring a 460 μm-thick sapphire base and an 850 nm-thick silicon epitaxial layer. A patterned photoresist layer was first formed on the silicon surface using UV photolithography. A 200 nm-thick aluminum film was then deposited on top of the photoresist via thermal evaporation. The sample was subsequently immersed in dimethyl sulfoxide to lift off the photoresist along with the unwanted aluminum, leaving behind the designed aluminum microstructure. Next, UV lithography was performed again to cover and protect both the silicon pattern and aluminum structures with photoresist. The exposed silicon epitaxial layer was removed using inductively coupled plasma (ICP) etching. Finally, the remaining photoresist was cleaned using dimethyl sulfoxide and acetone, resulting in the fabricated hybrid metasurface sample.

Measurements

The OPTP consists of three beam paths, including the detection beam path, the generation beam path and the pump beam path. Firstly, femtosecond pulses with 800 nm center wavelength, 100 fs pulse width and 1 kHz repetition frequency were divided into three beam paths by two beam splitters: the detection beam has a fixed optical range and is directly incident into the ZnTe crystal for detection. The generation beam pumps the ZnTe crystal and generates the THz wave undergoing a delay line to adjust the time of arrival of the THz pulse at the sample. The pump beam also undergoes a delay line to control the time of arrival of the pump pulse at the sample so that varying pump relaxation times of the THz wave are measured. Further details of the OPTP optical setup are provided in Supporting Information S2.

Numerical method

Numerical simulations (transmission spectrum matrix) were carried out using commercially available software (CST Microwave Studio) by a finite-element frequency domain solver with unit cell boundary conditions. The refractive index of silicon was set to n = 3.4, while the nondispersive refractive index of sapphire was set to n = 3.6. The conductivity of aluminum was defined as 7 × 106 S/m. The eigenmode analysis of the metasurface was carried out in COMSOL Multiphysics.