Single-pixel Terahertz Imaging Research Articles

Near-field terahertz single-pixel imaging with ultralow sampling ratio

Near-field terahertz single-pixel imaging with ultralow sampling ratio

Spatial Polarization Modulation for Terahertz Single-Pixel Imaging

Spatial Polarization Modulation for Terahertz Single-Pixel Imaging

Fast terahertz image classification with a single-pixel detector

A fast object classification scheme in terahertz (THz) domain is proposed. This scheme combines machine learning and THz single-pixel imaging (SPI) technologies but skips the image reconstruction in SPI. It can directly perform the linear pattern recognition task based on a few single-pixel values. This approach has advantages of low experimental complexity, simple optimization algorithms, and all-optical processing. It is verified in simulation and experiment with a classification accuracy of 90%. Our proposed scheme paves an avenue for fast classification of THz images in practical applications.

Terahertz single pixel imaging with frequency-multiplexed metasurface modulation

Single-pixel imaging is a very attractive technique at the terahertz band due to the lack of mature array detectors, over which the spatial light modulator is the most crucial component. Metasurfaces are usually introduced into the modulator to enhance the modulation depth of active materials. Here we take advantage of the flexible spectral response of pixelated metasurface resonators to encode different spatial masks into different frequency windows, without active materials and external stimuli. The measurements are obtained in parallel as opposed to in sequence in the time-domain spectroscopy system through a single terahertz signal. Images with 2 × 2 pixels as proof of the concept are reconstructed with high fidelity and plenty of choices of the frequency windows. As the measurement time does not increase with the number of pixels, this scheme can be generalized for imaging with higher resolution and increased number of pixels for practical applications in noninvasive inspection and detection.

High-efficiency terahertz single-pixel imaging based on a physics-enhanced network.

As an alternative solution to the lack of cost-effective multipixel terahertz cameras, terahertz single-pixel imaging that is free from pixel-by-pixel mechanical scanning has been attracting increasing attention. Such a technique relies on illuminating the object with a series of spatial light patterns and recording with a single-pixel detector for each one of them. This leads to a trade-off between the acquisition time and the image quality, hindering practical applications. Here, we tackle this challenge and demonstrate high-efficiency terahertz single-pixel imaging based on physically enhanced deep learning networks for both pattern generation and image reconstruction. Simulation and experimental results show that this strategy is much more efficient than the classical terahertz single-pixel imaging methods based on Hadamard or Fourier patterns, and can reconstruct high-quality terahertz images with a significantly reduced number of measurements, corresponding to an ultra-low sampling ratio down to 1.56%. The efficiency, robustness and generalization of the developed approach are also experimentally validated using different types of objects and different image resolutions, and clear image reconstruction with a low sampling ratio of 3.12% is demonstrated. The developed method speeds up the terahertz single-pixel imaging while reserving high image quality, and advances its real-time applications in security, industry, and scientific research.

Research Progress of Terahertz Single-Pixel Imaging and Its Dynamic Mask Materials

Research Progress of Terahertz Single-Pixel Imaging and Its Dynamic Mask Materials

Advances on terahertz single-pixel imaging

Single-pixel imaging is a novel imaging technique that can obtain image information through a single-pixel detector. It can effectively avoid the problem of lack of high-quality area array detectors in the terahertz band, and has attracted the attention of a large number of researchers in recent years. In this paper, the basic imaging principles, terahertz beam modulation methods and typical image reconstruction algorithms for terahertz single-pixel imaging are introduced and discussed, as well as its research progresses and developing trends.

Deep Learning Optimized Terahertz Single-Pixel Imaging

In this article, we demonstrate an efficient terahertz single-pixel imaging system incorporating deep learning networks. Experimental results show that by combining a Hadamard single-pixel imaging system with the deep learning network, the sampling time per pattern can be reduced to 1/20 of the conventional system and the number of Hadamard patterns can be reduced to 10% of the pixels while maintaining high image quality with acceptable signal-to-noise ratio above 20 dB and structural similarity of more than 0.85. We thus expect this article to advance the development of a real-time terahertz single-pixel imaging system and promote its applications.

FPGA-Based Tensor Compressive Sensing Reconstruction Processor for Terahertz Single-Pixel Imaging Systems

Terahertz (THz) imaging system has great potentials for material identification, security screening, circuit inspection, bioinformatics and bio-imaging because it can penetrate various non-metallic materials and inhibits unique spectral fingerprints of a great variety of optically opaque materials in our daily lives. However, THz emitters and detectors are still extremely expensive. Therefore, the single-pixel compressive sensing imaging technique becomes a potential solution for the implementation of a THz imaging system. This paper presents a tensor-based single-pixel compressive sensing model and a reconstruction algorithm for THz single-pixel imaging systems based on the generalized tensor compressive sensing framework. To accelerate the THz image reconstruction, a low-complexity 2-D compressive sensing processor based on power singular value decomposition method (2DCS-PSVD) was designed and implemented in this paper. In the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$32\times32$ </tex-math></inline-formula> single-pixel THz imaging system, the 2DCS-PSVD algorithm requires 78.9% complexity of the modified generalized tensor compressive sensing parallel algorithm (GTCS-P) with little image quality degradation. The 2DCS-PSVD processor was further designed and implemented in the Xilinx ZCU102 SOC FPGA plate-form. The proposed FPGA-based tensor-based compressive sensing processor achieved a throughput of 1127 frames/sec and had the highest normalized hardware efficiency compared to other state-of-the-art works in the literature.

Research progress of terahertz programmable metamaterials and applications in single-pixel imaging

Electromagnetic metamaterials have exhibited a powerful ability to control electromagnetic waves. With the introduction of programmable metamaterials, metamaterials are developing towards digitization and intelligence. In this article, we firstly review the research progress of terahertz programmable metamaterials, including the design methods, control principles and applications of terahertz programmable metamaterials using tunable materials such as semiconductors and liquid crystals. Next, the application of terahertz programmable metamaterials in single-pixel imaging is introduced. Electronically and optically controlled terahertz programmable metamaterials are used to realize spatial coding modulation of terahertz wave. Combined with imaging algorithms such as compressive sensing, they are used to realize terahertz single-pixel imaging. Finally, the development trend of terahertz programmable metamaterials and their application prospects are prospected.

Broadband high-resolution terahertz single-pixel imaging.

We report a simple single-pixel imaging system with a low mean squared error in the entire terahertz frequency region (3-13 THz) that employs a thin metallic ring with a series of directly perforated random masks and a subpixel mask digitization technique. This imaging system produces high pixel resolution reconstructed images, up to 1200 × 1200 pixels, and imaging area of 32 × 32 mm2. It can be extended to develop advanced imaging systems in the near-ultraviolet to terahertz region.

Terahertz Meta-Holograms Reconstruction Based on Compressed Sensing

The introduction of single-pixel imaging and compressed sensing (CS) techniques into terahertz (THz) imaging has sped up image acquisition and avoided raster scanning. At present, most single-pixel terahertz imaging developments are based on simple metal samples, researchers rarely study the reconstruction of complex structural samples with large attenuation in the terahertz domain, such as metasurface holographic images. Here, we present an implementation of the single-pixel compressed sensing approach into THz metasurface holography reconstruction. By laser projecting a set of binary patterns on a 500-μm thick silicon wafer using a digital micromirror device (DMD), THz wavefront of the holographic metasurface is spatially encoded. Single-element detector is used to measure electric field amplitude of the transmitted THz radiation for each pattern, and then the hologram is reconstructed by Total variation Augmented Lagrangian and Alternating Direction Algorithm (TVAL3). Besides, the reconstruction effects are also analyzed by reducing measurement number, it can maintain more than 95% of the image information under 20% compression. The demonstrated combination of terahertz holography and single-pixel compressed sensing imaging provides new possibilities for metasurface imaging, verifies the stability of terahertz single-pixel imaging, and the scheme may lead to advances in fast terahertz imaging.

Real-time terahertz imaging with a single-pixel detector

Terahertz (THz) radiation is poised to have an essential role in many imaging applications, from industrial inspections to medical diagnosis. However, commercialization is prevented by impractical and expensive THz instrumentation. Single-pixel cameras have emerged as alternatives to multi-pixel cameras due to reduced costs and superior durability. Here, by optimizing the modulation geometry and post-processing algorithms, we demonstrate the acquisition of a THz-video (32 × 32 pixels at 6 frames-per-second), shown in real-time, using a single-pixel fiber-coupled photoconductive THz detector. A laser diode with a digital micromirror device shining visible light onto silicon acts as the spatial THz modulator. We mathematically account for the temporal response of the system, reduce noise with a lock-in free carrier-wave modulation and realize quick, noise-robust image undersampling. Since our modifications do not impose intricate manufacturing, require long post-processing, nor sacrifice the time-resolving capabilities of THz-spectrometers, their greatest asset, this work has the potential to serve as a foundation for all future single-pixel THz imaging systems.

Terahertz Single-Pixel Imaging Improved by Using Silicon Wafer with SiO2 Passivation

We demonstrate terahertz single-pixel imaging is improved by using a photomodulator based on silicon passivated with SiO 2 . By exploring various SiO 2 thicknesses, we show that the modulation factor of the as-fabricated terahertz photomodulator can reach 0.9, three times that based on bare silicon. This improvement originates from chemical passivation, as well as anti-reflection. Single-pixel imaging experiments based on the compressed sensing method show that reconstructed images adopting the new photomodulator have better quality than the conventional terahertz modulator based on bare silicon. Since the passivation process is routine and low cost, we expect this work will reduce the cost of terahertz photomodulator and single-pixel THz imaging, and advance their applications.

Reflective Single-Pixel Terahertz Imaging Based on Compressed Sensing

The investigation of single-pixel terahertz (THz) imaging opens up a new research direction for the development of THz imaging technology. In this work, we exploit a reflective single-pixel THz imaging system based on photoinduced dynamic masks. By combining the compressed sensing and inverse Fresnel diffraction algorithms, a reflective THz spectral image is accurately reconstructed and the morphology of a sample is clearly observed. Three application potentials of the THz imaging system are fully proved, including time-of-flight measurement of a sample with multiple interfaces, noninvasive testing of a hidden object, and spectral identification of different chemical substances. The reflection-type measurement mode effectively improves the practicability of single-pixel THz imaging.

Fourier single-pixel imaging in the terahertz regime

We demonstrate Fourier single-pixel imaging in the terahertz regime. The experimental system is implemented using a photoinduced coded aperture setup, where monolayer graphene on a high-resistance silicon substrate illuminated by a coded laser beam works as a terahertz modulator. The results show that high-quality terahertz images can be reconstructed using a greatly reduced number of measurements. We further find that deep photoinduced terahertz modulation, by adding a monolayer graphene on the silicon substrate and by using high laser power, can significantly improve the image quality. Compared to Hadamard single-pixel imaging with a reordered Hadamard matrix, the Fourier approach has higher image quality. We expect that this work will speed up the efficiency of single-pixel terahertz imaging and advance terahertz imaging applications.

Electrically Programmable Terahertz Diatomic Metamolecules for Chiral Optical Control

Optical chirality is central to many industrial photonic technologies including enantiomer identification, ellipsometry-based tomography, and spin multiplexing in optical communications. However, a substantial chiral response requires a three-dimensional constituent, thereby making the morphology highly complex to realize structural reconfiguration. Moreover, an active reconfiguration demands intense dosage of external stimuli that pose a major limitation for on-chip integration. Here, we report a low bias, electrically programmable synthetic chiral paradigm with a remarkable reconfiguration among levorotatory, dextrorotatory, achiral, and racemic conformations. The switchable optical activity induced by the chiral conformations enables a transmission-type duplex spatial light modulator for terahertz single pixel imaging. The prototype delivers a new strategy towards reconfigurable stereoselective photonic applications and opens up avenues for on-chip programmable chiral devices with tremendous applications in biology, medicine, chemistry, and photonics.

Electrically Programmable Terahertz Diatomic Metamolecules for Chiral Optical Control.

Optical chirality is central to many industrial photonic technologies including enantiomer identification, ellipsometry-based tomography, and spin multiplexing in optical communications. However, a substantial chiral response requires a three-dimensional constituent, thereby making the morphology highly complex to realize structural reconfiguration. Moreover, an active reconfiguration demands intense dosage of external stimuli that pose a major limitation for on-chip integration. Here, we report a low bias, electrically programmable synthetic chiral paradigm with a remarkable reconfiguration among levorotatory, dextrorotatory, achiral, and racemic conformations. The switchable optical activity induced by the chiral conformations enables a transmission-type duplex spatial light modulator for terahertz single pixel imaging. The prototype delivers a new strategy towards reconfigurable stereoselective photonic applications and opens up avenues for on-chip programmable chiral devices with tremendous applications in biology, medicine, chemistry, and photonics.

A low-voltage high-speed terahertz spatial light modulator using active metamaterial

An all solid-state metamaterial based terahertz (THz) spatial light modulator (SLM) is presented which uses high mobility 2DEG to manipulate the metamaterial resonant frequency (0.45 THz) leading to terahertz wave modulation. The 2DEG is created by embedding pseudomorphic high-electron mobility transistors in the capacitive gap of each electrical-LC resonator, allowing the charge density to be controlled with very low voltage (1 V) and modulating speeds up to 10 MHz while consuming sub-milliwatt power. We have demonstrated our SLM as a 2 × 2 pixel array operating around 0.45 THz by raster scanning a 6 × 6 image of an occluded metal object behind a thick polystyrene screen using a single-pixel THz imaging setup.

A Nipkow disk integrated with Fresnel lenses for terahertz single pixel imaging

We present a novel Nipkow disk design for terahertz (THz) single pixel imaging applications. A 100 mm high resistivity (ρ≈3k-10k Ω·cm) silicon wafer was used for the disk on which a spiral array of twelve 16-level binary Fresnel lenses were fabricated using photolithography and a dry-etch process. The implementation of Fresnel lenses on the Nipkow disk increases the THz signal transmission compared to the conventional pinhole-based Nipkow disk by more than 12 times thus a THz source with lower power or a THz detector with lower detectivity can be used. Due to the focusing capability of the lenses, a pixel resolution better than 0.5 mm is in principle achievable. To demonstrate the concept, a single pixel imaging system operating at 2.52 THz is described.