The terahertz frequency band is located between the microwave and infrared bands in the electromagnetic spectrum. Compared with infrared radiation, terahertz radiation can transmit through most common clothing. A passive terahertz imager with a high spatial resolution is used to measure the whole-body temperature by our team. The calibration result of the temperature is provided, which shows that the temperature measurement error of our system is about ±0.7 K. More than 90 colleagues’ terahertz images and raw data were collected by our imager. The measured temperatures of forehead and palm of hand collected by our terahertz imager and an infrared camera are provided. The influence of clothing is also researched in our experiment.

When fielding near-surface hyperspectral imaging systems for computer vision applications, raw data from a sensor are often corrected to reflectance before analysis. This research presents an expedient and flexible methodology for performing spectral reflectance estimation using in situ asphalt cement concrete or Portland cement concrete pavement as a reference material. Then, to evaluate this reflectance estimation method’s utility for computer vision applications, four datasets are generated to train machine learning models for material classification: (1) a raw signal dataset, (2) a normalized dataset, (3) a reflectance dataset corrected with a standard reference material (polytetrafluoroethylene), and (4) a reflectance dataset corrected with a pavement reference material. Various machine learning algorithms are trained on each of the four datasets and all converge to excellent training accuracy (>94 % ). Models trained on the raw or normalized signals, however, did not exceed 70% accuracy when tested against new data captured under different illumination conditions, while models trained using either reflectance dataset saw almost no drop between training and testing accuracy. These results quantify the importance of reflectance correction in machine learning workflows using hyperspectral data, while also confirming practical viability of the proposed reflectance correction method for computer vision applications.

In recent years, bidirectional encoder representation from transformers (BERT) models have achieved superior performance in hyperspectral images (HSIs). It can capture the long-range correlations between HSI elements, but the local space and spectral band information of HSI is insufficient. We propose a spatially augmented guided sequence BERT network for HSI classification study, referred to as SAS-BERT, which makes more effective use of HSI’s spatial and spectral information by improving the BERT model. First, a spatial augmentation learning module is added in the preprocessing stage to obtain more significant spatial features before the input network and better guide the spatial sequence. Then a spectral correlation module was used to represent the spectral band features of the HSI and to establish a correlation with the spatial location of the images to obtain better classification performance. Experimental results on three datasets show that the method proposed achieves better classification performance than other state-of-the-art methods.

We introduce an approach for encoding a variety of independent outputs from a computer-generated diffractive optical element displayed on a spatial light modulator (SLM). In this approach, random binary 0-1 orthogonal patterns are multiplied to the different phase functions, effectively multiplexing the corresponding different outputs. We show experimental results with different examples of multiplexed phase functions. Additional functions can be multiplexed simply by adding more random binary patterns. We demonstrate the generation of up to eight different independent outputs. Although the technique was demonstrated years ago, nowadays it can be applied with high-resolution SLMs with a very large number of pixels, thus allowing for a larger number of multiplexed functions without significant degradation. Nevertheless, high-resolution SLMs are affected by pixel crosstalk caused by the fringing field effect. We show that the random patterns are quite sensitive to this effect, leading to a significant undesired DC order. Two alternative strategies to avoid this degradation and make the random multiplexing technique efficient are discussed.

Nowadays, bending workpiece angle measurement methods require touching the surface, which makes them prone to scratching the workpieces and inefficient. To solve the above problems, we propose a non-contact angle measurement system based on multi-line structured light. First, a bilinear laser is projected onto the surface of the workpiece and the machine tool lower die. However, reflections on the smooth workpiece will greatly destroy measurement accuracy. In this work, a UNet-based multi-exposure image fusion strategy is proposed to clip the reflection and increase the workpiece feature. Then, the Steger algorithm is used to achieve high-precision localization of the laser centerline. Finally, the angle of the workpiece is calculated indirectly according to fitting the laser centerline plane. The experimental results demonstrate that the measurement time of each workpiece is less than 100 ms and the measurement accuracy is ±0.3 deg in extreme installation locations and shadow. The proposed system can be extended to real industrial scenarios because of its high efficiency, accuracy, and robustness.

A rotating mirror high-speed imaging system can capture and track moving targets, obtaining high-resolution images of targets and it is suitable for capturing high-speed moving targets. Therefore, we propose a target velocity measurement method based on a rotating mirror high-speed camera. Since this system is based on monocular camera capture, traditional binocular vision-based visual velocity measurement methods are no longer applicable. We reconstruct the homography matrix of the plane where the target is located, calculate the virtual difference map of the target’s feature points, and reconstruct the three-dimensional (3D) coordinates of the feature points on the moving target. Then, based on calibration data, the actual 3D coordinates of the target are calculated, and the target’s motion speed is calculated using the frame rate of the camera. This method achieves 3D reconstruction of feature points of moving targets solely based on a monocular perspective and is highly suitable for a rotating camera model, allowing for continuous measurement of the motion speed of the target and observation of speed variations, expanding the range of velocity observation for high-speed moving targets. The experiment shows that this method has the advantages of low requirements for the field, simple construction of experimental equipment, and high robustness. It can still measure the speed of the target with high accuracy under relatively simple conditions. The average relative error of displacement measurement experiment using this method is 2.03%, which shows the feasibility and accuracy of this method. We believe it has significant application value for measuring the speed of high-speed moving targets.

A simple and effective phase-shift device is designed for the simultaneous and high-accuracy measurement of three-dimensional (3D) deformation using tri-wavelength electronic speckle pattern interferometry and a three-sensor charge-coupled device camera. The designed phase-shifter can provide tri-wavelength lasers quasi-π / 2 phase-step simultaneously. Multi-component phases related to 3D deformation information are extracted by a 90 deg step 4-frame technique from the separated red, green, and blue channels of color images. Six derivative components are further determined based on the retrieval phase maps. Experimental results demonstrate the validity and feasibility of the proposed method.

We present an adaptive phase unwrapping method based on geometric constraints and the gradient field without additional images for high-speed three-dimensional (3D) shape measurement. Specifically, we reconstruct the 3D geometry of moving objects frame by frame. We first create a reference phase map at the depth provided by the former frame. Then we optimize the depth value by validating the continuity of the computed unwrapped phase based on the modulus of the gradient field and recalculate the correct absolute phase map with the optimal depth value. After reconstructing the 3D geometry of the current frame, 3D data are delivered to the next frame. In particular, a geometric constraint-based method is applied in the first frame. Experiment results indicate that our approach, which requires only three phase-shifted fringe patterns per frame, can measure moving objects with high accuracy and robustness. Additionally, several isolated objects can also be measured by our method if they are continuous.

To resolve the disparity between accuracy and speed in the current surface flatness detection of medium and thick steel plates, which predominantly relies on the single-line laser vision method, we propose a high-efficiency flatness detection method for medium-thick steel plates based on multiline parallel laser vision. On the basis of building a flatness detection system, we present the adaptive cropping algorithm and improved variable threshold Otsu thresholding segmentation algorithm (IVT-Otsu) for image preprocessing. Then, the centerline of subpixel-level laser stripes is accurately extracted using a weighted quadratic grayscale center of gravity method. Meanwhile, a pruning algorithm-based multiline laser stripe center extraction method is proposed to address the phenomenon of spotting and branching in the center of multiline parallel laser, to efficiently obtain the surface depth information and flatness index of medium-thick steel plate. Results of the experiment indicate that the proposed method better fulfills the accuracy and efficiency requirements for online inspection when extracting the laser centers and calculating the flatness.

Glycine phosphite single crystals were grown by employing the slow evaporation solution growth technique. Grown crystals were subjected to shock waves generated by a pressure-driven Reddy Tube. The (001) plane of the grown crystal was subjected to various numbers of shock pulses of Mach number 1.7 whereby its structural, optical, and morphological properties were investigated by using the powder X-ray diffractometer, ultraviolet (UV)-visible spectrometer, impedance analyzer, and optical microscope, respectively. The powder X-ray diffraction analysis confirms that the crystals have comparatively higher structural stability along the (001) direction. The observed UV-visible spectrum reveals a considerable increase in optical transmission when increasing the number of shock pulses. The band gap of the crystal is also found to have increased from 4.15 to 4.17 eV after the fifth shock-loaded condition. The dielectric behaviour of the crystal under shocked conditions is studied in the frequency range of 1 Hz to 1 MHz.

Spatiotemporal optical solitons in strongly nonlocal nonlinear media (SNNM) are investigated theoretically and numerically by solving the ( 3 + 1 ) D Schrödinger equation in parabolic cylindric coordinates. The spatiotemporal optical solitons in parabolic cylindric coordinates are constructed by the Hermite–Gaussian pulses with topology charge l in the temporal domain and confluent hypergeometric beams with model number n, m in the spatial domain. The transverse field patterns of the solitons are manipulated by the confluent hypergeometric functions; meanwhile the Hermite–Gaussian pulses affect their transverse central peak’s intensity. Typical examples of the obtained soliton solutions are based on spatial mode numbers m, n, pulse topology charge l, and modulation depth q. The spatiotemporal hollow multi-ring optical soliton in SNNM with m ≠ 0 is first accessed. The spatiotemporal optical soliton keeps approximately non-dispersion properties in the temporal dimension, and their widths of packets remain steady in the spatial dimension. Their transverse central peak’s intensity vibrates and decays with the pulse topology charge l increasing. The spatiotemporal hollow multi-ring optical solitons in SNNM have potential applications in optical switches, optical communications, and three-dimensional microprinting.

Long-wave infrared (LWIR) imagers utilize self emission in 8 to 12 μm spectral band to image objects passively even during night time when the reflected radiation is not available. These are mostly used for surveillance purpose requiring large field of view (FOV). Achieving wide FOV and high-resolution image of megapixel (MP) order requires higher format detectors that are not readily available in LWIR. Further, the optical performance gets limited by fundamental limits of space bandwidth factor. An LWIR monocentric multiscale imager is proposed. The designed lens operates at f / 1.5 with effective focal length (EFL) of 50 mm and effective pixel count of 3.9 MP. It covers 80 deg × 16 deg FOV over five detector arrays. We discuss the basics of multiscale imaging, the specific issues in LWIR band and their mitigation, optical design approach and finally analyze the optical performance of the designed lens.

Photonic crystal fibers (PCFs) have been extensively studied to enhance communication capacity and spectral efficiency by supporting orbital angular momentum (OAM) modes. However, the structural fragility resulting from the central air hole in PCFs undermines the fiber’s roundness. We introduce a hybrid PCF that replaces the central air hole with a material with a high refractive index. This innovation not only enhances the fiber’s structural strength but also introduces an additional communication channel. Furthermore, this method increases the amount of OAM modes supported for transmission in the ring. Numerical results demonstrate that significant differences in refractive indices exist between adjacent vector modes, with high mode quality (ranging from 74.6% to 97.6%) and a small effective mode area (ranging from 23.5 to 59.5 μm²). The proposed hybrid PCF can transmit 20 OAM modes in the inner core and 54 OAM modes in the outer ring. The spacing between the two layers of air holes has a minimal impact on the effective mode area and mode quality. However, the effective mode area decreases and the mode quality increases with the enlargement of the diameter of air holes. In addition, a decrease in doping concentration results in lower mode quality and a larger effective mode area. Moreover, the proposed hybrid PCF can be employed in OAM-based mode division multiplexing for high-capacity short-range fiber optic communication.

A cost-efficient radio over fiber system based on a 21-tuple frequency binary phase-shift keying (BPSK) millimeter wave using a phase modulator (PM) and semiconductor optical amplifier (SOA) is theoretically proposed and demonstrated. In this scheme, the PM is driven by a radio frequency BPSK downlink signal at an appropriate modulation index to generate the +3rd-order sideband bearing BPSK signal and −4th-order sideband unmodulated generated signal, which is similar to the single sideband signal. New frequencies of sidebands are obtained after four-wave mixing in SOA. At the base station, after filtering, the −11th-order sideband bearing BPSK signal and +10th-order sideband unmodulated signal are abstracted, and then a photodiode is input to generate a 21-tuple frequency BPSK mm-wave signal, whereas the −4th-order sideband is used as the carrier for uplink. Simulation results show that, without precoding, a wideband 21-tuple frequency BPSK mm-wave signal with the frequency varying from 21 to 210 GHz can be obtained. Furthermore, the impact of SOA’s current and the laser linewidth on the system performance is also studied. The power penalty for the downlink signal is 2 dB and for the uplink signal is 1.7 dB after 50 km single-mode fiber transmission at a BER of 10 ^{− 9}, which shows good system performance.

We propose and experimentally demonstrate a bidirectional angled multimode interferometer (Bi-AMMI) for interleaved wavelength division multiplexing applications. The spectral response of the 2 × 4 Bi-AMMI is obtained using an eigenmode expansion method, including the cross coupling between the input and output ports at the same side of the multimode waveguide. To verify our design, both the standalone and interleaved Bi-AMMIs were fabricated and measured. The Bi-AMMI exhibits an insertion loss of 0.99 to 1.21 dB, and the unwanted cross coupling is lower than −20 dB. The interleaved device exhibits a measured optical loss of 4.77 to 5.02 dB, and the average crosstalk is calculated to be −18 dB.

Simplified coherence technology based on direct detection has been a hot topic because of its simple structure and low cost. However, some recently proposed simplified coherent receivers (SCRs) require extremely complex mathematical operations, resulting in high power consumption of digital signal processing. We design an asymmetric SCR (ASCR) based on a twin-single-sideband signal, and the field reconstruction algorithm only requires one Hilbert operation, avoiding the nonlinear mathematical operation and the digital up-sampling. Compared to the asymmetric direct detection receiver, the power consumption of the ASCR in the part of optical field reconstruction and dispersion compensation can be reduced by 79.83% under the same sensitivity. Besides, an optimal design of the optical filter and the channel equalization for the ASCR is proposed.

The loss of one bit of information causes energy dissipation in traditional logic gates at ambient temperature, but when the number of bits is greater, as in high-speed networks, the heat released by them is so great that it impacts performance and shortens component lifetime. Using reversible logic gates, which ideally result in zero energy dissipation, these problems in ordinary Boolean functions can be solved. At 100 Gb/s, an all-optical three-input-output reversible PNOR logic gate is numerically simulated in this article using semiconductor optical amplifiers (SOAs)-based switching units. The quality factor (Q-factor) and the bit error rate (BER) are the metrics against which the performance of reversible PNOR operation is assessed. The results indicate the feasibility of realizing all-optically the PNOR gate at 100 Gb/s since the SOA-based scheme, along with correct logic operation, manages to achieve more than acceptable Q-factor and BER.

A multilayered optical orthogonal frequency division multiplexing with offset quadrature amplitude modulation (LO-OFDM/OQAM) scheme is proposed for visible light communication (VLC) systems, which is inspired by the enhance optical OFDM/OQAM (EO-OFDM/OQAM) scheme. In this scheme, multiple layers of data are superimposed on the normal branch to further improve the spectral efficiency and power efficiency of the VLC systems. Specifically, the negative time-domain signals on each layer can be directly clipped as zeros without losing any information and demolishing the real-field orthogonal condition of the optical OFDM/OQAM system. Theoretical derivation is then given to prove the feasibility. Spectral efficiency, peak-to-average power ratio performance, bit error rate (BER) performance, and power efficiency of this proposed scheme are further investigated and compared with those of its counterparts. Simulation results show that the proposed LO-OFDM/OQAM scheme could achieve better BER performance in comparison with EO-OFDM/OQAM and DCO-OFDM/OQAM schemes, and at the same time, it is more power efficient. Our work would benefit the research and development of VLC systems.

Erratum corrects misspelling in an author name.