Polarization, the vector nature of electromagnetic waves, plays a vital role in optics. Polarization is characterized by the amplitude contrast and phase difference between two orthogonal polarization states. The present polarimeters usually perform a series of intensity measurements to carry out the polarization detection, making the process bulky and time-consuming. Thereby, compact and broadband-available polarimetry within a single snapshot is urgently demanded. We propose an all-liquid-crystal polarimeter for broadband polarization detection. It is cascaded by a q-plate and a polarization grating. The former is electrically tuned to meet the half-wave condition, whereas the latter is driven to deviate from this condition. After a polarized light passes through this device followed by a polarizer, its amplitude contrast and phase difference between orthogonal spins are read directly from the diffraction pattern. The intensity contrast between ±1st orders depicts the amplitude contrast, whereas the rotating angle of the dark split reveals the phase difference. The Stokes parameters can be calculated accordingly. The polarimeter works in a broad spectral range of 470 to 1100 nm. Through presetting a q-plate array, polarization imaging is demonstrated. It supplies an all-liquid-crystal and full-visible-band tunable Stokes polarimeter that significantly promotes advances in polarization optics.

Multiphoton entanglement with high information capacity plays an essential role in quantum information processing. The appearance of parallel beam splitting (BS) in a gradient metasurface provides the chance to prepare the multiphoton entanglement in one step. Here, we use a single metasurface to construct multiphoton path-polarization entanglement. Based on the parallel BS property, entanglement among N unentangled photons is created after they pass through a gradient metasurface. Also, with this ability, entanglement fusion among several pairs of entangled photons is set up, which can greatly enlarge the entanglement dimension. These theoretical results pave the way for manipulating metasurface-based multiphoton entanglement, which holds great promise for ultracompact on-chip quantum information processing.

Conventional superconducting nanowire single-photon detectors (SNSPDs) have been typically limited in their applications due to their size, weight, and power consumption, which confine their use to laboratory settings. However, with the rapid development of remote imaging, sensing technologies, and long-range quantum communication with fewer topographical constraints, the demand for high-efficiency single-photon detectors integrated with avionic platforms is rapidly growing. We herein designed and manufactured the first drone-based SNSPD system with a system detection efficiency (SDE) as high as 91.8%. This drone-based system incorporates high-performance NbTiN SNSPDs, a self-developed miniature liquid helium dewar, and custom-built integrated electrical setups, making it capable of being launched in complex topographical conditions. Such a drone-based SNSPD system may open the use of SNSPDs for applications that demand high SDE in complex environments.

Edge couplers, widely recognized for their efficiency and broad bandwidth, have gained significant attention as optical fiber-to-chip couplers. Silicon waveguides exhibit strong birefringence properties, resulting in substantial polarization-dependent loss for edge couplers in the O-band. We introduce a bilayer and double-tip edge coupler designed to efficiently couple both transverse electric (TE) and transverse magnetic (TM) modes while maintaining compatibility with standard manufacturing processes used in commercial silicon photonics foundries. We have successfully designed and fabricated this edge coupler, achieving coupling losses of <1.52 dB / facet for TE mode and 2 dB / facet for TM mode when coupled with a lensed optical fiber [4-μm mode field diameter (MFD)] within the wavelength range of 1260 to 1360 nm.

Holographic microscopy has emerged as a vital tool in biomedicine, enabling visualization of microscopic morphological features of tissues and cells in a label-free manner. Recently, deep learning (DL)-based image reconstruction models have demonstrated state-of-the-art performance in holographic image reconstruction. However, their utility in practice is still severely limited, as conventional training schemes could not properly handle out-of-distribution data. Here, we leverage backpropagation operation and reparameterization of the forward propagator to enable an adaptable image reconstruction model for histopathologic inspection. Only given with a training dataset of rectum tissue images captured from a single imaging configuration, our scheme consistently shows high reconstruction performance even with the input hologram of diverse tissue types at different pathological states captured under various imaging configurations. Using the proposed adaptation technique, we show that the diagnostic features of cancerous colorectal tissues, such as dirty necrosis, captured with 5× magnification and a numerical aperture (NA) of 0.1, can be reconstructed with high accuracy, whereas a given training dataset is strictly confined to normal rectum tissues acquired under the imaging configuration of 20× magnification and an NA of 0.4. Our results suggest that the DL-based image reconstruction approaches, with sophisticated adaptation techniques, could offer an extensively generalizable solution for inverse mapping problems in imaging.

We demonstrate an effective and optimal strategy for generating spatially resolved longitudinal spin angular momentum (LSAM) in optical tweezers by tightly focusing the first-order spirally polarized vector (SPV) beams with zero intrinsic angular momentum into a refractive index stratified medium. The stratified medium gives rise to a spherically aberrated intensity profile near the focal region of the optical tweezers, with off-axis intensity lobes in the radial direction possessing opposite LSAM (helicities corresponding to σ = + 1 and -1) compared to the beam center. We trap mesoscopic birefringent particles in an off-axis intensity lobe as well as at the beam center by modifying the trapping plane and observe particles spinning in opposite directions depending on their location. The direction of rotation depends on the particle size with larger particles spinning either clockwise or anticlockwise depending on the direction of spirality of the polarization of the SPV beam after tight focusing, while smaller particles spin in both directions depending on their spatial locations. Numerical simulations support our experimental observations. Our results introduce new avenues in spin–orbit optomechanics to facilitate novel yet straightforward avenues for exotic and complex particle manipulation in optical tweezers.

In traditional sensing, each parameter is treated as a real number in the signal demodulation, whereas the electric field of light is a complex number. The real and imaginary parts obey the Kramers–Kronig relationship, which is expected to help further enhance sensing precision. We propose a self-Bayesian estimate of the method, aiming at reducing measurement variance. This method utilizes the intensity and phase of the parameter to be measured, achieving statistical optimization of the estimated value through Bayesian inference, effectively reducing the measurement variance. To demonstrate the effectiveness of this method, we adopted an optical fiber heterodyne interference sensing vibration measurement system. The experimental results show that the signal-to-noise ratio is effectively improved within the frequency range of 200 to 500 kHz. Moreover, it is believed that the self-Bayesian estimation method holds broad application prospects in various types of optical sensing.

A microwave photonic prototype for concurrent radar detection and spectrum sensing is proposed. A direct digital synthesizer and an analog electronic circuit are integrated to generate an intermediate frequency (IF) linearly frequency-modulated (LFM) signal ranging from 2.5 to 9.5 GHz, with an instantaneous bandwidth of 1 GHz. The IF LFM signal is converted to the optical domain via an intensity modulator and filtered by a fiber Bragg grating to generate two second-order sidebands. The two sidebands beat each other to generate a frequency-and-bandwidth-quadrupled LFM signal. By changing the center frequency of the IF LFM signal, the radar function can be operated within 8 to 40 GHz. One second-order sideband works in conjunction with the stimulated Brillouin scattering gain spectrum for microwave frequency measurement, providing an instantaneous measurement bandwidth of 2 GHz and a frequency measurement range from 0 to 40 GHz. The prototype is demonstrated to be capable of achieving a range resolution of 3.75 cm, a range error of less than ±2 cm, a radial velocity error within ±1 cm / s, delivering clear imaging of multiple small targets, and maintaining a frequency measurement error of less than ±7 MHz and a frequency resolution of better than 20 MHz.

Optical and hybrid convolutional neural networks (CNNs) recently have become of increasing interest to achieve low-latency, low-power image classification, and computer-vision tasks. However, implementing optical nonlinearity is challenging, and omitting the nonlinear layers in a standard CNN comes with a significant reduction in accuracy. We use knowledge distillation to compress modified AlexNet to a single linear convolutional layer and an electronic backend (two fully connected layers). We obtain comparable performance with a purely electronic CNN with five convolutional layers and three fully connected layers. We implement the convolution optically via engineering the point spread function of an inverse-designed meta-optic. Using this hybrid approach, we estimate a reduction in multiply-accumulate operations from 17M in a conventional electronic modified AlexNet to only 86 K in the hybrid compressed network enabled by the optical front end. This constitutes over 2 orders of magnitude of reduction in latency and power consumption. Furthermore, we experimentally demonstrate that the classification accuracy of the system exceeds 93% on the MNIST dataset of handwritten digits.

Existing single-pixel imaging (SPI) and sensing techniques suffer from poor reconstruction quality and heavy computation cost, limiting their widespread application. To tackle these challenges, we propose a large-scale single-pixel imaging and sensing (SPIS) technique that enables high-quality megapixel SPI and highly efficient image-free sensing with a low sampling rate. Specifically, we first scan and sample the entire scene using small-size optimized patterns to obtain information-coupled measurements. Compared with the conventional full-sized patterns, small-sized optimized patterns achieve higher imaging fidelity and sensing accuracy with 1 order of magnitude fewer pattern parameters. Next, the coupled measurements are processed through a transformer-based encoder to extract high-dimensional features, followed by a task-specific plug-and-play decoder for imaging or image-free sensing. Considering that the regions with rich textures and edges are more difficult to reconstruct, we use an uncertainty-driven self-adaptive loss function to reinforce the network’s attention to these regions, thereby improving the imaging and sensing performance. Extensive experiments demonstrate that the reported technique achieves 24.13 dB megapixel SPI at a sampling rate of 3% within 1 s. In terms of sensing, it outperforms existing methods by 12% on image-free segmentation accuracy and achieves state-of-the-art image-free object detection accuracy with an order of magnitude less data bandwidth.

Deep ultraviolet coherent light, particularly at the wavelength of 193 nm, has become indispensable for semiconductor lithography. We present a compact solid-state nanosecond pulsed laser system capable of generating 193-nm coherent light at the repetition rate of 6 kHz. One part of the 1030-nm laser from the home-made Yb:YAG crystal amplifier is divided to generate 258 nm laser (1.2 W) by fourth-harmonic generation, and the rest is used to pump an optical parametric amplifier producing 1553 nm laser (700 mW). Frequency mixing of these beams in cascaded LiB3O5 crystals yields a 193-nm laser with 70-mW average power and a linewidth of less than 880 MHz. By introducing a spiral phase plate to the 1553-nm beam before frequency mixing, we generate a vortex beam carrying orbital angular momentum. This is, to our knowledge, the first demonstration of a 193-nm vortex beam generated from a solid-state laser. Such a beam could be valuable for seeding hybrid ArF excimer lasers and has potential applications in wafer processing and defect inspection.

Laser frequency combs, which are composed of a series of equally spaced coherent frequency components, have triggered revolutionary progress in precision spectroscopy and optical metrology. Length/distance is of fundamental importance in both science and technology. We describe a ranging scheme based on chirped pulse interferometry. In contrast to the traditional spectral interferometry, the local oscillator is strongly chirped which is able to meet the measurement pulses at arbitrary distances, and therefore, the dead zones can be removed. The distances can be precisely determined via two measurement steps based on the time-of-flight method and synthetic wavelength interferometry, respectively. To overcome the speed limitation of the optical spectrum analyzer, the spectrograms are stretched and detected by a fast photodetector and oscilloscope and consequently mapped into the time domain in real time. The experimental results indicate that the measurement uncertainty can be well within ±2 μm, compared with the reference distance meter. The Allan deviation can reach 0.4 μm at 4 ns averaging time and 25 nm at 1 μs and can achieve 2 nm at 100 μs averaging time. We also measured a spinning disk with grooves of different depths to verify the measurement speed, and the results show that the grooves with about 150 m / s line speed can be clearly captured. Our method provides a unique combination of non-dead zones, ultrafast measurement speed, high precision and accuracy, large ambiguity range, and only one single comb source. This system could offer a powerful solution for field measurements in practical applications in the future.