State Key Laboratory of Applied Optics

Photocatalytic water purification utilizes light to degrade the contaminants in water and may enjoy many merits of microfluidics technology such as fine flow control, large surface-area-to-volume ratio and self-refreshing of reaction surface. Although a number of microfluidic reactors have been reported for photocatalysis, there is still a lack of a comprehensive review. This article aims to identify the physical mechanisms that underpin the synergy of microfluidics and photocatalysis, and, based on which, to review the reported microfluidic photocatalytic reactors. These microreactors help overcome different problems in bulk reactors such as photon transfer limitation, mass transfer limitation, oxygen deficiency, and lack of reaction pathway control. They may be scaled up for large-throughput industrial applications of water processing and may also find niche applications in rapid screening and standardized tests of photocatalysts.

Abstract Artificial muscles possess a vast potential in accelerating the development of robotics, exoskeletons, and prosthetics. Although a variety of emerging actuator technologies are reported, they suffer from several issues, such as high driving voltages, large hysteresis, and water intolerance. Here, a liquid metal artificial muscle (LMAM) is demonstrated, based on the electrochemically tunable interfacial tension of liquid metal to mimic the contraction and extension of muscles. The LMAM can work in different solutions with a wide range of pH (0–14), generating actuation strains of up to 87% at a maximum extension speed of 15 mm s −1 . More importantly, the LMAM only needs a very low driving voltage of 0.5 V. The actuating components of the LMAM are completely built from liquids, which avoids mechanical fatigue and provides actuator linkages without mechanical constraints to movement. The LMAM is used for developing several proof‐of‐concept applications, including controlled displays, cargo deliveries, and reconfigurable optical reflectors. The simplicity, versatility, and efficiency of the LMAM are further demonstrated by using it to actuate the caudal fin of an untethered bionic robotic fish. The presented LMAM has the potential to extend the performance space of soft actuators for applications from engineering fields to biomedical applications.

Abstract Nanophotonic engineering provides an effective platform to manipulate thermal emission on-demand, enabling unprecedented heat management superior to conventional bulk materials. Amongst a plethora of nanophotonic structures, symmetries play an important role in controlling radiative heat transfer in both near-field and far-field. In physics, broken symmetries generally increase the degree of freedom in a system, enriching the understanding of physical mechanisms and bringing many exciting opportunities for novel applications. In this review, we discussed the underlying physics and functionalities of nanophotonic structures with broken geometrical symmetries, engineered mode symmetries, and broken reciprocity for the control of thermal emission. We overview a variety of physical phenomena and interesting applications, and provide the outlook for future development.

Abstract Gallium‐based room temperature liquid metal alloys have recently been explored to be an emerging functional material. They have attracted particular attentions in a variety of applications due to their unique properties. Many of the applications are based on the precise control over the motion of liquid metal, and yet, the fact that currently lacking the advanced and reliable controlling methods greatly hinders the potential of liquid metal to be applied in a wider range of fields. In this study, an innovative approach is developed to obtain functional liquid metal (FLM) by modifying it with copper–iron magnetic nanoparticles (Cu–Fe NPs). The magnetic modification process enables the Cu–Fe NPs to be suspended within the liquid metal and form the FLM. The FLM exhibits similar appearance, actuating behaviors, and deformability in alkaline solutions to those of pure liquid metal alloys. Meanwhile, the magnetic modification enables the precise and rapid manipulation of the liquid metal using a magnetic field. Most importantly, for the first time, the precise control and climbing locomotion of the FLM is demonstrated with the interworking of both electric and magnetic fields simultaneously. The remarkable features of the FLM may represent vast potentials toward the development of future intelligent soft robots.

Cr-doped Bi₄Ti₃O₁₂/Bi₂Ti₂O₇ nanofibers have been synthesized by electrospinning/calcination route, which shows good visible-light activity for photodegradation of methyl orange.

This review aims to describe the spectroscopic phenomena, discuss corresponding mechanisms and reveal the inherent clues hidden in the scattered literature of piezochromic luminescent materials under hydrostatic pressure.

Paper microfluidics has attracted much attention since its first introduction around one decade ago due to the merits such as low cost, ease of fabrication and operation, portability, and facile integration with other devices. The dominant application for paper microfluidics still lies in point-of-care testing (POCT), which holds great promise to provide diagnostic tools to meet the ASSURED criteria. With micro/nanostructures inside, paper substrates provide a natural 3D scaffold to mimic native cellular microenvironments and create excellent biointerfaces for cell analysis applications, such as long-term 3D cell culture, cell capture/phenotyping, and cell-related biochemical analysis (small molecules, protein DNA, etc.). This review summarizes cell-related applications based on various engineered paper microdevices and provides some perspectives for paper microfluidics-based cell analysis.

Ferromagnetic liquid crystals (FLCs), the suspensions of magnetic nanoparticles dispersed at different concentrations in liquid crystals (LCs), and their special magnetically induced birefringence characteristics have been investigated in the terahertz regime, mainly focusing on the interaction between magnetic cluster chains and LC molecules. We experimentally demonstrated the surface anchoring effect of the magnetic cluster chains on LC molecules in a mm-thick LC cell under an extremely weak external magnetic field (EMF), leading to a uniform anchoring arrangement of the LC molecules over the entire LC cell. Unlike pure 5CB LCs, the phase shift range of the FLCs at 1.45 THz up to π (no to ne or ne to no) can be achieved over the whole tunable range by simply changing the magnitude of the EMF without changing its direction, and the optical axis of LC molecules can be controlled to rotate by 90°, thereby realizing a tunable THz wave plate. This work provides a new way in the development of THz magneto-optic devices and phase devices.

Abstract As one of the three payloads for the Advanced Space-based Solar Observatory (ASO-S) mission, the Lyman-alpha (Ly α ) Solar Telescope (LST) is composed of three instruments: a Solar Corona Imager (SCI), a Ly α Solar Disk Imager (SDI) and a full-disk White-light Solar Telescope (WST). When working in-orbit, LST will simultaneously perform high-resolution imaging observations of all regions from the solar disk to the inner corona up to 2.5 R ⊙ (R ⊙ stands for the mean solar radius) with a spatial resolution of 4.8″ and 1.2″ for coronal and disk observations, respectively, and a temporal resolution of 30 – 120 s and 1 – 120 s for coronal and disk observations, respectively. The maximum exposure time can be up to 20 s due to precise pointing and image stabilization function. Among the three telescopes of LST, SCI is a dual-waveband coronagraph simultaneously and independently observing the inner corona in the HI Ly α (121.6±10 nm) line and white light (WL) (700±40 nm) wavebands by using a narrowband Ly α beam splitter and has a field of view (FOV) from 1.1 to 2.5 R ⊙ . The stray-light suppression level can attain <10 −6 B ⊙ (B ⊙ is the mean brightness of the solar disk) at 1.1 R ⊙ and ≤5×10 −8 B ⊙ at 2.5 R ⊙ . SDI and WST are solar disk imagers working in the Ly α line and 360.0 nm wavebands, respectively, which adopt an off-axis two-mirror reflective structure with an FOV up to 1.2 R ⊙ , covering the inner coronal edge area and relating to coronal imaging. We present the up-to-date design for the LST payload.

Noise significantly limits the accuracy and stability of retrieving gas concentration with the traditional direct absorption spectroscopy (DAS). Here, we developed an adaptively optimized gas analysis model (AOGAM) composed of a neural sequence filter (NSF) and a neural concentration retriever (NCR) based on deep learning algorithms for extraction of methane absorption information from the noisy transmission spectra and obtaining the corresponding concentrations from the denoised spectra. The model was trained on two data sets, including a computationally generated one and the experimental one. We have applied this model for retrieving methane concentration from its transmission spectra in the near-infrared (NIR) region. The NSF was implemented through an encoder-decoder structure enhanced by the attention mechanism, improving robustness under noisy conditions. Further, the NCR was employed based on a combination of a principal component analysis (PCA) layer, which focuses the algorithm on the most significant spectral components, and a fully connected layer for solving the nonlinear inversion problem of the determination of methane concentration from the denoised spectra without manual computation. Evaluation results show that the proposed NSF outperforms widely used digital filters as well as the state-of-the-art filtering algorithms, improving the signal-to-noise ratio by 7.3 dB, and the concentrations determined with the NCR are more accurate than those determined with the traditional DAS method. With the AOGAM enhancement, the optimized methane sensor features precision and stability in real-time measurements and achieves the minimum detectable column density of 1.40 ppm·m (1σ). The promising results of the present study demonstrate that the combination of deep learning and absorption spectroscopy provides a more effective, accurate, and stable solution for a gas monitoring system.

The limited underwater observation scenarios pose great challenges to the problem of object recognition from the low-resolution underwater images. This paper proposes a framework to explicitly learn the discriminative features from relatively low resolution images, by resorting to deep learning approaches and super-resolution method. Firstly, the framework tackles the problem of limited discriminative information of low resolution images by a single-image super resolution method. Then state-of-the-art deep learning approaches are employed to learn recognition models for the special underwater fish recognition task. The proposed framework can be effectively implemented for real-time underwater object recognition on autonomous underwater vehicles. To verify the effectiveness of our method, experiments on a public underwater image dataset of fishes are carried out. The results show that our framework achieves promising results for fish recognition on underwater image datasets.

A novel thermal reflow method for the monolithic fabrication of microlens arrays with ultrahigh focal numbers and tunable lens profiles.

Liquid metal has demonstrated an enormous potential for developing soft functional devices and machines. However, current liquid metal enabled machines suffer from several issues, such as the requirement of a liquid environment, generation of weak actuating forces, and insufficient maneuverability. To overcome these restrictions, here, a motor is developed based on the electrical actuation of liquid metal droplets without the need for conventional electromagnets. The approach is distinguished by (1) the encapsulation of electrolyte and multiple liquid metal droplets within an enclosed system, and (2) the creation of stable and continuous torque outside a liquid environment. In addition, a liquid metal electrical brush is introduced to operate the motor with low friction and low wear. The unique driving mechanism endows the motor with several advantages, including low friction, no sparking, low noise, versatile working environment, and being built from soft materials that could offer new opportunities for developing soft robotics.

Pure and Fe-doped MoO₃ nanobelts were synthesized by a facile one-step hydrothermal method and their xylene-sensing properties were investigated.

Centrifugal microfluidic chips offer rapid, highly integrable and simultaneous multi-channel microfluidic control without relying on external pressure pumps and pipelines. Current centrifugal microfluidic chips mainly separate particles of differing density based on the sedimentation method. However, in some biological cells, the volume difference is more notable than the density difference. In particular, cancer cells are generally larger than normal cells. The instability of particle velocity caused by the non-steady flow of the fluid in the centrifugal microfluidic chip leads to low separation purity of particles of different sizes. Thus, we propose herein a centrifugal microfluidic chip with a flow rectifier that transforms the centrifugal non-steady flow into locally steady flow with continuous flow. This chip resolves the problems caused by particle sedimentation in the sample chamber and non-steady flow and greatly improves the recovery ratio and separation purity of target particles. Therefore, it can be used to separate particles of differing size. The experimental results show that the chip can separate an equal-volume mixture of 25 μm and 12 μm polystyrene particles diluted 50 times with a ratio of 1 : 6 and obtain a recovery ratio and separation purity better than 95% for the 25 μm particles. In addition, rare tumour cells are separated from high-concentration white blood cells (ratio 1 : 25) with a recovery ratio of 90.4% ± 2.4% and separation purity of 83.0% ± 3.8%. In conclusion, this chip is promising for sorting of various biological cells and has significant potential for use in biomedical and clinical applications.

Cardiac troponin I (cTnI) is one of the most sensitive and specific markers of myocardial cell injury. In this study, a label-free biosensor that utilizes the birefringence property of liquid crystal (LC) for the detection of cTnI is demonstrated.

CdS nanowires (NWs) with an average diameter of 30 nm were synthesized by a solvothermal method and then Au nanoparticles with a size of 10–25 nm were decorated on the surface of the as-synthesized CdS NWs through a simple deposition process.

Gallium-based room-temperature liquid metals have enormous potential for realizing various applications in electronic devices, heat flow management, and soft actuators. Filling narrow spaces with a liquid metal is of great importance in rapid prototyping and circuit printing. However, it is relatively difficult to stretch or spread liquid metals into desired patterns because of their large surface tension. Here, we propose a method to fabricate a particle-based porous material which can enable the rapid and spontaneous diffusion of liquid metals within the material under a capillary force. Remarkably, such a method can allow liquid metal to diffuse along complex structures and even overcome the effect of gravity despite their large densities. We further demonstrate that the developed method can be utilized for prototyping complex three-dimensional (3D) structures via direct casting and connecting individual parts or by 3D printing. As such, we believe that the presented technique holds great promise for the development of additive manufacturing, rapid prototyping, and soft electronics using liquid metals.

To improve the accuracy of vibration location information of the Φ-OTDR system, a method of optical fiber sensing signal processing based on Compressed Sensing (CS) is proposed in this paper. First, a sensing matrix is constructed by sparse array and observation array, and the mathematical modeling of CS is established. Then the reconstruction algorithm is designed to complete the accurate reconstruction of the vibration signal with a small number of sampling values. Second, the time domain signal composed of all scattered light at the vibration source is analyzed to complete the measurement of vibration frequency. Finally, a heterodyne Phi-OTDR system is built, using PZT to simulate the vibration source. And 36 scattered light information is continuously collected at the frequency of 100 Hz and 500 Hz. The experimental verification of the CS method in this paper is carried out, besides, the signal-to-noise ratio (SNR) is compared with the traditional difference method, Empirical Mode Decomposition (EMD) method, and Variational Mode Decomposition (VMD) method. The experimental results show that the SNR of this method is improved to 40.41 dB and 30.62 dB, the optimal spatial resolution is 9m, and the maximum relative error of frequency measurement is 8.1%. Compared with the results of traditional I/Q demodulation, the frequency information obtained by the two methods is consistent, and there is no obvious deviation from the actual frequency of PZT. While improving the SNR of the system, this method can greatly simplify the signal processing process and improve the positioning accuracy of the system, which has a certain practical application value in the fields of infrastructure monitoring, resource exploration, and vibration detection.

copies per μL. In addition, it was verified that the fluorescence images obtained by this system were clearer than those obtained by a traditional system (using a PTFE spatial PCR microreactor) with two typical dyes and a probe tested-EvaGreen, SYBR Green and FAM.