Coaxial transceiving LiDAR based on a silicon photonic optical phased array.

A high performance optical phased array (OPA) combined with frequency-modulated continuous-wave (FMCW) technology is essential for coherent all-solid-state light detection and ranging (LiDAR). In this work, we propose and experimentally demonstrate a coaxial transceiver based on a single OPA for a LiDAR system, which releases the off-chip circulator and collimator. The proposed scheme is demonstrated on the commonly used silicon-on-insulator (SOI) platform. For realizing the long optical grating antenna with only one-step etching, the bound state in the continuum is harnessed to simplify the fabrication process and ease the fabrication precision. Experimental results indicate that the OPA is with 0.076° vertical beam divergence under a 1.5 mm-long grating antenna. The measured field of view (FOV) is 40° × 8° without grating lobes under a wavelength band of 60 nm. The coaxial transceiver of the single OPA is also demonstrated with the FMCW method for ranging measurement at different angles.

An acid-chromic luminescent lanthanide metallogel for time-dependent information encryption and anti-counterfeiting.

Luminescent materials with dynamic color transformation demonstrate significant potential in advanced information encryption and anti-counterfeiting. In this study, we designed multi-color luminescent lanthanide metallogels featuring time-dependent color transformation. These materials are based on Förster resonance energy transfer (FRET) platforms, facilitating cascade energy transfer from the ligand 4,4',4''-[1,3,5-benzenetriyltris (carbonylimino)]trisbenzoic acid (H3L) to Tb3+ ions and subsequently to Sulforhodamine 101. The emission color of the gels can be readily adjusted by the introduction of HCl, transitioning from initial green, yellow, light red, and red hues to blue, violet, pink, and deep red, respectively. Importantly, the color change in these gels is time-dependent, controlled by the hydrolysis time of glucono-δ-lactone, which modulates the luminescence intensity of H3L, Tb3+, and Sulforhodamine 101. Exploiting these characteristics, we developed methods for information encryption utilizing 3D color codes and anti-counterfeiting flower patterns. These patterns undergo time-dependent transformations, generating a series of 3D codes and flower patterns that can only be recognized in a predetermined manner. These findings highlight the promising application of lanthanide metallogels in advanced information protection strategies.

Polarization multiplexing silicon photonic optical phased array with a wide scanning range.

We propose and experimentally demonstrate a polarization multiplexed silicon optical phased array (OPA) with a wide scanning range. The two polarization states share the same power splitter tree and the phase shifter array. A polarization switch is introduced in front of the power splitter tree to manipulate the polarization state of the light in OPA. Through a polarization splitter-rotator (PSR), the light of two polarization states propagates into the superlattice grating antenna array. The wavelength tuning efficiency could be doubled by optimizing the parameters of the waveguide grating. We demonstrate the scheme on the commonly used 220 nm silicon-on-insulator (SOI) platform. Experimental results indicate that the 24.8° vertical scanning range could be realized with a high wavelength tuning efficiency of 0.31°/nm. The measured field of view (FOV) is 24.8 × 60°.

Metabolic Responses to Manganese Toxicity in Soybean Roots and Leaves.

Soybean is one of the most crucial beans in the world. Although Mn (manganese) is a kind of important nutritive element helpful to plant growth and health, excess Mn is harmful to crops. Nevertheless, the effect of Mn toxicity on soybean roots and leaves metabolism is still not clear. To explore this, water culture experiments were conducted on the development, activity of enzyme, and metabolic process of soybeans under varying levels of Mn treatment (5 and 100 µM). Compared with the control, the soybeans under Mn stress showed inhibited growth and development. Moreover, the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and the soluble protein content in leaves and roots of soybean were all increased. However, soluble sugar and proline contents in soybean roots and leaves showed the opposite trend. In addition, the Mg (magnesium) and Fe (iron) ion contents in soybean leaves significantly decreased, and the Mn ion content greatly increased. In roots, the Mn and Fe ion content increased, whereas the Mg ion content decreased. Furthermore, the metabolomic analysis based on nontargeted liquid chromatography-mass spectrometry identified 136 and 164 differential metabolites (DMs) that responded to Mn toxicity in roots and leaves of soybean, respectively. These DMs might participate in five different primary metabolic pathways in soybean leaves and roots, suggesting that soybean leaves and roots demonstrate different kinds of reactions in response to Mn toxicity. These findings indicate that Mn toxicity will result in enzymes activity being changed and the metabolic pathway being seriously affected, hence inhibiting the development of soybean.

Low-loss and power-efficient phase shifter based on an optimized multimode spiral silicon waveguide.

Low-loss and energy-efficient phase shifters are an effective tool to reduce the power consumption of large-scale photonic integrated circuits. In this work, a low-loss and power-efficient thermo-optic phase shifter has been demonstrated on the silicon-on-insulator platform. The multimode spiral waveguide is optimized to obtain lower power consumption and low cross talk. The waveguide width is beyond the single-mode region in consideration of low propagation loss. The optimized ultra-low loss 180° Bezier bends are used to further reduce the bending loss. The experimental results show that the excess loss of the phase shifter is only 0.36 dB at 1550-nm wavelength and the power consumption is 4.87 mW/π.

Transcriptome Sequencing Analysis of Root in Soybean Responding to Mn Poisoning.

Manganese (Mn) is among one of the essential trace elements for normal plant development; however, excessive Mn can cause plant growth and development to be hindered. Nevertheless, the regulatory mechanisms of plant root response to Mn poisoning remain unclear. In the present study, results revealed that the root growth was inhibited when exposed to Mn poisoning. Physiological results showed that the antioxidase enzyme activities (peroxidase, superoxide dismutase, ascorbate peroxidase, and catalase) and the proline, malondialdehyde, and soluble sugar contents increased significantly under Mn toxicity stress (100 µM Mn), whereas the soluble protein and four hormones' (indolebutyric acid, abscisic acid, indoleacetic acid, and gibberellic acid 3) contents decreased significantly. In addition, the Mn, Fe, Na, Al, and Se contents in the roots increased significantly, whereas those of Mg, Zn, and K decreased significantly. Furthermore, RNA sequencing (RNA-seq) analysis was used to test the differentially expressed genes (DEGs) of soybean root under Mn poisoning. The results found 45,274 genes in soybean root and 1430 DEGs under Mn concentrations of 5 (normal) and 100 (toxicity) µM. Among these DEGs, 572 were upregulated and 858 were downregulated, indicating that soybean roots may initiate complex molecular regulatory mechanisms on Mn poisoning stress. The results of quantitative RT-PCR indicated that many DEGs were upregulated or downregulated markedly in the roots, suggesting that the regulation of DEGs may be complex. Therefore, the regulatory mechanism of soybean root on Mn toxicity stress is complicated. Present results lay the foundation for further study on the molecular regulation mechanism of function genes involved in regulating Mn tolerance traits in soybean roots.

Manipulating leaky mode in silicon waveguides harnessing bound states in the continuum.

A low-loss ridge waveguide is proposed and demonstrated with a novel, to the best of our knowledge, bound state in the continuum (BIC)-based structure on the silicon-on-insulator (SOI) platform. The presented waveguide is designed appropriately to suppress TM-mode leakage, and has a theoretically low propagation loss of ∼0.0027 dB/cm at 1550 nm. In the wavelength range from 1530 nm to 1600 nm, the 2-mm-long waveguide can achieve an average loss suppression of ∼30 dB in the experiment. Such a novel ridge waveguide structure can also be introduced into narrowband optical filters. The fabricated Bragg grating filter working at the TM mode can achieve a narrow bandwidth of ∼1 nm and an extinction ratio of ∼14.8 dB.

Grating lobe-free silicon optical phased array with periodically bending modulation of dense antennas.

A grating lobe-free silicon optical phased array with large field of view is demonstrated. Antennas with periodically bending modulation are spaced at half wavelength or less. The experimental results show that the crosstalk between adjacent waveguides is negligible at 1550 nm wavelength. Additionally, to reduce the optical reflection caused by the sudden change of refractive index at the output antenna of the phased array, tapered antennas are added to the output end face so that more light will be coupled into the free space. The fabricated optical phased array shows a field of view of 120° without any grating lobes.

Ultra-broadband dual-polarization and arbitrary ratio power splitters based on Bezier curve optimized multimode interference.

We propose and demonstrate two types of 1 × 2 power splitters based on multimode interference (MMI), which are ultra-compact, fabrication friendly, and low loss. The contours of MMI and output tapers are optimized with Bezier curves, which can implement arbitrary ratio power splitters (ARPSs) and ultra-broadband dual-polarization power splitters (UDPSs). For ARPSs, the experimental results show that arbitrary power splitting ratios can be obtained with an average excess loss (EL) of 0.17 dB at 1550 nm for fundamental TE polarization. For UDPSs, the experimental results show that the ELs for fundamental TE and TM polarization are less than 0.63 dB and 0.44 dB over a large bandwidth of 415 nm (1260-1675 nm). The footprints of the proposed devices are less than 10 µm × 2.5 µm (without input straight waveguide) with large fabrication tolerance.

Comparative Transcriptome Analysis Reveals Complex Physiological Response and Gene Regulation in Peanut Roots and Leaves under Manganese Toxicity Stress.

Excess Manganese (Mn) is toxic to plants and reduces crop production. Although physiological and molecular pathways may drive plant responses to Mn toxicity, few studies have evaluated Mn tolerance capacity in roots and leaves. As a result, the processes behind Mn tolerance in various plant tissue or organ are unclear. The reactivity of peanut (Arachis hypogaea) to Mn toxicity stress was examined in this study. Mn oxidation spots developed on peanut leaves, and the root growth was inhibited under Mn toxicity stress. The physiological results revealed that under Mn toxicity stress, the activities of antioxidases and the content of proline in roots and leaves were greatly elevated, whereas the content of soluble protein decreased. In addition, manganese and iron ion content in roots and leaves increased significantly, but magnesium ion content decreased drastically. The differentially expressed genes (DEGs) in peanut roots and leaves in response to Mn toxicity were subsequently identified using genome-wide transcriptome analysis. Transcriptomic profiling results showed that 731 and 4589 DEGs were discovered individually in roots and leaves, respectively. Furthermore, only 310 DEGs were frequently adjusted and controlled in peanut roots and leaves, indicating peanut roots and leaves exhibited various toxicity responses to Mn. The results of qRT-PCR suggested that the gene expression of many DEGs in roots and leaves was inconsistent, indicating a more complex regulation of DEGs. Therefore, different regulatory mechanisms are present in peanut roots and leaves in response to Mn toxicity stress. The findings of this study can serve as a starting point for further research into the molecular mechanism of important functional genes in peanut roots and leaves that regulate peanut tolerance to Mn poisoning.

Silicon optical phased array with calibration-free phase shifters.

Optical phased array (OPA) based on silicon photonics is considered as a promising candidate for realizing solid-state beam steering. However, the high refractive index contrast of the silicon waveguides leads to conventional silicon based OPA suffering from large random phase errors, which require complex post-processing such as time-consuming phase calibration. We propose and demonstrate a calibration-free silicon OPA with optimized optical waveguides width as well as the compact 90° waveguide bends beyond the single mode regime. By using grouped cascaded phase shifters, it is able to reduce the number of control electrodes from N to log2(N). A 16-channel OPA has been demonstrated with continuous beam steering over the field of view controlled by only four control voltages without any calibration.

All-Solid-State Beam Steering via Integrated Optical Phased Array Technology.

Light detection and ranging (LiDAR), combining traditional radar technology with modern laser technology, has much potential for applications in navigation, mapping, and so on. Benefiting from the superior performance, an all-solid-state beam steering realized by integrated optical phased array (OPA) is one of the key components in the LiDAR system. In this review, we first introduce the basic principle of OPA for beam steering. Then, we briefly review the detailed advances of different solutions such as micro-electromechanical system OPA, liquid crystal OPA, and metasurface OPA, where our main focus was on the recent progress of OPA in photonic integrated chips. Finally, we summarize the different solutions and discuss the challenges and perspectives of all-solid-state beam steering for LiDAR.

Polarization tunable color filters based on all-dielectric metasurfaces on a flexible substrate.

Structural color filters based on all-dielectric materials are considered to be promising alternatives to metal nanostructures due to significant advantages, such as high-quality resonance effects and low losses of Ohmic effects. We demonstrate a polarization tunable color filter based on all-dielectric metasurfaces, which is based on the arrays of asymmetric monocrystalline silicon nanoblocks on the flexible substrate. By adjusting the physical dimensions of nanoblocks, the filter can exhibit a variety of bright transmission colors. Furthermore, the designed dielectric metasurfaces are sensitive to the linear polarization direction of the incident light, thus a wide range of color images can be created by changing the polarization angles. All of the color filter including the dielectric silicon nanoblocks, the overcladding, and the flexible substrate can be delaminated from the handler substrates and the optical property is reconfigurable, which will find applications in the functional color display, polarization detection and imaging, and secured optical tag.

On-chip simultaneous sensing of humidity and temperature with a dual-polarization silicon microring resonator.

It is still challenging to realize an on-chip optical sensor that can detect humidity and temperature at the same time. In this paper, we demonstrate a silicon-based dual-polarization micro-ring resonator (MRR) with a polyvinyl-alcohol (PVA) upper-cladding, which enables the simultaneous measurement of humidity and temperature. Due to the significant polarization-dependence of the silicon-on-insulator (SOI) nanophotonic waveguide, the transverse electric (TE) and transverse magnetic (TM) polarization modes have quite different sensitivities towards the changes of ambient relative humidity (RH) and temperature. Sensitivity, resolution, stability and cross-sensitivity are analyzed for the present dual-parameter sensor. The RH and temperature response sensitivity are measured to be 97.9 pm/%RH, 325.1 pm/%RH, 69.0 pm/°C and 30.6 pm/°C for TE and TM polarizations, respectively. To the best of our knowledge, it is the first on-chip optical sensor enabling the simultaneous measurement of RH and temperature.

Toward a Brain-Inspired System: Deep Recurrent Reinforcement Learning for a Simulated Self-Driving Agent.

An effective way to achieve intelligence is to simulate various intelligent behaviors in the human brain. In recent years, bio-inspired learning methods have emerged, and they are different from the classical mathematical programming principle. From the perspective of brain inspiration, reinforcement learning has gained additional interest in solving decision-making tasks as increasing neuroscientific research demonstrates that significant links exist between reinforcement learning and specific neural substrates. Because of the tremendous research that focuses on human brains and reinforcement learning, scientists have investigated how robots can autonomously tackle complex tasks in the form of making a self-driving agent control in a human-like way. In this study, we propose an end-to-end architecture using novel deep-Q-network architecture in conjunction with a recurrence to resolve the problem in the field of simulated self-driving. The main contribution of this study is that we trained the driving agent using a brain-inspired trial-and-error technique, which was in line with the real world situation. Besides, there are three innovations in the proposed learning network: raw screen outputs are the only information which the driving agent can rely on, a weighted layer that enhances the differences of the lengthy episode, and a modified replay mechanism that overcomes the problem of sparsity and accelerates learning. The proposed network was trained and tested under a third-party OpenAI Gym environment. After training for several episodes, the resulting driving agent performed advanced behaviors in the given scene. We hope that in the future, the proposed brain-inspired learning system would inspire practicable self-driving control solutions.

Polarization-insensitive silicon waveguide crossing based on multimode interference couplers.

A polarization-insensitive waveguide crossing based on multimode interference (MMI) couplers is proposed and demonstrated on a silicon-on-insulator (SOI) platform. By utilizing two orthogonal MMIs, the footprint of the device is about 23 µm×23 µm. The proposed device, easily fabricated with only one fully etched step, is characterized with low insertion losses and low crosstalks for both transverse-electric and transverse-magnetic polarizations from 1520 to 1610 nm bands.

Compact high-efficiency perfectly-vertical grating coupler on silicon at O-band.

A compact, high-efficiency grating coupler is demonstrated for interfacing a silicon waveguide and a perfectly-vertical fiber at O-band. The grating lies on a tilted silicon membrane for minimizing the reflections. Circular grating lines are adopted to shorten the overall device length to about 60µm. 57% peak coupling efficiency and >28nm 1-dB coupling bandwidth are obtained experimentally. Back reflections of 1% to the silicon waveguide and the single mode fiber are theoretically estimated. The processing flow to realize the proposed structure is discussed in detail. The fabrication control over the tilted angle of the silicon membrane is investigated. The approach by applying an oxide cladding to improve the stability of the membrane is also introduced. The present grating coupler is compatible to common fabrication processes for silicon photonic chips.

High sensitivity temperature sensor based on cascaded silicon photonic crystal nanobeam cavities.

We present the design, fabrication and characterization of a high sensitivity temperature sensor based on cascaded silicon photonic crystal (PhC) nanobeam cavities. Two PhC nanobeam cavities, one with stack width modulated structure and the other one with parabolic-beam structure are utilized to increase the sensitivity. Most of the light is designed to be confined in the cladding and the core for these two cavities, respectively. Due to the positive thermo-optic (TO) coefficient of silicon and the negative TO coefficient of SU-8 cladding, the wavelength responses red shift for parabolic-beam cavity and blue shift for stack width modulated cavity as the increase of the ambient temperature, respectively. Thus, the sensitivity for the temperature sensor can be improved greatly since the difference in resonant wavelength shifts is detected for the temperature sensing. The experimental results show that the sensitivity of the temperature sensor is about 162.9 pm/°C, which is almost twice as high as that of the conventional silicon based resonator sensors.