Low in-band spurious arbitrary waveform generator based on a 1-bit time-wavelength interleaved photonic digital-to-analog conversion.

We proposed an arbitrary waveform generator based on a 1-bit photonic digital-to-analog conversion (PDAC). The system is based on the principle of photonic pulse sampling and time interleaving. High-speed optical pulses are generated and modulated by digital signals and then synthesized in one path. The analog signals are obtained by an optical-to-electrical conversion of the time-interleaved pulses. Due to the 1-bit structure, there are no spurious components in principle. In the experiment, a 1-bit PDAC of 50 GSa/s is realized, and the X-band linear frequency-modulated (LFM) waveform with a bandwidth of 4 GHz is generated, the signal-to-spur-rejection ratio is as high as 50 dB, and the millimeter-wave 64QAM signal is generated, with an EVM of 4.27%.

Optical link encoding based simultaneous correction for crosstalk and nonlinearity in multi-site optical converged networks.

This paper reports a correction scheme to address the problem of modulation nonlinearity and optical switch crosstalk simultaneously for the multi-site optical converged network. Based on the optical link encoding and exclusive-or operation for the received signal, the present spectrum usage can be obtained among the confusion with interferences containing the modulated harmonic distortion and the crosstalk leakage from other sites. The proof-of-concept experiment is performed on various interferences involving the linear frequency modulated (LFM) waveform and the quadrature amplitude modulation (QAM) signal. The corrected spectrum has realized an improved signal-to-noise ratio (SNR) of over 22 dB compared to the uncorrected counterpart. Furthermore, it consistently maintains a superior SNR, surpassing the single impairment-corrected scenario by an impressive margin of at least 15.9 dB. Besides, the implementation would not introduce additional noise, making the corrected result agree well with the ideal case. Without any increase in hardware complexity, the presented scheme provides an effective technique to meet the correction challenge of large-scale and complicated optical networks with multiple optoelectronic devices.

Dual-comb generation with counter-propagating self-injection-locked solitons.

Microresonator-based optical frequency combs have been greatly developed in the last decade and have shown great potential for many applications. A dual-comb scheme is usually required for lidar ranging, spectroscopy, spectrometer and microwave photonic channelizer. However, dual-comb generation with microresonators would require doubled hardware resources and more complex feedback control. Here we propose a novel scheme for dual-comb generation with a single laser diode self-injection locked to a single microresonator. The output of the laser diode is split and pumps the microresonator in clockwise and counter-clockwise directions. The scheme is investigated intensely through numerical simulations based on a set of coupled Lugiato-Lefever equations. Turnkey counter-propagating single soliton generation and repetition rate tuning are demonstrated.

Bipolar segmented photonic digital-to-analog converter with wavelength multiplexing and balanced detection.

Photonic digital-to-analog converters (PDACs) with segmented design can achieve better performance than conventional binary PDACs in terms of effective number of bits (ENOB) and spurious-free dynamic range (SFDR). However, segmented PDACs generally require an increased amount of laser sources. Here, a structure of bipolar segmented PDAC based on laser wavelength multiplexing and balanced detection is proposed. The number of lasers is reduced by a half compared to a conventional segmented design with the same nominal resolution. Moreover, ideal bipolar output with no direct-current bias can be achieved with balanced detection. A proof-of-concept setup with a sampling rate of 10 GSa/s is constructed by employing only four lasers. The PDAC consists of four unary weighted channels and four ternary weighted channels. The measured ENOB and SFDR are 4.6 bits and 37.0 dBc, respectively. Generation of high-quality linear frequency-modulated radar waveforms with an instantaneous bandwidth of 4 GHz is also demonstrated.

Result-oriented lumped error correction for photonic-assisted broadband phased array processors.

Imperfect optoelectronic devices deteriorate the performance of microwave photonic (MWP) systems and then hinder further practical application. This paper proposes a result-oriented lumped error correction to address the problem in the photonic-assisted broadband phased array. Herein, we focus on the evolution of the ultimate output resulting from various errors due to the nonideality of components. By establishing the static calibration base set (CBS) with tangent line approximation, the correction procedure is simplified, and the output degradation is greatly improved. Experimental results show the effective number of bits (ENOB) at the final output has been enhanced from 2.5 to 6.1. Further, double objectives optimization and imaging correction are demonstrated experimentally. The range resolution has been boosted from 3.9 cm to 2.4 cm, and the quality of the inverse synthetic aperture radar (ISAR) images is improved using the proposed method.

Random code shifting based ultra-wideband photonic compressive receiver with image-frequency distinction.

We propose an ultra-wideband photonic compressive receiver based on random codes shifting with image-frequency distinction. By shifting the center frequencies of two random codes in large frequency range, the receiving bandwidth is flexibly expanded. Simultaneously, the center frequencies of two random codes are slightly different. This difference is used to distinguish the "fixed" true RF signal from the differently located image-frequency signal. Based on this idea, our system solves the problem of limited receiving bandwidth of existing photonic compressive receivers. In the experiments, with two channels of only 780-MHz outputs, the sensing capability in the range of 11-41 GHz has been demonstrated. A multi-tone spectrum and a sparse radar-communication spectrum, composed of a linear frequency modulated (LFM) signal, a quadrature phase-shift keying (QPSK) signal and a single-tone signal, are both recovered.

Weighted Gene Co-Expression Network Analysis of Oxymatrine in Psoriasis Treatment.

Purpose: Psoriasis is a common, chronic, inflammatory, recurrent, immune-mediated skin disease. Oxymatrine is effective for treating moderate and severe psoriasis. Here, transcriptional changes in skin lesions before and after oxymatrine treatment of patients with psoriasis were identified using full-length transcriptome analysis and then compared with those of normal skin tissues. Patients and Methods: Co-expression modules were constructed by combining the psoriasis area and severity index (PASI) score with weighted gene co-expression network analysis to explore the action mechanism of oxymatrine in improving clinical PASI. The expression of selected genes was verified using immunohistochemistry, quantitative real-time PCR, and Western blotting. Results: Kyoto Encyclopedia of Gene and Genome pathway analysis revealed that oxymatrine treatment reversed the abnormal pathways, with an improvement in lesions and a reduction in PASI scores. Gene Ontology (GO) analysis revealed that oxymatrine treatment led to altered GO terms being regulated with a decrease in the PASI score in patients. Therefore, oxymatrine treatment may improve the skin barrier, differentiation of keratinocytes, and alleviate abnormality of organelles such as desmosomes. Protein-protein interaction network interaction analysis revealed that the top five hub genes among many interrelated genes were CNFN, S100A8, SPRR2A, SPRR2D, and SPRR2E, associated with the epidermal differentiation complex (EDC). EDC regulates keratinocyte differentiation. This result indicates that oxymatrine treatment can restore keratinocyte differentiation by regulating the expression of EDC-related genes. Conclusion: Oxymatrine can improve erythema, scales, and other clinical symptoms of patients with psoriasis by regulating EDC-related genes and multiple pathways, thereby promoting the repair of epithelial tissue and maintaining the dynamic balance of skin keratosis.

Dispersion-less Kerr solitons in spectrally confined optical cavities.

Solitons are self-reinforcing localized wave packets that manifest in the major areas of nonlinear science, from optics to biology and Bose-Einstein condensates. Recently, optically driven dissipative solitons have attracted great attention for the implementation of the chip-scale frequency combs that are decisive for communications, spectroscopy, neural computing, and quantum information processing. In the current understanding, the generation of temporal solitons involves the chromatic dispersion as a key enabling physical effect, acting either globally or locally on the cavity dynamics in a decisive way. Here, we report on a novel class of solitons, both theoretically and experimentally, which builds up in spectrally confined optical cavities when dispersion is practically absent, both globally and locally. Precisely, the interplay between the Kerr nonlinearity and spectral filtering results in an infinite hierarchy of eigenfunctions which, combined with optical gain, allow for the generation of stable dispersion-less dissipative solitons in a previously unexplored regime. When the filter order tends to infinity, we find an unexpected link between dissipative and conservative solitons, in the form of Nyquist-pulse-like solitons endowed with an ultra-flat spectrum. In contrast to the conventional dispersion-enabled nonlinear Schrödinger solitons, these dispersion-less Nyquist solitons build on a fully confined spectrum and their energy scaling is not constrained by the pulse duration. Dispersion-less soliton molecules and their deterministic transitioning to single solitons are also evidenced. These findings broaden the fundamental scope of the dissipative soliton paradigm and open new avenues for generating soliton pulses and frequency combs endowed with unprecedented temporal and spectral features.

Broadband linear frequency-modulated waveform generation based on optical frequency comb assisted spectrum stitching.

In this paper, we propose and demonstrate a novel spectrum stitching method for broadband linear frequency-modulated waveform (LFMW) generation. An optical frequency comb (OFC) is modulated by a narrowband LFMW whose bandwidth matches the free spectral range of the OFC. Optical injection locking is employed in extracting one broadband frequency sweeping component from the modulated OFC. In this way, seamless spectrum stitching is realized and a broadband LFMW with a multi-fold time-bandwidth product (TBWP) is obtained. Our scheme has a simple structure, which requires only a single OFC, a modulation module and a baseband waveform generator. An LFMW as broad as 20 GHz is generated from a baseband LFMW with 2GHz bandwidth experimentally. The TBWP is 100 times as large as that of the baseband LFMW. Moreover, the power fluctuation and the phase jumps are both eliminated, ensuring an excellent pulse compression performance. Benefiting from the injection locking technique, the linearity reaches 2.0 × 10-6. The central frequency tuning ability of our scheme is also demonstrated.

Broadband photonic beam processor for simultaneous beamforming and high-resolution imaging.

In this paper, a broadband photonic beam processor is presented for the all-optical multifunction integrated receiver. By implementing echo signals with optical beam multi-domain processing based on space-to-time mapping and time-to-frequency mapping, the non-mechanical control of expected beam pointing is enabled while the target within the beam can be imaged simultaneously. A proof-of-concept experiment with a 4-element phased array is performed in Ka band. The beam pointing is set to be 0° and 12.5°, where two-dimensional images of moving targets inside the beam region are obtained, respectively. The suppression ratio to the beam region outside is measured to be 26.8 dB. And the range and cross-range imaging resolution is 0.042 m × 0.051 m. A comparison with a cascade mode of single-function microwave photonic modules shows that the multifunction integrated photonic beam processor has reduced the system loss by 32.4 dB. The proposed beam processor enables multi-element broadband phased arrays with less complexity and power consumption.

Photonic-assisted space-frequency two-dimensional compressive radar receiver for high-resolution and wide-range detection.

Existing photonic compressive receivers have the problem of resolution deterioration when applied in wide-range radar detection. In this study, we propose a photonic-assisted space-frequency two-dimensional (2D) compressive radar receiver capable of achieving high-resolution detection in wide-range scenarios. For the space dimension, the compression process is realized by employing a spatially adaptive photonic projection basis, which guarantees complete mapping of arbitrarily delayed echoes-the key to high-resolution wide-range detection. For the frequency dimension, photonic compressive sensing is employed to further compress the bandwidth of the projected sparse signal. Therefore, the proposed system can achieve wide-range radar detection without resolution deterioration with compressed output. Herein, with two channels of 630 MHz outputs, high-resolution distance detection within a range of 21 km with a resolution of up to 2.3 cm is achieved. Moreover, inverse synthetic aperture radar (ISAR) imaging of two sets of four-point turntables distributed within the range of 21 km with a resolution of 2.3 cm × 5.7 cm is realized. The proposed photonic-assisted 2D compressive radar receiver is a viable solution to overcome the tradeoff between detection resolution and range of existing photonic compressive receivers, which indicates a path for the further development of high-resolution wide-range radar detection.

Noise analysis of photonic digital-to-analog converters.

Photonic digital-to-analog converters (PDACs) have a broad application prospect due to the ability to overcome the non-idealities in electronic circuits. PDACs are usually implemented by quantizing and summing the optical intensities of multiple lasers. The relative intensity noise of laser sources plays a critical role in determining the signal-to-noise ratio (SNR) and effective number of bits (ENOB). We present a detailed noise analysis for PDACs. Both the traditional binary-weighted structure and the recently proposed segmented-weighted structure are investigated. The results show that laser noise imposes a fundamental limit to the maximum SNR and ENOB that can be achieved in binary-weighted PDACs, while segmented PDACs can break this limitation and have a continuously increasing SNR with the quantization bit number (QBN). A novel configuration based on laser multiplexing and balanced detection, to the best of our knowledge, is also proposed and analyzed to increase the number of bits when the number of lasers is limited. Numerical simulations are performed to evaluate the SNR evolution with the QBN in different types of PDACs. The results are in good agreement with the theoretical analysis. Our analysis provides useful insights and can be important guidance for implementing high-performance PDACs.

Tunable K/W-band OFDM integrated radar and communication system based on optoelectronic oscillator for intelligent transportation.

In this paper, we proposed a tunable K/W-band OFDM integrated radar and communication system based on Optoelectronic Oscillator (OEO) for intelligent transportation. All-optical signal processing including amplitude asymmetric filtering and quadratic phase manipulating is applied in OEO to achieve a high-frequency and tunable self-excited oscillation, which supports the K/W-band OFDM signal generation. Its product of maximum detection range and communication capacity is cB/4Δf (m·Gbaud), where c is light speed and Δf is subcarrier spacing of OFDM. A proof-of-concept experiment is carried out in K-band with bandwidth B = 2 GHz and W-band with bandwidth B = 10 GHz. The range resolution ΔR, detection range Rmax and communication capacity C of 0.075 m, 75 m, 12.8 Gbps, and 0.015 m, 300 m, 32 Gbps are experimentally demonstrated in K/W-band respectively.

Photonic time-frequency filter based on the software-defined time-frequency prism.

We propose a microwave photonic 2D time-frequency filter based on a photonic time-frequency prism. A time-varying frequency response is realized by deviating the passband of a 1D ordinary frequency filter in the 2D time-frequency plane. The proposed time-frequency filter features highly reconfigurable frequency-sweeping speed and bandwidth, thanks to the software-defined photonic time-frequency prism. With the proposed technique, separation of multiple linear and nonlinear chirp signals with overlapped spectra is experimentally demonstrated.

Full-Length Transcriptome Sequencing Analysis of Differentially Expressed Genes and Pathways After Treatment of Psoriasis With Oxymatrine.

Psoriasis is a recurrent chronic inflammatory skin disease. Unlike many of the latest psoriasis treatments that only confer limited curative effects and have certain side effects, oxymatrine effectively improves severe plaque psoriasis with mild adverse reactions. Here, we explored the genes and pathways underlying the effects of oxymatrine on psoriasis. Briefly, patients with severe plaque psoriasis were treated with oxymatrine and their lesioned skin samples were sequenced by full-length transcriptomics. Next, the differentially expressed genes (DEGs) in psoriatic lesions were identified and compared in oxymatrine-treated patients and healthy controls, their genes were functionally annotated, and protein-protein interaction network analysis and immunohistochemistry were performed. Both Psoriasis Area and Severity Index (PASI) and Body Surface Area (BSA) scores were recovered significantly from all 16 patients (all p < 0.001). The number of DEGs in patients before and after oxymatrine treatment was 4232, and 4105 DEGs were found between the psoriasis group (before oxymatrine treatment) and the normal control group [p < 0.01, |log2 fold change, (FC)| >1.5]. While most of the DEGs recovered significantly after oxymatrine treatment, only 650 DEGs were observed between the psoriasis group (after oxymatrine treatment) and the normal control group (p < 0.01, |log2FC|> 1.5). Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis showed that 64 pathways were significantly activated after oxymatrine treatment (p < 0.05). Only 12 pathways were statistically significant between after oxymatrine treatment and the normal control group (p < 0 .05). Among all the restored pathways, the improvement of the IL-17 signaling pathway was the most significant (p = 1.18E-06). Gene loci of oxymatrine action was assessed by protein interaction analysis on 205 DEGs that were co-expressed in 5 patients before and after oxymatrine treatment (p < 0.05, FC > 1.5). After oxymatrine treatment, the expression of two mitosis-related genes namely, cyclin dependent kinase 1 (CDK1) and cyclin B1 (CCNB1), that affect cell proliferation recovered significantly. In light of these results, we conclude that oxymatrine likely alters the abnormal expression of some genes and pathways in psoriasis patients. Multipathway and multitarget therapy can greatly ameliorate abnormalities in genes and pathways and effectively treat psoriasis. Importantly, among the DEGs, the proliferation-related genes, such as CDK1 and CCNB1, are likely important targets for treating psoriasis by oxymatrine. We believe that these findings may lead to a new treatment strategy for psoriasis.

Reconfigurable radar signal generator based on phase-quantized photonic digital-to-analog conversion.

A novel, to the best of our knowledge, scheme for reconfigurable radar signal generation is proposed based on the principle of photonic phase-quantized digital-to-analog conversion. Multi-level digital phase modulation with different modulation depths is combined to convert multi-channel digital data to the phase of an optical carrier. Frequency-modulated or phase-modulated radar signals are generated by beating the phase-synthesized optical carrier with a coherent reference light. The proposed radar signal generator features a simple structure, highly reconfigurable modulation format, and flexibly tunable frequency. A 3-bit photonic phase-quantized digital-to-analog converter with a 10-GSa/s sampling rate is constructed experimentally. The generation of linear frequency-modulated, nonlinear frequency-modulated, frequency-stepped, frequency-hopping, binary phase-coded, and polyphase-coded waveforms is demonstrated.

Photonics-assisted joint radar and communication system based on an optoelectronic oscillator.

This paper reports a photonics-assisted joint radar and communication system for intelligent transportation based on an optoelectronic oscillator (OEO). By manipulating the optical multi-dimensional processing module inserted in the OEO loop, two phase-orthogonal integrated signals are generated with low phase noise and high frequency, as the communication data loaded on the overall polarity of radar pulses. At the receiver, single-channel matched filtering and two-channel IQ data fusion are utilized to retrieve the communication data and the range profile, without any performance deterioration of either. In this way, the contradiction between the performance of two functions existing in the previous scheme is solved, and the integrated performance can be further optimized as bandwidth increases. A proof-of-concept experiment with 2 GHz bandwidth at 24 GHz, which is the operating frequency of short-range automotive radar, is carried out to verify that the proposed system can meet the requirement of the intelligent vehicles in the short-range scene. A communication capacity of 335.6 Mbps, a range profile with a resolution of 0.075 m, and a peak-to-sidelobe ratio (PSLR) of 20 dB is demonstrated under the experimental condition. The error vector magnitude (EVM) curve and constellation diagrams versus received power are measured, where the EVM is -8 and -14.5 dB corresponding to a power of -14 and 6 dBm, respectively.

High-resolution imaging of a high-speed target based on a reconfigurable photonic fractional Fourier transformer.

The previously reported photonics-based radar working with a large bandwidth has the advantages of realizing high-resolution imaging of targets with low velocity. However, the high velocity of a target will introduce Doppler dispersion to the echo signals, which severely deteriorates the imaging resolution. This problem becomes more noticeable as the bandwidth increases. In this paper, we propose a radar receiver based on a reconfigurable photonic fractional Fourier transformer (PFrFTer). The order of the PFrFTer can be reconstructed flexibly by changing the optical transform kernel. When the transform order matches the velocity of the target, the chirp echo signals behave as narrow impulses in the fractional Fourier domain, showing the range information with a high resolution. In the experiment, a PFrFTer is established and applied to process the echo signals with a bandwidth of 12 GHz. A lossless range resolution of 1.4 cm is obtained in range profiles and inverse synthetic aperture radar imaging for high-speed targets. This range resolution is much higher than that in the classical optical de-chirping receiver. These results demonstrate the PFrFTer is immune to the Doppler dispersion effect and is excellent for high-resolution imaging of high-speed target. The introduced technique would be of practical interest in the detection and recognition of targets.

Life cycle water footprint analysis for second-generation biobutanol.

Water is essential in conversion of crop to bioenergy. Therefore, it is important to carefully evaluate the impact of bioenergy technology on water source. Life cycle water footprints of biobutanol from wheat straw, corn grain and corn stover are analyzed in this study according to the characteristics of crop growing and climate conditions. The results show that life cycle water footprints of biobutanol from wheat straw, corn grain and corn stover are 271, 108 and 240 L H2O/MJ biobutanol, respectively. Life cycle water footprints of the crop production stage for wheat straw, corn grain and corn stover are 269.89, 107.84 and 238.95 L H2O/MJ biobutanol, respectively. Owing to the use of fertilizer in the crop production stage, gray water footprint of wheat straw, corn grain and corn stover accounts for 91.08%, 86.65% and 86.40% of the life cycle water footprint, respectively.

Research progress of catalysts for synthesis of low-carbon alcohols from synthesis gas.

In recent years, the application value of low-carbon alcohols (C1-C6 alcohols) in the fuel, chemical, environmental protection and other fields has become increasingly prominent. Catalytic conversion of synthesis gas to low-carbon alcohol is one of the important ways to realize the industrial production of low-carbon alcohol. Lack of high-performance catalysts is the main reason that restricts the industrial development of producing low-carbon alcohols from synthesis gas. The construction of a dual active-center catalyst with high activity and stability, and the study of its function and catalytic mechanism have become significantly important. In this paper, the characteristics of the reaction process of syngas to low-carbon alcohols, and the catalytic mechanism and preparation methods of different catalyst systems were reviewed, which provide the basis for further research on high performance catalysts.