Integrated lithium niobate microwave photonic processing engine.

Integrated microwave photonics (MWP) is an intriguing technology for the generation, transmission and manipulation of microwave signals in chip-scale optical systems1,2. In particular, ultrafast processing of analogue signals in the optical domain with high fidelity and low latency could enable a variety of applications such as MWP filters3-5, microwave signal processing6-9 and image recognition10,11. An ideal integrated MWP processing platform should have both an efficient and high-speed electro-optic modulation block to faithfully perform microwave-optic conversion at low power and also a low-loss functional photonic network to implement various signal-processing tasks. Moreover, large-scale, low-cost manufacturability is required to monolithically integrate the two building blocks on the same chip. Here we demonstrate such an integrated MWP processing engine based on a 4 inch wafer-scale thin-film lithium niobate platform. It can perform multipurpose tasks with processing bandwidths of up to 67 GHz at complementary metal-oxide-semiconductor (CMOS)-compatible voltages. We achieve ultrafast analogue computation, namely temporal integration and differentiation, at sampling rates of up to 256 giga samples per second, and deploy these functions to showcase three proof-of-concept applications: solving ordinary differential equations, generating ultra-wideband signals and detecting edges in images. We further leverage the image edge detector to realize a photonic-assisted image segmentation model that can effectively outline the boundaries of melanoma lesion in medical diagnostic images. Our ultrafast lithium niobate MWP engine could provide compact, low-latency and cost-effective solutions for future wireless communications, high-resolution radar and photonic artificial intelligence.

A Homochiral Fulgide Organic Ferroelectric Crystal with Photoinduced Molecular Orbital Breaking.

Thermally triggered spatial symmetry breaking in traditional ferroelectrics has been extensively studied for manipulation of the ferroelectricity. However, photoinduced molecular orbital breaking, which is promising for optical control of ferroelectric polarization, has been rarely explored. Herein, for the first time, we synthesized a homochiral fulgide organic ferroelectric crystal (E)-(R)-3-methyl-3-cyclohexylidene-4-(diphenylmethylene)dihydro-2,5-furandione (1), which exhibits both ferroelectricity and photoisomerization. Significantly, 1 shows a photoinduced reversible change in its molecular orbitals from the 3 π molecular orbitals in the open-ring isomer to 2 π and 1 σ molecular orbitals in the closed-ring isomer, which enables reversible ferroelectric domain switching by optical manipulation. To our knowledge, this is the first report revealing the manipulation of ferroelectric polarization in homochiral ferroelectric crystal by photoinduced breaking of molecular orbitals. This finding sheds light on the exploration of molecular orbital breaking in ferroelectrics for optical manipulation of ferroelectricity.

Effect of knee joint weight change on knee function recovery and gait after total knee arthroplasty.

BACKGROUND: Knee osteoarthritis (KOA) is a common disease based on degenerative pathological changes. Total knee arthroplasty (TKA) is an effective treatment for end-stage of KOA. However, only volume adaptation can be achieved with current knee prostheses, and it is difficult to achieve weight adaptation. This study focused on the weight difference of knee joints and initially explored the impact of this change on knee joint functional recovery and gait changes in patients after surgery. METHODS: From October 2015 to June 2019, patients who underwent primary unilateral TKA were enrolled in this prospective cohort study with the same brand of knee prostheses. General data were collected from patients who met the criteria. The resected bone and soft tissues were collected and weighed precisely during TKA, and multivariate regression analysis was used to determine the factors affecting the weight of the removed knee tissues. We compared the weight of excised tissues and the total weight of the knee prosthesis, and the weight difference was defined as the increased weight of the knee joint (IWKJ). All patients were evaluated by HSS score, gait analysis, and affected side knee X-ray at two weeks, three months, and the last follow-up after the operation. To further determine the influence of IWKJ on postoperative functional recovery, the relationship between IWKJ, HSS score, and gait analysis was analyzed by univariate regression. RESULTS: In total, 210 patients were eventually included in observation. All patients underwent postoperative follow-up for no less than two years. Multiple regression analysis showed that the course of the disease, body weight, and kellgren-Larencen stage(K-L stage)of the affected knee joint were independent factors affecting the weight of the removed knee tissues and were positively correlated with it. Univariate analysis showed that IWKJ was negatively correlated with HSS score at two weeks and three months after the operation. In addition, the values of spatiotemporal parameters and knee rotation ROM were negatively correlated with IWKJ two weeks after surgery, while outside food load response was positively correlated with IWKJ. Cadence, knee rotation ROM, and Ankle rotation ROM were negatively correlated with IWKJ, while outside food was positively correlated with IWKJ three months after surgery. At the last follow-up, only the hip rotation ROM was positively correlated with IWKJ. CONCLUSIONS: All Patients underwent TKA had varying degrees of increased knee weight. The increased weight was 298.98 ± 63.77 g. Patients' body weight, K-L staging, and disease duration are important factors that cause differences in resected knee tissue. Three months after the operation, the changes in knee joint weight had a negative correlation with the HSS score, which at the same time, it had varying degrees of linearity with gait parameters. However, the influence of weight diminished over time.

Salicylideneaniline is a Photoswitchable Ferroelectric Crystal.

Since the discovery of the first ferroelectric Rochelle salt, most ferroelectrics have been investigated showing thermally triggered symmetry-breaking phase transition. Although photochromism arising from geometrical isomerization was reported as early as 1867, such photoswitchable ferroelectric crystals have scarcely been developed to date. Herein, we report that salicylideneaniline is a photochromic ferroelectric crystal. Upon photoirradiation, the dielectric constant shows obvious switching between high and low dielectric states, and more importantly, the ferroelectric polarization demonstrates quick and reversible switching. This work opens the gate to developing photoswitchable ferroelectrics, which holds great potential for applications in optically controlled smart devices.

The effects of statins on hyperandrogenism in women with polycystic ovary syndrome: a systematic review and meta-analysis of randomized controlled trials.

Several clinical studies showed that statins were potential to treat polycystic ovary syndrome (PCOS). Through comprehensive search PubMed, EMBASE, the Web of Science, BIOSIS, the ClinialTrails.gov, and the Cochrane Library database up to 14 Feb 2020, we identified the randomized controlled trials about the treatment of statins on hyperandrogenism in PCOS women, and performed a systematic review and meta-analysis. The quality of the included studies was assessed by the Cochrane risk of bias tool and the Jadda score. Subgroup analysis and sensitivity analysis were conducted to analyze the pooled results. Nine trials included 682 PCOS patients were identified. Statins showed a significant potential to reduce testosterone (SMD = -0.47; 95% CI, - 0.76-- 0.18; P = 0.002) and dehydroepiandrosterone (SMD = -0.51; 95% CI, - 0.97-- 0.05; P = 0.03) levels, compared to the control treatments. The cutaneous symptoms hirsutism (SMD = -0.61; 95% CI, - 1.13-- 0.10; P = 0.02) and acne (SMD = -0.92; 95% CI, - 1.49-- 0.34; P = 0.002) were significantly improved by statins in PCOS women. Subgroup analysis showed that the two types of statins, and the different control treatments as well, presented no significantly different effect on testosterone and dehydroepiandrosterone. Sensitivity analysis confirmed the stability of the findings from the meta-analysis. In conclusion, statin treatment could significantly reduce androgen levels and improve cutaneous manifestations of hyperandrogenism of PCOS.

Tourniquet use in primary total knee arthroplasty is associated with a hypercoagulable status: a prospective thromboelastography trial.

STUDY DESIGN: Prospective study. PURPOSE: The main purpose of this study was to investigate whether the use of a tourniquet changes the blood coagulation state following primary total knee arthroplasty (TKA) by means of conventional coagulation tests and thromboelastography (TEG) analyses. METHODS: A total of 154 patients who underwent primary unilateral TKA from January 2018 to October 2020 were enrolled. Seventy-nine patients were randomized into a tourniquet group, and 75 were randomized into a no-tourniquet group. Demographic data, surgical time, intra-operative blood loss, transfusion rate, and wound complications were collected. Complete blood count, conventional coagulation tests, and TEG were performed the day before surgery, one day after surgery, three days after surgery, and seven days after surgery. Lower extremity Doppler ultrasound was performed the day before surgery and seven days after surgery. RESULTS: The baseline characteristics of the patients were similar between the two groups. Hidden blood loss, transfusion rate, and wound complications were similar between the two groups, but the intra-operative blood loss of the tourniquet group was lower than that of the no-tourniquet group. The calculated total blood loss of the tourniquet group was higher than that of the no-tourniquet group. In terms of conventional coagulation tests and TEG, the tourniquet group had higher values of fibrin degradation products, D-dimer, maximum amplitude, and coagulation index (p < 0.001). The incidence of deep vein thrombosis (DVT) in the tourniquet group was higher than that in the no-tourniquet group (21.5% compared with 8%; p = 0.019). CONCLUSION: The application of a tourniquet during TKA significantly increases the amount of calculated total blood loss and does not decrease the post-operative transfusion rate. Using a tourniquet in routine TKA exacerbates the early post-operative hypercoagulable status together with a higher incidence of below-knee asymptomatic DVT observed via conventional coagulation tests, TEG, and ultrasonic Doppler.

Unprecedented 2D Homochiral Hybrid Lead-Iodide Perovskite Thermochromic Ferroelectrics with Ferroelastic Switching.

Chiral perovskites have emerged as a significant class of materials showing promising optoelectronic and spintronic applications. Reports of chiral perovskite ferroelectrics, however, have been scarce. In this work, we have successfully synthesized homochiral lead-iodide perovskite ferroelectrics [(R)-N-(1-phenylethyl)ethane-1,2-diaminium]PbI4 and [(S)-N-(1-phenylethyl)ethane-1,2-diaminium]PbI4 by introducing a methyl group into the organic cation of the parent (N-benzylethane-1,2-diaminium)PbI4 . Vibrational circular dichroism spectra identify the chiral mirroring relationship. They both undergo 222F2-type paraelectric-ferroelectric behavior at around 378 K coupled with clear ferroelastic domain "ON/OFF" switching. Besides, they exhibit an evident thermochromism with color change from orange-yellow to orange-red. To our knowledge, the discovery of integrated ferroelectricity, ferroelasticity, and reversible thermochromism in chiral perovskites is unprecedented.

The First High-Temperature Supramolecular Radical Ferroics.

Organic radical ferroics such as TEMPO have attracted widespread interest. However, the relatively low Curie temperature of 287 K and melting point of 311 K severely hinder its application potential. Despite extensive interest, high-temperature radical ferroics have not yet been found. Here, taking advantage of chemical design and supramolecular radical chemistry, we designed two high-temperature organic supramolecular radical ferroics [(NH3 -TEMPO)([18]crown-6)](ReO4 ) (1) and [(NH3 -TEMPO)([18]crown-6)](ClO4 ) (2), which can retain ferroelectricity up to 413 K and 450 K, respectively. To our knowledge, they are both the first supramolecular radical ferroics and unprecedented high-temperature radical ferroics, where the supramolecular component is vital for the stabilization of the radical and extending the working temperature window. Both also have paramagnetism, non-interacting spin moments, and excellent piezoelectric and electrostrictive behaviors comparable to that of LiNbO3 .

Lateral bipolar junction transistor on a silicon photonics platform.

Integration of active electronics into photonic systems is necessary for large-scale photonic integration. While heterogeneous integration leverages high-performance electronics, a monolithic scheme can coexist by aiding the electronic processing, improving overall efficiency. We report a lateral bipolar junction transistor on a commercial silicon photonics foundry process. We achieved a DC current gain of 10 with a Darlington configuration, and using measured S-parameters for a single BJT, the available AC gain was at least 3dB for signal frequencies up to 1.1 GHz. Our single BJT demonstrated a transimpedance of 3.2mS/µm, which is about 70 times better than existing literature.

Photonic independent component analysis using an on-chip microring weight bank.

Independent component analysis (ICA) is a general-purpose technique for analyzing multi-dimensional data to reveal the underlying hidden factors that are maximally independent from each other. We report the first photonic ICA on mixtures of unknown signals by employing an on-chip microring (MRR) weight bank. The MRR weight bank performs so-called weighted addition (i.e., multiply-accumulate) operations on the received mixtures, and outputs a single reduced-dimensional representation of the signal of interest. We propose a novel ICA algorithm to recover independent components solely based on the statistical information of the weighted addition output, while remaining blind to not only the original sources but also the waveform information of the mixtures. We investigate both channel separability and near-far problems, and our two-channel photonic ICA experiment demonstrates our scheme holds comparable performance with the conventional software-based ICA method. Our numerical simulation validates the fidelity of the proposed approach, and studies noise effects to identify the operating regime of our method. The proposed technique could open new domains for future research in blind source separation, microwave photonics, and on-chip information processing.

Reconfigurable all-optical nonlinear activation functions for neuromorphic photonics.

We experimentally demonstrate all-optical reconfigurable nonlinear activation functions in a cavity-loaded Mach-Zehnder interferometer device on a silicon photonics platform, via the free-carrier dispersion effect. Our device is programmable to generate various nonlinear activation functions, including sigmoid, radial-basis, clamped rectified linear unit, and softplus, with tunable thresholds. We simulate benchmark tasks such as XOR and MNIST handwritten digit classifications with experimentally measured activation functions and obtain accuracies of 100% and 94%, respectively. Our device can serve as nonlinear units in photonic neural networks, while its nonlinear transfer function can be flexibly programmed to optimize the performance of different neuromorphic tasks.

High-speed all-optical thresholding via carrier lifetime tunability.

We theoretically study the effect of free-carrier lifetime on processing speed and strength of nonlinearity, pertaining to our all-optical thresholder. We find that optimal device performance necessitates tuning lifetime while optimizing for both speed and nonlinearity. We also experimentally demonstrate device processing speed improvement from 400 Mbps to 2.5 Gbps by incorporating PN-junction mediated free-carrier lifetime tuning mechanism. Our study on the significance of free-carrier lifetime is universally applicable to any optical signal processing system reliant on silicon photonic nonlinearities.

Blind source separation with integrated photonics and reduced dimensional statistics.

Microwave communications have witnessed an incipient proliferation of multi-antenna and opportunistic technologies in the wake of an ever-growing demand for spectrum resources, while facing increasingly difficult network management over widespread channel interference and heterogeneous wireless broadcasting. Radio frequency (RF) blind source separation (BSS) is a powerful technique for demixing mixtures of unknown signals with minimal assumptions, but relies on frequency dependent RF electronics and prior knowledge of the target frequency band. We propose photonic BSS with unparalleled frequency agility supported by the tremendous bandwidths of photonic channels and devices. Specifically, our approach adopts an RF photonic front-end to process RF signals at various frequency bands within the same array of integrated microring resonators, and implements a novel two-step photonic BSS pipeline to reconstruct source identities from the reduced dimensional statistics of front-end output. We verify the feasibility and robustness of our approach by performing the first proof-of-concept photonic BSS experiments on mixed-over-the-air RF signals across multiple frequency bands. The proposed technique lays the groundwork for further research in interference cancellation, radio communications, and photonic information processing.

An Above-Room-Temperature Molecular Ferroelectric: [Cyclopentylammonium]2CdBr4.

Molecular ferroelectrics as alternatives to the conventional inorganic ferroelectrics have been greatly developed in past decades; many of these have been discovered and designed through various chemical means due to their structural adjustability. However, it is still a huge challenge to obtain high (above room temperature) Curie temperature (Tc) molecular ferroelectrics to meet the application requirements. Here, we present a new organic-inorganic hybrid molecular ferroelectric, [cyclopentylammonium]2CdBr4 (1), showing a moderate above-room-temperature Tc of 340.3 K. The mechanism of the ferroelectric phase transition from Pnam to Pna21 in 1 is ascribed to the order-disorder transition of both the organic cations and inorganic anions, affording a spontaneous polarization of 0.57 µC/cm2 for the ferroelectric phase. Using piezoresponse force microscopy (PFM), we clearly observed the antiparallel 180° stripe domains and realized the polarization switching, unambiguously establishing the existence of room-temperature ferroelectricity in the thin film. These attributes make it attractive for use in flexible devices, soft robotics, biomedical devices, and other applications.

Accelerated secure key distribution based on localized and asymmetric fiber interferometers.

We propose and experimentally demonstrate an approach to generate and distribute secret keys over optical fiber communication infrastructure. Mach-Zehnder interferometers (MZIs) are adopted for key generation by transferring the environmental noise to random optical signals. A novel combination of wideband optical noise and an asymmetric MZI structure enables the secret keys to be securely transmitted and exchanged over public fiber links without being detected. We experimentally demonstrate this system and show reliable performance: keys are generated at the rate of 502 bit/s, and are successfully exchanged between two parties over a 10 km optical fiber with a bit error of ∼ 0.3%. System security analysis is performed by corroborating our experimental findings with simulations. The results show that our system can protect the key distribution under different attacks, attributed to wideband optical noise and asymmetric MZI structures. Compared to the previous schemes based on distributed MZIs, our scheme exploits localized MZI which provides twofold advantages. Firstly, the key generation rate can be increased by a factor of 5.7 at a negligible additional cost. Secondly, the system becomes robust to, in particular, active intrusion attack. The proposed system is a reliable and cost-effective solution for key establishment, and is compatible with the existing optical fiber communication infrastructure.

Raman-enhanced optical phase conjugator in WDM transmission systems.

Optical phase conjugation (OPC) can be applied to boost the performance of long-haul transmission by mitigating the impairments from fiber nonlinearity. Unfortunately, noticeable nonlinear noise in the conjugator for optical orthogonal frequency division multiplexing (OFDM) systems often degrades the signal quality. In this paper, we demonstrate nonlinear distortion mitigation in OPC by introducing backward Raman amplification to the conjugator. Raman amplification allows a lower input signal power, thus suppressing the OPC distortion while maintaining the conjugated output power. We investigate the performances of Raman-enhanced OPC in both back-to-back (BTB) and transmission systems with 3 × 25 Gbaud optical OFDM signals. In the BTB OPC system, Raman amplification boosts the tolerance to system nonlinearity, achieving a 3-dB improvement in the output power, a 2.4-dB improvement in the Q factor, and a 6-dB improvement in the input dynamic range. In the transmission system with Raman-enhanced OPC, the optimum launched power is increased by 2 dB and the maximum Q factor is increased by 0.4 dB compared to direct transmission. Similar performances are observed in all the wavelengths, indicating that our scheme works well with WDM transmission systems.

Simultaneous excitatory and inhibitory dynamics in an excitable laser.

Neocortical systems encode information in electrochemical spike timings, not just mean firing rates. Learning and memory in networks of spiking neurons is achieved by the precise timing of action potentials that induces synaptic strengthening (with excitation) or weakening (with inhibition). Inhibition should be incorporated into brain-inspired spike processing in the optical domain to enhance its information-processing capability. We demonstrate the simultaneous excitatory and inhibitory dynamics in an excitable (i.e., a pulsed) laser neuron, both numerically and experimentally. We investigate the bias strength effect, inhibitory strength effect, and excitatory and inhibitory input timing effect, based on the simulation platform of an integrated graphene excitable laser. We further corroborate these analyses with proof-of-principle experiments utilizing a fiber-based graphene excitable laser, where we introduce inhibition by directly modulating the gain of the laser. This technology may potentially open novel spike-processing functionality for future neuromorphic photonic systems.

SBS-enhanced FWM for polarization division multiplexed signals in coherent communication systems.

Stimulated Brillouin scattering (SBS) is applied to improve the performance of polarization insensitive four-wave mixing (FWM) realized with two orthogonal pumps. By manipulating the phase matching condition with SBS-induced phase change, we achieve conversion efficiency improvement up to 6 dB with negligible polarization dependence. Our approach is implemented in a coherent communication system where polarization division multiplexing (PDM) quadrature phase shift keying (QPSK) signal is applied. The quality of the converted idler is evaluated in both back-to-back (BtB) and transmission systems. Our experimental results show that the converted signal enjoys an improved conversion efficiency with negligible polarization-induced distortion. The SBS-enhanced Q factor leads to an extension of the transmission distance by 240 km. The results indicate that SBS-enhanced FWM can accommodate the advanced modulation formats and multiplexing schemes in today's optical networks.

Photonically assisted microwave waveform generation by gain-transparent SBS-induced carrier processing: erratum.

In our previous work [Opt. Lett.42, 3852 (2017)OPLEDP0146-959210.1364/OL.42.003852], there is an error in Fig. 1. That error is addressed here.

Photonically assisted microwave waveform generation by gain-transparent SBS-induced carrier processing.

We propose and experimentally demonstrate a new approach to generate microwave waveforms by phase modulation and optical carrier phase processing based on gain-transparent stimulated Brillouin scattering (SBS). By properly adjusting the SBS-induced-phase shift on the carrier and the following group velocity dispersion, microwave waveforms with controllable repetition rates and temporal profiles can be generated. In the experiment, we have successfully generated triangular waveforms at repetition rates of 5.64 and 7.87 GHz, and rectangular waveforms at repetition rates of 5.04 and 7.01 GHz.