Narrow-linewidth and low RIN Tm/Ho co-doped fiber laser based on self-injection locking.

A narrow-linewidth and low relative intensity noise (RIN) Tm/Ho co-doped fiber laser based on a saturable absorber and self-injection locking was demonstrated for the first time. Utilizing self-injection locking technology, the frequency noise power spectral density is remarkably reduced by more than 17.1 dB from 1.21 × 106 Hz2/Hz to 7.30 × 103 Hz2/Hz when the frequency is approximately 1 kHz. Furthermore, a laser with a linewidth compressed to a quarter of the original linewidth from 44.386 kHz to 2.850 kHz, a RIN of less than -127.74 dB/Hz, and an optical signal-to-noise ratio of more than 71.6 dB can be obtained. Using a delay fiber, the relaxation oscillation peak frequencies move to lower frequencies, from 27.9 kHz to 15.8 kHz. The proposed laser is highly competitive in advanced coherent light detection fields, including coherent Doppler wind lidar, high-speed coherent optical communication, and precise absolute distance coherent measurement.

Equalization system of low differential mode delay few-mode fibers based on the neural network MIMO algorithm.

In recent years, with the development of information networks, higher requirements for transmission capacity have been recommended. Yet, at the same time, the capacity of single-mode fiber is rapidly approaching the theoretical limit. The multidimensional multiplexing technique is an effective way to solve this problem. Since the high differential mode delay (DMD) of transmission fiber increases the complexity of demultiplexing in equalization algorithms, we use an intelligent design method to optimize the trench-assisted gradient refractive index structure in this paper. The maximum DMD of the optimized optical fiber structure is 19.6 ps/km. A least mean squares-feedforward neural network constant modulus algorithm (LMS-FNNCMA) is also designed by using the theory of the least mean squares (LMS), constant modulus algorithm (CMA), and the multiple input multiple output (MIMO) neural networks. In order to verify the accuracy of the algorithm, a polarization division multiplexing-wavelength division multiplexing-mode division multiplexing (PDM-WDM-MDM) optical transmission system is constructed through simulation. The algorithm successfully realizes the de-crosstalk over a transmission distance of 1200 km at a rate of 1.2 Tbps under simulation conditions.

Modulation of Nucleation and Growth Kinetics of Perovskite Nanocrystals Enables Efficient and Spectrally Stable Pure-Red Light-Emitting Diodes.

Perovskite light-emitting diodes (PeLEDs) based on CsPb(Br/I)3 nanocrystals (NCs) usually suffer from severe spectral instability under operating voltage due to the poor-quality PeNCs. Herein, zeolite was utilized to prepare high-quality CsPb(Br/I)3 NCs via promoting the homogeneous nucleation and growth and suppressing the Ostwald ripening of PeNCs. In addition, the decomposed zeolite interacted strongly with PeNCs through Pb-O bonds and hydrogen bonds, which inhibited the formation of defects and suppressed halide ion migration, leading to an improved photoluminescence quantum yield (PLQY) and enhanced stability of PeNCs. Moreover, the strong binding affinity of decomposed zeolite to PeNCs contributed to the formation of homogeneous perovskite films with high PLQY. As a result, pure-red PeLEDs with Commission International de I'Eclairage (CIE) coordinates of (0.705, 0.291) were fabricated, approaching the Rec. 2020 red primary color. The devices achieved a peak external quantum efficiency of 23.0% and outstanding spectral stability.

High resolution and large measurement range voltage sensing based on an optoelectronic oscillator utilizing an unbalanced Mach-Zehnder interferometer.

A voltage sensor with high resolution and large measurement range based on an optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The key component in the cavity to select the oscillating signal is a finite impulse response (FIR)-microwave photonic filter (MPF) which consists of a sinusoidal broadband optical signal, an unbalanced Mach-Zehnder interferometer (MZI), a section of dispersion compensating fiber, and a photodetector. The center frequency of the FIR-MPF is mainly determined by the free spectral range (FSR) of the FIR-MPF. In the lower arm of the MZI, a cylindrical piezoelectric ceramic (PZT) wrapped with a section of optical fiber acts as voltage sensing head. Due to the inverse piezoelectric effect of PZT, the variation of the voltage will cause radial deformation of the cylindrical PZT and then lead to the change of the FSR of the MZI, determining the shift of center frequency of FIR-MPF as well as the frequency of the oscillating signal of the OEO. Thus, by monitoring the shift of the oscillation frequency of the OEO using an electric spectrum analyzer or a digital signal processor, a high-speed interrogation and high-resolution voltage measurement can be realized. Additionally, in the proposed scheme, an infinite impulse response (IIR)-MPF consisting of a fiber ring resonator is cascaded with the FIR-MPF to ensure the single-mode oscillation of the OEO. The experimental results show that a total range of 1700 V voltage sensing from - 200 V to 1500 V is accomplished with the voltage sensitivity of 0.25 GHz/100 V and the resolution of 0.3 V. By adjusting the proportion of the length of single mode fiber between two branches of MZI, the impact of temperature can be greatly reduced. The proposed sensor offers advantages such as a large measurement range, high resolution, high-speed interrogation, and stability to temperature disturbances, making it highly suitable for sensing applications in smart grids.

Gain equalization for a few-mode erbium-doped fiber amplifier supporting eight spatial modes.

A trench-assisted ring few-mode erbium-doped fiber amplifier (FM-EDFA) supporting eight spatial modes is designed and proposed in this work. The gain equalization for the FM-EDFA is achieved by selecting the appropriate doping radius and concentration using a particle swarm optimization (PSO) algorithm when only the pump in the fundamental mode (L P 01) is applied. When the signals in the eight spatial modes are simultaneously amplified, the average modal gain is about 20 dB, and the DMG is less than 0.3 dB for a signal at 1550 nm. Considering the gain competition of six wavelength signals, the modal gain and DMG are more than 20 and 1 dB, respectively. In addition, the tolerance analysis for manufacturing with this design is also discussed. For a fluctuation in the refractive index, the average modal gain is about 19.5 dB, and the DMG is 0.77 dB, indicating that the structure has good fabrication tolerance.

Ultrasensitive refractive index sensor based on stainless steel metamaterial.

Terahertz metamaterial technology, as an efficient nondestructive testing method, has shown great development potential in biological detection. This paper presents a stainless steel terahertz metamaterial absorber that achieves a near-perfect absorption of incident metamaterial waves with a 99.99% absorption at 2.937 THz. We demonstrate the theoretical discussion about the absorber and the application in sensing. The effect of the metamaterial absorber's structural parameters on the sensing performance is also analyzed. Simulation results show that the sensor can detect analytes with a refractive index between 1.0 and 1.8. Additionally, the performance of the sensor in detecting analytes in three states (solid, liquid, and gas) is analyzed in detail, and the sensitivity and the FoM of the sensor to detect methane are 22.727 THz/RIU and 568.175R I U -1, respectively. In addition, the terahertz sensor has the advantage of wide incident angle insensitivity, maintaining a good sensing performance within a wide manufacturing tolerance range of -10% to 10%. Compared to metal-dielectric-metal or dielectric-metal structures, the proposed sensor adopts stainless steel as the only manufacturing material, which has the advantages of simple structure, low manufacturing costs, and high sensitivity, and has potential application prospects in label-free high-sensitivity biomedical sensing.

2†µm band four-wavelength-switchable narrow linewidth fiber laser enabled by fs-laser direct-written polarization-dependent parallel fiber Bragg gratings.

We propose and experimentally demonstrate a four-wavelength-switchable single-longitudinal-mode (SLM) narrow linewidth thulium-holmium co-doped fiber laser (THDFL) using two polarization-dependent parallel fiber Bragg gratings (PD-PFBGs). The PD-PFBGs, fabricated using femtosecond (fs) laser direct-writing technology in a standard single-mode fiber (SMF) via a point-by-point method, are used as a four-channel reflection filter. Two FBGs are inscribed in parallel in the fiber core along the axial direction and are uniquely positioned symmetrically on either side of the centerline. This configuration enables polarization-dependent multi-channel filtering capability, which further allows for polarization-control-based four-wavelength-switchable operations of the THDFL. SLM lasing is accomplished by utilizing a simple dual-ring sub-cavity filter. An exceptional output performance of the THDFL is achieved, including an optical signal-to-noise ratio (SNR) of >72 dB, maximum power and wavelength fluctuations of 0.350 dB and 0.024 nm, respectively, and a linewidth of <2 kHz, for all four single-wavelength operations lasing at ∼2000 nm. These performance indicators suggest that the THDFL can be applied in free-space optical communication, atmospheric monitoring, and Lidar.

Metamaterial graphene sensors for the detection of two food additives.

Food safety is an important consideration for the food industry and for daily life, and food additives are essential in the modern food industry. Graphene-based metamaterial sensors are of great value and have potential applications in the detection of food additives, due to their ultra-sensitivity. This paper proposes a metasurface sensor consisting of graphene and dual elliptical ring resonators (Gr-DERRs) sensor for the detection of two common food additives. The limit of detection (LOD) for Sudan I solution is 581.43 fg/ml and, for taurine, 52.86 fg/ml. This ultra-sensitive detection is achieved by exploiting the unique electromagnetic properties of electromagnetically induced transparency (EIT) resonance, together with the Fermi energy level of graphene moving to the Dirac point, resulting in a dramatic change in the dielectric environment. The Gr-DERRs sensor has brings significant improvement in the detection of food additives with detection limits reduced to the femtogram level.

Enrichment of anchoring sites by introducing supramolecular halogen bonds for the efficient perovskite nanocrystal LEDs.

Considering the multi-functionalization of ligands, it is crucial for ligand molecular design to reveal the landscape of anchoring sites. Here, a typical triphenylphosphine (TPP) ligand was employed to explore its effect on the surface of CsPbI3 perovskite nanocrystals (PNCs). Except for the conventionally considered P-Pb coordination, an P-I supramolecular halogen bonding was also found on the NC surface. The coexistence of the above two types of bonding significantly increased the formation energy of iodine vacancy defects and improved the photoluminescence quantum yield of PNCs up to 93%. Meanwhile, the direct interaction of P and I enhanced the stability of the Pb-I octahedra and dramatically inhibited the migration of I ions. Furthermore, the introduction of additional benzene rings (2-(Diphenylphosphino)-biphenyl (DPB)) increased the delocalized properties of the PNC surface and significantly improved the charge transport of the PNCs. As a result, the DPB passivated CsPbI3 NCs based top-emitting LEDs exhibite a peak external quantum efficiency (EQE) of 22.8%, a maximum luminance of 15, 204 cd m-2, and an extremely low-efficiency roll-off of 2.6% at the current density of 500 mA cm-2.

Highly Efficient and Flexible Perovskite Nanocrystal Light-Emitting Diodes on Disposable Paper Substrates.

Perovskite nanocrystals have been widely applied in the field of light-emitting diodes (LEDs) due to their excellent optoelectronic properties. However, there is generally a serious degradation of device efficiency when transferring the device from rigid to flexible substrates due to the high roughness, poor wettability, and low endurance temperature of flexible substrates. Herein, a highly flexible perovskite light-emitting diode (PeLED) by utilizing label paper as substrates and poly(methyl methacrylate) (PMMA) as the modified layer was reported. Compared with the reference device based on commonly used polyethylene terephthalate (PET) substrates, the label paper/PMMA-based devices did not show the degraded device performance when transferring from rigid to flexible substrates. This is mainly because of low roughness and good wettability of PMMA-modified label paper, which significantly improve the film-forming ability of the bottom electrode and functional layer. Furthermore, the flexibility of both devices was explored by a three-point bending flexural test, indicating that the label paper-based device has better bending stability than the polyethylene terephthalate-based one due to the lower flexural modulus for label paper. As a result, the label paper-based flexible PeLEDs exhibited the highest external quantum efficiency (EQE) of 14.3% among perovskite nanocrystal-based flexible LEDs and preeminent flexibility with 29% luminance degradation after bending for 1000 cycles at a small radius of 1.5 mm. This extension of the substrate to paper will widen the opportunity of PeLEDs in extremely flexible and inexpensive applications.

Sudden unexpected death in epilepsy: Investigation of autopsy-based studies.

Epilepsy is a common neurological disorder that is associated with increased morbidity and mortality. Sudden unexpected death in epilepsy (SUDEP) is one of the most common causes for epilepsy-related deaths and its characteristics remain largely unknown, particularly from a forensic autopsy perspective. The present study aimed to investigate the neurological, cardiac, and pulmonary findings for a total of 388 SUDEP decedents, encompassing three cases from our forensic center during 2011-2020 and 385 literature-reported autopsy cases. In the cases mentioned in this study, two of them presented with only mild cardiac abnormalities, such as focal myocarditis and mild coronary atherosclerosis of the left anterior coronary artery. The third one was negative of any pathological findings. After pooling together these SUDEP cases, we found that neurological changes (n = 218 cases, 56.2%) were the most common postmortem findings associated with SUDEP, with cerebral edema/congestion (n = 60 cases, 15.5%) and old traumatic brain injury (n = 58 cases, 14.9%) being the major findings. Interstitial fibrosis, myocyte disarray/hypertrophy, and mild coronary artery atherosclerosis were the most common findings related to primary cardiac pathology, documented in 49 (12.6%), 18 (4.6%), and 15 (3.9%) cases, respectively. Non-specific pulmonary edema was the major finding in the lungs. This is an autopsy-based study that reports the scenario of postmortem findings for SUDEP cases. Our study paves the way for understanding the pathogenesis of SUDEP and the interpretation of death.

Effective linewidth compression of a single-longitudinal-mode fiber laser with randomly distributed high scattering centers in the fiber induced by femtosecond laser pulses.

Femtosecond lasers can be used to create many functional devices in silica optical fibers with high designability. In this work, a femtosecond laser-induced high scattering fiber (HSF) with randomly distributed high scattering centers is used to effectively compress the linewidth of a fiber laser for the first time. A dual-wavelength, single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL) is constructed for the demonstration, which is capable of switching among two single-wavelength operations and one dual-wavelength operation. We find that the delayed self-heterodyne beating linewidth of the laser can be reduced from >1 kHz to <150 Hz when the length of the HSF in the laser cavity increases from 0 m to 20 m. We also find that the intrinsic Lorentzian linewidth of the laser can be compressed to several Hz using the HSF. The efficiency and effectiveness of linewidth reduction are also validated for the case that the laser operates in simultaneous dual-wavelength lasing mode. In addition to the linewidth compression, the EDFL shows outstanding overall performance after the HSF is incorporated. In particular, the optical spectrum and SLM lasing state are stable over long periods of time. The relative intensity noise is as low as <-150 dB/Hz@>3 MHz, which is very close to the shot noise limit. The optical signal-to-noise ratios of >85 dB for single-wavelength operation and >83 dB for dual-wavelength operation are unprecedented over numerous SLM fiber lasers reported previously. This novel method for laser linewidth reduction is applicable across gain-medium-type fiber lasers, which enables low-cost, high-performance, ultra-narrow linewidth fiber laser sources for many applications.

Sudden Cardiac Death in Schizophrenia During Hospitalization: An Autopsy-Based Study.

Schizophrenia is a severe mental disorder that is often comorbid with heart dysfunction and even sudden cardiac death (SCD). Clinical studies of SCD in schizophrenia have been largely reported, while there are limited autopsy studies that directly showed whole-scale information of such events. In this study, we present nine autopsy-based SCD cases in schizophrenia patients who died suddenly during hospitalization. Their medical records before and during hospitalization, and postmortem autopsy findings were summarized. These decedents had an average duration of schizophrenia for 6.83 ± 3.75 years with a male/female ratio of 4:5. They were all on intermittent antipsychotics medication before hospitalization and died within 15 days after hospitalization. Seven of the nine cases (77.8%) died of organic heart diseases such as severe coronary artery atherosclerosis (n = 4), myocarditis (n = 1), cardiomyopathy (n = 1), and pulmonary thromboembolism (n = 1). Two cases remained unexplained after systemic autopsy and toxicological examinations. Postmortem autopsy identified hepatic steatosis (n = 6) and respiratory inflammation (n = 3) as the most common associate extra-cardiac lesions. Our data provided autopsy-based data of SCD cases in schizophrenia and highlighted an intensive care of such patients during hospitalization.

Supermode noise suppression with polarization-multiplexed dual-loop for active mode-locking optoelectronic oscillator.

The active mode-locking (AML) technique has been widely used in erbium-doped fiber lasers to generate picosecond pulse trains. Here we propose a novel active mode-locking dual-loop optoelectronic oscillator (AML-DL-OEO), which can generate microwave frequency comb (MFC) signals with adjustable comb spacings. Based on this scheme, the order of harmonic mode-locking is dramatically decreased for a certain AML driving frequency compared with a single-loop AML-OEO. Thus, the supermode noise caused by harmonic mode-locking can be efficiently suppressed. In addition, the sidemodes are well suppressed by the dual-loop architecture. An experiment is performed. MFC signals with different comb spacings are generated under fundamental or harmonic mode-locking states. AML-DL-OEO systems with different length differences between two loops are implemented to evaluate supermode noise suppression capability. The performance of the generated MFC signals is recorded and analyzed.

Three-wavelength-switchable narrow linewidth thulium-doped fiber laser enabled by a compound-cavity filter and a sampled fiber Bragg grating.

A single-longitudinal-mode (SLM), narrow linewidth thulium-doped fiber laser with a sampled fiber Bragg grating (SFBG), switchable among three wavelengths, with a cascade dual-coupler-ring-based compound cavity (DCR-CC) filter, is proposed and demonstrated. The coupling design, simulation analysis, and characterization of the DCR-CC filter provide the foundation for the experiment. A nonlinear polarization rotation system was injected into the cavity to suppress gain competition and achieve a laser switchable among three wavelengths. The fluctuations of the wavelength and power of the output laser are less than 0.60 nm and 0.91 dBm, respectively. For demonstration, the laser maintained in SLM operation measured by the delayed self-heterodyne method has a linewidth of <3.7k H z and relative intensity noise of <-114d B/H z.

Wavelength-switchable ultra-narrow linewidth fiber laser enabled by a figure-8 compound-ring-cavity filter and a polarization-managed four-channel filter.

We propose and demonstrate a high-performance wavelength-switchable erbium-doped fiber laser (EDFL), enabled by a figure-8 compound-ring-cavity (F8-CRC) filter for single-longitudinal-mode (SLM) selection and a polarization-managed four-channel filter (PM-FCF) for defining four lasing wavelengths. We introduce a novel methodology utilizing signal-flow graph combined with Mason's rule to analyze a CRC filter in general and apply it to obtain the important design parameters for the F8-CRC used in this paper. By combining the functions of the F8-CRC filter and the PM-FCF assisted by the enhanced polarization hole-burning and polarization dependent loss, we achieve the EDFL with fifteen lasing states, including four single-, six dual-, four tri- and one quad-wavelength lasing operations. In particular, all the four single-wavelength operations are in stable SLM oscillation, typically with a linewidth of <600 Hz, a RIN of ≤-154.58 dB/Hz@≥3 MHz and an output power fluctuation of ≤±3.45%. In addition, all the six dual-wavelength operations have very similar performances, with the performance parameters close to those of the four single-wavelength operations, superior to our previous work and others' similar work significantly. Finally, we achieve the wavelength-spacing tuning of dual-wavelength operations for photonic generation of tunable microwave signals, and successfully obtain a signal at 23.10 GHz as a demonstration.

miR-3113-5p, miR-223-3p, miR-133a-3p, and miR-499a-5p are sensitive biomarkers to diagnose sudden cardiac death.

BACKGROUND: Sudden cardiac death (SCD) remains a great health threat and diagnostic challenge, especially those cases without positive autopsy findings. Molecular biomarkers have been urgently needed for the diagnosis of SCD displaying negative autopsy results. Due to their nature of stability, microRNAs (miRNAs) have emerged as promising diagnostic biomarkers for cardiovascular diseases. METHODS: This study investigated whether specific cardio-miRNAs (miR-3113-5p, miR-223-3p, miR-499a-5p, and miR-133a-3p) could serve as potential biomarkers for the diagnosis of SCD. Thirty-four SCD cases were selected, 18 categorized as SCD with negative autopsy (SCD-negative autopsy) findings and 16 as SCD with positive autopsy (SCD-positive autopsy) findings such as coronary atherosclerosis and gross myocardial scar. Carbon monoxide (CO) intoxication (n = 14) and fatal injury death (n = 14) that displayed no pathological changes of myocardium were selected as control group, respectively. Histological analyses were performed to reveal the pathological changes and real-time quantitative polymerase chain reaction (RT-qPCR) was used to determine the expression of those miRNAs. RESULTS: It showed that heart samples from the SCD-negative autopsy group displayed no remarkable difference with regard to the expression of cleaved-caspase3, CD31, and CD68 and the extent of fibrotic tissue accumulation when compared with control samples. The four cardio-miRNAs were significantly up-regulated in the SCD samples as compared with control. When discriminating SCD from controls, receiver operating characteristic (ROC) curve analysis revealed that the areas under the curve (AUC) of these 4 miRNAs were from 0.7839 to 0.9043 with sensitivity of 64.71-97.06% and specificity of 70-100%. Moreover, when discriminating the specific causes of SCD, the four miRNA expressions increased in the heart from the SCD-negative autopsy group as relative to that from the SCD-positive autopsy group, and a combination of two miRNAs presented higher diagnostic value (AUC = 0.7407-0.8667). CONCLUSION: miR-3113-5p, miR-223-3p, miR-499a-5p, and miR-133a-3p may serve as independent diagnostic biomarkers for SCD, and a combination of two of these miRNAs could further discriminate detailed causes of SCD.

Linearity improvement of analog photonic link based on a phase-coherent orthogonal light wave generator.

This Letter presents a novel, to the best of our knowledge, linearized analog photonic link (APL) based on a phase-coherent orthogonal light wave generator that consists of a polarization-dependent Mach-Zehnder modulator (MZM) and a polarization controller (PC). By adjusting the PC and bias voltage of MZM, the third-order intermodulation (IMD3) terms can be suppressed while retaining a high gain for the fundamental terms, which indicates that the spurious free dynamic range (SFDR) of the proposed APL can be much improved. To further verify the feasibility of the proposed APL, a proof-of-concept experiment is performed, and the performances are compared with conventional APL. The experimental results demonstrate that a 14 dB improvement in the fundamental to IMD3 power ratio and an SFDR of 100.2dB⋅Hz2/3 or 119.1dB⋅Hz2/3 for a noise floor of -139dBm/Hz or -163.9dBm/Hz are achieved. In addition, an orthogonal frequency division multiplexing signal with 30 MHz bandwidth centered at 2.5 GHz is delivered by our proposed APL, whose signal-to-noise ratio is increased by 10 dB, compared to conventional APL.

Ultrafast and temperature-insensitive strain interrogation using a PM-PCF based Sagnac loop interferometer and wavelength-to-time mapping.

A novel approach for ultrafast and temperature-insensitive strain interrogation using a polarization-maintaining photonic crystal fiber (PM-PCF) based Sagnac loop interferometer (SLI) and linear wavelength-to-time (WTT) mapping is proposed and experimentally demonstrated. The PM-PCF incorporated in the SLI is used as the sensing element to achieve stable strain sensing with ultra-low temperature-dependence due to its intrinsic thermal insensitivity, which can be used to eliminate the cross-sensitivity effect and increase the measurement accuracy. A dispersive element is employed to realize the WTT mapping and real-time strain interrogation is obtained by converting the strain-encoded wavelength shift to time shift in the temporal domain, which can be directly monitored by a real-time oscilloscope. The proposed system offers an ultrafast interrogation speed of 100 MHz and a strain sensitivity of -0.17 ps/µÎµ.

Widely tunable single-/dual-wavelength fiber lasers with ultra-narrow linewidth and high OSNR using high quality passive subring cavity and novel tuning method: erratum.

We provide a corrected equation of our previous publication [Opt. Express24, 19760 (2016)10.1364/OE.24.019760].