Highly precise timing alignment of multi-wavelength interleaved cavity-less pulse sources with FROG.

Strictly uniform time interval between adjacent channels is a crucial requirement for the multi-wavelength interleaved (MWI) pulse sources, which difficult alignment can be easily solved by what we believe to be our novel method based on frequency-resolved optical gating (FROG). By utilizing highly precise measurements from FROG, which provide fully two-dimensional information of the pulses in time and frequency domain, we can intuitively identify the time mismatches between different channels in the MWI pulse sources. This enables us to directly align the timing of each channel with sub-picosecond resolution at the first time. MWI pulse sources with total repetition rate of 20.8 GHz (four wavelengths) and 41.6 GHz (eight wavelengths) are precisely aligned by the proposed method, this achievement will pave the way for advancements in photonic analog-digital converters (PADC), high-speed optical communications and so on.

Refinement method for compressive hyperspectral data cubes based on self-fusion.

Compressive hyperspectral images often suffer from various noises and artifacts, which severely degrade the imaging quality and limit subsequent applications. In this paper, we present a refinement method for compressive hyperspectral data cubes based on self-fusion of the raw data cubes, which can effectively reduce various noises and improve the spatial and spectral details of the data cubes. To verify the universality, flexibility, and extensibility of the self-fusion refinement (SFR) method, a series of specific simulations and practical experiments were conducted, and SFR processing was performed through different fusion algorithms. The visual and quantitative assessments of the results demonstrate that, in terms of noise reduction and spatial-spectral detail restoration, the SFR method generally is much better than other typical denoising methods for hyperspectral data cubes. The results also indicate that the denoising effects of SFR greatly depend on the fusion algorithm used, and SFR implemented by joint bilateral filtering (JBF) performs better than SRF by guided filtering (GF) or a Markov random field (MRF). The proposed SFR method can significantly improve the quality of a compressive hyperspectral data cube in terms of noise reduction, artifact removal, and spatial and spectral detail improvement, which will further benefit subsequent hyperspectral applications.

Practical generation of arbitrary high-order cylindrical vector beams by cascading vortex half-wave plates.

A practical direct-view scheme for generating arbitrary high-order cylindrical vector (HCV) beams by cascading vortex half-wave plates (VHPs) is presented. The combination of odd number 2n-1 VHPs for n≥1 can realize (m2n-1-m2n-2+…+m1)-order CV beams, in which m is the order number of VHP and the corresponding subscript 2n-1 represents the arrangement number of VHPs, and the cascading of even number 2n ones can obtain (m2n-m2n-1+…+m2-m1)-order CV beams. All 1-12 order CV beams, including the high-order anti-vortex CV (ACV) beams, are generated only by selectively cascading the VHPs with m=1, 3 and 8. The polarization properties of the generated HCV beams are investigated by measuring the corresponding Stokes parameters. It is experimentally demonstrated that arbitrary HCV beams are effectively achieved by the proposed method. The order numbers of CV beams can be greatly expanded by cascading limited types of VHPs.

Measurement and Data Correction of Channel Sampling Timing Walk-Off of Photonic Analog-to-Digital Converter in Signal Recovery.

A two-channel, time-wavelength interleaved photonic analog-to-digital converter (PADC) system with a sampling rate of 10.4 GSa/s was established, and a concise method for measuring and data correcting the channel sampling timing walk-off of PADCs for signal recovery was proposed. The measurements show that for the two RF signals of f1 = 100 MHz and f2 = 200 MHz, the channel sampling timing walk-off was 12 sampling periods, which results in an ENOB = -0.1051 bits for the 100 MHz directly synthesized signal, while the ENOB improved up to 4.0136 bits using shift synthesis. In addition, the peak limit method (PLM) and normalization processing were introduced to reduce the impacts of signal peak jitter and power inconsistency between two channels, which further improve the ENOB of the 100 MHz signal up to 4.5668 bits. All signals were analyzed and discussed in both time and frequency domains. The 21.1 GHz signal was also collected and converted using the established two-channel PADC system with the data correction method, combining the PLM, normalization, and shift synthesis, showing that the ENOB increased from the initial -0.9181 to 4.1913 bits, which demonstrates that our method can be effectively used for signal recovery in channel-interleaved PADCs.

Generation and double-slit interference of higher-order vector beams.

A method for generating vector beams with higher-order states of polarization based on a setup with a one phase-only liquid crystal spatial light modulator is proposed. The polarization properties and double-slit interference of the higher-order vector beams were investigated in detail. The cross section intensity distributions were flower-like for higher-order vector beams when passing through a linear polarizer. Misplacements appeared in the double-slit interference fringes, which divided each fringe into several discrete parts, i.e., 2P-1 for P≥2, and 3 for P=1, where P is the polarization order number. When associated with optical petal orientations analysis of the beam spots behind a linear polarizer, the double-slit interference can be used to detect and analyze higher-order vector beams.

Effects of Optical Sampling Pulse Power, RF Power, and Electronic Back-End Bandwidth on the Performance of Photonic Analog-to-Digital Converter.

The effects of optical sampling pulse power, RF power, and electronic back-end bandwidth on the performance of time- and wavelength-interleaved photonic analog-to-digital converter (PADC) with eight-channel 41.6 GHz pulses have been experimentally investigated in detail. The effective number of bits (ENOB) and peak-to-peak voltage (Vpp) of converted 10.6 GHz electrical signals were used to characterize the effects. For the 1550.116 nm channel with 5.2 G samples per second, an average pulse power of 0 to -10 dBm input to the photoelectric detector (PD) has been tested. The Vpp increased with increasing pulse power. And the ENOB for pulse power -9~-3 dBm was almost the same and all were greater than four. Meanwhile, the ENOB decreased either when the pulse power was more than -2 dBm due to the saturation of PD or when the pulse power was less than -10 dBm due to the non-ignorable noise relative to the converted weak signal. In addition, RF powers of -10~15 dBm were loaded into the Mach-Zehnder modulator (MZM). The Vpp increased with the increase in RF power, and the ENOB also showed an increasing trend. However, higher RF power can saturate the PD and induce greater nonlinearity in MZM, leading to a decrease in ENOB, while lower RF power will convert weak electrical signals with more noise, also resulting in lower ENOB. In addition, the back-end bandwidths of 0.2~8 GHz were studied in the experiments. The Vpp decreased as the back-end bandwidth decreased from 8 to 3 GHz, and remained nearly constant for the bandwidth between the Nyquist bandwidth and the subsampled RF signal frequency. The ENOB was almost the same and all greater than four for a bandwidth from 3 to 8 GHz, and gradually increased up to 6.5 as the back-end bandwidth decreased from the Nyquist bandwidth to 0.25 GHz. A bandwidth slightly larger than the Nyquist bandwidth was recommended for low costs and without compromising performance. In our experiment, the -3 to -5 dBm average pulse power, about 10 dBm RF power, and 3 GHz back-end bandwidth were recommended to accomplish both a high ENOB more than four and large Vpp. Our research provides a solution for selecting optical sampling pulse power, RF power, and electronic back-end bandwidth to achieve low-cost and high-performance PADC.

Diabetic Striatopathy Complicated With Acute Ischemic Stroke: A Case Report.

Diabetic striatopathy (DS) is a rare complication secondary to hyperglycemia, featured by the choreiform movements and reversible striatal abnormalities on neuroimaging. Several studies have described the clinical characteristics of DS, however, the simultaneous occurrence of DS and acute ischemic stroke (AIS) in the striatum has not been reported. Herein, we report a 68-year-old man with uncontrolled type 2 diabetes who experienced the progressive involuntary movement of the right upper and lower limbs for 10 days. We initially considered this patient as an AIS with hemorrhage in the left basal ganglia and adjacent area because his brain magnetic resonance imaging (MRI) showed hyperintensity on fluid-attenuated inversion recovery (FLAIR) and diffusion-weighted imaging (DWI) images, as well as slight T1-hyperintensity around T1-hypointensity. However, his symptoms worsen persistently, which was inconsistent with neuroimaging findings. Further computed tomography (CT) scan revealed an extensive hyper-density and focal low-density in the left striatum, suggesting the diagnosis of DS and AIS. His symptoms were in complete remission after 2 months of glucose control. However, striatal hyperintensity on T1 images was significantly increased compared to the initial images, which disappeared 18 months later. Additionally, DWI hyperintensity on infarction lesions disappeared, while softening lesions and gliosis were observed on the follow-up MRI images. Therefore, we finally diagnosed the patient as DS complicated with AIS. This report highlights that DS and AIS could occur simultaneously in the striatum after hyperglycemia, which is easily misdiagnosed as AIS with hemorrhage and requires clinicians to pay more attention to avoid misdiagnosis and delayed treatment.

Design of Broadband Flat Optical Frequency Comb Based on Cascaded Sign-Alternated Dispersion Tellurite Microstructure Fiber.

We designed a tellurite microstructure fiber (TMF) and proposed a broadband optical frequency comb generation scheme that was based on electro-optical modulation and cascaded sign-alternated dispersion TMF (CSAD-TMF). In addition, the influence of different nonlinear effects, the ultrashort pulse evolution in the CSAD-TMF with the anomalous dispersion (AD) zones and the normal dispersion (ND) zones were analyzed based on the generalized nonlinear Schrodinger equations (GNLSE) modelling. According to the simulations, when the input seed comb had a repetition rate of 20 GHz and had an input pulse peak power of 30 W, the generation scheme could generate optical frequency combs with a 6 dB spectral bandwidth spanning over 170 nm centered at 1550 nm. Furthermore, the generated combs showed good coherence in performance over the whole 6 dB spectral bandwidth. The highly coherent optical frequency combs can be used as high-repetition-rate, multi-wavelength light sources for various integrated microwave photonics and ultrafast optical signal processing applications.