INTEGRATED COHERENT COMBINING OF ANGLED-GRATING BROAD-AREA LASERS: DESIGN, FABRICATION AND CHARACTERIZATION

In this thesis, we proposed, fabricated and demonstrated the coherent beam combining of angled-grating broad-area lasers. We have obtained the simultaneous coherent beam combining and single transverse mode operation completely on chip without any external phase control/components. Since the single transverse mode is the key to obtain diffraction-limit beam quality and high brightness, the proposed design is a good candidate for high power and high brightness applications. In the proposed coherently combined laser array, we use the angled-grating broad-area laser as the building block and overlap the adjacent emitters at one facet. The overlapped region becomes a 2D coupling region. And the coherent beam combining is obtained through the Bragg diffraction in these coupling regions. The scalability of the proposed structure is also studied through a simplified zigzag array with the same topographic structure. The random phase difference among emitters in the array is assumed to be Gaussian distribution. And the brightness of the laser array is calculated at different random phase strength in two extreme situations: one is that only adjacent emitters are correlated and the other one is that all the emitters in the array are correlated. In the real zigzag laser array, the power of one emitter can be coupled into multiple neighbouring emitters. The scalability of the proposed structure should be between the two extreme situations. It should be similar to the performance of common cavity laser arrays. The fabricated two coherently combined angled-grating broad-area lasers shows an interference pattern in the far field measurement indicating the two emitters are indeed coherently combined. However, the overall envelope shows double lobes. A further investigation reveals that the double lobes come from the uneven distribution of the injected current due to the lateral current leakage. The uneven current distribution excites the second order Bragg modes resulting in the double lobes in the far field. Therefore, we use ion implantation to increase the resistance outside the metal contact area to obtain a more uniform current distribution. And the laser diodes after ion implantation show a single lobe in the far field envelope with interference patterns within the envelope. The output power of the fabricated lasers is limited by the bad thermal management. There are obvious thermal rollover in the LI curves at high current level. By p-side-down bonding, we bring the active region closer to the heat sink to help with the heat dissipation. Both the single and two combined angled-grating broad-area lasers can deliver over 1W output power without obvious thermal rollover at 180K. They can also lase in room temperature pumped with quasi-CW current source. However the slope efficiency is still low and the threshold is relatively high, which may be due to the high optical and electrical loss induced by the deep III-V dry etching. In order to reduce the etched area for lower optical and electrical loss, we decide to substitute the TBR grating with 2D triangle lattice photonic crystal cavity. There are two advantageous of 2D PC cavity, one is to reduce the surface defect states for less total loss, the other one is to control the longitudinal mode to obtain single wavelength as well as single transverse mode, since structure along the propagation direction is also periodic. The reason for choosing triangle lattice is to easily combine the 2D PC Bragg cavity in the same way we did in the coherent combining of angled-grating broad-area lasers. We solve for the first several photonic bands using MPB and determine the periods along the transverse and propagation directions for design purpose. Since these two periods are geometrically related too, we find discrete tilted angles to satisfied both resonant and geometric requirements. And usually the wavevector along the propagation direction is resonant with a high order grating vector. We fabricated both single and two combined PC Bragg lasers. As expected, the single 2D PC Bragg laser diode presents stable single wavelength optical spectrum without mode hopping during the measurement period. The far field also indicates near diffraction-limited beam quality. However, the combined laser diode shows multiple peaks in the far field profile due to the shallow etching depth. Regrowth wafer is another way to reduce the total loss. In this project, since the grating is wet etched in the cladding layer which is much closer to the quantum well, the grating depth can be pretty shallow. Since we don\u27t have any epitaxy layer growth facilities and experience, the epitaxy layer growth and regrowth process is done by a foundry service. After the quantum well is grown, the wafer is shipped to us and after the grating is etched, we ship them back to the service for regrowth process. Unfortunately, due to the surface cleanness, the wafer after regrowth has a lot of defects in it. All the devices including the broad-area lasers do not lase. Therefore, we couldn\u27t evaluate the performance of the coherently combined lasers using regrowth epitaxy wafer. We also investigate another interesting laser cavity design based on the angled-grating broad-area laser, which is the folded angled-grating broad-area laser. By using the symmetry of the snake-like lasing mode in the angled-grating broad-area laser, the angled-grating broad-area laser can be folded at the center to the other direction without disturbing the lasing mode. The experiment results confirm that with a well design cavity length, the folded cavity has a similar performance to that of the angled-grating broad-area laser. The immediate benefit of this design is to reduce the laser area and increase the yield. More promising is to combine two folded cavity laser to increase the filling factor. It is obvious that in the previous combined laser design, the longer the cavity is, the smaller the filling factor is. By combining two folded cavity lasers, it is possible to increase the filling factor to nearly 1. The fabricated two combined folded cavity lasers show an increased angular distance between two interference fringes in the far field. However, due to the relative low output power, the aperture distance is still larger than designed distance

Diode Laser

A diode laser includes a p-contact layer, a n-contact layer, and a wafer body disposed between the p-contact layer and the n-contact layer, the wafer body having a front end and a back end. The diode laser further includes a first grating comprising a plurality of grooves defined in the wafer body and extending between the front end and the back end at a first tilt angle, and a second grating comprising a plurality of grooves defined in the wafer body and extending between the front end and the back end at a second tilt angle, the second tilt angle opposite to the first tilt angle. A coupling region is defined in the wafer body by interleaving portions of the first grating and the second grating. The interleaving portions provide coherent coupling of laser beams flowing through the first grating and the second grating

Difference between Pb and Cd Accumulation in 19 Elite Maize Inbred Lines and Application Prospects

In the last two decades, the accumulation of heavy metal in crop grains has become the study hotspot. In this study, 19 representative elite maize inbred lines and 3 hybrid varieties were investigated at the seedling stage, which can accumulate Pb and Cd in the stems and leaves, respectively. The results demonstrated that significant differences are among inbred lines for accumulation of heavy metals, implying that the Cd accumulation is significant correlation between the male parents and their hybrids and some inbred lines have been selected for cross-breeding with low Pb or Cd accumulation, such as S37, 9782, and ES40; Moreover, some inbred lines could be suitable for phytoremediation species for soil bioremediation with high levels of Pb and Cd accumulation, including 178, R08, 48-2, and Mo17ht

Xenotime-type high-entropy (Dy1/7Ho1/7Er1/7Tm1/7Yb1/7Lu1/7Y1/7)PO4: A promising thermal/environmental barrier coating material for SiCf/SiC ceramic matrix composites

Rare-earth phosphates (REPO4) are regarded as one of the promising thermal/environmental barrier coating (T/EBC) materials for SiCf/SiC ceramic matrix composites (SiC-CMCs) owing to their excellent resistance to water vapor and CaO–MgO–Al2O3–SiO2 (CMAS). Nevertheless, a relatively high thermal conductivity (κ) of the REPO4 becomes the bottleneck for their practical applications. In this work, novel xenotime-type high-entropy (Dy1/7Ho1/7Er1/7Tm1/7Yb1/7Lu1/7Y1/7)PO4 (HE (7RE1/7)PO4) has been designed and synthesized for the first time to solve this issue. HE (7RE1/7)PO4 with a homogeneous rare-earth element distribution exhibits high thermal stability up to 1750 ℃ and good chemical compatibility with SiO2 up to 1400 ℃. In addition, the thermal expansion coefficient (TEC) of HE (7RE1/7)PO4 (5.96×10−6 ℃−1 from room temperature (RT) to 900 ℃) is close to that of the SiC-CMCs. What is more, the thermal conductivities of HE (7RE1/7)PO4 (from 4.38 W·m−1·K−1 at 100 ℃ to 2.25 W·m−1·K−1 at 1300 ℃) are significantly decreased compared to those of single-component REPO4 with the minimum value ranging from 9.90 to 4.76 W·m−1·K−1. These results suggest that HE (7RE1/7)PO4 has the potential to be applied as the T/EBC materials for the SiC-CMCs in the future

Analysis of gut microbiotal diversity in healthy young adults in Sunan County, Gansu Province, China

ObjectiveTo examine gut microbiotal diversity in the Han Chinese and Yugur populations of Sunan County, Gansu Province, living in the same environmental conditions, and to analyze possible causes of differences in diversity.MethodsWe selected 28 people, ages 18–45 years old, all of whom were third-generation pure Yugur or Han Chinese from Sunan County. Fresh fecal samples were collected, and total bacterial deoxyribonucleic acid (DNA) was extracted. We performed 16S ribosomal ribonucleic acid (16S rRNA) high-throughput sequencing (HTS) and bioinformatics to study the relationships among between gut microbiota structure, genetics, and dietary habits in Yugur and Han Chinese subjects.ResultsWe found 350 differential operational taxonomic units (OTUs) in Han Chinese and Yugur gut microbiota, proving that gut microbiota differed between the two populations. That were less abundant among Yugurs than Han Chinese were Prevotella_9 and Alloprevotella. That were more abundant among Yugurs than Han Chinese were Anaerostipes and Christensenellaceae_R-7_group. And they were significantly associated with a high-calorie diet In addition. we found differences in predicted gut microbiota structural functions (The main functions were metabolic and genetic information) between the two populations.ConclusionYugur subjects demonstrated differences in gut microbiotal structure from Han Chinese subjects, and this difference influenced by dietary and may be influenced by genetic influences. This finding will provide a fundamental basis for further study of the relationships among gut microbiota, dietary factors, and disease in Sunan County

Pharmacokinetics/pharmacodynamics of polymyxin B in patients with bloodstream infection caused by carbapenem-resistant Klebsiella pneumoniae

Introduction: Polymyxin B is a last-line therapy for carbapenem-resistant microorganisms. However, a lack of clinical pharmacokinetic/pharmacodynamic (PK/PD) data has substantially hindered dose optimization and breakpoint setting.Methods: A prospective, multi-center clinical trial was undertaken with polymyxin B [2.5 mg/kg loading dose (3-h infusion), 1.25 mg/kg/12 h maintenance dose (2-h infusion)] for treatment of carbapenem-resistant K. pneumoniae (CRKP) bloodstream infections (BSI). Safety, clinical and microbiological efficacy were evaluated. A validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was applied to determine the concentrations of polymyxin B in blood samples. Population pharmacokinetic (PK) modeling and Monte Carlo simulations were conducted to examine the susceptibility breakpoint for polymyxin B against BSI caused by CRKP.Results: Nine patients were enrolled and evaluated for safety. Neurotoxicity (5/9), nephrotoxicity (5/9), and hyperpigmentation (1/9) were recorded. Blood cultures were negative within 3 days of commencing therapy in all 8 patients evaluated for microbiological efficacy, and clinical cure or improvement occurred in 6 of 8 patients. Cmax and Cmin following the loading dose were 5.53 ± 1.80 and 1.62 ± 0.41 mg/L, respectively. With maintenance dosing, AUCss,24 h was 79.6 ± 25.0 mg h/L and Css,avg 3.35 ± 1.06 mg/L. Monte Carlo simulations indicated that a 1 mg/kg/12-hourly maintenance dose could achieve >90% probability of target attainment (PTA) for isolates with minimum inhibitory concentration (MIC) ≤1 mg/L. PTA dropped substantially for MICs ≥2 mg/L, even with a maximally recommended daily dose of 1.5 mg/kg/12-hourly.Conclusion: This is the first clinical PK/PD study evaluating polymyxin B for BSI. These results will assist to optimize polymyxin B therapy and establish its breakpoints for CRKP BSI

Causative agent distribution and antibiotic therapy assessment among adult patients with community acquired pneumonia in Chinese urban population

<p>Abstract</p> <p>Background</p> <p>Knowledge of predominant microbial patterns in community-acquired pneumonia (CAP) constitutes the basis for initial decisions about empirical antimicrobial treatment, so a prospective study was performed during 2003–2004 among CAP of adult Chinese urban populations.</p> <p>Methods</p> <p>Qualified patients were enrolled and screened for bacterial, atypical, and viral pathogens by sputum and/or blood culturing, and by antibody seroconversion test. Antibiotic treatment and patient outcome were also assessed.</p> <p>Results</p> <p>Non-viral pathogens were found in 324/610 (53.1%) patients among whom <it>M. pneumoniae </it>was the most prevalent (126/610, 20.7%). Atypical pathogens were identified in 62/195 (31.8%) patients carrying bacterial pathogens. Respiratory viruses were identified in 35 (19%) of 184 randomly selected patients with adenovirus being the most common (16/184, 8.7%). The nonsusceptibility of <it>S. pneumoniae </it>to penicillin and azithromycin was 22.2% (Resistance (R): 3.2%, Intermediate (I): 19.0%) and 79.4% (R: 79.4%, I: 0%), respectively. Of patients (312) from whom causative pathogens were identified and antibiotic treatments were recorded, clinical cure rate with β-lactam antibiotics alone and with combination of a β-lactam plus a macrolide or with fluoroquinolones was 63.7% (79/124) and 67%(126/188), respectively. For patients having mixed <it>M. pneumoniae </it>and/or <it>C. pneumoniae </it>infections, a better cure rate was observed with regimens that are active against atypical pathogens (e.g. a β-lactam plus a macrolide, or a fluoroquinolone) than with β-lactam alone (75.8% vs. 42.9%, <it>p </it>= 0.045).</p> <p>Conclusion</p> <p>In Chinese adult CAP patients, <it>M. pneumoniae </it>was the most prevalent with mixed infections containing atypical pathogens being frequently observed. With <it>S. pneumoniae</it>, the prevalence of macrolide resistance was high and penicillin resistance low compared with data reported in other regions.</p

NTIRE 2020 Challenge on Spectral Reconstruction from an RGB Image

This paper reviews the second challenge on spectral reconstruction from RGB images, i.e., the recovery of whole- scene hyperspectral (HS) information from a 3-channel RGB image. As in the previous challenge, two tracks were provided: (i) a "Clean" track where HS images are estimated from noise-free RGBs, the RGB images are themselves calculated numerically using the ground-truth HS images and supplied spectral sensitivity functions (ii) a "Real World" track, simulating capture by an uncalibrated and unknown camera, where the HS images are recovered from noisy JPEG-compressed RGB images. A new, larger-than-ever, natural hyperspectral image data set is presented, containing a total of 510 HS images. The Clean and Real World tracks had 103 and 78 registered participants respectively, with 14 teams competing in the final testing phase. A description of the proposed methods, alongside their challenge scores and an extensive evaluation of top performing methods is also provided. They gauge the state-of-the-art in spectral reconstruction from an RGB image

Iterative Beam Hardening Correction for Multi-Material Objects.

In this paper, we propose an iterative beam hardening correction method that is applicable for the case with multiple materials. By assuming that the materials composing scanned object are known and that they are distinguishable by their linear attenuation coefficients at some given energy, the beam hardening correction problem is converted into a nonlinear system problem, which is then solved iteratively. The reconstructed image is the distribution of linear attenuation coefficient of the scanned object at a given energy. So there are no beam hardening artifacts in the image theoretically. The proposed iterative scheme combines an accurate polychromatic forward projection with a linearized backprojection. Both forward projection and backprojection have high degree of parallelism, and are suitable for acceleration on parallel systems. Numerical experiments with both simulated data and real data verifies the validity of the proposed method. The beam hardening artifacts are alleviated effectively. In addition, the proposed method has a good tolerance on the error of the estimated x-ray spectrum