High-Efficiency Frequency Doubling Blue-Laser VECSEL Based on Intracavity Beam Control.

Blue lasers are integral to a variety of applications, including marine communication, underwater resource exploration, cold laser processing, laser medicine, and beyond. Vertical external cavity surface-emitting lasers (VECSELs) have the advantages of high output power and tunable wavelength, and can output blue laser via frequency doubling. In this article, a new type of intracavity beam control external-cavity structure is introduced. The laser beam waist is effectively adjusted by intracavity beam control, and the frequency conversion efficiency is improved. A laser cavity stability analysis model was developed to investigate the impact of laser cavity lens parameters and relative positions on stability. The external resonant cavity of VECSELs utilizes two optical lenses to position the beam waist near the laser output coupling mirror and locates the frequency doubling crystal at a high optical power density position to optimize frequency conversion efficiency. The VECSEL straight external-cavity structure achieves a frequency conversion efficiency of up to 60.2% at 488 nm, yielding a blue laser output exceeding 1.3 W. The full width at half maximum of the 488 nm spectrum measures approximately 0.23 nm. This intracavity beam-controlled direct external-cavity structure effectively mitigates laser mode leakage and shows potential for the development of an efficient and compact blue laser source.

A 1-µm-Band Injection-Locked Semiconductor Laser with a High Side-Mode Suppression Ratio and Narrow Linewidth.

We demonstrate a narrow-linewidth, high side-mode suppression ratio (SMSR) semiconductor laser based on the external optical feedback injection locking technology of a femtosecond-apodized (Fs-apodized) fiber Bragg grating (FBG). A single frequency output is achieved by coupling and integrating a wide-gain quantum dot (QD) gain chip with a Fs-apodized FBG in a 1-µm band. We propose this low-cost and high-integration scheme for the preparation of a series of single-frequency seed sources in this wavelength range by characterizing the performance of 1030 nm and 1080 nm lasers. The lasers have a maximum SMSR of 66.3 dB and maximum output power of 134.6 mW. Additionally, the lasers have minimum Lorentzian linewidths that are measured to be 260.5 kHz; however, a minimum integral linewidth less than 180.4 kHz is observed by testing and analyzing the power spectra of the frequency noise values of the lasers.

2m-distance external cavity VECSEL for wireless charging applications.

We characterize laser generation in an ultralong air cavity (several meters in length) using an optical-pumped semiconductor gain chip for laser wireless charging applications. The study realizes laser generation in an external air cavity with a length of 200 cm, for the first time, and achieves a maximum output laser power of more than 86.3 mW. Furthermore, the laser oscillation can be maintained even when the output mirror of laser is off-axis within 1.6 cm. Thus, a long external cavity laser would ease the alignment between the laser beam and charging terminal, making it suitable for laser wireless charging applications.

Wavelength tuning robustness optimization for a high-temperature single-mode VCSEL used in chip-scale atomic sensing systems.

In this paper, the wavelength current tuning characteristics of high-temperature-operation single-mode vertical-cavity surface-emitting lasers (VCSELs) for chip-scale atomic sensing systems are studied. Excellent wavelength current tuning robustness is helpful to improve the stability of atomic sensing systems. By optimizing the size of the oxide aperture combined with surface relief mode control technology, the single-mode VCSEL with an 8 µm oxide aperture can achieve 2.02 mW output power at 355 K, and the wavelength current tuning coefficient is ∼0.25nm/mA. This excellent wavelength current tuning robustness results from the low active current density and device heat generation due to the optimized oxide aperture size.

Large-aperture single-mode 795 nm VCSEL for chip-scale nuclear magnetic resonance gyroscope with an output power of 4.1 mW at 80 °C.

Transverse optical confinement in oxide-confined vertical-cavity surface-emitting lasers (VCSELs) crucially depends on thickness of oxide layer and its position relative to a standing wave. Modifying the structure reduces the overlap between the oxide layer and the standing wave as well as effective refractive index difference between core and cladding of the VCSEL that subsequently decreases of the number of transverse modes and increases the mode extension beyond oxide aperture. A 795 nm VCSEL is designed and fabricated with this concept. The proposed device achieves high single-mode operation of 4.1 mW at 80 °C, SMSR of 41.68 dB, and OPSR of 27.4 dB. VCSEL is applied in a nuclear magnetic resonance gyroscope (NMRG) system as pump source due to its excellent device performance and satisfactory test results are obtained.

Simulation and experimental research of a high-order Bragg grating semiconductor laser.

In this paper, the influence of the epitaxial structure on distributed Bragg reflector (DBR) grating characteristics is studied by simulation analysis. Comparative analysis shows that the symmetrical epitaxial structure can achieve a lower threshold current and, thus, a higher power. Based on the simulated structure, a DBR laser based on a symmetric epitaxial structure was fabricated, and a single longitudinal mode laser output at ∼1060nm was obtained. The maximum power was 104.5 mW, and the side mode suppression ratio (SMSR) is 43 dB.

High-order DBR semiconductor lasers: effect of grating parameters on grating performance.

In this paper, a high-order distributed Bragg reflector (DBR) semiconductor laser operating at 1064 nm is demonstrated based on simulation analysis. To get optimal Bragg grating characteristics, four parameters of the Bragg grating were analyzed in detail. Forty-nine-order Bragg gratings were designed with a reflectivity of 6% and a FWHM of 3 nm, which can realize mode selection while lasing. The Bragg gratings were designed to maximize the use of light. Transmission of the rear laser facet is theoretically 0. This simulation result provides a simple and efficient DBR semiconductor laser scheme without cavity surface coating.

High-order DBR semiconductor lasers: effect of grating parameters on grating performance: publisher's note.

This publisher's note amends the author listing in Appl. Opt.59, 8789 (2020)APOPAI0003-693510.1364/AO.402699.

Optically Pumped Monolayer MoSe2 Excitonic Lasers from Whispering Gallery Mode Microcavities.

Developing integrable, nanoscale, and low-energy-consumption lasers is a crucial step toward on-chip optical communications and computing technologies. The strong exciton-photon interaction that emerged in monolayer transition metal dichalcogenides (TMDs) holds promise for engineering and integration. Herein, we prepare the MoSe2/microsphere cavities excitonic lasers by placing SiO2 microspheres on top of a monolayer MoSe2 film. By virtue of continuous-wave exciting MoSe2/microsphere whispering gallery mode (WGM) cavities, we realize multiple excitonic WGM lasing in the emission wavelength range of ∼750-875 nm at room temperature with tunable properties of free spectral range (FSR) and full width at half-maximum (fwhm) by varying the microsphere size. Theoretical calculations based on the finite element method (FEM) using COMSOL software were utilized to identify lasing modes and reveal the corresponding electric field distribution. These findings help to deepen fundamental understanding of excitonic WGM lasing and provide a promising research platform for integrable, scalable, and low-cost laser devices.

1550 nm external cavity diode laser with enhanced SMSR based on polarization mismatch by grating rotation.

A tunable external cavity diode laser (ECDL) with high side-mode suppression ratio (SMSR) is demonstrated. The ECDL is operated at both strong and weak feedback steady states with single longitudinal mode. Compared with the strong feedback mode, the SMSR of the weak feedback mode is significantly enhanced by rotating the grating along the axis of the incident beam, which changes the polarization orientation versus the grating grooves. The highest SMSR of the weak feedback mode is 54 dB at the injection current of 300 mA. The tunable range of the ECDL with weak feedback mode reaches 130.9 nm.

Microscopic View of Defect Evolution in Thermal Treated AlGaInAs Quantum Well Revealed by Spatially Resolved Cathodoluminescence.

An aluminum gallium indium arsenic (AlGaInAs) material system is indispensable as the active layer of diode lasers emitting at 1310 or 1550 nm, which are used in optical fiber communications. However, the course of the high-temperature instability of a quantum well structure, which is closely related to the diffusion of indium atoms, is still not clear due to the system’s complexity. The diffusion process of indium atoms was simulated by thermal treatment, and the changes in the optical and structural properties of an AlGaInAs quantum well are investigated in this paper. Compressive strained Al0.07Ga0.22In0.71As quantum wells were treated at 170 °C with different heat durations. A significant decrement of photoluminescence decay time was observed on the quantum well of a sample that was annealed after 4 h. The microscopic cathodoluminescent (CL) spectra of these quantum wells were measured by scanning electron microscope-cathodoluminescence (SEM-CL). The thermal treatment effect on quantum wells was characterized via CL emission peak wavelength and energy density distribution, which were obtained by spatially resolved cathodoluminescence. The defect area was clearly observed in the Al0.07Ga0.22In0.71As quantum wells layer after thermal treatment. CL emissions from the defect core have higher emission energy than those from the defect-free regions. The defect core distribution, which was associated with indium segregation gradient distribution, showed asymmetric character.

Transverse modal control of wide-stripe high power semiconductor lasers using sampled grating.

A transverse Bragg resonance (TBR) waveguide semiconductor laser with sampled grating is proposed and analyzed. The transverse phase shift in the middle of the grating is realized by shifting half of the sampling period, resulting in a good single transverse mode resonance. The characteristics such as the modal gain, the electric field distribution, the near and far field beam patterns are theoretically studied. Since the sampled grating is designed by combining a uniform basic grating with a micrometer scale sampling pattern, it can be easily fabricated by holographic exposure and conventional photolithography with low cost. Therefore, the proposed method would be beneficial to volume fabrication of wide-stripe high power semiconductor lasers.

High-power dual-wavelength lasing in bimodal-sized InGaAs/GaAs quantum dots.

In this paper, we demonstrate high power, dual-wavelength (dual-λ) lasing stemming from bimodal-sized InGaAs/GaAs quantum dots (QDs). The device exhibits simultaneous dual-λ lasing at 1015.2 nm and 1023.0 nm with total power of 165.6 mW at 700 mA under room temperature continuous wave (CW) mode. Gaussian fitting analyses of the electroluminescence (EL) spectrum attribute the excellent performance to independent carrier transitions from the first excited states of large dot ensemble (LD ES1) and small dot ensemble (SD ES1), respectively. This formation provides a new possibility to achieve high power dual-λ operation only using Fabry-Pérot (FP) cavity, which is significant for compact size and low fabrication cost.

Bimodal-sized quantum dots for broad spectral bandwidth emitter.

In this work, a high-power and broadband superluminescent diode (SLD) is achieved utilizing bimodal-sized quantum dots (QDs) as active materials. The device exhibits a 3 dB bandwidth of 178.8 nm with output power of 1.3 mW under continuous-wave (CW) conditions. Preliminary discussion attributes the spectra behavior of the device to carrier transfer between small dot ensemble and large dot ensemble. Our result provides a new possibility to further broadening the spectral bandwidth and improving the CW output power of QD-SLDs.

[Effects of insulin on pigment epithelium-derived factor expression in adipocytes of type 2 diabetic mellitus in rats].

OBJECTIVE: To explore the effects of insulin therapy on the expression of pigment epithelium-derived factor (PEDF) in adipocytes of type 2 diabetic mellitus (T2DM) in rats. METHODS: A total of 22 newly diagnosed type 2 diabetics received a 2-week intensive insulin therapy. The levels of fasting plasma glucose (FPG), serum triglyceride and PEDF were measured before and after therapy. T2DM was induced by a high-fat diet and a low-dose streptozotocin (STZ). The Spraque-Dawley rats were divided randomly into diabetic, insulin treatment and gliclazide treatment groups. Another group with a chow diet was designated as normal controls. Differentiated 3T3-L1 adipocytes were then incubated with tumor necrosis factor-alpha (TNF-α) and (or) insulin for 24 h. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and Western blot were used to detect the expression of PEDF in adipose tissue or adipocytes. The PEDF levels in both sera and cell supernatant were measured by enzyme-linked immunosorbent assay (ELISA). Glucose uptake was detected after treatment of PEDF or anti-PEDF antibody simultaneously together with insulin in mature 3T3-L1 adipocytes. RESULTS: Insulin therapy decreased the serum levels of FPG and triglyceride of T2DM patients ((12.9 ± 2.8) vs (5.9 ± 1.4) mmol/L, (3.1 ± 1.8) vs (1.7 ± 0.8) mmol/L, P < 0.05) while the serum level of PEDF decreased significantly after therapy ((22.85 ± 5.73) vs (18.38 ± 5.28) µg/L, P < 0.05). Consistently the serum level of PEDF of diabetic rats was remarkably higher than that of normal controls and insulin-treated group ((28.6 ± 0.5) vs (25.4 ± 0.6) and (25.3 ± 0.6) µg/L, P < 0.05). And the elevated levels of PEDF, TNF-α mRNA and protein in adipose tissue (P < 0.05) could be reduced by insulin treatment (P < 0.05). However, no obvious change was detected in gliclazide treatment group. Further evidences suggested that TNF-α could induce more secretion and expression of PEDF in 3T3-L1 adipocyte while this effect became ameliorated by insulin treatment. Furthermore, decreased capacity of glucose uptake by PEDF might be reversed by anti-PEDF antibody in 3T3-L1 adipocytes (P < 0.05). CONCLUSIONS: Insulin can down-regulate the expression of PEDF in adipocytes of T2DM and improve the glucose uptake of adipocytes. It may be one of the mechanisms through which insulin therapy improves peripheral insulin resistance.

PEDF expression is inhibited by insulin treatment in adipose tissue via suppressing 11ß-HSD1.

Early intensive insulin therapy improves insulin sensitivity in type 2 diabetic patients; while the underlying mechanism remains largely unknown. Pigment epithelium-derived factor (PEDF), an anti-angiogenic factor, is believed to be involved in the pathogenesis of insulin resistance. Here, we hypothesize that PEDF might be down regulated by insulin and then lead to the improved insulin resistance in type 2 diabetic patients during insulin therapy. We addressed this issue by investigating insulin regulation of PEDF expression in diabetic conditions. The results showed that serum PEDF was reduced by 15% in newly diagnosed type 2 diabetic patients after insulin therapy. In adipose tissue of diabetic Sprague-Dawley rats, PEDF expression was associated with TNF-α elevation and it could be decreased both in serum and in adipose tissue by insulin treatment. In adipocytes, PEDF was induced by TNF-α through activation of NF-κB. The response was inhibited by knockdown and enhanced by over expression of NF-κB p65. However, PEDF expression was indirectly, not directly, induced by NF-κB which promoted 11ß-hydroxysteroid dehydrogenase 1 (11ß-HSD1) expression in adipocytes. 11ß-HSD1 is likely to stimulate PEDF expression through production of active form of glucocorticoids as dexamethasone induced PEDF expression in adipose tissue. Insulin inhibited PEDF by down-regulating 11ß-HSD1 expression. The results suggest that PEDF activity is induced by inflammation and decreased by insulin through targeting 11ß-HSD1/glucocorticoid pathway in adipose tissue of diabetic patients.

Involvement of connective tissue growth factor (CTGF) in insulin-like growth factor-I (IGF1) stimulation of proliferation of a bovine mammary epithelial cell line.

The objective of this study was to determine the mechanism by which insulin-like growth factor-I (IGF1) stimulates proliferation of mammary epithelial cells, using the bovine mammary epithelial cell line MAC-T as a model. IGF1 significantly up- or down-regulated the expression of 155 genes in MAC-T cells. Among the most significantly suppressed was the gene for connective tissue growth factor (CTGF), a secretory protein that has both proliferative and apoptotic effects and is also a low-affinity binding protein of IGF1. IGF1 inhibited CTGF expression through the PI3K-Akt signaling pathway. Administration of growth hormone (GH), a strong stimulator of IGF1 production in vivo, decreased mammary CTGF mRNA in cattle; however, GH did not affect CTGF expression in MAC-T cells, suggesting that IGF1 may also inhibit CTGF expression in the mammary gland. Added alone CTGF stimulated proliferation of MAC-T cells, but in combination with IGF1 it attenuated IGF1's stimulation of proliferation of MAC-T cells. Excess IGF1 reversed this attenuating effect of CTGF. Despite being an IGF binding protein, CTGF did not affect IGF1-induced phosphorylation of IGF1 receptor (IGF1R) or IGF1R expression in MAC-T cells, indicating that the attenuating effect of CTGF on IGF1 stimulated proliferation of MAC-T cells was not mediated by decreasing IGF1's ability to bind to IGF1R or by decreasing IGF1R expression. Overall, these results suggest a novel biochemical and functional relationship between CTGF and IGF1 in the bovine mammary gland, where IGF1 may inhibit CTGF expression to reduce the attenuating effect of CTGF on IGF1 stimulated proliferation of epithelial cells.

The effects of interferon-gamma on the expression of the cyclin D isoforms in cord blood hematopoietic stem/progenitor cells.

To explore the hematopoiesis inhibition mechanisms of interferon-gamma (IFN-gamma), the effects of IFN-gamma on the expression of the cyclin D in the umbilical cord blood hematopoietic stem/progenitor cells were observed. In the experiments the CD34(+) cells were isolated from the cord blood with MIDI-MACS system; semi-solid methylcellulose culture technique was used to measure the formation of CFU-GM; the expression levels of cyclin D isoforms were assayed by semi-quantitative RT-PCR, after the hematopoietic stem/progenitor cells were incubated with IFN-gamma. The results indicated that IFN-gamma could inhibit the formation of CFU-GM and down-regulate the expression of cyclin D2 and cyclin D3 at the mRNA level. It is concluded that the IFN-gamma could inhibit the proliferation of hematopoietic stem cells and down-regulate the expression of cyclin D, that may be one mechanism underlying the hematopoietic inhibition of IFN-gamma.

[Effect of Ligustrazine on the expression of vascular endothelial growth factor in bone marrow stromal cells of radiation injured mice].

To evaluate the effect of Ligustrazine on the expression of VEGF in bone marrow stromal cells (BMSCs) of radiation injured mice and to explore the effect of VEGF on the recovery of hematopoiesis and the mechanism of signal transduction, the protein expression of VEGF, focal adhesion kinase (FAK) and mitogen-activated protein kinase (MAPK) in BMSCs were assayed by Western blot, the cell cycle and apoptosis rate of BMSCs were tested by flow cytometry. The effect of Ligustrazine on the hematopoiesis was evaluated at the same time. The results showed that the protein expression of VEGF in BMSCs was decreased significantly after irradiation and increased slowly with the time. The value in Ligustrazine-treated group almost reached normal level, but it remained lower than that in control group on day 14. The changes of phosphorylated FAK and MAPK protein expression had the same tendency. After (60)Co gamma-irradiation, the BMSCs were arrested in G0-G1 phase and apoptosis rate increased; these values recovered slowly with the time and remained higher than that in normal control group on day 14. The recovery of these values in Ligustrazine-treated group was sooner than that in irradiated control group, and they almost reached to the normal levels on day 14. It is concluded that irradiation could inhibit the expression of VEGF in BMSCs and induce apoptosis. The Ligustrazine promotes the recovery of bone marrow microenvironment probably by increasing the expression of phosphorylated FAK and MAPK in BMSCs.

Effects of platelet factor 4 on expression of bone marrow heparan sulfate in syngenic bone marrow transplantation mice.

To explore the effects of platelet factor 4(PF4) on hematopoietic reconstitution and its mechanism in syngenic bone marrow transplantation (BMT). The syngenic BMT mice models were established. 20 and 26 h before irradiation, the mice were injected 20 micrograms/kg PF4 or PBS twice into abdominal cavity, then the donor bone marrow nuclear cells (BMNC) were transplanted. On the 7th day, spleen clone forming units (CFU-S) were counted. On the 7th, 14th and 21st day after BMT, the BMNC and megakaryoryocytes in bone marrow tissue were counted and the percentage of hematopoietic tissue and expression level of heparan sulfate in bone marrow tissue were assessed. In PF4-treated groups, the CFU-S counts on the 7th day were higher than those in BMT groups after BMT. The BMNC and megakaryoryocyte counts and the percentage of hematopoietic tissue and heparan sulfate expression level were higher than those in BMT group on the 7th, 14th and 21st day after BMT (P < 0.01 or P < 0.05). PF4 could accelerate hematopoietic reconstitution of syngenic bone marrow transplantation. The promotion of the heparan sulfate expression in bone marrow may be one of mechanisms of PF4.