ABSTRACT
We demonstrate high-output-power and high-efficiency operation of 1.3-µm-wavelength InP-based photonic-crystal surface-emitting lasers (PCSELs). By introducing a metal reflector and adjusting the phase of the reflected light via optimization of the thickness of the p-InP cladding layer, we successfully achieve an output power of approximately 400â mW with the slope efficiency of 0.4 W/A and the wall-plug efficiency of 20% under CW conditions. In addition, this PCSEL exhibits a narrow circular beam with a divergence angle below 1.6° even at high output powers under CW conditions at temperatures from 15°C to 50°C. We have also demonstrated an output power of over 12 W under pulsed conditions at room temperature.
ABSTRACT
We demonstrate high-power continuous-wave (CW) lasing oscillation of 1.3-µm wavelength InP-based photonic-crystal surface-emitting lasers (PCSELs). Single-mode operation with an output power of over 100â mW, a side-mode suppression ratio (SMSR) of over 50â dB, and a narrow single-lobe beam with a divergence angle of below 1.2° are successfully achieved by using a double-lattice photonic crystal structure consisting of high-aspect-ratio deep air holes. The double lattice is designed to enhance both the in-plane optical feedback and the surface radiation effects in the photonic crystal. The coupling coefficients for 180 ∘, +90 ∘, and -90 ∘ diffractions are estimated from the measurements of the photonic band structure as κ1D = 417 cm-1, κ2D+ = 135 cm-1, and κ2D- = 65 cm-1, respectively. The stable single-mode, high-beam-quality operation is attributed to these large coupling coefficients introduced by the asymmetric double-lattice structure.
ABSTRACT
We report on electrically driven InP-based photonic-crystal surface-emitting lasers (PCSELs), which possess a deep-air-hole photonic crystal (PC) structure underneath an active region formed by metal-organic vapor-phase-epitaxial (MOVPE) regrowth. Single-mode continuous-wave (CW) lasing operation in 1.3-µm wavelength is successfully achieved at a temperature of 15°C. It is shown that the enhancement of lateral growth during the MOVPE regrowth process of air holes enables the formation of deep air holes with an atomically flat and thin overlayer, whose thickness is less than 100â nm. A threshold current of 120â mA (threshold current density = 0.68â kA/cm2) is obtained in a device with a diameter of 150â µm. A doughnut-like far-field pattern with the narrow beam divergence of less than 1° is observed. Strong optical confinement in the PC structure is revealed from measurements of the photonic band structure, and this strong optical confinement leads to the single-mode CW lasing operation with a low threshold current density.
ABSTRACT
Despite evidence that tripeptide glycyl-Ê-histidyl-Ê-lysine (GHK) is an endogenous antioxidant, its mechanism and importance are not fully understood. In the present study, the ability of GHK to reduce levels of reactive oxygen species (ROS) in Caco-2 cells was evaluated by flow cytometry with the oxidation-sensitive fluorescent dye 2',7'-dichlorodihydrofluorescein diacetate. Further, types of ROS diminished by GHK were assessed by utilizing an electron spin resonance (ESR) spin-trapping technique. GHK reduced the tert-butyl hydroperoxide-induced increase in ROS levels in Caco-2 cells at concentrations of 10 µM or less. Experiments utilizing an ESR spin-trapping technique revealed that, among hydroxyl (·OH), superoxide (O2-·), and peroxyl (ROO·) radicals generated by respective chemical reaction systems, GHK diminished signals of both ·OH and ROO·, but not O2-·. Additionally, the GHK effect on the signal of ·OH was much stronger than those of other well-known antioxidative, endogenous peptides, carnosine and reduced glutathione. These results suggest that GHK can function as an endogenous antioxidant in living organisms, possibly by diminishing ·OH and ROO·.
