To obtain high-power semiconductor lasers with stable operation in a single longitudinal mode and improve the characteristics of the output beam,an end-emitting surface second-order metal grating distributed feedback(DFB) laser emitting at around 940 nm is fabricated.The characteristics of the uncoated devices with and without gratings are tested under room temperature continuous-wave conditions without any temperature-control device and compared.The devices with gratings achieve high powers of up to 385 mW/facet and a small lateral far-field angle of 2.7° at 1.5 A,have only 4.13 nm/A wavelength-shift,and 0.09 nm spectral linewidth at 600 mA,and operate in a stable longitudinal mode.Devices without gratings operate in multimode,with a larger lateral far-field angle(7.3°) and spectral linewidth(1.3 nm),although with higher output powers.Because of the integration of second-order metal gratings and their very high coupling capability,the output beam quality is improved greatly,the lasing wavelength is stable and varies slowly with changes in injection current,while the spectrum is narrowed dramatically,and the far-field angles are greatly reduced.This opens the way for the realization of watt-scale power broad-stripe(>100 μm) surface second-order metal grating end and surface-emitting DFB lasers and arrays with single frequency,single mode operation and high output beam quality.
The output performance of a 980-nm broad-area vertical-cavity surface-emitting laser(VCSEL) is improved by optimizing the p-electrode diameter in this study.Based on a three-dimensional finite-element method,the current density distribution within the active region of the VCSEL is optimized through the appropriate adjustment of the p-electrode diameter,and uniform current-density distribution is achieved.Then,the effects of this optimization are studied experimentally.The L-I-V characteristics under different temperatures of the VCSELs with different p-electrode diameters are investigated,and better temperature stability is demonstrated in the VCSEL with an optimized p-electrode diameter.The far-field measurements show that with an injected current of 2 A,the far-field divergence angle of the VCSEL with an optimized p-electrode diameter is 9°,which is much lower than the far-field angle of the VCSEL without this optimization.Also the VCSEL with an optimized p-electrode diameter shows a better near-field distribution.
A single-mask dry-release process for fabrication of high aspect ratio SOI MEMS devices is presented,which takes advantage of the lag effect in silicon DRIE(deep reactive ion etching).The wide trenches and the releasing holes are etched to the buried oxide in the first-step DRIE whereas the narrow trenches are still connected due to the lag effect.After the buried oxide is removed by wet etching through the opened releasing holes and wide trenches,the narrow trenches are etched through by the second-step DRIE.Not only can the sticking problems be avoided,but also the footing effect during the DRIE can be partially suppressed.The feasibility of the proposed technique was verified by implementing a capacitive accelerometer.The scale factor and the non-linearity of the fabricated accelerometer were measured to be 63.4 mV/g and 0.1% with the measurement range of ±1 g,respectively.
