Abstract
The structure of a novel ring-shaped top-DBR etched microstructure VCSEL with a proton implantation high resistance region was designed. A ring column structure was formed from the upper electrode to the active region, which directly generated a hollow laser beam output. The optical field distribution of the etched microstructure VCSEL was calculated by FDTD software, and the obtained ring-shaped patterns maintained the hollow beam characteristics under the different mode numbers. We fabricated the etched microstructure VCSEL with a lasing wavelength of 848 nm at room temperature and investigated its performance. The threshold current was 0.27 A and the peak power was up to 170 mW. The near-field patterns of different currents clearly displayed hollow ring-shaped spots. The distribution curves of far-field light intensity matched the characteristics of a hollow beam as well. This novel VCSEL provides a new approach for the development of hollow beams and even array devices.
A hollow laser bea
The vertical cavity surface emitting laser (VCSEL) is a kind of semiconductor lasers with unique advantages such as low threshold, no cavity surface damage, and circular symmetric spo
In this article, we propose a new concept of using an etched microstructure VCSEL with a high-resistance area in the upper Distributed Bragg Reflector (DBR) to directly emit a hollow laser beam, to obtain a high-quality hollow laser beam more easily and directly. This structure utilizes the mode selection effect of artificial microstructure to reduce the effect of optical feedback gain in the central area to achieve mode control. A novel microstructure surface emitting laser and its hollow beam output are realized, and its transverse mode is simulated. An etched microstructure surface emitting laser with a high resistance region has been fabricated and its output characteristics have been tested and analyzed.
In the conventional surface emitting laser structure, the overall semiconductor process from the light output window to the active gain region is made into a cylindrical structure. The output beam of the VCSEL with this structure is a circularly symmetric Gaussian bea

Fig. 1 Structure schematic of the ring-shaped top-DBR etched microstructure VCSEL
图1 环形上DBR刻蚀微结构VCSEL结构示意图
To study the transverse mode of the etched microstructure VCSEL, the Finite Difference Time Domai
The transverse mode transmission pattern is simulated with device structural parameters and semiconductor material optical parameters, as shown in

Fig. 2 Calculated intensity profiles of different mode numbers (n) of ring-shaped top-DBR etched microstructure VCSEL obtained by FDTD: (a) n=1, (b) n=5, (c) n=9, (d) n=13
图2 FDTD计算得到的环形上DBR刻蚀微结构VCSEL不同模式数目(n)的强度分布:(a) n=1, (b) n=5, (c) n=9, (d) n=13
A single-mode with a ring-shaped pattern can be seen in
The hollow laser beam can be used for signal transmission in free space optical communicatio
The microstructure VCSEL was fabricated on the GaAs/Al0.3Ga0.7As triple quantum well laser material grown by metal organic chemical vapor deposition (MOCVD) on top of an N-doped 500 μm thick GaAs substrate. The active region is sandwiched between two DBRs. The upper DBR consists of 20 pairs of P-type Al0.9Ga0.1As/Al0.12Ga0.88As, while the lower DBR consists of 36 pairs of N-type Al0.9Ga0.1As/Al0.12Ga0.88As.
Then the first photolithography and inductively coupled plasma (ICP) etching were performed on the cleaned epitaxial wafer to etch the active region and above into a column. The etching depth is about 5 μm, and the mesa diameter is 200 μm. The central area etched microstructure with a depth of about 2.8 μm and an etching hole diameter of 50 μm was obtained by second photolithography and etching. After forming an oxide limiting layer by the wet oxidation process, a 200 nm thick layer of SiO2 was deposited on the device surface as an insulating layer. Then, the light window and central etched area were exposed through the third lithography and etching. Next, the lithography mask method was used to protect other areas and expose the central etched area. The chip was then placed into a high-energy ion implanter and

Fig. 3 Injection depth as a function of injection power (Down-right inset: SEM image of the central etched area)
图3 注入深度随注入能量的变化规律(右下插图:中心刻蚀区域的扫描电镜图像)

Fig. 4 Microscope image of the fabricated ring-shaped top-DBR etched microstructure VCSEL
图4 制备的环形上DBR刻蚀微结构VCSEL的显微镜图像
We measured the light emission characteristics of the etched microstructure VCSEL under the continuous-wave condition at room temperature. The output near-field pattern was photographed by a CCD camera, as shown in

Fig. 5 The near-field pattern of the ring-shaped top-DBR etched microstructure VCSEL
图5 环形上DBR刻蚀微结构VCSEL的近场发光图
The experimental measurement of the light output power-injection current-voltage (L-I-V) characteristic was carried out by using a photodiode power meter. The output power of the device was tested under continuous conditions, and no significant change in power was found during several hours of testing. The L-I-V curve and the corresponding near-field pattern are shown in

Fig. 6 Light output power and voltage as a function of injection current of the ring-shaped top-DBR etched microstructure VCSEL
图6 环形上DBR刻蚀微结构VCSEL的光输出功率和电压随注入电流的变化规律
The lasing spectrum of the microstructure VCSEL is analyzed by a spectrometer, as shown in

Fig. 7 The light spectrum of the ring-shaped top-DBR etched microstructure VCSEL at different injection currents: (a) 0.3 A, (b) 1.2 A
图7 环形上DBR刻蚀微结构VCSEL在不同注入电流下的光谱图:(a) 0.3 A, (b) 1.2 A

Fig. 8 The light intensity distribution curves of the ring-shaped top-DBR etched microstructure VCSEL in vertical and parallel directions
图8 环形上DBR刻蚀微结构VCSEL在垂直和平行方向的光强分布曲线
The reason that the central area isn’t completely dark may be, on the one hand, the rough wall and structural damage caused by etching will bring unnecessary light scattering. On the other hand, the light beam will scatter and diffract during the transmission process. Therefore, further research direction would be to optimize the device structure design to make the current injection more uniform, reduce the internal resistance of the device, and reduce the threshold current of the device. Additionally, it would be beneficial to improve the experimental process of the fabrication steps, reduce the damage to the device during the process steps, and realize the vertical cavity semiconductor laser to emit high-quality hollow laser beams more efficiently.
This paper designs a vertical cavity surface emitting semiconductor laser with an etched microstructure that uses a proton injection to form a high-resistance region. The microstructure VCSEL can directly obtain a hollow laser beam. The key technical issues such as the fabrication process were studied, and the lateral light field distribution was calculated by FDTD software. The ring-shaped top-DBR etched microstructure vertical cavity surface emitting semiconductor laser was successfully fabricated. And the output characteristics of the fabricated device were measured. The lasing wavelength is 848 nm, the threshold current is about 0.27 A, the output power is up to 170 mW, and the near-field pattern is a ring-shaped hollow beam pattern. Due to factors such as the etched surface can cause scattering and carrier diffusion, the central area of the beam is not completely dark. This research opens up a new direction in the research of semiconductor laser technology, proposes a new technical method for acquiring hollow laser beams, and provides technical support for the two-dimensional array integration of hollow beams. The two-dimensional array of hollow beams lays a good foundation for the future development of multi-particle manipulation and optical addressing devices.
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