According to the theory of DBR, with the P-type DBR as an example, the electrical characteristics and optical reflection of the DBR are analyzed by studying the energy band structure with various graded region widths and doping densities. The width and doping density of graded region are decided through a comparative study. The P-type DBR of 980 nm VCSELs is designed with Al0.9Ga0.1As and Al0.1Ga0.9As selected as the high and low refractive index material for the DBR. The 980 nm bottom VCSELs, which consists of 30 pairs P-type DBR and 28 pairs N-type DBR, are then fabricated. In P-type DBR, the width of graded region is 0.02 μm and the uniformity doping concentration is 2.5×10^18cm^-3. Its reflectivity is 99.9%. In N-type DBR, the width of graded region is also 0.02 μm and the uniformity doping concen- tration is 2×10^18cm^-3. Its reflectivity is 99.3%. The I-V curve shows that the series resistance of the device is about 0.05Ω. According to the theory of DBR, with the P-type DBR as an example, the electrical characteristics and optical reflection of the DBR are analyzed by studying the energy band structure with various graded region widths and doping densities. The width and doping density of graded region are decided through a comparative study. The P-type DBR of 980 nm VCSELs is designed, with Al0.9Ga0.1As and Al0.1Ga0.9As selected as the high and low refractive index material for the DBR. The 980 nm bottom VCSELs, which consist of 30 pairs P-type DBR and 28 pairs N-type DBR, are then fabricated. In P-type DBR, the width of graded region is 0.02μm and the uniformity doping concentration is 2.5×10^18cm^-3. Its reflectivity is 99.9%. In N-type DBR, the width of graded region is also 0.02 μm and the uniformity doping concentration is 2×10^18cm^-3. Its refiectivity is 99.3%. The I-V curve shows that the series resistance of the device is about 0.05Ω.
A 980 nm bottom-emitting vertical-cavity surface-emitting laser linear array with high power density and a good beam property of Gaussian far-field distribution is reported. This array is composed of five linearly arranged elements with a 200 μm diameter one at the center, the other two 150μm and 100μm diameter ones at both sides of the center with center to center spacing of 300μm and 250μm, respectively. A power of 880 mW at a current of 4 A and a corresponding power density of up to 1 kW/cm^2 is obtained. The temperature dependent characteristics of the linear array are investigated. The thermal interaction between the individual elements of the VCSEL linear array is smaller due to its optimized element size and device spacing, which make it more suitable for high power applications. A peak power of over 20 W has been achieved in pulsed operation with a 60 ns pulse length and a repetition frequency of 1 kHz.
The whispering-gallery-mode （WGM） photonic crystal microcavity can be potentially used for miniaturized photonic devices, such as thresholdless lasers. In this paper, we use plane wave expansion （PWE） method and study the WGM of H2 photonic crystal microcavities which are formed by removing seven center air holes in a photonic crystal. The WGM in these large- size cavities has some advantages compared with single defect WGM in the view of real device applications. We analyze the nearby air hole effect on WGM and conclude that WGM is more sensitive to moving towards the outside rather than moving towards the inside of a nearby air hole. In our case, if a nearby air hole is moved 0. la away from the center, the WGM will disappear. If a nearby air hole is moved 0.6a towards the center, however, the WGM will still exit. We also analyze the structure with an air hole （rm= 0.2a） in the center of the microcavity, and we fred that the WGM is not affected by the central hole sensitively. As we increase rm, the WGM remains unchanged until rm is 0.64 times greater than period a. It is found that the tolerance of WGM to the displacement of nearby air holes and the occurance of central holes is large enough to fabricate electrical injection structure.
