Objective 1550 nm transverse mode semiconductor laser has been applied in many fields such as optical fiber communication,spectral analysis,photoelectric detection,medical cosmetology. At the same time,it is also the research basis of communication band semiconductor optical amplifiers and narrow linewidth transverse mode semiconductor lasers. The kink effect refers to the fact that the P- I curve of the fundamental transverse mode device will be bent,which will greatly reduce the output power of lasers. At the same time,the steering effect will cause the far- field divergence angle of the horizontal direction of the device to shift and reduce the beam quality of the fundamental transverse mode device. For the 1550 nm semiconductor laser in the communication band,it will affect the efficiency of coupling with the single-mode fiber. In this paper,a 1550 nm high- power AlGaInAs/InP-based transverse mode semiconductor laser is designed and fabricated, and the kink effect is studied. Methods In this paper,a gradual Al component is introduced into the waveguide,and the atomic number fraction is 0. 310. 35. In addition,the atomic number fraction of Al component becomes lower when getting closer to the active region. This design can effectively reduce the oxidation of Al near the active region at the high-power output and improve the reliability of the device. At the same time,with the gradual increase in the Al atomic number fraction,the refractive index of AlGaInAs decreases gradually,which reduces the confinement factor of the whole device,improves the saturation power of the device, and lowers the far-field divergence angle. In order to realize the fundamental transverse mode output,the relationship between the residual thickness of cladding and ridge width is calculated according to the effective refractive index method. In view of the actual process,the final ridge width is 5. 4 mu m,and the etching depth is 2 mu m (Fig. 2). In order to analyze the kink effect occurring after device fabrication,a temperature model with high-order mode cutoff is established(Fig. 8). The mode output characteristics of the device before and after temperature rise are analyzed,and the influence of temperature on the kink effect is proved by measuring devices with different cavity lengths(Fig. 10). Results and Discussions The threshold current of the device designed and fabricated in this paper is 29 mA,the maximum slope efficiency is 0. 35 mW/mA,and the maximum output power is 138 mW(Fig. 3). At the highest output power of the device,the vertical and horizontal divergence angles are 32. 9 degrees and 11. 1 degrees,respectively (Fig. 4),which proves that the device has good fundamental transverse mode output characteristics,and the internal quantum efficiency and loss are 53. 6% and 6. 24 cm-1,respectively(Fig. 5). The P-I curve of the device at different operating temperatures is observed(Fig. 6). The current increasing curve tends to be flat at the same temperature,which is caused by the broadening and reduction of the gain spectrum due to the increase in the current and the saturation state of the device due to a large amount of carrier leakage. For the P-I folding phenomenon at a high temperature,according to the temperature model of the higher-order mode cut- off, it is believed that the temperature rise is more likely to make the higher-order mode compete with the fundamental transverse mode generation mode. Furthermore,as the gain of the higher-order mode increases,the gain of the fundamental transverse mode decreases,which leads to the kink effect. With the kink effect,the far-field divergence angle also has a steering effect. The peak of the far-field divergence angle shifts by 2. 2 degrees(Fig. 9),which is caused by the non-uniform lateral distribution of charge carriers. For devices with different cavity lengths,a longer cavity length is often accompanied by a higher current value of the kink effect. As the long cavity length structure has better heat dissipation,it proves not only that the temperature affects the occurrence of the kink effect but also that the long cavity length structure can better suppress the kink effect. Conclusions In this paper,a 1550 nm high- power AlGaInAs/ InP laser with the transverse mode is designed and fabricated. The device achieves a slope efficiency of 0. 35 mW/ mA and a power output of 138 mW at room temperature. The vertical and horizontal far-field divergence angles are 32. 9 degrees and 11. 1 degrees,respectively. By analyzing the kink effect in the P-I curve of the device at a high temperature and using the relationship between the refractive index of the waveguide and the temperature, a temperature model of the high-order mode cutoff is established. It shows that the heat changes the refractive index and then affects the high-order mode cutoff condition,which leads to the reduction of the gain of the fundamental transverse mode and the occurrence of the kink effect in the device. The non-uniform carrier distribution caused by the effect of hole burning in space makes the far-field divergence angle show the steering effect. By comparing the current at which the kink effect occurs in devices with different cavity lengths,it is proved that the device with a long cavity length can effectively prevent the occurrence of the kink effect.
