Results and Discussions In traditional tapered lasers, phenomena such as optical pumping, spatial hole burning, and beam filamentation cause the beam quality to deteriorate rapidly under high powers (Fig. 3). The residual reflected light on the front facet is transmitted in the tapered waveguide, and the optical field exhibits a significantly uneven distribution. With a decrease in the reflectivity of the front facet, the side lobes are suppressed. When the reflectivity of the front facet decreases below 1%, the light-field distribution tends to be stable. In particular, when the reflectivity of the front facet is 0.01%, the beam intensity in waveguide increases significantly (Fig. 4). The reflectivity of the rear facet directly induces an optical pumping effect. Reducing the reflectivity of the rear facet can weaken the optical pumping in the cavity (Fig. 5). Combined with the optimization of the front facet reflection, the mode characteristics are significantly improved, and an output close to the fundamental mode is obtained (Fig. 6). By optimizing the reflectivity of the facet, two optimization paths are proposed to achieve high beam quality (Figs. 7 and 8). Four optimized designs are selected to simulate the output characteristics. Compared with the traditional tapered lasers, the output characteristics are not significantly reduced, whereas the simulation of beam quality shows that the optimized design achieves a high beam quality with beam quality factor even lower than 2 (Fig. 9).

Tapered lasers undergo severe beam quality deterioration under high powers. Optical pumping, self-focusing, spatial hole burning, and beam filamentation are some phenomena that occur in traditional tapered lasers, severely degrading the beam quality. Facet reflection causes these problems, but the specific influence mechanism of facet reflection on beam quality is unclear. This study aims to clarify the effect of facet reflection on the beam quality of tapered lasers and proposes an optimization scheme to improve the beam quality.

Based on facet coating, this study establishes a physical model of a tapered laser without an antireflection structure. By varying the reflectivity of the front and rear facets and using the electro-optic model of the tapered lasers for simulations, the optical field distributions at different positions in the transmission direction in the facet are analyzed. In addition, the effect of facet reflection on the beam quality of the tapered laser is investigated. The output characteristics and beam quality factor of the optimized design are also verified using the simulation method.

Facet reflection is closely related to the beam quality. The residual reflection from the facets influences the field distribution in the cavity, causing the concentration of the local gain and refractive index, giving rise to nonlinear effects, and finally deteriorating the beam quality of the device. The reflection of the front facet plays a critical role in this process. The residual reflected light of the front facet is transmitted through a tapered waveguide owing to the unique structure of the tapered laser, and the optical field generates a significantly uneven distribution. In addition, the reflection of the rear facet directly causes optical pumping, which also significantly impacts the beam quality. By optimizing the reflectivity of the facet, two optimized paths are proposed to achieve high beam quality. Some optimal designs have their beam quality factor M2 less than 2 and maintain good output characteristics. Compared to previously designed schemes, there is no need to modify the overall structure. Adjusting only the reflectivity of the facet using the optical film can yield high beam quality. This study provides a reference for the design of a tapered laser.