We have designed a fiber coupling method based on the spatial beam combining of the Photonic Crystal (PC) Laser Diode (LD). The PC LD with a small fast-axis divergence angle makes it possible to reduce the requirements for the numerical aperture and the processing precision of the optical elements, increase the alignment tolerance of components, reduce the difficulty of shaping, and improve the product yield. In the module, there is no need for the collimation of the fast-axis and slow-axis beams, which can be simultaneously focused into the optical fiber through an aspheric cylindrical lens. The simulated results, obtained by the ray tracing method, have shown a coupling efficiency of around 91.4% when the PC LD is coupled into a fiber with a core diameter of 105 μm and the numerical aperture of 0.22. Then, we have performed the experiments, and the coupling efficiency of 71.5% has been achieved. By analyzing the deviation of the simulated and experimental coupling efficiency, we have proposed several solutions. Finally, according to the strategy of this beam shaping, we also list several promising arrangements, which further prove that the beam shaping method possesses broad application prospects.
Bound states in the continuum (BICs) remain localized even though they coexist with a continuous spectrum of radiating waves that can carry energy away. These modes can be almost perfectly localized in the structure, making lasers working at BIC or quasi-BIC have an ultrahigh quality factor (Q) and hence low threshold. Lowcontrast gratings (LCGs) have better mode selectivity than high-contrast gratings and promise higher single-mode output power for LCG-based vertical-cavity surface-emitting lasers. A quasi-BIC (i.e. supercavity mode) with a Q factor of 9.2 × 105 is obtained in the LCG, and a simplified three-layer slot laser with a Q factor of 9.66 × 106 is constructed. Further, a law of using the period of a grating to control resonant wavelength and using etched depth and width to control Q factor can be used for designing a high-Q structure at a specified wavelength. The calculated Q factor is optimized systematically by changing various parameters, and the highest Q factor obtained reaches 2.81 × 107 . The results of all these analyses are instructive to the design of grating-based low threshold electrically injected surface-emitting lasers or other high-Q devices.
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