第 44 卷 第 10 期/2024 年 5 月/光学学报 quality factor of the reflected X -LP beam is 1.11, and that of the reflected Y -LP beam is 1.12 (Fig. 5). Therefore, when X -LP and Y -LP beams are combined to propagate in the same direction, the beam quality factor of the combined beam is 1.12 [Fig. 6(a)]. The spectrum of the combined beam coincides well with the overlap of the two individual incident laser spectra [Fig. 6(b)]. Consequently, this study demonstrates that a polarization beam combiner based on the anomalous reflective metasurface has not only high combination efficiency but also broad operation bandwidth. It is suitable to be used for the midinfrared QCL power combining.
ConclusionsWe study a polarization beam combiner based on anomalous reflective metasurface, which is utilized to combine two incident beams with orthogonal linear polarizations. The beam combiner consists of periodic supercells with a dimension of 2 μm×20 μm. Each supercell contains 10 single cells of 2 μm×2 μm. The single cell comprises a metal substrate, a dielectric middle layer, and a top rectangular column. When the collimated X -LP and Y -LP beams with a central wavelength of 4.0 μm and incident angles of and − 11.54° reach the metasurface, both beams are reflected anomalously in the normal direction of the metasurface. The polarization beam combination is realized. Within a broad spectral band of 3.9 to 4.1 μm, high average anomalous reflectivity of 96.6% and 97.7% are obtained for X -LP and Y -LP incident beams, respectively. Based on the near field reflective intensity and phase distribution, the propagation of the combined beam in free space is simulated by the periodic field splicing method and Gaussian beam propagation law .Assuming both X -LP and Y -LP incident beams are fundamental Gaussian beams, the beam quality factor of the combined beam is 1.12. The metasurface beam combiner shows high design flexibility and can be prepared by mature MEMS technology. It has a good potential to solve the problems in midand longinfrared power beam combinations.
