深紫外倍频用KBBF晶体光栅耦合器设计

分析了氟硼铍酸钾(KBe2BO3F2,KBBF)晶体的倍频特性,结合基波光光栅耦合和KBBF晶体内全反射特性设计了新型KBBF晶体光栅耦合器。介绍了KBBF晶体光栅耦合器设计原理。在KBBF晶体表面制作光栅结构,使其衍射级次满足匹配角进而产生倍频光;结合在KBBF晶体内的全反射传输,增大光程,获得高的倍频转化效率。通过计算晶体匹配角、走离角、倍频系数等参数,获得合适的光栅匹配类型。优化设计匹配光栅参数,获得了槽型参数及较高的衍射效率;基于光栅衍射效率与倍频转化率的关系获得了KBBF晶体光栅耦合器的倍频转化率计算公式,并给出它们的适用范围。最后,基于5.2mm×5.2mm×1mm KBBF晶体研制了晶体光栅耦合器,该光栅耦合器能够实现深紫外波段倍频光的输出,总倍频转化效率达到了16.86%

Design of KBBF crystal grating coupler in deep ultraviolet band

The double frequency characteristics of KBe₂BO₃F₂(KBBF) crystals were analyzed. A new KBBF crystal grating coupler was designed with combination of the base wave grating coupling and the total reflection properties of KBBF crystals. The design principle of KBBF crystal grating coupler was introduced.By etching diffraction grating on the surface of a KBBF crystal, the diffraction order matching with the grating was chosen to generate double frequency. The total reflection in the KBBF crystal was used to increase optical path to obtain higher frequency conversion efficiency. Then, appropriate matching types were put forward by calculating matching angle, walk-off angle, frequency factor and other parameters. And the matched grating parameters were optimized to calculate groove parameters and diffraction efficiency of grating. Moreover, grating coupler frequency conversion formulas were given and their applicable ranges were shown. Finally, crystal grating coupler based on a 5.2 mm×5.2 mm×1 mm KBBF crystal was fabricated, and the results indicate that the grating coupler realizes double frequency outputs in deep ultraviolet waveband and its total frequency conversion efficiency reaches 16.86%.