研究了不同方向、不同强度的应变对Ge光学性质的影响。结果表明, Ge在单轴张应变和双轴张应变的调控下, 均可由间接带隙转向直接带隙, 其中, 单轴应变有更低的转变点。Ge在常用波段处（0.4 eV）的介电函数实部和虚部在张应变作用下, 均急速上升而后在一定应变范围内下降。对Ge进行［111］单轴应变调控能表现出更好的光学性能以及更便捷的器件设计（较低的应变量）。

To explore the changes of the optical properties for Ge in different orientations and different strains, we performed the first principle calculations based on density functional theory combined with GGA+U approach. The results show that Ge undergoes a transition from indirect- to direct-gap on uniaxially tensile strains (along ［100］, ［110］ and ［111］ directions) and biaxially tensile strains (parallel to (100), (110) planes).The band gaps of Ge with uniaxially strains (along ［110］ and ［111］ directions) are higher than those with biaxially strains, and the transition points of uniaxially strains are lower than those of biaxially strains. Under uniaxially and biaxially compressive strains, the changes of dielectric constants and loss factors of Ge between the frequency bands are both negligible. However, the dielectric constants and loss factors rise first and then fall in a definite range of strains when Ge is under uniaxially and biaxially tensile strains. Compared with unstrained Ge, Ge under ［111］ 1.22% strain possesses excellent optical properties: reasonable forbidden bandwidth, higher static dielectric, higher absorption coefficient, lower loss function and lower strains.