DMD光栅的衍射特性及其在可调谐激光中的应用

相比较于液晶空间光调制器,数字微镜晶片(DMD)具有开关速度快、显示精度高、偏振不相关、衍射效率高和宽带调制等优势。研究利用DMD的衍射效应作为波长选择器,将其应用于可调谐光纤激光器中,理论推导这种二维DMD光栅的衍射效率与入射光角度,像素间距等物理量之间的定量关系,重点讨论了两种不同像素间距的0.7″和0.55″DMD在单像素因子和多像素干涉共同作用下的衍射级数和强度分布。研究结果表明:0.7″DMD在光强不显著为零且满足实验约束条件下,允许出现4个干涉极大值,但由于极大值位置均远离闪耀条件,因此光强相对较弱。0.55″DMD仅出现1个干涉极大值,且接近闪耀条件,因此光强和效率均明显高于0.7″DMD的情况。由此可见,在可调谐光纤激光器中,利用0.55″DMD光栅作为波长选择器更有利于减小衍射损耗,提高系统稳定性。

Diffractive Properties of DMD Gratings and Its New Application in Tunable Fiber Lasers

Compared with widely-used liquid crystal spatial light modulators, digital micromirror devices (DMDs) have advantages in fast switching speed, high precision display, polarization-independent, high diffraction efficiency, and broadband capability. Therefore, we attempt to apply DMDs as wavelength selectors to tunable fiber lasers and analyze the dependence of diffraction properties of the two-dimension DMD grating on the incident angle, pixel spacing, etc. The diffraction orders and intensity distribution of DMDs in 0.7″ and 0.55″ sizes with different pixel spacings are discussed in detail. The theoretical results show that under the experimental constraint condition, a 0.7″ DMD allows four orders interference irradiance maxima. However, the light intensity is relatively weak due to the condition of far away from “blazed” grating. For a 0.55″ DMD, most of the diffracted radiation is concentrated in one order due to the approximate “blazed” condition. So, a 0.55″ DMD grating as a wavelength tuner is a better choice for the stability of laser systems.