利用变形镜抑制光纤模态噪声

光纤模态噪声限制了下一代高精度视向速度光谱仪的测量精度。特别是当使用相干光源进行波长定标时，模态噪声会引起视向速度测量误差，降低视向速度测量精度。为了抑制光纤模态噪声，提出了一种基于变形镜的动态改变散斑花样的技术方法，该方法是在单次曝光时间内通过动态改变变形镜的面型，平滑光纤引起的散斑花样，提高定标光谱的质心稳定性，从而保证视向速度的测量精度。通过实验，利用632.8 nm 氦氖激光器作为定标光源，验证了该方法的有效性。实验结果表明，单次曝光图像包含约105个变形镜形变模式时，可以有效抑制光纤模态噪声。针对分辨率R=100000的光谱仪，单根定标谱线的情况下，光纤模态噪声引起的视向速度定标误差约为19.8 cm/s，与国际上其他技术方法的精度持平，该方法不仅可以提高能量利用率，且不影响光纤的使用寿命。

Suppression of fiber modal noise by using deformable mirror

The modal noise in optical fiber limits the measurement accuracy of the next generation of high precision radial velocity spectrograph. Especially when using coherent light sources for wavelength calibration, modal noise can induce radial velocity errors that reduce the accuracy of radial velocity measurement. In order to suppress optical fiber modal noise, a technical method based on deformable mirror to dynamically change speckle pattern is proposed. The method smoothes the speckle pattern caused by optical fiber and improves the centroid stability of calibration spectrum by dynamically changing the shape of deformable mirror in one single exposure time, so as to ensure the measurement accuracy of radial velocity. A 632.8 nm He-Ne laser is used as a coherent calibration light source to verify the effectiveness of the device. Experimental results show that the optical fiber modal noise can be effectively suppressed when a single exposure image contains about 105 speckle patterns. For the spectrograph with resolution R=100000, the radial velocity calibration error caused by optical fiber modal noise is about 19.8 cm/s in use of one single calibration line, which is similar to the effect of other suppression methods in the world. And this method can not only improve the energy utilization rate but also not affect the service life of optical fiber.