Mitigating modal noise in multimode circular fibres by optical agitation using a galvanometer
Mitigating modal noise in multimode circular fibres by optical agitation using a galvanometer
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使用检流计通过光搅拌减轻多模圆形光纤中的模态噪声
DOI：
10.1093/rasti/rzad059
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发表时间：
2024
期刊：
影响因子：
--
通讯作者：
Ghosh S
中科院分区：
文献类型：
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作者：
Ghosh S
由于多模光纤中有限数目的模之间光强分布的不均匀和不稳定，出现了模噪声。它是制约光纤高分辨率光谱仪精确测量径向速度的重要因素。随着光纤纤芯变小，可以传播的模式数量减少，这个问题会变得特别严重。因此，在相对小的芯光纤中减轻模态噪声仍然是一个挑战。我们在这里提出了一种新的技术来抑制模态噪声。振镜形式的两个可移动反射镜将输入光纤的模式图案重新成像到输出光纤。耦合到输出光纤的模式的混合可以通过经由电压发生器施加两个正弦信号的反射镜的移动来控制。我们测试四个多模圆形光纤的技术：10和50米阶跃指数，50米渐变指数，和50米渐变指数和5：1锥形光纤（GI50 t）的组合。我们提出的模式抑制的结果，无论是在输出光纤的直接图像和白色光的光谱与高分辨率摄谱仪获得。我们发现，检流计减轻了所有测试光纤中的模态噪声，但对较小芯光纤最有用。然而，在模态噪声降低和光损失之间存在折衷。GI50t提供了最好的结果，以约5%的输出光损失为代价，降低了约60%的模态噪声。我们的解决方案易于使用，可在光纤光谱仪中实施。
Modal noise appears due to the non-uniform and unstable distribution of light intensity among the finite number of modes in multimode fibres. It is an important limiting factor in measuring radial velocity precisely by fibre-fed high-resolution spectrographs. The problem can become particularly severe as the fibre’s core become smaller and the number of modes that can propagate reduces. Thus, mitigating modal noise in relatively small core fibres still remains a challenge. We present here a novel technique to suppress modal noise. Two movable mirrors in the form of a galvanometer re-image the mode-pattern of an input fibre to an output fibre. The mixing of modes coupled to the output fibre can be controlled by the movement of mirrors applying two sinusoidal signals through a voltage generator. We test the technique for four multimode circular fibres: 10 and 50m step-index, 50m graded-index, and a combination of 50m graded-index and 5:1 tapered fibres (GI50t). We present the results of mode suppression both in terms of the direct image of the output fibre and spectrum of white light obtained with the high-resolution spectrograph. We found that the galvanometer mitigated modal noise in all the tested fibres, but was most useful for smaller core fibres. However, there is a trade-off between the modal noise reduction and light-loss. The GI50t provides the best result with about 60 per cent mitigation of modal noise at a cost of about 5 per cent output light-loss. Our solution is easy to use and can be implemented in fibre-fed spectrographs.