Performance evaluation of selective mode conversion based on phase plates for a 10-mode fiber.
Performance evaluation of selective mode conversion based on phase plates for a 10-mode fiber.
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DOI：
10.1364/oe.22.020881
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发表时间：
2014-08
期刊：
影响因子：
3.8
通讯作者：
K. Igarashi;Daiki Souma;T. Tsuritani;I. Morita
中科院分区：
文献类型：
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作者：
K. Igarashi;Daiki Souma;T. Tsuritani;I. Morita
本文对基于相位板的10模光纤高阶模转换性能进行了数值和实验研究。相位板在多个平面之间具有π的相位跳变，其匹配10 MF的线偏振（LP）模式的相位图案。首先，我们数值研究了相位板的相位差误差和斜率等制造误差对相位跳变的影响。对LP 11模式转换的模拟结果表明，这种误差使转换光束的空间方向图不对称。为了保持对称的图案，相位差误差要求小于± 2%，并且倾斜宽度与输入束腰的比率应被抑制为小于0.05。接下来，我们计算了当使用透镜将相位板之后的转换光束发射到10 MF时，10 MF中LP模式激发的耦合功率效率。作为计算结果，需要高度精确地调节输入束腰，以将由于不期望的LP模式的耦合而引起的串扰抑制小于-20dB。对于LP 11或LP 12的模式激发，即使小心地调节输入束腰，也不可避免大于-20 dB的串扰。相比之下，LP 21或LP 31的模式激发的串扰容易被抑制到小于-20dB，而无需仔细调整输入束腰。这些结果表明，相位板不适用于10 MF下的LP 11和LP 12模式转换，而适用于LP 02，LP 21和LP 31模式转换。最后，我们实验证明从LP 01到LP 21和LP 31模式在10 MF使用相位板转换。我们获得了接近理想的LP 21和LP 31模，由于其他不需要的LP模式的耦合，串扰很小。
We numerically and experimentally evaluate the performance of higher-order mode conversion based on phase plates for 10-mode fibers (10MFs). The phase plates have the phase jump of π between multiple planes, which match the phase patterns of linearly polarized (LP) modes of 10MF. First, we numerically investigate the effects of the fabrication errors such as the phase-difference error and the slope in the phase jump of the phase plate. The simulation results for the mode conversion to LP11 indicate that such errors make the spatial pattern of the converted beam asymmetric. In order to maintain the symmetric pattern, the phase-difference error is required to be less than ± 2%, and the ratio of the slope width to the input beam waist should be suppressed to be less than 0.05. Next, we calculate the coupling power efficiencies of the excitation of LP modes in 10MF when the converted beams after the phase plate are launched into 10MF using a lens. As the calculation results, highly accurate adjustment of the input beam waist is required to suppress the crosstalk due to coupling of undesirable LP modes by less than -20 dB. For mode excitation of LP11 or LP12, crosstalk of more than -20 dB is not avoidable even if the input beam waist is carefully adjusted. In contrast, the crosstalk for the mode excitation of LP21 or LP31 is easily suppressed to be less than -20 dB without careful adjustment of the input beam waist. These results suggest that phase plates are not applicable to mode conversion to LP11 and LP12 in 10MF while they are suitable for conversion to LP02, LP21 and LP31. Finally, we experimentally demonstrate conversion from LP01 to LP21 and LP31 modes in 10MF using phase plates. We obtain nearly ideal LP21 and LP31 modes with the small crosstalk due to the coupling of the other undesirable LP modes.