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本系统的指标参数如表1所示。
Parameter Data source Spectral range/nm 1 550±50 Fiber NA 0.12 Fiber diameter/μm 6 Chip receiving area/μm2 20×20 Angle between the optical axis and the chip normal/(°) 7 Coupling system vertical axis magnification −1× Monitoring system vertical axis magnification −3× Table 1. Optical design parameters
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表2为耦合系统透镜数据,图3为耦合系统结构图,光纤光束通过耦合系统高效的耦合到芯片式光谱仪上。左侧为输入光纤,右侧为芯片接收端,前两片透镜为耦合前部分系统,后三片透镜为复合共用系统。
Lens Material Radius Radius Thickness Diameter 1 H−K9L −15.214 −5.546 0.800 2.536 2 H−K9L 64.029 −11.388 0.800 2.706 Beam splitter H−K9L Infinity Infinity 0.500 3.748 3 H−ZK3 13.385 6.184 1.000 2.326 4 H−K9L 22.000 −10.332 1.000 2.364 5 H−ZK3 5.400 30.545 1.000 2.278 Table 2. Coupling system lens data
图4(a)、(b)为耦合系统的点列图,表明耦合系统在不同波长和视场下点列斑分布均匀,单个弥散斑半径在3 μm内,全视场光斑直径大小在12 μm内,小于集成芯片式光谱仪接收端尺寸。因此集成芯片式光谱仪接收端可接收到光纤发出的全部光束,避免能量浪费。
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将耦合系统导入LightTools中进行能量分析,图5 为耦合系统能量图,可见能量集中在光栅耦合器中央位置且分布均匀。光源发出的总功率为0.005 665 7 W,通过LightTools模拟可得接收端总功率为0.004 153 3,则在光栅面处耦合效率为0.733。
通过LightTools模拟及计算,可知光束耦合系统达到满足测试需求的耦合效率。
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表3为耦合系统透镜数据,图6为监测系统结构图,底端为芯片接收端,左侧为探测器,下端为复合共用系统,上端为监测后部分系统。由于物面与光轴成7°倾斜角,通过公式计算得出像面倾斜角度,如图6所示。
Lens Material Radius Radius Thickness Diameter 1 H-ZK3 30.545 5.400 1.000 2.278 2 H-K9L −10.332 22.000 1.000 2.364 3 H-ZK3 6.184 13.385 1.000 2.326 4 H-ZK3 −7.211 −20.437 1.000 2.336 5 H-K9L 20.708 −30.453 1.000 2.178 6 H-K9L 65.430 15.977 1.000 2.090 Table 3. Monitoring system lens data
图7和图8为监测系统的点列图和MTF曲线,表明监测系统在不同波长和视场下点列斑均小于一个像元大小,MTF曲线均贴近衍射极限,成像效果良好,可通过监测系统清晰地观测到芯片式光谱仪接收端情况。
System design for beam coupling and alignment monitoring of chip spectrometer
doi: 10.3788/IRLA20190532
- Received Date: 2019-12-05
- Rev Recd Date: 2020-02-15
- Available Online: 2020-09-22
- Publish Date: 2020-08-28
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Key words:
- chip spectrometer /
- beam coupling /
- composite shared optical path /
- alignment monitoring
Abstract: Aiming at the problem of the beam coupling and alignment monitoring of the chip spectrometer, an integrated optical system was proposed for avoiding the wear of the receiving end at chip spectrometer and the shielding of the optical fiber. The system consisted of a front coupling system, a rear monitor system and a composite sharing system. The composite sharing system needed to cooperate with the front coupling system and the rear monitor system to complete the beam coupling and alignment monitoring functions respectively. The final system was designed by multiple combinations, a coupling system and a monitoring system were designed for a 6 μm incident fiber and a 20 μm×20 μm chip spectrometer receiving end at (1 550±50) nm. The energy analysis of the coupled system was performed by LightTools. The coupling efficiency was 0.733. The final system has a simple structure and can perform beam coupling and alignment monitoring at the same time, which provides a new method for the beam coupling and monitoring of chip spectrometers.