Loozen Gyllion B, Karuna Arnica, Fanood Mohammad M R, Schreuder Erik, Caro Jacob
Department of Imaging Physics, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.
present address: Institute of Physical Chemistry, Friedrich Schiller University Jena, 07737 Jena, Germany.
Beilstein J Nanotechnol. 2020 May 27;11:829-842. doi: 10.3762/bjnano.11.68. eCollection 2020.
We realized integrated photonics multi-waveguide devices for optical trapping and Raman spectroscopy of particles in a fluid. In these devices, multiple beams directed towards the device center lead to a local field enhancement around this center and thus counteract the effect of light concentration near the facets, which is a disadvantage of dual-waveguide traps. Thus, a trapping region is created around the center, where a single particle of a size in a wide range can be trapped and studied spectroscopically, free from the influence of surfaces. We report the design (including simulations), fabrication and performance demonstration for multi-waveguide devices, using our SiN waveguiding platform as the basis. The designed ridge waveguides, optimized for trapping and Raman spectroscopy, emit narrow beams. Multiple waveguides arranged around the central microbath result from fanning out of a single input waveguide using Y-splitters. A second waveguiding layer is implemented for detection of light scattered by the trapped particle. For reliable filling of the device with sample fluid, microfluidic considerations lead to side channels of the microbath, to exploit capillary forces. The interference of the multiple beams produces an array of hot spots around the bath center, each forming a local trap. This property is clearly confirmed in the experiments and is registered in videos. We demonstrate the performance of a 2-waveguide and a 16-waveguide device, using 1 and 3 μm polystyrene beads. Study of the confined Brownian motion of the trapped beads yields experimental values of the normalized trap stiffness for the in-plane directions. The stiffness values for the 16-waveguide device are comparable to those of tightly focused Gaussian beam traps and are confirmed by our own simulations. The Raman spectra of the beads (in this work measured via an objective) show clear peaks that are characteristic of polystyrene. In the low-wavenumber range, the spectra have a background that most likely originates from the SiN waveguides.
我们实现了用于流体中粒子的光学捕获和拉曼光谱的集成光子学多波导器件。在这些器件中，多束光射向器件中心会导致该中心周围的局部场增强，从而抵消了双波导陷阱在小面附近光聚集的影响，而这是双波导陷阱的一个缺点。因此，在中心周围创建了一个捕获区域，在该区域中，宽范围内大小的单个粒子可以被捕获并进行光谱研究，不受表面影响。我们报告了以我们的氮化硅波导平台为基础的多波导器件的设计（包括模拟）、制造和性能演示。为捕获和拉曼光谱优化设计的脊形波导发射窄光束。围绕中央微池排列的多个波导是通过使用Y型分路器将单个输入波导展开而形成的。实现了第二层波导用于检测被捕获粒子散射的光。为了用样品流体可靠地填充器件，微流体方面的考虑导致了微池的侧通道，以利用毛细作用力。多束光的干涉在微池中心周围产生一系列热点，每个热点形成一个局部陷阱。这一特性在实验中得到了明确证实，并记录在视频中。我们使用1μm和3μm的聚苯乙烯珠展示了一个双波导和一个16波导器件的性能。对被捕获珠子的受限布朗运动的研究得出了面内方向归一化陷阱刚度的实验值。16波导器件的刚度值与紧密聚焦的高斯光束陷阱的刚度值相当，并得到了我们自己模拟的证实。珠子的拉曼光谱（在这项工作中通过物镜测量）显示出聚苯乙烯特有的清晰峰。在低波数范围内，光谱有一个很可能源自氮化硅波导的背景。
