Based on the balance between the scattering force and the trapping force of an evanescent field of a standing wave on silicon waveguides, we propose a structure for controllable trapping and releasing of nanoparticles, which can act as pause operation for nanoparticle flow control. The design is realized by the cascade of an optical switch with a structure of a ring-assisted Mach–Zehnder interferometer (RAMZI) and a Sagnac loop reflector which connects to one output of the switch. Through thermal tuning, with a tiny refractive index change of $4.3\times {10}^{-4}$ on a ring resonator, the output of a RAMZI can be switched between two ports. As for the release state of the nanoparticle flow, the light is guided to the port without a reflector. There is no standing wave or traps formed on a waveguide. Therefore, the scattering force dominates, which drives particles moving forward to output ports. Otherwise, for trapping a state, the light will be reflected by the Sagnac loop and form a stationary standing wave which provides an array of traps for nanoparticles. Most importantly, the structure can switch its state to trap or sequentially release particles without losing the control of samples which, to the best of our knowledge, has not been realized before. With the statistical description of particle motion, the balance between trapping and releasing is distinguished by the trapping time and tuned by reflectance. The feasibility of our design is verified using the three-dimensional finite-difference time domain and Maxwell stress tensor methods. Our structure possesses the merits of high compactness and time effectiveness and, thereby, it is highly suitable for on-chip optical manipulation of nanoparticle flow control, which brings great potential in integrated on-chip optofluidics.

中文翻译：

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通过驻波在光波导上可控地捕获和释放纳米颗粒

基于硅波导上驻波的渐逝场的散射力和俘获力之间的平衡，我们提出了一种可控制的俘获和释放纳米粒子的结构，该结构可以用作纳米粒子流控制的暂停操作。该设计是通过级联一个具有环辅助马赫曾德尔干涉仪（RAMZI）和连接到该开关一个输出的Sagnac环形反射镜的光开关来实现的。通过热调谐，折射率变化很小$4.3\times {10}^{-4}$在环形谐振器上，RAMZI的输出可以在两个端口之间切换。至于纳米颗粒流的释放状态，将光引导至没有反射器的端口。在波导上没有形成驻波或陷阱。因此，散射力占主导地位，这驱使颗粒向前移动到输出端口。否则，为了捕获状态，光将被Sagnac环反射并形成固定的驻波，该驻波为纳米粒子提供了一系列陷阱。最重要的是，该结构可以切换其状态以捕获或顺序释放颗粒，而不会失去对样品的控制，据我们所知，这是以前从未实现的。通过对粒子运动的统计描述，捕获和释放之间的平衡通过捕获时间来区分，并通过反射率进行调整。我们使用三维有限差分时域和麦克斯韦应力张量方法验证了我们设计的可行性。我们的结构具有高紧凑性和时间效率的优点，因此非常适合纳米颗粒流控制的片上光学操作，这在集成的片上光流体学中具有巨大的潜力。