Particle Manipulation In The Photonic Crystal Channel

Evanescent wave in the near-field has a strong intensity gradient and can overcome the shortcomings of traditional optical tweezers, which suffer from the diffraction limit and short operation length. At the same time, optical devices based on near-field optical manipulation can be integrated easily in lab-on-a-chip, which is a promising platform for multiple purposes including single molecule analysis, nano assembly and optical chromatography. Therefore, evanescent field based optical manipulation is intensively studied in particle trapping and transportation in various systems of optical waveguides, optical reson ant cavity, photonic crystals and surface plasmon. This thesis aims to capture and drive micro/nano-objects along or reverse the direction of light propagation in subwavelength channels, and its control by the polarization, wavelength, and geometry paramet ers.Based on the band theory of photonic crystal and the assistance of numerical simulation, we established a photonic crystal subwavelength channel and the corresponding simulation model. A negative optical force is obtained by optimizing the physical and geometrical parameters of the particles. Our results show that a particle is more susceptible to be pulled when its refractive index is larger, and its shape is elongated. The influence of the photonic crystal structural parameters to the optical tractor force is also systematically calculated and analyzed.The influences of the wavelength and polarization of incident light to optical field distribution is investigated. By tuning the wavelength and/or polarization of incident light, the ellipsoidal particles can be pushed away from the source along the direction of light propagation or be pulled to the source along the backward direction. According to this result, a photonic crystal channel that is able to bi-directionally manipulate an ellipsoidal particle is proposed, and the transportation speed of the particle is also investigated in a low Reynolds number liquid environment.The trapping behavior of single and multiple spherical particles is investigated in the photonic crystal channel. According to the influence of the particle radius to the optical field, a range of particle radius is determined, in which the particle can be captured stably. We also found that there are two potential wells with different potential depths in each period, and all of them have the stability coefficients much larger than 1, thus can trap objects stably. The capture stiffness around equilibrium positions is found to increase with the particle radius within certain region. Finally, we studied the trapping of multiple spherical particle systems, and result shows that the photonic crystal channel is able to capture multiple nanoparticles simultaneously, and achieve a periodic self-assembled nanoparticle chain.