Integrated Functional Devices Based On Grating Couplers

Grating coupler is a key device in integrated photonics.Here,we investigate integrated functional devices based on grating couplers for various applications.Recently,data traffic in long-haul telecom systems and data centers is growing exponentially and will reach the capacity limit of single mode fibers?SMFs?.The significantly increased requirement for telecom and datacom system capacity calls for mode division multiplexing,in which it is essential to combining light coupling between transceivers and fibers with mode conversion functions.We show that this can be done with a high efficiency.The proposed devices are very compact,with no extra fabrication efforts required.It is shown that the LP₀₁,LP_11a,LP_11b and LP_21b modes in a few-mode optical fiber can be excited directly from the proposed grating couplers,when the TE mode is used.The overall coupling efficiency,including mode conversion efficiency,can be 50%.We also analyze the performance of the grating couplers in terms of bandwidth,efficiency and tolerance to device fabrication errors.Optical manipulation and trapping of particles using integrated optical waveguides have been attractive.We present a method of estimating optical force using two-dimensional optical field distribution for large size structures waveguide,and verify its accuracy.We demonstrate an optical tweezer using a grating coupler that can radiate light with a divergence angle of 60°.The structure of the grating couplers are optimized by Particle Swarm Optimization.The analysis on field and the optical force distribution shows that particles of>6?m in size can be trapped to the grating coupler.Finally,we show an optical tweezer using surface plasmon polaritons of metal,which can be used together with grating couplers.This device is fabrication-friendly and cascadable.We study its field and force distributions.The force on particles with a radius of 300 nm can be sub-nN,high enough to trap particles stably.Also,we show an in-depth analysis of the trapping dynamics to the potential well and the trajectory of particles.We conclude that this novel structure can be successfully used for optical trapping and manipulation of nanoparticles by controlling water velocity.