| With the rapid growth of data traffic,optical interconnection has gradually replaced electrical connection and become the main connection way in short distance(between servers,boards)or even ultra short distance(intra-and inter-chips)data exchange.In particular,on-chip dense wireless optical interconnection,optical vortex coding and vortex multiplexing have become the research hotspots in the fields of communication and large capacity optical interconnection in recent years.On-chip dense wireless optical interconnection is a kind of optical interconnection with reflective backplanes.This method can give full play to the advantages of high density and interconnection flexibility of free space interconnection,so as to provide bigger interconnection capacity in limited space.Theoretically,there is no limit to the number of OAM(orbital angular momentum)states of vortex light.As a new coding state and a new multiplexing degree of freedom,OAM can be utilized to transfer more information on a given amount of energy or a given space link,making it promising in ultra-high capacity optical communication.On the other hand,recent research on light modulation with micro-nano structures,especially the research on matesurfaces,provides a powerful technical means for the development of interconnection devices.In this dissertation,silicon-based coupler,i.e.,the optical transceiver in chip level,is taken as the main research object,and the finite element method and finite difference time domain simulation are taken as the main research methods.Combined with theoretical analysis,various compact and high channel capacity couplers are designed based on the on-chip light field regulation of micro/nano structures,in order to improve the intra-and inter-chip optical interconnection performance effectively.The main research contents and achievements are as follows:A vertical light emitting and switchable coupler was designed for on-chip dense wireless optical interconnection.The coupler is essentially a metal relief grating excited by waveguide standing waves.Unlike most studies using TE wave as input light,the metal grating coupler here is excited by TM wave.The electric field radial component of the TM wave at core-cladding interface can excite the local surface plasmon resonance of the gold strips,which greatly enhances the light scattering of the grating,thus making it possible to miniaturize the coupler.Choosing TM standing wave for excitation can effectively overcome the problems of low radiation efficiency and deflection of radiation direction when a single TM wave is used.More importantly,the intensity of radiation can be modulated by adjusting the position of standing wave relative to gold strips.The study of the efficiency difference between on-and off-radiation showed that the local surface plasmon resonance scattering is the necessary condition for the grating coupler to have near ideal switching span(the ideal on-and off-radiation efficiency are 100% and 0%respectively).The proposed coupler,with the advantages of small area,high efficiency,high extinction ratio and vertical light emission,can be used as transmitters for on-chip wireless optical interconnections.Based on this,a new optical interconnection system was designed.A short slot waveguide Bragg grating was designed for in-plane light intensity modulation.The Bragg grating consists of seven gold nanoblocks,and the length of the whole grating is only about three mode wavelengths.Two kinds of waveguide mode selection gratings can be designed by adjusting the geometric parameters of the nanoblocks.First,the interactions between single gold nanoblock and two TE modes,i.e.the in-and anti-phase TE modes of slot waveguides,were analyzed to determine the design principle of the couplers.Then two kinds of waveguide mode selection gratings were designed,and the design parameters were optimized to improve the extinction ratio.The results showed that,at the center wavelength of1550 nm,the reflection and transmission light extinction ratio of type I grating is greater than 20.0 d B,and that of type ? grating is greater than 13.4 d B.Finally,the optical switch for modulating light reflection and transmission was designed,which can realize continuous modulation of light reflectance and transmittance.The slot waveguide Bragg grating is expected to be used in waveguide optical communication or on-chip laser Q-switching.In order to solve the problem of complex structure or narrow bandwidth of existing vortex emitters,a compact,non-resonant,energy-efficient on-chip vortex emitter was designed.The emitter can convert surface plasmon polaritons(SPPs)with different incident angles into free-space vortices with different topological charges.First,the concept of vortex synthesis method,which is a piecewise approximation method for generating vortices,was defined,and the vortex synthesis methods were classified into piecewise phase method(P-method)and piecewise phase gradient method(PG-method).Based on Rayleigh-Sommerfeld diffraction integral,the mathematical model of vortex generation by synthesis method was constructed,and the vortex spectrum analysis was expounded.Vortex spectrum analyses showed the superiority of PG-method over P-method.Then,a vortex emitter based on PG-method was designed by utilizing the wave vector manipulation of phase gradient metasurfaces.The simulation results showed that,for targeted topological charges range from-6 to 6,the effective vortex emission efficiency of the device is about 47%.Finally,an efficient on-chip matelens was designed.Combined with on-chip metalenses,the vortex emitter can convert the on-chip position coded information into the free-space topological charge coded information.On the contrary,this device can be used as the receiver to discriminate the vortex light.The compact vortex modulator/demodulator is expected to be used in wavelength division multiplexing compatible inter chip OAM interconnection.Metal nanoslit SPP arc-lens has the advantage of large range topological charge identification.The main drawback of this kind of structure is that the energy efficiency is very low.To solve this problem,a ring SPP arc-lens based on phase-gradient metasurface(PGM)was designed.Compared with nanoslits,the energy efficiency of PGM arc lens is increased by 14.5 times.First,a more accurate mathematical model of SPP arc-lens was constructed,and the focusing deviation method was proposed to analyze the focusing performance of SPP arc lens.The results showed that the quarter circle arc lenses perform a quasi ideal light focusing in a large range of topological charges.Then a quarter ring PGM arc-lens was designed based on metal-dielectric-metal(MIM)magnetic resonance antennas,and the spin sorting phenomenon of the arc-lens was analyzed.It was proved that the spin sorting mechanism is the same as that of vortex sorting.Finally,by coupling focal spots to waveguides,the low crosstalk and wide band on-chip fiber vortex mode sorting was demonstrated.The sorter can be used as the receiver for wavelength division multiplexing compatible inter chip fiber OAM communication. |
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