| The high speed electro-optic modulator is a key component in the current optical communication network,which can modulate electrical signals into optical carriers to achieve low loss,high speed and long-distance transmission of information.The integrated electro-optic modulator can not only realize the excellent electro-optic modulation function of the discrete electro-optic modulator,but also has the advantages of small footprint,low power consumption and easy system integration.In order to achieve high-speed,large bandwidth and low loss electro-optical integrated modulators,many novel modulator designs on silicon on insulator(SOI),lithium niobate on insulator(LNOI),silicon-graphene and other platforms have been proposed.Most of them still have to face the problem of polarization sensitivity,which leads to the polarization dependence of modulation efficiency.Therefore,once the polarization sensitive problem of the modulator can be solved,the modulation performance of the device will be effectively improved.In this paper,a series of innovative structures and schemes focusing on the polarization independent electro-optic modulator have been proposed and studied.The main studies of this paper are summarized as below:1.Two polarization beam splitter-rotators(PSRs)with an adjustable beam splitting ratio are designed on the SOI platform.Based on the principle of mode evolution and micro ring resonance,a PSR with low dynamic power consumption and reconfigurable beam splitting ratio is proposed and fabricated.In addition,based on the principle of mode evolution and interference,a PSR with large bandwidth and reconfigurable beam splitting ratio is proposed and fabricated.Such reconfigurable devices can not only realize polarization beam splitting and rotation,but also have the function of power devider,which can be flexibly applied to multi-functional optical chips.2.A high-performance polarization beam splitter(PBS)based on hetero-anisotropic metamaterials is proposed on the LNOI platform.Rather than the principle of PBS based on beatlength difference of transverse electric(TE)polarization and transverse magnetic(TM)polarization,the device can realize polarization beam splitting in single beat length,and the footprint of the proposed PBS can be reduced to 8 μm×160 μm(with S-bend).The proposed PBS has the advantages of small footprint,low insertion loss,large bandwidth,high polarization extinction ratio and large fabrication tolerance.3.A large bandwidth PSR based on LNOI strip waveguide is proposed.Due to the structural characteristics of the strip waveguide,the fabrication of PSR requires only one full etching process,which reduces the demand for etching accuracy and the difficulty of etching process.The device is composed of an adiabatic taper,a Y-splitter,and a multi-mode interferometer(MMI),which are wellknown for their large fabrication tolerances.The experimental results show that the device has the advantages of large bandwidth,low insertion loss and high polarization extinction ratio.4.By combining on-chip PSR,discrete Mach Zender modulator(MZM)and discrete PSR,a polarization independent modulation scheme is designed.This scheme can realize polarization independence of modulation efficiency and effectively reduce polarization dependence of loss.On this basis,a fully integrated polarization independent modulator based on the LNOI platform is proposed and analyzed.The simulation results show that the proposed integrated polarization independent modulator has almost the same electro-optical response intensity for TE and TM polarization.5.A slow wave electro-optic modulator with high modulation efficiency based on a fishbone-like grating structure is proposed on LNOI platform.By assembling the fishbone-like grating,the Pockels effect is significantly enhanced as a result of the compression of the local density of states.The simulation results show that the modulation efficiency of the slow wave modulator can be improved to 4.6 times of the original one. |
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