To improve the response speed of optical switches in the optical commu nication networks,a SiO₂/polymer hybrid waveguide structure is used in the design and fabrication of the Ybranch thermo -optica l switch.The silica with large thermal conductivity is adopted as the lower cladding of the waveguide.The low cost polymer of poly(meth yl methacylate-glyciclyl methacrylate) with favorable optical properties is adopt ed as the core and upper cladding material.The optical field propagation is simu lat ed by beam propagation method (BPM).According to optical mode calculations by Ma tlab,the width and height of this hybrid waveguide are optimized to be 3.5μm .Through methods of spin-coating,photolithography and inductively coupled plasm a etching,the switch waveguide is fabricated.Characterization by scanning electr on microscope (SEM) shows that the polymer waveguide has a vertical sidewall and square configuration,which is favorable for the confinement of optical mode and the reduction of optical loss.The experimental results indicate that the optica l insert loss and extinction ratio of the fabricated switch are 12dB and 18dB, respectively.Since hybrid waveguide structure can improve the diffusion of the t hermal field in the waveguide and reduce the response time effectively,the rise time an fall time are only 200μs.This switching speed is faster than that of thermo-optic switches adopting polymer as the lower cladding.