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Reducing the size of devices and the loss of waveguides are two significant research contents in integrated optics. Surface plasmon polariton (SPP) waveguides can break the diffraction limit and provide tight light confinement, however, they are subject to unavoidable high propagation loss due to the metallic ohmic loss. Traditional dielectric waveguides can propagate light with ultralow loss, but they are subject to the diffraction limit in each direction which will result in large mode size. In general, mode size and loss of waveguides are mutually restricted. Here, we proposed an all-dielectric nanowire waveguide which can confine light into nanoscale gap region and realize deep subwavelength mode confinement in two dimensions. A normalized mode area of 1.4×10-2 is achieved, which keeps on the same level with the plasmonic waveguides. The strong mode confinement is attributed to the discontinuity of the normal component of electric field at the interface of two materials. We determined the supported mode of the all-dielectric nanowire waveguide is quasi-TM mode by analyzing the electric vector distributions. The quasi-TM eigenmode is lossless in theory because of no metal components, which is consistent with our simulation results. The lossless propagation in theory is a significant breakthrough compared to the plasmonic waveguides. The all-dielectric nanowire waveguide realizes both subwavelength mode confinement and low-loss propagation simultaneously, conquers the trade-off between mode size and loss of waveguides in theory.
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