A polymer waveguide thermo-optical switch with loss compensation based on NaYF4∶ 18％ Yb3+,2％ Er3+ nanocrystals,fabricated by traditional semiconductor processes,has been investigated.NaYF4∶ 18％ Yb3+,2％ Er3+ nanocrystals were prepared by a pyrolysis method.The morphology and luminescent properties of the nanocrystals were characterized.The nanocrystals were doped into SU-8 as the core material of an optical waveguide amplifier.The size of the device was optimized for its optical and thermal fields as well as its transmission characteristics.The device was fabricated on a silica substrate by spin coating,photolithography,and wet etching.The insertion loss of the switch device is ～ 15 dB.The rise and fall times of the device are 240 μs and 380 μs,respectively,as measured by application of a 304 Hz square wave voltage.The extinction ratio of the device is about 14 dB at an electrode-driving power of 7 mW.When the pump light power is 230 mW and the signal light power is 0.1 mW,the loss compensation of the device is 3.8 dB at a wavelength of 1530 nm.Optical devices with loss compensation have important research significance.