A novel wavelength-division demultiplexer based on equilateral three-core optical fiber is proposed. Compared to the wavelength-division demultiplexer based on photonic crystal fiber, it has the advantage of being easier to make and to link with conventional optical fiber. Two parallel mismatched cores are designed to be phase-matched (or index-matched) at certain wavelength. Then the light in the two cores will be fully coupled, which will lead to filtering. By selecting a suitable fiber length, different wavelengths of the input light can be output at different cores end of the optical fiber to achieve the function of wavelength-division demultiplexer. Numerical simulation by beam propagation method demonstrates that a 10.25 mm long wavelength-division demultiplexer based on equilateral triangle arrangement three-core optical fiber can separate 1.31 μm wavelength light from 1.55 μm wavelength light.<网络出版日期?2014-05-16