A device for transmitting light signals includes two electrode plates, a spacing structure, a cladding fluid, and a core fluid. The spacing structure, the cladding and core fluids are disposed between the electrode plates. The refractive index of the core fluid is higher than that of the cladding fluid. The core fluid is located on an electrode of one of the electrode plates, and its shape corresponds to the shape of that electrode. The shape and position is changeable and programmable by the electrodes of one of the electrode plates. The core fluid is further surrounded by the cladding fluid, forming an optical waveguide. Via these arrangements, the interface between the core and cladding fluids is much smoother than that between a fluid and a solid, so that the light signals are less likely to scatter while transmitted, in the core fluid. Therefore, the attenuation and reduction of the intensity of the light signals can be decreased. A method for transmitting light signals is also provided.