A polymer-based waveguide device is for use in an optical amplifier or as a laser waveguide. The waveguide device includes a substrate (1), a polymer bottom cladding layer (21) on the substrate, a polymer channel waveguide (3) on the bottom cladding layer, and a polymer top cladding layer (22). The channel waveguide is doped with at least one kind of rare earth metal ion that can be excited to produce a laser. The bottom and top cladding layers have a same refractive index, which is substantially lower than a refractive index of the channel waveguide. When a light signal is input to the waveguide device, an amplified light signal is obtained and is transmitted within the channel waveguide.