Provided is an optical device having an optical waveguide including an organic Bragg grating sheet. The optical device includes a cladding layer, and an optical waveguide. The cladding layer is formed on a substrate, and the optical waveguide is formed within the cladding layer. The optical waveguide includes a core layer and an organic Bragg grating sheet located within the core layer. The organic Bragg grating sheet has a refractive index higher than that of the core layer to reflect or transmit light having a predetermined wavelength. Accordingly, light propagates through the optical waveguide with high reflectance and low loss. Besides, a high performance tunable wavelength filter or tunable dispersion compensator may be constructed by forming a thermal electrode on the optical waveguide, forming a tapered optical waveguide, or forming a chirped organic Bragg grating sheet in the middle of the core layer of the optical waveguide.