An optical filter and a method for fabricating an optical filter with a wide tuning range and a structure subject to miniaturization. The optical filter includes a bottom and a top dielectric layer with a stripe or film of metal between the dielectric layers which have dissimilar refractive index dispersion. The stripe of metal functions as a waveguide supporting a long-range surface plasmon polariton mode which will be achieved at wavelengths for which the refractive indices of the dielectric layers are the same thereby providing a bandpass filter. Furthermore, one of the dielectric layers is made of a material that allows its refractive index to be tuned, such as by changing its applied voltage or temperature. By tuning the refractive index of the dielectric layer, the wavelength at which the refractive indices of the dielectric layers match changes thereby effectively tuning the optical filter.