The GMR used in our group is comprised of one-dimensional surface relief structure. At normal incidence with a broadband light source, a particular wavelength of light excites the resonance of the structure and is reflected, and the rest of the light is transmitted through; hence, the GMR is essentially a bandstop filter. By varying the waveguide thickness or grating period across the device, we have demonstrated different kinds of linear variable bandstop filters, which  have applied to various applications.