US Patent 9310630 Tunable bragg stack

A tunable photonic crystal device comprising: alternating layers of a first material and a second material, the alternating layers comprising a responsive material, the responsive material being responsive to an external stimulus, the alternating layers having a periodic difference in refractive indices giving rise to a first reflected wavelength; wherein, in response to the external stimulus, a change in the responsive material results in a reflected wavelength of the device shifting from the first reflected wavelength to a second reflected wavelength.