Impurity effects in graphene

Polarization-independent and omnidirectional tunable bandpass filters have been proposed and demonstrated. It is seen that a bilayer period structure composed of single-negative materials can act as a tunable filter, which can be changed from a filter with two symmetrical passband to one with a single pass bandpass, or from one with a wide to one with a narrow pass band. Moreover, the proposed filter is insensitive to the incident angle and polarization of light, which is an omnidirectional, polarization-independent filter for incidence angles between 0° to 90°.