By means of introducing defect layers into multilayer structures composed by epsilon-negative material and mu-negative
material, the free modulation of single and double localized modes in <i>zero-φ<sub>eff</sub></i> gap is realized respectively through
adjusting the thickness of different kinds of defect layers in two designed structures. In addition, the defect modes in the
<i>zero-φ<sub>eff</sub></i> gap, being distinct from those in the Bragg gap, have the property of insensitivity to incident angle and
polarization in some degree, which would be applied widely in tunable omnidirectional filters.