Toward controllable photonic crystals for centimeter- and millimeter-wave devices

In this paper, we present several experimental and theoretical studies show ing the feasibility of active photonic crystals controlled either by electr ical elements or by light. The controllability of photonic crystals at cent imeter wavelengths is proposed with the periodic insertion of diodes along the wires of a two-dimensional (2-D) metallic structure. For only three cry stal periods with commercially available devices, more than 30 dB variation s of the crystal transmission are predicted over a multigigahertz range by switching the diodes. From calculation models, a tight analogy is shown bet ween these crystals and those consisting of discontinuous metallic rods wit h dielectric inserts. The numerical models as well as the proposed technolo gy are validated by experimental measurements on 2-D crystals with either c ontinuous or discontinuous metallic rods. The partial control of a 3-D laye r-by-layer dielectric structure at millimeter wavelengths is also demonstra ted in the second part of the work. A laser light is used to modulate the t ransmission level of defect modes by photo-induced free carrier absorption. The overall results are expected to contribute to further devopments of sw itchable electromagnetic windows as well as to tunable waveguide structures in the microwave and millimeter wave domains.