Browsing by Subject "Directivity"

Now showing 1 - 4 of 4

Open Access
Highly directional enhanced radiation from sources embedded inside three-dimensional photonic crystals
(Optical Society of America, 2005) Caglayan, H.; Bulu, I.; Özbay, Ekmel
We have experimentally studied emission of microwave radiation from a monopole source embedded in a three-dimensional photonic crystal. We have demonstrated enhancement of microwave radiation at the band edge and cavity mode frequencies. Furthermore, we have shown that it is possible to obtain highly directive microwave radiation sources operating at the band edge of the three-dimensional photonic crystal. We have measured half power beam widths of 13 degrees for both E and H planes, corresponding to a maximum directivity of 245. (c) 2005 Optical Society of America.
Open Access
Highly directional enhanced radiation from sources embedded inside two and three-dimensional photonic crystals
(SPIE, 2005) Çağlayan, Hümeyra; Bulu, İrfan; Özbay, Ekmel
In this work, we have experimentally and theoretically studied the emission of radiation from a monopole source embedded in a two and three dimensional photonic crystal. We have demonstrated the enhancement of radiation at the band edges and at the cavity modes including coupled cavity modes. We have shown that the emission of radiation from a source depends on the group velocities of the modes and on the electric field intensities of the modes at the source location. Moreover, we have studied the angular distribution of power emitted from a radiation source embedded inside a photonic crystal. Our results show that it is possible to obtain highly directive radiation sources operating at the band edge of the photonic crystal.
Open Access
Physics and applications of photonic crystals
(2000) Temelkuran, Burak
We first fabricated a dielectric based layer-by-layer photonic crystal, with a three-dimensional photonic band gap at microwave frequencies. We investigated the transmission, reflection and defect characteristics of the crystal. A Fabry-Perot cavity analogy was used to understand the localization of the electromagnetic (EM) fields around defects. We then showed the enhancement of the EM held within the defect volumes, and suggested a possible application: resonant cavity enhanced detectors built around photonic crystals. We demonstrated that a detector inserted inside the defect volume benefits from the frequency selectivity and the highly enhanced field of the cavity. Next, we investigated the radiation of the EM fields from a source inserted in the defect volume, and observed that the radiated field has a very high directivity and efficiency. The experimental results agreed well with the theoretical expectations. We demonstrated waveguiding structures built around photonic crystals. We showed that EM waves could be guided through a planar air gap between two photonic crystals, in which the wave is coupled inside the defect volume, and having no where else to go, propagates through this opening. The dispersion diagrams for these planar waveguide structures also agreed well with the theoretical expectations of our waveguide model. We also showed that, the wave could be guided along a single missing rod, and demonstrated the bending of the EM waves for these waveguide structures with “L” shaped openings. We tested metallic photonic crystals built in different dimensions and diflferent filling ratios. We observed many superiorities of these structures when compared to dielectric-based photonic crystals. A full characterisation of various metallic photonic crystals was performed. We also showed that metallic photonic crystals are suitable for some of the applications we have demonstrated for dielectric structures. We also fabricated a new layer-by-layer photonic crystal using highly doped silicon wafers processed by semiconductor micromachining techniques, with a band gap at millimeter wave frequencies. We showed that the transmission and defect characteristics of these structures are analogous to metallic photonic crystals, as we have predicted. The experimental results agree well with the predictions of the transfer matrix method (TMM) simulations. The method can be extended to fabricate these crystals at THz. frequencies.
Open Access
Radiation fields of a complex source in 2-D circular radome with metal gratings
(1997) Ouardani, Slim
In this thesis, the transmission effect of a two-dimensional circular radome with periodic metal gratings is analyzed. We started with the study of gratings consisting of periodic arrays of thin lossy strips surrounded by vacuum. Then we investigated the behavior of such gratings if a dielectric hiyer is inserted between them. Complex line sources are considered to simulate directed beam fields used in practice. The fields on the interior and exterior sides of the radome are represented by modal cylindrical waves. Taking advantage of theoretical considerations recently published, we propose an approximate method and stress the numerical aspect. Data is obtained for the far field solutions and the directivity, and their dependences on different radome parameters. It appecirs that directivity variations with beam orientation are decreased considerably by a proper insertion of the dielectric layer.