Browsing by Author "Temelkuran, Burak"

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Open Access
Characterization of photonic crystals at microwave frequencies
(1996) Temelkuran, Burak
VVe investigated the surface reflection properties of layer-by-layer photonic crystals, for dielectric and metallic based photonic crystals. By using a FabryPerot cavity analogy with the reflection-phase information of the photonic crystals, we predicted defect frequencies of planar defect structures. Our predictions were in good agreement with the measured defect frequencies. The Fabry-Perot cavity analogy was also used to relate the quality factors of the planar defect structures to the transmission of the mirrors of the cavity. A simple model was used to simulate the transmission spectra of planar defect structures, which agreed well with the experimental data. We also investigated the transmission and reflection properties of two different metallic crystal structures (face-centeredtetragonal and simple tetragonal). We obtained rejection rates of 7-8 dB per layer from metallic crystals. Defect modes created by removing rods resulted in high peak transmission (80%), and high quality factors (1740). Our measurements were in good agreement with theoretical simulations of metallic structures. Planar defect structures built around metallic structures resulted in higher quality factors (2250). We observed high reflection-rejection ratios (-80 dB) at defect frequencies for planar defect structures, which was explained by using the Fabry-Perot analogy. Finally, the enhanced field inside the defect volume was measured, by using a monopole receiver antenna inserted inside the defect. The maximum observed enhancement with respect to the incident field was around 200 for a planar defect structure. By placing a Schottky diode detector inside planar and box-like defects, we built resonant cavity enhanced (RCE) detectors and measured the enhanced field inside the defect.
Open Access
Highly directional resonant antennas built around photonic crystals
(IEEE, 1999) Özbay, Ekmel; Temelkuran, Burak; Bayındır, Mehmet; Biswas, R.; Sigalas, M. M.; Tuttle, G.; Ho, K. M.
We report a photonic crystal-based resonant antenna with a very high directivity and gain. The layer-by-layer dielectric photonic crystal we used in our experiments was designed to have a three dimensional band gap with a mid-gap frequency around 12 GHz. We used the output port of a microwave network analyzer and a monopole antenna to obtain EM waves. The input port of the network analyzer and a standard gain horn antenna were used to receive the radiated EM field from the monopole antenna. The receiver was kept free to rotate around the antenna. We investigated the radiation characteristics of this monopole antenna, which was inserted into the planar defect structures built around a photonic crystal that consisted of 20 layers. The planar defect was formed by separating the 8th and 9th layers of the structure. In order to suppress the radiation in the backward direction, we intentionally chose one of the mirrors of the cavity to have a higher reflectivity (/spl sim/18-20 dB) than the front mirror.
Open Access
Microwave applications of photonic band gap structures
(IEEE, 2000-10) Temelkuran, Burak; Bayındır, Mehmet; Özbay, Ekmel; Biswas, R.; Sigalas, M. M.; Tuttle, G.; Ho, K.-M.
We have investigated two major applications of photonic band gap materials. We demonstrated the guiding and bending of electromagnetic waves through planar waveguides built around layer-by-layer photonic crystals. We then investigated the radiation properties of an antenna that was formed by a hybrid combination of a monopole radiation source and a cavity built around the same photonic crystal structure. © 2000 IEEE.
Open Access
Photonic-crystal-based resonant-cavity-enhanced detectors
(IEEE, 1998) Temelkuran, Burak; Özbay, Ekmel; Kavanaugh, J. P.; Tuttle, G.; Ho, K. M.
A layer-by-layer three-dimensional photonic crystal, with a full photonic bandgap (PBG) in all directions is proposed. The electrical fields in the cavities of this crystal are usually enhanced, and by placing active devices such as resonant cavity enhanced (RCE) photodetectors and light emitting diodes. The RCE effect is demonstrated by placing microwave detectors within localized modes of photonic crystal, along with a monopole antenna. A network analyzer measured the enhanced field. Such RCE detectors are more sensitive and efficient as compared to conventional detectors, and can be used for various applications where sensitivity and efficiency are important parameters.
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
Reflection properties and defect formation in metallic photonic crystals
(IEEE, 1998-05) Özbay, Ekmel; Temelkuran, Burak; Sigalas, M.; Tuttle, G.; Soukoulis, C. M.; Ho, K. M.
The reflection properties of layer-by-layer metallic photonic crystals were investigated using metallic photonic crystals with simple-tetragonal (st) structure. The observed properties were used to predict defect formation in these crystals. The reflection and transmission amplitude characteristics were measured by a network analyzer and standard gain horn antennas. Transformation matrix method was employed for the theoretical simulations.
Open Access
Resonant cavity-enhanced detectors embedded in photonic crystals
(IEEE, 1996) Temelkuran, Burak; Özbay, Ekmel
Summary form only given. We demonstrate the resonant-cavity-enhanced effect by placing microwave detectors in a layer-by-layer photonic crystal. We used the output of a network analyzer as the microwave source, and fed the output to a horn antenna to obtain EM waves. The crystal was then replaced in the beam-path of the EM wave, and the electric field inside the cavity was measured by a probe that consisted of a monopole antenna. The output of the antenna was measured by use of two different techniques: network analyzer and microwave detector within the cavity. The first cavity structure was similar to a one-dimensional Fabry-Perot resonator made of two mirrors separated by a distance.