Samad Roshan Entezar

Bio: Samad Roshan Entezar is an academic researcher from University of Tabriz. The author has contributed to research in topics: Photonic crystal & Graphene. The author has an hindex of 11, co-authored 47 publications receiving 393 citations.

Optical properties of one-dimensional photonic crystals containing graphene sheets

Abstract: The transmission properties of a one-dimensional photonic crystal containing graphene monolayers are investigated using transfer matrix method. It is shown that the structure has a new type of the photonic band gap in the THz region which is almost omnidirectional and insensitive to the polarization. The results show that the characteristic properties of this band gap depend on the optical parameters of the graphene sheets and can be controlled via a gate voltage. The difference between this gap and the structural Bragg gaps is investigated by plotting the electromagnetic field profiles inside the one-dimensional photonic crystal for some critical frequencies.

Photonic transmission spectra in one-dimensional fibonacci multilayer structures containing single-negative metamaterials

Abstract: We investigate the transmission properties of the Fibonacci quasiperiodic layered structures consisting of a pair of double positive (DPS), epsilon-negative (ENG) or/and mu-negative (MNG) materials. It is found that there exist the polarization-dependent transmission gaps which are invariant with a change of scaling and insensitive to incident angles. Analytical methods based on transfer matrices and efiective medium theory have been used to explain the properties of transmission gaps of DPS-MNG, DPS-ENG and ENG- MNG Fibonacci multilayer structures.

Optical properties of a one-dimensional photonic crystal containing a graphene-based hyperbolic metamaterial defect layer.

Abstract: The transmission properties of a one-dimensional defective photonic crystal have been investigated using the transfer matrix method. A layer of graphene-based hyperbolic metamaterial whose optical axis is tilted with respect to the interface is taken as a defect. It is shown that two kinds of the defect modes can be found in the band gaps of the structure for TM-polarized waves. One kind is created at the frequency range in which the principle elements of the effective permittivity tensor of the defect layer have the same signs. The frequency of this kind of defect mode is independent from the orientation of the optical axis of the defect layer. The other one is created at the hyperbolic dispersion frequency range. Such a defect mode appears due to the anisotropic behavior of the defect layer and its frequency strongly depends on the orientation of the optical axis. Unlike the conventional defect modes, the magnetic field of this defect mode is localized around the defect layer.

Terahertz tunable photonic crystal optical filter containing graphene and nonlinear electro-optic polymer

Abstract: In this paper, new photonic crystal optical filters with very unique optical characteristics are presented. The designed structures are composed of stacked SiO2 isotropic dielectric slabs separated by monolayer graphene sheets. Defect layers of nonlinear electro-optical polymer materials are also inserted to behave as the resonant areas. Results obtained by using the transfer matrix method approach clearly reflect the possibility of the wide photonic band gap generation in the absorption spectra of the proposed crystals in the terahertz frequency range. Furthermore, a very strong relation is seen between the defect layer(s) induced resonant modes and the location/number of the defect(s) inside the crystal. To widen the scope of our findings, in addition to studying the dependencies on the structural characteristics, the tunability of the optical features using the external parameters is investigated systematically. It is shown that the number and central frequencies of the resonant modes are controllable in the far-infrared range by adjusting the temperature and wave incident angle. Thus, the proposed crystals might have remarkable applications in the fabrication of multi-channel tunable filters used in optical integrated circuits.

Photonic crystals

Abstract: The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

Controlling the dynamics of spontaneous emission from quantum dots by photonic crystals

Abstract: Control of spontaneously emitted light lies at the heart of quantum optics. It is essential for diverse applications ranging from miniature lasers and light-emitting diodes, to single-photon sources for quantum information, and to solar energy harvesting. To explore such new quantum optics applications, a suitably tailored dielectric environment is required in which the vacuum fluctuations that control spontaneous emission can be manipulated. Photonic crystals provide such an environment: they strongly modify the vacuum fluctuations, causing the decay of emitted light to be accelerated or slowed down, to reveal unusual statistics, or to be completely inhibited in the ideal case of a photonic bandgap. Here we study spontaneous emission from semiconductor quantum dots embedded in inverse opal photonic crystals. We show that the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal. Modified emission is observed over large frequency bandwidths of 10%, orders of magnitude larger than reported for resonant optical microcavities. Both inhibited and enhanced decay rates are observed depending on the optical emission frequency, and they are controlled by the crystals’ lattice parameter. Our experimental results provide a basis for all-solid-state dynamic control of optical quantum systems.

Semiconductor-Laser Physics

Abstract: 1. Semiconductor Laser Diodes 2. Basic Concepts 3. Free-Carrier Theory 4. Coulomb Effects 5. Many-Body Gain 6. Band Mixing and Strain in Quantum Wells 7. Semiclassical laser Theory 8. Multimode Operation 9. Quantum Theory of the Laser 10. Propagation Effects 11. Beyond Quasiequilibrium Theory, Appendices A-e, Index

Highly Directional Emission from Photonic Crystal Waveguides of Subwavelength Width

Abstract: Recently it has been shown that it is possible to achieve directional emission out of a subwavelength aperture in a periodically corrugated metallic thin film. We report on theoretical and experimental studies of a related phenomenon concerning light emitted from photonic crystal waveguides that are less than a wavelength wide. We find that the termination of the photonic crystal end facets and an appropriate choice of the wavelength are instrumental in achieving very low numerical apertures. Our results hold promise for the combination of photonic crystal waveguides with conventional optical systems such as fibers, waveguides, and freely propagating light beams.

Optical Shop Testing

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