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    Analytical expression of giant Goos-Hanchen shift in terms of proper and improper modes in waveguide structures with arbitrary refractive index profile

    , Article Optics Letters ; Volume 35, Issue 11 , 2010 , Pages 1759-1761 ; 01469592 (ISSN) Mehrany, K ; Alishahi, F ; Sharif University of Technology
    We analytically relate the giant Goos-Hanchen shift, observed at the interface of a high refractive index prism and a waveguide structure with an arbitrary refractive index profile, to the spatial resonance phenomenon. The proximity effect of the high refractive index prism on modal properties of the waveguide is discussed, and the observed shift is expressed in terms of proper and improper electromagnetic modes supported by the waveguide with no prism. The transversely increasing improper modes are shown playing an increasingly important role as the high refractive index prism comes closer to the waveguide  

    Tube length-assisted optimized aerosol trapping

    , Article Optics Communications ; Vol. 329, issue , 2014 , pp. 196-199 ; ISSN: 00304018 Taheri, S. M. R ; Sadeghi, M ; Madadi, E ; S. Reihani, S. N ; Sharif University of Technology
    Trapping a single aerosol using optical tweezers could be of great importance for environmental sciences. Though a single nanoparticle as small as 10 nm is successfully trapped in aqueous media using optical tweezers, due to spherical aberration only large clusters of nanoparticles were stably trapped in air. In this paper we provide our theoretical and experimental results on optimized trapping of aerosols as small as 400 nm in radius by the introduction of an extra spherical aberration source in order to minimize the total spherical aberration of the system. Our method allows for trapping of high refractive index particles such as polystyrene beads in air. It also provides considerably... 

    Optimized three-dimensional trapping of aerosols: The effect of immersion medium

    , Article Journal of the Optical Society of America B: Optical Physics ; Volume 32, Issue 7 , 2015 , Pages 1494-1498 ; 07403224 (ISSN) Taheri, S. M. R ; Madadi, E ; Sadeghi, M ; Reihani, S. N. S ; Sharif University of Technology
    OSA - The Optical Society  2015
    Optical tweezers have proven to be indispensable micromanipulation tools especially in aqueous solutions. Because of the significantly larger spherical aberration induced by the refractive index mismatch, trapping aerosols has always been cumbersome if not impossible. We introduce a simple but very efficient method for optimized aerosol trapping at a desired depth. We show that a wise selection of the immersion medium and the mechanical tube length not only enables trapping of objects that are known to be untrappable but also provides a way to tune the trappable depth range  

    Refractive index correction in optical coherence tomography images of multilayer tissues

    , Article Journal of Biomedical Optics ; Volume 23, Issue 7 , 2018 ; 10833668 (ISSN) Turani, Z ; Fatemizadeh, E ; Xu, Q ; Daveluy, S ; Mehregan, D ; Nasiriavanaki, M ; Sharif University of Technology
    SPIE  2018
    We propose an algorithm to compensate for the refractive index error in the optical coherence tomography (OCT) images of multilayer tissues, such as skin. The performance of the proposed method has been evaluated on one-and two-layer solid phantoms, as well as the skin of rat paw. © 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)  

    Simultaneous measurement of refractive index and physical thickness of multiple layers using the results of Fourier domain optical coherence tomography

    , Article Iranian Journal of Physics Research ; Volume 18, Issue 1 , April , 2018 , Pages 115-124 ; 16826957 (ISSN) Amjadi, A ; Ghasemi Falavarjani, K ; Moazami Gudarzi, N ; Sharif University of Technology
    Isfahan University of Technology  2018
    In the Fourier domain optical coherence tomography, a picture of the optical thickness (multiplication of the refractive index n in physical thickness d) is obtained; e.g. for the retinal layers, it is used to diagnose many diseases throughout the hospitals in the country. In this work, we introduce a method for a discrete and simultaneous measurement of the refractive index and the physical thickness of multiple layers using Fourier domain optical coherence tomography, without additional information regarding the structure of the sample under investigation. In this method, the only input data are the spectrum of the FD-OCT system and the optical thickness of the sample layers (OPLs),... 

    Creation of artificial surface conductivity on metallic metamaterials

    , Article Journal of Lightwave Technology ; Volume 30, Issue 12 , February , 2012 , Pages 1789-1794 ; 07338724 (ISSN) Edalatipour, M ; Khavasi, A ; Rezaei, M ; Mehrany, K ; Sharif University of Technology
    Metal films with a periodic arrangement of cut-through slits are studied to show that artificial surface conductivity is created at the flat interface between the periodic slits and the cover/substrate. The presence of surface conductivity when the periodic structure is modeled by an effective refractive index can describe how non-specular higher diffracted orders affect the specular zeroth diffracted order. The magnitude of this surface conductivity is controlled geometrically. The artificial surface conductivity is pure imaginary and thus reactive if all non-specular orders are evanescent. This is usually the case in the low frequency regime. At higher working frequencies when some... 

    Tunable wide-band graphene plasmonic nano-color-sorter: Application in scanning near-field optical microscopy

    , Article Journal of the Optical Society of America B: Optical Physics ; Volume 36, Issue 2 , 2019 , Pages 435-442 ; 07403224 (ISSN) Heydarian, H ; Yazdanfar, P ; Shahmansouri, A ; Rashidian, B ; Sharif University of Technology
    OSA - The Optical Society  2019
    Tunability of the Fermi level of graphene is exploited to implement a plasmonic nano-color-sorter for scanning near-field optical microscope (SNOM) applications capable of handling large tip sample couplings. Nano-color-sorting has been used in SNOM through creating multiple spatially separated hot spots for different incident wavelengths. We show that in the presence of high-refractive-index samples an unwanted redshift in the spectral response of the dual-color probe occurs. This limitation can be compensated for using graphene and adjusting its chemical potential to obtain a blueshift in probe spectral response. The Method of Moments analysis technique is employed to engineer the probe... 

    A new method for solving nonhermitian perturbation theory for the microdisc resonators with phi-periodic refractive index

    , Article Proceedings of SPIE- Silicon Photonics and Photonic Integrated Circuits, Strasbourg, 7 April 2008 through 10 April 2008 ; Volume 6996 , 2008 ; 0277786X (ISSN) ; 9780819471949 (ISBN) Keyvaninia, S ; Karvar, M ; Bahrampour, A ; Sharif University of Technology
    The radiation loss in the whispering gallery resonators causes the eigenvalues of the Maxwell equations with the corresponding boundary conditions complex. The corresponding operators are nonhermitian and for these operators the standard perturbation techniques have some difficulties. In this paper by employing the Floquet theorem a new technique for the φ periodic perturbations is developed. The method is applied to obtain the change of resonance frequencies and losses of φ -perturbed microresonators with cylindrical symmetry. The results are compatible with that are obtained by the Volume Current Method  

    A novel omega shaped microwave absorber with wideband negative refractive index for C-band applications

    , Article Optik ; Volume 242 , 2021 ; 00304026 (ISSN) Bilal, R. M. H ; Baqir, M. A ; Iftikhar, A ; Ali, M. M ; Rahim, A. A ; Niaz Akhtar, M ; Mughal, M. J ; Naqvi, S. A ; Sharif University of Technology
    Elsevier GmbH  2021
    This paper reports a polarization controllable and angle-insensitive perfect metamaterial absorber (PMA). The proposed PMA consists of periodically arranged asymmetric omega-shaped resonators made of metallic copper. The absorptivity was analyzed considering the microwave C-band from 4 GHz to 8 GHz. The proposed PMA shows an absorption peak with almost 100% absorptivity at 6.2 GHz. Also, wideband negative index of refraction is observed. Further, the absorber is inspected for the different rotation angles of the top metasurface (omega-shaped ring) along the optical axis, and obliquity of incidence angle for both TE and TM polarized waves. Moreover, surface electric field and surface current... 

    Oriented hyperlens based on passivated porous graphene phases for sub-diffraction visible imaging

    , Article Optical Materials Express ; Volume 11, Issue 9 , 2021 , Pages 2839-2853 ; 21593930 (ISSN) Sadeghi, M. N ; Yazdanfar, P ; Rashidian, B ; Sharif University of Technology
    The Optical Society  2021
    The performance of conventional imaging lenses, relying on the phase transformation of propagating waves, is impairing due to the aberration and diffraction limits. For imaging beyond the diffraction limit, different superlens designs have been proposed. Although subdiffraction resolution imaging in the near field has been realized by the superlenses with negative refractive index, magnification of the subwavelength objects into the far field has not been fulfilled. Imaging using “hyperlens” is promising to overcome the energy spreading associated with diffraction, by utilizing negative permittivity parallel to the optical axis, and positive permittivity perpendicular to it. Among various... 

    Accurate and fast extraction of the bloch eigenmodes of fiber gratings

    , Article Progress In Electromagnetics Research M ; Volume 34 , 2013 , Pages 29-37 ; 19378726 (ISSN) Jazayeri, A. M ; Sharif University of Technology
    Based on Bloch-Floquet's theorem and ordinary matrix calculations, a rigorous method for extraction of the eigenmodes of fiber gratings is developed. This method is also applicable to fiber gratings which are either physically multilayer or mathematically divided into layers along the radial coordinate. Although the well-known coupled mode theory (CMT) is accounted a method for extraction of the coefficients of reflection and transmission of finite-length FBGs, its inadequacy for extraction of the Bloch eigenmodes of FBGs is illustrated, even if the modulation depth of refractive index is small and the Bragg condition is satisfied  

    Investigation of humidity effect on the air refractive index using an optical fiber design

    , Article Journal of Applied Sciences ; Volume 11, Issue 16 , 2011 , Pages 3022-3027 ; 18125654 (ISSN) Mehrabani, A ; Golnabi, H ; Sharif University of Technology
    In this study operation of an optical design based on the intensity modulation for the refractive index change has been described. The reported instrument measures the transmitted output power depending up on the medium refractive index in the light path of a fiber-to-fiber design. A liquid cell is located between the fibers in the light path and power variations for different cold and hot water levels in the cell are measured. By using a reference humidity meter the calibration curve representing the relative humidity (%RH) as a function of the transmitted output power is obtained. For the hot water with the final temperature of T = 32.7°C the output power range of 255.0 -313.OnW is... 

    Simultaneous Measurement of Refractive Index and Physical Thickness Using Fourier-Domain Optical Coherence Tomography

    , M.Sc. Thesis Sharif University of Technology Moazami Gudarzi, Nilufar (Author) ; Amjadi, Ahmad (Supervisor)
    In Fourier domain optical coherence tomography, we can measure the optical thickness (refractive index n times thickness d), of sample’s layers. In this work, we introduce a new method for measurement of refractive index and physical thickness of multiple layers simultaneously by Fourier domain optical coherence tomography, without additional information about the structure of the sample under investigation. The input data to the formulation are the optical path lengths (OPLs) and suitable set of wavenumber of the FD-OCT interference spectrum. The output of simulation suggest that, the accuracy of the extracted parameters depend on the difference in the refractive index gradient of sample... 

    Analysis of Graphene Plasmonic Waveguide with Inhomogeneous Substrate in Terahertz Band

    , M.Sc. Thesis Sharif University of Technology Rezaei, Zohreh (Author) ; Borji, Amir (Supervisor) ; Rajaei, Behzad (Supervisor)
    Due to its extensive applications in imaging, data security, medication, etc., Terahertz has attaracted an ever-inceasing attention. Design and implementation of Terahertz sources and circuits as waveguide, filters, etc. in this band have attracted attention. The unique elec-tric characteristics of graphene, like showing plasmonic characteristics in Terahertz frequency band, made this recently recognized matter a promising one to build super-integrated plas-monic circuits in Terahertz band. In this text, the first section represents an introduction for a number of graphene waveguides as well as studying the effective refractive index method to analyze graphene waveguides. Due to the small... 

    Opposing trends of geometrical parameters in maximisation of micro-ring resonator quality factor

    , Article Electronics Letters ; Volume 47, Issue 25 , 2011 , Pages 1388-1390 ; 00135194 (ISSN) Jalaly, S ; Rezaei, M ; Mehrany, K ; Sharif University of Technology
    Opposing trends of geometrical parameters in minimisation of bending loss and thus in maximising the quality factor are briefly discussed for micro-ring resonators. It is shown that, while the quality factor of low order modes is an oscillatory function of geometrical parameters, the quality factor of high order modes is a monotonic function. The former has discrete pairs of optimum inner and outer ring radii which maximises the quality factor. In contrast, the quality factor of the latter has no local maximum. Introduction of slight inhomogeneities does not change the overall behaviour of the quality factor but can increase its overall level when the refractive index of the ring region... 

    Wideband and polarisation-independent antireflection coating using metamaterials

    , Article IET Optoelectronics ; Volume 14, Issue 5 , 2020 , Pages 266-273 Sepehripour, F ; Karimi, P ; Khavasi, A ; Sharif University of Technology
    Institution of Engineering and Technology  2020
    Here, the authors propose a new approach for realising wideband and polarisation-independent antireflection coating, based on a metamaterial composed of a subwavelength array of metallic pillars with a square cross-section. The effective impedance of the array can be duly adjusted by the size and distance of the pillars. As such, the authors design the effective impedance of the antireflection coating to be the geometrical mean of the impedance of upper and lower media and choose its height to be quarter of operating wavelength. Doing so, the reflection vanishes at the desired frequency and fractional bandwidth of 56% is achieved with a criterion of 10% reflectance (the refractive index of... 

    Differential-transfer-matrix based on Airy's functions in analysis of planar optical structures with arbitrary index profiles

    , Article IEEE Journal of Quantum Electronics ; Volume 44, Issue 4 , February , 2008 , Pages 324-330 ; 00189197 (ISSN) Zariean, N ; Sarrafi, P ; Mehrany, K ; Rashidian, B ; Sharif University of Technology
    A novel analytical method for solution of planar optical structure with arbitrary refractive index profile is proposed. This new method is founded on differential-transfer-matrices, whose field solutions are based on Airy's trial functions. In contrast to conventional Wentzel, Kramers, and Brillouin (WKB) solutions, which diverge around the turning points, this approach can be successfully used for exact calculation of various functions, including eigenvalues of optical waveguides with arbitrary index profiles, and complex reflection and transmission coefficients, even at the presence of turning points. The method is rigorous and can be applied for both major polarizations. © 2008 IEEE  

    Analytical extraction of leaky modes in circular slab waveguides with arbitrary refractive index profile

    , Article Applied Optics ; Volume 46, Issue 36 , 2007 , Pages 8656-8667 ; 1559128X (ISSN) Sarrafi, P ; Zareian, N ; Mehrany, K ; Sharif University of Technology
    Circular slab waveguides are conformally transformed into straight inhomogeneous waveguides, where-upon electromagnetic fields in the core are expanded in terms of Legendre polynomial basis functions. Thereafter, different analytical expression of electromagnetic fields in the cladding region, viz. Wentzel-Kramers-Brillouin solution, modified Airy function expansion, and the exact field solution for circular waveguides, i.e., Hankel function of complex order, are each matched to the polynomial expansion of the transverse electric field within the guide. This field matching process renders different boundary conditions to be satisfied by the set of orthogonal Legendre polynomial basis... 

    Improved differential-transfer-matrix method for inhomogeneous one-dimensional photonic crystals

    , Article Journal of the Optical Society of America B: Optical Physics ; Volume 23, Issue 7 , 2006 , Pages 1451-1459 ; 07403224 (ISSN) Eghlidi, M. H ; Mehrany, K ; Rashidian, B ; Sharif University of Technology
    Optical Society of American (OSA)  2006
    A band structure of one-dimensional periodic media having an arbitrary inhomogeneous refractive index profile is extracted based on the modification committed on the differential-transfer-matrix method (DTMM). Furthermore, the most recently modified differential transfer matrix is improved by reshaping the formulation in terms of which the electromagnetic fields are expanded and closed form formulas, providing the allowed values of Bloch wavenumbers, which were not available before. Although the frequency gaps in previously published results that we derived by using the conventional DTMM were not in agreement with the well-known Bragg law at the edge of each Brillouin zone, the new results... 

    Legendre polynomial expansion for analysis of linear one-dimensional inhomogeneous optical structures and photonic crystals

    , Article Journal of the Optical Society of America B: Optical Physics ; Volume 23, Issue 5 , 2006 , Pages 969-977 ; 07403224 (ISSN) Chamanzar, M ; Mehrany, K ; Rashidian, B ; Sharif University of Technology
    Optical Society of American (OSA)  2006
    A Legendre polynomial expansion of electromagnetic fields for analysis of layers with an inhomogeneous refractive index profile is reported. The solution of Maxwell's equations subject to boundary conditions is sought in a complete space spanned by Legendre polynomials. Also, the permittivity profile is interpolated by polynomials. Different cases including computation of reflection-transmission coefficients of inhomogeneous layers, band-structure extraction of one-dimensional photonic crystals whose unit-cell refractive index profiles are inhomogeneous, and inhomogeneous planar waveguide analysis are investigated. The presented approach can be used to obtain the transfer matrix of an...