Sharif Digital Repository

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  

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... 

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  

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)  

A high sensitive optical MEMS accelerometer is proposed, which works by changing the effective refractive index of a microring relied on intensity modulation of light wave. The proposed optical sensing system consists of a microring, waveguide, and a proof mass. Acceleration causes lateral displacement of the proof mass. The proof mass is in the optical coupling length of the microring, and the displacement of the proof mass changes effective refractive index of the microring. Changes of the effective refractive index of the microring result in wavelength shift. The mechanical and optical parts of the proposed accelerometer are designed, and the obtained functional characteristics are... 

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),... 

The present study demonstrates numerically a novel approach to perform a controllable single-mode random laser, using stimulated Raman gain. Due to the narrow linewidth of the Raman line shape, only one of the modes of the passive random system can lase. The robust control on the emission spectrum was achieved through the selection of any desired quasi-modes, by adjusting the pump wavelength in order to place the center of Raman line shape on desired quasi-modes. This approach was proved using a developed nonlinear transfer matrix method for a 1D Raman random system. The proposed method includes the Raman gain saturation and the frequency-dependent index of refraction  

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... 

It is has been long known that the curved space in the presence of gravitation can be described as a non-homogeneous anisotropic medium in flat geometry with different constitutive equations. In this article, we show that the eigenpolarizations of such medium can be exactly solved, leading to a pseudo-isotropic description of curved vacuum with two refractive index eigenvalues having opposite signs, which correspond to forward and backward travel in time. We conclude that for a rotating universe, time-reversal symmetry is broken. We also demonstrate the applicability of this method to Schwarzschild metric and derive exact forms of refractive index. We derive the subtle optical anisotropy of... 

We show that a plasmonic semiconductor substrate can support highly confined surface plasmons when it is covered by a graphene layer. This occurs when the imaginary part of graphene conductivity and real part of the effective permittivity of the surrounding medium become simultaneously negative. Full-wave electromagnetic simulations demonstrate the occurrence of negative refraction and two-dimensional lensing at the interface separating regions supporting conventional right-handed graphene plasmons and left-handed surface plasmon polaritons. © 2018 Optical Society of America  

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... 

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  

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... 

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... 

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  

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...