Sharif Digital Repository

This paper models the dielectric corona pre-ionization, capacitor transfer type of flat-plane transmission line traveling wave transverse excited atmospheric pressure nitrogen laser by a non-linear lumped RLC electric circuit. The flat-plane transmission line and the pre-ionizer dielectric are modeled by a lumped linear RLC and time-dependent non-linear RC circuit, respectively. The main discharge region is considered as a time-dependent non-linear RLC circuit where its resistance value is also depends on the radiated pre-ionization ultra violet (UV) intensity. The UV radiation is radiated by the resistance due to the surface plasma on the pre-ionizer dielectric. The theoretical predictions... 

In this paper, a distributed relative humidity (RH) or moisture sensor is proposed. The proposed structure is a single mode telecommunication optical fiber coated by humidity sensitive and insensitive polymers periodically. The polymer coated fiber is surrounded by a high Young's modulus material such as stainless steel mesh. The swelling of the coated Humidity Sensitive Polymers (HSPs) as a result of moisture absorption induces fiber gratings in the single mode fiber. Depending on the coating period relative to the light wavelength, the induced fiber grating can be Fiber Bragg Grating (FBG) or Long Period Fiber Grating (LPFG). The light reflected by the induced FBG or losses due to the... 

Leak detection based on acoustic emission needs robust time delay estimation in the presence of various types of noise. Considering several aspects of leakage signal and noise, the present work introduces wavelet based optimized residual complexity (WORC), in order to minimize the probability of false alarms in the presence of correlated, uncorrelated, and impulsive noise. The proposed method utilizes two approaches simultaneously. First, it optimizes residual complexity “for robustness against both correlated and uncorrelated noise”, then it employs wavelet basis in order to reduce the complexity of mixture of correlated and impulsive noise. In order to compare the resolution and percentage... 

The deposition of tetrakis (4-sulonatophenyl) porphyrin (TPPS) thin film on optical fibers presents many possibilities for sensing applications. The J-form aggregation with a narrow and sharp spectral feature at about 490 nm and its sensitivity to humidity have been discussed; a fast change of wavelength occurs according with variation in the humidity level. The reproducibility and high sensitivity of TPPS-coated fibers, along with the capabilities of optical fibers, suggest the device as a good candidate for humidity sensing in harsh environments. © 2018, The Author(s)  

Oil leakage of transportation pipelines causes a change in its environmental temperature. This effect is employed to detect the leakage and its positions. The Raman Optical Time Domain Reflectometer (ROTDR) and Brillouin Optical Time Domain Amplifier (BOTDA) sensors are two of the most precise oil pipeline leak detector systems operate based on this effect. The position of leakage is determined by the time difference between the sending and backscattered laser pulses. In this paper, the transient response of BOTDA and ROTDR sensors are obtained through solution of the mass, energy and heat transfer in soil and fiber cable. It is shown that the mechanical rise time is of the order of a few... 

We theoretically study a hybrid plasmonic-photonic cavity setup that can be used to induce and control long-distance heat transfer between molecular systems through optomechanical interactions. The structure we propose consists of two separated plasmonic nanoantennas coupled to a dielectric cavity. The hybrid modes of this resonator can combine the large optomechanical coupling of the sub-wavelength plasmonic modes with the large quality factor and delocalized character of the cavity mode that extends over a large distance (∼µm). We show that this can lead to effective long-range heat transport between molecular vibrations that can be actively controlled through an external driving laser. ©... 

The photon orbital and/or spin angular-momentum absorption in absorbing plasma medium causes the circular motion of electrons and generate the azimuthal component of current density. The axial magnetic field generation due to the azimuthal component of generated current density is known as inverse Faraday effect. In this paper, the axial magnetic field generation in an absorbing plasma with ramped density by the propagation of linear polarized Laguerre-Gaussian beam is taken into consideration. It is shown that the positive slope of the initial electron density causes a considerable enhancement of self-generated axial magnetic field. The magnetic field enhancement depends on the twisted... 

The non-paraxial and vectorial effects have an important role in the dynamics of highly confined beam in nonlinear medium. In this paper, we study the vectorial non-paraxial propagation of Gaussian field in the saturable absorber media numerically with the aim of nano-lithography. It is shown that in the optimal regimes for nanolithography, the mutual coupling between components of optical field and mode coupling between different orders of Hermite-Gaussian mode lead to generation of various patterns upon propagation through saturable absorber media. The vectorial effect is responsible for the symmetry breaking. For converging input beam, while the intense part of the beam goes toward the... 

Quantum optical coherent-state comparison amplifiers are nondeterministic devices which can amplify rather noiselessly a weak coherent state with an unknown phase from a finite discrete set. The high fidelity and high success probability of this amplifier are accomplished by a comparison stage and some photon subtraction stages. Due to the heralding nature of these amplifiers, they work part of the time. Here, we propose a feedforward protocol to increase the heralded times by correcting the incorrect guess. Hence, we enhance the fidelity and success probability more. Finally, the schematic experimental configuration of the feedforward-assisted coherent-state comparison amplifier is... 

Time-dependent model is presented to simulate random lasers in the presence of an inhomogeneous gain medium. PbSe quantum dots (QDs) with an arbitrary size distribution are treated as an inhomogeneous gain medium. By introducing inhomogeneity of the PbSe QDs in polarization, rate, and Maxwell's equations, our model is constructed for a one-dimensional disordered system. By employing the finite difference time-domain method, the governing equations are numerically solved and lasing spectra and spatial distribution of the electric field are calculated. The effect of increasing the pumping rate on the laser characteristics is investigated. The results show that the number of lasing modes and... 

Governing equations of a Raman fiber distributed temperature sensor supported by a counter propagating pumped Raman amplifier are written in the form of integral equations. Forward pump and backward going probe are in the pulsed and continuous wave modes of operation respectively. It is shown that powers of the forward and backward Raman signals (stokes and anti stokes) approximately are the convolution of the input forward pump pulse and corresponding optical fiber impulse responses. The Fourier Wavelet Regularized Deconvolution (ForWaRD) method is employed to improve the spatial resolution in fiber Raman distributed temperature sensor without reducing the pulse width of the laser source  

We explore whether localized surface plasmon polariton modes can transfer heat between molecules placed in the hot spot of a nanoplasmonic cavity through optomechanical interaction with the molecular vibrations. We demonstrate that external driving of the plasmon resonance indeed induces an effective molecule-molecule interaction corresponding to a heat transfer mechanism that can even be more effective in cooling the hotter molecule than its heating due to the vibrational pumping by the plasmon. This mechanism allows us to actively control the rate of heat flow between molecules through the intensity and frequency of the driving laser. © 2019 American Physical Society  

In this paper quasi photonic crystal fibers (QPCFs) based on 8-fold and Penrose symmetries are analyzed. The confinement loss of both proposed QPCFs with employing perfect matching layer by finite element method has been calculated. It is shown for both presented structures, the confinement loss is negligible relative to Rayleigh scattering loss. The birefringence of Penrose tile QPCF, is 80 times greater than that of Amnan Beenker quasicrystal fiber. We present numerically the existence of endlessly single mode fiber and zero birefringence QPCFs as advantage of employing novel rotational symmetry. © 2017, National Institute of Optoelectronics. All rights reserved  

In our previous work, a distributed moisture sensor based on the induced long-period fiber grating in the presence of moisture is proposed. The proposed structure is analyzed numerically (Opt Laser Technol 117:126–133, 2019). In this article, due to the axial symmetry and periodic structure of the proposed sensor, the Love’s potential and Fourier series are employed to obtain an analytical solution for the refractive index variation along the sensor versus moisture density. The analytical method reduces the computation time relative to our numerical calculation drastically. The analytical results are in good agreement with those that are obtained by numerical calculations. The analytical... 

Optical fiber torsion sensors have significant importance for structural health monitoring. In this paper, an optical fiber torsion sensor based on computer-generated-hologram (CGH) is proposed and investigated theoretically. In the proposed structure a dual mode fiber (DMF) is used as a sensing element. An acoustic source can be employed to induce a fiber grating. The acoustic induced fiber grating (AIFG) causes the fundamental LP01 mode of DMF couples to LP11 o and LP11 e fiber modes. In the presence of torsion in DMF, the profiles of LP01, LP11 o and LP11 e modes rotate relative to the absence of fiber torsion. At the end of DMF a suitable CGH can be employed to resolve spatially the... 

Careful studies of coupling show that transmittance power between microring and waveguide is dependant to field intensity. Also more researches show that optical multistable behavior of microring had been affected by nonlinear power coupling efficiency in high field intensities. Operation of microring in nonlinear regions can be so useful in designing all optical switches and control techniques. In this paper has been proposed an all-optical flip-flop based on nonlinear treatment of microring. © 2008 Elsevier B.V. All rights reserved  

We present a new class of hollow core photonic crystal fibers taking the advantages of quasi-crystals structures. We analyze two structures based on modified 8-fold and 12-fold symmetries and we presente the ability of air guiding propagation having two photonic bandgap in the λ/Λ<1 In this paper bandgap of both structures as well as the behavior of the guided modes via finite element method are investigated  

Fiber optic sensors have emerged as a promising technology for precise measurements in various applications. In this study, we propose an integrated all-fiber Cascade Fabry–Perot (CFP) sensor that uses the harmonic Vernier effect to enhance its sensitivity. The sensor consists of a Silica Capillary Tube (SCT) fusion spliced to a Single-Mode Fiber (SMF), and its cavity length is optimized to locate Vernier's internal envelopes for three different Vernier harmonic orders within the spectral range of 1500 nm–1600 nm. Three CFPs were fabricated and utilized as strain and temperature sensors. By analyzing and tracing Vernier's internal envelopes, we experimentally demonstrated that sensitivity... 

In our previous works, we presented a theoretical approach to describe the behavior of a single-mode step-index optical fiber or polymer optical fiber such as poly (methyl methacrylate) or PMMA fiber coated by moisture-sensitive polymers (MSPs) and moisture-insensitive polymers periodically. The periodic structure is surrounded by a high young's modulus material such as stainless steel mesh. Absorption of the moisture by the MSPs causes to deform the optical fiber, such that the optical fiber gratings are induced. Induced fiber gratings are the basis of the proposed relative moisture sensor. Due to the low Young's modulus of polymers, the polymer fiber sensors are more sensitive relative to... 

Precise acoustical leak detection calls for robust time-delay estimates, which minimize the probability of false alarms in the face of dispersive propagation, multiple reflections, and uncorrelated background noise. Providing evidence that higher order modes and multi-reflected signals behave like sets of correlated noise, this work uses a regression model to optimize residual complexity in the presence of both correlated and uncorrelated noise. This optimized residual complexity (ORC) is highly robust since it takes into account both the level and complexity of noise. The lower complexity of the dispersive modes and multiple reflections, compared to the complexity of the plane mode, points...