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nonlinear-optics
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Analysis of Nonlinear and Plasmonic Nano-Photonic Structures
, M.Sc. Thesis Sharif University of Technology ; Mehrany, Khashayar (Supervisor) ; Khorasani, Sina (Supervisor)
Abstract
Different methods of shifting and shaping of space-time electromagnetic pulses are in this work investigated by nonlinearity and/or dispersion. Developing two dimensional (2D) finite difference time domain (FDTD) codes in the nonlinear regime and taking the optical dispersion of ideal metals into account, nanophotonic and plasmonic structures are analyzed in this thesis.
Goos-Hänchen shift, superprism effect, and optical bistability are particularly emphasized. A heuristic approximation is presented to extract the Goos-Hänchen shift at the interface of 1D and 2D photonic crystals. The superprism effect for electric polarization – where the electric field vector is perpendicular to the 2D...
Goos-Hänchen shift, superprism effect, and optical bistability are particularly emphasized. A heuristic approximation is presented to extract the Goos-Hänchen shift at the interface of 1D and 2D photonic crystals. The superprism effect for electric polarization – where the electric field vector is perpendicular to the 2D...
The Measurement of Ultrashort Optical Parametric Oscillator Pulses
, M.Sc. Thesis Sharif University of Technology ; Anvari, Abbas (Supervisor) ; Ebrahim-Zadeh, Majid (Supervisor) ; Sadighi Bonabi, Rasoul (Co-Advisor)
Abstract
The picosecond (ps) pulses in a synchronously pumped optical parametric oscillator (SPOPO) is generated by a 20W and 81.1 MHz Yb fiber laser at 1064nm, providing 11.7 W of total average power in near to mid-IR at 73% efficiency so that the signal pulse with a wavelength of 1560 nm and 7.1W average power and 3330 nm idler pulse with an average power of about 4.6W has been produced. The optical parametric oscillator (OPO), based on a 50 mm MgO:PPLN crystal with 5 gratings which is capable of withstanding large average powers without thermal effects.
The duration of these ultrashort infrared signal pulse generated by the described SPOPO is measured by using homemade interferometric...
The duration of these ultrashort infrared signal pulse generated by the described SPOPO is measured by using homemade interferometric...
Designing an Optical Processing Unit for Non-Linear Operations in Deep Neural Networks
, M.Sc. Thesis Sharif University of Technology ; Koohi, Somayyeh (Supervisor)
Abstract
Abstract: In this thesis, we tackled the problem of nonlinear activation function in optical artificial neural networks, and in particular in convolutional and recurrent neural networks. In the end, we propose an all-optical recurrent neural network in free-space optics for the first time. Artificial neural networks are a branch of artificial intelligence, which can be adopted to solve a wide variety of problems. While very powerful, these networks can be very power hungry and slow when it comes to solving very complicated problems. Optical versions of these networks bring the promise of solving both of these issues and provide a fast and power efficient platform for these networks. However,...
Two new swinging interferometers
, Article Journal of Optics A: Pure and Applied Optics ; Volume 9, Issue 7 , 2007 , Pages 560-564 ; 14644258 (ISSN) ; Rashidian, B ; Sharif University of Technology
2007
Abstract
The most important disadvantage of swinging interferometers is that the optical path difference created in them is a nonlinear function of the rotation angle. In this paper, two new swinging interferometers are presented which have good linearity and provide a larger path difference in response to the rotation angle compared to other interferometers. This makes them suitable for applications such as high-resolution spectroscopy, and precision micro and nanopositioning. In one of these two interferometers, the optical path difference is created by rotation of a system composed of four mirrors, and in the other one it is created by rotation of a system consisting of two mirrors. They are not...
A semiclassical approach for the phase matching effect in the nonlinear optical phenomena
, Article Journal of Optics A: Pure and Applied Optics ; Volume 10, Issue 12 , 2008 ; 14644258 (ISSN) ; Kaatuzian, H ; Amjadi, A ; Sharif University of Technology
2008
Abstract
In this paper we present a semiclassical model for explanation of the nonlinear optical effect and phase matching. We calculate momentary quantities of the delay time of photon-electron interaction in each layer. We show that for phase matching, the average delay time for the fundamental photons must be equal to the average delay time for the harmonic photons. Additionally, we calculate the number of layers that the harmonic photon needs to be absorbed or converted to fundamental photons. This calculation applies to different wavelengths with different phase matching angles. Our simulation results are in good agreement with experimental data. © 2008 IOP Publishing Ltd
Theoretical study of high repetition rate short pulse generation with fiber optical parametric amplification [electronic resource]
, Article Journal of Lightwave Technology ; May 2012, Volume 30, Issue 9, PP. 1263-1268 ; Ariaei, A. M ; Jadidi, M. M ; Salehi, J. A ; Sharif Unversity of Technology
Abstract
In this paper, we study theoretically the generation of high repetition rate short pulses using fiber optical parametric amplification. We show that the pulse shape and duration depend on the signal location relatively to the pump frequency. We demonstrate that in order to get the shortest pulse width, the signal must be located at one of the extremities of the gain spectrum associated with the pump peak power. We derive the analytical expression of the pulse shape in this case and compare it to the exponential gain regime case. Using numerical simulations, we also analyze the impact of walk-off and pump phase modulation that is required to suppress Stimulated Brillouin Scattering and derive...
Theoretical study of high repetition rate short pulse generation with fiber optical parametric amplification
, Article Journal of Lightwave Technology ; Volume 30, Issue 9 , 2012 , Pages 1263-1268 ; 07338724 (ISSN) ; Ariaei, A. M ; Jadidi, M. M ; Salehi, J. A ; Sharif University of Technology
2012
Abstract
In this paper, we study theoretically the generation of high repetition rate short pulses using fiber optical parametric amplification. We show that the pulse shape and duration depend on the signal location relatively to the pump frequency. We demonstrate that in order to get the shortest pulse width, the signal must be located at one of the extremities of the gain spectrum associated with the pump peak power. We derive the analytical expression of the pulse shape in this case and compare it to the exponential gain regime case. Using numerical simulations, we also analyze the impact of walk-off and pump phase modulation that is required to suppress Stimulated Brillouin Scattering and derive...
Resonant second harmonic generation in plasma by self-focused twisted beam
, Article Optics Communications ; Volume 341 , April , 2015 , Pages 295-301 ; 00304018 (ISSN) ; Sohailya, S ; Bahrampour, A ; Sharif University of Technology
Elsevier
2015
Abstract
The resonant second harmonic generation in the presence of a wiggler magnetic field by twisted laser plasma interaction is surveyed. The wiggler magnetic field provides additional momentum required for the phase matching. The Laguerre-Gaussian modes can be used to control the self-focusing and improve the second harmonic generation in laser plasma interaction. The wave equations for the fundamental and the second harmonic fields have been solved in the paraxial approximation. The generation of the second harmonic considering self-focusing is investigated. Also, the dependence of the second harmonic power on the propagation distance for different values of initial fundamental beam intensity,...
Generation and compression of dissipative soliton using fiber arrays
, Article Optical Fiber Technology ; Volume 33 , 2017 , Pages 1-6 ; 10685200 (ISSN) ; Niknafs, A ; Rooholamininejad, H ; Bahrampour, A ; Sharif University of Technology
Academic Press Inc
2017
Abstract
Compression of dissipative soliton (DS) and dissipative soliton resonance (DSR) have attracted considerable attention for generation of short pulse lasers. Generation of DS/DSR is investigated numerically in circular fiber array with optical central fiber. Parameter management can generate the DS and DSR in circular fiber array with central optical fiber and in normal or anomalous dispersion. The nonlinear circular fiber arrays can be used as an optical pulse compressor. In this paper, compression of DS and DSR versus the nonlinearity and dispersion parameters in circular fiber array with central fiber, are taken into investigation. © 2016 Elsevier Inc
The effect of higher order harmonics on second order nonlinear phenomena
, Article Optics Communications ; Volume 343 , May , 2015 , Pages 124-130 ; 00304018 (ISSN) ; Borji, A ; Sharif University of Technology
Elsevier
2015
Abstract
A new method which is a combination of the harmonic balance and finite difference techniques (HBFD) is proposed for complete time-harmonic solution of the nonlinear wave equation. All interactions between different harmonics up to an arbitrary order can be incorporated. The effect of higher order harmonics on two important nonlinear optical phenomena, namely, the second harmonic generation (SHG) and frequency mixing is investigated by this method and the results are compared with well-known analytical solutions. The method is quite general and can be used to study wave propagation in all nonlinear media
Electromagnetically induced grating in the microwavedriven four-level atomic systems
, Article Applied Optics ; Volume 54, Issue 3 , 2015 , Pages 368-377 ; 1559128X (ISSN) ; Naseri, T ; Navadeh Toupchi, M ; Sharif University of Technology
Abstract
A new scheme to investigate an electromagnetically induced grating in an N-type configuration in the presence of a strong-standing coupling field, additional coherent fields, and microwave driven fields is presented. By considering the coherent population trapping (CPT) condition in a four-level microwave drivenN-type atomic system, a novel nonlinear optical storage is obtained via linear absorption vanishing and giant Kerr nonlinearity during light propagation. It is revealed that nonlinear properties in this atomic medium are maximum in the CPT condition, and these nonlinear properties could be affected and modulated by means of a microwave driven field. In this condition high-phase...
Free-Space optical neural network based on optical nonlinearity and pooling operations
, Article IEEE Access ; Volume 9 , 2021 , Pages 146533-146549 ; 21693536 (ISSN) ; Koohi, S ; Paranj, A. F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2021
Abstract
Despite various optical realizations of convolutional neural networks (CNNs), optical implementation of nonlinear activation functions and pooling operations are still challenging problems. In this regard, this paper proposes an optical saturable absorption nonlinearity and its atomic-level model, as well as two various optical pooling operations, namely optical average pooling and optical motion pooling, by means of 4f optical correlators. Proposing these optical building blocks not only speed up the neural networks due to negligible optical processing latency, but also facilitate the concatenation of optical convolutional layers with no optoelectrical conversions in-between, as the...
High-Speed multi-layer convolutional neural network based on free-space optics
, Article IEEE Photonics Journal ; Volume 14, Issue 4 , 2022 ; 19430655 (ISSN) ; Koohi, S ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2022
Abstract
Convolutional neural networks (CNNs) are at the heart of several machine learning applications, while they suffer from computational complexity due to their large number of parameters and operations. Recently, all-optical implementation of the CNNs has achieved many attentions, however, the recently proposed optical architectures for CNNs cannot fully utilize the tremendous capabilities of optical processing, due to the required electro-optical conversions in-between successive layers. To implement an all-optical multi-layer CNN, it is essential to optically implement all required operations, namely convolution, summation of channels' output for each convolutional kernel feeding the...
Exact solitary optical wave solutions and modulational instability of the truncated Ω- fractional Lakshamanan–Porsezian–Daniel model with Kerr, parabolic, and anti-cubic nonlinear laws
, Article Optical and Quantum Electronics ; Volume 54, Issue 5 , 2022 ; 03068919 (ISSN) ; Das, P. K ; Pashrashid, A ; Rezazadeh, H ; Sharif University of Technology
Springer
2022
Abstract
In this article we have acquired exact solitary wave solutions for the truncated Ω- fractional Lakshamanan–Porsezian–Daniel model with Kerr, parabolic, and anti-cubic nonlinear laws employing extended auxiliary technique. Diverse set of exponential function solutions acquired relying on a map between the considered equation and an auxiliary ODE. Obtained solutions are recast in several hyperbolic and trigonometric forms based on different restrictions between parameters involved in equations and integration constants that appear in the solution. A few significant ones among the reported solutions are pictured to perceive the physical utility and peculiarity of the considered model using...
Theoretical Studies of Ultrashort Light Pulse Spectrally-Phase-Encoded OCDMA System Using Power-Cubic Optical Nonlinear Preprocessor
, Article Journal of Lightwave Technology ; Volume 33, Issue 24 , October , 2015 , Pages 5062-5072 ; 07338724 (ISSN) ; Salehi, J. A ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2015
Abstract
In this paper, a spectral-phase-encoded ultrashort light pulse optical code division multiple access (SPE-OCDMA) system employing a novel nonlinear power-cubic optical preprocessor at its receiver's front end is theoretically investigated. The system's mathematical model and the statistical distribution of the decision variable Y, prior to the decision module of the receiver, are discussed. The first three moments of the random decision variable Y are obtained in the context of the above OCDMA system and subsequently used in an appropriate Log-Pearson type 3 (LP3) distribution to represent the random decision variable $Y$. Multiple access interference (MAI) and amplified spontaneous emission...
Statistical modeling and performance characterization of ultrashort light pulse communication system using power-cubic optical nonlinear preprocessor
, Article IEEE Transactions on Communications ; Volume 63, Issue 8 , 2015 , Pages 2948-2958 ; 00906778 (ISSN) ; Salehi, J. A ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2015
Abstract
In this paper, we present an analytical approach in obtaining the probability density function (pdf) of the random decision variable Y, which is formed at the output of the power-cubic all-optical nonlinear preprocessor followed by the photodetector, with applications in ultrafast optical time-division multiplexing and optical code-division multiple-access systems. Our approach can be used to accurately evaluate the performance of ultrafast pulse detection in the presence of Gaussian noise. Through rigorous Monte Carlo simulation, the accuracy of the widely used Gaussian approximation of decision variable Y is refuted. However, in this paper, we show that the so-called log-Pearson type-3...
Statistical characterization of the output of nonlinear power-cubic detection unit for ultrashort light pulse communication in the presence of Gaussian noise
, Article IWCIT 2015 - Iran Workshop on Communication and Information Theory ; 2015 ; 9781479982356 (ISBN) ; Salehi, J. A ; Sharif University of Technology
Abstract
In this paper, an accurate model for the probability density function (pdf) of the random decision variable Y in an ultrafast digital lightwave communication system, utilizing power-cubic all-optical nonlinear preprocessor is presented. The proposed model can replace the prevalent Gaussian approximation, as the accuracy of the latter is discredited by Monte-Carlo simulation. The Log-Pearson type-3 probability density function (LP3 pdf) is shown to appropriately represents the random decision variable Y. Three characteristic parameters of the LP3 pdf are also obtained through the three moments of the decision variable Y. Finally, the system error probability is revisited using the obtained...
Square-hexagonal nanostructured photonic crystal fiber at 1550 nm wavelength
, Article 10th International Symposium on Communication Systems, Networks and Digital Signal Processing, CSNDSP 2016, 20 July 2016 through 23 July 2016 ; 2016 ; 9781509025268 (ISBN) ; Nikoosohbat, A ; Mohebzadeh Bahabady, A ; Chizari, A ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2016
Abstract
Photonic crystal fibers (PCFs) are widely used in optical communications systems, nonlinear devices, gas sensors, high power transmission, and so on. Photonic crystal fiber with minimum values of confinement loss, nonlinear effects, and chromatic dispersion is used in optical communication. But in some applications, high nonlinear coefficient is required. This paper presents new design of index-guiding photonic crystal fiber (IGPCF) with characteristics appropriate for nonlinear applications. In the present design with a square-hexagonal nano-structure having air holes with unequal diameters, nearly zero dispersion at the wavelength range of 1540 to 1550 nm is achieved. The simulation...
Chromatic dispersion and nonlinear phase noise compensation based on KLMS method
, Article Optics Communications ; Volume 351 , September , 2015 , Pages 149-154 ; 00304018 (ISSN) ; Shayesteh, M. G ; Farhangian, N ; Sharif University of Technology
Elsevier
2015
Abstract
In this study, kernel least mean square (KLMS) algorithm with fractionally spaced equalizing structure is proposed for electrical compensation of chromatic dispersion (CD) and nonlinear phase noise (NLPN) in a dual polarization optical communications system with coherent detection. We consider single mode fiber channel. At the receiver, the additive optical noise is represented as additive white Gaussian noise. Phase modification is utilized at high signal powers to maintain the validity of Gaussian model of noise. We consider QAM and PSK modulations and evaluate the performance of the proposed method in terms of error rate, phase error, and error vector magnitude (EVM). The results are...
Optical bistable switching with Kerr nonlinear materials exhibiting a finite response time in two-dimensional photonic crystals
, Article Volume 7713 ; Proceedings of SPIE - The International Society for Optical Engineering, 12 April 2010 through 15 April 2010 , 2010 ; 0277786X (ISSN) ; 9780819481863 (ISBN) ; Monem Haghdoost, Z ; Abediasl, H ; Khorasani, S ; Mehrany, K ; Sharif University of Technology
Abstract
Effect of relaxation time on the performance of photonic crystal optical bistable switches based on Kerr nolinearity is discussed. This paper deals with optical pulses with the duration of about 50 ps. In such cases the steady state response of the optical device can be used to approximate the pulse evolution if the nonlinearity is assumed instantaneous, hence analytical solutions such as the coupled mode theory can be used to obtain the time evolution of the electromagnetic fields. However if the relaxation time of the material nonlinear response is also considered, changes in the power levels and in the shape of the hystersis loop is observed. In this case, we use the nonlinear finite...