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nonlinear-optics
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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...
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...
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,...
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...
Mathematical modeling and statistical analysis of SPE-OCDMA systems utilizing second harmonic generation effect in thick crystal receivers
, Article 2009 Asia Communications and Photonics Conference and Exhibition, ACP 2009 ; 2009 ; 9781557528773 (ISBN) ; Salehi, J. A ; Sharif University of Technology
Optical Society of America
2009
Abstract
In this paper we evaluate the performance of a spectrally-phase-encoded-OCDMA system using a receiver structure based on second harmonic generation effect. We approximate the decision variable moment generating function and obtain the error probability using saddle-point approximation. The impact of different parameters, e.g., code length, and photodetectors' speed, is studied. © 2009 OSA/ACP 2009
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...
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...
NLOS identification in range-based source localization: statistical approach
, Article IEEE Sensors Journal ; Volume 18, Issue 9 , 1 May , 2018 , Pages 3745-3751 ; 1530437X (ISSN) ; Behnia, F ; Amiri, R ; Marvasti, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
Least squares estimation is a widely-used technique for range-based source localization, which obtains the most probable position of mobile station. These methods cannot provide desirable accuracy in the case with a non line of sight (NLOS) path between mobile station and base stations. To circumvent this drawback, many algorithms have been proposed to identify and mitigate this error; however, they have a large run-time overhead. On the other hand, new positioning systems utilize a large set of base stations, and a practical algorithm should be fast enough to deal with them. In this paper, we propose a novel algorithm based on subspace method to identify and eliminate the NLOS error....
Energy-efficient transponder configuration for FMF-based elastic optical networks
, Article IEEE Communications Letters ; Volume 22, Issue 5 , 2018 , Pages 970-973 ; 10897798 (ISSN) ; Pakravan, M. R ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
We propose an energy-efficient procedure for transponder configuration in few-mode fiber-based elastic optical networks in which bit error rate and physical constraints are guaranteed and joint optimization of temporal, spectral, and spatial resources are addressed. We use geometric convexification techniques to provide convex formulations for the signal-to-interference plus noise ratio, transponder power consumption, and transponder configuration problem. Simulation results demonstrate that the proposed convex formulation for the transponder configuration problem is considerably faster than its mixed-integer nonlinear counterpart. We consider transmit optical power as a configurable...
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...
All-optical recurrent neural network with reconfigurable activation function
, Article IEEE Journal of Selected Topics in Quantum Electronics ; 2022 , Pages 1-1 ; 1077260X (ISSN) ; Koohi, S ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2022
Abstract
Optical Neural Networks (ONNs) can be promising alternatives for conventional electrical neural networks as they offer ultra-fast data processing with low energy consumption. However, lack of suitable nonlinearity is standing in their road of achieving this goal. While this problem can be circumvented in feed-forward neural networks, the performance of the recurrent neural networks (RNNs) depends heavily on their nonlinearity. In this paper, we first propose and numerically demonstrate a novel reconfigurable optical activation function, named ROA, based on adding or subtracting the outputs of two saturable absorbers (SAs). RAO can provide both bounded and unbounded outputs by facilitating an...
Sensitive and accurate dispersion map extraction of HNLFs by frequency tuning of a degenerate FWM
, Article Journal of Lightwave Technology ; Volume 34, Issue 18 , 2016 , Pages 4197-4204 ; 07338724 (ISSN) ; Vedadi, A ; Shoaie, M. A ; Bres, C. S ; Mehrany, K ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
Abstract
A sensitive and accurate method for dispersion map extraction along an arbitrarily profiled highly nonlinear fiber (HNLF) is proposed. High sensitivity is achieved by positioning the wavelength of a signal at the band edge of the modulation instability (MI) spectrum generated by an intense degenerate four wave mixing (FWM) pump. In doing so, the to-be-extracted dispersion fluctuations leave a more drastic effect on the FWM-generated power since they either inflate or deflate the MI spectrum. The accuracy of the method is increased by monitoring the distribution of power along the fiber. Once the power distribution is measured along the fiber, dispersion map of the HNLF is extracted using an...
Temporal analog optical computing using an on-chip fully reconfigurable photonic signal processor
, Article Optics and Laser Technology ; Volume 111 , 2019 , Pages 66-74 ; 00303992 (ISSN) ; Kavehvash, Z ; Khavasi, A ; Koohi, S ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
This paper introduces the concept of on-chip temporal optical computing, based on dispersive Fourier transform and suitably designed modulation module, to perform mathematical operations of interest, such as differentiation, integration, or convolution in time domain. The desired mathematical operation is performed as signal propagates through a fully reconfigurable on-chip photonic signal processor. Although a few numbers of photonic temporal signal processors have been introduced recently, they are usually bulky or they suffer from limited reconfigurability which is of great importance to implement large-scale general-purpose photonic signal processors. To address these limitations, this...
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...
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
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
A high-performance guidance filter scheme with exact dynamic modeling of a pitch-yaw gimballed seeker mechanism
, Article Mechanical Systems and Signal Processing ; Volume 144 , 2020 ; Haeri, M ; Sharif University of Technology
Academic Press
2020
Abstract
This paper is concerned with the problem of guidance filter design for a homing air defense missile using measurements of an on-board pitch-yaw gimballed seeker mechanism. This problem possess a highly nonlinear dynamic which is influenced by various error sources such as seeker's stabilization loop torque disturbances originated from pursuer's accelerations and angular velocities, significant channel couplings, time-delayed and noisy measurements of optical sensor besides the unknown target maneuvers. To handle the inherent nonlinearity of problem a wide variety of assumptions are made in literature to derive simplified engagement kinematics. In present work, performance degradations which...