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    Optical bistability in fiber ring resonator containing an erbium doped fiber amplifier and quantum dot doped fiber saturable absorber

    , Article Applied Optics ; Volume 51, Issue 29 , 2012 , Pages 7016-7024 ; 1559128X (ISSN) Tofighi, S ; Farshemi, S. S ; Sajjad, B ; Shahshahani, F ; Bahrampour, A. R ; Sharif University of Technology
    2012
    Abstract
    In this paper we study the optical bistability in a double coupler fiber ring resonator which consists of an erbium doped fiber amplifier (EDFA) in half part of the fiber ring and a quantum dot doped fiber (QDF) saturable absorber in the other half. The bistability is provided by the QDF section of the ring resonator. The EDFA is employed to reduce the switching power. The transmitted and reflected bistability characteristics are investigated. It is shown that the switching power for this new bistable device is less than 10 mW  

    High performance of finite element method applied to plastic analysis of reinforced materials with application in optoelectronic devices

    , Article Journal of Optoelectronics and Advanced Materials ; Volume 17, Issue 9-10 , 2015 , Pages 1545-1548 ; 14544164 (ISSN) Monfared, V ; Daneshmand, S ; Fazaeli, D ; Sharif University of Technology
    National Institute of Optoelectronics  2015
    Abstract
    Finite element analysis of creeping short fiber composites is carried out in the second stage creep with application in microelectronic and optoelectronic/photonic devices. Prediction of the creep behavior is very significant for designing the optoelectronic and photonic composites with optical fibers. Study on the creep behavior is necessary for failure, fracture, fatigue, and creep resistance of the optoelectronic/photonic composites. The creep behavior of the short fiber composites is estimated by FEM. Study on the creep behavior is necessary for defect analysis and creep resistance of the short fiber composites. In this research work, prediction of the creep behavior of the short fiber... 

    Comparison of prism-based optical probes for liquid monitoring

    , Article Modern Physics Letters B ; Volume 24, Issue 11 , May , 2010 , Pages 1111-1126 ; 02179849 (ISSN) Golnabi, H ; Razani, M ; Sharif University of Technology
    2010
    Abstract
    In this article, two possible applications of prism-based probes for liquid-switching, level-sensing, and as a refractometer are described. Theoretical formulation is developed for the emergent intensity for each system and possible range of operation for each system is reported. By comparing the theoretical investigations, some hints are given in optimum usage of prism in each case. Variation of the beam divergence, incident angle, and prism glass index are major parameters that are considered in this investigation. The obtained results are compared with some available experimental results and practical points concerning the effective application of each geometry is reported. Theoretical... 

    Tensile properties of GFRP laminates after exposure to elevated temperatures: Effect of fiber configuration, sample thickness, and time of exposure

    , Article Composite Structures ; Volume 238 , 2020 Ashrafi, H ; Bazli, M ; Jafari, A ; Ozbakkaloglu, T ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    This study investigates the tensile properties of various GFRP laminates after exposure to elevated temperatures. Fiber configuration, exposure temperature and laminate thickness were considered as the test variables. A total number of 180 specimens were tested in tension to obtain the mechanical properties of GFRP laminates. Alongside the mechanical tests, SEM analyses were conducted on selected samples before testing to investigate the resin, fiber, and their interface damages. Regardless of the sample type, it was generally observed that the reduction rate in the tensile strength increased with an increase in the exposure time and a decrease in the laminates’ thickness. The results of... 

    Beam profile and image transfer study in multimode optical fiber coupling

    , Article Journal of Applied Sciences ; Volume 8, Issue 22 , 2008 , Pages 4210-4214 ; 18125654 (ISSN) Asadpour, A ; Golnabi, H ; Sharif University of Technology
    2008
    Abstract
    In this study the optical beam transfer and imaging in an optical fiber coupling is discussed. In coupling two fibers, some measurements from intensity perspective are performed and intensity profile is investigated. A theoretical model for the power transmission in fiber coupling is developed and theoretical function is compared with the experimental results. The amount of light delivered to the receiving fiber depends on the acceptance angle of the receiving fiber and the core cross sections of both fibers. Intensity profile function obtained theoretically agrees well with the measured results. The intensity variation as a function of the air gap variation is investigated in this article.... 

    Potentials of plastic optical fibers for sensor technology

    , Article Multi-functional Materials and Structures - International Conference on Multifunctional Materials and Structures, Hong Kong, P.R., 28 July 2008 through 31 July 2008 ; Volume 47-50 PART 1 , 2008 , Pages 161-164 ; 10226680 (ISSN); 0878493786 (ISBN); 9780878493784 (ISBN) Golnabi, H ; Kavei, M ; Azizi, Kh ; Sharif University of Technology
    Trans Tech Publications  2008
    Abstract
    Optical fibers, in particular, glass fibers, are mostly used in the field of optical communication, however in recent years new optical sensors based on the optical fibers have been reported in literature and produced commercially. Extrinsic and intrinsic character of the fibers have been implemented in development of such sensing devices. Glass Optical Fibers (GOF) because of low attenuation are more suitable for the optical communication purposes while Plastic Optical Fibers are advantageous for the linking purpose and some sensing operations. Considering this point different (POF) optical fiber sensors have been developed by author to show potential applications of POFs in sensor... 

    Experimental Investigation on Debonding between FRP sheets and Structures

    , M.Sc. Thesis Sharif University of Technology Haghighi, Sina (Author) ; Toufigh, Vahab (Supervisor)
    Abstract
    This study has investigated the effects of different environmental conditions on the bond at the interface between two fiber reinforced polymer (FRP) layers. A total of 945 single lap splice coupons with three bond length were made using wet lay-up technic. There were used three unidirectional fabrics and one type of epoxy resin. A Uniaxial tensile test was performed on samples after 2, 4, 12, 20, 28, 36 and 48 weeks of exposure. Also series of test were conducted in order to determine the minimum lap splice length of single splice FRP samples. The experimental results indicated reduction of bond strength in glass specimens that was 17 % after 48 weeks of exposure while for same amount of... 

    Investigation of bending and temperature effects in optical fibers

    , Article Microwave and Optical Technology Letters ; Volume 55, Issue 1 , NOV , 2013 , Pages 82-86 ; 08952477 (ISSN) Golnabi, H ; Sharifian, M ; Sharif University of Technology
    2013
    Abstract
    Fiber bending and temperature loss mechanisms in plastic optical fibers are reported.A simple arrangement is used to monitor the fiber bending and temperature by output power variation. Powers in the fibers in bend-free situation at room temperature and under rolling deforming force at different water bath temperatures (20-60°C) are measured and compared. Reported arrangements can be used as a temperature sensor  

    Numerical study on the creep behavior of the metal matrix short fiber composites with application in optoelectronic and photonic devices

    , Article Optoelectronics and Advanced Materials, Rapid Communications ; Volume 9, Issue 9-10 , 2015 , Pages 1088-1092 ; 18426573 (ISSN) Monfared, V ; Daneshmand, S ; Fazaeli, D ; Sharif University of Technology
    Abstract
    FEM study is carried out for predicting the behavior of the short fiber composites in the steady state creep with application in optoelectronic and photonic devices. The study on the creep behavior is necessary in order for failure, fracture, fatigue, and creep resistance of the short fiber composites. In this article, the creep behavior of the short fiber composite is predicted under tensile axial loading by the numerical method. One of the significant applications of the work is in the short fiber composite designing and optimizing. Also, the available experimental results [10] are used for the FEM simulation  

    Comparison of beam shapes and transmission powers of two prism ducts

    , Article Australian Journal of Basic and Applied Sciences ; Volume 4, Issue 10 , 2010 , Pages 4922-4929 ; 19918178 (ISSN) Emami, Z ; Golnabi, H ; Sharif University of Technology
    2010
    Abstract
    Design and performance of two-stage optical beam shaping system based on a plastic fiberbundle, prism coupled waveguide, is described in this study. Such systems offer practical means to modify and change the output beam shape at two stages and also provide quantitative information concerning the output beam intensity. It is possible to investigate output power and image transmittance data by using a light source for illumination and image analysis by a CCD/digital camera. The photograph picture of the illuminating LED beam shows a circular shape with a diameter of about 10 mm at its output point. Picture of the fiber-bundle output beam is also taken, which shows a rectangular shape with a... 

    Interface behavior between carbon-fiber polymer and sand

    , Article Journal of Testing and Evaluation ; Volume 44, Issue 1 , 2016 , Pages 385-390 ; 00903973 (ISSN) Toufigh, V ; Ouria, A ; Desai, C. S ; Javid, N ; Toufigh, V ; Saadatmanesh, H ; Sharif University of Technology
    ASTM International  2016
    Abstract
    Interface shear strength between soil and structural materials is dependent on the confining pressure. To increase the confining pressure, different methods of reinforcement and materials, such as carbon-fiber-reinforced polymer (CFRP) can be used. The shear strength of CFRP-improved soil is dependent on the interface properties of the soil and CFRP. The objective of this study is to investigate the interface properties (friction angle and adhesion) of sand and FRP experimentally using the direct shear test apparatus. To increase the surface roughness to improve the interface properties, a layer of sand was placed on saturated carbon fiber during the curing period [spark plasma sintering... 

    Environmental effects on the bond at the interface of fiber-reinforced polymer and masonry brick

    , Article Journal of Reinforced Plastics and Composites ; Volume 36, Issue 18 , 2017 , Pages 1355-1368 ; 07316844 (ISSN) Toufigh, V ; Yarigarravesh, M ; Mofid, M ; Sharif University of Technology
    Abstract
    This study examined the bond at the interface of masonry bricks and fiber-reinforced polymer when exposed to five environments. Three fabrics (aramid, carbon, and glass) and one type of epoxy resin were used. A total of 375 brick-fiber-reinforced polymer specimens were made using wet lay-up technic and exposed to chemical solutions at four pH values (2.5, 7, 10, and 12.5) and substitute seawater. The effect of dry heat on the bond at the interface was also investigated. Single-lap shear tests were then carried out on the samples after 2, 4, 6, 8, 10, and 13 weeks of exposure. The experimental results indicated that freshwater and seawater had a considerable effect on the bond strength of... 

    A proposal for distributed humidity sensor based on the induced LPFG in a periodic polymer coated fiber structure

    , Article Optics and Laser Technology ; Volume 117 , 2019 , Pages 126-133 ; 00303992 (ISSN) Dehghani Sanij, M ; Esmailzadeh Noghani, F ; Bahrampour, A ; Bahrampour, A. R ; Sharif University of Technology
    Elsevier Ltd  2019
    Abstract
    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... 

    Design and operation of a fiber optic sensor for liquid level detection

    , Article Optics and Lasers in Engineering ; Volume 41, Issue 5 , 2004 , Pages 801-812 ; 01438166 (ISSN) Golnabi, H ; Sharif University of Technology
    2004
    Abstract
    Design and construction of an optical fiber sensor for liquid level detection are reported. This sensor operates based on light intensity modulation, and such modulation results from alteration of total internal reflection into partial reflection at the interface. The modulated intensity has been measured by using a pair of fibers, one transmitting source light, another acting as receiving fiber, and a glass prism providing the total and partial reflections. During the level measurements, when a liquid in a vessel touches the 45° faces of the 45-90-45° prism, the total internal reflection is disturbed, and the reflected light is modulated. The performance of this sensor is tested with... 

    Mass measurement using an intensity-modulated optical fiber sensor

    , Article Optics and Lasers in Engineering ; Volume 38, Issue 6 , 2002 , Pages 537-548 ; 01438166 (ISSN) Golnabi, H ; Sharif University of Technology
    2002
    Abstract
    Design and operation of an opto-mechanical sensor for mass measurements is reported. This device uses a pair of optical fibers and a reflecting coated lens. The light intensity modulation is based on the relative motion of the lens due to a given mass with respect to the optical fibers. The modulated intensity because of the weighing mass has been measured by using a digital voltmeter. A full-range sensitivity of about 11.5 mV/g for a dynamic range of 80 g is obtained. A mass resolution of better than 0.25 g has been measured with this device. The measured output response is checked against the expected theoretical one and a general agreement observed. A comparison with similar experimental... 

    Design of an optical fiber sensor for linear thermal expansion measurement

    , Article Optics and Laser Technology ; Volume 34, Issue 5 , 2002 , Pages 389-394 ; 00303992 (ISSN) Golnabi, H ; Sharif University of Technology
    2002
    Abstract
    Design and operation of an optical fiber device for temperature sensing and thermal expansion measurement are reported. The modulated intensity has been measured by using a pair of 450 μm core fiber, one acting as the source and the other one as receiving fiber. In this design, the light intensity modulation is based on the relative motion of the optical fibers and a reflective coated lens. By using displacement calibration data for this sensor, the linear thermal expansion of the aluminum rod is determined. This sensor shows an average sensitivity of about 11.3 mV/°C for temperature detection and 7 μm/°C for thermal expansion detection. Device resolution for a linear expansion measurement... 

    Enhancement of bond characteristics of ribbed-surface GFRP bars with concrete by using carbon fiber mat anchorage

    , Article Construction and Building Materials ; Volume 134 , 2017 , Pages 507-519 ; 09500618 (ISSN) Ashrafi, H ; Bazli, M ; Vatani Oskouei, A. V ; Sharif University of Technology
    Abstract
    The bond of fiber-reinforced polymer (FRP) reinforcement is expected to be more sensitive to the strength and geometry of the ribs than conventional steel reinforcement. In this study, the effect of carbon fiber mat anchorage on the pullout behavior of glass fiber-reinforced polymer (GFRP) bars embedded in normal concrete is studied. The studied parameters were the compressive strength of the concrete (16 MPa, 24 MPa, and 37 MPa), and, the length and diameter of the anchorage. In total, 15 variables were studied. Ribbed GFRP bars with 10 mm nominal diameter and 80 mm embedment length, ld, (which is 8 times the bar diameter) were considered. Based on the results for concretes with the... 

    Power modulation in axial and lateral fiber displacements in a fiber-to-fiber design

    , Article Optics and Lasers in Engineering ; Volume 48, Issue 10 , 2010 , Pages 987-993 ; 01438166 (ISSN) Golnabi, H ; Kargaran, A ; Heidari, F ; Sharif University of Technology
    2010
    Abstract
    In this study power transmission modulation for different fibers in a fiber-to-fiber design using two different light sources is reported. A fiber-to-fiber arrangement is used in which the source light is directly coupled to the first fiber and the second fiber delivers the light to a power meter. Arrangements with three sets of different type fibers are tested in this study and output powers are monitored with the white lamp or red LED as illumination light sources. Using this arrangement the variations of the power as a result of axial (Z-direction) and lateral (X- and Y-direction) displacements of the second fiber are monitored. Theoretical models are also used to evaluate the power... 

    Fiber Bragg grating-based band edge delay line for radio frequency (RF) photonics applications

    , Article AEU - International Journal of Electronics and Communications ; Volume 64, Issue 3 , 2010 , Pages 267-272 ; 14348411 (ISSN) Rajabvand, M ; Behnia, F ; Sharif University of Technology
    2010
    Abstract
    A fiber Bragg grating (FBG)-based delay line (or phase shifter) has been developed for microwave over fiber and phased array antenna (PAA) applications. The scheme uses band edge time delay of tunable fiber gratings to provide a continuously controllable microwave time delay or phase shift. Following the formulation and analysis of the device behavior, simulations of amplitude and phase responses are conducted. The results confirm the validity of theoretical predictions  

    Numerical study of index guiding quasi-crystal fibers by employing FEM method

    , Article Optoelectronics and Advanced Materials, Rapid Communications ; Volume 11, Issue 3-4 , 2017 , Pages 134-138 ; 18426573 (ISSN) Bahrampour, A ; Dehghanisanij, M ; Rooholamininejad, H ; Bahrampour, A ; Sharif University of Technology
    National Institute of Optoelectronics  2017
    Abstract
    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