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Optics Express (10944087)33(3)pp. 4550-4562
All-optical switches (AOSs) with the unique functionality of light controlling by light are the essential components of advanced photonics. However, it is still a grand challenge to propose materials with appropriate nonlinear effects and structures with high-performance all-optical switching. This study proposes an AOS with a hybrid silica-azopolymer optical microfiber coupler configuration. This structure is characterized by in-line switching functionality, extremely high extinction ratio of 22 dB at λ = 1550 nm, low-insertion loss (<1 dB), and ease of fabrication process. It is shown that, because of the photo-induced birefringence in the azopolymer microfiber, the functionality of the introduced switch depends on the polarizations of the controlling and propagating light signals. Moreover, using full-wave electromagnetic simulations, the performance of the hybrid AOS is explained and clarified. © 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement.
IEEE Sensors Journal (1530437X)24(24)pp. 40994-41002
Optical microfiber couplers (OMCs) with simple structure, low loss, and high sensitivity have been broadly involved in physicochemical fiber sensing applications. Until now, the fabrication of OMCs using arc discharge as a fast, clean, and low-cost method has not been explored. In this study, an arc-discharge fiber heating and pulling process for OMC manufacturing is presented and the characteristics of the arc-induced structures are investigated. It is shown that, in addition to high spectral visibility and refractive index (RI) sensitivity, importantly, the arc-induced OMCs exhibit ultralow temperature dependency of less than 1.9 pm/°C, over the wide testing range of 15 °C to 315 °C. Finally, an exact theoretical explanation is presented for the observed different temperature coefficients using analytical expressions and full-wave simulations based on the modal analysis of OMCs. Thus, the introduced arc-discharge technique and the resultant OMCs with ultralow temperature dependency could be useful for real-world applications of microfiber (MF) couplers. © 2001-2012 IEEE.
Journal of Industrial and Engineering Chemistry (1226086X)130pp. 623-637
A new high-efficiency continuous photocatalytic system composed of a microreactor and an optical fiber coated with a ZnO nanorod array/TiO2/GO with a retention time of 4–7 min was introduced. Using a new step-by-step chemical bath deposition method, a ZnO nanorod array coated with TiO2 and GO was grown on the surface of an optical fiber with different mass ratios. The coated photocatalytic layer was characterized using XRD, XPS, Raman spectra, UV-drs, TEM, and SEM. The photocatalytic degradation efficiency of Cefixime (CEF) in the microreactor was studied under irradiation from two diffusing and focusing light sources to determine the effect of light radiation type on the efficiency. ZnO nanorods/TiO2 coated optical fiber (Ti/Zn weight ratio = 0.37) and GO deposition during the growth of ZnO nanorods demonstrated the highest degradation efficiency. The operational and geometrical parameters were optimized as fiber length = 15 cm, fiber diameter = 500 µm, CEF concentration = 10 ppm, and pH = 4.8. The removal efficiency under these conditions was approximately 67 % with a diffused light source and 80.1 % with a focused light source. The coated photocatalytic composite showed high stability to the liquid flow after 1200 min of continuous operation, indicating the ZnO nanorods/TiO2/GO coating method's success. © 2023 The Korean Society of Industrial and Engineering Chemistry
IEEE Sensors Journal (1530437X)23(14)pp. 15570-15577
With strong evanescent waves, optical microfibers (MFs) provide guided lights the ability to directly interact with surrounding environments, whereby several fiber optics chemical sensors have been realized. In this study, based on MFs external refractive index (RI) sensitivity, a multimode optical fiber (MMF) specklegram RI sensor with MMF-MF-MMF configuration is presented. As the MF Section is exposed to the liquids of different RIs (in the range of 1.333-1.368), the interaction between the liquids and evanescent waves modulates the guidance status of the MF, thereby changes the excited modes within the end MMF Section and affects the output speckle pattern accordingly. The evaluation of the functionalities of the MFs with different waist diameters (11, 18, 33, and 42 μ m ) shows that the MF with 33- μ m waist diameter results in the highest output specklegram RI sensitivity, which has been quantified by the zero-mean normalized cross correlation coefficient (ZNCC). Moreover, the response time and sensitivity of the proposed fiber specklegram sensor (FSS) have been simultaneously improved by applying spacial filter on the captured speckles. The RI sensor has also been studied for the temperature detection and showed 0.013°C-1 linear sensitivity within the range of 25 °C-65 °C. Finally, the theoretical analysis of the supported modes by the MFs of the specified waist diameters verifies that 33- μ m sample with high number of guided modes and strong total evanescent waves is the optimum case for the MMF-MF-MMF specklegram RI sensor. © 2001-2012 IEEE.
Journal of Lightwave Technology (15582213)40(24)pp. 7930-7936
Optical microfiber long period gratings (MLPGs) with advantages such as low insertion loss, polarization independence, high resonance dip, and simple configuration are broadly involved in different applications, including fiber optics micro-scale components and sensors. However, it is still a grand challenge to fabricate MLPGs by using current long-time multistep processes. Herein, based on the typical arc-discharge fiber heating and pulling technique, a very fast single-step process for MLPGs fabrication is presented. In this process, the applied fiber heating arc-discharge is functionalized by a series of narrow OFF-pulses to simultaneously modulate the being pulled microfibers. Through the developed one-step technique, a low-loss adiabatic optical microfiber with a periodic array of micro-tapers along its waist region is implemented in less than 100 s, which is much faster than current methods. It is shown that the realized single-step MLPGs with the diameter of 20 μm are characterized by high resonance dip (>27 dB), low transmission loss (≤1.2 ± 0.2 dB), narrow FWHM (<20 nm), and high repeatability. The measured external refractive index (RI) sensitivity and temperature dependency of the gratings are 744 nm/RI-unit and 12 pm/°C, respectively. The results of this study could be of interest for the applications of the MLPGs for miniature fiber optics elements and sensors realization. © 1983-2012 IEEE.
Optics Communications (00304018)522
Based on an attainable cost-effective homemade arc-discharge fiber heating and pulling setup, a fast and highly controllable process for fabricating low-loss adiabatic optical microfibers (AMFs) is presented. For this purpose, two linear translation stages driven at the same direction with different speeds stretch and shift a silica fiber through a heating arc-discharge zone induced between two tungsten electrodes. In this process, the amplitude of the inducing arc voltage and the relative positions of the electrodes and the tapering fiber adjust the characteristics of the heating zone. This technique is relatively fast and takes only about 55 s to form a low-loss (<0.2 dB) AMF. By this setup, the fabricated microfiber samples with the input and output transitions of about 12 mm lengths and the waists diameters of 3, 5, and 8μm exhibit very low insertion losses of 0.16, 0.13, and 0.07 dB, respectively. The adiabaticity of the resultant microfibers is experimentally examined by monitoring their spectral responses and is theoretically investigated based on fiber tapers adiabaticity criteria. Finally, as an important application of the microfibers, two knot resonator configurations are manually implemented on the 5μm AMFs, and their external sensitivities are investigated using the ethanol/water solutions of different concentrations. This study shows the functionality of an affordable arc-discharge setup and appropriate process for fabricating high-performance AMFs, which could be useful for their future applications. © 2022 Elsevier B.V.
AEU - International Journal of Electronics and Communications (16180399)140
Sensor nodes and IoT systems require blocks that not only consume low power but also have good accuracy. Voltage reference generators are also considered important building blocks in sensor interface circuits. This paper presents a solution to increase the accuracy of low power subthreshold voltage generators by lowering the circuit sensitivity to temperature and supply voltage variations. The enhancement is achieved by using two separate stages for temperature coefficient (TC) and line sensitivity (LS) correction. A 0.18 µm standard CMOS process has been used for the proposed structure. The effects of parameter variations in the fabrication process are investigated using post-layout simulation and Monte Carlo analysis. In the supply voltage of 0.4–2 V, an LS of 143.8 ppm/V is obtained. In typical corner conditions, the achieved TC is 7.45 ppm/°C over the temperature range of 0–80 °C. Due to process changes, and mainly affected by threshold voltage variations, the average TC can change to 39.2 ppm/°C. The minimum power consumption at 0 °C and at a supply voltage of 0.4 V is 3.25 pW while the power consumption increases to 2.84 nW in 80 °C and at the maximum supply voltage of 2 V. © 2021 Elsevier GmbH
Flexible and Printed Electronics (20588585)6(4)
The developments and advances achieved in organic semiconductors have promised lower costs for integrated circuit production and also fabrication of electronic circuits using printed technology on unconventional substrates such as plastic, clothing, and even skin. An important building block essential to most electronic circuits is a voltage, process, and temperature independent potential generator which can be used to bias amplifiers and produce a fixed reference for sensor devices. The generation of a voltage reference is also important for voltage regulators. Currently, most reported organic integrated circuits use only p-type OFETs in their circuits due to simpler fabrication procedures. Furthermore, air stable p-type organic semiconductors such as pentacene and CuPc are well characterized. In this paper, a low power two stage all PMOS voltage reference generator is proposed. Since properties such as threshold voltage value and device aging are dependent on the OFET structure, the type of device chosen for this purpose will have a direct impact on the circuit performance. Three different types of OFETs with silver, copper, and gold drain/source electrodes are studied in this work. Performance factors such as line sensitivity (LS), temperature coefficient (TC), power consumption, time constant, and output drifts of the fabricated integrated circuits are measured and reported to verify the characteristics of the proposed circuits. It is shown that the drain/source metal choice affects the threshold voltage dependent output potential of the reference generators. © 2021 IOP Publishing Ltd.
Proceedings of SPIE - The International Society for Optical Engineering (1996756X)11927
A single-step approach based on heating and pulling single-mode fiber optics via a modulated-arc discharging process is investigated, resulting in microfiber long period gratings (MF-LPGs) structures. In this process, a modulated-arc signal controls the effective axial tension over the fused fiber. Consequently, both microfiber and periodic down-tapers are generated simultaneously through a single-step. This pulse signal period determines the pitch of the induced gratings and adjusts the resonance wavelength of the MF-LPGs. The sample with the diameters of microfiber and tapers equal 30 μm and 15 μm, respectively, provides a high resonance dip up to 26 dB at the wavelength of 1547 nm. The proposed low-cost and fast fabrication technique should be useful for in-line microfiber devices and sensors based on MF-LPGs. © 2021 SPIE.
IEEE Sensors Journal (1530437X)19(5)pp. 1788-1795
In this paper, exploiting a new single-step process, in-line Mach-Zehnder interferometers (M-MZIs) on microfibers of different diameters are fabricated and their refractive-index (RI) sensitivities and temperature stabilities are characterized. The M-MZI comprises a microfiber with two functionalizing miniature down-Tapers inscribed along its longitudinal direction. It is fabricated exploiting a selectively modulated arc-discharge assisted fiber heating and pulling one-step process. In this new technique, inserted short time off-switches in the heating arc signal, while the fiber ends are pulled, induce additional micro-Tapers on the thinned fiber is being fabricated. The resultant one-step M-MZIs show extremely high interference visibilities up to 34 dB and high RI sensitivities up to 2271.3 nm/RI-unit around RI = 1.368. The results show that, with reducing the diameter of the structures, in addition to the higher RI sensitivity, very low temperature coefficient (5.2 pm/°C for 8μm sample) will be achieved. These M-MZIs have high stability, flexibility, reproducibility, and low fabrication cost. © 2001-2012 IEEE.
In this paper, using a new technique, microfiber knot resonators (MKRs) with single and double twist on 8 μm biconical arc induced microfibers are implemented and their transmission spectrums are investigated. To fabricate these MKRs, first the microfibers have been functionalized with polymeric films to facilitate and make repeatable knotting process and finally, the added layer is stripped by a suitable organic solvent. Exploiting this simple and low cost technique makes the fabrication process of the simple and complex MKRs very fast and repeatable. The results show that, the implemented resonator with double twist exhibits extremely high interference visibility up to 30 dB. © 2019 IEEE.
IEEE Photonics Technology Letters (10411135)30(10)pp. 915-918
Based on a novel modulated arc-discharge technique, a single step process for taper-functionalized optical microfiber in-line Mach-Zehnder interferometers (MZIs) fabrication is presented. By this process, microfiber and its added down-tapers are fabricated exploiting an amplitude modulated arc-discharge heating in one-step. In this letter, included short-time arc OFF switches during an arc-assisted microfiber fabrication process result in the formation of miniature down-tapers along the microfiber being pulled. The arrangement and time duration of these arc OFF pulses determine the functionality of the resultant microfiber structure. The first single step taper-functionalized microfiber in-line MZI exhibits an extremely high interference dip (29 dB) with low full width at half maximum (5 nm) and high external refractive index (RI) sensitivity of 1840 nm per RI unit around 1.368. © 1989-2012 IEEE.
Journal of Applied Physics (10897550)121(10)
We have developed analytical models for bias dependent contact resistance (RC) and output characteristics of staggered organic field-effect transistors (OFETS) based on a bulk resistance-approximated and mobility-modified current-crowding method. Numerical evaluations of RC and its resistive components show that the bias dependency of the bulk resistance is negligible. Consequently, the properties of the active layer interfaces determine RC and its characteristics. Effective parameters include a normally constant charge injection barrier at the organic-metal interface (Eb) and a gate induced surface carrier-concentration (PS0) at the organic-insulator boundary. The energy barrier pertains to the fabrication process, and its related resistance (rc) can be determined as the fitting parameter of the theoretical model. However, PS0 is strongly gate bias dependent and the results of the numerical model indicate that the resulting component (rch) is dominant and has a considerable effect on RC and its characteristics. More importantly, PS0 as the key parameter of the contact resistance is analytically expressible and by using a proposed mobility-modified current-crowding model, the contact resistance can be analytically formulated. Accordingly, the output characteristics of the OFETs in the triode region can be also analytically modeled using the developed relation of RC © 2017 Author(s).
Iranian Conference on Machine Vision and Image Processing, MVIP (21666776)2017pp. 114-118
In fiber optic sensors, laser source produces a coherent light which is transmitted through a fiber cable. The output of this laser forms a speckle. This speckle is captured by a CCD and then analyzed by a PC. The intensity and shape of the speckle change when external force is applied on the cable. In this paper, Laplacian of Gaussian (LoG) filter is used to improve the dynamic range and accuracy of the fiber optic sensor. Capturing images is done in a dark room and the simulation is done by Matlab. The difference between the intensities of a normal and abnormal state image was 4.0556 when using 2D Discrete Wavelet transform (DWT) filter. It is increased into 14.6191 when LoG filter is used, thus increasing the dynamic range and accuracy of the sensor. In addition, the time is decreased by about 24.5 %. The number of changed blocks is increased by about 22 % leading to double increase in the accuracy and dynamic range. © 2017 IEEE.
Journal of Applied Physics (10897550)119(10)
In this paper, using a mobility modified current crowding formalism, we have modeled the gate-bias dependence of contact resistance in staggered organic field effect transistors. For this purpose, the gate modulation of the potential and carrier-concentration in the organic semiconductor layer has been investigated by solving the 1-D Poisson's equation. Due to this effect, the charge hopping mobility (μ) and therefore the conductivity of this layer which are carrier-concentration dependent are also modulated. Using an analytical carrier-concentration dependent model for μ with current crowding formalism, the gate-bias dependence of the contact resistance has been exactly simulated. Based on the obtained mobility relation, bulk and channel resistive components of the current crowding model are calculated. This method has been used for simulation of experimental data, and results confirm the reliability of the presented approach. © 2016 AIP Publishing LLC.
Thin Solid Films (00406090)590pp. 214-218
In this paper, we have investigated experimentally the effect of different drain/source (D/S) electrodes and charge injection buffer layers on the electrical properties and operational stability of a stilbene organic field effect transistor (OFET). The results show that the organic buffer layer of copper phthalocyanine (CuPc) considerably improves the electrical properties of the transistors, but has a negligible effect on their temporal behavior. On the other hand, inorganic metal-oxide buffer layer of molybdenum oxide (MoO3) drastically changes both the electrical properties and operational stability. The functionalities of this metal-oxide tightly depend on the properties of the D/S metallic electrodes. OFETs with Al/MoO3 as the bilayer D/S electrodes have the best electrical properties: field effect mobility μeff = 0.32 cm2 V- 1 s- 1 and threshold voltage VTH = - 5 V and the transistors with Ag/MoO3 have the longest operational stability. It was concluded that the chemical stability of the metal/metal-oxide or metal/organic interfaces of the bilayer D/S electrodes determine the operational stability of the OFETs. © 2015 Elsevier B.V.
Journal of Applied Physics (10897550)115(9)
In this paper, we have investigated experimentally the photo-response of the organic field effect transistors (OFETs) based on π-conjugated stilbene oligomers with mutual optical and electrical properties. The cis-trans photoisomerization of these oligomers in the active layer of the OFETs disturbs the intermolecular interactions. This perturbation disrupts the charge transport in the conduction channel and turns-off the transistor. We used this phenomenon to modulate the drain current of the OFETs optically. The photo-response activity of the transistors is temperature dependent, in agreement with the isomerization of the stilbenes. Photoluminescent evaluations verify the isomerization of the oligomers in the thin film. © 2014 AIP Publishing LLC.
Vacuum (0042207X)99pp. 204-210
Al-Al2O3-Al nanocapacitors are fabricated using hard and mild anodization methods which is simple and inexpensive. Samples are prepared with various effective areas and dielectric thicknesses below 10 nm. The experiments are carried out for glass slides and porous anodic alumina as substrates. The capacitance characteristics of the fabricated capacitors were measured and studied. The capacitance of capacitor with a higher ratio of surface to volume has a good stability in high frequencies. The higher traps on a surface are responsible for this effect. The breakdown electric fields of all capacitors are close to each other. The capacitor with a smaller ratio of surface to volume has a lesser leakage current density. Capacitance densities ranged between 0.623 and 1.659 μF/cm2 at 1 kHz, with a low leakage current. The highest value of the capacitance density was obtained for the sample anodized at 3.5 V on the porous anodic alumina substrate. © 2013 Elsevier Ltd. All rights reserved.
Journal of Lightwave Technology (15582213)30(5)pp. 700-703
We have designed and fabricated an add/drop multiplexer on an azo-functionalized polymeric film using four slanted gratings. The gratings were placed on the corners of a rectangular formation. The gratings were made using the interference pattern of two overlapping laser beams and were used as 90° reflectors. Two channels were separated from the main beam with centers at 1546 and 1560 nm with a 3 dB bandwidth of 6 nm. These channels were then added together by two other gratings and sent out of the integrated circuit. © 2011 IEEE.
Journal of Applied Physics (10897550)112(7)
In this paper we have investigated theoretically the effect of top gate voltage on the threshold voltage of a double gate organic field effect transistor. We have solved the 1-D Poissons equation in organic semiconductor active layer of this structure. Using the calculated local potential profile in the active layer, the total surface charge density was obtained. By considering the linear variation of this charge quantity with bottom gate voltage, the modulation of threshold voltage was studied as a function of different top gate voltages. It appears that the shielding effect of the top gate charges attenuates the effect of top gate voltage on the threshold voltage. In situations where shielding charges do not exist, the top gate voltage drastically affects the threshold voltage. © 2012 American Institute of Physics.
Optics Letters (01469592)36(21)pp. 4125-4127
In this Letter, we have introduced a technique, new to our knowledge, to fabricate gratings on a waveguide of azo-functionalized polymeric films using a slit mask and a fast, direct-writing method. To prevent the destruction of the waveguide by the grating formation on the waveguide, we placed a slit mask on the waveguide. By properly adjusting the resonance, this grating can be used as an integrated wavelength filter. We have produced an attenuation of 13:4dB at 1562nm with a FWHM of 3:45 nm. The grating has been fabricated as narrow as the width of the waveguide to couple filtered light into the waveguide by using a slit mask. Any light shifted from the resonance will pass through the waveguide undisturbed. © 2011 Optical Society of America.
Journal of Lightwave Technology (15582213)29(18)pp. 2801-2804
An all-optical switch was fabricated using azo polymers in a directional coupler form where the index of the coupling region was change via cis-trans of azo dyes in the polymer matrix. Exposing the coupling region to green or violet light caused switching action with a response time of about 10 s. © 2006 IEEE.
Optics InfoBase Conference Papers (21622701)
Using cis-trans isomerization of azo polymers we can fabricate waveguides, gratings and other periodic structures. Here we have fabricated a two dimensional photonic crystal which acts as an active Add/Drop WDM switch. © 2009 OSA.
Applied Optics (21553165)48(17)pp. 3250-3254
We have fabricated a two-dimensional photonic crystal that functions as a two-channel add/drop filter on azo-functionalized polymeric films using a fast, direct-writing method. By properly adjusting the resonance, this structure can be used as a multichannel add/drop filter in the plane of the film. Here, we were able to separate two channels at 1555.7 and 1570:7nm with attenuation of 13:1 dB and FWHM of 6:7nm for each channel. The separated channels were directed towards the sides at an approximately 90° angle with respect to the input direction. © 2009 Optical Society of America.
Karimi alavijeh, H.R.,
Baghban, M.,
Parsanasab, G.,
Sarailou, E.,
Gharavi, A.,
Javadpour, S. Optics Letters (01469592)33(18)pp. 2152-2154
We have fabricated in-plane slanted gratings on azo-functionalized polymeric films using a fast, direct-writing method. By properly adjusting the resonance, these gratings can be used as 90° integrated reflectors and add/drop filters in the plane of the film. We have produced an attenuation of 14.8 dB at 1560.2 nm with a FWHM of 6.47 nm. Also, a signal of 1548 nm wavelength was added to the output from a different direction. Any light shifted from the resonance will pass through the filter undisturbed. © 2008 Optical Society of America.
Karimi alavijeh, H.R.,
Parsanasab, G.,
Baghban, M.,
Sarailou, E.,
Gharavi, A.,
Javadpour, S.,
Shkunov, V. Applied Physics Letters (10773118)92(4)
Fast direct writing of waveguides on polymers using low power continuous-wave lasers has been investigated. Using the cis-trans property of a functionalized sulfonated azo chromophores, we have fabricated graded index waveguides with low loss, which is due to graded index sidewalls. Fabrication is done by exposing the polymer film to a 532 nm wavelength laser beam focused to about 5 μm spot at the film. Losses were calculated to be 0.48±0.04 dBcm at 830 nm wavelength with no surface deformation. This technique enables us to fabricate integrated optical circuits including directional couplers, dividers, filters, switches, etc., as they are currently investigated in our laboratory. © 2008 American Institute of Physics.
We have fabricated a 2-D photonic crystal which functions as a two-channel add/drop filter on azo-functionalized polymeric films using a fast, direct-writing method. By properly adjusting the resonance, this structure can be used as a multi-channel add/drop filter in the plane of the film. Here, we were able to separate two channels at 1555.7 nm and 1570.7 nm with attenuation of 13.1 dB and FWHM of 6.7 nm for each channel. The separated channels were directed towards the sides at an approximately 90° angle with respect to the input direction. ©2008 IEEE.
