S. D. Emami

Multimedia University, Kuala Lumpor, Kuala Lumpur, Malaysia

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Publications (50)55.79 Total impact

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    ABSTRACT: A new method of soot deposition to improve the characteristics of a solution-doped optical fibre preform is reported. The soot was generated using a modified chemical vapour deposition (MCVD) technique. A better longitudinal uniformity of the core refractive index profile and a higher degree of dopant incorporation were obtained when two layers of soot were deposited in the core. These improvements were further extended by depositing each layer at different temperatures. A variation of 0.15 × 10−2 (%RSD 3.5%) in the refractive index difference along 23 cm of the preform and a core-to-cladding refractive index difference of approximately 0.012 were achieved using a 1.2 M AlCl3 solution.
    Full-text · Article · Mar 2016 · Optical Fiber Technology
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    ABSTRACT: This paper describes a low pass filter based on photonics crystal fiber (PCF) partial ASE suppression, and its application within a 1.7 µm to 1.8 µm band thulium-doped fiber amplifier (TDFA) and a thulium-doped fiber laser (TDFL). The enlargement of air holes around the doped core region of the PCF resulted in a low-pass filter device that was able to attenuate wavelengths above the conventional long cut-off wavelength. These ensuing long cut-off wavelengths were 1.85 μm and 1.75 μm, and enabled a transmission mechanism that possessed a number of desirable characteristics. The proposed optical low-pass filter was applied within a TDFA and TDFL system. Peak spectrum was observed at around 1.9 μm for conventional TDF lasers, while the proposed TDF laser with PCF setup had fiber laser peak wavelengths measured at downshifted values of 1.74 μm and 1.81 μm.
    Full-text · Article · Sep 2015 · Optics Express
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    ABSTRACT: Grating inscription in a Ga-doped silica core fiber (∼5 wt. % Ga) has been demonstrated using ArF (193 nm) and KrF (248 nm) excimer lasers. In a comparative study with germanosilicate fiber with similar Ge concentration, a Ga-doped silica core fiber shows greater photosensitivity to an ArF excimer laser due to the higher absorbance in the region of 190-195 nm. In addition, the photosensitivity of a Ga-doped silica core fiber has been greatly enhanced with hydrogenation. Ga-doped fibers are potential photosensitive fibers for fiber Bragg grating production with an ArF excimer laser.
    Full-text · Article · Jun 2015 · Applied Optics
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    ABSTRACT: A new approach for the generation of an optical frequency comb, based on chirping of modulators, is proposed and numerically demonstrated. The setup includes two cascaded Mach–Zehnder Modulators (MZMs), a sinusoidal wave oscillator, and an electrical time delay. The first MZM is driven directly by a sinusoidal wave, while the second MZM is driven by a delayed replica of the sinusoidal wave. A mathematical model of the proposed system is formulated and modeled using the Matlab software. It is shown that the number of the frequency lines is directly proportional to the chirp factor. In order to achieve the highest number of frequency comb lines with the best flatness, the time delay between the driving voltages of the two MZMs is optimized. Our results reveal that at least 51 frequency lines can be observed at the output spectrum. In addition, 27 of these lines have power fluctuations of less than 1 dB. The performance of the proposed system is also simulated using a split-step numerical analysis. An optical frequency comb, with tunable frequency spacing ranging from 5 to 40 GHz, is successfully generated.
    Full-text · Article · Jun 2015 · Optics Communications
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    ABSTRACT: The potential for higher spectral efficiency has increased the interest in all-optical orthogonal frequency division multiplexing (OFDM) systems. However, the sensitivity of all-optical OFDM to fiber non-linearity, which causes nonlinear phase noise, is still a major concern. In this paper, an analytical model for estimating the phase noise due to self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM) in an all-optical OFDM system is presented. The phase noise versus power, distance, and number of subcarriers is evaluated by implementing the mathematical model using Matlab. In order to verify the results, an all-optical OFDM system, that uses coupler-based inverse fast Fourier transform/fast Fourier transform without any nonlinear compensation, is demonstrated by numerical simulation. The system employs 29 subcarriers; each subcarrier is modulated by a 4-QAM or 16-QAM format with a symbol rate of 25 Gsymbol/s. The results indicate that the phase variance due to FWM is dominant over those induced by either SPM or XPM. It is also shown that the minimum phase noise occurs at −3 dBm and −1 dBm for 4-QAM and 16-QAM, respectively. Finally, the error vector magnitude (EVM) versus subcarrier power and symbol rate is quantified using both simulation and the analytical model. It turns out that both EVM results are in good agreement with each other.
    Full-text · Article · Feb 2015 · Optics Express
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    Full-text · Article · Jan 2015 · IEEE Sensors Journal
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    MRK Soltanian · IS Amiri · SD Emami · H Ahmad

    Full-text · Chapter · Jan 2015
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    ABSTRACT: An extended method for gain and noise figure enhancement in the S-band using a thulium-doped photonic crystal fiber amplifier (TD-PCFA) is proposed and shown by numerical simulation. The principle behind the enhancement is the suppression of unwanted amplified spontaneous emission (ASE) using the PCF structure. This proposed PCF achieves the intended band-pass by doping the cladding with high index material and realizes appropriate short and long cut-off wavelengths by enlarging the air-holes surrounding the doped core region. The PCF geometrical structure is optimized so that high losses occur below the short cut-off wavelength (800 nm) and beyond the long cut-off wavelength (1750 nm). Furthermore, the PCF geometrical structure design allows for high ASE suppression at 800- and 1800-nm band, thus increasing the population inversion needed for amplification in S-band region as the 1050-nm pump propagates light in the band-pass. The proposed TD-PCFA demonstrates gain enhancements of 3–6 dB between 1420 and 1470 nm.
    Full-text · Article · Dec 2014 · IEEE Photonics Journal
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    ABSTRACT: This paper presents the representation circuit model for Fano resonance of plasmonic nanoparticles in the optical domain. An intuitive explanation is provided for the physical nature of Fano resonance based on the three-level quantum system, and the Fano resonance effects of three basic nanoparticle arrangements, namely tetramer, pentamer, and symmetry broke pentamer are discussed. A coupling capacitor is calculated as an equivalent component in the proposed circuit model in order to describe the coupling effect between subradiant and superradiant mode in the Fano resonance. The circuit impedances of tetramer, pentamer, and broken symmetry pentamer are simulated, with resultant circuit models in agreement with the calculated results based on S-parameters.
    Full-text · Article · Dec 2014 · Plasmonics
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    ABSTRACT: This paper describes an analytical model developed to study the Fano resonance effect in clusters of spherical plasmonic nanoparticles under local excitation. The model depicted the case of a parallel single dipole emitter that was near-field coupled to a pentamer or heptamer cluster of nanospheres. Spatial polarization and field distributions of the optical states and resonance spectra for these cluster configurations were calculated. It was discovered that polarization interference between the nanoparticles triggered the formation of a second peak in the directivity spectra at 690 nm, and this in turn provided a mechanism for the occurrence of subradiant mode effects. The directivity calculation was analyzed in order to qualify the redirection of emission. Performances of various nanoantennae were investigated and fully characterized in terms of spatial geometric differences and the Fano resonance effect on plasmonic nanoparticles in the optical domain. Light radiation patterns were found to be significantly affected by nanosphere sizes and positioning of nanospheres with respect to the dipole. The analytical treatment of these modeled nanoantennae yielded results that are applicable to physical design and utilization considerations for pentamer and heptamer clusters in nanoantennae mechanisms.
    Full-text · Article · Oct 2014 · Applied Physics A
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    ABSTRACT: This work proposes a new method to enhance the performance of an S-band fiber laser by using a thulium-doped photonic crystal fiber (PCF). The proposed method is based on amplified spontaneous emission (ASE) suppression provided by the thulium-doped PCF unique geometric structure. The enhanced performance of this filter based PCF is dependent on the short and long cut-off wavelength characteristics that define the fiber transmission window. Realizing the short wavelength cut-off location requires the PCF cladding to be doped with a high index material, which provides a refractive index difference between the core and cladding region. Achieving the long cut-off wavelength necessitates enlarging the size of the air holes surrounding the rare-earth doped core region. The PCF structure is optimized so as to achieve the desired ASE suppression regions of below 0.8 μm and above 1.8 μm. The laser performance is simulated for different host media, namely pure silica, alumino-silicate, and fluoride-based fiber ZBLAN based on this thulium-doped PCF design. The host media spectroscopic details, including lifetime variations and quantum efficiency effect on the lasing emission are also discussed. Information on the filter based PCF design is gathered via a full-vectorial finite element method analysis and specifically a numerical modelling solution for the energy level rate equation using the Runge–Kutta method. Results are analyzed for gain improvement, lasing cavity, laser efficiency and effect of core size diameter variation. Results are compared with conventional thulium-doped fiber and thulium-doped PCF for every single host media. We observe that the ZBLAN host media is the most promising candidate due to its greater quantum efficiency.
    Full-text · Article · Sep 2014 · Laser Physics
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    ABSTRACT: A fiber based high sensitive bend sensor is proposed and demonstrated using a uniquely designed partially doped core fiber (PDCF). The fabrication method of PDCF with two core regions, namely an undoped outer region with a diameter of ${sim}{rm 9.5}~mu{rm m}$ encompassing a doped, inner core region with a diameter of 4.00 $mu{rm m}$ is explained. The mechanism of bending effect in proposed PDCF and the experimental setup for amplified spontaneous emission (ASE) based sensor and fiber laser based sensor is illustrated. For ASE sensor, the higher ASE power level loss as the spooling radius is reduced from 20 to 3 cm is measured. The gain peak shift to shorter wavelength with respect to the decrease of the spooling radius from 20 to 3 cm due to higher bending loss at smaller bending radius is observed. The results are in agreement with overlap factor variation of PDCF. As expected from ASE peaks variation, the fiber laser sensor spectral operation is changed from 1539 to 1530 nm range. This phenomenon is due to higher mode field diameter of longer wavelength and result of optical filtering at longer wavelengths. The experimental results showed the output of the ASE is also highly stable, with no observable variation in the power output over a measurement period of 1 h. The PDCF is also temperature insensitive.
    Full-text · Article · Apr 2014 · IEEE Sensors Journal
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    ABSTRACT: This paper details the effect of Thulium and Bismuth concentration ratio on gain-shift at 1800 nm and 1400 nm band in a Thulium-Bismuth Doped Fiber Amplifier (TBDFA). The effect of Thulium and Bismuth's concentration ratio on gain shifting is experimentally established and subsequently numerically modeled. The analysis is carried out via the cross relaxation and energy transfer processes between the two dopants. The energy transfer in this process was studied through experimental and numerical analysis of three samples with different Tm/Bi concentration ratio of 2, 0.5 and 0.2, respectively. The optimized length for the three samples (TBDFA-1, TBDFA-2 and TBDFA-3) was determined and set at 6.5, 4 and 5.5 m, respectively. In addition, the experimental result of Thulium Doped Fiber Amplifier (TDFA) was compared with the earlier TBDFA samples. The gain for TBDFA-1, with the highest Tm/Bi ratio, showed no shift at the 1800 nm region, while TBDFA-2 and TBDFA-3, possessing a lower Tm/Bi concentration ratio, shifted to the region of 1950 and 1960 nm, respectively. The gain shifting from 1460 nm to 1490 nm is also observed. The numerical model demonstrates that the common <sup>3</sup>F<sub>4</sub> layer for 1460 nm emission (<sup>3</sup>H<sub>4</sub>→<sup>3</sup>F<sub>4</sub>), and 1800 nm emission (<sup>3</sup>F<sub>4</sub>→<sup>3</sup>H<sub>6</sub>) inversely affects the 1460 nm and 1800 nm gain shifting.
    Full-text · Article · Mar 2014 · Optics Express
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    ABSTRACT: A new method for gain enhancement in S-band Thulium-doped fiber amplifier (TDFA) co-doped with Aluminum is demonstrated using a photonic crystal fiber and macro-bending approach. The photonic crystal fiber and macro-bending methods suppresses both amplified spontaneous emissions (ASEs) at 800 nm and 1800 nm band and thus increases the population inversion in S-band region. Gain enhancements of about 5∼8 dB are obtained at the wavelength region between 1420 and 1470 nm.
    Full-text · Conference Paper · Jan 2014
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    ABSTRACT: A new design of an S-band Thulium-doped modified Silica fiber co-doped with aluminum is presented. The design goal is high gain and low noise figure in the wavelength range of 1450 - 1520 nm. The optimization considers design parameters such as the cut-off wavelength, dopant concentration, waveguide structure, index profile and numerical aperture. These design parameters are optimized to achieve long fluorescence lifetime, high overlap factor and selected mode excitation. The amplifier performance is theoretically modelled and simulated considering the proposed design optimization. We show that the amplifier can achieve a gain of 16 dB and 3dB noise figure.
    No preview · Conference Paper · Oct 2013
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    ABSTRACT: A return-to-zero differential quadrature phase-shift keying (DQPSK) modulation scheme is proposed for all-optical orthogonal frequency-division multiplexing transmission systems. The system uses coupler-based inverse fast Fourier transform/fast Fourier transform to support a 700 km single-mode fiber link and a transmission rate of 40 Gb/s without any nonlinear compensation. The performance of the proposed system is evaluated using simulation and four performance measures are obtained, namely, the eye diagram, the eye-opening penalty (EOP), the power spectral broadening, and the bit error rate(BER). The effect of self-phase modulation is taken into account in the performance evaluation. In addition, the performance of the proposed system is compared to that of a traditional one adopting a non-return-to-zero DQPSK scheme. Our results reveal that the proposed system outperforms the traditional one in all four aforementioned performance measures, yet the spectral efficiency is almost preserved. Specifically, for an input average power of 12 dBm, a reduction in both the required optical-signal-to-noise ratio of about 4 dB (to achieve a BER of 10-6) and the EOP of about 5 dB are reported when adopting the proposed system, as compared to the traditional one.
    Full-text · Article · Sep 2013 · Journal of Optical Communications and Networking
  • R. Parvizi · S.D. Emami
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    ABSTRACT: This chapter describes one of the main applications of photonic crystal fibre (PCF) as a nonlinear gain medium to generate multi-wavelength fiber laser based on stimulated Brillouin scattering (SBS) and four-wave mixing (FWM) nonlinear effects. Firstly, the threshold power condition of SBS for a piece of 100 m long PCF has been theoretically studied in terms of fibre parameters and input pump power. The threshold exponential gain, Gth, can be anticipated by this simulation which strongly depends on the fibre length Brillouin gain content and effective area. This value varies from 14 to 18 depending on the fibre length according to the Smith's definition. In order to characterize completely, the frequency shift of Brillouin Stokes in the PCF is measured nearly 9.75 GHz via heterodyne measurement method. To demonstrate the PCF application in fiber laser generation process, a simple multi-wavelength Brillouin fibre laser (BFL) is illustrated using the PCF in conjunction with a fibre Bragg grating (FBG) to produce at least 7 Stokes and 4 anti-Stokes lines with a line spacing of 0.08 nm. To produce double-spacing Brillouin lines, a compact multi-wavelength Brillouin fibre laser in conjunction with a figure-of-eight configuration is proposed. At a BP power of 15.3 dBm, at least 4 simultaneous lines with 20 GHz or 0.16 nm line spacing is achieved by removing the odd-order Stokes lines. The anti-Stokes lines are also generated via FWM process in the laser cavity. The output spectrum of the proposed BFL can be tuned by 80 nm, dependent on the availability of an appropriate BP source. These results show that the use of a highly nonlinear PCF is capable to produce a compact and efficient multi-wavelength laser for many applications such as wavelength division multiplexing system (WDM) optical communication network system and sensors.
    No preview · Article · May 2013
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    ABSTRACT: A new approach for filtering an optical band-pass in optical amplifier is proposed using a macro bending. The proposed filter leverages the bending loss of higher order modes at shorter wavelengths. At longer wavelengths, the filter increases fiber's bending loss as the fundamental mode 'tail' is leak out from the cladding. The combination of wavelength dependent loss at longer and shorter wavelength gives rise to the optical band-pass filter characteristic inside the fiber. The simulated spectral response of the filter is found to be in good agreement with the experimental results. Subsequently, the proposed optical band-pass filter is applied in Thulium-doped fiber amplifiers (TDFA) system for gain and noise figure enhancements. The filter functions to suppress both the amplified spontaneous emission (ASE) at 800 nm and 1800 nm wavelength regions and thus improves both gain and noise figure performances in S-band region. By bending of the gain medium, gain and noise figure of the TDFA are improved by about 2 dB and 0.5 dB respectively, within a wavelength region from 1440 and 1500 nm when the 1050 nm pump power is fixed at 250 mW.
    Full-text · Article · Dec 2012 · Optics Express
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    ABSTRACT: Energy transfer processes in Thulium–Bismuth co-doped germanate fiber amplifier at 1800 nm region have been studied quantitatively in this work. Energy transfer models are utilized in order to investigate the effect of dopants concentration on energy transfer parameters. A series of non-linear rate equations were derived using the energy transfer parameters and solved by means of a semi-analytical method. A general model of optical fiber amplifier in conjunction with rate equations is employed to simulate Thulium and Bismuth ions population distribution along the fiber. Thulium and Bismuth concentrations are noted as critical factors that control the output power and saturation length. The optimum values of Thulium and Bismuth concentration which result in maximum gain at 1800 nm are 0.5 wt.% and 2 wt.% respectively.
    No preview · Article · Dec 2012 · Optical Materials
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    ABSTRACT: A tunable multiwavelength Brillouin-erbium fiber laser is experimentally demonstrated with a double-Brillouin-frequency spacing. This double-frequency shifter is constructed by incorporating a four-port circulator to isolate and circulate the odd-Stokes signals through the 10 km long non-zero dispersion shifted fiber, which acts as a Brillouin gain medium. The output even-order Stokes signals are amplified in the erbium gain block formed in a ring cavity. Up to 15 lasing lines with a wavelength spacing of 0.173 nm have been achieved at a 980 nm pump power of 50 mW and a Brillouin pump of 3 dB m. The multiwavelength laser source exhibits a 10 nm tuning range from 1552 to 1562 nm with the optical signal-to-noise ratio of the desired output channels at around 34.5 dB.
    No preview · Article · Nov 2012 · Laser Physics

Publication Stats

209 Citations
55.79 Total Impact Points

Institutions

  • 2008-2016
    • Multimedia University
      • Faculty of Engineering
      Kuala Lumpor, Kuala Lumpur, Malaysia
    • University of Kuala Lumpur
      Kuala Lumpor, Kuala Lumpur, Malaysia
  • 2007-2015
    • University of Malaya
      • • Photonics Research Centre
      • • Faculty of Engineering
      • • Department of Electrical Engineering
      Kuala Lumpor, Kuala Lumpur, Malaysia