S. D. Emami

University of Malaya, Kuala Lumpor, Kuala Lumpur, Malaysia

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Publications (40)60.77 Total impact

  • [Show abstract] [Hide abstract]
    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.
    Plasmonics 12/2014; · 2.43 Impact Factor
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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.
    Applied Physics A 10/2014; · 1.69 Impact Factor
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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.
    Laser Physics 09/2014; 24(11):115201. · 2.55 Impact Factor
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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.
    Optics Express 03/2014; 22(6):7075-86. · 3.55 Impact Factor
  • Optical Fiber Communications Conference and Exhibition (OFC), 2014; 01/2014
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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.
    IEEE Sensors Journal 01/2014; 14(4):1295-1303. · 1.48 Impact Factor
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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.
    Journal of Optical Communications and Networking 01/2013; 5(9):932-944. · 1.43 Impact Factor
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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.
    Photonics (ICP), 2013 IEEE 4th International Conference on; 01/2013
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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.
    Optics Express 12/2012; 20(28):29784-97. · 3.55 Impact Factor
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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.
    Laser Physics 11/2012; 23(1):015103. · 2.55 Impact Factor
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    Selected Topics on Optical Amplifiers in Present Scenario, 02/2012; , ISBN: 978-953-51-0391-2
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    ABSTRACT: We present the Fano resonance effects of plasmonic nanoparticles in the optical domain. An intuitive explanation on the physical nature of fano resonance based on the three-level quantum system is presented. The Fano resonance effects of three basic nanoparticle arrangements, namely quadrumer, pentamer and heptamer are discussed. The mass spring model of quadrumer, pentamer and heptamer are presented. The calculated results from mass spring model are found to be in agreement with the calculated results from CST Microwave Studio result.
    Photonics (ICP), 2012 IEEE 3rd International Conference on; 01/2012
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    ABSTRACT: Due to the tremendous growth in applications for fiber laser in medical science, sensor solution, and light detection and ranging system at 1.8 to 2-μm region, more research efforts have been directed toward developing highly efficient broadband fiber amplifiers in this range. In order to amplify this region, Thulium-Bismuth-doped fiber amplifier (TBDFA) is proposed in conjunction with 800-nm pumping. Optimal Thulium ion concentration of 4.17 × 1026 ion/m3 and Bismuth ion concentration of 2.08 × 1026 ion/m3 together with low phonon energy of germanate glass lead to the highest energy transfer rates. Effective energy transfer mechanism from Bismuth to Thulium in addition to the cross relaxation process between Thulium ions results in higher amplification, efficiency, and super broadband amplification in TBDFA. We analytically solve the rate equations of TBDFA including the effect of energy transfer in order to calculate the broadband amplifier gain.
    IEEE Journal of Quantum Electronics 01/2012; 48(8):1052-1058. · 2.11 Impact Factor
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    ABSTRACT: A new method for gain and noise figure enhancements in S-band thulium-doped fiber amplifier (TDFA) co-doped with aluminum is demonstrated using a macro-bending approach. The macro-bending suppresses both the amplified spontaneous emission (ASE) at 800 and 1,800 nm wavelength region and consequently improves the S-band gain of the TDFA. Gain enhancements between 5 and 8 dB are obtained with the macro-bending between 1,420 and 1,480 nm. The macro-bending also reduces the noise figure of the S-band TDFA.
    Applied Physics B 01/2012; 108(4):807-813. · 1.78 Impact Factor
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    ABSTRACT: This paper presents the analysis of a coupler based NRZ-DQPSK all-optical orthogonal frequency division multiplexing system with a rate of 80 Gb/s. The transmission line used is SSMF that is over 1000 km long with 21 km DCF for each span. The performance of the system is characterized in terms of BER, eye diagram and Q values. The power tolerance of the system as a function of fiber dispersion is also surveyed.
    Photonics (ICP), 2012 IEEE 3rd International Conference on; 01/2012
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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.
    Optical Materials 01/2012; 35:231-239. · 2.08 Impact Factor
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    ABSTRACT: A new method for gain enhancement in a S-band thulium-doped fiber amplifier (TDFA) co-doped with aluminum is demonstrated using a macro-bending approach. The macrobending of the doped fiber in a small radius suppresses both amplified spontaneous emissions (ASEs) at 800 and 1800 nm band and thus increases the population inversion in the S-band region. The numerical aperture and core radius of the doped fiber are optimized so that 800 nm ASE propagates with higher order modes to achieve a significant suppression while the loss is minimum in the S-band region. Meanwhile, the 1050 nm pump wavelength should propagate in the fundamental mode to maximize the overlap factor and thulium ion absorption so that the ASE loss is maximum at the 1800 nm region. Gain enhancements of about 5-8 dB are obtained with macrobending at the wavelength region between 1420 and 1470 nm.
    Journal of Lightwave Technology 01/2012; 30(20):3263-3272. · 2.56 Impact Factor
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    ABSTRACT: A new method for optical bandpass filters using macro bending approach is proposed. The proposed optical bandpass filter leverages on bending loss of higher order modes for shorter wavelengths. For longer wavelengths, the filter banks on fiber bending loss as the fundamental mode 'tail' is lost in the cladding. The combination of wavelength dependent loss at longer and shorter wavelength gives rise to the optical bandpass filter characteristics. We report both simulation and experimental results, which demonstrates agreement in the spectral response.
    Photonics (ICP), 2012 IEEE 3rd International Conference on; 01/2012
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    Modeling, Programming and Simulations Using LabVIEW&#8482; Software, 01/2011; , ISBN: 978-953-307-521-1
  • Ukr. J. Phys. Opt. 01/2011; 13:74-81.