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ABSTRACT: Spherical CdSe-CdS core-shell quantum dots (QDs) are found to be flexible in the transition between the type-I regime and the type-II regime with different core/shell dimensions. The quasi-type-II feature of the colloidal dots is confirmed with time-resolved photoluminescence (PL) measurements. Two recombination paths of the excitons with significantly different decay rates are observed and analyzed. The spherical CdSe-CdS core-shell QDs are numerically simulated to investigate the carrier separation. A relatively long radiative lifetime and high degree of spatial carrier separation provide good potential to achieve lasing under continuous-wave excitation. Amplified spontaneous emission at room temperature is detected from the QDs embedded in the polymer matrix. It is shown that a larger shell thickness results in a lower pumping threshold, while a smaller shell thickness leads to higher PL efficiency.
Applied Optics 01/2013; 52(1):105-9. · 1.41 Impact Factor
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ABSTRACT: We study polarization-dependent transmission of light through arrays of single-slit split-ring resonator (SSRR) based systems at normal incidence using finite integration time domain (FITD) and finite element methods (FEM). It is found that a conventional planar array of SSRRs acts as an effective optical wave plate at certain polarizations of incident light. The effect is attributed to the intrinsic linear birefringence of individual SSRRs. A comparison is made with other split-ring resonator-based systems exhibiting wave-plate-like properties due to inter-SSRR coupling.
Optics Letters 06/2012; 37(11):2043-5. · 3.40 Impact Factor
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ABSTRACT: We report results on experimental and theoretical characterisation of self-pulsing in high concentration erbium doped fibre
laser which is free from erbium clusters. Unlike previous models of self-pulsing accounting for pair-induced quenching (PIQ)
on the clustered erbium ions, new model has been developed with accounting for statistical nature of the excitation migration
and upconversion and resonance-like pumpto-signal intensity noise transfer. The obtained results are in a good agreement with
the experimental data.
Keywordsfibre lasers–upconversion–erbium–optical instabilities
Central European Journal of Physics 04/2012; 8(2):159-163. · 0.91 Impact Factor
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ABSTRACT: Bragg grating reflectors placed along microcavity facets can improve the efficiency of a polymer dye laser built with such
a microcavity. The impact of different reflector designs on the mode pattern and resonance frequencies of the microcavity
is numerically simulated and analyzed. This rigorous physical model is based on solving the Maxwell equations and includes
such material properties as absorption, dispersion, fluorescence and optical gain. In certain cases, an asymmetrical layout
of the reflectors can be more preferable than the pair of reflectors located on opposite sides of the microcavity as it is
implemented for typical design.
Keywordsmicrocavity laser–Bragg grating reflector–polymer dye laser
Central European Journal of Physics 04/2012; 8(2):202-206. · 0.91 Impact Factor
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ABSTRACT: By using two-section fibre where the first section has no spin and the second one is periodically spun, we demonstrate reduced
polarization dependent gain and polarization mode dispersion (0.3 dB and 0.0072 ps·km−1/2 correspondently) in a distributed fibre Raman amplifier.
Keywordspolarization mode dispersion–spun fibre–fibre Raman amplifier
Central European Journal of Physics 04/2012; 8(2):164-168. · 0.91 Impact Factor
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ABSTRACT: A radio frequency (RF) carrier can be used to mitigate the phase noise impact in n-level PSK and QAM systems. The systems performance is influenced by the use of an RF pilot carrier to accomplish phase noise compensation through complex multiplication in combination with discrete filters to compensate for the chromatic dispersion (CD). We perform a detailed study comparing two filters for the CD compensation namely the fixed frequency domain equalizer (FDE) filter and the adaptive least-mean-square (LMS) filter. The study provides important novel physical insight into the equalization enhanced phase noise (EEPN) influence on the system bit-error-rate (BER) versus optical signal-to-noise-ratio (OSNR) performance. Important results of the analysis are that the FDE filter position relative to the RF carrier phase noise compensation module provides a possibility for choosing whether the EEPN from the Tx or the LO laser influences the system quality. The LMS filter works very inefficiently when placed prior to the RF phase noise compensation stage of the Rx whereas it works much more efficiently and gives almost the same performance as the FDE filter when placed after the RF phase noise compensation stage.
Optics Express 04/2012; 20(8):8862-70. · 3.59 Impact Factor
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ABSTRACT: We report the lasing performance and photobleaching of gain material containing a water solution of Rhodamine 6G dye and gold nanoparticles (NPs). In comparison to a pure dye solution, the investigated material demonstrated both enhancement and quenching of the lasing output, depending on the relative concentration of the gold NPs. Although the presence of NPs with an optimized concentration looks preferable in terms of the lasing output enhancement, such additives deteriorate the operational resource of the gain material; i.e., the photobleaching rate speeds up.
Optics Letters 01/2012; 37(1):34-6. · 3.40 Impact Factor
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ABSTRACT: Synthesis of colloidal nanocrystals of II-VI semiconductor materials has been refined in recent decades and their size dependent optoelectronic properties have been well established. Here we report a facile synthesis of CdSe-CdS core-shell heterostructures using a two-step hot injection process. Red-shifts in absorption and photoluminescence spectra show that the obtained quantum dots have quasi-type-II alignment of energy levels. The obtained nanocrystals have a heterostructure with a large and highly faceted tetrahedral CdS shell grown epitaxially over a spherical CdSe core. The obtained morphology as well as high resolution electron microscopy confirms that the tetrahedral shell have a zinc blende crystal structure. A phenomenological mechanism for the growth and morphology of the nanocrystals is discussed.
Nanotechnology 09/2011; 22(42):425202. · 3.98 Impact Factor
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ABSTRACT: We study the phenomenon of the electromagnetically induced transparency in planar and stacked plasmonic metamaterials (MMs) using the finite integration time domain and finite element methods. For such structures, the dependence of the tunability of the inherent structural resonances on geometry design is clarified. We also analyze the performance of recently demonstrated MM designs in terms of the achievable group refractive index and losses, which are of great interest for slowing light applications.
Applied Optics 07/2011; 50(21):3958-61. · 1.41 Impact Factor
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ABSTRACT: In this paper, a novel method for extracting an RF pilot carrier signal in the coherent receiver is presented. The RF carrier is used to mitigate the phase noise influence in n-level PSK and QAM systems. The performance is compared to the use of an (ideal) optically transmitted RF pilot tone. As expected an electronically generated RF carrier provides less efficient phase noise mitigation than the optical RF. However, the electronically generated RF carrier still improves the phase noise tolerance by about one order of magnitude in bit error rate (BER) compared to using no RF pilot tone. It is also found, as a novel study result, that equalization enhanced phase noise--which appears as correlated pure phase noise, amplitude noise and time jitter-cannot be efficiently mitigated by the use of an (optically or electrically generated) RF pilot tone.
Optics Express 07/2011; 19(15):14487-94. · 3.59 Impact Factor
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ABSTRACT: We present a novel investigation on the enhancement of phase noise in coherent optical transmission system due to electronic chromatic dispersion compensation. Two types of equalizers, including a time domain fiber dispersion finite impulse response (FD-FIR) filter and a frequency domain blind look-up (BLU) filter are applied to mitigate the chromatic dispersion in a 112-Gbit/s polarization division multiplexed quadrature phase shift keying (PDM-QPSK) transmission system. The bit-error-rate (BER) floor in phase estimation using an optimized one-tap normalized least-mean-square (NLMS) filter, and considering the equalization enhanced phase noise (EEPN) is evaluated analytically including the correlation effects. The numerical simulations are implemented and compared with the performance of differential QPSK demodulation system.
Optics Express 04/2011; 19(8):7756-68. · 3.59 Impact Factor
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ABSTRACT: We report an experimental study of low-frequency (~10 kHz) self-pulsing of the output intensity in a high-concentration erbium-doped fiber laser. We suggest that the fast intensity fluctuations caused by multimode and polarization instabilities play the role of an external noise source, leading to low-frequency auto-oscillations through a coherence resonance scenario.
Optics Letters 11/2010; 35(22):3736-8. · 3.40 Impact Factor
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ABSTRACT: The spectral response of crescent-like metallic nanostructures, a sub-class of U-shaped split-ring resonators, on a glass substrate at normal incidence is studied numerically. Also, the interpretation of transmission resonances arising from periodic conventional standard split-ring resonators with rectangular edges (SSRR) at normal incidence is revisited. In particular, we focus on one specific transmission resonance which is present for nano-crescents (NC) but absent in the case of SSRRs used for metamaterials. It is proposed that for a U-shaped metallic structure of arbitrary geometry, coupling of plasmonic eigen modes at all the surfaces of the three-dimensional structure is essential to be considered. The manner in which the coupling takes place between plasmonic modes at all the surfaces of the three-dimensional structure is what completely characterizes transmission resonances, and it is unique for each given resonance.
Optics Express 08/2010; 18(17):17719-28. · 3.59 Impact Factor
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ABSTRACT: We present a comparative analysis of three popular digital filters for chromatic dispersion compensation: a time-domain least mean square adaptive filter, a time-domain fiber dispersion finite impulse response filter, and a frequency-domain blind look-up filter. The filters are applied to equalize the chromatic dispersion in a 112-Gbit/s non-return-to-zero polarization division multiplexed quadrature phase shift keying transmission system. The characteristics of these filters are compared by evaluating their applicability for different fiber lengths, their usability for dispersion perturbations, and their computational complexity. In addition, the phase noise tolerance of these filters is also analyzed.
Optics Express 07/2010; 18(15):16243-57. · 3.59 Impact Factor
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ABSTRACT: The transmission of light through metallic films with periodic double nanoholes is studied using vectorial three-dimensional finite element method. Special emphasis is given on understanding different transmission resonances arising in gold and silver films with periodic sub-wavelength holes of different shapes. The spectral shift of the hole-shape resonance resulting from a variation of the hole refractive index is analyzed for a double nanohole geometry in the transmission mode using numerical simulations. Specifically, the role of field enhancement at the apexes of the double nanohole in the sensing of medium within the hole cavity is pointed out and discussed. The presence of sharp apexes within the double nanoholes significantly improves the resonance sensitivity as compared to rectangular holes of comparable area. Impact of possible manufacturing errors on the overall sensitivity is also characterized. Robustness and a relatively simple fabrication procedure make these kinds of refractive index sensors practically attractive.
Optics Express 01/2010; 18(1):193-203. · 3.59 Impact Factor
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ABSTRACT: Picosecond 4×40 GHz multi-colored optical pulses have been generated using a single two-arm modulated Mach-Zehnder modulator. In the same time the pulses can be aligned in the time domain to form a uniform 160 GHz multi-colored pulse train.
Communications and Photonics Conference and Exhibition (ACP), 2009 Asia; 12/2009
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ABSTRACT: We report a novel vector model of Raman amplification in a fiber with randomly varying birefringence and unidirectional spin profile. Applying the model, we demonstrate for the first time simultaneous mitigation of polarization mode dispersion and polarization dependence of the Raman gain.
Optics Express 10/2008; 16(19):14380-9. · 3.59 Impact Factor
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ABSTRACT: Wavelength tunability of a microcavity solid-state dye laser is modeled and demonstrated by simulations making use of the finite element method. We investigate the application of two phenomena, thermoelastic expansion of the microcavity material and thermo-induced change of the refractive index, to tune the microcavity mode frequencies by a variation of the effective optical path. An optimized size of the laser microcavity is defined depending on the operation wavelength bandwidth and the glass transition temperature of the gain material.
Optics Express 11/2007; 15(20):12971-8. · 3.59 Impact Factor
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ABSTRACT: We report a new vector model of a fiber Raman amplifier with a randomly varying birefringence. We find that the analysis of gain fluctuations and polarization-dependent gain can be used for measurements of beat and birefringence correlation lengths and the polarization mode dispersion value on a long single-mode fiber. Results are consistent with a standard technique based on differential group delay measurements.
Journal of Optics A Pure and Applied Optics 10/2007; 9(12):1119. · 1.92 Impact Factor
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ABSTRACT: Applying a pair-correlation function of erbium ions that is known from x-ray absorption fine structure spectroscopy, we develop a new statistical model of migration-assisted upconversion in erbium-doped glasses. The results of modeling show that short-range coordination order of erbium ions contributes to the upconversion rate for both low and high population inversion. In addition, we report the methods of suppression of the short-range order of erbium ions in multicomponent glasses.
Optics Letters 07/2005; 30(11):1258-60. · 3.40 Impact Factor
