839 research outputs found
Book Review: Urban Structure Matters
No full textJTLU, vol. 2, no. 1, (2009) pp. 81-83.The author reviews the book Urban Structure Matters by Petter Naess (Routledge, 2006).Chen, Xueming. (2009). Book Review: Urban Structure Matters. Retrieved from the University Digital Conservancy, 10.5198/jtlu.v2i1.107
Mechanism of high-energy pulse generation without wave breaking in mode-locked fiber lasers
No full textThe mechanism and intrinsic conditions of high-energy wave-breaking-free pulse generation in fiber lasers mode-locked by a nonlinear polarization rotation technique are investigated numerically and experimentally. Both numerical and experimental results show that the pulses along the two orthogonal polarization axes of the fiber have a large difference in pulse energy. The numerical simulations show that the ratio of the energy of two components is limited and ranges from about 8 to about 65. The slope of the instantaneous frequency at the central position of the pulse decreases rapidly with the increase of the pulse duration and energy, whereas the slope at the pulse edge changes slightly. The accumulation of instantaneous frequency throughout the pulse width approaches a constant in a higher pulse energy regime. Understanding the mechanism and intrinsic conditions of the wave-breaking-free pulse generation could be useful in generating high-energy pulses delivered from fiber lasers
Pulse evolution without wave breaking in a strongly dissipative-dispersive laser system
No full textWe report on pulse evolution without wave breaking in a strongly dissipative-dispersive laser system where pulses encounter significant amounts of positive and negative dispersions. In contrast to conventional soliton, dispersion-managed soliton, and self-similar pulse evolutions, a different type of pulse shaping in mode-locked lasers is theoretically investigated and experimentally observed. The pulses of this laser have very low frequency chirp and exhibit as the quasirectangle temporal and Gaussian spectral profiles, and the spectral width is almost independent of the pumping strength. The temporal and spectral widths fluctuate as low as similar to 3% of the relative fluctuation throughout the laser cavity. Both numerical and experimental results show that the pulses exist with energies much greater than can be tolerated in self-similar pulse shaping
Beam dynamics in disordered PT-symmetric optical lattices based on eigenstate analyses
No full text
Wave functions will experience a localization process when evolving in disordered lattices. Here, we have demonstrated the effects of disordered PT-symmetric potentials on wave- function characteristics in optics based on eigenstate analyses. In weak- disorder cases, by using the tight-binding approximation method, a conclusion is obtained that the increasing of the imaginary part of potential can enhance the diffraction, while the increasing disorder will block the diffraction and lead to localization. In the general case, band theory is used for band-structure analysis of three bands. We find that the disorder has a smaller effect on the higher- order band, which is proved by the beam evolutions. Our work may be instructive for realizing beam path control by manipulating the strengths of disorder and gain and/ or loss of lattice.</p
Tunable multiple phase-coupled plasmon-induced transparencies in graphene metamaterials
No full textWe demonstrate the existence of multiple electromagnetically induced transparencies (EIT)-like spectral responses in graphene metamaterials consisting of a series of self-assembled graphene Fabry-Perot (FP) cavities. By exploiting the graphene plasmon resonances and phase-coupling effects, the transfer matrix model is established to theoretically predict the EIT-like responses, and the calculated results coincide well with numerical simulations. It is found that high-contrast (similar to 90%) multiple EIT-like windows are observed over a broad range of mid-infrared. Additionally, these optical responses can be efficiently tuned by altering the Fermi level in graphene and the separations of FP cavities. The proposed scheme paves the way toward control of the multiple EIT-like responses, enabling exploration of the on-chip multifunctional electro-optic devices including multi-channel-selective filters, sensors, and modulators. (C) 2014 Optical Society of Americ
MoS2-clad microfibre laser delivering conventional, dispersion-managed and dissipative solitons
No full text
Molybdenum disulfide (MoS2), whose monolayer possesses a direct band gap, displays promising applications in optoelectronics, photonics, and lasers. Recent researches have demonstrated that MoS2 has not only a significant broadband saturable absorption performance, but also a higher optical nonlinear response than graphene. However, MoS2 shows much lower optical damage threshold owing to the poorer thermal conductivity and mechanical property. Here, we exploit a MoS2-clad microfibre (MCM) as the saturable absorber (SA) for the generation of ultrashort pulses under different dispersion conditions. The improved evanescent field interaction scheme can overcome the laser-induced thermal damage, as well as take full advantage of the strong nonlinear effect of MoS2. With the MCM SA, conventional, dispersion-managed, and dissipative solitons are generated around 1600 nm in Er-doped fibre lasers with anomalous, near-zero, and normal cavity dispersions, respectively. Our work paves the way for applications of 2D layered materials in photonics, especially in laser sources.</p
Nonlinear Saturable and Polarization-induced Absorption of Rhenium Disulfide
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Monolayer of transition metal dichalcogenides (TMDs), with lamellar structure as that of graphene, has attracted significant attentions in optoelectronics and photonics. Here, we focus on the optical absorption response of a new member TMDs, rhenium disulphide (ReS2) whose monolayer and bulk forms have the nearly identical band structures. The nonlinear saturable and polarization-induced absorption of ReS2 are investigated at near-infrared communication band beyond its bandgap. It is found that the ReS2-covered D-shaped fiber (RDF) displays the remarkable polarization-induced absorption, which indicates the different responses for transverse electric (TE) and transverse magnetic (TM) polarizations relative to ReS2 plane. Nonlinear saturable absorption of RDF exhibits the similar saturable fluence of several tens of mu J/cm(2) and modulation depth of about 1% for ultrafast pulses with two orthogonal polarizations. RDF is utilized as a saturable absorber to achieve self-started mode-locking operation in an Er-doped fiber laser. The results broaden the operation wavelength of ReS2 from visible light to around 1550 nm, and numerous applications may benefit from the anisotropic and nonlinear absorption characteristics of ReS2, such as in-line optical polarizers, high-power pulsed lasers, and optical communication system.</p
Various soliton molecules in large anomalous dispersion fiber laser
No full textSoliton molecules (SMs) induced by the spectral filtering with the phase difference of 0, π, π/2 and multiple separations are observed. It is found that the equilibrium distances of SMs are multiple and discrete. © 2015 IEEE
Coexistence of strong and weak pulses in a fiber laser with largely anomalous dispersion
No full textThe coexistence of weakly sech-shaped solitons and strongly dissipative solitons is experimentally observed in an ultra-large net-anomalous-dispersion mode-locked fiber laser for the first time to author's best knowledge. Both sech-shaped and dissipative solitons appear to be the asymmetrically combined pulse state with one pulse component much smaller than the other. The energy of dissipative solitons is over three orders of magnitude larger than that of sech-shaped solitons. Two different types of pulse-shaping mechanisms coexist in the laser: one is the dissipative processes and the other is the balance between anomalous dispersion and nonlinear Kerr effect. Numerical simulations and analysis confirm the experimental observations. (c) 2011 Optical Society of Americ
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