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Terahertz generation in quantum-cascade lasers through down-conversion optical nonlinearity: Design and modeling
摘要： In this paper, we propose an electrically driven optically excited laser structure for terahertz (THz) generation in quantum cascade lasers (QCLs) through frequency down-conversion optical nonlinearity. In our distinct design, both the pump and THz radiations are generated simultaneously by optical and electronic intersubband transitions (ISTs) between the quantized states within the conduction band of the same active region of a QCL. The modeling of laser bandstructure is achieved using a self-consistent solution of Schrodinger-Poisson equations, and the detailed analysis of electronic transport of the proposed structure is performed using the density matrix approach and energy-density balance equation that self-consistently consider the optical, electrical and thermal interactions in the structure. Additionally, the waveguide loss for the THz optical mode is considered using the bulk Drude model. Using a stationary solution of the density matrix equations, an expression for the THz intensity gain is derived as a function of pump field intensity, carrier distributions and quantum coherence contributions. Using the presented model, we analyze the steady-state and transient characteristics of the device for two different heatsink temperatures, 220 and 300 K. Simulation results show that the proposed structure has a potential to generate room-temperature THz radiation in QCLs.
关键词： Quantum-cascade laser (QCL),terahertz (THz) generation,down-conversion optical nonlinearity,density-matrix formalism
更新于2025-09-23 15:21:01
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Relativistic Self Focusing and Frequency Shift of super-Gaussian Laser Beam in Plasma
摘要： Relativistic self focusing and frequency shift of laser beam having super-Gaussian profile in space and Gaussian profile in time is studied in a plasma. The relativistic mass nonlinearity is found to cause time dependent self focusing of the laser pulse and the saturation effect of nonlinearity avoids point focusing of the beam. For ultrashort laser pulse, the front of the pulse undergoes frequency down shift while that of the tail undergoes up shift. Frequency shift increases and self focusing becomes stronger for higher intensity of the laser. The self focusing is also stronger for the laser beam carrying larger wavelength.
关键词： Beam width parameter,Self focusing,Frequency shift,super-Gaussian laser,Moment Theory,Relativistic nonlinearity
更新于2025-09-23 15:21:01
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Amplification and cross-Kerr nonlinearity in waveguide quantum electrodynamics
摘要： We explore amplification and cross-Kerr nonlinearity by a three-level emitter (3LE) embedded in a waveguide and driven by two light beams. The coherent amplification and cross-Kerr nonlinearity were demonstrated in recent experiments, respectively, with a V and a ladder-type 3LE coupled to an open superconducting transmission line carrying two microwave fields. Here, we consider (cid:2), V, and ladder-type 3LE, and compare the efficiency of coherent and incoherent amplification as well as the magnitude of the cross-Kerr phase shift in all three emitters. We apply the Heisenberg-Langevin equations approach to investigate the scattering of a probe and a drive beam, both initially in coherent states. We particularly calculate the regime of the probe and drive powers when the 3LE acts most efficiently as a coherent amplifier and derive the second-order coherence of amplified probe photons. Finally, we apply the Kramers-Kronig relations to correlate the amplitude and phase response of the probe beam, which are used in finding the coherent amplification and the cross-Kerr phase shift in these systems.
关键词： waveguide quantum electrodynamics,three-level emitter,cross-Kerr nonlinearity,amplification,Heisenberg-Langevin equations,Kramers-Kronig relations
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Using Artificial Neural Network for Compensation of Semiconductor Thermistor Nonlinearity
摘要： A method for correcting the transformation function of a semiconductor thermistor using a nonlinearity compensator based on a three-layer perceptron is proposed. Using of computer simulation, the operability of the proposed method has been investigated, a comparative analysis has been carried out with polynomial compensators of nonlinearity.
关键词： compensation of nonlinearity,learning,perceptron,artificial neural network
更新于2025-09-23 15:21:01
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Ring modes supported by concentrated cubic nonlinearity
摘要： We consider the one-dimensional Schr?dinger equation on a ring, with the cubic term, of either self-attractive or repulsive sign, con?ned to a narrow segment. This setting can be realized in optics and Bose-Einstein condensates. For the nonlinearity coef?cient represented by the δ function, all stationary states are obtained in an exact analytical form. The states with positive chemical potentials are found in alternating bands for the cases of the self-repulsion and attraction, while solutions with negative chemical potentials exist only in the latter case. These results provide a possibility to obtain exact solutions for band-gap states in the nonlinear system. Approximating the δ function by a narrow Gaussian, stability of the stationary modes is addressed through numerical computation of eigenvalues for small perturbations, and veri?ed by simulations of the perturbed evolution. For positive chemical potentials, the stability is investigated in three lowest bands. In the case of the self-attraction, each band contains a stable subband, the transition to instability occurring with the increase of the total norm. As a result, multipeak states may be stable in higher bands. In the case of the self-repulsion, a single-peak ground state is stable in the ?rst band, while the two higher ones are populated by weakly unstable two- and four-peak excited states. In the case of the self-attraction and negative chemical potentials, single-peak modes feature instability which transforms them into persistently oscillating states.
关键词： cubic nonlinearity,Bose-Einstein condensates,stationary states,optics,Schr?dinger equation,stability analysis
更新于2025-09-23 15:21:01
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Symmetric and antisymmetric surface plasmon polariton solitons in a metal-dielectric-metal waveguide with incoherent pumping
摘要： We propose a scheme to realize stable linear and nonlinear propagation of symmetric and antisymmetric surface plasmon polaritons (SPPs) solitons by doping ladder-type three-level quantum emitters into the middle layer of a metal-dielectric-metal (MDM) waveguide. In linear propagation regime, we show that both symmetric and antisymmetric SPPs can acquire a gain from electromagnetically induced transparency (EIT) effect with an incoherent pumping. The EIT can be used not only to completely compensate the Ohmic loss in the metal but also to acquire a subluminal group velocity for the SPPs. We also show that in nonlinear propagation regime a huge enhancement of Kerr nonlinearity of the symmetric and antisymmetric SPPs can be obtained but with different incoherent pumping intensities. As a result, gain-assisted (1+1)-dimensional symmetric and antisymmetric subluminal surface polaritonic solitons may be produced based on the strong confinement of electric field in the MDM waveguide. Our study may have promising applications in light information processing and transmission at nanoscale level based on MDM waveguides.
关键词： solitons,surface plasmon polaritons,electromagnetically induced transparency,Kerr nonlinearity,metal-dielectric-metal waveguide
更新于2025-09-23 15:21:01
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Solitons in magnetoa??optic waveguides with quadratica??cubic nonlinearity
摘要： This paper implements unified Riccati equation expansion scheme as well as extended auxiliary equation method to obtain bright, dark and singular solitons in magneto–optic waveguides. The quadratic–cubic form of nonlinear refractive index is the focus of the paper. These solitons emerge after a limiting value when the modulus of ellipticity approaches unity.
关键词： Quadratic–cubic nonlinearity,Solitons,Magneto–optic waveguide
更新于2025-09-23 15:21:01
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Ultra high birefringence and lower beat length for square shape PCF: Analysis effect on rotation angle and eccentricity
摘要： In this article, a circular air hole organized in a square manner cladding with porous core using elliptical holes index-guiding photonic crystal fiber (IG-PCF) has been proposed and numerically examined. The numerical study is obtained by using finite element method (FEM) inclusion with an electromagnetic absorption boundary perfectly matched layer (PML). Investigation process runs over a broader wavelength range near IR region from 1.20 mm to 1.80 mm for evaluating modal properties of proposed square shaped PCF. S-PCF expresses higher birefringence (2.2 (cid:1) 10(cid:3)3), high nonlinearity (23.46 W(cid:3)1 km(cid:3)1) along with lower beat length (553.86 mm) at the pumping wavelength k = 1.20 mm. Core holes angle orientation and eccentricity are tuned for gaining higher birefringence. Furthermore, beat length, Veff, spot size, beam divergence are inquired in details. Finally, this research is focused on birefringence and nonlinearity behaviors are highly affected by angle effect and eccentricity.
关键词： Beat length,Birefringence,Nonlinearity,Single mode PCF,Eccentricity,Spot size
更新于2025-09-23 15:21:01
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Optical Fréedericksz transition and director field structure recording in dye-doped nematic liquid-crystalline polymer
摘要： Dye-doped nematic liquid-crystalline polymers exhibit much higher orientational optical response than the systems based on low-molar-mass liquid crystals. In addition, polymer materials possess the glassy state, which allows one to record their supramolecular structure. We study the effect of light field inhomogeneity on the director deformation in the geometry of Fréedericksz transition and recording of corresponding phase structures. The relationship of the light beam width with the threshold light intensity and the size of the induced and recorded deformation region was determined. An influence of the beam waist radius on the polymer director relaxation time was detected. The results of numerical calculations based on the continuum theory and the independence of the enhancement factor of the optical torque on light–polymer interaction geometry agree with the experimental data.
关键词： Fréedericksz transition,recording optical,optical nonlinearity,liquid-crystalline polymer,supermolecular structure
更新于2025-09-23 15:21:01
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Design of quad core photonic crystal fibers with flattened zero dispersion
摘要： Two photonic crystal fiber structures with quad-core have been investigated in this paper. Both the structures are geometrically similar but have different background materials. Both PCF structures exhibit very high birefringence. However, structure with silica background material reports birefringence of the order 10-2. It is to be noted that, this PCF structure has also shown zero dispersion behavior over a wide range of telecommunication wavelength. Moreover, the other structure with lead silicate as background material has also reported very low dispersion. Thus both the PCF structures simulated show ability to mitigate the effect of polarized mode dispersion. Besides this, other propagation characteristics like confinement loss, normalized frequency and non linear coefficient have been reported.
关键词： confinement loss,dispersion,birefringence,nonlinearity,Photonic crystal fibers
更新于2025-09-23 15:21:01