Compensating losses in negative-index metamaterials by optical parametric amplification

Optical parametric amplification controlled by the auxiliary electromagnetic field enables transparency, amplification, and oscillation with no cavity in strongly absorbing negative-index metamaterials. The opposite directions of the wave vector and the Poynting vector in such materials result in extraordinary optical properties, including "backward" phase matching and the generation of entangled pairs of left- and right-handed counterpropagating photons.     

Four-wave mixing in coupled semiconductor quantum dots

We present a theoretical analysis of four-wave mixing in coupled quantum dots subject to inhomogeneous broadening. For the biexciton transitions, a clear signature of interdot-coupling appears in the spectra. The possibility of experimental observation is discussed.     

Four-wave mixing in microstructure fiber

We report what we believe to be the first experimental demonstration of nondegenerate four-wave mixing in a microstructure fiber. The effect of the chi((3)) nonlinearity is enhanced in such a fiber because of the small core area, and we achieve phase matching by operating near the zero-dispersion wavelength (?750 nm) . We have observed parametric gains of more than 13 dB in 6.1-m-long fiber with a pump peak power of only 6 W. We compare our experimental gain results with those predicted by theory and explore the effects of Raman shift and (or) amplification and cascaded nonlinear mixing.     

砷化镓晶体中的四波混频

本文报道了以1.06μm调QNd:YAG激光脉冲,采用简并四波混频的方法,在未掺杂的GaAs单晶中产生红外位相共轭短脉冲。研究了该光脉冲的主要特性。用实验的方法探讨了影响共轭光强弱的主要因素。     

Resonant nonlinear optics of backward waves in negative-index metamaterials

The extraordinary properties of resonant four-wave mixing of backward and ordinary electromagnetic waves in doped negative-index materials are investigated. The feasibility of independent engineering of the negative refractive index and the nonlinear optical response as well as quantum control of the nonlinear propagation process in such composites is shown due to the coherent energy transfer from a control field to a signal field. Laser-induced transparency, quantum switching, frequency-tunable narrow-band filtering, amplification, and realizing a miniature mirrorless optical parametric generator of the entangled backward and ordinary waves are among the possible applications of the investigated processes.     

Four-wave mixing: Photon statistics and the impact on a co-propagating quantum signal

We reconstruct the photon statistics of a single-photon source based on the stimulated four-wave mixing (FWM) process. We find that the statistics of the source goes from thermal, at a low power regime, to Poissonian, at a high power regime. We also study the impact of the FWM process on a co-propagating coherent quantum signal in a wavelength-division multiplexed (WDM) lightwave system. The statistics of the quantum signal changes from Poissonian to thermal when a low power is used, and remains Poissonian for a higher power. A multithermal regime is also observed when a moderate power is used.     

Four-wave mixing self-stability based on photonic crystal fiber and its applications on erbium-doped fiber lasers

The analytic solutions of coupled-mode equations of four-wave mixings (FWMs) are achieved by means of the undepleted approximation and the perturbation method. The self-stability mechanism of the FWM processes is theoretically proved and is applicable to design a new kind of triple-wavelength erbium-doped fiber lasers. The proposed fiber lasers with excellent stability and uniformity are demonstrated by using a flat-near-zero-dispersion high-nonlinear photonic-crystal-fiber. The significant excellence is analyzed in theory and is proved in experiment. Our fiber lasers can stably lase three waves with the power ripple of less than 0.4 dB.     

Effect of unbalanced and common losses in quantum photonic integrated circuits

Loss is inevitable for the optical system due to the absorption of materials, scattering caused by the defects, and surface roughness. In quantum optical circuits, the loss can not only reduce the intensity of the signal, but also affect the performance of quantum operations. In this work, we divide losses into unbalanced linear losses and shared common losses, and provide a detailed analysis on how loss affects the integrated linear optical quantum gates. It is found that the orthogonality of eigenmodes and the unitary phase relation of the coupled waveguide modes are destroyed by the loss. As a result, the fidelity of single-and two-qubit operations decreases significantly as the shared loss becomes comparable to the coupling strength. Our results are important for the investigation of large-scale photonic integrated quantum information processes.     

Four-wave mixing and hyper-Raman scattering in CuCl

Non-degenerate four-wave mixing using two non-collinear laser beams with frequencies (wavevectors) ω_p, ω_t (k_p, k_t) respectively is studied in CuCl. Two emission lines at frequencies ω⁽¹⁾=2ω_t-ω_p, and ω⁽²⁾=2ω_p-ω_t are observed. Their excitation spectrum is sharply peaked if the phase-match condition k⁽¹⁾=2k_t-k_p is fulfilled. This is the case, if ω_p coincides with the hyper-Raman lines (R⁺_T, R^-_T) of the laser labelled (t) in a well-defined geometrical configuration.     

Propagation of Gaussian beams in negative-index metamaterials with cubic nonlinearity

Propagation of Gaussian beams in the negative-index metamaterials (NIMs) with cubic nonlinearities is investigated, both theoretically and numerically. The role of the status of the incident Gaussian beam, which is scaled by a converging parameter in this paper, in beam self-focusing and self-defocusing in NIMs is specially identified. The expressions for beam self-focusing and self-defocusing for different converging parameter cases, and the dependence of the critical power and the focus location of self-focusing in NIMs on the converging parameter are obtained. It is found that it is the divergent rather than convergent incident beams which are self-focused more quickly in NIMs with defocusing nonlinearities, in sharp contrast with the propagation property of Gaussian beams in conventional Kerr media, in which beam self-focusing only occurs in the media with focusing nonlinearities and a convergent incident beam self-focuses more quickly than a divergent one. By adjusting the converging parameter of incident Gaussian beam or the controllable magnetic permeability of NIM, or both, one can manipulate the beam self-focusing in NIMs at will.     

Four-wave mixing in hollow photonic-crystal fibers

A radical enhancement of four-wave mixing in hollow-core photonic-crystal fibers is experimentally demonstrated. An enhancement ratio of about 800 relative to the regime of tight focusing is achieved for the four-wave mixing process 3ω=2ω+2ω?2ω, where ω and 2ω are the frequencies of fundamental radiation and the second harmonic of picosecond Nd:YAG laser pulses.     

Four-wave mixing and six-wave mixing in a four-level confined atomic system

We have investigated coexisting four-wave mixing and six-wave mixing (SWM) in ultra-thin, micrometre and long vapour cells. There exists competition between Dicke-narrowing features and polarization interference in the micrometre cell. The oscillation behaviour of SWM signal intensities and linewidths results from destructive interference. With a larger destructive interference, the SWM signal in ultra-thin cells shows a narrow spectrum, in contrast to the long cell case. Due to the Dicke-narrowing features, a narrow spectrum can be obtained, and such spectra can be used for high precision measurements and metrological standards.     

Four-wave mixing in long wavelength III-nitride QD-SOAs

Four wave mixing analysis is stated for quantum dot semiconductor optical amplifiers (QD SOAs) using the propagation equations (including nonlinear propagation contribution) coupled with the QD rate equations under the saturation assumption. Long wavelength III-nitride InN and AIInN QD SOAs are simulated. Asymmetric behavior due to linewidth enhancement factor is assigned. P-doping increases efficiency. Lossless efficiency for InAlN QDs for longer radii is obtained. Carrier heating is shown to have a considerable effect and a detuning dependence is expected at most cases. InN QD SOAs shown to have higher efficiency.     

Four-wave mixing of optical and microwave fields

We demonstrate degenerate four-wave mixing involving both optical and microwave fields. This four-wave mixing process, with fields that differ in frequency by 5 orders of magnitude, results from stimulated Raman scattering of the optical field from an atomic ground-state Zeeman coherence in warm rubidium vapor, which is induced and maintained by the microwave field.     

Dyakonov surface waves in photonic metamaterials

We show that suitable photonic metamaterial structures can support lossless surface waves of the form envisaged by Dyakonov. The idea we put forward is based on the birefringent properties of photonic crystals in the long-wavelength limit, and uses the metamaterial anisotropy of the structures to meet the resonance conditions at which Dyakonov surface waves exist. Implementation of this concept can lead to the first experimental observation of Dyakonov waves, and might open the door to the realization of widely tunable sensing devices based on the unique properties of such waves.     

Four-wave mixing assisted stability enhancement: theory, experiment, and application

Stability enhancement on the basis of four-wave mixing (FWM) is proposed and proved for the first time to our knowledge. This technique is applied to dual-wavelength erbium-doped fiber lasers. Significant uniformity and stability of the novel fiber lasers are demonstrated experimentally.     

Four-wave mixing and biphoton generation in a two-level system

We find that in a two-level system there are two kinds of four-wave mixing processes which destructively contribute to the third-order nonlinear susceptibility. In a paired-photon generation scheme by using a single retroreflected pump beam, these two processes occur with definite time orders. The biphoton temporal correlation, which is measured with a back-to-back geometry in a laser-cooled two-level atomic ensemble, shows a damped Rabi oscillation and photon antibunching. Without suppressing the background of Rayleigh scattering, the upper limit of Cauchy criteria is estimated.     

Four-wave mixing in alkali halide crystals and aqueous solutions

Noncollinear phase-matched nonresonant four-photon frequency mixing _p+ _p– _{L s} in crystals and aqueous solutions of LiCl, CsCl, KF, and KI is studied. The concentration of the aqueous solutions is varied between 0.5 mol/l and saturation. Picosecond laser pulses of a mode-locked Nd-glass laser are applied as pump pulses. The energy conversion of laser light at frequency _L to frequency _S is measured and the nonlinear susceptibilities ⁽³⁾ are calculated. The dependence of the hyperpolarizabilities on concentration is analysed and gives information on the solute-solvent interaction.     

Four-wave mixing dipole soliton in laser-induced atomic gratings

We demonstrate a novel type of stable multicomponent vector solitons consisting of two perpendicular four-wave mixing (FWM) dipole components induced by electromagnetically induced gratings. We analyze the formation and steering of the steady dipole solitons and their dynamical (energy transfer) effects. The dipole-mode solitons of two FWM processes have horizontal and vertical orientations, respectively. Omnidirectional Bragg reflections are also investigated.     

Four-wave mixing of quasi-monochromatic waves and few-cycle pulses

Four-wave coherent mixing models for two quasi-monochromatic pumping fields and pulses of a two-component Stokes field with an elliptic polarization and a duration on the order of the period of oscillations have been derived for a two-level medium with a forbidden dipole transition. It is shown that, under the unidirectional wave propagation conditions and in the absence of depletion of pumping, the system of Maxwell-Bloch equations can be reduced to a new completely integrable system of equations. Nonsoliton radiation dynamics of generation of Stokes field pulses is studied in the framework of the integrable reduction of this model. The apparatus for the inverse problem algorithm corresponding to the solvable problem is developed. An approximate asymptotic expression for the leading front of the pulse packet being generated is obtained for various initial and boundary conditions. The application of these results for describing parametric processes involving various types of waves is discussed.