Polarization multistability of cavity polaritons

New effects of polarization multistability and polarization hysteresis in a coherently driven polariton system in a semiconductor microcavity are predicted and theoretically analyzed. The multistability arises due to polarization-dependent polariton-polariton interactions and can be revealed in polarization resolved photoluminescence experiments. The pumping power required to observe this effect is 4 orders of magnitude lower than the characteristic pumping power in conventional bistable optical systems.     

Optical multistability in three-level atoms inside an optical ring cavity

Optical multistability in an optical ring cavity filled with a collection of three-level Lambda-type rubidium atoms has been experimentally demonstrated. The observed multistability is very sensitive to the induced atomic coherence in the system and can evolve from a normal bistable behavior with the change of the coupling field as well as the atomic number density. The underlying mechanism for the formation of such multistability is also discussed.     

Polarization bistability in a nonlinear birefringent Fabry-Perot cavity

Polarization bistability and switching are described theoretically and demonstrated experimentally for a birefringent nonlinear Fabry-Perot cavity.     

Dispersive optical bistability in a ring cavity

Equations governing the behaviour of a single mode high-Q ring cavity are obtained for a coherent driving field (detuned to both cavity and atoms) and inhomogeneously broadened atomic transitions using a Hamiltonian approach. We find the region of bistability and critical points in the homogeneous broadening case. Numerical results including inhomogeneous broadening show that bistability is obtained more readily by detuning both the atomic transition and the cavity mode relative to the driving field.     

Vibration insensitive optical ring cavity

The mounting configuration of an optical ring cavity is optimized for vibration insensitivity by finite element analysis. A minimum response to vertical accelerations is found by simulations made for different supporting positions.     

Controllable optical bistability and multistability in a rare-earth-ion-doped optical fiber

We investigated the optical bistability and multistability in an Er³⁺-doped ZrF₄–BaF₂–LaF₃–AlF₃–NaF optical fiber inside an optical ring cavity. It is found that the optical bistability and multistability can be easily controlled via adjusting properly the parameters of the corresponding system. Our scheme may provide some new possibilities for technological applications in optoelectronics and optical-fiber communication.     

Broadband source generated by stimulated Raman scattering and four-wave mixing in a highly nonlinear optical fiber ring cavity

A novel high-power broadband source based on the combined action of stimulated Raman scattering and parametric four-wave mixing in a highly nonlinear dispersion-shifted fiber ring cavity is investigated experimentally. An output spectrum of 1510-1580 nm with a stable power of 91 mW is demonstrated with a dual-wavelength pumping scheme.     

Continuous-wave supercontinuum laser based on an erbium-doped fiber ring cavity incorporating a highly nonlinear optical fiber

We experimentally demonstrate a novel erbium-doped fiber based continuous-wave (cw) supercontinuum laser. The laser has a simple ring-cavity structure incorporating an erbium-doped fiber and a highly nonlinear dispersion-shifted fiber (HNL-DSF). Differently from previously demonstrated cw supercontinuum sources based on single propagation of a strong Raman pump laser beam through a highly nonlinear fiber, erbium gain inside the cavity generates a seed light oscillation, and the oscillated light subsequently evolves into a supercontinuum by nonlinear effects such as modulation instability and stimulated Raman scattering in the HNL-DSF. High quality of the depolarized supercontinuum laser output with a spectral bandwidth larger than 250 nm is readily achieved.     

Stability conditions for two-photon optical bistability in a ring cavity

A stability analysis in the good-cavity and mean-field limits, of two-photon optical bistability arising when two beams at different frequencies interact with a nonlinear medium in a ring cavity, is presented. Another metastable state has been found to occur in the double-absorption case in certain circumstances, and the system may be described as exhibiting a form of tristability.     

Optical bistability and multistability in a photorefractive bidirectional ring oscillator

We consider optical bistability and multistability based on the theory of bidirectional oscillations induced by four-wave mixing (FWM) in a photorefractive (PR) phaseconjugate ring resonator model. Bistable and multistable effects of the intensity of oscillation have been established numerically using a successive bisection method that can predict repeated roots as well as discontinuities.Oscillation intensities are studied as a function of parameters such as the nonlinear coupling strength (gL), the ratio of pump beam intensities (R) and the product of reflection coefficients of three cavity mirrors (|r|). It is shown that for certain combinations of these parameters and assuming that gL exceeds its threshold value, the oscillation intensity becomes double-valued or multivalued corresponding to the number of oscillating modes in the cavity. The multiplicity of solutions as well as the possible regions of bistable/multistable branches are greatly affected by the sign of gL and also depend on whether R and |r| are greater than or less than unity.     

Spatial symmetry breaking and coexistence of attractors in a nonlinear ring cavity

We consider a passive optical system consisting of a ring cavity and a homogeneously broadened two-level medium. We find that a spatial modulation of the input beam imposes processes of competition between the external modulation frequency and the internal space frequencies which emerge from modulation instabilities. This leads to symmetry breaking phenomena when both the amplitude and the wavelength of the modulation are increased and results in the coexistence of periodic attractors. We numerically analyze the corresponding bifurcations and find that they can be explained by a generalization of the concept of cooperative frequency locking although the bifurcating attractors are periodic and are not related to linear resonator modes.     

Pattern formation by spatially incoherent light in a nonlinear ring cavity

Modulation instability and pattern formation by spatially incoherent light is investigated experimentally in a nonlinear ring cavity using a photorefractive strontium barium niobate crystal as the nonlinear medium. A step-like threshold for the onset of pattern formation is observed experimentally for the case of high optical feedback. When compared to the case without feedback, this threshold is shifted towards smaller nonlinearities and a significant increase of the modulation degree of the obtained patterns is obtained. Our measurements also show that, above threshold, the dominating spatial frequency of the patterns decreases monotonically with both increasing nonlinearity and increasing feedback. PACS 42.65.Tg; 42.65.Sf; 89.75.Kd     

Dynamics of a nonlinear ring cavity: Excitability and coherent resonance

The phenomena of excitability and coherent resonance in a nonlinear ring cavity in the presence of excitons and biexcitons are considered. A bifurcation analysis of the dynamics of the nonlinear ring cavity indicates that both self-pulsation and excitability can exist in the system. It is demonstrated that coherent resonance can be observed in an excitable exciton-biexciton system in the ring cavity. The optimum conditions for the manifestation of these phenomena are investigated, and their possible applications are discussed.     

Excitable wave patterns in a spatially extended nonlinear optical cavity

We show that finite external excitation can lead to a traveling wave in an excitable passive optical system with one-dimensional space geometry. We have studied the excitable behavior of this system in parallel with that of its diffusive counterpart and show the effects of optical phase on the traveling-wave solution and its velocity. In two-dimensional space we observe numerically rotating optical spiral waves evolving from a truncated planar wave front.     

非线性波导腔耦合特性研究

对一种非线性波导耦合腔进行了理论和实验研究。研究表明,该系统的透过率随入射光强变化。对于不同的初始偏置、耦合区长度和入射功率系统具有微分放大、限幅、反常耦合和双稳运行等不同的响应。     

Polarization and amplitude hybrid modulation of longitudinally polarized subwavelength-sized optical needle

We present a method of both polarization and amplitude modulations on an incident beam to obtain a longitudinally polarized subwavelength-sized optical needle.A 4-f system with a spatial light modulator is used to generate experimentally a two-mode alternate cylindrical vector beam by polarization modulation,enhancing performance and facilitating implementation.We optimize the beam focusing properties after passing the beam through an annular aperture to obtain amplitude modulation by the simulated annealing algorithm.Numerical results indicate that a sharp focal spot(0.417λ) with a long focal depth(8λ) and a strong longitudinally polarized field can be easily achieved.     

Controlled observation of a nonequilibrium Ising-Bloch transition in a nonlinear optical cavity

We report the controlled observation of the nonequilibrium Ising-Bloch transition in a broad area nonlinear optical cavity (a quasi-1D single longitudinal-mode photorefractive oscillator in a degenerate four-wave mixing configuration). Our experimental technique allows for the controlled injection of the domain walls. We use cavity detuning as control parameter and find that both Ising and Bloch walls can exist for the same detuning values within a certain interval of detunings; i.e., the Ising-Bloch transition is hysteretic in our case. A complex Ginzburg-Landau model is used for supporting the observations.     

Excitability mediated by localized structures in a dissipative nonlinear optical cavity

We find and characterize an excitability regime mediated by localized structures in a dissipative nonlinear optical cavity. The scenario is that stable localized structures exhibit a Hopf bifurcation to self-pulsating behavior, that is followed by the destruction of the oscillation in a saddle-loop bifurcation. Beyond this point there is a regime of excitable localized structures under the application of suitable perturbations. Excitability emerges from the spatial dependence since the system does not exhibit any excitable behavior locally. We show that the whole scenario is organized by a Takens-Bogdanov codimension-2 bifurcation point.