Summary form only given. Optical bistability has raised a sustained interest in the 1990s. However it is commonly admitted that transverse mechanisms such as diffraction and carrier diffusion can seriously limit the applications developed in the frame of a plane wave (PW) analysis in increasing the energy consumption or introducing crosstalk mechanisms. In particular, several authors have predicted the existence of switching waves arising from the spatial coexistence of two different PW solutions, connected by an inhomogeneous intensity profile. We report on the first experimental observation of transverse switching waves in a passive resonator hosting a fast nonlinear active medium in a resonator composed by two Bragg mirrors.
Summary form only given. Optical bistability has raised a sustained interest in the 1990s. However it is commonly admitted that transverse mechanisms such as diffraction and carrier diffusion can seriously limit the applications developed in the frame of a plane wave (PW) analysis in increasing the energy consumption or introducing crosstalk mechanisms. In particular, several authors have predicted the existence of switching waves arising from the spatial coexistence of two different PW solutions, connected by an inhomogeneous intensity profile. We report on the first experimental observation of transverse switching waves in a passive resonator hosting a fast nonlinear active medium in a resonator composed by two Bragg mirrors.
Transverse effects are known to play a central role in nonlinear-optical systems.Since experiments are generally performed with lasers with finite transverse dimensions, the transverse nature of the field must be considered.Experimental evidence, for example, indicates that mechanisms in the form of diffusive and diffractive coupling within the medium, free-space diffraction, or some combination of these, can create transverse structures which are important in optical bistability and self-focusing/defocusing.In particular, transverse coupling is attributed to such phenomena as radial dependence of the switch up times of bistable loops, spatial hysteresis, and the formation of solitary waves in passive systems.The dynamical effects of free-space diffraction in a unidirectional ring cavity containing a thin resonant absorber driven by an external coherent signal is considered.Minimal focusing effects exist in this system by incorporating a thin medium whose width is small compared to the cavity length and Raleigh range.There is no restriction on the medium response time relative to the round trip time; i.e. the time-dependent polarization is not adiabatically eliminated from the equations of motion.Free-space diffraction effects are isolated and diffraction and diffusive coupling within the medium is negligible.In this model where free-space diffraction is the dominant mechanism for changing the field profile in the system, shifting, deformation, and radial variation of the bistable loop and spatial hysteresis is attributed to an inherent dispersion induced by the free-space diffraction.
Optical bistability is a first-order nonequilibrium phase transition, which is characterized by the spatial or temporal coexistence of two phases. In systems with resonators this phase coexistence can be realized in the form of transverse patterns of high and low intensity values, whereas in a resonatorless optical bistability the phase coexistence becomes manifest in a longitudinal intensity variation. In systems in which strong diffusion of the elementary excitations suppresses spatial phase coexistence, random fluctuations establish at least in principal a temporal phase coexistence by stochastic switching between the two bistable states.
We discuss a novel type of optical instability, which leads to the spontaneous formation of a stationary spatial structure, instead of to the onset of oscillations or pulsations. A passive system is contained in an optical cavity, to which we add two lateral mirrors. Under appropriate conditions, diffraction of radiation can induce the onset of a transverse-stripe structure in an initially uniform plane-wave field configuration. In this paper, we consider the case of a homogeneously broadened two-level system. The model on which our analysis is based is derived from the Maxwell-Bloch equations in the paraxial approximation, using the mean-field limit and assuming a large Fresnel number. We show that, with respect to the bistability parameter C, the threshold of the spatial instability coincides with the bistability threshold for absorptive, resonant optical bistability. The spatial instability requires, however, a detuned configuration and can arise both in the absence and presence of bistability. In the latter case, it can occur both in the lower and in the upper branch of the steady-state curve. The instability is caused by competition between different transverse modes, which realize a situation of spatial coexistence, different from the state of temporal coexistence which characterizes the spontaneous oscillations that arise from the previously known multimode instabilities. Finally, we discuss some points relevant for an experimental observation of this phenomenon.
We analyze transverse-electric (TE) wave reflection at a planar interface between a linear medium and a Kerr nonlinear half-space. Using an amplitude-phase formalism, we derive exact expressions for the reflection coefficient and the incident intensity as functions of the permittivity at the interface. Under total internal reflection, the spatial evolution of the permittivity is described by a first-order differential equation and decays monotonically to the linear value. The incident intensity on the evanescent branch is shown to possess a maximum when 2𝛽2 > 𝜀1 +𝜀𝑙, where 𝛽 is the conserved propagation constant, 𝜀1 the linear permittivity, and 𝜀𝑙 the low-intensity permittivity of the Kerr medium. For intensities between the threshold 𝑆𝑐 and the maximum 𝑆max, three steady states coexist: two evanescent (TIR) solutions (one stable, one unstable) and one propagating solution. The propagating branch rises with an infinite slope at 𝜀 = 𝛽2 (square-root singularity), leading to an ultra-sharp switching transition. The relation between the normalized decay constant 𝜇 and the incident intensity exhibits a folded curve, revealing an “internal” bistability in the TIR regime. Both self-focusing (𝛼 > 0) and self-defocusing (𝛼 < 0) Kerr nonlinearities are treated. The propagation constant 𝛽 appears as a free design parameter, allowing the switching intensity to be tuned through waveguide geometry. These results provide a unified picture of optical bistability at a nonlinear interface, with potential applications in all-optical switching and sensing.
We analyze transverse-electric (TE) wave reflection at a planar interface between a linear medium and a Kerr nonlinear half-space. Using an amplitude-phase formalism, we derive exact expressions for the reflection coefficient and the incident intensity as functions of the permittivity at the interface. Under total internal reflection, the spatial evolution of the permittivity is described by a first-order differential equation and decays monotonically to the linear value. The incident intensity on the evanescent branch is shown to possess a maximum when 2𝛽2 > 𝜀1 +𝜀𝑙, where 𝛽 is the conserved propagation constant, 𝜀1 the linear permittivity, and 𝜀𝑙 the low-intensity permittivity of the Kerr medium. For intensities between the threshold 𝑆𝑐 and the maximum 𝑆max, three steady states coexist: two evanescent (TIR) solutions (one stable, one unstable) and one propagating solution. The propagating branch rises with an infinite slope at 𝜀 = 𝛽2 (square-root singularity), leading to an ultra-sharp switching transition. The relation between the normalized decay constant 𝜇 and the incident intensity exhibits a folded curve, revealing an “internal” bistability in the TIR regime. Both self-focusing (𝛼 > 0) and self-defocusing (𝛼 < 0) Kerr nonlinearities are treated. The propagation constant 𝛽 appears as a free design parameter, allowing the switching intensity to be tuned through waveguide geometry. These results provide a unified picture of optical bistability at a nonlinear interface, with potential applications in all-optical switching and sensing.
This thesis presents the theory of the driven optical ring cavity containing a nonlinear material. First, an overview of the history of bistability and spatial solitons in driven nonlinear cavities is outlined. Then, the basic theory of the optical Kerr effect is presented and two of its consequences are outlined: optical bistability and spatial solitons. Within this background, the mirror feedback model is derived from the Maxwell-Bloch equations and considerations of the classical optics of the cavity. This model is analytically shown to exhibit bistability in the plane wave case. The mean-field model is subsequently derived by applying the mean-field limit to the Maxwell-Bloch equations and the cavity optics. In addition, the mean-field model is analytically shown to exhibit bistability in the plane wave case. Numerical simulations are performed on the mean-field model demonstrating the existence of: (i) plane wave bistability, (ii) transverse modulational bistability, (iii) the ability to “switch†between bistable states in both the plane wave and modulated case, (iv) instabilities in the modulated case and (v) the possibility for optimization of the switching process. Finally, an application of bistable driven cavities is explored: an all-optical digital information processor and storage device.