Bistable Optical Response Research Articles

Bistable optical response of a nanoparticle heterodimer: Mechanism, phase diagram, and switching time

We conduct a theoretical study of the bistable optical response of a nanoparticle heterodimer comprised of a closely spaced semiconductor quantum dot and a metal nanoparticle. The bistable nature of the response results from the interplay between the quantum dot's optical nonlinearity and its self-action (feedback) originating from the presence of the metal nanoparticle. The feedback is governed by a complex valued coupling parameter G = G(R) + iG(I). We calculate the bistability phase diagram within the system's parameter space: spanned by G(R), G(I), and Δ, the latter being the detuning between the driving frequency and the transition frequency of the quantum dot. Additionally, switching times from the lower stable branch to the upper one (and vice versa) are calculated as a function of the intensity of the driving field. The conditions for bistability to occur can be realized, for example, for a heterodimer comprised of a closely spaced CdSe (or CdSe/ZnSe) quantum dot and a gold nanosphere.

Optical response from dual-frequency hybrid-aligned nematic liquid crystal cells

Dual-frequency hybrid-aligned nematic liquid crystal cells and the influence of the parameters of a control electric field on their optical response are studied. It is found that the harmonic oscillations of the optical transmission in such cells are observed in the interval between low frequency-to-high frequency voltage switchings unlike in conventional twisted nematic cells. A V-shaped bistable optical response is obtained by successively applying sinusoidal electric fields with frequencies of 1 and 30 kHz to a twisted nematic cell. For a liquid crystal layer 8 μm thick and an applied voltage of 50 V, the response time is 10 ms. In a hybrid-aligned twisted-nematic cell with a large initial tilt angle of the director (about 70°), the V-shaped optical response is observed when the inclined homeotropic state is switched to the twisted state by applying a 30-kHz field. The initial structure of the layer recovers as a result of natural elastic relaxation, and the response time increases roughly fourfold.

Low-power optical bistability in a free-standing silicon ring resonator

We demonstrate low-power thermo-optic-based optical bistability in a free-standing silicon ring resonator. A bistable optical response is achieved at reduced pump powers by thermally isolating the ring resonator from its supporting substrate with an air gap. The conversion efficiency from optical power to temperature change in the silicon core is enhanced. The optical transfer function of the resulting free-standing resonator exhibits a hysteresis loop for 80 microW input optical power. Similar nonthermally isolated resonators at the same detuning do not exhibit a bistable mode for input powers less than 2 mW.

Bistability of an optical response of a photonic crystal with a dense resonant medium as a defect

Optical characteristics of a system consisting of a photonic crystal with a defect layer of a dense resonant medium described by the modified Bloch equation are considered. Transmission spectra are calculated and regions of existence of bistable optical response of the system are found. It is shown that the effect of internal reflection demonstrated by the dense resonant medium results in variation of reflection and transmission spectra of the photonic crystal and the loop width of the bistable response of the dense resonant medium is determined by the structure of the photonic crystal.

Bistable optical response in quantum well semiconductor microcavity

We report an experimental study of the optical bistability in a semiconductor microcavity (MC), consisting of a wedged λ GaAs spacer containing a single 8.5 nm In0.04Ga0.96As quantum well (QW). Increasing the excitation power, a transition between the normal coupling and the weak coupling regime of the MC modes is observed. At intermediate excitation power the reflectivity spectrum shows the simultaneous presence of three resonances, with a third peak spectrally lying between the two normal modes. Monitoring the reflected signal for different laser energy as a function of the excitation power, we found that optical bistability is observed only at the energy of the third peak. The experimental findings do not agree with transfer matrix calculations based on exciton bleaching, suggesting that more complex nonlinear mechanisms are relevant in the observed bistable behaviour.

Optical bistability driven by a first order phase transition

A new general method of obtaining an bistable optical response, which makes use of a change in the optical properties of the medium induced by a first order phase transition, is investigated. The properties of this type of optical bistability are found to be substantially dependent on the assumptions concerning the role of metastable states in the phase transition. Possible steady-state regimes are analyzed, and universal expressions are derived for the figures of merit describing the bistable response in the vicinity of a critical point of the phase transition.

Theoretical and experimental aspects of the nonlinear spectroscopy of biexcitons in CuCl

Forward degenerate fourwave mixing in CuCl in the vicinity of the two-photon absorption on the biexciton can be analyzed from two complementary theoretical points of view :(a) In terms of the traditional perturbational formulation of nonlinear optics, the low intensity observations can be accounted for in terms of interferences and re-normalizations among different-order elementary mixing processes (b) In terms of a perturbational scheme which provides directly an analytic expression for the intensity-dependent dielectric function of the material. This last approach points to a potentially bistable optical response when local field effects are included in the calculation.