Chen Li-Xue

Finite-difference time-domain analysis of optical bistability with low threshold in one-dimensional nonlinear photonic crystal with Kerr medium

Abstract We present a nonlinear finite-difference time-domain (NFDTD) analysis of optical bistability (OB) in a one-dimensional nonlinear photonic crystal (1D-NPC) with Kerr medium under Debye relaxation. The properties of the defect modes in a symmetrical structure 1D-NPC and the way to obtain low threshold of OB is discussed in detail. The OB threshold depends on the optical thickness and refractive index of defect layer and the number of symmetrical layers. When the half-width of defect mode is small enough and frequency of incident light and linear refractive index are selected carefully, the low threshold OB is able to be obtained. By numerical simulation threshold ∼ 130 KW / m 2 is obtained, correspond refractive index change is only about 0.04.

Low Threshold Bistable Switching by the Nonlinear One-Dimensional Photonic Crystal

In the approximation of the fast Debye relaxation of a nonlinear Kerr medium, the nonlinear finite-difference time-domain method is derived to simulate numerically the one-dimensional nonlinear photonic crystal sandwiched by the Kerr medium. Bistable switching with a low threshold intensity of 0.01kW/cm2 is obtained, and the corresponding refractive index change of the Kerr media is about 0.038.

Localization and Threshold of Bistable Switching by Gap-Edge Shifting

We numerically investigate the localization behaviour of light propagation in a one-dimensional nonlinear photonic crystal (1D-NPC). It is found that the localization of a high gap-edge mode is better than that of a low one, so that the switching threshold of the 1D-NPC with plus Kerr L-layers is much lower than that with minus Kerr H-layers. For a structure of 16 periods, the threshold of the structure with nonlinear L-layers is about 1/10 of that with nonlinear H-layers in the same level of nonlinear refractive coefficient.

Intrinsic Bistability and Critical Slowing in Tm3+/Yb3+ Codoped Laser Crystal with the Photon Avalanche Mechanism

We present theoretically a novel intrinsic optical bistability (IOB) in the Tm3+/Yb3+ codoped system with a photon avalanche mechanism. Numerical simulations based on the rate equation model demonstrate distinct IOB hysteresis and critical slowing dynamics around the avalanche thresholds. Such an IOB characteristic in Tm3+/Yb3+ codoped crystal has potential applications in solid-state bistable optical displays and luminescence switchers in visible-infrared spectra.

Periodic and chaotic behaviors in optical bistability

The periodic and chaotic behaviors for both long and short delay time are demonstrated successfully using a hybrid OBD. The degree of stability S is introduced into the dynamic equations of optical bistability with a delayed feedback. The instability threshold is S = 2 for long delay time and S = 1 + π/2Q for short delay time.

Large Bandwidth Optical Limiting by Kerr Medium Doped One-Dimensional Coupled Cavity Optical Waveguides

We present a new method to realize large bandwidth optical limiting using Kerr nonlinearity doped one-dimensional coupled cavity optical waveguides (CCOWs). When the incident intensity is weak, the structure is a perfect CCOW that supports a high transmission band. When the intensity is increased, the Kerr effects change the refractive index of the Kerr cavity which results in a large decrease of transmission coefficients in the whole band. We numerically analyse the limiter using the nonlinear transfer matrix method and nonlinear finite difference in time domain method. Optical limiting effects are observed in the whole transmission band, and optimization methods are also discussed.

Emissions of Photonic Crystal Waveguides with Discretely Modulated Surfaces

Transmission properties of photonic crystal (PC) waveguides with discretely modulated exit surfaces are investigated numerically using the unite-difference time-domain (FDTD) method. Unlike the case of periodically modulated surfaces, where the transmission beam tends to be a single and directional beam, when the exit surfaces are modulated only at several discrete points, the emission power tends to split into multiple and directional beams. We explain this phenomenon using a multiple point source interference model. Based on these results, we propose a 1-to-N beam splitter, and numerically realized high efficiency coupling between a PC sub-wavelength waveguide and three traditional dielectric waveguides with a total efficiency larger than 92%. This simple, easy fabrication, and controllable mechanism may find more potential applications in integrated optical circuits.

Photonic Crystal Waveguide Intersection Based on Self-Imaging of Multi-Mode Interference

A new mechanism of intersection formed by two line defect photonic crystal (PC) waveguides are numerically investigated using the finite-difference time-domain method. The results show that the normalized crosstalk is smaller than 10−4; the reflection is smaller than 10−3, and the transmission is larger than 0.999. The authors analyse the physical origins and find that a modified self-imaging process in the intersected multi-mode region is the main reason of the excellent performance. This kind of multi-mode interference based intersection may find potential applications in PC optical circuits.

An Optical Parametric Amplifier in Photonic Crystals of Nondispersive Medium with Perfect Bloch Phase Matching

One-dimensional photonic crystal of second-order nonlinearity is studied. Among the three waves of the parametric interaction process of down-conversion with a nondispersive medium, two gap-edge localized modes and one travelling-mode are proposed, and an exact phase matching condition is realized using the periodic condition of the Bloch phase. Numerical simulation is implemented by the slow-envelope finite difference time domain method. In the case of a pulse wave pump of amplitude half-width 5.2×10−13 s, an intense optical parametric pulse with half-width about 5×10−14 s is observed.

Broadband Frequency Down-Conversion Using Coupled Cavity Structures in One-Dimensional Photonic Crystals

The frequency down-conversion of one-dimensional photonic crystals with the coupled cavity structure is investigated by the nonlinear finite-difference time-domain method. The efficient frequency conversion is obtained by utilizing the advantages of the broad eigenfrequency band, the strong localization and the Bloch phase matching of the coupled cavity structure. More importantly, the signal frequency could be tuned continuously within the whole band of the coupled cavity structure (with a bandwidth to central frequency ratio of 5.4%), and the gains are homogeneous in the band.