基于光纤Fabry-Perot滤波器的电光混合光学双稳态

提出了一种新型的电光混合光纤光学双稳装置,它由波长为1.55μm带尾纤的DFB半导体激光器、全光纤可调谐Fabry_Perot滤波器和电光反馈电路构成。实验中通过改变输入光强实现了光学双稳运转。讨论了该双稳器件在激光光强稳定器和光纤传感器方面的应用。     

带延时光学双稳装置分岔点处的光放大效应

调节在倍周期分岔第一个分岔点处的带延时光学双稳装置(OBD),对与系统谐振的光学小信号具有放大作用.本文对此作了理论分析.     

Optical bistability in fiber ring resonator containing an EDFA

In this paper, we study on optical bistability behaviors in a double-coupler ring resonator, in which an erbium-doped fiber amplifier (EDFA) is inserted into the ring for counteracting the loss by the gain of EDFA. The two groups of transmitted and reflected optical bistability loops under different parameters are investigated symmetrically. According to our optimum design of this new optical bistable device, the switching power can be less than 60 mW.     

Multiple bistability in an optical fibre double-ring resonator by using degenerate two-wave mixing

A theoretical study is presented of multiple bistability in a single-mode optical fibre double-ring resonator using an all-fibre scheme involving degenerate two-wave mixing. Two successive bistable hysteresis loops (one is a normal type and another an inverting type) are formed in the input-output transmission curve. The dependence of the multiple bistability on major parameters of the fibres and the couplers is investigated.     

Temperature switch based on optical bistability

We have demonstrated a temperature switch based on an optically bistable device integrated with an optical fibre. The principle demonstrated here might lead to the development of new types of all-optical temperature sensors.     

Fully automatic system for the coupling alignment of optical fibres

To realize the low-loss connection of two optical fibres intended as a transmission medium for optical signals, very tight tolerances have to be observed on account of the small geometrical dimensions involved. The present work describes a fully automatic system for the alignment of optical fibres in thex-y planes relative to a light source, which has only a single intensity peak, so that maximum optical power is launched into the fibre. The light source can be, for instance, the radiating end of a fibre, a semi-conductor laser or a light-emitting diode. The optical power coupled into the fibre serves as the control signal. Three precision displacement stages driven by stepping motors serve to align the fibres. Various sequential control algorithms for optimal coupling are investigated with reference to theory. Two algorithms are tested with the aid of a computer with reference to the alignment accuracy and speed requirements which have to be met and the one shown by theoretical simulation to be the more favourable is selected for technical realization. The resulting system was used for numerous alignment operations for the coupling of two graded-index fibres. The alignment time is below 1 s and the coupling efficiency compared with manual coupling alignment efficiency (= 100%) is above 99%, corresponding to an additional loss of <0.05 dB.     

Analysis of dynamic pattern formation in nonlinear Fabry-Perot resonators

We present a detailed analysis of transverse effects and pattern formation in bistable optical elements. The system we investigate consists of a Fabry-Perot resonator for the optical feedback element with a nematic liquid-crystal cell used as an optically nonlinear intracavity medium. On illumination with a cw-laser beam, the system causes the beam to break up into several individual spots, passing through several transitions before finally reaching a stationary state. We devise a theoretical model which is used as the basis for numerical simulations of the system. The simulation results are in good agreement with experiment. Finally, we characterize the principal instability of the system using a linear stability analysis of the theoretical model.     

Spatial coherence properties of light from optical fibres

The mutual intensity of the optical field in the Fraunhofer diffraction region produced from the end of an optical fibre under illumination of a coherent beam, is theoretically analysed by using an optical fibre-end source model. In this source model, the optical field at the end of the fibre is expressed as an aggregation of independent plane waves with random directions and phases, because the guided modes propagating through the fibre may be regarded as a stochastic process. It is found that the optical field in the diffraction region from the multimode optical fibre is not homogeneous butquasi homogeneous in a statistical sense. The spatial coherence properties in the field are discussed in connection with theV number (the normalized frequency) of the fibre and in comparison with those in the field produced from an incoherent source obeying the van Cittert-Zernike theorem.     

Noticeable positive Doppler effect on optical bistability in an N-type active Raman gain atomic system

We theoretically investigate the Doppler effect on optical bistability in an N-type active Raman gain atomic system inside an optical ring cavity.It is shown that the Doppler effect can greatly enhance the dispersion and thus create the bistable behaviour or greatly increase the bistable region,which has been known as the positive Doppler effect on optical bistability.In addition,we find that a positive Doppler effect can change optical bistability from the hybrid dispersion-gain type to a dispersive type.     

Millimetre-wave fibre–wireless transmission systems with reduced effects of fibre chromatic dispersion

This paper describes two techniques for the implementation of millimetre-wave (mm-wave) wireless communication systems incorporating optical fibre distribution networks. Fibre chromatic dispersion can exhibit severe effects on the transportation of mm-wave frequencies over fibre, resulting in greatly reduced post-detection rf powers. Each mm-wave fibre–wireless system demonstrated here incorporates a method for the generation and modulation of an optical mm-wave carrier, which enables the effect of fibre dispersion to be significantly reduced. One set-up is a direct-detection scheme where optical single-sideband (SSB) with carrier modulation is used to overcome fibre dispersion effects. The other system employs a self-heterodyne arrangement in which a dual-frequency optical source generates a low phase-noise mm-wave beat signal. Data transmission is achieved by externally modulating the dual-mode signal and reduced effects of fibre dispersion are observed.     

一种实现二进制加法符号替换规律的光逻辑系统

为了实现二进制加法符号替换规律,本文提出了一种简单的光逻辑系统,它仅包括一片二维列阵光学双稳器件.本实验采用同时具有NXOR和OR逻辑功能的透反射型ZnS光学双稳干涉滤光片作光逻辑器件.该光学逻辑系统完成了二进制加法四个符号替换规律的并行替换.光学系统采用固定的自由空间互连方法,具有光学硬件少,光功率损耗低,结构简单、实用的优点.     

Chaotic Oscillator in Frequency by Using Tunable Laser with Fibre Bragg Grating

A novel chaotic oscillator in wavelength domain by using a tunable fibre laser is proposed. The generator of chaos in wavelength is composed of fibre Bragg grating （FBG） with hybrid delayed feedback loop which induces wavelength nonlinearity. The dynamical regime of wavelength is ruled by a differential difference equation. We give the numerical simulation of the experimental setup and discuss its application in an optical encryption system.     

Mean First-Passage Time in Optical Bistable Systems

The transient properties of an optical bistable system driven by multiplicative and additive noises are investigated. The effects of multiplicative and additive noises intensities on the mean first-passage times （MFPTs） in two opposite directions are discussed. The results show that the intensities of multiplicative and additive noises affect the MFPTs on two directions in the same way.     

Theory of optical bistability in a non-linear quasi-waveguide

Optical bistable behavior in a quasi-waveguide containing non-linear film has been experimentally investigated in several publications in the past years; however, the physical mechanism for optical bistability has not been theoretically explained. In the present letter, we propose a theoretical model and successfully explain the observed optical bistability of both the reflected light and the scattered light (m-lines) in a non-linear quasi-waveguide. The optical bistability in the non-linear quasi-waveguide is due to the scattering-type wavevector mismatch mechanism. Received: 10 July 2002 / Revised version: 10 September 2002 / Published online: 20 December 2002 RID="*" ID="*"Corresponding author. Fax: +86-25/359-5535, E-mail: htwang@nju.edu.cn     

Optical bistability in a triple semiconductor quantum well structure with tunnelling-induced interference

We study the behavior of optical bistability (OB) in a triple semiconductor quantum well structure with tunnelling-induced interference, where the system is driven coherently by the probe laser inside the unidirectional ring cavity. The results show that we are able to control efficiently the bistable threshold intensity and the hysteresis loop by tuning the parameters of the system such as laser frequency and tunnelling-induced frequency splitting. This investigation can be used for the development of new types of nanoelectronic devices for realizing switching process.     

Spatial coherence of laser light propagating in an optical fibre

The modulus of the complex degree of spatial coherence at the exit face of an optical fibre is determined for a quasi-monochromatic, spatially coherent source. It is found that the contribution of the cross-terms between many modes to the formulus of pointwise correlation is negligible for a highly multimode fibre in which even and odd modes are equally excited, although care must be taken when even or odd modes only are selectively excited in the waveguide. Experimental results obtained by using a Koesters prism in the wavefront reversing interferometer are also presented for a graded-index multimode fibre and a quasi-single mode fibre. Modal contents of the propagating field in the optical fibre can be successfully determined, provided that the coherence time of a quasi-monochromatic source and the path difference of the wavefront reversing system are knowna priori.     

Light-driven molecular switches and motors

Technology is omnipresent in our modern-day society and it is hard to imagine a world without machines, computers or robots. One of the main current scientific challenges is the bottom-up construction of systems that represent nanosize analogues of switches, devices and motors. Our efforts in this area have focussed on the construction of devices based on sterically overcrowded alkenes. In this paper, we present our ongoing research on the construction of binary molecular switches, which has recently led to genuine molecular motors. The control of chirality in a molecular switching system allows interconversion between molecules of opposite helicity using different wavelengths of light. Such bistable chiral switches are of potential use in optical data storage and processing at the molecular level. The control of molecular chirality is even more subtle in the case of molecular motor systems. The exquisite control of chirality using light as an energy source has resulted in a controlled, repetitive 360° unidirectional rotation in two generations of molecular motor systems. Received: 21 January 2002 / Accepted: 11 February 2002 / Published online: 22 April 2002     

Dynamic characteristics of nonlinear Bragg gratings in photonic crystal fibres

We study numerically the temporal and spatial dynamics of light in Bragg gratings in highly nonlinear photonic crystal fibre for a CW input signal. Our numerical model is based on the plane wave mode solver and a set of nonlinear coupled-mode equations which we solve using a variation of implicit fourth order Runge-Kutta method. We observe not only bistability of the intensity versus transmitted and reflected light but also complex dynamics. We demonstrate that for values of input intensity above the bistable region the steady state may undergo a supercritical Hopf bifurcation. For some ranges of the input intensity we also observe a coexistence of two periodic attractors. The dynamics found, in particular the features in the bifurcation diagram, strongly depend on the parameters of the fibre. Consequently, we suggest that by proper design of the photonic crystal in the cladding we can adjust such nonlinear features of the Bragg gratings as the width of the bistable region, the intensity at which the bifurcation occurs and also the characteristics of the dynamics at high values of input intensity.     

Bistable switching using an optical Tamm cavity with a Kerr medium

All-optical bistable switching is proposed to realize by using an optical Tamm cavity in which a Kerr medium is sandwiched between a metal layer and a Bragg mirror. Results show that the excitation of clockwise and counterclockwise bistable switching under the control of external optical injection is due to the presence of optical Tamm states. In addition, the bistable characteristics of optical Tamm cavities are found to be sensitive to the polarization of external optical injection.     

Investigation into the power-law dependence of fibre Bragg grating growth

We have undertaken a detailed experimental and numerical investigation of fibre Bragg grating growth rates over relatively long timescales, in which we consider the influence of zero-order UV irradiation, jitter and drift. In contrast to other studies, our results show that measurements of grating growth dynamics are in good agreement with numerical expressions describing exponential decay of a population of defect sites if the influence of small lateral displacements between the optical fibre and the modulated UV beam (jitter) are accounted for.