Low-light-level all-optical switching

We propose an all-optical switch that utilizes the technique of storage and retrieval of light pulses. A single photon (probe pulse) switched by another (switching pulse) is feasible, and the on-off ratio can be as large as 10 dB. We have experimentally demonstrated that the energy of the retrieved probe pulse is reduced to about 10% because of the presence of a switching pulse with an energy per unit area of one photon per lambda(2)/(2pi). The achieved result does not depend on the coupling intensity, the atomic optical density, or the width and shape of the switching pulse.     

Observation of all-optical bump-on-tail instability

We demonstrate an all-optical bump-on-tail instability by considering the nonlinear interaction of two partially coherent spatial beams. For weak wave coupling, we observe momentum transfer with no variation in intensity. For strong wave coupling, modulations appear in intensity and evidence appears for wave (Langmuir) collapse at large scales. Borrowing plasma language, these limits represent regimes of weak and strong spatial optical turbulence. In both limits, the internal spectral energy redistribution is observed by recording and reconstructing a hologram of the evolving dynamics. The results are universal and can appear in any wave-kinetic system with short-wave-long-wave coupling.     

基于石墨烯的宽带全光空间调制器

提出了单层石墨烯包裹微纳光纤的全光空间调制.石墨烯作为可饱和吸收体包裹在通过二氧化碳激光器加热制备的微纳光纤上,当信号光沿着微纳光纤传输时部分光将以倏逝场的形式沿着微纳光纤表面传递,并与石墨烯产生作用被吸收.同时将波长为808 nm的抽运光从空间垂直入射到石墨烯包裹的微纳光纤处,依据石墨烯的优先吸收特性,通过抽运光控制石墨烯对信号光的吸收,实现了宽带全光空间调制.在1095 nm波长处获得最大调制深度约为6 dB,调制带宽约为50 nm,调制速率约为1.5 kHz.空间全光调制器具有输出信号光“干净”的特点.与传统石墨烯微纳光纤全光调制器相比,输出端不需要对抽运光进行光学滤波而直接获得已调信号.该复合波导全光空间调制器以更为灵活、高效的方式打开了微纳超快信号处理的大门.     

Phase-locked all-optical differential polarization demodulation

A novel scheme of differential polarization demodulation is presented and demonstrated based on a polarized asym- metrical Mach-Zehnder interferometer configuration with polarization control. To enhance the stability of the demodulator, a phase-lock device is designed, and it is composed of a symmetric 3 × 3 coupler and a feedback circuit. For further estab- lishing a differential polarization-shift keying （DPolSK） transmission system, we successfully carry out the demodulation experiments on 10-Gb/s DPolSK optical signals for the first time. Due to the all-optical structure with phase-lock, our scheme is available to realize the DPolSK optical communication in practical optical fiber systems.     

Micromagnetic investigation of all-optical switching

This Letter investigates all-optical magnetization switching from micromagnetic perspective. The influence of circularly polarized light on a magnetic sample was considered to be both directly through the inverse Faraday effect and indirectly aided by thermal induced effects by the laser beam. Dependence of all-optical switching on pulse duration, laser intensity and the magneto-optical susceptibility strength is studied. An important aspect of this investigation is the analysis of how the cooling process influences the successive switches, especially through limiting the successive writing time.     

Near-deterministic efficient all-optical quantum computation

We propose a flexible scheme to prepare various kinds of useful entangled coherent states using weak cross-Kerr nonlinearities and strong laser fields. We then show that, with such entangled states as off-line resources, near-deterministic quantum gates needed for coherent-state-based quantum computation can be efficiently implemented by means of in-line linear-optics elements.     

第九讲光速减慢和光缓存技术

高速光信号的存储是光信息科学的重要分支,全光缓存器是当今高速光信号处理的瓶颈.本文介绍了全光缓存器的研究进展,着重介绍了光速减慢的原理、物理基础, 以及在半导体量子点中利用电磁诱导透明效应发展全光缓存器的思路.     

Passive, “self-trapped family” all-optical half adder using all-optical XOR and AND gates

The paper presents an alternative novel approach to obtain all-optical logic. We show that XOR, NOT, and AND logic could be obtained by appropriately setting parameter of all-optical passive transistor. An AND gate followed by NOT gives NAND logic (building block) that, in principle can provide complete set of passive, fiber compatible “self-trapped family” all-optical logic gates (with Boolean completeness) and may find many possibilities in the area of all-optical computing. To give one example, we propose all-optical half adder.     

An all-optical WDM-to-TDM conversion scheme with simultaneous all-optical synchronization for WDM/OTDM network nodes

We present an all-optical WDM-to-TDM conversion scheme with simultaneous all-optical synchronization that can be utilized in switching nodes of very high-speed WDM/OTDM hybrid communication systems. The scheme, which utilizes a nonlinear optical loop mirror in conjunction with a synchronously modelocked semiconductor laser, is experimentally demonstrated by WDM-to-TDM conversion of two optical channels in a switching node. The optical time division multiplexed output has a potential total throughput of ≈40 Gb/s. This all-optical scheme removes limitations of restricted bandwidth of electronics at switching nodes and also has advantages over existing optical time division multiplexing schemes.     

Silicon photonic crystal all-optical logic gates

All-optical logic gates, including OR, XOR, NOT, XNOR, and NAND gates, are realized theoretically in a two-dimensional silicon photonic crystal using the light beam interference effect. The ingenious photonic crystal waveguide component design, the precisely controlled optical path difference, and the elaborate device configuration ensure the simultaneous realization of five types of logic gate with low-power and a contrast ratio between the logic states of “1” and “0” as high as 20 dB. High power is not necessary for operation of these logic gate devices. This offers a simple and effective approach for the realization of integrated all-optical logic devices.     

Time-dependent all-optical logic-gates with bacteriorhodopsin film

In this paper, we proposed time-dependent AND, NOT and operation based on the relation between input and output intensities of the first-order diffraction beams in degenerate multi-wave coupling. When two coherent green beams are coupled in bacteriorhodopsin (bR) film with a small angle, the intensities of the diffraction beams decrease along with writing time. Based on the phenomenon that the diffraction beams decay along with writing time and the relation between the intensities of input and output beams, we demonstrated the time-dependent optical AND, NOT and operations.     

Micrometer-scale all-optical wavelength converter on silicon

We demonstrate a highly integrated micrometer-scale low-power wavelength converter based on the free-carrier dispersion effect in silicon. The conversion is achieved through all-optical modulation of a silicon ring resonator by use of modulated cw control light. The ring resonator has a radius of 5 microm and a Q of approximately 10,000. Both inverted and noninverted modulation are achieved at a bit rate of 0.9 Gbits/s with a control power of 4.5 mW. The scaling of the required control power for operation with respect to the characteristics of the ring resonator is established.     

Mach-Zehnder interferometer-based all-optical reversible logic gate

In recent years, reversible logic has emerged as a promising computing paradigm having application in low-power CMOS, quantum computing, nanotechnology and optical computing. Optical logic gates have the potential to work at macroscopic (light pulses carry information), or quantum (single photons carry information) levels with great efficiency. However, relatively little has been published on designing reversible logic circuits in all-optical domain. In this paper, we propose and design a novel scheme of Toffoli and Feynman gates in all-optical domain. We have described their principle of operations and used a theoretical model to assist this task, finally confirming through numerical simulations. Semiconductor optical amplifier (SOA)-based Mach-Zehnder interferometer (MZI) can play a significant role in this field of ultra-fast all-optical signal processing. The all-optical reversible circuits presented in this paper will be useful to perform different arithmetic (full adder, BCD adder) and logical (realization of Boolean function) operations in the domain of reversible logic-based information processing.     

An all-optical, high-sensitivity magnetic gradiometer

Optical magnetometers have reached sensitivities that make them interesting candidates for the measurement of weak magnetic fields also outside physics laboratories. In order to overcome problems with stray magnetic fields a common solution with existing magnetometers is to operate a pair of them in a gradiometer configuration: one sensor measures the signal plus the stray fields, while the other one is mounted such that it is only influenced by the stray fields. In the difference signal the stray fields cancel. We have constructed such a gradiometer consisting of two sensors based on coherent population trapping (CPT) resonances in a thermal cesium vapor. Using a magnetic bias field the intrinsically scalar CPT magnetometer can be turned into a true vector magnetometer that is insensitive to magnetic fields perpendicular to a chosen measurement direction. We describe how to align and calibrate the gradiometer. Stray field suppression by more than two orders of magnitude has been achieved, limited by the sensitivity of the magnetometer. This makes possible the detection of picotesla flux density changes in a weakly shielded or even unshielded environment. Received: 3 April 2002 / Published online: 15 November 2002 RID="*" ID="*"New address: Département de Physique, Université de Fribourg, Chemin du Musée 3, 1700 Fribourg, Switzerland RID="**" ID="**"Corresponding author. Fax: +41-26/300-9631, E-mail: robert.wynands@unifr.ch     

Blocking in wavelength-routed all-optical WDM networks

In this paper, we have developed a low complexity mathematical model which is used for the calculation of blocking probability of network and this model does not require any simulation statistics. The implementation of the model proposed has less complexity and the computation used in this model is quite efficient. This paper suggests an optimum path as a solution to routing problem and the appropriate number of wavelengths have also been suggested which should be free in a network to have the least blocking probability. This model can be implemented on different network topologies. Further, the model is also used to evaluate the blocking performance of NSFNet topology and hence used to improve its performance on the basis of blocking probability.     

Noncontact all-optical measurement of corneal elasticity

We report on a noninvasive and noncontact all-optical method to measure the elasticity of the cornea. We use a pulsed laser to excite surface acoustic waves (SAW) that propagate on the corneal surface, then use a phase-sensitive optical coherence tomography system to remotely record the SAWs from which the corneal elasticity is estimated. In addition, the system is able to provide real-time tomographic images of the cornea being examined, an important consideration for clinical studies. While precisely maintaining a range of intraocular pressures (IOP), a series of measurements is performed on ex vivo intact primate eyes. The measurement results not only demonstrate the feasibility of the proposed system to remotely measure the corneal elasticity, but also suggest a strong correlation between the corneal stiffness and the true IOP.