Static and synchronized switching noise management of replicated optical pulse trains

Demonstration is provided for the generation of high quality replicated optical pulse trains, from a single pulse. This uses the storage capability of an electro-optically switched recirculating fibre loop. For better understanding, the first step involves the development of general purpose derivations related to the evolution of the noise with near-unity loop gains. This is a basic tool to evaluate the propagation of the noise and the temporal evolution of the signal to noise ratio during the replication process. In a second step, the comparison of theoretical and experimental results will be shown to evidence good agreement, up to more than 1000 replica. Finally, experiments are performed on synchronised gain-switching inside the loop to help optimise the dynamic range of replication at the output of the system.     

Photonics applications in switching: An ATM optical node

An ATM optical node architecture that carries out cell routing and buffering by photonic means, controlled by electronic circuits, is presented. An evolutionary approach, where cell aggregation and compression are introduced to achieve a large throughput, with a high performance, is also described. And we report experimental results that demonstrate the feasibility of all the relevant photonic functions, based on advanced optoelectronic devices, namely: fast wavelength reassignment, suitable for multigigabit operation, based on fast tunable lasers and semiconductor optical amplifiers; high bit rate packet storage in a multiwavelength fiber loop memory including fast optical gates; dynamic wavelength selection, based on distributed feedback (DFB) filters with nanosecond tuning response; and all optical demultiplexing of multigigabit/s time division multiplexing (TDM) signals by means of saturated semiconductor optical amplifiers.     

Laser optical fibre heterodyne interferometer with frequency indicating of the phase shift of a light signal in an optical waveguide

Self-sustained oscillations in a laser optical fibre heterodyne interferometer are discussed; oscillations were produced by closing into a loop the single-mode optical fibres of the interferometer. Such oscillatory systems are shown to feature high-frequency stability. It is proposed to use this oscillating interferometer as a high-sensitivity sensor of external factors affecting the optical waveguide.     

Efficient broadband simulations for thin optical structures

The thickness of the layers comprising optical structures is usually very thin. When modelling such thin features using a traditional numerical method, for instance the transmission-line modelling (TLM) method, a very small space step is often used to properly discretize the material geometry. This consequently results in large memory storage and longer run time. In this paper a new technique embedding thin structures between TLM nodes is investigated. The key features of this technique are the acquisition of the formulations in the frequency domain and the utilisation of digital filter theory and an inverse Z transform to change the formulations to the time domain. This technique has been successfully applied to calculate the reflection and transmission coefficients of optical structures incorporating thin layers, including antireflection coatings and fibre Bragg grating structures.     

Current status of lightguide component and device technologies in Korea

We review the current state of lightwave component and device technology in South Korea, particularly focusing on the recent progress in research, development and implementation in conjunction with a government programme. The plan for the communications infrastructure is being conducted in three stages. The first stage consists of installation of optical fibre cables interconnecting all the cities in South Korea as well as digitalization of the telecommunications networks by 1997. The second stage (1997 to 2001) will make available optical fibre network for CATV to apartment complexes and densely populated areas to provide the subscribers with multimedia services of the future. The third stage of the plan will start in 2002, and will offer broader applications of B-ISDN for user networks supporting broadband local loop. Along with these major projects, our current activities in the three major areas of optical fibre components and devices, microoptics and integrated optics, and optical fibre sensors are discussed.     

Easily tuneable nonlinear optical loop mirror including low-birefringence,highly twisted fibre with invariant output polarisation

We investigate theoretically the operation of a versatile nonlinear optical loop mirror (NOLM) structure to be used in optical communication systems. The proposed device is a fibre Sagnac interferometer that includes a low-birefringence, highly twisted fibre and a quarter-wave plate retarder in the loop. We study, both analytically and numerically, the evolution of the intensity-dependent NOLM transmission for both output polarisation components, using different models for the NOLM. From this analysis, we propose an easy way to adjust the position of the NOLM maximum transmission, simply by tuning the angle of the retarder. This procedure is particularly useful for amplitude regularisation of an optical signal. We also demonstrate that, if a tuneable optical attenuator is inserted in the loop, the positions of both maximum and minimum transmission can be tuned separately, using a perfectly reproducible procedure. It is therefore possible to optimise the NOLM transmission for both pedestal and amplitude fluctuations removal in an optical pulse train. For a circular input polarisation, this procedure ensures the highest possible contrast between minimum and maximum transmission, and an output polarisation state that is linear and independent of the input power. Finally, we demonstrate that the transmission characteristic of this NOLM is robust to environmentally induced changes in the fibre birefringence. Thanks to its versatility, robustness and polarisation invariance, this device is thought to be of primary interest for applications such as passive mode locking, pulse compression and pedestal suppression, amplitude regularisation in harmonically mode-locked, rational-harmonically mode-locked or subharmonic synchronous mode-locked lasers, as well as damping of relaxation oscillations.     

Photonics applications in switching: An ATM optical node

Abstract

An ATM optical node architecture that carries out cell routing and buffering by photonic means, controlled by electronic circuits, is presented. An evolutionary approach, where cell aggregation and compression are introduced to achieve a large throughput, with a high performance, is also described. And we report experimental results that demonstrate the feasibility of all the relevant photonic functions, based on advanced optoelectronic devices, namely: fast wavelength reassignment, suitable for multigigabit operation, based on fast tunable lasers and semiconductor optical amplifiers; high bit rate packet storage in a multiwavelength fiber loop memory including fast optical gates; dynamic wavelength selection, based on distributed feedback (DFB) filters with nanosecond tuning response; and all optical demultiplexing of multigigabit/s time division multiplexing (TDM) signals by means of saturated semiconductor optical amplifiers.     

Demonstration and characterisation of a non-inverting all-optical read/write regenerative memory

An all-optical regenerative memory device using a single loop mirror and a semiconductor optical amplifier is experimentally demonstrated. This configuration has potential for a low power all-optical stable memory device with non-inverting characteristics where packets are stored by continuously injecting the regenerated data back into the loop.     

Proposal for loadable and erasable optical memory unit based on dual active microring optical integrators

A novel approach for loadable and erasable optical memory unit based on dual microring optical integrators is proposed and studied. The optical integrator, which can generate an optical step function for data storing, is synthesized using active media for loss compensation and a tunable phase shifter for data reading at any time. The input data into the memory is return-to-zero (RZ) signal, and the output data read from the memory is also RZ format with a narrower pulse width. An optical digital register based on the proposed optical memory unit is also investigated and simulated, which shows the potential for large scale data storage and serial-to-parallel data conversion. A great number of such memory units can be densely integrated on a photonic circuit for future large scale data storage and buffer.     

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.     

Quantum memory with optically trapped atoms

We report the experimental demonstration of quantum memory for collective atomic states in a far-detuned optical dipole trap. Generation of the collective atomic state is heralded by the detection of a Raman scattered photon and accompanied by storage in the ensemble of atoms. The optical dipole trap provides confinement for the atoms during the quantum storage while retaining the atomic coherence. We probe the quantum storage by cross correlation of the photon pair arising from the Raman scattering and the retrieval of the atomic state stored in the memory. Nonclassical correlations are observed for storage times up to 60 mus.     

基于有机薄膜晶体管的光写入多级存储器

由于依靠不断缩小存储单元尺寸来提升单位面积存储能力的传统方法将会面临着器件尺寸的物理极限等瓶颈,人们逐渐将目光投向了能够在单一器件上实现高密度存储的多级存储器件。本文利用有机薄膜晶体管中存在的持续光电导率(PPC)效应制备了一个光写入操作的多级存储器件,有效地避免了电写入操作对器件的接触破坏性和较大功耗问题。研究了在不同功率(60,100,150μW/cm²)和不同持续时间(50～1 000 ms)700 nm光写入脉冲作用下的器件存储状态,器件在光功率为60μW/cm²、持续时间为100 ms的光脉冲下展现出了低至0.189 nJ的极低工作功耗。通过对器件施加16个连续光写入脉冲证实器件具有16个有效的存储状态,实现了存储容量为4 bits的多级光写入存储功能。     

High-speed all-optical long-term memory using SOA MZIs: Simulation and experiment

We propose and demonstrate a novel all-optical memory to store high-speed optical data for long term. The key elements of the memory are Mach–Zehnder Interferometers (MZIs) incorporating semiconductor optical amplifiers (SOAs), acting as AND gate and regenerator in a loop configuration. The simulations show that the memory can be operated up to 80 Gb/s. In addition, the memory was demonstrated at 21.3 Gb/s.     

利用光子回声技术对光的相干态进行存储的研究

具备有效存储和读取光的相干态的能力是实现连续变量量子信息存储的关键。本文研究了利用混合光子回声技术对光场的相干态进行存储和读取。光量子态被记录在原子系综的基态的两个相干能级中从而实现长时间的量子态存储。考虑到由于原子退相干的噪声效应,我们发现在目前可实现的技术条件下存储保真度仍然高于保真度阈值2/3。我们的研究为实现高效准确的基于量子回声技术的光量子态存储提供了一些切实可行的实践指导。     

Generation of 207-femtosecond pulses from a ytterbium figure-of-eight fibre laser

We report the generation of 207-fs pulses with 1.2mW average power at 1036nm directly from a passively mode-locked Yb-doped fibre laser with a nonlinear optical loop mirror for mode-locking and pairs of diffraction gratings for intracavity dispersion compensation. These results imply a 4-fold reduction in pulse duration over previously reported figure-of-eight cavity passively mode-locked Yb-doped fibre lasers. Stable pulse trains are produced at the fundamental repetition rate of the resonator, 24.0MHz. On the other hand, this laser offers a cleaner spectrum and greater stability and is completely self-starting.     

Experimental demonstration and cascadability analysis of a tunable optical buffer based on a re-circulating loop consisting of optical SSB modulator and FBG filter

We demonstrate a tunable optical buffer with variable time delays for label switching applications using an optical single sideband modulator in a fiber Bragg grating-filter loop. This optical buffer realizes payload storage with optional wavelength conversion function, providing flexibility in packet router design. Small sensitivity penalty is observed in our experiment after the payload circulating in the buffer loop three times. The cascadability of the tunable optical buffer is investigated. We provide analysis of the optical signal to noise ratio degradation due to accumulated amplified spontaneous emission noise, and the penalty caused by loss ripple and group delay ripple of the fiber Bragg grating.     

Highly nonlinear optical fibre loop mirror for reshaping femtosecond pulses from a soliton-compressed electro-absorption modulator source over a wide repetition rate and wavelength range

Highly nonlinear fibre (HNF) applied to a nonlinear optical fibre-loop mirror (NOLM) proves very effective for high quality femtosecond pulses shaping. The HNF exhibiting about four times larger nonlinearity than either dispersion flattened fibre or dispersion-shifted fibre excites higher-order soliton propagation enabling significant pulse compression, while shortening the loop length required for efficient switching, which advantageously reduces both the detrimental higher-order chromatic dispersion effects and sensitivity to environmental perturbations. A short NOLM consisting of a 60 m HNF demonstrates effective reshaping and compression of 254–394 fs pulses from a fibre-soliton compressed electro-absorption modulator source to produce pedestal-free and transform-limited 186–243 fs pulses over a wide wavelength (1550–1570 nm) and repetition-rate (6.8–18 GHz) range.     

Optical pulse shaping at moderate power using a twisted-fibre NOLM with single output polarisation selection

We demonstrate theoretically and experimentally that efficient signal shaping operation can be obtained at moderate power by using the transmission characteristic of a power-symmetric nonlinear optical loop mirror (NOLM) including highly twisted fibre and operating through nonlinear polarisation rotation, when the circular polarisation state orthogonal to the input polarisation is selected at the NOLM output. By adjusting the angle of the quarter-wave retarder inserted in the loop, the phase bias of the transfer characteristic can be adjusted precisely to enable proper signal shaping for moderate values of input power, remaining well below switching power. The tolerance of the procedure to deviations of the input polarisation from the ideal circular case is investigated numerically. We demonstrate experimentally the capabilities of this setup for both power equalisation and extinction ratio enhancement. Finally, we show that this setup is also useful to shape ultrashort optical pulses from the relaxation oscillations of a DFB semiconductor laser. In comparison with other NOLM-based techniques, the proposed approach allows to reduce by a factor of 8-10 the peak power required for pulse shaping, for the same fibre length and Kerr coefficient.     

Time-domain optical data storage by photon echo

Principles and applications of time-domain optical data storage using stimulated photon echo are briefly reviewed. Special emphasis is laid upon the comparison of this memory with holography; both memories use the interference between two optical waves. Some new experimental developments are introduced using samples of europium-ion-doped crystals, one of the most promising candidates in time-domain data storage. Some other topics, such as ultrafast data storage, time-domain data processing, and time- and spatial-image storage using photon echo, are also discussed.     

冷原子系综中两正交光场偏振模高效率存储的实验研究

高效率光量子信息存储是可扩展光量子信息处理的一个重要工具.本文对一个冷原子系综中两正交光场偏振模的高效率存储进行了实验研究.通过在雪茄型冷原子系统上施加一个中等强度的磁场,消除了原子Zeeman子能级的简并性,从而使磁敏感自旋波从电磁感应透明系统中被移出,由此完成了两正交光场偏振模高效率、长寿命的量子存储.实验测量了两偏振模存储效率与存储时间以及实验重复频率的关系,结果表明,随着重复频率的增加,存储效率逐渐降低,在10 Hz时,测量得到两偏振模存储效率为30%,同时存储寿命达到3 ms.测量结果为偏振纠缠在冷原子系统中的存储提供了重要的实验基础.