A new alternative approach of all optical frequency encoded clocked S-R flip-flop exploiting the non-linear character of semiconductor optical amplifiers

In all optical networking and computing system, the role of all-optical flip-flops is very much essential. For signal synchronization with a reference clock and for storage of digital bits the flip-flop has no alternative. In this communication the authors propose a method of developing an all optical frequency encoded clocked R-S flip-flop using the non-linear character of semiconductor optical amplifiers. Frequency is the basic character of light and several encoding/decoding problems in computations and communications can be solved using the frequency encoding principle of optical data. The proposed system is all-optical and therefore it can extend a super fast speed of operation (far above THz limit).     

Optical properties of microcavity polaritons

This work contains a theoretical analysis of the optical properties of semiconductor quantum wells embedded in planar Fabry-Perot microcavities. In particular, the properties of the system in correspondence to the excitonic transition are studied by means of the polariton formalism. The polariton states in microcavities are derived and the polar-iton dispersion is presented. Particular emphasis is put on the existence of two well distinct regimes depending on the exciton and cavity parameters: strong coupling and weak coupling regime. The main experimental results are reviewed and compared with the prediction of the theory. After the polariton states have been characterized, the optical response of the system is discussed, with particular attention to the photoluminescence measurements. The polariton formation and relaxation through phonon scattering and the effect of the exciton inhomogeneous broadening are considered and, finally, a phe-nomenological model for the polariton photoluminescence spectra is presented.     

Alternating approach of implementing frequency encoded all-optical logic gates and flip-flop using semiconductor optical amplifier

In conduction of parallel logic, arithmetic and algebraic operations, optics has already proved its successful role. Since last few decades a number of established methods on optical data processing were proposed and to implement such processors different data encoding/decoding techniques have also been reported. Currently frequency encoding technique is found be a promising as well as a faithful mechanism for the conversion of all-optical processing as the frequency of light remains unaltered after refection, refraction, absorption, etc. during the transmission of light. There are already proposed some frequency encoded optical logic gates. In this communication the authors propose a new and different concept of frequency encoded optical logic gates and optical flip-flop using the non-linear function of semiconductor optical amplifier.     

Photoinduced non-linear optical diagnostic of InI ferroelastic nanocrystals

Photoinduced second harmonic generation was established in the centrosymmetric layered crystals of InI. The effect was grounded on occurrence of photoinduced optical second harmonic generation in the ferroelastic phase of the InI crystals. As a subject of investigations layered ferroelastic crystal of InI was chosen. It was found that the ferroelastic phase disappears during decrease of the nanolayers from 15 nm up to 6 nm. Such effects are explained by occurrence of anharmonic phonon modes confined by the walls of the layered crystals. We have found that the effect may be of importance for the further investigations of the layered nanocrystals. At the same time the giant value of the photoinduced SHG indicates on a possible using the nanolayered crystals like promising non-linear optical crystals.     

Full-vectorial analysis of optical vortex propagation in anisotropic cubic-quintic non-linear optical medium

This paper presents for the first time a full-vectorial analysis of optical vortex propagation in anisotropic cubic-quintic (CQ) non-linear medium. The purpose is to investigate the energy transfer mechanism and stability between orthogonal field components and how they are affected by the presence of material anisotropy in CQ materials. The numerical simulations were carried out via a three-dimensional finite difference based beam propagation method (3D-FD-BPM) which is capable of handling variations in any of the permittivity tensor components. Therefore, in this work we allowed all tensor components to vary independently and simulate vortex propagation for distances several times longer than the diffraction length. We expect that this work can provide new and important information regarding the behavior of these objects that may become valuable for the design of new photonic devices.     

A method of optical implementation of frequency encoded different logic operations using second harmonic and difference frequency generation techniques in non-linear material

Optics has already been proved its successful roles for conduction of parallel logic, arithmetic and algebraic operations. Since last few decades many types of optical data processors were proposed. To implement these processors different data encoding/decoding techniques have been reported. In this context polarization encoding technique, tristate, quartenary logic, multivalued logic, symbolic substitution techniques etc. may be mentioned. Very recently, frequency encoding/decoding technique have also been well established. The potential advantage of frequency dependent encoding/decoding is that, as the frequency being the fundamental character of a signal; it will remain unaltered in reflection, refraction, absorption etc. during transmission of the signal. In this communication the authors propose a scheme for implementing different logic operations adopting frequency based encoding technique. For this purpose the second harmonic generation and difference frequency generation techniques are used by exploiting the non-linear response character of some materials.     

微盘腔垂直耦合器特性的拓展分析

利用垂直于微盘腔边界的波导与腔耦合是一种新开发的耦合技术. 采用有限元数值模拟方法对垂直耦合器的腔尺寸适应性、波长适应性和端口扩展性做出详细分析. 结果证实: 垂直耦合器在大尺寸腔中或者多个波段均有效; 并且多个垂直耦合器可以和同一盘腔交换能量, 实现滤波、分束、光路交叉的功能. 垂直耦合器在以微腔为元件的集成光路中的应用将使材料选取和光路排布更为灵活. 关键词： 微纳光学 微腔 回音壁模式 垂直耦合器     

Numerical study of an optical regenerator exploiting self-phase modulation and spectral offset filtering at 40 Gbit/s

In this work, we numerically investigate the performances of optical regenerators based on self-phase modulation and spectral offset filtering at 40 Gbit/s. We outline the different effects affecting the device performances and explain the choice of the optimal working power. The impact of the regenerator on the output signal is also analysed through a statistical approach. Both single- and double-stage configurations are investigated.     

Polarization selection rules in scattering of cavity polaritons

We theoretically discuss scattering of polaritons in semiconductor microcavities by means of a microscopic model. Taking into account the composite character of excitons (formed by an electron and a hole), we analyze the relation between polarizations of incoming and outgoing polariton states under resonant excitation by linearly polarized laser beams with opposite in-plane momenta. In addition to these polarization selection rules, we investigate the nonlinear processes up to the sixth order and we show the origin of an induced anisotropy due to the excitation beams which is responsible for the operation of an optical gate based on polariton–polariton scattering in a microcavity.     

表面等离子体波在金属纳米缝超强透射中的作用(英文)

A single metallic nanoslit is employed for investigating the contribution of Surface Plasmon Polaritons(SPPs) to Extraordinary Optical Transmission(EOT) based on rigorous electromagnetic theory and the Spectrum Analysis Method(SAM). Numerical results shows that the SPP is the main factor responsible for the EOT, and a phase singularity is observed.     

表面等离子体波在金属纳米缝超强透射中的作用

A single metallic nanoslit is employed for investigating the contribution of Surface Plasmon Polaritons（SPPs） to Extraordinary Optical Transmission （EOT） based on rigorous electromagnetic theory and the Spectrum Analysis Method （SAM）. Numerical results shows that the SPP is the main factor responsible for the EOT, and a phase singularity is observed.     

Proposal for loss reduction and output enhancement of silicon Raman laser using bi-directional pumping scheme

Based on a novel loss analysis, we numerically demonstrate that bi-directional pumping scheme is an effective technique to achieve loss reduction and maximum output power enhancement in silicon Raman laser. We then investigate the influence of cavity end-facet reflectivity under the bi-directional pumping scheme. Low end-facet reflectivity cavity simultaneously maximizes the output power and enhancement effect of bi-directional pumping, resulting in a fully optimized peak Stokes output.     

Longitudinal mode competition in semiconductor lasers under optical feedback: Regime of short-external cavity

This paper introduces a theoretical study of longitudinal mode competition in semiconductor lasers subject to optical feedback. The study is based on a model of time-delay multimode rate equations taking into account both symmetric and asymmetric suppressions of modal gain. The model is numerically solved and applied to the case of a short-external cavity. Mode competition is characterized along the feedback-induced period-doubling route to chaos as well as under chaotic dynamics. Contributions of symmetric and asymmetric gain suppressions to both mode dynamics and modal operation under OFB are clarified. The results show that under chaotic dynamics, mode competition induces multimode hopping giving rise to asymmetric multimode output spectra. In regimes of continuous-wave operation, mode competition supports single-mode oscillation, and the side-mode suppression ratio improves with the increase of feedback. In the regime of strong feedback, the lasing mode moves to either long- or short-wavelength side in a seemingly random fashion, which is strongly related to asymmetric gain suppression.     

两种谐振腔长度的微腔有机电致发光器件模拟

微腔的谐振腔长度直接影响微腔有机电致发光器件(MOLED)的发光特性,根据微腔器件的相关计算公式运用传输矩阵法,分别对微腔长度L=λ/2和L=λ(λ:中心波长)时,在微腔内不同位置激子复合发光的电致发光谱(EL)进行模拟计算和比较。发现:微腔长度为L=λ/2时,峰值均为520nm,半峰全宽均为17nm,激子处在微腔的中心位置时,峰值强度和积分强度均为最大。L=λ时,激子在腔内不同位置时,峰值均为520nm,半峰全宽均12nm,在腔的中心区域时,与L=λ/2时正好相反,峰值强度和积分强度最小。分析后判断是因为两种长度的微腔内电场强度分布不同,激子位于腔内电场的最大值处发光性能最好。说明要制作出高效率的MOLED,要区别不同谐振腔长度,并使激子处于腔内电场最大处。     

The non-linear refractive index of colloidal PbSe nanocrystals: Spectroscopy and saturation behaviour

A spectroscopic study of the optical non-linearities of PbSe colloidal solutions was performed with the Z-scan technique, at wavelengths between 1200 and 1750 nm. No non-linear absorption is observed, while the third-order non-linear refractive index n₂ shows clear resonances, somewhat blueshifted relative to the exciton transitions in the absorbance spectrum. The occurrence of thermal effects is ruled out by time-resolved measurements. At resonance, measured n₂ values exceed typical bulk semiconductor values by two orders of magnitude. At high optical intensity, the refractive index change saturates, indicating that state filling lies at the origin of the observed effect.     

Dielectric,ferroelectric and non-linear optical behavior of crystalline erbium tartrate dihydrate

The dielectric, ferroelectric and non-linear optical behavior of erbium tartrate dihydrate crystals is studied. The dielectric constant has been measured as a function of temperature and frequency. The crystals of erbium tartrate dihydrate show an anomalous dielectric behavior as a function of temperature: the dielectric constant increases with temperature, attains a peak around 235 °C and then decreases as the temperature goes beyond 235 °C. The dielectric anomaly at 235 °C is suggested to be due to ferroelectric phase transition brought about in the material. The experiment on polarization versus electric field shows a hysteresis loop thereby establishing the ferroelectric nature of erbium tartrate dihydrate. The results of thermal study show that the material is thermally stable up to a temperature of about 240 °C. The non-linear optical study shows that erbium tartrate dihydrate has second harmonic generation efficiency comparable to that of potassium dihydrogen phosphate (KDP).     

Optical limiting behavior of new fullerene derivatives

The optical limiting behavior of C₆₀Ph₅Cl, C₆₀Cl₆, and C₇₀Cl₁₀ in toluene solution has been measured at 532 nm with nanosecond pulses. The limiting threshold for C₆₀Ph₅Cl, C₆₀Cl₆, and C₇₀Cl₁₀ were 4, 8, and 8 J/cm², respectively. The limiting action was strongly influenced by the number of conjugated double bonds and the nature of the ligand. Both lower limiting thresholds and throughputs make these new fullerene derivative compounds good promising candidates for optical limiting materials in the toluene solution.     

静压下半导体微腔内激子与光子行为的研究

由于腔模与激子对压力的依赖关系不同,所以可以选择不同的压力使激子和光场处于不同的耦合状态,从而实现对耦合的调谐。利用这种办法,我们观测到了代表激子与光场强耦合作用的Rabi分裂。由于在我们现有样品结构中压力对激子本征行为的影响很小,与以前报道的温度、电场等调谐方式相比,这种调谐方法不仅可以有效地调谐半导体微腔内激子与腔模的耦合程度,而且能够保持激子的本征性质在整个调谐过程中基本不变。这有助于研究在强耦合过程中激子极化激元的本征性质。将实验结果与压力下激子与腔模耦合理论进行拟合,得出了正确的Rabi分裂值。     

Temperature dependence of symmetric and asymmetric structured Au stripe waveguides

The thermal effects on pigtailed 22-nm-thick, 5-μm-wide and 1-cm-long Au stripe long-range surface plasmon polariton (LRSPP) waveguides, embedded in polymer/polymer layers and in polymer/silica layers, are theoretically and experimentally demonstrated. The polymer and silica cladding layers have thermo-optic coefficients of opposite signs. As the temperature varies the Au stripe LRSPP waveguide embedded in the polymer/polymer layers retains its symmetry in the refractive index, but that embedded in the polymer/silica layers becomes asymmetric in the refractive index. The thermal sensitivity in the optical output power of the symmetric structure is smaller than 0.02 dB/°C but the sensitivity of the asymmetric structure is ∼ 0.3 dB/°C. These structures open up potential applications of the LRSPP waveguides for temperature independent/dependent photonic devices.