Wavelength division multiplexed loop buffer memory based optical packet switch

Photonic all-optical switching is widely considered as one of the technique to utilize the enormous optical bandwidth. Optical packet switching provides high speed, data rate transparency, data format transparency, efficient use of bandwidth and flexibility. To resolve the conflict during contention, packets are needed to be buffered. Due to the lack of optical RAM, fiber delay lines (FDLs) are the most suited option to buffer the packets. This paper proposes new optical packet switch architecture alongwith feedback shared buffer utilizing the advantage of WDM loop buffer memory. The loop buffer module used in this switch architecture is a new approach towards WDM buffering of packets. The mathematical modeling is done to validate the results obtained from simulation.     

AWG and EDFA based optical packet switch using feedback shared loop buffer memory

Optical packet switching provides high speed, data rate/format transparency, efficient use of bandwidth and flexibility. The major problem in the implementation of “all-optical” switching is contention which occurs when two or more packets arrive at the same time for the same destination. To resolve the contention, we have proposed an optical packet switch architecture based on WDM loop buffer memory in the feedback configuration. In that architecture, the contending packets are stored in a loop buffer module, and routed in the free time slots. The buffering duration in the recirculating loop is limited by a circulation limit. The analysis was been done to obtain the maximum number of allowed circulations. This paper proposes improved version of that optical packet switch architecture, to increase the number of maximum allowed circulations. The modification is done either by adding an extra erbium doped fiber amplifier (EDFA) in the original switch or by replacing the core space switch with arrayed waveguide grating (AWG). The performance analysis has been done by the simulations.     

Modeling and design of WDM optical buffers in asynchronous and variable-length optical packet switches

This paper aims to analyze the influence of wavelength conversion on the design of optical fiber delay line (FDL) buffers in a wavelength-division multiplexing (WDM) packet switch. We focus on the network scenario that variable-length packets arrive at the optical switch asynchronously. Through a detailed analysis of the behaviors of packets in the WDM FDL buffer, an approximate analytical traffic model is established. And the theoretical model is proved to be reasonable by simulations. Based on the model, it is clear that, under the same traffic load per wavelength channel, the utilization of tunable wavelength converters (TWCs) to resolve the output contention significantly reduces the number of fiber delay lines (FDLs) in optical buffers, and to achieve a given packet loss probability under a certain number of FDLs, the required number of tunable wavelengths can be predicted. The model can also estimate the optimal value of the basic time unit of the FDLs, and examine the influence of WDM on the optimal value. Finally, the impact of wavelength conversion on the optical switch size is analyzed. To the best of our knowledge, it is the first time that modeling on this problem is presented.     

一种反馈FDL结构竞争解决丢包率的研究

对反馈FDL结构的光分组交换竞争解决方案建立了数学模型并进行了理论分析,推导出了在反馈FDL输入分组比输入光纤输入分组具有更高输出优先级时的系统丢包率公式,对系统丢包率与负载、输入光纤端口数和FDL数目的关系进行了数值计算和讨论.结果表明：由于FDL缓存分组的概率与输入分组负载的非线性关系导致了反馈FDL结构在低负载时对丢包率的改善非常明显,对高负载的改善却十分有限.随着FDL数目的增加,对系统丢包率的改善不会趋于一个极限值,这是与使用波长转换器进行竞争解决的不同之处,因此使用反馈FDL结构可以降低波长转换器的丢包率极限.     

波长转换器和光纤延迟线在WDM光分组交换中的结构设计和性能研究

介绍了两种新颖的光分组交换结构——MOD1和MOD2,用于解决分组冲突问题.其特点在于,MOD1共享了一组非简并的延迟线,而MOD2则是共享了一组简并的延迟线和波长转换器.研究表明,对于非突发业务,两种结构都只需要少量的延迟线即可获得理想的性能.此时,MOD1比MOD2更加能降低系统体积和成本.而对于突发业务,如果MOD1所共享的延迟线数量和MOD2所共享的延迟线和转换器的总数量相等,MOD2的分组丢弃率要远远低于MOD1.随着业务突发程度的增加,MOD2中的转换器数量也需要增加才能维持给定的分组丢弃率,但即使业务突发程度很高,MOD2在体积、成本和性能等三方面均可取得较理想的折衷.     

光纤延迟线和可调谐波长转换器在光分组交换网络竞争解决结构中的性能分析

研究了光分组交换网络中的两种竞争解决方案.结合课题研究的进展,基于突发和非突发业务,对这两种竞争处理结构进行了深入分析,得出了几点重要结论,首先,在竞争处理上,对于非突发业务,光纤延迟线比可调谐波长转换器有效;而对于突发业务而言,可调谐波长转换器比光纤延迟线有效.其次,在突发业务下反馈式光纤延迟线结构（FFA）是一种较为理想的竞争解决结构,但对非突发业务而言,反馈式光纤延迟线和可调谐波长转换器结构（FFTA）在成本上和结构尺寸上比FFA要有效的多.随着平均突发长度的增加,FFTA中的可调谐波长转换器数目也要增加才能获得合理的分组丢失率。但无论是针对突发业务还是非突发业务,FFTA都是一种成本有效的竞争解决结构.     

Large capacity optical router based on arrayed waveguide gratings and optical loop buffer

This paper presents optical packet switch architecture with large buffering capacity for the contention resolution of the packets. The main feature of the architecture is no requirement of Demux/Mux and splitter/combiner which are used in most of the other loop buffer based switch architectures. Therefore physical loss of the architecture is very less, and switch performance is not limited by the physical degradation of the signal. In the buffer, TWCs/SOAs are replaced by Tunable Fiber Bragg Gratings (TFBGs). The use of TFBGs inside the buffer is a novel approach towards buffering structure. The architecture presented here can be modeled as output queue buffer scheme. This paper investigates the advantages of the proposed architecture over the earlier architecture. The performance of the architecture in terms of physical layer parameters (loss analysis, power analysis and noise analysis), packaging volume and optical cost is done.     

High-capacity and security packet switching using the nonlinear effects in micro ring resonators

We propose a new design of secured packet switching generated by using nonlinear behaviors of light in a micro ring resonator. The use of chaotic signals generated by the micro ring resonator to form the filtering and packet switching characteristics is described, where the high-capacity and security switching using such form is presented. The key advantage is that the high capacity of communication data can be secured in the transmission link, where the nonlinear penalty of light traveling in the device is beneficial. For instance, the required information can be transmitted and retrieved by using the proposed packet switching scheme. In principle, the chaotic signals are generated by a Kerr effects nonlinear type of light in a micro ring resonator, where the control input power can be specified by the required output filtering signals. The ring radii used range between 10 and 20 μm, κ=0.0225, α=0.5 dB and n₂=2.2×10⁻¹⁵ m²/W. Simulation results obtained have been described based on the practical device parameters. Three forms of the applications have been simulated, the potential of using for the tunable band pass and band stop filters, in which high-capacity packet switching data can be performed, and the fs switching time is plausible.     

Anisotropic nonlinear optical absorption of gold nanorods in a silica matrix

Nanocomposite films consisting of gold nanospheres or gold nanorods embedded in a silica matrix have been prepared using a hybrid deposition technique consisting of plasma-enhanced chemical vapor deposition of SiO₂ and co-sputtering of gold, followed by annealing at 900 °C. Subsequent irradiation with 30 MeV heavy ions (Cu⁵⁺) was used to form gold nanorods. Linear and nonlinear optical properties of this material are closely related with the surface plasmon resonance in the visible. The nonlinear absorption coefficient (α₂@532 nm) for the films containing gold nanospheres was measured by Z-scan and P-scan techniques, and it was found to be isotropic and equal to −4.8 × 10⁻² cm/W. On the contrary, gold nanorods films exhibited two distinct surface plasmon resonance absorption bands giving rise to a strong anisotropic behavior, namely a polarization-dependent linear absorption and saturable absorption. Z-scan and P-scan measurements using various light polarization directions yielded nonlinear absorption coefficient (α₂@532 nm) values varying from −0.9 × 10⁻² cm/W up to −3.0 × 10⁻² cm/W. Linearity of the P-scan method in the context of nanocomposite saturable absorption is also discussed.     

Optimal design of 32 channels spectrum slicing WDM for optical fiber access network system

In this article, the spectrum sliced dense wavelength division multiplexed passive optical network (SS-DWDM–PON) has been investigated as a power efficient and cost effective solution for optical access networks. In this work an AWG demultiplexer is used to operate as slicing system. The high speed SS-DWDM system has been realized and investigated for 32 channels with data rate up to 3 Gb/s using broadband ASE source (LED). The 3 Gb/s signals both non-return-to-zero (NRZ) and return-to-zero (RZ) were demonstrated in 40 km optical fiber link with BER < 10⁻¹². The results obtained here demonstrate that SS-DWDM is well suited for Fiber-to-the-Home (FTTH) network.     

Giga-bit optical receiver for plastic optical fibre

An optical receiver with high sensitivity and linearity specially designed for Giga-bit communications over small-bandwidth high-attenuation multimode plastic optical fiber is presented. An automatic gain control transimpedance amplifier and linear post amplifiers are used to maintain a good performance with multilevel modulation. Using multilevel signaling and large-diameter integrated photodiodes make the presented optical receiver suitable for large core plastic optical fiber. For a wavelength of 675 nm, a sensitivity of −26.3 dB m (BER = 10⁻⁹) at 500 Mb/s is presented by a binary signal. A data rate of 1 Gb/s and a sensitivity of −19.8 dB m (BER = 10⁻⁹) are achieved with four-level pulse amplitude modulation.     

Polarization maintaining large nonlinear coefficient photonic crystal fibers using rotational hybrid cladding

In this paper, we present and explore a new hybrid cladding design for improved birefringence and highly nonlinear photonic crystal fibers (PCFs) in a broad range of wavelength bands. The birefringence of the fundamental mode in such a PCF is numerically analyzed using the finite element method (FEM). It is demonstrated that it is possible to design a simple highly nonlinear hybrid PCF (HyPCF) with a nonlinear coefficient of the about 46 W⁻¹ km⁻¹ at a 1.55 μm wavelength. According to simulation, the highest modal birefringence and lowest confinement loss of our proposed structure at the excitation wavelength of λ = 1.55 μm can be achieved at a magnitude of 1.77 × 10⁻² and of the order less than 10² dB/km with only five rings of air-holes in the fiber cladding.     

Characterization of hybrid electrolytes prepared from the Li2S-P2S5 glasses and alkanediols

Inorganic-organic hybrid electrolytes were prepared by the mechanochemical method using the Li⁺ ion conductive 70Li₂S·30P₂S₅ glass and various alkanediols. Local structure of the prepared electrolytes was analyzed by FT-IR and Raman spectroscopy. The effects of the proportion and chain length of alkanediols on conductivity of the hybrid electrolytes were investigated. The hybrid electrolyte with 2 mol.% of 1,4-butanediol exhibited the conductivity of 9.7 × 10^− 5 S cm^− 1 at room temperature and the unity of lithium ion transference number. The use of alkanediols with shorter chain length was effective in increasing conductivity of hybrid electrolytes. The electrolyte using ethyleneglycol showed the highest conductivity of 1.1 × 10^− 4 S cm^− 1 at room temperature. Lowering glass transition temperature by incorporation of alkanediols is responsible for the enhancement of conductivity of hybrid electrolytes.     

CdSe quantum dots decorated by mercaptosuccinic acid as fluorescence probe for Cu

Water-soluble CdSe quantum dots (QDs) were synthesized using mercaptosuccinic acid (MSA) as a stabilizer. The growth process and characterization of CdSe quantum dots were determined by transmission electron microscopy (TEM), X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, Ultraviolet-visible (UV-vis) spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy. Results demonstrated the MSA-capped CdSe QDs were highly crystalline and possessed good optical properties. Further, the resulting products could be used as fluorescent probes to detect Cu²⁺ ions in physiological buffer solution. The response was linearly proportional to the concentration of Cu²⁺ ion in the range 2×10⁻⁸- 3.5×10⁻⁷ mol L⁻¹ with a detection limit of 3.4 nmol L⁻¹.     

High birefringence and low loss circular air-holes photonic crystal fiber using complex unit cells in cladding

We propose a high birefringence and low loss index-guiding photonic crystal fiber (PCF) using the complex unit cells in cladding by the finite-element method. Results show that the birefringence and confinement loss in such PCF fiber is determined not only by the whole cladding asymmetry but also the shape of the PCF core. The maximal modal birefringence and lowest confinement loss of our proposed structures at the excitation wavelength of λ = 1550 nm can be achieved at 8.7 × 10⁻³ and 5.27 × 10⁻⁵ dB/km, respectively.     

A novel dispersion-shifted single mode optical fiber design with ultra-high-bit-rate and very low loss for long-haul communications

In this paper, a novel dispersion-shifted multi-clad optical fiber with very small bending loss and ultra-high bit-rate applicable for large capacity information transmission systems is presented. To decrease dispersion and higher-order dispersion effects at λ = 1.55 μm, a weighted pulse broadening factor and genetic algorithm (GA) optimization technique is used. Compared to the works reported previously, this method can precisely set the zero-dispersion wavelength. This kind of dispersion-shifted fibers has dispersion, dispersion slope, mode field diameter (MFD), effective area and quality factor within −1.40 × 10⁻⁴ to −8.44 × 10⁻² ps/km nm, 3.06 × 10⁻² to −4.07 × 10⁻² ps/km nm², 5.56−5.85 μm, 119.25−176.42 μm² and 3.49-5.27 at λ = 1.55 μm, respectively. Besides, by applying dispersion at λ = 1.55 μm as the cost function, dispersion of about 1.31 × 10⁻⁸ ps/km nm is obtained. Thus, this novel optical fiber can be used in long-haul high information-transmission capacity communication systems.     

χ measurement and optical limiting studies of urea picrate

The molecular charge complex urea picrate (UP) was synthesized and its third order nonlinear optical properties have been investigated using a single beam Z-scan technique with nanosecond laser pulses at 532 nm. Open aperture data of the compound indicates two photon absorption at this wavelength. The nonlinear refractive index n₂, nonlinear absorption coefficient β, magnitude of effective third order susceptibility χ⁽³⁾, the second order hyperpolarizability γ_h and the coupling factor ρ have been estimated. The experimentally determined values of β, n₂, Re χ⁽³⁾ and Im χ⁽³⁾, γ_h and ρ of the compound UP are 2.146 cm/GW, −1.258×10⁻¹¹ esu, −1.347×10⁻¹³ esu, 0.377×10⁻¹³ esu, 0.69×10⁻³² esu and 0.28, respectively. The compound exhibits good optical limiting at 532 nm with the limiting threshold of 80 μJ/pulse. Our studies suggest that compound UP is a potential candidate for optical device applications such as optical limiters.     

Single beam Z-scan measurement of the third order optical nonlinearities of styryl7 dye

The optical nonlinearity of styryl7 dye in ethanol solution at different concentrations has been studied using pulsed Nd:YAG laser at 532 nm as the source of excitation. The optical responses were characterized by measuring the intensity dependent refractive index (n₂) of the medium using the Z-scan technique. The open aperture Z-scan trace of the dye in solution displayed saturable absorption. The closed aperture Z-scan trace of the dye exhibited a negative nonlinearity. The styryl7 dye at 1 mM concentration exhibited nonlinear refractive co-efficient n₂ = −1.24 × 10⁻⁸ cm²/W, nonlinear absorption coefficient β = − 3.9 × 10⁻⁴ cm/W and real and imaginary parts of third-order nonlinear optical susceptibility χ³ = 3.26 × 10⁻⁶ esu in ethanol. These results showed that the dye has potential application in nonlinear optics.     

Effects of swift heavy ion irradiation on the electrical characteristics of Au/n-GaAs Schottky diodes

Metal-semiconductor diode of Au/n-GaAs is studied under the irradiation of swift heavy ion (SHI) beam (80 MeV ¹⁶O⁶⁺), using in situ current-voltage characterization technique. The diode parameters like ideality factor, barrier height, and leakage current are observed to vary with irradiation fluence. Significantly, the diode performance improves at a high fluence of 2 × 10¹³ ions cm⁻² with a large decrease of reverse leakage current in comparison to the original as deposited sample. The Schottky barrier height (SBH) also increases with fluence. At a high irradiation fluence of 5 × 10¹³ ions cm⁻² the SBH (0.62 ± 0.01 eV) is much larger than that of the as deposited sample (0.55 ± 0.01 eV). The diode parameters remain stable over a large range of irradiation up to fluence of 8 × 10¹³ ions cm⁻². A prominent annealing effect of the swift ion beam owing to moderate electronic excitation and high ratio of electronic energy loss to the nuclear loss is found to be responsible for the improvement in diode characteristics.     

Holographic properties of Fe3O4 nanoparticle-doped organic–inorganic hybrid photopolymer

An organic–inorganic hybrid photopolymer doped with sodium-citrate-coated Fe₃O₄ nanoparticles was fabricated. The experimental results showed that the maximum diffraction efficiency could be increased from 69 to 90%, and the maximum refractive index modulation improved from 1.386 × 10⁻³ to 2.083 × 10⁻³. It also found that the volume shrinkage during holographic exposure was noticeably suppressed without affecting the optical quality of the photopolymer.