Limitations Due to Er-Doped Optical Amplifier Noise and Stimulated Raman Scattering in Optic-Frequency Division Multiplexed Communications

In this paper, system limitations of an optic-frequency division multiplexed commu nication link are evaluated due to stimulated Raman scattering and noise in erbium-doped optical fiber amplifiers. It is shown that the product of the number of optical amplifiers and the gain (i.e., total gain) are limited by a factor that depends upon the number of channels, channel spacing and required signal-to-noise ratio (bit-error-rate), etc. Thus an indefinite increase in the number of amplifiers and or amplifier gain may not extend the repeaterless distance significantly while keeping the bit-error-rate above a minimum level. Numerical results show that appropriate choice of optical amplifier gain can improve the bit-error-rate of the worst effected channel without adding significant requirements on the receiver. However, large changes in the amplifier gain cannot be allowed if the receiver dynamic range is to be kept small.     

All optical frequency encoding method for converting a decimal number to its equivalent binary number using tree architecture

In any kind of computing and data processing system the use of binary numbers are found very much suitable and reliable. On the other hand several natural representations have been realized using decimal numbers. So conversion of a decimal number to its binary equivalent and vise-versa are of great importance in the field of computation technology. There lie already a number of established methods regarding such conversion processes. Again optical tree architecture is one of the most promising systems for realizing the optical conversion of any decimal number to its equivalent binary. Here in this communication the authors propose a new method for optical conversion of a decimal number to its binary equivalent using tree architecture based system and frequency encoding principle. In frequency encoding system, frequency of light is used for encoding of decimal digits or binary bits instead of intensity variation. For example 0 and 1 bits of binary number are coded by two different frequencies of light signal, instead of representing the presence of light as 1 and absence by 0. The proposed conversion process has multifaceted advantages in communication, as well as in data processing. To implement the above conversion some characteristic features of semiconductor optical amplifier (SOA) have been used massively. The wavelength conversion property, cross gain modulation and some nonlinear properties of SOA are exploited to get the frequency encoded response. The proposed system carries all the basic advantages of optical processing as well as those of frequency encoding also.     

微弱光学图像的光参量放大特性的研究

研究了微弱光学图像在光参量图像放大中的放大特性,分析了相位匹配和晶体的空间频率带宽对图像信号增益的影响,从实验上验证了不同的相位匹配时输入图像信号在傅里叶平面上的增益分布.结果表明,当晶体的空间频率带宽大于输入图像信号的空间频率带宽且完全相位匹配时,光参量图像放大器能够对输入图像信号实现无失真、高增益的理想放大;有相位失配时,图像信号的增益峰值向高空间频率范围移动,并且在峰值附近范围变窄,随相位失配量大小的变化能够对图像信号光场中某特定空间频率实现放大,对图像信号进行滤波处理,突出图像特定频率的信息,实现图像边缘增强.     

用楔形柱面光纤微透镜耦合的1.3μm SOA组件

运用激光模式耦合理论分析了半导体光放大器(SOA)与单模通信光纤的连接损耗,并设计制作了楔形柱面光纤微透镜用来实现两者的模斑匹配,有效地降低了器件的光耦合损耗.本文介绍了楔形柱面光纤微透镜耦合的1.3 μm半导体光放大器(SOA)组件及其制作方法.该组件的最大增益不小于14 dB,其偏振灵敏度小于1 dB,增益波动不大于0.5 dB.     

Optical arithmetic unit using bit-WDM

A novel arithmetic unit is proposed consisting of a pipelined optical ripple carry adder that adds two words with bits multiplexed by different wavelengths on a single fiber. The addition result is returned to a fiber bus in the same format as the incoming words. The corresponding operand bit pairs are split off the fiber using wavelength division demultiplexers. Full adders compute the sum for each bit pair and the carry from the next lower significant bit pair. The full adder uses couplers and NOT, NOR and novel XOR logic gates constructed using semiconductor optical amplifiers for gain and wavelength shifting.     

Intensity modulation and multi modes hopping induced by phase change in external cavity Nd:YAG lasers

Intensity modulation and multi modes hopping in Nd:YAG lasers subjected to optical feedback have been studied experimentally and theoretically. Their dependence on the external-cavity-phase has been studied. The results are compared with the predictions of the model of threshold gain modulation. As the initial length of external cavity is changed the number of hopping modes also changes.     

Analysis of Wavelength-Routed Optical Burst-Switched Network Performance

This paper studies a novel scalable network architecture combining optical burst switching (OBS) with dynamic wavelength allocation to guarantee quality of service (QoS), forming a wavelength-routed optical burst-switched network. All processing and buffering functions are concentrated at the network edge and bursts are assigned to fast tuneable lasers and routed over a bufferless optical transport core using dynamic wavelength assignment. Different burst aggregation mechanisms are evaluated for a range of traffic statistics in terms of delay and packet loss rate. New network performance parameters in an analytical model quantify the advantages of dynamic wavelength allocation. The results define the operational gain achievable with dynamic wavelength assignment compared to quasi-static wavelength routed optical networks.     

Analysis of Wavelength-Routed Optical Burst-Switched Network Performance

This paper studies a novel scalable network architecture combining optical burst switching (OBS) with dynamic wavelength allocation to guarantee quality of service (QoS), forming a wavelength-routed optical burst-switched network. All processing and buffering functions are concentrated at the network edge and bursts are assigned to fast tuneable lasers and routed over a bufferless optical transport core using dynamic wavelength assignment. Different burst aggregation mechanisms are evaluated for a range of traffic statistics in terms of delay and packet loss rate. New network performance parameters in an analytical model quantify the advantages of dynamic wavelength allocation. The results define the operational gain achievable with dynamic wavelength assignment compared to quasi-static wavelength routed optical networks.     

基于垂直谐振腔结构的半导体光放大器理论分析

由新型垂直腔半导体光放大器（VCSOAs）器件结构出发,在反射模式和透射模式两种 情况下,计算了VCSOAs的分布布拉格反射堆（DBR）反射率、单程增益与增益、带宽的关系 ,其中DBR反射率的增大伴随着增益的上升,但也伴随着带宽的减小.通过引入增益-带宽 积的概念,以均衡增益与带宽.计算中表明:10 dB以上增益,50 GHz以上带宽可以实现. 计算结果与文献实验相吻合,对优化VCSOAs的结构设计和性能有所裨益.     

光纤参量放大饱和增益特性研究

通过数值分析的方法推导出光纤参量放大饱和信号增益和信号输出功率的数学表达式.计算分三步, 首先数值求解描述参量放大过程的非线性耦合方程得出一系列数值, 然后用控制变量法找到饱和信号增益的函数形式, 最后用最小二乘法拟合出系数（与数字积分结果比较, 最大相对误差不超过0.46‰）.同样也得出了饱和信号输出功率的表达式.计算结果与已有实验结果相吻合.     

Design and performance analysis of various one dimensional codes using different data formats for OCDMA system

In this paper, the design, implementation and performance analysis of various one dimensional codes in an OCDMA system for different data formats is presented. A number of different codes are used with optical CDMA to improve its error performance. Here, three such codes, optical orthogonal codes (OOC), Walsh Hadamard codes and zero cross-correlation (ZCC) codes have been compared using different data formats, NRZ raised cosine, NRZ rectangular, RZ raised cosine and RZ rectangular. It is found that NRZ raised cosine has the best system performance for all the codes used. After that, the three codes have been compared in terms of the BER, eye diagrams and received optical power using NRZ raised cosine modulation format. It is analyzed that ZCC codes have zero cross-correlation property. The simulation results revealed that ZCC codes can provide a better BER compared to the OOC and Walsh Hadamard codes and it is most suitable to be employed in the OCDMA systems.     

Radiative properties of optical board embedded with optical black holes

Unique radiative properties, such as wavelength-selective transmission or absorption, have been intensively studied. Historically, geometries for wavelength-selective of light absorption were developed based on metallic periodical structures, which were only applied in the case of TM wave incidence due to the excitation of surface plasmons. In this paper, we develop an alternative approach to selective wavelength of light absorption (both TE and TM waves), based on an optical board periodical embedded with optical black holes. Numerical work was carried out to study such structure’s radiative properties within the wavelength range of 1-100 μm. The electromagnetic wave transmission through such a structure is predicted by solving Maxwell’s equations using the finite-difference time-domain (FDTD) method. Spectral absorptance varies with the period of optical black holes. When the incidence wavelength is much larger than the inner core radius, most of the light energy will be transmitted through the inner core. Otherwise, the energy will be mainly absorbed. Numerical results of the radiative properties of the optical board with different incidence wavelengths are also obtained. The effect of the oblique incidence wave is investigated. This study helps us gain a better understanding of the radiative properties of an optical board embedded with optical black holes and develop an alternative approach to selective light absorption.     

双波长全光自动增益箝制掺铒光纤放大器的实验研究

提出了结构简单的光纤布喇格光栅（FBG）双波长全光自动增益箝制方案,并进行了相关实验.结果表明,在三种不同的箝制波长组合1535.64nm+1562.68nm、1530.48nm+1562.68nm、1530.48 nm+1551.36 nm条件下,1540 nm信号的输出增益大小和输入信号功率动态范围几乎一致.对应此三种箝制波长组合,环路内的损耗分别为：14.7 dB、15 dB、15 dB.由此证明,在相同泵浦条件和环路损耗条件下,此三种不同箝制波长组合具有近似相同的箝制效果.而1551.36 nm+1562.68 nm箝制波长组合得到的结果相差甚远.此结果说明,在设计双波长全光自动增益箝制掺铒光纤放大器（OAGC-EDFA）时,为了取得足够大的信号增益,两箝制波长的波长间隔应尽量较大.     

A novel all-optical label processing based on multiple optical orthogonal codes sequences for optical packet switching networks

This paper proposes an all-optical label processing scheme that uses the multiple optical orthogonal codes sequences (MOOCS)-based optical label for optical packet switching (OPS) (MOOCS-OPS) networks. In this scheme, each MOOCS is a permutation or combination of the multiple optical orthogonal codes (MOOC) selected from the multiple-groups optical orthogonal codes (MGOOC). Following a comparison of different optical label processing (OLP) schemes, the principles of MOOCS-OPS network are given and analyzed. Firstly, theoretical analyses are used to prove that MOOCS is able to greatly enlarge the number of available optical labels when compared to the previous single optical orthogonal code (SOOC) for OPS (SOOC-OPS) network. Then, the key units of the MOOCS-based optical label packets, including optical packet generation, optical label erasing, optical label extraction and optical label rewriting etc., are given and studied. These results are used to verify that the proposed MOOCS-OPS scheme is feasible.     

氧碘化学激光中的增益光导效应

 发现和分析了氧碘化学激光中的增益光导效应。碘注入的不均匀等导致增益在该方向的不均匀。采用预混模型和Fabry Perot腔模型，推导了碘不均匀分布情况下的单重态氧的产额和激光束横向分布的解析表达式。计算结果表明，由于增益光导效应，引起激光横向分布的变化，可导致光束在碘注入方向的倾斜，以及输出功率的下降。     

Separation of label and payload using FP-SOA

A novel scheme of separating the label and payload with different pulse width by using FP-SOA is proposed in this paper. Due to the facet reflectivity of FP-SOA, the gain is rippled with the variation of carrier density and the opposite characteristics of gain and carrier density appear at either side of the gain peak. Since the different pulse widths deplete different number of carriers, the working region in carrier density shifts adaptively with the pulse width. The wide pulse label extraction can be performed in the region where the gain decreases with the increment of carrier density. The label suppression can be realized in another region where the gain increases with increment of carrier density. The numerical simulation shows that the label extraction with 10.5 dB contrast ratio and the label suppression with 7 dB. The application in 10 Gb/s optical packet switching is discussed. The relationship of the pulse peak gain and pulse width is investigated on considering the impact of the pulse peak power and pulse period.     

A clustered speckle approach to optical trapping

An in situ study of the clustered speckle 3D structure using an optical tweezer setup is presented. Clustered speckles appear when a coherently illuminated diffuser is imaged through a pupil mask with several apertures, properly distributed over a closed path, which is placed before the objective lens of a standard optical trapping system. Thus, light volumes are reduced several times when compared with standard speckles, being even smaller than the focus volume of a Gaussian beam commonly used to trap. Moreover, clustered speckles have odd statistical properties which differentiated it from standard speckles. Then, geometrically ordered multiple trapping arrays, with statistical random distribution of intensities, can be created with this technique. This fact could enable different studies concerning optical binding or new developments in coherent matter wave transport where Optical Trapping has been proven with standard speckles. In this work, a qualitative analysis of clustered speckles in an optical tweezer setup relative to the number of apertures in the mask and their size is carried on. Besides, in the Rayleigh regime, a general quantitative method to characterize the trapping capability of an optical field is proposed. Then, it is applied to clustered speckles. As a result, a relation between aperture size and the maximum size of the particles that could be trapped is found. This fact opens the possibility of engineering the statistic of the trapped particles by properly selecting the pupil mask.     

Optical transitions in CdSe quantum dots: From discrete levels to broad gain spectra

The optical transition energies have been determined for the lowest electron-hole pair states of CdSe quantum dots embedded in glass. The data obtained by photoluminescence, differential absorption and photoluminescence excitation spectroscopy have been compared and a general size dependence could be established. Based on theoretical calculations, the dominant features in the spectra have been assigned to the different transitions from the ground state to the one-pair states. Within the lowest one pair transition, a fine structure due to exchange interaction has been observed. The change in the optical properties with increasing intensity has been studied and the two-pair states identified in luminescence. Spectrally broad optical gain has been found due to stimulated transitions involving both one- and two-pair states.     

An interference-based optical authentication scheme using two phase-only masks with different diffraction distances

A new method to eliminate the security risk of the well-known interference-based optical cryptosystem is proposed. In this method, which is suitable for security authentication application, two phase-only masks are separately placed at different distances from the output plane, where a certification image (public image) can be obtained. To further increase the security and flexibility of this authentication system, we employ one more validation image (secret image), which can be observed at another output plane, for confirming the identity of the user. Only if the two correct masks are properly settled at their positions one could obtain two significant images. Besides, even if the legal users exchange their masks (keys), the authentication process will fail and the authentication results will not reveal any information. Numerical simulations are performed to demonstrate the validity and security of the proposed method.     

Multiplexing Techniques for Noninterferometric Optical Point-Sensor Networks: A Review

This article presents a review of the strategies that have been both demonstrated and proposed for the multiplexing of multiple noninterferometric optical fiber point sensors to form a sensor network. The focus, which avoids consideration of interferometric sensor types, enables discussion of conventional multiplexing tech niques, namely, spatial, time division, frequency division, and wavelength division prior to dealing with combined or hybrid schemes, which exhibit the potential for increased multiplexing gain. Specific advantages and potential drawbacks of the different strategies are provided together with an indication of the number of point sensors that each multiplexing scheme can support.