Modified signed-digit addition by using binary logic operations and its optoelectronic implementation

In this work, a three-step modified signed-digit (MSD) addition by using binary logic operations is proposed. Each input digit is encoded with two binary bits. Through binary logic operations, all of the weight and transfer digits and the final sum digits represented with the same encoding scheme will be generated. The operations can be performed at each digit position in parallel. In our suggested optical arithmetic and logic unit (ALU), a single electron trapping (ET) device is employed to serve as the binary logic device. This technique based on ET logic possesses the advantage of high signal-to-noise ratio (SNR). The optoelectronic system can be constructed in a simple, compact and general-purpose form.     

Optical binary logic gate-based modified signed-digit arithmetic

A new design approach for a three-step modified signed-digit (MSD) adder is presented that can be optically implemented using binary logic gates. The proposed scheme depends on encoding each MSD digits into a pair of binary digits using a two-state and multi-position encoding scheme. The proposed design algorithm depends on constructing the addition truth table of binary-coded MSD numbers and then using Karnaugh map to achieve output minimization. The optical binary logic gates are obtained by simply programming the decoding masks of a shadow-casting-based optical logic gate system. The proposed scheme results in a simple, compact, and efficient optical binary gate-based parallel addition system.     

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.     

Simulation of a flat optical frequency comb using a single-drive multi-RF Mach–Zehnder modulator in a cascaded intensity modulator chain

We proposed a scheme based on two cascaded lithium niobate intensity modulators to generate an optical frequency comb with very high flatness. Single-drive multi-RF waveforms are used for driving the first intensity modulator, and 9 lines within 1 dB power variation can be obtained. When cascading with another intensity modulator, by specially adjusting the DC bias and the drive amplitudes of the RF signals of the two intensity modulators, 27 or 45 comb lines with a spectral power variation about 1 dB are obtained. The scheme is relatively simple and adjustable, and the frequency interval of the OFC varies with microwave frequency applied on modulators.     

All-optical conversion scheme: Binary to quaternary and quaternary to binary number

To achieve the inherent parallelism in optics a suitable number system and efficient encoding/decoding scheme for handling the data are very much essential. Binary number is accepted as the best representing number system in almost all types of existing electronic computers. But, binary number (0 and 1) is insufficient in respect to the demand of the coming generation. Multi-valued logic (with radix >2) can be viewed as an alternative approach to solve many problems in transmission, storage and processing of large amount of information in digital signal processing. Here, in this paper all-optical scheme for the conversion of binary to quaternary number and vice versa have been proposed and described. Simulation has also been done. In this all-optical scheme the numbers are represented by different discrete polarized state of light.     

An all optical method of implementing a wavelength encoded simultaneous binary full adder-full subtractor unit exploiting nonlinear polarization rotation in semiconductor optical amplifier

Full adders and full subtractors are the basic circuit elements of any digital data processor in electronics as well as in the all optical domain. Again the wavelength dependent encoding/decoding techniques have established itself as a very promising and efficient tool having some inherent and unique advantages relative to the other well known intensity or polarization or phase dependent optical data encoding mechanisms. In this communication, the authors therefore propose a new scheme of implementing a wavelength encoded complete binary full adder-full subtractor unit in the all optical domain using the wavelength conversion by the nonlinear polarization rotation in a single semiconductor optical amplifier. The interacting signals are counter propagating in the semiconductor optical amplifier and hence can be set at the same wavelength. To realize the binary logic wavelength dependent encoding/decoding mechanism is exploited in our proposed scheme of full adder-full subtractor unit. Also the optical add/drop multiplexing employing the special filtering property of the semiconductor optical amplifier is utilized for the designing of the all optical system.     

A bidirectional 60 GHz RoF system based on FWM in a semiconductor optical amplifier

In this study, a bidirectional 60 GHz RoF systems based on four-wave mixing (FWM) in semiconductor optical amplifier (SOA) is proposed. Two key techniques are included in such a scheme, namely, generation of 60 GHz modulating signals and distribution of 60 GHz local oscillator. The analytical model is theoretically analyzed and then confirmed by numerical simulations. Results of this study demonstrate that such a scheme can offer realistic solutions to support future mobile broad-band applications.     

Fully reconfigurable optical add-drop multiplexer based on parallel configuration using Mach-Zehnder module

Reconfigurable optical add-drop multiplexer (ROADM) with the ability of dynamic configuration will be one of the core equipment for the future optical transport networks. This paper proposes an effective scheme for fully ROADM with parallel modularized structure and ability of upgrading. Each module consists of a Mach-Zehnder interferometer based on fiber Bragg grating (FBG), a 1 × 2 optical switch and a Y-model combiner. Optical signal with single wavelength or multiwavelength could be dropped or added at one drop port or add port by configuring the optical switch in each module. The proposed ROADM with four-stage parallel connection is designed and experimentally investigated to prove its performance and advantage in dynamic selection of the wavelengths and upgrading. It is also showed that this ROADM can also reduce the ununiformity of power at output port and drop port to improve the optical signal to noise ration (OSNR) of the whole system.     

Nonorthogonal unitaries in two-way quantum key distribution

Two-way Quantum Key Distribution (QKD) schemes commonly make use of a set of unitaries corresponding to binary encodings which can in principle be distinguished perfectly. In this paper, inline with the proposal in Chiribella et al. (2008) [13], we introduce a non-entangled two-way QKD scheme with two sets of unitaries of which the elements in one set can be viewed as ‘nonorthogonal’ to elements in the other with the aim of naturally suppressing an eavesdropper's information to provide for a higher security threshold. Security analysis is done in the context of individual attack strategies for a quick comparison with the conventional two-way QKD scheme. Given the richer structure of the improvement, future direction is also discussed.     

Chaos generation in a semiconductor ring laser with an optical injection

Two chaos generation schemes are demonstrated numerically based on a semiconductor ring laser (SRL) with either a constant or a chaotic optical injection from an external distributed feedback (DFB) laser. Under a certain bias current, the chaotic output can be generated by the SRL with appropriate injection parameters. Parameter map is achieved numerically to show types of oscillation in the SRL. Bifurcation diagrams and Lyapunov exponent spectra roughly describe the routes to chaos for the SRL with disturbance. A bandwidth-enhanced chaos generation can be describes based on the chaotic optical injection scheme. The bandwidth of the bandwidth-enhanced chaos generated is about 12 GHz, which achieves approximately a two-fold increase compared with the constant injection scheme.     

Binary and ternary oscillations in a cubic numerical scheme

We study a central difference semi-discretization of the cubic scalar conservation law. Both spatial period-2 (binary) and period-3 (ternary) oscillations are stationary solutions of this scheme, and we find where each type is linearly stable. We observe numerically the formation of ternary oscillations, to the left of Riemann shock initial data with u_r = 0, while binary oscillations form to the right of Riemann rarefaction data having u_l = 0. We derive modulation equations for both wave patterns, using them to show that binary oscillations generated by the scheme are numerical artifacts, while computing an explicit solution for the ternary modulation equations. For positive initial data, the ternary modulation equations remain hyperbolic, while the solutions enter an elliptic region for data of both signs. Conditions under which solutions of the ternary modulation equations can be inverted to yield period-3 oscillations are also discussed.     

驱动函数切换调制实现超混沌数字保密通信

在主动-被动分解同步的基础上,提出了一种利用不同超混沌系统的驱动函数切换调制实现数字保密通信的方案.根据二进制信号“0”和“1”的传输情况交替发射两个不同的驱动函数,这就增加了发射信号的复杂度,减少了信号的相关性.且通过进行多次非线性变换加密,进一步设置了新的密钥,使得基于预测法的攻击完全失效.理论分析和模拟结果均表明本方案在实现超混沌数字保密通信时的有效性. 关键词： 超混沌 主动-被动分解法 切换调制 保密通信     

Trellis ternary line coding scheme for asynchronous optical CDMA systems

In this paper, we investigate the employment of a ternary line coding technique based on Ungerboeck's trellis-coded method in asynchronous optical CDMA systems. The ternary coding we use is predicated upon the equal-weight orthogonal (EWO) scheme. Each user transmits two mutually orthogonal signature sequences to represent “+1” and “−1”, respectively, and nothing is transmitted for “0”. The receiver employs a maximum-likelihood soft-decoder to select the path with minimum Euclidean distance as the preferred path. This trellis ternary coding scheme applies set partitioning with partially overlapping subsets to increase the free Euclidean distance, which considerably improves system performance. Furthermore, due to line coding technique, such scheme comprises sufficient clock information, and thus benefits for baseband timing extraction (i.e. clock recovery). Numerical results reveal that the proposed trellis ternary coding scheme can significantly reduce the error floor and allow more active users to be accommodated in the network.     

光双二进制传输系统的性能研究

光双二进制信号的谱宽是传统二进制信号的一半,采用双二进制传输比二进制传输色散限制的中继距离可增加一倍.本文对采用传统光接收机的光双二进制传输系统用MATLAB进行了通信仿真.结果表明:在完全消光条件下,10 Gb/s双二进制信号在常规单模光纤上传输可达160 km,40 Gb/s双二进制信号在非零色散光纤上为30 km,均比二进制增加了一倍;详细考察了消光比对传输的影响,只有消光比大于25 dB时,双二进制相对于二进制传输的优越性才呈现出来.     

A multi-parameter optical fiber sensor with interrogation and discrimination capabilities

A multi-parameter and multi-function, but low-cost, optical fiber grating sensor with self-interrogation and self-discrimination capabilities is presented theoretically and experimentally. The sensor bases on three fiber Bragg gratings (FBG) and one fiber long period grating (LPG). Strain, vibration, pressure, ordinary temperature (−10 to 100 °C) and high temperature (100–800 °C) can be measured by the sensor. When high temperature (100–800 °C) is measured, the LPG is used as a high temperture sensor head and FBG₁ is used as an interrogation element. Alternatively, when one of the other four measurands is measured, FBG₁ (or FBG₂) is used as a sensor head and LPG is used as an interrogation element. When two of the other four measurands are measured simultaneously, FBG₁ and FBG₂ are used as sensor heads and LPG is used as a shared interrogation element. FBG₃ is used as a reference element to eliminate the errors resulted from light source fluctuation and the cross-sensitivity between measurand and environmental temperature. The measurands can be interrogated according to the signals of the photodiodes (PDs), which are related to the relative wavelength shift of the LPG and the FBGs. Experimental results agree well with theoretical analyses. The interrogation scheme is immune to light source fluctuation and the cross-sensitivity between measurands and enviromental temperature, and also the dynamic range is large.     

An efficient scheme for optimizing channel utilization in OBS networks

Optical burst switching (OBS) is an emerging technology that allows variable size data bursts to be transported directly over DWDM links. In order to make OBS a viable solution, the wavelength scheduling algorithms need to be able to utilize the available wavelengths efficiently, while being able to operate fast enough to keep up with the burst incoming rate. Unfortunately, horizon scheduling cannot utilize the voids created by previously scheduled bursts, resulting in low bandwidth utilization. To date, Min-SV is the fastest scheduling algorithm that can schedule wavelengths efficiently. However, its complexity is O (log m) and it requires 10 log (m) memory accesses to schedule a single burst. This means that it can take upto several microseconds for each burst request, which is still too slow to make it a practical solution for OBS deployment. In this paper, an efficient scheme has been proposed for optimizing channel utilization in OBS networks. In the proposed approach, a burst is represented by an interval of time. The process of scheduling a number of bursts, thus, turns to be a process of fitting a set of the corresponding time intervals on a channel time line that represents a channel-time resource. By doing so, the scheduling process can be formulated as a combinatorial optimization problem. Then, graph theory is applied to schedule as many non-overlapping intervals as possible onto the channel time line. The underlying concept of the proposed scheduling scheme is that of briefly delaying the scheduling of a burst so that a much better decision can be made about a number of bursts all-together. This scheme is shown, through simulations, to improve performance in terms of burst loss probability, channel utilization, fairness-control and data throughput over existing schemes. Thus the proposed scheme is well suited for high performance networks in terms of reliability.     

All optical logic NAND gate based on two-photon absorption in semiconductor optical amplifiers

We propose a new scheme to realize all optical logic NAND operating at high speeds up to 250 Gb/s utilizing the ultrafast phase response during two-photon absorption (TPA) process in semiconductor optical amplifiers (SOA). NAND gate is important because other Boolean logic elements and circuits can be realized using NAND gates as basic building blocks. Rate equations for semiconductor optical amplifiers (for input data signals with high intensity) configured in the form of a Mach-Zehnder interferometer have been solved. The input intensities are high enough so that the two-photon induced phase change is larger than the regular gain induced phase change. The performance of this scheme is analyzed by calculating the quality factor of the resulting data streams. The results show that both AND and NAND operations at 250 Gb/s with good signal to noise ratio are feasible.     

基于N+2(B2∑+u→X2∑+g)的电弧等离子体振动温度和转动温度测量

通过光谱诊断系统测量大气压直流氩氮等离子体射流的发射光谱,在光谱紫外波段观察到氮的第一负带系N 2(B2∑ u→X2∑ g),利用N 2(B2∑ u→X2∑ g)跃迁的△v=0谱带系v'=0→v"＝0和v'＝1→v"＝1谱带,对实验测得的谱带和模拟计算得到的谱带进行点对点对比,得到了等离子体射流的振动温度和转动温度,并就仪器展宽、振动温度和转动温度对谱带结构和形状的影响进行了分析.结果表明在文章所述的实验条件下,等离子体的电子温度、振动温度、转动温度和化学动力学温度基本相等,大气压直流氩氮等离子体射流达到局域热力学平衡.     

Optical implementation of flip-flops using single-LCD panel

A novel scheme for implementation of flip-flop operations in a hybrid optical architecture using a single-LCD panel is proposed. Since flip-flops are sequential logic elements, the present inputs along with the previous output determine the present output state. In the proposed system, the previous state is considered as the third input to the system and three inputs are spatially coded and superimposed. A light source array projects an output binary pattern, which is decoded using a specially designed decoding mask so that both the present output Q and its complement are obtained simultaneously. The switching modes of the light sources in the array decide the operation of S-R, J-K, T and D flip-flops in a single architecture.     

Quasi-reciprocal reflective optical voltage sensor based on Pockels effect with digital closed-loop detection technique

A novel Pockels effect based optical voltage sensor (OVS) consisting of quasi-reciprocal reflective optical circuit is proposed and demonstrated in this paper. The quasi-reciprocal reflective optical circuit is realized so that a digital closed-loop detection technique adopted from fiber gyroscopes can be introduced to obtain the voltage-induced Pockels phase. Due to the digital closed-loop detection scheme, the proposed OVS is insensitive to the fluctuation of the light intensity and the dynamic range is independent of the half-wave voltage of the Pockels crystal compared to the conventional crystal bulk-type with the light intensity based detection scheme. A prototype of the proposed OVS is designed and evaluated. The calculated results of the electric field distribution show that the maximal measured voltage of the sensing element is up to 15 kV. The dc voltage from 0 to 3000 V and 50 Hz ac voltage from 0 to 5000 V are measured with good linearity. The proposed OVS achieves accuracy within ± 1% and ± 0.44% with the measured dc voltage above 800 V and ac voltage above 500 V, respectively. The influences of the alignment error in the sensing element on the measurement accuracy are also theoretically analyzed and experimentally verified.