All-optical analog-to-digital converters, hardlimiters, and logicgates

The authors propose and analyze the optical signal processing functionality of periodic structures consisting of alternating layers of materials possessing different Kerr nonlinearities. They explore structure-materials-performance relationships in all-optical analog-to-digital converters, hardlimiters, and AND and OR gates. They show that their proposed analog-to-digital converters can extract a binary word from multilevel optical signals in a single bit interval. They also propose a family of optical limiters whose output signal clamps to a set upper logic level for any input value exceeding a chosen threshold. They explore the performance of an all-optical logic gate whose forward-directed output implements a binary AND and whose backward-directed output implements an OR function     

Implementation of quantum optical tristate oscillators based on tristate Pauli-X, Y and Z gates by using joint encoding of phase and intensity

Oscillator circuit has the significant role to always repeat the same signal at the output after certain time interval. In quantum computing, intensity and phase of light signal can be made oscillatory at the output of a quantum optical oscillator circuit. In this paper, we have implemented quantum optical tristate oscillator circuits based on tristate Pauli-X, Y and Z gates using phase and intensity encoding technique of light signal. Here, three different oscillator circuits are developed. The phase of light signal is chosen as the oscillating parameter in all proposed circuits. The truth tables and oscillating phase diagrams are also shown for each oscillator circuit in this paper. The operation of one of the oscillator circuits is simulated with MATLAB to prove its feasibility.     

Frame time-hopping fiber-optic code-division multiple access using generalized optical orthogonal codes

A new spreading technique for intensity modulation direct detection fiber-optic code-division multiple-access (FO-CDMA) communication systems is proposed. This new spreading technique is based on generalized optical orthogonal codes (OOC) with large cardinality and minimal degradation in performance when compared with a more optimum system, namely, an optical CDMA system using OOC with autocorrelation and cross-correlation value bounded by one, i.e., OOC (/spl lambda/=1). To obtain the performance of such systems, we use a communication scheme, namely, frame time-hopping (FTH)-CDMA with random coding. Systems with generalized OOC patterns and random time-hopping coding are close in structure and performance. Furthermore, the performance of such systems is near the performance of optical CDMA with optimum but low cardinality OOC (/spl lambda/=1), which further renders the practicality of the proposed technique with very large cardinality. Two new receiver structures for FO-CDMA, namely, chip-level detector with optimum comparator threshold and correlation receiver with an electrical hard limiter, are also proposed. The performance analysis for a binary pulse position FTH-FO-CDMA network is considered for the correlation receiver, chip-level detector, correlation receiver with an optical hard limiter, optimum receiver, and the two newly proposed receiver structures. The results also show that a chip-level detector with optimum comparator threshold is superior to a chip-level detector for received low signal powers, and predict that the performance of the correlation receiver with an electrical hard limiter is superior to all other considered receiver structures, e.g., requiring one third of transmission power to achieve a desired bit error rate when compared with other receiver structures.     

A Generalized "Polarity-Type" Costas Loop for Tracking MPSK Signals

A generalized tracking loop is proposed for tracking MPSK signals at high SNR. It is similar in form to the polarity-type Costas loop used for tracking QPSK signals, in which limiters in the arms provide the data estimates needed for data wipeoff in forming the loop error signal. For the MPSK signal, the hard limiters are replaced by "multivalued limiters" withM/4 (M geq 4)positive and negative values. The outputs of the multivalued limiters in each arm are theIandQprojections of the data. TheScurve is computed for this MPSK loop, and plotted for different SNR's. A comparison is made to theScurve for theMth power loop (orM-phase Costas loop), which is optimum for low SNR. From this comparison, a rough value of the "boundary" SNR can be obtained; this value may be used by the designer to determine which loop structure should be used. The advantage of the high SNR structure proposed here is that it is much simpler to implement than the corresponding low SNR structures.     

Quadratic Electro-Optic Kerr Effect: Applications to Photonic Devices

We propose novel applications of the quadratic electro-optic Kerr effect to photonic devices. Specifically in this work, two new illustrative examples are described, namely an electrically controlled multistable switch (ECMS), and an electrically tunable Bragg grating (ETBG). Their functionality is based on the third-order nonlinearity in an isotropic medium. On one hand, we note that the first key feature is the all-optical as well as electro-optical control/tunability. This can be achieved only in the third-order nonlinear material as opposed to a more frequently used linear electro-optic effect exploited in optical crystals. On the other hand, the second important key feature is the availability of integrated and compatible materials that show third order nonlinearity. In the first application proposed here, ECMS, the interplay between the quadratic electro-optic and all-optical Kerr effects is crucial for its tunable operation and leads to an interesting feature of storing an electrical information optically. In the second example, ETBG, employing the quadratic electro-optic effect makes it attractive thanks to the existence of the third-order nonlinearity in many interesting isotropic materials that are suitable for device integration. Devices such as modulators, switches, mixers, variable attenuators or optical limiters can be designed.     

光纤光栅和环行器构成的多路光分插复用器

讨论由光纤光栅和光环行器构成的光分插复用器的结构,性能和特点,提出采用一段刻有多个光纤布拉格光栅的光纤,两个光环行器,WDM复用器和解复用器等器件,构造能够对WDM的多个信道实施分插操作的光分插复用器,该光分插复用器的插入损耗要比简单地把多个单路的光分插复用器进行级联时小得多,波分复用全光网络中的光分插复用技术,是实现波分复用网络的关键技术之一。     

Fiber-optic lattice signal processing

We discuss the implementation of fiber-optic lattice structures incorporating single-mode fibers and directional couplers. These fiber structures can be used to perform various high-speed time-domain and frequency-domain functions such as matrix operations and frequency filtering. In this paper we mainly consider systems in which the signals (optical intensities) and coupling coefficients are nonnegative quantities; these systems fit well in the theory of positive systems. We use this theory to conclude, for example, that for such systems the pole of the system transfer function with the largest magnitude is simple and positive-valued (in the Z-plane), and that the magnitude of the frequency response can nowhere exceed its value at the origin. We also discuss the effects of various noise phenomena on the performance of fiber-optic signal processors, particularly considering the effects of laser source phase fluctuations. Experimental results are presented showing that the dynamic range of the fiber systems, discussed in this paper, is limited, not by the laser source intensity noise or shot noise, but by the laser phase-induced intensity noise. Mathematical analyses of lattice structures as well as additional applications are also presented.     

Multiwavelength cross-connects for optical transport networks

Multiwavelength cross-connects (M-XCs) will play a key role in future optical multiwavelength transport networks. In this paper, we propose a class of optical wavelength interchange devices that can be used as basic building-blocks for multiwavelength optical cross-connects. We describe three different multiwavelength cross-connect structures that can be constructed using these building blocks. We investigate their blocking performance and examine issues such as complexity, modularity, and wavelength channel spacing associated with the proposed cross-connect structures     

Scheduling with interference decoding: Complexity and algorithms

In this article we study the problem of scheduling wireless links in the physical interference model with interference decoding capability. We analyze two models with different decoding strategies that explore the fact that interfering signals should not be treated as random noise, but as well-structured signals. The first model makes use of successive interference cancelation, which allows the strongest signal to be iteratively decoded and subtracted from a collision, thus enabling the decoding of weaker simultaneous signals. The second model explores the fact that routers are able to forward the interfered signal of a pair of nodes that wish to exchange a message and these nodes are able to decode the collided messages by subtracting their own contribution from the interfered signal. We prove that the scheduling problem remains NP-complete in both models. Moreover, we propose a polynomial-time scheduling algorithm that uses successive interference cancelation to compute short schedules for network topologies formed by nodes arbitrarily distributed in the Euclidean plane. We prove that the proposed algorithm is correct in the physical interference model and provide simulation results demonstrating the performance of the algorithm in different network topologies. We compare the results to solutions without successive interference cancelation and observe that considerable throughput gains are obtained in certain scenarios.     

Nonlinear disordered media for broad-band optical limiting

We analyze broad-band limiting behavior in nonlinear structures that are, on average, periodic. Introduction of a controlled degree of randomness in layer thicknesses results in widening of the stopband. Light at all of the frequencies in this broadened effective stopband of the structure with randomly perturbed layer thicknesses exhibits true optical limiting-clamping of the transmitted intensity below a fixed level independent of incident intensity. We explore the impact of the degree of randomization and the strength of the nonlinear mechanism on the smoothness and regularity of the limiting spectrum and on the localization of the light within these cyclostationary media. Optical limiting in integrable devices is of interest in optical logic, signal processing, and personnel and sensor protection     

DS-OCDMA Receivers Based on Parallel Interference Cancellation and Hard Limiters

In an incoherent direct-sequence optical code-division multiple-access (DS-OCDMA) system, multiple-access interference (MAI) is one of the principal limitations. To mitigate MAI, the parallel interference cancellation (PIC) technique can be used to remove nondesired users' contribution. In this paper, we study four DS-OCDMA receivers based on the PIC technique with hard limiters placed before the nondesired users or before the desired user receiver, or both. We develop, for the ideal synchronous case, the theoretical upper bound of the error probability for the four receivers. Significant performance improvement is obtained by comparison with conventional receivers in the case of optical orthogonal codes. The paper highlights that the number of active users with null error probability is doubled, compared with conventional receivers. Finally, we show that, thanks to their good performances, the PIC structures permit considerably reducing the minimal code length required to have 30 users with bit-error rate$≪10^-9$. So, the hardware constraints are relaxed for realistic application.     

Electronic Feedback System for Stabilization of Fiber Ring Resonator

We propose a simple technique to stabilize the optical output intensity of a fiber ring resonator. The electronic feedback circuit system, which consists of two voltage control oscillators, a phase comparator, and a low pass filter, is applied to the fiber ring resonator in order to compensate the optical phase shift in the ring loop. The reference electrical signal determines the operating condition of the fiber ring resonator for the desired optical output signal. The experimental results within the operating range agree well with the analytical results. The simulated performance of the proposed model is also compared with that of other existing models and shows significant improvement over them.     

Full-Duplex Radio-Over-Fiber System Using Phase-Modulated Downlink and Intensity-Modulated Uplink

We propose and demonstrate a full-duplex radio- over-fiber system employing a phase-modulated downlink and an intensity-modulated uplink over a single optical carrier. Each downlink and uplink is encoded with 200-Mb/s 16-quadrature amplitude modulation and a 100-Mb/s quadrature phase-shift keying signal carried in the 6-GHz band, respectively. The demonstration results show that the constraints on modulation index of the downlink signal as well as power budget of uplink signal can be relaxed thanks to the constant intensity of the phase-modulated downlink signal. The results also show the good error vector magnitude performance in both downlink and uplink signals after transmission over a 25-km fiber link. The effect of phase modulation to intensity modulation conversion of the downlink signal is also measured and evaluated for the scalability of the proposed technique.      

MDSI: Signal Integrity Interconnect Fault Modeling and Testing for SoCs

Unacceptable loss of signal integrity may cause permanent or intermittent harm to the functionality and performance of SoCs. In this paper, we present an abstract model and a new test pattern generation method of signal integrity problems on interconnects. This approach is achieved by considering the effects for testing inputs and parasitic RLC elements of interconnects. We also develop a framework to deal with arbitrary interconnection topology. Experimental results show that the proposed signal integrity fault model is more exact and more powerful for long interconnects than previous approaches.     

FSK Modulation Scheme for High-Speed Optical Transmission

In this paper,we describe the generation,detection,and performance of frequency-shift keying (FSK) for high-speed optical transmission and label switching.A non-return-to-zero (NRZ) FSK signal is generated by using two continuous-wave (CW) lasers,one Mach-Zehnder modulator (MZM),and one Mach-Zehnder delay interferometer (MZDI).An RZ-FSK signal is generated by cascading a dual-arm MZM,which is driven by a sinusoidal voltage at half the bit rate.Demodulation can be achieved on 1 bit rate through one MZDI or an array waveguide grating (AWG) demultiplexer with balanced detection.We perform numerical simulation on two types of frequency modulation schemes using MZM or PM,and we determine the effect of frequency tone spacing (FTS) on the generated FSK signal.In the proposed scheme,a novel frequency modulation format has transmission advantages compared with traditional modulation formats such as RZ and differential phase-shift keying (DPSK),under varying dispersion management.The performance of an RZ-FSK signal in a 4 × 40 Gb/s WDM transmission system is discussed.We experiment on transparent wavelength conversion based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) and in a highly nonlinear dispersion shifted fiber (HNDSF) for a 40 Gb/s RZ-FSK signal.The feasibility of all-optical signal processing of a high-speed RZ-FSK signal is confirmed.We also determine the receiver power penalty for the RZ-FSK signal after a 100 km standard single-mode fiber (SMF) transmission link with matching dispersion compensating fiber (DCF),under the post-compensation management scheme.Because the frequency modulation format is orthogonal to intensity modulation and vector modulation (polarization shift keying),it can be used in the context of the combined modulation format to decrease the data rate or enhance the symbol rate.It can also be used in orthogonal label-switching as the modulation format for the payload or the label.As an example,we propose a simple orthogonal optical label switching technique based on 40 Gb/s FSK payload and 2.5 Gb/s intensity modulated (IM) label.     

Performance improvement of phase-shift-keying signal transmission by means of optical limiters using four-wave mixing in fibers

Improvement of transmission performance of phase-shift-keying signals by the use of ultrafast optical limiters (amplitude regenerators) based on four-wave mixing (FWM) in fibers is theoretically and numerically studied. Theoretical analysis focuses on the nonlinear phase noise (the Gordon-Mollenauer effect) and its reduction by the limiters. It is shown that the cubic growth of the phase variance as the distance extends can be suppressed by the limiters that are periodically inserted in the system, although some additional phase noise is introduced by them. Numerical simulation is performed for nonreturn-to-zero (NRZ) differential phase-shift-keying (DPSK) transmission in a quasi-linear highly dispersed-pulse system with and without limiters. The results show that the maximum transmission distance is extended by the limiters. A clear indication of nonlinear phase-noise reduction at the high-signal-power regime, however, is not seen. This is attributed to the existence of intrachannel-FWM-induced phase fluctuation, which cannot be effectively suppressed by the amplitude limiter.     

Performance of APD-based, PPM free-space optical communication systems in atmospheric turbulence

In this paper, we characterize the performance of a direct-detection, avalanche photodiode-based free-space optical (FSO) communication system in terms of the overall bit-error rate. The system of interest uses pulse-position modulation (PPM) and is subjected to scintillation due to optical turbulence. Two scenarios are considered. In one case, a weak turbulence (clear-air) scenario is considered, for which the received signal intensity may be modeled as a log-normal random process. In the other case, we consider a negative exponentially distributed received signal intensity. To arrive at the desired results, it is assumed that the system uses a binary PPM (BPPM) modulation scheme. Furthermore, it is assumed that the receiver thermal noise is nonnegligible, and that the average signal intensity is large enough to justify a Gaussian approximation at the receiver. Union bound is used to assess the performance of M-ary PPM systems using the results of the BPPM scenario. Numerical results are presented for the BPPM case to shed light on the impact of turbulence on the overall performance.     

基于Nyquist脉冲副载波调制的短距离光纤传输技术研究

提出了一种适用于强度调制直接检测(IM/DD) 光系统的信号调制格式。这种基于Nyquist脉冲half cycle副载波调制(SCM)信号能有效提高频谱效率,为了减少传递函数引起的系统的性能 恶化,采 用了数字预均衡和后均衡实现对光纤损伤的补偿;建立了偏振复用(PDM)IM/DD系统 平台, 分析了Nyquist脉冲SCM信号在系统中的PAPR性能,实现了72Gbit/s 64-QAM N yquist脉冲SCM信号经过20km标准单模光纤(SMF)传输后其误码性能 小于前向纠错(FEC)阀值3．8×10－3。     

Relative Intensity Noise Suppression for RF Photonic Links

We propose and experimentally demonstrate a novel technique to reduce laser relative intensity noise (RIN). A RIN suppression servo is usually implemented by inserting an intensity modulator in the optical path and controlling measured light intensity with a closed-loop servo system. We utilize the intensity modulator already present in a photonic link to perform the task of RIN suppression as well as encoding the optical signal with the microwave subcarrier. This technique provides suppression of 10 to 50 dB of laser RIN over a bandwidth of 10 MHz. Furthermore, we implement this technique in an optoelectronic oscillator, significantly improving its phase noise performance due to the reduced effect of RIN on the phase noise of the oscillator.