All-optical buffer and shaper based on complex-modulated long-period-grating coupler and self-closed fiber loop

We propose a novel all-optical buffer and shaper based on the adjustable power transferring characteristics of the complex-modulated long-period-grating coupler(CM-LPGC)and the multiple circulations of the self-closed fiber loop.By turning on the external optical pumps,the signals can be stored by utilizing the nonreciprocal power transferring of the CM-LPGC.When the buffer time is satisfied,the signals can be extracted discretionarily by turning off the external optical pumps.In addition,by controlling the spectral bandwidth of the CM-LPGC,the temporal rectangular pulse can be obtained by re-shaping the Gaussian input signal.     

GaAs MESFET Regenerator for Phase-Shift Keying Signals at the Carrier Frequency

This paper describes a GaAs metal-semiconductor FET (GaAs MESFET) phase regenerator for biphase phase-shift keying (PSK) signals at the carrier frequency. By using this regenerator, decision and reshaping of the signals can be made without detection, thus repeaters can be simplified. This paper shows that phase regeneration is characterized by the symbol m, which denotes the ratio of the normal signal to the phase-inverted signal. Ideal phase regeneration is obtained for m = 1. An analysis of the ratio m for the MESFET regenerator is presented, and it is shown that, if the gate bias or the local-oscillator power level are selected at a slightly higher point than that minimizing the conversion loss, then m = 1.03 is obtained at an excess loss of 3 dB. To verify this analysis, the ratio m was measured experimentally and it was found to agree with the analysis. Static and dynamic characteristics were also measured, and it is shown that the MESFET regenerator has decision and reshaping ability.     

Performances of a Fully Integrated All-Optical Pulse Reshaper Based on Cascaded Coupled Nonlinear Microring Resonators

We propose a simple way to design a fully integrated and passive all-optical pulse reshaper in the aim of reamplifying and reshaping (2R) regeneration of optical digital signals. The device could be achieved from a coupled microresonator structure with Kerr nonlinearity. By using time-domain simulation, we show that we can obtain a clear nonlinear power transfer that is capable of improving signal-to-noise ratio and reducing bit error rate for digital signals. The reshaping performances are estimated by calculating Q-factor enhancement. Since we take benefit from field enhancement at resonance, this integrated reshaper could be much smaller than other gates based on nonlinear fibers or waveguides.     

Tunable All-Optical Wavelength Conversion of 160-Gb/s RZ Optical Signals by Cascaded SFG-DFG Generation in PPLN Waveguide

We report, for the first time, tunable all-optical wavelength conversion of 160-Gb/s return-to-zero (RZ) optical signals based on cascaded sum- and difference-frequency generation in a periodically poled LiNbO₃ waveguide. The distorted signals due to limited phase-matching bandwidth during conversion were compensated by spectral reshaping. We achieved error-free tunable wavelength conversion with a bit-error rate of less than 10^-9 for 160-Gb/s RZ signals in a 23-nm tuning range over the C-band     

Optical Reshaping of 40-Gb/s NRZ and RZ Signals Without Wavelength Conversion

We experimentally demonstrate a scheme for all-optical reshaping at 40 Gb/s that is wavelength preserving and transparent to both nonreturn-to-zero and return-to-zero on-off keying signals. Eye-diagram reshaping is confirmed by means of bit-error rate versus threshold measurements on both modulation formats. The scheme is based on cross-gain compression in an semiconductor optical amplifier (SOA) and uses two SOAs that are not in interferometric configuration. Due to its working principle, this method is polarization-independent and suitable, in principle, for higher bit rates.     

All-optical signal reshaping by means of four-wave mixing inoptical fibers

It is experimentally demonstrated that the four-wave mixing (FWM) effect in an optical fiber can be exploited to achieve all-optical reshaping. The injection of a signal and a strong continuous-wave (CW) pump into a common dispersion-shifted fiber results in several wavelength-converted replicas of the signal. These spectral components exhibit various reshaping behaviors. Selecting low-order FWM waves, we observe a sinusoidal-like transfer function. However, unlike other reshaping devices, a step-like transfer function is obtained for higher order mixing products. A significant noise compression is observed at the converted output, starting from an input noisy nonreturn-to-zero (NRZ) signal stream     

基于雷达料位仪信号处理的整形放大电路设计

重点描述了雷达料位仪中信号处理电路部分的整形放大电路的基本原理与设计方法。首先信号处理方法的优劣对雷达料位仪的测距精度指标有着很重要的作用,因此对雷达料位仪的信号处理方法的研究十分重要,然而整形放大电路在整个信号处理部分有着至关重要的作用。采用2个LM324N运放组合设计出整形放大电路。经使用表明,该电路性能稳定,精度高。     

Investigation of 43-Gb/s Transmission With a Wavelength Preserving SOA-Based Optical Regenerator

Transmission with cascaded optical regeneration based on synchronous modulation combined with optical reshaping by cross-gain compression in a semiconductor optical amplifier is investigated at 43 Gb/s over transoceanic distances (10 000 km). The proposed optical regenerator configuration performs signal reshaping and retiming while preserving the input signal wavelength. The regenerator cascadability properties are investigated using a reconfigurable loop to assess the impact of different inter-regeneration spacing on the transmission signal properties.      

QPSK Direct Regenerator with a Frequency Tripler and a Quadrupler

This paper describes a regenerator for quadriphase phase shift keying (QPSK) signals at the carrier frequency, which is called a "direct regenerator." The direct regenerator proposed here is realized using a tripler and a quadrupler. This regenerator is characterized by the symbolsm,nands, which denote the intermediate combiner amplitude ratio, the final combiner amplitude ratio and the limiter dynamic range, respectively. Complete regeneration is obtained atm = n = 1ands = infty. Even if this condition is not satisfied, sufficient regenerative performance for practical use is preserved, when0.8 < m < 1.25, 0.7 < n < 1.4ands > 5dB. To verify the operation principle, an experiment was carried out for 1.7 GHz QPSK signals transmitted at 40 Mbits/s. It is shown that this regenerator has satisfactory decision and reshaping capability in dynamic operation. Using this direct regenerator, decision and reshaping of the QPSK signals can be made without detection. Thus, a repeater can be simplified, compared to a conventional repeater composed of a detector, a baseband regenerator and a modulator.     

Statistical Properties of Timing Jitter in a PAM Timing Recovery Scheme

A new technique is presented for evaluating the performance of a popular type of timing recovery circuit for baseband synchronous pulse amplitude modulation (PAM) data signals. The timing circuit consists of a square-law device followed by a narrowband filter tuned to the pulse repetition frequency along with provision for reshaping the pulses entering the timing path (prefiltering). The output of the timing circuit is a nearly sinusoidal timing wave whose zero crossings indicate the appropriate sampling instants for demodulation of the PAM signal. For a random data sequence, the timing wave exhibits phase fluctuations which are strongly dependent on the pulse shapes entering the timing path and the passband shape of the narrow-band filter. Expressions for rms phase fluctuation in the timing wave as a function of the prefiltering and postfiltering characteristics of the filters preceding and following the square-law device are presented. These expressions have a form which is especially suitable for studying the case where the baseband PAM signal is band-limited to frequencies less than the pulse repetition frequency. A condition on prefiltering and postfiltering which gives error-free timing recovery is presented. Results obtained from some specific examples serve to illustrate several aspects of the timing recovery problem.     

Robust detection with the gap metric

In a multipath communication channel, the optimal receiver is matched to the maximum likelihood (ML) estimate of the multipath signal. In general, this leads to a computationally intensive multidimensional nonlinear optimization problem that is not feasible in most applications. We develop a detection algorithm that avoids finding the ML estimates of the channel parameters while still achieving good performance. Our approach is based on a geometric interpretation of the multipath detection problem. The ML estimate of the multipath signal is the orthogonal projection of the received signal on a suitable signal subspace S. We design a second subspace G, which is the representation subspace, that is close to S but whose orthogonal projection is easily computed. The closeness is measured by the gap metric. The subspace G is designed by using wavelet analysis tools coupled with a reshaping algorithm in the Zak transform domain. We show examples where our approach significantly outperforms the conventional correlator receiver (CR) and other alternative suboptimal detectors     

Variable group delay and pulse reshaping of high bandwidth optical signals

We present the dispersive characteristics of an electronically tunable optical filter, with application toward delaying high speed digital and analog signals. Square waves can be dynamically delayed and reshaped through a change in injection current to the filter. Since the filter is of an all-pass nature, its usable bandwidth is limited primarily by the phase response (dispersion). We show that for 2-GHz square waves, dispersion is not a limiting factor and the filter can be operated over the full range of delays. At 5 GHz, the pulses can still be delayed, however the range of operation is dispersion limited. Additionally, at 5 GHz this dispersion can be harnessed for pulse reshaping applications. The filter is studied both experimentally and theoretically, demonstrating good agreement.     

Spatial optical beam-forming network for receiving-mode multibeamarray antenna - proposal and experiment

This paper proposes an array antenna for multibeam reception with a beam-forming network (BFN) that uses spatial optical signal processing and also presents experimental results. In this antenna, signals received at individual antenna elements are converted to optical signals, and are optically divided from the directions of signal arrival by means of optical spatial Fourier transformation, and then the optical signals are reconverted into microwave signals at the BFN. In this BFN, to maintain optical path-length conditions, an optical integrated circuit is employed. We have experimentally investigated the optical signal processing performances of the BFN for multibeam reception. The experimental results show that optical beam direction is changed according to the signal arrival direction of an array antenna. Two multiple RF signals with different phase distributions are separated. The sidelobe level of the optical signal is reduced when amplitude distributions of optical signals are Chebyshev distributions. We also present the signal transmission behavior of this BFN. The measured carrier-to-noise-ratio degradation of this BFN is 2 dB at BER=10^-6 when 118.125-Mb/s QPSK modulated signal is input into the BFN     

Noise-resistant pulse oximetry using a synthetic reference signal

We describe a noise-resistant pulse oximetry algorithm suited to both signal reconstruction and oxygen saturation estimation. The algorithm first detects relatively clean signal sections from which the heart rate is estimated. The heart rate is used to construct a synthetic reference signal that matches an idealized pulse signal. An adaptive filter continuously processes the sensor signals, reconstructing signals in a linear subspace defined by the reference signal. A projective subspace algorithm is then applied to find the oxygenation level of the blood. We show that under specific circumstances this algorithm solves the sufficiency condition for signal reconstruction in linear saturation estimators. The core principle of using a frequency modulated synthetic reference signal can be applied to adaptive filtering of other physiological signals controlled by the heartbeat, such as blood pressure and electrocardiogram.     

Impairment constraint multicasting in translucent WDM networks: architecture, network design and multicasting routing

The popularity of broadband streaming applications requires communication networks to support high-performance multicasting at the optical layer. Suffering from transmission impairments in multi-hop all-optical (transparent) WDM multicasting networks, the signal may be degraded beyond the receivable margin at some multicast destinations. To guarantee the signal quality, we introduce a translucent WDM multicasting network to regenerate the degraded signals at some switching nodes with electronic 3R (reamplification, reshaping and retiming) functionality. The translucent network is built by employing three kinds of multicasting capable switching architectures: (1) all-optical multicasting capable cross connect (oMC-OXC), (2) electronic switch and (3) translucent multicasting capable cross connect (tMC-OXC). Among them both the electronic switch and tMC-OXC are capable of electronic 3R regeneration. Furthermore, we propose a multicast-capable nodes placement algorithm based on regeneration weight, and two multicasting routing algorithms called nearest hub first and nearest on tree hub first to provide signal-quality guaranteed routes for the multicasting requests. The numerical simulation on two typical mesh networks shows that it is sufficient to equip 30% of the nodes or less with signal-regeneration capability to guarantee the signal quality.     

基于小波变换的信号调制方式的识别研究

根据小波理论,利用小波变换的尺度分解和局部放大的能力,对调制信号进行小波变换和分解,挖掘调制信号在间断点的瞬态特性,成功建立了不同调制方式和其调制特征间的对应关系。在不需要同步和符号速率等先验知识的情况下,实现了对MASK、MFSK、MPSK、MQAM等数字调制方式的完全识别。通过理论分析和计算机仿真验证了所提方法的有效性和实用性,具有很高的应用价值。     

Application of signal subspace algorithms to scattered geometricoptics and edge-diffracted signals

This paper addresses a signal processing problem arising from a high-frequency radar scattering problem. Signal subspace algorithms apply to signals which are a sum of sinusoids and are widely studied in this context. We consider the application of existing signal subspace algorithms to signals of a more general type. We analyze the accuracy of model parameters estimated and show that the signal subspace algorithms are in a certain sense robust. Thus these algorithms have potential for solving a signal processing problem arising in conventional radar target identification problems     

Signal enhancement by time-frequency peak filtering

Time-frequency peak filtering (TFPF) allows the reconstruction of signals from observations corrupted by additive noise by encoding the noisy signal as the instantaneous frequency (IF) of a frequency modulated (FM) analytic signal. IF estimation is then performed on the analytic signal using the peak of a time-frequency distribution (TFD) to recover the filtered signal. This method is biased when the peak of the Wigner-Ville distribution (WVD) is used to estimate the encoded signal's instantaneous frequency. We characterize a class of signals for which the method implemented using the pseudo WVD is approximately unbiased. This class contains deterministic bandlimited nonstationary multicomponent signals in additive white Gaussian noise (WGN). We then derive the pseudo WVD window length that gives a reduced bias when TFPF is used for signals from this class. Testing of the method on both synthetic and real life newborn electroencephalogram (EEG) signals shows clean recovery of the signals in noise level down to a signal-to-noise ratio (SNR) of -9 dB.     

Approximate Time-Variable Coherence Analysis of Multichannel Signals

We present a new method for signal extraction from noisy multichannel epileptic seizure onset EEG signals. These signals are non-stationary which makes time-invariant filtering unsuitable. The new method assumes a signal model and performs denoising by filtering the signal of each channel using a time-variable filter which is an estimate of the Wiener filter. The approximate Wiener filters are obtained using the time-frequency coherence functions between all channel pairs, and a fix-point algorithm. We estimate the coherence functions using the multiple window method, after which the fix-point algorithm is applied. Simulations indicate that this method improves upon its restriction to assumed stationary signals for realistically non-stationary data, in terms of mean square error, and we show that it can also be used for time-frequency representation of noisy multichannel signals. The method was applied to two epileptic seizure onset signals, and it turned out that the most informative output of the method are the filters themselves studied in the time-frequency domain. They seem to reveal hidden features of the epileptic signal which are otherwise invisible. This algorithm can be used as preprocessing for seizure onset EEG signals prior to time-frequency representation and manual or algorithmic pattern classification.