All-Optical 40-GHz Time-Domain Fourier Transformation Using XPM With a Dark Parabolic Pulse

We demonstrate a 40-GHz all-optical time-domain Fourier transformation, in which an ideal parabolic phase modulation is applied to a signal by cross-phase modulation (XPM) with a dark parabolic pulse. The dark optical parabolic pulse is generated by the line-by-line spectral manipulation of a 40-GHz picosecond optical pulse source using an arrayed waveguide grating pulse shaper. By applying the parabolic XPM, the time interval for eliminating linear waveform distortions is expanded to a full bit slot. Dispersion slope-induced distortion is successfully eliminated with this scheme.      

Fast and robust control of systems with multiple flexible modes

This paper derives shaped time-optimal servomechanism (STOS) closed-loop control laws using a phase-plane approach to address flexible structures having multiple flexible modes. The STOS control laws for systems having two and three flexible modes are detailed. The flexible modes are addressed by using multimode input shapers to shape the time-optimal control for the rigid body portion of the system. The altered rigid body phase-plane trajectories resulting from this shaping are solved and used to determine an STOS closed-loop controller. Both "convolution" and "simultaneous" method multimode input shapers are considered. We also improve the robustness to modeling errors of the STOS control. The more robust zero vibration and derivative (ZVD) shaper is used. The ZVD shaper consists of more impulses and has a longer time duration than the simpler zero vibration (ZV) shaper which leads to the more robust STOS (RSTOS) control derived from the ZVD shaper having more switches and longer time response than the STOS control derived from the ZV shaper. Simulation results show that using the ZVD shaper in deriving the RSTOS control improves the robustness to modeling errors in frequency and damping of the flexible mode.     

Design, Fabrication and Characterization of an InP-Based Tunable Integrated Optical Pulse Shaper

In this paper a tunable integrated semiconductor optical pulse shaper is presented. The device consists of a pair of arrayed waveguide gratings with an array of electrooptical phase modulators in between. It has been fabricated in InP-InGaAsP material for operation at wavelengths around 1.55 mum. Multimode inputs to the waveguide gratings are used to flatten their optical passband. We have used a new short-pulse characterization technique to fully characterize pulse shaping by the device, i.e., both the power and the phase profile. A fourfold decrease in pulse ringing was observed for the devices with flattened passbands. Moreover these devices showed a 25% increase in pulse peak power. The possibilities for using the device as a dispersion (pre-) compensator have been investigated. Pulse reconstruction could be obtained for dispersion values of up to 0.2 ps/nm. The fabrication technology of the pulse shaper is compatible with the fabrication of integrated mode-locked lasers, which makes further integration of complete arbitrary pulse generators possible.     

Ultrafast Response of Arrayed Waveguide Gratings

The ultrafast limit of the response of arrayed waveguide gratings is studied both theoretically and experimentally. We present new experimental results that show that interference occurs inside of an arrayed waveguide pulse shaper even when pulses that travel through different paths do not overlap. A comprehensive discussion of this extreme case is presented     

Complete dispersion compensation for 400-fs pulse transmission over10-km fiber link using dispersion compensating fiber and spectral phaseequalizer

We have demonstrated essentially complete dispersion compensation for 400-fs pulses over a 10-km fiber link using dispersion compensating fiber and a programmable femtosecond pulse shaper functioning as a spectral phase equalizer. The pulse shaper impresses adjustable quadratic and cubic phases onto the spectrum and removes all the residual dispersion and dispersion slope in the dispersion compensated fiber link. Our work shows that the pulse shaper technique provides a powerful and convenient tool for programmable fiber dispersion compensation over broad optical bandwidth. This allows distortion-free femtosecond pulse transmission over a fiber link in excess of 10 km without requiring the exact trimming of the dispersion-compensating fiber     

A Design of Flattop-beam Shaper at Millimeter Wavelengths

Beam shaping technique for generating flattop beam has long been used in optics, and there are many methods to design flattop-beam shapers in optics. Flattop beam is also important in some applications at millimeter wavelengths such as in the quasi-optical power divider, however, there are few design method for the flattop-beam shaper used at millimeter wave frequencies and the design method of optics are not suitable to the beam shaper at millimeter wave frequencies, so a design method for the flattop-beam shaper at millimeter wave frequencies is presented in this paper. Several flattop-beam shapers in the form of diffractive element have been designed and simulation results are presented.     

Priority shaping of traffic streams sharing a policed virtual path in an ATM network

Traffic streams with differing service requirements, sharing a single contract for use of a policed virtual path in an ATM network, may be jointly shaped to make the best use of bandwidth available in the path. The shaper may use the information about the network policer to perform self-policing with a form of priority service to ensure satisfactory levels of cell loss and delay for both real-time and non-real-time traffic. Two such shapers are considered assuming a mean bit-rate contract with the network in which a leaky-bucket mechanism performs the policing function. The performance of the shapers is analysed using Markov-modulated models of bursty traffic sources and stochastic fluid methods, and the analytical results are corroborated by simulations. The choice of the shaper type and optimization of the shaper design parameters are discussed using correlated and non-correlated source models.     

A femtosecond pulse-shaping apparatus containing microlens arraysfor use with pixellated spatial light modulators

We discuss a modified femtosecond pulse shaper that uses microlens arrays to convert the continuous band of frequencies normally obtained at the mask plane of a pulse shaper to a series of discrete spots. Two possible modified pulse-shaping geometries are described and the optimum geometry is chosen. Our experiments demonstrate that this modification can improve pulse-shaping quality when modulator arrays with large interpixel gaps are used for Fourier-plane filtering     

The distributed Bragg pulse shaper: demonstration and model

The distributed Bragg pulse shaper (DBPS) is a series of electrically switchable Bragg mirrors on a semiconductor waveguide. The DBPS encodes data packets using parallel electrical signals to set the states of the Bragg mirrors. A broad-band source pulse then probes the device to generate a high bandwidth serial wavepacket from the train of partially reflecting mirrors. This paper describes a DBPS constructed in AlGaAs. Using this device and a mode-locked Ti:sapphire laser, we create a 4-bit packet with 0.37 Tb/s burst bit rate and are demonstrate for the first time that bits in the wavepacket can be switched by electrical modulation of individual Bragg segments. We also describe a model collaborating the observed data     

Designing unity magnitude input shaping by using PWM technique

This paper proposes a method for reducing vibrations in flexible systems by using the input shaping. A new input shaper technique based on Pulse Width Modulation (PWM) is used to shape the input.Since unity magnitude (UM) input shaping is easy to implement and provides less control duration, it has been preferred for many application areas. An analytical solution to time locations of the UM shaper requires very complex mathematical expressions due to involving in dependent constraint equations. This paper presents a simple PWM based input shaping method. The proposed technique allows designing UM shapers without analytical solution especially for the shapers having higher order impulse sequence. The method requires only the estimated value of system natural frequency and damping ratio. Desired numbers of impulses can be obtained by comparing reference signal amplitude and carrier wave frequency of a PWM. Analysis and experimental results demonstrate the effectiveness of the proposed method.     

基于高斯脉冲导数的正交UWB波形最优化设计

超宽带无线通信由于其在短距离高速率无线通信中的潜在应用已经引起了广泛的关注.超宽带信号要符合FCC发布的辐射掩蔽,并且要充分利用分配的频谱,这就要求合理的脉冲波形设计.本文分别采用4阶和5阶高斯脉冲导数,进行组合来合成用于UWB通信的脉冲波形,设计中采用归一化有效信号功率作为频谱利用的衡量标准,将波形设计问题转化成为线性规划问题,线性规划问题可以高效地求解,得到的波形具有很高的频谱利用率,并且4阶和5阶高斯脉冲导数合成的脉冲是相互正交的,可以进一步扩大通信的容量.     

Optical frequency domain differential phase shift keying infemtosecond-pulse spectral modulation systems

We propose a novel scheme of differential phase shift keying (DPSK) in the optical frequency domain. We take advantage of the intrinsic coherence among spectral elements derived by spectrum slicing a femtosecond optical pulse, introducing differential phase modulation between adjacent spectral elements with a femtosecond-pulse shaper. Detection of the differential phase is achieved by a Mach-Zehnder (MZ) or Sagnac interferometric receiver without requirement of any external phase reference     

Some properties of variable length packet shapers

The min-plus theory of greedy shapers has been developed from R.L. Cruz's results (1991) on the calculus of network delays. The theory of greedy shapers establishes a number of properties such as the series decomposition of shapers or the conservation of arrival constraints by reshaping. It applies either to fluid systems or to packets of constant size such as ATM. For variable length packets, due to the distortion introduced by packetization, the theory is no longer valid. We elucidate the relationship between shaping and packetization effects. We show a central result, the min-plus representation of a packetized greedy shaper. We find a sufficient condition under which series decomposition of shapers and conservation of arrival constraints still holds in the presence of packetization effects. This allows us to demonstrate the equivalence of implementing a buffered leaky bucket controller based on either virtual finish times or on bucket replenishment. However, in some examples, if the condition is not satisfied, then the property may no longer hold. Thus, for variable size packets, there is a fundamental difference between constraints based on leaky buckets and constraints based on general arrival curves, such as spacing constraints. The latter are used in the context of ATM to obtain tight end-to-end delay bounds. We use a min-plus theory and obtain results on greedy shapers for variable length packets which are not readily explained with the max-plus theory of C.S. Chang (see "Performance Guarantees in Communication Networks", Springer-Verlag, 2000)     

Optical arbitrary waveform generation and characterization using spectral line-by-line control

This paper demonstrates optical arbitrary waveform generation (O-AWG) and its characterization using spectral line-by-line control with high-resolution grating-based pulse shapers. Such integrated capabilities are the enabling techniques for high-fidelity O-AWG.     

Tunable modulation format conversion based on spectral line-by-line pulse shaper for all-optical signal processing

A tunable modulation format converter based on spectral line-by-line pulse shaper is proposed to realize different format conversions. The pulse shaper works as a format converter by setting its frequency response equivalent to the transform function between two formats. The working principles show that the format converter is suitable for different formats by adjusting its frequency response. Examples of format conversion from return to zero differential phase-shift keying （RZ-DPSK） to on-off keying （OOK） with different data packets and from return to zero （RZ） to non-return to zero （NRZ） are given. The results show that the format converter is not only suitable for different formats but also for random data packets.     

Design of command shapers for residual vibration suppression in Duffing nonlinear systems

Residual vibrations generated from rest-to-rest maneuvers are crucial for applications in precision engineering, active structural control, space engineering, and other mechatronics applications. In certain applications, the structures to be controlled could be highly nonlinear yet lightly damped. Although the traditional input shaping techniques, which utilize destructive interference, work well for linear and weakly nonlinear systems, they show little effects on systems with strong nonlinearity. In this paper, a general input shaper design methodology for single-degree-of-freedom systems with Duffing nonlinearity is developed by an energy approach. Following this approach, two-step and three-step shapers, as well as their design procedures, are developed, which in the linear limit reduce to the traditional zero-vibration and zero-vibration-and-derivative shapers, respectively. The robustness of these nonlinear shapers is investigated numerically through case studies. The results show that the three-step shapers are sufficiently robust to resist certain level of parameter variations (from their designed values) without exciting significant residual vibrations. The two-step shapers, however, are less robust in comparison. Meanwhile, it is also found that the presence of damping effectively disturbs the energy flow and thus induces residual vibrations. For the less robust two-step shapers, an effective ‘online tuning’ scheme is also proposed here to further improve its performance in a damped nonlinear system. These shaping schemes, as well as their practical adjustment routing, could be applied to the particular structural or mechatronics systems with Duffing or other nonlinearities for vibration suppression to enhance the performance of mechatronics systems.     

Design guidelines and comparison of detector readout front end integrated S-G shapers using transconductance circuits

An analysis of readout front end electronics semi-gaussian (S-G) shapers is carried out. Innovative design methodology is proposed and an advanced filter design technique based on operational transconductance amplifiers (OTA) is used, in order to implement fully integrated structures. Three respective novel CMOS shaper topologies are designed and compared in terms of noise performance, total harmonic distortion, dynamic range and power consumption as to examine which is the most preferable in readout applications. Analysis is supported by simulations results using SPICE in a 0.6?µm process by the Austria Mikro Systeme (AMS). The optimum implementation appears to be the OTA based cascade shaper structure with the inductor simulation. The specific shaper implementation is used in a fully integrated preamplifier-shaper system for a space application silicon strip detector of 2?pF capacitance. The readout system achieves an equivalent noise charge of 327 electrons at 1.7?µs peaking time in ?40°C.     

Phase-Only Matched Filtering of Ultrawideband Arbitrary Microwave Waveforms via Optical Pulse Shaping

We demonstrate compression of ultrawideband (UWB) microwave arbitrary waveforms via phase-only matched filtering implemented in a programmable hyperfine resolution optical pulse shaper. We synthesize spread-time UWB electrical waveforms and utilize programmable microwave photonic phase filters to impose the opposite of a waveform's spectral phase on its spectrum. This enables us to compress an UWB microwave waveform to its corresponding bandwidth-limited pulse duration via phase filtering. As an example, we present compression of a linear frequency-modulated electrical waveform with ${>}15$ GHz frequency content with almost 200% fractional bandwidth with ${sim}733$ ps temporal window to a 40-ps duration pulse with more than 14-dB gain in peak power. Our technique is programmable and we believe it is applicable to a wide range of arbitrary spectral phase modulated UWB radio frequency (RF) waveforms.      

Multichannel Differential Group Delay Emulation and Compensation via a Phase Pulse Shaper

We developed a differential group delay (DGD) emulator which is based on a high spectral resolution phase pulse shaper. DGD generation has been demonstrated for up to four wavelength channels independently and simultaneously, with DGD accuracy of approximately 1 ps for up to 400-ps DGD range. For each channel, DGD versus frequency profiles can be arbitrarily programmed to user specifications. Multichannel DGD compensation has also been demonstrated using the same setup.     

基于光纤环形镜的全光脉冲整形器

提出了一种基于光纤环形镜的全光脉冲整形器。该全光脉冲整形器利用波分复用器将控制光脉冲引入光纤环形镜中，控制光脉冲由于交叉相位调制在信号光上产生了非线性附加相移。信号光在耦合器中发生干涉，经过整形的信号光脉冲从脉冲整形器的出射端出射，信号脉冲的波形由非线性附加相移的波形决定。实验中．利用对控制脉冲光谱整形和啁啾展宽的方法来对控制脉冲进行时间脉冲的整形，该全光脉冲整形器实现了对单纵模激光的脉冲整形，同时实现了飞秒脉冲和单纵模整形脉冲的精确同步。在理论上数值计算了该全光脉冲整形器的输出特性，理论计算结果和实验结果相一致，并为“快点火”实验提供了一条可行的技术途径。