Phase shift keying using optical delay modulation formillimeter-wave fiber-optic radio links

We propose a novel phase shift keying technique that uses optical delay modulation for fiber optic radio links. Using only a 2×1 switch and a delay line, this technique enables modulation of a millimeter-wave carrier at bit rates of several gigabits per second or higher, where high-speed devices are not needed. Binary phase shift keying (BPSK) was experimentally demonstrated, 2-Gb/s data signal on a 40-GHz carrier was transmitted over a 5-km optical fiber without any error. The coherent crosstalk noise, due to insufficient extinction ratio of optical switches, was evaluated. The BPSK modulation technique can he extended to multiphase shift-keying modulation     

Dual-mode composite-right/left-handed transmission line ring resonator

The phase response of composite right/left-handed transmission lines is used in the design of a dual-mode ring resonator. The phase can be designed to change the spacing of the resonant modes. Simulation and measured results for a dual-mode ring demonstrate this technique. The designed structure exhibits the elimination of the singlemode resonance at the second harmonic.     

A femtosecond waveform transfer technique using type II second harmonic generation

We present a novel waveform frequency conversion technique by type II second harmonic generation (SHG). We have theoretically studied and experimentally demonstrated femtosecond waveform transfer from 800 to 400 nm wavelength by type II SHG in a lithium triborate (LBO) crystal. The output second harmonic (SH) waveform is a temporally magnified or compressed version of the input fundamental waveform, depending on the experimental configuration. Our experiments demonstrate that this technique can transfer not only the intensity profiles of the fundamental waveform, but also the phase profiles. This technique shows promise for programmable generation of shaped ultrafast optical waveforms down to the UV range, where direct pulse shaping is challenging.     

General optical all-pass filter structures for dispersion controlin WDM systems

All-pass filters (APFs) are devices that allow phase correction or equalization without introducing any amplitude distortion. An optical implementation of such devices is very attractive since they can be used for dispersion compensation. In contrast to other dispersion control devices, optical APFs can correct any order of dispersion. This can be achieved by careful design of multistage APFs to approximate a target phase profile. However, large dispersion is usually narrow band or requires many filter stages. These performance tradeoffs and the general phase properties of optical APFs are reviewed and clarified in the first part of this paper. In the second part, a general design methodology of optical APFs is introduced. We show that any all-pass structure may be constructed from simple N-port devices (such as directional couplers or Mach-Zehnder interferometers) with N-1 outputs fed back to any of the N-1 inputs. The feedback paths may contain delays or further APFs (recursive design). This set of design rules allows for constructing complex all-pass filters of any number of stages starting with very simple elements. We use this technique to demonstrate a number of optical all-pass structures that may be implemented in planar waveguide or using thin-film filter technology     

Timing Recovery in Synchronous Equalized Data Communication

The best estimation of sampler timing in adaptively equalized systems is examined. First, two previous approaches to the estimation problem are reviewed and are found to have fundamental shortcomings. The first technique sets the timing instants coincident with the peak of the unequalized system impulse response. Under certain circumstances this technique can produce nulls in the spectrum of the sampled system, thus preventing efficient operation of the equalizer. The second technique sets the timing instants so as to minimize the residual distortion of the equalized system. This does assure proper operation but requires a second equalizer structure and also requires an accurate initial estimate of sampler phase which it cannot provide itself. A timing recovery technique based on band-edge component maximization which circumvents these problems is presented. Although the scheme is not optimal, it efficiently and effectively recovers timing in synchronous equalized data communication systems.     

Design of High-Channel-Count Multichannel Fiber Bragg Gratings Based on a Largely Chirped Structure

We propose a novel technique to design a high-channel-count, multichannel fiber Bragg grating (FBG) based on a largely chirped structure. The minimization of refractive-index modulation has been widely discussed in the previously demonstrated multichannel grating designs. The complexity of the grating structure, however, is also important from the point of view of practical fabrication. In this paper, the degree of grating complexity (DGC) is defined. We show that the DGC of a multichannel grating can be significantly reduced by designing a grating with a largely chirped structure. A detailed grating design process based on this technique is discussed, by which four multichannel gratings are designed and numerically studied, for applications such as periodic and nonperiodic spectral filtering, chromatic dispersion compensation and dispersion slope compensation. The proposed theory and examples show that different gratings with high-channel-count and multichannel responses can be designed and fabricated using a single commercially available phase mask, and all the gratings can be realized by a conventional FBG fabrication facility since the gratings have a low DGC with low index modulation.      

A data-gathering antenna array for transhorizon propagation research

A versatile vertical antenna array and receiving system have been developed for measuring relative phase and amplitude along the wavefront of anS-band transhorizon signal. The array, which operates at 3.200 GHz, consists of 12 parabolic antennas 1.22 meters (4 feet) in diameter which are spaced 1.39 meters apart on a tower for a total effective vertical aperture of 15.24 meters (162 lambda). The raw data outputs from the array are amplitude and differential phase successively sampled from the 12 elements. Data can be taken at variable rates of up to 100 passes per second over the 12 elements. The data are processed in a computer to form conventional uniformly illuminated array beams 0.3 degree wide with a grating lobe spacing of 3.9 degrees or to produce many combinations of correlation functions. A reference signal is used to cancel the effects of relative motion of the array support structure from the phase data. The array and receiving system and actual performance characteristics are described.     

A tool for power and phase noise optimization in frequency synthesizers

In this paper, we present a CAD technique to design low-power and low phase noise integrated frequency synthesizers. This technique introduces a key parameter, Phase Noise per Unit Power, which correlates phase noise and power among all the sub-circuits in the frequency synthesizer. By correlating the performance of all the independent circuits together, sophisticated synthesizer design and optimization can be significantly simplified. We demonstrate a 1.8 GHz frequency synthesizer design in a 0.18 μm CMOS process achieving −132 dBc/Hz phase noise at 100 kHz offset with less than 4.3 mW power consumption.     

Narrowband fiber grating filters

Two techniques for the fabrication of fiber gratings with a narrowband filter response are reported. In the first technique, the reflection bandwidth is reduced by increasing the grating length. Fiber gratings 10 mm long have been made with a bandwidth of ~0.3 nm. In the second technique, a phase shift is incorporated into the grating to form a resonant structure. Fiber resonators with resonant dips in reflection and peaks in transmission having full-width half-maximum (FWHM) bandwidths of ~0.08 nm have been fabricated. A corresponding narrowband transmission peak was also measured     

ASK multiport optical homodyne receivers

Several types of ASK multiport homodyne receivers are investigated, and the impact of the phase noise and of the shot noise on these receivers is analyzed. The simplest structure is the conventional multiport receiver with a matched filter in each branch. This structure can tolerateDeltavT[deltavis the laser finewidth andTis the bit duration) of several percent with a small power penalty (3.6 percent for 1-dB penalty and 5.2 percent for 2-dB penalty). Optimization of branch filters of conventional multiport receivers does not help when the linewidth (and the penalty) is small but does improve the receiver performance for larger linewidths. The most important point of the paper is the novel wide-band filter-rectifier-narrow-band filter (WIRNA) structure, proposed and investigated here for the first time for optical communication systems. It is shown that the optimized WIRNA homodyne receivers are extremely robust with respect to the phase noise: the WIRNA tolerable value ofDeltavTis 3.6 percent for 1-dB penalty and more than 50 percent for 2-dB penalty. Thus, the WIRNA structure opens, for the first time, the possibility of constructing homodyne receivers operating at several hundred megabits per second with conventional DFB lasers without complicated external cavities. Under no-phase-noise conditions, all the multiport receivers investigated here have the same performance, which is identical to that of heterodyne ASK receivers. In addition, the optimized WIRNA receivers can tolerate tapproximately) the same laser linewidth as the heterodyne ASK receivers. Thus, the main difference between the WIRNA multiport homodyne and heterodyne receivers is that the former shifts the processing to a lower frequency range, in return for a more complicated implementation. This difference makes the WIRNA multiport homodyne receivers particularly attractive at high (say, several gigabit per second) bit rates.     

A novel phase noise reduction technique in oscillators usingdefected ground structure

A new technique to reduce the phase noise in microwave oscillators is developed using the resonant characteristic of the defected ground structure (DGS). Two kinds of oscillators have been designed and measured for the examination of the reduction of phase noise by the DGS. The first adopts the DGS section under the microstrip line at the gate circuit, while the second has only the conventional microstrip line. Measurement shows reduced phase noise by 10-15 dB in the oscillator with the DGS compared to the conventional one     

Continuously phase-matched M-waveguides for second-order nonlinearupconversion

We present an analysis of an M-waveguide structure in lithium niobate that provides a new method for second-order nonlinear upconversion processes. M-waveguides can be designed to be continuously phase matched without the use of birefringence or quasi phase matching, and the output wave profile produced is single-lobed in the core region. M-waveguides provide a novel phase-matching technique and are ideal candidates for monolithically integrated circuits     

Alternatives for on-board digital multicarrier demodulation

In this paper alternatives for digital multicarrier demodulators (MCD) suitable for advanced digital satellite communications systems are presented. The MCD permits the direct on-board interfacing of FDMA and TDM communication links by digital signal processing techniques. Two main functions are implemented by a MCD: demultiplexing (DEMUX) and demodulation (DEMOD). We focus here only on a digital implementation of the MCD, looking at its advantages, flexibility, better performance and VLSI integrability. The DEMUX may be implemented in a number of ways: the analytic signal method, fast Fourier transform with polyphase network technique, or multistage methods. For all the implementation methods considered it is shown that a certain degree of integration of DEMUX and DEMOD functions is possible. To this end, in the proposed MCD schemes the receiver pulse-shaping filter has been integrated in the DEMUX structure, reducing the overall implementation complexity. It is shown that, for the per-channel structure based on the analytic signal method, a highly modular and flexible implementation can also be achieved. Coherent demodulation is used to reduce the signal-to-noise ratio required to achieve a specified bit error rate. The coherent demodulation is carried out by using the maximum likelihood (ML) estimation method. Two different approaches to receiver synchronization have been studied. For the first, the carrier phase and symbol timing estimates are independently derived by suitable techniques. The second approach makes use of the maximum a posteriori probability method to estimate both the carrier phase and symbol timing of the receivied signal. In particular, for this technique it is shown that, by a suitable choice of the architecture of the digital coherent receiver, the ML demodulator can be integrated in the joint carrier and clock recovery circuit, with no increase in the overall system complexity. The digital architecture of the proposed MCD can be adapted to different digital modulation techniques. However, here we consider only the application for QPSK signals, as this modulation scheme is the most promising for digital satellite communications. A theoretical analysis and computer simulation have been used to evaluate the performance degradation of the proposed MCD, including finite-arithmetic implementation effects.     

Maximization of Good Chips Per Wafer by Optimization of Memory Redundancy

In the optimization of the number of good chips per wafer, yield is obviously one key factor. It plays the major role in the manufacturing phase, as at this time circuit design and chip area cannot be modified. In the design phase, however, chip area as the second factor defining good chips per wafer can still be influenced. If there are no strong relationships between yield and chip area, both can be optimized independently. In some cases, however, there are such strong relationships, and an optimum of yield gain versus area growth has to be found. Maybe the most important example where strong relationships between area and yield have to be considered is the estimation of optimum memory redundancy. In this paper, we will review and discuss relationships between yield and area and present methods for optimization of good chips per wafer, with special focus on the optimization of memory redundancy     

Recovery of Spectral Moments from Overlaid Echoes in a Doppler Weather Radar

This paper presents a technique that enables the estimation of spectral moments of overlaid first and second trip weather echo signals in a pulsed Doppler radar. The transmitted pulses are phase coded with a sequence that allows manipulation of the signal spectrum in such a way that either the first or the second trip signal autocorrelation can be made zero, thus removing the bias error in mean velocity estimates due to overlaid echo. With a sufficiently large number of samples, desired mean velocities can be recovered using autocovariance processing provided that the interfering overlying echo power is not more than 10 dB higher than the desired echo power. Also presented is a spectral processing technique that, in conjunction with autocovariance processing, can recover all three spectral moments of both the first and second trip echoes, when their spectrum widths are narrow compared to the Nyquist interval and their power ratio is in the range ±15 dB. An algorithm is developed that can be easily implemented in existing Doppler radars, with the addition only of a lowpower switchable phase shifter and associated drive circuit.     

Algorithm for complete and rapid retrieval of ultrashort pulseamplitude and phase from a sonogram

We describe an algorithm based on principal-component generalized projections that is capable of unambiguous retrieval of the amplitude and phase of an ultrashort pulse from a measurement of its sonogram. Running on a personal computer, the algorithm can complete more than 50 iterations per second which enables real-time display of an ultrashort pulse intensity and phase profile. Retrieval is demonstrated for a range of pulses with commonly encountered phase errors including linear chirp, self-phase modulation, and cubic spectral phase, and experimental results illustrate good agreement between the retrieved pulse characteristics and independent spectral measurements     

Analytical analysis and feedback linearization tracking control ofthe general Takagi-Sugeno fuzzy dynamic systems

The Takagi-Sugeno (TS) fuzzy modeling technique, a black-box discrete-time approach for system identification, has widely been used to model behaviors of complex dynamic systems. The analytical structure of TS fuzzy models, however, is unknown, causing at two major problems. First, the fuzzy models cannot be utilized to design controllers of the physical systems modeled. Second, there is no systematic technique for designing a controller that is capable of controlling any given TS fuzzy model to achieve the desired tracking or setpoint control performance. In this paper, we provide solutions to these problems. We have proved that a general class of TS fuzzy models is a nonlinear time-varying ARX (Auto-Regressive with eXtra input) model. We have established a simple condition for analytically determining the local stability of the general TS fuzzy dynamic model. The condition can also be used to analytically check the quality of a TS fuzzy model and invalidate the model if the condition warrants. We have developed a feedback linearization technique for systematically designing an output tracking controller so that the output of a controlled TS fuzzy system of the general class achieves perfect tracking of any bounded time-varying trajectory. We have investigated the stability of the tracking controller and established a condition, in relation to the stability of non-minimum phase systems, for analytically deciding whether a stable tracking controller can be designed using our method for any given TS fuzzy system. Three numerical examples are provided to illustrate the effectiveness and utility of our results and techniques     

视频压缩编码器的研究与设计

设计并实现了一种基于TMS320C64x系列高性能通用DSPs的MPEG-4 Simple Profile编码器。详细介绍了系统的硬件结构和工作流程。为了解决高分辨率视频编码的实时性问题,研究了采用预测技术的运动估计算法以及基于C64xCPU的软件优化技术。实验结果表明,编码器对D1分辨率(720×576)视频的编码速率达到25帧/秒以上,且具有较低的码率和较好的图像质量。     

Indirect Controlled Phased Source

We propose here a novel phase controllable oscillator to realize phase shift for the phased array. The phase of the oscillator is controlled by the phase of reference frequency of a phase locked loop. Since the reference frequency is usually lower than 100MHz, the phase shifting can be much easier, have a lower cost, and be more accurate than that in microwave phase shifters. A four-element scanning array antenna using this novel phase control technique is demonstrated with a scanning range of plusmn40deg in this letter