Spl Pi Research Articles

Equivolumetric partition of solid spheres with applications to orientation workspace analysis of robot manipulators

Orientation workspace analysis is a critical issue in the design of robot manipulators, especially the spherical manipulators. However, there is a lack of effective methods for such analysis, because the orientation workspace of a robot manipulator is normally a subset of SO(3) (the special orthogonal group) with a complex boundary. Numerical approaches appear more practical in actual implementations. For numerical analysis, a finite partition of the orientation workspace in its parametric domain is necessary. It has been realized that the exponential coordinates parameterization is more appropriate for finite partition. With such a parameterization, the rigid body rotation group, i.e., SO(3), can be mapped to a solid sphere D/sup 3/ of radius /spl pi/ with antipodal points identified. A novel partition scheme is proposed to geometrically divide the parametric domain, i.e., the solid sphere D/sup 3/ of radius /spl pi/, into finite elements with equal volume. Subsequently, the volume of SO(3) can be numerically computed as a weighted volume sum of the equivolumetric elements, in which the weightages are the element-associated integration measures. In this way, we can simplify the partition scheme and also reduce the computation efforts, as the elements in the same partition layer (along the radial direction) have the same integration measure. The effectiveness of the partition scheme is demonstrated through analysis of the orientation workspace of a three-degree-of-freedom spherical parallel manipulator. Numerical convergence on various orientation workspace measures, such as the workspace volume and the global condition index, are obtained based on this partition scheme.

Pulse shaping for differential offset-QPSK

Pulse shaping is examined as a means to improve the performance of a differential offset quadrature phase-shift keying system in a bandwidth-constrained environment. Through optimization with respect to a composite Nyquist criterion, the derived pulse shapes have comparable performance to a /spl pi//4-differential quadrature phase-shift keying in an additive white Gaussian noise (AWGN) channel and better performance in a hard-limited AWGN channel.

Optical DPSK demodulator based on /spl pi/-phase-shifted fiber Bragg grating with an optically tunable phase shifter

We propose and demonstrate a novel optical differential phase-shift keying (DPSK) demodulator with an optically tunable phase shifter. The proposed DPSK demodulator is implemented by using a pi-phase-shifted fiber Bragg grating and an Yb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -Al <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+ </sup> codoped optical fiber. A 10-Gb/s DPSK signal was successfully demodulated by the proposed demodulator, showing clearly open eye diagrams as well as bit-error-free performance. Moreover, the phase of delayed optical signal can be tuned by the phase shifter that is controlled by a pumping light at around 980nm

A quarter-wave phase-stepping algorithm for fiber-optic electronic speckle pattern interferometry using zero-crossing triggers

An efficient phase-stepping method for the use in fiber-optic electronic speckle pattern interferometry is proposed. A fiber-optic Michelson interferometer is phase-modulated, and the zero-crossing points of a back-reflected interference signal, that have consecutive /spl pi/ phase difference, are used to trigger the charged-coupled device camera to capture specklegrams with /spl pi//2 phase difference. A phase error of less than 3 mrad with 100-Hz image capture speed has been obtained in an open-loop configuration. Also, it has been experimentally shown that the phase-stepping accuracy of the proposing method does not depend on the nonlinear actions of the phase modulator.

Boundless-range optical phase modulator for high-speed frequency-shift and heterodyne applications

Optical phase modulators are used for many applications in optical communication systems and signal processing, but they are fundamentally limited in the amount of a monotonic phase change that can be induced due to practical physical limits on the drive-signal magnitude. In this paper, the necessary drive conditions are derived to achieve a boundless monotonic phase change on the output while keeping the drive inputs within practical physical bounds, i.e., comparable to an amplitude modulator. A simulation of a three-section modulator with two distinct drive signals is provided whereby a continuous phase change on the output is achieved with only a maximum phase shift of /spl pi//2 created in any individual section. The architecture has two outputs, therefore a design tradeoff can be made in choosing the power splitting ratio between the outputs. The amplitudes are kept constant as the phase is modulated. The other output is not frequency shifted and may provide a convenient heterodyne signal for subsequent coherent processing.

Particle-in-cell simulations of start-up dynamics in a grounded cathode magnetron

Simulations results of a relativistic magnetron using the MAGIC particle-In-cell (PIC) code are reported. The time evolution of the buildup process for different magnetron azimuthal modes is studied for a variety of initial voltages, with and without a second, oscillatory small voltage in addition to the drive. The self-field is seen to evolve so that the anode-cathode voltage nears the Buneman-Hartree voltage of a particular mode. Simulations show that the output power is larger in the case where the voltage dynamically approaches the Buneman-Hartree value from above than when it is approached from below. The time evolution of a pure mode (without mode competition) resembles the time evolution of some autoresonant systems. An oscillatory voltage, of relatively small amplitude, fixed or chirped in frequency is seen to modify mode competition. The frequency of the first occurring mode is shown to follow the external drive with small phase deviations. This appears to be the beginning of an autoresonance process driven by the external drive, which stops abruptly at the mode transition. Small changes in the azimuthal structure are seen to lead to different mode dynamics; when the /spl pi/-mode symmetry is enforced other competing modes are suppressed to some extent.

Radio frequency priming of a long-pulse relativistic magnetron

Rapid startup, increased pulsewidth, and mode locking of magnetrons have been explored experimentally on a relativistic magnetron by radio frequency (RF) priming. Experiments utilize a -300 kV, 2-8 kA, 300-500-ns electron beam to drive a Titan six-vane relativistic magnetron (5-100 MW output power in each of the three waveguides). The RF priming source is a 100-kW pulsed magnetron operating at 1.27-1.32 GHz. Tuning stubs are utilized in the Titan structure to adjust the frequency of the relativistic magnetron to match that of the priming source. Experiments are performed on rising sun as well as standard anode configurations. Magnetron start-oscillation time, pulsewidth, and /spl pi/-mode locking are compared with RF priming versus the unprimed case. The results show significant reductions in microwave output delay and mode competition even when Adler's Relation is not satisfied.

Wideband Monopole Antenna Integrated Within the Front-End Module Package

A novel wideband monopole antenna integrated within the front-end module package for WLAN and/or WiMAX operation in the 5 GHz band for a mobile device is presented. The front-end module package mainly comprises a bent /spl pi/-shaped wideband monopole antenna for 5 GHz band operation and a shielding metal case for accommodating the associated module and circuitry. The antenna is integrated to the shielding metal case through short-circuiting. For practical applications, the proposed front-end module package is to be mounted at one of the corners of the system circuit board of the mobile device. In this case, the shielding metal case not only performs as part of the ground plane of the antenna, but also functions as a shielding metal block to shield the antenna from the undesired coupling with nearby electronic or conducting elements in the mobile device. The proposed design of the front-end module package with an embedded antenna is studied, and obtained results of the constructed prototypes are presented.

Electrooptic modulation of multisilicon-on-insulator photonic wires

This paper proposes and analyzes electrically modulated submicrometer-size high-index-contrast waveguides (photonic wires) based on a multisilicon-on-insulator (MSOI) platform. Metal-oxide-semiconductor junctions are used to control the effective refractive index of the waveguides. The electrooptic structures are electrically and optically modeled. The performances of the studied configurations are analyzed and compared in terms of phase modulation efficiency, optical losses, and operation speed, and the feasibility of their fabrication is discussed. Calculations indicate that the proposed schemes can be used to achieve highly efficient phase shifters (V/sub /spl pi//L/sub /spl pi//<1 V-cm) based on photonic wires on MSOI, with data transmission rates ranging from 3 to 10 Gb/s.

High-speed optical modulator in LiNbO/sub 3/ with cascaded resonant-type electrodes

A high-speed optical modulator with cascaded resonant-type electrodes is presented. To reduce the drive power and switch voltage V/sub /spl pi// and to maintain high-modulation efficiencies, resonant reduced-length electrode structures were cascaded and integrated on LiNbO/sub 3/. Electrical power coupling into the resonators was realized by a single-input source distributed with electrical power dividers and delay lines. As a result, an optical modulator with four resonant-type cascaded electrodes was fabricated and characterized. This device, with a total active-electrode length as short as 3.4 (4 /spl times/ 0.85) mm, achieved a switch efficiency V/sub /spl pi///spl middot/ L of 68 V /spl middot/ mm at 25 GHz at 1.55-/spl mu/m wavelength, resulting in a drive power 8.7 dB less than that required for a traveling wave modulator with the same active length.

Performance analysis of single-MZM APRZ transmitters

In this paper, an efficient single Mach-Zender modulator (MZM) implementation of alternate-phase return to zero (APRZ), which combines carrier-suppressed return to zero (CSRZ)'s ease of implementation with APRZ's nonlinear tolerance, is analyzed. In particular, the first numerical study of 67%-duty-cycle single-MZM APRZ over a 40-Gb/s 5 /spl times/ 100-km link, in terms of nonlinear, dispersion, and filtering tolerance, comparing it with 33% RZ, 33% APRZ, and standard 67% CSRZ, is presented. The results show that APRZ with phase shift close to /spl pi//2 is the optimum choice, independent of specific transmitter implementation. A new mechanism is also discovered, based on the interference of ghost pulses with the original pulse train, which improves the nonlinear tolerance of CSRZ in a 40-Gb/s transmission.

Cost-Effective Chip-On-Heat Sink Leadframe Package for 800-Mb/s/Lead Applications

Chip-on-heat sink leadframe (COHS-LF) packages offer a simple, low-cost chip encapsulation structure with advanced electrical and thermal performance for high-speed integrated circuit applications. The COHS-LF package is a novel solution to the problems of increased power consumption and signal bandwidth demands that result from high-speed data transmission rates. Not only does it offer high thermal and electrical performance, but also provides a low-cost short time-to-market package solution for high-speed applications. In general, there are two main memory packages employed by the most popular high-speed applications, double data rate (DDR) SDRAM. One is the cheaper, higher parasitic leadframe packages, such as the thin small outline packages (TSOPs), and the other is the more expensive, lower parasitic substrate-based packages, such as the ball grid array (BGA). Due to the requirement for higher ambient temperature and operating frequency for high-speed devices, DDR2 SDRAM packages were switched from conventional TSOPs to more expensive chip-scale packages (i.e., BGA) with lower parasitic effects. And yet, by using an exposed heat sink pasted on the surface of the chip and packed in a conventional leadframe package, the COHS-LF is a simpler, lower cost design. Results of a three-dimensional full-wave electromagnetic field solver and SPICE simulator tests show that the COHS-LF package achieves less signal loss, propagation delay, edge rate degradation, and crosstalk than the BGA package. Furthermore, transient analysis using the wideband T-3/spl pi/ models optimized up to 5.6 GHz for signal speeds as high as 800 Mb/s/lead demonstrates the accuracy of the equivalent circuit model and reconfirms the superior electrical characteristics of COHS-LF package.

Broadband hitless bypass switch for integrated photonic circuits

A new microphotonic hitless switch is proposed. By enabling continuous, uninterrupted transition to a bypass path, it permits tuning of wavelength add-drop filters without disturbing intermediate channels. The scheme comprises two symmetrically actuated, 2 /spl times/ 2 /spl Delta//spl beta/-type optical switches, antisymmetrically cascaded in a balanced Mach-Zehnder configuration, and a /spl pi/ differential phase shift in the interferometer arms. By symmetry, it provides for wavelength-independent hitless operation before, during and after switch reconfiguration, permitting slow switching independent of bit rate. Compact implementations using high-index-contrast microelectromechanical-system (MEMS)-actuated switches are proposed.

A novel uniplanar compact photonic bandgap power plane with ultra-broadband suppression of ground bounce noise

A novel /spl pi/-bridged photonic bandgap (PBG) power/ground planes is proposed with ultra-broadband suppression of the ground bounce noise(GBN) in the high-speed printed circuit boards. The S-parameters of the proposed low-period structures show that the novel uniplanar compact photonic bandgap (UC-PBG) structures could omni-directionally suppress the GBN in RF/analog circuits and digital circuits. The high omnidirectionally suppressions of the GBN for the proposed structure are validated both experimentally and numerically in the noise bandwidth from 300MHz to 6GHz, almost the whole noise band.

A novel way to improve the dispersion-limited transmission distance of electroabsorption modulated lasers

We propose and demonstrate a way to improve the dispersion-limited reach of electroabsorption modulated lasers (EMLs). We generate continuous-phase frequency-shift keying/amplitude-shift keying (ASK) signals with the EML by applying a small current modulation to the laser diode (LD) on top of electroabsorption-modulated ASK signals. The amount of frequency deviation induced by the current modulation is adjusted to have the EML output signals experience /spl pi/ phase shift at every space. The experimental demonstration shows that with the proposed scheme we can increase the dispersion-limited transmission distance of the EML-based transmitter by 25%-75%, and it can be further improved by employing an LD with flat frequency-modulation response.

Novel high-response electromagnetic actuator for electronic engraving system

We describe a new moving-iron electromagnetic actuator that utilizes cantilever-beam-type springs, /spl pi/ type armature, full-bridge magnetic circuits, and a single driving coil. The actuator is suitable for electromechanical converters with high response and minor displacement for use in electronic engraving systems. We analyzed its static and dynamic characteristics by using a three-dimensional finite-element method. We used a simple and practical measuring method based on light reflection to detect the actuator's real hysteresis loop and amplitude frequency response characteristics. The results show that the actuator has a displacement of /spl plusmn/65 /spl mu/m, hysteresis of less than 5.5%, and amplitude cutoff frequency of 3.1 kHz. We tested the actuator on a real engraving system and confirmed its characteristics by the engraving results.

Scalable compact circuit model and synthesis for RF CMOS spiral inductors

A scalable industry-oriented, 24-element 2-/spl pi/ compact circuit model for on-chip RF CMOS spiral inductors is presented. It has a good accuracy up to self-resonant frequency (SRF). Two levels of modeling approaches are provided, which are: 1) the fixed model, which extracts the values of circuit elements directly from the measured S-parameters of a given device, achieving high accuracy, but no scalability and 2) the scalable model, in which circuit elements are related to the geometry (i.e., layout) through a set of formulas with model parameters calibrated upon a few testing devices. The synthesis procedure is also discussed, which includes the scalable model and a SPICE simulator as the evaluation method within the iteration loop.

A broadband and scalable model for on-chip inductors incorporating substrate and conductor loss effects

A new T-model has been developed to accurately simulate the broadband characteristics of on-Si-chip spiral inductors, up to 20 GHz. The spiral coil and substrate RLC networks built in the model play a key role responsible for conductor loss and substrate loss in the wideband regime, which cannot be accurately described by the conventional /spl pi/-model. Good match with the measured S-parameters, L(/spl omega/), Re(Z/sub in/(/spl omega/)), and Q(/spl omega/) proves the proposed T-model. Besides the broadband feature, scalability has been justified by good match with a linear function of coil numbers for all model parameters employed in the RLC networks. The satisfactory scalability manifest themselves physical parameters rather than curve fitting. A parameter extraction flow is established through equivalent circuit analysis to enable automatic parameter extraction and optimization. This scalable inductor model will facilitate optimization design of on-chip inductor and the accuracy proven up to 20 GHz can improve RF circuit simulation accuracy demanded by broadband design.

Operational Design on High-Speed Semiconductor Optical Amplifier With Assist Light for Application to Wavelength Converters Using Cross-Phase Modulation

Using the newly developed time-dependent transfer matrix method with nonlinear effects, we analyzed the characteristics of cross-phase modulation (XPM), cross-gain modulation and gain recovery time of a semiconductor optical amplifier (SOA) with an assist light injection, which is introduced to speed up the gain recovery of the SOA. Particularly for the application to high-speed wavelength converters using XPM with an interferometer structure where /spl pi/-phase change is required, various parameters such as SOA lengths, wavelengths and powers of injected lights, and their propagation directions are designed via numerical simulation. Discussions concerning the conditions of an SOA structure and the parameters of injected lights for high-speed operation are described to show the potential of fast gain recovery with a response time as low as 25 ps.

Threshold performance of MUSIC when using the forward-backward data matrix

The multiple signal classification (MUSIC) frequency estimator is a suboptimal method for estimating the frequencies of multiple sinusoids buried in white noise and has a threshold of around 14 dB for the well-known two-sinusoid example (equal amplitudes f/sub 1/=0.52, f/sub 2/=0.5, /spl phi//sub 1/=/spl pi//4, and /spl phi//sub 2/=0). We point out that this threshold value is the result of estimating the autocorrelation estimates using the forward data matrix alone. Instead, if the autocorrelation estimates are obtained from the data matrix, the threshold is lowered to 4 dB (lower than Kumaresan-Tufts method's 7 dB and within 1 dB of maximum-likelihood estimator). We offer an explanation of why the threshold is lowered by examining the noiseless autocorrelation matrix based on the forward and data matrices. Also, it is well known that the Crame/spl acute/r-Rao lower bound (CRLB) is also a function of the relative phases. We point out that when /spl phi//sub 1/=/spl pi//2, the estimates obtained using MUSIC become increasingly biased and cause the variance to fall below CRLB at 23 dB for the forward-backward root MUSIC and at 25 dB for forward-only root MUSIC. The use of the data matrix in spectral estimation is not novel, but to our knowledge, the improvement in threshold for /spl phi//sub 1/=/spl pi//4 has not been reported, nor the comparative performance as /spl phi//sub 1/ varies.