We report the generation of time- and wavelength-interleaved optical pulses using the principle of sub-harmonic pulse gating in a dispersion-managed fiber cavity. The pulsed source has been applied to the processing of electrical and optical signals including analog-to-digital conversion, wavelength multicast, and serial-to-parallel optical data conversion.

Next generation free electron lasers aim to generate x-ray pulses with pulse durations down to 30 fs, and possibly even sub-fs. Synchronization of various stages of the accelerator and the probe laser system to the x-ray pulses with stability on the order of the pulse width is necessary to make maximal use of this capability. We are developing an optical timing synchronization system in order to meet this challenge. The scheme is based on generating a train of short optical pulses, with a precise repetition frequency, from a mode-locked laser oscillator and distributed via length-stabilized optical fibers to points requiring synchronization. The timing information is embedded in the repetition frequency and its harmonics. A significant advantage of the optical synchronization system is that multiple mode-locked Ti:sapphire seed oscillators typically present in an accelerator facility can be replaced by the master mode-locked fiber laser. In this paper, we briefly review progress on the development of the synchronization system and then discuss the implementation of this new possibility. Several technical issues related to this approach are analyzed.

Gaussian pulse has no beginning point, so has no Laplace transform and is non-physical. We propose sinnt pulse (referred to as pseudo-Gaussian pulse or PGP) as an approximation of the Gaussian pulse. PGP has the Laplace transform and approaches the Gaussian pulse as n→∞. The propagation of PGP-modulated wave packet in the highly anomalous dispersion band of a Lorentz medium is investigated by numerical inversion of Laplace transform. Our results are greatly different from the conventional results obtained by the saddle point method. Our results show that the velocity of a Gaussian wave packet cannot be explained only by the concept of the group velocity as has been done so far.

The UWB (ultra-wideband) pulse radar is a promising candidate as an environment measurement method for rescue robots. Radar imaging to locate a nearby target is known as an ill-posed inverse problem, on which various studies have been done. However, conventional algorithms require long computational time, which makes it difficult to apply them to real-time operations of robots. We have proposed a fast radar imaging algorithm, the SEABED algorithm, for UWB pulse radars. This algorithm is based on a reversible transform, BST (Boundary Scattering Transform), between the target shape and the observed data. This transform enables us to estimate target shapes quickly and accurately in a noiseless environment. However, in a noisy environment the image estimated by the SEABED algorithm is degraded because BST utilizes differential operations. We have also proposed an image stabilization method, which utilizes the upper bound of the smoothness of received data. This method can be applied only to convex objects, not to concave ones. In this paper, we propose a fractional BST, which is obtained by expanding the conventional BST, and an image stabilization method by using the fractional BST. We show that the estimated image can be stabilized regardless of the shape of target.

In the design of an active matrix LCD (Liquid Crystal Display), the ratio of the pixel voltage to the video voltage (RPV) of a pixel is an important factor of the performance of the LCD, since the pixel voltage of each pixel determines its transmitted luminance. Thus, of practical importance is the issue of how to maintain the admissible allowance of RPV of each pixel within a prescribed narrow range. This constraint on RPV is analyzed in terms of circuit parameters associated with the sampling switch and sampling pulse of a column driver in the LCD. With the use of a minimal set of such circuit parameters, a design procedure is described dedicatedly for the sampling switch, which intends to seek an optimal sampling switch as well as an optimal sampling pulse waveform. A number of experimental results show that an optimal sampling switch attained by the proposed procedure yields a source driver with almost 18% less power consumption than the one by manual design. Moreover, the percentage of the RPVs within 1001% among 270 cases of fluctuations is 88.1% for the optimal sampling switch, but 46.7% for the manual design.

A novel UWB system for a new indoor short distance radio-communication is examined. Various types of UWB systems have been proposed in the literature. Particularly direct sequence (DS) systems and time hopping (TH) systems are attractive due to low power consumption and a simple transceiver construction. In this paper, we consider to apply modulated and modified Hermite pulses (MMHP) for both DS-UWB and TH-UWB systems. Furthermore, MMHP are extended to a novel pulse set referred as limited bandwidth MMHP set in order to reduce various interferences. It is composed of pseudo-orthogonal pulses that have both good auto-correlation characteristics in all orders and low cross-correlation characteristics between different orders. The proposed pulse set also have some specific notches, which can be used to reduce narrow-band interference (NBI). Additionally, we propose a novel pulse shape hopping that employs the proposed MMHP set. Multi-user interference (MUI) and inter-symbol interference (ISI) can be reduced by such a pulse shape hopping scheme for the DS or TH UWB signal format. Simulation results show significant performance improvements by using the proposed UWB system.

Pulse-shaping OFDM is well-known that it performs well in a mobile environment compared with conventional OFDM. However, in a highly mobile environment intersymbol and intercarrier interferences (ISI/ICIs) increase and can no longer be neglected. These ISI/ICIs deteriorate the performance of the systems. Proper channel equalization is needed for further improvement of the systems. In this paper, a more general case, namely Biorthogonal Frequency Division System based on Offset QAM (BFDM/OQAM) is considered. We propose a multi-input multi-output (MIMO) transversal filter to equalize the time-frequency dispersive channel. Tap weights are calculated using the zero-forcing (ZF) algorithm. We also propose maximum-likelihood channel estimator and its low-complexity version. The proposed system can significantly improve the performance of BFDM/OQAM systems in the highly mobile environment.

In this letter, it is shown that a MAP detector can be employed with differential pulse-position modulation (L-DPPM) in an indoor optical wireless system. The MAP detector error performance is evaluated and compared with that of a hard-decision detector and MLSD over an intersymbol interference channel. It is shown that a MAP detector provides superb performance even in a dispersive channel with high DT.

Optical fiber communications require multiple-access schemes to access a shared channel among multiple users. The coherent ultrashort light pulse code-division multiple-access (CDMA) system is one such scheme, and it also offers asynchronous-access communication. This system usually employs 2-level, i.e., binary, m-sequences as signature codes because of their low correlation. If the number of active users is greater than the length of the m-sequence, i.e., code length, distinct m-sequences are used. However, the distinct 2-level m-sequences do not exhibit low correlation, resulting in performance degradation. We therefore propose a coherent ultrashort light pulse CDMA communication system with distinct 4-level, i.e., quaternary, m-sequences to improve system performance when the number of users is greater than the code length. We created the 4-level m-sequences from 2-level m-sequences, and assess the correlation of the 4-level m-sequences. We also theoretically derive the bit error rate (BER) of the proposed system taking into account multiple-access interference (MAI), beat noise, amplified spontaneous emission (ASE), shot noise, and thermal noise. The numerical results show that BER for distinct 4-level m-sequences is more than an order of magnitude smaller than that for distinct 2-level m-sequences. BER is limited by MAI and beat noise when the power of the received signal is high, otherwise BER is limited by ASE, shot noise, and thermal noise.

This letter develops theoretical analysis of the normalized LMS algorithm (NLMSA) for use in complex-domain adaptive filters in the presence of impulse noise at filter input. We propose a new "stochastic" model for such impulse noise, and assume that filter reference input process is a white process, e.g., digital QAM data, White & Gaussian process, etc. In the analysis, we derive a simple difference equation for mean square tap weight misalignment (MSTWM). Experiment is carried out to demonstrate effectiveness of the NLMSA in robust filtering in the presence of the impulse noise at the filter input. Good agreement between simulated and theoretically calculated filter convergence, in a transient phase as well as in a steady-state, proves the validity of the analysis.

UWB pulse radars that offer target shape estimation are promising as imaging techniques for household or rescue robots. We have already proposed an efficient algorithm for a shape estimation method SEABED which is a fast algorithm based on a reversible transform. SEABED extracts quasi wavefronts from received signals with the filter that matches the transmitted waveform. However, the scattered waveform is, in general, different from the transmitted one depending on the shape of targets. This difference causes estimation errors in SEABED. In this paper, we propose an accurate algorithm for a polygonal-target based on scattered waveform estimation. The proposed method is presented first, followed by results of numerical simulations and experiments that show the efficiency of the proposed method.

Self-controlled sub-nanosecond pulse generator was demonstrated with an ytterbium-doped fiber. This fiber laser consisted simply of all non-polarization fiber without any devices for polarization control and birefringence compensation. The self-pulse operation system gave an average output power of 0.9 mW in 800-ps duration pulses.

A self-starting pulse laser with an erbium-doped fiber cooled at liquid-nitrogen temperature was demonstrated. The self-starting-pulse fiber-ring laser can produce an approximately 1 ns pulse train without the need for devices for polarization control and compensation of birefringence.

This paper describes the Differential Pass Transistor Pulsed Latch (DPTPL) which enhances D-Q delay and reduce power consumption using NMOS pass transistors and feedback PMOS transistors. The proposed flip-flop uses the characteristic of stronger drivability of NMOS transistor than that of transmission gate if the sum of total transistor width is the same. Positive feedback PMOS transistors enhance the speed of the latch as well as guarantee the full-swing of internal nodes. Also, the power consumption of proposed pulsed latch is reduced significantly due to the reduced clock load and smaller total transistor width compared to conventional differential flip-flops. DPTPL reduces ED by 45.5% over ep-SFF. The simulations were performed in a 0.1 µm CMOS technology at 1.2 V supply voltage with 1.25 GHz clock frequency.

The objective of this paper is to propose the Pulse Position Modulation (PPM) system which embeds the synchronizing signal in the information frame. In the proposed system, the frame for transmitting information is also the frame for acquiring frame timing. The data transmission rate of the proposed system is independent of the length of the synchronization signal because the proposed system does not require the synchronization frame. The data transmission rate and the synchronization performance for the proposed system are better than those of the conventional system.

An all-digital clock deskew buffer with variable duty cycles is presented. The proposed circuit aligns the input and output clocks with two cycles. A pulsewidth detector using the sequential time-to-digital conversion is employed to detect the duty cycle. The output clock with adjustable duty cycles can be generated. The proposed circuit has been fabricated in a 0.35 µm CMOS technology. The measured duty cycle of the output clock can be adjusted from 30% to 70% in steps of 10%. The operation frequency range is from 400 MHz to 600 MHz.

The present letter deals with the blind equalization problem of a single-input single-output infinite impulse response (SISO-IIR) channel with additive Gaussian noise. To solve the problem, we propose a new criterion for maximizing constrainedly a fourth-order cumulant. The algorithms derived from the criterion have such a novel property that even if Gaussian noise is added to the output of the channel, an effective zero-forcing (ZF) equalizer can be obtained with as little influence of Gaussian noise as possible. To show the validity of the proposed criterion, some simulation results are presented.

We theoretically analyze the performance of coherent ultrashort light pulse code-division multiple-access (CDMA) communication systems with a nonlinear optical thresholder. The coherent ultrashort light pulse CDMA is a promising system for an optical local area network (LAN) due to its advantages of asynchronous transmission, high information security, multiple access capability, and optical processing. The nonlinear optical thresholder is based on frequency chirping induced by self-phase modulation (SPM) in optical fiber, and discriminates an ultrashort pulse from multiple access interference (MAI) with picosecond duration. The numerical results show that the thermal noise caused in a photodetector dominates the bit error rate (BER). BER decreases as the fiber length in the nonlinear thresholder and the photocurrent difference in the photodetector increase. Using the nonlinear optical thresholder allows for the response time of the photodetector to be at least 100 times the duration of the ultrashort pulses. We also show that the optimum cut-off frequency at the nonlinear thresholder to achieve the minimum BER increases with fiber length, the total number of users, and the load resistance in the photodetector.

In this paper, two new modulation schemes, Multi-Pulse Modulation (MPM) and Differential Multi-Pulse Modulation (DMPM) have been proposed in order to increase the total data rate and improve the error performance. By these schemes, the modulated pulse that had been used for transmitting only one data bit in each pulse-pair in conventional TR-UWB system, can be used for transmitting more than one bit data depending on the level of modulation. Moreover, the error performance has been improved by these new modulation schemes because for the same Eb/N0, the energy per pulse has increased. In addition, these new modulation schemes are applied to a multiple access system. The simulation results show that the total throughput performance of the proposed system has been improved, nearly 2-4 times when compared to the conventional TR-UWB communication system.

A highly collision-resistive RFID system multiplexes communications between thousands of tags and a single reader in combination with time-domain multiplexing code division multiple access (TD-CDMA), CRC error detection, and re-transmission for error recovery. The collision probability due to a random selection of CDMA codes and TDMA channels bounds the number of IDs successfully transmitted to a reader during a limited time frame. However, theoretical analysis showed that the re-transmission greatly reduced the collision probability and that an ID error rate of 2.510-9 could be achieved when 1,000 ID tags responded within a time frame of 400 msec in ideal communication channels. The proposed collision-resistive communication scheme for a thousand multiplexed channels was modeled on a discrete-time digital expression and an FPGA-based emulator was built to evaluate a practical ID error rate under the presence of background noise in communication channels. To achieve simple anti-noise communication in a multiple-response RFID system, as well as unurged re-transmission of ID data, adjusting of correlator thresholds provides a significant improvement to the error rate. Thus, the proposed scheme does not require a reader to request ID transmission to erroneously responding tags. A reader also can lower noise influence by using correlator thresholds, since the scheme multiplexes IDs by CDMA-based communication. The effectiveness of the re-transmission was confirmed experimentally even in noisy channels, and the ID error rate derived from the emulation was 1.910-5. The emulation was useful for deriving an optimum set of RFID system parameters to be used in the design of mixed analog and digital integrated circuits for RFID communication.