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We investigated optical packet signal distortion due to crosstalk of an optical switch by adopting an intensity trimming technique. Less than −17 dB is required for error-free operation.

We demonstrated synthesis of picosecond pulse train from a continuous-wave laser source using low-driving-voltage Mach-Zehnder modulator (MZM) asymmetrically large-amplitude driven with step-recovery diodes, without using high-power driver amplifiers. 2-GHz, 5.2-ps pulse train was successfully generated.

We proposed and experimentally investigated a frequency swapping technique for two lightwaves by using a LiNbO 3 optical switch where only Mach-Zehnder structures were nested. 10-GHz opposite frequency shifts for two lightwaves were successfully obtained.

We review electro-optic synthesis of high-speed and high-spectral-efficient optical QAM, where a multi-parallel MZM is utilized. It is shown that QAM and other multi-level formats are synthesized superposing BPSK signals.

We proposed a method for millimeter and terahertz wave generation using a Mach-Zehnder-modulator-based flat comb generator, and showed a 100 GHz beat signal by extracting two modes from 12.5 GHz-spaced comb signals.

A new electro-optic duo-binary modulator is proposed. Utilizing non-periodic polarization reversal structures, a pair of Gaussian-like modulation frequency responses with an opposite sign is obtainable. It operates with a single duo-binary signal without electrical/optical filters.

We propose a method to synthesize optical 8PSK with linear phasor trajectory by using a quad-parallel Mach-Zehnder modulator, where BPSK signals are linearly superposed to form 8PSK. Modulation and demodulation of 30-Gb/s 8PSK are demonstrated.

An automatic system to measure the zirconium liner thickness and Zircaloy-2 thickness of Zircaloy tubes with a zirconium liner for nuclear reactors has been developed. This system uses an electromagnetic probe connected to a data processing unit for measuring the liner thickness, an ultrasonic inspection system for measuring the wall-thickness, and a computer for calculating the Zircaloy-2 thickness from the liner thickness and wall-thickness. Fully automatic measurements on zirconium liner thickness and Zircaloy-2 thickness are performed with high accuracy to an order of 2μm. This newly developed system is very useful in assuring the liner layer and Zircaloy-2 thickness in the production of high-quality cladding tubes.

We demonstrate highly pure 160-GHz two-tone lightwave generation using a high extinction-ratio optical intensity modulator and a delay interferometer. The undesired sideband suppression ratio was more than 39 dB.

Amplitude and phase characterization of the output from a dual-electrode LiNbO3 Mach-Zehnder modulator based ultra-flat optical frequency comb generator is investigated for well-known ldquoin-phaserdquo operation and a new ldquoout-of-phaserdquo regime. The out-of-phase regime may be realized with a single-electrode Mach-Zehnder modulator.

We investigate auto-bias control of Mach-Zenhder-modulator-based flat comb generator (MZM-FCG). Ultra-flat frequency comb was generated with a single-stage electro-optic Mach-Zehnder modulator exhibiting great long-term stability. In this paper applications of the MZM-FCG are also introduced.

We have demonstrated wideband frequency-tunable ultrashort pulse generation using a Mach-Zehnder-modulator-based flat comb generator (MZ-FCG) and a dispersion- flattened dispersion-decreasing fiber. Continuous wave lights were converted to ultraflat comb signals by the MZ-FCG. The comb signals were formed into picosecond pulse trains by chirp compensation, and they are compressed into femtosecond ones by a soliton compression technique. Pulse trains of 200 fs width were successfully generated in a repetition rate range of 5-17 GHz. Our pulse source is very simple configuration and possesses high stability and low timing jitter.

The variability of meteorological observables is known to crucially depend on the geographical conditions and the considered spatial as well as temporal scales. In this contribution, we explicitly take the spatial dimension into account. Recent studies on this aspect have considered individual investigations of spatially distributed records from different stations, which form network structures with interesting statistical properties. However, the results of such studies are strongly influenced by the preprocessing of the time series, in the case of temperature records particularly by the applied deseasonalisation strategy. As a complementary approach, we investigate whether the interdependences between pairs of meteorological records can be used to extract additional information about the regularity of temporal variations of the regional climate and its potential change with time. As an alternative to the consideration of univariate estimates of fractal dimensions, the concept of multivariate dimension estimates is introduced. Different quantitative measures for the complexity of linear correlations are introduced and thoroughly compared. After studying the results for stationary model systems, our approach is used to characterise the variability of temperature records from 13 Japanese meteorological stations. The complexity of the complete record varies on an annual period with a larger complexity during the summer season, which is possibly related to the action of the East Asian monsoonal circulation.

By combining a Mach–Zehnder-modulator-based flat comb generator (MZ-FCG) with a dispersion-flattened dispersion-decreasing fiber, femtosecond pulses have been generated from a cw light. Near-Fourier-transform-limit picosecond pulses generated from the MZ-FCG were compressed into femtosecond order by pulse compression. Our system enables flexible tuning of the repetition rate and pulse width, because those depend on the driving signal of the MZ-FCG. Pulse trains of 200 fs width were continuously and stably generated without mode hopping, with a repetition rate range from 5 to 17 GHz. Our system consists of a modulator and compression fiber; thus, the configuration is simpler and more stable.

Pure two-tone signal generation with spurious suppression ratio of 47 dB was demonstrated by using an optical Mach-Zehnder modulator with precisely balanced operation, where extinction ratio and chirp parameter were respectively 64 dB and 0.0099.

We study the impact of modulator extinction-ratio on duobinary signal generation. Duobinary transmission with 2 % modulation depth was achieved at 10 Gb/s, where the extinction-ratio was enhanced by an active trimming technique.

Adaptive symbol discrimination for optical multilevel signal distorted in a constellation map is proposed. A 50-Gb/s 16-level optical quadrature amplitude modulation signal is demodulated with a bit error rate less than forward error correction limit.

We have demonstrated simple and practical femtosecond pulse generation using Mach-Zehnder-modulator-based optical comb generator and adiabatic soliton compression techniques. 10-GHz, 200-fs pulses with excellent extinction ratio (>20-dB) were obtained.

We demonstrated two-color picosecond pulse generation using Mach-Zehnder-modulator-based flat comb generator. Parabolic phase compensation of the comb with a dispersion-flattened fiber yields colorless operation. 10-GHz 4-ps pulse trains were simultaneously generated at two different wavelengths.

We present a high-speed dual-parallel Mach-Zehnder modulator with thin substrate. Modulator frequency response was investigated by network analyzer and optical spectrum analyzer based techniques. Clear eye opening was achieved at 87 Gbaud with on-off-keying.

Broadband wavelength tunable femtosecond pulse generation has been demonstrated using a Mach-Zehnder-modulator-based comb generator. 200 fs, 10 GHz pulses were generated in the wavelength range of 1545 to 1570 nm.

We investigated transmission of 50 Gb/s 16 QAM over 50 km SMF. 16 QAM was electro-optically synthesized with a quad-parallel MZM; demodulated by off-line digital homodyne employing electric equalizers.

This paper discusses the possibility of applying the high extinction ratio Mach-Zehnder LiNbOs optical modulator to a high stability and high frequency (over 100 GHz) optical reference signal generator for Astronomical Radio Interferometer. ALMA (Atacama Large Millimeter/sub-millimeter Array) is a high-frequency radio interferometer array currently under development, and each of the ALMA antennas has a 10-band receiver, and its highest receiving frequency reaches 950 GHz. To receive such high frequencies, higher reference frequency is required for the 1st local (as much as over 100 GHz), and stability to maintain the signal coherence is also required. To address these issues, we have developed a new method to generate and transmit a reference signal in the form of frequency difference between two coherent light waves. The reference frequency is calculated using heterodyne conversion. Current optical two-tone generators of the ALMA baseline plan are based on an optical phase lock schemes. In the high-extinction ratio lithium niobate (LiNbO3) Mach-Zehnder intensity modulator, the optical frequency difference between two optical signals is exactly twice (or four times) the modulation frequency. Compared to the optical phase lock scheme, the Mach-Zehnder modulator has significant advantages in terms of robustness to mechanical vibration and acoustic noise, stability (free from the influence of the input laser line-width), and capability of maintaining polarization state of the input laser.

We demonstrate an ultra-wideband light source using multi-wavelength single-sideband modulation (SSB) frequency sweep technique, aiming at optical coherence tomography (OCT). The light source consists of an optical SSB frequency sweeper with an optical frequency comb generator cascaded with a multi-wavelength laser. Ultra-wideband signal was generated by sweeping frequency of each components of an optical multi-wavelength light source. The proposed system can achieve much faster and more precise spectrum measurement than the conventional OCT system.

We optimize electro-optic frequency comb generation using a conventional Mach-Zehnder modulator. It is theoretically and experimentally proved that a conventional Mach-Zehnder modulator can generate optical frequency comb with excellent spectral flatness. In this technique, the modulator is asymmetrically dual-driven by large-amplitude sinusoidal signals with different amplitudes. The optimal driving condition is theoretically derived, and translated to practical formulas. 10-GHz spaced ultraflat optical frequency comb generation with a 10-dB bandwidth of 230 GHz was demonstrated to confirm the concept.

We propose and demonstrate ultra-flat frequency comb generation using a "push-pull" operated Mach-Zehnder modulator (MZM), where the MZM is dual driven with out-of-phase signals having different amplitudes. 10-GHz spaced 210-GHz-wide comb is flatly generated.

We demonstrated 55-dB extinction ratio port selection using an integrated LiNbO3 2times2 optical switch with two intensity trimmers, in addition to a possibility of its quick response less than 0.1 ns.

We propose an agile wideband light source, which targeted on optical coherence tomography (OCT), consists of an optical single-sideband modulation (SSB) frequency sweeper cascaded with an optical frequency comb generator and a multi-wavelength light source.

We review a simple and highly-stable ultra-flat frequency comb generator employing a single-stage electro-optic Mach-Zehnder modulator. Synthesis of a picosecond/sub-picosecond pulse train from the frequency comb using linear/nonlinear pulse compression technique is also reported.

We theoretically prove that a conventional Mach-Zehnder modulator can generate an optical frequency comb with excellent spectral flatness. The modulator is asymmetrically dual driven by large amplitude sinusoidal signals with different amplitudes. The driving condition to obtain spectral flatness is analytically derived and optimized, yielding a simple formula. This formula also predicts the conversion efficiency and bandwidth of the generated frequency comb.

We describe integrated optical modulators based on LiNbO3 waveguide device technologies, which can be applicable for advanced modulation formats. Over 100 Gb/s transmission can be achieved by differential quadrature-phase-shift-keying (DQPSK).

We present high-speed differential quadrature-shift-keying modulators based on LiNbO3 waveguide device technologies, which can be applicable for over 80 Gb/s transmission systems. Bias condition monitor technique is also investigated for automatic bias stabilization scheme.

We demonstrate the use of an optical equalizer to allow a 42.7-Gbaud (85.4-Gb/s) NRZ-DQPSK signal to tolerate the narrow optical filtering required in high-spectral-efficiency systems. The equalizer passbands are repetitive, enabling equalization of multiple channels.

We propose a high-speed CPFSK/MSK modulation technique using a single-stage monolithic-integrated dual-arm driven FSK modulator. By measuring phase trajectory, we directly confirmed that the externally modulated lightwave was truly continuous in phase to form CPFSK/MSK.

We analyzed the nature of temporal fluctuations of wind speed by Higuchi’s fractal dimension. The upward wind and east wind were nearly random because they were disturbed by the ground and a building before the anemometer, respectively, and therefore hard to be predicted. The north wind was not random and is promising for prediction.

In dynamic optical networking scenarios, it is desirable that the optical transmitter chooses the most suitable modulation format in order to achieve optimal transmission performance. Owing to the ability of switching among different modulation formats, flexible optical transmitters based on reconfigurable optical devices are becoming a key component for the implementation of future flexible optical networks. In this paper, we experimentally demonstrate a flexible 8-ary transmitter to achieve adaptive switching between 8-ary phase-shift keying (8PSK) and circular 8-ary quadrature-amplitude modulation (8QAM) through reconfiguration of two cascaded in-phase/quadrature (IQ) modulators with different driving signals and biasing conditions. An arbitrary binary quadrature-amplitude modulation (2QAM) with constant or non-constant amplitude is proposed and experimentally demonstrated using an IQ modulator. Then, optical 8PSK or 8QAM modulation formats are successfully synthesized when a standard squared QPSK modulator is cascaded with a constant-amplitude or non-constant-amplitude 2QAM, respectively.

By using rapid optical frequency sweep technique, we demonstrated ultra-wideband frequency chirp millimeter-wave wave signal generation whose bandwidth was 6.4 GHz. Ultra fast and precise optical frequency sweep was achieved by using single-sideband modulation, where the theoretical limit of resolution due to the uncertainty between time and frequency was almost obtained. Ultra-wideband frequency chirp signals from 9.6 GHz to 16 GHz, which were generated by using a computer controlled arbitrary waveform generator and a wideband frequency multiplier, were fed to an optical single-single sideband modulator consisting of two sub Mach-Zehnder interferometers.

By using a high extinction-ratio optical Mach-Zehnder modulator biased at a maximum transmission point, we demonstrated generation of a two-tone lightwave consisting of the second order sideband components whose frequency separation was 160 GHz

In this paper, we demonstrate an optical 2times2 switch having an extinction ratio of more than 42 dB over C- and L-band wavelengths by adopting Mach-Zehnder structures to balance optical powers at the two waveguides in the switch. In addition, we also demonstrate the possibility of ultrafast switching, by measurement of high-frequency response at the drop port of the switch when we apply 10-GHz voltage signal

We proposed a stable and agile picosecond pulse generator using a single-stage conventional Mach-Zehnder modulator that generates ultra-flat frequency comb. 10-GHz 2.9-ps pulse trains were generated with a timing jitter of less than 130 fs.

We demonstrated stable 470 GHz clock signal generation, by using a reciprocating optical modulator with uniform fibre Bragg gratings having narrow passbands adjacent to reflection bands, which enables effective generation of high-order sideband components.

80 different optical-code (OC)-labels are generated simultaneously using an optical spectrum synthesizer (OSS) and multi-wavelength electro-optic frequency comb generator. 40 parallel matched-filtering is performed by an OSS. Its application to optical CDMA is also demonstrated.

A wideband transmittance/reflectivity measurement system for fine-structured components is proposed. The optical single-sideband frequency sweeper with an ultra wideband Hilbert transformer enables excellent frequency sweep range between 2GHz-30GHz. Frequency resolution of 4.7MHz is experimentally obtained.

Optical frequency comb generation by using a novel optoelectronic oscillator (OEO) is proposed and demonstrated with the emphasis placed on self-oscillating operation. In the OEO, a wideband LiNbO3 phase modulator is driven with a large-amplitude radio-frequency (RF) feedback signal to generate a deeply phase-modulated light wave; accordingly, an optical frequency comb with a bandwidth greater than the RF signal is generated by self-oscillation. Although it generates multifrequency components, the OEO exhibits characteristics of a single-mode oscillator. Its operation is stable and self-starting. An optical frequency comb with a 120 GHz bandwidth and 9.95 GHz frequency spacing was successfully generated by self-oscillation at a single frequency.

We demonstrated ultra-flat optical frequency comb generation only using a set of conventional Mach-Zehnder modulator asymmetrically dual-driven by large-amplitude sinusoidal signals with different amplitudes. 19-channel 10-GHz-spaced frequency comb with

We demonstrated 80 Gb/s optical differential quadrature-shift-keying modulation, by using a single-chip integrated LiNbO 3 modulator with two sub Mach-Zehnder interferometers, where 40 Gb/s in-phase and quadrature data were, simultaneously, fed to the modulator.

We investigated high-speed optical differential quadrature-shift-keying (DQPSK) modulation using an integrated LiNbO3 modulator with two sub Mach-Zehnder structures. A bias condition monitor technique was also proposed for automatic bias control in DQPSK modulation.

We demonstrated high extinction ratio intensity modulation for two-tone lightwave generation, by using an integrated Mach-Zehnder modulator with active trimmers which can compensate imbalance in the modulator due to fabrication errors. The extinction ratio was larger than 70 dB.

We demonstrated effective generation of high-order sideband components whose frequency deviation was 312 GHz by using a reciprocating optical modulator. Enhancement factor in the eighth-order sideband was 65.9 dB with respect to conventional modulation methods.