Widely wavelength-tunable ultra-flat frequency comb generation using conventional dual-drive Mach-Zehnder modulator

Wavelength-tunable ultra-flat optical frequency comb generation is demonstrated using only a conventional Mach-Zehnder modulator that is asymmetrically dual-driven by large-amplitude sinusoidal signals with different amplitudes. A 10 GHz-spaced frequency comb with a 10 dB bandwidth of 230 GHz was experimentally generated. In addition, 50 nm widely wavelength tunable operation was achieved.     

Pulmonary arterial impedance analysis by the use of the oscillated assist flow

Pulmonary arterial impedance is an important and interesting characteristic that can be used to evaluate the physiological properties of the pulmonary vessel. However, power spectrum analysis of the pulmonary artery pressure and flow pattern have suggested that peak power in the relatively high frequency range (> 10 Hz) is significantly low; thus, we cannot analyze the vessel properties in the high frequency range. In this study, we used the newly developed vibrating flow pump (VFP), which can generate oscillated blood flow with a relatively high frequency (10-50 Hz) for right heart bypass, to evaluate the pulmonary arterial impedance pattern in the high frequency range. Acute animal experiments of the right heart bypass from the right atrium to the pulmonary artery using 6 healthy adult goats were performed. The flow pattern and pressure of the pulmonary artery, electrocardiograms (ECGs), and arterial and right atrial pressures were continuously monitored during the experiments. Spectral analysis of the hemodynamic parameters using the fast Fourier transform (FFT) method was performed to evaluate the spectral properties. The coherence function, transfer function, and phase patterns were calculated to analyze the impedance pattern in the relatively high frequency area. Previously, various investigators had tried to analyze the impedance patterns of the pulmonary artery; however, they could not analyze the impedance patterns over 10 Hz because the spectral patterns of the pulmonary flow do not have high power at high frequencies. These physiological analyses may be useful in designing the optimal pulmonary circulation.     

10-Gb/s external modulation in optical CPFSK format

We demonstrated a synchronous control technique for external optical modulation in a format of continuous-phase frequency-shift keying (CPFSK) at 10 Gb/s. In this method, the FSK signal in the upper- or lower-sideband state synchronously shifts to the other state at the timing when their phases are the same. We investigated the accuracy of the timing control required for the synchronous control. Experimental results show that the allowable timing misalignment to keep power penalty of the receiver sensitivity less than 1 dB was more than 25 ps, 25% of each bit period.     

Involvement of calcium in interactions between gingival epithelial cells and Porphyromonas gingivalis

Porphyromonas gingivalis, a periodontal pathogen can invade primary cultures of gingival epithelial cells. This invasion was significantly inhibited (74-81%) by thapsigargin and 1,2-bis(2-aminophenoxy)ethane-N,N,N1,N1-tetraacetic acid, acetoxymethyl ester (BAPTA/AM), but not by EDTA or amiloride. Release of Ca2+ from an intracellular store and the subsequent increase in cytosolic [Ca2+] may, therefore, be involved in the invasion process, while Ca2+ influx is not. Moreover, cytosolic [Ca2+] was found to increase transiently in about 30% of gingival epithelial cells acutely exposed to P. gingivalis, but not in unexposed cells, or in cells exposed to noninvasive Escherichia coli. These findings indicate that P. gingivalis invasion of epithelial cells is correlated with activation of [Ca2+]-dependent host cell signaling systems.     

Optical-waveguide microdisplacement sensor

As a novel application of integrated optics, a detection method of microdisplacement is proposed and its first demonstration is reported. The sensor has the Michelson interferometer configuration composed of an optical waveguide hybrid coupler. The operation was confirmed by building and testing the sensor using a Ti-diffused LiNbO3 waveguide.     

Low-drive-power asymmetric Mach-Zehnder modulator with band-limitedoperation

A novel 2×2 asymmetric Mach-Zehnder interferometric modulator is fabricated on Ti:LiNbO₃ waveguide and tested at microwave frequency. Band-limited operation was realized by using a traveling-wave periodic polarity reversed structure with the asymmetric strip line as the modulator electrode instead of the conventional coplanar waveguide. For a modulator with a three-section polarity reversed electrode, a 3-dB bandwidth of 7 GHz was obtained experimentally from 9 to 16 GHz centered at 12 GHz     

Picosecond pulse response of broad-band guided-wave interferometric light modulators

Picosecond pulse operation of the guided-wave light modulator is reported in this paper. First, we analyze the time responses of phase and intensity modulators of the traveling-wave type, and the modulated output waveforms related to the modulating pulses are discussed. It is shown that there is an optimum interaction (or electrode) length of the modulator whereby the drive voltage is minimized for a desired output pulse width. The traveling-wave push-pull light intensity modulator of Ti-diffused LiNbO3waveguides was modulated by a pulse train of 1 GHz repetition frequency, and the modulated output was observed by the image tube streak camera modified for sinusoidal scan at the same frequency. The duration of the modulated light pulses was less than 45 ps, which shows good agreement with the predicted one.