Akito Chiba

Dynamic and high-resolution live cell imaging by direct electron beam excitation.

We propose a direct electron-beam excitation assisted optical microscope with a resolution of a few tens of nanometers and it can be applied for observation of dynamic movements of nanoparticles in liquid. The technique is also useful for live cell imaging under physiological conditions as well as observation of colloidal solution, microcrystal growth in solutions, etc. In the microscope, fluorescent materials are directly excited with a focused electron beam. The direct excitation with an electron beam yields high spatial resolution since the electron beam can be focused to a few tens of nanometers in the specimens. In order to demonstrate the potential of our proposed microscope, we observed the movements of fluorescent nanoparticles, which can be used for labelling specimens, in a water-based solution. We also demonstrated an observation result of living CHO cells.

50-km SMF transmission of 50-Gb/s 16 QAM generated by quad-parallel MZM

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.

Coherent synthesis of optical multilevel signals by electrooptic digital-to-analog conversion using multiparallel modulator

This paper presents an electrooptic vector digital-to-analog converter (EO-DAC) for coherent synthesis of optical multilevel signals, such as quadrature-amplitude modulation (QAM) signals. For generation of an optical multilevel/QAM signal, the inphase (I) and quadrature (Q) components of a carrier lightwave should be orthogonally modulated in multi-levels. Conventionally, inphase-quadrature (IQ) orthogonal modulators have been utilized for this purpose. In the scheme, however, the symbol rate available for multilevel/QAM signals is limited, and it is difficult to obtain a clear constellation because of the difficulty involved in handling with electrical multilevel signals. The EO-DAC employing multiparallel modulator, described in this paper, can be used to synthesize multilevel signals through the combination of binary data streams. Using this proposed technology, multilevel signals can be coherently synthesized at a high bit rate, and clearer constellations can be obtained. Further, because of its flexibility, and versatility, the EO-DAC can be used for the several types of multilevel modulation formats. In this paper, we describe the EO synthesis of optical multilevel signals especially focusing on the method based on the EO-DAC, along with comparisons with other conventional methods.

Ultra high extinction-ratio and ultra low chirp optical intensity modulation for pure two-tone lightwave signal generation

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.

High-speed dual-parallel Mach-Zehnder modulator using thin lithium niobate substrate

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.

Duobinary signal generation using high-extinction ratio modulation

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.

Reconfigurable multilevel transmitter using monolithically integrated quad Mach-Zehnder IQ modulator for optical 16-QAM and 8-PSK generation.

We propose and demonstrate a reconfigurable multilevel transmitter using a monolithically-integrated quad Mach-Zehnder in-phase/quadrature (QMZ-IQ) modulator with binary driving electronics. Different from previous parallel-integrated quadrature amplitude modulation (QAM) transmitter solutions, only one electrode is required to adjust the relative phase offset among embedded sub-Mach-Zehnder modulators in the proposed IQ superstructure. By feeding different RF driving electronics and operating the integrated modulator as different bias conditions, different advanced multilevel modulation formats, such as QAM and 8-ary phase-shift keying (8-PSK), could be synthesized. In this paper, a 40-Gb/s 16-QAM and a 30-Gb/s 8-PSK are generated using the proposed multilevel transmitter, respectively. Offline digital processing is employed for bit-error rates estimation and constellation reconstruction.

Low-Crosstalk Balanced Bridge Interferometric-Type Optical Switch for Optical Signal Routing

Crosstalk is one of the significant measures of an optical cross-bar switch. In this paper, we describe a configuration for crosstalk suppression of a balanced-bridge interferometric type optical switch and its application to an optical-signal routing device. Since crosstalk of the optical switch originates from imbalance in the amplitude of a lightwave propagating within the arm of the interferometer, additional Mach-Zehnder structures were embedded for trimming the amplitude of the light. By adjusting the transmittance of the trimmers, crosstalk of less than -56 dB is achieved for dc voltage. Also, for high-frequency voltages, a crosstalk estimation procedure was developed, and crosstalk at 10-GHz sinusoidal voltage was evaluated to be -48 dB. Furthermore, based on the transient response measurement, its switching time was evaluated to be 26 ps. For a demonstration utilizing extremely low crosstalk and quick response, a guard-time-free optical signal routing experiment is also described.

Adaptive symbol discrimination method for distorted multi-level optical signal and its application to decoding of high-speed optical quadrature amplitude modulation

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.

Crosstalk Suppression of a Balanced Bridge Interferometric-Type LiNbO

Crosstalk in a balanced bridge interferometric-type optical switch is highly suppressed by using Mach-Zehnder (MZ) structures as intensity trimmers. An imbalance in optical power is caused by deviations from the ideal dividing ratio of directional couplers in the switch, which causes an increase in the crosstalk. This imbalance was compensated for by adjusting the transmittances of the nested MZ structures. A crosstalk of less than 55 dB has been achieved even for alternating voltage signals. It is also shown that the crosstalk reduction is possible for a control voltage signal of more than 10 GHz, which is based on double-sideband suppressed-carrier modulation spectra measurement results.