Tetsuya Kawanishi

Compensation of third-order intermodulation distortion of electro-optic modulator by using frequency chirp modulation

A new electro-optic modulator for compensating the nonlinear distortion is proposed. The third-order intermodulation distortion (IMD3) in receiver output is optically suppressed by the frequency-chirp modulation in the dual-parallel Mach-Zehnder modulator (DPMZM) structure. All of optical branches of the DPMZM are symmetric. The performance was analyzed by numerical calculations. First, we made an experiment to confirm the performance using a DPMZM with a microwave hybrid coupler for applying 10GHz two-tone signals to each electrode of the DPMZM. The chirp parameters of two Mach-Zehnder modulators (MZMs) of the DPMZM were set to opposite signs to each other, +1 and −1. It is seen from the experiment that the intensity ratio of IMD3 to signal in the receiver output was less than −58dB at modulation indices below 0.55 (0.175π) rad and that the minimum of the ratio was less than −80dB at around 0.5 (0.16π) rad. In contrast, for a conventional single-MZM the ratio was less than −27dB below 0.55rad modulation indices. These experimental results agreed well with the calculation ones. Next, we designed and fabricated the modulator of the single-chip structure and the single-input operation for smallsizing and simple operation. The microwave rat-race circuit (RR), which operates as a 180° hybrid coupler, was designed on a Lithium Niobate (LN) substrate at 10GHz and was integrated with modulation electrodes of the DPMZM. The RR and modulation electrodes were formed with a gold thin film pattern at a time. The IMD3 suppression operation was confirmed for the fabricated modulator as well.

Study of high power generation in UTC-PD at 110-210 GHz

We designed and fabricated a low-bias operational uni-travelling carrier photodiode (UTC-PD) structure, which can be operated at over 100 GHz. The main structure of the device consisted of p-doped InGaAs for the photo-absorption layer and non-doped InP for the carrier collector layer, to obtain both a high electron drift velocity at a low bias and a small CR time constant based on the pn-junction capacitance. Through an on-wafer probing test, the frequency response was measured up to 210 GHz using a 1 mm coaxial connecter type (DC-110GHz), W-band (75–110 GHz) and G-band (140–220 GHz) waveguide probe with a spectrum analyzer. In the measurement results, a large bandwidth of 10 MHz-110 GHz could be obtained with good flatness within ±1 dB. When the W-band and G-band performance were characterized, the high-power characteristic of -3.8 dBm could be achieved at 106 GHz. and the output power level of - 19.8 dBm could be confirmed at 210 GHz as well.

Radio over fiber network technologies for linear cell systems in millimeter-wave bands

Millimeter-wave signal feeding technique to remote radio transceivers via an optical fiber network is discussed particularly in linear cell configurations using radio over fiber technologies. Double-sideband and single-sideband modulation schemes with suitable modulation frequency are demonstrated under 10-km-class optical fiber network configuration.

W-band millimeter-wave patch antennas on optical modulator for runway security systems

We propose and report W-band millimeter-wave patch antennas on an optical modulator for foreign object debris (FOD) detection to support runway security systems. The proposed device can be used for receiving wireless millimeter-wave signals and converting to lightwave signals trough optical fiber networks for distribution. In experiment, the proposed device was fabricated successfully in an array structure. In measurement, about 40dB optical sidebands to carrier ratio was obtained. Approximately 6GHz bandwidth was also obtained using the fabricated devices.

Modulator bias optimization of a high extinction-ratio optical Mach-Zehnder intensity modulator for linear-cell radar systems

We propose a bias operation method with high stability using a high extinction-ratio optical modulator. Even in the high extinction-ratio optical modulator, there is instability of the bias fluctuation under a null-point bias operation, in general. We set the bias point at a slope for improvement of tracking performance without significant spurious emissions. When the bias voltage is changed in operation by bias drifts of the modulator, slope-set bias operation can easily provide direction of the voltage change, and finally, can realize quick restoration of the bias condition without unwanted bias changes. Numerical and experimental analyses are discussed in the study with a discussion of nonlinear distortion effect at bias conditions.

30-GHz OFDM radar and wireless communication experiment using radio over fiber technology

We present both OFDM radar and wireless communication experiments with 30-GHz RoF technology using the same experimental set-up. Two of key technologies of a newly developed 30-GHz wideband photoreceiver module and digital pre-distortion techniques allow a high space resolution with high signal-to-noise ratios. From the wireless communication experiment, 14.5-Gbps high data rate up to a distance of 10-m is achieved with a 1 × 10−3 bit error rate using single carrier signal, which can be easily switched to a multi-carrier signal system, such as orthogonal frequency-division multiplexing (OFDM). In the OFDM radar experiment (10.1 GHz bandwidth, 1683 subcarriers) including low crest factor OFDM reference signal, highly reflected signals from “known refractors” located at a 5-m distance could be clearly detected.

Radio over fiber-based radio relay link for indoor and in-car applications towards 5G/IoT era

Radio over single-mode, multimode, and plastic optical fiber links are demonstrated as a radio relay link for improvement of coverage areas. These techniques are capable for different deployment scenarios in several indoor conditions.

A semiconductor optical amplifier consisting of highly stacked InAs quantum dots fabricated by using the strain-compensation technique

A semiconductor optical amplifier was fabricated by incorporating highly stacked InAs quantum dots (QDs) as gain media. Twenty InAs QD layers were successfully stacked through the strain-compensation technique, without any deterioration of crystal quality. A wide-range 1.55 μm band gain was observed. The maximum gain reached 15 dB at 1510 nm when the input power was below -20 dBm.

Large-scale space division multiplexed transmission through multi-core fiber

Rapid progress in multi-core fibers and space division multiplexing technologies has enabled large-capacity transmission exceeding the conventional single-core fiber capacity limit of approximately 100 Tb/s. In this invited paper, we review such progress and achievements.

Wideband frequency conversion with LiNbO/sub 3/ optical single-sideband modulator

We demonstrated a wideband frequency conversion with a LiNbO/sub 3/ optical single-sideband modulator. The operation wavelength more than 80 nm was attained at the 10 GHz frequency conversions. No degradation in the 10 Gb/s signals was found.