Makoto Yaita

120-GHz-Band Wireless Link Technologies for Outdoor 10-Gbit/s Data Transmission

Our progress in 120-GHz-band wireless link technologies enables us to transmit 10-Gbit/s data transmission over a distance of more than 1 km. The 120-GHz-band wireless link uses high-speed uni-traveling carrier photodiodes (UTC-PD) and InP high-electron mobility transistor (HEMT) millimeter-wave (MMW) monolithic integrated circuits (MMICs) for the generation of MMW signals. We investigate the maximum output power of these devices and compare the phase noise of MMW signals generated by UTC-PDs and InP HEMT MMICs. We describe the antennas we used and their operation technologies. Finally, we investigate the dependence of transmission distance on availability using the statistical rain attenuation data. The calculation results show that the 120-GHz-band wireless link can transmit 10-Gbit/s data over a distance of 1 km with availability of 99.999%.

Fully Integrated ASK Receiver MMIC for Terahertz Communications at 300 GHz

An ASK receiver MMIC operating at 300 GHz for future terahertz communications is presented. In the receiver IC, we fully integrated all necessary components-a receiving dipole antenna, high gain RF amplifier, envelop detector for demodulating ASK signal and output differential data amplifier-in a 1000×2500 μm2 area. A silicon lens was used to compensate for the small gain of the on-chip antenna. To ensure reliable and stable operation, we designed the MMIC with a thin-film microstrip line, which is expected to suppress crosstalk between the on-chip antenna and the RF amplifier through the substrate and silicon lens. The packaged receiver module with the silicon lens is expected to provide approximately 24-dBi beam directivity. Measured RF and baseband bandwidths are around 30 and 15 GHz, respectively, when a single bias of 3.3 V and total current of around 86 mA are applied. With the receiver module, simple wireless data transmission was conducted for up to 24 Gbps in the 300-GHz band. At 12.5 Gbps, error-free data transmission (bit error rate <; 10-9) over 0.3 m was achieved with the transmission power of - 16-dBm and a 25-dBi transmitting antenna. With -10-dBm transmission power, measured Q-factors of the received eye patterns were larger than 6 for up to 20 Gbps, which implies that the bit error rate will be less than 10-9.

10-80-Gb/s highly extinctive electrooptic pulse pattern generation

A pulse-rate-tunable, highly extinctive, ultra-highspeed electrooptic pulse pattern generator has been developed. The optical short pulse generation is based on sinusoidal electrooptic phase modulation and linear chirp compensation using a dispersive medium. Filtering the nonlinear chirp components generated by sinusoidal phase modulation drastically improves the pulse extinction, and makes nearly background-free picosecond pulsation over a wide pulse-rate range even when the group delay dispersion value is fixed.

50-Gb/s Direct Conversion QPSK Modulator and Demodulator MMICs for Terahertz Communications at 300 GHz

We demonstrate direct quadrature modulator and demodulator monolithic microwave integrated circuits for future terahertz communications at 300 GHz based on the quadrature phase-shift keying (QPSK) modulation format. For the modulating and demodulating signal, we employed half-Gilbert cell mixers, which provide balanced signaling and moderate performance in conversion efficiency with a simple circuit configuration. In order to maintain the balance performance of the modulator and demodulator, passive baluns and couplers are implemented with thin-film microstrip lines, which exhibit less insertion loss than inverted microstrip lines (IMSLs), while the active mixers are based on IMSLs for short interconnections. The half-Gilbert-cell mixers have a wide enough operation bandwidth for high-throughput communications of more than 10% at 300 GHz. According to the static constellation of the modulator, imbalance is expected to be less than approximately ±0.6 dB ∠4°. A nonchip back-to-back experiment was conducted at up to 60 Gb/s, and 50-Gb/s operation was verified with a low bit error rate on the order of 10-8 or less. The results demonstrate that the QPSK modulation scheme can be applied to double the data rate at terahertz frequencies.

300-GHz Step-Profiled Corrugated Horn Antennas Integrated in LTCC

This paper presents 300-GHz step-profiled corrugated horn antennas, aiming at their integration in low-temperature co-fired ceramic (LTCC) packages. Using substrate integrated waveguide technology, the cavity inside the multi-layer LTCC substrate and a surrounding via fence are used to form a feeding hollow waveguide and horn structure. Owing to the vertical configuration, we were able to design the corrugations and stepped profile of horn antennas to approximate smooth metallic surface. To verify the design experimentally, the LTCC waveguides and horn antennas were fabricated with an LTCC multi-layer process. The LTCC waveguide exhibits insertion loss of 0.6 dB/mm, and the LTCC horn antenna exhibits 18-dBi peak gain and 100-GHz bandwidth with more than 10-dB return loss. The size of the horn antenna is only 5×5×2.8 mm3, which makes it easy to integrate it in LTCC transceiver modules.

A differential photoconductive AND gate with Be-doped low-temperature-grown InGaAs-InAlAs MQW MSM-PD's

A novel photoconductive AND gate that overcomes the problems of: 1) the long tail of photoconductive switches and 2) signal leakage via switch capacitance (signal feedthrough) is proposed. We use Be-doped low-temperature (LT)-grown InGaAs-InAlAs MQW metal-semiconductor-metal photodetectors (MSM-PDs) to get a shorter turn-off time and propose a differential AND gate to cancel the signal feedthrough. A comparison between LT-grown MSM-PDs and those fabricated by ion implantation shows that the LT-grown ones are ultrafast with a full width at half maximum of 5.3 ps and are suitable for low-bias operation. It is experimentally confirmed that the differential AND gate completely cancels the signal feedthrough in the picosecond region. The differential AND gate: with the LT MSM-PDs achieves return-to-zero (RZ) 20 Gb/s AND operation.

Continuous-Wave THz Homodyne Spectroscopy and Imaging System With Electro-Optical Phase Modulation for High Dynamic Range

We present a terahertz (THz) continuous-wave coherent homodyne spectroscopy and imaging system based on THz phase control using electrooptic (EO) phase modulation for fast measurement without mechanical delay movement. After describing the degradation effects of detection signal by the optical laser noise and parasitic amplitude modulation, we propose the push-pull EO phase modulation with optical delay control for dynamic range enhancement. Using wideband unitraveling-carrier photodiode and InGaAs photoconductive antenna, spectroscopy up to a 1.5-THz frequency range and imaging are demonstrated.

Compact and stable THz vector spectroscopy using silicon photonics technology

We present a compact and stable terahertz (THz) vector spectroscopy system using silicon photonics technology. A silicon-based integrated phase control circuit greatly reduces the physical size of the continuous-wave THz spectroscopy system and enhances environmental phase stability. Differential lightwave phase control using two carrier-injection electro-optic modulators enables fast and linear phase sweeps of THz-waves. Using the silicon-photonic circuit, we demonstrate a THz vector spectrometer; the dynamic ranges are 65 and 35 dB at 300 GHz and 1 THz with 1-ms integration time and phase variation is less than ± 10° without thermal packaging.

CW-THz vector spectroscopy and imaging system based on 1.55-µm fiber-optics

We present a continuous-wave terahertz (THz) vector spectroscopy and imaging system based on a 1.5-µm fiber optic uni-traveling-carrier photodiode and InGaAs photo-conductive receiver. Using electro-optic (EO) phase modulators for THz phase control with shortened optical paths, the system achieves fast vector measurement with effective phase stabilization. Dynamic ranges of 100 dB · Hz and 75 dB · Hz at 300 GHz and 1 THz, and phase stability of 1.5° per minute are obtained. With the simultaneous measurement of absorbance and relative permittivity, we demonstrate non-destructive analyses of pharmaceutical cocrystals inside tablets within a few minutes.

InP HBT voltage controlled oscillator for 300-GHz-band wireless communications

We present a 300-GHz-band fundamental voltage controlled oscillator (VCO) for wireless communications using 0.25-μm InP HBT technology. The VCO exhibits about -2-dBm differential output power and 10-GHz frequency tuning range with dc power consumption of 46.2 mW. The oscillation frequency band of the VCO can be extended over 360 GHz in the same structure.