Atsushi Wakatsuki

Terahertz wireless communication link at 300 GHz

We present a terahertz wave wireless link operating at 300 GHz which has a potential for use in ultra fast future wireless services in short range. Terahertz wave was generated and modulated with photonic technologies in the transmitter, allowing us to use radio on fiber system concept as well. For the receiver, we used a Schottky barrier diode detector integrated with a planar antenna. With the link, error free data transmission at 12.5 Gbps was experimentally demonstrated. Taking the performance margin of the transmitter and receiver into consideration, we believe that even up to 20-Gbps data can be transmitted.

Uni-Travelling-Carrier Photodiode Module Generating 300 GHz Power Greater Than 1 mW

In this letter, we demonstrate over 1 mW power generation at 300 GHz with a uni-travelling-carrier photodiode (UTC-PD) packaged in a WR-3 waveguide module. To increase the maximum power, two identical UTC-PDs were monolithically integrated along with a T-junction to combine the power from the two PDs. The UTC-PD module exhibited peak saturated output power of approximately 1.2 mW at 300 GHz with photocurrent of around 20 mA per PD and bias voltage of -3.9 V. In addition, 3 and 10 dB bandwidths were measured to be around 70 GHz or 23% and over 150 GHz or 50%, respectively.

High-power and broadband sub-terahertz wave generation using a J-band photomixer module with rectangular-waveguide output port

A high-output-power photomixer module operating at 200-500 GHz has been developed. The module consists of a uni-traveling-carrier photodiode, a PD-waveguide mode-conversion coupler, and a compact metal package with a rectangular-waveguide that outputs sub-terahertz wave. The fabricated module exhibits a 10- dB down bandwidth of about 300 GHz and an output power as high as -2.7 dBm at 350 GHz. This is the highest value ever reported for a photomixer module operating at 350-GHz band.

A 0.2–0.5THz single-band heterodyne receiver based on a photonic local oscillator and a superconductor-insulator-superconductor mixer

We have demonstrated that a superconductor-insulator-superconductor (SIS) mixer pumped by a photonic local oscillator (LO) covers the whole frequency range of 0.2–0.5THz. In the bandwidth of 74% of the center frequency, this single-band receiver exhibits noise temperature of TRX⩽20hf∕kB, where h is Planck’s constant, f is the frequency, and kB is Boltzmann’s constant. Resultant TRX is almost equal to TRX of the identical SIS mixer pumped by three conventional frequency-multiplier-based LOs which share the 0.2–0.5THz band. This technique will contribute to simple, wide-band, and low-noise heterodyne receivers in the terahertz region.

Multi-gigabit wireless data transmission at over 200-GHz

Error-free data transmission at 8 Gbps in the 250-GHz millimeter-wave band over 0.5-m distance was demonstrated. A J-band uni-travelling-carrier photodetector (UTC-PD) module and an InP-Schottky barrier diode detector integrated with a slot ring antenna and an output low-pass filter were used for the transmitter and receiver, respectively. Taking the maximum available power from the UTC-PD module into consideration, it is expected that 8-Gbps data can be transmitted over a distance of 2 meter.

Absorption Spectra of Smoke Emitted from Heated Nylon Fabric Measured with a Continuous-Wave Sub-Terahertz Spectrometer

The absorption spectra of smoke emitted from heated nylon fabric are studied in the sub-terahertz band. The transmission loss of 1.5-µm-wavelength light in the smoke is 50 dB/m or more. Even in such dense smoke, the loss for waves with the frequency ranging from 200 to 500 GHz is so small that absorption lines of gas molecules in the smoke can be detected in this frequency range. Spectral analysis indicates that the smoke contains molecules of toxic gas, such as HCN and CH3CN, generated due to incomplete combustion of the nylon fabric when heated to 500 °C with air.

Toward practical applications over 100 GHz

This paper discusses practical applications of the frequency band starting at 100 Ghz—a band that has yet to be fully exploited. It considers the feasibility of future applications driven by the sub-terahertz and terahertz bands, examining this feasibility from two perspectives: (1) market needs and the standards being released to meet these needs mainly in the area of communications applications, and (2) advances in semiconductor technologies and their peripheral technologies. To discuss approaches to implementing these applications, we present two transmission technologies that we are developing.

High-sweeping-speed optically synchronized dual-channel terahertz-signal generator for driving a superconducting tunneling mixer and its application to active gas sensing

We propose a high-sweeping-speed optically synchronized dual-channel terahertz (THz) signal generator for an active gas-sensing system with a superconductor-insulator-superconductor (SIS) mixer. The generator can sweep a frequency range from 200 to 500 GHz at a speed of 375 GHz/s and a frequency resolution of 500 MHz. With the developed gas-sensing system, a gas-absorption-line measurement was successfully carried out with N(2)O gas in that frequency range.

Continuous-wave terahertz spectroscopic imaging at over 1 THz for pharmaceutical applications

Spectroscopic images were obtained using a system combining a tunable continuous-wave terahertz laser with an InP-based Schottky barrier diode detector integrating a broadband log-periodic antenna. The distribution of polymorphic forms in pharmaceutical tablets was observed in obtained at images over 1 THz.

Subterahertz noise signal generation using a photodetector and wavelength-sliced optical noise signals for spectroscopic measurements

We present a photonic technique for generating a subterahertz time-continuous noise signal, which provides not only fine resolution and a potential for broadband measurements but also a higher output power resulting in high signal to noise ratio for the spectroscopy measurement. To increase the output noise power at subterahertz frequencies, the optical noise is sliced with the arrayed waveguide gratings (AWGs), resulting in the power level of −126.1 dBm/Hz at 350 GHz, which is approximately 17 dB higher than that without the AWGs. Using the implemented subterahertz noise signal source, we demonstrate a simple spectroscopic measurement of the H2O absorption line at around 380 GHz.