Kazuisao Tsuruda

Extremely low-loss terahertz waveguide based on silicon photonic-crystal slab

We pursued the extremely low loss of photonic-crystal waveguides composed of a silicon slab with high resistivity (20 kΩ-cm) in the terahertz region. Propagation and bending losses as small as <0.1 dB/cm (0.326-0.331 THz) and 0.2 dB/bend (0.323-0.331 THz), respectively, were achieved in the 0.3-THz band. We also developed 1.5-Gbit/s terahertz links and demonstrated an error-free uncompressed high-definition video transmission by using a photonic-crystal waveguide with a length of as long as 50 cm and up to 28 bends thanks to the low-loss properties. Our results show the potential of photonic crystals for application as terahertz integration platforms.

Millimeter-Wave and Terahertz-Wave Applications Enabled by Photonics

This paper describes continuous millimeter-wave and terahertz (THz)-wave applications, where telecom-based photonics technologies are efficiently employed to enhance their performance. First, 300-GHz-band wireless communications are described toward real-time error-free transmissions at 50 Gbit/s and beyond. Next, a novel approach to increase a phase measurement sensitivity in THz frequency-domain spectroscopy systems is explained, and a similar technique is successfully applied to the visualization of electric-field radiation and propagation. Finally, as a futuristic study, the manipulation of THz waves with a concept of photonic crystals and its possible applications to platforms in THz integrated systems are presented.

Modeling and Simulation of Terahertz Resonant Tunneling Diode-Based Circuits

Circuit models of transmission line elements and of a terahertz resonant tunneling diode (RTD) have been developed. The models allow for a reliable design of RTD-based oscillator and detector circuits. The transmission line elements have been modeled based on electromagnetic field simulations and dc measurements. Their accuracy has been verified through S-parameter measurements. The RTD has been modeled on the basis of dc and S-parameter measurements. The models have been used for the circuit design. A new circuit has been developed that can provide a load impedance that allows for high-output-power oscillators and high-sensitivity detectors. The circuit has been manufactured and measured as an oscillator and as a detector at frequencies around 300 GHz. An excellent agreement between measurement and simulation has been obtained, proving the accuracy of the developed models.

Integration of resonant tunneling diode with Terahertz photonic-crystal waveguide and its application to gigabit terahertz-wave communications

We integrate a resonant tunneling diode chip with a terahertz-wave photonic-crystal waveguide for the development of terahertz-wave integrated circuits. The propagation frequency band of the photonic-crystal waveguide is successfully observed from the integrated device through the resonant tunneling diode as a terahertz detector. Finally, we achieve 3-Gbit/s error-free terahertz-wave communication using the device in the 300-GHz band.

Ultralow-loss photonic-crystal waveguides for gigabit terahertz-wave communications

We demonstrate terahertz photonic-crystal waveguides with ultra-low propagation loss (~0.2 dB/cm) and ultra-low bending loss (<;0.2 dB/bend) in planar compact structure, which is promising to develop a terahertz-wave integrated circuit. 1.5-Gbit/s error free terahertz-wave communications are achieved in the photonic-crystal waveguides as long as 47-cm length with 28-times bends, for the first time.

Terahertz sensing based on photonic crystal cavity and resonant tunneling diode

We report terahertz sensing applications of photonic crystal cavity with a high quality factor (~9300). The frequency response of the cavity was measured using a compact terahertz source based on a resonant tunneling diode (RTD), and the results were compared with the results obtained using a bulky, precise frequency multiplier. The oscillation frequency of the RTD was tuned by changing the applied bias voltage resulting from the voltage-dependent capacitance of the diode. We successfully observed the resonant spectrum of the cavity at 318 GHz using a spectroscopic system. As a preliminary experiment for the sensing application, we measured a clear frequency shift of the resonant spectrum when a thin dielectric tape with a thickness of 5 μm, which is smaller than 1/100 the wavelength, is attached to the surface of the cavity.

Terahertz resonant tunneling diode systems for next generation wireless communication

For low cost and short distance wireless data communication systems in the THz frequency range, resonant tunneling diodes (RTDs) are very promising. To obtain a large signal-to-noise ratio, thus high data rate, the transmitter output power and receiver sensitivity have to be high. In this paper, we discuss how to overcome the limitations of current RTD-based systems for wireless communication with respect to circuit design, showing our latest experimental results.

Packaging of THz circuits using a HDPE lens and an impedance-matched carrier substrate

A concept a for low-cost and robust packaging is presented. It is applied to a resonant tunneling diode (RTD) circuit fabricated on an InP substrate. The RTD circuit has been designed for wireless data transfer in the 300 GHz frequency range. The proposed system uses a substrate integrated lens made of high density polyethylene (HDPE) and a λ/4 matching layer to match the different wave impedances of HDPE and InP. The matching layer also works as a carrier substrate for the baseband circuit. The system has a simulated directivity of 21 dBi and a measured 3-dB bandwidth of 17 GHz.