Abstract- Experimental characterization of terajet generated from dielectric cuboid under different illumination conditions

Hai Huy Nguyen Pham, Shintaro Hisatake,  Tadao Nagatsuma,  Igor Vladilenovich Minin,  Oleg Vladilenovich Minin

http://ieeexplore.ieee.org/document/7970306/

The terajet, which is the generation of a jet in the terahertz (THz) frequency band (0.1 THz-10 THz), has attracted significant research interest owing to its subwavelength hotspot that can be exploited in THz imaging applications. To date, the generation of the terajet from a dielectric cuboid has been studied and verified under planar incidences. In practical applications of high-resolution THz imaging, it is essential to take into consideration the alignment of the cuboid, as well as the efficient use of the THz power. Here, we experimentally study the generation of the terajet under different oblique and compressed incidences, in order to verify the characteristics of the terajet, such as the position, direction, and full width at half maximum (FWHM) properties. We discover that the terajet can be generated under compressed incidence. The output angle of the terajet under oblique incidence is linear and identical to the input angle of the incident beam. The position of the generated terajet is varied within two wavelengths. The FWHW below one wavelength was maintained under those illumination conditions. Consequently, the cuboid can function as a novel focusing device, which can enhance the resolution by simply placing it in the imaging system with a flexible alignment.

Abstract-Terahertz Sensor Using Photonic Crystal Cavity and Resonant Tunneling Diodes

Kazuma Okamoto, Kazuisao Tsuruda, Sebastian Diebold, Shintaro Hisatake, Masayuki Fujita Tadao,  Nagatsuma

https://link.springer.com/article/10.1007%2Fs10762-017-0391-0

In this paper, we report on a terahertz (THz) sensing system. Compared to previously reported systems, it has increased system sensitivity and reduced size. Both are achieved by using a photonic crystal (PC) cavity as a resonator and compact resonant tunneling diodes (RTDs) as signal source and as detector. The measured quality factor of the PC cavity is higher than 10,000, and its resonant frequency is 318 GHz. To demonstrate the operation of the refractive index sensing system, dielectric tapes of various thicknesses are attached to the PC cavity and the change in the resonator’s refractive index is measured. The figure of merit of refractive index sensing using the developed system is one order higher than that of previous studies, which used metallic metamaterial resonators. The frequency of the RTD-based source can be swept from 316 to 321 GHz by varying the RTD direct current voltage. This effect is used to realize a compact frequency tunable signal source. Measurements using a commercial signal source and detector are carried out to verify the accuracy of the data obtained using RTDs as a signal source and as a detector.

Abstract-Terahertz balanced self-heterodyne spectrometer with SNR-limited phase-measurement sensitivity

Shintaro Hisatake, Yuki Koda, Ryosuke Nakamura, Norio Hamada, and Tadao Nagatsuma
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-20-26689

Photonics-based frequency-domain terahertz (THz) wave measurement systems have received significant attention in both scientific and industrial fields due to their high-frequency resolution. Highly sensitive phase-measurement systems have been desired in the chemical, material, and biomedical sciences to facilitate microanalysis of materials. Here, we demonstrate a balanced self-heterodyne technique that, for the first time, simultaneously offers wide frequency tunability of more than 2.5 THz and high phase sensitivity, which is limited only by the signal-to-noise ratio (SNR) of the amplitude measurement. Using free-running lasers for THz wave generation and detection, the experimentally achieved minimum detectable optical path length change was 400±50 nm at 2 THz for a SNR of 37.7 ± 0.7 dB, even though the theoretically expected SNR-limited value was 310 ± 20 nm. The phase measurement sensitivity of our system is almost one order of magnitude better than that of the conventional systems in which limitations arise from phase instabilities in the optical components and/or laser linewidth.

© 2015 Optical Society of America

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Abstract-Terahertz wireless communications based on photonics technologies

Tadao Nagatsuma, Shogo Horiguchi, Yusuke Minamikata, Yasuyuki Yoshimizu, Shintaro Hisatake, Shigeru Kuwano, Naoto Yoshimoto, Jun Terada, and Hiroyuki Takahashi  »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-21-20-23736

There has been an increasing interest in the application of terahertz (THz) waves to broadband wireless communications. In particular, use of frequencies above 275 GHz is one of the strong concerns among radio scientists and engineers, because these frequency bands have not yet been allocated at specific active services, and there is a possibility to employ extremely large bandwidths for ultra-broadband wireless communications. Introduction of photonics technologies for signal generation, modulation and detection is effective not only to enhance the bandwidth and/or the data rate, but also to combine fiber-optic (wired) and wireless networks. This paper reviews recent progress in THz wireless communications using telecom-based photonics technologies towards 100 Gbit/s.

© 2013 Optical Society of America

Abstract-Continuous-wave terahertz field imaging based on photonics-based self-heterodyne electro-optic detection

Shintaro Hisatake and Tadao Nagatsuma
http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-38-13-2307

We demonstrate a photonics-based self-heterodyne electro-optic field imaging technique at terahertz (THz) frequency. An optical intensity beat generated by mixing two frequency-detuned free-running lasers is used for both the generation and the detection. The frequency of the beat for detection is shifted by an optical frequency shifter to realize coherent heterodyne measurement with free-running lasers. Neither mechanical delay lines nor phase-locked synthesizers are required for the amplitude and the phase imaging of the THz field, and the system simplicity is thus improved. The amplitude and phase of the THz field (125 GHz) radiated from a horn antenna are simultaneously imaged, and the standard deviation of the phase measurement is found to be 0.18 rad.
© 2013 Optical Society of America