Nonlinear optical detection of terahertz-wave radiation from resonant tunneling diodes

Significance Statement

Terahertz waves have received more research attention recently than any other time. This is in view of the many potential applications, for example, in wireless communication and nondestructive imaging. To realize these special applications, compact terahertz-wave sources as well as sensitive detectors operating at room temperatures are extremely important.

Resonant tunneling diode is an important extremely compact terahertz wave source. At around 1 Terahertz region, the resonant tunneling diode devices can generate continuous wave and monochromatic terahertz wave output in the order of microwatts at room temperature.

Frequency up conversion in the nonlinear optical crystals appears to be a promising approach for detection of terahertz wave radiation at room temperature. In this process, terahertz-wave radiation is normally mixed with an optical pump wave in a nonlinear crystal to yield an optical up-converted wave. Then the up-converted wave can be separated from the residual pump wave and detected implementing a commercial sensitive photodetector designed with nanosecond time resolution.

Yuma Takida, Kouji Nawata and Hiroaki Minamide at RIKEN and in collaboration with Safumi Suzuki and Masahiro Asada at Tokyo Institute of Technology demonstrated a nonlinear optical detection of terahertz-wave radiation from continuous-wave resonant tunneling diode gadgets with frequencies of 0.58, 0.78, and 1.14 terahertz at room temperature. They demonstrated that the terahertz-wave radiation from resonant tunneling diode gadgets is up-converted to near-infrared waves in a nonlinear optical magnesium-oxide-doped lithium niobate crystal. They achieved a detection limit of the continuous-wave terahertz-wave power of 5nW at 1.14 terahertz, which corresponded to 2-aJ energy and about 2.7×103 photons. Their research work is now published in Optics Express.

The authors collimated the continuous wave terahertz-wave radiation from the resonant tunneling device and focused the wave on a magnesium-oxide-doped lithium niobate. Magnesium-oxide-doped lithium niobate crystals were used as the nonlinear medium for this study. A normal incidence configuration implementing a trapezoidal crystal was applied to effectively couple the waves into the nonlinear crystal.

In view of the nonlinear phase-matching condition in the crystal, the difference-frequency up-converted wave was produced, and then amplified during propagation through the crystal. The authors implemented a spatial filter to separate the up-converted wave from the residual pump wave. In the experiment, no phase-locking between the terahertz and pump waves was necessary since the difference-frequency up-conversion process was sensitive to the intensity of the two only.

The research team was able to achieve a minimum detection limit of as low as 5 nW at 1.14 terahertz. This was corresponding to 2-aJ energy and 2.7×103 photons. The results of their experiment indicated the the input frequency as well as the power of the resonant tunneling devices could be calibrated by determining, respectively, the output wavelength and energy of the up-converted waves.

Comparing the detection performance of the continuous wave resonant tunneling diode gadgets and a pulsed injection-seeded THz-wave parametric generator helped the authors observe that the method was not only applicable to resonant tunneling diodes, but also other terahertz wave sources.

The proposed detection technique can be implemented in real-time spectroscopic detection with multi-frequency terahertz-wave sources since, in the experiment; the non-collinear phase matching achieved simultaneous up-conversion from superposed terahertz waves. Therefore, this optical detection for the compact terahertz wave sources will be helpful in opening new opportunities for terahertz wave applications.

Nonlinear optical detection of terahertz-wave radiation from resonant tunneling diodes

(a) Photograph of typical resonant tunneling diode (RTD) device. (b) Schematic experimental setup for nonlinear optical detection of THz-wave radiation from RTD device. (c) Measured optical spectra of pump and up-converted waves with 1.14-THz RTD device.

About The Author

Yuma Takida received the Ph.D. degree in physical electronics and Informatics from Osaka City University, Osaka, Japan in 2013. In 2013, he joined the Tera-Photonics Research Team, RIKEN Center for Advanced Photonics (RAP), RIKEN, Sendai, Japan, as a Postdoctoral Fellow of the Japan Society for the Promotion of Science (JSPS), and since 2015, he has been a Special Postdoctoral Researcher of RIKEN, where he is involved in frequency-domain THz-wave generation and detection based on nonlinear wavelength conversions, and their applications.

His current research interests include laser sources, nonlinear optics, THz-wave generation and detection, and THz-wave spectroscopy.

About The Author

Kouji Nawata received the Ph.D. degree in engineering from Chiba University, Chiba, Japan, in 2010. In 2010, he joined Tera-Photonics research team in RIKEN as a Postdoctoral Researcher. He was a Special Postdoctoral Researcher from 2014 to present. His current research interests include high power THz-wave generation/sensitive THz-wave detection based on nonlinear optics and its applications.

About The Author

Safumi Suzuki received the D.E. degree in electronics and applied physics from the Tokyo Institute of Technology, Tokyo, Japan, in 2009. From 2009 to 2014, he was an Assistant Professor with the Department of Electronics and Applied Physics and, from 2014 to 2016, an Associate Professor with the Department of Physical Electronics, Tokyo Institute of Technology, respectively. Since 2016, he has been an Associate Professor with the Department of Electrical and Electronic Engineering, Tokyo Institute of Technology. His research interests include terahertz electronic devices and applications.

About The Author

Masahiro Asada received the D.E. degree in Physical Electronics from the Tokyo Institute of Technology, Japan in 1984. In 1984, he joined the Department of Physical Electronics, Tokyo Institute of Technology as a Research Associate. From 1986 to 1987, he was with the Physics Institute of Stuttgart University, Stuttgart, Germany, as a Research Fellow of the Alexander von Humboldt Foundation. From 1988 to 1999, he was an Associate Professor in the Department of Electrical and Electronic Engineering, Tokyo Institute of Technology and was a Professor in the Interdisciplinary Graduate School of Science and Engineering from 1999-2016. He is currently a Professor in the Institute of Innovative Research, Tokyo Institute of Technology. His current research is on terahertz devices using semiconductor nanostructures.

About The Author

Hiroaki Minamide (M’13) received the B.S. degree in communication engineering and M.S. and Ph.D. degrees in electronic engineering from Tohoku University, Sendai Japan, in 1993, 1996, and 1999, respectively. In 1999, he joined as a Frontier Researcher with the Photo-Dynamics Research Center of RIKEN and started to study developing terahertz-wave source using nonlinear optical effect. He demonstrated a frequency-agile THz-wave parametric oscillator in a ring-cavity configuration, which covers a wide frequency region from 1 to 3 THz. And he continuously joined in a new project of Teraphotonics team from 2005, RIKEN Sendai and he was a deputy team leader from 2007 to September 2010.

His research is spread into the development of ultra-wide tunable THz-wave in the frequency region from sub-THz to several tens THz using organic nonlinear crystal. Additionally, high-sensitive THz-wave detection with rapid time-response and room-temperature operation using nonlinear optical up-conversion is studied. Since October 2010, he has led the Teraphotonics team as a Team Leader in the second term of RIKEN THz research project. He is currently a Team Leader in the new THz research project which started April 2013 in RIKEN. Recently, his research interests include high-power THz-wave generation and extremely sensitive THz-wave detection using nonlinear optics and their unique THz applications.

Reference

Yuma Takida, Kouji Nawata, Safumi Suzuki, Masahiro Asada, and Hiroaki Minamide. Nonlinear optical detection of terahertz-wave radiation from resonant tunneling diodes. Vol. 25, No. 5 | 6 Mar 2017 | OPTICS EXPRESS 5390.

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