Spectral Narrowing of a Varactor-Integrated Resonant-Tunneling-Diode Terahertz Oscillator by Phase-Locked Loop

  • Kota Ogino
  • Safumi Suzuki
  • Masahiro Asada


Spectral narrowing of a resonant-tunneling-diode (RTD) terahertz oscillator, which is useful for various applications of terahertz frequency range, such as an accurate gas spectroscopy, a frequency reference in various communication systems, etc., was achieved with a phase-locked loop system. The oscillator is composed of an RTD, a slot antenna, and a varactor diode for electrical frequency tuning. The output of the RTD oscillating at 610 GHz was down-converted to 400 MHz by a heterodyne detection. The phase noise was transformed to amplitude noise by a balanced mixer and fed back into the varactor diode. The loop filter for a stable operation is discussed. The spectral linewidth of 18.6 MHz in free-running operation was reduced to less than 1 Hz by the feedback.


Terahertz source Resonant-tunneling diode Frequency-tunable oscillator Phase-locked loop 



The authors thank Honorary Prof. Y. Suematsu and Emeritus Prof. K. Furuya of the Tokyo Institute of Technology for the continuous encouragement. The authors also acknowledge Dr. M. Kumagai and Dr. S. Nagano of the National Institute of Information and Communications Technology, Profs. S. Arai, and Y. Miyamoto, Assoc. Profs. M. Watanabe and N. Nishiyama of the Tokyo Institute of Technology for stimulating discussions. This work was supported by a scientific grant-in-aid (16H06292) from the JSPS, the CREST program (JPMJCR1534) of the JST, and the SCOPE from the Ministry of Internal Affairs and Communications, Japan.


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Copyright information

© Springer Science+Business Media, LLC 2017

Authors and Affiliations

  1. 1.Department of Electrical and Electronic EngineeringTokyo Institute of TechnologyTokyoJapan
  2. 2.Institute of Innovative Research, Tokyo Institute of TechnologyTokyoJapan

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