Abstract-Optical frequency switching scheme for a high-speed broadband THz measurement system based on the photomixing technique

Hajun Song, Sejin Hwang, and Jong-In Song

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-10-11767&origin=search

This study presents an optical frequency switching scheme for a high-speed broadband terahertz (THz) measurement system based on the photomixing technique. The proposed system can achieve high-speed broadband THz measurements using narrow optical frequency scanning of a tunable laser source combined with a wavelength-switchable laser source. In addition, this scheme can provide a larger output power of an individual THz signal compared with that of a multi-mode THz signal generated by multiple CW laser sources. A swept-source THz tomography system implemented with a two-channel wavelength-switchable laser source achieves a reduced time for acquisition of a point spread function and a higher depth resolution in the same amount of measurement time compared with a system with a single optical source.

© 2017 Optical Society of America

Abstract-Robust terahertz self-heterodyne system using a phase noise compensation technique

Hajun Song and Jong-In Song*
Department of Information and Communications, Gwangju Institute of Science and Technology (GIST), 1 Oryongdong, Buk-gu, Gwangju, 500-712, South Korea * jisong@gist.ac.kr

https://www.osapublishing.org/view_article.cfm?gotourl=https%3A%2F%2Fwww%2Eosapublishing%2Eorg%2FDirectPDFAccess%2F21FB87F3-A3E9-DA0D-2777700B69C274C6_323774%2Foe-23-16-21181%2Epdf%3Fda%3D1%26id%3D323774%26seq%3D0%26mobile%3Dno&org=

Abstract: We propose and demonstrate a robust terahertz self-heterodyne system using a phase noise compensation technique. Conventional terahertz self-heterodyne systems suffer from degraded phase noise performance due to phase noise of the laser sources. The proposed phase noise compensation technique uses an additional photodiode and a simple electric circuit to produce phase noise identical to that observed in the terahertz signal produced by the self-heterodyne system. The phase noise is subsequently subtracted from the terahertz signal produced by the self-heterodyne system using a lock-in amplifier. While the terahertz self-heterodyne system using a phase noise compensation technique offers improved phase noise performance, it also provides a reduced phase drift against ambient temperature variations. The terahertz self-heterodyne system using a phase noise compensation technique shows a phase noise of 0.67 degree in terms of a standard deviation value even without using overall delay balance control. It also shows a phase drift of as small as approximately 10 degrees in an open-to-air measurement condition without any strict temperature