Measurement of absolute frequency of continuous-wave terahertz radiation in real time using a free-running, dual-wavelength mode-locked, erbium-doped fibre laser

• Published in: Scientific reports 2017-02, Vol.7 (1), p.42082-42082, Article 42082
• Main Authors: Hu, Guoqing, Mizuguchi, Tatsuya, Zhao, Xin, Minamikawa, Takeo, Mizuno, Takahiko, Yang, Yuli, Li, Cui, Bai, Ming, Zheng, Zheng, Yasui, Takeshi
• Format: Article
• Language: English
• Subjects: 639/624/1111/1112; 639/624/400/561; Antennae; Erbium; Humanities and Social Sciences; Lasers; multidisciplinary; Science; Terahertz frequencies; Wavelength; Wavelengths
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/srep42082

A single, free-running, dual-wavelength mode-locked, erbium-doped fibre laser was exploited to measure the absolute frequency of continuous-wave terahertz (CW-THz) radiation in real time using dual THz combs of photo-carriers (dual PC-THz combs). Two independent mode-locked laser beams with different wavelengths and different repetition frequencies were generated from this laser and were used to generate dual PC-THz combs having different frequency spacings in photoconductive antennae. Based on the dual PC-THz combs, the absolute frequency of CW-THz radiation was determined with a relative precision of 1.2 × 10 −9 and a relative accuracy of 1.4 × 10 −9 at a sampling rate of 100 Hz. Real-time determination of the absolute frequency of CW-THz radiation varying over a few tens of GHz was also demonstrated. Use of a single dual-wavelength mode-locked fibre laser, in place of dual mode-locked lasers, greatly reduced the size, complexity, and cost of the measurement system while maintaining the real-time capability and high measurement precision.