Widely and continuously tunable terahertz synthesizer traceable to a microwave frequency standard Takeshi Yasui, 1,2,* Hisanari Takahashi, 3,4 Kohji Kawamoto, 1 Yutaka Iwamoto, 3,4 Kaoru Arai, 3,4 Tsutomu Araki, 1 Hajime Inaba, 3 and Kaoru Minoshima 3,4 1 Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531, Japan 2 Institute of Technology and Science, The University of Tokushima, 2-1 Minami-Josanjima, Tokushima 770-8506, Japan 3 National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8563, Japan 4 Faculty of Science and Technology, Tokyo University of Science, 2641 Yamasaki, Noda, Chiba 278-8510, Japan *[email protected] Abstract: We constructed a widely and continuously tunable terahertz frequency synthesizer traceable to a hydrogen maser linked to coordinated universal time. Photomixing of two optical frequency synthesizers, linked to the hydrogen maser via dual optical frequency combs, gave this THz synthesizer frequency uncertainty of 10 12 . To demonstrate the potential of wide and continuous tunability in the THz synthesizer, we tuned its output frequency up to 50 GHz discretely and 1.26 GHz continuously in the F-band while maintaining the unprecedented frequency uncertainty by using a uni- traveling-carrier photodiode as a photomixer. This THz synthesizer will be a powerful tool for broadband, high-precision THz spectroscopy and THz frequency metrology. ©2011 Optical Society of America OCIS codes: (120.3930) Metrological instrumentation; (120.6200) Spectrometers and spectroscopic instrumentation; (140.3425) Laser stabilization; (300.6320) Spectroscopy, high- resolution; (300.6495) Spectroscopy, terahertz. References and links 1. T. Yasui, S. Yokoyama, H. Inaba, K. Minoshima, T. Nagatsuma, and T. Araki, “Terahertz frequency metrology based on frequency comb,” IEEE J. Sel. Top. Quantum Electron. 17(1), 191–201 (2011). 2. T. Nagatsuma, H. Ito, and T. Ishibashi, “High-power RF photodiodes and their applications,” Laser Photonics Rev. 3(1-2), 123–137 (2009). 3. A. J. Deninger, T. Göbel, D. Schönherr, T. Kinder, A. Roggenbuck, M. Köberle, F. Lison, T. Müller-Wirts, and P. Meissner, “Precisely tunable continuous-wave terahertz source with interferometric frequency control,” Rev. Sci. Instrum. 79(4), 044702 (2008). 4. K. Kawase, J. Shikata, and H. Ito, “Terahertz wave parametric source,” J. Phys. D Appl. Phys. 35(3), R1–R14 (2002). 5. J. Ward, E. Schlecht, G. Chattopadhyay, A. Maestrini, J. Gill, F. Maiwald, H. Javadi, and I. Mehdi, “Capability of THz sources based on Schottky diode frequency multiplier chains,” in Proceedings of IEEE MTT-S International Microwave Symposium (Institute of Electrical and Electronics Engineers, Fort Worth, 2004), pp. 1587–1590. 6. Th. Udem, R. Holzwarth, and T. W. Hänsch, “Optical frequency metrology,” Nature 416(6877), 233–237 (2002). 7. T. Yasui, Y. Kabetani, E. Saneyoshi, S. Yokoyama, and T. Araki, “Terahertz frequency comb by multi- frequency-heterodyning photoconductive detection for high-accuracy, high-resolution terahertz spectroscopy,” Appl. Phys. Lett. 88(24), 241104 (2006). 8. S. Barbieri, P. Gellie, G. Santarelli, L. Ding, W. Maineult, C. Sirtori, R. Colombelli, H. Beere, and D. Ritchie, “Phase-locking of a 2.7-THz quantum cascade laser to a mode-locked erbium-doped fibre laser,” Nat. Photonics 4(9), 636–640 (2010). 9. S. P. Khanna, M. Salih, P. Dean, A. G. Davies, and E. H. Linfield, “Electrically tunable terahertz quantum- cascade laser with a heterogeneous active region,” Appl. Phys. Lett. 95(18), 181101 (2009). 10. Q. Quraishi, M. Griebel, T. Kleine-Ostmann, and R. Bratschitsch, “Generation of phase-locked and tunable continuous-wave radiation in the terahertz regime,” Opt. Lett. 30(23), 3231–3233 (2005).