Frequency detection of focused sub-THz waves using a high-T c Josephson junction T. Miyadera a,b , I. Kawayama a,b, * , T. Kiwa c , K. Tsukada c , M. Tonouchi a,b a Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka 565-0871, Japan b CREST-JST., 2-6 Yamadaoka, Suita, Osaka 565-0871, Japan c Okayama University, 3-1-1 Tsusimanaka, Okayama, Okayama 700-0082, Japan Received 23 November 2004; accepted 14 February 2005 Available online 20 July 2005 Abstract We have proposed a new type of frequency detection system of sub-terahertz electromagnetic waves using a photomix- ing technique and a Josephson junction detector. The photomixer illuminated by two lasers with different wavelengths generates coherent electromagnetic waves that include a frequency component corresponding to the frequency difference of the two lasers. The generated electromagnetic waves were radiated from a horn antenna and focused to the Josephson junction detector with Si lens. The high-T c Josephson junction operates as a frequency detector for electromagnetic waves. Using this system, we observed the Shapiro steps of 188 lV that correspond to the frequencies of 90.8 GHz. Ó 2005 Elsevier B.V. All rights reserved. PACS: 07.57.Hm; 85.25.Cp Keywords: Photomixing; Josephson junction; Shapiro step 1. Introduction In recent years, terahertz (THz) and sub-THz frequency region has attracted considerable atten- tion and various applications, e.g. terahertz local oscillator, THz imaging and THz time domain spectroscopy (THz-TDS), have been developed. In particular, THz imaging is expected to be a powerful tool in biological and biomedical areas [1]. However, most of the THz systems are bulky and need vibration isolation system due to a com- plicate optical system, therefore, such a system is not ideal for practical applications. Recently, we have proposed a compact and ro- bust sub-THz generation and detection system using a photomixer and high-T c Josephson junction 0921-4534/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2005.02.136 * Corresponding author. Address: Institute of Laser Engi- neering, Osaka University, 2-6 Yamadaoka, Suita, Osaka 565- 0871, Japan. Tel.: +81 6 6879 7983; fax: +81 6 6879 7964. E-mail address: kawayama@ile.osaka-u.ac.jp (I. Kawaya- ma). Physica C 426–431 (2005) 1726–1730 www.elsevier.com/locate/physc