Terahertz Technology Research Center

Terahertz Laboratory (Frontier ICT Technology)

Core technology for terahertz radio testbed

To realize 100 Gbps-class terahertz communication technology, we are developing technologies to generate terahertz signals based on fiber-radio and advanced optical fiber communication technologies. In FY2019, we studied a technique for generating a single ultra-wide-band signal by combining multiple transmitters, each having a limited bandwidth. We used digitalsignal processing to partition a single-carrier multi-level modulated signal with 85 GHz bandwidth (modulation rate of 80 Gbaud) into three frequency bands, and assigned them to each of three transmitters with bandwidths of under 45 GHz. We then tested a method to receive and demodulate them together as a single, wideband signal at the receiver. A schematic diagram and spectral distribution for the system are shown in Fig. 2. Comparing the received and demodulated signal with the one transmitted using a single wideband transmitter showed that the wideband signal can be generated by partitioning the bandwidth, with no particular degradation.

Fig.2:Ultra wideband signal generation technology

Fundamental technologies for terahertz spectrum measurements

In spectrum measurement, we require an octave-spanning bandwidth(0.3 to 0.6THz) to enable measurement of spurious signal characteristics specified by the Radio Regulations. Our goal is to establish fundamental technology able to take spectrum measurements more quickly and accurately than previously, while handling this bandwidth in a single instrument. One method that has been proposed to realize this is to convert to multiple bands using a filter bank that partitions the measurement band into several equal bands, and to measure each of the partitioned frequency bands simultaneously using frequency comb signals as local oscillators. In FY2019, we conducted experiments to check the multi-band spectrum measurement concept using technology elements developed earlier(Fig.3).

Fig.3: Evaluation system concept for 3-band receiver and a photo of the inside of the cryostat (top), Ch.2 filter characteristics (middle) and receiver noise temperatureat different LO frequencies (bottom)

International standardization activities

We performed standardization activities according to WRC-19 agenda item 1.15, "Identification of frequency bands for use by administrations for the land-mobile and fixed services applications operating in the frequency range from 275 to 450 GHz," achieving the following results in FY2019:
(1) Completed ITU-R report SM.2450, "Sharing and compatibility studies between land-mobile, fixed and passive ser-vices in the frequency range from 275 to 450 GHz," in ITU-R WP1A (Spectrum engineering technology).
(2) Completed the APC (APT joint proposal) regarding WRC-19 agenda item 1.15 in APG19-5 (APT WRC-19 preparatory meeting) and input it from the APT to WRC-19.
(3) Collaborated with the APT coordinator and CEPT coordinator in WRC-19 to add a new note identifying the four bandwidths shown in Fig.4 (275 to 296 GHz, 306 to 311 GHz, 318 to 333 GHz, and 356 to 450 GHz) for land-mobile and fixed services applications in the radio communication regulations.

Fig.4: Standardization of Terahertz band: WRC-19 frequency identification results

Archive_NICT Report 2020