Frequency Down-Conversion Device and Communication Device

A frequency down-conversion device receiving input of an optical data signal and an optical subcarrier signal having different frequencies in an infrared optical frequency band, and outputting a data signal having a frequency in a radio wave band or a baseband, wherein

• the device has a structure of a field effect transistor in which a source electrode, a drain electrode, a first gate electrode having a plurality of first fingers arranged in parallel at regular intervals, and a second gate electrode having a plurality of second fingers arranged in parallel at regular intervals are arranged on a mesa, the plurality of first fingers and the plurality of second fingers being arranged in a nested manner, and
• a local oscillation signal having a predetermined frequency that is close to a difference frequency between a frequency of the optical data signal and a frequency of the optical subcarrier signal and that is in a band from sub-terahertz to terahertz, is input to the second gate electrode, and the device is configured to output, from the first gate electrode, the data signal having a frequency corresponding to an absolute difference between the predetermined frequency and the difference frequency.