Heterodyne detection at 216, 432, and 648Â GHz based on bilayer graphene field-effect transistor with quasi-optical coupling

Graphene field-effect transistors (G-FETs) are being developed with ever increasing sensitivity as terahertz direct detectors at room temperature. The noise-equivalent power is being reduced towards the order of 1pW/Hz with frequency about 650 GHz. G-FET-based frequency multipliers and subharmonic mixers are becoming new active components for both millimeter and terahertz wave technologies. We report a 650-GHz G-FET coupled with terahertz antennas and a quasi-optical silicon lens for heterodyne/subharmonic detection. Heterodyne detection at 216 and 648 GHz, second-subharmonic detection at 432 GHz, and third-subharmonic detection at 648 GHz were demonstrated and characterized. Self-mixing/homodyne detection was used as a calibration tool for the power levels of the local pump source and the source to be detected. The conversion losses of heterodyne mixing at 216 GHz (off-resonant) and 648 GHz (resonant) were 38.4 dB and 57.9 dB with 12.8 dBm and −14 dBm of local pump power, respectively. The conversion loss of the second-harmonic mixing at 432 GHz is about 8 dB higher than that of the heterodyne mixing at 216 GHz. Calculations based on our quasi-static mixing model agree well with the measured conversion losses. To improve the conversion loss, more details on the G-FET noise, the optimal pump power, and the antenna should be examined.

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