THz-TDS Characterization of the Digital Communication Channels of the Atmosphere and the Enabled Applications

Our measurements and complete linear dispersion theory calculations of amplitude and phase show that it is possible to have seven high performance point-to-point, 10.7 Gb/s to 28.4 Gb/s, digital THz ground links in the atmosphere. At a RH 58% (10g/m(3)) and 20 degrees C including O-2 absorption, and for an absorption loss of 10 dB, the seven links are: Channel 1: at 96 GHz, Bandwidth (BW) 30 GHz, 10.7 Gb/s for 17.5 km, Channel 2: at 144 GHz, BW 30 GHz, 12.0 Gb/s for 7.4 km, Channel 3: at 252 GHz, BW 50 GHz, 25.2 Gb/s for 2.5 km, Channel 4: at 342 GHz, BW 24 GHz, 11.4 Gb/s for 840 m, Channel 5: at 408 GHz, BW 30 GHz, 13.6 Gb/s for 440 m, Channel 6: at 672 GHz, BW 60 GHz, 22.6 Gb/s for 140 m, and Channel 7: at 852 GHz, BW 60 GHz, 28.4 Gb/s for 120 m. The enabled long-path THz links are discussed. Two applications are presented in detail, namely, a long-path 17.5 km THz ground-link operating at 96 GHz, BW 30 GHz, 10.7 Gb/s, and a GEO satellite link at 252 GHz, BW 50 GHz, 25.2 Gb/s. In addition, Channel 7 at 852 GHz is studied by calculated pulse propagation to understand the relationships between high bit-rates and propagation distance. It is shown that good digital transmission could be obtained with 852 GHz, BW 108 GHz, 56.8 Gb/s for a 160 m propagation distance in the atmosphere with RH 58% (10g/m(3)) and 20 degrees C. Good digital transmission could also be obtained with 852 GHz, BW 108 GHz, 71.0 Gb/s for 80 m. These results are discussed with respect to high bit-rate, short-path applications. These digital THz communication channels were determined together with a new measurement of the water vapor continuum absorption from 0.35 to 1 THz. The THz pulses propagate though a 137 m long humidity-controlled chamber and are measured by THz time-domain spectroscopy (THz-TDS). The average relative humidity along the entire THz path is precisely obtained by measuring the difference between transit times of the sample and reference THz pulses to an accuracy of 0.1 ps. Using the measured total absorption and the calculated resonance line absorption with the Molecular Response Theory lineshape, an accurate continuum absorption is obtained within five THz absorption windows, that agrees with the empirical theory.