Fig. 7: Wireless link experimental setup.

The first input is a dual wavelength optical signal, indicated as LO. A baseband quadrature phase shift keying (QPSK) datastream (IF) with CF 2 GHz is generated using a Digital-to-Analog Converter (DAC). The data rate of the signal has been tuned between 1 Gbit/s and 4 Gbit/s. The optical and electrical inputs signals are applied to the G-OEM, as indicated in the optical image in the inset: the LO is coupled to the chip using a lensed fiber. The LO frequency is 91 GHz The IF is applied using an RF probe. The output port (RF) provides the sub-THz CF carrying the upconverted information. Since the LO frequency is 91 GHz and the IF carrier is 2 GHz, the upconverted signal is carried around a carrier frequency of 91 GHz + 2 GHz = 93 GHz (upper sideband). This electrical signal is collected by a second RF probe. After being filtered and amplified, it is transmitted through a wireless link using a horn antenna, and then is detected by a receiver composed by a second antenna and a commercial downconverter. A real-time oscilloscope is finally used to analyze the received QPSK sequence. On the bottom, the schematic electrical spectrum of the datastream is depicted, as it flows along the various elements of the system: the baseband signal is first upconverted by the G-OEM in the sub-THz domain, and then downconverted again in baseband after the wireless link, to be visualized on the oscilloscope. At each Input/Output stage of the wireless link chain, the electrical (black) or optical (red) maximum powers used during the experiment are indicated.