## 2 Description of the THz Wireless Communication Setup
### THz Receiver Setup  
The receiver configuration, as illustrated in Figure 1, comprises a WR3.4 antenna connected to a selection of mixers, which is the focal point of this investigation. Unlike Schottky Barrier Diodes (SBDs) [30; 33], the high performance of the mixers used in this study avoids the use of any RF amplifier, considerably reducing the power consumption and the receiver noise figure. The down-converted IF signal is connected to a Low-Noise Amplifier (LNA), and the output goes to an oscilloscope (Agilent DSO-X 93304Q) to measure and capture the received signal. This study explores two distinct approaches of LO, optical and electrical pumping techniques, which are defined as follows:  
* Optical pumping consists of a similar approach as the transmitter, as is seen in Figure 1c). The optical signal from the two different lasers is coupled to a 50:50 coupler. The output is amplified using an EDFA which is again connected to a probed MUTC-PD which acts as an LO source to pump the mixers. This is possible due to the high output power of the diodes provided by the UDE [32; 34] and the low LO power requirements of the InGaAs mixers. The photodiodes used in this study were not able to achieve the required output power to pump the GaAs mixer. However, recent advancements in photodiode technology have demonstrated the ability to generate a few milliwatts of output power at higher frequencies [35; 36]. * The second approach is to use multiplication chains based on GaAs diodes; see Figure 1d). This technique has been widely used in extenders, sources, and active multiplier chains (AMCs) to reach frequencies above 500 GHz [37]. The AMC used in this study is provided by ACST. Its typical 10 dBm of output power is enough to be used as an LO source in both the GaAs and InGaAs mixers. Although, to be used with InGaAs diodes, a waveguide variable attenuator is placed between the mixer's LO port and the AMC output to reduce the power to levels below the damage threshold. Figure 1: THz transmission and reception architecture. **(a)** shows photonic transmitter based on optical heterodyne mixing in a probed modified uni-traveling-carrier photodiode (MUTC) to generate THz signals, where data are provided by modulating one of the laser arms. After transmission in the wireless channel, the signal is down-converted to IF using a sub-harmonic mixer (SMH) pumped by two different approaches. The first case is similar to the TX, using the beating of two lasers, and the second case uses electrical pumping. **(b)** shows a picture of the THz transmitter consisting of the probed MUTC connected to a horn antenna pointing to the receiver. **(c)** shows a picture of the receiver; here, the mixer is connected to a probed MUTC, which generates the LO signal to pump the mixer. **(d)** shows a picture of the electrically pumped receiver, consisting of an AMC connected to the mixer. The different characteristics in terms of operational frequency, IF bandwidth, conversion loss, and local oscillator power requirements are presented in Table 1. These key parameters are given for the two different mixers that will be compared in this study: narrow band mixers employing GaAs and InGaAs diodes. In terms of the frequency range, both narrow band mixers using GaAs and InGaAs diodes cover part of the WR3.4 range spanning from 270 to 320 GHz. Regarding the IF bandwidth, both mixers employ high-quality SMA connectors, enabling IF frequencies beyond 25 GHz. Focusing on the conversion loss, which quantifies the power loss during the down-conversion process, we observe variations among the different mixers. The narrow-band mixers using GaAs diodes show double-side-band (DSB) conversion loss of 6 dB, and those mixers with InGaAs show values of 13 dB. Generally, lower conversion losses are preferred to ensure higher efficiency in signal processing. Lastly, we consider the LO power requirements for each mixer type.