# 100 Gbit/s and Beyond IEEE 802.15.3d Channelization Compatible THz Communications Enabled by a Broadband MUTC Photodiode

Ezgi Abacıoğlu, Abdu Subahan Mohammed, Jonas Tebart, Marcel Grzeslo, Tom Neerfeld, José Luis Fernández Estévez, Pascal Szriftgiser, Guillaume Ducournau, Andreas Stöhr

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## ► To cite this version:

Ezgi Abacıoğlu, Abdu Subahan Mohammed, Jonas Tebart, Marcel Grzeslo, Tom Neerfeld, et al., 100 Gbit/s and Beyond IEEE 802.15.3d Channelization Compatible THz Communications Enabled by a Broadband MUTC Photodiode. IEEE Transactions on Terahertz Science and Technology, 2025, 15 (3), pp.389 - 399. 10.1109/TTHZ.2025.3541824. hal-04963122

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# 100 Gbit/s and Beyond IEEE 802.15.3d Channelization Compatible THz Communications Enabled by a Broadband MUTC Photodiode

Ezgi Abacıoğlu, Graduate Student Member, IEEE, Abdu Subahan Mohammed, Jonas Tebart, Marcel Grzeslo, Tom Neerfeld, José Luis Fernández Estévez, Pascal Szriftgiser, Guillaume Ducournau, Member, IEEE, and Andreas Stöhr, Senior Member, IEEE

**Abstract**—We present photonics-driven high data rate IEEE 802.15.3d compliant terahertz (THz) communication links operated at a center frequency of 280 GHz. We analyze wireless data transmission within selected single and dual channels of the IEEE 802.15.3d and assess the outcomes through additional back-to-back (B2B) data transmission measurements and calibrated link budgets of the THz link. The system architecture uses on-wafer probing of a single high-power and highly linear broadband modified unitraveling-carrier photodiode (MUTC-PD). Using the MUTC-PD as THz transmitter, we report 16-QAM 100 Gbit/s 25-cm wireless links for single and dual channel data transmission with significantly low error vector magnitude (EVM) levels, that is, 12.3% and 10.9%, respectively. As for B2B demonstration, we successfully transmit 200 Gbit/s (32-QAM) in a single channel with 7.5% EVM and 160 Gbit/s (16-QAM) in dual channel with 7.8% EVM. We further display the highly linear nature of the MUTC-PD by efficient data transmission with higher modulation formats, which is also supported by the power-saturation characteristics of the PD. To the best of the authors' knowledge, this is the first study investigating the IEEE 802.15.3d channelization compliancy

Received 25 June 2024; revised 15 October 2024 and 12 January 2025; accepted 2 February 2025. Date of publication 13 February 2025; date of current version 28 April 2025. This work was supported in part by the European TERAOPTICS project under Grant 956857, in part by the German Research Foundation - CRC 196 MARIE C06 and C07 under Grant 287022738, in part by the Federal Ministry of Education and Research - 6GEM under Grant 16KISK039, in part by the Open6GHub under Grant 16KISK017, and terahertz.NRW under Grant NW21-068C, in part by the Contrat de Plan Etat Region WAVETECH @HdF project and Haut de-France Regional Council, IEMN UHD Flagship Project, the IEMN CHOP Platform, France 2030-PEPRFUNTERA and SYSTERA projects, funded by Agence Nationale de la Recherche under Grant ANR-22-PEEL-0006 and Grant 22-PEFT-0006, and in part by the French RE-NATECH network, the Equipex + Nanofutur under Grant IA-21-ESRE-0012. (Corresponding author: Ezgi Abacıoğlu.)

Ezgi Abacıoğlu, Jonas Tebart, Marcel Grzeslo, Tom Neerfeld, José Luis Fernández Estévez, and Andreas Stöhr are with the Department of Optoelectronics, University of Duisburg-Essen, 47057 Duisburg, Germany (e-mail: ezgi.abacıoglu@uni-due.de; jonas.tebart@uni-due.de; marcel.grzeslo@uni-due.de; tom.neerfeld@uni-due.de; jose.fernandez-estevez@uni-due.de; andreas.stoehr@uni-due.de).

Abdu Subahan Mohammed and Guillaume Ducournau are with the CNRS, Centrale Lille, Univ. Polytechnique Hauts-de-France, UMR 8520-IEMN, Institut d'Electronique de Microélectronique et de Nanotechnologie, University of Lille, 59000 Lille, France (e-mail: abdu-subahan.mohammed@iemn.fr; guillaume.ducournau@univ-lille.fr).

Pascal Szriftgiser is with the CNRS, Laboratoire de Physique des Lasers, Atomes et Molécules, PhLAM, UMR 8523, University of Lille, F-59000 Lille, France (e-mail: pascal.szriftgiser@univ-lille.fr).

Color versions of one or more figures in this article are available at https://doi.org/10.1109/TTHZ.2025.3541824.

Digital Object Identifier 10.1109/TTHZ.2025.3541824

through system level design and spectral verification while at the same time achieving 100 Gbit/s and beyond data rates with notably low EVM values.

**Index Terms**—Complex modulation, IEEE 802.15.3d, modified unitraveling-carrier photodiode, multichannel transmission, terahertz (THz) communications, wireless communications.

## I. INTRODUCTION

WIRELESS communications has undergone an exceptional growth in the past decades, with data rates increasing exponentially following Moore's law [1]. This growth is accelerated by the ever-increasing global demand for wireless technologies in the recent years. Accordingly, the global mobile network data traffic almost doubled itself between the first quarters of the years 2021 and 2023 from 66 EB (exabyte) per month to 126 EB per month, respectively, and it was predicted to reach 160 EB per month by the end of 2023 [2], [3]. By the end of 2029, the total mobile network traffic is even anticipated to reach 563 EB per month, including the traffic generated by fixed wireless access (FWA). This projection study takes into account a significant increase in video traffic as well as the future contribution of new applications into data traffic, such as extended reality services. In the same report, the share of 5G communications in mobile data traffic is forecasted to grow to 76% in 2029, while it was only 15% at the end of 2022 [3]. To meet this demand, the “6G” research is very active, covering frequencies from the sub-6 GHz up to the 300 GHz bands [4], [5], [6], [7]. One of the bottlenecks is to increase the capacity of the FWA systems. To reach this objective, the preliminary research focuses on improving the data exchange efficiencies in the lower FWA bands between 28 and 86 GHz in order to circumvent the complexities of employing higher millimeter-wave frequencies [8], [9], [10]. Looking beyond, these efforts are to be succeeded by the exploitation of frequencies above 100 GHz to realize efficient 6G and beyond communication systems [11], [12].

All of the above-mentioned prospects are creating a further drive for the development of reliable, low-latency, high data rate, and large bandwidth wireless technologies. In this context, terahertz (THz) communications (covering the operating frequencies from 100 GHz to 10 THz) is attractive as it enables broad data bandwidths and high data rates, especially for front- and backhaul applications [13], [14], [15]. This great potential
<table><caption>TABLE I
IEEE 802.15.3D THZ PHY CHANNELIZATION AND TRANSMIT SPECTRUM MASK PARAMETERS [16]</caption><thead><tr><th rowspan="2">IEEE 802.15.3d Channel</th><th rowspan="2">Bandwidth (GHz)</th><th rowspan="2">Start Frequency (GHz)</th><th rowspan="2">Center Frequency (GHz)</th><th rowspan="2">Stop Frequency (GHz)</th><th colspan="4">Transmit Spectrum Mask Parameters</th></tr><tr><th>f<sub>1</sub> (GHz)</th><th>f<sub>2</sub> (GHz)</th><th>f<sub>3</sub> (GHz)</th><th>f<sub>4</sub> (GHz)</th></tr></thead><tbody><tr><td>Ch 66</td><td rowspan="2">25.92</td><td>252.72</td><td>265.68</td><td>278.64</td><td rowspan="2">12.82</td><td rowspan="2">12.98</td><td rowspan="2">13.48</td><td rowspan="2">14.08</td></tr><tr><td>Ch 67</td><td>278.64</td><td>291.6</td><td>304.56</td></tr><tr><td>Ch 68</td><td rowspan="2">51.84</td><td>252.72</td><td>278.64</td><td>304.56</td><td rowspan="2">25.78</td><td rowspan="2">25.94</td><td rowspan="2">26.44</td><td rowspan="2">27.04</td></tr><tr><td>Ch 69</td><td>252.72</td><td>287.28</td><td>321.84</td></tr></tbody></table>

is acknowledged by the first standard dedicated to THz wireless communications, namely the IEEE Std 802.15.3d, which was officially approved in 2017 [16]. The IEEE 802.15.3d defines a physical layer (PHY) at a sub-THz frequency band (253-322 GHz) for wireless point-to-point links with data rates of 100 Gbit/s and higher. The standard covers wireless distances from a few centimeters up to several hundred meters.

According to the IEEE 802.15.3d, the THz PHY layer can have one of the two modes:

1) THz single carrier mode PHY (THz-SC PHY).

2) THz on-off keying mode PHY (THz-OOK PHY).

The THz-SC PHY is designed for high data rates up to 100 Gbit/s and supports various modulation types: $\pi/2$ BPSK, $\pi/2$ QPSK, $\pi/2$ 8-PSK, $\pi/2$ 8-APSK, 16-QAM, and 64-QAM. The THz-SC-PHY mode mainly targets bandwidth-oriented applications, such as front- and backhaul links. The second mode, THz-OOK PHY, is designed for cost-effective, low-complexity devices and supports only a single modulation format—OOK [16].

The channel allocation plan of the IEEE 802.15.3d defines altogether 69 channels between 252.72 GHz and 321.84 GHz. The narrowest supported channels (Ch 1–Ch 32) have a bandwidth of 2.16 GHz each and can all be aggregated, whereas the widest channel (Ch 69) covers the full bandwidth of 69.12 GHz between 252.72 and 321.84 GHz. Depending on the application and device capabilities, either a single channel or multiple aggregated channels can be used. For all defined channels, there is a specified transmit mask for both THz-SC PHY and THz-OOK PHY modes in order to frame the allowed channel spectrums within the standard [12], [16]. Table I shows the IEEE 802.15.3d THz PHY channelization for channels from 66 to 69 (the ones utilized in this study) and knee frequencies of the spectral emission masks defined in the standard [16]. The recently released latest revision of the standard covers additional channels up to 425 GHz [17].

In recent years, many technologies have been developed and exploited for terahertz communications. Table II provides an overview on the state-of-the-art in THz communication systems operating within the frequency range defined by the IEEE 802.15.3d standard [15], [18], [19], [20], [21], [22], [23], [24], [25]. As can be seen from Table II, both all-electronic and optoelectronic technologies are being used. In either case, the THz receivers are usually electronic-based devices, such as subharmonic mixers (SHM) or Schottky barrier diodes (SBD). For THz transmitters, either all-electronic or photonic technologies are exploited. Electronic THz transmitters are commonly

developed using III-V or silicon (Si) multipliers or oscillators [15], [18], [19], [20]. Here, it should be noted that electronic multipliers usually suffer from increased phase noise which is proportional to $20 \times \log(N)$, with N being the multiplication factor, despite providing high-power solutions. Photonic THz transmitters usually exploit pin-photodiodes (pin-PD) or unitraveling-carrier photodiodes (UTC-PD) [21], [22], [23], [24]. Critical figures of merit for these PDs include a broad operational bandwidth, high saturation output power, and quantum efficiency [26]. Especially the broadband and high output power capabilities of UTC-PDs are beneficial for their use in high data rate THz communications [23]. This is because UTC-PDs leverage high mobility electrons while suppressing the hole transport, which in turn reduces the junction transit time and improves the high frequency response [27]. By optimizing the E-field distribution through the device junction, thanks to an optimized epilayer design, the so-called modified UTC-PD (MUTC-PD) can provide even further improved performances in terms of carrier transition time and power saturation [28]. Consequently, photonics-based transmitters offer highly linear THz signal generation over a broad bandwidth, which is beneficial for spectral efficient complex modulation. Another advantage of photonic solutions is the potential for a more straightforward multichannel transmission by increasing the number of lasers used in the signal generation. In any case, the transmitted power is a limiting factor for the reach of the wireless links. In this regard, employing high output power THz transmitters can be advantageous to contribute to the overall link budget.

Table II also provides an overview on the achieved system performances. In [15] and [18], monolithic millimeter-wave integrated circuit (MMIC) based superheterodyne systems were demonstrated in the 300 GHz band. In [18], 16-QAM 100 Gbit/s signals were successfully transmitted over a 2.22 m long wireless link in single channel configuration. In [15], it is shown that a wireless distance of 10 m is achievable with a single channel data rate of 56 Gbit/s using again 16-QAM. The same group also reported on multichannel transmission using two channels, each with a bandwidth of 2.295 GHz, which is a little wider than the IEEE 802.15.3d defined channel bandwidth of 2.16 GHz. In this experiment, the aggregated data rate was measured to be 20.4 Gbit/s (10.2 Gbit/s per channel) using 64-QAM signal modulation. In their work using CMOS-based superheterodyne wireless links, Lee et al. [19], [20] targeted the single channels 66 and 67 of the IEEE 802.15.3d and achieved 80 Gbit/s (3 cm link) and 40 Gbit/s (1 m link), respectively. However, none of
<table><caption>TABLE II
STATE-OF-THE-ART OF THZ COMMUNICATION LINKS WITHIN IEEE 802.15.3D FREQUENCY BAND USING ALL-ELECTRONIC AND OPTOELECTRONIC TECHNOLOGIES</caption><thead><tr><th>Ref.</th><th>Technology</th><th>Channel Format</th><th>Center Frequency (GHz)</th><th>IEEE 802.15.3d Channel</th><th>Mod. Type</th><th>Distance (m)</th><th>Data Rate (Gbit/s)</th><th>EVM (%)</th><th>BER</th></tr></thead><tbody><tr><td>[18]</td><td>80 nm InP-HEMT</td><td>SC</td><td>287</td><td>—</td><td>16-QAM</td><td>2.22</td><td>100</td><td></td><td>&gt;10<sup>-3</sup></td></tr><tr><td rowspan="2">[15]</td><td rowspan="2">35 nm InGaAs mHEMT</td><td>SC</td><td rowspan="2">300</td><td rowspan="2">—</td><td>16-QAM</td><td rowspan="2">10</td><td>56</td><td>12.2**</td><td></td></tr><tr><td>MC</td><td>64-QAM</td><td>20.4</td><td>6</td><td></td></tr><tr><td>[19]</td><td>40 nm CMOS</td><td>SC</td><td>265.7</td><td>Ch 66*</td><td>16-QAM</td><td>0.03</td><td>80</td><td>12</td><td></td></tr><tr><td>[20]</td><td>40 nm CMOS</td><td>SC</td><td>291.6</td><td>Ch 67*</td><td>16-QAM</td><td>1</td><td>40</td><td>14.5</td><td></td></tr><tr><td>[21]</td><td>pin-PD + electronic mixer</td><td>SC</td><td>300</td><td>—</td><td>16-QAM</td><td>0.50</td><td>128</td><td></td><td>8×10<sup>-3**</sup></td></tr><tr><td>[22]</td><td>RCE UTC-PD + electronic mixer</td><td>SC</td><td>280</td><td>Ch 69*</td><td>16-QAM</td><td>0.50</td><td>100</td><td></td><td>10<sup>-4</sup></td></tr><tr><td>[23]</td><td>UTC-PD + SBD</td><td>SC</td><td>300</td><td>—</td><td>16-QAM</td><td>0.50</td><td>100</td><td></td><td>16.95</td></tr><tr><td>[24]</td><td>UTC-PD + electronic intradyne receiver MMIC</td><td>SC</td><td>300</td><td>—</td><td>16-QAM</td><td>52</td><td>200</td><td></td><td>3×10<sup>-3**</sup></td></tr><tr><td>[25]</td><td>UTC-PD + electronic mixer</td><td>SC</td><td>300</td><td>—</td><td>32-QAM</td><td>214</td><td>220</td><td></td><td>3.75×10<sup>-3</sup></td></tr><tr><td rowspan="6">This work</td><td rowspan="6">MUTC-PD + electronic mixer</td><td rowspan="3">SC</td><td rowspan="3">280</td><td>Ch 69</td><td>16-QAM</td><td>B2B</td><td>160</td><td>8.8</td><td>&lt;10<sup>-3</sup></td></tr><tr><td>32-QAM</td><td></td><td>200</td><td>7.5</td><td>&lt;10<sup>-2</sup></td></tr><tr><td></td><td>B2B</td><td></td><td>6.4</td><td>&lt;10<sup>-4</sup></td></tr><tr><td rowspan="2">Ch 68</td><td>16-QAM</td><td>0.25</td><td>100</td><td>12.3</td><td>&lt;10<sup>-2</sup></td></tr><tr><td>32-QAM</td><td></td><td>125</td><td>5.5</td><td>&lt;10<sup>-3</sup></td></tr><tr><td></td><td>64-QAM</td><td></td><td>150</td><td>5.5</td><td>~10<sup>-2</sup></td></tr><tr><td></td><td>MC</td><td>265.7 &amp; 291.6</td><td>Ch 66 &amp; Ch 67</td><td>16-QAM</td><td>B2B</td><td>160</td><td>7.8</td><td>&lt;10<sup>-4</sup></td></tr><tr><td></td><td></td><td></td><td></td><td></td><td>0.25</td><td>100</td><td>10.9</td><td>~10<sup>-3</sup></td></tr></tbody></table>

Note: Ref.: Reference; SC: Single Channel; MC: Multi Channel; Mod. Type: Modulation Type; B2B: Back-to-Back; EVM: Error Vector Magnitude; BER: Bit Error Rate; *No mask analysis provided for IEEE 802.15.3d compliance.; **Estimated from measurement results.

these studies provided spectral verification to prove compliance with the IEEE Std 802.15.3d.

In optoelectronic solutions, a broadband *pin*-PD was employed to demonstrate 128 Gbit/s with 16-QAM modulation over a 50 cm single channel wireless link at 300 GHz [21]. In the same frequency band, Chinni et al. [22] reported a single 100 Gbit/s THz channel (targeting the IEEE 802.15.3d Ch 69) with 16-QAM signaling by using a linear resonant cavity enhanced (RCE) UTC-PD. Here again, compliance with the standard is not verified by spectral data. Previously, our group demonstrated 100 Gbit/s single channel transmission at 300 GHz over 50 cm using 16-QAM [23] and even 200 Gbit/s long distance wireless transmission over 52 m [24]. However, in these previous demonstrations, we did not prove compatibility to the IEEE 802.15.3d standard. In another recent study in the 300 GHz band, Maekawa et al. reported a 220 Gbit/s single channel long distance wireless link over 214 m with 32-QAM modulation by using a UTC-PD [25].

In this article, we report on photonics-driven single and multi-channel THz communication links using IEEE 802.15.3d channelization. The operation conditions of the THz communication system such as the baud rate were adapted to be in accordance with the standard. Compatibility to IEEE 802.15.3d was then

investigated by comparing the data spectra to the spectral masks defined in the standard. In the system reported here, a single high-power and highly linear broadband MUTC-PD was employed in the THz transmitter for all measurements. The impact of the high linearity and high-power saturation characteristics of the MUTC-PD were demonstrated by thorough experimental single channel and multichannel studies for back-to-back (B2B) and wireless transmission experiments. Thanks to the high linearity of the MUTC-PD, very low EVM figures for 100 Gbit/s wireless transmission and 200 Gbit/s B2B transmission were achieved.

## II. MUTC PHOTODIODE STRUCTURE

The epilayers of the MUTC-PD are grown via metal organic chemical vapor deposition. The photodiode junction design includes a hybrid InGaAs absorber, which is sandwiched between two InP regions: A highly doped top InP layer serving as diffusion blocker and another InP layer functioning as compensated collector and waveguide cladding. To prevent carrier accumulation, InGaAsP spacer layers are incorporated. An inhomogeneous doping profile is realized by inserting p-type doped and n-type doped cliff layers in the absorber region and
<figure><img src="image_3.png" /><figcaption>Fig. 1. (a) System architecture of the PD characterization setup. Signal generation is based on optical heterodyne mixing in an MUTC-PD. The RF-power of the probed PD is measured using a calorimetric power meter (PM5B). (c) shows the fiber-chip coupling and MUTC-PD probing using a GSG probe, which can be seen more closely in the optical microscope image given in (b).</figcaption></figure>

collector region, respectively. The p- and n-type contact layers are p⁺-InGaAs and n⁺-InP, respectively.

The p-contacts are fabricated via metallization process, which is followed by structuring of the mesas (p- and n-) and the passive optical waveguide using wet chemical etching technique. A second metallization process is employed for the fabrication of n-contacts. Continuously, a post-annealing process is performed to obtain low contact resistances. For passivation and isolation of the mesas, diluted benzocyclobutene coating is used. The final fabrication step includes the metallization of the coplanar waveguide (CPW) with 50 Ω load. The signal and gap widths of the CPW are 35 and 25 µm, respectively.

Details about the layer structure and fabrication process of the waveguide-integrated MUTC-PDs can be found in previous study [29]. For this work, a 6 × 30 µm² MUTC-PD was fabricated.

### III. RF-CHARACTERISTICS OF THE MUTC PHOTODIODE

Among the key features of using a photonics-based transmitter for THz communications, the output power and linearity of the devices are to be checked first. High linearity is an important figure to minimize signal distortion and maintain large spurious-free dynamic range [30]. Here, the RF-characteristics of the fabricated 6 × 30 µm² CPW-integrated MUTC-PD (with a responsivity of 0.2 A/W) are measured in continuous-wave frequency domain for a better understanding of the expected PD behavior in THz communication links. Fig. 1(a) shows the optical heterodyne setup for the RF-response characterization. Here, the carrier signals of two tunable external cavity laser diodes (ECL1 and ECL2) are used to generate a beat signal at 280 GHz, which corresponds to the difference frequency of the two laser lines (both in the range of 193.5 THz). The produced optical signal is then preamplified by an erbium-doped fiber amplifier (EDFA1). The output power of the signal is adjusted using a variable optical attenuator (VOA) before being injected in a second EDFA (EDFA2). Subsequently, the signal is coupled into the facet of the MUTC-PD waveguide with a lensed optical fiber as shown in Fig. 1(b) and (c). The optical power at the tip of the fiber was measured to be 20.6 dBm (measured in free space with a 1.55-µm sensitive optical power meter). The MUTC-PD is on-wafer probed using a T-wave type WR-3.4 band (220–325 GHz) probe with 50 µm pitch. The RF-power levels are measured using a calorimetric power meter (PM5B

<figure><img src="image_4.png" /><figcaption>Fig. 2. RF output power and relative power at 280 GHz for varying reverse bias for the 6 × 30 µm² MUTC-PD with 50 Ω load.</figcaption></figure>

from Virginia Diodes). As the PM5B has a WR10 input, a WR3.4–WR10 taper is used in front of the power meter. The losses from both the waveguide taper [31] and the RF-probe (from probe manufacturer data) are taken into account.

The measured saturation characteristics and compression of the 6 × 30 µm² MUTC-PD for different dc biasing conditions are shown in Fig. 2. As can be seen, the PD exhibits high saturation currents along with a linear power response to the photocurrent at the carrier frequency of 280 GHz for varying reverse bias voltage between –1.4 and –2 V. The highest output powers were measured at the –1.4 V biasing condition, reaching –5.4 dBm at a photocurrent level of 22 mA. Details to the reverse bias dependency of the output power at varying THz frequencies can be found in our recent study covering the identical MUTC-PD epilayer design [32]. The relative power in Fig. 2 is the difference between the measured power and expected power with 50 Ω load. The 1 dB compression point can be determined from this curve, which is defined as the point where the relative power drops for 1 dB from its constant value [33]. From the figure, it is estimated to be between 13 and 15 mA for reverse bias varying between –1.4 and –2 V. These values indicate a good power handling capability of the MUTC-PD. Moreover, the 6 × 30 µm² CPW-integrated MUTC-PD used in this study has recently been shown to exhibit ultrabroadband capabilities up to 500 GHz [34]. Given the high-power handling capability, favorable saturation characteristics with linear behavior, and broad operational bandwidth, the 6 × 30 µm² MUTC-PD was further employed in THz communication measurements.

### IV. TERAHERTZ COMMUNICATION MEASUREMENTS

The configuration of the THz communication links in this study is designed to investigate the compatibility with the single and multichannel definitions in the IEEE 802.15.3d standard as well as to characterize B2B data transmission in the same frequency range. Accordingly, B2B and wireless communication setups are built to test high data rate single and dual carrier data
<figure><img src="image_5.png" /><figcaption>Fig. 3. Transmission architecture of the THz communication links. On the transmitter side (a), an optical heterodyning approach is used to generate the THz signal and one of the optical carriers is modulated by means of an MZM. For dual channel measurements, a third laser (ECL3) is integrated to create a further LO tone. After the MUTC-PD, the down-converted THz signal carrying the data waveform is extracted with a GSG probe. In B2B configuration, the extracted signal is directly fed into the THz receiver (b), where it is down-converted into an IF by a SHM. After subsequent amplification, the signal is analyzed in a real-time oscilloscope. The system is extended with horn antennas and lenses for the 25-cm wireless link as shown in (c). Photographs of the wireless link are shown in (d), (e), and (f).</figcaption></figure>

<table><caption>TABLE III
TESTED FREQUENCY PLAN FOR SINGLE AND DUAL CHANNEL MEASUREMENTS</caption><thead><tr><th></th><th>2×LO<br>(GHz)</th><th>f<sub>c</sub><br>(GHz)</th><th>IF<sub>1</sub><br>(GHz)</th><th>IF<sub>2</sub><br>(GHz)</th><th>IEEE<br>802.15.3d<br>Channel</th></tr></thead><tbody><tr><td>SC<sub>1</sub></td><td>302.4</td><td>280</td><td>20</td><td></td><td>Ch 69</td></tr><tr><td>SC<sub>2</sub></td><td>302.4</td><td>280</td><td>20</td><td></td><td>Ch 68</td></tr><tr><td rowspan="2">DC</td><td rowspan="2">303</td><td>265.7</td><td></td><td>38</td><td>Ch 66</td></tr><tr><td>291.6</td><td>12</td><td></td><td>Ch 67</td></tr></tbody></table>

SC: Single Channel; DC: Dual Channel; LO: Local Oscillator; f<sub>c</sub>: Center Frequency; IF: Intermediate Frequency.

transmission using the high-power broadband MUTC-PD discussed in the previous section. All measurements are performed in the linear region below the P<sub>1dB</sub>-photocurrent of the PD, as characterized in Fig. 2, to circumvent the saturation effects. Table III lists the frequency plan for single channel (Ch 68 and Ch 69) and dual channel (Ch 66 and Ch 67) use defined in the IEEE 802.15.3d standard. These channels were used in the experimental demonstrations. To assure that the transmit spectrum for each channel is within the spectral mask set by the standard, central frequencies, symbol rates, and power levels were adapted accordingly.

In this study, the figure of merit for the performance assessment of the measured THz transmission links is the measured EVM. The bit error rate (BER) limits are also shown to allow for a comparison between the performances of different proposed systems. Accordingly, the BER is evaluated by direct comparison of the transmitted data patterns (pseudo random bit sequences, PRBS, from arbitrary waveform generator, AWG, baseband *I* and *Q* data) and detected *I* and *Q* signals after constellation analysis, which also indicates the EVM. The PRBS length used in this work is 2<sup>13</sup> − 1.

## A. Back-to-Back Link

Similar to the photodiode characterization setup already described in Section III, the approach used for communication

applications is also based on the use of optical heterodyne mixing in a broadband MUTC-PD. A schematic diagram is given in Fig. 3. Here, instead of using the classical concept of up-conversion as used in all-electronic systems, we use down-conversion (from optical to THz, namely the photomixing process), which can provide spurious-free signals along with larger tunability and easy modulation, leveraging the techniques widely used in fiber-optic communications. To be able to use the system for communication purposes (with single or dual channel) and the systematic investigation of the transmission properties of the THz link, the transmitter side is adapted according to the block diagram shown in Fig. 3(a). Here, the THz transmitter is used in a B2B transmission in combination with the receiver shown in Fig. 3(b). The modulated data signal itself is a complex signal obtained with two baseband waveforms, *I* and *Q*, both generated by an AWG allowing the flexible use of different symbol rates and modulation orders. These *I* and *Q* signals are fed into a Mach-Zehnder modulator (MZM), resulting in a quadrature amplitude modulation (QAM). Subsequently, the fiber output of the modulator is combined (using a fiber coupler) with a second laser (ECL2) which acts as a local oscillator (LO). By adding further LO tones, i.e., adding additional lasers, the same data signal can be generated simultaneously at different THz carrier frequencies according to the channels defined in the standard. This way, it is also possible to analyze the transmission system for multichannel applications. The optical tones of the three lasers are not correlated for all measurements. After combining the data and LO signals, an initial optical preamplification is performed using EDFA1. In the next step, its output power is adapted to the optimum input power of the second amplifier stage (EDFA2) by means of a VOA so that both EDFAs can operate in the optimum range and can provide up to 22 dBm of optical input power to the MUTC-PD, without any optical filtering. The down-converted THz signal containing the data waveform at the targeted THz transmission frequency is then extracted via a ground-signal-ground (GSG) probe and, in the case of the B2B configuration, directly fed to the THz receiver as an input signal via a waveguide. The THz
receiver itself is based on an electrically pumped SHM (WR2.8 model from VDI [35]) allowing the modulated THz signal to be down-converted from the THz carrier frequency into an intermediate frequency (IF) (<40 GHz). The roll-off effect of the SHM (frequency dependence of the IF path) is corrected during equalization applied in the signal analysis. This SHM requires an LO tone around 150 GHz which is provided by a signal generator (SMA100B from Rohde & Schwarz) with a subsequent ×12 multiplier. The generated baseband signal is then first amplified and subsequently captured by a wideband 70 GHz real-time oscilloscope (UXR from Keysight). This allows for a real-time analysis of usual performance metrics such as the EVM at different symbol rates and modulation orders. The DSP routine used in the experiments is the following: First, time sequences (typical lengths < 1 µs) are sampled on the real-time oscilloscope in order to limit the effect of the lasers' phase noise. The center IF frequency is fixed at a value which is not 0, and the demodulation of the IQ signal is directly done using the commercial “digital demodulation” tool from the Keysight vector signal analysis (VSA) software. A frequency equalization is done on the signal to compensate mostly for the frequency response induced by the UTC-PD, probe and frequency-dependent IF losses inside the SHM used to down-convert the 300 GHz signal. The BER evaluation is done by direct comparison of the PRBS sequences used for I and Q baseband signals and the detected I and Q data after demodulation.

Using the specified B2B link, the THz signal is kept inside the IEEE 802.15.3d channels 68 and 69 for single carrier data transmission, and inside the channels 66 and 67 simultaneously for dual carrier data transmission. The spectra of the received signal for all channels with the corresponding IEEE 802.15.3d masks (see Table I for mask parameters) are shown in Fig. 4. As it is seen from the figure, the measured channel spectra are within the predefined channelization scheme for all occupied channels and therefore IEEE 802.15.3d compatible. It should be noted that the measured frequency drift of the utilized tunable lasers is in the 1–10 MHz range. Taking into account the given margin with regard to the boundary values of the spectrum masks up to a few GHz (see Fig. 4), it is expected that the boundary conditions of the individual channels can still be met even under the given drift phenomena due to the measurement setup.

Fig. 5 presents the evolution of the EVM with the photocurrent level inside the MUTC-PD for the Ch 69 as well as the measured constellations. Along with 16-QAM, a higher modulation format of 32-QAM was also employed to observe the data transmission behavior and to display the linearity of the MUTC-PD. 40 Gbaud signals were successfully transmitted for both 16-QAM and 32-QAM resulting in data rates of 160 Gbit/s and 200 Gbit/s, respectively. It is also seen from Fig. 5 that the measured EVM is reduced as the output photocurrent of the MUTC-PD increases. For 16-QAM signal (160 Gbit/s), the EVM hits a minimum at 8.8%, which corresponds to a level below the BER threshold of $10^{-4}$. For QAM-32 (200 Gbit/s), the EVM reaches 7.5% at 5.5 mA, which corresponds to a BER level less than $10^{-2}$.

Data transmission within the Ch 68 is investigated using the same technique. Fig. 6 demonstrates the achieved EVM with respect to PD photocurrent and constellation diagrams for 16-,

<figure><img src="image_6.png" /><figcaption>Fig. 4. Spectra of the received signal with the corresponding IEEE 802.15.3d masks for single channel (Ch 69 and Ch 68) and dual channel (Ch 66 and Ch 67) measurements.</figcaption></figure>

32-, and 64-QAM signals, all at 25 Gbaud. For all modulation formats, data rates above 100 Gbit/s were achieved, with the highest data rate of 150 Gbit/s for 32-QAM signal. For 64-QAM, the minimum EVM is 5.5% at 6 mA photocurrent level. BER levels less than $10^{-4}$, $10^{-3}$, and $10^{-2}$ were achieved for 16-, 32-, and 64-QAM, respectively, making the system compliant with forward error correction (FEC) techniques. These results, as well
<figure><img src="image_7.png" /><figcaption>Fig. 5. Measured EVM versus output photocurrent (top) and constellation diagrams (bottom) of different QAM signals for single channel (Ch 69) B2B link. The 40 Gbaud signals were successfully transmitted within the Ch 69, reaching data rates of 160 Gbit/s for 16-QAM and 200 Gbit/s for 32-QAM.</figcaption></figure>

as the observed shapes of *I/Q* maps, confirm negligible nonlinear impairments in the case of all three modulation formats used, as expected from the linear behavior of the MUTC-PD. Additionally, in comparison with Ch 69, better constellations were obtained in the case of Ch 68 due to the lower symbol rate and higher signal to noise ratio.

In dual channel demonstration, the three optical signals to generate the two modulated signals are coupled to the MUTC-PD at the same time; in other words, the two modulated THz signals are simultaneously generated in the MUTC-PD for transmission. These two signals are further analyzed at the reception stage, using a different intermediate frequency for each. The two IF signals are then analyzed in real-time using the VSA software from Keysight. Fig. 7 shows the EVM evolution and constellation diagrams for dual channel data transmission in channels 66 and 67. Here, the symbol rate is kept at 20 Gbaud to stay in the channel masks defined by the standard for the channels 66 and 67. As it is seen from the Fig. 7, 16-QAM signals were successfully transmitted in two channels with a data rate of 80 Gbit/s per channel, i.e., total data rate of 160 Gbit/s for dual channel. The measured EVM is as low as 7.8%, which corresponds to a BER level less than $10^{-4}$, compatible with FEC in both channels. It should be noted that for a fixed current in the MUTC-PD, the performance is reduced for the two channels since the current flowing in the MUTC-PD is shared by the two THz signals as the carriers are generated at the same time. The dual channel test confirms that the MUTC-PD enables the dual

<figure><img src="image_8.png" /><figcaption>Fig. 6. Measured EVM versus output photocurrent (top) and constellation diagrams (bottom) of different QAM signals for single channel (Ch 68) B2B link. The 25 Gbaud signals with 16-, 32-, and 64-QAM were successfully transmitted within the Ch 68, achieving data rates of 100, 125, and 150 Gbit/s, respectively.</figcaption></figure>

carrier generation with a good level of performance, thanks to the device linearity. This is essential for efficient data transmission through different channels simultaneously.

## B. Wireless Link

The THz communication system described in Section IV-A is adapted for transmission in a wireless THz link, i.e., using an over-the-air (OTA) or “free-space” THz path. The extension of the system architecture is shown in Fig. 3(b). Here, instead of feeding the THz output signal of the photodiode directly to the THz receiver, it is now radiated into the air using a WR3.4 conical horn antenna (23.5 dBi typical gain at 280 GHz). The gain of the horns used in the experiment is shown in Fig. 8. On the receiver side, another identical horn antenna is implemented for the reception of the signal after 25 cm of wireless transmission distance. In addition, polymer lenses (Zeonex, 25 mm diameter and 30 mm focal length) are used on both the transmitting and receiving sides to further compensate for the free space path loss (FSPL). Photos of the probed PD, the Tx horn antenna with lens, and the receiver are given in Fig. 3(d)–(f).

The transmission losses of the OTA path are determined by measuring the $S_{21}$ parameter in the entire WR3 range to be able to make a statement about the expected attenuation impact of the wireless transmission path in comparison with the B2B link. To this end, a set of frequency extenders (Rohde & Schwarz ZVA-Z325) connected to a vector network analyzer (VNA) are
<figure><img src="image_9.png" /><figcaption>Fig. 7. Measured EVM versus output photocurrent of the dual channel (Ch 66 and Ch 67) B2B link (top). The 20 Gbaud 16-QAM signals were successfully transmitted through both channels, leading to a data rate of 80 Gbit/s on each channel (1CH) and a total data rate of 160 Gbit/s for the dual channel (2CH). The BER lines refer to 16-QAM limits. At the bottom, constellation diagrams of the dual channel analyses for Ch 66 (left) and Ch 67 (right) are shown.</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>Fig. 8. Gain of the horn antennas used in the OTA measurements. Inset shows the WR3.4 conical antenna.</figcaption></figure>

first waveguide calibrated using the thru-reflect-match technique. Then, the wireless path is measured according to the setup consisting of two horn antennas and two lenses. The result, which is shown in Fig. 9, allows for determining the expected signal degradation caused by the FSPL. As an example, the mean FSPL over the frequency range of 268–293 GHz (Ch 68 range) is determined to be 4.6 dB. Fig. 10 shows the results of the EVM

<figure><img src="image_11.png" /><figcaption>Fig. 9. $S_{21}$ parameters measured through the VNA at a frequency range between 220 and 325 GHz with a mean loss of 4.6 dB between 268 and 293 GHz.</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>Fig. 10. Measured EVM versus output photocurrent of the 25 Gbaud 16-QAM single channel B2B and wireless (WL) link. Inset shows the constellation of the wireless channel measured at 6.7 mA photocurrent. For both measurements, a data rate of 100 Gbit/s was achieved. The FSPL curve shows the expected EVM trend after implementing a mean loss of 4.6 dB to the measured B2B data. The BER lines refer to 16-QAM limits.</figcaption></figure>

measurements of the B2B and OTA cases. The comparison of the EVM curves for B2B and OTA cases enable to determine a power penalty, i.e., the power increase required at the transmitter in the case of OTA to reach the same value of EVM in B2B. Obviously, a pure FSPL should lead to an equal power penalty if there is constant group delay and no amplitude distortion. Such a comparison is interesting in terms of comparing the performances of B2B and THz OTA transmission quantitatively. In Fig. 10, the blue squares are the Ch 68 B2B measurement results with 25 Gbaud 16-QAM signals from Section IV-A. The red dots in Fig. 10 show the expected EVM vs. photocurrent behavior for OTA, when considering only a pure additional mean FSPL of 4.6 dB. This curve has been determined from
the measured photocurrent for B2B ($I_{B2B}$) using

$$20 \log \left( \frac{I_{FSPL}}{I_{B2B}} \right) = 4.6 \text{ dB.} \qquad (1)$$

However, it should be noted that this is an optimistic estimate as average losses are used (only a pure power penalty is considered here) without considering any other degradation (dispersion in the OTA part, standing waves of the THz link) or nonlinear effects. When compared to the actual wireless measurement (green triangles) that is performed with the same symbol rate and modulation format, a higher penalty can be observed.

We believe that at least two combined effects could explain the observed degradation of the EVM: 1) distortion, dominating at lower currents and 2) beginning of nonlinear degradation for higher currents. For lower currents, i.e., in the range of 3–5 mA, the slope of the EVM curve is different from the B2B case, while the MUTC-PD is operated in a highly linear region. This may reveal some additional distortions in the OTA link as it is expected from Fig. 9 and could be caused by standing wave effects from the lenses or even some near field effects as the distance is not very high. Beyond 6 mA, the EVM is stabilized and then starts to increase, which could be due to saturation effects in the MUTC-PD. Indeed, the MUTC-PD is biased at –1.7 V, and for this bias, Fig. 2 reveals that the 1dB compression of the MUTC-PD occurs at ~14 mA. Then, considering a 6 dB back-off from 1 dB compression, the operating current should be limited to 7 mA. This reduction of the power back-off beyond 7 mA is certainly the most important contribution of the EVM final degradation.

Despite the loss mechanisms affecting the wireless link performance, a data rate of 100 Gbit/s with EVM values as low as 12.3% was achieved. The constellation diagram of the wireless channel measured at 6.7 mA photocurrent level is given in the inset of Fig. 10, showing a clear IQ-mapping.

For dual channel wireless data transmission, 12.5 Gbaud 16-QAM signals are transmitted in channels 66 and 67 simultaneously. To allow for a comparison, the measurement was repeated inside the B2B link by using the same symbol rate and modulation format. Fig. 11 shows the EVM evolution and constellation diagrams for wireless and B2B measurements using a 12.5 Gbaud 16-QAM signal for both channels, i.e., a data rate of 50 Gbit/s for single channel and 100 Gbit/s for dual channel operation. It can be seen from Fig. 11 that the slope of the curve for each channel remains approximately consistent for wireless and B2B transmission. However, a significant shift is observed in their EVM evolution when changing from B2B to wireless, which is similar to the behavior observed for single channel 68 transmission presented in Fig. 10. Using (1) for Fig. 11, the observed FSPL penalty for Ch 66 (265.8 GHz carrier frequency) is about 4.4 dB, while the penalty is a bit higher (about 6 dB) for Ch 67 at 291 GHz carrier frequency. These two values are quite close to the measured $S_{21}$ of the OTA link (see Fig. 9), showing a penalty close to –3.5 dB at 265 GHz and close to –6 dB for 291 GHz. This confirms the origin of the observed shifts of the curves while the increased penalty at higher currents can be attributed to nonlinear degradation as explained for the single channel case.

<figure><img src="image_13.png" /><figcaption>Fig. 11. Measured EVM versus output photocurrent of the dual channel B2B and wireless links (top). The 12.5 Gbaud 16-QAM signals were successfully transmitted through both channels, leading to a data rate of 50 Gbit/s on each channel and a total data rate of 100 Gbit/s for the dual channel (2CH). The BER lines refer to 16-QAM limits. At the bottom, constellation diagrams of the wireless link are shown.</figcaption></figure>

The lowest measured EVM values are 10.9% and 11.2% for dual channel wireless analyses of Ch 67 and Ch 66, respectively. These values correspond to BER levels of around $10^{-3}$. Even lower EVM values were achieved from B2B measurements, reaching 8.4% for Ch 67 and 7.8% for Ch 66, which corresponds to a level below the BER threshold of $10^{-4}$. The constellation diagrams presented in Fig. 11 visualize the deviation in the measured EVM when comparing the B2B measurement with the wireless. We can also note that, as expected, the lowest EVMs obtained for both channels in wireless are not as low as the one obtained in B2B as the MUTC-PD is operated at higher current levels to mitigate the OTA losses. Nevertheless, successful transmission of at least 100 Gbit/s signals was achieved for single and dual channel transmission. As a result, we believe that the proposed photonics-driven approach can be exploited for future ultrafast multicarrier 6G communication applications.

## V. CONCLUSION

We report on photonics-driven THz communication systems through systematical analyses of wireless and back-to-back links accomplishing single and dual carrier transmission within IEEE 802.15.3d channelization. In this regard, a full set of experiments from power measurements to single and dual channel wireless data transmission was carried out. Accordingly, 100 Gbit/s single and dual channel 25-cm wireless transmission of 16-QAM signals is reported with EVM levels of 12.3% and 10.9%,
respectively. When performed in B2B links, single carrier data rates up to 200 Gbit/s (32-QAM) and a dual carrier data rate of 160 Gbit/s (16-QAM) were achieved. The EVM values are 7.5% and 7.8% for single and dual carrier, respectively. The lowest measured EVM belongs to the 64-QAM 150 Gbit/s signal, being only 5.5%, transmitted through B2B link. As a result, we achieved significantly low EVM values, which proves efficient data transmission in different system configurations. By measuring the B2B performance and over-the-air response, it is possible to individually study the penalties arising from FSPL and linearity effects occurring at high photocurrent levels. This characterization also reveals the importance of developing high-saturation photocurrent THz MUTC photodiodes for ultrafast sub-THz 6G communications. Looking beyond, to transfer the results shown in this article to the application scenarios envisaged in the IEEE 802.15.3d standard, which include switched point-to-point wireless links for front- and backhaul, kiosk downloads and intradevice communications, the packaging of the MUTC-PDs would play an important role. In this respect, current efforts are focusing on integrating our devices in a waveguide block to mitigate the RF loss of the currently used CPW-probe and on utilizing locked lasers to pave the way towards a future application in IEEE 802.15.3d long-range THz communications.

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<figure><img src="image_14.png" /></figure>

**Ezgi Abacıoğlu** (Graduate Student Member, IEEE) received the B.Sc. degree in chemical engineering from Gazi University, Ankara, Türkiye, in 2013, the M.Sc. degree in micro and nanotechnology from the Department of Physics, Middle East Technical University, Ankara, in 2017. She is currently working toward the Ph.D. degree in Marie Skłodowska-Curie TERAOPTICS network with the University of Duisburg-Essen, Duisburg, Germany.

She completed her master's degree as a Member of Center for Solar Energy Research and Applications (GÜNAM). From 2018 to 2021, she was a Systems Engineer with Roketsan Missiles Inc., Ankara. After three years in defence industry, she joined the Department of Optoelectronics, University of Duisburg-Essen. Her research focuses on high-power broadband THz photodiodes for different system Configurations.

<figure><img src="image_15.png" /></figure>

**Abdu Subahan Mohammed** received the bachelor's and master's dual degree in physics from IISER Thiruvananthapuram, India, in 2020. His master's degree focused on intensity modulator-based frequency comb generation and phase noise characteristics. He is currently working toward the Ph.D. degree in smart THz integration using III-V and silicon technologies in University of Lille, Lille, France.

He served as a Junior Research Fellow with the Advanced Photonics and Microscopy Laboratory, Electrical and Communication Engineering Department, IISc Bangalore, where he contributed to the development of on-chip quantum devices for quantum applications. He is a Member of the Terahertz Photonics group at the Institute of Electronics, Microelectronics, and Nanotechnology (University of Lille), France.

<figure><img src="image_16.png" /></figure>

**Jonas Tebart** received the B.Sc. and M.Sc. degrees in electrical engineering and information technology in 2016 and 2019, respectively, from the University of Duisburg-Essen, Duisburg, Germany, where he is currently working toward the Ph.D. degree under the supervision of Prof. Andreas Stöhr.

After his studies with focus on microelectronics and optoelectronics, he joined the Department of Optoelectronics, University of Duisburg-Essen, as a Research Assistant. His research interests include radio-over-fiber techniques, millimeter-wave (mm-wave) and THz communications, 5G, B5G and 6G mobile networks, photonic radars, as well as mm-wave beam-steering antennas.

<figure><img src="image_17.png" /></figure>

**Marcel Grzesło** received the M.Sc. degree in nano-engineering from the University of Duisburg-Essen, Duisburg, Germany, in 2019. Since 2019, he has been working toward the Ph.D. degree in the Department of Optoelectronics, University of Duisburg-Essen, with a focus on THz mixers involving the monolithic integration of fermi-level managed barrier diodes with unitraveling-carrier photodiodes.

<figure><img src="image_18.png" /></figure>

**Tom Neerfeld** received the B.Sc. degree in nanoengineering and the M.Sc. degree in electrical engineering from the University of Duisburg-Essen, Duisburg, Germany, in 2020 and 2023, respectively. He is currently working toward the Ph.D. degree in the Department of Optoelectronics, University of Duisburg-Essen, with a focus on high-speed photodiodes and system integration.

<figure><img src="image_19.png" /></figure>

**José Luis Fernández Estévez** received the degree in microtechnology of semiconductor technology from the Chamber of Commerce and Industry in Dortmund (IHK zu Dortmund), Dortmund, Germany, in 2000.

He is currently a member of the Center for Semiconductor Technology and Optoelectronics (ZHO), Department of Optoelectronics, as a Technical Assistant with the University of Duisburg-Essen, Duisburg, Germany.

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**Pascal Szriftgiser** received the Ph.D. degree in quantum physics from the Laboratoire Kastler Brossel, University Paris VI (Sorbonne University today), Paris, France, in 1996.

In 1996, as a researcher, he joined CNRS (Centre National de la Recherche Scientifique), Laboratory PhLAM (Physique des Lasers Atomes et Molécules). Since 2012, he has been a CNRS Research Director. From 2014 to 2021, he was the Leader of the Cold Atoms Group and Deputy Director of the Laboratory PhLAM from 2019 to 2021. Since 2021, he has been a PI of Contrat de Projet Etat Région (CPER) WaveTech at HdF, a consortium that brings together six research laboratories in Hauts-de-France country. He has authored or coauthored 137 publications in peer-reviewed international journals or conference proceedings. His research interests include cold atoms physics, quantum chaos, topology and nonlinear optics in optical fibers to high-speed coherent optical communications for THz applications.

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**Guillaume Ducournau** (Member, IEEE) received the M.Sc. degree from ESIGELEC, Rouen, France, in 2002, and the Ph.D. degree from the University of Rouen, France, 2005, with a focus on high-speed telecommunications. He has been with the Institute of Electronics, Microelectronics and Nanotechnology (IEMN), University of Lille, Villeneuve d'Ascq, France, since 2007. He is the Leader of the THz wireless communications activity with IEMN using optoelectronic THz photomixers, electronic receivers, THz instrumentation, and millimeter-wave (mm-wave) characterization. He worked on several European projects: STREP ROOTHz 2010-2013, ThoR H2020, GRAPH-X, TIMES (6G SNS) as well as the Marie-Skłodowska Curie TERAOPTICS network. At national level he was the Coordinator of the COM'TONIQ Project from 2014 to 2017 funded by ANR (INFRA 2013) dedicated to THz communications in the 300 GHz band, the ANR/DFG TERASONIC project for the use of THz photonics technologies and electrical solid-state technologies for THz communications and SPATIOTERA for spatially distributed photomixers. He is involved in national France 2030 programs gathering several French laboratories under the "PEPR" programs funded by the ANR (Agence Nationale de la Recherche). In this framework, the FUNTERA project (six partners) is investigating THz converters, while the SYSTERA project (12 partners) is dedicated to beyond 90 GHz systems for future networks. He also participates to the ST-IEMN common laboratory, and more specifically involved in the mm-wave technologies characterization part. He has authored or coauthored more than 180 publications in peer-reviewed international journals or peer-reviewed conferences proceedings and holds 1 patent.

Mr. Ducournau was the recipient of the 2020 ISAP BEST PAPER Award.

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**Andreas Stöhr** (Senior Member, IEEE) received the Dipl.-Ing. and Dr.-Ing. degrees in electrical engineering from Gerhard-Mercator University, Duisburg, Germany, in 1991 and 1997, respectively.

From 1996 to 2013, he was a Research Scientist with the University of Duisburg-Essen (UDE), Duisburg. Between 1998 and 1999, he joined the Communications Research Laboratory, Tokyo, Japan. He was with France Telecom Orange Labs, France, in 2009, and Corning, in 2015. Since 2011, he has been a Professor and the Head of the Center for Semiconductor Technology and Optoelectronics, Optoelectronics Department, UDE. He has authored or coauthored more than 200 papers in journals and conferences. His research interests include III/V integrated microwave photonics and RF photonic integration for millimeter-wave and THz communications, measurement systems, and sensing applications.

Mr. Stöhr is a Senior Member of the IEEE Photonics and MTT Society, a committee member and the Chair of a number of international conferences, and the Guest Editor of IEEE/OSA.