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This project is co-funded by Horizon 2020 HRCP Photonics approaches for THz coms Second Towards TeraHertz Communications Workshop Brussels, 7 March 2019 Guillaume Ducournau, Prof. University of Lille, France guillaume.ducournau@univ-lille.fr

  1. This project is co-funded by Horizon 2020 HRCP Photonics approaches for THz coms Second Towards TeraHertz Communications Workshop Brussels, 7 March 2019 Guillaume Ducournau, Prof. University of Lille, France guillaume.ducournau@univ-lille.fr

  2. Context Photomixers, Tx/Rx Some systems Project Exemples Conclusions/challenges Guillaume Ducournau | Photonic approaches for THz communications | Brussels, 7 March 2019| 2/29 ThorProject.eu

  3. Massive data + Beyond 5G + urban cases: > 100 user/cell Needs Tbps/cell + Fast cell-to-cell links! Context • Why using THz for coms? • Point to point? B: bandwidth • Looking at Shannon S/N = signal/noise C = capacity (bit/s) THz RADIO : Small B, High S/N (MIMO, RF performances) THz : High Bandwidth, limited RF performances (power) Fluidmesh.com Photonics can help! Main focus/challenge Fixed points for THz Tx / Rx : optical fibers can be coupled to deliver / collect the BW to the antennas (concept of RAU, Remote Antenna Unit ) Guillaume Ducournau | Photonic approaches for THz communications | Brussels, 7 March 2019| 3/29 ThorProject.eu

  4. What source for Datacoms? • Sources  Opto-electronics:  Electronic sources: - Photodiodes, photoconductors - TMICs, Multiplication chains, RTD, transistors, diodes, TWTA … (tunable, very easy to modulated) low power Direct (not easy) or mixing (low power) for modulation But active devices on the way « No source land » Optical fibers (1.55 µm) 1 THz 1 ps 300 µm 4,1 meV 49 K  Direct generation - QCL, non-linear optics, molecular lasers (power = ok , but generally requires external modulation of the THz beam) Guillaume Ducournau | Photonic approaches for THz communications | Brussels, 7 March 2019| 4/29 ThorProject.eu

  5. Photomixing Photodiodes (UTC-PD, SiPho PD Ge, …) / Photoconductor (LT-GaAs, InGaAs, ErAs , …) Optical signals (modulated) x bit/s 1,55 µm THz Laser 1, F 1 f B Terahertz/sub-THz P f B = F 2 - F 1 OPTICS x Hz F I=s.P opt THz noise Laser 2, F 2 Challenges : max ASE optical power on the device, effciency Optical Noise What is already used in optical fibers => THz can leveraged on that!! Guillaume Ducournau | Photonic approaches for THz communications | Brussels, 7 March 2019| 5/29 ThorProject.eu

  6. The photonics emitter… the so called “ photomixer ” 2 families: Photodiodes (ex. UTC-PD) and Photoconductors (PC) h  CB VB Uni-travelling carrier PD Most simple UTC-PD,  = 1.5 µm Low-temperature grown GaAs PC p absorbing layer (not PIN) LTG-GaAs PC,  = 0.8 µm / Short-carrier lifetime Guillaume Ducournau | Photonic approaches for THz communications | Brussels, 7 March 2019| 6/29 ThorProject.eu

  7. Photomixing : results examples… photodiodes [Rouvalis et al., IEEE MTT (2012)] [Song et al., IEEE MWCL (2012)] TW-UTC: 110 µW @ 300 GHz 2 × UTC-PD integrated (module): 1.2 mW @ 300 GHz (20 mA/PD @ -3.9 V) RCE-UTC-PD: 0.8 mW @ 300 GHz NBUTC-PD: 0.67 mW @ 260 GHz P. Latzel IEEE Flip-chip on AlN TTST2017. [Wun et al., IEEE PTL (2014)] • Advantage of PM devices: the relative bandwidth. • 1 device = compatible with multi-carrier THz emission Guillaume Ducournau | Photonic approaches for THz communications | Brussels, 7 March 2019| 7/29 ThorProject.eu

  8. RCE-UTC : resonant cavity enhanced UTC-PD … ~ mW level (per device) is ok now Illumination Nano grid SoTA on UTC-PD : mW level, key point / optical driving power! P. Latzel et al ., IEEE Transactions on Terahertz Science and Technology , vol. 7, no. 6, pp. 800- 807, Nov. 2017. Typical power from utc-pd output: now mW level, still need more! [18] Rouvalis, E. et al. Opt. Express 18, 11105 – 10 (2010). [20] J.M. Wun, et al. IEEE Photonics and Technology Letters, 26(4) :pp. 2462 – 2464, 2014. -> arrays or ampl. [29] A. Wakatsuki et al., 2008 33rd International Conference on Infrared, Millimeter and Terahertz Waves, Pasadena, CA, 2008, pp. 1-2. doi: 10.1109/ICIMW.2008.4665566 Guillaume Ducournau | Photonic approaches for THz communications | Brussels, 7 March 2019| 8/29 ThorProject.eu

  9. … but not enough… why not use amplifiers or arrays? • Photodiode: simple devices, good for wide band modulation, limited power + low level of integration (if PD only )… The photodiodes/photoconductors could be a good « driver » of integrated amplifier, other active structures… However, interconnexion losses using several technologies… to be investigated Or TWT! Future systems: integrated/co-designed UTC-PD arrays Challenges : interconnections, integration of different technologies Guillaume Ducournau | Photonic approaches for THz communications | Brussels, 7 March 2019| 9/29 ThorProject.eu

  10. Tx architecture: comparison  Modified from IG THz study Group (15-10-0149-01) High power, Less signal integrity > 10 mW @ BW of the TWT? Oscillators 20-40 GHz 300 G (PA) Good phase noise Next steps + Amp. And 20.log(N) TWT photodiodes degradation from amp? reference -> SiPho? I/Q Mixer, SHM 1 mW @ 300 G (UTC-PD) 4.5 THz BW Up to THz Amp Be carefull to (C-band) phase noise… + Use combs + Good power, stabilized lines High signal 1535- integrity* 1565 nm The ‘famous’ Mach - Amp. BW Zehnder modulator Guillaume Ducournau | Photonic approaches for THz communications | Brussels, 7 March 2019| 10/29 ThorProject.eu

  11. Using photonics, efficient optical modulations MACH ZEHNDER MODULATOR (MZM) Modulated laser Discrete or integrated OOK = amplitude modulation (SiPho PIC, …) P/P 0 Voltage The spectrum BW Spectral efficiency = Data-rate/BW Guillaume Ducournau | Photonic approaches for THz communications | Brussels, 7 March 2019| 11/29 ThorProject.eu

  12. Combining I/Q at optical level then to THz Optical domain Fiber optics X Gbit/s technologies 2X Gbit/s  X Gbit/s THz domain Access network,  1 P2P back-haul 1-Pol  pilot UTC-PD THz-QPSK Guillaume Ducournau | Photonic approaches for THz communications | Brussels, 7 March 2019| 12/29 225 ThorProject.eu

  13. In a nutshell… what optics can do for wide - band THz … Optical domain Advantages : WDM channels 10-40 Gbit/s Frequency aglity (25 GHz spacing) Re-use of the Optical QPSK spectrum Optical fiber core networks Dynamic allocation F opt ~ 193 THz Multi  , 2-Pol WDM Optical Baseband QPSK optical PIN-PD signals THz domain Access network,  1 Mobile Rx P2P back-haul 1-Pol  pilot UTC-PD THz-QPSK Carrier freq (GHz) 225 250 275 300 Guillaume Ducournau | Photonic approaches for THz communications | Brussels, 7 March 2019| 13/29 ThorProject.eu

  14. What about receiving: -> photonics? • For a global THz system, we need Tx AND Rx . • Up to now, photonic-driven Tx are combined with electronic Rx (Schottky). • For a full « optically transparent » system, the Rx is to be done as well. Need to be investigated towards « seamless integration » Less studies on photonics based Rx! Optics -> THz -> Optics 32 dB conv. Gain - Use of UTC-PD as receivers (possible but @ 100 GHz structure has to be adapted) - Use of photoconductors (possible but devices Peytavit et al. , Appl. Phys. Lett. 103 , 201107 (2013). to be optimized for 1.55 µm) - Use of silicon-plasmonic based systems (works, overall efficiency has to be increased) Guillaume Ducournau | Photonic approaches for THz communications | Brussels, 7 March 2019| 14/29 ThorProject.eu

  15. Examples. LT-GaAs & plasmonic-based • Use photoconductive switches f B f IF Optical injection Current f B =  2 -  1 Voltage f r THz homodyne ( f IF =0) if f r = f B 28 dB @ 300 GHz Wideband, scalable beyond 1THz O/T conversion using silicon -55 dBm @ 300 GHz (Tx) 66 dB conv losses at Rx. Silicon based Guillaume Ducournau | Photonic approaches for THz communications | Brussels, 7 March 2019| 15/29 15 ThorProject.eu

  16. Photonics: where could (should) it also be usefull?? • Beam steering, forming, switching? Arrays of Indoor THz beam control, alignment of Optics can help here! P2P links… Easy to get multi- feed (low optical losses) + adjusting the relative phases Beam forming phase Challenges : delay in opt domain? Should consider interconnections, array integrated optics fab (yield), polarization [Modified from Wikipedia] (SiPho might help) control… Guillaume Ducournau | Photonic approaches for THz communications | Brussels, 7 March 2019| 16/29 ThorProject.eu

  17. System-level demos Photonics is pushing the data-rate More compact systems for future… So far, the compactness is not More data-rate scaling for decrease of wavelenght … 1000 -> Tbs More distance Mastering simple schemes for Tx/Rx Data rate (Gbps) locking [19] [17] 100 [17] [26] Electronics is [18] [23] [20] pulling the [21] [25] [24] 10 [6] distance Photonics Tx [22] With moderately-sized Electronics Tx 1 antennas (ie not > 50 dBi); 0,1 1 10 100 1000 Distance (m) Highest schemes/complexity of mod. scheme: photonic-based Tx usually Guillaume Ducournau | Photonic approaches for THz communications | Brussels, 7 March 2019| 17/29 ThorProject.eu

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