TERAHERTZ COMMUNICATION: A STORY OF BANDWIDTH AND SILICON PHOTONIC INTEGRATION PHOTONICS RESEARCH GROUP & IDLAB, DEPARTMENT OF INFORMATION TECHNOLOGY (INTEC) Dennis Maes, Emilien Peytavit, Bart Kuyken, Sam Lemey Contact dennis.maes@ugent.be linkedin.com/in/dennis-maes/ Wireless networks are hungry for bandwidth The need for higher wireless data rates makes the radio spectrum congested. In addition to spatial multiplexing and spectral optimization, higher carrier frequencies with more available bandwidth can be used to accommodate this need. The mmWave and terahertz (THz) spectrum (100 GHz and beyond) offer this much needed bandwidth. (IEEE 802.15.3d- 2017) >50 Gbit/s - 300 GHz 69 GHz (1), 13 GHz(5) 5G NR (3GPP rel.15) sub-6 GHz mmWave THz 4G) (LTE) 300 Mbit/s - 800, 1800, 2600 MHz BE 20 MHz (10s) WiFi 5 (IEEE 802.11ac) 6.9 Gbit/s - 5 GHZ 160 MHz (2)EU WiFi 4 (IEEE 802.11n) 900 Mbit/s - 2.4, 5 GHz 40 MHz (2+12)EU WiGig (IEEE 802.11ad) 7 Gbit/s - 60 GHz 2 160 MHz (6) 4G+ (LTE-A) 1 Gbit/s - 800, 1800, 2600 MHz BE 100 (5x20) MHz (10s) WiFi 6E (IEEE 802.11ax) 9.6 Gbit/s - 2.4, 5, 6 GHz 160 MHz (0,3,3)EU Max. data rate - Carrier frequency Max. channel bandwidth (supported # of channels) > 10 Gbit/s - 0.7, 3.8, 26, 36 GHz BE 100 MHz (<10), 400 MHz (<10) Phased Antenna Array (PAA) Array of integrated opto-electronic antenna elements Low-loss optical Si3N4 waveguides Optical beam forming network (OBFN) On-chip modulatorIntegrated amplifiers Integrated laser sources Ultra fast photodetector Laser 2 Laser 1 Modulator νopt λ1 > λ2 Optical waveguides Electrical waveguide fRF fTHz fTHz THz signals can be efficiently generated by on-chip photomixing Beating two optical signals on a photodetector (photomixing) will result in a radio signal at their offset frequency. The only limitation is the conversion efficiency of the photodetector, a very high bandwidth photodiode is thus needed. Beamforming improves signal strength but requires a low-loss feed network A phased antenna array (PAA) is used to generate narrow, high-gain beams. Beamforming not only improves signal strength to overcome higher path loss at THz frequencies, but it also allows more spectral reuse. # of antenna elements Gain [dB] 1 2 5 10 20 50 100 200 500 20 17 13 10 7 3 0 -3 -7 -10 -13 -17 Optical power splitterPRF∽Popt2Feed network (CMOS) Feed network (III/V) Feed network (SiPh) Optical (SiPh full-passive)Distributed amplifier Optical (SiPh + III/V optical amplifiers) Electrical (CMOS)Power splitter Electrical (III/V)More antennas+10 dB/dec -10dB/dec -20dB/dec Array gain A Silicon Photonic (SiPh) beamforming chip leverages the low-loss waveguides for efficient RF signal routing and allows distributed optical amplification to overcome power splitting losses. A high-speed photodiode on a low-loss SiPh platform enables data rates beyond 100 Gbit/s at 280 GHz 16-QAM at 35 GBaud (140 Gbit/s) 11% EVM 32-QAM at 25 GBaud (125 Gbit/s) 7% EVM By means of micro transfer printing, we have heterogeneously integrated a Uni- Traveling-Carrier photodiode (UTC-PD) on a Silicon Nitride (SiN) waveguide. This ultra-fast photodetector has a bandwidth of 155 GHz. We demonstrated a back-to-back THz link at 280 GHz achieving data rates beyond 100 Gbit/s. Electrical contact pads to extract THz signal SiN optical grating coupler SiN low-loss waveguide Waveguide-coupled photodiode 100 µm 10 µm PD coupon just after transfer-printing Conclusion Immense bandwidths are available in the THz spectrum Photonic chips offer compact solutions for beamforming Heterogenous integration of UTC-PDs on SiN waveguides results in ultra-fast detectors needed for photomixing These detectors enable super-fast THz links at 280 GHz with a data rate of more than 100 Gbit/s More information? D. Maes et al., “High-Speed Photodiodes on Silicon Nitride with a Bandwidth beyond 100 GHz“, 2022 Conference on Lasers and Electro-Optics (CLEO), 2022