Photonics-based techniques spearhead the generation of high-frequency signals in the millimeter-andTerahertz wave, crucial for ultrabroadband mobile wireless link development. Photonic integration is enabling to provide the photonic approach with added advantages of energy-efficiency, flexibility and scalability, in addition to signal quality. We present an optical heterodyne system based on a novel dual laser module containing two InP-Si 3 N 4 hybrid lasers with intracavity wavelength selective optical filters with output optical power per laser of up to 15 dBm (31 mW), wide wavelength tuning of about 60 nm, and narrow optical linewidth below 100 kHz. To the best of our knowledge, we present for the first time the continuous-wave generation of RF frequencies over a wide tuning range from C-band (4 GHz -8-GHz) to W-band (75 GHz -110 GHz) achieving record low RF electrical linewidth around 108 kHz and long-term drift < 12 MHz with two free-running lasers. This is the best beat-note linewidth obtained with such an integrated source in a free-runnning regime and with a wide tuning range ever reported.Index Terms-photonic integration, millimeter-waves, hybrid laser, laser tuning.
I. INTRODUCTIONT is expected that networks will utilize frequency bands in the millimeter-wave range (30 to 300 GHz) to deliver extreme link capacities and miniaturize transceivers [1]. These are key parameters to unlock the radio access densification in urban scenarios through wireless backhaul of small cells,
We for the first time, the optical injection locking (OIL) to a frequency comb of a hybrid InP-Si 3 N 4 dual laser source for high-purity mm-wave generation through optical heterodyning. Key performance parameters of the comb line demultiplexing functionality provided by this source under OIL -such as adjacent-comb-line side mode suppression ratio (SMSR) and locking range -are reported. It is also shown that the amount of free-running drift exhibited by the hybrid lasers (which should be as little as possible to keep them within the locking range) can be minimized by reducing the amount of bias level applied to the heater-based phase actuators present in such lasers. According to the measured drift, locking range and SMSR, these lasers have potential to achieve continuous locking with SMSR levels of more than 45 dB at comb line separations higher than 9 GHz. Successful carrier generation at 93 GHz is demonstrated by locking the two lasers to an optical frequency comb achieving an ultra-stable International Telecommunication Union (ITU)-compliant signal. Both real-time and DSP-aided data transmissions are demonstrated at this frequency achieving data rates of 12.5 and 28 Gbit/s, respectively.
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