Photonic generations of millimeter-wave (mmW) frequencies (30 GHz – 300 GHz) have been attracted more and more interest for applications in 5G and beyond wireless networks. To generate high-quality mmW signals, it requires optical sources with ultra-narrow optical linewidth and low relative intensity noise (RIN). In recent years, we have demonstrated InAs/InP quantum dot / dash (QD) multi-wavelength lasers (QD MWLs) around 1550 nm with the frequency spacing from 10 GHz to 1000 GHz and output power of up to 50 mW. Those QD MWLs have low RIN, ultra-narrow optical linewidth, small timing jitters, compact size, low power consumption and the ability for hybrid integration with silicon substrates. As examples we present a monolithic dual-wavelength (DW) DFB laser based on synthesized aperiodic gratings on InAs/InP QD gain medium and its application as an optical beat source for mmW signal generation. The QD DW-DFB laser is capable of generating spectrally pure mmW signals between 46 GHz and 48 GHz with the 3-dB RF beating linewidth of less than 16 KHz and the RIN of -158 dB/Hz from 10 MHz to 20 GHz. By using this QD DW-DFB laser, we have experimentally demonstrated a multi-gigabit/s mmW radio-over-fiber (mmW-RoF) communication system operating at 47 GHz with 16QAM, 32QAM and 64QAM modulated signals over single mode fiber (SMF) in terms of clear eye and constellation diagrams. We have achieved an optical-heterodyne mmW-RoF system with broadband 4-meter wireless links through 25.22-km SMF featuring a high bitrate of 24-Gbit/s (64QAM × 4-GBaud) using a QD DW-DFB laser.
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