Local oscillators-free chip-enabled W-band wireless IM-DD PAM-4 data transmission with simultaneous dual-laser...

Wireless data traffic is expected to exponentially increase in the future, and meeting this demand will require high data rate photonic-wireless links operating in the W-band (75-110 GHz). For this purpose, pulse-amplitude-modulation with four levels (PAM-4)-based intensity modulation and direct detection (IM-DD) photonic-wireless systems are preferred due to their simplified configuration. In this Letter, we present an experimental demonstration of an IM-DD PAM-4 photonic-wireless link in the W-band, leveraging a monolithic dual-laser photonic chip to enhance integration. Through injection-locking by an optical comb, the chip generates a W-band wireless signal via photo-mixing with a photodiode. This comb injection approach facilitates the phase correlation of the chip's two modes, resulting in a stabilized beat note. Additionally, the on-chip integration of the dual lasers enables the modulation of the two modes with a single modulator, improving the signal-to-noise ratio (SNR) while eliminating the need for extra splitters or combiners. Meanwhile, the envelope detector (ED) plays a crucial role in the simplified configuration, contributing to the overall decrease in size, weight, power, and complexity of the system. The integration of the chip-based phase-locked light source and the utilization of the ED thus signify noteworthy features of our experimental setup, which functions without the necessity of both optical and electrical local oscillators. PAM-4 signal modulation is simultaneously applied to the two coherent optical carriers. Our experiments have effectively transmitted 5 and 10 Gbaud PAM-4 W-band wireless signals in a cost-effective, lightweight, and straightforward configuration, achieving a line data rate of up to 20 Gbit/s economically. These experimental results demonstrate the practical potential of implementing fully integrated photonic-wireless transmitters.