Photonic True-Time Delay Beamforming Assisted By Multi-Core Fiber For 5g Wireless Communications

This paper describes and evaluates experimentally two versions of Si3N4 photonic integrated devices based on optical ring resonators (ORRs) and multi-core fiber (MCF) that enable radio beamsteering for operating 5G and beyond in the K-band. The RF beamsteerer depends on the optical delay induced by the ORRs that can be modified by heater tuning (slow switching) or by wavelength shift (fast switching). The first version of the beamforming chip permits multi-wavelength operation by keeping the heaters' configuration and changing the wavelength. The second version of the chip includes independent dual-wavelength operation with dedicated heaters' configurations for each wavelength. The experimental evaluations are performed for both short-reach and long-reach applications with the transmission of the photonic TTD over 150-m of 4-core MCF and over 1-km of 7-core MCF for the first and second version of the chip, respectively. In addition, the stability and delay variation were measured experimentally over 1-hour run time for different heater configurations. A maximum delay variation of 4 ps was measured, which translates to a 9 degrees steering angle resolution at 19 GHz RF. The impact of the delay variation applied to one of the antenna elements in the resulting beam steering is analyzed in more detail in this work, confirming the suitability of the proposed technique.