Development of a SiN photonic circuit for the stabilization of C-band semiconductor lasers

The future of high-bandwidth communications requires the on-chip generation of several lines with the aim of improving the spectral efficiency of optical channels and reduce the power consumption. With the recent technological advancements, semiconductor lasers could address this challenge. Unfortunately, these components are very sensitive to thermal fluctuations and their operational frequency could be severely affected by the action of closely spaced devices. A compact and dynamic method to account for the thermal crosstalk is represented by feedback based solutions. In this work, the frequency locking of multiple lines is implemented on a single photonic integrated circuit (PIC). Specifically, the architecture features a packaged silicon nitride (SiN) on insulator PIC arranged in a negative feedback configuration with the capability of stabilizing the frequency of 16 semiconductor lasers. The system was entirely developed and characterized. To explore the system’s effectiveness in stabilizing high-bandwidth channels, a set of advanced experiments was carried out. Initially, a 2-channel DDO-OFDM system was created by loading each carrier with a 50.244 Gb/s data rate. The ability of the system of retaining a narrow guard band of ∼160 MHz was tested under unstable conditions, leading to improved performance. Finally, the generation of stable sub-THz waves (100 GHz and 150 GHz) was demonstrated out of two properly frequency spaced lasers. The native lasers were also fed to a 183.8 km long installed optical link. A stability of 0.8 ±30 MHz and -3 ±30 MHz was detected on site for the two configurations (100 GHz and 150 GHz, respectively), when a slow frequency ramp (-125 MHz/hour) aimed to mimic the effect of thermal cross-talk in densely integrated circuits was applied to the sub-THz waves. These experiments paved the way to implement tightly spaced optical carriers (superchannel) and stable sub-THz/THz waves onto a single chip.