Ultrafast tunable laser integrated with lithium niobate and silicon nitride

thin-film lithium niobate (LiNbO3) has enabled low-loss photonic integrated circuits, modulators with increased half-wave voltages, electro-optical frequency combs, and electro-optical devices on chip for applications ranging from microwave photonics to microwave-to-optical interfaces. Although recent advances have demonstrated tunable integrated lasers based on LiNbO3 lithium niobate, the full potential of thin-film lithium niobate platforms to demonstrate frequency-agile, narrow-linewidth integrated lasers has yet to be realized.

Recently, a research team from IBM and the Swiss Federal Institute of Technology in Lausanne (EPFL) reported in Nature a rapidly tuned laser based on a hybrid silicon nitriding Si3N4-Linbo3 photon platform and demonstrated its application in coherent laser ranging, which could have a significant impact on optical ranging technology. The laser is based on lithium niobate and has the potential to revolutionize light detection and ranging (LiDAR) applications due to its low noise and fast wavelength tuning properties.

Lithium niobate is a commonly used material in the field of optical modulators because it has a high optical power capacity and has a high "Pockels coefficient," which means that it can change its optical properties when an electric field is applied. IBM and EPFL researchers have implemented a new type of hybrid integrated tunable laser by combining lithium niobate with silicon nitride.

Figure 1: Heterogeneous, low-loss Si3N4 -- lithium niobate LiNbO3 photonic integrated platform for a rapidly tunable self-injected lock-in laser.

To build the laser, the team built photonic integrated circuits based on silicon nitride at EPFL, which were then combined with lithium niobate wafers at IBM. The platform is based on the heterointegration of an ultra-low loss Si3N4 photonic integrated circuit with a thin film LiNbO3, with a low propagation loss of 8.5B/m, unlike the previously demonstrated chip-level integration, through direct bonding at the chip level. A narrow linewidth laser (natural linewidth of 3 KHZ) is achieved by self-injection locking into the laser diode. The hybrid mode of the resonator allows for electro-optical laser frequency tuning at 12 PHz/s, maintaining a narrow linewidth while maintaining high linearity and low hysteresis.

Figure 2: A hybrid heterogeneous Si3N4 -- LiNbO3 platform characterizing integration.

The low noise and fast wavelength tuning characteristics of the laser make it an ideal choice for lidar applications. The team then carried out optical ranging experiments using lasers, achieving a high precision measurement of distance. The new laser also has potential beyond lidar applications. The hybrid platform has the potential to enable integrated transceivers for telecommunications and microwave optical transducers for quantum computing.

Figure 3: Self-injection locked distributed feedback, electro-optical frequency tuning of a DFB laser

Figure 4: Demonstration of a coherent frequency modulated continuous wave using a hybrid integrated laser, Frequency Modulated Continuous wave, FMCW Lidar.

The original link: https://www.nature.com/articles/s41586-023-05724-2