EPFL and IBM scientists create new lithium niobate laser technology

16 Mar 2023

New type of laser could have “significant impact” on lidar and optical ranging, say developers.

Scientists at EPFL and IBM have developed a new type of laser that could have a significant impact on optical ranging technology. The laser is based lithium niobate, often used in the field of optical modulators, which controls the frequency or intensity of light that is transmitted through a device.

Lithium niobate is useful because it can handle a lot of optical power and has a high Pockels coefficient, which means that it can change its optical properties when an electric field is applied to it.

The researchers achieved their breakthrough by combining lithium niobate with silicon nitride, which allowed them to produce a new type of hybrid integrated tunable laser. To do this, the team manufactured integrated circuits for light (photonic integrated circuits) based on silicon nitride at EPFL, and then bonded them with lithium niobate wafers at IBM.

The work is described in a March 15th paper in Nature.

Lidar applications

The approach produced a laser with low frequency noise, which is a measure of how stable a laser’s frequency is, and simultaneously with fast wavelength tuning—both great qualities for a laser used in light detection and ranging (lidar) applications. Then the developers performed an optical ranging experiment in which they used the laser to measure distances with high precision.

Beyond integrated lasers, the hybrid platform has the potential to realize integrated transceivers for telecommunications as well as microwave-optical transducers for use in quantum computing.

“What is remarkable about the result is that the laser simultaneously provides low phase noise and fast petahertz-per-second tuning, something that has never before been achieved with such a chip-scale integrated laser,” said Professor Tobias J. Kippenberg, who led the EPFL side of the project.

Nature paper abstract

The Nature paper abstract explains, “Although recent advances have demonstrated tunable integrated lasers based on LiNbO₃, the full potential of this platform to demonstrate frequency-agile, narrow-linewidth integrated lasers has not been achieved. Here we report such a laser with a fast tuning rate based on a hybrid silicon nitride (Si₃N₄– LiNbO₃) photonic platform and demonstrate its use for coherent laser ranging.

“Our platform is based on heterogeneous integration of ultralow-loss Si₃N₄ photonic integrated circuits with thin-film LiNbO₃ through direct bonding at the wafer level, in contrast to previously demonstrated chiplet-level integration, featuring low propagation loss of 8.5 decibels per metre, enabling narrow-linewidth lasing by self-injection locking to a laser diode.

“The hybrid mode of the resonator allows electro-optic laser frequency tuning at a speed of 12 × 10¹⁵Hz with high linearity and low hysteresis while retaining the narrow linewidth. Using a hybrid integrated laser, we perform a proof-of-concept coherent optical ranging (FMCW lidar) experiment. Endowing Si₃N₄ photonic integrated circuits with LiNbO₃ creates a platform that combines the individual advantages of thin-film LiNbO₃ with those of Si₃N₄, which show precise lithographic control, mature manufacturing and ultralow loss.”