Despite all the advances in integrated lithium-niobate optical circuits, from frequency combs and frequency converters to modulators, one component remains frustratingly difficult to integrate: lasers.

Lasers are used to create optical carriers for data transmission in long-haul telecommunication networks, data centers optical interconnects and microwave photonics systems. Lasers can be used as a stand-alone device, independent of the modulators. This makes the entire system less reliable and more costly.

Researchers from Harvard John A. Paulson School of Engineering and Applied Sciences have now developed the first integrated high-power laser using a lithium niobate-chip. This will open the door to high-powered telecommunications systems, fully integrated spectrometers and optical remote sensing and efficient frequency conversions for quantum networks.

“Integrated lithium niobate opticals is a promising platform to develop high-performance chip scale optical systems. However, getting a laser onto a Lithium Niobate chip has proven to be one the greatest design challenges,” stated Marko Loncar (the Tiantsai Lin Professor in Electrical Engineering at SEAS, and the senior author of this study. To overcome these challenges, we utilized all of the nanofabrication techniques and tricks learned from previous developments in integrated Lithium Niobate Photonics to achieve our goal of integrating an efficient laser onto a thin-film platform.

Loncar and his team used small, but powerful distributed feedback lasers to create their integrated chip. The lasers are embedded in tiny trenches or wells in the lithium niobate. They deliver up to 60 mW of optical power through waveguides that were fabricated on the same platform. To create a high-power transmitter, the researchers used a 50 gigahertz lithium niobate electro-optic modulator to combine the laser.

Amirhassan Shamsan Shamsan-Ansari, a SEAS graduate student and the first author of this study, stated that “Integrating high performance plug-and-play lasers would significantly reduce cost, complexity and power consumption for future communication systems.” It’s a building block that can easily be integrated into larger optical system for a variety of applications in data telecommunications, lidar and sensing.

This research is a major step towards low-cost, large-scale optical networks and transmitter arrays. It combines thin-film lithium-niobate with high-power lasers in an industry-friendly way. The team plans to improve the laser’s power, scalability and adaptability for more applications.