Breakthrough: Low-Cost, High-Efficiency Photonic IC Developed by Researchers

The field of photonic integrated circuits (PICs) is on the brink of a transformation thanks to a groundbreaking development leveraging the unique properties of lithium tantalate. Recently published in Nature, this breakthrough has the potential to make high-quality PICs more economically viable than ever before.

For years, silicon-based PICs have been the go-to choice due to their cost-effectiveness and seamless integration with existing semiconductor manufacturing technologies. Despite their widespread use, silicon PICs have faced limitations, particularly in terms of their electro-optical modulation bandwidth. However, the commercial success of silicon-on-insulator optical transceiver chips has played a crucial role in driving information traffic through the intricate networks of modern data centers.

Emerging as a superior material for photonic integrated electro-optical modulators, the lithium niobate-on-insulator wafer platform has shown great promise thanks to its strong Pockels coefficient, essential for high-speed optical modulation. Yet, the high costs and complex production requirements associated with lithium niobate have hindered its widespread adoption, limiting its commercial integration.

Enter lithium tantalate (LiTaO3), a material closely related to lithium niobate but with distinct advantages. Offering similar excellent electro-optic qualities, lithium tantalate boasts scalability and cost-effectiveness, with widespread use in 5G radio frequency filters by telecom industries. This positions lithium tantalate as a promising candidate to overcome existing barriers in the field of PICs.

The researchers behind this groundbreaking development devised a wafer-bonding method for lithium tantalate that is compatible with silicon-on-insulator production lines. By masking the thin-film lithium tantalate wafer with diamond-like carbon and employing advanced etching techniques, they were able to fabricate optical waveguides, modulators, and ultra-high quality factor microresonators.

Through a meticulous process involving deep ultraviolet (DUV) photolithography and dry-etching techniques, originally developed for lithium niobate, the team optimized the etch parameters to minimize optical losses in lithium tantalate. This approach resulted in the fabrication of high-efficiency lithium tantalate PICs with an impressively low optical loss rate of just 5.6 dB/m at telecom wavelengths.

One of the standout achievements of this research is the development of an electro-optic Mach-Zehnder modulator (MZM) using lithium tantalate. With a half-wave voltage-length product of 1.9 V cm and an electro-optical bandwidth reaching 40 GHz, the lithium tantalate MZM offers significant advancements for high-speed optical fiber communication.

Chengli Wang, the study's first author, highlights the generation of soliton microcombs on the lithium tantalate platform, featuring a multitude of coherent frequencies. When combined with electro-optic modulation capabilities, these soliton microcombs hold great potential for applications such as parallel coherent LiDAR and photonic computing.

The reduced birefringence of lithium tantalate PICs allows for dense circuit configurations and broad operational capabilities across all telecommunication bands. This work sets the stage for scalable and cost-effective manufacturing of advanced electro-optical PICs, marking a significant milestone in the evolution of photonic integrated circuits.