A new, low-cost, high-efficiency PIC?
EPFL-led team creates PIC platform based on lithium tantalate
Silicon-based PICs have dominated photonics due to their cost and easy integration with existing semiconductor manufacturing technologies. However, they have limitations with electro-optical modulation bandwidth. .
The lithium niobate-on-insulator wafer platform has emerged as a superior material for photonic integrated electro-optical modulators due to its strong Pockels coefficient, which is essential for high-speed optical modulation. Nonetheless, high costs and complex production requirements, have kept lithium niobate from being adopted more widely, limiting its commercial integration.
Now scientists led by Tobias J. Kippenberg at EPFL (École Polytechnique Fédérale de Lausanne) and Xin Ou at the Shanghai Institute of Microsystem and Information Technology (SIMIT) have created a new PIC platform based on lithium tantalate (LiTaO3), a close relative of lithium niobate, that promises to overcome these barriers.
It features similar excellent electro-optic qualities but has an advantage over lithium niobate in scalability and cost, as it is already being widely used in 5G radiofrequency filters by telecom industries.
The team says that PIC leverages the material's inherent advantages and can transform the field by making high-quality PICs more economically viable. The breakthrough was published in Nature in the paper 'Ultrafast tunable lasers using lithium niobate integrated photonics'.
The researchers have developed a wafer-bonding method for LiTaO3, which is compatible with silicon-on-insulator production lines. They then masked the thin-film LiTaO3 wafer with diamond-like carbon and proceeded to etch optical waveguides, modulators, and ultra-high quality factor microresonators.
The etching was achieved by combining deep ultraviolet (DUV) photolithography and dry-etching techniques, developed initially for lithium niobate and then carefully adapted to etch the harder and more inert lithium tantalate. This adaptation involved optimising the etch parameters to minimise optical losses, a crucial factor in achieving high performance in photonic circuits.
With this approach, the team was able to fabricate high-efficiency lithium tantalate PICs with an optical loss rate of just 5.6 dB/m at telecom wavelength. Another highlight is the electro-optic Mach-Zehnder modulator (MZM), a device widely used in today’s high-speed optical fiber communication. The LiTaO3 MZM offers a half-wave voltage-length product of 1.9 V cm and an electro-optical bandwidth reaching 40 GHz.
“While maintaining highly efficient electro-optical performance, we also generated soliton microcomb on this platform,” says Chengli Wang, the study’s first author. “These soliton microcombs feature a large number of coherent frequencies and, when combined with electro-optic modulation capabilities, are particularly suitable for applications such as parallel coherent LiDAR and photonic computing.”
The LiTaO3PIC’s reduced birefringence (the dependence of refractive index on light polarisation and propagation direction) allows dense circuit configurations and ensures broad operational capabilities across all telecommunication bands. The work paves the way for scalable, cost-effective manufacturing of advanced electro-optical PICs.
