Lithium tantalate photonic integrated circuits. Credit: Tobias Kippenberg (EPFL) New photonic integrated circuit technology based on lithium tantalate enhances cost-efficiency and scalability, making significant developments in optical communications and computing.Optical communications and computing systems have been reinvented by the rapid development in photonic integrated circuits (PICs), which combine numerous optical devices and performances on a single chip.For years, silicon-based PICs have dominated the field due to their cost-effectiveness and their integration with existing semiconductor manufacturing innovations, in spite of their constraints with regard to their electro-optical modulation bandwidth. Nonetheless, silicon-on-insulator optical transceiver chips were successfully advertised, driving information traffic through countless glass fibers in contemporary information centers.Emerging Lithium Niobate PlatformsRecently, the lithium niobate-on-insulator wafer platform has become a remarkable product for photonic integrated electro-optical modulators due to its strong Pockels coefficient, which is essential for high-speed optical modulation. High costs and complex production requirements, have kept lithium niobate from being embraced more widely, limiting its commercial integration.Lithium tantalate (LiTaO3), a close relative of lithium niobate, promises to overcome these barriers. It features similar excellent electro-optic qualities but has an advantage over lithium niobate in scalability and expense, as it is currently being widely utilized in 5G radiofrequency filters by telecom industries.Now researchers led by Professor Tobias J. Kippenberg at EPFL and Professor Xin Ou at the Shanghai Institute of Microsystem and Information Technology (SIMIT) have developed a new PIC platform based upon lithium tantalate. The PIC leverages the materials inherent benefits and can change the field by making high-quality PICs more economically practical. The development was published on May 8 in Nature.Technological Innovations in FabricationThe scientists established a wafer-bonding technique for lithium tantalate, which is suitable with silicon-on-insulator production lines. They then masked the thin-film lithium tantalate wafer with diamond-like carbon and proceeded to engrave optical waveguides, modulators, and ultra-high quality aspect microresonators.The etching was achieved by combining deep ultraviolet (DUV) photolithography and dry-etching strategies, established at first for lithium niobate and then thoroughly adjusted to engrave the harder and more inert lithium tantalate. This adjustment included enhancing the etch specifications to decrease optical losses, a vital element in attaining high performance in photonic circuits.Achievements and Future ProspectsWith this method, the group was able to fabricate high-efficiency lithium tantalate PICs with an optical loss rate of simply 5.6 dB/m at telecom wavelength. Another highlight is the electro-optic Mach-Zehnder modulator (MZM), a gadget commonly utilized in todays high-speed fiber optics communication. The lithium tantalate MZM offers a half-wave voltage-length product of 1.9 V cm and an electro-optical bandwidth reaching 40 GHz.” While preserving highly effective electro-optical efficiency, we also generated soliton microcomb on this platform,” says Chengli Wang, the research studys very first author. “These soliton microcombs feature a great deal of meaningful frequencies and, when integrated with electro-optic modulation abilities, are particularly appropriate for applications such as parallel meaningful LiDAR and photonic computing.” The lithium tantalate PICs minimized birefringence (the dependence of refractive index on light polarization and propagation direction) enables thick circuit setups and ensures broad functional capabilities throughout all telecommunication bands. The work paves the method for scalable, affordable production of innovative electro-optical PICs.Reference: “Lithium tantalate photonic incorporated circuits for volume production” by Chengli Wang, Zihan Li, Johann Riemensberger, Grigory Lihachev, Mikhail Churaev, Wil Kao, Xinru Ji, Junyin Zhang, Terence Blesin, Alisa Davydova, Yang Chen, Kai Huang, Xi Wang, Xin Ou and Tobias J. Kippenberg, 8 May 2024, Nature.DOI: 10.1038/ s41586-024-07369-1.