Zhejiang University builds 8.64 Tbps lithium niobate optical transmitter

Researchers at Zhejiang University have unveiled a lithium niobate on insulator transmitter chip that combines mode and wavelength multiplexing to push aggregate capacity to 8.64 Tbps. The device could help ease bottlenecks in data centers and backbone networks as AI and cloud traffic keep rising.

Why it matters: - Data traffic tied to AI, big data and cloud computing is growing about 25% a year, straining conventional optical interconnects. - The new chip targets higher-speed, lower-power and smaller-footprint links for backbone networks, data centers and chip-scale optical interconnects. - The design pushes lithium niobate integrated photonics closer to practical high-density transmission at 8.64 Tbps.

What happened: - A research team from Zhejiang University developed a lithium niobate on insulator hybrid mode/wavelength division multiplexing transmitter chip. - The chip combines 6 spatial modes and 6 wavelengths to create 36 independent channels. - Each channel carries 240 Gbps, for a total capacity of 8.64 Tbps. - The work was published in Opto-Electronic Advances under DOI 10.29026/oea.2026.250341.

The details: - The team used Z-propagating LNOI waveguide structures to suppress mode hybridization in lithium niobate. - The mode multiplexer and demultiplexer support stable handling of six modes from TE0 to TE5. - The adiabatic coupling design provides broad operating bandwidth and fabrication tolerance. - Measured insertion loss is below 0.3 dB. - Inter-mode crosstalk is less than -15 dB. - For wavelength multiplexing, the chip uses a cascaded Fabry–Pérot cavity structure. - The wavelength filter delivers flat-top dense wavelength division multiplexing. - The fabricated filter has a 3 dB bandwidth of about 1.8 nm. - Channel spacing follows the ITU-T standard of 400 GHz, or 3.2 nm. - The integrated Mach–Zehnder modulators show a 3 dB electro-optic bandwidth above 67 GHz. - The modulators also have a low half-wave voltage-length product. - Experiments demonstrated 120 GBaud OOK and PAM4 signal modulation. - Clear eye diagrams were observed across all 36 channels without obvious inter-symbol interference.

Between the lines: - Silicon photonics remains the mainstream platform for scale, but its electro-optic limits make ultrahigh-speed modulation harder beyond 100 Gbps per channel. - Lithium niobate offers a stronger electro-optic coefficient, lower propagation loss and a broad transparent window. - Thin-film lithium niobate on insulator gives researchers a CMOS-compatible route to subwavelength waveguides and denser integration. - The work also highlights a harder problem on LNOI: crystalline anisotropy can create mode hybridization and complicate wavelength-selective device design.

What's next: - The chip provides a chip-scale approach for high-spectral-efficiency optical transmission in next-generation networks. - The measured results suggest the platform could support further scaling of multidimensional multiplexing on LNOI. - The publication positions lithium niobate transmitter chips as a candidate path for higher-capacity optical interconnects as traffic demand rises.

The bottom line: - Zhejiang University’s chip shows that combining mode and wavelength multiplexing on lithium niobate can deliver terabit-scale transmission in a single integrated device.