Isolator-Free Optical Transmitter Reaches 180 Gbit/s for Data Centers
Japanese researchers combine silicon nitride resonators and lithium niobate modulators to eliminate bulky optical isolators.
Engineers from Japan have developed an integrated optical transmitter that operates stably without an optical isolator, achieving data transmission rates of up to 180 Gbit/s. The hardware invention solves reflection problems that destabilize lasers in high-capacity links designed for cloud services and artificial intelligence workloads.
Managing optical reflections without bulky shields
Modern computing centers rely on fast optical links to share data between servers, but hardware miniaturization faces a recurring physical barrier in optical innovation. When tunable lasers built on silicon photonics are integrated with modulators made from different materials, light reflects backward into the laser cavity. These reflections destabilize the laser beam and degrade high-speed data transmission.
Standard optical assemblies fix the problem by inserting a magneto-optic isolator, a component that blocks backward-traveling light. Optical isolators add bulk, increase assembly costs, and resist integration onto standard semiconductor chips. To bypass this constraint, a team led by professor and inventor Tomohiro Kita from the Department of Applied Physics at Waseda University designed a transmitter that suppresses the destabilizing feedback through spectral engineering, an invention reported by TechXplore.
“This architecture provides a promising pathway toward compact, isolator-free optical transmitters for next-generation photonic integrated circuits and high-speed optical communication systems.”
— Tomohiro Kita, Professor at Waseda University
Co-design across silicon nitride and lithium niobate
The research team included Shotaro Hirata, Shingo Takano, Yu Kataoka, and Ryo Shimizu from Sumitomo Osaka Cement Co. Ltd., alongside Dr. Yuya Yamaguchi from Japan's National Institute of Information and Communications Technology. Their study appeared in the Journal of Lightwave Technology on October 7, 2026.
The hardware prototype pairs an external-cavity tunable laser with a thin-film lithium niobate modulator. Inside the laser cavity, two silicon nitride ring resonators act as a Vernier filter to select specific operational wavelengths. The modulator integrates an asymmetric Mach-Zehnder interferometer, which has its own wavelength-dependent transmission curve. By matching the optical response of the modulator to the response of the laser filter, the researchers shaped the returning feedback so it no longer upsets single-mode laser emission.
Broad tuning range and high data capacity
Laboratory evaluations showed that the isolator-free transmitter maintains stable laser performance across an operating span of approximately 67 nm. The setup maintained signal clarity without active temperature control, which simplifies thermal management in high-density rack systems.
During high-speed evaluation, the device sustained data transmission at 180 Gbit/s, the top rate examined during testing. Because the transmitter tunes across 67 nm, it supports wavelength-division multiplexing, a technique that sends several data channels across different optical wavelengths down one fiber. Representing valuable new intellectual property, the design provides a pathway for patent licensing and technology transfer into production lines for next-generation optical interconnects.
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