Thin-film lithium niobate photonics

In plain language

Lithium niobate is a crystal whose optical properties change when a voltage is applied to it. This is called the electro-optic effect. In thin-film form, a very thin layer of the crystal is bonded onto an insulating base wafer and carved into narrow channels that guide light. An electrical signal applied to the channel can then switch the light or write data onto it.

Engineers want this platform because the switching voltage can be low enough for ordinary electronic chips to drive directly, which saves power and space. A 2018 peer-reviewed paper reported chip-scale modulators with a CMOS-compatible drive that carried data at up to 210 gigabits per second. The same thin layers also make frequency combs, which are rulers of evenly spaced colours of light used in measurement and communications. Commercial production is still early. Companies say they will supply chips in large volumes, but most of their figures have no published test conditions.

Technical explanation

Bulk lithium niobate has a strong, linear electro-optic effect and low optical loss, but bulk modulators are large because the drive voltage depends on the length of the interaction region. Thin-film lithium niobate on insulator (LNOI) confines light in a high-contrast ridge waveguide, which lets electrodes sit close to the optical mode and reduces the voltage needed for a given length. Wang and colleagues (2018) report monolithic modulators with a CMOS-compatible drive voltage, data rates up to 210 Gb/s and on-chip optical loss below 0.5 dB. The sources read here do not give the test conditions, bandwidth or device length for these figures.

Low-loss microring resonators on the same platform support frequency combs. Zhang and colleagues (2019) drove an electro-optic microring with a microwave signal and measured a comb of over 900 lines, spaced about 10 GHz apart, across the telecom L-band. Line spacing could be tuned from 10 Hz to 100 MHz by changing the modulation frequency, and the same device produced two combs at once. The authors describe an octave-spanning comb as a future goal that would need further dispersion engineering. Zhu and colleagues (2021) review the platform and report that some thin-film devices, such as modulators and wavelength converters, reportedly outperform their bulk-crystal counterparts.

The main device limits are optical and DC instability. At higher optical power, the photorefractive effect can add instability, and the operating bias of a lithium niobate modulator can drift under DC voltage. A 2024 preprint from the Lončar group reports that a quadrature-biased thin-film lithium tantalate modulator stayed within 1 dB over 46 hours at 12.1 dBm input, compared with about 5 dB for thin-film lithium niobate under the same test. The preprint abstract does not give a cause for the difference.

What the evidence says

Each statement is typed by the strength of its evidence and linked to the source that supports it.

Limitations and open problems

• Bias drift and photorefractive effects at higher optical power can make lithium niobate modulators unstable. A 2024 preprint reports that thin-film lithium tantalate is more stable under the same test, but this is one group's comparison, and the sources reviewed do not show the approach as standard practice.
• Wafer supply is a constraint. A Lightium co-founder named volume wafer supply as the top challenge for the industry, and the lithium niobate on insulator supply chain has depended on a single commercial supplier outside the EU, according to the ELENA consortium as reported from LASER World of Photonics 2025.
• Early foundry access is through multi-project wafer runs with application deadlines, such as the September 2025 deadline for CCRAFT's first run.
• The headline figures for commercial products, such as data rates per lane and bandwidth, are given by companies without stated test conditions, and the sources reviewed did not give independent measurements.
• The strongest comb result is a single chip-scale device spanning the telecom L-band. An octave-spanning comb, which the authors describe as a future goal, has not been shown in the sources reviewed.
• Cost and yield figures for thin-film lithium niobate wafers and chips were not found in the sources reviewed, so none are quoted.

Possible future uses

Timeline

1. Oct 2018Wang and colleagues publish monolithic lithium niobate modulators with a CMOS-compatible drive voltage, data rates up to 210 Gb/s and on-chip loss below 0.5 dB in Nature. Sources: [1], [2]
2. Mar 2019Zhang and colleagues report an electro-optic frequency comb of over 900 lines spaced about 10 GHz apart in a thin-film lithium niobate microring, in Nature. Sources: [3]
3. 2021Zhu, Shao, Lončar and colleagues publish a review of integrated photonics on thin-film lithium niobate in Advances in Optics and Photonics. Sources: [4]
4. 2025CCRAFT, a CSEM spin-out, announces a thin-film lithium niobate foundry and plans multi-project wafer runs, with the first application deadline in September 2025. Company volume targets are for about 2028. Sources: [5]
5. Mar 2026HyperLight announces a partnership with UMC and Wavetek for high-volume foundry production of its thin-film lithium niobate chiplet platform. Sources: [6]

Glossary

Electro-optic effect

A change in a material's optical properties when an electric field is applied, used to switch or modulate light with an electrical signal.

Half-wave voltage (Vπ)

The voltage needed to shift the phase of light by half a cycle in a modulator. Lower values mean the modulator can be driven by smaller electronic circuits.

Optical frequency comb

A light source that emits many evenly spaced frequencies of light at once, like the marks on a ruler.

Photorefractive effect

A light-induced change in refractive index in some crystals, which can cause drift and instability in lithium niobate devices at higher optical power.

Sources

1. peer reviewed paper
   Integrated lithium niobate electro-optic modulators operating at CMOS-compatible voltages
   Cheng Wang, Mian Zhang, Xi Chen et al.. Nature, Oct 2018. DOI: 10.1038/s41586-018-0551-y. Accessed 22 Oct 2026.
2. news
   Monolithic integrated lithium niobate modulator operates at CMOS voltages of about a volt
   John Wallace. Laser Focus World, Sept 2018. Accessed 22 Oct 2026.
3. peer reviewed paper
   Broadband electro-optic frequency comb generation in a lithium niobate microring resonator
   Mian Zhang, Brandon Buscaino, Cheng Wang et al.. Nature, Mar 2019. DOI: 10.1038/s41586-019-1008-7. Accessed 22 Oct 2026.
4. review article
   Integrated photonics on thin-film lithium niobate
   Di Zhu, Linbo Shao, Mengjie Yu et al.. Advances in Optics and Photonics, 2021. DOI: 10.1364/AOP.411024. Accessed 22 Oct 2026.
5. news
   Laser 2025: CCRAFT and Lightium push thin film lithium niobate PICs
   Optics.org, 2025. Accessed 22 Oct 2026.
6. company announcement
   HyperLight Corporation homepage
   HyperLight Corporation, Publication date not stated. Accessed 22 Oct 2026.
7. preprint
   Stable electro-optic modulators using thin-film lithium tantalate
   Keith Powell, Xudong Li, Daniel Assumpcao et al.. arXiv, May 2024. Accessed 22 Oct 2026.

Revision history

3 changes since this profile was created.