Ghent University, imec and Stanford collaborate to extend lithium niobate photonics capabilities with integrated light sources

The micro-transfer printing technique allows to add different materials to the lithium niobate circuit, such as a layer of silicon and a III-V semiconductor optical amplifier. (large view)

The micro-transfer printing technique allows to add different materials to the lithium niobate circuit, such as a layer of silicon and a III-V semiconductor optical amplifier.

(05-11-2021) Lithium niobate is an important material for quantum computing and high-speed communications.

Scientists from Ghent University and imec have joined forces with Stanford University to integrate light sources on the lithium niobate photonic platform. They demonstrated the first fully integrated laser whose lasing characteristics can be controlled using the (quasi-)instantaneous electro-optic effect which is present in lithium niobate. The addition of these III-V semiconductor based light sources to the lithium niobate platform paves the route towards dense wafer-scale integration: a big contribution towards commercial viability for several applications. These applications include quantum computing, high-speed communications and ranging. Lasers that can change color almost instantaneously are much sought for as they allow to rapidly change between different optical communication bands. Moreover, they allow for the cointegration with beyond 100GHz modulators needed in the next generation networks

Lithium niobate is a so-called electro-optic material, meaning that its optical properties can be modified by applying a voltage over the material. This effect can be used to imprint digital data onto an optical signal. Owing to this, the material played a pioneering role in the commercial deployment of  integrated photonics: lithium niobate components were critical in the realization of the world wide web as we know it. However, a more widespread use was hindered by the lack of high-density scaling capabilities. The modulators are too large to use them for the optical interconnects in e.g. datacenters. In the past twenty years, the field of integrated photonics was instead spearheaded by the CMOS-compatible silicon and silicon nitride platforms.

Consistent research efforts during this time have led to a new and improved lithium niobate platform for integrated photonics, with better scaling capabilities and capable of exploiting the electro-optic effect more efficiently. Several recent scientific breakthroughs such as efficient frequency conversion or optical modulators with bandwidths exceeding 100 GHz have been achieved thanks to its attractive properties. However, as the platform lacks the capability for electrically pumped, on-chip light generation, external light sources are used in these demonstrations. Although this is satisfactory in an R&D setting, it increases packaging costs and reduces fabrication throughput, which could be prohibitive for commercial deployment.

Ghent University, imec and Stanford University have combined their expertise to realize the integration of III-V semiconductor based light sources on lithium niobate. Researchers at the Ginzton lab at Stanford University fabricated a photonic integrated circuit on the lithium niobate platform they developed. The researchers at the Photonics Research Group at Ghent University then used their experience in heterogeneous integration to develop a novel back-end compatible integration process for the light sources, based on the micro-transfer printing technique. Their work resulted in the first ever demonstration of a fully integrated, electrically pumped laser with electro-optic wavelength tuning capability and promises to boost future developments on the lithium niobate platform. Particular strengths of the used method are that there is no need to alter the previously optimized fabrication flow of the lithium niobate circuit, and that the used techniques are all scalable to wafer-scale production. The reported work was supported by grants of the Research Foundation Flanders, the European Research Council, Interreg, the U.S. National Science Foundation, the U.S. Department of Energy and the U.S. Air Force Office of Scientific Research.

More information

Optica,  Vol. 8, Issue 10, pp. 1288-1289 (2021) - III/V-on-lithium niobate amplifiers and lasers 
Camiel Op de Beeck, Felix M. Mayor, Stijn Cuyvers, Stijn Poelman, Jason F. Herrmann, Okan Atalar, Timothy P. McKenna, Bahawal Haq, Wentao Jiang, Jeremy D. Witmer, Gunther Roelkens, Amir H. Safavi-Naeini, Raphaël Van Laer, and Bart Kuyken