A sketch of the all-optical SH polarization modulation. The control pulse is polarized along the ZZ direction whereas the probe pulse is polarized along the AC direction of an MoS2 sample.

High-speed modulation by crystalline symmetry

ACP physicists and chemists are working methods for non-linear optical signal modulation in 2D materials. A team led by ACP principal scientist Giancarlo Soavi has developed a method for non-linear signal modulation.
A sketch of the all-optical SH polarization modulation. The control pulse is polarized along the...
Illustration: Soavi research group, published in Nature Photonics.
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Published: 9 September 2021, 02:00 | By: Sebastian Hollstein, translated and adapted by Christian Helgert

Nonlinear optics are of outstanding importance in numerous areas of science and technology and are a key target direction in our CRC/SFB 1375 "NOA - Nonlinear Optics down to Atomic scales". Frequency doubling is routinely used to achieve new wavelengths that are not available with conventional laser sources. In addition, there are significant applications in the field of photonic data transmission and quantum communication or sensor technology, since information can be written into the light by modulating the signal - i.e. switching the conversion on and off. In order to fully exploit the potential of this technology, the laser must be modulated as quickly and efficiently as possible. ACP scientists have now developed a particularly effective method together with colleagues from Politecnico di Milano and have published their findings in the recent issue of Nature Photonics.

In order to generate the second harmonic, the Jena researchers' team under the lead of ACP principal scientist Giancarlo Soavi applies ultrashort laser pulses to a 2D material. Such ultra-thin materials, which only consist of a layer of atoms, are particularly suitable for nanoscale components, as they can be easily integrated on photonic platforms thanks to their flexibility and mechanical properties.

Soavi and his colleagues combine the advantages of two different approaches for their new method: “On the one hand, you can change the properties of the material by applying an electrical voltage and thus influence the intensity of the light emitted. It works very efficiently but relatively slowly, ”explains Soavi. “On the other hand, it is possible to stimulate the material with a second light beam. This happens extremely quickly, but the modulation of the second harmonic that is achieved is rather weak.” With their new method, the Jena scientists now combine the advantages of electrical and optical modulation. This development from the SFB 1375 NOA and the European Graphene Flagship research initiative may pave the way for new types of integrated high-speed frequency converters that can be used, for example, in fast data transmission.

S. Klimmer et al., "All-optical polarization and amplitude modulation of second-harmonic generation in atomically thin semiconductors," Nature Photon., online (2021).

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