Optical frequency conversion via a 'spatiotemporal boundary' works even for weak light

A team at KAIST (Daejeon, Korea) has developed an optical frequency-conversion technique based on spatiotemporal boundaries (areas with properties that change in time) in materials.¹ The research focuses on realizing a spatiotemporal boundary with a much higher degree of freedom than the results of previous studies by fabricating a thin metal metamaterial structure on a semiconductor surface.

The device contains two types of metallic meta-atoms, and is activated by an ultrafast pulse of terahertz radiation that merges the two types of meta-atoms into one.

Optical frequency-conversion devices, which play key roles in precision measurement and communications technology, conventionally function via optical nonlinearity, usually by the interaction between a high-intensity laser and a nonlinear medium.

In the KAIST approach, frequency conversion is observed by temporally modifying the optical properties of the medium through which light travels using an external stimulus; this approach does not rely on optical nonlinearities in materials. Since frequency conversion in this way can be observed even in weak light, such a technique could be particularly useful in communications technology.

The KAIST researchers developed the optical metamaterial by arranging a metal microstructure so that it mimics an atomic structure, and then created a spatiotemporal boundary by changing the optical property of the artificial material abruptly. While previous studies only slightly modified the refractive index of the medium, the KAIST study provided a spatiotemporal boundary as a platform for freely designing and changing the spectral properties of the medium. Using this, the research team developed a device that can control the frequency of light to a large degree.

Source: https://www.kaist.ac.kr/_prog/_board/?code=ed_news&mode=V&no=89341&upr_ntt_no=89341&site_dvs_cd=en&menu_dvs_cd=0601

REFERENCE:

1. Kanghee Lee et al., Nature Photonics (2108); https://doi.org/10.1038/s41566-018-0259-4