Optical frequency conversion via a 'spatiotemporal boundary' works even for weak light
Activated by a terahertz pulse, the metamaterial device frequency-converts light without using a nonlinear optical material.
|Frequency conversion of light using a spatiotemporal boundary. (Image: KAIST)|
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.
1. Kanghee Lee et al., Nature Photonics (2108); https://doi.org/10.1038/s41566-018-0259-4