Heat tunes polarization in new dielectric metasurface design

Controlling polarization, a fundamental property of light, is necessary for many applications including telecommunications, optical sensors, lasers and three-dimensional displays. Most devices that regulate polarization, known as polarization synthesizers, are up to several millimeters thick. At less than one micron, dielectric metasurfaces are emerging as a thinner alternative.

Most metasurfaces manipulate light but are not tunable. For the first time, Bosch et al. present a germanium-based dielectric metasurface design that allows thermal tuning of light polarization.

The authors deposited an array of nanoscale germanium resonators, which have a high refractive index and thermo-optic coefficient, on a calcium fluoride surface. When they heated the metasurface, it modulated the phase retardance between the two transmitted principal polarization states of the linearly polarized light incident on the sample. This allowed generation and control of a wide range of output polarization states. By varying the temperature of the metasurface between 25 and 125 degrees Celsius and altering the angle of incident polarization, the researchers found that the polarization tuning range of the device covers 36 percent of the upper half of the Poincaré sphere, a graphical representation of polarized light.

Author Melissa Bosch said the results establish thermo-optic actuation as an important tuning mechanism for polarization control in dielectric metasurfaces. This technique is easy to access and could be further applied to other active optical components including dynamic notch filters, phase shifters or lenses.

Because the tunable dielectric metasurface is thin, these results also create new possibilities for compact tunable polarization synthesizers with potential applications in free-space and integrated photonics.

Source: “Polarization states synthesizer based on a thermo-optic dielectric metasurface,” by M. Bosch, M. R. Shcherbakov, Z. Fan, and G. Shvets, Journal of Applied Physics (2019). The article can be accessed at https://doi.org/10.1063/1.5094158 .