Programmable optical reflection: turning mirrors to absorbers
Each element composing a photonic system is chosen according to its optical reflection, transmission or absorption properties. For example, a highly reflective material will be chosen for the manufacture of mirrors, while highly absorbing materials will be the basis of photodetectors and solar cells. These optical properties are generally intrinsic to the materials used and fixed in time.
However, the class of so-called phase change materials (PCMs) departs from this rule: their refractive indices and absorption coefficients can be modified quickly and reversibly. By combining the unique properties of these PCMs with nanophotonic design techniques, we have demonstrated a very broad modulation of the reflection/absorption properties of a single stack of materials including nanoscale layers of GeSbTe. In particular, we have experimentally demonstrated the transformation of a highly reflective device (R = 80%) into a perfect absorber device (A ~ 99.9995%), thus reducing its reflectivity by a factor greater than 10,000 at telecom wavelengths. On the other hand, by means of partial crystallizations of the PCM, 100 distinct reflectivity levels between 80% and 0% were successively “programmed” in a single sample.
The proposed device, which does not require lithography, can now be manufactured on a large scale and could easily be implemented in optical components of large dimensions, thus giving them versatile and reconfigurable optical properties.
Sébastien Cueff & Lotfi Berguiga
In partnership with CRHEA, l’Institut Fresnel and ST Microelectronics
S. Cueff, A. Taute, A. Bourgade, J. Lumeau, S. Monfray, Q. Song, P. Genevet, B. Devif, X. Letartre and L. Berguiga : Reconfigurable Flat Optics with Programmable Reflection Amplitude Using Lithography-Free Phase-Change Materials Ultra-Thin Films. Advanced Optical Materials 2001291 (2020); https://doi.org/10.1002/adom.202001291