Electrically tuned optical reflection band for an artificial helicoidal structure

ABSTRACT

We analysed the control of optical band gaps for axially propagating electromagnetic waves throughout a nanocomposite structurally chiral medium under the influence of a low-frequency (dc) electric field aligned along the same axis as the periodic structure. This medium is made of metallic nanoballs (silver) randomly dispersed in a structurally chiral material whose dielectric properties can be represented by a resonant effective uniaxial tensor. Structurally chiral material is taken to possess locally a $\overline{4}2m$ point group symmetry and the Pockels effect is assumed. By establishing the Maxwell equations in a $4\times 4$ matrix representation, we have computed the eigenvalues and eigenvectors of the corresponding matrix in the system rotating along with the helical structure as function of the filling factor and the electric field. We found that the band gap properties of the periodic system depend strongly on the applied low-frequency electric field which is able to increase the bandwidths of the two sub-band gaps generated by the presence of the metallic inclusions obtained above a given filling factor. The applied electric field is even able to open the mentioned band gaps when they are initially closed. We note that by increasing the filling factor, also by keeping the inclination angle and the electric field fixed, the bands are opened and closed. Then when changing the angle of inclination and the electric field the bands shift, they break and new sub-band gaps appear.

KEYWORDS:

• Nanocomposite medium
• structurally chiral medium
• band gap
• electrical tuning

Acknowledgements

M Franco-Ortiz acknowledges the support of the Universidad de Sonora and STAUS. J.A.R. acknowledges partial financial support from DGAPA UNAM grant [IN 101316]. This work was partially supported by grant from CONACYT 258366.

Disclosure statement

No potential conflict of interest was reported by the authors.