Electric field tuning of magnetically assembled photonic crystals

Electrically tunable photonic crystals are fabricated by encapsulating magnetically assembled colloidal crystals inside an electrolytic cell, and their reflection decreases or recovers when an electric field is applied or removed. The reflection changes are caused by the change in the order degree of the colloidal crystals, which can be further explained by the migration of Fe ₃O₄ nanoparticles and the change of localized ionic strength in different electric fields. A stronger electric field is needed to tune the colloidal crystals assembled by a strong magnetic field, and a good match between their strengths is significant to improve the sensitivity and reversibility of the reflection switching. Generally, the reflection falls within 1 s and recovers after 4-5 s depending on the field strength. Since the electric field can be well restricted in the space between two electrodes and precisely controlled by the applied potentials, it is possible to fabricate adjacent magnetic photonic crystal cells whose reflection signals can be independently controlled by the electric field, which reveals a possible solution to high-resolution photonic crystal based optical devices.