Engineering the refractive index of three-dimensional photonic crystals through multilayer deposition of CdS films

Abstract

Woodpile photonic crystals are amongst the preferred candidates for the next generation of photonics components. However, the photocurable resists used to produce them still lack the optical properties (high-n, non-linearity) suitable for photonics applications. A chemical bath deposition protocol has been adapted to deposit high-n/non-linear chalcogenide CdS on the surface of Ormocer woodpiles. The deposition parameters have been adjusted to obtain heterogeneous growth of CdS layers on the Ormocer surface. The layers shift the photonic band-gap and increase its amplitude by more than 15%. Software simulation confirmed that the woodpile effective refractive index underwent an excess of 30% increase.

Tuning the Refractive Index in Gyroid Photonic Crystals via Lead‐Chalcogenide Nanocrystal Coating

“…Achieving complete PBGs with the DLW technique requires the conversion of the polymeric structures to high refractive‐index PhCs. This can be achieved with inversion techniques, and coating methods . Backfilling 3D templates allows gaining strong PBGs, but these methods can be challenging due to severe constraints on the mechanical strength of the structures, the materials that can be utilized and the complex procedures involved .…”

“…Backfilling 3D templates allows gaining strong PBGs, but these methods can be challenging due to severe constraints on the mechanical strength of the structures, the materials that can be utilized and the complex procedures involved . Alternatives, represented by coating techniques, are generally less complex, but the refractive‐index contrast that these methods can achieve is low, and there can be problems in uniformly coating structures with intricate 3D geometries.…”

“…In this communication, we report on an alternatively charged layer‐by‐layer (AC‐LBL) deposition protocol with lead‐chalcogenide nanocrystals ( Figure a–e) to tune the effective refractive index of a 3D PhC and precisely engineer position, width, and amplitude of the PBG. Compared with the other approaches used to tune the dielectric contrast of 3D structures, our AC‐LBL method offers significant advantages because the use of charged compounds ensures that the coating penetrates deep and uniformly inside 3D complex structures. Moreover, this low cost, fast and room‐temperature method can be applied to different coating materials, such as quantum dots and other nanocrystals .…”

“…The simulated spectra were filtered to account for the finite opening angle used in experiments. The redshift of the PBG is related to a combination of the increase of the effective refractive index and the change in the filling fraction, while the improved transmission suppression is a consequence of the increment in the effective refractive index only …”

“…This result is caused by the morphology of the PbS cladding layer, where the presence of empty spaces between the nanocubes reduces the average refractive index of the coating and increases the surface roughness and scattering. The reduction in transmission for short wavelengths is caused by both an increase in scattering losses as the number of PbS particles forming the cladding layer is increased, and by a decrease in coupling‐strength to the higher‐order modes as the effective‐index is increased. In order to obtain a smoother surface, it is possible to use a filter with smaller pores, follow a different protocol to synthetize smaller PbS nanocubes or alternatively choose other nanoparticles.…”