Fabrication of Flexible Photonic Crystal Slabs

Abstract

Two methods for the fabrication of flexible and stretchable photonic crystal slabs are demonstrated and compared. In both cases a periodically nanostructured polydimethylsiloxane (PDMS) membrane is used as substrate. The first method is based on oblique-angle vapor deposition of SiO as a high refractive index material onto the nanostructured membrane. The deposition is made at an angle of 45° to the surface. The grooves of the nanostructure are aligned such that shading effects cause an inhomogeneous layer thickness distribution on the surface. This supports controlled, periodic cracking of the high index layer upon stretching. In the second approach ZnO nanoparticles are spin-coated on the nanostructured PDMS membrane. Here, the membrane can be stretched and serves as a photonic crystal slab without the need of any further treatment. For both types of flexible photonic crystal slabs a shift of the guided mode resonances to longer wavelengths is observed upon stretching. For a 20% strain perpendicular to the grating grooves a resonance shift of more than 50 nm is obtained.

Flexible photonic crystal membranes with nanoparticle high refractive index layers

“…The wavevector of the mode k mode = n eff k 0 is related to the grating vector k Gx = 2π/Λ by Eq. 1 [ 15 ].…”

“…k 0 = 2π/λ is the vacuum-wavevector, λ is the resonance wavelength in vacuum, Λ is the grating period, m is the resonance order, θ is the incidence angles to the surface normal, and φ is the angle between the grating lines and the projection of the incidence light onto the surface [ 15 ]. In our setup we use φ = 0° and θ = 0°.…”

“…The samples were stretched up to 3.75% and 5% strain, respectively. We previously identified cracking of continuous high-index waveguide layers as a limitation for the performance of flexible photonic crystals and demonstrated a nanoparticulate high-index layer [ 15 ]. Our previous study [ 12 ] showed first promising results in the use of flexible photonic crystals.…”

Pressure sensor based on flexible photonic crystal membrane

“…The layer of randomly arranged TiO 2 -particles forms a waveguide that has a geometric periodic structure due to the linear grating in the PDMS layer below it. We diluted the dispersion to 4 wt% of TiO 2 -particles in H 2 O together with 0.5 wt% of fluorosurfactant (PFT) (NOVEC FC-4430 from 3M) to further reduce the contact angle and spin-coated it onto the nanostructure with 2000 rpm and a ramp of 5000 rpm/s for 20 s [12]. Afterwards the bottom and top part were pealed from the molds and assembled by using the "Stamp-and-Stick (SAS)" method with uncured PDMS as described by Satyanarayana et al [16] to form the sealed chamber.…”

“…The flexible photonic crystal slab is formed by a high refractive index layer of TiO 2 nanoparticles on a periodically nanostructured surface. We employ a nanoparticle layer to prevent cracking in the photonic crystal surface under strain [12]. Under illumination a quasi-guided mode is excited.…”