All-optical switching in an optofluidic polydimethylsiloxane: Liquid crystal grating defined by cast-molding

Abstract

We report an optofluidic photoswitchable grating, based on a polydimethylsiloxane periodic structure on a glass substrate, separated by a thin liquid crystal film. The polydimethylsiloxane microstructure was realized via high resolution replica molding and was employed to both confine and align a photosensitive nematic liquid crystal. In the absence of any surface treatment, the liquid crystal exhibited homeotropic alignment. By inducing planar alignment on the glass substrate, a hybrid orientation of the liquid crystal was achieved, inducing polarization sensitive transmission. The photosensitivity of the liquid crystal enabled the all-optical control of the grating transmission and 20% diffraction efficiency was measured. © 2010 American Institute of Physics. ͓doi:10.1063/1.3377801͔Light responsive materials are promising candidates for the realization of optically addressed devices. In particular, dye-doped nematic liquid crystal ͑NLC͒ has attracted significant attention for its potential applications in the areas of all-optical holographic gratings 1,2 and optical phase conjugation.3 These light sensitive liquid crystals ͑LC͒ contain photochromic molecules, which can undergo reversible trans-cis isomerization. This transition can be induced with UV/visible light and reversed by heating or irradiation with light at longer wavelength. 4,5 The combination of the NLC properties with on-chip photonic structures have been widely explored, 6 however the integration of NLCs with costeffective and high-resolution nanostructures remains an open challenge. To this end, polydimethylsiloxane ͑PDMS͒ has attracted significant attention as a high-quality optical material, namely, due to its transparency, low surface energy, low dielectric constant and Young's modulus, and thermally and optically enabled polymerization. The emergence of optofluidics, where microfluidics are integrated with optics, has sparked renewed interest in PDMS for optical applications. 7,8 The birefringent properties of LCs with the enhanced optical characteristics of PDMS have been recently combined to realize tuneable high-Q microresonators and transmission gratings.9,10 In these, the NLC is dispersed in a PDMS matrix and the photonic structure was defined either via self-assembly, or holographically, placing thus a limit in the morphology and shape control. In this letter, we report the integration of NLCs with a PDMS microstructure realized by cast-molding lithography and demonstrate an optically controlled transmission grating. Such hybrid device combines the advantage of cost-effective and high resolution diffractive structures with the tuneability of LCs. Its applications may involve optical switching or lab-on-a-chip optofluidic applications. The construction strategy of the device was based on high-resolution cast molding lithography, opening thus an alternative path toward cost-effective and highly multiplexed optical functionalities for lab-on-a-chip and information processing applications. 11 We found that the low surface energy of the PDM...

Liquid crystal bubbles forming a tunable micro-lenses array

“…Even if nematics have been used for displays for the past forty years, nematics continue to find applications in novel optical and electro-optical devices such as optical waveguides, optical switches, and light modulators or deflectors. [1][2][3][4][5][6][7] Moreover, some have proposed that nematics may be used for constructing a tunable lens, 8 and surface relief profiles, 9 linear or circular hole-patterned electrodes, 10 and Fresnel zone type [11][12][13] examples have been presented. All these devices sandwich the nematic material between suitable electrode structures, and the application of an electric field induces a centro-symmetric distribution of the refractive index within the nematic layer, making it possible to control the focal length.…”

Tunable high aspect ratio polymer nanostructures for cell interfaces

“…One current limitation is the maximum feature height of about 1 µm, which is at the shorter end of the spectrum of high aspect ratio nanostructures reported in the literature 6 . However, EBL systems with higher acceleration voltages are available (typically 100-125 kV compared to 30 kV in our system), which would further increase the potential aspect ratio and height of the features 44 , due to significantly lower electron scattering in the resist (see ESI † Figure S3). Other direct-write techniques such as direct laser writing (DLW) or two-photon polymerization could potentially increase device production throughput, but suffer from lower feature resolution 45,46 .…”

All-optical switching of diffraction gratings infiltrated with dye-doped liquid crystals

“…A different approach exploits DDLC to infiltrate a polymer grating after its fabrication. 5 Following this strategy, in this work we report the fabrication and characterization of an all-optical switching device based on a polymeric grating containing a DDLC. Our device consists of a thin ͑thickness d = 0.5 m͒ diffraction grating holographically recorded in SU-8 polymeric film, developed and then infiltrated with a DDLC.…”