Nowadays, nanoporous films are widely employed in biochemical applications or in opto‐photonic devices such as displays, solar cells, or light‐guiding systems. In particular, the technological feasibility of nanoporous layers with low refractive indices has recently enabled the development of high‐efficiency anti‐reflection coatings. In this paper, we report on hybrid polymer nanoporous films that can be fabricated in a single coating step with an industrial aqueous‐based method on very large surfaces. Both high transparency and low refractive index are simultaneously achieved over the entire visible spectrum. We eventually demonstrate the potential of such films for broadband AR applications by combining them in a graded‐index multilayer that reduces the surface reflectivity of a polymer substrate from 10% to few ‰.

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Multimode planar polymer waveguides were fabricated on hybrid polymer nanoporous layers with a fast industrial aqueous-based method well adapted to coat large-surface plastic substrates and easily scalable up to economical mass production volumes. Using a fiber probe internal light source technique, we were able to measure quantitatively the modal propagation losses. In particular, attenuation coefficients lower than 0.5 dB/cm were found for the fundamental modes, thus showing the potential of our polymer nanoporous layers as optical isolation layers in waveguiding applications. Optical planar waveguides are fundamental building blocks in numerous optoelectronic devices, where signal transmission is needed. While inorganic materials have extensively been used to develop the best performing optical waveguides so far, in the last few years, the interest for organic materials has been rapidly growing.1 Polymer waveguides provide indeed a very attractive solution for the fabrication of optical systems characterized by low intrinsic losses, mechanical flexibility, and large surface, with the possibility of using simple, rapid, and cost-competitive production techniques. Moreover, the recent progresses in the material engineering of organic compounds make polymer multilayer films an ideal platform for the development of complex optical systems.2 In particular, several conventional polymers have been studied to fabricate optical waveguides: with poly(methyl methacrylate) (PMMA), for instance, waveguides were fabricated with propagation losses in the order of 0.1 dB/cm or higher in the infrared spectral region. 1More recently, optimized optical polymers have been developed such as deuterated and halogenated polyacrylates, whose physical properties (refractive index, transparency, adhesion, surface energy, birefringence, etc.) and synthesis procedures are generally well mastered. With these latter polymers, monomode and multimode waveguides were fabricated with losses in the order of 0.01 dB/cm in the infrared and red spectral intervals, respectively. Both fluorinated polyimides and perfluorocyclobutyl aryl ether polymers were also used to coat polymer-based waveguides with losses in the order of 0.1 dB/cm in the infrared spectral region. Nevertheless, with the first materials, birefringence cannot be avoided and waveguide losses depend on polarization.In general, the optical performances of planar waveguides strongly depend on the refractive index contrast Dn between the core and the cladding layers, 3 i.e., by increasing Dn, the light confinement in the guiding structure is improved, thus reducing the intrinsic contribution to propagation losses. In this respect, nanoporous layers have recently appeared as very attractive materials due to the possibility of achieving a very low refractive index n (between 1.0 and 1.2) that can, thus, enhance Dn in the existing waveguiding systems. More generally, these nanoporous layers are also being studied for applications in several other optical systems such as interferential anti...