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Laser Manufacturing of 3D nanostructured optics using Advanced Photochemistry

Periodic Reporting for period 2 - PHENOMENON (Laser Manufacturing of 3D nanostructured optics using Advanced Photochemistry)

Reporting period: 2019-07-01 to 2021-04-30

Optics are in the core of many technological innovations, since displays and interfaces, imaging, lighting, surveyance/security and telecom heavily rely on high quality and novel optics. Conventional optical systems have reached their limit in terms of miniaturization and performance to satisfy the demands of the new applications.
The PHENOmenon project pursued a fabrication technology to produce ultraslim custom optics, by exploiting 2D and 3D nanoscale architectures which break the limits of conventional optics in terms of light manipulation. The main challenge is the precise, industrial scale and cost-effective fabrication of such optical structures. The project tackled that in two ways:
1– R&D in three main areas: a) Laser based nanofabrication: multiphoton polymerization for freeform 3D printing beyond the diffraction limit using parallel laser writing. b) Chemistry and materials science, for high performance materials. c) Optical engineering, simulation and design of the 3D optical nanostructures.
2– Demonstration of optically nanostructured surfaces and metaoptics, developing simulation frameworks and models. The industrial partners provided product designs with extreme optical demands, to be fulfilled by PHENOmenon technology.
The multidisciplinary development of the fabrication technology, comprising the design and modelling of micro/nanostructures for different optical applications, the materials for high resolution fabrication and the optics and strategies for massive laser beam parallelization and, thus, fast fabrication speed established the foundations for a new fabrication paradigm, overcoming the main objectives of the project:
1: 3D nanofabrication. Developing a robust and flexible technology to produce 3D nanostructures with the desired optical behavior.
2: Ultra high resolution over large areas: Fabricating 100 cm2 areas with subwavelength resolution.
3: High productivity mass customization: Producing microstructures with fabrication speeds beyond 5 cm2/min with full optical functionality.
4: New optostructures: making use of new materials with extreme refraction indexes and resolution below 100 nm.
5: Disruptive applications: demonstrating the PHENOmenon technology in new foreseen products, such as holographic imaging, surveillance optics or compact LED lighting.
A multidisciplinary approach involving three lines of research were developed in parallel within the PHENOmenon Project:
i) Materials and Photochemistry: New complete chemical systems were developed (resins, photoinitiators, sensitizers), to control the characteristics of the fabricated optostructure, and the mechanism of the optical writing. CNRS explored cost effective and environmentally friendly synthesis routes to obtain the required materials with new optical properties, like high refraction index materials (n>2).
ii) Laser Writing: development and realization of new and unique laser writing setups to realize the concept of Massively Parallelized Laser Writing. The strategies include diffractive optical elements (DOEs), dynamic amplitude and phase modulation (with SLM devices like LCOS or LCDs), and holographic projection. IMT-A designed the optical elements which allow for massive parallelization (up to 100k simultaneous individually addressed voxels). The parallelization strategies were tested at laser writing facilities of different partners (AIMEN, IMT-A, CNRS, MPO), and the results were complemented with wafer level postprocessing (THALES).
iii) Advanced nano-optostructured optical system design: modelling and design of functional optostructures with sub-wavelength features, with the development of the wave propagation models at nanostructure level, and its link with micro, meso and macroscale model and design frameworks. The project started from existing tools and developments in the consortium partners (THALES, FLUXIM, IMT-A, ICFO, CNRS), further developing the models to fit the characteristics of the target microstructures, and fitting together the models to make them compatible. The project has already resulted in a new version of the LAOSS software by FLUXIM, to successfully deliver the designs for ultraflat microlenses, nanostructured concentrator Fresnel optics, and a flat microprism based optostructured diffuser layer for finetuned LED backlighting. Novel approaches were proposed to calculate and design color 3D holograms reconstructed with white LEDs or natural light, and different 3D effects.
The demonstration of the technology was carried out through the combination of the achievements of the three lines of research. In this way, the fabrication of five challenging products was reached: antifogging optics for surveillance (THALES), machine readable color holograms (FNMT), holographic virtual button (PSA), high visibility curved display (FLEXENABLE) and ultraflat LED lighting surfaces (DLED); analyzing the outcome of the fabrication against benchmarks established based on the characteristics and performance of existing state of the art equipment and praxis.
The work in the synthesis of new resins and Photoinitiators provided outstanding results. Compared to a common Photoinitiator (Michler’s ketone), an octupolar chromophore developed in the project requires six times less energy for writing, with 25 times larger TPA cross-section, exceeding initial expectations. Writing at ultra-low laser energy levels with 2 photon absorption is also beyond the state of the art. A new type of sensitizer was demonstrated to enable nonlinear photopolymerization of resins with CW lasers at energy densities as low as 16 W/cm2, many orders of magnitude below what was possible before. This result opens the opportunity for fabrication with much simpler and cheaper laser systems than the lasers currently used. High refractive index materials were also developed with relevant results through sol-gel synthesis. A value of n=1.9 for Zr based resins, and n>2 for ZrO2 based resins, were attained after calcination opens a wide range of possibilities for different optical functions.
In Laser Writing technology, the use of a 11x11 fixed DOE enabled to fabricate 121 simultaneous structures with optimal energy distribution, with no zeroth-order effect, at sub-wavelength 2D/3D resolution (300 nm and below). The fabrication of optical microstructures in 100 cm2 areas with fabrication speed over 5cm2/min represented one of the highlights of the project, with developments well beyond the state of the art, boosting the competitiveness of 2pp for the fabrication of tailored microoptics.
In the field of structure calculation, ultraflat microoptics were designed in the form of a field of multiple nanorods from 100 to 500 nm in diameter, all with only 1 micron high, to produce the concentration of solar light in the visible and NIR spectrum with nearly no dispersion or chromatic aberrations. New methods for designing computer generated holograms (monochrome and color) with different 3D effects in their reconstruction were also published as advances beyond the state of the art.
Paper FNMT
MPO piramids
Holographic button
PC card FNMT
LAOSS software
support F14 T0.3