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Laser Manufacturing of 3D nanostructured optics using Advanced Photochemistry

Periodic Reporting for period 1 - PHENOMENON (Laser Manufacturing of 3D nanostructured optics using Advanced Photochemistry)

Reporting period: 2018-01-01 to 2019-06-30

Optics are in the core of many technological innovations, as 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 pursues 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 tackles 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 provide product designs with extreme optical demands, to be fulfilled by PHENOmenon technology.
The specific objectives of the project:
1: 3D nanofabrication. Robust and flexible technology to produce 3D nanostructures with the desired optical behavior.
2: Ultra high resolution over large areas: Realistic applications demand cm2 of active optical surfaces.
3: High productivity mass customization. Full control of the nanostructure allows for free design of optical functionality.
4: New optostructures: the project ambitions to offer the industry radical and unedited optical functions, particularly metaoptics and flat microoptics.
5: Disruptive applications: practical applications and new products are foreseen, such as holographic imaging, surveillance optics or compact LED lighting.
In this first period of the project, R&D and demonstration were handled coordinately towards the main objective: competitive production of optical nanostructures which enable new products and characteristics.
General specifications were established for five challenging products: 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). Benchmarks were established based on the characteristics and performance of existing State of the Art equipment and praxis. Three lines of research were developed in parallel:
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 plasmonic structures and high refraction index materials (n>1.8) using nanoparticle dispersion and photocoagulation, or photoreduction.
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-wavelenght 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 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. The work will continue the development of similar molecules with improved performance, solubility and stability.
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. A new photochemical route based in oxide nanoparticle aggregation is expected to provide nanostructures with n as high as 2.5.
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). From that point, 25x25, 51x51 and up to 101x101 arrays of spots were optimized for parallel fabrication, 3 to 4 orders of magnitude larger productivity than standard 2PP.
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.
In the second period, the project will focus in the results directly related with the deployment of practical applications of the new materials, techniques and fabrication technologies. These results will be attained with a fabrication system which is nearly 10 times less costly than EBL, easier to operate, faster and more flexible. The ultimate impact is to unleash the full potential of metaoptics and ultraflat optics fabrication in new sectors and applications.
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Detail_DOE_fabricated
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Structures were fabricated with a beam splitting diffractive optical element which splits the incomi
Design of metaoptics requires elements with subwavelength size
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