Micro - nanoscale 3D printing of silica-based GLASses for optical SENSors – 3DGLASSENS

The 3D GLASSENS project was structured around five interconnected work packages: «Results Management and Dissemination,« «New Formulations and Resins for Two-Photon Polymerization,« «Modeling/Design of Metallic Coatings, Mirrors, and Multi-Material Printing,« «Additive Manufacturing of Advanced Multifunctional Micro- and Nanofiber Optical Sensors: Towards the Lab-on-Fiber Concept,« and «Testing of 3D-Printed Fiber Microsensors for Monitoring Next-Generation Aircraft Engines.« New resins were developed and tested by PhLAM. The partners (PhLAM, CEA, and Safran) then proposed, modeled, produced, tested, modified, and optimized the shapes of 3D-printed components through collaborative exchanges between the different work packages. The goal was to create optical sensors for the harsh conditions of aircraft engines.

The major results of the 3D GLASSENS project are:
- the development of a new family of resins called «Solmers,« photopolymerizable by two photons, based on an innovative combination of the sol-gel process and organic monomers. This new family enables the additive synthesis of silica glasses with high optical qualities (surface roughness, refractive index control, etc.). In this new family of organic-inorganic hybrid resins, reactions take place at the molecular scale without the limitations related to the size of silica nanoparticles, unlike Glassomer-type resins already studied in the literature. After 3D printing and sintering (1100-1300 °C), high-optical-quality glasses with low surface roughness (< 0.2 nm) were obtained. Structural analyses confirmed the amorphous structure of the silica glasses. Various single- or multi-material microstructures were successfully fabricated on fused silica substrates. Furthermore, this approach has been extended to the functionalization of optical fibers for optical sensing applications in extreme environments (1000 °C).

- Improvement of 3D printing processes (printing parameters: laser power, scanning speed, development, etc., and post-processing: debinding and sintering) to reduce micro/nanobubbles in optical parts and, more specifically, to achieve a record resolution of 23 nm.

- Development of new resins adapted for the localized deposition of metallic layers after 3D printing.

- A new multi-material printing method has been patented.

- Demonstration of a new type of optical sensor (temperature, pressure, and humidity) based on lamellar Bragg gratings.

- Demonstration of multi-core fiber optic sensors, showcasing the potential of fiber optic micro-laboratories. - Demonstrations of optical sensors based on Fabry-Pérot interferometers, designed for temperature and pressure measurement, with micrometer-sized elements printed on the ends of optical fibers (one patent).

- These demonstrators were tested in harsh environments similar to real-world conditions (800°C, 70 bar) where hysteresis phenomena are undetectable. Above 800°C, very low hysteresis appears, limiting their use to temperatures up to 100°C for long-term applications.

- Exploration of other alumina-based materials resistant to temperatures above 1000°C.

- Dissemination of results through several summer schools, 10 national and international conferences, the publication of 3 articles in open-access international journals, and the filing of 2 patents.

During testing in harsh environments at temperatures above 800°C, although the temperature sensor operates at 1000°C, long-term temperature hysteresis is observed and increases with temperature as the temperature rises from 800°C to 1000°C. The use of Solmers resins significantly increased the stability of 3D-printed silica components compared to Ormocomp resins, which exhibit hysteresis even at 180°C, despite being usable up to 250°C in the short term. The use of silica as a base material for optical components, such as sensors, appears limited at temperatures above 800°C. This also highlights the limitations of conventional silica-based fibers. This limitation can be overcome by changing the base material to materials such as alumina or zirconia, which demonstrate temperature resistance close to 2000°C. This project has enabled the initiation of tests on this new approach, which appears feasible for these optically complex materials. This path constitutes our next step in this research area.
Compared to organic or organic-inorganic resins based on prefabricated particles, Solmers hybrid resins allow the 3D printing of dense silica-based glasses with improved optical and structural properties. These resins also offer new perspectives for multi-material 3D printing, paving the way for optoelectronic applications. Furthermore, doping with gold nanoparticles allows for localized metallization, opening up possibilities in microelectronics, microfluidics, and plasmonics. All these demonstrations attest to the great versatility of Solmers resins; for example, optical pressure and temperature sensors have demonstrated the full potential of these new resins for the production of optical components whose aging, and therefore use in real-world environments, is greatly improved compared to the previous state of the art.

Dissemination of results through several summer schools, 10 national and international conferences, publication of 3 articles in open-access international journals, and the granting of 2 patents, or example:
ves Quiquempois, Ayan Mondal, Priya Dominic, Halima El Aadad, Hicham El Hamzaoui, et al.. Impression 3D de verre (de silice) : Applications à la réalisation de composants photoniques. Ecole thématique USTV «Verre et optique«, Oct 2025, Presqu'Ile de Giens, France. ?hal-05322514?

Ayan Mondal, Halima El Aadad, Hicham El Hamzaoui, Marc Douay, Franz Enno Morel, et al.. Highly stable 3D printed microsensors at optical fiber tips. Sensors and Actuators A: Physical , 2025, 390, pp.116620. ?10.1016/j.sna.2025.116620?. ?hal-05085216?

Ayan Mondal, Halima El Aadad, Hicham El Hamzaoui, Marc Douay, Yves Quiquempois. 3D Printing of High Stable Fabry-Perot Sensors on Optical Fiber Tips for High Temperature Sensing. Optica Sensing Congress 2025, Jul 2025, Long Beach (California), United States. ?hal-05322453?

Ayan Mondal, Halima El Aadad, Hicham El Hamzaoui, Marc Douay, Yves Quiquempois. Laser-assisted additive manufacturing of silica-based glasses for photonic applications. Optica Advanced Photonics Congress 2025, Novel Optical Materials and Applications (NOMA), Jul 2025, Marseille, France. ?hal-05322438?

Two-photon 3D printed Fabry-Perot cavity combined with a femtosecond fiber Bragg grating on a single fiber for simultaneous sensing of pressure and temperature at high temperatures -Franz-Enno Morel,Guillaume Laffont, Marc Douay
Proceedings Volume 13639, 29th International Conference on Optical Fiber Sensors; 136396Z (2025) doi.org/10.1117/12.3062572

Halima El Aadad, Hicham El Hamzaoui, Yves Quiquempois, Marc Douay. Additive Manufacturing of Binary and Ternary Oxide Systems Using Two-Photon Polymerization and Low-Temperature Sintering. Nanomaterials, 2024, 14 (23), pp.1977. ?10.3390/nano14231977?. ?hal-05322404?

Yves Quiquempois, Halima El Aadad, Hicham El Hamzaoui, Ayan Mondal, Marc Douay. Impression 3D de verre à base de silice pour des applications photoniques. Journées VERRE, Nov 2024, Dijon, France. ?hal-05085331?

Halima El Aadad, Hicham El Hamzaoui, Gaëlle Brévalle-Wasilewski, Rémy Bernard, Christophe Kinowski, et al.. Solmers: Versatile hybrid resins for nanometric 3D printing of silica-based photonic components. Materials Today Advances, 2024, 22, pp.100500. ?10.1016/j.mtadv.2024.100500?. ?hal-04739174?

Halima El Aadad, Hicham El Hamzaoui, Rémy Bernard, Marc Douay, Yves Quiquempois. 20 nm Resolution 3D Printing of Doped Silica Glass Micro-objects for Optical Applications. 10th World Congress of Advanced Materials (WCAM 2024), May 2024, Osaka, Japan. ?hal-04739121?

Halima El Aadad, et al. 3D printing of doped silica glass microstructures by two-photon polymerization for photonics applications. 3D Printing & Additive Manufacturing, Oct 2023, Amsterdam, Netherlands. ?hal-04414329?

Photonics is omnipresent in our society in a growing number of industrial activity sectors. Customers are increasingly demanding more “personalized”, smarter, cleaner and lower-priced products that ultimately have a significant impact on production lines. Photonics is therefore evolving towards a personalized supply market which requires a new flexible, agile and reconfigurable production organization.

Like the 3D printing of metals or organic polymers, there is an urgent need in the 3D printing of silica glasses for optical components in order to bring to photonics the same revolution as additive manufacturing of metal ( for example) brings to other disciplinary areas. In addition, 3D printing of optical silica at the micro-nanometric scale will boost research projects and applications in multiple fields: communications, medical, energy, security and surveillance of structures, defense, metrology, photonic integrated circuits.

Breakthroughs proposed in this project are based on an innovative combination of the sol-gel process and polymers for 3D printing by two-photon polymerization. It aims to master the 3D fabrication of micro-objects, with micro-nanometric resolution, by mastering the 3D printing parameters and subsequent heat treatments. A demonstrator proposed by Safran is planned in this project, it will clearly illustrate the interest of 3D printing of optical quality silica glasses. This demonstrator will illustrate the advances related to this project which can be used for the realization of many other photonic components.

The objectives of the 3D GLASSENS project are then: - to develop new formulations of silica or Ge doped silica (in order to locally modify the refractive index) with photopolymerizable organic monomers (Two Photon Polymerization: TPP) which will lead to silica glasses with the required optical qualities (diffusion, absorption, surface roughness, refractive index control, etc.). In these new inks, the reaction takes place at the scale of the molecule and is no longer limited by the size of the nanoparticles as for the Glassomer solutions already demonstrated – to improve 3D printing processes (power, time, debinding, sintering) - Develop new inks for the deposition of local metallic layers. – to push high resolution TPP 3D printing of silica-based glass micro-objects down to a resolution of 70 nm - to perform direct functionalizations of optical fibers with these silica glass-based micro-objects of silica will be carried out – to realize 3D printed optical sensors in a relevant environment: test these new sensors in aeronautical applications, in particular the Health Monitoring of any structure and / or process involving extreme conditions. This environment combines temperatures up to 1000 ° C and pressure variations of up to 70 bars under high vibration levels.

3D Glassens will bring the following advantages for 3D printing of silica photonic components: performance gain, weight reduction, increased mechanical and thermal resistance of parts, original design of new functions, design freedom, rapid prototyping, reduction of development and manufacturing costs, waste reduction, design and manufacturing agility, multi-material achievements, implementation of the Industry 4.0 concept.