3D Femtosecond Laser Manufacturing of low cost integrated optical components for IR applications – FLAG-IR

FLAG-IR project is to exploit the femtosecond laser 3D direct writing technique in InfraRed (IR) glasses structuring for achieving low cost and integrated optical components for SWaP applications (reduction of Size, Weight and Power). The interaction of femtosecond laser with transparent materials is such that refractive index change can be as large as +/-10-2 in most transparent oxide glasses [1-3] and even -5.10-2 in some Ge-Sb based chalcogenide [4-5], the broadband linear birefringence [6-7] can be as large as 10-2 with a fine control of the orientation (a unique feature), the attenuation can be lower than 1dB/cm but the writing speed can be as large as a few cm/s! Furthermore, thanks to non-linear interactions, structuring can be achieved in 3D with a sub-micron lateral resolution. These features lead to think to tremendous progress in low cost photonics with such a flexible tool. The ability to control the direction of the slow axis and to induce high refractive index contrasts leads to the engineering of unique integrated optical devices with spatially varying birefringence and refractive index changes.
FLAG-IR proposes specifically to apply this 3D manufacturing technique to create compact and low cost optical components in IR materials. Indeed, in IR instrumentation, there is a need for miniaturized, low weight and low cost optical systems for civilian (domotics, smartphone, automobile) but also security and military applications (vehicles steering, survey, weapons guidance, unmasking, countermeasure identification). The constraints on size and weight of optical systems are so demanding that traditional optical systems with a single optical axis are reaching their limits. Therefore, new breakthroughs in optical design have been proposed that consist in developing bio-inspired multichannel architectures and integrating optical functions using planar optical components. In this field, new IR materials mainly gallo-germanate glasses (Ga2O3-GeO2-BaO-K2O glass system) transparent up to 5,5µm [8-9] in this project but also Gex-Sb10-S100-x chalcogenide family are excellent candidates for on-demand and low-cost production. One major advantage of the chosen chalcogenide is the transparency up to 11µm and high laser induced index changes up to -0,1 in Ge-Sb-S family [10-11]. In contrast gallo-germanate offer high durability in harsh environment and also the possibility to create a strong form birefringence based on nanogratings formation [6-7], which cannot form in others classical IR glass like ZBLAN. In addition, the possibility of making 3D direct shaping by use of femtosecond lasers enlarges the panel of optical functions we could encode into a small device, as it has been done earlier in pure silica glass.
The main objective of FLAG-IR project is to master femtosecond laser interaction with some well-chosen IR materials in the view to achieve low cost integrated optical components for IR applications and in particular SWaP reduction (Size, Weight and Power). More specifically we propose “to extend” to IR materials the results already obtained in SiO2 and GeO2 that were an important source of new discoveries, which can be explained and therefore further exploited both by defense and by civil companies. Driven by the specifications of the planned IR applications given by ONERA and its industrial partners like SOFRADIR, we will apply results already obtained in silicate glasses to gallo-germanate glasses (transparency up to 5.5µm), which is the heart of the project. In addition we will perform “preliminary investigations” on Gex-Sb10-S100-x chalcogenide family for long wave range (up to 11µm for thin samples involved here) for which we have already available samples and femtosecond laser processing windows based on recent investigations within our consortium and partners.