MANUFACTURING with short pulse lasers FOCUS optical-axis orientation, such as lenses, gratings, beam shapers, or multi-plane light converters.
A key perspective is to broaden the range of written properties beyond linear birefringence which includes linear and circular dichroism and other circular effects( optical activity, circular birefringence). Advanced anisotropy does not necessarily require explicit laser nano-structuring only and a promising route is to exploit the residual stress field as a design parameter: controlling the spatial distribution of stress can generate and orientate birefringence and more complex circular properties indirectly. Progress along these directions relies on spatio-temporal engineering of the writing laser field. Transversal and longitudinal spatial shaping( elongated foci, Bessel beams, vortex beams [ 8 ]) offers additional degrees of freedom by tailoring energy deposition along propagation( Fig. 3b shows an example of such laser-induced microstructures with chiral optical properties). Temporal structuring( laser pulse, pulse trains, and newly coming GHz burst regimes) provides further control over absorption dynamics, heat accumulation, and stress build-up, which collectively determines anisotropy, losses, and repeatability. Looking further ahead, emerging research highlights the potential for achieving sub-wavelength modification limits( few nm to few tens of nm). At this scale, an open question is whether laser-driven processes can be engineered to impose controlled optical anisotropy or chirality through structural rearrangements approaching interatomic-bond length scales, shifting the paradigm from writing shapes to writing material properties at the most fundamental level.
Besides laser writing processes, material science and glass composition engineering are of equal importance. While silica and borosilicate glasses remain the materials of choice for most visible and near-infrared applications, their performance is inherently limited by intrinsic absorption bands, particularly in extended
Figure 3. Examples of advanced laser-written nano-microstuctures. a) Waveguide Bragg grating written in a silver doped phosphate glass with 500 nm period [ adapted from L. Loi et al. Opt. Mat. Exp. 14, 1837( 2024)]. b) Microstructures with chiral optical properties inscribed in silica glass with a polarized Bessel laser beam [ adapted from J. Lu et al. APL Photonics 8, 060801( 2023)]. c) Laser-induced dissolution of dielectric nanoparticles embedded in the core of a scattering silica optical fiber( Credits: F. Orange, F. Pellerin, W. Blanc, M. Bellec).
spectral ranges. As the demand for advanced photonic functionalities grows, there is increasing interest in exploring alternative glass compositions, including soft-glass systems such as fluorides, heavy-metal oxides, and chalcogenides. However, their distinct thermomechanical behaviors and photoinduced responses present significant challenges for femtosecond laser structuring. Developing novel processing strategies is essential to achieve high reproducibility, low optical loss, and long-term stability of engineered optical properties.
CONCLUSION Femtosecond laser processing has revolutionized the fabrication of 3D photonic nano-microstructures in glasses, enabling precise control over various linear, nonlinear, passive or active optical
REFERENCES properties for advanced applications in photonics. Laser inscription is evolving to integrate subtractive and additive techniques. By inducing defects and stress, it enables laser-assisted etching for precise 3D microstructures, such as microfluidic channels and optical cavities, which can be infiltrated with active materials to incorporate functionalities in the bulk of robust glass host matrices. Additionally, laser-driven polymerization allows the fabrication of complex 3D architectures, including metamaterials and interconnects, enhancing photonic integration. Within this flourishing context, next generation of photonic platforms embedding sources, light transport, sensing and signal processing will certainly incorporate multiple functionalities obtained by combining various manufacturing abilities.
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