**6.2 Micromachining via interference**

FSL has enabled the imprinting of large-scale periodic micro/nanostructures directly on the surface of hard materials or within transparent materials. By adjusting the laser energy, angle of incidence, the number of interference beams, the focal length of the focusing lens, exposure time, laser wavelength, and other parameters, we can modify the period, morphology, and dimension of the structures. Stable and applicable coaxial multi-beam interference can be produced by splitting lenses with a beam splitter and gratings and used for the fabrication of 3D spiral optical fields and chiral microstructures. Michelson interferometer-based FSL spatiotemporal interference approach was proposed for efficient and flexible surface patterning, which can produce a custom-designed gray-scale patterning on a bulk material with a single laser SLM pulse. Direct interference patterning has also been used for nanoparticles size distribution tailoring and multifunctional metal surface modification. This technique, FSL interference, enables the fabrication of periodic functional micro/ nanostructures, used in information storage, biomedical engineering, and metamaterials, owing to the invaluable features of this laser technique, including single-step processing, high efficiency, and controllable period [9].

The advantages of FSL have made it appropriate for the fabrication of various optical devices. In the following, we provide a summary of its applications:


for multiplexing. Multi-components fiber sensors, 3D waveguides, X-couplers, Bragg gratings, microholes, mirrors, optofluidic components, and microfluidic structures can also be processed within a single-mode fiber. Optical fiber using FSL can be used for on-surface and sub-surface fabrication of optical devices and microfluidic devices, which can be integrated onto an optical platform for various materials with diverse physical, chemical, mechanical, and biological properties.
