**4. Conclusion**

In this chapter, the authors presented an overview of laser-induced periodic surface structures (LIPSS) produced by ultrashort laser pulses. A part of its historical background was provided; the formation mechanism of LIPSS in femtosecond pulse regimes was described. Experimental results obtained by our studies were also presented as a practical use of femtosecond micromachining even though a part of the result is still under investigation.

Section 4 shows the functionalization of optical fibers using femtosecond laser drilling. Highfluence femtosecond laser microstructuring was described with recent experimental data in our research group. The investigation not only to explain the formation mechanism of LIPSS but also to have a microscale perspective should be important for material removal because a high-throughput fabrication of 3D microstructures to microdevices requires a large number of pulses and high fluence. We therefore expect that the obtained results can contribute to practical aspects.
