**5. Acknowledgements**

The author wishes to thank Mr. P.M. Latino for his technical support in the development of the technological processes and the HTA.

### **6. References**


**27** 

**Applications of In–Fiber Acousto–Optic Devices** 

Nowadays, in-fiber acousto-optic devices are increasingly used as frequency shifters, multiplexers, modulators, and tunable filters. They can be easily spliced into optical fiber systems, and the consequent low insertion loss, make them an attractive alternative to bulk optics devices. Our group, established at the Institute of Materials Science, Department of Applied Physics, of the Valencia University (ICMUV, Valencia, Spain), has been involved in this field for the last ten years, and our fabrication facilities allow us the development of new in-fiber acousto-optic devices for novel applications in different fields such as sensors, microwave photonics, lasers, and optical communications. Our aim here is to present the great potential shown by in-fiber acousto-optic devices for different photonic applications. Although this chapter is focused in our latest developments, the reader will also find discussed the work done by other research groups in the field. This chapter is divided in two main sections: Section 2 is focused on novel applications of acousto-optic fiber devices based on flexural acoustic waves, and Section 3 is focused on applications of the acoustooptic devices based on the interaction of longitudinal acoustic waves with fiber Bragg

**2. Applications of acousto-optic devices based on flexural acoustic waves**  In a standard single mode fiber, when a flexural acoustic wave propagates along an optical fiber a periodic perturbation is introduced in its refractive index, and it can induce coupling between the fundamental mode guided by the core and the modes supported by the cladding (Kim et al., 1997). This acousto-optic interaction can be seen as the dynamic counterpart of a long period grating (LPG). LPGs are usually fabricated by creating a periodic perturbation of the refractive index by UV radiation; this of course fixes its spectral characteristics. On the other hand, when the perturbation is introduced by an acoustic wave, its period and strength can be controlled through the frequency and amplitude of the acoustic wave, respectively. Thus, the spectral properties of the optical device can be controlled dynamically through the characteristics of the acoustic perturbation. The optical

gratings (FBG). Finally, our conclusions are shown in Section 4.

\**1Departamento de Física Aplicada y Electromagnetismo, ICMUV,* 

*3Centro de Investigaciones en Óptica, León, Guanajuato, Mexico*

*Universidad de Valencia, Burjassot, Valencia, Spain 2CONICET La Plata, Buenos Aires, Argentina,* 

**1. Introduction** 

\*C. Cuadrado-Laborde1,2, A. Díez1, M. V. Andrés1, J. L. Cruz1, M. Bello-Jimenez1, I. L. Villegas1,3, A. Martínez-Gámez3 and Y. O. Barmenkov1,3

