Optical communication and fiber-optic sensing require a technique for extracting a specific wavelength from signals consisting of multiple wavelengths. Murata's acousto-optic tunable filter (AOTF) does this by exploiting the interaction between acoustic waves (surface acoustic waves) and optical waves. By controlling the frequency of the excited surface acoustic wave, the filter is able to select the required wavelength or even multiple wavelengths. Murata's unique technologies make this possible. For example, our microfabrication technology allows for high-precision forming of optical waveguides and acoustic waveguides on piezoelectric substrates, while our design technology permits us to control surface acoustic waves at will.

AOTF can be used for optical wavelength monitoring. The figure shows optical wavelength monitor measurements of the reflections (with different wavelengths) from five FBG sensors. If force acts on any of the sensors (FBG 3 in this example) and strains it, a change occurs in the wavelength of the reflection from the sensor. By installing FBG sensors in buildings and on cliffs, it is possible to detect vibrations and impending landslides.