**1. Introduction**

There is a growing interest in finding detection technologies enabling real-time and on-line monitoring of many elements having remarkable, (in some cases dramatic), impacts on our everyday lives. Consequently, a huge effort has been devoted to designing and building instruments with capabilities that would not even be thought of a few years ago. Nowadays are required instruments to analyse many fields of high interest ranging from environmental pollutants or pathogens in air and water, up to the Security and Safety in the urban ambient or in the logistic chain of food production and transport, as well as many other applications.

In most cases, the realisation of this kind of device involves analytical techniques that should avoid chemical reactants, difficult to be used outside specialised laboratories. Moreover, the device has to be routinely applied by almost untrained people that should also be able to read and understand the measurement result. At the same time, the analytical equipment must be self-contained and available at a very low cost.

Nowadays, the only available solution suitable to satisfy the whole of these requirements is to develop highly miniature integrated equipment to allow mass production using technologies likewise the planar technologies driven by the development of microelectronics. At the present state of the art, most of these requirements can be satisfied when it is possible to develop sensing techniques belonging to the family of the optical integrated microdevices.

Optical detection can concern different properties of light such as Intensity, (in the case of photometric analyses), Wavelength, (in the case of spectroscopic analyses), Refractive Index, (in the case of Index change due to the presence of the analyte molecules at the Sensor Surface), etc.

A large variety of optical and photonic microdevices, based on interferometric, energy dispersive elements, photonic micro and nanofluidic devices, has been designed, studied and reported in the literature [1–6].

The development at industrial quality level of active optical materials, (particularly Lithium Niobate, LiNbO3), joined to the use of planar technology, has allowed the fabrication of monolithic integrated optical microdevices having sensing capabilities comparable to the correspondent standard laboratory equipment.

As highlighted in the next paragraphs, IO and Photonics microfabrication techniques, offer the possibility to generate in monolithic and miniaturised systems, nearly all the equivalents of classical optical components (mirrors, splitters, combiners, phase shifters, etc.). Furthermore, such IO components can be integrated into and interfaced with guided wave circuits, such as integrated optical waveguides and optical fibres. These characteristics often strongly simplify all issues related to optical alignment and maintenance, the flow of the luminous signal, carrying the information, being firmly confined within fixed and well defined optical channels. In the following an overview of the characteristics and potentialities of IO devices is presented, in particular for a wide range of interferometric sensing applications.
