Electromagnetic field (EMF) sensors are widely used in several industrial, scientific and medical applications and for measurements of fields yield by a huge set of communication devices. We focuses on some experiences on the use of an integrated optical device which implements a Mach-Zehnder interferometer, and on its further development as an electromagnetic field sensor. The probe is mainly made by non conductive materials, making such device suitable for experimental measurement of electromagnetic fields in near field region (or Fresnel's one) of transmitting antennas. Here no simple theory is available in order to evaluate the fields and mutual coupling between antennas and standard probes strongly affect the measurements: the optical probe avoids the coupling of the fields with metallic structures and the loss of antenna calibration which typically yield measurement errors.