Micro-processing by using an ultrashort pulsed laser has been previously reported and developed in the past decade for fabricating micro devices. Using tightly focused short pulse laser beam, the laser intensity easily can reach more than 10<sup>13</sup> W/cm<sup>2</sup>. Under such conditions non-linear phenomena are triggered, hence multiphoton ionization and self-focusing are notably induced in a medium. Femtosecond laser enables micro-fabrication without critical heat damage owing to extremely shorter pulse width and very fast multi-photon absorption at the laser focal point, compared with longer pulse irradiation. In this report, a micro-voids array was created in optical fiber line by using a femtosecond laser to produce sensing area only at local micro-region of the fiber line. At sensing portion consisted of the voids array, transmitted light was partially scattered by voids after that the leaked light could be reflected on the interface of cladding and outsides, which held the incident angle depending on structures of the micro-voids array. Voids array played as a role of scattering sources to transmitted light and consequently it was expected that the transmitted light can be broadly leaked out from the fiber core to the cladding. Furthermore, optical losses attributed to the creation of micro voids were quantitatively obtained so as to figure out the sensor characteristics. Consequently the reflection region which was considered as a sensing area showed the re-coupling rate of 0.04 dB (3.03%) to insertion loss of 1.32 dB, and the incident angle existed between 67.2 -71.9°.