**4. Conclusions**

outcomes suggest that, by an appropriate selection of the above mentioned parameters, LPGs can be produced either to be radiation hardened or with pronounced radiation sensitivity, appropriate to be used in radiation dosimetry. No change in the temperature sensitivity of

A new proposed approach in studying gamma irradiation effects on LGPs Includes several

**•** the use of an OFDR model LUNA OBR 4600, operating in the transmission mode or, for

**•** LPGs on-line monitoring when the irradiation is on and off, which makes possible the

**•** the comparative evaluation of the radiation induced LPG changes for grating produced in standard communication and specially designed radiation hardened optical fibers.

The use of the OFDR improved drastically the detection S/N as compared to classical reading with an optical spectrum analyzer. During the irradiation the sensors were encapsulated into ceramic radiation transparent cases to avoid any strain induced changes in the LPG spectrum, and in the mean time, the gratings were placed into a thermally insulated box. The temperature was permanently monitored both inside this box and in the irradiation chamber and temper‐ ature related corrections were applied to the LPG characteristics. Based on the referred papers, **Figure 11** illustrates comparatively the behaviour of gamma irradiation on the LPG developed into a standard communication optical fiber (LPGsc) and one written in a radiation hardened optical fiber (LPGrh). The wavelength deep of the two samples move in opposite directions, the wavelength of the grating produced in the standard communication fiber increases with the dose increase, while for the other one the wavelength decreases with the dose increase. Besides that, it can be noticed the magnitude of the two changes, LPGsc being by far more

**Figure 11.** The change of the wavelength deep for two LPGs written in standard communication optical fibers LPGsc

comparative purpose, of an optical fiber interrogator model sm125;

LPGs upon irradiation was observed [101].

observation of room temperature recovery;

and in F-doped core optical fiber LPGrh.

novelties [102, 103]:

56 Radiation Effects in Materials

The last four to five years brought additional data concerning radiation effects in optical fibers and optical fiber-based devices as new materials, technologies and possible applications in radiation environments emerged. In the frame of this chapter, the major trends were presented and some novel techniques and applications promoted recently were addressed, in relation to different types of irradiations (i.e. electron beam, synchrotron radiation). In this way, the data reviewed in previous publications are updated and the extensive possibilities offered by new materials and experimental setups in using radiation effects on optical fibers were demon‐ strated. By focusing such type of research on newly developed fibers (plastic, micro-structured, multi-core) and by using novel photonic devices based on optical fibers, new classes of equipment will emerge for terrestrial applications (dosimetry, medicine, remote and distrib‐ uted monitoring) and for space missions.
