Radiation Tolerant Optical Fibers for Fiber Optic Gyroscopes
The application space for Fiber Optic Gyroscopes (FOGs) has been constantly growing with many applications in ground based vehicles, marine and aerospace sectors. As the FOG technology matures and gains better acceptance the use of FOGs in high value projects, such as satellites, continues to grow. TV channel broadcasting drives the growth of the satellite industry and with momentum behind the lower cost micro-satellites there will be many new opportunities for the inclusion of FOGs into future satellite projects.
For most FOG fiber coils, polarization maintaing (PM) highly birefringent fibers are used which have an inner cladding region made from phosphorus doped silica. The addition of phosphorus into the inner cladding aids the manufacturing process and is suitable for most terrestial applications. However with exposure to radiation, the phosphorus causes the attenuation of the fiber to increase. The rate of attenuation increase is relative to the radiation dose and the operating state of the fiber. Therefore PM optical fibers which are to be used in space applications or other applications that require radiation resistance need to be designed without phosphorous.
The effect of radiation on erbium doped fibers will also be discussed to give a balanced view on the possibility of using erbium doped fibers as ASE light sources for FOGs in radiation environments. The radiation causes a change in the spectral response that is not constant over the full spectral range of the absorption and emission of the erbium doped fiber. The level of spectral change is relative to the type and concentration of dopants used within the fiber, giving significant constraints in the ability to design an erbium doped fiber suitable for space applications.
The theory will be analysed and discussed and experimental results will be shown comparing the performance of phosphorus doped and phosphorus free PM fibers before and after exposure to radiation and the effects on erbium doped fibers will also be measured and discussed.