Rewritable densification gratings in boron-doped fibers.

We show that the strength of long-period gratings recorded in boron-doped fibers by CO2 radiation can be significantly enhanced by a uniform pre-exposure by the same laser. The resultant gratings could be erased by a similar uniform exposure and then recorded again multiple times with no loss of fiber sensitivity. We suggest that such gratings are formed by reversible densification of the fiber core. These densification gratings have higher thermal stability than gratings written with ultraviolet light.