Observation of the photoscattering effect from supercontinuum-generating germanosilicate fiber

We observe a photosensitivity apparently different from that associated with fiber grating inscription in a supercontinuum-generating germanosilicate fiber. Transmission of intense femtosecond ~800 nm pulses in the heavily Ge-doped fiber progressively produces a waveguide at the entrance of the fiber. The waveguide behaves as a multi-millimeter long fiber bandpass filter which scatters away light with wavelength shorter or longer than 850 nm. This photosensitivity is therefore termed as the photoscattering effect. A model incorporating color center formation is proposed to explain the underlying mechanism. A 5-photon absorption process likely serves as the common origin of this effect and the ~800 nm photosensitivity producing low-loss waveguides in bulk silica glass and Type I-IR fiber Bragg gratings in side written optical fibers.

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