The asymmetry of the UV-induced refractive-index profile in photosensitive optical fibers causes a deformation of the modal fields, resulting in transition losses between UV-exposed and unexposed fiber sections up to 0.1 dB for UV-induced index changes of the order of ≤10<sup>−2</sup>. A numerical analysis of the transition losses is developed. It is verified experimentally that the loss is caused by coupling of power of the fundamental mode to cladding modes at such a transition.
© 2000 Optical Society of America
(060.0060) Fiber optics and optical communications : Fiber optics and optical communications
(060.2270) Fiber optics and optical communications : Fiber characterization
(060.2310) Fiber optics and optical communications : Fiber optics
(130.2790) Integrated optics : Guided waves
(230.7370) Optical devices : Waveguides
Hagen Renner, Dietmar Johlen, and Ernst Brinkmeyer, "Modal Field Deformation and Transition Losses in UV Side-Written Optical Fibers," Appl. Opt. 39, 933-940 (2000)