Fiber mode converters: point-by-point fabrication of index gratings, visualization using thermoluminescence, and applications

Recently, we reported a technique for making a LP0l → LP11 fiber mode converter device.1 The technique differs from holographic techniques2,3 in that the periodic mode converter refractive index grating is written point-by-point in the, core of a two-mode photosensitive fiber with ultraviolet light, thereby allowing control of the pitch, length, and blaze of the perturbations. This paper provides further details on these fiber mode converters and reports the first direct observation of the index perturbations with thermoluminescence.