Abstract
Since its development in 2003, the technique of Bragg grating inscription in optical fibers and waveguides with ultrafast infrared radiation and a phase mask has proven to be as simple as the standard UV-laser grating writing techniques but far more versatile. The ultrafast IR laser-based process allows for the creation of grating structures in glassy and crystalline materials that are not typically UV photosensitive. In this article, we will review the studies that have been performed at the Communications Research Centre Canada on the grating formation processes as well as applications of the ultrafast laser technique to fabricate gratings in various optical fibers and waveguides.
Highlights
High-power femtosecond lasers systems are being used extensively for laser-material processing of glassy materials in order to fabricate microfluidic and photonic devices
The process of induced index change in bulk glasses resulting from femtosecond-IR laser exposure is thought to result from a multiphoton absorption/ionization process resulting in material compaction and/or defect formation depending on the intensity of the exposure [1]
Combining the ultrafast IR laser and the phase mask approach, we successfully demonstrated the efficient fabrication of retroreflecting fiber Bragg grating (FBG) in standard telecom and pure silica core single mode fibers [11, 12]
Summary
High-power femtosecond (fs) lasers systems are being used extensively for laser-material processing of glassy materials in order to fabricate microfluidic and photonic devices. Femtosecond laser systems have been used to induce large index changes and fabricate long-period fiber grating structures in a step-and-repeat fashion [3, 4]. Ith, another regime of induced index change has been observed that can be erased by annealing with temperatures below the material tg [5] In this regime, multiphoton absorption likely results in defect formation similar to that seen for ultraviolet—(UV-) induced index changes in photosensitive germanium doped silica glasses. A limitation of this technique is that lower pulse intensities need to be employed since high nonlinear absorption and group velocity dispersion would otherwise occur within the mask Such nonlinear absorption reduces the amount of light transmitted through the mask that is available to induce an index change in the fiber and simultaneously degrades the phase mask with time. We will summarize our investigations into the processes of ultrafast IR laser-induced FBGs with a phase mask along with many of the applications that have arisen from the use of this technique, such as direct fabrication of gratings through protective fiber coatings, fabrication of fiber laser cavities, and the fabrication of hightemperature-stable grating sensors
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