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25 April 2012 Microstructure-assisted grating inscription in photonic crystal fibers
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One of the recent methods of grating inscription is based on inducing an array of highly localized index changes in the silica core of a fiber by tightly focused high intensity laser pulses. There were already several reports of such point-by-point gratings in conventional step index fibers. Applying this technique to photonic crystal fibers (PCFs) is still not straightforward. The main reason is the air holed microstructure which distorts the wave front of the inscribing laser beam and counters the focusing of the light in the core. We propose a new concept of microstructure-assisted grating inscription in photonic crystal fibers by introducing a focusing microstructure in the cladding of the fiber. We designed special types of photonic crystal fibers with a photonic crystal Mikaelian lens (PCML) in their cladding. Such a PCML is the implementation of a conventional Mikaelian or gradient index lens in a photonic crystal lattice. The effective index variation in a PCML is achieved via a variable air hole radius. In a fiber that is equipped with a PCML the inscribing laser beam can be tightly focused to the fiber core. This concept allows increasing optical power densities in the core of a PCF by an order of magnitude. We present a numerical model of a PCF with a PCML designed for 800 nm wavelength 125 femtosecond laser pulses.
© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Tigran Baghdasaryan, Thomas Geernaert, Francis Berghmans, and Hugo Thienpont "Microstructure-assisted grating inscription in photonic crystal fibers", Proc. SPIE 8426, Microstructured and Specialty Optical Fibres, 842606 (25 April 2012);

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