The recently observed laser wavelength self-sweeping is known for its large sweeping range up to tens of nanometers, single- or few-longitudinal mode operation and self-pulsing output [1-5]. The self-sweeping can be explained by spatial hole burning along the active fiber. The spatial hole burning cause also weak refractive index modulation [6-7]. Self-swept fiber lasers recently attained attention thanks to its practical applications in laser spectroscopy and fiber sensor systems as well as revealing physical insight view into important laser physics phenomena, e.g., the origin of self-Q-switching regime and longitudinal mode-instabilities in fiber lasers.
We present evaluation of the reflectivity of superimposed transient fiber Bragg gratings (FBG) using a numerical model of fiber laser with refractive index gratings build-up. In contrast to single refractive index grating demonstrated earlier [6-7] we present more realistic case of several superimposed gratings with damped modulation depth. We show that the 100 % reflectivity and thus sudden enhancement of the cavity Q-factor can be easily achieved despite small modulation depth of the gratings. The differences of reflectivities of the single FBG and of the multiple superimposed damped FBGs are discussed. This work was supported by the Czech Science Foundation, project No. 16-13306S.
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 P. Peterka, P. Honzátko, P. Koška, F. Todorov, J. Aubrecht, O. Podrazký, and I. Kašík, "Reflectivity of transient Bragg reflection gratings in fiber laser with laser-wavelength self-sweeping," Opt. Express 22:30024-30031, 2014.
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Pavel Peterka, Pavel Koška, and Jirí Ctyroký, "Reflectivity of superimposed transient gratings in self-swept fiber lasers (Conference Presentation)," Proc. SPIE 10232, Micro-structured and Specialty Optical Fibres V, 1023208 (Presented at SPIE Optics + Optoelectronics: April 26, 2017; Published: 25 January 2018); https://doi.org/10.1117/12.2266696.5463398304001.
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Study of self-shadowing effect as a simple means to realize nanostructured thin films and layers with special attentions to birefringent obliquely deposited thin films and photo-luminescent porous silicon