Nonlinear optical properties of microfiber resonators are investigated. First, a miniature optical resonator standing in air is realized out of a silica microfiber, and measurements of the intensity transfer function show a wide variety of hysteresis cycles obtained at low scanning frequency of the input power. The results are satisfactorily interpreted through the action of thermally-induced nonlinear phase shifts. Secondly, we discuss the conditions under which the fast Kerr nonlinearity can be used efficiently in microfiber resonators under pulsed optical operation.
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