Electronic Kerr effect in a polyfluorene derivative is used to reversibly switch near infrared probe beam resonantly coupled to a hybrid polymer-silica microspherical resonator. NIR pumping at 780 nm in pulsed laser regime is used for non-linear switching of the WGM resonances that shift as much as 2 GHz for 50 mW of average pump power, compared to a shift of 250 MHz for the same average pump power at CW regime. The absence of temporal drift and the magnitude of this shift confirm the Kerr nature of the switching, ruling out thermooptical effects.