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We report the development of a novel optical switching technique consisting of a silica microsphere optical resonator coated by a conjugated polymer. A 250-μm diameter silica microsphere was coated by dipping into a toluene solution of poly(2,5-dioctyloxy-1,4-phenylenevinylene). The resonator properties were characterized by evanescently coupling 1.55-μm light propagating along a stripline-pedestal antiresonant reflecting optical waveguide into optical whispering gallery modes (WGMs) of the microsphere. WGM resonant frequency shifts as large as 3.2 GHz were observed when 405-nm pump light with a power density of /spl sim/104 mW/cm2 was incident on the microsphere. The time constant of the observed frequency shifts is approximately 0.165 s, leading us to attribute the frequency shift to thermooptic effects. As microsphere resonators with WGM linewidths less than 2 MHz (corresponding to cavity Q>10/sup 8/) can be easily fabricated, initial measurements indicate that such a system is capable of thermooptically switching the WGM resonant frequency at speeds on the order of 100 ms.