No mirror Switch for ipad mini. Only speaker icon appear

After update to iOS version 9.3.1, I tried to mirror my ipad on computer. After check whether my ipad and computer are in the same network, I proceed to the airplay option. But after I get into airplay, I couldn't find mirror button. The only thing that I can see is the speaker icon in front of my computer name instead of the screen icon as usual. Anyone knows how to fix this problem?