Abstract: An ultrahigh-resolution fiber-optic confocal microscope has an illumination system; three single-mode optical fibers, each optically coupled to a fiber coupler; a sample support stage arranged to receive illumination radiation from an end of one of the single-mode optical fibers; a detector arranged to receive output radiation from one of the single-mode optical fibers; and a lock-in amplifier electrically connected to the detector and the illumination system. The illumination system is adapted to provide illumination radiation that has a time-varying strength that is correlated with the detector by the lock-in amplifier.