A compact and low cost microscope illuminator capable of generating 3-D optical images includes a first light source and a second light source. The two light sources lead two optical paths: one to illuminate a sample and another to project a pattern onto the focal plane of a microscope objective lens. The two light sources are controlled by a processor and can be turned on and off rapidly. A 3-D optical microscope equipped with said microscope illuminator and a method of creating a 3-D image on said 3-D optical microscope are also described.