A fiber optic rotary coupler is invented using both single mode and multi-mode optic fibers. This device has a rotatable optic fiber and a stationary optic fiber in an assembly to convey a light beam in the optic fibers. The assembly also includes a stationary fiber holder for fixing the tip of stationary optic fiber in a central hole and a rotatable fiber holder for fixing the body of the rotatable optic fiber with the tip of the rotatable fiber protruding out of the rotatable fiber holder. The two fiber holders can be rotated relatively each other so as to allow the tip of rotatable optic fiber to rotate in the central hole on the stationary fiber holder with the tips of the two optic fibers adjacent very closely.