The current multi-touch interactions are mainly relying on the contact between objects and diplay screens, which is restricted in a two dimensional plane. To expand the dimension of human-machine interaction, we propose a kind of remote multi-point optical 'touch' technology in which users can control the displays from distant laser pens. The touching system consists of a laser pen used as touching light, double layered transparent optical films with sub-wavelength gratings, and photodetector arrays set around the sidewalls of the optical films. The working mechanism is: when the incident light hits the optical films, it will be converted to waveguide light propagating along the films by the gratings on the films and eventually reaches detectors on the sidewalls for position detection. In this work, touch time response up to millisecond level is superior to conventional optical touch technologies. The design overcomes the problem that the touch point caused by direct contact technology is beyond the reach of human body under the touch of large screen. Optical touch based on sub-wavelength grating couplers will make touch more intelligent and natural.