Laser beam scanning apparatus having a variable focal distance device and the variable focal distance device for use in the apparatus

摘要

In a variable density scanning apparatus, a variable focal distance device is provided in a scanning optical system. This variable focal distance device is formed of a light waveguide having a plurality of electrodes, of which the lengths along the direction of an incident laser beam are decreased or increased with the increase of the distance from the central electrode. The voltage to be applied between the electrodes is controlled in accordance with a desired dot pattern so as to change the refractive index of the light waveguide through which the laser beam is passed, thereby effectively changing the focal distance so that the diameter of the scanning laser beam spot can be changed in one dimension.