Optical fibers have cores with diameters ranging from 10 to 50 microns. Optical signals are fed into the cores of these fibers using devices known as LD (laser diode) modules. Laser light generated by a high-output laser diode is passed through the lenses of the LD module to be fed into the fiber core. Two types of lens-an elliptical collimating lens and a rod-shaped line generation lens-are used to focus the laser beam and direct it towards the optical fiber core.