an integrated optical device for magneto - optical recording and / or reading employs elements that may be fabricated on a substrate using semiconductor manufacturing technology . such elements include , but are not limited to , a system of waveguides for transmitting light energy beams from lasers to end portions of the waveguides exposed to the outside of the substrate , and from those end portions to detectors , so that reading , writing , focusing , and tracking operations may be performed . the waveguide systems include , e . g ., polarization controllers and mode splitters .