Optical memory device

Claim 1

An optical memory device for recording and reproducing signals on an amplitude detection type disc-type data recording medium, and which detects erroneous data writing, comprising: radiating means for radiating a recording light beam which is modulated in accordance with recording data; objective lens means for focusing the light beam from said radiating means onto said recording medium, said recording medium being arranged in a focal plane of said objective lens means, and said recording medium being movable relative to the focused light beam; photosensing means for detecting the light beam radiated from said radiating means and reflected by the recording medium, said photosensing means being arranged at a focal point of said objective lens means and including first and second segments placed so that one follows the other along a direction corresponding to the direction of relative movement between said recording medium and the focused light beam; subtracting means coupled to said photosensing means for calculating a difference between outputs from said first and second segments of said photosensing means, said first and said second segments and said subtracting means being operative so that said subtracting means produces an output corresponding to data recorded by the focused light beam on the recording medium after the data is recorded by said light beam and the recording medium moves relative to said light beam; and judging means coupled to the output of said subtracting means and to a source of the recording data for detecting an erroneous writing operation in accordance with the output from said subtracting means and the source of the recording data.