Patent ID: 7688874

Claim:
A semiconductor laser driving device, comprising: a current supply unit supplying current to a semiconductor laser; a first control unit controlling said current supply unit to supply a first current which is half or less of a lasing threshold of the semiconductor laser; a second control unit controlling said current supply unit to supply a second current which is larger than the lasing threshold after a first time is passed from an edge of a clock signal; an input unit inputting a signal representing light-emission intensity of the semiconductor laser, and a signal representing a second time from the edge of the clock signal to a start of light-emission of the semiconductor laser; a first decision unit deciding the first current based on the difference between the first and second times, the first current being the half or less of the lasing threshold; a second decision unit deciding the sum of the first and second current based on the light-emission intensity; and a third decision unit deciding the second current based on the sum and the decided first current.