Laser driving device, optical scanning device, and image forming apparatus

#The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2010-132727 filed in Japan on Jun. 10, 2010.

#1. Field of the Invention

#The present invention relates to a laser driving device, an optical scanning device, and an image forming apparatus, and more specifically relates to a laser driving device including a semiconductor laser driving circuit that controls a light output from, for example, a light source of a laser printer, an optical disk device, a digital copying machine, an optical communications apparatus, and an optical scanning device including the laser driving device, and an image forming apparatus including the optical scanning device.

#FIGS. 1A1 to 1C2 are schematics illustrating droop characteristics of a typical semiconductor laser;

#FIGS. 2A1 to 2C2 are schematics exemplarily illustrating high-speed optical response waveforms of the typical semiconductor laser;

#FIG. 3 is a schematic illustrating an exemplary structure of a laser driving device according to the present embodiment;

#Characteristics of a laser and driving control of the laser are generally described below prior to the description of an embodiment according to the present embodiment. FIGS. 1A1 to 1C2 illustrate droop characteristics of a typical semiconductor laser. In FIGS. 1A1 to 1C2, illustrated are relations between driving current 1, 2, and 3 and waveforms of light outputs (light waveforms). The driving currents 1, 2, and 3 have three different driving current levels. In FIGS. 1A1 to 1C2, ΔP is roughly depicted as a same value regardless of the levels of the driving currents for ease of explanation. However, it is known that the value actually slightly fluctuates. The value, however, can be almost the same regardless of the levels of the driving currents because the fluctuation amount does not change with a driving current change, i.e., a peak light amount change.

#In a typical laser, it is known that an absolute amount of a droop due to an efficiency drop caused by self-heating of the laser does not really depend on a light amount. Accordingly, as illustrated in FIGS. 1A1 to 1C2, the light outputs drop by almost the same power (ΔP) regardless of the levels of the driving currents. Because of almost the same power drop, the more influenced by the droop characteristic of the semiconductor laser is the smaller light amount one (a light output under a steady state); because a ratio of the power drop to a peak light amount (initial light output) becomes larger, i.e., a ratio of light amount fluctuation becomes larger.

#In order to achieve a more uniform light amount, i.e., more uniform image density, it is preferable that the light amount of the semiconductor laser is increased so that the semiconductor laser is used in an operational condition in which the effect (ratio) of a droop with respect to a peak light amount is further reduced. For example, when a semiconductor laser is used in an image forming apparatus, the driving current 1 is suitable for achieving a uniform image density out of driving currents in FIGS 1A1, 1B1 and 1C1; because the driving current 1 has a large driving current value and a large light emission amount as illustrate in FIGS. 1A1 and 1A2, so that the droop value is relatively small. As a result, more stable images can be formed.