Optical scanning device, image forming apparatus, and controlling method

An image forming apparatus comprising an optical scanning device that includes:

• a vertical cavity surface emitting laser;
• a driving unit that controls modulation driving for the vertical cavity surface emitting laser;
• a coupling optical system that couples a beam output from the vertical cavity surface emitting laser;
• an aperture that is configured to define a beam spot diameter on a target surface;
• a deflecting unit that deflects a laser beam incoming from the aperture;
• and
• a scanning optical system that guides the laser beam incoming from the deflecting unit to the target surface, wherein
• the driving unit controls so as to satisfy conditions 1 and 2 below:
• P1>P100 condition 1
• Wm<Ws condition 2
• where P1 is an amount of light at a time after a period T1 corresponding to a minimum pixel unit has elapsed since beginning of light emission,
• P100 is an amount of light at a time after a time period of 100×T1 has elapsed since the beginning of light emission,
• Wm is a static beam spot diameter in a main-scanning direction, and
• Ws is a static beam spot diameter in a sub-scanning direction.

A controlling method employing an optical scanning device that includes:

• a vertical cavity surface emitting laser;
• a driving unit that controls modulation driving for the vertical cavity surface emitting laser;
• a coupling optical system that couples a beam emitted from the vertical cavity surface emitting laser;
• an aperture that is configured to define a beam spot diameter on a target surface;
• a deflecting unit that deflects a laser beam incoming from the aperture;
• and
• a scanning optical system that guides the laser beam incoming from the deflecting unit to the target surface,
• the controlling method comprising;
• controlling so as to satisfy conditions 1 and 2 below by the driving unit:
• P1>P100 condition 1
• Wm<Ws condition 2
• where P1 is an amount of light at a time after a period T1 corresponding to a minimum pixel unit has elapsed since beginning of light emission,
• P100 is an amount of light at a time after a time period of 100×T1 has elapsed since the beginning of light emission,
• Wm is a static beam spot diameter in a main-scanning direction, and
• Wm is a static beam spot diameter in a sub-scanning direction.