Method and device for controlling semiconductor laser

A semiconductor laser control device comprising:

• a semiconductor laser permitting a light amount control in accordance with current;
• light amount monitoring means for monitoring a light amount of said semiconductor laser;
• feedback control means for controlling a feedback of said light amount of said semiconductor laser with a predetermined time constant based on a monitoring result from said light amount monitoring means;
• low pass filter for passing a low frequency component of a monitoring signal from said light amount monitoring means;
• and
• selecting means for inputting a light amount monitoring signal to a feedback control means without passing through a low pass filter till the light amount of said semiconductor laser reaches a first light amount not being zero, based on said monitoring result from said light amount monitoring means, and inputting said monitoring signal from said light amount monitoring means to said feedback control means through said low pass filter when the light amount of said semiconductor laser is larger than said first light amount.

A semiconductor laser control device comprising:

• a semiconductor laser permitting a light amount control in accordance with current;
• light amount monitoring means for monitoring a light amount of said semiconductor laser;
• feedback control means for controlling a feedback of said light amount of said semiconductor laser with a predetermined light amount based on a monitoring result from said light amount monitoring means;
• low pass filter for passing a low frequency component of a monitoring result from said light amount monitoring means;
• and
• selecting means for first inputting said monitoring signal from said light amount monitoring means to said feedback control means through said low pass filter after a first period of time not being zero when a light amount is larger than a second light amount not being zero based on said monitoring result from said light amount monitoring means and for second inputting said light amount monitoring signal to said feedback control means via no low pass filter during time period other than said first inputting operation.

A semiconductor laser control device comprising:

• a semiconductor laser permitting a light amount control in accordance with current;
• light amount monitoring means for monitoring a light amount of said semiconductor laser;
• feedback control means for controlling a feedback of said light amount of said semiconductor laser with a predetermined light amount based on a monitoring result from said light amount monitoring means;
• low pass filter for passing a low frequency component of a monitoring result from said light amount monitoring means;
• on/off control means for controlling the on/off operation of said semiconductor laser;
• and
• selecting means for first inputting a monitoring signal from said light amount monitoring means to said feedback control means via said low pass filter after a second period of time not being zero when semiconductor laser has been changed from an off state to an on state by said on/off control means and for second inputting said light amount monitoring signal to said feedback control means via no low pass filter, during time period other than said first inputting operation.