Laser Diode - Toshiba e-studio3511, e-studio4511 Manual

8.3 Laser Diode

The laser used in this equipment is a A1GaAs type semiconductive laser. It is generated in the single-
horizontal mode, and its wavelength is approx. 785 nm. This semiconductive laser outputs 10mW with
standard DC power supply. Laser intensity is controlled by using the output from the PIN diode for
monitoring light output in the semiconductive laser.
The relation between the current and optical output
of the semiconductive laser is as shown at right.
Light emission is started when the forward current
reaches or becomes larger than the threshold
current and outputs the monitor current which is
proportionate to the optical output. The threshold
current and monitor current differs depending on
each semiconductive laser. So optical output has
to be adjusted to maintain a constant value.
Since the optical output of the semiconductive laser
is decreased as the temperature of the laser rises,
APC control needs to be performed to maintain a
constant optical output.
Laser power
comparison
circuit
Fig. 8-302 shows a block diagram of the semiconductive laser control circuit. The semiconductive laser
performs monitor efficiency regulation (a process to control monitor current for the light amount), and
laser itself is adjusted to initial output emission of approx. 3.0 mW (approx. 408 µW on the drum surface).
The regulated voltage of the monitor output is feedback to the laser power comparison circuit. This
monitor output voltage is compared with the laser power voltage set for the control circuit for every
scanning. Laser driver circuit increases the forward current if the laser power is insufficient, and decreases
the current when the power is excessive to maintain a constant optical output.
November 2003 © TOSHIBA TEC
Power source
Laser driver
circuit
Constant
optical output
Monitor efficiency
regulation circuit
Fig. 8-302
8 - 7 e-STUDIO3511/4511 LASER OPTICAL UNIT
High temp.
Regulation
Low temp.
Forward current
Monitor current
Current (mA)
Threshold current
Fig. 8-301
Semiconductive laser
Monitor output
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