Semconductve laser

8.3 Laser Diode

The laser used in this equipment is a AlGaAs type semiconductive laser. It is generated in the single- horizontal mode, and its wavelength is approx. 785 nm. This semiconductive laser outputs 5mW 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.

)

Regulaton

Hgh temp.

mW

 

 

 

 

 

Light emission is started when the forward cur-

(

 

 

 

 

Output

 

 

 

 

rent reaches or becomes larger than the threshold

Low temp.

 

 

current and outputs the monitor current which is

calOpt

 

 

 

 

proportionate to the optical output. The threshold

 

 

 

 

 

 

 

 

 

current and monitor current differs depending on

 

 

 

Forward current

 

 

 

Montor current

each semiconductive laser. So optical output has

 

 

 

 

 

 

 

 

to be adjusted to maintain a constant value.

 

 

Current (mA)

 

 

 

 

 

 

 

Since the optical output of the semiconductive

 

 

 

 

 

 

Threshold current

 

 

laser is decreased as the temperature of the la-

 

Fig. 8-301

 

 

 

 

 

 

ser rises, APC control needs to be performed to maintain a constant optical output.

Power source

8

Laser power comparson crcut

Laser drver crcut

Montor eff- cency regula- ton crcut

Constant

optcal output

Montor output

Fig. 8-302

Fig. 8-302 shows a block diagram of the semiconductive laser control circuit. The semiconductive la- ser 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. 2.11 mW (approx. 421 µW on the drum surface). The regulated voltage of the monitor output is fed back to the laser power comparison cir- cuit. 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.

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e-STUDIO350/352/353/450/452/453

 

LASER OPTICAL UNIT

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Toshiba 353 Laser Diode, Light emission is started when the forward cur, Rent reaches or becomes larger than the threshold
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350, 353, 453, 452 specifications

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