High Power Laser Diode
that Achieves High-Speed CD-R Recording
SLD234VL
In the optical disc area, including CD, MD, and now DVD as well,
Sony continues to lead the industry.
The laser diode is the critical device in optical disc systems, and
Sony continues to provide the most advanced technology in this
area as well.
Now, Sony has developed a new high power laser diode for CD-R
recording, an area with increasing demand as a large-capacity com-
puter data storage medium.
The SLD234VL achieves the high power levels of 60 mW in CW
(continuous wave) mode and 80 mW in pulsed mode and thus makes
4
× speed CD-R recording a possibility.
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Real index guide laser
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High power:
60 mW CW, 80 mW pulsed
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Low operating current:
Iop = 70 mA at 50 mW CW (Iop = 100
mA at 80 mW pulsed mode)
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High reliability
VOICE
The key point for this device was
to achieve the highest possible
power while still assuring reliabil-
ity. Thus, while the directions in
which we should proceed were
naturally limited, from those
possibilities we determined which
aspects to aim for based on current
requirements and costs, and by
introducing new technologies as
well, arrived at the product
described here. I think this device
can also be applied to high-speed
recording in other optical discs as
well as CD-R. I hope you will
consider this product for your
other applications as well.
The following points must be consid-
ered to achieve both high power and
high reliability in laser diodes.
· Lowering the density of the light at the
point the light is emitted to prevent
melting of the crystals in the laser
diode itself by the emitted light.
· Increasing the efficiency with which
the supplied current is converted to
light.
· Suppressing absorption of light within
the semiconductor material.
We adopted the structure described
below, which is made possible by
Sony’s superlative MOCVD crystal
growth technology that allows nanom-
eter order (a nanometer is one billionth
of a meter) fine control, and achieved
both high power and high reliability.
Multi-Quantum Well
Structure
A multi-quantum well (MQW) structure
is adopted in the active layer in the
SLD234VL. This technique acquires
quantum effects by making the layers
that contribute to active layer optical
emissions extremely thin, having thick-
nesses of about 10 nm, and thus
achieves even more efficient optical
conversion. Also, optical enclosure was
suppressed by reducing the thickness of
the whole of the active layer region,
which reduced the optical density at the
emission point.
Real Index Guide Structure
A real index guide structure, which has
minimal internal absorption is used as
the laser diode internal optical
waveguide. (See figure 1.) Improve-
ments to the crystal growth and fabri-
cation processes that started with an
analysis of this structure resulted in a
60% reduction in internal absorption in
sections other than the optically active
sections as compared to the earlier Sony
SLD203BVL. Figure 2 shows the
characteristics of the SLD234VL which
result from this concentration of tech-
nology. This device achieves an
operating current, Iop, of 70 mA at 50
mW CW and 100 mA at 80 mW pulsed,
and exhibits no crystal melting even at
150 mW in pulsed mode. (See figure
2-1.) The FFP (far field pattern) is 8.8
degrees (typical) for the active layers in
the horizontal direction (
θ ⁄⁄), and is 22
degrees (typical) for the active layers in
the vertical direction (
θ⊥). (See figure
2-2.) Also, the oscillation wavelength
is 784 nm (typical), which matches the
sensitivity of CD-R discs. (See figure
2-3.) In addition, this device has super-
lative thermal characteristics, and, as
shown in figure 3, can operate at over
100 mW in pulsed mode even at 80
°C.
In reliability testing, no degradation was
seen after 1000 hours of 80 mW pulsed
mode operation at 75
°C, and thus this
device provides more than adequate
reliability for practical application. (See
figure 4.)
Sony will continue striving to develop
devices with even higher power.
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