Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1999-06-25
2003-11-11
Young, W. R. (Department: 2655)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S044120, C369S112150, C369S120000
Reexamination Certificate
active
06646975
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a semiconductor laser array and its manufacturing method, optical integrated unit, optical pickup and optical disk driving apparatus. More specifically, the invention relates to a semiconductor laser array for a short wavelength band and its manufacturing method; compact high-performance optical integrated unit, optical pickup and optical disk driving apparatus suitable for use in a compatible optical disk system such as DVD system ensuring compatibility with CD or CD-R, for example, using such a laser.
Optical disk systems are under wide practical use because they are compact but capable of recording a large amount of data. DVD (digital versatile disc) systems, in particular, are under rapid development toward practical use as major systems such as next-generation movies, ROMs and RAMs. On the other hand, CD (compact disc) systems or CD-R (compact disc-recordable) systems have been widely diffused for years, and DVD systems are desired to be compatible with CD systems. That is, DVD systems are required to be capable of reading and writing data on and from CDs or CD-Rs.
In these optical disc systems, an optical pickup using a semiconductor laser (LD) is used to read and write information on and from a disc.
FIG. 26
is an explanatory view showing a typical construction proposed as an optical pickup for conventional DVD systems. The optical pickup shown here has a compatibility with CDs, and includes an optical integrated unit
101
for DVDs and another optical unit
102
for CDs and CD-Rs.
Laser light of the wavelength 650 nm released from the DVD-compatible optical integrated unit
101
passes through a dichroic prism
103
, then through a collective lens
104
, re-orienting mirror
105
, wavelength selecting filter
106
and objective lens
107
, and reaches an optical disc
109
. On the other hand, laser light of the wavelength 780 nm released from the CD-compatible optical integrated unit
102
is first reflected by the prism
103
, then travels the same path as the laser light of 650 nm for DVDs, and reaches CD or CD-R
108
.
Return light from the disc travels the optical path in the opposite direction, and reaches the DVD-compatible optical integrated unit
101
or CD-compatible optical integrated unit
102
.
In general, since the spot size by the objective lens
107
is slightly different between CD
108
DVD-ROM disk
109
, the effective NA (numerical aperture) is changed by using the wavelength selecting filter
106
, for example.
Next explained is a conventional optical integrated unit used with the optical pickup shown above.
FIG. 27
is a perspective view schematically showing construction of typical conventional optical integrated units. Optical integrated units
101
,
102
have a stem
138
and a heat sink
141
mounted thereon. Adequately provided on the stem
138
are leads
109
for predetermined electrical connection. The heat sink
141
is made of a material having a good heat conductivity, such as copper, and a LD chip
135
and a detecting PD (photodiode)
136
are provided thereon. Monitoring PD
137
is provided behind the LD chip
135
to feedback-control the LD optical output.
Above those elements, a hologram element, not shown, is provided. A stem encapsulating cap is omitted from illustration in FIG.
27
.
Light released from the LD chip
135
in the direction shown with an arrow in
FIG. 27
reaches the disk through the path explained with reference to FIG.
26
. Return light from the disk is diffracted by the hologram, and enters the error detecting PD
136
as shown with an arrow in FIG.
27
. PD is divided into some regions for detecting the optical focus and tracking errors on the disk. For example, PD can be designed to equalize quantities of incident light among respective divisional regions when the disk is positioned at a focal point. If it moves from the focal point, then a difference is produced in quantities of incident light among the divisional regions. Therefore, by detecting it as a current difference, it is fed back via a mechanical servo mechanism, not shown, to return the disk to the focal point. Detection of errors in radial directions also follows the same process.
The conventional optical pickup, however, involved problems, namely, complicated construction, difficulty in reducing its size and weight, and the need for complicated assemblage. These problems are discussed below in greater detail.
In the conventional optical pickup shown in
FIG. 26
, beams of light from two different optical integrated units
101
,
102
must be synthesized into a single optical axis because the angular difference of light from LD relative to the optical axis of the pickup must be maintained minimum. For this purpose, it required optical parts like the dichroic prism
103
, and this resulted in complicating the construction, increasing the size, complicating the assembling process and increasing the cost.
Moreover, the conventional optical pickup is subject to degradation of the ratio of acceptable products through the assembling process because of the need for the process of adjusting optical axes of two different optical integrated units
101
,
102
used therein. That is, also for the positional accuracy (X, Y, &thgr;) of return light from the disk (diffracted light from the hologram), there is a strict requirement. Especially in DVD, the positional accuracy is desired to be within ±5 &mgr;m, ±0.50° between LD and PD. Even if the light from LD is within a desired accuracy, expected characteristics are not obtained unless relative positions of PD and LD in each optical integrated unit are held within the above-mentioned acceptable range. That is, since bifurcated optical integrated units are used, relative positional accuracy must be sufficiently high between two LDs and two PDs. The increased number of steps for adjustment required to realize it and degradation in the ratio of acceptable products of the pickup through assemblage are serious problems.
Furthermore, the use of two divisional optical integrated units limits miniaturization of the entirety. Especially when DVD systems are mounted in portable personal computers whose demand is expected to greatly grow in the future, reduction of the size and the weight is indispensable. However, it has been significantly difficult to reduce the size and the weight with the conventional structure as shown in FIG.
26
.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a high-performance semiconductor laser array of a multi-wavelength type and its manufacturing method, and to provide a compact, high-performance optical integrated unit, optical pickup and optical disk driving apparatus which can be realized by using such semiconductor lasers.
According to the invention, there is provided a semiconductor laser array comprising: a GaAs substrate; a first laser element portion provided on said substrate to release laser light of a first wavelength; and a second laser element portion provided on said substrate to release laser light of a second wavelength different from said first wavelength in a direction substantially parallel to the laser light of the first wavelength, said first laser element portion including a first cladding layer, an active layer formed by epitaxially growing a first semiconductor material on said first cladding layer, a second cladding layer formed on said active layer and a current-blocking layer to confine an electrical current injected into said first laser element portion, said second laser element portion including a first cladding layer, an active layer formed by epitaxially growing a second semiconductor material on said first cladding layer, a second cladding layer formed on said active layer and a current-blocking layer to confine an electrical current injected into said second laser element portion, and said current-blocking layer of said first laser element portion and said current-blocking layer of said second laser element portion are made of same semiconductor material.
Ac
Mori Kazushige
Shiozawa Hideo
Uchizaki Ichiro
Hogan & Hartson LLP
Young W. R.
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