Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
1998-02-24
2001-03-13
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C250S216000, C250S225000, C369S044140
Reexamination Certificate
active
06201228
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improvement in an optical pickup used in an optical recording and reproducing apparatus for recording and reproducing of an optical recording medium such as a magneto-optical disk. More specifically, the present invention relates to an improvement in an optical pickup integrated with optical system.
2. Description of the Background Art
When a signal recorded on a magneto-optical disk is reproduced by using an optical pickup, a beam of linearly polarized light is directed to the magneto-optical disk by the optical pickup. The plane of polarization of the beam reflected from the magneto-optical disk is rotated to right or left slightly dependent on magnetic direction on the magneto-optical disk by Kerr effect. With this reflected beam being passed through an analyzer, the direction of rotation of plane of polarization of the beam is detected as a variation in the amount of light, and recorded signal is reproduced.
FIG. 9
is a plan view of an optical pickup employing an optical waveguide device for a magneto-optical disk disclosed in Japanese Patent Laying-Open No.
8-171747.
FIGS. 10 and 11
are a side view and a plan view respectively, of the optical waveguide device shown in FIG.
9
.
When a signal recorded on the magneto-optical disk is to be detected (reproduced), the optical pickup generally directs a beam emitted from a laser diode to the magneto-optical disk. The beam is reflected and splitted into a beam for detecting a servo error signal and a beam for detecting the recorded signal, and the splitted beams are used by the optical pickup for detecting signals. At this time, a beam splitter is used for splitting the beam.
In the optical pickup PC
1
shown in
FIG. 9
, a beam
102
emitted from laser diode
101
provided in a package
118
is divided into a main beam and a tracking beam by a grating
103
in package
118
, passed through a hologram
104
in package
118
, and incident on a beam splitter
105
formed by adhering a plate glass
113
and a prism
114
. The beam entering beam splitter
105
is reflected by a mirror at an interface a between plane glass
113
and prism
114
, passes through a collimator lens
106
, reflected vertically upward by a mirror
107
, and collected onto the magneto-optical disk (not shown) by an objective lens
108
.
Thereafter, the beam reflected from the magneto-optical disk passes through objective lens
108
, mirror
107
and collimator lens
106
and enters beam splitter
105
, where the beam is splitted into a beam
109
for detecting a servo error signal, and a beam
110
for detecting the recorded signal. Beam
109
enters from beam splitter
105
to hologram
104
, where the beam is diffracted, and thereafter the beam enters a photodiode
111
and detected by photodiode
111
as a servo error signal. Beam
110
is reflected by a mirror surface on a rear surface b of plane glass
113
which constitutes beam splitter
105
, and therefore, it does not pass through hologram
104
but enters a coupler portion of optical waveguide device
112
. Beam
110
which is coupled to the optical waveguide at this coupler portion is divided into TE beam and TM beam, and enter a photodetector, where the beams are detected (reproduced) as the information signal.
Referring to
FIGS. 10 and 11
, the coupler portion of optical waveguide device
112
will be described. The coupler portion includes a prism
121
and a microlens
122
. Beam
110
reflected at the surface b of beam splitter
105
passes the right side of hologram
104
, enters package
118
and is once converged and thereafter diverged. Then, the beam passes through microlens
122
and enters prism
121
. At this time, the diverged beam
110
is converted to a collimated beam by microlens
122
provided on prism
121
, and the collimated beam is coupled to optical waveguide
123
at a prescribed incident angle. The beam coupled to optical waveguide
123
is divided into TE and TM beams by a polarized beam splitter
129
, and detected (reproduced) as the information signal, by photodiode
124
.
In optical pickup PC
1
of
FIG. 9
, laser diode
101
and optical waveguide device
112
are attached to package
118
and, thereafter, beam splitter
105
is attached to package
118
. Therefore, offset in the position of attachment of optical waveguide
112
, or relative positional offset between the beam reflected from the magneto-optical disk and optical waveguide device
112
caused by error in manufacturing plate glass
113
of beam splitter
105
must be compensated for by position adjustment of beam splitter
105
.
FIG. 12
shows a principle of compensation of the relative positional offset between the beam reflected from the magneto-optical disk and optical waveguide device
112
by adjusting attitude of beam splitter
105
shown in FIG.
9
. Referring to
FIG. 12
, assume that optical waveguide device
112
is arranged offset in the direction of the arrow Y. At this time, the beam emitted from laser diode
101
proceeds along an optical path L
101
, is reflected by a surface a of prism
114
, proceeds along an optical path L
102
and is incident on the magneto-optical disk. Thereafter, the beam reflected from the magneto-optical disk proceeds along optical path L
102
, is reflected at surface b of plate glass
113
and proceeds along an optical path L
103
to optical waveguide device
112
. At this time, assume that relative position between optical path L
103
and optical waveguide device
112
is offset. When beam splitter
105
is rotated by &thgr; about the X axis, the beam reflected from the magneto-optical disk would proceed along optical paths L
202
→L
203
denoted by the dotted lines, and correctly enter optical waveguide device
112
.
In the optical pickup PC
1
of
FIG. 9
, beam splitter
105
is arranged between collimator lens
106
and hologram
104
, which means that it is at a considerable distance from the light source, and therefore it requires a large effective aperture (the scope through which the beam passes in beam splitter
105
). As a result, beam
110
converges very close to a lower surface of a member
117
on which grating
103
is formed, and therefore the point of convergence cannot directly be coupled to optical waveguide
123
. From this reason, microlens
122
for converting the divergent beam
110
to a collimated beam has been required. Focal distance of microlens
122
is about 1 mm. It is difficult to form a lens having such a short focal distance on prism
121
of the coupler.
Further, since the surface a is inclined when the attitude of beam splitter
105
is adjusted, optical path L
101
of the beam emitted from laser diode
101
is offset from the original optical path L
102
by
2
&thgr;, to optical path L
202
. As a result, the center of the beam emitted from laser diode
101
may possibly be offset from the center of collimator lens
106
, or the collimated beam emitted from collimator lens
106
may proceed obliquely. It has been difficult to work out and apply a solution to such problems.
Further, in the optical pickup PC
1
shown in
FIG. 9
, in order that one main beam spot and two tracking beam spots have matched orientation on a track of the magneto-optical disk, a separate mechanism for rotating package
118
containing laser diode
101
and beam splitter
105
about an optical axis (see chain-dotted line CL in the figure) of collimator lens
106
has been required.
The beam emitted from laser diode
101
, passed through surface a and reflected at surface b is reflected from the magneto-optical disk and is detected (reproduced) as a signal by a photodetector. In order to prevent deterioration of quality of the detected signal, it has been necessary to form an antireflection film
116
partially at a portion of surface b which opposes to laser diode
101
. This lowers efficiency in mass production of beam splitter
105
.
Further, since optical waveguide device
112
is directly arranged in package
118
, three-dimensional positional adjustm
Conlin David G.
Dike Bronstein, Roberts & Cushman LLP
Le Que T.
Sharp Kabushiki Kaisha
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