Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1995-11-29
2001-07-17
Shafer, Ricky D. (Department: 2872)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C257S082000, C257S098000, C359S507000, C359S514000, C359S831000, C359S833000
Reexamination Certificate
active
06262413
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a composite optical device and its manufacturing method suitable for a composite optical device in which an optical element such as prism, for example, is bonded to a support body with an adhesive.
2. Related Art
Among conventional composite optical devices of this type, there is a device called laser coupler. Such a conventional laser coupler used as an optical pickup of a CD player, for example, is shown in
FIGS. 1 and 2
.
FIG. 1
is a perspective view of the laser coupler, and
FIG. 2
is a longitudinal cross-sectional view of the same laser coupler. As shown in
FIGS. 1 and 2
, the laser coupler comprises a microprism
102
made of optical glass and a LOP (laser on photodiode) chip consisting of a photodiode
103
and a semiconductor laser
104
supported thereon, which are mounted on a photodiode IC
101
in a close relationship. The photodiode IC
101
includes a pair of photodiodes PD
1
and PD
2
for detecting an optical signal, a current-to-voltage (I-V) converting amplifier and an arithmetic processing unit (not shown) which all are incorporated into IC. The photodiode
103
is configured to monitor light output from a rear end surface of the semiconductor laser
104
and to control light output from a front end surface of the semiconductor laser
104
.
As shown in
FIG. 2
, the microprism
102
has a half mirror
105
on its slanted surface
102
a
, a total reflection film
106
on its top surface
102
b
, an antireflection film
107
on its bottom surface
102
c
, a mirror plane comprising its end surface
102
d
facing to the LOP chip, and a light absorbing film
108
on its end surface
102
e
opposite from the LOP chip. The antireflection film
107
on the bottom surface
102
c
of the microprism
102
is covered by a SiO
2
film
109
. The microprism
102
is mounted on the photodiode IC
101
by an adhesive
110
applied to the SiO
2
film
109
. The SiO
2
film
9
is used to reinforce the adhesive force of the adhesive
110
for holding the microprism
102
on the photodiode IC
101
. Used as the half mirror
105
is, for example, an amorphous Si film which is made by vacuum evaporation. Used as the total reflection film
106
is, for example, a dielectric multi-layered film including 20 layers of SiO
2
and 20 layers of TiO
2
which are stacked alternately. Used as the antireflection film
107
is, for example, a CeF
3
film. Used as the light absorbing film
108
is, for example, a Cr/CrO-based multi-layered film. In certain cases, the microprism
102
has a half mirror on one half of the antireflection film
107
on the bottom surface
102
c
located nearer to the LOP chip.
The laser coupler having the above construction is contained in a flat package
111
made of, for example ceramics, and sealed by a window cap, as shown in FIG.
3
.
As shown in
FIGS. 1 and 2
, in the laser coupler described above, a laser beam L exerted from the front end surface of the semiconductor laser
104
is reflected by the half mirror
105
on the slanted surface
102
a
of the microprism
102
, and runs toward a disc (not shown) for reading a signal from the laser beam L. The laser beam L reflected by the disc passes through the half mirror
105
and enters in the microprism
102
from its slanted surface
102
a
. One half of the beam enters into the photodiode PD
1
, and the other half beam enters into the photodiode PD
2
after sequentially reflected by the surface of the photodiode PD
1
and the top surface
102
b
of the microprism
102
. When the laser beam L focalizes on a recording plane of the disc, spot sizes on front and rear photodiodes PD
1
and PD
2
are equal; however, if the focalization is out of the recording plane, then the spot sizes on the photodiodes PD
1
and PD
2
differ from each other. Then, if the deviation of focalization appears as a difference between output signals from the photodiodes PD
1
and PD
2
, a focus error signal can be detected. The point where the focus error signal is zero corresponds to the point in which the focalized position lies on the recording plane of the disc, that is, the just focus point. By a feedback control of a focus servo system such that the focus error signal becomes zero, the just-focus state can be maintained, and the disc can be reproduced in a good condition.
Conventional laser coupler, as described above, are manufactured in the following method.
As shown in
FIG. 4
, a photodiode IC wafer
111
is first prepared through a given wafer process. Reference numeral
111
a
denotes a chip region corresponding to a single photodiode IC.
Next, as shown in
FIG. 5
, LOP chips are mounted on respective chip regions
111
a
of the photodiode IC wafer
111
by silver paste (not shown) and then subjected to an appropriate curing treatment.
In the next step, as shown in
FIG. 6
, bar-shaped microprisms
102
each extending over a plurality of chip regions
111
a
, e.g. ten chip regions, on the photodiode IC wafer
111
are provisionally fixed by using a silicone-resin-based adhesive (not shown) which cures when exposed to ultraviolet rays. After that, a curing treatment is effected, that is, the adhesive is set by irradiation of ultraviolet rays.
In the next step, the back surface of the photodiode IC wafer
111
is bonded to an extensible sheet (not shown). Then, as shown in
FIG. 7
, each bar-shaped microprism
102
is half-cut by using an appropriate dicer (dicing unit, not shown).
After that, each bar-shaped microprism
102
, adhesive
110
and photodiode IC wafer
111
are full-cut with the dicer to finally obtain separate chips, i.e. individual photodiode ICs, as shown in FIG.
8
.
Then the extensible sheet is extended to isolate the respective chips from each other, and each chip is picked up and packaged as shown in FIG.
3
.
In the conventional laser coupler manufacturing method described above, when the photodiode IC wafer
111
is full-cut by the dicer, the bar-shaped microprism
102
, adhesive
110
and photodiode IC wafer
111
are cut sequentially. In this cutting process, swarf is produced and adheres on the surfaces of the microprism
102
and the photodiode IC
101
. Since the slanted surface
102
a
and the top surface
102
b
of the microprism
102
behave as the plane of incidence of light and the light reflective plane, contamination of these surfaces adversely affect incidence and reflection of the laser beam L. To prevent this, the conventional method washes away the swarf by spraying water to the cut portion and the blade of the dicer during the cutting, and removes dust by spraying water and blowing dry air after the cutting.
Silicone resin, however, which is used as the adhesive
110
, has a stickiness, its swarf adheres onto the surfaces of the microprism
102
and other element and remains even after the washing mentioned above.
This problem is not limited to laser couplers but applies to composite optical devices, in general, which are made by bonding a bar-shaped optical element on a support body by means of an adhesive, especially a resin-based adhesive, and subsequently cutting the semi-product into individual devices with an appropriate dicer or a like apparatus. Therefore, there is a strong demand for solution of the problem.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a composite optical device and its manufacturing method which can effectively prevent contamination of surfaces of an optical element by swarf produced upon cutting the optical element, adhesive and support body.
The present inventors made efforts to solve the above problem, and realized that washing by sprayed water, etc. is insufficient to prevent adhesion of dust or swarf onto surfaces of microprisms and other optical elements while the semi-product is cut by a dicer and that this problem is not overcome unless using a structural improvement to prevent swarf or dust from staying on surfaces of the optical element. As a result of a further progress of the study, the present inventors found that
Fujimaki Yoshitsugu
Taniguchi Tadashi
Shafer Ricky D.
Sonnenschein Nath & Rosenthal
Sony Corporation
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