Abstrict A silicon base optical waveguide manufacturing method including
the steps of preparing a silicon wafer having a plurality of embedded
optical waveguides, performing first-stage dicing of the silicon
wafer to form a cut groove by using a first resin diamond blade
having a thickness t1 and performing second-stage dicing of the
silicon wafer along the cut groove to polish an end face of each
optical waveguide by using a second resin diamond blade having a
thickness t2 greater than the thickness t1. The second resin diamond
blade includes diamond abrasive grains having a grain diameter of
2 .mu.m or less, and the relation between the thicknesses t1 and
t2 is set to t1+0.01 mm.ltoreq.t2.ltoreq.t1+0.05 mm.
Claims What is claimed is:
1. A silicon base optical waveguide manufacturing method comprising
the steps of: performing first-stage dicing of a silicon wafer having
a silicon substrate and a plurality of optical waveguides formed
on said silicon substrate to form a cut groove by using a first
resin diamond blade having a thickness t1; and performing second-stage
dicing of said silicon wafer along said cut groove to polish an
end face of each of said optical waveguides by using a second resin
diamond blade having a thickness t2 greater than said thickness
t1; said second resin diamond blade including diamond abrasive grains
having a grain diameter of 2 .mu.m or less; the relation between
said thickness t1 and said thickness t2 being set to t1+0.01 mm.ltoreq.t2.ltoreq.t1+0.05
mm.
2. A silicon base optical waveguide manufacturing method according
to claim 1 wherein said second resin diamond blade further includes
cerium oxide abrasive grains having an average grain diameter of
0.1 to 5.0 .mu.m and a purity of 35 to 95 wt %.
3. A silicon base optical waveguide manufacturing method according
to claim 2 wherein: the total content of said diamond abrasive
grains and said cerium oxide abrasive grains with respect to the
volume of said second resin diamond blade is 20 to 40 vol %; and
the content of said cerium oxide abrasive grains with respect to
the total volume of said diamond abrasive grains and said cerium
oxide abrasive grains is 35 to 70 vol %.
4. A silicon base optical waveguide manufacturing method according
to claim 2 wherein the rotational speed of said first and second
resin diamond blades is 10000 to 30000 rpm, and the depth of cut
per stroke is 0.02 to 1.5 mm.
5. A silicon base optical waveguide manufacturing method according
to claim 4 wherein the feed speed of said silicon wafer is 0.1
to 1.5 mm/sec in cutting said optical waveguides and 0.1 to 5.0
mm/sec in cutting said silicon substrate.
6. A silicon base optical waveguide manufacturing method comprising
the steps of: bonding a first silicon wafer having a plurality of
optical waveguides on a second silicon wafer; performing first-stage
dicing of said first and second silicon wafers to form a first cut
groove by using a first resin diamond blade having a thickness t1;
and performing second-stage dicing of said first and second silicon
wafers along said first cut groove to form a second cut groove shallower
than said first cut groove by using a second resin diamond blade
having a thickness t2 greater than said thickness t1; said second
resin diamond blade including diamond abrasive grains having a grain
diameter of 2 .mu.m or less.
7. A silicon base optical waveguide manufacturing method according
to claim 6 wherein said second resin diamond blade further includes
cerium oxide abrasive grains having an average grain diameter of
0.1 to 5.0 .mu.m and a purity of 35 to 95 wt %.
8. A silicon base optical waveguide manufacturing method according
to claim 7 wherein: the total content of said diamond abrasive
grains and said cerium oxide abrasive grains with respect to the
volume of said second resin diamond blade is 20 to 40 vol %; and
the content of said cerium oxide abrasive grains with respect to
the total volume of said diamond abrasive grains and said cerium
oxide abrasive grains is 35 to 70 vol %.
9. A resin diamond blade comprising: diamond abrasive grains having
a grain diameter of 2 .mu.m or less; cerium oxide abrasive grains
having an average grain diameter of 0.1 to 5.0 .mu.m and a purity
of 35 to 95 wt %; a bonding resin for bonding said diamond abrasive
grains and said cerium oxide abrasive grains; the total content
of said diamond abrasive grains and said cerium oxide abrasive grains
with respect to the volume of said resin diamond blade being 20
to 40 vol %; and the content of said cerium oxide abrasive grains
with respect to the total volume of said diamond abrasive grains
and said cerium oxide abrasive grains being 35 to 70 vol %.
10. A resin diamond blade according to claim 9 wherein said cerium
oxide abrasive grains have an average grain diameter of about 3
.mu.m and a purity of about 60 wt %.
11. A resin diamond blade according to claim 9 wherein: the total
content of said diamond abrasive grains and said cerium oxide abrasive
grains with respect to the volume of said resin diamond blade is
about 25 vol %; and the content of said cerium oxide abrasive grains
with respect to the total volume of said diamond abrasive grains
and said cerium oxide abrasive grains is about 50 vol %.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resin diamond blade and a silicon
base optical waveguide manufacturing method using the blade.
2. Description of the Related Art
An optical device using an optical waveguide is becoming increasingly
necessary with the evolution of optical communication, and the development
of optical components such as an optical brancher/coupler, optical
multiplexer/demultiplexer, optical modulator, optical switch, and
optical wavelength converter is accordingly becoming important.
Typical examples of the optical waveguide well known in the art
include an optical waveguide formed by diffusing Ti in a single-crystal
substrate of LiNbO.sub.3 an optical waveguide formed by depositing
SiO.sub.2 on a silicon substrate, and a polymer optical waveguide.
A light incidence end face and a light emergence end face of the
optical waveguide correspond to portions for optical coupling of
lightwaves propagating in the optical waveguide and lightwaves propagating
outside of the optical waveguide. Accordingly, the finished condition
of each end face has an important effect on optical loss in the
whole of the optical waveguide device.
Each end face of the optical waveguide is conventionally formed
by various techniques such as polishing, cleaving, and cutting.
The formation of the end face by polishing is superior both in surface
roughness of a finished surface and in generation rate of chipping,
and this technique is applied to a LiNbO.sub.3 optical waveguide
and a so-called silicon base optical waveguide formed by depositing
SiO.sub.2 on a silicon substrate. However, much time is required
for polishing, causing a reduction in throughput and an increase
in working cost. The formation of the end face by cleaving is applied
to a semiconductor optical waveguide of GaAs, for example, and this
technique has an advantage that the end face can be quickly obtained
with smoothness at a crystal lattice level. However, since this
technique is a method utilizing the anisotropy of crystal, the application
of this method is limited to a high-cleavage orientation of a high-cleavage
material, and this method cannot be applied to a low-cleavage material.
To the contrary, the formation of the end face by abrasive cutting
using a diamond blade or the like is applicable also to a low-cleavage
material. Moreover, this technique is superior in throughput and
working cost because the end face can be formed faster than polishing.
Accordingly, this abrasive cutting method has recently been examined
as a method for forming the end faces of various optical waveguides.
For example, Japanese Patent Laid-open No. Hei 8-68913 discloses
a technique of simultaneously performing dicing of a silicon wafer
and polishing of the end face of a silicon base optical waveguide
by using a resin bonded diamond blade for cutting the optical-waveguide.
According to this method described in the above publication, the
silicon wafer having the optical waveguide is mounted on a bonded
structure, and the resin bonded diamond blade is rotated at a high
speed (18000-35000 rpm) to cut the silicon wafer being fed at
an appropriate speed, thereby simultaneously performing dicing of
the silicon wafer and polishing of the end face of the optical waveguide.
The optical waveguide manufacturing method described in the above
publication has been followed by the present inventor. As the result,
it has been found that the smoothness of the end face of the optical
waveguide is insufficient and it cannot be put to practical use
unless additional polishing is performed. That is, the end face
of the optical waveguide must have a surface roughness (smoothness)
of .lambda./4 or less where .lambda. is the wavelength of light
for use, so as to sufficiently suppress optical loss in the whole
of the optical waveguide device. However, such a smooth end face
cannot be obtained by the method described in the above publication,
according to the test made by the present inventor.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
silicon base optical waveguide manufacturing method which can form
a satisfactory end face of each optical waveguide.
It is another object of the present invention to provide a resin
diamond blade which can perform polishing of the end face of each
optical waveguide simultaneously with dicing of a silicon wafer.
In accordance with an aspect of the present invention, there is
provided a silicon base optical waveguide manufacturing method comprising
the steps of performing first-stage dicing of a silicon wafer having
a silicon substrate and a plurality of optical waveguides formed
on the silicon substrate to form a cut groove by using a first resin
diamond blade having a thickness t1; and performing second-stage
dicing of the silicon wafer along the cut groove to polish an end
face of each of the optical waveguides by using a second resin diamond-blade
having a thickness t2 greater than the thickness t1. The second
resin diamond blade includes diamond abrasive grains having a grain
diameter of 2 .mu.m or less. The relation between the thickness
t1 and the thickness t2 is set to t1+0.01 mm.ltoreq.e t2.ltoreq.t1+0.05
mm.
Preferably, the second resin diamond blade further includes-cerium
oxide abrasive grains having an average grain diameter of 0.1 to
5.0 .mu.m and a purity of 35 to 95 wt %. More preferably, the total
content of the diamond abrasive grains and the cerium oxide abrasive
grains with respect to the volume of the second resin diamond blade
is 20 to 40 vol %. Further the content of the cerium oxide abrasive
grains with respect to the total volume of the diamond abrasive
grains and the cerium oxide abrasive grains is 35 to 70 vol %. Further,
the rotational speed of the first and second resin diamond blades
is 10000 to 30000 rpm, and the depth of cut per stroke is 0.02
to 1.5 mm. More preferably, the feed speed of the silicon wafer
is 0.1 to 1.5 mm/sec in cutting the optical waveguides and 0.1 to
5.0 mm/sec in cutting the silicon substrate.
In accordance with another aspect of the present invention, there
is provided a silicon base optical waveguide manufacturing method
comprising the steps of bonding a first silicon wafer having a plurality
of optical waveguides on a second silicon wafer; performing first-stage
dicing of the first and second silicon wafers to form a first cut
groove by using a first resin diamond blade having a thickness t1;
and performing second-stage dicing of the first and second-silicon
wafers along the first cut groove to form a second cut groove shallower
than the first cut groove by using a second resin diamond blade
having a thickness t2 greater than the thickness t1. The second
resin diamond blade includes diamond abrasive grains having a grain
diameter of 2 .mu.m or less.
Preferably, the second resin diamond blade further includes cerium
oxide abrasive grains having an average grain diameter of 0.1 to
5.0 .mu.m and a purity of 35 to 95 wt %.
In accordance with a further aspect of the present invention, there
is provided a resin diamond blade comprising diamond abrasive grains
having a grain diameter of 2 .mu.m or less; cerium oxide abrasive
grains having an average grain diameter of 0.1 to 5.0 .mu.m and
a purity of 35 to 95 wt %; and a bonding resin for bonding the diamond
abrasive grains and the cerium oxide abrasive grains. The total
content of the diamond abrasive grains and the cerium oxide abrasive
grains with respect to the volume of the resin diamond blade is
20 to 40 vol %; the content of the cerium oxide abrasive grains
with respect to the total volume of the diamond abrasive grains
and the cerium oxide abrasive grains being 35 to 70 vol %.
Preferably, the cerium oxide abrasive grains have an average grain
diameter of about 3 .mu.m and a purity of about 60 wt %. Further,
the total content of the diamond abrasive grains and the cerium
oxide abrasive grains with respect to the volume of the resin diamond
blade is about 25 vol %. The content of the cerium oxide abrasive
grains with respect to the total volume of the diamond abrasive
grains and the cerium oxide abrasive grains is about 50 vol %.
The above and other objects, features and advantages of the present
invention and the manner of realizing them will become more apparent,
and the invention itself will best be understood from a study of
the following description and appended claims with reference to
the attached drawings showing some preferred embodiments of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a dicing device usable in the optical
waveguide manufacturing method according to the present invention;
FIG. 2 is a schematic view of a double-cut dicing device;
FIG. 3 is a plan view illustrating a dicing method for a silicon
base optical waveguide work;
FIG. 4 is an elevational view of the silicon base optical waveguide
work shown in FIG. 3;
FIG. 5A is a sectional view illustrating first-stage dicing; and
FIG. 5B is a sectional view illustrating second-stage dicing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1 there is shown a schematic view of a dicing
device usable in the optical waveguide manufacturing method according
to the present invention. The dicing device has a spindle 4 on which
a resin diamond blade 2 is mounted. The resin diamond blade 2 is
rotated at a speed of about 10000 to 30000 rpm in a direction
of arrow R by the rotation of the spindle 4. In a specific example,
the resin diamond blade 2 is rotated at a speed of about 15000
rpm. Reference numeral 6 denotes a silicon wafer having a plurality
of embedded optical waveguides. During dicing of the silicon wafer
6 by the resin diamond blade 2 a cutting water 14 is sprayed from
a front nozzle 8 and a pair of opposite side nozzles 10 and 12 onto
the blade 2.
The cutting water 14 is preferably provided by pure water. However,
normal water may be used as the cutting water 14. By spraying the
cutting water 14 onto the resin diamond blade 2 chips generated
by the dicing of the silicon wafer 6 are washed away by the cutting
water 14 and loading of the resin diamond blade 2 is also prevented.
The resin diamond blade 2 is detachably mounted on the spindle 4
so that various blades having different abrasive grain sizes are
selectively used according to applications. For example, a blade
having diamond abrasive grains with a grain size of #1000 (grain
diameter of 8 to 20 .mu.m) or a blade having diamond abrasive grains
with a grain size of #6000 (grain diameter of 2 .mu.m or less) may
be used.
FIG. 2 is a schematic view of a double-cut dicing device. The double-cut
dicing device includes a first dicing unit 18 having a first resin
diamond blade 2 and a second dicing unit 26 having a second resin
diamond blade 22. Reference numeral 24 denotes a spindle in the
second dicing unit 26. The first resin diamond blade 2 is used for
first-stage-dicing, and the second resin diamond blade 22 is used
for second-stage dicing. The first resin diamond blade 2 has relatively
coarse diamond abrasive grains, and the second resin diamond blade
22 has relatively fine diamond abrasive grains. The silicon wafer
6 to be diced is set on a table 16 by suction, for example. The
table 16 is movable in X and Y directions orthogonal to each other.
The first and second resin diamond blades 2 and 22 are movable in
a vertical direction (Z direction).
FIG. 3 is a plan view illustrating a dicing method for a silicon
base optical waveguide work (silicon wafer having optical waveguides)
6 and FIG. 4 is an elevational view of the silicon base optical
waveguide work 6 shown in FIG. 3. As shown in FIG. 4 the silicon
base optical waveguide work 6 is bonded by a wax to a lower silicon
wafer 38 for dicing, and the lower silicon wafer 38 is bonded by
a wax to a glass plate 40 for suction. Referring back to FIG. 3
the silicon wafer 6 is formed with a plurality of embedded optical
waveguides 28 arrayed in one direction. The silicon wafer 6 is a
6-inch wafer, for example. Each optical waveguide 28 has a width
of 5 to 10 mm, for example. The silicon wafer 6 is diced in the
Y direction along three cutting lines 30 perpendicular to the longitudinal
direction of the optical waveguides 28 and in the X direction along
5 to 15 cutting lines 32 parallel to the longitudinal direction
of the optical waveguides 28 thereby cutting and separating the
optical waveguides 28.
Referring again to FIG. 4 the silicon wafer 6 has a thickness
of 1.04 mm. The silicon wafer 6 includes a silicon substrate 34
and the optical waveguides 28 of SiO.sub.2 formed on the silicon
substrate 34. Each optical waveguide 28 has a thickness of 0.04
mm. The lower silicon wafer 38 has a thickness of 1.00 mm, and the
glass plate 40 has a thickness of 5.00 mm. Reference numeral 42
denotes a dicing stop position. According to the dicing method of
the present invention, the silicon wafer 6 having the optical waveguides
28 is fully cut across its thickness, and the lower silicon wafer
38 is partially cut to such a depth as shown by the dicing stop
position 42.
The resin diamond blade according to the present invention and
the silicon base optical waveguide manufacturing method using this
blade according to the present invention will now be described in
more detail with reference to FIGS. 5A and 5B. The first resin diamond
blade 2 shown in FIG. 5A is a known blade, which is configured by
bonding diamond abrasive grains having a grain size of #1000 (grain
diameter of 8 to 20 .mu.m) with phenolic resin, for example. The
first resin diamond blade 2 has an outer diameter of 76.2 mm and
a thickness of 200 .mu.m. The first resin diamond blade 2 is used
for the first-stage dicing.
The second resin diamond blade 22 shown in FIG. 5B is a novel blade
having the following configuration. The second resin-diamond blade
22 has an outer diameter of 76.2 mm and a thickness of 220 .mu.m.
In embodying the optical waveguide manufacturing method according
to the present invention, the relation between the thickness t1
of the first resin diamond blade 2 and the thickness t2 of the second
resin diamond blade 22 is especially important. This relation will
be hereinafter described in detail.
The second resin diamond blade 22 has such a structure that diamond
abrasive grains and cerium oxide abrasive grains adhere to a bonding
resin as a resin bond. Thermosetting phenolic resin (e.g., manufactured
by Sumitomo Durez Co., Ltd., solid content of 70%), polyimide resin,
etc. may be adopted as the bonding resin. The diamond abrasive grains
of the blade 22 preferably have a grain diameter of 2 .mu.m or less,
that is, finer than a grain size of #6000. If the grain diameter
of the diamond abrasive grains is greater than 2 .mu.m, a sufficient
polishing performance cannot be exhibited. In other words, if diamond
abrasive grains having a grain diameter of greater than 2 .mu.m
are used, a surface roughness of .lambda./4 or less required for
the end face of the optical waveguide cannot be achieved, where
.lambda. is the wavelength of light propagating in the optical waveguide.
Preferably, the cerium oxide abrasive grains have an average grain
diameter of 0.1 to 5.0 .mu.m and a purity of 35 to 95 wt %. If the
average grain diameter of the cerium oxide abrasive grains is less
than 0.1 .mu.m, the polishing rate becomes extremely low. Conversely,
if the average grain diameter is greater than 5.0 .mu.m, scratches
due to the coarse grains are generated on the end face of the optical
waveguide, causing an increase in the surface roughness. There are
various purities of products for cerium oxide. If the content of
cerium oxide in the cerium oxide abrasive grains is less than 35
wt %, the polishing performance of cerium oxide cannot be sufficiently
exhibited because of a larger content of impurities, so that the
polishing rate becomes extremely low. Conversely, if the content
of cerium oxide in the cerium oxide abrasive grains is greater than
95 wt %, the polishing rate similarly becomes low. Moreover, an
added cost of purification is required, causing an increase in unit
price of the cerium oxide abrasive grains to result in an increase
in polishing cost. In a specific example, the cerium oxide abrasive
grains have an average grain diameter of about 3 .mu.m and a purity
of about 60 wt %.
Preferably, the total content of the diamond abrasive grains and
the cerium oxide abrasive grains with respect to the volume of the
blade 22 is 20 to 40 vol %. In a specific example, the total content
of the diamond abrasive grains and the cerium oxide abrasive grains
with respect to the volume of the blade 22 is set to about 25 vol
%. Furthermore, the content of the cerium oxide abrasive grains
with respect to the total volume of the diamond abrasive grains
and the cerium oxide abrasive grains is preferably set to 35 to
70 vol %. In a specific example, the ratio of the diamond abrasive
grains and the cerium oxide abrasive grains is set to about 1:1
by volume.
The second resin diamond blade 22 is manufactured in the following
manner. The diamond abrasive grains, the cerium oxide abrasive grains,
the phenolic resin powder (manufactured by Sumitomo Durez Co., Ltd.,
solid content of 70%), and additives (minute amounts of Cu, Ni,
and Al) are mixed together with stirring. The contents of the diamond
abrasive grains and the cerium oxide abrasive grains are equal to
each other by vol %. The mixture thus prepared is charged into a
given die, and pressed to be solidified. The molding thus obtained
is next heat-treated at about 150.degree. C. for three hours for
hardening.
There will now be described in detail the two-stage dicing method
according to the present invention using the first resin diamond
blade 2 and the second resin diamond blade 22. As shown in FIG.
5A, the first-stage dicing of the silicon wafer 6 is performed by
using the first resin diamond blade 2 having a thickness of 200
.mu.m. The rotational speed of the first resin diamond blade 2 is
set to 10000 to 30000 rpm. In a specific example, the speed is
set to 15000 rpm. The depth of cut by the first resin diamond blade
2 per stroke is set to 0.02 to 1.5 mm. In this case, the depth is
set to 0.05 mm.
While the silicon wafer 6 is fed in the X direction or the Y direction
during dicing, the feed speed of the silicon wafer 6 is set to 0.1
to 1.5 mm/sec, preferably, in cutting the optical waveguides 28
and 0.1 to 5.0 mm/sec, preferably, in cutting the silicon substrate
34 and the lower silicon wafer 38. In a specific example, the feed
speed of the silicon wafer 6 is set to 0.2 mm/sec in cutting the
optical waveguides 28 and 2.0 mm/sec in cutting the silicon substrate
34 and the lower silicon wafer 38.
As shown in FIG. 5A, the optical waveguides 28 of SiO.sub.2 as
a principal component are formed on the silicon substrate 34 by
CVD. Each optical waveguide 28 includes an under cladding 44 a
core 46 and an over cladding 48. Each of the under cladding 44
and the over cladding 48 is doped with B and P, and the core 46
is doped with Ge and P. In the first-stage dicing shown in FIG.
5A, the total depth of cut is set to 1.4 mm from the surface of
each optical waveguide 28. Accordingly, the silicon wafer 6 is fully
cut across its thickness of 1.04 mm, and the lower silicon wafer
38 is partially cut to its mid position of the thickness. The grain
size of the diamond abrasive grains of the first resin diamond blade
2 is #1000 (grain diameter of 8 to 20 .mu.m).
After the first-stage dicing is finished, the second-stage dicing
shown in FIG. 5B is performed by using the second resin diamond
blade 22 and applying it to a cut groove 50 formed in the first-stage
dicing. The second resin diamond blade 22 has a thickness of 220
.mu.m. The rotational speed of the second resin diamond blade 22
is set to 10000 to 30000 rpm. In this case, the speed is set to
15000 rpm.
The depth of cut by the second resin diamond blade 22 per stroke
is set to 0.02 to 1.5 mm. In a specific example, the depth is set
to 0.05 mm. The feed speed of the silicon wafer 6 is set to 0.1
to 1.5 mm/sec, preferably, in cutting the optical waveguides 28
and 0.1 to 5.0 mm/sec, preferably, in cutting the silicon substrate
34 and the lower silicon wafer 38. In a specific example, the feed
speed of the silicon wafer 6 is set to 0.2 mm/sec in cutting the
optical waveguides 28 and 2.0 mm/sec in cutting the silicon substrate
34 and the lower silicon wafer 38. Both in the first-stage dicing
and in the second-stage dicing, the cutting water 14 is sprayed
at a rate of 1 liter/min from the front nozzle 8 and the side nozzles
10 and 12 onto the first and second resin diamond blades 2 and 22
as shown in FIG. 1. By spraying the cutting water, chips of the
silicon wafers 6 and 38 during dicing are washed away and loading
of the resin diamond blades 2 and 22 is prevented.
In the second-stage dicing shown in FIG. 5B, the total depth of
cut is set to 1.2 mm, which is smaller than the total depth of cut
in the first-stage dicing. By stopping the second-stage dicing at
such a shallower cut position than that in the first-stage dicing,
the chips of the silicon wafers 6 and 38 during the second-stage
dicing can be sufficiently washed away by the cutting water. By
the above-mentioned two-stage dicing, the end face of each optical
waveguide 28 can be polished to a sufficient smoothness, i.e., a
surface roughness of .lambda./4 or less. In particular, since the
second resin diamond blade 22 includes a predetermined amount of
cerium oxide abrasive grains, the smoothness of the end face of
each optical waveguide 28 is considered to be improved. It is considered
that chemical etching by the cerium oxide abrasive grains contributes
to this improvement in smoothness. After the second-stage dicing
is finished, the wax bonding the silicon wafer 6 to the lower silicon
wafer 38 is melted to separate the silicon wafer 6 from the lower
silicon wafer 38. Thus, a plurality of optical waveguide devices
each having a sufficient smoothness at each end face can be manufactured.
The relation between the thickness t1 of the first resin diamond
blade 2 and the thickness t2 of the second resin diamond blade 22
for obtaining a sufficient smoothness of the end face of each optical
waveguide was examined by a test. The test results are shown in
Table 1.
TABLE 1 t1 (mm) t2 (mm) t2 - t1 (mm) Evaluation 0.157 0.233 0.076
Poor 0.185 0.230 0.045 Good 0.205 0.227 0.022 Good 0.209 0.225 0.016
Good 0.210 0.218 0.008 Poor
As understood from the results shown in Table 1 the relation of
t1+0.01 mm.ltoreq.t2.ltoreq.t1+0.05 mm must be satisfied to obtain
a sufficient smoothness of the end face of each optical waveguide.
The present invention is not limited to the details of the above
described preferred embodiments. The scope of the invention is defined
by the appended claims and all changes and modifications as fall
within the equivalence of the scope of the claims are therefore
to be embraced by the invention. |