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Claims  |
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What is claimed is:
1. An optical waveguide device comprising:
an optical waveguide formed on a substrate and enabling a light to
bidirectionally propagate therethrough; and
a trench-shaped space formed in the optical waveguide near at least one end
of the optical waveguide to cross a direction of light propagation, the
trench-shaped space being capable of switching the light propagating
through the optical waveguide,
wherein the trench-shaped space has a first boundary surface capable of
internally reflecting a coming light propagating through the optical
waveguide, thereby guiding the coming light out of the optical waveguide,
and a second boundary surface capable of passing therethrough a
transmitting light traveling in the direction opposite to the direction of
propagation of the coming light, thereby guiding the transmitting light
into the optical waveguide,
wherein when n denotes a refractive index of a material constituting a
principal part of the optical waveguide,
an angle .theta.1(.degree.) of the first boundary surface to the direction
of light propagation and an angle .theta.2(.degree.) of the second
boundary surface to the direction of light propagation satisfy the
following expressions:
.theta.1<90-sin.sup.-1 (1/n)
.theta.2>90-sin.sup.-1 (1/n).
2. An optical waveguide device according to claim 1, wherein the optical
waveguide includes:
a core which the light propagates through; and
a cladding formed to surround the core.
3. An optical waveguide device according to claim 2, wherein the
trench-shaped space is formed to cross at least the core.
4. An optical waveguide device according to claim 1, wherein at least one
end of the optical waveguide forms an end surface which is substantially
perpendicular to the direction of light propagation and which is capable
of passing therethrough the externally incoming transmitting light in
substantially the same direction as the incoming direction, and
the transmitting light entering through the end surface passes the second
boundary surface, the trench-shaped space, and the first boundary surface
in sequence so that the transmitting light is guided into the optical
waveguide.
5. An optical waveguide device according to claim 1, wherein at least one
end surface of the optical waveguide forms an end surface which forms a
predetermined angle with the direction of light propagation to cross the
direction of light propagation and which is capable of internally
reflecting the transmitting light entering through an upper surface or a
side surface of the optical waveguide, and
the transmitting light reflected by the end surface passes the second
boundary surface, the trench-shaped space, and the first boundary surface
in sequence so that the transmitting light is guided into the optical
waveguide.
6. An optical waveguide device according to claim 5, wherein when n denotes
the refractive index of the material constituting the principal part of
the optical waveguide,
an angle .theta.3(.degree.) of the end surface to the direction of light
propagation satisfies the following expression:
.theta.3>sin.sup.-1 (1/n).
7. An optical waveguide device according to claim 1, wherein the optical
waveguide comprises a high polymeric material.
8. An optical waveguide device according to claim 1, wherein the substrate
comprises an inorganic material containing at least one of silicon,
quartz, glass and ceramics or an organic material.
9. An optical transmitting and receiving device comprising:
an optical waveguide formed on a substrate and enabling a light to
bidirectionally propagate therethrough;
a trench-shaped space formed in the optical waveguide near at least one end
of the optical waveguide to cross the direction of light propagation, the
trench-shaped space being capable of switching the light propagating
through the optical waveguide;
a photodetector for receiving a coming light switched by the trench-shaped
space; and
a light emitting device for emitting a transmitting light toward the
trench-shaped space,
wherein the trench-shaped space has a first boundary surface capable of
internally reflecting the coming light propagating through the optical
waveguide, thereby guiding the coming light out of the optical waveguide,
and a second boundary surface capable of passing therethrough the
transmitting light traveling in the direction opposite to the direction of
propagation of the coming light, thereby guiding the transmitting light
into the optical waveguide,
wherein when n denotes a refractive index of a material constituting a
principal part of the optical waveguide,
an angle .theta.1(.degree.) of the first boundary surface to the direction
of light propagation and an angle .theta.2(.degree.) of the second
boundary surface to the direction of light propagation satisfy the
following expressions:
.theta.1<90-sin.sup.-1 (1/n)
.theta.2>90-sin.sup.-1 (1/n).
10. An optical transmitting and receiving device according to claim 9,
wherein the optical waveguide includes:
a core which the light propagates through; and
a cladding formed to surround the core.
11. An optical transmitting and receiving device according to claim 9,
wherein the trench-shaped space is formed to cross at least the core.
12. An optical transmitting and receiving device according to claim 9,
wherein the photodetector is arranged on the upper surface or the side
surface of the optical waveguide near the first boundary surface, and the
photodetector can receive the coming light reflected by the first boundary
surface.
13. An optical transmitting and receiving device according to claim 9,
wherein at least one end of the optical waveguide forms an end surface
which is substantially perpendicular to the direction of light propagation
and which is capable of passing therethrough the externally incoming
transmitting light in substantially the same direction as the incoming
direction, and
the transmitting light entering through the end surface passes the second
boundary surface, the trench-shaped space, and the first boundary surface
in sequence so that the transmitting light is guided into the optical
waveguide.
14. An optical transmitting and receiving device according to claim 13,
wherein the light emitting device is arranged to face the end surface and
emits the transmitting light toward the end surface.
15. An optical transmitting and receiving device according to claim 14,
wherein the light emitting device has a light emitting layer having an end
surface which the light exits through.
16. An optical transmitting and receiving device according to claim 9,
wherein at least one end of the optical waveguide forms an end surface
which forms a predetermined angle with the direction of light propagation
to cross the direction of light propagation and which is capable of
internally reflecting the transmitting light entering through the upper
surface or the side surface of the optical waveguide, and
the transmitting light reflected by the end surface passes the second
boundary surface, the trench-shaped space, and the first boundary surface
in sequence so that the transmitting light is guided into the optical
waveguide.
17. An optical transmitting and receiving device according to claim 16,
wherein the light emitting device is arranged on the upper surface or the
side surface of the optical waveguide.
18. An optical transmitting and receiving device according to claim 16,
wherein the light emitting device has a light emitting layer having a main
surface which the light exits through.
19. An optical transmitting and receiving device according to claim 16,
wherein when n denotes the refractive index of the material constituting
the principal part of the optical waveguide,
an angle .theta.3(.degree.) of the end surface to the direction of light
propagation satisfies the following expression:
.theta.3>sin.sup.-1 (1/n).
20. A method of manufacturing an optical waveguide device comprising the
steps of:
forming on a substrate an optical waveguide enabling a light to
bidirectionally propagate therethrough; and
forming a trench-shaped space in the optical waveguide near at least one
end of the optical waveguide to cross the direction of light propagation,
the trench-shaped space having a first boundary surface and a second
boundary surface, the first boundary surface being capable of internally
reflecting a coming light propagating through the optical waveguide and
thereby guiding outward the coming light through the upper surface or the
side surface of the optical waveguide, the second boundary surface being
capable of passing therethrough a transmitting light traveling in the
direction opposite to the direction of propagation of the coming light and
thereby guiding the transmitting light into the optical waveguide through
the first boundary surface,
wherein when n denotes a refractive index of a material constituting a
principal part of the optical waveguide,
an angle .theta.1(.degree.) of the first boundary surface to the direction
of light propagation and an angle .theta.2(.degree.) of the second
boundary surface to the direction of light propagation satisfy the
following expressions:
.theta.1<90-sin.sup.-1 (1/n)
.theta.2>90-sin.sup.- 1(1/n).
21. A method of manufacturing an optical waveguide device according to
claim 20, wherein at least one end of the optical waveguide forms an end
surface which is substantially perpendicular to the direction of light
propagation and which is capable of passing therethrough the externally
incoming transmitting light and thereby guiding the transmitting light
toward the second boundary surface.
22. A method of manufacturing an optical waveguide device according to
claim 20, wherein at least one end of the optical waveguide forms an end
surface which forms a predetermined angle with the direction of light
propagation to cross the direction of light propagation and which is
capable of internally reflecting the transmitting light entering through
the upper surface or the side surface of the optical waveguide and thereby
guiding the transmitting light toward the second boundary surface.
23. A method of manufacturing an optical waveguide device according to
claim 22, wherein when n denotes the refractive index of the material
constituting the principal part of the optical waveguide,
an angle .theta.3(.degree.) of the end surface to the direction of light
propagation satisfies the following expression:
.theta.3>sin.sup.-1 (1/n).
24. A method of manufacturing an optical transmitting and receiving device
comprising the steps of:
forming on a substrate, an optical waveguide enabling a light to
bidirectionally propagate therethrough;
forming a trench-shaped space in the optical waveguide near at least one
end of the optical waveguide to cross the direction of light propagation,
the trench-shaped space having a first boundary surface and a second
boundary surface, the first boundary surface being capable of internally
reflecting a coming light propagating through the optical waveguide and
thereby guiding outward the coming light through the upper surface or the
side surface of the optical waveguide, the second boundary surface being
capable of passing therethrough a transmitting light traveling in the
direction opposite to the direction of propagation of the coming light and
thereby guiding the transmitting light to the optical waveguide through
the first boundary surface;
forming a photodetector for receiving the coming light reflected by the
first boundary surface, on the upper surface or the side surface of the
optical waveguide near the first boundary surface; and
forming near the end surface a light emitting device for emitting the
transmitting light toward the end surface,
wherein when n denotes a refractive index of a material constituting a
principal part of the optical waveguide,
an angle .theta.1(.degree.) of the first boundary surface to the direction
of light propagation and an angle .theta.2(.degree.) of the second
boundary surface to the direction of light propagation satisfy the
following expressions:
.theta.1<90-sin.sup.-1 (1/n)
.theta.2>90-sin.sup.-1 (1/n).
25. A method of manufacturing an optical transmitting and receiving device
according to claim 24, wherein at least one end of the optical waveguide
forms an end surface which is substantially perpendicular to the direction
of light propagation and which is capable of passing therethrough the
externally incoming transmitting light in substantially the same direction
as the incoming direction.
26. A method of manufacturing an optical transmitting and receiving device
according to claim 24, wherein at least one end of the optical waveguide
forms an end surface which forms a predetermined angle with the direction
of light propagation to cross the direction of light propagation and which
is capable of internally reflecting the transmitting light entering
through the upper surface or the side surface of the optical waveguide.
27. A method of manufacturing an optical transmitting and receiving device
according to claim 26, wherein when n denotes the refractive index of the
material constituting the principal part of the optical waveguide,
an angle .theta.3(.degree.) of the end surface to the direction of light
propagation satisfies the following expression:
.theta.3>sin.sup.-1 (1/n). |
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Claims |
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Description |
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RELATED APPLICATION DATA
The present application claims priority to Japanese Application No.
P11-029258 filed Feb. 5, 1999 which application is incorporated herein by
reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an optical waveguide device including an optical
waveguide capable of propagating a light, an optical transmitting and
receiving device, a method of manufacturing an optical waveguide device
and a method of manufacturing an optical transmitting and receiving
device.
2. Description of the Related Art
In the field of an integrated circuit (IC), a large scale integration (LSI)
or the like, the technological advance improves an operating speed and a
scale of integration, thereby rapidly promoting an enhancement in
performance of a microprocessor and an increase in a capacity of a memory
chip. However, the increase in a transmission rate of an electric signal
and the increase in density of signal wiring are bottlenecks for an
improvement in the performance of these electronic devices. Moreover, a
problem of signal delay in electrical wiring arises. Furthermore, a
provision for EMI/EMC (Electro-Magnetic Interference/Electro-Magnetic
Compatibility) is indispensable for achieving the increase in the
transmission rate of the electric signal and the increase in the density
of the signal wiring. Attention is paid to an optical interconnection
(optical wiring) as means for eliminating the bottlenecks in these
wirings.
This optical interconnection is considered to be applicable to various
situations such as the interconnection between devices, between in-device
boards or between in-board chips. An optical transmission communication
system, in which an optical waveguide formed on a substrate is used as a
transmission line, is considered to be suitable for a transmission over
relatively short distances such as the distance between the chips, for
example. For the optical transmission communication system using such an
optical waveguide, an important problem is to establish a process of
making the optical waveguide.
Requirements for such an optical waveguide are a low optical loss and
easiness in making. Optical waveguides for satisfying these requirements
include a low-loss optical waveguide using a quartz base material, for
example. As has been proved by an optical fiber, quartz is excellent in
light transmittance. Thus, the loss can be reduced to 0.1 dB/cm or less
when the optical waveguide is made of quartz. However, the use of quartz
has problems such as a long time required to make the optical waveguide, a
high temperature (800.degree. C. or higher) at the time of the making, a
difficulty in increasing an area and a high cost. It is considered that a
high polymeric material such as polymethyl methacrylate (PMMA) or
polyimide is used as the material for solving these problems and making it
possible to make the optical waveguide by a low-temperature process.
Taking into consideration the increase in the density of an optical
transmission using the optical waveguide, it is desirable t hat an optical
signal is bidirectionally propagated through the optical waveguide.
However, the system for intending the optical signal to bidirectionally
propagate has various problems to be solved, such as the form of an entry
of the light from a light emitting device into the optical waveguide, the
form of an exit of the light from the optical waveguide to a
photodetector, an arrangement of the light emitting device and the
photodetector with respect to the optical waveguide, or crosstalk between
the signals bidirectionally propagated.
The invention is designed to overcome the foregoing problems. It is an
object of the invention to provide an optical waveguide device and an
optical transmitting and receiving device which enable bidirectional
communication by allowing the optical signal to bidirectionally propagate
by using the optical waveguide formed on the substrate and used as the
optical wiring, a method of manufacturing an optical waveguide device and
a method of manufacturing an optical transmitting and receiving device.
SUMMARY OF THE INVENTION
An optical waveguide device of the invention comprises an optical waveguide
formed on a substrate and enabling a light to bidirectionally propagate
therethrough; and a trench-shaped space formed in the optical waveguide
near at least one end of the optical waveguide so as to cross a direction
of light propagation, the trench-shaped space being capable of switching
the light propagating through the optical waveguide. The optical waveguide
can comprise a high polymeric material. Moreover, the substrate can
comprise an inorganic material containing at least one of silicon, quartz,
glass and ceramics or an organic material.
An optical transmitting and receiving device of the invention comprises an
optical waveguide formed on a substrate and enabling a light to
bidirectionally propagate therethrough; a trench-shaped space formed in
the optical waveguide near at least one end of the optical waveguide so as
to cross the direction of light propagation, the trench-shaped space being
capable of switching the light propagating through the optical waveguide;
a photodetector for receiving a coming light switched by the trench-shaped
space; and a light emitting device for emitting a transmitting light
toward the trench-shaped space.
In the optical waveguide device or the optical transmitting and receiving
device of the invention, the optical waveguide can include a core which
the light propagates through; and a cladding formed so as to surround the
core. In this case, it is desirable that the trench-shaped space is formed
so as to cross at least the core.
Moreover, in the optical waveguide device or the optical transmitting and
receiving device of the invention, the trench-shaped space can have a
first boundary surface capable of internally reflecting a coming light
propagating through the optical waveguide, thereby guiding the coming
light out of the optical waveguide; and a second boundary surface capable
of passing therethrough a transmitting light traveling in the direction
opposite to the direction of propagation of the coming light, thereby
guiding the transmitting light into the optical waveguide. Preferably,
when n denotes a refractive index of a material constituting a principal
part of the optical waveguide, an angle .theta.1(.degree.) of the first
boundary surface to the direction of light propagation satisfies
.theta.1<90-sin.sup.-1 (1/n), and an angle .theta.2(.degree.) of the
second boundary surface to the direction of light propagation satisfies
.theta.2>90-sin.sup.-1 (1/n).
Moreover, in the optical waveguide device or the optical transmitting and
receiving device of the invention, at least one end of the optical
waveguide can form an end surface which is substantially perpendicular to
the direction of light propagation and which is capable of passing
therethrough the externally incoming transmitting light in substantially
the same direction as the incoming direction, and the transmitting light
entering through the end surface passes the second boundary surface, the
trench-shaped space and the first boundary surface in sequence so that the
transmitting light is guided into the optical waveguide.
Moreover, in the optical waveguide device or the optical transmitting and
receiving device of the invention, at least one end of the optical
waveguide may form an end surface which forms a predetermined angle with
the direction of light propagation so as to cross the direction of light
propagation and which is capable of internally reflecting the transmitting
light entering through an upper surface or a side surface of the optical
waveguide, and the transmitting light reflected by the end surface passes
the second boundary surface, the trench-shaped space and the first
boundary surface in sequence so that the transmitting light is guided into
the optical waveguide. In this case, preferably, when n denotes the
refractive index of the material constituting the principal part of the
optical waveguide, an angle .theta.3(.degree.) of the end surface to the
direction of light propagation satisfies .theta.3>sin.sup.-1 (1/n).
A method of manufacturing an optical waveguide device of the invention
comprises the steps of forming on a substrate an optical waveguide
enabling a light to bidirectionally propagate therethrough; and forming a
trench-shaped space in the optical waveguide near at least one end of the
optical waveguide so as to cross the direction of light propagation, the
trench-shaped space having a first boundary surface and a second boundary
surface, the first boundary surface being capable of internally reflecting
a coming light propagating through the optical waveguide and thereby
guiding outward the coming light through the upper surface or the side
surface of the optical waveguide, the second boundary surface being
capable of passing therethrough a transmitting light traveling in the
direction opposite to the direction of propagation of the coming light and
thereby guiding the transmitting light into the optical waveguide through
the first boundary surface.
A method of manufacturing an optical transmitting and receiving device of
the invention comprises the steps of forming on a substrate an optical
waveguide enabling a light to bidirectionally propagate therethrough;
forming a trench-shaped space in the optical waveguide near at least one
end of the optical waveguide so as to cross the direction of light
propagation, the trench-shaped space having a first boundary surface and a
second boundary surface, the first boundary surface being capable of
internally reflecting a coming light propagating through the optical
waveguide and thereby guiding outward the coming light through the upper
surface or the side surface of the optical waveguide, the second boundary
surface being capable of passing therethrough a transmitting light
traveling in the direction opposite to the direction of propagation of the
coming light and thereby guiding the transmitting light to the optical
waveguide through the first boundary surface; forming a photodetector for
receiving the coming light reflected by the first boundary surface, on the
upper surface or the side surface of the optical waveguide near the first
boundary surface; and forming near the end surface a light emitting device
for emitting the transmitting light toward the end surface.
In the optical waveguide device of the invention, the light propagating
through the optical waveguide is switched by the trench-shaped space which
is formed in the optical waveguide near at least one end of the optical
waveguide formed on the substrate so as to cross the direction of light
propagation. Herein, the phrase "the light is switched"means that the
light propagating through the optical waveguide is guided to routes
differing in accordance with the direction of propagation of the light.
In the optical transmitting and receiving device of the invention, the
light propagating through the optical waveguide is switched by the
trench-shaped space which is formed in the optical waveguide near at least
one end of the optical waveguide formed on the substrate so as to cross
the direction of light propagation. The coming light switched by the
trench-shaped space is received by the photodetector, while the
transmitting light is emitted from the light emitting device toward the
trench-shaped space.
Other and further objects, features and advantages of the invention will
appear more fully from the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross sectional view of an optical transmitting and receiving
device according to one embodiment of the invention, showing a sectional
structure taken along the direction of light propagation;
FIG. 2 is a cross sectional view of the optical transmitting and receiving
device according to one embodiment of the invention, showing the sectional
structure taken along the direction perpendicular to the direction of
light propagation;
FIG. 3 is a perspective view of an external constitution of the optical
transmitting and receiving device according to one embodiment of the
invention;
FIG. 4 is a cross sectional view of one process of a method of
manufacturing the optical transmitting and receiving device according to
one embodiment of the invention;
FIG. 5 is a cross sectional view of the process following the process of
FIG. 4;
FIG. 6 is a cross sectional view of the process following the process of
FIG. 5;
FIG. 7 is a cross sectional view of another sectional structure of an
optical waveguide in the process shown in FIG. 6;
FIG. 8 is a cross sectional view of the process following the process of
FIG. 7;
FIG. 9 is a cross sectional view of the process following the process of
FIG. 8;
FIG. 10 is a cross sectional view of the optical transmitting and receiving
device according to a second embodiment of the invention, showing the
sectional structure taken along the direction of light propagation; and
FIG. 11 is a cross sectional view of the optical transmitting and receiving
device according to a modification of the embodiments of the invention,
showing the sectional structure taken along the direction perpendicular to
the direction of light propagation.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the invention will be described in detail below with
reference to the accompanying drawings.
[First embodiment]
FIGS. 1 to 3 show a principal part of a constitution of an optical
transmitting and receiving device according to one embodiment of the
invention applied to a bidirectional optical transmission system. FIG. 3
is a perspective view of an external constitution of the principal part of
the optical transmitting and receiving device. FIG. 1 shows a cross
section taken along line I--I of FIG. 3. FIG. 2 shows a cross section
taken along line II--II of FIG. 3. Since an optical waveguide device
according to the embodiment of the invention and a method of manufacturing
the same are embodied by the optical transmitting and receiving device
according to the embodiment and a method of manufacturing the same, the
former device and method will be described in conjunction with the latter
device and method.
As shown in these drawings, the optical transmitting and receiving device
of this embodiment comprises a substrate 11, an optical waveguide formed
on the substrate 11, light emitting devices 23a and 23b arranged on the
substrate 11 and facing ends 18a and 18b of the optical waveguide 15,
respectively, and photodetectors 25a and 25b arranged on an upper surface
(a side surface) of the optical waveguide 15 near the ends of the optical
waveguide 15, respectively. The substrate 11 is typically composed of an
inorganic material such as silicon, quartz or glass, and the substrate
flattened with high precision specifically for an optical circuit is used
as the substrate 11. Besides, the substrate 11 may be an electrical wiring
substrate having relatively great roughness because of electrical wiring
formed thereon. Furthermore, such an electrical wiring substrate may be,
for example, the substrate made of an inorganic material such as ceramics
or the substrate made of a glass-epoxy-family organic material. The
optical waveguide 15 corresponds to "an optical waveguide"of the
invention, and the ends 18a and 18b correspond to "end surfaces"of the
invention.
The optical waveguide 15 has a core 13, and claddings 12 and 14 which are
formed so that the upper, lower, left and right sides of the core 13 may
be surrounded by the claddings 12 and 14, each of which has a refractive
index lower than the refractive index of the core 13. The core 13 is made
of a high polymeric material described below, and the claddings 12 and 14
are made of the same high polymeric material. The claddings 12 and 14
correspond to "claddings"of the invention, and the core 13 corresponds to
"a core"of the invention.
An angle .theta.3 between each of the ends 18a and 18b of the optical
waveguide 15 and the surface of the substrate 11 is about 90.degree. in
this embodiment. The light emitting device 23a is arranged on the
substrate 11 on one transmitting and receiving end side (hereinafter
referred to as an A side) of the optical waveguide 15 so as to face the
end 18a. The light emitting device 23b is arranged on the substrate 11 on
the other transmitting and receiving end side (hereinafter referred to as
a B side) of the optical waveguide 15 so as to face the end 18b. Only the
A side is shown in FIG. 3. The light emitting device 23a has a base layer
21a formed on the substrate 11 and a light emitting layer 22a formed on
the base layer 21a. Similarly, the light emitting device 23b has a base
layer 21b and a light emitting layer 22b. An edge emitting type light
emitting device such as an edge emitting type semiconductor laser, for
example, can be used as the light emitting devices 23a and 23b. In this
case, the light exiting through the end of the light emitting layer 22a of
the light emitting device 23a enters through the end 18a substantially
perpendicularly to the end 18a. On the other hand, the light exiting
through the end of the light emitting layer 22b of the light emitting
device 23b enters through the end 18b substantially perpendicularly to the
end 18b.
The optical waveguide 15 has trench-shaped spaces 31a and 31b in the A and
B sides thereof, respectively. The trench-shaped spaces 31a and 31b are
made so as to cross the direction in which the light propagates through
the optical waveguide 15 (a longitudinal direction of the optical
waveguide 15). More specifically, as shown in FIGS. 1 and 3, the
trench-shaped space 31a is made so as to diagonally cross three parts,
i.e., the cladding 14 on the core 13, the core 13 and the cladding 12
under the core 13, in this order. Thus, the trench-shaped space 31a has
only to cross at least the core 13 and does not have to cross the
claddings 12 and 14. However, the trench-shaped space 31a is increased in
size in the longitudinal direction of the trench-shaped space 31a (the
direction perpendicular to the surface of a sheet in FIG. 1) so that the
trench-shaped space 31a may cross not only the three parts, i.e., the
cladding 14 on the core 13, the core 13 and the cladding 12 under the core
13 but also the claddings 12 and 14 on both the sides of the core 13,
whereby the optical waveguide 15 may be completely separated by the
trench-shaped space 31a. In this embodiment, it is assumed that the
trench-shaped space 31a is filled with an external medium (e.g., the air)
of the optical waveguide 15.
The trench-shaped space 31a is delimited mainly by a boundary surface 16a
and a boundary surface 17a. The boundary surface 16a forms an angle
.theta.1 with the surface of the substrate 11, and the boundary surface
17a forms an angle .theta.2 with the surface of the substrate 11, where
.theta.2>.theta.1. The angle .theta.1 is set to such an angle that all
the coming lights propagating through the optical waveguide 15 along the
direction of light propagation from the left side (the B side) in FIG. 1
can be internally reflected by the first boundary surface 16a and can exit
outward through the upper surface of the optical waveguide 15. Moreover,
the angle .theta.2 is set to such an angle that the transmitting light
entering through the end 18a and propagating in the direction (the
direction from right to left in FIG. 1) opposite to the direction of
propagation of the coming light (the direction from left to right in FIG.
1) can pass through the second boundary surface 17a and can enter through
the first boundary surface 16a. The angles .theta.1 and .theta.2 will be
further described below. Since the structure and shape of the
trench-shaped space 31b are the same as those of the trench-shaped space
31a, the description thereof is omitted. The trench-shaped space 31a or
31b corresponds to "a trench-shaped space"of the invention. The boundary
surface 16a corresponds to "a first boundary surface"of the invention, and
the boundary surface 17a corresponds to "a second boundary surface"of the
invention.
The photodetectors 25a and 25b are arranged on the optical waveguide 15 on
the A and B sides of the optical waveguide 15, respectively. For example,
a surface photo-detection type photodetector such as a Pin type
photodetector or an MSM (Metal-Schottky-Metal) type photodetector can be
used as the photodetectors 25a and 25b.
Next, a function of the optical transmitting and receiving device having
the above constitution will be described with reference to FIG. 1. An
optical principle of transmission and reception on the A side, one
transmitting and receiving end will be described. Since the principle of
the transmission and reception on the other transmitting and receiving end
(the B side) is the same as that on one transmitting and receiving end
(the A side), the description thereof is omitted.
First, the principle of the transmission will be described. The
transmitting light, which exits through the end of the light emitting
layer 22a of the light emitting device 23a substantially parallel to the
substrate 11, enters through the end 18a that is the end of the optical
waveguide 15, as shown in FIG. 1. The end 18a is substantially
perpendicular to the direction of light propagation (the longitudinal
direction of the optical waveguide 15) as described above. Thus, the
transmitting light entering through the end 18a travels in straight lines
as it is, and the light reaches the boundary surface 17a of the
trench-shaped space 31a close to the light emitting device 23a. The
boundary surface 17a is formed so as to form the angle .theta.2 at which
the incident transmitting light is not totally reflected, with respect to
the direction of light propagation (equal to the direction of the surface
of the substrate 11). That is, the angle .theta.2 is such an angle that an
incident angle of the transmitting light incident on the boundary surface
17a does not exceed a critical angle. More specifically, the angle
.theta.2 (in units of degrees) depends on a refractive index n of the
material constituting the core 13 of the optical waveguide 15, and the
angle .theta.2 is set in accordance with Snell's law so as to satisfy the
following expression (1).
.theta.2>90-sin.sup.-1 (1/n) (1)
As long as the expression (1) is satisfied, the transmitting light from the
light emitting device 23a is not totally reflected by the boundary surface
17a but is refracted by the boundary surface 17a in accordance with
Snell's law and passes through the boundary surface 17a. For example,
assuming that the refractive index n of the core 13 is 1.5,
.theta.2>48.2.degree. is obtained from the expression (1). That is, in
this case, if the angle .theta.2 is 50.degree. or more for example, the
transmitting light can sufficiently pass through the boundary surface 17a
and thus an optical switching operation is ensured during the
transmission.
The transmitting light, which has passed through the boundary surface 17a,
travels through the trench-shaped space 31a and reaches the boundary
surface 16a of the trench-shaped space 31a. The transmitting light is
refracted by the boundary surface 16a in accordance with Snell's law, then
the light travels into the core 13 of the optical waveguide 15, and
further the light travels through the core 13 toward the B side. The
direction in which the transmitting light travels from the boundary
surface 16a into the core 13 forms a small angle with the direction of
light propagation. However, as long as the optical waveguide 15 has such a
numerical aperture (NA) as may be capable of propagating the transmitting
light and may be permissible, the transmitting light can propagate through
the optical waveguide 15 at sufficient power. The greater a difference
between the refractive index n of the core 13 and the refractive index of
each of the claddings 12 and 14, the higher the numerical aperture of the
optical waveguide 15 and thus the higher an efficiency of propagation of
the transmitting light.
Next, the principle of the reception will be described. As described above,
the angle .theta.1 of the boundary surface 16a of the trench-shaped space
31a close to the photodetector 25a to the direction of light propagation
is such an angle that the light propagating through the optical waveguide
from the B side is totally reflected by the boundary surface 16a. In other
words, the angle .theta.1 is such an angle that the incident angle of the
coming light incident on the second boundary surface is equal to or more
than the critical angle. More specifically, the angle .theta.1 (in units
of degrees) depends on the refractive index n of the material constituting
the core 13 of the optical waveguide 15, and the angle .theta.1 is set in
accordance with Snell's law so as to satisfy the following expression (2).
.theta.1<90-sin.sup.-1 (1/n) (2)
As long as the expression (2) is satisfied, the coming light propagating
through the core 13 of the optical waveguide 15 from the B side does not
pass through the boundary surface 16a but is totally reflected by the
boundary surface 16a and received by the photodetector 25a arranged on the
upper surface of the optical waveguide 15. For example, assuming that the
refractive index n of the core 13 of the optical waveguide 15 is 1.5,
1<48.2.degree. is obtained. That is, in this case, if the angle
.theta.1 is 45.degree. or less for example, the light from the B side is
totally reflected by the boundary surface 16a and enters into the
photodetector 25a. Therefore, the optical switching operation is ensured
during the reception, and an efficiency of photo-detection is maximized.
For example, assuming that the refractive index n of the material of the
core 13 is 1.5, that .theta.1 is 45.degree. and that .theta.2 is
50.degree., the angle, at which the transmitting light from the light
emitting device 23a reenters into the optical waveguide 15 through the
boundary surfaces 17a and 16a, is an angle of about 4.degree. to the
direction of light propagation. Thus, the optical waveguide having a
typical NA (e.g., NA=about 0.2 to about 0.3) would be sufficiently capable
of optical coupling. A width of the trench-shaped space 31a, namely, a
distance between the boundary surfaces 16a and 17a may be minimized as
long as these two boundary surfaces are such that they have no optical
effect on each other. Specifically, the width such that the boundary
surfaces have no optical effect on each other means the width equal to or
more than a wavelength order (e.g., a few micrometers) of the light. In
this case, a multi-mode optical waveguide having a core diameter of tens
of micrometers to hundreds of micrometers, for example, permits sufficient
optical coupling. On the other hand, the coming light from the B side is
totally reflected by the boundary surface 16a and received by the
photodetector 25a.
As described above, according to the optical transmitting and receiving
device of this embodiment, the trench-shaped space 31a having the boundary
surfaces 16a and 17a is located in the optical waveguide near one end of
the optical waveguide 15 so that the trench-shaped space 31a may cross the
direction of light propagation. Thus, the coming light propagating through
the optical waveguide 15 from the B side is internally reflected by the
boundary surface 16a and exits outward through the upper surface of the
optical waveguide 15, and the transmitting light entering through the end
18a on the A side of the optical waveguide 15 passes through the boundary
surface 17a and enters through the boundary surface 16a. Thus, a single
optical waveguide formed on the substrate can bidirectionally switch an
optical signal by a relatively simple constitution. Therefore, a
bidirectional optical transmission and reception system can achieve a
high-density optical transmission by low-density optical wiring.
Next, the method of manufacturing the optical transmitting and receiving
device according to this embodiment will be described with reference to
FIGS. 4 to 9.
First, the optical waveguide 15 including the core 13 and the claddings 12
and 14 is formed on the substrate 11 by processes shown in FIGS. 4 to 6.
FIGS. 4 to 6 show the cross section taken along the direction
perpendicular to the direction of light propagation.
Specifically, as shown in FIG. 4, a lower cladding layer 12p made of an
organic material and having a thickness of about tens of micrometers is
formed on the flat substrate 11 such as a silicon substrate or a glass
substrate by spin coating, for instance. Furthermore, the lower cladding
layer 12p is cured by heat treatment, exposure to ultraviolet light, or
the like. For example, acrylic resin such as polyimide or PMMA (polymethyl
methacrylate), epoxy resin whose base resin is bisphenol or the like,
polyolefine resin such as polyethylene or polystyrene, or any of these
substances doped with fluorine can be used as the lower cladding layer
12p.
Then, a core layer 13p having the refractive index higher than the
refractive index of the lower cladding layer 12p and a thickness of about
tens of micrometers is formed on the lower cladding layer 12p by the
process of spin coating, the process of heat treatment and so on. The
material having the refractive index sufficiently higher than the
refractive index of the material selected as the lower cladding layer 12p
is selected as the core layer 13p among, for example, the above-described
materials (the acrylic resin such as polyimide or PMMA, the epoxy resin
whose base resin is bisphenol or the like, the polyolefine resin such as
polyethylene or polystyrene, and any of these substances doped with
fluorine).
Then, as shown in FIG. 5, the core layer 13p is patterned by a
photolithography process, a reactive ion etching (RIE) process and so on,
whereby the core 13 having a rectangular section is formed. In this case,
the width of the core 13 is about 30 .mu.m, for example.
Then, as shown in FIGS. 6 and 7, an upper cladding layer made of the same
material as that of the lower cladding layer 12p is formed over the whole
surface of the substrate 11 with a thickness of about a few micrometers by
the process of spin coating, the process of heat treatment and so on.
Then, the upper cladding layer and the lower cladding layer 12p are
selectively etched, whereby the optical waveguides are separated from one
another. Thus, a plurality of separate optical waveguides 15, each of
which has the core 13 surrounded by the claddings 12 and 14, are formed on
the substrate 11. FIG. 7 is a cross sectional view taken along line
VII--VII of FIG. 6, showing the optical waveguide 15 in a state shown in
FIG. 6.
Then, as shown in FIG. 8, the trench-shaped spaces 31a and 31b and the ends
18a and 18b are formed. Furthermore, as shown in FIG. 9, the light
emitting device 23a and the photodetector 25a are formed. FIGS. 8 and 9
show the cross section taken along the same direction as the direction
shown in FIG. 7, i.e., the cross section of the optical waveguide 15 taken
along the direction of light propagation.
The trench-shaped spaces 31a and 31b are formed by various etching
processes such as laser processing using a high-power light beam such as
an excimer las | | |
