Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2000-04-19
2002-08-20
Spyrou, Cassandra (Department: 2872)
Optical waveguides
With optical coupler
Input/output coupler
C385S034000, C385S040000, C385S049000, C385S074000, C385S088000, C385S093000, C385S052000, C372S092000, C372S107000, C372S065000
Reexamination Certificate
active
06438289
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a light emitting and receiving device for bidirectional optical communications with one optical fiber.
2. Description of the Related Art
FIG. 5
is a basic block diagram of an optical bidirectional communications system proposed in Japanese Patent Application Unexamined Publication No. 61-9610. Below is description of the system construction.
Denoted
101
is a light emitting and receiving device which consists of a light emitter
102
for converting electrical signals to optical signals, a light receiver
103
for converting optical signals to electrical signals, and an optical branching filter
104
. Denoted
105
is also a light emitting and receiving device which consists of a light emitter
106
, a light receiver
107
and an optical branching filter
108
, all having the same constructions as those in the light emitting and receiving device
101
. The light emitting and receiving devices
101
and
105
are optically connected to each other via one optical fiber
109
.
The publication as mentioned above also discloses a light emitting and receiving device
101
′,
105
′ which is of one-piece structure as shown in FIG.
6
. In this structure, light from a light emitting element
110
is converted into parallel lights at a lens
111
, gathered via a half mirror
112
at a lens
113
, and passed to an optical fiber
114
. On the other hand, light from the optical fiber
114
is reflected at the half mirror
112
, gathered at a lens
115
, and passed to a light receiving element
116
.
The publication as mentioned above further discloses a light emitting and receiving device
101
″,
105
″ as shown in
FIG. 7
, which consists of a light emitting element
117
, an optical fiber
118
, a first lens
119
, a glass block
120
, a second lens
121
and a light receiving element
122
.
The optical fiber
118
has its front end portion received at a center axis in a glass tube
123
and has its front end surface obliquely ground at an angle of about 45° with the glass tube
123
.
The first lens
119
is disposed between the light emitting element
117
and the optical fiber
118
and gathers light from the light emitting element
117
to pass to the optical fiber
118
.
The glass block
120
has a surface
120
a
in opposition to an end surface of the first lens
119
, which is ground at right angles to the center axis of the optical fiber
118
, and a surface
120
b
ground at an angle of about 45° relative to the center axis of the optical fiber
118
and coated with a half mirror
124
.
The second lens
121
gathers light from the optical fiber
118
which is reflected at the half mirror
124
.
A holder
126
, which has the glass tube
123
and an outer sheath
125
of the optical fiber
118
fixed in its hollow interior, the light emitting element
117
, the first and second lenses
119
and
121
, the light receiving element
122
and the glass block
120
are received in a housing
127
.
Another system is also proposed in Japanese Patent Application Unexamined Publication No. 63-175539, which is as shown in FIG.
8
.
In this system, as shown in
FIG. 8
, light emitted from a light emitting means
129
of a light emitting and receiving device
128
passes through a half mirror
130
, enter and travel through an optical fiber
131
, is reflected at a half mirror
133
of a light emitting and receiving device
132
, and pass through a diffraction grating
134
into a light receiving means
135
.
Description of the operation in the opposite direction will be omitted. Denoted
136
is a light receiving means and
137
is a light emitting means.
With the above systems, however, because each light emitting and receiving device is provided with a half mirror as an indispensable component, loss of optical power has been inevitable. In other words, if light passes through a half mirror in optical communications, its amount becomes one half the amount before passing through (reflection at) the half mirror, resulting in the loss mentioned above.
Further, because of the structure in which the light receiving means receives light after it is reflected at the half mirror, it is necessary that the receiving means is situated at a position perpendicular to the axis of the optical fiber, the light emitting and receiving device becomes unfavorably upsized.
SUMMARY OF THE INVENTION
This invention has been accomplished to overcome the above drawbacks and an object of this invention is to provide a light emitting and receiving device which reduces loss of optical power, and which is downsized.
In order to attain the object, according to this invention, there is provided a light emitting and receiving device which comprises: an optical fiber; a light propagating member capable of propagating light therethrough, which is provided with a light emitting means, the light emitting means converting first electrical signals into first optical signals; and a light receiving means which receives second optical signals and converts the second optical signals into second electrical signals, the light receiving means being disposed coaxially with the optical fiber, wherein the light propagating member is situated between an end of the optical fiber and the light receiving means, such that the light emitting means emits the first optical signals into the optical fiber at the end, and that the light propagating member receives from the optical fiber and propagates therethrough the second optical signals to the light receiving means.
In the above light emitting and receiving device, due to the arrangement in which the light propagating member with the light emitting means is situated between an end of the optical fiber and the light receiving means, the light having traveled through the optical fiber passes through the light propagating member to the light receiving means, and the light emitted from the light emitting means passes through the light propagating member or directly into the optical fiber.
Without a half mirror which has conventionally been used as an indispensable component, in the present device, for example the light from the optical fiber is prevented from being reduced by half, thereby to realize a better optical communication.
Further, due to the arrangement in which the light receiving means is disposed coaxially with the optical fiber and the light emitting means is provided on the light propagating member between the light receiving means and the optical fiber, a more compact light emitting and receiving device than the conventional one is attained. In other words, because no half mirror is employed which reflects light, no main component needs to be located at a position in a direction of reflection of light from the half mirror or direction perpendicular to the axis of the optical fiber, a compact light emitting and receiving device is attained.
Thus, loss of optical power is suppressed, while attaining a downsized light emitting and receiving device.
Incidentally, during propagation of light through the light propagating member to the light receiving means, part of the light may be obstructed by the light emitting means. This, however, can be coped with by reducing the surface area of the light emitting means facing the optical fiber. The loss can be minimized in this way and will cause no problem.
Preferably, the light propagating member has a cavity formed therein for mounting the light emitting means in an integrated manner with the light propagating member.
In this way, the light emitting means may be prepared in advance, in a separate process, in conformity to the shape of the cavity and combined integrally with the light propagating member by mounting same in the cavity.
Preferably, the cavity is formed at such position as to open to an end surface of the light propagating member opposed to the end of the optical fiber.
This arrangement allows the light from the light emitting means to directly enter the optical fiber, while reducing the number of boundary surfaces between the li
Armstrong Westerman & Hattori, LLP
Yazaki -Corporation
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