Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2002-08-02
2004-04-06
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S060000, C385S088000, C385S093000
Reexamination Certificate
active
06718091
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a bi-directional optical transmission and reception system for executing transmission and reception by using one-core optical fiber. The present invention also relates to an optical transmission and reception module and an optical cable for use in the optical transmission and reception system. In particular, the present invention relates a digital communication system such as IEEE 1394 and USB2 capable of making high-speed transmission.
A plastic optical fiber cable has been hitherto used in optical communication at home. The plastic optical fiber cable is flexible, can be wired easily, and costs low. Therefore, audio digital signals are actually transmitted in domestic networks, such as audiovisual devices and personal computers, through the plastic optical fiber cable.
At home, it is expected that various factors such as rearrangement of furniture in a room cause frequent alteration of wiring of the optical fiber cable, accompanied with the removal and installation of an optical plug and/or elongation of the optical fiber cable. It is also expected that a user switches a communication medium, depending on use conditions. That is, in a short-distance low-speed communication, optical spatial transmission will be used, whereas in long-distance high-speed communication, the optical fiber cable will be used. To meet the need, development of optical transmission and reception systems are being made.
The protocols (communication methods) in the optical transmission and reception system are classified into a full duplex communication method and a half duplex communication method. The former is capable of accomplishing transmission and reception simultaneously, whereas the latter is incapable of accomplishing reception unless transmission has terminated. It is conceivable that real time transmission of information will be mainly made even at home in the near future. Thus, the construction of the optical transmission and reception system adopting the full duplex communication method is desired.
As an example of a conventional optical transmission and reception module for realizing such an optical transmission and reception system, an optical transmission and reception module proposed in the Japanese Patent Application Laid-Open No. 7-248429 is described below with reference to FIG.
1
. The optical transmission and reception module is intended to be compact and inexpensive by adopting the Foucault prism as an optical branching element.
According to the proposed optical transmission and reception module, transmission light T emitted by a light emitting element
101
transmits through a cover glass
102
installed on a package and is divided into halves by a Foucault prism
103
. After condensed by a condenser lens
104
, a half is coupled to, or incident on, an optical fiber
107
through a rod lens
105
. On the other hand, reception light rays R discharged from an optical fiber
107
having the rod lens
105
disposed at its front end are condensed by the condenser lens
104
, incident on the Foucault prism
103
, and then divided into halves. After they pass through the cover glass
102
, only a half is coupled to a light receiving element
106
.
However, the disposition relationship between the light emitting element
101
and the light receiving element
106
shown in
FIG. 1
forces the light receiving element
106
to be located at a position apart from the condensed point of the reception light R. Accordingly, to detect the diverged reception light R, it is necessary to prepare a large light receiving element
106
. Consequently, the electrostatic capacity of the light receiving element
106
is large. Thus it is difficult to realize a high-speed communication.
The limitative position of the light receiving element
106
may be caused by that the light-condensing system consists of the single condenser lens
104
interposed between the optical fiber
107
and the Foucault prism
103
and that the vertical angle of the Foucault prism is as small as 2-3 degrees, as described in a paragraph denoted by [0018] of the Japanese Patent Application Laid-Open No. 7-248429.
As another prior art example, there is an optical transmission and reception module proposed in the Japanese Patent Application Laid-Open No. 10-39181, which module carries out optical transmission and reception through one optical fiber by the half duplex communication method, as shown in FIG.
2
.
According to the optical transmission and reception module, half of transmission light rays T emitted by a laser diode LD serving as a light emitting element are reflected from a 50%-beam splitter film BS formed on a prism
121
provided on a light receiving element PD, condensed by a lens
122
, and connected to an optical fiber
123
. On the other hand, half of reception light rays R discharged from the optical fiber
123
pass through the beam splitter film BS and are connected to the light receiving element PD.
This prior art is advantageous in that one optical fiber is used to carry out the optical transmission and reception by the half duplex communication method. However, because light is branched by means of the beam splitter film BS formed on the prism
121
, the optical amount is reduced to half in each of the transmission and the reception. Thus, the optical transmission and reception module is not suitable for a long-distance transmission and reception of an optical signal.
As still another prior art example, there is an optical transmission and reception module proposed in the literature “Miniaturized Transceiver using Simplex POF for IEEE 1394 (International POF Conference '99, pages 205-208)”. The optical transmission and reception module carries out optical transmission and reception through one optical fiber by the full duplex communication method, as shown in FIG.
3
.
According to the optical transmission and reception module, transmission light rays T are emitted by an LD serving as the light emitting element, condensed by a cylindrical lens
131
, reflected from a reflection film
133
(99%) formed on a prism
132
, and converged. The converged light is connected to, or incident on, an end surface of the optical fiber. On the other hand, reception light rays R are discharged from the optical fiber and are mostly connected to a photodiode PD, although a part of the light rays R is lost by the reflection film
133
. According to the method, because the light rays are connected to the optical fiber, with the light rays converged, in principle, Fresnel light on the end surface of the optical fiber is not connected to the photodiode PD. Thus, the full duplex transmission and reception can be accomplished with one optical fiber.
The prior art shown in
FIG. 3
has merits because it can accomplish transmission and reception by using one optical fiber, has only a small light loss in a transmission time, and the transmission light T and the reception light R can be almost completely separated from each other, i.e., the full duplex optical system can be realized. However, in the prior art, the reflection film
133
is formed on the prism, and the cylindrical lens
131
is formed on the reflection film
133
. That is, a large number of processes are required in the stage of preparing the optical branching elements. Consequently, the manufacturing cost is high. Further, because the reception light rays R do not pass through a lens, the light receiving element PD is required to be large. Consequently, the electrostatic capacity of the light receiving element PD is large. That is, the conventional art is unsuitable for high-speed communication.
Sharp Kabushiki Kaisha has proposed an optical transmission and reception system as shown in
FIGS. 4A and 4B
in the Japanese Patent Application No. 11-5872 (filed on Jan. 12, 1999).
In the optical transmission and reception system, it is possible to use a digital audio optical fiber cable which has already spread, and execute two-way communication through one optical cable having one-core optical fi
Ishihara Takehisa
Kashida Hajime
Terashima Kentaro
Conlin David G.
Edwards & Angell LLP
Hartnell, III George W.
Palmer Phan T. H.
Sharp Kabushiki Kaisha
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