Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2001-08-09
2003-09-30
Chang, Audrey (Department: 2872)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S049000, C385S089000, C385S093000
Reexamination Certificate
active
06626584
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a two-way optical communication device and a two-way optical communication system both capable of transmitting and receiving optical signals bidirectionally, and a method for assembling the two-way optical communication device. More particularly, the present invention relates to a two-way optical communication device and a two-way optical communication system both employed for home communication, device-to-device communication, a local area network (LAN), and the like, in which a multi-mode optical fiber, such as a plastic optical fiber, is used as a transmission path.
2. Description of the Related Art
As an information society develops, network technologies using fiber-optic communication have been a focus of attention. Particularly, such technologies are applied to household communication and device-to-device communication with the advent of recent plastic optical fibers having low light loss and broad band capabilities. Hereinafter, plastic optical fibers are also referred to as POFs.
Conventionally, a dominating optical communication system for transmitting and receiving optical signals having the same wavelength through an optical fiber(s) as a transmission medium is a system in which two optical fibers are used to perform full duplex optical communication. However, when two optical fibers are employed, it is difficult to reduce the size of an optical communication device, and the cost of the optical fibers is increased with an increase in a transmission distance. Therefore, a two-way optical communication device has been proposed in which a single optical fiber is used to perform full duplex optical communication.
In such a two-way optical communication device, transmission and reception are performed on the same optical fiber, so that it is important as to how to prevent interference between transmitted light and incoming light. Causes of incoming light interfering with transmitted light are: (1) when transmitted light enters an optical fiber, a portion of the light is reflected by an end surface of the optical fiber (hereinafter referred to as near-end reflection); (2) when transmitted light which has propagated through an optical fiber is emitted from the optical fiber, a portion of the light is reflected by an end surface of the optical fiber (hereinafter referred to as far-end reflection); (3) transmitted light is reflected by the two-way optical communication device on the other end (hereinafter referred to as reflection on the other-end module); (4) internally scattered light within the two-way optical communication device (hereinafter referred to as stray light); and the like. Further, there are problems other than the optical interference between transmitted light and incoming light, such as (5) electrical or electromagnetic noise. In this case, a signal-to-noise (S/N) ratio is reduced.
Japanese Laid-Open Publication No. 10-153720 discloses a representative method which has been conventionally proposed in order to solve the above-described problems. In this method, a polarization separation device (polarization separation film) is used to separate transmitted light from incoming light. This conventional technique will be described with reference to FIG.
16
.
In a two-way optical communication device
1600
as shown in
FIG. 16
, transmitted light
108
emitted from a laser diode
104
, which is in the form of S-polarization, enters a polarization reflection film
107
provided on a tilted surface of a prism
111
. The transmitted light
108
is mostly reflected by the polarization reflection film
107
, condensed by a lens
106
, and coupled to an optical fiber
102
. Incoming light
109
emitted from the multi-mode optical fiber
102
is condensed by the lens
106
and enters the polarization reflection film
107
in the form of random polarization. The substantial half of the incoming light
109
is reflected by the polarization reflection film
107
while the remaining half is transmitted by the polarization reflection film
107
to be coupled to a photodetector
105
. In this case, the transmitted light
108
reflected by the optical fiber
102
is in the form of S-polarized light and therefore, is substantially perfectly reflected by the polarization reflection film
107
so as not to be coupled to the photodetector
105
. Therefore, transmitted light of near-end reflection can be prevented from interfering with the incoming light.
Further, there is another known method which prevents transmitted light of near-end reflection from interfering with incoming light by providing a light blocking plate between a transmitter portion and a receiver portion. This conventional technique will be described with reference to FIG.
17
.
In a two-way optical communication device
1700
as shown in
FIG. 17
, transmitted light
208
emitted from a light emitting element
204
is condensed by a transmission optical system
206
and coupled to an optical fiber
202
. Incoming light
209
emitted from the optical fiber
202
is condensed by a reception optical system
224
and coupled to a photodetector
205
. Further, a light blocking plate
207
made of metal or the like is provided between a transmitter portion and a receiver portion so that the transmitted light
208
reflected by the optical fiber
202
is prevented from being coupled to the photodetector
205
.
Furthermore, Japanese Laid-Open Publication No. 62-222211 discloses a method in which transmitted light is condensed by a spheroid type mirror and coupled to an optical fiber. In this method, transmitted light emitted from a light emitting element is reflected from a concave mirror toward an optical fiber, condensed and coupled to an optical fiber. This concave mirror is in the shape of a spheroid. A light emitting element is provided at one of the two focus positions of the concave mirror, while an end surface of the optical fiber is provided at the other focus position. Therefore, transmitted light emitted from the light emitting element is conversed on the end surface of the optical fiber and coupled to the optical fiber. Similarly, if a photodetector is provided instead of the light emitting element, it is possible to efficiently receive incoming light emitted from an optical fiber.
In the method disclosed in the above-described Japanese Laid-Open Publication No. 10-153720, the substantial half of incoming light is reflected by the polarization reflection film
107
, resulting in a reception loss of about 3 dB. Therefore, light cannot be efficiently used. In this conventional technique, transmitted light of near-end reflection can be prevented from interfering with incoming light. However, since light of far-end reflection and of reflection on an other-end module has random polarization directions, it is difficult to separate between transmitted light and incoming light. Further, since the conventional technique utilizes polarization, an inexpensive light emitting diode (LED) cannot be used as the light emitting element. Furthermore, in the conventional technique, an expensive polarization separation film (polarization reflection film) is required, leading to an increase in cost. Further still, in the conventional technique, the laser diode
104
is disposed close to the photodetector
105
, both of which are provided on a substrate. Furthermore, since the laser diode
104
is not shielded, electrical or eletromagnetic noise easily occurs.
A problem with the two-way optical communication device
1700
, in which the light blocking plate
207
is used to separate the transmitter portion and the receiver portion, is that the number of parts is increased raising the cost, and that a region of the optical fiber
202
corresponding to the thickness of the light blocking plate
207
cannot be used, resulting in a reduction in reception efficiency. Further, in this conventional technique, the degree of freedom in disposing the light emitting element
204
and the photodetector
205
is low. Therefore, the transmission optical sys
Fujita Hideaki
Ishii Yorishige
Iwai Yoshifumi
Kurata Yukio
Matsushima Toshiyuki
Allen Denise
Chang Audrey
Edwards & Angell LLP
Neuner George W.
Sharp Kabushiki Kaisha
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