Optical transmitter-receiver

Details Optical transmitter-receiver Optical transmitter-receiver

2001-01-29

2004-04-20

Chan, Jason (Department: 2633)

Optical communications

Diagnostic testing

C398S012000, C398S015000, C398S016000, C398S020000, C398S022000, C398S037000

Reexamination Certificate

active

06724993

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an optical transmitter-receiver in an optical communications system using optical fibers, and particularly to an optical transmitter-receiver suitable for a system employing plastic optical fibers. In addition, the present invention relates to a mechanism for preventing the adverse effects of laser light from the optical transmitter-receiver on humans.
BACKGROUND ART
FIG. 13
is an explanatory diagram showing a conventional fiber-optic communications system. As shown in FIG.
13
(
a
) the system includes optical transmitter-receivers
101
and
102
linked by optical fibers
103
and
104
. An optical signal
105
is transmitted from the optical transmitter-receiver
101
to the optical transmitter-receiver
102
via the optical fiber
103
. Similarly, an optical signal
106
transmitted from the optical transmitter-receiver
102
is transferred to the optical transmitter-receiver
101
via the optical fiber
104
. This fiber-optic communications system is referred to as a point-to-point type.
FIG.
13
(
b
) shows a shared bus type communications system. This system comprises optical transmitter-receivers
111
,
112
,
113
, and
114
and a passive optical splitter
115
. Optical signals transmitted from the optical transmitter-receiver
111
are transferred to the optical transmitter-receivers
112
through
114
after being branched by the optical splitter
115
. Optical signals transmitted from the optical transmitter-receivers
112
through
114
are merged by the optical splitter
115
and transferred to the optical transmitter-receiver
111
. In actual operations, the system uses a time-sharing method to prevent the optical transmitter-receivers
112
through
114
from transmitting optical signals simultaneously. The optical splitter
115
can be thought of as a device functioning to combine the optical signal channels.
FIG. 14
is a timing chart illustrating how optical signals are transferred in a conventional fiber-optic communications system. FIG.
14
(
a
) shows the state of optical signal transmission in a fiber-optic communications system using the point-to-point method, as shown in FIG.
13
(
a
). As shown in the diagram, valid data
122
and
124
are transmitted when available, and idle signals
121
and
123
are transmitted when there is no valid data. During normal operations, therefore, some type of optical signal is being exchanged between the two optical transmitter-receivers
101
and
102
at all times.
FIG.
14
(
b
) is a time chart for the state of optical signals in the shared bus optical communications system of FIG.
13
(
b
). In this method, valid data
125
and
126
are transmitted, but idle signals are not transferred therebetween. Therefore, there are periods in which no optical signals are being transferred.
The above-described optical transmitter-receivers do not give rise to problems when properly connected by cables. However, if an optical transmitter-receiver
131
is not connected to an optical fiber, as shown in FIG.
15
(
a
), a laser light
132
is emitted from the optical transmitter-receiver
131
into free space. Such laser light
132
can have an adverse effect on a human eye
133
. The laser light can adversely affect the human eye even when a cover or the like is provided over the optical fiber connection point on the optical transmitter-receiver. For example, when an optical fiber
135
is connected on one end to the optical transmitter-receiver
131
and while the other end is open to free space, as shown in FIG.
15
(
b
), a laser light
136
is emitted into free space from the open end of the optical fiber
135
and can cause harm to the human eye
133
. Conventionally, the output of the laser light from the optical transmitter-receiver has been limited to avoid harming the human eye. In other words, the optical transmitter-receiver is designed to prevent effects on the human eye even when the laser light is emitted into free space.
With the increasing transfer rates of laser light, however, a high output laser light is becoming more necessary to enable proper reception of the laser signals that decay from long-distance transfers through optical fibers. Recently, a graded index plastic optical fiber (GI-POF) was developed. This optical fiber is far less expensive than conventional quartz optical fibers and has a broad transmission band, which is thought to be suitable for application to local area networks (LAN) and communication networks of information appliances. At this stage, however, the GI-POF still has a greater loss than quartz optical fibers and cannot be transmitted reliably over long distances.
As a safety measure, a mechanism has been proposed in U.S. Pat. No. 5,428,471 that automatically shuts down operations of an optical amplifier locally when there is a disruption in the optical fiber and automatically restores operations when the connection has been restored.
DISCLOSURE OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide a mechanism that improves the transmission output of an optical transmitter-receiver suitable for a point-to-point fiber-optic communications system, while preventing adverse effects on the human eye.
These objects and others will be attained by an optical transmitter-receiver for use in a point-to-point fiber-optic communications system connected by optical fibers. The optical transmitter-receiver comprises a dummy signal generator; a detector for detecting an optical signal received from another optical transmitter-receiver; a switch for switching between a dummy signal and a normal signal and transmitting a dummy signal when an optical signal is detected from another optical transmitter-receiver; and a mechanism for changing the transmission power and reducing the transmission power when an optical signal is detected from another optical transmitter-receiver.
An optical transmitter-receiver for point-to-point optical transmission and having the construction described above can prevent harm to the human eye by laser light emitted into free space when an optical fiber connection is broken. Further, the transmitter-receiver can automatically resume proper transmission when the optical fiber is properly reconnected.
The dummy signal generator can be provided either separately from a mechanism for outputting normal signals or together with the same. The above features and others will be described in more detail below within the scope of the attached claims.


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