Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-03-19
2001-08-21
Negash, Kinfe-Michael (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06278536
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to an optical transmission device for bi-directional optical communications, which performs bi-directional optical communications by transmitting optical signals having different wavelengths in two ways.
(2) Description of the Related Art
For a transmission type communication system designed to construct a multimedia network, an optical communication system capable of increasing transmission capacity has been used in recent years. Various multiplexing systems have been available in order to attain extra-large capacity in the optical communication system. Such multiplexing systems include, for example, a time-division multiplexing (abbreviated as TDM) transmission system, an optical time-division multiplexing (OTDM) transmission system, a wavelength-division multiplexing (WDM) transmission system, and so on.
Among these multiplexing systems, the WDM transmission system is promising, because it facilitates flexible construction of an optical communication network (lightwave network) by using an erbium-doped optical fiber amplifier (EDFA) having a wide gain band so as to perform optical level cross connection, branching/insertion of optical signals or multiplexing of various services.
In the lightwave network employing such a WDM transmission system, for example, an optical add/drop multiplexer (ADM) is used. This optical ADM includes transit points called nodes provided in the middle way of a transmission line, and enables free branching or insertion of optical signals by selectively transmitting, among multiplexed optical signals, an optical signal having a specified wavelength through the nodes and receiving the other optical signals having wavelengths different from the specified one by the nodes.
In other words, in the WDM transmission system, by utilizing the optical ADM, a speed for performing transmission among the nodes can be increased, and the network can be made flexible.
The lightwave network employing the foregoing WDM transmission system typically uses a uni-directional wavelength-division multiplexing system, which transmits optical signals by using optical fibers [single mode fiber (SMF)] individually allocated to clockwise and counterclockwise directions.
Referring to
FIG. 19
, there is shown an example of a wavelength-division multiplexing communication system
50
which employs the foregoing uni-directional wavelength-division multiplexing system. The wavelength-division multiplexing system
50
shown includes two opposing optical transmission devices
501
and
502
which are connected to each other by two uni-directional optical fibers
81
A and
81
B.
Specifically, between the optical transmission devices
501
and
502
, optical signal transmission is performed as follows. Optical signals (&lgr;
1
-&lgr;
8
) are transmitted from the optical sender (OS)
80
A of the optical transmission device
501
. These optical signals are then received through the optical fiber
81
A by the optical receiver (OR)
82
A of the optical transmission device
502
. Optical signals (&lgr;
1
-&lgr;
8
) are transmitted from the OS
80
B of the optical transmission device
502
. These optical signals are then received through the optical fiber
81
B by the OR
82
B of the optical transmission device
501
.
Thus, in the wavelength-division multiplexing communication system
50
shown in
FIG. 19
, the optical fibers
81
A and
81
B are individually allocated to the two directions of the optical signals. All the optical signals transmitted through each of the optical fibers
81
A and
81
B are transmitted in the same direction.
However, in the wavelength-division multiplexing communication system
50
, it may become impossible to perform normal communications between the optical transmission devices
501
and
502
. This problem occurs because the transmission of the clockwise optical signals is interrupted if, among the two optical fibers
81
A and
81
B, for example, as shown in
FIG. 20
, a failure occurs in one optical fiber
81
A and the communications are cut off (may be referred to as communication cut-off, hereinafter).
SUMMARY OF THE INVENTION
The present invention was made in order to solve the problems discussed above. It is an object of the invention to provide an optical transmission device for bi-directional optical communications, which enables bi-directional wavelength-division multiplexing optical communications to be performed by unifying transmission routes (flows) of optical signals transmitted in two ways in a single direction and using the existing optical transmission device for uni-directional optical communications.
In order to achieve the objective, according to an aspect of the present invention, an optical transmission device for bi-directional optical communications is provided. This optical transmission device used for bi-directional optical communications is positioned between bi-directional communication optical transmission lines for performing bi-directional optical communications by transmitting optical signals having wavelengths different between clockwise and counterclockwise directions, and performs specified optical transmission processing for optical signals transmitted through the bi-directional communication optical transmission lines. The optical transmission device used for bi-directional optical communications comprises a uni-directional optical signal processing unit for performing specified optical signal processing for optical signals transmitted in a single direction and a uni-direction/bi-direction changing unit for unifying the flows of clockwise and counterclockwise optical signals in a single direction, then inputting these flow-unified optical signals to the uni-directional optical signal processing unit and dividing the flow of optical signals from the uni-directional optical signal processing unit into two ways between clockwise and counterclockwise directions.
In the optical transmission device of the present invention used for bi-directional optical communications, the uni-directional optical signal processing unit includes at least one input port and one output port. The uni-direction/bi-direction changing unit inputs clockwise optical signals inputted through one bi-directional communication optical transmission line and counterclockwise optical signals inputted through the other bi-directional communication optical transmission line to the input port of the uni-directional optical signal processing unit. The uni-direction/bi-direction changing unit outputs, among optical signals outputted from the output port of the unidirectional optical signal processing unit, clockwise optical signals to the latter bi-directional communication optical transmission line and counterclockwise optical signals to the former bi-directional communication optical transmission line.
In the optical transmission device of the present invention used for bi-directional optical communications, the uni-direct-on/bi-direction changing unit includes an optical wavelength multiplexing unit for multiplexing clockwise and counterclockwise optical signals and outputting the multiplexed optical signals to the input port of the uni-directional optical signal processing unit, an optical wavelength demultiplexing unit for demultiplexing processed optical signals from the output port of the uni-directional optical signal processing unit into clockwise and counterclockwise optical signals, a first optical signal branching unit for branching clockwise optical signals from the former bi-directional communication optical transmission line to the optical wavelength multiplexing unit and counterclockwise optical signals obtained by demultiplexing performed in the optical wavelength demultiplexing unit to the former bi-directional communication optical transmission line, and a second optical signal branching unit for branching counterclockwise optical signals from the latter bi-directional communication optical transmission line to the optical wavelength multiplexing unit and clo
Chikama Terumi
Kai Yutaka
Fujitsu Limited
Negash Kinfe-Michael
Staas & Halsey , LLP
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