Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-05-25
2002-12-24
Negash, Kinfe-Michael (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200
Reexamination Certificate
active
06498664
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wavelength discriminating function, and more particularly to a wavelength division multiplexing transmission device and method having a wavelength discriminating function applicable to a wavelength division multiplexing transmission system in an optical communication system.
Recently, there has been considerable activity of increasing communication channels due to an abrupt demand for communications in optical transmission systems. However, an extension work of optical fiber cables needs a huge amount of cost. Hence, a wavelength division multiplexing transmission system is positioned as a key scheme because such a system efficiently utilizes the existing optical fiber cables and can increase the channel capacity by increasing the degree of multiplexing. Nowadays, four-wave multiplexing, eight-wave multiplexing, 16-wave multiplexing and 32-wave multiplexing have been used in practice in the wavelength division multiplexing transmission system.
2. Description of the Related Art
FIG. 1
is a block diagram of a conventional wavelength division multiplexing transmission system (four-wave multiplexing). Line terminal equipment LTE receives four data signals STM-M of a relatively low bit rate and multiplexes the data signals into an optical signal STM-N of a relatively high bit rate having a given wavelength by a method which will be described with reference to FIG.
2
.
A line terminal equipment (LTE)
11
multiplexes
1
multiplexes four data signals STM-M#
1
-#
4
of a relatively low bit rate into a single optical signal STM-N of a relatively high bit rate having a wavelength &lgr;
1
to an optical coupler
15
. Similarly, line terminal equipment LTE
12
,
13
and
14
respectively output multiplexed optical signals STM-N having wavelengths &lgr;
2
, &lgr;
3
and &lgr;
4
and supply them to the optical coupler
15
, which has a wavelength multiplexing function (MUX).
The wavelengths &lgr;
1
-&lgr;
4
are arranged as shown in FIG.
3
. As shown in
FIG. 3
, the wavelengths &lgr;
1
-&lgr;
4
are respectively set equal to 1548.51 nm, 1551.72 nm, 1554.94 nm and 1558.17 nm. With this arrangement, the wavelength division multiplexing can be realized. Further, 8-wave multiplexing and 16-wave multiplexing can be realized as shown in FIG.
3
.
Turning to
FIG. 1
again, the optical coupler
15
combines the four high-bit-rate optical signals STM-N having the different wavelengths from the line terminal equipment
11
-
14
, and outputs a combined, namely, multiplexed optical signal to an optical coupler
17
via an optical fiber cable
16
.
The optical coupler
17
, which has a wavelength demultiplexing function (DMUX), demultiplexes the multiplexed STM-N signal received from the optical fiber cable
15
into four optical signals STM-N having the different wavelengths. Then, the optical coupler
17
outputs the optical signal STM-N of the wavelength &lgr;
1
to line terminal equipment LTE
18
. Similarly, the optical coupler
17
outputs the optical signals STM-N of the wavelengths &lgr;
2
-&lgr;
4
to line terminal equipment LTE
19
-
21
, respectively.
The line terminal equipment
18
is supplied with the high-bit-rate optical signal STM-N of the wavelength &lgr;
1
and demultiplexes it into four low-bit-rate data signals STM-M by a method which will be described later with reference to FIG.
2
. Similarly, the line terminal equipment
19
,
20
and
21
are respectively supplied with the high-bit-rate optical signals STM-N of the wavelengths &lgr;
2
-&lgr;
4
and demultiplex them into four low-bit-rate data signals STM-M.
The line terminal equipment LTE will be described with reference to
FIG. 2
, which is a block diagram thereof. The line terminal equipment
11
receives the four low-bit-rate data signals STM-M#
1
-STM-M#
4
from an external device, and outputs these signals to a multiplexer (MUX)
29
via interface parts
25
-
28
, respectively. The multiplexer
29
inserts OHBs (Over Head Bit or Over Head Byte), which are used to transfer maintenance information between communication devices.
A system controller
30
performs various control procedures in accordance with information and data supplied from a local terminal
33
and/or a remote terminal
23
such as a workstation (WS) connected to a network management system (NMS)
22
. The remote terminal
23
enables a remote maintenance work.
The multiplexer
29
multiplexes the four data signals STM-M supplied thereto into a single high-bit-rate data signal, and adds OHB data thereto. Then, the multiplexer
29
supplies an electro-optic converter (E/O)
34
with the multiplexed data signal with the OHB data added thereto.
The electro-optic converter
34
converts the received electric signal into a corresponding optical signal. Although not shown in
FIG. 2
, the optical signal outgoing from the electro-optic converter
34
is supplied to the optical coupler
15
shown in
FIG. 1
, which coupler multiplexes other optical signals generated similarly. Then, the multiplexed optical signal is output from the optical coupler
15
to the optical coupler
17
via the optical fiber cable
16
.
An opto-electric (O/E) converter
36
receives the multiplexed optical signal from the optical fiber cable
16
. The converter
36
converts the received optical signal into a corresponding electric signal, which is supplied to a demultiplexer (DMUX)
37
. The demultiplexer
37
demultiplexes the received signal into the data signals STM-M#
1
-STM-M#
4
and the OHB data. The data signals STM-M#
1
-STM-M#
4
are respectively supplied to devices of the next stage via interface parts
43
-
46
. The OHB data is supplied to a system controller
38
, which performs various controls in accordance with instructions supplied from a local terminal
42
or the aforementioned remote terminal
23
.
A description will now be given of a transfer of the maintenance information between the communication devices using the OHB data. The wavelength division multiplexing transmission is used in an SDH (Synchronous Digital Hierarchy) optical communication system which conforms to the international standard of synchronous multiplexing recommended by ITU-T. In the SDH optical communication system, the maintenance information is transferred between the communication devices using the OHB data provided in the STM-N frame which is the unit for multiplexing. The way of using the OHB data is defined.
The minimum management interval between the communication devices in the SDH optical communication system is called “section”, and the OHB data for managing the section is called RSOH (Reg. Section Over Head). Conventionally, the RSOH has a section trace function of performing the inter-section management, called J
0
byte. The section tracing function using the J
0
byte shows from where the signal being transferred comes.
The section trace function will be described with reference to
FIG. 4. A
station (A)
50
is now located on the transmission side. The optical coupler
15
of the station
50
combines the optical signals respectively having the wavelengths &lgr;
1
-&lgr;
4
generated by the line terminal equipment
11
-
14
, and sends the multiplexed signal to a station (B)
51
located on the reception side. The interval between the stations
50
and
51
is the section, and the section trace function using the J
0
byte manages information on the section including the country number, the name of the station and the name of the transmitter device
However, in the wavelength division multiplexing transmission system, the J
0
bytes of all the wavelength-division-multiplexed signals having different wavelength have the same value because the J
0
bytes show from which the respective signals come from (station
50
in the case shown in FIG.
4
). Hence, it is impossible to check each of the wavelength-division-multiplexed signals having the different wavelengths by referring to the respective J
0
bytes. Conventionally, a spectrum analyzer is used to measure
Fujitsu Limited
Negash Kinfe-Michael
Staas & Halsey , LLP
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