Optical communications – Multiplex – Broadcast and distribution system
Reexamination Certificate
1998-07-24
2003-09-16
Pascal, Leslie (Department: 2633)
Optical communications
Multiplex
Broadcast and distribution system
C398S082000
Reexamination Certificate
active
06619865
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an information transmission system employing optical communication, and more particularly to a network with high reliability and flexibility using optical frequency selection and optical frequency conversion functions.
Recently, with the advance of coherent communication techniques, there has been proposed a network utilizing optical frequency division multiplexing (or optical wavelength division multiplexing) transmission.
Typical examples of the optical frequency or wavelength division multiplexing network are found in paper (1) “IEEE Journal of Lightwave Technology, Vol. 7, No. 11, pp. 1759-1768, 1989” and paper (2) “Proceedings of IOOC, '90, pp. 84-95, 1990”. Networks described in other papers are similar to those described in the above two papers.
A network configuration described in the paper (1) is shown in
FIG. 2
of the paper and part thereof corresponding to the present invention is shown in
FIG. 2
of the accompanying drawings.
FIG. 2
shows a line distribution and collection system of the network shown in the paper (1). The system of
FIG. 2
includes a remote node
10
having a wavelength demultiplexer
500
and a wavelength multiplexer
501
connected through optical fibers
100
and
200
, respectively, to a central office and subscriber terminals
20
-
1
~N connected through optical fibers
300
-
1
~N to
400
-
1
~N to the remote node. Signals having wavelength &lgr;
11
to &lgr;
1n
transmitted from the central office in wavelength division multiplexing fashion are demultiplexed into signals having the respective optical frequencies by the wavelength demultiplexer to be transmitted to the subscriber terminals
20
-
1
~N. On the countrary, signals having wavelength &lgr;
21
to &lgr;
2n
transmitted from the subscriber terminals
20
-
1
~N are wavelength-multiplexed by the wavelength multiplexer to be transmitted to the central office.
In the above-mentioned system, the subscriber terminals
20
-
1
~N must transmit and receive signals having different wavelengths, respectively. In the paper (1), as shown in
FIG. 4
thereof, receivers are common to the subscriber terminals, while transmitters employ lasers having different wavelengths for each subscriber terminal. Accordingly, a laser having stable wavelength must be provided in each subscriber terminal and hence there is a problem in reliability and flexibility. Further, movement of the subscriber terminal is not easy.
In the paper (1), transmission employs the conventional intensity modulation optical communication and accordingly it is difficult that the multiplex degree of optical signal exceeds 100. Even in this system, a coherent receiver capable of effecting multiplexing with the multiplex degree of 1000 or more can be used. In this case, receivers capable of receiving signals having wavelengths &lgr;
11
to &lgr;
1n
transmitted from the central office assigned to the subscriber terminals
20
-
1
~N with wavelength division multiplexing are required. Accordingly, the receivers are expensive as compared with the present invention described later.
Further, coherent receivers having variable transmission wavelength and common to the subscriber terminals
20
-
1
~N can be employed. In this case, however, signals having wavelength &lgr;
21
to &lgr;
2n
transmitted from the subscriber terminals are also multiplexed and accordingly the wavelength must be stable. It is difficult to remotely control the wavelength and hence the reliability of the network is also degraded.
Furthermore, when it is to be attempted that the optical fibers
300
-
1
~N and
400
-
1
~N are combined to effect bi-directional transmission by means of a single optical fiber per subscriber terminal, “it is basically required that all of wavelengths &lgr;
11
to &lgr;
1n
and &lgr;
21
to &lgr;
2n
are different” and utilization efficiency of frequency is deteriorated.
A network configuration described in the paper (2) is shown in
FIG. 1
of the paper and is shown in
FIG. 3
of the accompanying drawings. in corresponding manner to the present invention. The system includes a remote node (not shown in the paper (2)) having a power divider
502
and a transport star coupler or wavelength multiplexer
501
connected to a central office (not shown in the paper (2)) through optical fibers
100
and
200
and fixed wavelength receivers and tunable transmitters or subscriber terminals
20
-
1
~N connected to the remote node through optical fibers
300
-
1
~N and
400
-
1
~N. All optical signals having wavelengths &lgr;
11
to &lgr;
1n
transmitted from the central office with wavelength division multiplexing are transmitted to the subscriber terminals
20
-
1
~N by means of the power divider and the subscriber terminals
20
-
1
~N receive only necessary signals by receivers for receiving only particular wavelength. On the contrary, signal-having wavelength; &lgr;
21
to &lgr;
2n
transmitted from the subscriber terminals are wavelength-multiplexed by the wavelength multiplexer to be transmitted to the central office.
This system is featured in that an inexpensive power divider is used instead of the wavelength demultiplexer of the paper (1) and wavelength selection reception which is a maximum advantage of coherent transmission can be utilized.
The maximum drawback of this system is that all of the subscriber terminals
20
-
1
~N can receive all signals. Thus, there is a problem in privacy characteristic.
Accordingly, in the system of the paper (2), receivers having fixed receive frequency are disposed in each of the subscriber terminals
20
-
1
~N. However, there remains the problem in the privacy characteristic for malicious operation.
Further, when coherent transmitter and receiver are used, the transmitter and receiver of the system have also the same problem as in the transmitter and receiver of the paper (1).
The conventional network utilizing the wavelength division multiplexing has drawbacks as follows. Particularly, since the wavelength employed between the central office and the remote node and between the remote node and the subscriber terminals is the same, a failure occurring in one subscriber terminal influences all of the subscriber terminals connected to the remote node to which the subscriber terminal having the failure is connected. Further, since the transmitter and receiver of the subscriber terminal must deal with a multiplicity of frequencies and require the same reliability as that of the central office, it is very expensive. In addition, expansion of the network and rearrangement of the subscriber terminals are not made easily and the flexibility of the network is lacking.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a network having transmitters and receivers for terminals utilizing inexpensive common optical frequency division multiplexing and having good privacy characteristic, high reliability and flexibility.
In order to achieve the above object, the present invention has the following measures.
1. A node for distributing signals transmitted in optical frequency division multiplexing to terminals selects an optical frequency corresponding to the terminal from the transmitted signals and converts the selected optical frequency into an optical frequency common to the terminals as determined in an interface so as to be transmitted to the terminals.
2. A node for collecting signals transmitted from the terminals and transmitting the signals in optical frequency division multiplexing fashion converts the signals transmitted with the optical frequency determined in the interface common to the terminals into optical frequencies to be transmitted in the optical frequency division multiplexing fashion.
FIG. 1
shows a basic logical configuration of the present invention. It comprises a remote node
10
connected through optical speech paths or optical channels
100
and
200
to an upper node and terminals
20
-
1
~N connected to the remote node
10
through optical fibers
300
-
1
~N and
400
-
1
~N. The remote node
10
inc
Takai Atsushi
Takase Akihiko
Takeyari Ryoji
Pascal Leslie
Singh Dalzid
LandOfFree
Optical frequency division multiplexing network does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical frequency division multiplexing network, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical frequency division multiplexing network will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3020927