Optical communications – Transmitter – Having particular modulation
Reexamination Certificate
2000-09-11
2004-08-10
Sedighian, M. R. (Department: 2633)
Optical communications
Transmitter
Having particular modulation
C398S183000, C398S190000, C398S198000, C398S200000
Reexamination Certificate
active
06775483
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to wavelength-division multiplex optical transmission systems, and more particularly to a wavelength-division multiplex optical transmission system for transmitting signals to be supplied individually to a plurality of optical receiving parts and signals to be supplied equally thereto on a wavelength-division-multiplexed optical signal.
2. Description of the Background Art
Recently, in fields such as optical CATV systems, data communications services providing digital signals for data communications are offered together with conventional video-broadcast services. In such services, it is specifically required to offer a specific data communications service to each of a plurality of optical receiving parts while offering the same video-broadcast services equally to all optical receiving parts. Further, due to increasing data amount in data communications, a system for supplying large communications data individually to each optical receiving part at the same time of offering the conventional video-broadcast service is required and is under study.
A wavelength-division multiplex transmission technique is appropriate for simultaneously supplying large communications data to each of the optical receiving parts. With the technique, a plurality of signals are each superimposed on optical signals having different wavelengths from each other and multiplexed to become a single optical signal. After being transmitted through an optical transmission path such as an optical fiber, the multiplexed optical signal is separated for each wavelength, and thereby the optical signals before multiplexing are obtained.
Conventionally, a wavelength-division multiplex optical transmission system using the above technique is disclosed in “OPTCOM”, No. 115, June 1999 issue, pp. 46 to 50.
FIG. 7
is a block diagram showing the structure of the conventional wavelength-division multiplex optical transmission system. The system is described next below.
In
FIG. 7
, the conventional wavelength-division multiplex optical transmission system includes: a data communications central station
109
; a video-broadcast central station
209
; a repeater station
309
; a plurality of optical receiving parts
411
to
41
n
; and a plurality of optical fibers
570
,
580
, and
591
to
59
n
. The data communications central station
109
is provided with a plurality of optical modulators
111
to
11
n
and a wavelength-division-multiplexing part
120
. The video-broadcast central station
209
is provided with an optical modulator
290
, and the repeater station
309
is provided with a demultiplexing part
310
, a branching part
380
, and a plurality of multiplexing parts
391
to
39
n
. The operation of the system is described next below.
In the data communications central station
109
, a plurality of communications signals
11
to
1
n
, which are to be supplied individually to each of the plurality of optical receiving parts
411
to
41
n
as the data communications services, are inputted to the plurality of optical modulators
111
to
11
n
, respectively. The plurality of optical modulators
111
to
11
n
each output optical signals modulated by the incoming communications signals
11
to
1
n
and each having different wavelengths &lgr;
1
, &lgr;
2
, . . . , &lgr;
n
. The output optical signals are multiplexed in the wavelength-division-multiplexing part
120
and transmitted to the repeater station
309
through the optical fiber
570
. In the video-broadcast central station
209
, a broadcast signal
20
, which is to be supplied equally to the plurality of optical receiving parts
411
to
41
n
as the video-broadcast service, is inputted to the optical modulator
290
. The optical modulator
290
outputs an optical signal modulated by the incoming broadcast signal
20
and having a wavelength &lgr;
b
that is different from any of the wavelengths of the optical signals outputted from the optical modulators
111
to
11
n
. The output optical signal is transmitted to the repeater station
309
through the optical fiber
580
. In the repeater station
309
, the optical signal transmitted through the optical fiber
570
from the data communications central station
109
is separated, based on the wavelengths, in the demultiplexing part
310
into the optical signals having the wavelengths &lgr;
1
, &lgr;
2
, . . . , &lgr;
n
. Also, the optical signal transmitted through the optical fiber
580
from the video-broadcast central station
209
is branched in the branching part
380
to a plurality of optical signals all having the wavelength &lgr;
b
. Each of the separated optical signals separated in the demultiplexing part
310
is supplied to the respective multiplexing parts
391
to
39
n
, and therein, multiplexed with each of the branched optical signals also supplied thereto. The multiplexed optical signals are each transmitted through the optical fibers
591
to
59
n
to the optical receiving part
411
to
41
n
. That is to say, the optical signal obtained by multiplexing the optical signal having the &lgr;
1
wavelength and the optical signal having the &lgr;
b
wavelength is supplied to the optical receiving part
411
, and the optical signal obtained by multiplexing the optical signal having the &lgr;
2
wavelength and the optical signal having the &lgr;
b
wavelength is supplied to the optical receiving part
412
. Other optical receiving parts
413
to
41
n
are similarly supplied with the multiplexed optical signals. Each of the optical receiving parts
411
to
41
n
separates, by using a wave separator not shown in the drawing, the optical signal supplied thereto into the optical signal having any one of the wavelengths &lgr;
1
, &lgr;
2
, . . . , &lgr;
n
that carries the corresponding communications signal
11
to
1
n
, and the optical signal having the &lgr;
b
wavelength that carries the broadcast signal
20
. Thereafter, each of the optical receiving parts
411
to
41
n
converts, by using two optical receivers not shown in the drawing, each of the separated optical signals into electrical signals. Note, although omitted in the drawing, optical amplification is carried out in each part of the system, as required, to compensate for the transmission loss and the splitting loss.
As described, according to the conventional wavelength-division multiplex optical transmission system, path selection is made based on the wavelength, thereby enabling simultaneous transmission of the communications signals individually supplied to each of the optical receiving parts and the broadcast signal equally supplied to the optical receiving parts. In other words, with such system, the video-broadcast service offered to all optical receiving parts and the data communications service offered to a specific optical receiving part can be combined.
In the system shown in
FIG. 7
, however, to combine the video-broadcast service offered to all optical receiving parts and the data communications service offered to a specific optical receiving part, the repeater station
309
is required to first separate, for each wavelength, the received optical signal obtained by wavelength-division-multiplexing the optical signals carrying the communications signals, and then again multiplexing each separated signal with the optical signal carrying the broadcast signal
20
. Accordingly, the problem comes up that the structure of the repeater station
309
becomes complex. Moreover, each of the optical receiving parts
411
to
41
n
is required to be provided with the wave separator and two optical receivers in order to receive the optical signal obtained by multiplexing two types of optical signal, i.e., the optical signal for carrying the respective communications signals
11
to
1
n
; and the optical signal for carrying the broadcast signal
20
. As a result, another problem comes up that the cost of the optical receiving parts
411
to
41
n
increases.
To solve the problems above, considered is a method that each of the communications signal
Fuse Masaru
Ikushima Tsuyoshi
Sasai Hiroyuki
Sedighian M. R.
Wenderoth , Lind & Ponack, L.L.P.
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