Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-09-03
2003-01-28
Wu, Daniel J. (Department: 2632)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C385S027000
Reexamination Certificate
active
06512613
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a WDM (Wavelength Division Multiplexing) transmission system which transmits a plurality of signal lights having wavelengths different from each other, a WDM transmission repeater provided in an optical transmission line in the WDM transmission system, and a WDM transmission method in such a WDM transmission system.
BACKGROUND ART
By transmitting a WDM signal group including a plurality of signal lights with wavelengths different from each other through an optical fiber line as a transmission line, a WDM transmission system enables high-speed, large-capacity optical communications. It enables large-capacity optical communications, e.g., 32 channels (utilizing 32 signal lights) at 2.5 Gb/s, even in the case where an existing single-mode optical fiber line network is employed. As a consequence, the introduction of WDM transmission system has recently been under way in order to respond to rapid increases in communication demands such as those in Internet or the like.
In such a WDM transmission system, there are cases where a repeater base station having a WDM transmission repeater is disposed somewhere in the transmission line from a transmitter within a transmitter base station to a receiver within a receiver base station. The WDM transmission repeater is equipped with an optical amplifier, an optical ADM (Add-Drop Multiplexer), and the like. The optical amplifier functions to collectively optically amplify the WDM signal group propagating through the transmission line. The optical ADM functions to demultiplex the WDM signal group into a first group of signal lights and a second group of signal lights different from those of the first group, receive the second group of signal lights, multiplex a separate third group of signal lights with the first group of signal lights, and send the resulting new WDM signal group into the transmission line again.
DISCLOSURE OF THE INVENTION
As a result of studies of the conventional WDM transmission systems thus configured, the inventors have found the problems as follows.
Namely, the conventional WDM transmission systems and WDM transmission repeaters are designed so as to be applicable to long-haul main lines, so that the distance between adjacent repeaters is long, e.g., on the order of 60 km to 80 km, in such a WDM transmission system. As a consequence, the optical amplifier within each WDM transmission repeater is required to have such properties as a wide band and high gain, a minimum gain deviation (fluctuation in gain between individual signal lights having their respective wavelengths), and the like in order to collectively compensate for the transmission loss of the whole signal lights propagating between the repeaters having such a long distance therebetween. However, not only such a high-performance optical repeater is expensive, but also its reliability is hard to secure.
In the local inter-station transmission, by contrast, the distance between the adjacent repeaters is relatively short, i.e., a few km to ten plus several km, and the received signal light level at each repeater is high, whereby it is often unnecessary to utilize optical amplifiers having a high gain or any optical amplifiers at all. Also, in general, since signal lights are received and transmitted by each repeater, it is often unnecessary for all the signal lights having wavelengths different from each other to be optically amplified with a uniform gain. Consequently, the conventional WDM transmission repeaters for long-haul main lines, equipped with high-performance expensive optical repeaters, are not suitably applicable to local interstation WDM transmission systems in terms of cost and equipment. It is not so economical to apply such conventional WDM transmission repeaters to the local inter-station WDM transmission system as in the case of applying the WDM transmission system with a long-haul main line.
In order to overcome the problems such as those mentioned above, it is an object of the present invention to provide a WDM transmission system suitable as optical communication means between local stations, a WDM transmission repeater suitable for the WDM transmission system, and a WDM transmission method in such a WDM transmission system.
The WDM transmission system according to the present invention comprises a plurality of WDM transmission repeaters, whereas the interval between these WDM transmission repeaters is not greater than 20 km, thereby enabling optical communications suitable for relatively short inter-station transmission.
In such a WDM transmission system, it is unnecessary to use a wide-band optical amplifier which can amplify all of a plurality of signal lights, and a narrow-band amplifier which can optically amplify a small number of demultiplexed signal lights is sufficiently applicable thereto. Here, the distance between the respective center wavelengths of the individual signal lights is not greater than a few nm. Specifically, there are transmission modes of 1.6 nm, 0.8 nm, 0.6 nm, and the like. As a consequence, though the number of employed WDM transmission repeaters, i.e., the number of optical amplifiers, increases, these optical amplifiers can utilize inexpensive products, and the optical amplifiers become unnecessary in some instances, whereby the system as a whole can be realized at a low cost. Also, since the distance between the repeaters is relatively short, i.e., 20 km or less, no high output is required for the optical amplifiers employed, whereby a sufficient degree of reliability is secured. In addition, since only a small number of signal lights in the WDM signal group propagating through the transmission line are optically amplified by each WDM transmission repeater, the risk of all the channels (all the signal lights) failing to establish communications is low in the event of failure of an optical amplifier in any of the WDM transmission repeaters.
The WDM transmission repeater according to the present invention has a configuration suitable for the above-mentioned WDM transmission system and is installed in a transmission line through which a WDM signal group including a plurality of signal lights having wavelengths different from each other within a usable wavelength band propagates. The WDM transmission repeater comprises an optical ADM having an entrance end for receiving the WDM signal group from the transmission line; a first port for taking out, from first and second groups each composed of one or more signal lights and separated from the WDM signal group taken in by way of the entrance end, the second group of signal lights; a second port for receiving a third group of signal lights composed of one or more signal lights within the usable wavelength band, each having a wavelength different from those of the first group; and an output end for sending to the transmission line a new WDM signal group including the first group of signal lights and the third group of signal lights taken in by way of the second port.
Also, the WDM transmission repeater according to the present invention may be configured so as to comprise, in addition to the optical ADM, at least one of a first optical amplifier for amplifying the second group of signal lights taken out from the first port of the optical ADM and a second optical amplifier for amplifying the third group of signal lights to be received from the second port of the optical ADM.
In a configuration such as that mentioned above, the taken-out second group of signal lights is amplified by the first optical amplifier, whereby a sufficient receiving sensitivity is assured in the WDM transmission repeater at the next stage. On the other hand, as the newly introduced third group of signal lights is amplified by the second optical amplifier, the light intensity of the crosstalk component in each of the signal lights in the not-demultiplexed second group can be lowered relative to the light intensity of the WDM signal group (mainly including the first and third groups of signal lights). Namely, it becomes more likely to determine that s
Murakami Yasunori
Nishimura Masayuki
Shigematsu Masayuki
Tanaka Shigeru
McDermott & Will & Emery
Sumitomo Electric Industries Ltd.
Wu Daniel J.
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