Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-03-01
2002-08-13
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06433900
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a redundant structure in an optical wavelength multiplexing system.
2. Description of the Related Art
With the increase in the processing speed and the capacity of information, the need for broadening the band of/increasing the capacity of a network and a transmission system has been required. Therefore, as one of the means of realizing this, the configuration of an optical network based on a wavelength division multiplexing technology has been desired. When configuring an optical network, a key point is an optical path cross connection system in an optical wavelength multiplexing system (a device for routing optical signals inputted from a plurality of optical fibers, whose wavelengths have been multiplexed, to desired output optical fibers for each wavelength).
On the other hand, with the increase in a transmission capacity, faults which occur in the transmission line and a node have a great influence. Therefore, it is necessary to provide a redundant configuration in the transmission line and the node in order to increase the reliability at the time of faults.
FIGS. 1A and 1B
show examples of a redundant configuration in a conventional optical wavelength multiplexing system.
FIG. 1A
shows an example of a redundant configuration of a node output portion in the conventional optical wavelength multiplexing system (for example, optical path cross connection system; optical XC system).
A node is duplexed (0-system/1-system), and is provided with optical selectors
2700
and
2701
at the output. Monitor circuits
2702
and
2703
detect whether output optical signals are normal or abnormal for all the wavelengths outputted from each node, and control the switching of protection switches (optical selectors
2700
and
2701
).
In
FIG. 1A
, a set of an optical XC node, a protection switch, and monitor circuits
2702
and
2703
is provided. Actually, however, the same number of optical selectors and the same number of monitor circuits are provided as that of a 0-system line
2704
and a 1-system line
2705
, outputted from the optical XC nodes.
The monitor circuits
2702
and
2703
input both the 0-system line
2704
and the 1-system line
2705
, which correspond to the optical XC node (
0
) and the optical XC node (
1
), respectively. Then, the circuits receive optical signals, and monitor whether or not faults occur on the lines. When the 0-system line is being used, if the monitor circuit
2702
or
2703
detects the occurrence of a fault in this 0-system line, the optical selector
2700
or the optical selector
2701
is controlled to switch to the 1-system line.
FIG. 1B
shows an example of a redundant configuration in an input transmission line to a node in a conventional optical XC system.
The transmission line is duplexed (0-system/1-system), and a protection switch
2708
is provided at the preceding stage of the optical XC system. The protection switch
2708
is composed of optical selectors
2709
and
2710
, and monitor circuits
2706
and
2707
corresponding to these optical selectors. The optical transmission line which has redundancy to provide a 0-system and a 1-system is configured by a set of a 0-system transmission line and a 1-system transmission line, and this set of transmission lines is connected to the optical selector
2709
or
2710
. The monitor circuits
2706
and
2707
detect whether the input optical signals from each transmission line are normal or abnormal for all the wavelengths. When a fault is detected in the optical signals, the protection switch
2708
is controlled to be switched. In the case of
FIG. 1B
, the optical XC node is not provided with a redundant configuration, but this node can further be provided with a 0-system node and a 1-system node as shown in FIG.
1
A. In this case, the optical selectors
2709
and
2710
should be provided with two inputs and two outputs.
FIGS. 2A and 2B
show examples of the configuration of a conventional protection switch (optical selector).
FIG. 2A
shows the case where an optical selector is configured by 2×2 optical switches. When a transmission line to be inputted to the optical selector has redundancy to provide a 0-system and a 1-system as shown in
FIG. 1A
or
1
B, only one output is used.
FIG. 2B
shows a configuration where gate-type optical switches and an optical coupler are combined.
These switches are basically the same as a conventionally known optical switch, but they make use of a function of switching the optical path of the inputted optical signal. That is, these optical switches are configured in such a way that the optical signal whose optical path has been switched is prevented from being externally outputted by using a photo absorption material or the like, which is provided along the optical path. The optical switches having such a configuration are used as optical gates. An optical coupler can be a conventionally-known optical coupler, and only transmit the optical signal outputted from the optical gate to the transmission line.
As an example of such an optical switch, an optical switch which is composed of an inductive material such as LiNbO
3
or a semiconductor such as InP, GaAs or the like, can be adopted. This switch performs ON/OFF control by being applied by a voltage or a current. As one example of the details of such an optical switch, please refer to the document “IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 6, NO. 7, pp.
1267-1272 (1988)” or the like.
According to the conventional configuration, one wavelength transmission system is used. Accordingly, when a monitor circuit detects a fault only in one wavelength of an optical signal having a plurality of wavelengths which have been multiplexed, even the remaining normal optical signals are simultaneously switched to the other system by a protection switch.
In the case of one wavelength transmission, since the optical signal to be transmitted has one wavelength, that is, one channel, no problem will arise. In an optical wavelength multiplexing system, however, since an optical signal of a plurality of wavelengths is transmitted to one transmission line, even optical signals in which faults do not occur are also switched.
Therefore, in an originally normal optical signal, a signal disconnection is generated at the time of the switching so that the transmission efficiency will deteriorate. Even if an optical switch which performs processings at high speed up to a level where any error will not occur in directing a signal, a circuit is required for matching a phase of an optical signal of the 0-system with that of the 1-system before the protection switch. The same number of these circuits is required as that of the wavelengths so that the amount of hardware will increase. Further, it is more difficult to perform the switching and the phase matching for a high speed optical switch, as the transmission speed increases.
In spite of the above-mentioned problems, however, no specific configuration other than a configuration of one wavelength transmission is proposed at present, for the redundant configuration of an optical wavelength multiplexing system.
SUMMARY OF THE INVENTION
The present invention provides an optical wavelength multiplexing system having a redundant configuration only for switching the optical signal of a wavelength in which a fault occurs, among optical signals whose wavelengths have been multiplexed.
In the optical wavelength multiplexing system according to a first aspect of the present invention, a plurality of input and output optical fibers transmitting wavelength-multiplexed optical signals are included. Further, in this optical wavelength multiplexing system for processing the optical signals for each wavelength, a protection switch is provided on an output side of a node duplexed into a first system and a second system. This protection switch comprises a demultiplexer for demultiplexing an optical signal to be inputted after its wavelengths have been multiplexed, into optical signals fo
Kuroyanagi Satoshi
Maeda Takuji
Nakajima Ichiro
Nishi Tetsuya
Tsuyama Isao
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Pascal Leslie
Phan Hanh
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