Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1997-12-18
2001-04-24
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200
Reexamination Certificate
active
06222659
ABSTRACT:
The present invention consists in a repeater for soliton signal fiber optic transmission systems and a method of transmitting information in a transmission system including a repeater of this kind.
It applies in particular to monitoring or surveillance of the repeaters of the transmission system or to location of faults in the transmission system.
Finally, it concerns a fiber optic transmission system including a repeater of the above kind.
The transmission of soliton pulses or solitons in the abnormal dispersion part of an optical fiber is known in itself. Solitons are pulse signals having a sech” shape. With this pulse shape, the non-linearity in the corresponding part of the fiber compensates the dispersion of the optical signal. The transmission of solitons is modeled in a manner known in itself using the non-linear Schrödinger equation.
Various effects limit the transmission of such pulses, such as the jitter induced by the interaction of the solitons with the noise present in the transmission system, as described for example in the article by J. P. Gordon and H. A. Haus, Optical Letters, vol. 11 No. 10, pages 665-667. This effect, known as the Gordon-Haus effect, imposes a theoretical limit on the quality or on the bit rate of transmission using solitons. Systems have been proposed using sliding guide filters to control the jitter of the transmitted solitons so that this limit can be exceeded—see for example EP-A-0 576 208. The use of intensity or phase modulators to regenerate the signal on the line has also been proposed.
Using control frequencies different from the frequencies used for the transmission of signals for repeater surveillance or monitoring in fiber optic transmission systems is known in itself. A fiber optic transmission system using such monitoring for optical repeaters is described in U.S. Pat. No. 4,899,043.
The conventional solution of U.S. Pat. No. 4,889,043 cannot be applied in a soliton signal fiber optic transmission system including sliding filters or synchronous modulators, for example. If a low-frequency signal were used as suggested in the above document it could not be transmitted through the system because of the presence of the sliding filters or the synchronous modulators.
U.S. Pat. No. 5,080,505 describes a soliton signal fiber optic transmission system in which optical amplifiers at regular intervals along the fiber have their gain controlled by a feedback signal from the next amplifier. To resolve indeterminacy regarding the gain, each amplifier uses low-frequency, for example sinusoidal, interference transmitted by the immediately upstream amplifier. GB-A-2 273 838 also describes a soliton signal fiber optic transmission system in which a low-frequency interference signal is used locally, i.e. in a repeater.
U.S. Pat. No. 5,080,505 and GB-A-2 273 838 propose the use of low-frequency interference in soliton signal fiber optic transmission systems to control modulators or amplifiers. In both the above documents the low-frequency signals are in the form of sinusoidaL interference with the transmitted signals and used only locally i.e. in the same repeater or from one repeater to another.
Using extending optical time domain reflectometery (EOTDR) for locating faults in a transmission system using optical amplifiers in the form of erbium-doped fibers is also known in itself, as described in the article by S. Furukawa et al, IEEE Photonics Technology Letters, vol. 7, No. 5. The above document specifies that the OTDR optical power must be kept as uniform as possible to prevent optical transients in the repeaters. This solution therefore cannot be used in soliton signal fiber optic transmission systems, the optical part of which includes at least one soliton signal monitoring device, such as a synchronous modulator or a filter.
The present invention proposes a novel and simple solution to the problem of optical repeater monitoring or surveillance in a soliton signal optical fiber transmission system. It also proposes a novel and simple solution to the problem of locating faults in a transmission system of the above kind. In the conventional way the repeaters can include filters, synchronous modulators or any other device known in itself or a combination of such devices. Using limited means, the invention enables the use of low-frequency signals for repeater monitoring or surveillance. It also enables the transmission of signals for locating faults, for example extended optical time domain reflectomertry type signals.
To be more precise, the invention proposes a repeater for soliton signal optical fiber transmission systems the optical part of which includes at least a soliton signal monitoring device, such as a filter or a synchronous modulator, and a branch connection for signals having a frequency or a format that would be cut off by the monitoring device.
The branch connection preferably includes a demultiplexer upstream of the monitoring device, a length of optical fiber and a multiplexer downstream of the monitoring device. It can also include a coupler upstream of the monitoring device, a length of optical fiber and a multiplexer downstream of the monitoring device.
The branch connection can include an amplifier for signals having a frequency that would be cut off by the monitoring device, for example an optical fiber doped with erbium.
An optical fiber doped with erbium can be provided for amplifying soliton signals and a common light source for pumping the optical fiber for amplifying the signals having a frequency or a format that would be cut off by the monitoring device and the optical fiber for amplifying the soliton signals.
The invention also proposes a method of transmitting information in a soliton signal optical fiber transmission system including at least one repeater of the above kind wherein not only soliton signals but also signals having a frequency or a format that would be cut off by the monitoring device are transmitted.
The signals having a frequency that would be cut off by the monitoring device can be low-frequency signals, for example signals transmitted under normal dispersion conditions in the optical fiber, or continuous wave signals modulated at a low frequency, or NRZ signals.
The signals having a format that would be cut off by the monitoring device can be extended optical time domain reflectometery type signals.
The invention also consists in the application of a method of the above kind to repeater monitoring or surveillance or to fault location.
Finally, the invention also proposes an optical transmission system including at least one repeater of the above kind.
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M. Nakazawa et al, “40GBit/s WDM (10GBits/s×4 Unequally Spaced Channels) Colition Transmission Over 10000KM Using Synchronous Modulation and Narrow Band Optical Filtering”,Electronics Letters, vol. 32, No. 9, Apr. 25, 1996, pp. 828-830.
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Alcatel
Bello Agustin
Pascal Leslie
Sughrue Mion Zinn Macpeak & Seas, PLLC
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