Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-11-10
2002-06-11
Chan, Jason (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200
Reexamination Certificate
active
06404524
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to Dense Wavelength Multiplex Systems (DWDMs) and specifically to securing information or channels in these systems.
BACKGROUND OF THE INVENTION
Dense Wavelength Division Multiplex (DWDM) technology has provided a cost-effective solution to fiber exhaust in communications networks by increasing the data throughput of the network without requiring the installation of new fiber and is the enabling technology for the emerging all optical networking. In a DWDM system each of several input signals enter a DWDM node or network element and is assigned or converted to a specific wavelength, typically, in the 1550 nanometer (nm) band. After wavelength conversion each individual signal wavelength or channel is then multiplexed by wavelength division multiplexing and transmitted onto the same fiber. Consequently, a single fiber carries more than one wavelength. In fact each wavelength carried by a DWDM system may be considered a virtual fiber.
In order for DWDM technology to be truly viable as a network solution, DWDM systems must be secure. As opposed to re al fibers, the signal carried on the virtual fibers of DWDM systems may be susceptible to eavesdropping. In DWDM systems different channels travel through the same fiber and the same components. As a result of cross-talk, nonlinearity, etc., at the receiving end, there is a residual of signal(s) from other channels that can be isolated, amplified, and detected.
The potential for eavesdropping may be better appreciated by reference to
FIG.1
where there is depicted a receiving node
100
in a DWDM network. Receiving node
100
may be an optical demultiplexer or add drop multiplexer, a wavelength converter, or an optical cross-connect that serves as a drop off or interchange point for one or more channels.
FIG. 2
shows, on a logarithmic scale, the optical spectrum of channel
10
in
FIG. 1
as it dropped from node
100
. As
FIG. 2
shows, although the goal was to drop only channel
10
, channel
11
is clearly visible. In
FIG. 3
, I used a notch filter to reduce the optical signal to noise ratio (OSNR) for channel
10
. As
FIG. 3
shows, channel
11
is still present with enough power to be recoverable. In fact, in
FIG. 4
, I have turned off the channel
10
transmitter and as
FIG. 4
shows there is a significant amount of residual power still present from channel
11
. I have also achieved similar results shown in
FIG. 4
by introducing a second filter to attenuate channel
10
in the received spectrum. In either case, in
FIG. 4
, channel
11
is leaked with large enough OSNR to be recoverable after optical amplification. I have achieved better than 20 dB OSNR for the leaked signal for this particular optically amplified DWDM system. I expect better eavesdropping performance (larger OSNR than 20 dB for the leaked signal) for DWDM systems without the amplified stimulated emission (ASE) associated with the optical amplification process. Accordingly, the user of channel of
10
may be able to recover channel
11
without the network operator ever knowing of the breach in security. On another level, residual power from each channel may be available on all the channels thereby providing for security akin to having a party line.
Of utility then would be a method and system for securing DWDM networks against potential eavesdropping.
SUMMARY OF THE INVENTION
My invention is a method and system for securing DWDM networks by introducing noise into the fiber channel or cable up to the level of cross-talk (leakage) or ASE noise, which ever is larger, so that unauthorized recovery of channels is prevented or not permitted.
In accordance with my invention, a white noise source inputs white noise into the fiber channel up to amplified spontaneous emission level so that only the signal intended to be dropped or terminated can be recovered. In accordance with my invention the added noise masks the leaked signal without affecting the performance of the channel intended to be dropped or terminated.
By using only a noise source the network is secured against eavesdropping without the need of any sophisticated monitoring or processing software. Accordingly, a DWDM system designed in accordance with my invention will not incur a substantial increase in cost.
In one aspect of my invention the noise source is included as part of the DWDM node at the point the multiwavelength signal is being received, i.e., at the point within the equipment before the multiwavelength signal is optically demultiplexed. Although the noise can be injected anywhere along the path of the multiwavelength signals, it is most effective if injected at the receiving end.
In another aspect of my invention the noise source is coupled onto the fiber after the optical demultiplexer and just before the single channel optical signal is being handed over. In this case only the channels that have to be secure get the noise injection. In accordance with this aspect of my invention, DWDM systems that have been already deployed may be protected by my invention.
REFERENCES:
patent: 3737584 (1973-06-01), Kaneko et al.
patent: 4573205 (1986-02-01), Nash
patent: 5612805 (1997-03-01), Fevrier
patent: 5923667 (1999-07-01), Poiraud et al.
“Data Communication via Chaotic Encoding and Associated Security Issues”, Jaafar M. H. Elmirhani, Dept. of Electrica Electronic Engineering and Physics, University of Northumbria at Newcastle, Newcastle Upon Tyne, NE1 8ST, UK, IEEE 1995, pp. 1188-1192.
“Point-to-Point and Multi-User Communication Based on Chaotic Sequences”, Jaafar M.H. Elmirghani and Robert A. Cryan, Dept. of Electrical, Electronic Engineering and Physics, University of Northumbria at Newcastle, UK, IEEE 1995, pp. 582-584.
“Communication using Chaotic Masking”, J.M.H. Elmirghani and R. A. Cryan, Centre for Communication Networks Research, Department of Electrical and Electronic Engineering, The Manchester Metropolitan University, Chester St., Manchester, M1 5GD, UK, pp. 12/1—12/6.
Cockings Orville R.
Telcordia Technologies Inc.
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