Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-02-17
2002-09-17
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200
Reexamination Certificate
active
06452707
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to fiber-optic communication systems. More specifically, the present invention relates to applying error-correction codes to improve spectral efficiency in wavelength-division multiplexing (WDM) fiber optic communication systems.
Error correction codes have been applied with varying degrees of success to various types of optical systems, including WDM systems, in attempts to improve system performance. First, for example, error codes have been applied to provide a performance margin to compensate for minute device and subsystem flaws. See, e.g.,
Optical Fiber Telecommunications IIIA,
§3.6.1, Ed. Kaminow and Koch, Academic Press, 1997. As a result, less expensive and more mass-producible optoelectronics can be used, and the overall system lifetime can be extended as devices slowly degrade.
Second, error-correction codes also have been applied to reduce the required system is designed for an optimal signal power that is sufficiently high to overcome optical signal power. See e.g.,
Optical Fiber Telecommunications IIIA,
§3.6.2. Because error correction codes allow an optical system to operate at lower optical signal powers, the number of optical amplifies necessary in a long distance fiber-optic link can be reduced. The is particularly important in, for example, transoceanic fiber-optic links traversing long distances through difficult-to-acess environments that are hostile to system equipment that rely on electronic components. Such transoceanic fiber-optic links often use optical amplification to increase the optical-signal power rather than electronic regeneration which is less reliable and more expensive to maintain in such inaccessible and hostile environments. By applying error-correction codes to reduce the number of required optical amplifiers for a given fiber-optic link, the overall cost of installing that link is reduced and the overall reliability of that link is improved.
Third, error correction codes also have been applied to shift the operation point of WDM channels, thereby allowing more cross talk and nonlinearitieds. See, e.g.,
Optical Fiber Telecommunications IIIA,
§3.6.3; Livas, J. C., et al., “Forward error correction in a 1 Gbit/s/chanel wavelength-division multiplexed system, ”
IEEE/LEOS Summer Topical Meeting on Optical Networks and their Enabling Technologies,
July 1994. As
FIG. 1
illustrates, the bit-error rate is an exponential function of the channel density. In other words, as the channel spacing for a WDM system is decreased, the bit-error rate of the receiver system increases relatively slightly until some point (i.e., the “operation point” labeled in
FIG. 1
as
10
a
) at which the bit-error rate dramatically increases. After the operation point for a system has been determined, error correction codes have been applied to shift this operation point (labeled in
FIG. 1
as
10
b
) so that WDM channels can be spaced closer together without dramatically increasing the bit-error rate. This application of error-correction codes to a WDM system has yielded an increase in channel packing density of a factor 2.5for an error correction code with a coding gain of 3.7 dB.
These known applications have applied error-correction codes to WDM system in only a limited sense with limited results. Known applications of error correction codes have not provided the fullest performance benefits possible.
SUMMARY OF THE INVENTION
Embodiments of the present invention address the shortcomings of the known applications of error-correction codes. One embodiment of the present invention is a method for designing an optical system. The optical system launches optical signals with data into a fiber link having a property of inducing nonlinear distortion of the optical signals as a function of signal power of the optical signals and distance traversed in the fiber link. A Q-factor curve for the fiber link is determined as a function of the signal power. A signal power is preselected based on the Q-factor curve. The preselected signal power is associated with a set of channels. A coding gain is preselected based on the preselected signal power and a desired channel spacing for the set of channels.
Another embodiment is a method for launching optical signals modified with data into a fiber link. The data is error-correction coded with a coding gain to produce encoded data signals. The encoded data signals is multiplexed to produce channels each of which carries optical signals based on the encoded data signals. A preselected coding gain is based on a preselected signal power associated with the channels and a desired channel spacing for the channels.
REFERENCES:
patent: 5351148 (1994-09-01), Maeda et al.
patent: 5715076 (1998-02-01), Alexander et al.
patent: 5896211 (1999-04-01), Watanabe
patent: 6040933 (2000-03-01), Khaleghi et al.
“Optical Fiber Telecommunications IIIA”, Ivan P. Kamonow, Thomas L. Koch, Academic Press (1997), pp. 58-61.
“Forward Error Correction In a 1 Gbit/S/Channel Wavelength-Division-Multiplexed System”, J.C. Livas et al., IEEE/LEOS Summer topical meeting on optical networks and their enabling technologies Jul. 11, 1994.
“Near Shannon Limit Error-Correcting Coding and Decoding: Turbo-Codes(1)”, Claude Berrou et al., IEEE Int'l Conf. On Comm. (1993), pp. 1064-1070.
Pilipetskii Alexei N.
Puc Andrej B.
Singh Dalzid
TyCom (US) Inc.
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