Optical waveguides – Optical fiber waveguide with cladding
Reexamination Certificate
2002-03-11
2004-02-17
Bovernick, Rodney (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
C385S001000, C359S199200, C359S199200
Reexamination Certificate
active
06694081
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to dispersion compensated optical waveguide fiber telecommunication systems, and particularly to such telecommunication systems that incorporate wavelength division multiplexing.
2. Technical Background
In optical waveguide fiber telecommunication systems designed to operate at high data rates over distances of the order of at least a hundred kilometers, compensation of total dispersion has been recognized as an efficient means of facilitating the system by reducing the number of electronic regenerators required. The concept of total dispersion compensation is, generally, the incorporation into the system of a compensating waveguide fiber having total dispersion sign opposite that of the primary transmission fiber. (The sign convention in common use is that dispersion of a waveguide is said to be positive if light of shorter wavelength travels faster in the waveguide than does light of longer wavelength).
Because wavelength division multiplexed systems can accommodate higher data rates over the same waveguide fiber, the concept of total dispersion slope compensation, i.e., compensation of total dispersion over a range of wavelengths, was introduced. Perfect compensation over a range of wavelengths can be achieved by selecting the total dispersion and dispersion slope of the compensating fiber to be the same multiple of the total dispersion and dispersion slope of a transmission fiber, respectively, while having signs opposite to those of the transmission fiber. This choice of total dispersion slope in the compensating fiber provides the capability of equally compensating the total dispersion of each of a number of signal wavelengths in the operating wavelength range of the system. That is, substantially equal total dispersion compensation is provided for each of the channels in the wavelength division multiplexed system.
Non-linear optical effects, which become important in these high performance telecommunication systems, can be mitigated through use of relatively higher effective area optical waveguide fiber. In certain dispersion compensated systems, both relatively high as well as relatively low effective area waveguide fibers are used. Non-linear effects can be held to a minimum by placing the lower effective area fiber at locations in the system where signal intensity is lower, so that non-linearity has less negative impact on system performance.
Recent investigations have focused on waveguide fiber combinations including large effective area transmission waveguide fibers used in conjunction with compensating waveguide fibers that compensate the total dispersion over a wavelength range (total dispersion slope compensation). Because the refractive index profile design of total dispersion slope compensating fibers does not in general include the property of large effective area, strategies have been developed in which transmission fiber and compensating fiber have been optimally placed to limit non-linear effects as well as compensate total dispersion over an operating wavelength range of the optical waveguide system.
An advantageous system or link configuration is one using a compensating fiber that has total dispersion and total dispersion slope related to the corresponding parameters in the transmission fiber by the same integral multiple. For example, a transmission fiber having total dispersion D and total dispersion slope S can be compensated by a fiber having total dispersion −2D and total dispersion slope −2S by using in the system a transmission fiber length to compensating fiber length ratio of 2 to 1 within each of multiple sections of the total transmission path. The system is said to be perfectly compensated because the ratio of total dispersion to total dispersion slope, &kgr;, is identical for the fibers making up the system. A disadvantage of this scheme of perfect compensation is that the average total dispersion is zero for the compensated spans that together make up the waveguide transmission path for the system. When wavelength division multiplexed signals spend a significant amount of travel time in waveguide sections having zero or near zero total dispersion, the non-linear-effects cross phase modulation and four wave mixing can adversely affect system performance and increase the physical bit error rate.
One can effectively move away from the perfect compensation format using fibers having identical total dispersion to total dispersion slope ratio, by adjusting the length ratio of transmission to compensating waveguide fiber. However there are drawbacks in this system design because additional lengths of either the transmission fiber or the compensating fiber must be inserted into the system to remove accumulated total dispersion or accumulated total dispersion slope. In systems where average negative total dispersion is desired within each section or span, the compensating fiber is relatively longer than the transmission fiber. In effect, the lower effective area, compensating fiber is located in parts of the system where signal intensity is relatively higher, so that non-linear effects are more pronounced. In the alternative case, systems where average positive dispersion is desired, a long span of compensating fiber is needed to remove accumulated positive total dispersion and positive total dispersion slope, thereby introducing pulse distortion due to self phase modulation. An alternative to the use of the span of compensating fiber is the introduction into the span of a dispersion compensating module designed to compensate either total dispersion, total dispersion slope, or both. The drawback in this case is that additional optical amplifiers must be used to offset the signal attenuation in the dispersion compensating module.
There is therefore a need for a compensation format that provides for spans making up a system, wherein the spans have a net negative or net positive average total dispersion without incurring the penalties associated with prior art compensation schemes. The present invention addresses this need.
SUMMARY OF THE INVENTION
One aspect of the present invention is an optical waveguide fiber telecommunications link including a plurality of spans optically coupled in series, i.e., end to end. As used in this specification, an optical waveguide fiber link refers to the total length of waveguide fiber that propagates light from a light signal transmitter to a receiver. The term link will be understood to include components such as optical amplifiers, optical couplers, or wavelength division multiplexers used in telecommunication systems. Each span includes a first and a second optical waveguide fiber. Each of these waveguide fibers is characterized by a total dispersion (the sum of waveguide and material dispersion) at a particular wavelength &lgr; and by a total dispersion slope over a wavelength range, that includes &lgr;, of operation of the link. The total dispersion slope of the respective first and second optical waveguide fibers are selected to be opposite in sign. The magnitudes of the respective total dispersion slopes are selected to provide a particular accumulated total dispersion over the span at the wavelength &lgr;. Further, the respective total dispersion slopes are selected to provide, at the wavelengths over the operating wavelength range, accumulated total dispersion having a value within +/−10% of the value at wavelength &lgr; or +/−10 ps
m, whichever is larger. That is, the end to end dispersion of a span, measured in units of ps
m, exhibits the same value to within the larger of +/−10 ps
m or +/−10% at each wavelength over the wavelength range. The span is said to be compensated over the wavelength range. Accumulated total dispersion, the dispersion experienced by a signal pulse traversing a length of waveguide fiber, is the product of fiber total dispersion times fiber length.
The total dispersion of each span is not completely compensated, i.e., total disper
Bickham Scott R.
Cain Michael B.
Grochocinski James M.
Bovernick Rodney
Chervenak William J.
Corning Incorporated
Homa Joseph M.
Pak Sung
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