The present invention is directed toward optical communication systems incorporating dispersion compensation and particularly such systems having an adjustable amount of dispersion compensation and to components of such systems.
Optical signals transmitted in a fiber optic communication system typically constitute a series of pulses of digital information. Although the pulses are usually at a single nominal wavelength, each pulse is actually composed of different spectral components. The spectral components of each pulse propagate through the transmission fiber at different speeds with higher frequency components traveling slower than lower frequency components in non-dispersion shifted optical fiber. This effect, known as xe2x80x9cchromatic dispersionxe2x80x9d, can result in spectral components of one pulse arriving at a receiver at substantially the same time as a succeeding pulse, thereby causing degraded receiver sensitivity. Chromatic dispersion becomes increasingly pronounced at higher bit rates, e.g. those associated with synchronous optical network (SONET) OC-192 transmission speeds.
Typically, optical signals propagating through transmission optical fiber experience a positive dispersion. Accordingly, dispersion compensated fiber (DCF) having a negative dispersion can be coupled to the transmission optical fiber in order to offset the chromatic dispersion thereof. The amount of dispersion experienced by an optical signal depends on the distance traveled through the transmission optical fiber. Shorter lengths of transmission optical fiber require less compensation than longer lengths. Likewise, longer lengths of DCF are used when more compensation is required, and shorter lengths of DCF are provided when less compensation is needed. Each segment of transmission optical fiber, however, requires a unique length of DCF in order to provide an appropriate amount of dispersion compensation.
In a fiber optic network, many different lengths or spans of transmission optical fiber are used to connect various points within the network. According to the conventional approach to dispersion compensation described above, a unique length of DCF must be cut for each span. If the network contains many spans, a corresponding number of DCF fibers must be provided, each having a different length. As a result, the conventional approach to dispersion compensation in such instances can be inefficient and time consuming.
Dispersion compensating modules have been proposed including segments of DCF fiber of varying length to provide tailored dispersion compensation. Some of the DCF segments have a positive dispersion, while others have a negative dispersion. Selected DCF segments are coupled to one another to provide a desired net dispersion to offset the dispersion associated with the transmission optical fiber. Thus, rather than provide a unique segment of DCF for each span, the same dispersion compensationmodule can be used for spans of varying length and fiber types by simply connecting appropriate segments of DCF within the module.
The segments of DCF to be included in the dispersion compensation module are typically wound about standard-sized spools. The spools, in turn, are housed within a package. If used in the United States, however, the package should conform to a Network Equipmentxe2x80x94Building System (xe2x80x9cNEBSxe2x80x9d) standard, as well as other standards dictating fiber packaging dimensions in order to be a commercially attractive. Moreover, the spools should be readily coupled to one another in order to provide the desired compensation, but still conform to these, as well as any other pertinent, standards.
Consistent with the present invention, a dispersion compensation module is provided which comprises a housing accommodating one or more spools of DCF. Each spool is provided in a respective package, which can be slidably inserted into or removed from the housing along a track provided within the housing. xe2x80x9cJumpersxe2x80x9d or relatively short pieces of fiber can be used to interconnect the spools through adapters external to the packages. As a result, spools of DCF can be readily coupled to one another to provide a desired amount of dispersion compensation. Moreover, the adapters are geometrically configured so that connections can be made to the spools without excessively bending fiber interconnecting the DCF and the DCF itself, while permitting the module to conform to fiber optic packaging standards.