1. Field of the Invention
The present invention generally relates to a wavelength dispersion compensation design method, and a system thereof; and especially relates to a wavelength dispersion compensation design method for compensating for a wavelength dispersion generated in an optical transmission system, and a design system thereof.
2. Description of the Related Art
When planning a wavelength division multiplexing (WDM) optical transmission system with a transmission speed of 10 Gbps, it is required that an optical network be designed at low cost in a short period, the importance of which will increase with a WDM optical transmission system with 40 Gbps of transmission speed, or even higher.
Generally, a wavelength dispersion compensator is used by a relay section (span) of the WDM transmission system such that degradation of a waveform due to wavelength dispersion in the transmission line is compensated for. Amounts of wavelength dispersion compensation differ from system to system.
In an optical transmission system where the transmission speed is 10 Gbps or higher per wavelength, the wavelength dispersion compensator is used in the span of the system such that degradation of signal properties due to the wavelength dispersion generated in the transmission line may be compensated for.
When designing wavelength dispersion compensation, a predetermined amount of transmission degradation is tolerated in each span, and an amount of wavelength dispersion compensation is set up so that waveform degradation due to wavelength dispersion may fall within the predetermined transmission degradation. For example, a Q value is defined as an index of a transmission characteristic, and 1 dB of degradation is tolerated in terms of the Q value.
Here, the amount of wavelength dispersion compensation has a tolerance in a transmission section (path) of each transmission signal, and the difference between the amount of wavelength dispersion of the transmission section and the amount of wavelength dispersion compensation that is within the tolerance is made into a tolerable residual dispersion range. That is, a signal transmission at a guaranteed transmission characteristic is attained by designing the network so that wavelength dispersion may fall within the tolerable residual dispersion range (the amount of wavelength dispersion is compensated for so as to be within the tolerable residual dispersion range).
Here, there is a point that should be taken into consideration in designing the wavelength dispersion compensation. In the case of a point-to-point system that does not include an optical add/drop (OADM) function, wherein a signal is input only from a transmitting station and is output to a receiving station, what is necessary is to adjust the amount of wavelength dispersion compensation at the last transmission section on the side of the receiving station so that the amount of wavelength dispersion may fall within the tolerable residual dispersion range of the system.
However, in the case of a system including the OADM function, the amount of wavelength dispersion compensation in each relay section has to be arranged such that an adequate signal transmission may be attained within the tolerable residual dispersion range in every path of the link that is the design target section, given that the signal may be added/dropped in a node having the OADM function in the system.
Further, in order to determine the amount of wavelength dispersion compensation for each relay section at this time, the fact that the tolerable residual dispersion range varies with a self-phase modulation (SPM) generated by the optical input power to the transmission line has to be taken into consideration. That is, even if transmission lines have the same relay section length and the same amount of wavelength dispersions, the tolerable residual dispersion ranges may differ if optical input power is different.
Conventional technologies disclose methods of optimizing the amount of wavelength dispersion compensation of a certain given system in consideration of the above described problems. For example, Patent Reference 1 discloses a method of designing the amount of wavelength dispersion compensation of all spans concerning a point-to-point system equipped with the OADM function.
Further, Patent Reference 2 and Patent Reference 3 disclose point-to-point system configurations.
Patent reference 1 JPA 2002-117422
Patent reference 2 JPA 11-344768
Patent reference 3 JPA 2000-261376
However, the Patent References disclose an application only to a given point-to-point long-distance WDM transmission system. That is, a method of optimizing the amount of the wavelength dispersion compensation for any desired point-to-point transmission systems and metro systems of a ring structure is not available in a commonly applicable and formulized manner. For this reason, when designing an optical network, various design methods have to be used depending on link form, making it difficult to design the network in a short period.