1. Field of the Invention
The present invention relates to a dispersion compensating system used for bi-directional optical communication using wavelength division multiplexed transmission. More specifically, the present invention relates to a dispersion compensating system which reduces the required number of compensators.
2. Description of Related Art
In the field of optical communication using an optical fiber, a plurality of signal lights having different wavelengths are sometimes transmitted on a single optical transmission path, which is called wavelength division multiplexing (abbreviated as WDM hereinafter). WDM increases transmission capacity of the optical transmission path, for example, it enables bi-direction transmission for a single optical fiber. However, an optical fiber has different optical fiber has different propagation periods for different wavelength components, which result in waveform distortion. On the other hand, the wavelength dispersion has little effect on waveform in a wavelength near the zero dispersion wavelength of the optical fiber. However, it is very difficult to manufacture an optical fiber in which wavelength dispersion is substantially equal to zero for all wavelengths used in WDM.
Thus, various device and methods for compensating overall chromatic dispersion of multiplied signal lights have been published, for example, Japanese Patent Application Laid-open Nos. 7-327012, 8-307347, 8-234255, 8-204258, 7-202798, etc. However, these devices and methods substantially comprise optical fiber paths for respective propagation directions, on which dispersion compensators are arranged. An optical transmission system needs an amplifier such as an erbium doped optical fiber amplifier which essentially includes an optical isolator so that an optical fiber path is required in each direction. Thus, the conventional bi-directional communication system using WDM consists of two one-way optical fiber paths, each of which has an amplifier and a dispersion compensator.
The dispersion compensator is so expensive that the conventional bi-directional communication system using WDM becomes very expensive.
Accordingly, it is an object of the present invention to provide a bi-directional optical communication system which uses wavelength division multiplex transmission and at the same time reduces the number of dispersion compensator.
Various dispersion compensating systems that address the foregoing objects and needs as well as other objects and needs are disclosed. In one embodiment, a dispersion compensating system includes a bi-directional optical fiber path and a dispersion compensator provided on said bi-directional optical fiber path. Optical circulators/couplers are disposed on both ends of the bi-directional optical fiber path. An optical amplifier is disposed on each divisional optical fiber path connected to the optical circulators/couplers, wherein the divisional optical fiber paths are configured for uni-directional signal transmissions. The system also includes at least one supplemental dispersion compensator disposed on the divisional optical fiber paths connected to the optical circulators/couplers.
According to the invention, the dispersion compensator may be a dispersion compensating fiber having positive dispersion in signal wavelength, such as a 1.3 xcexcm zero-dispersion single mode fiber.
The dispersion compensator may also be a dispersion compensated fiber having a negative dispersion in signal wavelength, such as a double clad type fiber.
According to still another aspect of the invention, there is provided a bi-directional optical communication system using wavelength division multiplex transmission comprising at least one optical path formed of a single optical fiber wherein signal lights bi-directionally pass through the single optical fiber and the single optical fiber comprises a dispersion compensating fiber.
In another embodiment, a dispersion compensating system comprises a first optical fiber path for bi-directional transmission and a first 3-port coupler connected to the first optical fiber path. A second optical fiber path is provided for transmission in a first direction connected between the first 3-port coupler and a second 3-port coupler, and a third optical fiber path is provided for bi-directional transmission connected between the second 3-port coupler and a third 3-port coupler. The dispersion compensating system further includes a fourth optical fiber path for transmission in the first direction connected between the third 3-port coupler and a fourth 3-port coupler, and a fifth optical fiber path for bi-directional transmission connected to the fourth 3-port coupler. A sixth optical fiber path is provided for transmission in a second direction connected between the first 3-port coupler and the second 3-port coupler, and a seventh optical fiber path is provided for transmission in the second direction connected between the third 3-port coupler and the fourth 3-port coupler. The optical amplifiers are provided on the second, fourth, sixth and seventh optical fiber paths. Optionally, a dispersion compensator is provided on the third optical fiber path. At least one supplemental dispersion compensator is disposed on the second, the fourth, the sixth or the seventh optical fiber path.
According to still another aspect of the invention, there is provided a bi-directional optical communication system using wavelength division multiplex transmission comprising at least one optical path formed of a single optical fiber wherein signal lights bi-directionally pass through the single optical fiber and the single optical fiber comprises a dispersion compensated fiber.
The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings.