The present invention in general relates to an optical transmission system. More particularly, this invention relates to an optical wavelength division multiplexing transmission system.
In recent years, with still more expanding expectations for development of an optical communication technique to provide high bit rates, large capacity transmission path as an infrastructure of the information-oriented society, there have been promoted global and vigorous researches and developments of high rate, large capacity optical communication systems.
On land, an optical wavelength division multiplexing transmission system of a 10 Gb/s transmission rate using a transmission path of a 1.3 μm band single mode fiber (SMF) and a 1.55 μm band dispersion shift fiber (DFS) has come into practice.
Under the ocean, on the other hand, an optical wavelength division multiplexing transmission system of a 10 Gb/s transmission rate using a transmission path of a non-zero dispersion shift fiber having a zero-dispersion wavelength at a 1.58 μm band has come into practice.
Generally, a transmission waveform deterioration occurs in the optical fiber due to interaction (called SPM-GVD effect) between a self-phase modulation (SPM) and a group-velocity dispersion (GVD). Therefore, a possibly smaller value should be set as a value of the (group-velocity) dispersion to be caused by a difference in transmission time in optical fiber between optical signals of different wavelength.
However, as the wavelengths of the optical signals approach a zero-dispersion wavelength, there is an increased tendency for a four-wave mixing (FWM) to cause a crosstalk, with an increased deterioration of transmission characteristic. Therefore, the optical wavelength division multiplexing transmission requires a wavelength layout in consideration of a zero-dispersion wavelength of optical fiber.
An optical wavelength division multiplexing transmission system is disclosed in Japanese Patent Application Laid-Open Publication No. 8-97771. This conventional system uses a transmission path of a 1.55 μm band dispersion shift fiber (DSF), in which the effect of a conventional four-optical-wave mixing is suppressed.
At present, if two different networks (transmission paths), such as for land use and submarine use, are to be connected at a connection point therebetween, then the two different networks are electrically terminated. However, it is necessary for aiming at a practical low-cost system to implement a connection-less simplified structure for structural integration of two networks.
In the conventional system, however, optical fibers in use have different zero-dispersion wavelengths, and a direct use for transmission accompanies a crosstalk due to the SPM-GVD effect or FWM, as a significant problem.
The optical wavelength division multiplexing transmission system according to the present invention comprises a first optical fiber transmission path for a wavelength division multiplex signal to be input therefrom, a second optical fiber transmission path having a zero-dispersion wavelength different from the first optical fiber transmission path, and an optical repeater in which the wavelength division multiplex signal input from the first optical fiber transmission path is wavelength-converted with respect to respective wavelengths thereof, for an output thereof to the second optical fiber transmission path.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.
Preferred embodiments of the present invention are explained below with reference to the accompanying drawings.
The optical repeater 1 operates as explained next. An optical signal with multiplexed wavelengths λ1 to λn is input into the wavelength selector 5. The wavelength selector 5 separates the received multiplexed wavelengths λ1 to λn into optical signals by the wavelengths λ1 to λn and supplies the separated wavelength to the wavelength converters 6.
Based on a control signal, the wavelength converters 6 respectively convert the wavelengths, such that λ1 into λ1′ and λ2 into λ2′ etc. The wavelength converters 6 provide the converted wavelengths to the wave combiner 7. The wave combiner combines the wavelengths λ1′, λ2′, . . . , λn′ and outputs the result.
Thus, a connection-less simplified structure can be implemented for structural integration of the two networks (transmission paths).
As explained above, the optical repeater 1 is provided between the first optical fiber transmission path 2 and the second optical fiber transmission path 3, wherein the second optical fiber transmission path 3 has a zero-dispersion wavelength different from the first optical fiber transmission path 2. This optical repeater 1 wavelength-converts with respect to respective wavelengths a wavelength division multiplex signal input from the first optical fiber transmission path 2, and output the result to the second optical fiber transmission path 3. Therefore, the SPM-GVD effect and FWM in the second optical fiber transmission path 3 are minimized, thereby implementing a connection-less simplified structure for structural integration of the two networks (transmission paths).
An optical signal with multiplexed wavelengths λ1, λ2, . . . , λn is input to the wave divider 4, wherefrom optical signals of all channels are likewise output to be sent to the wavelength selectors 5, where they have their wavelengths λ1, λ2, . . . , λn selected, to be sent to wavelength converters 6. Thereafter, actions are like the case of
Thus, with the second embodiment, a connection-less simplified structure can be implemented for structural integration of the two networks (transmission paths).
Because the optical amplifier 8 is inserted after every wavelength converter 6, the gain of each optical amplifier 8 is individually adjustable depending on a wavelength conversion efficiency of associated wavelength, thereby permitting compensation of an optical loss.
The compensation may preferably be effected of both transmission path loss and wavelength conversion loss, as shown in the optical repeater 61 in
The opto-electrical converter 9 may be a photo-diode, avalanche photo-diode, photo-counter, etc. The electro-optical converter 10 can be constituted with ease by use of a semiconductor laser.
Legend 12 denotes a light source, legend 13 denotes a photo-coupler, legend 14 denotes an optical filter, and legend 15 denotes the semiconductor optical amplifier. An optical signal (wavelength: λi) and pump light (wavelength: λp) are combined in the photo-coupler 13, to strike the semiconductor optical amplifier 15, which then generates a new wavelength-converted optical signal (wavelength: λi′) by way of a four-wave mixing. Only the wavelength-converted optical signal is filtered by the optical filter 14, to be output.
Legend 16 denotes the electric field absorption type modulator. The other elements are same as those shown in
Legend 17 denotes an optical fiber. The other elements are same as those shown in
The following tenth to thirteenth embodiments are each addressed to a changing process in an optical repeater 1 (or optical repeaters 11, 21, 31, and 61), where wavelength intervals are changed from an even interval layout to an uneven interval layout, or from an uneven interval layout to an even interval layout.
The tenth embodiment corresponds to a case of changing the wavelength intervals in the optical repeater 1 from an even interval layout to an uneven interval layout.
The eleventh embodiment corresponds to a case of changing the wavelength intervals in the optical repeater from an uneven interval layout to an even interval layout.
The twelfth embodiment corresponds to a case of changing the wavelength intervals in the optical repeater from a constant value Δλ to another constant value Δλ′.
The thirteenth embodiment corresponds to a case of changing the number of wavelengths in the optical repeater by a branching or insertion of wavelength.
Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.
Number | Date | Country | Kind |
---|---|---|---|
11-337937 | Nov 1999 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
4560246 | Cotter | Dec 1985 | A |
5170273 | Nishio | Dec 1992 | A |
5438445 | Nakano | Aug 1995 | A |
5442476 | Yamazaki et al. | Aug 1995 | A |
5629994 | Huber et al. | May 1997 | A |
5657144 | Tanaka et al. | Aug 1997 | A |
5696614 | Ishikawa et al. | Dec 1997 | A |
5717795 | Sharma et al. | Feb 1998 | A |
5781673 | Reed et al. | Jul 1998 | A |
5786916 | Okayama et al. | Jul 1998 | A |
5894362 | Onaka et al. | Apr 1999 | A |
6005698 | Huber et al. | Dec 1999 | A |
6115173 | Tanaka et al. | Sep 2000 | A |
6118561 | Maki | Sep 2000 | A |
6188511 | Marcenac et al. | Feb 2001 | B1 |
6188823 | Ma | Feb 2001 | B1 |
6285480 | H.o slashed.rlyck | Sep 2001 | B1 |
6304348 | Watanabe | Oct 2001 | B1 |
6377375 | Taga et al. | Apr 2002 | B1 |
6445473 | Suemura et al. | Sep 2002 | B1 |
6469813 | Leclerc et al. | Oct 2002 | B1 |
Number | Date | Country |
---|---|---|
0 703 680 | Mar 1996 | EP |
07-107069 | Apr 1995 | JP |
08-97771 | Apr 1996 | JP |
09-247091 | Sep 1997 | JP |