Patent Grant
6917743
1. Field of the Invention
The present invention relates to an optical fiber capable of compensating both the chromatic dispersion and dispersion slope of a positive-dispersion optical fiber, an optical transmission line constructed by splicing the optical fiber and a positive-dispersion optical fiber, and an optical communications system incorporating the optical transmission line.
2. Description of the Background Art
The wavelength division multiplexing (WDM) optical communications system multiplexes a plurality of component signals having mutually different wavelengths with an optical transmitter to transmit them. A signal lightwave composed of the component signals travels over an optical transmission line to arrive at an optical receiver. The WDM communications system can transmit and receive a large volume of information at a high rate. The conventional WDM communications system uses the C-band (1,530 to 1,565 nm) as a wavelength band for signal lightwaves. To increase the transmission capacity further, the use of the L-band (1,565 to 1,625 nm) is also being studied as the wavelength band for signal lightwaves.
It is desirable that the optical transmission line for the WDM communications system have a small absolute value of the chromatic dispersion over the entire wavelength band of the signal lightwave in order to transmit the signal lightwave with high quality. However, it is difficult to reduce the absolute value of the chromatic dispersion over the entire wavelength band of the signal lightwave when the optical transmission line is constructed by using only one type of optical fiber. Consequently, an optical transmission line is usually constructed by using two types of optical fibers to reduce the absolute value of the average chromatic dispersion of the entire optical transmission line over the wavelength band of the signal lightwave.
For example, published Japanese patent application H6-11620 has disclosed an optical transmission line for the application where the C-band is used as the wavelength band of the signal lightwave. The optical transmission line is constructed by splicing a standard single-mode optical fiber and a dispersion-compensating optical fiber. Here, the single-mode optical fiber is a positive-dispersion optical fiber having a zero dispersion wavelength at a wavelength of 1.3 μm or so, and a positive chromatic dispersion of 15 ps/nm/km or so and a positive dispersion slope of 0.06 ps/nm2/km or so at a wavelength of 1.55 μm. The dispersion-compensating optical fiber has a negative chromatic dispersion and a negative dispersion slope at a wavelength of 1.55 μm, and compensates both the chromatic dispersion and dispersion slope of the single-mode optical fiber.
U.S. Pat. No. 5,838,867 has disclosed another optical transmission line. The optical transmission line is constructed by splicing a non-zero dispersion-shifted fiber and a dispersion-compensating optical fiber. Here, the non-zero dispersion-shifted fiber is a positive-dispersion optical fiber having a zero-dispersion wavelength shifted to a wavelength of more than 1.3 μm, and a positive chromatic dispersion between 1 and 10 ps/nm/km and a positive dispersion slope at a wavelength of 1.55 μm. The dispersion-compensating optical fiber has a negative chromatic dispersion and a negative dispersion slope at a wavelength of 1.55 μm, and compensates both the chromatic dispersion and dispersion slope of the dispersion-shifted optical fiber.
The foregoing optical transmission lines constructed by splicing a positive-dispersion optical fiber (a single-mode optical fiber or a non-zero dispersion-shifted fiber) and a dispersion-compensating optical fiber has a small absolute value of the chromatic dispersion over the entire C-band and can perform high-quality WDM optical communication. However, the absolute value of the chromatic dispersion is not sufficiently small in the L-band. Therefore, they are not suitable for performing WDM optical communication in the L-band.
S. Bigo, et al. have reported in ECOC'99, PD 2-9 (p. 40) a non-zero dispersion-shifted fiber having a chromatic dispersion of 8 ps/nm/km and a dispersion slope of 0.057 ps/nm2/km at a wavelength of 1,550 nm (a chromatic dispersion of 10.3 ps/nm/km and a dispersion slope of 0.06 ps/nm2/km at a wavelength of 1,590 nm). D. W. Peckham, et al. have reported in ECOC'98 (p. 139) a non-zero dispersion-shifted fiber having a chromatic dispersion of 3.7 ps/nm/km and a dispersion slope of 0.0457 ps/nm2/km at a wavelength of 1,550 nm (a chromatic dispersion of 5.5 ps/nm/km and a dispersion slope of 0.046 ps/nm2/km at a wavelength of 1,590 nm). Published international application WO 00/65387 has disclosed a non-zero dispersion-shifted fiber having a chromatic dispersion of +7.7 ps/nm/km and a dispersion slope of +0.08 ps/nm2/km at a wavelength of 1,590 nm. However, no report has so far been published on a dispersion-compensating optical fiber capable of compensating in the L-band both the chromatic dispersion and dispersion slope of the above-described non-zero dispersion-shifted fibers.
An object of the present invention is to offer an optical fiber capable of compensating in the L-band both the chromatic dispersion and dispersion slope of a non-zero dispersion-shifted fiber. Another object is to offer an optical transmission line constructed by splicing the optical fiber and a non-zero dispersion-shifted fiber for performing high-quality WDM optical communication in the L-band. Yet another object is to offer an optical communications system incorporating the optical transmission line.
According to the present invention, the foregoing object is attained by offering an optical fiber having at a wavelength of 1,590 nm a chromatic dispersion, D, and a dispersion slope, S, that satisfy the formulae
−200 ps/nm/km≦D≦−50 ps/nm/km, and
0.009/nm≦S/D.
The optical fiber may comprise the following regions:
In accordance with another aspect of the present invention, an optical transmission line is offered that comprises the following components:
In accordance with yet another aspect of the present invention, an optical communications system is offered that comprises the following components:
Advantages of the present invention will become apparent from the following detailed description, which illustrates the best mode contemplated to carry out the invention. The invention can also be carried out by different embodiments, and its several details can be modified in various respects, all without departing from the invention. Accordingly, the accompanying drawing and the following description are illustrative in nature, not restrictive.
The present invention is illustrated to show examples, not to show limitations, in the figures of the accompanying drawing. In the drawing, the same reference numeral and sign refer to a similar element.
In the drawing:
−200 ps/nm/km≦D2≦−50 ps/nm/km (1a).
0.009/nm≦S2/D2 (1b)
The chromatic dispersion D2 may have a lower limit of −110 ps/nm/km. The ratio S2/D2 may have an upper limit of 0.015/nm. The upper limit may be reduced to 0.011/nm.
In the optical transmission line 10 and the optical communications system 1 incorporating it, both the chromatic dispersion and dispersion slope of the optical fiber 11 in the L-band are compensated by the optical fiber 12. Consequently, a signal lightwave having a multitude of wavelengths in the L-band can be transmitted with high quality. It is desirable that the optical transmission line 10 have a variation range of at most 0.4 ps/nm/km in the average chromatic dispersion of the entire optical transmission line in a wavelength range of 1,570 to 1,610 nm. Here, the term “variation range” is used to mean the difference between the maximum value and the minimum value. In this optical transmission line, the ratio of the length of the positive-dispersion optical fiber to that of the optical fiber of the present invention is properly determined. As a result, the absolute value of the chromatic dispersion in the L-band is considerably reduced, which enables the high-quality WDM optical communication.
It is desirable that the optical fiber 12 have an effective core area (hereinafter referred to as “effective area”) of at least 12 μm2 at a wavelength of 1,590 nm. In this case, the generation of non-linear optical phenomena can be suppressed, which can further increase the quality of the optical communication. It is desirable that the optical fiber 12 have a cutoff wavelength of at least 1.2 μm. In this case, even when the optical fiber is bent in a coil to form a module, the increase in bend loss can be suppressed. It is desirable that the optical fiber 12 have a transmission loss of at most 1.0 dB/km at a wavelength of 1,590 nm. It is desirable that the optical fiber 12 have a total loss of at most 7 dB in a wavelength range of 1,565 to 1,610 nm. In these two cases, the loss of a signal lightwave can be substantially reduced, which enables the long-distance transmission.
The optical fiber 12 can be produced by the following method:
It is desirable that the optical fiber 12 have a structure such that (a) the central core region 12a has a relative refractive-index difference, Δn1, of at least 1.2% and (b) the first cladding region 12b has a relative refractive-index difference, Δn2, of at most −0.3%. It is desirable that the ratio 2a/2c be at least 0.20, where 2a is the diameter of the central core region 12a, and 2c is the outer diameter of the second cladding region 12c. Furthermore, it is desirable that when the outer diameter 2c of the second cladding region 12c varies by 2%, the ratio S2/D2 vary by at most 15%. This condition facilitates the production of the optical fiber 12.
Examples of the optical fiber 12 are explained below. Table I shows dimensions and properties of Examples 1 to 10 of the optical fiber of the present invention. The optical fibers of Examples 1 to 10 have the refractive-index profile shown in FIG. 3B. The effective area (denoted as Aeff in Table I), bend loss, and transmission loss (denoted as Loss in Table I) are the values at a wavelength of 1,590 nm. The bend loss shows an increment in loss when the optical fiber is bent on a mandrel having a diameter of 20 mm.
When the optical fiber of Example 4 was coiled with a coiling diameter of 140 mm, its total loss was measured in a wavelength range of 1,565 to 1,610 nm. The maximum loss was 5.6 dB, and it occurred at a wavelength of 1,565 nm. The same measurement was conducted on the optical fiber of Example 5 under the same conditions as above. The maximum loss was 6.8 dB, and it occurred at a wavelength of 1,565 nm.
The present invention is described above in connection with what is presently considered to be the most practical and preferred embodiments. However, the invention is not limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
The entire disclosure of Japanese patent application 2002-218449 filed on Jul. 26, 2002 including the specification, claims, drawing, and summary is incorporated herein by reference in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2002-218449 | Jul 2002 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5361319 | Antos et al. | Nov 1994 | A |
| 5838867 | Onishi et al. | Nov 1998 | A |
| 20020164138 | Saitou et al. | Nov 2002 | A1 |
| 20020164139 | Saitou et al. | Nov 2002 | A1 |
| 20030021563 | Jiang et al. | Jan 2003 | A1 |
| Number | Date | Country |
|---|---|---|
| 06-11620 | Jan 1994 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20040017988 A1 | Jan 2004 | US |
