LOW-DISPERSION SINGLE-MODE OPTICAL FIBER

Abstract

A low-dispersion single-mode fiber includes a core and claddings covering the core. The core layer has a radius in a range of 3-5 μm and a relative refractive index difference in a range of 0.15% to 0.45%. The claddings comprise a first depressed cladding, a raised cladding, a second depressed cladding, and an outer cladding arranged sequentially from inside to outside. The first depressed cladding has a unilateral width in a range of 2-7 μm and a relative refractive index difference in a range of −0.4% to 0.03%. The raised cladding has a unilateral width in a range of 2-7 μm and a relative refractive index difference in a range of 0.05% to 0.20%. The second depressed cladding has a unilateral width in a range of 0-8 μm and a relative refractive index difference in a range of 0% to −0.2%. The outer cladding is formed of pure silicon dioxide glass.

Claims

1. A low-dispersion single-mode fiber, comprising a core layer and claddings, wherein the core layer has a radius R1 in a range from 3 μm to 5 μm and a relative refractive index difference Δ1 in a range from 0.15% to 0.45%, and the claddings comprise a first depressed cladding, a raised cladding, a second depressed cladding, and an outer cladding from inside to outside, wherein the first depressed cladding has a unilateral width (R2-R1) in a range from 2 μm to 7 μm and a relative refractive index difference Δ2 in a range from −0.4% to 0.03%; the raised cladding has a unilateral width (R3-R2) in a range from 2 μm to 7 μm and a relative refractive index difference Δ3 in a range from 0.05% to 0.20%; the second depressed cladding has a unilateral width (R4-R3) in a range from 0 μm to 8 μm and a relative refractive index difference Δ4 in a range from 0% to −0.2%; and the outer cladding is a layer made of pure silicon dioxide glass.

2. The low-dispersion single-mode fiber according to claim 1, wherein the radius of the core layer is in a range from 3.5 μm to 4.5 μm.

3. The low-dispersion single-mode fiber according to claim 1, wherein the relative refractive index difference Δ1 of the core layer is in a range from 0.20% to 0.40%.

4. The low-dispersion single-mode fiber according to claim 1, wherein the core layer is a silicon dioxide glass layer co-doped with germanium Ge and fluorine F, and has a contribution amount of doped F, wherein ΔF1 is in a range from −0.2% to −0.02%.

5. The low-dispersion single-mode fiber according to claim 1, wherein the unilateral width of the first depressed cladding (R2-R1) is in a range from 2.5 μm to 5.5 μm.

6. The low-dispersion single-mode fiber according to claim 1, wherein a difference value between the relative refractive index difference of the core layer and the relative refractive index difference of the first depressed cladding, wherein Δ1-Δ2 is in a range from 0.3% to 0.5%.

7. The low-dispersion single-mode fiber according to claim 1, wherein a value of annular area integral for the relative refractive index difference of the first depressed cladding, wherein Δ2×(R2.sup.2−R1.sup.2) is in a range from −15%.Math.μm.sup.2 to −2%.Math.μm.sup.2.

8. The low-dispersion single-mode fiber according to claim 7, wherein the first depressed cladding is a silicon dioxide glass layer co-doped with Ge and F, and has a contribution amount of doped F, wherein ΔF2 is in a range from −0.45% to −0.04%.

9. The low-dispersion single-mode fiber according to claim 1, wherein a value of annular area integral for the relative refractive index difference of the raised cladding, wherein Δ3×(R3.sup.2−R2.sup.2) is in a range from 4%.Math.μm.sup.2 to 21%.Math.μm.sup.2.

10. The low-dispersion single-mode fiber according to claim 9, wherein the raised cladding is a silicon dioxide glass layer doped with Ge or co-doped with Ge and F, and has a contribution amount of doped F, wherein ΔF3 is in a range from −0.20% to 0%.

11. The low-dispersion single-mode fiber according to claim 1, wherein the fiber has an MFD at a wavelength of 1310 nm in a range from 8.5 μm to 9.5 μm.

12. The low-dispersion single-mode fiber according to claim 1, wherein the fiber has a cable cutoff wavelength λ.sub.cc smaller than or equal to 1260 nm.

13. The low-dispersion single-mode fiber according to claim 1, wherein the fiber has attenuation smaller than or equal to 0.45 dB at a waveband ranging from 1270 nm to 1380 nm.

14. The low-dispersion single-mode fiber according to claim 1, wherein the fiber has dispersion in a range from −12 ps/nm/km to 5 ps/nm/km at a waveband ranging from 1270 nm to 1380 nm.

15. The low-dispersion single-mode fiber according to claim 1, wherein the fiber has dispersion in a range from −3.5 ps/nm/km to 3.5 ps/nm/km at a waveband ranging from 1340 nm to 1380 nm.

16. The low-dispersion single-mode fiber according to claim 1, wherein the fiber has a dispersion slope smaller than or equal to 0.08 ps/nm.sup.2.Math.km at a waveband ranging from 1270 nm to 1380 nm.

17. The low-dispersion single-mode fiber according to claim 1, wherein the fiber has a zero dispersion wavelength in a range from 1300 nm to 1400 nm.

18. Use of the fiber according to claim 1 as a low-dispersion single-mode fiber in a communication system, wherein the fiber is used for a WDM transmission system at a waveband ranging from 1270 nm to 1380 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 schematically shows a refractive index profile in an embodiment of the present disclosure;

[0035] FIG. 2 schematically shows a refractive index profile in another embodiment of the present disclosure;

[0036] FIG. 3 schematically shows material dispersion, waveguide dispersion, and total dispersion of a fiber;

[0037] FIG. 4 schematically shows doping in an embodiment of the present disclosure;

[0038] FIG. 5 schematically shows doping in another embodiment of the present disclosure; and

[0039] FIG. 6 shows a dispersion-wavelength graph for some embodiments of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] Total dispersion of a single-mode fiber is the sum of material dispersion and waveguide dispersion, as shown in the following equation:

D(λ)=D.sub.mat(λ)+D.sub.wg(λ).

[0041] Broadband dispersion can be realized by adjusting the material dispersion and the waveguide dispersion. Main factors affecting the material dispersion are doping components and doping concentrations thereof. Doping of germanium increases the material dispersion and the dispersion slope; and a low concentration of F has little influence on the dispersion.

[0042] In the single-mode fiber, only about 80% of optical power is transmitted in a fiber core, and 20% of the optical power is transmitted in a cladding. When pulses are transmitted in the fiber core and the cladding at the same time, a transmission speed in the fiber core and a transmission speed in the cladding are different due to different refractive index, so that waveguide dispersion is caused. Refractive indexes of the fiber core and the cladding and a profile structure can be adjusted so as to adjust the value and the slope of the waveguide dispersion. The waveguide dispersion is dependent on the mode field distribution between the fiber core and the cladding, that means it dependent on MFD, while the MFD is also dependent on wavelength.

[0043] Reasonable design of parameters for a first depressed cladding can reduce the dispersion slope of the fiber. When a width of the first depressed cladding is increased, most energy is limited in a core layer, so that the dispersion slope is reduced; and when the width of the first depressed cladding is further increased, influence of a raised layer is weakened, which leads to increasing of the dispersion slope. In addition, when a relative reflective index difference of the first depressed cladding is reduced, more energy is limited in the core layer, so that the slope of the waveguide dispersion is reduced, thereby reducing the total dispersion slope. However, the above method of reducing the dispersion slope is essentially to change an energy distribution by reducing an effective area, in which case MFD is also reduced.

[0044] In order that the fiber is compatible with the conventional G.652 single-mode fiber, it is required that MFD of the fiber should be large enough. By disposing a raised cladding designed with reasonable parameters in the cladding, a transmission speed of the pulses in the cladding can be reduced, so that the transmission speed difference between the fiber core and the cladding is reduced, thereby reducing the dispersion slope. In addition, the raised cladding allows for transmission of part of the energy, which can increase the effective area and increase the MFD. A second depressed cladding outside the raised cladding may restrict transmission of the optical power to an outer cladding, which can enhance a bending-insensitive property of the fiber.

[0045] Specific embodiments will be provided below to further describe the present disclosure.

[0046] The fiber of the present disclosure includes a core layer and claddings. The core layer has a radius R1 and a relative refractive index difference Δ1. The claddings include a first depressed cladding, a raised cladding, a second depressed cladding, and an outer cladding from inside to outside. The first depressed cladding has a radius R2 and a relative refractive index difference Δ2. The raised cladding has a radius R3 and a relative refractive index difference Δ3. The second depressed cladding has a radius R4 and a relative refractive index difference Δ4. The outer cladding is a layer made of pure silicon dioxide glass, and has a radius of 62.5 μm.

[0047] According to the description of present disclosure, a group of preformed rods were prepared and drawn into fibers, and a double-layer coating was applied to the fibers. Structural parameters and main performance parameters of the fibers are shown in Table 1.

[0048] As shown in Embodiment 1 and Embodiment 3, arranging the second depressed cladding can enhance a bending-resistance property of the fiber, but would slightly increase the dispersion slope. Based on this, the first depressed cladding and the raised cladding may be adjusted to reduce the dispersion slope.

[0049] With decreasing of annular area integral for the relative refractive index difference of the first depressed cladding, i.e., Δ2×(R2.sup.2−R2.sup.1), the dispersion slope is reduced significantly, as shown in Embodiments 2 to 5. It is required that Δ2×(R2.sup.2−R2.sup.1) be at least smaller than −2%.Math.μm.sup.2. However, at this time, the MFD is reduced, and the dispersion is reduced. Therefore, it is required that Δ2×(R2.sup.2−R2.sup.1) be larger than −15%.Math.μm.sup.2 so as to ensure an MFD matching the conventional G.652 single-mode fiber and a reasonable dispersion value.

[0050] With increasing of annular area integral for the relative refractive index difference of the raised cladding, i.e., Δ3×(R3.sup.2−R2.sup.1), the dispersion slope is decreased, and the dispersion is reduced, as shown in Embodiments 6 to 8. For another example, in Embodiment 12, when Δ3×(R3.sup.2−R2.sup.1) is very large, the dispersion slope is very small, but the dispersion is further reduced. Therefore, in order to ensure a small enough dispersion slope and a proper dispersion value, it is required that Δ3×(R3.sup.2−R2.sup.1) be in a range from 4%.Math.μm.sup.2 to 2.sup.1%.Math.μm.sup.2.

[0051] Embodiments 2 and 9 show that increasing of the annular area integral for the relative refractive index difference of the raised cladding, i.e., Δ3×(R3.sup.2−R2.sup.1) only is not sufficient enough to improve the dispersion slope.

[0052] In actual application of the fiber, there are requirements for the MFD, a dispersion value, and the bending-resistance property. When relatively large Δ2×(R2.sup.2−R2.sup.1) and Δ3×(R3.sup.2−R2.sup.1) are ensured, influence of the second depressed cladding on respective parameters is far smaller than that of the first depressed cladding and the raised cladding. Therefore, a very deep and wide second depressed cladding may be prepared, so as to enhance the bending-resistance property. In view of the above limiting condition of multiple claddings, in order to reduce the material dispersion and attenuation, a method of reducing doping of germanium in the core layer may be adopted to adjust and optimize parameters of the core layer in a certain range, so as to prepare a broadband low-dispersion single-mode fiber having a relatively small absolute value of dispersion at a waveband ranging from 1270 nm to 1380 nm, a small dispersion slope, a relatively large MFD, as shown in Embodiments 10 and 11.

TABLE-US-00001 TABLE 1 Main structural parameters and performance parameters of the fibers Embodiment Embodiment Embodiment Embodiment Embodiment Embodiment Fiber Parameters 1 2 3 4 5 6 R1 (um) 4.01 3.97 3.98 3.98 4.01 4.03 Δ1 (%) 0.303 0.304 0.301 0.300 0.299 0.303 Δ1-Δ2 (%) 0.400 0.347 0.411 0.440 0.479 0.426 Δ3-Δ2 (%) 0.202 0.186 0.212 0.240 0.330 0.267 Δ4-Δ2 (%) 0.097 −0.030 0.070 0.100 0.140 0.069 Δ2 × (R2.sup.2 − R1.sup.2) −3.2 −2.5 −3.8 −4.6 −6.0 −5.2 Δ3 × (R3.sup.2 − R2.sup.2) 5.3 8.1 5.3 5.0 7.7 7.7 Δ4 × (R4.sup.2 − R3.sup.2) 0.0 −5.9 −2.6 −2.6 −2.7 −4.0 MFD@1310 nm (um) 8.93 9.08 8.78 8.64 8.59 8.69 Disp@1270 nm (ps/nm/km) −7.32 −6.02 −6.50 −6.49 −7.70 −6.56 Disp@1380 nm (ps/nm/km) 0.06 2.31 1.46 1.21 −0.70 0.99 S@1270~1380 (ps/nm.sup.2/km) 0.067 0.076 0.072 0.070 0.064 0.069 λ0 (um) 1.371 1.347 1.358 1.361 1.393 1.364 S0 (ps/nm.sup.2/km) 0.061 0.073 0.067 0.063 0.053 0.060 Embodiment Embodiment Embodiment Embodiment Embodiment Embodiment Fiber Parameters 7 8 9 10 11 12 R1 (um) 4.02 4.01 3.84 4.41 4.41 4.41 Δ1 (%) 0.300 0.304 0.337 0.263 0.213 0.263 Δ1-Δ2 (%) 0.423 0.427 0.400 0.450 0.450 0.450 Δ3-Δ2 (%) 0.246 0.225 0.221 0.297 0.327 0.327 Δ4-Δ2 (%) 0.083 0.083 0.013 0.112 0.077 0.077 Δ2 × (R2.sup.2 − R1.sup.2) −5.2 −5.2 −2.5 −9.7 −12.2 −0.6 Δ3 × (R3.sup.2 − R2.sup.2) 8.9 10.8 8.3 8.4 8.6 16.4 Δ4 × (R4.sup.2 − R3.sup.2) −3.1 −3.4 −3.5 −6.1 −30.5 −22.1 MFD@1310 nm (um) 8.70 8.68 8.67 8.90 8.99 9.03 Disp@1270 nm (ps/nm/km) −6.82 −6.87 −7.40 −3.90 −4.47 −5.37 Disp@1380 nm (ps/nm/km) 0.37 0.02 0.67 3.43 2.54 0.99 S@1270~1380 (ps/nm.sup.2/km) 0.065 0.063 0.073 0.067 0.064 0.058 λ0 (um) 1.374 1.380 1.370 1.323 1.335 1.359 S0 (ps/nm.sup.2/km) 0.057 0.052 0.068 0.064 0.061 0.051