JP2009198945A - Single mode optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a single mode optical fiber that can materialize expansion of an effective core cross section and reduction of bending loss while having chromatic dispersion equivalent to that of an ordinary single mode optical fiber. <P>SOLUTION: The single mode optical fiber is characterized in that cable cutoff wavelength is ≤1,260 nm, that an effective core cross section at 1,550 nm wavelength is ≥100 μm<SP>2</SP>, that bent loss when bent ten times with a bending radius of 20 mmϕ is ≤30 dB, and that zero-scattering wavelength is in the range of 1,300-1,324 nm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a single mode optical fiber in which an effective core area (hereinafter referred to as A _eff ) having a zero dispersion wavelength in the 1.3 μm wavelength band is enlarged. The single mode optical fiber of the present invention is suitable as an optical fiber for transmission in a transmission system that needs to suppress stimulated Raman scattering and stimulated Brillouin scattering, for example, a three-wave multiplex transmission system.

  Transmission systems using optical fibers are being developed from long-haul and ultra-long haul transmission systems such as trunk systems connecting large cities and submarine systems connecting continents to FTTH (Fiber To The Home). . As a transmission system for FTTH, data communication and video distribution systems using three-wave multiplexing are expected to spread.

  FIG. 1 is a block diagram showing an example of this three-wave multiplex transmission system. This transmission system guides a signal from a center side 1 to an optical fiber 2 and transmits the signal from an optical fiber 2 by an optical coupler 4. The optical fibers are branched and guided to a large number of subscribers 3 to enable data communication and video distribution to the subscribers 3. In this transmission system, an optical signal having a wavelength of 1.31 μm and a wavelength of 1.49 μm is used for uplink / downlink of data communication, and a video signal is distributed using an optical signal having a wavelength of 1.55 μm.

As a transmission line of such a system, ITU-T (International Telecommunication Union Telecommunication Standardization sector) G.I. A single mode optical fiber as defined in 652 is used. As a video signal distribution method, there are a method using IP (Internet Protocol) and a method using analog intensity modulation as in the case of data communication. Distribution by analog intensity modulation is widely used because the conventional image receiving unit can be used as it is if the receiving unit performs demodulation.
For example, Patent Documents 1 and 2 and Non-Patent Document 1 are cited as conventional techniques related to a single mode optical fiber in which A _eff of the present invention is expanded.
US Pat. No. 6,337,942 US Pat. No. 6,385,379 Aikawa, et al., “Single-mode optical fiber with effective core area larger than 160μm2,” ECOC 1999, Proceeding of ECOC 1999, P1.15

In the three-wave multiplexing system, problems of signal degradation due to stimulated Brillouin scattering (hereinafter referred to as SBS) and stimulated Raman scattering (hereinafter referred to as SRS) are pointed out.
FIG. 2 shows an example of SBS measurement. As shown in FIG. 2, in the region where the incident power is relatively low, the output power is increased as compared with the incident power. However, when the power exceeds a certain level, the output power hardly increases. This phenomenon occurs because the power reflected by the SBS in the optical fiber increases. SBS is said to be a significant problem in systems that transmit video signals by analog modulation. As a method for suppressing SBS, there are known a method for changing the wavelength of a light source on the transmission system side and a method for suppressing the occurrence of SBS on the fiber itself. By suppressing SBS, it is possible to increase the power incident on the optical fiber. In addition to the effect of extending the transmission distance of the three-wave multiplex system, this has advantages such as an increase in the number of signal branches in a system using a PON (Passive Optical Network).

  When a high-intensity light (pump light) having a certain wavelength is incident on an optical fiber, the SRS generates an amplification characteristic having a peak on the long wavelength side of about 100 nm from the wavelength. If pump light is incident at an appropriate wavelength with respect to signal light, an optical fiber can be used as an amplification medium. On the other hand, it is known that SBS causes noise in a three-wave multiplexing system. As shown in FIG. 1, in the three-wave multiplexing system, the downstream data signal is arranged in the 1.49 μm band, and the video signal is arranged in the wavelength 1.55 μm band. Therefore, a data signal with a wavelength of 1.49 μm acts as pump light, a Raman gain is generated in the wavelength band of the video signal, and noise is generated in the video signal. The amount of SBS generated increases as the pump light power increases.

By using the above-described system and optical fiber for suppressing SBS, it is possible to increase the power incident on the optical fiber from the viewpoint of SBS. On the other hand, in terms of SRS, there is a restriction on the incident power. To do. It is known that increasing the A _{eff of} an optical fiber is effective in suppressing SRS (Nonlinear Fiber Optics, GP Agrawel, Academic Eress). A normal single mode optical fiber has an A _eff of about 80 μm ² at a wavelength of 1550 nm. On the other hand, an optical fiber in which A _eff is expanded to about 110 to 160 μm ² is known (see, for example, Patent Documents 1 and 2 and Non-Patent Document 1).

These conventional A _eff magnifying optical fibers are designed for ultra-long distance DWDM (Dense Wavelength Division Multiplexing) systems such as submarine cables. The DWDM system generally uses a wavelength of C band (1530 to 1565 nm) or more, and the cutoff wavelength of the conventional A _eff expansion optical fiber is set to 1530 nm or less. For this reason, it cannot be applied to a system that uses a wavelength of 1310 nm for transmission, such as a three-wave multiplexing system.

An ordinary single mode optical fiber or a conventional A _eff magnifying optical fiber often uses a refractive index distribution structure as shown in FIG. The refractive index distribution in FIG. 3 is a so-called step index type, in which there is a region of the core 5 with a high refractive index at the center in the radial direction of the fiber, and a region of the cladding 6 with a low refractive index on the outer periphery. Both the refractive index distribution and the refractive index distribution in the cladding 6 region are flat. In FIG. 3, symbol r ₁ is the radius of the core 5 and Δ ₁ is the relative refractive index difference of the core with respect to the cladding. FIG. 4 shows characteristics when a design for expanding A _eff is performed under the condition of a cut-off wavelength comparable to that of a normal single mode optical fiber (cable cut-off wavelength is 1260 nm). 4A is a graph showing the relationship between the mode field diameter (hereinafter referred to as MFD) and bending loss at a wavelength of 1310 nm, and FIG. 4B is a graph showing the relationship between A _eff and bending loss at a wavelength of 1550 nm. is there.
In a normal single mode optical fiber, for example, a single mode optical fiber having an MFD of about 9.2 μm at a wavelength of 1310 nm and an A _eff of about 80 μm ^{2 at} a wavelength of 1550 nm, the bending loss at 20 mmφ and 1550 nm is about 10 dB / m. On the other hand, when A _eff is increased to about 110 μm ² , the bending loss increases to about 100 dB / m, and it cannot be put into practical use. Also, the zero-dispersion wavelength is less than 1300 nm, and compatibility with a normal single mode optical fiber cannot be ensured.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a single mode optical fiber capable of realizing _Aeff expansion and bending loss reduction while having chromatic dispersion characteristics equivalent to those of a normal single mode optical fiber.

In order to achieve the above object, the present invention has a cable cutoff wavelength of 1260 nm or less, an A _{eff at} a wavelength of 1550 nm of 100 μm ² or more, a bending loss of 10 dB or less when bent at a bending diameter of 20 mmφ, and a zero dispersion wavelength. Provided is a single mode optical fiber having a range of 1300 nm to 1324 nm.

In the single mode optical fiber of the present invention, a central core having a radius r _1, a first cladding having a radius r ₂ provided on the outer periphery of the central core, and a _first core having a radius r ₃ provided on the outer periphery of the first cladding. 2 clads and a third clad having a radius r ₄ provided on the outer periphery of the second clad, and the central core, the first clad, and the second clad have a maximum refractive index n _1max , n _2max , n _3max , _respectively . a minimum refractive index _{n 1min, n 2min,} the refractive index distribution becomes _{n 3min,} the third cladding has a constant refractive index _{n c, n 1max> n c} , n 1max> n 2max, n 2max> n 3max _{, n 1min> n 2min, n} 2min> n 3min, it is preferable to satisfy the made _n 3min _{<n c} related.

  The single mode optical fiber of the present invention preferably has a maximum refractive index at the center of the central core.

In the single mode optical fiber of the present invention, a first layer having a central layer having a maximum relative refractive index Δ _{c1 based} on the refractive index of the third cladding and a minimum refractive index Δ _c2 provided on the outer periphery of the central layer. an annular region preferably has a core composed of a second annular region having a maximum refractive index delta _c3 provided on the outer periphery of the first annular region.

The single mode optical fiber of the present invention can suppress the generation of SBS and SRS by expanding A _eff .
Since the single mode optical fiber of the present invention has the same wavelength dispersion characteristic as that of a normal single mode optical fiber and has an expanded A _eff , the compatibility with the normal single mode optical fiber is ensured. Can do.
Since the single mode optical fiber of the present invention has an expanded A _eff and a small bending loss, it is less deteriorated in signal when used as a transmission fiber in a three-wave multiplex transmission system or the like, and has high quality transmission. You can build a system.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 5 is a diagram showing the refractive index distribution of the first embodiment of the single mode optical fiber according to the present invention. Single-mode optical fiber 10 of the present embodiment includes a central core 11 of radius r _1, a first cladding 12 having a radius r ₂ which is provided on the outer periphery of said central core 11, provided on the outer periphery of the first cladding 12 and a second cladding 13 of radius _{r 3,} and Do from the third cladding 14 of radius _{r 4} provided on the outer periphery of the second cladding 13. The refractive index of each part is in the order of the central core> the third cladding> the first cladding> the second cladding. In the present embodiment, the refractive indexes of the respective parts of the central core 11, the first cladding 12, the second cladding 13, and the third cladding 14 of the single mode optical fiber 10 are uniform.

The single mode optical fiber of this embodiment has a cable cutoff wavelength of 1260 nm or less, an A _{eff at} a wavelength of 1550 nm of 100 μm ² or more, a bending loss of 30 dB or less when bent 10 times with a bending diameter of 20 mmφ, and a zero dispersion wavelength of 1300 nm. The range is ˜1324 nm.

The single mode optical fiber 10 of the present embodiment can suppress the occurrence of SBS and SRS by expanding A _eff .
The single-mode optical fiber 10 of the present embodiment has a wavelength dispersion characteristic equivalent to that of a normal single-mode optical fiber and has an expanded A _eff , so that compatibility with a normal single-mode optical fiber is ensured. can do.
Since the single mode optical fiber 10 of the present embodiment has an expanded A _eff and a small bending loss, the signal quality is less deteriorated when used as a transmission fiber in a three-wave multiplex transmission system, etc. Can be constructed.

In the present invention, the refractive index of each part of the central core 11, the first cladding 12, and the second cladding 13 of the single mode optical fiber 10 is not necessarily uniform, and the refractive index distribution of any part is stepped. Or may be changed in a curved line. The central core 11, first clad 12 and second clad 13, respectively have the maximum refractive index _{n 1max, n 2max, n 3max} , minimum refractive index _{n 1min,} n _2min, the refractive index distribution becomes _{n 3min,} third If cladding 14 that has a constant refractive index _{n c,} the respective refractive _{index, n 1max> n c, n} 1max> n 2max, n 2max> n 3max, n 1min> n 2min, n 2min> n 3min It may satisfy composed _n 3min _{<n c} related.

  FIG. 6 is a diagram showing the refractive index distribution of the second embodiment of the single mode optical fiber according to the present invention. The single mode optical fiber 20 of the present embodiment is provided on the outer periphery of the center core 21 having a maximum refractive index at the center and a refractive index distribution in which the refractive index gradually decreases toward the outside. The first clad 22, the second clad 23 provided on the outer periphery of the first clad 22, and the third clad 24 provided outside the second clad 23. The refractive indexes of the respective parts are in the order of the central core> the first and third claddings> the second cladding.

The single mode optical fiber 20 of the present embodiment has a refractive index distribution structure shown in FIG. 6, so that, similarly to the first embodiment, a cable cutoff wavelength of 1260 nm or less and an A _{eff at} a wavelength of 1550 nm of 100 μm ² or more. In addition, it is possible to achieve transmission characteristics with a bending loss of 30 dB or less and a zero dispersion wavelength in the range of 1300 nm to 1324 nm when bent 10 times with a bending diameter of 20 mmφ, and the same effects as in the first embodiment can be obtained. .

FIG. 7 is a diagram showing the refractive index distribution of the third embodiment of the single mode optical fiber according to the present invention. The single mode optical fiber 30 of this embodiment includes a central core 31 having a plurality of layers having different refractive indexes, a first cladding 32 provided on the outer periphery of the central core 31, and an outer periphery of the first cladding 32. The second clad 33 and the third clad 34 provided outside the second clad 33. The refractive indexes of the respective parts are in the order of the central core> the first and third claddings> the second cladding. The central core 31 has a central layer 35 having a maximum relative refractive index Δ _{c1 based} on the refractive index of the third cladding 34, and a first refractive index Δ _c2 provided on the outer periphery of the central layer 35. the annular region 36, which is a second annular region 37 and having a maximum refractive index delta _c3 provided on the outer periphery of the first annular area 36.

The single-mode optical fiber 30 of the present embodiment has a refractive index distribution structure shown in FIG. 7, so that, similarly to the first embodiment, a cable cutoff wavelength of 1260 nm or less and an A _{eff at} a wavelength of 1550 nm of 100 μm ² or more. In addition, it is possible to achieve transmission characteristics with a bending loss of 30 dB or less and a zero dispersion wavelength in the range of 1300 nm to 1324 nm when bent 10 times with a bending diameter of 20 mmφ, and the same effects as in the first embodiment can be obtained. .
Hereinafter, the effects of the present invention will be demonstrated by examples.

[Example 1]
Five types of single-mode optical fibers of Examples 1-1 to 1-4 having the refractive index distribution structure shown in FIG. 5 and having different radii and relative refractive index differences as shown in Table 1, Each _Aeff , MFD, chromatic dispersion value, dispersion slope, zero dispersion wavelength, and bending loss were measured. The results are summarized in Table 1.

As shown in Table 1, the four types of single mode optical fibers of Examples 1-1 to 1-4 have a cable cutoff wavelength of 1260 nm or less, an A _{eff at} a wavelength of 1550 nm of 10 μm ² or more, and a bending diameter of 20 mmφ 10 times. The bending loss when bent was 30 dB or less, and the zero dispersion wavelength was 1300 nm to 1324 nm.

FIG. 8 shows the relationship between the MFD and the bending loss (FIG. 4 (a)) of the conventional optical fiber shown in FIG. 4 (when A _eff is designed to be increased in a normal single mode optical fiber), and A _eff and the bending. It is the figure which plotted the bending loss measurement result of Examples 1-1 to 1-4 shown in Table 1 on the graph which shows the relationship (FIG.4 (b)) with loss. 8A and 8B, it can be seen that the four types of single-mode optical fibers of Examples 1-1 to 1-4 according to the present invention can remarkably reduce the bending loss as compared with the conventional optical fiber. .

[Example 2]
A single mode optical fiber of Example 2 having the refractive index distribution structure shown in FIG. 6 and having different radii and relative refractive index differences as shown in Table 2 was manufactured. Each A _eff , MFD, chromatic dispersion The value, dispersion slope, zero dispersion wavelength and bending loss were measured. The results are summarized in Table 2.

[Example 3]
A single mode optical fiber of Example 3 having the refractive index distribution structure shown in FIG. 7 and having different radii and relative refractive index differences as shown in Table 2 was manufactured, and each A _eff , MFD, and chromatic dispersion were produced. The value, dispersion slope, zero dispersion wavelength and bending loss were measured. The results are summarized in Table 2.

As shown in Table 2, the single mode optical fibers of Examples 2 and 3 are bent when the cable cutoff wavelength is 1260 nm or less, A _{eff at} the wavelength of 1550 nm is 100 μm ² or more, and the bending diameter is 10 times with a bending diameter of 20 mmφ. The performance was such that the loss was 30 dB or less and the zero dispersion wavelength was in the range of 1300 nm to 1324 nm.

Figure 9 shows the relationship between MFD and a bending loss of the conventional optical fiber shown in FIG. 4 (when the design to increase the A _eff at ordinary single mode optical fiber) (FIG. 4 (a)) and A _eff and It is the figure which plotted the bending loss measurement result of Example 2 and Example 3 shown in Table 2 on the graph which shows a relationship with a bending loss (FIG.4 (b)). 9 (a) and 9 (b), it can be seen that the single-mode optical fibers of Examples 2 and 3 according to the present invention can significantly reduce the bending loss as compared with the conventional optical fiber.

It is a block diagram which shows an example of a three-wave multiplex transmission system. It is a graph which illustrates the measurement waveform of SBS. It is a figure which shows an example of the refractive index distribution of the conventional single mode optical fiber. It is a graph which shows the relationship between (a) MFD and a bending loss, (b) Relationship between _Aeff and a bending loss about the conventional optical fiber designed to expand _Aeff in a normal single mode optical fiber. It is a refractive index distribution map which shows 1st Embodiment of the single mode optical fiber of this invention. It is a refractive index distribution diagram showing a second embodiment of the single mode optical fiber of the present invention. It is a refractive index profile showing a third embodiment of the single mode optical fiber of the present invention. It is a graph which shows the bending loss measurement result of the single mode optical fiber of Example 1 which concerns on this invention. It is a graph which shows the bending loss measurement result of the single mode optical fiber of Example 2, 3 which concerns on this invention.

Explanation of symbols

  10, 20, 30 ... single mode optical fiber, 11, 21, 31 ... first cladding, 12, 22, 32 ... second cladding, 13, 23, 33 ... third cladding, 14, 24, 34 ... fourth cladding 35 ... center layer, 36 ... first annular region, 37 ... second annular region.

Claims (4)

Cable cutoff wavelength of 1260 nm or less, effective core area at wavelength of 1550 nm is 100 μm ² or more, bending loss when bending 10 times with a bending diameter of 20 mmφ is 30 dB or less, and zero dispersion wavelength is in the range of 1300 nm to 1324 nm. Characteristic single mode optical fiber. A central core having a radius r _1, a first cladding having a radius r ₂ provided on the outer periphery of the central core, a second cladding having a radius r ₃ provided on the outer periphery of the first cladding, and a third cladding radius _{r 4} that is provided on the outer periphery, a central core, a first cladding and a second cladding each maximum refractive index _{n 1max, n 2max, n 3max} , minimum refractive index _{n 1min, n 2min,} It has a refractive index distribution which becomes n _3min, the third cladding has a constant refractive index _{n c, n 1max> n c} , n 1max> n 2max, n 2max> n 3max, n 1min> n 2min, n 2min > _{n 3min,} single-mode optical fiber according to claim 1, characterized in that satisfy _n 3min _{<n c} the relationship.   The single-mode optical fiber according to claim 2, wherein the single-mode optical fiber has a maximum refractive index at a central portion of the central core. A central layer having a maximum relative refractive index Δ _{c1 based} on the refractive index of the third cladding, a first annular region having a minimum refractive index Δ _c2 provided on the outer periphery of the central layer, and the first annular single-mode optical fiber according to claim 2, characterized in that it comprises a core composed of a second annular region having a maximum refractive index delta _c3 provided on the outer periphery of the region.

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