JP2006038898A - Single mode optical fiber and distributed Raman amplification transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a single mode optical fiber suitable for wide wavelength region distributed Raman amplification transmission and a distributed Raman amplification transmission system.
[Solution]
The single mode optical fiber has a core portion using pure quartz and a cladding portion having a refractive index lower than that of the core portion, a theoretical cutoff wavelength is 1.36 μm or less, a zero dispersion wavelength is 1.36 μm or less, The bending loss under a predetermined condition is designed to be 0.5 dB or less.
[Selection] Figure 6

Description

  The present invention relates to a single-mode optical fiber and a distributed Raman amplification transmission system to which the single-mode optical fiber is applied. For example, in a wide wavelength band of wavelengths from 1.46 μm to 1.625 μm, distributed Raman by backward pumping is provided. It is a single mode optical fiber that can be applied to an amplification transmission system, and is a distributed Raman amplification transmission system using the single mode optical fiber.

  In order to expand the transmission capacity per optical fiber, a high transmission rate and wavelength division multiplexing (WDM) technology have been widely studied.

  Along with this, for the purpose of application of long-distance / high-speed WDM transmission in the low loss band of wavelengths from 1.46 μm to 1.625 μm, an optical fiber designed to have non-zero chromatic dispersion in the wavelength band, A dispersion slope type optical fiber has been proposed (see Patent Document 1 and Non-Patent Document 1 below).

  On the other hand, distributed Raman amplification is excellent in signal-to-noise ratio (SNR) characteristics, and an arbitrary signal wavelength can be amplified in a wide band by selecting an excitation wavelength. Is widely studied (see Non-Patent Documents 2 and 3 below).

  In addition, it has been reported that the effect of improving transmission characteristics by adapting distributed Raman amplification can be improved by reducing the amount of dopant added to the optical fiber core used in the transmission line (see Non-Patent Document 4 below). . Furthermore, a pure silica glass core optical fiber has been proposed as an optical fiber in which the amount of dopant added to the optical fiber core portion is reduced (see Patent Document 2 below).

JP-T-2002-526807 JP-A-11-326670 D.Molin, L.Fleury, M.Gorlier, F.Beaumont, L.Expert, L.de Montmorillon, P.Sillard, P.Nouchi, "Ultra-Low Slope Medium-Dispersion Fiber for Wide-Band Transmissions", Proceeding of Optical Fiber Communication Conference & Exposition, 2003, pp.150-151 (TuB2) C. Fludger, A. Maroney, N. Jolley, R. Mears, "An analysis of the improvements in OSNR from distributed Raman amplifiers using modern transmission fibers", Proceeding of Optical Fiber Communication Conference, 2000, vol. 4, pp. 100 -102 B.Zhu, L.Leng, LENelson, Y.Qian, S.Stulz, C.Doerr, L.Stulz, S.Chandrasekar, S.Radic, D.Vengsarkar, Z.Chen, J.Park, K.Feder , H.Thiele, J.Bromage, L.Gruner-Nielsen, S.Knudsen, "3.08Tb / s (77 × 42.7Gb / s) Transmission over 1200km of Non-zero Dispersion-Shifted Fiber with 100-km Spans using C -and L-Band Distributed Raman Amplification "Proceeding of Optical Fiber Communication Conference and Exhibit, 2001, vol.4, PD23. C, Fukai, K. Nakajima, J. Zhou, K. Tajima, K. Kurokawa, I. Sankawa, "A Study of the Optimum Fiber Design for a Distributed Raman Amplification Transmission System", IEEE Photonics Technology Letters, 2003, vol. 15, No.11, pp.1642-1644 T. Mizuochi, K. Kinjo, S. Kajiya, T. Tokura, K. Motoshima, "Bidirectional Unrepeatered 43Gb / s WDM Transmission With C / L Band-Separated Raman Amplification", Journal of Lightwave Technology, 2002, vol. 20, No.12, pp.2079-2085

  In distributed Raman amplification, signal light existing at a wavelength in the frequency shift region of about 13 THz from the pumping light wavelength to the long wavelength side is amplified (see Non-Patent Document 5 above). Therefore, in order to perform single-mode WDM transmission adapted to distributed Raman amplification in the wavelength band from 1.46 μm to 1.625 μm, the wavelength corresponding to the frequency shift position from 1.46 μm to about 13 THz is shorter by 1. It is necessary to design the theoretical cutoff wavelength to 36 μm or less.

  In distributed Raman amplification, when a zero-dispersion wavelength exists in the wavelength band of signal light and pumping light, transmission characteristics are degraded by four-wave mixing. In Non-Patent Document 5, when the zero dispersion wavelength is less than or equal to the wavelength band of the signal light and the excitation light, the four-wave mixing is suppressed, and the zero dispersion wavelength exists in the wavelength band of the signal light and the excitation light. It is shown that the transmission characteristics are improved.

  For this reason, in order to suppress the four-wave mixing of the signal light and the excitation light in the wavelength band of 1.46 μm to 1.625 μm, it is necessary to design the optical fiber so that the zero dispersion wavelength is also 1.36 μm or less. Arise.

  However, the fiber described in Patent Document 2 is assumed to be used in a wavelength band of 1.55 μm, and has a problem that the cutoff wavelength characteristic does not always satisfy the above condition. Further, the fibers described in Patent Document 1 and Non-Patent Document 1 have a problem in that germanium is added to the core portion, which is not necessarily suitable for a distributed Raman amplification transmission system.

  The present invention has been made in view of such a problem, and a single mode optical fiber suitable for a WDM transmission system adapted for distributed Raman amplification in a wide wavelength band ranging from 1.46 μm to 1.625 μm, and An object is to provide a distributed Raman amplification transmission system.

The single mode optical fiber according to the present invention that solves the above problems is
Having a core part made of pure quartz and a cladding part having a lower refractive index than the core part,
A single mode optical fiber having a theoretical cutoff wavelength of 1.36 μm or less.

In the single mode optical fiber,
A single mode optical fiber having a zero dispersion wavelength of 1.36 μm or less.

In the single mode optical fiber,
A single-mode optical fiber characterized in that a bending loss at a wavelength of 1.625 μm when wound 100 times with a bending radius of 30 mm is 0.5 dB or less.

The single mode optical fiber according to the present invention that solves the above problems is
A core part formed of pure quartz and having a uniform refractive index, a cladding part having a refractive index lower than that of the core part and a uniform refractive index,
The theoretical cutoff wavelength is 1.36 μm or less, the zero-dispersion wavelength is 1.36 μm or less, the bending loss at a wavelength of 1.625 μm when wound 100 times with a bending radius of 30 mm is 0.5 dB or less,
A single mode optical fiber, wherein the radius of the core part is 2.4 μm to 4.6 μm, and the relative refractive index difference of the core part with respect to the cladding part is 0.3% to 1.2%.

The distributed Raman amplification transmission system according to the present invention that solves the above problems is as follows.
A transmission path composed of the single mode optical fiber; a pumping light source that is disposed behind the single mode optical fiber and injects pumping light that propagates in the direction opposite to the propagation direction of the signal light; and the single mode A distributed Raman amplification transmission system comprising a dispersion compensation element that compensates for cumulative dispersion of an optical fiber and an optical amplifier.

  According to the single mode optical fiber of the present invention, an optical fiber having a core portion using pure quartz and a cladding portion having a refractive index lower than that of the core portion is used, and the core radius and relative refractive index difference of the optical fiber are used. The ideal cutoff wavelength characteristics, zero-dispersion wavelength characteristics, and bending loss characteristics that have no practical problems in the wavelength band of 1.46 μm to 1.625 μm are realized by designing the HF appropriately. There is an effect such as.

  Specifically, by setting the theoretical cutoff wavelength to 1.36 μm or less, the single-mode characteristics of the excitation light at wavelengths of 1.36 μm or more are maintained, and good distributed Raman amplification of signal light at wavelengths of 1.46 μm or more is possible. The effect is as follows.

  On the other hand, when the theoretical cutoff wavelength condition is not satisfied, the single-mode transmission band of the pumping light is reduced, and the lower limit of the signal light wavelength enabling the distributed Raman amplification is limited to a wavelength longer than the wavelength of 1.46 μm. End up. This leads to a loss that the entire band cannot be sufficiently used in long-distance / high-speed WDM transmission using a low loss band of wavelengths from 1.46 μm to 1.625 μm.

  In addition, by setting the zero dispersion wavelength to 1.36 μm or less, it is possible to suppress deterioration in transmission characteristics due to four-wave mixing between signal light and between signal light and excitation light.

  On the other hand, when the condition of the zero-dispersion wavelength is not satisfied, the transmission characteristic is deteriorated due to the four-wave mixing between the signal light and the pumping light, and a signal that enables good transmission characteristics when applying distributed Raman amplification. The lower limit of the light wavelength is limited to the longer wavelength side than the wavelength of 1.46 μm. The loss caused by this is as described above.

  Furthermore, the current ITU-T Recommendation G. ITU-T Recommendation G.1 is used by setting the bending loss at a wavelength of 1.625 μm when wound 100 times with a bending radius of 30 mm to 0.5 dB or less. An effect of satisfying the transmission characteristics equivalent to the single mode fiber defined in 652 is also achieved.

  On the other hand, when the bending loss condition is not satisfied, an increase in loss due to bending occurs particularly on the long wavelength side, and the optical signal wavelength that can be used for optical signal transmission is limited to the shorter wavelength side than 1.625 μm. . The loss caused by this is as described above.

  Further, it has a core part made of pure quartz and a clad part having a refractive index lower than that of the core part, a theoretical cutoff wavelength is 1.36 μm or less, a zero dispersion wavelength is 1.36 μm or less, a bending radius A core portion having a bending loss of 0.5 dB or less at a wavelength of 1.625 μm when wound 100 times at 30 mm and having a uniform refractive index, and a clad portion having a refractive index lower than that of the core portion and a uniform refractive index. And the radius of the core portion is 2.4 μm to 4.6 μm, and the relative refractive index difference of the core portion with respect to the cladding portion is 0.3% to 1.2%. It is possible to apply good distributed Raman amplification to signal light of 46 μm to 1.625 μm, and at the same time, for example, design chromatic dispersion at a wavelength of 1.55 μm in the range of 5 ps / nm · km to 17 ps / nm · km. For example, when a dispersion compensation fiber is used as a dispersion compensation element by realizing good transmission characteristics because the accumulated dispersion in the optical transmission path is reduced and reducing the amount of dispersion compensation. There is also an effect that the length of the dispersion compensating fiber and insertion loss can be reduced.

  Hereinafter, although an embodiment of the present invention is described in detail using a drawing, the present invention is not limited to this. FIG. 1 is a schematic configuration diagram illustrating a distributed Raman amplification transmission system according to an embodiment.

  As shown in the figure, a distributed Raman amplification transmission system 1 according to the embodiment includes an optical fiber 2 serving as a transmission line, a pumping light source 3 for distributed Raman amplification, and pumping light from the pumping light source 3 to the optical fiber 2. It comprises an incident optical circulator 5, a dispersion compensation element 6, and lumped constant optical amplifiers 7a and 7b.

  Excitation light from the excitation light source 3 is incident in a direction opposite to the propagation direction of the signal light 4 and is connected to the dispersion compensation element 6 and the optical amplifiers 7a and 7b via the optical circulator 5 and the like. The dispersion compensating element 6 is an element that compensates for accumulated dispersion generated in the optical fiber 2. Hereinafter, the optical fiber 2 (single mode optical fiber) which is a transmission line will be described in detail.

  FIG. 2 is a conceptual diagram showing the refractive index distribution in the cross-sectional direction of the single-mode optical fiber 2 applied to the distributed Raman amplification transmission system 1 according to the embodiment. The core portion of the single mode optical fiber 2 is made of pure quartz and has a uniform refractive index as shown in FIG. The clad part has a lower refractive index than the core part and a uniform refractive index.

The relative refractive index difference Δ _S of the core with respect to the cladding is defined by the following formula (1) using the refractive index n _SiO2 of the core made of pure quartz and the refractive index n _clad of the cladding. In addition, in the same figure, a represents the radius of a core part.

FIG. 3 is a diagram illustrating a calculation example of equal wavelength dispersion characteristics at a wavelength of 1.55 μm with respect to the relative refractive index difference Δ _S of the single mode optical fiber 2 and the radius a of the core portion. In the figure, lines showing the characteristics of equal wavelength dispersion (unit: ps / nm · km) are shown every 2 ps / nm · km from 0 ps / nm · km to 18 ps / nm · km.

FIG. 4 shows the relative refractive index difference Δ _S when the single-mode optical fiber 2 satisfies the condition α _R where the bending loss at a wavelength of 1.625 μm is 0.5 dB or less when wound 100 times with a bending radius of 30 mm. It is a figure showing the relationship of the radius a of a core part.

By designing the relative refractive index difference Δ _S and the radius a of the core portion in the region on the right side from the solid line indicating the condition α _R in FIG. 4 (the region on the oblique line side: see the following formula (2)), A single-mode optical fiber that satisfies the loss condition α _R can be obtained. The following formula (2) is an approximate formula obtained from the solid line indicating the condition α _R in FIG.

FIG. 5 shows the relationship between the relative refractive index difference Δ _S and the radius a of the core portion when the condition α _R is satisfied and the condition λ _C is 1.36 μm or less in the single mode optical fiber 2. FIG.

By designing the relative refractive index difference Δ _S and the core radius a in the region on the left side of the solid line indicating the condition λ _C in FIG. 5 (the region on the oblique line side: see the following formula (3)), the above theory is obtained. It is possible to satisfy the cutoff wavelength condition λ _C. Note that the following equation (3) is an approximate equation obtained from a solid line indicating the condition λ _C in FIG. Furthermore, by designing the relative refractive index difference Δ _S and the radius a of the core portion in a region surrounded by a solid line indicating the condition α _R and a solid line indicating the condition λ _C , the bending loss condition α _R and the theoretical cutoff wavelength are determined. The condition λ _C can be satisfied at the same time.

FIG. 6 shows the relative refractive index difference Δ _S when the condition α _R and the condition λ _C are satisfied and the condition λ ₀ where the zero-dispersion wavelength is 1.36 μm or less is satisfied in the single mode optical fiber 2. It is a figure showing the relationship of the radius a.

By designing the relative refractive index difference Δ _S and the radius a of the core portion in the region above the solid line indicating the condition λ _{0 in} FIG. 6 (the region on the oblique line side: see the following formula (4)), the above zero is obtained. The dispersion wavelength condition λ ₀ can be satisfied. The following formula (4) is an approximate formula obtained from the solid line indicating the condition λ ₀ in FIG. Furthermore, by designing the relative refractive index difference Δ _S and the core radius a in a region surrounded by a solid line indicating the condition α _R , a solid line indicating the condition λ _C and a solid line indicating the condition λ ₀ , It is possible to simultaneously satisfy α _R , the theoretical cutoff wavelength condition λ _C, and the zero dispersion wavelength condition λ ₀ .

In FIG. 6, the intersection of the solid line indicating the condition α _R and the solid line indicating the condition λ _C is established under the design condition of a relative refractive index difference of 0.3% and a core radius of 4.6 μm, and the solid line indicating the condition α _R And the solid line indicating the condition λ ₀ is established under the design condition of a relative refractive index difference of 0.4% and a core radius of 3.1 μm. The intersection of the solid line indicating the condition λ _C and the solid line indicating the condition λ ₀ is This is established under design conditions of a relative refractive index difference of 1.2% and a core radius of 2.4 μm.

  As described above, in the case of the single mode optical fiber having the refractive index distribution shown in FIG. 2, the radius of the core portion is 2.4 μm to 4.6 μm, and the relative refractive index difference of the clad portion with respect to the core portion is 0.3. % To 1.2%, a theoretical cutoff wavelength characteristic of 1.36 μm or less, a zero dispersion wavelength of 1.36 μm or less, a bending radius of 30 mm, 100 turns, 0.5 dB or less at a wavelength of 1.625 μm It can be seen that the chromatic dispersion at a wavelength of 1.55 μm can be changed from 5 ps / nm · km to 17 ps / nm · km.

1 is a schematic configuration diagram illustrating a distributed Raman amplification transmission system according to an embodiment. It is a conceptual diagram showing the refractive index distribution of the cross-sectional direction of the single mode optical fiber applied to the distributed Raman amplification transmission system which concerns on embodiment. It is a figure showing the example of a calculation of the equal wavelength dispersion characteristic in wavelength 1.55micrometer with respect to the relative refractive index difference of the single mode optical fiber applied to the distributed Raman amplification transmission system which concerns on embodiment, and the radius of a core part. In the single-mode optical fiber applied to the distributed Raman amplification transmission system according to the embodiment, when the condition α _R where the bending loss at a wavelength of 1.625 μm when wound 100 times with a bending radius of 30 mm is 0.5 dB or less is satisfied It is a figure showing the relationship between the relative refractive index difference of this, and the radius of a core part. In a single mode optical fiber applied to the distributed Raman amplification transmission system according to the embodiment, the relative refractive index difference and the core satisfying the condition α _R and satisfying the condition λ _C where the theoretical cutoff wavelength is 1.36 μm or less It is a figure showing the relationship of the radius of a part. In the single mode optical fiber applied to the distributed Raman amplification transmission system according to the embodiment, the relative refraction when the condition α _R and the condition λ _C are satisfied and the condition λ ₀ where the zero dispersion wavelength is 1.36 μm or less is satisfied It is a figure showing the relationship between a rate difference and the radius of a core part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Distributed Raman amplification transmission system 2 Optical fiber 3 Excitation light source 4 Signal light 5 Optical circulator 6 Dispersion compensation element
7a, 7b Optical amplifier

Claims (5)

Having a core part made of pure quartz and a cladding part having a lower refractive index than the core part,
A single mode optical fiber having a theoretical cutoff wavelength of 1.36 μm or less. The single mode optical fiber according to claim 1, wherein
A single mode optical fiber having a zero dispersion wavelength of 1.36 μm or less. The single mode optical fiber according to claim 1 or 2,
A single-mode optical fiber, wherein a bending loss at a wavelength of 1.625 μm when wound 100 times with a bending radius of 30 mm is 0.5 dB or less. A core part formed of pure quartz and having a uniform refractive index, a cladding part having a refractive index lower than that of the core part and a uniform refractive index,
The theoretical cutoff wavelength is 1.36 μm or less, the zero-dispersion wavelength is 1.36 μm or less, the bending loss at a wavelength of 1.625 μm when wound 100 times with a bending radius of 30 mm is 0.5 dB or less,
A single mode optical fiber, wherein the radius of the core part is 2.4 μm to 4.6 μm, and the relative refractive index difference of the core part with respect to the cladding part is 0.3% to 1.2%.   A transmission line constituted by the single mode optical fiber according to any one of claims 1 to 4, and pumping light that is arranged behind the single mode optical fiber and propagates in a direction opposite to the propagation direction of the signal light. A distributed Raman amplification transmission system comprising: an excitation light source to be injected; a dispersion compensation element that compensates for the accumulated dispersion of the single mode optical fiber; and an optical amplifier.

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