JP2007298885A - Dispersion compensating optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dispersion compensating optical fiber improved in bending loss with respect to the dispersion compensating optical fiber conventionally having complexity and a large specific refractive index difference. <P>SOLUTION: The dispersion compensating optical fiber 1 is provided with a core 2 and two or more clad layers 3-6 covering the core 2 and having different refractive indexes. In the boundary between the core 2 and a first clad layer 3 outside the core, there is provided a first gradient layer 8 in which a specific refractive index difference gradually decreases. Also, in the boundary between the first clad layer 3 and the second clad layer 4 outside the first, a second gradient layer 9 is provided in which the specific refractive index difference gradually increases. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a dispersion compensating optical fiber including a core and two or more clad layers having different refractive indexes covering the core, and in particular, has a complicated refractive index profile and a large relative refractive index difference Δ. The present invention relates to a dispersion compensating optical fiber.

  Due to the explosive increase in data communications such as the Internet in recent years, a dramatic increase in transmission capacity has been demanded. At present, a WDM (Wavelength Division Multiplexing) transmission system that simultaneously transmits a plurality of signal lights having different wavelengths in one optical fiber has been put into practical use and is used in a trunk transmission line and a submarine optical cable. Usually, such optical fiber transmission lines are provided with repeaters at regular intervals.

  A conventional repeater is a so-called re-repeater that converts signal light once into an electrical signal in order to compensate and amplify the signal light, and synchronously reproduces and amplifies the electrical signal to convert it into an optical signal. However, in WDM transmission, since reproduction and amplification must be performed for each of a plurality of signal lights having slightly different wavelengths, devices corresponding to the number of waves are required.

  For this reason, the increase in the wave number for increasing the capacity of WDM transmission has limitations in terms of cost and mounting space.

  However, with the development of EDFA (Erium-Doped Fiber Amplifier), signal light of all wavelengths can be amplified as a whole without converting the signal light into an electrical signal. It was. Although this EDFA has rapidly increased the transmission capacity, various problems have arisen due to an increase in wave number and an increase in the bit rate of signal light.

  For example, due to the chromatic dispersion inherent in the optical fiber, different dispersion occurs at both ends of the used wavelength band, and there is a problem that the waveform of the signal light after transmission is deteriorated or a nonlinear phenomenon occurs. The non-linear phenomenon is a phenomenon caused by a local change in refractive index distribution (generally depending on the optical power density) of the optical fiber constituting the transmission path, and corresponds to FWM (Four Wave Mixing) and the like.

  These dispersion and non-linear phenomena can cause the transmission quality of signal light to deteriorate. This is particularly serious when a large number of signal lights having different wavelengths are transmitted over a long distance as in WDM transmission.

  The prior art document information related to the invention of this application includes the following.

JP 2003-207664 A JP 2005-4216 A

  Here, in order to prevent the signal waveform from being deteriorated due to the chromatic dispersion of the optical fiber, it is effective to shift the so-called zero dispersion wavelength to the use wavelength so as to make the dispersion value of the use wavelength band as small as possible. For example, a DSF (Dispersion Shift Fiber) having a zero dispersion wavelength of 1550 nm is widely applied regardless of whether it is on land or on the seabed.

  However, in WDM transmission in which a plurality of signal lights are transmitted, the dispersion values generated in the signal light on the shortest wavelength side and the signal light on the longest wavelength side are different. That is, the wave number itself is limited by the presence of the dispersion slope. This is because a dispersion range (that is, a wavelength band) within which the signal light after transmission through the optical fiber is within a limit that can be discriminated is determined by hardware and transmission speed, and as a result, the maximum wave number is determined.

  Therefore, it is important to increase the transmission capacity to reduce the value of the dispersion slope as much as possible.

By changing the single-peak type refractive index profile (refractive index distribution) of a conventional optical fiber to a complicated refractive index profile such as a W type or a triple clad type, for example, 0.05 ps / nm ² / km or less A low dispersion slope can be achieved.

  However, on the other hand, as the wave number increases, the power density of the optical signal incident on the optical fiber increases, and the above-mentioned nonlinear phenomenon has become a big problem. For example, recent research has revealed that the above-described FWM amplifies WDM signal light in the vicinity of a zero dispersion wavelength and significantly degrades signal transmission characteristics. In order to increase the wave number of signal light while preventing this non-linear phenomenon, it is sufficient to use an optical fiber having a large effective area as much as possible while keeping the dispersion and dispersion slope small in the entire transmission line.

For example, using an optical fiber that has a relatively large effective cross-sectional area and a small dispersion and dispersion slope at a portion where the optical density immediately after amplification by an amplifier such as an EDFA is high, suppress the occurrence of nonlinear phenomena and compare it to the output end of the optical fiber. By connecting an optical fiber having a small effective effective cross-sectional area and a relatively small dispersion and dispersion slope, dispersion can be non-zero and the slope can be suppressed to 0.1 ps / nm ² / km or less in the entire transmission line.

  In addition, an optical fiber having an extremely large effective area and large dispersion is used immediately after amplification by an amplifier such as an EDFA (the first half of the amplification section of the rare earth-doped optical fiber), and then (the latter half of the amplification section of the rare earth-doped optical fiber) is used in the first half. A hybrid transmission line using an optical fiber that completely compensates for the generated accumulated dispersion and dispersion slope has also been proposed.

  FIG. 3 is a diagram showing cumulative dispersion of a hybrid transmission line by an optical fiber with an enlarged effective area and a dispersion / dispersion slope compensating optical fiber during wavelength division multiplexing transmission. In FIG. 3, the horizontal axis indicates the fiber length, and the vertical axis indicates the cumulative dispersion.

  An SCDCF (Slope Compensation Dispersion Compensation Fiber) used in the latter half of the transmission line can realize large negative dispersion and negative dispersion slope, but has a relatively small effective area. For this reason, an SCDCF having a large MFD (mode field diameter) has been proposed when fusion splicing with a different type optical fiber such as an optical fiber having an extremely large effective area used in the first half.

  However, these SCDCFs do not take the bending loss value into consideration, and it is difficult to accurately evaluate the transmission loss. In addition, there is a problem that the transmission loss is likely to decrease after the cable is formed.

  Accordingly, an object of the present invention is to provide a dispersion compensating optical fiber that solves the above-described problems and has improved bending loss in a dispersion compensating optical fiber that is complex and has a large relative refractive index difference, such as a conventional dispersion compensating optical fiber. It is in.

  The present invention was devised to achieve the above object, and the invention of claim 1 is a dispersion compensating optical fiber comprising a core and two or more clad layers having different refractive indexes covering the core. Providing a first inclined layer in which the relative refractive index difference gradually decreases at the boundary between the core and the first outer cladding layer, and at the boundary between the first cladding layer and the second outer cladding layer. This is a dispersion compensating optical fiber provided with a second inclined layer in which the relative refractive index difference gradually increases.

  According to a second aspect of the present invention, the refractive index distribution of the core has a trapezoidal shape, the first inclined layer is provided in the first cladding layer, and the second inclined layer is provided in the first cladding layer. 1. The dispersion compensating optical fiber according to 1.

  The invention according to claim 3 is the dispersion compensation according to claim 2, wherein the thickness of the first gradient layer is 0.75 to 0.95 μm, and the thickness of the second gradient layer is 1.75 to 1.85 μm. It is an optical fiber.

  According to a fourth aspect of the present invention, the two or more cladding layers are composed of first to fourth cladding layers in order from the inside, and the relative refractive index difference Δn1 of the core and the relative refractive index difference Δn3 of the second cladding layer are determined. The relative refractive index difference Δn0 of the fourth cladding layer is made larger than the relative refractive index difference Δn2 of the first cladding layer and the relative refractive index difference Δn4 of the third cladding layer is made smaller than the relative refractive index difference Δn0 of the fourth cladding layer. The dispersion compensating optical fiber according to claim 1.

  In the invention of claim 5, the relative refractive index difference Δn1 of the core is 0.85 to 1.05%, the radius r1 of the core is 2.05 to 2.15 μm, and the relative refractive index difference Δn3 of the second cladding layer is 0.10 to 0.13%, the radius r3 of the second cladding layer is 8.75 to 8.95 μm, the relative refractive index difference Δn2 of the first cladding layer is −0.45 to −0.40%, The radius r2 of the first cladding layer is 5.50 to 5.90 μm, the relative refractive index difference Δn4 of the third cladding layer is −0.07 to −0.03%, and the radius r4 of the third cladding layer is 9. The dispersion compensating optical fiber according to claim 1, wherein the dispersion compensating optical fiber is 95 to 10.15 μm.

  According to the present invention, bending loss can be suppressed lower than that of a conventional dispersion compensating optical fiber, and an increase in transmission loss after being cabled can be suppressed.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a refractive index distribution diagram of a dispersion compensating optical fiber showing a preferred embodiment of the present invention. In FIG. 1, the horizontal axis indicates the distance (fiber diameter) from the center O of the core, and the vertical axis indicates the relative refractive index difference.

  As shown in FIG. 1, the dispersion compensating optical fiber 1 according to this embodiment includes a core 2 having a radius r1 and two or more clad layers having different refractive indexes that cover the core 2, and the radius r2 (layer) in order from the inside. A first cladding layer 3 having a thickness (r2-r1)), a second cladding layer 4 having a radius r3 (layer thickness (r3-r2)), a third cladding layer 5 having a radius r4 (layer thickness (r4-r3)), And a fourth cladding layer 6 having a radius r5 (layer thickness (r5-r4)).

  The dispersion compensating optical fiber 1 is provided with the first inclined layer 8 in which the relative refractive index difference gradually decreases at the boundary 23 between the core 2 and the first cladding layer 3 outside the core 2. There is a feature in that the second inclined layer 9 in which the relative refractive index difference is gradually increased is provided at the boundary portion 34 of the second cladding layer 4.

  In the present embodiment, the refractive index distribution of the core 2 is made constant at the relative refractive index difference Δn1 of the core 2 from the center O to the boundary portion 23 between the core 2 and the first cladding layer 3, and from the boundary portion 23 to the first A trapezoidal shape having an inclined portion 7 in which the relative refractive index difference gradually decreases from the relative refractive index difference Δn1 to 0 up to the cladding layer 3 was adopted.

  The layer thickness b0 of the inclined portion 7 is preferably 0.74 to 0.79 μm.

  Here, the relative refractive index difference Δ means the difference (n−n0) / n0 between the refractive index n of the target and the refractive index n0 of the fourth cladding layer with respect to the refractive index n0 of the fourth cladding layer 6.

  Further, in the first cladding layer 3, the first gradient layer 8 in which the relative refractive index difference gradually decreases from 0 to the relative refractive index difference Δn2 of the first cladding layer 3, and in the first cladding layer 3, The second gradient layer 9 is provided in which the relative refractive index difference gradually increases from the relative refractive index difference Δn2 to less than 0. That is, in the present embodiment, the first clad layer 3 is configured by the first graded layer 8, the portion where the relative refractive index difference Δn 2 is constant, and the second graded layer 9.

  In this dispersion compensating optical fiber 1, the relative refractive index difference Δn 1 of the core 2 and the relative refractive index difference Δn 3 of the second cladding layer 4 are made larger than the relative refractive index difference Δn 0 of the fourth cladding layer 6. The relative refractive index difference Δn2 of the third cladding layer 5 and the relative refractive index difference Δn4 of the third cladding layer 5 are made smaller than the relative refractive index difference Δn0 of the fourth cladding layer 6.

  In the present embodiment, the refractive index distribution of the dispersion compensating optical fiber 1 is set such that the fluctuation width of the relative refractive index difference decreases as the distance from the core 2 increases, and at the boundary between the first to fourth cladding layers 3 to 6. It was formed by meandering to have corners.

  More specifically, the relative refractive index difference Δn1 of the core 2 is set to 0.85 to 1.05%, the radius r1 of the core 2 is set to 2.05 to 2.15 μm, and the relative refractive index difference Δn3 of the second cladding layer 4 is set. Is 0.10 to 0.13%, the radius of the second cladding layer 4 is 8.75 to 8.95 μm, and the relative refractive index difference Δn2 of the first cladding layer 3 is −0.45 to −0.40%. The radius r2 of the first cladding layer 3 is set to 5.50 to 5.90 μm, the relative refractive index difference Δn4 of the third cladding layer 5 is set to −0.07 to −0.03%, The radius r4 is preferably 9.95 to 10.15 μm.

  The layer thickness b1 of the first gradient layer 8 is preferably 0.75 to 0.95 μm, and the layer thickness b2 of the second gradient layer 9 is preferably 1.75 to 1.85 μm.

  The chromatic dispersion and dispersion slope of the dispersion compensating optical fiber 1 are mainly the diameter of the core 2 and the first cladding layer 3 and their Δn1 and Δn2, the mode field diameter is mainly the diameter of the core 2 and its Δn1, and the cutoff wavelength is It depends mainly on the diameters of the first and second cladding layers 3 and 4 and their Δn2 and Δn3. Each parameter such as relative refractive index difference Δ and diameter of each layer can be optimized to obtain desired chromatic dispersion, dispersion slope, mode field diameter, and cutoff wavelength.

  Here, the value of the radius r4 of the third cladding layer 5 theoretically has little influence on the chromatic dispersion. Although the cut-off wavelength relatively changes, this cut-off wavelength decreases as the radius r4 increases, so the limit of the radius r4 is only the lower limit. However, in terms of manufacturing conditions, it is preferable that the cladding thickness is thin, and the upper limit is preferably 10.15 μm including manufacturing errors.

  The operation of this embodiment will be described.

  The dispersion compensating optical fiber 1 includes a core 2 and first to fourth cladding layers 3 to 6 having different refractive indexes, and a first inclined layer 8 is provided at a boundary portion 23 between the core 2 and the first cladding layer 3. The second inclined layer 9 is provided at the boundary 34 between the first cladding layer 3 and the second cladding layer 4.

  The first graded layer 8 connects the core 2 and the first clad layer 3 that have significantly different relative refractive index differences so that the refractive index distribution does not change suddenly (vertically). The first clad layer 3 and the second clad layer 4 that are greatly different in refractive index difference are connected so that the refractive index distribution does not change abruptly.

  In particular, the core 2 and the first clad layer 3, and the first clad layer 3 and the second clad layer 4 are portions where the relative refractive index difference is greatly different and the materials are different from each other. For this reason, if bending is applied to the dispersion compensating optical fiber 1, stress concentration is likely to occur at the boundary between these layers, which causes an increase in bending loss.

  However, even if the dispersion compensating optical fiber 1 concentrates stress at the boundary portion 23 between the core 2 and the first cladding layer 3 and the boundary portion 34 between the first cladding layer 3 and the second cladding layer 4 due to bending, the stress is reduced. Since the first gradient layer 8 and the second gradient layer 9 are relaxed, the first gradient layer 8 and the second gradient layer 9 function as buffer layers.

  Therefore, the dispersion compensating optical fiber 1 is bent more than the conventional one while maintaining its characteristics even in a complicated dispersion compensating optical fiber having a large relative refractive index difference such as a W-type or a triple clad like the conventional dispersion compensating optical fiber. Loss can be kept low, and an increase in transmission loss after cable formation can be suppressed.

  In particular, the dispersion compensating optical fiber 1 has a core 2 with a trapezoidal shape, and a first inclined layer 8 and a second inclined layer 9 are provided in the first cladding layer 3. Bending loss can be reduced while maintaining the function.

  Further, at the boundary portion 23 between the core 2 and the first cladding layer 3, the inclined portion 7 is provided to make the core 2 trapezoidal. For this reason, the portion where the relative refractive index difference Δn1 of the core 2 is constant and the first inclined layer 8 can be connected so that the refractive index distribution does not change rapidly, and the bending loss can be reduced while maintaining the function of the core 2. .

  Further, by setting the layer thickness b1 of the first inclined layer 8 to 0.75 to 0.95 μm and the layer thickness b2 of the second inclined layer 9 to 1.75 to 1.85 μm, the bending loss at a diameter of 20 mm is 30 dB. / Km or less.

  By setting the relative refractive index difference Δn1 of the core 2 to 0.85 to 1.05%, chromatic dispersion at a wavelength of 1550 nm can be set to −50 to −40 ps / nm / km.

  By setting the radius r1 of the core 2 to 2.05 to 2.15 μm, chromatic dispersion at a wavelength of 1550 nm can be set to −50 to −40 ps / nm / km.

  By setting the relative refractive index difference Δn1 of the core 2 to 0.85 to 1.05% and the radius r1 of the core 2 to 2.05 to 2.15 μm, the chromatic dispersion at a wavelength of 1550 nm is −50 to −40 ps / nm. / Km and the mode field diameter (MFD) can be 6.0 μm or more.

  Here, the MFD is preferably as large as possible. However, if the MFD is too large, the bending loss is increased. Therefore, the MFD is preferably 6.6 μm or less.

By setting the relative refractive index difference Δn2 of the first cladding layer 3 to −0.45 to −0.40%, the dispersion slope at a wavelength of 1550 nm can be set to −0.16 to −0.10 ps / nm ² / km.

By setting the radius r2 of the first cladding layer 3 to 5.50 to 5.90 μm, the chromatic dispersion at a wavelength of 1550 nm can be made −50 to −40 ps / nm / km, and the dispersion slope at a wavelength of 1550 nm is −0.16. It can be set to ˜−0.10 ps / nm ² / km.

  By setting the relative refractive index difference Δn3 of the second cladding layer 4 to 0.10 to 0.13%, the cutoff wavelength at the reference length of 2 m can be made 1500 nm or less.

By setting the radius r3 of the second cladding layer 4 to 8.75 to 8.95 μm, the dispersion slope at the wavelength of 1550 nm can be set to −0.16 to −0.10 ps / nm ² / km, and the reference length is 2 m. The cutoff wavelength can be 1500 nm or less.

By setting the relative refractive index difference Δn4 of the third cladding layer 5 to −0.07 to −0.03%, the cutoff wavelength at the reference length of 2 m can be made 1500 nm or less, and the dispersion slope at the wavelength of 1550 nm is −0. .16 to -0.10 ps / nm ² / km.

  By setting the radius r4 of the third cladding layer 5 to 9.95 to 10.15 μm, the cutoff wavelength at the reference length of 2 m can be made 1500 nm or less.

  In the said embodiment, although the clad demonstrated in the example which consists of the 1st-4th clad layers 3-6, the clad should just consist of two or more layers.

Example 1
The dispersion compensating optical fiber 1 is manufactured by an MCVD (internal) method, a VAD (axial) method, an OVD (external) method, or the like, which is a general optical fiber manufacturing method. Hereinafter, although the manufacturing method of the dispersion compensation optical fiber 1 by MCVD method is demonstrated, this invention is not limited to the optical fiber manufactured by MCVD method.

  FIG. 2 is a schematic diagram of a core rod manufacturing method by the MCVD method.

Pure oxygen is supplied to the bubbler 21 through the bubbler oxygen supply pipe 20, and the raw material gas g bubbled with the pure oxygen is introduced into the quartz pipe 23 rotating around the axis through the rotation introduction terminal 22 formed of a rotary joint. Examples of the source gas g include SiCl ₄ , GeCl ₄ , O ₂ , He, Cl ₂ , and C ₂ F ₆ .

  These source gases g are heated from the outside of the quartz tube 23 by the oxyhydrogen burner 24 moving along the longitudinal direction of the quartz tube 23, and soot particles 25 are generated by a chemical reaction. A part of the soot particles 25 adheres and accumulates on the inner surface of the quartz tube 23, and the rest passes through the exhaust pipe 26 and is discharged to the soot box 27. The soot particles 25 adhering to the inner surface of the quartz tube 23 are heated again by the oxyhydrogen burner 24 to become transparent glass.

  The above steps are repeated as necessary, and the fourth cladding layer 6, the third cladding layer 5, the second cladding layer 4, the first cladding layer 3 (including the second inclined layer 9 and the first inclined layer 8), the core 2 Are formed in this order.

  At this time, the relative refractive index difference Δn1 of the core 2 is 0.917%, the radius r1 after drawing is 2.106 μm, the relative refractive index difference Δn2 of the first cladding layer 3 is −0.436%, and after the drawing. Radius r2 = 5.681 μm, relative refractive index difference Δn3 = 0.116% of the third cladding layer 4, radius r3 = 8.848 μm after drawing, relative refractive index difference Δn4 = −0.3 of the third cladding layer 5. 051%, radius r4 after drawing = 10.55 μm, layer thickness b0 = 0.766 μm of inclined portion 7, layer thickness b1 = 0.912 μm of first inclined layer 8, layer thickness b2 = second inclined layer 9 = It is formed in consideration of the relative refractive index difference Δ of each layer, the ratio of the outer diameter between each layer, and the ratio of the layer thickness of each inclined layer so as to be 1.775 μm.

  Moreover, the 1st inclination layer 8 and the 2nd inclination layer 9 are formed by changing manufacturing conditions, such as the addition amount of the dopant added to the raw material used as glass, in steps.

  After the deposition of the soot particles 25 and the transparent vitrification is completed, the thermal power of the oxyhydrogen burner 24 is increased to close the remaining space in the center, and the core rod is made solid by the surface tension of the quartz tube 23. .

  The core rod thus obtained is externally attached with pure quartz soot, for example, by the VAD method, and sintered to obtain a drawing base material (fiber base material). The drawing base material is drawn at a drawing speed of 200 m / min to obtain the dispersion compensating optical fiber 1.

As a result, the dispersion compensating optical fiber 1 has a light transmission loss of 0.249 dB / km at a wavelength of 1550 nm, an MFD of 6.13 μm, a dispersion of −44.24 ps / nm / km, and a wavelength of 1550 nm. The dispersion slope at −0.133 ps / nm ² / km, the cable cutoff wavelength was 1468 nm, the bending loss at a diameter of 20 mm was 10.1 dB / km, and good characteristics were obtained.

(Example 2)
Similar to Example 1, the refractive index distribution shown in FIG. 1 was obtained, the relative refractive index difference Δn1 = 0.870% of the core 2, the radius r1 = 2.153 μm, the relative refractive index of the first cladding layer 3 Difference Δn2 = −0.412%, radius r2 = 5.986 μm, relative refractive index difference of third cladding layer 4 Δn3 = 0.100%, radius r3 = 9.229 μm, relative refractive index difference of third cladding layer 5 Δn4 = −0.056%, radius r4 = 10.426 μm, layer thickness b0 = 0.833 μm of inclined portion 7, layer thickness b1 = 0.801 μm of first inclined layer 8, layer thickness b2 of second inclined layer 9 = 1.828 μm A dispersion-compensating optical fiber 1 was manufactured.

As a result, the dispersion-compensating optical fiber 1 has a light transmission loss of 0.278 dB / km at a wavelength of 1550 nm, an MFD of 6.23 μm, a dispersion of −43.78 ps / nm / km, and a wavelength of 1550 nm. The dispersion slope at −0.152 ps / nm ² / km, the cable cut-off wavelength was 1430 nm, and the bending loss at a diameter of 20 mm was 16.6 dB / km.

(Example 3)
Similar to Example 1, the refractive index distribution shown in FIG. 1 was obtained, the relative refractive index difference Δn1 of the core 2 was 0.914%, the radius r1 = 2.111 μm, and the relative refractive index of the first cladding layer 3 Difference Δn2 = −0.411%, radius r2 = 5.849 μm, relative refractive index difference of third cladding layer 4 Δn3 = 0.113%, radius r3 = 8.827 μm, relative refractive index difference of third cladding layer 5 Δn4 = −0.051%, radius r4 = 10.129 μm, layer thickness b0 = 0.768 μm of inclined portion 7, layer thickness b1 = 0.96 μm of first inclined layer 8, layer thickness b2 of second inclined layer 9 = Dispersion compensating optical fiber 1 having a thickness of 1.772 μm was manufactured.

As a result, the dispersion-compensating optical fiber 1 has a light transmission loss of 0.242 dB / km at a wavelength of 1550 nm, an MFD of 6.16 μm, a dispersion of −46.09 ps / nm / km, and a wavelength of 1550 nm. The dispersion slope was −0.128 ps / nm ² / km, the cable cutoff wavelength was 1419 nm, and the bending loss at a diameter of 20 mm was 11.1 dB / km.

It is a refractive index distribution diagram of a dispersion compensating optical fiber showing a preferred embodiment of the present invention. It is a schematic diagram of the core rod manufacturing apparatus by MCVD method used for manufacture of the optical fiber shown in FIG. It is a figure which shows the cumulative dispersion | distribution of the hybrid transmission line by the effective area expansion optical fiber and dispersion | distribution / dispersion slope compensation optical fiber at the time of wavelength division multiplexing transmission.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dispersion compensation optical fiber 2 Core 3 1st clad layer 4 2nd clad layer 5 3rd clad layer 6 4th clad layer 8 1st gradient layer 9 2nd gradient layer

Claims (5)

  In a dispersion compensating optical fiber comprising a core and two or more cladding layers having different refractive indexes covering the core, the relative refractive index difference is gradually reduced at the boundary between the core and the first outer cladding layer. And a second gradient layer in which the relative refractive index difference gradually increases at the boundary between the first cladding layer and the second cladding layer outside the first gradient layer. fiber.   The dispersion compensating optical fiber according to claim 1, wherein the refractive index distribution of the core is trapezoidal, the first inclined layer is provided in the first cladding layer, and the second inclined layer is provided in the first cladding layer. .   The dispersion compensating optical fiber according to claim 2, wherein the thickness of the first gradient layer is 0.75 to 0.95 µm, and the thickness of the second gradient layer is 1.75 to 1.85 µm.   The two or more clad layers are composed of first to fourth clad layers in order from the inside, and the relative refractive index difference Δn1 of the core and the relative refractive index difference Δn3 of the second clad layer are determined as the relative refractive index of the fourth clad layer. 4. The refractive index difference Δn2 of the first cladding layer and the relative refractive index difference Δn4 of the third cladding layer are made smaller than the relative refractive index difference Δn0 of the fourth cladding layer. The dispersion compensating optical fiber according to 1. The core relative refractive index difference Δn1 is set to 0.85 to 1.05%, the core radius r1 is set to 2.05 to 2.15 μm, and the relative refractive index difference Δn3 of the second cladding layer is set to 0.10 to 0.13. %, The radius r3 of the second cladding layer is 8.75 to 8.95 μm, the relative refractive index difference Δn2 of the first cladding layer is −0.45 to −0.40%, and the radius r2 of the first cladding layer is Is 5.50 to 5.90 μm, the relative refractive index difference Δn4 of the third cladding layer is −0.07 to −0.03%, and the radius r4 of the third cladding layer is 9.95 to 10.15 μm. The dispersion compensating optical fiber according to claim 1.

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