Single mode optical fiber with low bending losses

Single-mode fiber technology field

[0001] The present invention relates to the field of optical fiber transmission, and more specifically, to a line optical fiber with reduced bending loss and microbending loss.

Background technique

[0002] For optical fibers, the refractive index profile is generally defined with respect to a graph showing a function relating the refractive index of the optical fiber to the radius of the optical fiber. Conventionally, the distance to the center of the optical fiber is shown along the abscissa axis, and the difference between the refractive index and the refractive index of the fiber cladding is shown along the ordinate axis. Therefore, the refractive index profile is described as "stepped", "trapezoidal" or "rectangular" for graphs showing stepped, trapezoidal, or rectangular shapes, respectively. These curves usually represent the theoretical or group distribution of the optical fiber, where the stress produced by the optical fiber may result in a substantially different distribution.

[0003] An optical fiber is traditionally composed of an optical fiber core and an optical fiber cladding. The function of the optical fiber core is to transmit and optionally amplify optical signals, while the function of the optical fiber cladding is to confine the optical signals within the core. For this reason, the refractive index Q of the core and the refractive index of the cladding ear are made rabbit>n_gOAs we all know, the propagation of an optical signal in a single-mode fiber is decomposed into a basic mode guided in the core and an auxiliary mode guided at a specific distance in the core-cladding combination and called the cladding mode.

[0004] As a line optical fiber used in an optical fiber transmission system, a single-mode optical fiber (SMF) is generally used. These fibers exhibit dispersion and dispersion slope that meet specific communication standards.

[0005] In order to require compatibility between optical systems of different manufacturers, the International Telecommunication Union (ITU) has developed a standard reference ITU-T G..652, in which standard single-mode fiber (SSMF) must meet this standard.

[0006] The G. 652 standard of the transmission fiber specifically recommends that the mode field diameter (MFD) at a wavelength of 1310nm is in the range of [8.6; 9. 5um]; the cut-off wavelength of the optical cable is 1260nm; expressed as input . The dispersion elimination wavelength is [1300; 1324nm]; the maximum dispersion slope is 0.093ps/nm²-km_oThe cut-off wavelength of an optical cable is usually measured as the wavelength at which the optical signal is no longer single-mode after being propagated over 22 meters of the optical fiber, for example, as defined by the subcommittee 86A of the International Electrotechnical Commission under the standard IEC 60793-1-44.

[0007] Similarly, for a given optical fiber, the so-called MAC value is defined as the ratio of the optical fiber's mode field diameter at 1550 nm to the effective cut-off wavelength (also called cut-off wavelength). The cut-off wavelength is usually measured as the wavelength at which the optical signal is no longer single-mode after propagating on 2 meters of the optical fiber, for example, as defined by the subcommittee 86A of the International Electrotechnical Commission under the standard IEC 60793-1-44. The MAC value is used to evaluate fiber performance, especially to find the trade-off between the mode field diameter, effective cut-off wavelength and bending loss.

[0008] Figure 1 depicts the applicant's experimental results, given the MAC value relative to the wavelength of 1550nm, in the standard SSMF fiber with a bending radius of 15mm and a wavelength of 1625, the bending loss. It can be seen that the MAC value affects the bending loss of the optical fiber, and these bending losses can be reduced by reducing the MAC value.

[0009] However, reducing the MAC value by reducing the mode field diameter and/or by increasing the effective cutoff wavelength may result in overstepping the G.652 standard, making the optical fiber commercially incompatible with some transmission systems.

[0010] Conforms to the G652 standard and reduces bending loss. For fiber optic systems in the home (called fiber to the home system (FTTH)) or to the roadside or to the fiber optic system of the building (the so-called fiber to the curb (FFTC)) It is a real challenge.

CN 1982928 Β

[0011] Indeed, the transmission system via optical fiber includes a storage box in which excessively long optical fibers are provided for future emergency; these excessively long optical fibers are wound in the box. Because the intention is to miniaturize these boxes for FTTH or FTTC applications, single-mode fibers in this context will be wound on smaller and smaller diameters (in order to reach a bend radius of 15mm or 11mm). Moreover, in the scope of FTTH or FTTC applications, the risk of optical fiber is subject to stricter installation constraints for longer-distance applications, that is, there are accidental bends related to the low cost of installation and the environment. Provision must be made for the occurrence of accidental bending radii equal to 7.5 mm or even 5 mm. Therefore, in order to meet the constraints and installation constraints related to the storage box, it is absolutely necessary that the single-mode fiber used for FTTH or FTTC applications limits the bending loss. Even so, it should be understood that this reduction in bending loss should not lead to the adverse effect of signal single mode loss (which will severely reduce the signal), or introduce the adverse effect of extremely large splice light loss.

[0012] The publication Bend-insensitive and Low Splice-Loss Optical Fiber for Indoor Wiring in FTTH, OFC '04 Proceedings, paper Thl3 (2004) by S. Matsuo et al. describes the refractive index profile for single-mode optical fiber (SMF) , Making it possible to reduce bending loss. However, this fiber shows a dispersion between 10.2 ps/nm-km and 14. lps/nm-km, which is outside the G.652 standard.

[0013] I. Publications by Sakabe et al. ^uEnhanced Bending Loss InsensitiveFiber and New Cables for CWDM Access Network, 53" IWCS Proceedings, pp. 112-118 (2004) proposes to reduce the mode field diameter to reduce bending loss. However, this reduction in mode field diameter leads to an increase in G. 653 standard.

[0014] k. Bandou et al.s publication Development of Premise Optical WiringComponents Using Hole-Assisted FiberIWCS Proceedings, pp. 119-122 (2004) proposed a hole fiber with the optical characteristics of SSMF fiber with reduced bending loss . The cost of manufacturing the optical fiber and the current high attenuation (>0.25 dB/km) make it difficult to commercially use in FTTH systems.

[0015] T. Yokoawa et al.s publication Ultra-Low Loss and Bend Insensitive Pure-Silica-Core Fiber Complying with G. 652 C/D and its Applications to a Loose Tube Cabled3^rd IWCS Proceedings, pp. 150-155 (2004) proposed a pure silicon core optical fiber PSCF with reduced transmission and bending losses, but with a reduced mode field diameter outside the G.652 standard.

[0016] US6771865 describes a distribution of transmission fibers with reduced bending losses. The optical fiber has a central core, a ring inner cladding and an optical outer cladding. The ring-shaped cladding layer is doped with both fault and fluorine. The information given in this document does not provide for determining whether the fiber meets the specifications established by the G.652 standard.

[0017] US4852968 describes the distribution of transmission fibers with reduced bending losses. However, the fiber has a dispersion that does not meet the specifications of the G.652 standard: the G.652 standard requires dispersion cancellation at a wavelength between 1300nm and 1324nm, but the fiber described in US4852962 shows a wavelength between 1400nm and 1800nm The dispersion at the place is eliminated.

[0018] WO-A-2004/092794 describes the distribution of transmission fibers with reduced bending losses. The optical fiber has a central core, a first inner cladding, a second embedded inner cladding, and an outer optical cladding. Some of the fiber examples described in this document also meet the specifications of the G.652 standard. The optical fiber described in this document is manufactured by vapor phase axial deposition (VAD) or chemical vapor deposition (CVD) type technology. However, the optical fiber described in this document does not identify the problem of microbend loss.

[0019] Therefore, there is a need for a transmission fiber that can meet the specifications of the G.652 standard, that is, the fiber can be used commercially in FTTH or FTTC type transmission systems, and exhibit reduced bending loss and reduced microbending loss . In FTTH or FTTC applications, optical fibers are subject to higher bending and microbending stresses than in long-distance transmission applications. Indeed, in FFTH or FTTC applications, an excessively long optical fiber is usually wound in an increasingly miniaturized storage box, and the optical fiber will experience extreme bending stress related to its installation environment.

Summary of the invention

[0020] To this end, the present invention proposes an optical fiber distribution, including a central core, a first inner cladding, a deeply buried second inner cladding, and an outer cladding. The second inner cladding contains errors.

[0021] Even if the fault is a dopant, its effect is to increase the refractive index of silicon, but the presence of the fault in the deep buried cladding layer makes it possible to increase the elastic-optical coefficient of the buried cladding layer. Therefore, when stress is applied to the optical fiber, especially when the optical fiber undergoes bending or microbending, the presence of a deep buried cladding containing faults allows to limit the influence of the stress on the change of the refractive index of the optical fiber. Therefore, when such stress is applied to the second deep buried cladding layer with errors, the light loss is reduced.

[0022] More specifically, the present invention proposes an optical transmission fiber, including:

[0023]-The central core, having a refractive index difference with the outer optical cladding;

[0024]-a first inner cladding layer having a refractive index difference ratio with that of the outer cladding layer;

[0025]-The second buried inner cladding layer, the refractive index difference between it and the outer cladding layer is less than -3×10-³, And contains errors with a weight concentration of 0.5% to 7%.

[0026] According to one characteristic, the refractive index difference between the second inner cladding layer and the outer cladding layer is greater than -15×10-3.

[0027] According to another characteristic, the refractive index difference between the center core and the first inner cladding (An Factory 41¾) is 3.9X10^ to 5. 9X10^-3between.

[0028] According to another characteristic, the radius of the second buried cladding is between 12 μm and 25 μm.

[0029] According to another characteristic, the radius of the central core is between 3.5 um and 4.5 U m, and the refractive index difference with the outer cladding layer is between 4.2X10 "3 to 6. 1 X10 "3. .

[0030] According to another characteristic, the radius of the first inner cladding layer is between 7.5 um and 14. 5 μm, and the refractive index difference with the outer cladding layer is T· 2 X 10 bow to 1.2 X Between 10 bows.

[0031] According to another characteristic, the integral of the central core is defined as:

[0032] ή = f Δ»(Γ)ί/Γ «η x,

[0033] The integral is at 17X10^_3Between μ m and 24X10^ μ m.

[0034] According to another characteristic, at a wavelength of 1310 nm, the optical fiber of the present invention shows a dispersion slope of 0.0093 ps/nmLkm or less.

[0035] According to another characteristic, the optical fiber of the present invention exhibits dispersion cancellation at a wavelength between 1300 nm and 1324 nm.

[0036] According to another characteristic, the optical fiber of the present invention has a cable cut-off wavelength of 1260 nm or less.

[0037] According to another characteristic, at a wavelength of 1625 nm, for a winding around a 15 mm bend radius of 100 turns, the optical fiber of the present invention shows a bending loss of 1 db or less.

[0038] According to another characteristic, at a wavelength of 1625nm, for a winding around a bending radius of 11mm, the optical fiber of the present invention exhibits a bending loss of 0.5dB or less.

[0039] According to another characteristic, at a wavelength of 1625 nm, for a winding around a bending radius of 5 mm, the optical fiber of the present invention shows a bending loss of 2 dB or less.

[0040] According to another characteristic, up to a wavelength of 1625 nm, the optical fiber of the present invention exhibits a microbending loss of 0.8 dB/km or less measured by the so-called fixed diameter drum method.

[0041] The present invention also relates to a method for manufacturing the optical transmission fiber of the present invention, the method comprising the steps:

[0042]-Provide a silicon tube and position the silicon tube on a lathe;

[0043]-Oxygen Ο?, silicon SiCl₄,Fluorine C₂F₆And wrong Ge0₂The gas mixture is injected into the tube;

CN 1982928 Β

[0044]-ionize the gas mixture by microwave heating to obtain plasma, so as to deposit the doped silicon layer forming the second buried inner cladding layer;

[0045]-Continuously injecting a gas mixture and ionizing the mixture to deposit a doped silicon layer forming a first inner cladding layer and a central core.

[0046] The present invention further relates to a fiber to the home (FTTH) or fiber to the roadside (FTTC) fiber optic system, which at least includes an optical module or a storage box according to the present invention.

Description of the drawings

[0047] By reading the detailed description of the embodiments of the present invention given as an example and with reference to the accompanying drawings, other characteristics and advantages of the present invention will become more apparent, among which:

[0048] FIG. 1 is a schematic diagram of the previous description, describing the bending loss at a wavelength of 1625nm in a standard single-mode fiber (SSMF) with a bending radius of 15mm relative to the MAC value at a wavelength of 1500nm;

[0049] FIG. 2 is a diagram showing the group distribution of a single mode fiber (SMF) according to an embodiment of the present invention;

[0050] FIGS. 3a to 3c are several schematic diagrams, describing for different standard single-mode fibers (SSMF) and for different fibers of the present invention, relative to the MAC value at a wavelength of 150nm, for different bending radii at a wavelength of 1625nm Bending loss; and

[0051] FIGS. 4a and 4b are schematic diagrams describing the loss through microbending.

Detailed ways

[0052] The optical fiber of the present invention has a central core, a first inner cladding and a second buried inner cladding. By embedding the cladding means the radial part of the fiber whose refractive index is lower than that of the cladding. The refractive index difference between the second embedded inner cladding layer and the outer cladding layer is less than -3X10 bar and can reach -15X103. Similarly, the embedded cladding layer contains errors with a weight concentration of 0.5% to 7%.

[0053] As known per se, the optical fiber is obtained by drawing a preform. For example, the preform can be a high-quality glass tube (pure silicon) that forms part of the outer cladding and surrounds the central core and inner cladding of the optical fiber; then it can be given before the drawing operation in the draw tower. The tube is fitted with a sleeve or refilled to increase its diameter. In order to manufacture the preform, the tube is usually installed horizontally, and the tube is held in place at its ends by a glass rod in the lathe; then the tube is rotated and the tube is locally heated to determine the accumulation of the preform The components of the composition. This composition determines the optical characteristics of future optical fibers.

[0054] The components deposited in the tube are usually referred to as "doping", that is, adding "impurities" to silicon to modify its refractive index. Thus, Ge or phosphorus (P) increases the refractive index of silicon; they are often used to dope the central core of optical fibers. Similarly, fluorine (F) or boron (B) lowers the refractive index of silicon; they are often used to form buried cladding or as doping with co-doping when it is desired to compensate for the increase in refractive index in the photosensitive cladding.

[0055] Preforms with embedded cladding are difficult to manufacture. When the heating exceeds a certain temperature, fluorine is not easily incorporated into silicon, and high temperature is required to manufacture glass. The trade-off between the high temperature required for glass manufacturing and the low temperature that promotes proper fluorine incorporation makes it impossible to obtain a refractive index that is significantly lower than that of silicon.

[0056] It is proposed to use the PCVD technology (plasma chemical vapor deposition) to manufacture the preform of the optical fiber of the present invention because it allows the reaction at a lower temperature than the conventional technology (CVD, VAD, OVD) by ionizing the reactive components. The manufacturing technique is described in documents US RE 30635 and US 4314833; it allows more fluorine to be incorporated into silicon in order to form a deep buried cladding.

[0057] The use of PCVD technology to manufacture the optical fiber of the present invention also makes it possible to add errors to the buried cladding. As above

CN 1982928 Β

As mentioned, the error increases the refractive index of silicon; therefore, it is generally not recommended to incorporate the error into the part of the optical fiber that seeks to obtain a refractive index lower than that of silicon. However, PCVD makes it possible to generate a large amount of highly reactive fluoride ions; then it is possible to add error to the reaction, and thus obtain a buried inner cladding.

[0058] Therefore, the optical fiber of the present invention includes a fault in the combination of the inner cladding, wherein the inner cladding includes a refractive index less than -3×10 "³ofcladding. The presence of errors in the embedded cladding corrects the viscosity of silicon and the elastic-optical coefficient in the cladding.

[0059] FIG. 2 depicts the refractive index profile of the transmission fiber of the present invention. The distribution shown is a group distribution, that is, it represents the theoretical distribution of the optical fiber, which is actually obtained after drawing from a preform that may give a substantially different distribution.

[0060] The single-mode transmission optical fiber of the present invention includes: a central core having a refractive index difference Ani with an outer cladding layer, the outer cladding layer is used as an optical cladding layer; a first inner cladding layer having a refractive index difference ratio with the outer cladding layer ; The second inner cladding layer is deeply buried and has a refractive index difference with the outer cladding layer. The refractive index in the central core, the first cladding and the second inner cladding is basically constant over their entire width; therefore, the group distribution is truly a single-mode fiber. The width of the core is defined by its radius, and the width of the cladding is defined by their respective outer diameter r₂And r₃definition.

[0061] In order to define a set of refractive index distributions of an optical fiber, the refractive index of the outer cladding is usually used as a reference. Then give the refractive index values of the central core, the buried cladding and the ring as the refractive index difference of 411,2,3°. Usually, the outer cladding is formed of silicon, but it can be doped to the outer cladding to increase or decrease its refractive index. , For example, to modify signal propagation characteristics.

[0062] Therefore, the integral that associates the refractive index change with the radius of each fiber portion can be used to define each portion of the fiber distribution.

[0063] Therefore, three integrals can be defined for the optical fiber of the present invention, which represent the core surface A, the first inner cladding surface [2, and the second buried inner cladding surface [3. The expression "surface" is not interpreted geometrically, but corresponds to the value of the considered size. These three points can be expressed as:

[0064] I_} = f M(r)dr «η x A®

[0065] =f Aw(r)tZr «(r₂ -η) χ Δ«₂

[0066] =Ρ Δ«(Γ)ό/Γ «-r₂) χ Δη₃ **2

[0067] The following Table I gives the limit value of the radius and refractive index difference and the limit value of the integral A, they are required to make the optical fiber show reduced bending loss and micro-bending loss, while satisfying G for transmission fiber. 652 standard light propagation specification. The values given in the table correspond to the group distribution of optical fibers.

[0068] Table I

[0069]

<td>(μηι)</td><td>2 (μηι)</td><td>Work 3 (μηι)</td><td>Mouth/Ya 2</td><td>Δ ratio (ΧΙΟ³)</td><td>^Δη₂(ΧΙΟ³)</td><td>^Δη₃(ΧΙΟ³)</td><td>Δ η]- Δ η₂</td><td>Ι/μηι ΧΙΟ³)</td>

<td>3. 5</td><td>7. 5</td><td>12. 0</td><td>0. 27</td><td>4. 2</td><td>-1. 2</td><td>-15</td><td>3. 9</td><td>17</td>

<td>4. 5</td><td>14. 5</td><td>25. 0</td><td>0. 5</td><td>6. 2</td><td>1. 2</td><td>-3</td><td>5. 9</td><td>24</td>

[0070] The value of the integral Ij of the central core affects the basic propagation mode of the signal in the optical fiber. 17X ΙΟ³μ m to 24X ΙΟ³The integrated value of the central core of μ m makes it possible to maintain the mode field diameter that meets the G.652 standard.

[0071] Table II below gives possible refractive index profiles for the transmission fiber according to the present invention. The first column assigns a reference to each distribution. The following columns give the radius value of each part (from mouth to and), and the following columns give the refractive index difference between each part and the outer cladding (Ani to 41¾)° The refractive index value measured at a wavelength of 633nm.

CN 1982928 Β

[0072] Table II

[0073]

<td>example</td><td>r_x (μ m)</td><td>r₂ (μ m)</td><td>r₃ (μ m)</td><td>Δ_ηι(Χ10³)</td><td>Δη₂(Χ10³)</td><td>Δη₃(Χ10³)</td>

<td>1</td><td>2. 86</td><td>6. 90</td><td>13. 24</td><td>5. 41</td><td>2.00</td><td>-3. 70</td>

<td>2</td><td>3. 86</td><td>9. 50</td><td>15</td><td>5. 16</td><td>0. 69</td><td>-5. 0</td>

<td>3</td><td>4. 02</td><td>9. 55</td><td>15</td><td>5. 31</td><td>0. 45</td><td>-5. 0</td>

<td>4</td><td>3. 86</td><td>8. 66</td><td>15</td><td>5. 41</td><td>0. 85</td><td>-5. 0</td>

[0074] The transmission optical fiber of the present invention having a refractive index profile such as the above-mentioned exhibits reduced bending loss and microbending loss at useful wavelengths.

[0075] In addition, the optical fiber of the present invention meets the specifications of the G.652 standard.

[0076] The following Tables III and IV describe simulated optical characteristics for the transmission fiber corresponding to the refractive index profile of Table II.

[0077] In Table III, the first column reproduces the reference to Table II. For each fiber distribution, the effective cut-off wavelength is given in the following columns-the cut-off wavelength of the optical cable is cc, the mode field diameter for 1310nm and 1550nm wavelengths is 2W02, the dispersion elimination wavelength is °, and the dispersion slope at human ο is Ρ . , For the dispersion C of 1550nm wavelength and 1625nm wavelength.

[0078] In Table IV, the first column reproduces the reference to Table III. The following column gives the MAC value at a wavelength of 1550nm. The next three columns give the value of the bending loss BL for each bending radius of 5, 11, and 15 mm at a wavelength of 1625 nm. The next column gives the relative bending loss normalized to the standard bending loss of SSMF fiber with the same MAC value at 1550 nm for a radius of 15 mm. The penultimate column gives the microbending loss obtained using the pin array test (10 pins in 1.5mm) at a wavelength of 1550nm.

[0079] The test used an array of 10 polishing needles with a diameter of 1.5 mm and a spacing of 1 cm. The optical fiber passes through the array orthogonal to the axis of the needle, and the optical fiber and the array are compressed between two rigid plates covered with approximately 3 mm of high-density polyethylene foam. The combination layer (board, array, fiber) is positioned horizontally, and the combination is covered with a weight of 250g. The last column shows the microbending loss measured using a fixed diameter drum method at a wavelength of 1625nm. This method is described in the technical recommendations of the International Electronic Technology Committee (refer to the sub-committee under IEC TR-62221). The diameter of the drum used is 60 cm; the drum is covered with ultra-fine sandpaper. The value of the bending loss BL at the wavelength of 1625 nm is shown.

Table III

[0081]

<td>Ν°</td><td>^xcoff 3 m)</td><td>λ _cc (μ m)</td><td>2W02@1310nm(μ m²)</td><td>2W02@1550nm(μ m²)</td><td>(nm)</td><td>Po(ps/ μ m²-km)</td><td>C@1550nm (ps/ μ m-km)</td><td>C@1625nm (ps/ μ m -km)</td>

<td>1</td><td>1. 13</td><td>&lt; 1. 26</td><td>9. 10</td><td>10. 18</td><td>1308</td><td>0. 097</td><td>19. 2</td><td>23. 9</td>

<td>2</td><td>1. 23</td><td>&lt; 1. 26</td><td>9. 16</td><td>10. 36</td><td>1312</td><td>0. 091</td><td>18. 1</td><td>22. 9</td>

<td>3</td><td>1. 25</td><td>&lt; 1. 26</td><td>9. 01</td><td>10. 13</td><td>1318</td><td>0. 089</td><td>17. 3</td><td>22. 0</td>

<td>4</td><td>1. 25</td><td>&lt; 1. 26</td><td>9. 00</td><td>10. 08</td><td>1318</td><td>0. 091</td><td>17.8</td><td>22. 5</td>

[0082] Table IV

[0083]

CN 1982928 Β

<td>N⁰</td><td>MAC@155Onm</td><td>BLR - 5mm@1625nm (dB/ circle)</td><td>BLR - 11mm@1625nm (dB/ circle)</td><td>BLR - 15mm@1625nm (dB/100 circle)</td><td>BLrelR - 15mm@1625nm</td><td>BL μ pin array test @1550nm (dB)</td><td>BL μ drum method @1625nm (dB/km)</td>

<td>1</td><td>9. 0</td><td>W 5</td><td>W 2</td><td></td><td>1/5</td><td></td><td></td>

<td>2</td><td>&amp; 4</td><td>2</td><td>W 0.5</td><td>W 1</td><td>1/5</td><td>0. 025</td><td>W 0.8</td>

<td>3</td><td>8. 1</td><td>1</td><td>W 0.1</td><td>&lt;0.4</td><td>1/5</td><td>W 0. 025</td><td>&lt; 0. 8</td>

<td>4</td><td>8. 1</td><td>1</td><td>W 0.1</td><td>&lt;0.4</td><td>1/5</td><td>W 0. 025</td><td>&lt; 0. 8</td>

[0084] As can be seen in Table III, Examples 2 to 4 do indeed comply with the G.652 standard, and Example 1 shows a dispersion slope that is slightly outside the G.652 standard.₀ο

[0085] In particular, the fibers in Examples 2 to 4 show dispersion cancellation for wavelengths between 1300 nm and 1324 nm; this is in compliance with the G.652 standard. The fibers in Examples 2 to 4 also show a dispersion slope of 0.093 ps/nm for a wavelength of 1310 nm²-km or less, which meets the G.652 standard. Also in Examples 2 to 4, the optical fibers show a cable cut-off wavelength of 1260 nm or less, which complies with the specifications of the G.652 standard, which requires the cable cut-off wavelength to be 1260 nm or less.

[0086] In addition, as can be seen in Table IV, Examples 2 to 4 exhibit significantly improved bending loss relative to the loss of standard SSMF transmission fiber. The microbending loss is also improved.

[0087] The schematic diagrams in FIGS. 3a, 3b, and 3c show the bending loss obtained when the bending radius is R=5mm, R=11mm and R=15mm at the wavelength of 1625nm for the optical fiber and standard optical fiber manufactured according to the present invention Measurement results. The bending loss here is given at the end of one turn (for R = 5mm and R = 11mm) or at the end of 100 turns (for R = 15mm).

[0088] FIG. 4a shows the microbending loss of the optical fiber manufactured according to the present invention, which is characterized by: for different SSFM fibers and the optical fiber of the present invention, relative to the MAC value at a wavelength of 1500nm, a pin test is used and the wavelength is 1500nm Measured at.

[0089] FIG. 4b shows the microbending loss of the SSM fiber and the optical fiber of the present invention with MAC values of &amp; 11 and &amp; 31 at a wavelength of 1550 nm, relative to the wavelength, measured using a fixed diameter drum.

[0090] Similarly, the schematic diagrams in FIGS. 4a and 4b clearly show that the sensitivity of the optical fiber of the present invention to microbending is significantly reduced relative to the sensitivity of SSMF to microbending. It can be seen in Figure 4a that the measured microbend loss (pin array test) for the fiber of the present invention with a MAC value of &amp; 44 at a wavelength of 1550nm is 0.025dB, and they are ten times higher than the SSMF fiber with the same MAC value. . It can also be seen in FIG. 4b that, compared with the microbending loss for the SSMF fiber with a larger MAC value at a wavelength of 1550 nm, the microbending loss for the fiber of the present invention increases significantly more slowly with wavelength. In the schematic diagram, it can be seen that the optical fiber of the present invention guarantees the sensitivity to microbending loss up to the long wavelength, that is, greater than 1650 nm, which is equivalent to the sensitivity that can be guaranteed for the SSMF fiber, up to the wavelength of 1550 nm.

[0091] The transmission optical fiber of the present invention can be manufactured by drawing a preform having one of the above-mentioned refractive index profiles. For example, the preform distribution can be made from a silicon sleeve, and a doped silicon layer is deposited in the silicon sleeve. The deposition is performed by the plasma chemical vapor deposition (PCVD) type deposition method mentioned above. Chemical deposition in the form of vapor excited by plasma is particularly suitable for obtaining the embedded inner cladding of the optical fiber of the present invention, the embedded cladding containing a weight concentration of between 0.5% and 7% of the fault. The weight concentration of the fault is preferably between 0.5% and 1.5%, because this allows an optimal balance between lower cost and easier manufacturing on the one hand, and good fiber characteristics on the other hand.

CN 1982928 Β

[0092] Provide a pure silicon tube and install it on a lathe. Then, the tube is rotated, and a gas mixture of silica and dopant is injected into the tube. The tube passes through a microwave cavity in which the gas mixture is locally heated. Microwave heating generates plasma by ionizing the gas injected into the tube, and the ionized dopant reacts strongly with silicon particles, so that a doped silicon layer is deposited on the inside of the tube.

[0093] The strong reaction of the dopant heated by microwaves makes it possible to incorporate high-concentration dopants in the silicon layer. Especially for fluorine (which is difficult to incorporate silicon using local burner heating), the PCVD technology allows the silicon layer to be doped with a high concentration of fluorine to form a deep buried layer.

[0094] Within the scope of the present invention, the second buried cladding layer is obtained by depositing a silicon layer doped with fluorine and aluminum; oxygen-containing ones will be included. 2. SiCl containing silicon₄, C containing fluorine₂F₆And Ge0 that contains errors₂The gas mixture is injected into the tube. The gas mixture is ionized in the microwave cavity of the PCVD installation, and fluorine and zirconium ions are incorporated into the silicon particles.

[0095] The proportion of the injected gas is monitored so that a doped silicon layer is obtained, containing a weight concentration of 0.5% to 7% of the wrong, and a concentration of fluorine required to obtain the target refractive index.

[0096] The high concentration of fluorine ensures the required reduction of the refractive index of the embedded cladding, and the low concentration of the fault leads to changes in viscosity and elastic-optical coefficient, which are required to reduce the bending loss and microbending of the obtained optical fiber loss.

[0097] The transmission optical fiber according to the present invention can be used in the transmission and reception module of the FTTH or FTTC system or in the high-speed and long-distance optical transmission cable. The optical cable of the present invention is compatible with systems on the market because it complies with the G.652 standard. Specifically, the excessively long optical fiber according to the present invention can be wound in a storage box associated with the optical module of the FTTH or FTTC system. The optical fiber according to the present invention can be wound with a bending radius of less than 15mm, or even less than 5mm, without causing Strong light loss. The optical fiber according to the present invention can also be adapted to support accidental bending associated with installation in various homes, with a bending radius ranging as low as 5 mm.

[0098] Obviously, the present invention is not limited to the embodiment described as an example. In particular, if a manufacturing method other than PCVD allows incorporation of errors in the buried layer according to the claimed ratio and refractive index difference, this method may be considered. In addition, the optical fiber according to the present invention can also be used in applications other than FTTH or FTTC.

CN 1982928 Β