Single mode optical fiber

TECHNICAL FIELD 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.

2. Description of the Related Art For optical fibers, the refractive index distribution is generally defined relative 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 a "step shape", a "trapezoid shape", or a "rectangular shape" for a graph showing a stepped shape, a trapezoidal shape, or a rectangular shape, 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.

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 the optical signal, and the function of the optical fiber cladding is to confine the optical signal within the core. For this reason, the refractive index of the core n_cAnd the refractive index ng of the cladding is n_c>n_go It is well known that 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.

As line fibers used in optical fiber transmission systems, single-mode fibers (SMF) are generally used. These fibers exhibit dispersion and dispersion slope that meet specific communication standards.

In order to be compatible 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.

The G..652 standard of the transmission fiber specifically recommends that the mode field diameter (MFD) range at the 1310nm wavelength is [8.6; 9.5μπι]; the maximum cut-off wavelength of the optical cable is 1260nm; expressed as input. The dispersion elimination wavelength is [1300; 1324nm]; the maximum dispersion slope is

200610144536.6 No.

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 propagating 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.

Similarly, for a given fiber, the so-called MAC value is defined as the ratio of the 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 the performance of the fiber, especially to find the trade-off between the mode field diameter, the effective cut-off wavelength and the bending loss.

Figure 1 depicts the applicant's experimental results, and shows the bending loss at a wavelength of 1625 in a standard SSMF fiber with a bending radius of 15 mm and a wavelength of 1625 relative to the MAC value at a wavelength of 1550 nm. 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.

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

Compliance with G652 standard and reduction of bending loss are suitable for fiber applications in home fiber systems (called fiber to the home system (FTTH)) or to the roadside or building fiber system (so called fiber to the roadside (FFTC)) A real challenge.

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, within 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 7.5mm or even 5mm. Therefore, in order to meet the constraints and installation constraints associated with storage boxes, it is absolutely necessary that single-mode fibers used in FTTH or FTTC applications limit bending losses. Even so, it should be understood that this reduction in bending loss should not lead to single-mode signal loss (this will severely reduce the signal)

200610144536.6 The adverse effect of the first, or the adverse effect of the introduction of a great splice light loss.

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) such that Can reduce bending loss. However, this fiber shows a dispersion between 10. 2ps/nm-km and 14. lps/nm-km, which is outside the G.652 standard.

I. Sakabe et al. Publication Enhanced Bending Loss Insensitive Fiber and New Cables for CWDM Access Network, 53^rd IWCS Proceedings, pp. 112-118 (2004) proposed to reduce the mode field diameter to reduce bending loss. However, this reduction in the mode field diameter has exceeded the G.653 standard.

k. Bandou et al.'s publication ``Development of Premise Optical Wiring Components Using Hole-Assisted Fiber 53^rd IWCS 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 (>0.25dB/km) make it difficult to commercially use in FTTH systems.

Publications by T. Yokoawa et al. ^UU1 tra-Low Loss and Bend Insens it ive Pure-Si1ica-Core Fiber Complying with G.652 C/D and its Applications to a Loose Tube Cable 53^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.

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 fault and fluorine at the same time. The information given in this document does not provide for determining whether the fiber meets the specifications established by the G.652 standard.

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 Dispersion at the place is eliminated.

WO-A-2004/092794 describes the distribution of transmission fibers with reduced bending losses.

200610144536.6 The first optical fiber has a central core, a first inner cladding, a second buried 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 techniques. However, the optical fiber described in this document does not identify the problem of microbend loss.

Therefore, there is a need for a transmission optical fiber that can meet the specifications of the G.652 standard, that is, the optical 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, too long an optical fiber is usually wound in an increasingly miniaturized storage box, and the optical fiber will experience extreme bending stresses related to its installation environment.

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

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 cladding layer containing the handcuffs, the optical loss is reduced.

More specifically, the present invention provides an optical transmission fiber, including:

-The central core has a refractive index difference with the outer optical cladding

-The first inner cladding layer has a refractive index difference with the outer cladding layer

-The second embedded inner cladding layer has a refractive index difference Am less than -3x1 (Γ[ and contains a weight concentration of 0.5% to 7% between the wrong layer.

According to one characteristic, the refractive index difference between the second inner cladding layer and the outer cladding layer is greater than T5 χ 10^_3_o According to another characteristic, the refractive index difference (Δη?) between the central core and the first inner cladding layer is 3. 9χ10^-3To 5.9 χ 1 (between Τ.

According to another characteristic, the radius of the second buried cladding is between 12 angstroms and 25 angstroms.

200610144536.6 According to another feature, the radius of the central core is between 3.5 divisions to 4.5wn, and the refractive index difference with the outer cladding layer is between 4.2 X ΙΟ to 6. 1 X 1(Γ'between .

According to another characteristic, the radius of the first inner cladding layer is between 7.5 angstroms and 14.5 angstroms, and the refractive index difference with the outer cladding layer is between -1.2 X 1(ΓTo1.2 X ).

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

Zi = f Dn(r)dr «η x Dn_}, The integral is at 17 χ 10^_3Between μπι and 24 χ ΙίΤμπι.

According to another characteristic, at a wavelength of 1310nm, the optical fiber of the present invention shows 0.00093ps/nm²-km or smaller dispersion slope.

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

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

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

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

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.

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

The present invention also relates to a method for manufacturing the optical transmission fiber of the present invention. The method includes the steps:

-Provide a silicon tube and position the silicon tube on a lathe;

-Put oxygen. 2. The gas mixture of silicon SiCS, fluorine C2F6 and GeO? is injected into the tube;

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

-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.

200610144536.6 The present invention further relates to fiber to the home (FTTH) or fiber to the roadside (FTTC) fiber optic system, which at least includes the optical module or storage box according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS 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. The MAC value at a wavelength of 1500nm, a bending radius of 15mm and a bending loss at a wavelength of 1625nm in a standard single-mode fiber (SSMF); Figure 2 shows the group distribution of a single-mode fiber (SMF) according to an embodiment of the present invention; Figures 3a to 3c are several schematic diagrams describing the bending loss of different standard single-mode fibers (SSMF) and for different optical fibers of the present invention, relative to the MAC value at a wavelength of 150nm, for different bending radii at a wavelength of 1625nm; And Figures 4a and 4b are schematic diagrams describing the loss through microbending.

DETAILED DESCRIPTION OF THE INVENTION 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 buried inner cladding layer and the outer cladding layer is less than -3χ 10'³, And can reach -15x103. Similarly, the embedded cladding contains a weight concentration of between 0.5% and 7%.

As I know, 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 a 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 properties of future optical fibers.

The components deposited in the tube are usually called "doping", that is, adding "impurities" to the silicon to modify its refractive index. Therefore, wrong (Ge) or phosphorus (P) increases the refractive index of silicon; it

200610144536.6 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 handcuffs when it is desired to compensate for the increase in refractive index in the photosensitive cladding.

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.

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, 0VD) 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.

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 mentioned above, errors increase the refractive index of silicon; therefore, it is generally not recommended to incorporate errors into the part of the optical fiber that seeks to obtain a lower refractive index than 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 layer.

Therefore, the optical fiber of the present invention includes faults in the combination of the inner cladding, wherein the inner cladding includes a refractive index less than -3 X 10'³ofcladding. The presence of errors in the embedded cladding corrects the viscosity of silicon and the elastic-optical coefficient in the cladding.

Figure 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.

The single-mode transmission optical fiber of the present invention includes: a central core having a refractive index difference Δ m from 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 Δ n from the outer cladding layer₂; The second inner cladding layer is deeply buried and has a refractive index difference from that of the outer cladding layer. The refractive index in the central core, the first cladding and the second inner cladding is substantially constant over their entire width; therefore, the set of distributions are truly single-mode fibers. The width of the core is defined by its radius , and the width of the cladding is defined by their respective outer diameters and 3.

In order to define a set of refractive index distributions of the optical fiber, the refractive index of the outer cladding is usually used as a reference. Then the refractive index values of the central core, the embedded cladding and the ring are given as the refractive index difference m,2,3.

200610144536.6 No. Normally, the cladding layer is formed of silicon, but the cladding layer can be doped to increase or decrease its refractive index, for example, to modify the signal propagation characteristics.

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.

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

Z] = f Dn{r}dr «η x Dn_}

I₂ = p Dn(r)dr »(r₂ -r,) x Dn₂ =Dn(r)dr «(r₃ -r₂) x Dn₃ The following Table I gives the limit values of radius and refractive index difference and the limit value of integral II, which are required to make the optical fiber show reduced bending loss and micro-bending loss, while meeting the G.652 standard for transmission fiber Light propagation specification. The values given in the table correspond to the group distribution of optical fibers.

Table I

<td>Τι(Mm)</td><td>r₂(Mm)</td><td>r₃(Pm)</td><td>Γι/γ₂</td><td>Δπι (χ 10³)</td><td> m (χ 10³)</td><td>Δη₃(χ 10³)</td><td>Δη-Δη₂</td><td>ΐιplus X ΙΟ³)</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>

The value of the integral A of the central core affects the basic propagation mode of the signal in the optical fiber. 17χ10³μπι to 24 X ΙΟ³ The integrated value of the central core of μοι makes it possible to maintain a mode field diameter that meets the G.652 standard.

Table II below gives possible refractive index profiles for the transmission fiber according to the invention. The first column assigns a reference to each distribution. Each part (door to r₃), and the following columns give the refractive index difference between each part and the outer cladding layer (Ani to. At 633nm

200610144536.6 Measure the refractive index value at the first wavelength.

Table II

<td>example</td><td>ri (Mm)</td><td>r₂ (Mm)</td><td>r₃ (Mm)</td><td> η](χ 10³)</td><td> m (x 10³)</td><td>Δη₃(χ 10³)1</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>&amp; 66</td><td>15</td><td>5. 41</td><td>0. 85</td><td>~5. 0</td>

The transmission optical fiber of the present invention having a refractive index profile such as that described above shows reduced bending loss and microbending loss at useful wavelengths.

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

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

In Table III, the first column reproduces the reference to Table II. For each fiber distribution, the effective cut-off wavelength into C is given in the following columns. , The cut-off wavelength of the optical cable enters CC, the mode field diameter of 1310nm wavelength and 1550nm wavelength is 2W02, and the dispersion elimination wavelength enters. , Is entering. The dispersion slope Po at, the dispersion C for the wavelength of 155nm and the wavelength of 1625nm.

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 mni at a wavelength of 1625 nm. The next column gives the relative bending loss normalized to the standard bending loss of the SSMF fiber with the same MAC value at the 1550nm wavelength for a radius of 15mm. The penultimate column shows the microbending loss obtained using the pin array test (10 pins in 1.5mm) at a wavelength of 1550nm.

The test used an array of 10 polishing needles with a diameter of 1.5 mm and spaced 1 cm apart. 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 25Og. The last column shows the microbending loss measured using a fixed diameter drum method at a wavelength of 1625nm. In the International Electrotechnical Commission (in reference to IEC

200610144536.6 No.

This method is described in the technical recommendation of the subcommittee under 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

<td>N⁰</td><td>λ Corr(Pm)</td><td>λ cc( Wn)</td><td>2W02®1310nm(Mm²)</td><td>2W02B) 1550nm (chi)</td><td>λ ο(nm)</td><td>Po(ps/Mm²-km)</td><td>cS1550nm(ps/Mm-km)</td><td>c ®1625nm (ps/wn -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>1&amp; 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>

Table IV

<td>N°</td><td>MACQ155Onm</td><td>BLR=5mm01625nm(dB/circle)</td><td>BL R=llmm B)1625nm (dB/circle)</td><td>BLR=15mm ®1625nm (dB/100 circle)</td><td>BLrelR=15mm®1625nm</td><td>BL Jie pin array test 0155 Onm (dB)</td><td>BL4 drum method 6) 1625nm (dB/km)</td>

<td>1</td><td>9. 0</td><td>&lt;5</td><td>&lt;2</td><td></td><td>1/5</td><td></td><td></td>

<td>2</td><td>8.4</td><td>2</td><td>&lt;0. 5</td><td>&lt;1</td><td>1/5</td><td>0. 025</td><td>&lt;0. 8</td>

<td>3</td><td>8. 1</td><td>1</td><td>&lt;0. 1</td><td>&lt;0. 4</td><td>1/5</td><td>&lt; 0. 025</td><td>&lt;0. 8</td>

<td>4</td><td>&amp; 1</td><td>1</td><td>&lt;0. 1</td><td>&lt;0. 4</td><td>1/5</td><td>&lt;0. 025</td><td>&lt;0.8</td>

As can be seen in Table III, Examples 2 to 4 do comply with the G. 652 standard, and Example 1 shows a dispersion slope Poo slightly outside the G. 652 standard. In particular, the fibers in Examples 2 to 4 show a difference in the range of 1300 nm. Between 1324nm

200610144536.6 The dispersion cancellation of the first wavelength; this is in line with the G.652 standard. The fibers in Examples 2 to 4 also show a dispersion slope of 0.093 ps/nmLkni or less for a wavelength of 1310 nm, which conforms to 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.

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

The schematic diagrams in Figures 3a, 3b, and 3c show the bending loss measurement results 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. The bending loss here is given at the end of one turn (for R=5mm and R=llmm) or at the end of 100 turns (for R=15mm).

Figure 4a shows the microbending loss of the optical fiber manufactured according to the present invention, which is characterized by: for different SSFM optical 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 performed at a wavelength of 1500nm measuring.

Figure 4b shows the microbending loss of the SSM fiber and the fiber of the present invention with MAC values of 8.11 and &amp; 31 at a wavelength of 1550 nm, relative to the wavelength, measured using a fixed diameter drum.

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 compared to the sensitivity of SSMF to microbending. It can be seen in Figure 4a that the measured microbend loss (pin array test) of 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. Times. 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 155 nm, the bending 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.

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. Through the plasma chemical vapor deposition (PCVD) type deposition method mentioned above

200610144536.6 The first method to carry out accumulation. The 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, and the embedded cladding contains a weight concentration of 0.5% to 7%. The weight concentration of the cast is preferably between 05% 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.

Provide pure silicon tube and install it on the lathe. Then, the tube is rotated, and a gas mixture of silica and dopant is injected into the tube. The tube passes through the 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.

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.

Within the scope of the present invention, the second buried cladding layer is obtained by depositing a silicon layer doped with fluorine and aluminum; it will contain oxygen. 2. Silicon SiCh&gt;Fluorine C2F6 and &lt;Ge0₂The gas mixture is injected into the tube. The gas mixture is ionized in the microwave cavity of the PCVD installation, and fluorine and pig ions are incorporated into the silicon particles.

The proportion of the injected gas is monitored so that a doped silicon layer is obtained, including pigs with a weight concentration of 0.5 to 7%, and fluorine at a concentration required to obtain the target refractive index.

The high concentration of fluorine ensures the required reduction of the refractive index of the buried 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 loss of the obtained optical fiber.

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. .

200610144536.6 It is obvious that 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.

200610144536.6