Patent Application
20200319398
The invention relates to single-mode optical fibres used in optical transmission systems, optical transmission systems comprising such single mode fibres, and fabrication methods thereof. More specifically, the present invention relates to single-mode optical fibres, which are bending-loss insensitive, and compliant with the ITU-T G.657.A2 standard.
Telecommunication systems require optical fibre, which is capable of transmitting signals for a long distance without degradation. Such optical-fibre transmission systems often use single-mode optical fibres (SMFs), such as, for example, so-called “standard” single-mode fibres (SSMFs), which are used in terrestrial transmission systems.
To facilitate compatibility between optical systems from different manufacturers, the International Telecommunication Union (ITU) has defined several standards with which a standard optical transmission fibre should comply. Among these standards, the ITU-T G. 652 recommendation (Last revision of November 2016) describes the characteristics of single-mode fibre and cable-based networks, which can answer the growing demand for broadband services. The ITU-T G. 652 recommendation has several attributes (i.e. A, B, C and D) defining the fibre attributes of a single mode optical fibre.
As the specific use in an optical access network puts different demands on the fibre and cable, which impacts its optimal performance characteristics, the ITU-T G. 657 recommendation focuses more precisely on bending-loss insensitive single mode optical fibres, which show strongly improved bending performance compared with the existing ITU-T G.652 single-mode fibre and cables. Actually, such improved bending performance is necessary, due to the high density network of distribution and drop cables in the access network, as well as to the limited space and the many manipulations needed, which ask for operator-friendly fibre performance and low bending sensitivity.
Both ITU-T G. 652 and ITU-T G. 657 standards are herein incorporated by reference in their entirety.
The ITU-T G. 657 recommendation describes two categories (A and B) of single-mode optical fibre cable which are suitable for use in access networks, including inside buildings at the end of these networks. Both categories A and B contain two subcategories which differ in macrobending loss.
Category A fibres are optimized for reduced macrobending loss and tighter dimensional specifications compared to ITU-T G.652.D fibres and can be deployed throughout the access network. These fibres are suitable to be used in the 0, E, S, C and L-band (i.e., throughout the 1260 to 1625 nm range). Fibres and requirements in this category are a subset of ITU-T G.652.D and therefore compliant with ITU-T G.652.D fibres and have the same transmission and interconnection properties.
Subcategory ITU-T G.657.A1 fibres are appropriate for a minimum design radius of 10 mm. Subcategory ITU-T G.657.A2 fibres are appropriate for a minimum design radius of 7.5 mm.
Table 1 in the ITU-T G.657 Recommendation (ITU-T G.657 category A attributes; November 2016 Issue) provides the ranges or limits on values of the single-mode fibre characteristics in order for them to comply with the ITU-T G.657.A recommendation.
Macrobending loss observed in uncabled fibres varies with wavelength, bend radius and the number of turns about a mandrel with a specified radius. In order for a SMF to comply with the ITU-T G.657.A recommendation, macrobending loss shall not exceed the maximum value given in the below table for the specified wavelength(s), bend radii and number of turns.
Although the ITU-T G.657.A recommendation does not provide any specific requirement as regards the refractive index profile of the optical fibre, which does not need to be known according to the standard, it must be noted that single mode optical fibres with trench assisted refractive index profiles have been introduced in the market. Thanks to this design, improved macro-bending losses can be reached, compared to legacy step index designs. Nowadays, it is this profile design type which is used to manufacture fibres compliant with the ITU-T G. 657. A2 recommendation.
city
(Notes 1, 2)
nm
nm
00
24
fitting
× km)
nm to
nm)
× km)
nm
× km)
nm to
nm)
nm
× km)
nm
× km)
nm
× km)
nm to
nm (Note 4)
nm
nm after
(Note 5)
indicates data missing or illegible when filed
More precisely, up to day, in order to comply with the tightest ITU-T G. 657. A2 specification, bend insensitive single mode fibres require a deep trench in the cladding. Actually, for the time being, single mode fibres without such a deep trench in the cladding can comply with the worst G.657.A category, i.e. G.657.A1, but not with the G.657.A2 category, because of their high macro-bending losses level for 7.5 mm and 10 mm bend radii.
Moreover, as appears in the above table, the ITU-T G. 657. A2 specification accepts nominal Mode Field Diameter (MFD) at a wavelength of 1310 nm comprised between 8.6 μm and 9.2 μm. The ITU-T G. 652.D standard also accepts nominal Mode Field Diameter (MFD) at a wavelength of 1310 nm comprised between 8.6 μm and 9.2 μm. However, while commercialized G. 652.D fibres are generally targeting a nominal MFD at 1310 nm at the high end of the specification, that is, between 9.0 μm and 9.2 μm, the currently commercialized G. 657.A fibres are generally designed to have a Mode Field Diameter at the low end of the specification, i.e. between 8.6 μm and 8.8 μm. Actually, most G. 657.A fibres manufacturers had to play on the Mode Field Diameter, and lower it, in order to achieve the demanding requirements of the G. 657.A standard as regards macrobending losses.
To improve backward compatibility (in particular regarding splices and reduce misinterpretation with OTDR (“Optical Time Domain Reflectometer”)) with standard step-index G.652.D fibres, it is preferable to have a G.657.A2 fibre without trench and that is targeting a nominal MFD at 1310 nm between 9.0 and 9.2 μm.
Patent document WO2015/092464, in the name of the Applicant, describes a single mode optical fibre having a core and a cladding, the core refractive index profile having a trapezoid-like shape. The transition part of the trapezoid-like core refractive index profile is obtained by gradually changing a concentration of at least two dopants from a concentration in the centre part of the core to a concentration in a cladding part adjacent to the core.
Actually, trapezoid core shape is a well-known solution to control extra losses or to design non-zero dispersion shifted fibres, and is also easier to manufacture than well-known alpha core shapes, used for multimode fibres. However, the profile designs disclosed in this patent document are not compliant with the ITU-T G.657.A2 recommendation, and have Mode Field Diameters at 1310 nm below 9.0 μm.
Patent document U.S. Pat. No. 7,187,833 discloses an optical waveguide fibre having a multi-segmented core surrounded by a cladding, the core having a central segment and an annular segment surrounding the central segment. The central segment has a positive relative refractive index profile, and the annular segment has a negative relative refractive index profile. The optical fibre exhibits an effective area of greater than about 75 μm2 at a wavelength of about 1550 nm, a dispersion slope of less than 0.07 ps/nm2/km at a wavelength of about 1550 nm, a zero-dispersion wavelength of between about 1290 and 1330 nm, and an attenuation of less than 0.20 dB/km, and preferably less than 0.19 dB/km, at a wavelength of about 1550 nm.
Contrarily to patent document WO2015/092464, this document does not disclose a trapezoid core. Moreover, the respective core and trench volumes disclosed in this document do not allow achieving a single mode fibre profile fulfilling the above-listed requirements.
Patent document U.S. Pat. No. 8,849,082 discloses an optical fibre comprising: (I) a germania doped central core region having outer radius r1 and (II) a maximum relative refractive index Δ1max and a cladding region including (i) a first inner cladding region having an outer radius r2>5 microns and refractive index Δ2; (ii) a second inner cladding region having an outer radius r3>9 microns and comprising refractive index Δ3; and (iii) an outer cladding region surrounding the inner cladding region and comprising refractive index Δ4, wherein Δ1max>Δ4, Δ2>Δ3, and wherein 0.01%≤Δ4−Δ3≤0.09%, said fibre exhibits a 22 m cable cutoff less than or equal to 1260 nm, and 0.25≤r1/r2≤0.85.
Contrarily to patent document WO2015/092464, this document does not disclose a trapezoid core. Moreover, although the single mode fibres disclosed in this document are compliant with the ITU-T G.652 standard, it is not clear whether they also comply with the requirements of the ITU-T G.657.A2 standard as regards macrobending losses.
In summary, none of these prior art designs corresponds to a single mode fibre which would be compliant with the ITU-T G.657.A2 recommendation, which cladding would not comprise a deep trench, and which would target a nominal MFD at 1310 nm ranging from 9.0 μm to 9.2 μm.
There is therefore a need for an improved Single Mode Fibre profile, which would be compliant with the ITU-T G.657.A2 recommendation, while being easily spliced with a standard Single Mode Fibre without trench, compliant with the ITU-T G. 652.D standard.
In an embodiment of the present disclosure, a bending-loss insensitive single mode optical fibre having a Mode Field Diameter greater than or equal to 9.0 μm at a 1310 nm wavelength is disclosed. Such an optical fibre has a core surrounded by a cladding, the core refractive index profile having a trapezoid-like shape.
A centre part of the core has a radius r0 and a refractive index n0 and a transition part of the trapezoid-like core refractive index profile ranges from radius r0 to a radius r1>r0 with a trapezoid ratio r0/r1 of the centre part of the core's radius r0 to the transition part's radius r1 between 0.1 and 0.6, preferably between 0.2 and 0.5, and more preferably between 0.25 and 0.45.
The cladding comprises at least one region of depressed refractive index, called a trench, ranging from radius r2≥r1 to radius r3>r2 and having a refractive index nt, and an outer cladding ranging from radius r3 to the end of a glass part of the single mode fibre and having a refractive index n4. The refractive-index difference of the trench with respect to the outer cladding Δnt=nt−n4 is between −2×10−3 and −0.9×10−3. The core has a surface integral V01 between 20.10−3 μm and 24.10−3 μm, the surface integral being defined according to the following equation: V01=∫0r
The cladding has a surface integral V02 between −25×10−3 μm and −9×10−3 μm, the surface integral being defined according to the following equation: V02=∫r
Moreover, the single mode optical fibre fulfils the following criterion:
25.7×10−3≤V01−0.23261V02≤26.8×10−3.
The present disclosure thus relies on a novel and inventive approach to the design of bending-loss insensitive single mode fibres. Actually, a single mode optical fibre according to an embodiment of the present disclosure has a core with a refractive index profile showing a trapezoid shape, instead of the more usual step shape. It is well known that such a trapezoid shape allows reducing the extra scattering losses in the single mode optical fibre, without degrading Rayleigh scattering, or to design non-zero dispersion shifted fibres. However, such a trapezoid shape is here used to enable the single mode optical fibre to be compliant with the ITU-T G.657.A2 standard, while avoiding adding a deep trench in the cladding. Such a trapezoid shape of the core is instead combined with a large, but shallow, trench in the cladding (as defined by the range of allowed values for V02), which advantageously replaces the deep trench needed so far for achieving compliance with the ITU-T G.657.A2 standard.
Replacing the deep trench with a shallow and large trench eases splicing with a ITU-T G. 652.D compliant standard SMF, which has no trench.
Moreover, such a trapezoid shape is easier to manufacture, as compared to the alpha-shaped refractive index profile from the prior art, which is not adequate for the small core diameter of single mode optical fibres.
Such a trapezoid shape may be achieved through a gradual change in the concentration of two or more dopants in the transition part from the centre part of the core to the cladding, as disclosed for example in patent document WO2015/092464 in the name of the Applicant which is herein integrated by reference in its entirety.
Moreover, such a bending-loss insensitive single mode optical fibre according to embodiments of the present disclosure has a nominal Mode Field Diameter at the 1310 nm wavelength, which is between 9.0 and 9.2 μm, i.e. at the high end of the ITU-T G.657.A2 standardized range: these nominal MFD values are hence compatible with those of the commercialized ITU-T G.652.D compliant single mode fibres. Their splicing is easier for the user, as it does not induce artefacts in the OTDR.
In addition, for a nominal MFD at 1310 nm between 9.0 and 9.2 μm, the inventors have observed that it was necessary to have 25.7×10−3≤V01−0.2326V02, in order to achieve macrobending losses at bending radii of 15 mm and 10 mm compliant with the requirements of the ITU-T G. 657.A2 Recommendation.
They have also observed that it was necessary to have V01−0.2326V02≤26.8×10−3 in order to ensure a targeted cable cut-off wavelength below 1240 nm, when the Mode Field Diameter at 1310 nm is at 9.0 μm.
Actually, it is known that macrobending losses decrease when the core surface integral V01 increases and when the cladding surface integral V02 decreases. The inventors have hence worked out that there must be a positive number k, which allows describing macrobending losses by a mathematical function of the type:
f=V
01
−k×V
02.
The same reasoning applies with the cable cutoff wavelength, which tends to increase when the core surface integral V01 increases and when the cladding surface integral V02 decreases. Hence, there must also be a positive number g, which allows describing the behaviour of the cable cut off wavelength by a mathematical function of the type:
f=V
01
−g×V
02.
By trial and error, the inventors have found out that for k=g=0.2326, there is a strong correlation between the f function and the macrobending losses at bending radii of 15 mm and 10 mm on the one hand, and the cable cut-off wavelength on the other hand.
They have hence derived that the optical fibre of the present disclosure should fulfil the criterion: 25.7×10−3−V01−0.2326V02≤26.8×10−3, in order for it to comply with the requirements of the ITU-T G.657.A2 Recommendation at a MFD at 1310 nm between 9.0 and 9.2 microns.
Moreover, a range for the ratio r0/r1 between 0.1 and 0.6 is required to have a Zero chromatic Dispersion Wavelength (ZDW) between 1300 nm and 1324 nm (which is required for compliance with the ITU G657.A2 standard). A preferred range for r0/r1 is between 0.2 and 0.5, while an even narrower range between 0.25 and 0.45 provides a robust working range.
According to a first embodiment of the present disclosure, r2=r1 and a trench ranging from r2 to r3 surrounds the core. The core surface integral may hence be approximated as
where Δn0=n0−n4 is the refractive-index difference of the centre part of the core with respect to the outer cladding, and the cladding surface integral may be approximated as V02≈(r3−r2)×Δt.
According to a second embodiment of the present disclosure, the cladding comprises an intermediate cladding ranging from radius r1 to radius r2>r1 and having a refractive index n2, and the trench surrounds the intermediate cladding.
Such an intermediate cladding eases the optical fibre manufacturing process when it relies on the OVD (“Outside Vapor Deposition”) technique.
According to this second embodiment, the core surface integral may hence be approximated as
where Δn0=n0−n4 is the refractive-index difference of said centre part of said core with respect to said outer cladding and where Δn2=n2−n4 is the refractive-index difference of said intermediate cladding with respect to said outer cladding, and the cladding surface integral may be approximated as V02≈(r2−r1)×Δn2+(r3−r2)×Δnt.
According to a preferred aspect of this second embodiment, the refractive index difference of the intermediate cladding with respect to the outer cladding Δn2=0. The intermediate cladding hence presents a refractive index which is equivalent to that of the external cladding. Such an intermediate cladding is void of any dopant and constitutes a buffer zone between the up-doped core and the down-doped trench.
According to an embodiment of the present disclosure, the core outer radius r1 is between 5.4 μm and 8.0 μm.
According to an embodiment of the present disclosure, the trench outer radius r3 is between 16 μm and 22 μm.
According to an embodiment of the present disclosure, the refractive-index difference of the centre part of the core with respect to the outer cladding Δn0=n0−n4 is between 5×10−3 and 6×10−3.
According to an embodiment of the present disclosure, such an optical fibre has a Mode Field Diameter at 1310 nm between 9.0 μm and 9.2 μm.
According to an embodiment of the present disclosure, said optical fibre has a maximum Cable cut-off wavelength of 1240 nm.
Actually, the ITU-T G.657.A2 Recommendation specifies a maximum value of the Cable Cut-off Wavelength of 1260 nm. However, it appears reasonable to target a lower maximum Cable Cut-off Wavelength, around 1240 nm, to ensure that all manufactured optical fibres will pass the cable cut-off recommendation. Targeting a cable cut-off wavelength at 1260 nm is not robust as it would induce 50% of the produced optical fibres out of the G. 657.A2 Recommendation, because of manufacturing defects. Targeting cable cut-off wavelength below 1240 nm is needed to ensure a robust production.
Throughout this document, the Cable Cut-Off wavelength (CCO) corresponds to the cut-off wavelength in cable λcc such as defined by Subcommittee 86A of the International Electrotechnical Commission in the IEC 60793-1-44 standard.
According to an embodiment of the present disclosure, said optical fibre complies with the requirements of the ITU-T G.657.A2 standard.
The present invention also relates to an optical fibre transmission system comprising at least one single mode fibre according to the invention.
Other features and advantages of embodiments of the invention shall appear from the following description, given by way of an indicative and non-exhaustive example and from the appended drawings, of which:
The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
Reference will now be made in detail to embodiments of single mode optical fibers, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.
One embodiment of a bending-loss insensitive single mode optical fiber according to the present disclosure is schematically depicted in isometric view in
In embodiments of the present disclosure with no intermediate cladding 102, the trench 130 directly abuts the core 101, and ranges from an inner radius r1 to an outer radius r3.
In embodiments of the present disclosure, the glass core 101 generally has an outer radius r1 between 5.4 μm and 8.0 μm. Moreover, the depressed cladding 103 has an outer radius r3 between 16 μm and 22 μm. The core 101 has a trapezoid shape, with a small basis radius r0 and a large basis radius r1. The small basis over large basis trapezoid ratio r0/r1 is ranging from 0.1 to 0.6, typically ranging from about 0.2 to about 0.5, preferably from about 0.25 to about 0.45.
In the embodiments shown and described herein, the core 101 and the cladding generally comprise silica, specifically silica glass. The cross-section of the optical fiber 10 may be generally circular-symmetric with respect to the center of the core 101. In some embodiments described herein, the radius of the glass portion of the optical fiber 10 is about 62.5 μm. However, it should be understood that the dimensions of the cladding may be adjusted so that the radius of the glass portion of the optical fiber may be greater than or less than 62.5 μm. The optical fiber 10 also comprises a coating surrounding the cladding. Such a coating may comprise several layers, and it may notably be a dual-layer coating, although these different layers are not shown on
The different portions in the cladding may comprise pure silica glass (SiO2), silica glass with one or more dopants, which increase the index of refraction (e.g. GeO2 or any other known dopant), such as when the portion of the cladding is “up-doped” (e.g. for the intermediate cladding 102), or silica glass with a dopant, which decreases the index of refraction, such as fluorine, such as when the portion of the cladding is “down-doped” (e.g. for the trench 103).
The trapezoid shape of the core 101 may be obtained by gradually adjusting the concentration of at least two dopants in the center part of the core.
In the first embodiment illustrated by
The centre part of the core 101 has a radius r0 and an index difference Δn0 relative to the outer cladding. In the transition part of the core, the refractive index difference decreases substantially linearly. The refractive index of the core typically has a trapezoid shape. Accordingly, the refractive-index difference Δn(r) between the central core and the outer cladding depends on the distance r from the centre of the optical fibre (e.g. decreasing as the distance from the centre of the optical fibre increases). As used herein, the term “refractive-index difference” does not exclude a refractive-index difference of zero.
The depressed cladding, or buried trench, 103 has a radius r3 and a refractive-index difference Δnt with respect to the outer cladding that is typically constant. As used herein, the term “buried trench” is used to designate a radial portion of the optical fibre having a refractive index lower than the refractive index of the outer cladding.
The outer cladding 104 ranges from a radius r3 to the end of the glass part of the single mode fibre.
In the second embodiment illustrated by
Like in the embodiment of
The intermediate cladding 102 has a radius r2 and a refractive-index difference Δne with respect to the outer cladding that is typically constant. In the peculiar embodiment illustrated by
The outer cladding 104 ranges from a radius r3 to the end of the glass part of the single mode fibre.
In both
Table 2 below draws a comparison of the refractive index designs of two exemplary embodiments Ex1 and Ex2 of
The first column of Table 2 lists the exemplary and comparative optical fibres. The following columns provide, for each single mode fibre listed in the first column:
The refractive index differences in Table 2 (as well as in all the other tables throughout the present document) have been multiplied by 1000, as are the ordinate values in
Table 3 below details the refractive index design of exemplary embodiments Ex3 and Ex4 of
The first column of Table 3 gives the reference of the exemplary optical fibres. The following columns provide for the single mode fibres listed in the first column:
Both in the embodiments of
Table 4 (below) shows optical transmission characteristics for optical single mode fibres having the refractive-index profiles depicted in Table 2 and Table 3, compared with the optical transmission characteristics recommended in the ITU-T G.657.A2 standard. The first column identifies the minimum and maximum G.657.A2 recommended range, and the exemplary and comparative optical fibres. The next columns provide, for each optical fibre:
The comparative example Comp Ex, corresponding to a step-index single mode fibre, presents the same MFD at 1310 nm and Cable Cut-off as examples Ex1 to Ex3. However, examples Ex1 to Ex4 are all compliant with ITU-T G.657.A2 Recommendation, which is not the case of the comparative example Comp Ex.
It must be noted that the cable cutoff target needs to be significantly below the maximum accepted level of 1260 nm. Targeting a cable cutoff at 1260 nm is not robust as it will by definition induce 50% of the production out of the ranges of values recommended by the G.657.A2 standard. In the above examples, the cable cutoff wavelength is targeted to be around 1210 nm that is ensuring robust production, i.e nearly all fibers can pass the cable cutoff recommendation. More generally, targeting cable cutoff below 1240 nm is recommended to ensure a robust production.
As may be observed in Table 4, all the exemplary fibers Ex1 to Ex4 target a nominal Mode Field Diameter at 1310 nm of 9 microns.
Table 5 (below) shows macrobending losses for optical fibres having the refractive-index profiles depicted in Tables 2 and 3 for the wavelengths of 1550 nanometres and 1625 nanometres for radii of curvature of 15 millimetres, 10 millimetres, 7.5 millimetres and 5 millimetres, such as:
Table 5 also provides the maximum recommended value by the ITU-T G.657.A2 standard.
In accordance with Tables 4 and 5 (above), the optical fibres according to embodiments of the invention show bending losses, which are less than the comparative optical fibre, which has a step-index profile.
The four refractive index profile examples Ex1, Ext, Ex3 and Ex4 according to embodiments of the invention, described in Tables 2 to 5, as well as in
Table 6 below provides the features of three other exemplary optical fibres Ex5 to Ex7, which refractive index profile corresponds to the one depicted in
The structure and units of Table 6 is identical to that of Table 2 and is therefore not detailed here. Similarly, Table 7 below corresponds to Table 4 above and provides the optical characteristics of exemplary optical fibres Ex5-Ex7; Table 8 below corresponds to Table 5 above and provides the macrobending losses of exemplary optical fibres Ex5-Ex7.
We now present interesting tools and methods for defining acceptable profile ranges for single mode optical fibres according to the present disclosure.
Each section of the optical fibre profile may be defined using surface integrals. The term “surface” should not be understood geometrically but rather should be understood as a value having two dimensions.
Accordingly, the central core may define a surface integral V01 and the cladding may define a surface integral V02 respectively defined by the following equations:
For exemplary optical fibres which refractive index profile corresponds to the first embodiment of
V
02≈(r3−r2)×Δnt
Table 9 (below) completes Tables 2, 3 and 6 (above) with the values of the surface integrals V01 and V02 described above for the exemplary embodiments of the invention Ex1 to Ex7, as well as for their comparative step index single mode fibre Comp Ex. All the examples in Table 9 are hence the same as in Tables 2, 3 and 6. The values in Table 9 correspond to the theoretical refractive-index profiles.
The first column in Table 9 lists the exemplary and comparative optical fibres. The three other columns provide respective values for the surface integrals V01 and V02, as well as for the polynomial V01−0.2326V02. The integrals in Table 9 have been multiplied by 1000.
Tables 10 to 13 (below) provide the features of further exemplary optical fibres Ex8 to Ex35, according to embodiments of the present disclosure, which refractive index profile corresponds to the one depicted in
Similarly, Table 11 below corresponds to Table 4 above and provides the optical characteristics of exemplary optical fibres Ex8-Ex35; Table 12 below corresponds to Table 5 above and provides the macrobending losses of exemplary optical fibres Ex8-Ex35. Last, Table 13 below corresponds to Table 9 above and provides the values of the surface integrals V01 and V02 described above for the exemplary embodiments of the invention Ex8 to Ex35. The structure and units in Tables 10-13 are the same as in the previously described corresponding tables.
Optical fibres according to embodiments of the invention typically target a MFD at 1310 nm greater than or equal to 9 microns, and have the following properties:
Actually, it is known that macrobending losses decrease when the core surface integral V01 increases and when the cladding surface integral V02 decreases. The inventors have hence worked out that there must be a positive number k, which allows describing macrobending losses by a mathematical function of the type:
f=V
01
−k×V
02.
The same reasoning applies with the cable cutoff wavelength, which tends to increase when the core surface integral V01 increases and when the cladding surface integral V02 decreases. Hence, there must also be a positive number g, which allows describing the behaviour of the cable cut off wavelength by a mathematical function of the type:
f=V
01
−g×V
02.
By trial and error, the inventors have found out that for k=g=0.2326, there is a strong correlation between the f function and the macrobending losses at bending radii of 15 mm and 10 mm on the one hand, and the cable cut-off wavelength on the other hand.
As may be observed, the values of macrobending losses and cable cut-off wavelength are dispersed.
The same may be observed on
However,
Hence, as may be observed on
We now describe an exemplary method of manufacturing an optical fibre according to embodiments of the present disclosure. Such a manufacturing method comprises a first step of Chemical Vapour Deposition to form a core rod. During the Chemical Vapour Deposition doped or non-doped glass layers are deposited. The deposited glass layers form the core refractive index profile of the final optical. In a second step the core rod is provided with an external overcladding for increasing its diameter to form a preform. The overcladding may be derived from pre-formed silica tubes or by deposition of glass layers on the outer circumference of the core rod. Various techniques could be used for providing an overcladding by deposition of glass layers, such as Outside Vapour Deposition (OVD) or Advanced Plasma and Vapour Deposition (APVD). In a third step, the optical fibre is obtained by drawing the preform in a fibre drawing tower.
In order to fabricate the core-rod, a tube or substrate is generally mounted horizontally and held in a glass-making lathe. Thereafter, the tube or substrate is rotated and heated or energised locally for depositing components that determine the composition of the core-rod. Those of ordinary skill in the art will appreciate that the composition of the core-rod determines the optical characteristics of the fibre.
In this regard, both the centre part and the transition part of the core, the intermediate cladding and the trench are typically obtained using plasma chemical vapour deposition (PCVD) or furnace chemical vapour deposition (FCVD), which enable large quantities of fluorine and germanium to be incorporated into the silica and which enable a gradual change of their concentrations in the transition part of the core. The PCVD technique is for example described in patent document U.S. Pat. No. Re30,635 or U.S. Pat. No. 4,314,833.
Other techniques could also be used to form the core-rod, such as vapour axial deposition (VAD) or outside vapour deposition (OVD).
Optical fibres in accordance with the present invention are well suited for use in various optical communication systems. They are particularly suited for terrestrial transmission systems, as well as for fibre-to-the-home (FTTH) systems.
Moreover, they are typically compatible with conventional optical fibres, which make them appropriate for use in many optical communication systems. For example, the optical fibres according to embodiments of the invention are typically compatible with conventional optical fibres with respect to mode field diameter, thereby facilitating good fibre-to-fibre coupling.
In the specification and/or figure, typical embodiments of the invention have been disclosed. The present invention is not limited to such exemplary embodiments.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2017/001722 | 12/21/2017 | WO | 00 |
