Patent Application
20210032153
The present disclosure generally relates to methods of forming an optical fiber using a fiber drawing system, and more particularly relates to tension-based methods for forming bandwidth-tuned optical fibers for bi-modal optical data transmission.
Standard single mode optical fiber is the preferred type of optical fiber for use in hyperscale data centers because it has a higher bandwidth than multimode fibers, which provides benefits of higher data rate, longer system reach and future-proof. Hyperscale data centers also include short optical links in the range from 1 meter to 100 meters. For this short-distance range, multimode fibers are preferred, especially when used with multimode light sources, such as vertical cavity surface emitting lasers (VCSELs).
On the other hand, hyperscale data center operators prefer to use standard single mode optical fiber for both the short and long optical data links to simplify fiber cable management. Unfortunately, this simplified cable management approach comes at the expense of optical transmission performance for the short-distance optical links that use multimode light sources because standard single mode optical fibers have relatively poor bandwidth performance at the wavelength range of the multimode light sources. Also, it is difficult to efficiently couple the light from a multimode VCSEL into standard single mode optical fibers due to mismatched optical properties.
Optical fibers suitable for both single mode and few mode data transmission for use with VCSELs have been developed. However, due to manufacturing errors, it can be difficult to form such optical fibers to have the exact refractive index profile that yields a suitably high or optimum (target) bandwidth for few mode operation within a select wavelength band or at a select wavelength of interest for optical data transmission when using a multimode light source such as a VCSEL.
Single mode (SM) VCSELs can offer better data transmission performance than multimode (MM) VCSELs over multimode fibers. SM or few mode (FM) VCSELs can be made through similar process as multimode (MM) VCSELs with similar costs. On the other hand, the lower numerical aperture (NA) and smaller spot size of the light emitted from SM VCSELs make them more suitable for launching into smaller core optical fibers. VCSELs typically operate at a wavelength of 850 nm, but it is also feasible for VCSELs to be made for operating at one or two wavelengths in the range from 850 nm to 1100 nm, e.g., at 850 nm and at 910 nm. For such wavelengths, a standard SM fiber (e.g., Corning® SMF-28® Ultra optical fiber) designed for SM operation at wavelengths above 1260 nm (the cable cut-off wavelength) can support a few modes, such as two or three mode groups, but with poor bandwidth since a standard SM fiber is not optimized for bandwidth performance below its cut-off wavelength.
The fibers formed using the draw tensioning methods disclosed herein are bandwidth tuned, meaning that they are formed to have suitably high if not optimal bandwidth for BM (bimodal) operation at a select (target) wavelength λ in a BM wavelength range from 850 nm to 1100 nm.
An embodiment of the disclosure is directed to a method of forming a bandwidth-tuned optical fiber for short-length data transmission systems, comprising: a) establishing a relationship between a change Δτ in a modal delay τ, a change ΔT in a draw tension T and a change Δλ in a bimodal (BM) wavelength λ of light in a BM wavelength range from 840 nm and 1100 nm for a test optical fiber that supports BM operation at the BM wavelength; and b) drawing the bandwidth-tuned optical fiber by setting the draw tension based on said relationship between the change in the modal delay ΔT, the change in the draw tension ΔT and a change Δλ in the BM wavelength λ so that the bandwidth-tuned optical fiber has a target bandwidth greater than 2 GHz·km at a target wavelength within the BM wavelength range.
Another embodiment of the disclosure is directed to a method of forming a bandwidth-tuned optical fiber, comprising: a) for a test optical fiber supporting BM operation in a BM wavelength range comprising a plurality of BM wavelengths, establishing a correlation between a modal delay τ, a draw tension T and a BM wavelength λ, the correlation comprising data measured for the test optical fiber; b) selecting a target draw tension TT for the bandwidth-tuned optical from the correlation, the target draw tension TT selected so that the bandwidth-tuned optical fiber has a target bandwidth BWT at a target BM wavelength λT within the BM wavelength range; and c) drawing the bandwidth-tuned optical fiber at the target draw tension TT.
Another embodiment of the disclosure is directed to a method of forming a bandwidth-tuned non-test optical fiber for short-length data transmission systems, comprising: a) establishing a relationship between a change Δτ in a modal delay τ and a change ΔT in a draw tension T for a BM target wavelength λT of light in a BM wavelength range from 840 nm and 1100 nm for a test optical fiber that supports BM operation at the BM target wavelength λT; and drawing the bandwidth-tuned optical fiber by changing the amount of draw tension according to the relationship between the change Δτ in the modal delay and the change ΔT in the draw tension T so that the bandwidth-tuned optical fiber has a target bandwidth greater than 2 GHz·km at the target wavelength T.
Another embodiment of the disclosure is directed to a method of forming a bandwidth-tuned optical fiber, comprising: a) for a test optical fiber supporting BM operation in a BM wavelength range comprising a plurality of BM wavelengths, establishing a correlation between a modal delay τ and a draw tension T for a BM target wavelength λT, the correlation comprising data measured for the test optical fiber; b) selecting a target draw tension TT for the bandwidth-tuned optical from the correlation, the target draw tension TT selected so that the bandwidth-tuned optical fiber has a target bandwidth BWT at the BM target wavelength λT; and c) drawing the bandwidth-tuned optical fiber at the target draw tension TT.
Another embodiment of the disclosure is directed to a method of forming a bandwidth-tuned optical fiber for short-length data transmission systems, comprising: a) establishing a relationship between a change Δλp in a peak wavelength λp of light that resides within a BM wavelength range from 840 nm and 1100 nm and a change ΔT in a draw tension T, for a test optical fiber that supports BM operation with the BM wavelength range; and b) drawing the bandwidth-tuned optical fiber with the draw tension T set according to the relationship between the change Δλp in the peak wavelength λp and the change ΔT in the draw tension T to cause the optical fiber to have a target peak wavelength λpT at which the bandwidth-tuned optical fiber has a bandwidth of greater than 2 GHz·km.
Another embodiment of the disclosure is directed to a method of forming a bandwidth-tuned optical fiber, comprising: a) for a test optical fiber supporting BM operation in a BM wavelength range comprising a plurality of BM wavelengths, establishing a correlation between a peak wavelength λp and a draw tension T, the correlation comprising data measured for the test optical fiber; b) selecting a target draw tension TT for the bandwidth-tuned optical from the correlation, the target draw tension TT selected so that the bandwidth-tuned optical fiber has a target bandwidth BWT at the peak wavelength λp; and c) drawing the bandwidth-tuned optical fiber at the target draw tension TT.
Another embodiment of the disclosure is directed to method of forming an optical fiber data transmission system comprising: forming an optical fiber link using the bandwidth-tuned optical fibers disclosed herein, wherein the optical fiber link has an input end, an output end and a link length LL between the input and output ends, wherein LL<1000 meters; optically coupling the input end of the optical fiber link to a SM VCSEL that emits light having a VCSEL wavelength λV that is substantially equal to the target wavelength and that carries optical signals at a data rate of at least 10 Gb/s; and optically coupling a photodetector to the output end of the optical fiber link to receive and convert the optical signals to electrical signals.
Another embodiment of the disclosure is directed to a method of forming an optical fiber data transmission system comprising: forming an optical fiber link using the bandwidth-tuned optical fiber disclosure herein, wherein the optical fiber link has an input end, an output end and a link length LL between the input and output ends, wherein LL<1000 meters; optically coupling the input end of the optical fiber link to a SM VCSEL that emits light having first and second VCSEL wavelengths λV1 and λV2 that respectively carry first and second optical signals at a data rate of at least 10 Gb/s, and wherein the target wavelength is substantially midway between the first and second VCSEL wavelengths λV1 and λV2; and optically coupling first and second photodetectors to the output end of the optical fiber link to respectively receive and convert the first and second optical signals to electrical signals.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary and are intended to provide an overview or framework to understanding the nature and character of the claims. The accompanying drawings are included to provide a further understanding and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiments, and together with the description explain the principles and operation of the various embodiments.
Reference is made in detail to example embodiments illustrated in the accompanying drawings. Whenever possible, the same reference numerals are used throughout the drawings to refer to the same or like parts.
The claims as set forth below are incorporated into and constitute part of this detailed description.
Cartesian coordinates are used in some of the Figures for the sake of reference and ease of illustration and are not intended to be limiting as to direction or orientation. The z-direction is taken as the axial direction of the optical fiber.
U.S. Pat. No. 10,131,566, entitled “Methods for modifying multi-mode optical fiber manufacturing processes,” is incorporated by reference herein.
U.S. Patent Application Ser. No. 62/803,956, entitled “Optical fibers for single mode and few mode VCSEL-based optical fiber transmission systems,” is incorporated by reference herein.
The coordinate r is a radial coordinate, where r=0 corresponds to the centerline of the fiber.
The symbol “μm” is used as shorthand for “micron,” which is a micrometer, i.e., 1×10−6 meter.
The symbol “nm” is used as shorthand for “nanometer,” which is 1×10−9 meter.
The term “fiber” as used herein is shorthand for optical fiber.
The term “single mode” is abbreviated as SM and when referring to an optical fiber means that the optical fiber supports a single linear polarization (LP) mode at an operating wavelength equal to or greater than the cut-off wavelength.
A standard SM optical fiber referred to herein and such as mentioned above has optical properties according to the G.652 industry standards known in the art and as set forth by Telecommunication Industry Association (TIA). A standard SM optical fiber has a relatively small core of about 9 microns in diameter and a numerical aperture (NA) of about 0.12. A standard single-mode fiber is designed to have a cable cut-off wavelength λC below (i.e., less than) 1260 nm so the fiber supports only one mode at 1310 nm and supports a few modes at 850 nm. Typically, a standard SM fiber has a step index profile associated with a very high alpha parameter (e.g., α≥10). The step index profile is simple, but the bandwidth at 850 nm is low. Consequently, a standard single-mode fiber with a step index is not suitable for few mode or bi-mode transmission at 850 nm.
The term “few mode” is abbreviated FM and when referring to an optical fiber means that the optical fiber supports two or three linear polarization (LP) modes, and typically refers to a single mode fiber operating below the cut-off wavelength (defined below). A given optical fiber can be both SM and FM since SM and FM operation is determined by the wavelength of light used.
The term “bi-mode” or “bi-modal” is abbreviated BM and when referring to an optical fiber means a special case of an FM optical fiber that supports only two modes, e.g., LP01 and LP11 modes. The optical fiber 6 discussed below is designed for BM operation (and is thus referred to as a BM fiber) in a BM (bimodal) wavelength range from 840 nm to 1100 nm, where BM wavelength range refers to a range of operating wavelengths over which the optical fiber supports only two modes.
The term “bandwidth tuning” is used herein to describe the process of forming the BM fiber to have a select bandwidth performance (“target bandwidth” BWT) at a select or target wavelength λT within the BM wavelength range between 840 nm and 1100 nm. In an example, the bandwidth-tuned BM fiber has a select or “target” bandwidth BWT, which in an example is in the range from 1 GHz·km to 50 GHz·km or above. A wavelength within the BM wavelength range is referred to as a bimodal or BM wavelength and is denoted λ. The target wavelength is an example of a BM wavelength λ.
The limits on any ranges cited herein are inclusive and thus lie within the range, unless otherwise specified.
The terms “comprising,” and “comprises,” e.g., “A comprises B,” is intended to include as a special case the concept of “consisting,” as in “A consists of B.”
Some non-italicized parameters and variables are shown in italics in the equations set forth below by way of equation conventions used in the art.
The terms “drawing tension” and “draw tension” or just “tension” are used interchangeably herein and are denoted by T and have units of grams, g. However, it should be understood that drawing tension measurements provided in grams may be converted to tension measurements in Newtons or dynes. To convert grams of drawing tension to Newtons of drawing tension, the drawing tension in grams is multiplied by 0.0098. To convert grams of drawing tension to dynes of drawing tension, the drawing tension in grams is multiplied by 980.
The phrase “bare optical fiber” or “bare fiber” as used herein means an optical fiber directly drawn from a heated glass source (i.e., a “preform”) and prior to applying a protective coating layer to its outer surface (e.g., prior to the bare optical fiber being coated with a polymeric-based material). In the discussion below, the term “fiber” can mean a bare optical fiber or a coated optical fiber unless expressly stated otherwise.
The “relative refractive index” as used herein is defined as:
where n(r) is the refractive index of the fiber at the radial distance r from the fiber's centerline AC (r=0) at a wavelength of 1550 nm, unless otherwise specified, and ncl is the index of the outer cladding at a wavelength of 1550 nm. When the outer cladding is essentially pure silica, ncl=1.444 at a wavelength of 1550 nm. As used herein, the relative refractive index percent (also referred herein as the “relative refractive index” or “relative index percent” for short) is represented by Δ (or “delta”), Δ% (or “delta %”), or %, all of which can be used interchangeably, and its values are given in units of percent or %, unless otherwise specified. Relative refractive index is also expressed as Δ(r) or Δ(r)%. Relative refractive index is also defined for specific regions “i” of a fiber, where the regions “i” include in one example a core (i=1), inner cladding (i=2), trench (i=3), and/or outer cladding (i=4), or in another example a core (i=1), a trench (i=2), and a cladding (i=4), or in yet another example a core (i=1), and a cladding (i=4). The relative refractive index of region “i” is expressed as Δi, where, unless otherwise specified, Δi refers to the average value of Δ in region “i”. The minimum and maximum values of Δ in region “i” are expressed as Δi,min and Δi,max, respectively.
In cases where the refractive index of a region is less than the reference index ncl, the relative index percent is negative and is referred to as having a depressed region or depressed-index (also referred to as a “trench”), and the minimum relative refractive index is calculated at the point at which the relative index is most negative unless otherwise specified. In cases where the refractive index of a region is greater than the reference index ncl, the relative index percent is positive and the region can be said to be raised or to have a positive index.
The term “dopant” as used herein refers to a substance that changes the relative refractive index of glass relative to pure undoped SiO2. One or more other substances that are not dopants may be present in a region of an optical fiber (e.g., the core) having a positive relative refractive index Δ. The dopants used to form the core of the optical fiber disclosed herein include GeO2 (germania) and Al2O3 (alumina). The parameter a (also called the “profile parameter” or “alpha parameter”) as used herein relates to the relative refractive Δ(%) where r is the radius (radial coordinate), and which is defined by:
Δ(r)=Δ0{1−[(r−rm)/(r0−rm)]α}
where rm is the point where Δ(r) is the maximum Δ0, r0 is the point at which Δ(r)=0 and r is in the range rinitial to rfinal, where Δ(r) is defined above, rinitial is the initial point of the α-profile, rfinal is the final point of the α-profile and α is an exponent that is a real number. For a step index profile, α>10, and for a gradient-index profile, α<5.
The “trench volume” is denoted by V and is defined for a trench with a relative refractive index ΔT as a constant:
V=Δ
T·[(rOUT)2−(rIN)2].
where rOUT and rIN are the outer and inner radii that define the trench. In an example where the trench relative refractive index ΔT varies with radial coordinate (i.e., ΔT(r)), then the trench volume is given by
V=2∫ΔT(r)rdr
with the limits on the integration being from rIN to rOUT and the units in “%-μm2”.
Thus, for the example refractive index profile shown in
V=Δ
3·[(r3)2−(r2)2].
And in an example where the relative refractive index Δ3 varies with radial coordinate (i.e., Δ3(r)), then the trench volume is given by
V=2∫Δ3(r)rdr
with the limits on the integration being from r2 to r3 and the units in “%-μm2”. The trench 20 in the example refractive index profile of
The “mode field diameter” or “MFD” of an optical fiber is determined using the Peterman II method, which is the current international standard measurement technique for measuring the MFD of an optical fiber. The MFD is given by:
where f(r) is the transverse component of the electric field distribution of the guided optical signal and r is radial position in the fiber. The MFD depends on the wavelength of the optical signal and is reported herein at selected wavelengths as indicated below.
A related concept to MFD is the “effective area” of an optical fiber, which is defined as: Aeff=2π(∫(f(r))2 r dr)2/(∫(f(r))4 r dr), where r is the radial coordinate, the integration limits are 0 to ∞, and f(r) is the transverse component of the electric field associated with light propagated in the optical fiber. Effective area depends on the wavelength of the optical signal and is reported herein at selected wavelengths as indicated below.
“Chromatic dispersion”, herein referred to as “dispersion” unless otherwise noted, of an optical fiber is the sum of the material dispersion, the waveguide dispersion, and the intermodal dispersion. In the case of single mode waveguide fibers, the inter-modal dispersion is zero. Dispersion values in a two-mode regime assume intermodal dispersion is zero. Dispersion is reported herein in units of ps/nm-km.
The zero-dispersion wavelength is denoted λ0 and is the wavelength where material dispersion and waveguide dispersion cancel each other. In silica-based optical fibers, the zero-dispersion wavelength is about 1300 nm, e.g., between 1300 and 1324 nm, depending on the dopants used to form the optical fiber.
The operating wavelength is denoted by λ and is a wavelength at which the optical fiber can operate while supporting (guiding) a single mode, two modes, or a few modes. An operating wavelength at which the optical fiber supports only two modes is referred to as a BM wavelength.
The VCSEL wavelength is denoted λV and represents one or more output wavelengths of a VCSEL. Example VCSEL wavelengths λV can include one wavelength λV=850 nm or two wavelengths λV1=850 nm and λV2=910 nm for two-wavelength VCSEL output.
The term “bandwidth” as used herein and denoted BW and is measured in units of MHz·km or GHz·km. For the bandwidth measurement, the two propagating modes in the BM fiber (e.g., LP01 and LP11) are excited with comparable weights, which is essentially the overfilled bandwidth. The bandwidth BW of a BM fiber is defined by the modal delay τ between the two propagating modes when the two modes are equally excited and is related to the modal delay τ in one embodiment via the equation:
BW(τ)=b·(1/τ)=(1/3)·(1/τ)
and is hereinafter referred to as the “bandwidth equation” where b is a constant coefficient. In some other embodiments, the coefficient b in the bandwidth equation can be larger than 1/3. The values for the bandwidths BW referred to herein are based on the above equation with the coefficient b of (1/3) unless otherwise noted. A value of b=1/3 provides conservative or “worst case” value for calculating the bandwidth from the modal delay.
The target bandwidth BWT is a select bandwidth associated with a target wavelength λT (see below).
The target wavelength is denoted λT and is a wavelength in the BM wavelength range from 840 nm to 1100 nm associated with the target bandwidth BWT. It is noted that the target wavelength λT need not be equal to a VCSEL wavelength λV. In an example, the target wavelength λT can be substantially the same as a VCSEL wavelength λV of light emitted by the VCSEL, while in another example can reside between (e.g., substantially midway between) two VCSEL wavelengths λV1 and λV2 of light emitted by the VSCEL.
The term “peak wavelength” λp means a wavelength of light that maximizes the bandwidth of the BM fiber formed using the methods disclosed herein. Techniques for measuring the peak wavelength of the BM fiber based on multi-wavelength measurement techniques and differential mode delay techniques are known in the art and are described for example in the aforementioned U.S. Pat. No. 10,131,566. The BM fibers formed using the tension-based bandwidth-tuning methods disclosed herein can have a target peak wavelength λpT between 840 nm and 1100 nm.
A target draw tension TT is a draw tension used to establish a target peak wavelength λpT or a target bandwidth BWT at a target wavelength λT.
The cut-off wavelength is denoted λC and is the minimum wavelength at which the optical fiber will support only one propagating mode. For wavelengths below (less than) the cut-off wavelength λC, multimode (or few mode or bimodal) transmission may occur and an additional source of modal dispersion may arise to limit the fiber's bandwidth. Thus, the SM operating wavelength λ has a lower limit of λC. The cut-off wavelength λC is reported herein as a cable cut-off wavelength. The cable cut-off wavelength is based on a 22-meter cabled fiber length. The 22-meter cable cut-off wavelength is typically less than the 2-meter cut-off wavelength due to higher levels of bending and mechanical pressure in the cable environment. The cable cut-off wavelength λC is equal to or below 1300 nm or equal to or below 1260 nm, and further in an example is in the wavelength range from 1160 nm to 1260 nm or in the range from 1160 nm to 1300 nm. Wavelengths at or above the cut-off wavelength λC reside in what is referred to herein as the single mode or SM wavelength range of operation of the optical fiber.
As used herein, the term “modal delay” (also called differential mode delay) is denoted T and is the relative delay measured between the two guided modes of the BM fiber. A detailed testing procedure for measuring the mode delay is defined in TIA-455-220-A: FOTP-220 Differential Mode Delay Measurement of Multimode Fiber in the Time Domain.
Optical Fiber Configurations and Characteristics
The BM fiber 6 can have a number of different physical configurations as set forth below that provide it with desired the optical characteristics for use with SM or FM VCSELs. In an example, the physical configuration of the fiber 6 defines a cut-off wavelength λC below 1260 nm and an MFD in the range from 8.2 μm≤MFD≤11 μm at a wavelength λ of 1310 nm. This ensures that the fiber 6 is SM at a wavelength λ above 1260 nm and is compatible with the standard SM fiber for splicing and connectorization. The fiber 6 also has a bandwidth of at least 1 GHz·km or at least 2 GHz·km or at least 4 GHz·km or in the range from 1 GHz·km to 50 GHz·km for at least one wavelength in the BM wavelength range from 840 nm and 1100 nm, where the fiber operates as an BM fiber. More specifically, the fiber 6 is formed using the tension-based bandwidth-tuning methods disclosed herein to have a target bandwidth BWT at a select or target wavelength λT in the BM wavelength range from 840 nm and 1100 nm.
The fiber 6 has a centerline AC shown by way of example as running in the z-direction. The fiber 6 comprises a glass core region (“core”) 10 that is centered on the centerline AC and that has a radial extent r1 and a gradient relative refractive index Δ1(r) with a maximum value Δ1(r)=A1max on the centerline AC (i.e., at r=0) and decreasing to Δ1(r)=0 at r=r1. The core 10 has a graded index as defined by an alpha value α in the range from 2≤α≤3.
The core 10 is immediately surrounded by a glass cladding region (“cladding”) 50 that extends from the core radius ri out to a cladding outer radius r4. The cladding 50 has an outer surface 52, which constitutes the outer surface of a bare fiber 6. In an example, the fiber 6 includes a protective coating 60 applied to the cladding outer surface 52. In an example, the protective coating 60 is made of a non-glass material 61, such as a polymeric material. When the fiber 6 includes the protective coating 60, it is referred to as a coated fiber.
In the example fiber 6 shown in
In the example shown in
The example shown in
Fiber Drawing System
Aspects of the disclosure are directed to methods that involve adjusting the tension on the fiber 6 during the drawing process to a target tension TT to “tune” the fiber to have an optimal (maximum) or higher bandwidth BWT at a target wavelength λT in the BM range from 840 nm and 1100 nm.
The fiber preform 6P generally comprises silica-based glass. In embodiments in which the fiber preform 6P comprises silica-based glass, the fiber preform 6P may include dopants that increase or decrease the refractive index of the silica-based glass relative to pure silica glass. In some embodiments, the fiber preform 6P comprises a core surrounded by cladding in a scale-up configuration of the fiber 6 as shown in
In the embodiment depicted in
The draw furnace 114 includes a heating element (not shown) that supplies heat to at least a bottom portion of the fiber preform 6P. In some embodiments, the draw furnace 114 may heat the bottom portion of the fiber preform 6P to a draw temperature of about 1700° C. to about 2100° C.
The fiber 6 (or test fiber 6T) is drawn from the heated fiber preform 6P and through the various stages of the drawing system 100 and collected with the fiber take-up system 140. The fiber take-up system 140 utilizes various drawing mechanisms 142 and pulleys 141 to provide a desired amount of tension Tin the axial direction of the fiber 6 as the fiber 6 is drawn through the drawing system 100.
In the embodiment of the drawing system 100 depicted in
Still referring to
The process controller 150 may include a processor 152 communicatively coupled to a memory 154. The memory 154 can contain a (non-transitory) computer readable medium and computer readable and executable instructions, which are executed by the processor to control the process for manufacturing fiber 6 in the manner disclosed herein. In some embodiments, the computer readable and executable instructions are executed by the processor 152 to adjust the tension T to modify the process for manufacturing the fiber 6, as described in further detail below.
In the embodiment depicted in
As noted hereinabove, the peak wavelength determination system 160 determines a measured peak wavelength λp of a test fiber 6T as shown in
In some embodiments, such as the embodiment depicted in
In other embodiments, the peak wavelength determination system 160 may determine the measured peak wavelength λp of the drawn test fiber 6T before the test fiber is separated from the fiber perform 6P. For example, in some embodiments, the peak wavelength determination system 160 may determine the measured peak wavelength λp of the drawn test fiber 6T via an online peak wavelength measurement system that measures the peak wavelength of the drawn test fiber 6T in real time as the test fiber is drawn. Such an online measurement system allows the peak wavelength λp of the drawn test fiber 6T to be measured and process parameters to be adjusted in substantially real time.
With continuing reference to
In some examples, the relative refractive index profile Δ(r) of a sample fiber 6TS is obtained using measurement techniques known in the art. Such a measurement requires only a small length of the sample fiber 6TS, e.g., 10 cm. The optical properties of the drawn fiber 6 are then deduced from the measured relative refractive index profile Δ(r) using methods known in the art.
Forming the BM Fiber
Aspects of the disclosure are directed to using the drawing system 100 of
Experiments were conducted wherein 1 km lengths of example test fibers 6T having the refractive index profile of
Δτ=C1*ΔT=−0.003246*ΔT (EQ. 1)
EQ. 1 can be obtained using a linear fit to the data. Using EQ. 1, the results from test fibers 6T can be used to adjust the tension T when forming the (non-test) fiber 6 to be drawn later so that the later drawn fiber has a reduced or minimum modal delay τ and thus a greater bandwidth for the target wavelength λT. The test fibers 6T and later (non-test) fibers 6 can be from the same preform 6P, or can formed from a closely related preform 6PR (see
For example, if an example test fiber 6T is measured to have a modal delay of τ=0.2 ns/km (corresponding to a bandwidth BW of 1.67 GHz·km according to the relationship BW(τ)=(1/3)·(1/τ)) for a target wavelength λT=850 nm, then increasing the draw tension T by 40 g (i.e., ΔT=40 g), the modal delay τ for the later (non-test) fiber 6 can be reduced to 0.07 ns/km (i.e., Δτ=−0.13 ns/km, which is the modal delay difference induced by the increased draw tension T), which corresponds to a substantially larger bandwidth of BW 4.76 GHz·km, which is almost a factor of 3× improvement in the bandwidth. Different target wavelengths λT of interest will yield similar coefficients C1 for EQ. 1.
Δτ=C2*Δλ.=0.004858*Δλ (EQ. 2)
Different tensions Twill yield similar constant coefficients C2 for EQ. 2.
Equations EQ. 1 and EQ. 2 can be combined as follows so that one can predict the effect of both a tension change ΔT and wavelength change Δλ on the change in the modal delay Δτ:
Δτ=C1*ΔT+C2*Δλ=−0.003246*ΔT+0.004858*Δλ (EQ. 3)
Using EQ. 3, knowing the modal delay τ at one wavelength λ under a specific draw tension T, the modal delay τ at other wavelengths λ and with another draw tension T can be determined. Likewise, EQ. 3 can be used to set a proper tension change ΔT for the non-test fiber 6 relative to the test fiber 6T to have a lower modal delay τ (and thus a higher bandwidth BW) at another wavelength λ.
Example 1: if a test fiber 6T is measured to have a modal delay τ of 0.4216 ns/km at a wavelength λ of 850 nm as formed with a draw tension T of 30 g, then the modal delay τ at a target wavelength ΔT of 880 nm and a draw tension T of 60 g for a non-test fiber 6 can calculated to be:
τ=042−0003246*30+0004858*30=0.4696 ns/km,
which is very close to the measured value as shown in Table 1A, and using the bandwidth equation BW(τ), corresponds to a bandwidth BW(τ) of 0.71 GHz·km, which is close to the corresponding value in Table 1B.
Example 2: if a test fiber 6T is measured to have a modal delay τ of 0.2 ns/km at a wavelength λ of 850 nm with a draw tension T of 30 g, then by EQ. 3 the tension T can be set to a target tension TT of 136 g for a non-test fiber 6 so that the modal delay τ at a target wavelength λT of 880 nm for the non-test fiber is essentially 0 ns/km, which corresponds to a bandwidth BW(τ) approaching infinity. This is interpreted to mean that limitations on the bandwidth are due to effects other than delays between the two propagation modes. Such effects can include optical fiber attenuation, chromatic dispersion, etc.
Measurements of the peak wavelength λp on a test fiber 6T drawn with different tensions T or separate test fibers 6T drawn with different tensions T allows one to find a correlation between the tension T and the peak wavelength λp . In an example, this can include quantifying the relationship for a tension change ΔT and a change in the peak wavelength Δλp.
Δλp=C3*ΔT=0.82*ΔT (EQ. 4)
Using EQ. 4 above, it can be found that every gram of tension change shifts the peak wavelength λp by 0.82 nm in the same direction, i.e., an increase in tension increases the peak wavelength. It should be noted that this relationship is opposite to that of a multimode fiber with a 50 micron core size, i.e., the relationship coefficient (slope) has the opposite sign and a different value. This allows for determining a change in tension ΔT to achieve a target peak wavelength λpT.
The detailed changes in
It is seen that an increase in the draw tension T causes the peak delta Δ1max, the core radius r1 and alpha value α to all increase. Thus, effect of changing the draw tension is to change the profile parameters of the fiber.
The optical properties of the fibers formed using the different tensions per Table 2 are set forth in Table 3. The optical properties considered are the dispersion D (ps/nm/km), the fiber effective area Aeff (μm2), and the MFD (μm), considered for two different wavelengths λ of 1310 nm and 1550 nm.
The optical properties listed in Table 3 vary from one tension to another, but all fall within an acceptable range. This illustrates that changes in draw tension can be used to change the optical properties of a fiber as well as the physical dimensions of the fiber.
Example Data Transmission Systems
An example transmitter 310 includes a light source 320 such as a VCSEL and a transmitter electronics unit 330 configured to operably support the operation of the light source. In an example, the transmitter electronics unit 330 comprises a transmitter electronic integrated circuit (IC) 340 operably supported by a transmitter circuit board (e.g., a printed circuit board or PCB) 350. In an example, the transmitter electronic IC 340 is configured with a VCSEL driver and related electronic components (not shown) as known in the art.
With reference to the close-up inset IN2 of
In an example, the receiver 410 comprises at least one photodetector 420 optically coupled to the output end 504 of the optical fiber link 500. The photodetector 420 is operably supported by a receiver electronics unit 430 configured to operably support the photodetector 420. In an example, the receiver electronics unit 430 comprises a receiver IC 440 operably supported by a receiver circuit board (e.g., a printed circuit board or PCB) 450. In an example, photodetector 420 is configured to convert the optical signals OS encoded on the light 324 into electrical signals ES (see the close-up inset IN4 in
The system 300 is configured by virtue of the fiber 6 for SM optical transmission when the light 324 has a wavelength λ above 1260 nm and BM optical transmission in the system 300 is compliant/compatible with the cut-off wavelength λC and mode field diameter MFD of a standard SM fiber at 1310 nm and 1550 nm for SM operation and is optimized for bandwidth at a target wavelength λT in the BM wavelength range between 840 nm and 1100 nm for BM transmission with the light source 320, which in an example is a SM or FM light source such as a SM or FM VCSEL.
As discussed above, the target wavelength λT can be substantially equal to the wavelength λV of the light source 320 when the optical signals OS are encoded onto a single wavelength λV. In another embodiment, the target wavelength λT can be substantially midway between two wavelengths λV1 and λV2 of the light source 320 when the optical signals OS are encoded in the two different λV1 and λV2.
The systems 300 disclosed herein can be configured to meet a broad range of needs and data transmission applications. In general, the optical signals OS can be modulated using an NRZ modulation format, a PAM4 modulation format or other modulation format used in the art of high-data-rate signal transmission.
For example, for 100 G transmission, most of short distance transmission is based on the QSFP28 form factor with 4×25 G data streams transmitted in and out. The SM/FM VCSELs 320 can be packaged in a VCSEL array 320A to enable 4×25 G transmission using a 25 G NRZ modulation format or a 25 G four-level pulse amplitude (PAM4).
In another example, the light source 320 can comprises a VCSEL driven by 50 G PAM4 electrical signals from the transmitter IC 320 just like a 100 G bidirectional (BiDi) transceiver to achieve 100 G transmission using two wavelengths, for example 850 nm and 900 nm.
In another example, different light sources 320 can be implemented to operate at different wavelengths to enable short wavelength division multiplexing (SWDM) transmission in the manner of conventional 100 G SWDM transceivers. The transceivers can also be implemented to adopt the 400 G transceiver form factor by using one or more of the base technology, such as 50 G PAM4, parallel optics, SWDM to achieve 400 G data rate per transceiver. The fiber and cable structure can be maintained the same as they are used for SM transmission while having the added BM functionality discussed above.
Aspects of the Description
The following Aspects of the description set forth example general properties of the fibers 6 disclosed herein, as well as optical data transmission systems using the fibers, noting that the bandwidth tuning methods can be carried out to form the fibers to have an optimum or near optimum bandwidth (or equivalently, a target peak wavelength) consistent with the described fiber refractive index profile configurations.
Aspect 1 of the description is:
a) establishing a relationship between a change Δτ in a modal delay τ, a change ΔT in a draw tension T and a change Δλ in a bimodal (BM) wavelength λ of light in a BM wavelength range from 840 nm and 1100 nm for a test optical fiber that supports BM operation at the BM wavelength; and
b) drawing the bandwidth-tuned optical fiber by setting the draw tension based on said relationship between the change in the modal delay Δτ, the change in the draw tension ΔT and a change Δλ in the BM wavelength Δτ, so that the bandwidth-tuned optical fiber has a target bandwidth greater than 2 GHz·km at a target wavelength within the BM wavelength range.
Aspect 3 of the description is:
during said drawing of the test fiber, varying an amount of the draw tension T on the test optical fiber to create different sections of the test optical fiber formed using different amounts of the draw tension T;
measuring a modal delay τ for the different sections of the test optical fiber for different BM wavelengths of light within the BM wavelength range; and
quantifying the interrelation between the change Δτ in the modal delay τ, the change ΔT in the draw tension T and the change Δτ in the BM wavelength.
Aspect 4 of the description is:
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Aspect 12 of the description is:
Aspect 13 of the description is:
forming an optical fiber link using the bandwidth-tuned optical fiber formed by the method of any of Aspects 1-12, wherein the optical fiber link has an input end, an output end and a link length LL between the input and output ends, wherein LL<1000 meters;
optically coupling the input end of the optical fiber link to a single mode (SM) VCSEL that emits light having a VCSEL wavelength λV that is substantially equal to the target wavelength and that carries optical signals at a data rate of at least 10 Gb/s; and
optically coupling a photodetector to the output end of the optical fiber link to receive and convert the optical signals to electrical signals.
Aspect 14 of the description is:
forming an optical fiber link using the bandwidth-tuned optical fiber formed by the method of any of Aspects 1-12, wherein the optical fiber link has an input end, an output end and a link length LL between the input and output ends, wherein LL<1000 meters;
optically coupling the input end of the optical fiber link to a single mode (SM) VCSEL that emits light having first and second VCSEL wavelengths λV1 and λV2 that respectively carry first and second optical signals at a data rate of at least 10 Gb/s, and wherein the target wavelength is substantially midway between the first and second VCSEL wavelengths λV1 and λV2; and
optically coupling first and second photodetectors to the output end of the optical fiber link to respectively receive and convert the first and second optical signals to electrical signals.
Aspect 15 of the description is:
a) for a test optical fiber supporting bimodal (BM) operation in a BM wavelength range comprising a plurality of BM wavelengths, establishing a correlation between a modal delay τ, a draw tension T and a BM wavelength λ, the correlation comprising data measured for the test optical fiber;
b) selecting a target draw tension TT for the bandwidth-tuned optical from the correlation, the target draw tension TT selected so that the bandwidth-tuned optical fiber has a target bandwidth BWT at a target BM wavelength λT within the BM wavelength range; and
c) drawing the bandwidth-tuned optical fiber at the target draw tension TT.
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Aspect 29 of the description is:
a) establishing a relationship between a change Δτ in a modal delay τ and a change ΔT in a draw tension T for a bimodal (BM) target wavelength λT of light in a BM wavelength range from 840 nm and 1100 nm for a test optical fiber that supports BM operation at the BM target wavelength λT; and
b) drawing the bandwidth-tuned optical fiber by changing the amount of draw tension according to the relationship between the change Δτ in the modal delay and the change ΔT in the draw tension T so that the bandwidth-tuned optical fiber has a target bandwidth greater than 2 GHz·km at the target wavelength λT.
Aspect 30 of the description is:
Aspect 31 of the description is:
during said drawing of the test fiber, varying an amount of a draw tension T on the test optical fiber to create different sections of the test optical fiber formed using different amounts of the draw tension T;
measuring the modal delay τ for the different sections of the test optical fiber at a target wavelength with the BM wavelength range; and
quantifying the interrelation between the change Δτ in the modal delay τ and a change ΔT in the draw tension T at the target wavelength.
Aspect 32 of the description is:
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Aspect 41 of the description is:
forming an optical fiber link using the bandwidth-tuned optical fiber formed by the method of any of Aspects 29-40, wherein the optical fiber link has an input end, an output end and a link length LL between the input and output ends, wherein LL<1000 meters;
optically coupling the input end of the optical fiber link to a single mode (SM) VCSEL that emits light having a VCSEL wavelength λV that is substantially equal to the target wavelength and that carries optical signals at a data rate of at least 10 Gb/s; and
optically coupling a photodetector to the output end of the optical fiber link to receive and convert the optical signals to electrical signals.
Aspect 42 of the description is:
forming an optical fiber link using the bandwidth-tuned optical fiber formed by the method of any of Aspects 29-40, wherein the optical fiber link has an input end, an output end and a link length LL between the input and output ends, wherein LL<1000 meters;
optically coupling the input end of the optical fiber link to a SM VCSEL that emits light having first and second VCSEL wavelengths λV1 and λV2 that respectively carry first and second optical signals at a data rate of at least 10 Gb/s, and wherein the target wavelength is substantially midway between the first and second VCSEL wavelengths λV1 and λV2 ; and
optically coupling first and second photodetectors to the output end of the optical fiber link to respectively receive and convert the first and second optical signals to electrical signals.
Aspect 43 of the description is:
a) for a test optical fiber supporting bimodal (BM) operation in a BM wavelength range comprising a plurality of BM wavelengths, establishing a correlation between a modal delay τ and a draw tension T for a BM target wavelength λT, the correlation comprising data measured for the test optical fiber; and
b) selecting a target draw tension TT for the bandwidth-tuned optical from the correlation, the target draw tension TT selected so that the bandwidth-tuned optical fiber has a target bandwidth BWT at the BM target wavelength λT; and
c) drawing the bandwidth-tuned optical fiber at the target draw tension TT.
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Aspect 56 of the description is:
during said drawing of the test fiber, varying an amount of a draw tension T on the test optical fiber to create different sections of the test optical fiber formed using different amounts of the draw tension T;
measuring the peak wavelength λp for the different sections of the test optical fiber; and
quantifying the interrelation between the change Δλp in the peak wavelength λp and the change ΔT in the draw tension T.
Aspect 57 of the description is:
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Aspect 66 of the description is:
forming an optical fiber link using the bandwidth-tuned optical fiber formed by any of the methods of any of Aspects 54-65, wherein the optical fiber link has an input end, an output end and a link length LL between the input and output ends, wherein LL<1000 meters;
optically coupling the input end of the optical fiber link to a SM VCSEL that emits light having a VCSEL wavelength λV that is substantially equal to the target peak wavelength λpT and that carries optical signals at a data rate of at least 10 Gb/s; and
optically coupling a photodetector to the output end of the optical fiber link to receive and convert the optical signals to electrical signals.
Aspect 67 of the description is:
forming an optical fiber link using the bandwidth-tuned optical fiber formed by the method of any of Aspects 54-65, wherein the optical fiber link has an input end, an output end and a link length LL between the input and output ends, wherein LL<1000 meters;
optically coupling the input end of the optical fiber link to a SM VCSEL that emits light having first and second VCSEL wavelengths λV1 and λV2 that respectively carry first and second optical signals at a data rate of at least 10 Gb/s, and wherein the target peak wavelength λpT is substantially midway between the first and second VCSEL wavelengths λV1 and λV2; and
optically coupling first and second photodetectors to the output end of the optical fiber link to respectively receive and convert the first and second optical signals to electrical signals.
Aspect 68 of the description is:
a) for a test optical fiber supporting bimodal (BM) operation in a BM wavelength range comprising a plurality of BM wavelengths, establishing a correlation between a peak wavelength λp and a draw tension T, the correlation comprising data measured for the test optical fiber; and
b) selecting a target draw tension TT for the bandwidth-tuned optical from the correlation, the target draw tension TT selected so that the bandwidth-tuned optical fiber has a target bandwidth BWT at the peak wavelength λp ; and
c) drawing the bandwidth-tuned optical fiber at the target draw tension TT.
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The bandwidth-tuning methods disclosed herein result in improving the manufacturing yields the BM fibers disclosed and result in lower manufacturing cost for these optical fibers while also providing the highest-value fibers. In particular, the ability to accurately define the fiber bandwidth at a target wavelength means that spools of the BM fiber will more readily meet target design parameters and thus more readily meet target optical performance. This means that the spools of the bandwidth-tuned BM fiber will fall into a higher-priced category of fiber. This is in contrast to the usual practice of measuring the fiber bandwidth of BM fibers after the fact and then categorizing the prices of the spools based on measured bandwidth performance, which varies widely from spool to spool using conventional fiber drawing techniques.
It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the claims.
This Application claims priority under 35 USC § 119(e) from U.S. Provisional Patent Application Ser. No. 62/880,242, filed on Jul. 30, 2019, and which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62880242 | Jul 2019 | US |
