LOW BEND LOSS SINGLE MODE OPTICAL FIBER

[0001] This application claims the benefit of priority under 35 U.S.C. § 1 19 of U.S.

Provisional Application Serial No. 62/413,605, filed on October 27, 2016, the content of which is relied upon and incorporated herein by reference in its entirety.

Field

[0002] The present invention relates to optical fibers having low bend losses and suitable for use with silicon photonic devices.

Technical Background

[0003] The need for greater bandwidth and higher data transmission rates has motivated efforts to develop next-generation platforms for information storage and delivery. It is widely believed that optical information systems will provide superior performance to today's microelectronics-based systems. Integrated optical systems based on silicon photonics are a leading replacement technology for microelectronic systems. Silicon photonics interfaces with standard CMOS technologies and WDM (wavelength division multiplexing) to convert electrical signals to optical signals, to transmit optical signals, and to reconvert optical signals to electrical signals. In disaggregated systems, transfer of signals between units occurs through optical links that provide high bandwidth and high data transfer rates.

[0004] Data centers with disaggregated architecture are being proposed for future data centers, involving use of silicon photonics and WDM technology. While a number of these systems have focused on using multimode optical fibers, system architectures using single- mode fibers are also contemplated.

[0005] Consequently, there is a need for suitable optical fibers for such data center applications and like applications

SUMMARY

[0006] Disclosed herein are optical waveguide fibers comprising:

a core region comprising an outer radius ri and 3.0 < ri < 7.0 microns and a relative refractive index ΔΙ _ΠΒΧ and 0.32% < ΔΙ _ΠΗΧ < 0.5%; a depressed index cladding region surrounding the core region, the depressed index cladding region comprising an outer radius r ₃ and a relative refractive index Δ ₃ less than -0.2%, and an absolute volute of trench volume V ₃ such 45 %A-micron ² < | V ₃ |≤ 200 %Δ- micron ² ;

a first outer cladding region surrounding the depressed index cladding region, the outer cladding region comprising a relative refractive index Δ ₄ and an outer radius r ₄ ; and a second outer cladding layer a relative refractive index Δ5, said second outer cladding region comprising silica based glass doped with 5 to 20 wt% titania and having a thickness TM, such that 2 micron < T _M ≤ 30 microns, the second outer layer having an outer radius r ₅ of not greater than 65 microns;

wherein the optical fiber has a mode field diameter at 1550 nm (MFD1550) and 8.3 microns < MFD1550≤ 10.5 microns, a single mode cutoff wavelength <1550 nm when bent 1 turn around a 2.5 mm radius mandrel, an effective area at 1550 nm of at least 65 micron ² and less than 85 micron ² _, and a bending loss at 1550 nm as determined by the mandrel wrap test using a mandrel comprising a radius of 2.5 mm-of < 1.0 dB/turn.

[0007] According to at least some exemplary embodiments of the optical fiber disclosed herein, the single mode cutoff wavelength is between 1 lOOnm and 1450 nm when the fiber bent 1 turn around a 2.5 mm radius mandrel. According to at least some exemplary embodiments disclosed herein 60 %A-micron ² < | V ₃ | < 200 %A-micron ² .

[0008] According to at least some exemplary embodiments disclosed herein the fiber exhibits bending loss at 1550 nm as determined by the mandrel wrap test using a mandrel comprising a radius of 2.5 mm-of < 0.55 dB/turn, and in some embodiments < 0.4dB/turn, in some embodiments < 0.2 dB/turn, for example < 0.1 dB/turn, or even < 0.01 dB/turn.

[0009] According to at least some exemplary embodiments disclosed herein the fiber the outer radius of the core region is 3.0 < rl <6, and the trench volume V ₃ is such that 70 %A- micron ² < | V ₃ |≤ 150%A-micron ² .

[0010] According to at least some exemplary embodiments 80 %A-micron ² < | V ₃ | < 200%A-micron ² , and in some emodiments 100 %A-micron ² < | V ₃ | <150%A-micron ² .

According to at least some exemplary embodiments 60 %A-micron ² < | V ₃ | < 140%Δ- micron ² , and in some embodiments 70 %A-micron ² < | V ₃ | <140%A-micron ² . In some embodiments 80 %A-micron ² < | V ₃ | <140%A-micron ² . [0011] According to at least some exemplary embodiments 10 microns < rs <63 microns for example 30 microns < rs <63 microns, or 30 microns < rs <62.5 microns, and in some embodiments 30 microns < r ₅ <50 microns. According to at least some exemplary embodiments 40 microns < <62.5 microns. For example, in some exemplary embodiments, the outer radius r ₅ of the second outer cladding is 62.5, 60, 55, 50, 42, 41.7, 35, 31.25, or 30 microns.

[0012] According to at least some exemplary embodiments the optical fiber has a fiber cutoff wavelength <1550 nm when bent 1 turn around a 2.5 mm radius mandrel, an effective area at 1550 nm of at least 65 micron ² and less than 85 micron ² , and a bending loss at 1550 nm as determined by the mandrel wrap test using a mandrel comprising a radius of 2.5 mm-of ≤ 1.0 dB/turn.

[0013] According to at least some exemplary embodiments the optical fiber has a 22m cable cutoff wavelength less than 1550 nm. According to at least some exemplary embodiments the optical fiber has a 22m cable cutoff wavelength less than 1300 nm, for example between 1000 nm and 1350 nm, for example between 1000 nm and 1300 nm.

According to at least some exemplary embodiments the optical fiber has a 22 m cable cutoff wavelength between 1200 nm and 1550 nm, for example between 1200 nm and 1350 nm.

[0014] According to at least some exemplary embodiments the optical fiber the second outer cladding layer comprises 5 to 15 wt% titania, and 3 micron < TM≤ 15 microns.

[0015] In some exemplary embodiments 2 micron < TM≤ 20 microns. In some exemplary embodiments 2 micron < TM≤ 15 microns. In some exemplary embodiments 3 micron < TM < 15 microns. In some exemplary embodiments 2 micron < TM≤ 10 microns. In some embodiments 2 micron < TM≤ 5 microns.

[0016] In some embodiments the mode field diameter at 1550 nm (MFD155 ₀ ) is 9 microns < MFD1550≤ 10 microns. In some embodiments the mode field diameter at 1550 nm (MFD1550) 9.5 microns < MFD1550≤ 10.3 microns.

[0017] In some embodiments the relative refractive index of the depressed index cladding region, Δ ₃ , is -0.2% < Δ ₃ ≤ -0.7%, and in some embodiments -0.3% < Δ ₃ ≤ -0.5%.

[0018] According to the exemplary described herein the core region comprises a, and 10 < a <100 . However, in some exemplary embodiments 1 < a <10.

[0019] According to at least some exemplary embodiments disclosed herein the fiber includes a coating surrounding the second outer cladding layer, the coating comprises: a primary coating P having a Young's modulus 0.1 to 1 MPa; and a secondary coating S having a Young's modulus of 1100 MPa to 2500 MPa, wherein the secondary coating has an outer coating diameter of not greater than 260 microns, in some embodiments not greater than 250 nm, and in some embodiments not greater than 242 microns, for example less than 210 microns

[0020] According to at least some exemplary embodiments a micro-optic device comprises:

a. a silicon-photonics chip;

b. an optical fiber having a section bent to a bend radius of < 5mm; the fiber comprising:

a core region comprising an outer radius ri in the range from 3.0 to 7.0 microns and a relative refractive index ΔΙ _ΠΒΧ in the range from 0.32% to 0. 5%;

a depressed index cladding region surrounding the core region, the depressed index cladding region comprising an outer radius r ₃ and a relative refractive index Δ ₃ less than -0.2%, and a trench volume V ₃ such that of 45%A-micron ² < | V ₃ | ≤ 200 %A-micron ² ; a first outer cladding region surrounding the depressed index cladding region, the outer cladding region comprising a relative refractive index Δ ₄ and an outer radius r ₄ ; and a second outer cladding layer a relative refractive index Δ ₅ the second outer cladding region comprising silica based glass doped with 5 to 20 wt% titania and having a thickness TM, such that 3 micron < T _M ≤ 30 microns, the second outer layer having an outer radius r ₅ of not greater than 65 microns;.

wherein the optical fiber has a mode field diameter at 1550 nm (MFD1550) is 8.3 microns < MFD155 ₀ ≤ 10.5 microns, a single mode cutoff wavelength <1550 nm when bent 1 turn around a 2.5 mm radius mandrel, an effective area at 1550 nm of at least 65 micron ² and less than 85 micron ² , and a bending loss at 1550 nm as determined by the mandrel wrap test using a mandrel comprising a radius of 2.5 mm-of < 1.0 dB/turn.

[0021] In some embodiments the optical fiber has a section that is bent to a bend radius r _b of not greater than 3 mm, for example 0.5mm to 2.5 mm. In some embodiments the bend radius r _b is 2.5 mm> r _b >l mm, and in some embodiments 2.5 mm> r _b >1.5mm.

[0022] In some embodiments the optical fiber has a section that is bent to a bend radius of

< 2.5 mm, and the fiber exhibits bending loss at 1550 nm as determined by the mandrel wrap test using a mandrel comprising a radius of 2.5 mm-of < 0.55 dB/turn, and in some embodiments < 0.1 dB/turn, or even of < 0.01 dB/tum. In some embodiments the optical fiber has a section that is bent to a bend radius of < 2 mm, and the fiber exhibits bending loss at 1550 nm as determined by the mandrel wrap test using a mandrel comprising a radius of 2 mm-of < ldB/turn, for example < 0.55 dB/turn, and in some embodiments < 0.1 dB/turn, or even < 0.01 dB/turn.

[0023] Reference will now be made in detail to the present preferred embodiments, examples of which are illustrated in the accompanying drawings.

Brief Description of the Drawings

[0024] FIG. 1 illustrates an optical fiber coupled to a Si photonic waveguide through a ferrule connector with a curved hole for supporting a section of the optical fiber;

[0025] FIG. 2A a cross-sectional view of an example optical fiber according to the disclosure;

[0026] FIG 2B. illustrates schematically a refractive index profile corresponding to the optical fiber of FIG. 2A;

[0027] FIG. 3 illustrates the relationship between minimum bend radius (mm) and fiber cladding diameter (microns); and

[0028] FIG. 4 illustrates refractive index profile of another optical waveguide fiber disclosed herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0029] Additional features and advantages will be set forth in the detailed description which follows and will be apparent to those skilled in the art from the description or recognized by practicing as described in the following description together with the claims and appended drawings.

Definitions and terminology

[0030] The "refractive index profile" is the relationship between refractive index or relative refractive index and the radial position within the waveguide fiber. The radius for each segment of the refractive index profile is given by the abbreviations r _1; r ₂ , r ₃ , r ₄ , etc. and lower and upper case are used interchangeably herein (e.g., ri is equivalent to Ri).

[0031] The term "relative refractive index percent" (also referred to herein as "relative refractive index", and "refractive index delta") is defined as Δ% = 100 x ¾ ² -n _c ² )/2ni ² , and as used herein, unless stated otherwise, n _c is the average refractive index of the first outer cladding region 40 (which in some embodiments is undoped silica). As used herein, the relative refractive index is represented by Δ and its values are given in units of "%", unless otherwise specified. The terms: delta, Δ, A%, %A, delta%, %delta and percent delta may be used interchangeability herein. That is, as used herein, relative refractive index percent (or relative refractive index, or refractive index delta) of a given fiber region is measured relative to undoped silica. In cases where the refractive index of a region is less than the average refractive index of undoped silica, the relative index percent is negative and may be referred to as having a depressed region or depressed index. In cases where the refractive index of a region is greater than the average refractive index of undoped silica, the relative index percent is positive. An "updopant" is herein considered to be a dopant which has a propensity to raise the refractive index relative to pure undoped S1O2. A "downdopant" is herein considered to be a dopant which has a propensity to lower the refractive index relative to pure undoped S1O2. Examples of updopants include GeC>2 (germania), AI2O3, P2O5, T1O2, CI, Br. Examples of down dopants include fluorine and boron.

[0032] "Chromatic dispersion", herein referred to as "dispersion" unless otherwise noted, of a waveguide fiber is the sum of the material dispersion, the waveguide dispersion, and the inter-modal dispersion. In the case of single mode waveguide fibers the inter-modal dispersion is zero. Zero dispersion wavelength is a wavelength at which the dispersion has a value of zero. Dispersion slope is the rate of change of dispersion with respect to wavelength.

[0033] "Effective area" is defined as:

A _eff = 2n (Jf ² r dr) ² /(Jf ⁴ r dr),

where the integration limits are 0 to∞, and f is the transverse component of the electric field associated with light propagated in the waveguide. The effective area A _e ff depends on the wavelength of the optical signal and is reported herein for wavelengths of 850 nm, 980 nm, 1060 nm and 1550 nm. As used herein, unless otherwise noted, "effective area" or "A _e fr" refers to optical effective area at a wavelength of 1550 nm.

[0034] The term "alpha parameter" or "a-parameter" or "alpha value" or just "a" refers to a parameter used to define a relative refractive index profile of the core, expressed in terms of A(r) which is in units of "%", where r is radius, which follows the equation,

Δ(Γ) = Δ(Γ ₀ )(1 -[ I r-r ₀ 1 / (r r ₀ )] ^a ), where r ₀ is the point at which Δ(Γ) is maximum (also referred herein as Δ _{; ;;ΔΛ} ), ri is the point at which Δ(Γ)% is zero, and r is in the range r; < r < r _f , where Δ is defined above, η is the initial point of the a-profile, rf is the final point of the a-profile, and a is an exponent which is a real number. In some embodiments of the optical fiber described herein (for example in fibers that do not have a centerline dip in the fiber core) Δ(Γ ₀ ) = Δ(Γ;). In some embodiments ri≡ r _£

[0035] The terms "trench" and "depressed index cladding region" are used interchangeably herein and refer to a cladding region that has a minimum relative refractive index that is lower than that of the adjacent regions that are in contact therewith. The trench volume V3 is defined herein as wherein Δ _3-2 (Γ) = Δ ₃ - Δ ₂ (Γ) for a given radial position r situated between the radial positions of r ₃ and r ₂ , where r ₂ is the inner radius of cladding region 30 and r ₃ is the outer radius of cladding region 30 Thus, the limits of integration for V ₃ are from r ₂ to

Γ3.

The terms "μπι" and "microns" are used interchangeably herein.

[0037] The mode field diameter (MFD) is measured using the Peterman II method wherein,

2w = MFD, and w ^! = (2/f ² r dr/J[df/d r] r dr), the integral limits being 0 to∞, and MFD1550 is mode field diameter at 1550 nm wavelength.

[0038] The bend resistance of a waveguide fiber can be gauged by induced attenuation under prescribed test conditions, for example by deploying or wrapping the fiber around a mandrel of a prescribed diameter, e.g., by wrapping 1 turn around a either a 6 mm, 10 mm, or 20 mm or similar diameter mandrel (e.g. "1x10 mm diameter macrobend loss" or the "1x20 mm diameter macrobend loss") and measuring the increase in attenuation per turn.

[0039] Fiber cutoff (also referred to herein as fiber cutoff wavelength) is measured by the standard 2m fiber cutoff test, FOTP-80 (EIA-TIA-455-80), to yield the "fiber cutoff wavelength", also known as the "2m fiber cutoff or "measured cutoff. The FOTP-80 standard test is performed to either strip out the higher order modes using a controlled amount of bending, or to normalize the spectral response of the fiber to that of a multimode fiber. [0040] By fiber cutoff wavelength when bent 1 turn around a 2.5 mm radius mandrel we mean the fiber cutoff wavelength as measured by the standard 2m fiber cutoff test, FOTP-80 (EIA-TIA-455-80) deployed with an additional single bend around a 2.5 mm radius mandrel situated within 20 cm distance from the end of the fiber where the light is launched.

Similarly, by fiber cutoff wavelength when bent 1 turn around a 2mm radius mandrel we mean the fiber cutoff wavelength as measured by the standard 2m fiber cutoff test, FOTP-80 (EIA-TIA-455-80) deployed with an additional single bend around a 2 mm radius mandrel situated within 20 cm distance from the end of the fiber where the light is launched.

[0041] By cabled cutoff wavelength, or "cabled cutoff as used herein, we mean the single mode cutoff as measured by the 22 m cabled cutoff test described in the EIA-445 Fiber Optic Test Procedures, which are part of the EIA-TIA Fiber Optics Standards, that is, the

Electronics Industry Alliance - Telecommunications Industry Association Fiber Optics Standards.

[0042] By cable cut off with a 2.5mm radius bend, we mean the single mode cutoff as measured by the 22 m cabled cutoff test described in the EIA-445 Fiber Optic Test

Procedures measured with an additional single bend around a 2.5 mm radius mandrel.

Similarly, by cable cut off with a 2 mm radius bend, we mean the single mode cutoff as measured by the 22 m cabled cutoff test described in the EIA-445 Fiber Optic Test

Procedures measured with an additional single bend around a 2 mm radius mandrel.

[0043] Unless otherwise noted herein, optical properties (such as dispersion, dispersion slope, etc.) are reported for the LP01 mode.

[0044] One challenging problem is to couple light from a silicon photonic device to a single mode fiber with low cost. An attractive approach is to use a grating to couple the light out of the surface of a silicon (Si) waveguide to an optical fiber as shown in FIG. 1. Because the tight space above the Si waveguide (about 4 - 5 mm, or less), the fiber needs to be bent with a quarter of turn at bend radius of approximately 3 mm or less, for example < 2.5mm. The bent fiber connector may be, for example, a glass or ceramic ferrule with curved hole. The fiber is stripped of the coating down to the glass cladding, and the stripped portion of the fiber is inserted into the hole and glued with an epoxy. The ordinary comparative fibers fiber can be easily damaged during stripping and subsequent the fiber insertion process through the hole in the coupling device 7 (connector 7), causing fiber mechanical failure due to fiber break, which results from surface flows undergoing stress due to being under stress because it is bent to a such a small diameter. Thus in comparative fibers, under stress, the surface defects would propagate deeper into glass, causing mechanical failure (fiber break) and/or shortened life cycle. However, the optical fibers 100 disclosed herein can be coupled to silicon photonic device even when bent to radii of 3mm or less without mechanical failure due or fiber break. Optical fibers 100 advantageously can be advantageously inserted through the hole in the coupling device 7 that has a bend radius r _b of 2.5mm or less (e.g., lmm< r _b ≤ 2 mm, and in at least some embodiments even 0.5 mm< ¾≤ 2 mm), without causing fiber mechanical failure due to fiber break, and thus can be bent to a such a small diameter without substantial loss of strength or significant loss of lifetime. Optical fibers 100 advantageously have improved surface damage resistance and low bending loss.

[0045] Optical fibers 100 disclosed herein are capable of exhibiting an effective area Aeff at 1550 nm which is greater than about 55 microns ² , preferably between 60 and 85 microns ² . In some preferred embodiments, the effective area at 1550 nm is between about 75 and 82 micron ² .

[0046] FIG. 2A is a cross-sectional view of one exemplary embodiment of the optical fiber (100). The optical fiber (100) comprises a central core region 10 centered around a central axis AC, and an optional inner cladding region 20, a third region 30 in the form of a trench and thus referred to as "trench region" 30 or "depressed cladding region," and a fourth region 40 making up a first outer cladding and thus referred to as an "outer cladding region" 40 (also referred to herein as a first outer cladding region 40). The optional inner cladding 20, the trench region 30, and the first outer cladding region 40 collectively define a cladding section 50 (also to referred herein as "cladding" (50). In the exemplary embodiments described herein cladding regions 20 30, 40 of the cladding 50 are preferably glass and is surrounded by a mechanical reliability layer ML (the outer most cladding layer or region 60) that comprises titania (T1O2) doped silica. The outer cladding layer 60 (i.e., the mechanical stability layer M _L ) may be surrounded by a coating 70 that includes a primary coating P and a secondary coating S, which can be stripped from a fiber 100 prior to bending and of the fiber 100 to a silicon-photonic device.

FIG. 2B illustrates schematically relative refractive index profile Δ(%) versus fiber radius r of one exemplary embodiment of the optical fiber (100). The plot is from the central axis AC radially outward, i.e., from r = 0. The core region 10 has outer radius ri and relative refractive index Δι. The inner cladding region 20 extends from the radial position ri to a radial position r ₂ and has relative refractive index Δ ₂ . The trench region 30 (i. e., the depressed index cladding region) extends from the radial position r ₂ to a radial position r ₃ and has relative refractive index Δ ₃ . The outer cladding region 40 extends from the radial position r ₃ to radial position r ₄ and has relative refractive index Δ ₄ . The second outer cladding 60 (i. e., the outer most cladding region 60) surrounds the first outer cladding region 40. The second outer cladding region 60 extends from the radial position r ₄ to radial position rs and has relative refractive index Δ5 > Δ4. In the fiber embodiments disclosed herein the outer diameter ds of the second outer cladding 60 (ds=2rs) is not greater than 130 microns, for example, not greater than 126 microns, not greater than 125 microns, and in some embodiments not greater than 100 microns or even not greater than 82 microns. For example, in some embodiments ds is not greater than 80 microns, not greater than 75 microns, not greater than 60 microns, not greater than 5 microns, or not greater than 50 microns. In some embodiments 20 microns < ds <126 microns. In some embodiments 20 microns < ds <110 microns, or 20 microns < rs <100 microns, or 20 microns < rs <90 microns, or even 20 microns < rs <80 microns. In some embodiments 20 microns < rs <70 microns, in some embodiments 20 microns < rs <50 microns, and in some embodiments 60 microns < rs <126 microns. In some embodiments 30 microns < ds <126 microns. In some embodiments 30 microns < ds <1 10 microns, or 30 microns < ds <100 microns, 30 microns < rs <90 microns, or even 30 microns < rs <80 microns. In some embodiments 30 microns < rs <70 microns. In some embodiments 30 microns < rs <50 microns. . In some embodiments 40 microns < ds <126 microns. In some embodiments 40 microns < ds <100 microns, 40 microns < ds <90 microns or even 40 microns < rs <80 microns. In some embodiments 40 microns < rs <70 microns, and in some embodiments 40 microns < rs <60 microns. According to some embodiments the diameter ds of the cladding layer 60 is, for example, 50 to 125 microns, or 60 to 125 microns; and in some embodiments 70 to 100 microns. In some embodiments 60 microns < ds <126 microns, 60 microns < ds <125 microns, in some embodiments in some embodiments 60 microns < ds <110 microns, and in some embodiments 80 microns < ds <125 microns.

[0047] A coating 70 surrounds the cladding layer 60. The coating 70 extends to an outer diameter r ₆ .

[0048] As stated above, optical fibers 100 are capable of providing low bend loss at tight radii of curvature and high resistance to surface damage for bent fiber connector applications, for example when used with a ferrule connector 5 coupling it to a silicon photonics chip 7, as shown in FIG. 1. In FIG. 1, inside the connector 5 the optical fiber is bent to about quarter of turn at a bend radius r _b of about 3 mm or less (e.g. , 0.5 mm < r _b < 3 mm, 1 mm < r _b < 2.5 mm, 1 mm < r _b ≤ 2 mm, 1 mm < r _b < 1.5mm, or 1mm < r _b < 2 mm) and coupled to a grating 7G situated within a Si waveguide 7 '. According to at least some the embodiments of the optical fiber 100 disclosed herein, the optical fiber 100 has a single mode cutoff wavelength <1550 nm when bent 1 turn around a 2.5 mm radius mandrel, and also has an effective area at 1550 nm of at least 65 micron ² and less than 85 micron ² , and bending loss at 1550 nm as determined by the mandrel wrap test using a mandrel comprising a radius of 2.5 mm-of < 1.0 dB/turn.

[0049] According to at least some of the embodiments of the optical fiber 100 disclosed herein, the bending loss at 1550 nm around a mandrel with a bend radius r _b of 2.5 mm is < 0.8 dB/turn, in some embodiments < 0.5 dB/turn, in some embodiments < 0.4 dB/turn, in some embodiments < 0.2 dB/turn, in some embodiments < 0.1 dB/turn, in some embodiments < 0.05 dB/turn, and in some embodiments < 0.01 dB/turn. Also, according to at least some the embodiments of the optical fiber 100 disclosed herein, the bending loss at 1550 nm with a bend radius r _b of 2 mm is < 1 dB/turn, in some embodiments < 0.5 dB/turn, and in some embodiments < 0.4 dB/turn. Also, according to at least some the embodiments of the optical fiber 100 disclosed herein the bending loss at 1550 nm with a bend radius r _b of 2 mm is < 0.2 dB/turn, in some embodiments < 0.1 dB/turn, and in some embodiments < 0.05 dB/turn. Also, according to at least some the embodiments of the optical fiber 100 disclosed herein the bending loss at 1550 nm with a bend radius r _b of 2 mm is < 0.02 dB/turn, and in some embodiments < 0.01 dB/turn. Also, according to at least some the embodiments of the optical fiber 100 disclosed herein, the bending loss at 1550 nm with a bend radius r _b of 1.5 mm is < 1 dB/turn, in some embodiments < 0.5 dB/turn, and in some embodiments < 0.4 dB/turn, and in some embodiments < 0.2 dB/turn. Also, according to at least some the embodiments of the optical fiber 100 disclosed herein, the bending loss at 1550 nm with a bend radius r _b of 1 mm is < 1 dB/turn, in some embodiments < 075 dB/turn, in some embodiments < 0.5 dB/turn, and in some embodiments < 0.4 dB/turn, and in some embodiments < 0.2 dB/turn.

[0050] The outer most cladding layer 60 (also referred to herein as layer M _L, or the second outer cladding layer) comprises T1O2 (titania) and protects the outer glass surface of the first outer cladding 40 also referred to herein as the (first outer cladding region 40) from damage during handling and also during stripping of the coating 70, as well as improves fiber' s mechanical reliability, especially in the presence of abrasions to the glass surfaces as can happen during assembly of miniature glass components.

[0051] In the profile of FIG. 2B, the trench region 30 in the cladding may have a constant refractive index that is less than the refractive indices of the inner cladding region 20 and the first outer cladding region 40. Core region 10 of the optical fiber 100 has the highest relative refractive index than fiber regions 20, 30 or 40. In some embodiments the core region 10 may include a lower index region at or near the centerline (known in the art as a "centerline dip"), which not shown in FIG. 2B.

[0052] It should be noted that the inner cladding region 20 is optional and may be eliminated as noted hereinabove. When inner cladding region 20 is missing, depressed index region 30 is directly adjacent core region 10. The relative ordering of relative refractive indices Δ _1; Δ ₃ , and Δ4 satisfy the conditions Δι > Δ4 > Δ ₃ .

[0053] In the embodiments disclosed herein the relative ordering of relative refractive indices Δι, Δ ₂ , Δ ₃ , and Δ4 satisfy the conditions Δι > Δ4 > Δ3 and Δι > Δ ₂ > Δ ₃ . The values of Δ ₂ and Δ4 may be equal or either may be greater than the other, but both Δ ₂ and Δ4 are between Δι and Δ ₃ .

[0054] According to the embodiments of the optical fiber 100 described herein, the maximum relative refractive index Δι of the core region 10 (relative to Δ4 of the the outer cladding region 40) is between 0.3 % to 0.6%, more preferably between 0.32% to 0.5%. According to some embodiments the core region 10 has radius ri is between 3 to 6 μιτι, more preferably between 4 μιτι and 5 μιτι. The core region 10 can have a step index profile with a >10, or alternatively can exhibit a graded index profile with a < 10, for example a< 5 (e.g., 1 <a< 10, or 1 < a < 5). The relative refractive index Δ ₂ of the inner cladding region 20 (relative to Δ ₄ of the the outer cladding region 40) is between -0.05 to 0.05%. The inner cladding region 20 can be pure silica glass, or silica glass doped with an up-dopant such as CI, or Ge0 ₂ . The minimum relative refractive index Δ3 of the trench region 30 (relative to Δ4 of the the outer cladding region 40) is between -0.2 to -0.7%, and in some embodiments between -0.3 to -0.5%. In the exemplary embodiments the trench region 30 is silica based glass doped with boron or fluorine. The width w of the trench region 30 (w= r ₃ - r ₂ ) is between 3 to 20 microns, in some embodiments between 4 and 15 microns. The outer cladding region 40 can be pure silica glass, or silica glass doped with an up-dopant such as CI, or GeC>2. The cladding layer 60 (also referred to herein as "outer most cladding layer ", the second outer cladding layer, or a "mechanical reliability layer") comprises 5 to 20 wt. % T1O2, and in some embodiments, between 5-15 wt. % T1O2. The outer most cladding layer 60 has a radial thickness T _M between 3 to 30 microns, and in some embodiments, between 5 to 15 microns. The outer most cladding layer 60 improves mechanical stability/reliability of the fiber 100. In at least some embodiments As> Δι.

[0055] The outer cladding region 40 of the fiber 100, surrounds the lower index trench region 30. In the exemplary embodiments described herein the outer cladding starts at a radius Γ3 has an outer radius n. The outer cladding region 40 of the fiber 100 comprises relative refractive index Δ4 which is higher than the relative refractive index Δ3 of trench region 30 thereby forming a region which is "updoped" with respect to trench region 30. The trench region 30 is preferably downdoped relative to pure silica, for example with fluorine or boron. Note, however that the outer cladding region 40 may be either pure silica, or may be updoped relative to pure silica.

[0056] The absolute value | V3 | of the volume V3 of the trench region 30 may be greater than 45 % Amicron ² , and in some embodiments may be greater than 50% Amicron ² . The absolute value for the volume V3 of the trench region 30 is in some embodiments is at least 60% Amicron ² , and in some embodiments is at least 80% Amicron ² . In some embodiments, the absolute value for the volume V3 of the first cladding region (2) is less than 200% Amicron ² , in some embodiments less than 150 % Amicron ² , and in some other embodiments less than 125 % Amicron ² According to some embodiments the absolute value of the volume V3 is between about 45 and 200 % Δ microns ² , for example between 60 and 200 % Δ microns ² , or for example between 60 and 190 % Δ microns ² , or between 45 and 175 % Δ microns ² , or between 60 and 175 % Δ microns ² , for example between 45 and 150 % Δ microns ² , or between 60 and 150 % Δ microns ² , between 80 and 150 % Δ microns ² , or between 60 and 125 % Δ microns ² , or between 80 and 125 % Δ microns ² According to some embodiments 80 %A-micron ² < | V3 | < 200%A-micron ² microns ² According to some embodiments 70 %A-micron ² < | V3 | < 150%A-micron ² According to some embodiments 100 %A-micron ² ≤ | V ₃ | ≤150%A-micron ² . [0057] The core and cladding regions of fiber 100 may be produced in a single-step process or multi-step process by methods which are well known in the art. Suitable methods include: the double crucible method, rod-in-tube procedures, and doped deposited silica processes, also commonly referred to as chemical vapor deposition ("CVD") or vapor phase oxidation. A variety of CVD processes are known and are suitable for producing the core and cladding layer used in the coated optical fibers of the present invention. They include external CVD processes, axial vapor deposition processes, modified CVD (MCVD), inside vapor deposition, and plasma-enhanced CVD (PECVD).

[0058] The glass portion of the coated fibers may be drawn from a specially prepared, cylindrical preform which has been locally and symmetrically heated to a temperature sufficient to soften the glass, e.g., a temperature of about 2000 °C for a silica glass. As the preform is heated, such as by feeding the preform into and through a furnace, a glass fiber is drawn from the molten material. See, for example, U.S. Patent Nos. 7,565,820; 5,410,567; 7,832,675; and 6,027,062; the disclosures of which are hereby incorporated by reference herein, for further details about fiber making processes.

[0059] FIG. 3 illustrates a plot of modeled and measured minimum fiber bend radius as a function of fiber diameter (outer diameter of the cladding region 60). The plot line represents a 10 ^"10 probability of failure over a 5 year lifetime for an 82° bend. The modeled results indicate the long term reliability limits of narrower cladding diameter fibers. The

calculations for fiber reliability are for the optical fibers that can be used in short reach (fiber length 1 is <10 m, for example <1 m, and in some embodiments between 1 cm and 1 m, for example 1 cm to 50 cm, or even 1cm to 25cm) interconnects within data centers, especially hyperscale data centers. The short reach interconnects should have a fairly short usage lifetime (3-5 years), which is the same lifetime as the electronic equipment they will be connected to. These very short reach interconnects can be deployed within a rack or even within a server. (This is distinct from the optical fiber for use in trunk cables, etc., which is designed for operations over longer lengths (>50m, e.g., lOOm-lkm), and which should have a longer usage lifetime.) The measured results (shown by circles in FIG.3) are in agreements with the modeled results.

[0060] FIG. 3 illustrates that when the optical fiber 100 has an outer diameter of the cladding layer 60 of 125 mm the optical fiber 100 can be bent to a bent radius of about 2.3mm with 10 ^" probability of failure over a 5 year lifetime (i.e., the expectant life time of the bent fiber 100 is at least 5 years). Similarly, FIG. 3 illustrates that when the optical fiber 100 has an outer diameter of the cladding layer 60 of 100 microns the optical fiber 100 can be bent to a bent radius of about 1.9 mm with 10 ^"10 probability of failure over a 5 year lifetime (i.e., the expectant life time of the bent fiber 100 is at least 5 years). In addition, FIG. 3 illustrates that when the optical fiber 100 has an outer diameter (i.e., the diameter ds of the cladding layer 60) of 62.5 microns, the optical fiber 100 can be bent to a bent radius of about 1.2 mm (with 10 ^"10 probability of failure over a 5 year lifetime (i.e., the expectant life time of the bent fiber 100 is at least 5 years). FIG. 3 also illustrates that when the optical fiber 100 has an outer diameter of the cladding layer 60 of about 53 microns or less (e.g., 40-52 microns), the optical fiber 100 can be bent to a bent radius of about 1 mm or less with about 10 ^"10 probability of failure over a 5 year lifetime (i.e., the expectant life time of the bent fiber 100 is at least 5 years).

[0061] FIG. 3 also indicates that when the cladding layer 60 the optical fiber 100 has an outer diameter ds of about 40 to 50 microns (or 20-50 microns), the optical fiber 100 can be bent to a bent radius of about 0.75 mm with 10 ^"10 probability of failure over a 5 year lifetime (i.e., the expectant life time of the bent fiber 100 is at least 5 years). FIG. 3 also indicates that when the cladding layer 60 the optical fiber 100 has an outer diameter ds of 20-30 microns, the optical fiber 100 can be bent to a bent radius of about 0.5 mm with 10 ^"10 probability of failure over a 5 year lifetime (i.e., the expectant life time of the bent fiber 100 is at least 5 years). Thus, the embodiments of the optical fibers 100 with an outer cladding layer 60 having an outer diameter of ds of not greater than 125 microns, for example not greater than 100 microns, or not greater than 82 microns (e.g., 80, 75, 65, 62.5, 50, 40, 30, 25, or 20 microns, or therebetween) can be bent to very tight bend radii r _b and advantageously provide improved the mechanical reliability under tight bending conditions.

[0062] Based on our analysis the optical fibers 100 with an outer cladding layer 60 having an outer diameter of ds of not greater than 126 microns can be bent to very tight bend radii r _b and advantageously provide improved the mechanical reliability under tight bending conditions even in the presence of small abrasions to the glass surfaces,, as can happen during assembly of miniature glass assemblies, or due to stripping off of the coating layer 70 from the fiber. [0063] According to some exemplary embodiments (for example those of Tables 1-4) the inner cladding region 20 and/or the outer cladding region 40 has a substantially constant relative refractive index profile, i. e. the difference between the relative refractive index at any two radii within the inner cladding region is less than 0.02%, and in some preferred embodiments less than 0.01 %. Thus, according to at least some embodiments disclosed herein the relative refractive index profile of the outer cladding region 40, has substantially flat shape. Also, according to at least some embodiments disclosed herein the relative refractive index profile of the inner cladding region 20 has substantially flat shape.

[0064] The central core region (1) may be a step index core, or as shown, for example in FIG. 2B, it may comprise an alpha (a) shape (also see, for example, FIG. 4, below).

[0065] According to some embodiments the optical fiber exhibits:

(i) MFDi55o> 8 microns (e.g. , 8.3 microns < MFDi ₅₅₀ ≤ 10.5 microns , and in some embodiments MFDi55o> 9 microns, for example 9 microns to 10.3 microns);

(ii) cable cutoff wavelength greater than 1260 nm and less than <1540 nm;

(iii) macrobend loss and is measured at 1550 nm wavelength at 2.5mm radius mandrel <1 dB/turn; and

(iv) macrobend loss and is measured at 1550 nm wavelength at 5 mm radius mandrel <0.5 dB/turn.

[0066] According to some embodiments 1200 nm <cable cutoff wavelength <1540 nm. According to some embodiments 1200 nm <cable cutoff wavelength <1540 nm, when deployed with an additional single bend around a 2.5 mm radius mandrel.

[0067] According to some embodiments the optical fiber exhibits:

(i) MFDi55o> 8 microns (e.g., 8.3 microns < MFD155 ₀ ≤ 10.5 microns or 8.5 microns < MFD1550 < 10.5 microns, and in some embodiments MFDi55o> 9 microns, for example 9 microns to 10.3 microns);

(ii) cable cutoff wavelength greater than 1260 nm and less than <1540 nm;

(iii) bend loss at 2.5mm radius mandrel <ldB/turn;

(iv) bend loss at 5 mm radius mandrel <0.5 dB/turn

wherein the bend loss is macrobend loss and is measured at 1550 nm wavelength/

[0068] According to some embodiments the optical fiber exhibits 0.001 dB/turn < macrobend loss at 2.55 mm bend radius <0.55 dB/turn; and 0.001 dB/turn < macrobend loss at 5 mm bend radius < 0.5 dB/turn; wherein the macrobend loss is measured at 1550 nm wavelength.

[0069] According to some exemplary embodiments the fiber exhibits:

MFDi55o> 8 microns (e.g., 8.3 microns < MFD155 ₀ ≤ 10.5 microns, for example 8.3 microns <

MFD155 ₀ ≤ 10.5 microns, and in some embodiments MFDi55o> 9 microns, for example 9 microns to 10.3 microns));

Cable Cutoff <1570 nm;

Macrobend loss at 2.5 mm radius <0.5 dB/turn dB/turn, measured at a 1550 nm wavelength.

[0070] The fibers disclosed herein may be drawn from optical fiber preforms made using conventional manufacturing techniques and using known fiber draw methods and apparatus, for example as is disclosed in US Patent No. 7,565,820; 5,410,567; 7,832,675 ; 6,027,062, the specifications of which is hereby incorporated by reference.

[0071] Various exemplary embodiments will be further clarified by the following examples. 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.

[0072] Tables 1A, IB, and 2-5, below, list characteristics of illustrative modeled fiber examples 1 -21 having a refractive index similar to that shown in Figs. 2B. In particular, set forth below for each example is the relative refractive index Δ _1; core alpha, and outer radius ri of the central core 10, relative refractive index Δ2 and outer radius xi of the first cladding region 20 and profile volume V3 of the trench region 30, which is calculated between r ₂ and r ₃ , as well as the relative refractive index Δ ₃ . Also set forth are chromatic dispersion and dispersion slope at 1310 nm, chromatic dispersion and dispersion slope at 1550 nm, mode field diameter at 1310 nm and 1550 nm, fiber cutoff wavelength, MAC number at 1310 nm, and macro bend induced losses (dB/turn) calculated at 1550 nm wavelength when the bend radius ¾ is 2.5 mm and 5 mm, respectively. In the exemplary embodiments of Tables 1A-1C and Tables 2-4 the outer cladding region 40 is pure silica, and Δ ₄ =0. Similarly, in the exemplary embodiments of Tables 1A-1C and Tables 2-4 the inner cladding region 20 is pure silica and Δ ₂ =0; and in these exemplary embodiment delta (Δ ₅ ) of the outer cladding layer 60 was about 2%. Thus in these exemplary embodiments the refractive index of the inner cladding region 20 is the same as that of the outer cladding region 40.

Table 1A Parameter Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5

Core delta (%) 0.31 0.31 0.31 0.31 0.33

Core dopant Ge02 Ge02 Ge02 Ge02 Ge02

Core alpha 20 20 20 20 20

Core radius (ri, microns) 4.7 4.7 4.7 4.7 4.5

(Optional) Inner cladding delta 0 0 0 0 0

Outer radius of the optional inner cladding

(r ₂ , microns) 7.23 7.23 7.23 7.23 8.2

Trench start (r ₂ , microns) 7.23 7.23 7.23 7.23 8.2

Trench delta (%) -0.4 -0.4 -0.4 -0.4 -0.4

Trench dopant F F F F F

Trench end (r ₃ , microns) 13.23 15.23 17.23 19.23 14.2

Trench volume, (%»microns ² ) -49.1 -71.9 -97.8 -127.0 -53.8

Outer radius r ₄ , of the outer cladding region

40 ) 60.0 60.0 60.0 60.0 60.0

Outer radius r ₄ , of the outer cladding region

40 ) 60.0 60.0 60.0 60.0 60.0

Outer cladding delta, Δ ₄ (%) 0 0 0 0 0

Mechanical stability layer (second outer

cladding 60) outer radius (r ₅ , microns) 62.5 62.5 62.5 62.5 62.5

Mechanical layer dopant Ti02 Ti02 Ti02 Ti02 Ti02

Mechanical layer dopant (wt. %) 10 10 10 10 10

Outer radius (micron) of the glass portion

of the fiber cladding 62.5 62.5 62.5 62.5 62.5

Theoretical Cutoff wavelength (nm) 1199 1199 1199 1199 1217

MFD at 1310 nm (microns) 9.1 9.1 9.1 9.1 9.0

Effective area at 1310 nm (microns ² ) 67.8 67.8 67.8 67.8 65.5

Dispersion at 1310 nm (ps/(nm»km) 3.5 3.5 3.5 3.5 2.2

Dispersion slope at 1310 nm (ps/(nm2»km) 0.0927 0.0927 0.0927 0.0927 0.0921

MFD at 1550 nm (microns) 9.8 9.8 9.8 9.8 9.9

Effective area at 1550 nm (microns ² ) 78.0 78.0 78.0 78.0 77.5

Dispersion at 13550 nm (ps/(nm»km) 21.7 21.7 21.7 21.7 20.4

Dispersion slope at 1550 nm (ps/(nm2»km) 0.0635 0.0637 0.0638 0.0638 0.0642

Cable Cutoff 1309 1373 1446 1528 1308 macro bend induced loss when bend

around 2.5 mm bend radius (r _b ), at 1550

nm (dB/turn) 1.75 0.32 0.045 0.005 0.96 macro bend induced loss when bend

around 5 mm bend radius (r _b ), at 1550 nm

(dB/turn) 0.4062 0.0753 0.0110 0.0013 0.2169

Table 1 B

Parameter Ex. 2B Ex. 3B Ex. 4B Ex. 5B

Core delta (%) 0.31 0.31 0.31 0.33

Core dopant Ge02 Ge02 Ge02 Ge02 Core alpha 20 20 20 20

Core radius (ΙΊ, microns) 4.7 4.7 4.7 4.5

(Optional) Inner cladding delta 0 0 0 0

Trench start (r ₂ , microns) 7.23 7.23 7.23 8.2

Trench delta (%) -0.4 -0.4 -0.4 -0.4

Trench dopant F F F F

Trench end (r ₃ , microns) 15.23 17.23 19.23 14.2

Trench volume, (%»microns ² ) -71.9 -97.8 -127.0 -53.8

Mechanical layer start r ₄ , microns) 30.0 35 30.0 27.0

Mechanical layer end (r ₅ , microns) 32.5 40 35 30

Mechanical layer dopant Ti02 Ti02 Ti02 Ti02

Mechanical layer dopant (wt. %) 10 10 10 10

Outer radius (micron) 30 40 35 30

Theoretical Cutoff wavelength (nm) 1199 1199 1199 1217

MFD at 1310 nm (microns) 9.1 9.1 9.1 9.0

Effective area at 1310 nm (microns ² ) 67.8 67.8 67.8 65.5

Dispersion at 1310 nm (ps/(nm»km) 3.5 3.5 3.5 2.2

Dispersion slope at 1310 nm (ps/(nm2»km) 0.0927 0.0927 0.0927 0.0921

MFD at 1550 nm (microns) 9.8 9.8 9.8 9.9

Effective area at 1550 nm (microns ² ) 78.0 78.0 78.0 77.5

Dispersion at 13550 nm (ps/(nm»km) 21.7 21.7 21.7 20.4

Dispersion slope at 1550 nm (ps/(nm2»km) 0.0637 0.0638 0.0638 0.0642

Cable Cutoff 1373 1446 1528 1308 macro bend induced loss when bend

around 2.5 mm bend radius (r _b ), at 1550

nm (dB/turn) 0.32 0.045 0.005 0.96 macro bend induced loss when bend

around 5 mm bend radius (r _b ), at 1550 nm

(dB/turn 0.0753 0.0110 0.0013 0.2169

Table 2

Parameter Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10

Core delta (%) 0.33 0.33 0.33 0.34 0.34

Core dopant Ge02 Ge02 Ge02 Ge02 Ge02

Core alpha 20 20 20 20 20

Core radius (microns) 4.5 4.5 4.5 4.3 4.3

Trench start (:·.·. microns) 8.2 8.2 8.2 13 13

Trench delta (%) -0.4 -0.4 -0.4 -0.4 -0.4

Trench dopant F F F F F

Trench end (¾ microns) 16.2 18.2 20.2 17 19

Trench volume, (%»microns ² ) -78.1 -105.6 -136.3 -48.0 -76.8

Mechanical layer start (microns) 60.0 60.0 60.0 60.0 60.0

Mechanical layer end (microns) 62.5 62.5 62.5 62.5 62.5

Mechanical layer dopant Ti02 Ti02 Ti02 Ti02 Ti02

Mechanical layer dopant (wt. %) 10 10 10 10 10 Outer radius (micron) 62.5 62.5 62.5 62.5 62.5

Theoretical Cutoff wavelength (nm) 1217 1217 1217 1234 1234

M FD at 1310 nm (microns) 9.0 9.0 9.0 9.0 9.0

Effective area at 1310 nm (microns ² ) 65.5 65.5 65.5 64.2 64.2

Dispersion at 1310 n m (ps/(nm»km) 2.2 2.2 2.2 -0.2 -0.2

Dispersion slope at 1310 nm (ps/(nm ² »km) 0.0921 0.0921 0.0921 0.0867 0.0867

M FD at 1550 nm (microns) 9.9 9.9 9.9 10.3 10.3

Effective area at 1550 nm (microns ² ) 77.5 77.5 77.5 80.6 80.6

Dispersion at 13550 nm (ps/( nm»km) 20.4 20.4 20.4 16.9 16.9

Dispersion slope at 1550 nm (ps/(nm ² »km) 0.0643 0.0644 0.0644 0.0609 0.0610

Cable Cutoff 1376 1453 1539 1252 1333 macro bend induced loss when bend

around 2.5 mm bend radius (r _b ), at 1550

nm (dB/turn) 0.15 0.02 0.002 1.58 0.18 macro bend induced loss when bend

around 5 mm bend radius (r _b ), at 1550 nm

(d B/turn 0.0359 0.0047 0.0005 0.36 0.04

Table 3

Parameter Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15

Core delta (%) 0.34 0.34 0.34 0.34 0.34

Core dopant Ge02 Ge02 Ge02 Ge02 Ge02

Core alpha 20 20 20 20 20

Core radius (microns) 4.3 4.3 4.3 4.4 4.4

Trench start ( . microns) 13 13 13 9.7 9.7

Trench delta (%) -0.4 -0.4 -0.4 -0.4 -0.4

Trench dopant F F F F F

Trench end (¾ microns) 21 23 25 15.7 16.7

Trench volu me, (%»microns ² ) -108.8 -144.0 -182.4 -61.0 -73.9

Mechanical layer start (· _¾ .. microns) 60.0 60.0 60.0 60.0 60.0

Mechanical layer end (rv. microns) 62.5 62.5 62.5 62.5 62.5

Mechanical layer dopant Ti02 Ti02 Ti02 Ti02 Ti02

Mechanical layer dopant (wt. %) 10 10 10 10 10

Outer radius (micron) 62.5 62.5 62.5 62.5 62.5

Theoretical Cutoff wavelength (nm) 1234 1234 1234 1235 1235

M FD at 1310 nm (microns) 9.0 9.0 9.0 9.0 9.0

Effective area at 1310 nm (microns ² ) 64.2 64.2 64.2 64.7 64.7

Dispersion at 1310 n m (ps/(nm»km) -0.2 -0.2 -0.2 1.0 1.0

Dispersion slope at 1310 nm (ps/(nm ² »km) 0.0867 0.0867 0.0867 0.0902 0.0902

M FD at 1550 nm (microns) 10.3 10.3 10.3 10.1 10.1

Effective area at 1550 nm (microns ² ) 80.6 80.6 80.6 78.7 78.7

Dispersion at 1350 n m (ps/(nm»km) 16.9 16.9 16.9 18.9 18.9

Dispersion slope at 1550 nm (ps/(nm ² »km) 0.0610 0.0610 0.0610 0.0639 0.0639

Cable Cutoff 1423 1521 1629 1318 1354 macro bend induced loss when bend

around 2.5 mm bend radius (r _b ), at 1550

nm (dB/turn) 0.02 0.001 0.0001 0.51 0.19 macro bend induced loss when bend

around 5 mm bend radius (r _b ), at 1550 nm

(dB/turn) 0.004 0.0003 0.00002 0.11 0.0437

Table 4

Parameter Ex. 16 Ex. 17 Ex. 18

Core delta (%) 0.34 0.34 0.34

Core dopant Ge02 Ge02 Ge02

Core alpha 20 20 20

Core radius (microns) 4.4 4.4 4.4

Trench start (microns) 9.7 9.7 9.7

Trench delta (%) -0.4 -0.4 -0.4

Trench dopant F F F

Trench end (microns) 17.7 19.7 21.7

Trench volume, (%»microns ² ) -87.7 -117.6 -150.7

Mechanical layer start (microns) 60.0 60.0 60.0

Mechanical layer end (microns) 62.5 62.5 62.5

Mechanical layer dopant Ti02 Ti02 Ti02

Mechanical layer dopant (wt. %) 10 10 10

Outer radius (micron) 62.5 62.5 62.5

Theoretical Cutoff wavelength (nm) 1235 1235 1235

MFD at 1310 nm (microns) 9.0 9.0 9.0

Effective area at 1310 nm (microns ² ) 64.7 64.7 64.7

Dispersion at 1310 nm (ps/(nm»km) 1.0 1.0 1.0

Dispersion slope at 1310 nm (ps/(nm ² »km) 0.0902 0.0902 0.0902

MFD at 1550 nm (microns) 10.1 10.1 10.1

Effective area at 1550 nm (microns ² ) 78.7 78.7 78.7

Dispersion at 1350 nm (ps/(nm»km) 18.9 18.9 18.9

Dispersion slope at 1550 nm (ps/(nm ² »km) 0.0639 0.0639 0.0639

Cable Cutoff 1393 1476 1569

macro bend induced loss when bend

around 2.5 mm bend radius (r _b ), at 1550

nm (dB/turn) 0.07 0.007 0.0006

macro bend induced loss when bend

around 5 mm bend radius (r _b ), at 1550 nm

(dB/turn) 0.02 0.002 0.0001

Table 5

Parameter Ex. 19 Ex. 20 Ex. 22 Core delta (%) 0.34 0.34 0.31

Core dopant Ge02 Ge02 Ge02

Core alpha 20 20 20

Core radius (ri, microns) 4.4 4.4 4.7

Trench start (r _2, microns) 9.7 9.7 7.23

Trench delta (%) -0.4 -0.4 -0.4

Trench dopant F F F

Trench end (r ₃ , microns) 17.7 19.7 15.23

Trench volume, (%»microns ² ) -87.7 -117.6 -71.9

Mechanical layer start (r ₄ , microns) 20.0 22.7 18.0

Mechanical layer end (r ₅ , microns) 22.5 26 20

Mechanical layer dopant Ti02 Ti02 Ti02

Mechanical layer dopant (wt. %) 10 10 10

Outer radius (micron) 22.5 26.5 20.5

Theoretical Cutoff wavelength (nm) 1235 1235 1199

MFD at 1310 nm (microns) 9.0 9.0 9.1

Effective area at 1310 nm (microns ² ) 64.7 64.7 67.8

Dispersion at 1310 nm (ps/(nm»km) 1.0 1.0 3.5

Dispersion slope at 1310 nm (ps/(nm ² »km) 0.0902 0.0902 0.0927

MFD at 1550 nm (microns) 10.1 10.1 9.8

Effective area at 1550 nm (microns ² ) 78.7 78.7 78.0

Dispersion at 1350 nm (ps/(nm»km) 18.9 18.9 21.7

Dispersion slope at 1550 nm (ps/(nm ² »km) 0.0639 0.0639 0.0637

Cable Cutoff 1393 1476 1373

macro bend induced loss when bend

around 2.5 mm bend radius (r _b ), at 1550

nm (dB/turn) 0.07 0.007 0.32

macro bend induced loss when bend

around 5 mm bend radius (r _b ), at 1550 nm

(dB/turn) 0.02 0.002 0.0753

According to the exemplary embodiments of Tables 1A-5, the optical fiber has a mode field diameter at 1550 nm (MFD1550) of 8.3 microns < MFD1550≤ 10.5 microns (e.g., 8.5 microns < MFD1550≤ 10.5 microns), a single mode cutoff wavelength <1550 nm when bent 1 turn around a 2.5 mm radius mandrel, an effective area at 1550 nm of at least 65 micron ² and less than 85 micron ² _, and a bending loss at 1550 nm as determined by the mandrel wrap test using a mandrel comprising a radius of 2.5 mm-of < 1.0 dB/turn.

[0073] The optical fiber has Fig. 4 shows a measured refractive index profile of the manufactured optical fiber 100 according to one embodiment. In the profile of the exemplary embodiment shown in Fig. 4, the core region 10 which comprises Δι is surrounded by depressed cladding inner cladding region 30 comprising Δ ₂ . Inner cladding region 20 is situated between the core region 10 and is surrounded by the trench cladding region 30 comprising Δ ₃ . The outer cladding region 40 surrounds the trench region 30. The absolute difference between Δ ₄ and Δ ₃ is about 0.4%, and Δ ₅ is about 2%. In the embodiment illustrated in Fig. 5, the first cladding region (2) is substantially undoped silica and the second cladding region (3) is silica doped with chlorine. The optical fiber disclosed in Table 2 has cladding (60) that has an outer diameter of about 125 micron.

[0074] The manufactured fiber 100 that has the refractive index profile of FIG. 4 had a MFD of 8.8 microns and 9.7 microns at 1310 and 1550 nm, respectively, a 1409 nm 22 m cutoff, attenuation of 0.2 dB/km at 1550 nm, and ultra-low bend loss (measured at 1490 nm) on small diameter mandrels (4 mm, 5 mm, or 6 mm diameter [2 mm, 2.5 mm, or 3 mm radii]) as shown in Table 6, below. Table 6 indicates that when the optical fiber 100 is bent by about a quarter turn (see, for example, FIG. 1 ) to a bend radius r _b = 2mm, the bend loss ( measured for example at a 1 1490 nm wavelength) will be less than 0.02dB. More specifically, when the optical fiber 100 is bent by about a quarter turn to a bend radius i¾= 2mm, the bend loss is expected to be O.OldB or less.

Table 6

Total

# of wraps 2 mm Radius Rod, Loss in dB Per wrap_

loss, dB

0.5 0.02 0.04

1 0.16 0.16

2 0.46 0.23

3 1.02 0.34

5 2.65 0.53

10 5.8 0.58

# of wraps 2.5 mm Radius Rod, Loss Per wrap_

0.5 0.13 0.26

1 0.24 0.24

2 0.43 0.22

3 0.62 0.21

5 1.15 0.23

10 2.2 0.22

# of wraps 3 mm Radius Rod, Loss Per wrap_

0.5 0.02 0.04

1 0.14 0.14

2 0.15 0.08 3 0.26 0.09

5 0.4 0.08

10 0.8 0.08

[0075] The optical fibers (100) disclosed herein may be surrounded by the protective coating 70 that surrounds the second outer cladding layer 60, The protective coating may comprise a primary coating P contacting and surrounding the outer cladding region 60, the primary coating P having a Young's modulus of less than 1.0 MPa, preferably less than 0.9 MPa, and in some embodiments not more than 0.8 MPa, and in some embodiments not more than 0.5 MPa, and in some embodiments not more than 0.3 MPa, for example 0.1 to 1 MPa, and in some embodiments 0.1 to 0.5 MPa. The protective coating 70 further comprises a secondary coating S contacting and surrounding the primary coating P, the secondary coating S having a Young's modulus of greater than 1200 MPa, and in some embodiments greater than 1400 MPa, for example at least 1500MPa, or at least 1600MPa, at least 1800MPa, or 1400MPa to 2500MPa or 1500MPa to 2500MPa. The lower modulus of the primary coating (e.g. < 0.5MPa supports good microbend performance, and higher modulus secondary coating (e.g., > 1500MPa) supports improve puncture resistance of the secondary coating, even when its thickness is reduced. According to some embodiments the outer diameter of the secondary coating S is not greater than 250 microns, for example not greater than 242 microns (e.g., <225 microns, <210 microns, or <200 microns), for example 175-242 microns, or 175 to 225 microns, or 180 to 200 microns. The above fiber designs enable good micro and macro bending performance even with coating diameters of less than 225 microns, which enables smaller diameter, lower cost, higher fiber density cables with excellent optical performance.

[0076] As used herein, the Young's modulus, elongation to break, and tensile strength of a cured polymeric material of a primary coating is measured using a tensile testing instrument (e.g. , a Sintech MTS Tensile Tester, or an INSTRON Universal Material Test System) on a sample of a material shaped as a film between about 0.003" (76 micron) and 0.004" (102 micron) in thickness and about 1.3 cm in width, with a gauge length of 5.1 cm, and a test speed of 2.5 cm/min.

[0077] Additional description of suitable primary and secondary coatings can be found in PCT Publication WO2005/010589 which is incorporated herein by reference in its entirety. [0078] The fibers disclosed herein exhibit low PMD values particularly when fabricated with OVD processes. Spinning of the optical fiber may also lower PMD values for the fiber disclosed herein.

[0079] It is to be understood that the foregoing description is exemplary only and is intended to provide an overview for the understanding of the nature and character of the fibers which are defined by the claims. The accompanying drawings are included to provide a further understanding of the preferred embodiments and are incorporated and constitute part of this specification. The drawings illustrate various features and embodiments which, together with their description, serve to explain the principals and operation. It will become apparent to those skilled in the art that various modifications to the preferred embodiments as described herein can be made without departing from the spirit or scope of the appended claims.