The present disclosure relates to optical fibers, and in particular, relates to ultra-low loss optical fibers for long haul communications.
5 BACKGROUND
[0002] With the advancement of science and technology, various modern technologies are being employed for communication purposes. One of the most important modern communication technologies is optical fiber communication technology using a variety of optical fibers. An optical fiber is used to transmit
10 information as light pulses from one end to another. One such type of optical fiber is a single mode optical fiber. The single mode optical fiber is used in FTTx and long haul communications. The telecommunications industry is continuously striving for designs to achieve high data rate capacity and low losses. The ongoing research suggests that the single mode optical fiber of G657 and G652D categories are used
15 for the FTTx and long-haul applications. However, the single mode optical fiber of G652D and G657 categories face major challenges in 400G transmission in territorial long haul communication systems due to non-linear effects that occur due to small effective area, higher attenuation and low SNR (Signal-to-Noise Ratio).
[0003] Thus, there exists a need to develop an optical fiber which has an
20 optimize design and addresses the aforementioned drawbacks.
OBJECT OF THE DISCLOSURE
[0004] A primary object of the present disclosure is to provide an ultra-low
loss optical fiber for long haul communications.
25 [0005] Another object of the present disclosure is to provide an optical fiber
having an optimize design with large effective area and mode field diameter (MFD), reduced non-linear effects, low attenuation, low latency, high OSNR (Optical Signal to Noise Ratio).
30

SUMMARY
[0006] Accordingly, an ultra-low loss optical fiber for long haul communications is provided. The optical fiber comprises a core region defined by a core relative refractive index and a cladding region, surrounding the core region, 5 defined by a cladding relative refractive index. The cladding region is down-doped for entire radial cladding thickness and the core region comprises a relative refractive index in a range of-0.06% to +0.06%.
[0007] The cladding region further comprises an inner cladding region and an outer cladding region. The inner cladding region is defined by an inner cladding
10 relative refractive index and the outer cladding region is defined by an outer cladding relative refractive index. The inner cladding relative refractive index is less than the outer cladding relative refractive index. The inner cladding relative refractive index ranges between -0.29% and -0.32% and the outer cladding relative refractive index ranges between -0.24% and -0.28%. Further, the inner cladding region is defined by
15 an inner cladding radius ranging between 21 um and 25 um and the inner cladding relative refractive index ranging between -0.29% and -0.32% and the outer cladding region is defined by an outer cladding radius of 62.5+0.7 um. and the outer cladding relative refractive index ranging between -0.24% and -0.28%. The inner cladding relative refractive index is less than the outer cladding relative refractive index.
20 [0008] The inner cladding region has a first fluorinated region Tl defined
by a thickness r2 - n, which is a difference between the inner cladding radius and the core radius and the outer cladding region has a second fluorinated region T2 defined by a thickness r3 - ri, which is a difference between the outer cladding radius and the inner cladding radius.
25 [0009] The optical fiber is characterized by an attenuation of less than or
equal to 0.17 dB/km at 1550 nm wavelength and an attenuation of less than or equal to 0.20 dB/km at 1625 nm wavelength and a mode field diameter (MFD) of 12.5+0.5 at 1550 nm wavelength. The optical fiber has a macro-bend loss of less than or equal to 0.1 dB per 100 turns at 30 mm radius and at 1625 nm wavelength and a macro-
30 bend loss of less than or equal to 0.03 dB per 100 turns at 30 mm radius and at 1550 nm wavelength.

[0010] These and other aspects herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions are given by way of illustration and not of limitation. Many changes and 5 modifications may be made within the scope of the invention herein without departing from the spirit thereof.
BRIEF DESCRIPTION OF FIGURE
[0011] The invention is illustrated in the accompanying drawings, 10 throughout which like reference letters indicate corresponding parts in the drawings. The invention herein will be better understood from the following description with reference to the drawings, in which:
[0012] FIG. 1 illustrates a cross-sectional view of an ultra-low loss optical
fiber.
15 [0013] FIG. 2 illustrates a refractive index profile of the ultra-low loss
optical fiber.
[0014] It should be noted that the accompanying figures are intended to present illustrations of few examples of the present disclosure. The figures are not intended to limit the scope of the present disclosure. It should also be noted that 20 accompanying figures are not necessarily drawn to scale.
DETAILED DESCRIPTION
[0015] In the following detailed description of the invention, numerous specific details are set forth in order to provide a thorough understanding of the 25 invention. However, it will be obvious to a person skilled in the art that the invention may be practiced with or without these specific details. In other instances, well known methods, procedures and components have not been described in details so as not to unnecessarily obscure aspects of the invention.
[0016] Furthermore, it will be clear that the invention is not limited to these 30 alternatives only. Numerous modifications, changes, variations, substitutions and

equivalents will be apparent to those skilled in the art, without parting from the scope of the invention.
[0017] The accompanying drawings are used to help easily understand various technical features and it should be understood that the alternatives presented 5 herein are not limited by the accompanying drawings. As such, the present disclosure should be construed to extend to any alterations, equivalents and substitutes in addition to those which are particularly set out in the accompanying drawings. Although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are
10 generally only used to distinguish one element from another.
[0018] Unlike conventional optical fibers, the present disclosure proposes an ultra-low loss optical fiber for long haul communications having an optimize design with a large effective area and mode field diameter (MFD), reduced non-linear effects, a low attenuation, a low latency, a high OSNR (Optical Signal to Noise Ratio)
15 as compared to G652D optical fiber.
[0019] Now, simultaneous reference is made to FIG. 1 through FIG. 2, in which FIG. 1 illustrates a cross-sectional view of an ultra-low loss optical fiber (interchangeably referred to as optical fiber) 100 and FIG. 2 illustrates a refractive index profile 200 of the ultra-low loss optical fiber 100. In general, an optical fiber
20 is a thin strand of glass or plastic or combination thereof capable of transmitting optical signals. The optical fiber 100 is configured to transmit information over long distances with low non-linear effects. The optical fiber 100 may include a core region 102 and a cladding region.
[0020] The core region 102 may be formed by pure silica (aka "silica"). The
25 core region 102 may comprise a relative refractive index in a range of -0.06% to +0.06%). That is, the core region 102 may be the pure silica or the core region 102 may be up-doped or the core region 102 may be down-doped. The up-doping increases a refractive index of the silica, whereas the down-doping lowers the refractive index of the silica. The dopant may be, but not limited to, germanium oxide
30 (Ge02), fluorine, boron, chlorine, phosphorus. Preferably, the dopant is germanium oxide (Ge02).

[0021] The core region 102 may be defined by a core relative refractive index Ai and a core radius n. Generally, a relative refractive index is a measure of relative difference in refractive index between two optical materials. The value of the core relative refractive index Ai may be between -0.06% and 0.06% depending upon 5 doping of the core region 102 and the core radius n may be between 6.1 um and 6.5 um. Preferably, the value of the core relative refractive index Ai may be zero (0) and the core radius n may be 6.4 um. Alternatively, the value of the core relative refractive index Ai and the core radius n may vary.
[0022] The core region 102 may be surrounded by the cladding region. The
10 cladding region may be defined by a cladding relative refractive index and a cladding radius. Specifically, the cladding region may comprise an inner cladding region 104 and an outer cladding region 106. The inner cladding region 104 may be defined by an inner cladding relative refractive index A2 and an inner cladding radius ft. The outer cladding region 106 may be defined by an outer cladding relative refractive
15 index A3 and an outer cladding radius ft. The inner cladding relative refractive index A2 may be less than the outer cladding relative refractive index A3.
[0023] The value of the inner cladding relative refractive index A2 may be between -0.29% and -0.32% and the inner cladding radius ft may be between 21 um and 25 um. Preferably, the value of the inner cladding relative refractive index A2
20 may be -0.30% and the inner cladding radius ft may be 22 um. Similarly, the value of the outer cladding relative refractive index A3 may be between -0.24% and -0.28% and the outer cladding radius ft may be 62.5+0.7 um. Preferably, the value of the outer cladding relative refractive index A3 may be -0.26% and the outer cladding radius ft may be 62.5 um. Alternatively, the value of the outer cladding relative
25 refractive index A3 and the outer cladding radius ft may vary.
[0024] The cladding region may be doped with a down-dopant, such as fluorine, for entire radial cladding thickness (T). Alternatively, other down-dopants (known to a person skilled in the art) may be used. The down-dopant has propensity to lower the refractive index of the silica. Accordingly, the cladding region may have
30 a fluorinated region . That is, the inner cladding region 104 may have a first fluorinated region Tl defined by a thickness ft - n (i.e., difference between the inner

cladding radius and the core radius) and the outer cladding region 106 may have a second fluorinated region T2 defined by a thickness r3 - r2 (i.e., difference between the outer cladding radius and the inner cladding radius). The first fluorinated region Tl and the second fluorinated region T2 may extend radially outwards from the core 5 region 102.
[0025] The fluorinated cladding region with the fluorinated region and lower or no doping of Ge02 in the core region result in the optical fiber 100 having the large effective area and mode field diameter (MFD), reduced non-linear effects, low attenuation, low latency, higher OSNR as compared to G652D.
10 [0026] The optical fiber 100 may be characterized by an attenuation of less
than or equal to 0.17 dB/km at 1550 nm wavelength and an attenuation of less than or equal to 0.20 dB/km at 1625 nm wavelength, a cable cut-off wavelength of less than or equal to 1530 nm and a chromatic dispersion (CD) ranging between 17 picosecond/(nanometer-kilometer) and 23 picosecond/(nanometer-kilometer) at
15 1550 nm wavelength and less than or equal to 27 picosecond/(nanometer-kilometer) at 1625 nm wavelength. Generally, the attenuation corresponds to signal loss, the cut¬off wavelength is a minimum wavelength in which the optical fiber acts as a single mode fiber and the chromatic dispersion is a phenomenon of optical signal spreading over time resulting from the different speeds of light rays.
20 [0027] Further, the optical fiber 100 may have a dispersion slope in a range
between 0.05-0.07 ps/nm2-km and an MFD of 12.5±0.5 um at 1550 nm wavelength. In general, mode field diameter defines a section or area of optical fiber in which the optical signals travel.
[0028] Furthermore, the optical fiber 100 may have a macro-bend loss of
25 less than or equal to 0.1 dB per 100 turns at 30 mm radius and at 1625 nm wavelength and a macro-bend loss of less than or equal to 0.03 dB per 100 turns at 30 mm radius and at 1550 nm wavelength. The macro bend loss is defined by a loss occurred when an optical fiber cable is subjected to a significant amount of bending.
[0029] It will be apparent to those skilled in the art that other alternatives of
30 the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention. While the foregoing written description

of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific aspect, method, and examples herein. The invention should therefore not be limited 5 by the above described alternative, method, and examples, but by all aspects and methods within the scope of the invention. It is intended that the specification and examples be considered as exemplary, with the true scope of the invention being indicated by the claims.
[0030] Conditional language used herein, such as, among others, "can,"
10 "may," "might," "may," "e.g.," and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain alternatives include, while other alternatives do not include, certain features, elements and/or steps. Thus, such conditional language is not generally intended to imply that features, elements and/or steps are in any way required for one or more
15 alternatives or that one or more alternatives necessarily include logic for deciding, with or without other input or prompting, whether these features, elements and/or steps are included or are to be performed in any particular alternative. The terms "comprising," "including," "having," and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements,
20 features, acts, operations, and so forth. Also, the term "or" is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term "or" means one, some, or all of the elements in the list.
[0031] Disjunctive language such as the phrase "at least one of X, Y, Z," unless specifically stated otherwise, is otherwise understood with the context as used
25 in general to present that an item, term, etc., may be either X, Y, or Z, or any combination thereof (e.g., X, Y, and/or Z). Thus, such disjunctive language is not generally intended to, and should not, imply that certain alternatives require at least one of X, at least one of Y, or at least one of Z to each be present.
[0032] While the detailed description has shown, described, and pointed out
30 novel features as applied to various alternatives, it can be understood that various omissions, substitutions, and changes in the form and details of the devices or

algorithms illustrated can be made without departing from the scope of the disclosure. As can be recognized, certain alternatives described herein can be embodied within a form that does not provide all of the features and benefits set forth herein, as some features can be used or practiced separately from others.

CLAIMS
We Claim:

1. An optical fiber (100), comprising:
a core region (102) defined by a core relative refractive index; and a cladding region surrounding the core region (102), wherein the cladding region is down-doped for entire radial cladding thickness.
2. The optical fiber (100) as claimed in claim 1, wherein the core region (102) comprises a relative refractive index in a range of-0.06% to +0.06%.
3. The optical fiber (100) as claimed in claim 1, wherein the cladding region further comprising an inner cladding region (104) and an outer cladding region (106), wherein the inner cladding region (104) is defined by an inner cladding relative refractive index and the outer cladding region (106) is defined by an ouer cladding relative refractive index such that value of relative refractive index of the inner cladding is less than value of relative refractive index of the outer cladding.
4. The optical fiber (100) as claimed in claim 3, wherein the inner cladding relative refractive index is less than the outer cladding relative refractive index.
5. The optical fiber (100) as claimed in claim 3, wherein the inner cladding region (104) has a first fluorinated region Tl defined by a thickness r2 - n, which is a difference between an inner cladding radius and a core radius and the outer cladding region (106) has a second fluorinated region T2 defined by a thickness r3 - T2, which is a difference between an outer cladding radius and the inner cladding radius.

6. The optical fiber (100) as claimed in claim 5, wherein the thickness of the first fluorinated region Tl is less than the thickness of the second fluorinated region T2.
5 7. The optical fiber (100) as claimed in claim 3, wherein the inner cladding region (104) is defined by an inner cladding radius ranging between 21 um and 25 um and an inner cladding relative refractive index ranging between -0.29% and -0.32%.
10 8. The optical fiber (100) as claimed in claim 3, wherein the outer cladding region (106) is defined by an outer cladding radius ranging between 61.8 um to 63,2 um and an outer cladding relative refractive index ranging between -0.24% and -0.28%.
15 9. The optical fiber (100) as claimed in claim 1, wherein the optical fiber (100) is characterized by an attenuation of less than or equal to 0.17 dB/km at 1550 nm wavelength and an attenuation of less than or equal to 0.20 dB/km at 1625 nm wavelength and a mode field diameter (MFD) of 12.5±0.5 at 1550 nm wavelength.
20
10. The optical fiber (100) as claimed in claim 1, wherein the optical fiber (100) has a macro-bend loss of less than or equal to 0.1 dB per 100 turns at 30 mm radius and at 1625 nm wavelength and a macro-bend loss of less than or equal to 0.03 dB per 100 turns at 30 mm radius and at 1550 nm wavelength.