WO2002027367A1 - Dispersion optimized fiber with low dispersion and optical loss - Google Patents

Dispersion optimized fiber with low dispersion and optical loss Download PDF

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Publication number
WO2002027367A1
WO2002027367A1 PCT/IN2000/000092 IN0000092W WO0227367A1 WO 2002027367 A1 WO2002027367 A1 WO 2002027367A1 IN 0000092 W IN0000092 W IN 0000092W WO 0227367 A1 WO0227367 A1 WO 0227367A1
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WIPO (PCT)
Prior art keywords
core
fiber
dispersion
side core
refractive index
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PCT/IN2000/000092
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French (fr)
Inventor
Samaresh Changdar
Sanjit Singh Bhatia
Senthil Kumar Nageswaran
Prakash Satyan
Ashok Agarwal
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Sterlite Optical Technologies Ltd.
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Application filed by Sterlite Optical Technologies Ltd. filed Critical Sterlite Optical Technologies Ltd.
Priority to AU2001225460A priority Critical patent/AU2001225460A1/en
Priority to PCT/IN2000/000092 priority patent/WO2002027367A1/en
Publication of WO2002027367A1 publication Critical patent/WO2002027367A1/en

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
    • G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
    • G02B6/03661—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 4 layers only
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02214—Optical fibres with cladding with or without a coating tailored to obtain the desired dispersion, e.g. dispersion shifted, dispersion flattened
    • G02B6/02219—Characterised by the wavelength dispersion properties in the silica low loss window around 1550 nm, i.e. S, C, L and U bands from 1460-1675 nm
    • G02B6/02266—Positive dispersion fibres at 1550 nm
    • G02B6/02271—Non-zero dispersion shifted fibres, i.e. having a small positive dispersion at 1550 nm, e.g. ITU-T G.655 dispersion between 1.0 to 10 ps/nm.km for avoiding nonlinear effects
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02214—Optical fibres with cladding with or without a coating tailored to obtain the desired dispersion, e.g. dispersion shifted, dispersion flattened
    • G02B6/02219—Characterised by the wavelength dispersion properties in the silica low loss window around 1550 nm, i.e. S, C, L and U bands from 1460-1675 nm
    • G02B6/02228—Dispersion flattened fibres, i.e. having a low dispersion variation over an extended wavelength range
    • G02B6/02238—Low dispersion slope fibres
    • G02B6/02242—Low dispersion slope fibres having a dispersion slope <0.06 ps/km/nm2
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/028—Optical fibres with cladding with or without a coating with core or cladding having graded refractive index
    • G02B6/0281—Graded index region forming part of the central core segment, e.g. alpha profile, triangular, trapezoidal core

Definitions

  • the present invention relates to dispersion optimized fiber with low dispersion and optical loss, particularly it relates to a dispersion optimized fiber to provide low dispersion and optical loss between 1530 to 1565.
  • nm (C-band) transmissions more particularly it relates to single mode dispersion optimized fiber, which is suitable for transmission of higher, bandwidth over long distances and yet has optimized effective area, cut-off wavelength and mode field diameter to achieve a high level of bend resistance for high bandwidth transmission.
  • optical fibers have been developed and installed as the backbone of interoffice networks for voice, video and data transmission. These are becoming important with growing and expanding telecommunication infrastructure. Their importance is further increasing because of their high bandwidth applicability. The higher bandwidth demand is further increasing exponentially with time because of rapid growth of information technology.
  • the multi-mode fiber at wavelength of 850 nm were used, which were replaced by single mode fibers with zero dispersion wavelength near 1310 nm.
  • the single mode or monomode optical fibers have greater bandwidth than that of the multimode fibers. Therefore, the research has been directed towards the development of the single mode fibers, as these fibers were observed to have lower attenuation between the wavelength range from 1300 nm to 1550 nm.
  • the transmission loss of single mode fibers is observed to be as low as 0.5 dB/km at 1300 nm wavelength and 0.2 dB/km at 1550 nm wavelength.
  • the single mode fibers were observed to have very high dispersion.
  • the optical fibers with minimum attenuation of light transmission and the dispersion shifted fibers with zero dispersion in the wavelength region of 1500 nm to 1600 nm band are being used.
  • the fibers with simple step like refractive index profile have ⁇ poor practical advantages.
  • the dispersion shifted fibers with convex refractive index profile have better practical advantages and less flexural loss.
  • the known dispersion shifted fibers have higher refractive index in the center core and lower refractive index in the outer region.
  • the relative difference in the refractive index is achieved by using different dopants.
  • the commonly used dopants are germanium and fluorine, however, their flow rate and the temperature of doping are different in different known methods.
  • the specific refractive index profile having selected refractive indexes and outer diameters of core and cladding region of the optical fiber is decided by the selection of dopants, their flow rates and temperatures of doping of the core and/or cladding regions, demarcation of core region into one or more core regions with one or more set of refractive indexes, the demarcation of cladding region into one or more cladding regions with one or more set of refractive indexes, the shape of core and cladding regions etc. These parameters decide the characteristic properties of thus obtained fiber and the applications of thus obtained fiber.
  • the fibers known in the art are distinguished by way of their characteristic properties, which in-turn are decided by various parameters as stated herein above.
  • the fibers as known in the prior art either have . low non- linearity but high bend loss or have low bend loss but less effective area or may have higher non-linearity and higher bend loss.
  • the main object of the present invention is to make a complete disclosure of a dispersion optimized fiber, which has low dispersion and optical loss, particularly between 1530 to 1565 nm wavelength band.
  • the another object of "the present invention is to make a complete disclosure of a dispersion optimized fiber, which is suitable for long haul transmission.
  • Still another object of the present invention is to make a disclosure' of a dispersion optimized fiber which not only has low dispersion and optical loss in 1530 to 1565 nm wavelength band but also has optimized effective area, cut-off wavelength and mode field diameter.
  • dispersion optimized fiber with low dispersion and optical loss between 1530 to 1565 nm (C-band) transmissions particularly a dispersion optimized fiber, which is suitable for transmission of higher bandwidth over long distances and yet has optimized effective area, cutoff wavelength and mode field diameter, herein after referred to as MFD, to achieve a high level of bend resistance for high bandwidth transmission, minimized non-linearities and low chromatic dispersion with a low .
  • optical loss in the C-Band region comprising a centre core, two side cores, a cladding region and a outer glass, wherein the first side core is provided onto the outer periphery of the center core, second side core is provided onto the outer periphery of the first side core and cladding region is provided onto the outer periphery of the second side core.
  • the centre core, first side core, second side core and cladding region have ni, n 2 , n 3 and n 4 refractive index respectively and 2a, 2b 1 , 2b 2 and 2b 3 outer diameter respectively.
  • the refractive index of outer glass is n 5 and its diameter is selected to suit the requirement of desired fiber.
  • the refractive indexes of said members are characterized by relationship n ⁇ n 5 ⁇ n 3 ⁇ n 2 ⁇ ni, and outer diameters ' of each member are characterized by 5.1>2a>6.2 ⁇ m, 7>2b ⁇ >9 ⁇ m, 13>2b 2 >15 ⁇ m, 19>2b 3 >22 ⁇ m relationships.
  • the cladding region is depressed cladding region and the side cores have lower refractive index than the center core.
  • the refractive index of centre core, two side cores are positive and refractive index of cladding region is negative with respect to the refractive index of outer glass.
  • Figure 1a of figure 1 shows a cut-section of dispersion optimized fiber in accordance to the preferred embodiments of the present invention.
  • Figure 1 b of figure 1 shows the refractive index profile of dispersion optimized fiber in accordance to the preferred embodiments of the present invention.
  • Figure 2 shows the chromatic dispersion in the C-band region of dispersion optimized fiber in accordance to the preferred embodiments of the present invention.
  • Figure 3 shows the cut-off wavelength, using 2m-fiber as a reference length and measured on spectral analyzer, of the dispersion optimized fiber in accordance to the preferred embodiments of the present invention.
  • Figure 4 shows the intensity distribution along the diameter of the presently disclosed fiber for measuring the MFD of dispersion optimized fiber in accordance to the preferred embodiments of the present invention.
  • Figure 5 shows the attenuation spectra of dispersion optimized fiber in accordance to the preferred embodiments of the present invention. .
  • the dispersion optimized fiber T comprises of a centre core 2, two side cores 3 and 4, which are referred to as first side core 3 and second side core 4, a cladding region 5 and a outer glass 6, and in accordance to the present invention the first side core 3 is provided onto the outer periphery of the center core 2, second side core 4 is provided onto the outer periphery of the first side core 3, cladding region 5 is provided onto the outer periphery of the second side core 4 and outer glass 6 is provided onto the outer periphery of the cladding region 5.
  • centre core 2 has refractive index ni
  • the first side core 3 has refractive index n 2
  • the second side core 4 has refractive index n 3
  • the cladding region 5 has refractive index n 4
  • the outer glass 6 has refractive index n 5 ⁇ and the centre core 2 has outer diameter 2a
  • the first side core 3 has outer diameter 2b ⁇
  • the second side core 4 has outer diameter 2b 2
  • the cladding region 5 has outer diameter 2b 3 .
  • the diameter of the outer glass 6 can be selected to suit the requirement of desired dispersion optimized fiber.
  • the relative refractive index difference between center core 2 and outer glass 6 is ⁇ -i
  • the relative refractive index difference between first side core 3 and outer glass 6 is ⁇ 2
  • the relative refractive index difference between second .side core 4 and outer glass 6 is ⁇ 3
  • ⁇ 2 n 2 -n 5
  • ⁇ 3 n 3 -n 5
  • ⁇ 4 n -n 5 .
  • the refractive index of center core 2, side cores 3 and 4, cladding region 5 and outer glass are characterized by the following relationship - n 4 ⁇ n 5 ⁇ n 3 ⁇ n 2 ⁇ n , which indicates that the refractive indexes n 2 , n 3 , and n 4 of first side core 3, second side core 4 and cladding region 5 respectively are lower than the refractive index ni of the center core 2, and the refractive index n 4 of cladding region 5 is also lower than the refractive index n 5 of the outer glass 6.
  • refractive indexes n-i, n 2 and n 3 of center core 2, first side core 3 and second side core 4 respectively are positive, and refractive index n of cladding region 5 is negative with respect to the refractive index ns of outer glass 6, which is assigned zero value as reference.
  • the cladding region 5 is depressed cladding region.
  • the relative refractive index differences ⁇ i, ⁇ 2 , ⁇ g and ⁇ 4 between center core 2 and outer glass 6, between first side core 3 and outer glass 6, between second side core 4 and outer glass 6 and between cladding region 5 and outer glass 6 respectively are characterised by the following relationships :
  • the outer diameters of the centre core 2, first side core 3, second side core 4 and cladding region 5 are characterised by following relationships :
  • the ratio of radius 'bi'of first side core 3 and of radius 'a' of centre core 2 [b ⁇ a] is about 1.5 ⁇ 0.2
  • the ratio of radius 'b 2 ' of second side core 4 and of radius 'a' of centre core 2 [b 2 /a] is about 2.5 ⁇ 0.2
  • the ratio of radius 'b 3 ' of cladding region 5 and of radius 'a' of centre core 2 [bs/a] is about 3.7 ⁇ 0.2.
  • the presently disclosed dispersion optimized fiber having the profile as described and disclosed herein above has attenuation less than or equal to about 0.22 dB/km at 1550 nm, mode field diameter about 8.4 to 9.4 micrometer at 1550 nm, the effective area between about 55 to 65 micron 2 at 1550 nm, the cut-off wavelength less than about 1250 nm, the chromatic dispersion between about 2 to 8 ps/nm-km in 1530 - 1565 nm range, the polarized mode dispersion less than about 0.25 ps/km 5 and the microbending loss less than about 0.04 dB at 1550 nm.
  • the dispersion slope of the presently disclosed dispersion optimized fiber is about 0.060 ⁇ 0.015 ps/nm 2 km over the predefined wavelength region and the zero chromatic dispersion lies in between about 1470 - 1510 nm wavelength region.
  • the dispersion optimized fiber as disclosed in the present invention has low dispersion and optical loss between 1530 to 1565 nm (C-band) transmissions and is suitable for transmission of higher bandwidth. over long distances.
  • the presently disclosed dispersion optimized fiber not only has optimized effective area, cut-off wave length and mode filed diameter but also has achieved a high level of bend resistance for high bandwidth transmission, minimized non- linearities and low chromatic dispersion with a low optical loss in the C-Band region.
  • the center core 2 of the presently disclosed dispersion optimized fiber 1 is doped with germanium doped in Si0 2
  • the first, side core 3 is doped with germanium and fluorine doped in Si0 2
  • the second side core 4 is doped with germanium and fluorine doped in Si0 2
  • the depressed cladding region 5 is doped with germanium'and fluorine doped in SiO ⁇ .
  • the doped dispersion optimized fiber' of the present invention can be manufactured in accordance to any known process.
  • the center core 2 of the presently disclosed dispersion optimized fiber 1 is doped with germanium doped in Si0 2 preferably at 55 to 166 SCCm (standard cubic centimeter) flow rate and preferably at 1920 to 1960°C temperature
  • the first side core 3 is doped with germanium and fluorine doped in Si0 2 preferably at 116 to 130 SCCm flow rate of germanium and preferably at 0.19 to 0.44 SCCm flow rate of fluorine and preferably at 1900 to 1916°C temperature
  • the second side core 4 is doped with germanium and fluorine doped in Si0 2 preferably at 105 to 115 SCCm flow rate of germanium and preferably at 0.19 to 0.78 SCCm flow rate of fluorine and preferably at 1860 to 1892°C temperature
  • the depressed cladding region 5 is doped with germanium and fluorine doped in Si0 2 preferably at 90.4 to 100.4 SCCm flow rate of germanium and preferably at 0.75 to 1.1
  • germanium dioxide (Ge0 2 ) is doped to quartz glass of the center core
  • first side core 3, and second side core 4 to increase the refractive index n 1? n 2) n 3 .
  • the refractive index ni, n 2 and n 3 of the center core 2, first side core 3, and second side core 4 respectively is increased only by the doping of Ge0 2 , Rayleigh scattering in the glass increases which in turn increases the attenuation of light transmission of the optical fiber.
  • the solution of this problem has been achieved by fluorine doping in the outer cladding region 5.
  • the doping of fluorine decreases the viscosity mismatch between center core 1 , first side core 3 and second side core 4 and at the same time increases the total refractive index difference between the core, comprising of center core 2, first side core 3, and second side core 4, and clad 5, that is, it reduces the attenuation by reducing the amount of Ge0 2 incorporation in the core.
  • the dispersion optimized fiber design, as disclosed herein above has a unique profile which results in significantly less microbendi ⁇ g sensitivity.
  • SPM Self Phase Modulation
  • XPM Cross Phase Modulation
  • Figures 2 to 5 illustrate various characteristics of the presently disclosed dispersion optimized fiber.
  • Figure 2 discloses the chromatic dispersion characteristics of dispersion optimized fiber in accordance with the present invention, particularly, it discloses low dispersion and low slope that have been achieved from the preferred combination of refractive indices ni, n 2 , n 3) n 4 and n 5 and diameters 2a, 2b ⁇ , 2b 2 , 2b 3 of the said members, as defined and described herein above, of the refractive index profile of the presently disclosed dispersion optimized fiber.
  • Figure 5 discloses spectral attenuation, characteristics of the presently disclosed dispersion optimized fiber in accordance with the present invention, particularly it discloses a combination of low loss in the previously defined C-band and low OH .peak, which has been created from the selection of flow rate of the dopants in accordance to the present invention.
  • the dispersion optimized fiber 1 is an optical fiber having a step index profile in case of first side core 3 and second side core 4 and trapezoidal profile in case of the center core 2.
  • the profile volume of the presently disclosed dispersion optimized fiber can be defined as follows :
  • the calculated profile volume of the presently disclosed dispersion optimized fiber 1 is in the range of 8 % ⁇ m 2 to 23 % ⁇ m 2 .
  • the refractive index profile of the presently disclosed dispersion optimized fiber 1 as disclosed in figure 1 comprises of a germanium doped silica core, germanium and fluorine doped first and second side cores, germanium, fluorine doped depressed cladding and silica outer cladding, which is not intended to limit the scope of the present invention.

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Abstract

A dispersion optimized fiber comprising a centre core, two side cores, a cladding and a outer glass, wherein first side core is provided onto outer periphery of center core, second side core is provided onto outer periphery of first side core and cladding region is provided onto outer periphery of second side core is disclosed, wherein centre core, first side core, second side core and cladding region have n1, n2, n3 and n4 refractive index respectively and 2a, 2b1, 2b2 and 2b3 outer diameter respectively.. The refractive index of outer glass is n5 and its diameter is selected to suit the requirement of desired fiber. The refractive indexes of said members are characterized by relationship n4<n5<n3<n2<n1, and outer diameters of each member are characterized by 5.1≥2a≥6.2 νm, 7≥2b1≥9 νm, 13≥2b2≥15 νm, 19≥2b3≥22 νm relationships.

Description

TITLE OF INVENTION
Dispersion Optimized Fiber with Low Dispersion and Optical Loss
Technical Field
The present invention relates to dispersion optimized fiber with low dispersion and optical loss, particularly it relates to a dispersion optimized fiber to provide low dispersion and optical loss between 1530 to 1565. nm (C-band) transmissions, more particularly it relates to single mode dispersion optimized fiber, which is suitable for transmission of higher, bandwidth over long distances and yet has optimized effective area, cut-off wavelength and mode field diameter to achieve a high level of bend resistance for high bandwidth transmission.
Background Art
Over the last decade, the optical fibers have been developed and installed as the backbone of interoffice networks for voice, video and data transmission. These are becoming important with growing and expanding telecommunication infrastructure. Their importance is further increasing because of their high bandwidth applicability. The higher bandwidth demand is further increasing exponentially with time because of rapid growth of information technology.
Conventionally, the multi-mode fiber at wavelength of 850 nm were used, which were replaced by single mode fibers with zero dispersion wavelength near 1310 nm. The single mode or monomode optical fibers have greater bandwidth than that of the multimode fibers. Therefore, the research has been directed towards the development of the single mode fibers, as these fibers were observed to have lower attenuation between the wavelength range from 1300 nm to 1550 nm. The transmission loss of single mode fibers is observed to be as low as 0.5 dB/km at 1300 nm wavelength and 0.2 dB/km at 1550 nm wavelength. However, when single wavelength moved through 1550 nm window for lower attenuation, the single mode fibers were observed to have very high dispersion.
The major disadvantage of the single mode fibers with high dispersion at 1550 nm was that, it obstructed higher bit rate transmission. This disadvantage of single mode fibers has been overcome by the improved single mode fibers, known as dispersion shifted fibers, which have zero dispersion even when the wavelength shifted to 1550 nm.
In the prior art the optical fibers with minimum attenuation of light transmission and the dispersion shifted fibers with zero dispersion in the wavelength region of 1500 nm to 1600 nm band are being used. The fibers with simple step like refractive index profile have ■ poor practical advantages. The dispersion shifted fibers with convex refractive index profile have better practical advantages and less flexural loss.
The known dispersion shifted fibers have higher refractive index in the center core and lower refractive index in the outer region. The relative difference in the refractive index is achieved by using different dopants. The commonly used dopants are germanium and fluorine, however, their flow rate and the temperature of doping are different in different known methods. The specific refractive index profile having selected refractive indexes and outer diameters of core and cladding region of the optical fiber is decided by the selection of dopants, their flow rates and temperatures of doping of the core and/or cladding regions, demarcation of core region into one or more core regions with one or more set of refractive indexes, the demarcation of cladding region into one or more cladding regions with one or more set of refractive indexes, the shape of core and cladding regions etc. These parameters decide the characteristic properties of thus obtained fiber and the applications of thus obtained fiber.
Therefore, the fibers known in the art are distinguished by way of their characteristic properties, which in-turn are decided by various parameters as stated herein above. The fibers as known in the prior art either have. low non- linearity but high bend loss or have low bend loss but less effective area or may have higher non-linearity and higher bend loss.
Therefore, the attempt had been to develop the fiber, which will have optimum characteristic properties, that is which will not sacrifice one of the characteristic property to achieve another characteristic property.
Objects of the Invention
The main object of the present invention is to make a complete disclosure of a dispersion optimized fiber, which has low dispersion and optical loss, particularly between 1530 to 1565 nm wavelength band.
The another object of "the present invention is to make a complete disclosure of a dispersion optimized fiber, which is suitable for long haul transmission.
Still another object of the present invention is to make a disclosure' of a dispersion optimized fiber which not only has low dispersion and optical loss in 1530 to 1565 nm wavelength band but also has optimized effective area, cut-off wavelength and mode field diameter.
*
This is further an object of the present invention to make a disclosure of a dispersion optimized fiber which not only has high level of bend resistance for high bandwidth transmission but also has minimized non-linearities and low chromatic dispersion.
The other objects and preferred embodiments and advantages of the present invention will be more apparent from the following description when it is read in conjunction with the accompanying figures which are not intended to limit the scope of the present invention. Brief Disclosure of the Invention
In accordance to the present invention dispersion optimized fiber with low dispersion and optical loss between 1530 to 1565 nm (C-band) transmissions, particularly a dispersion optimized fiber, which is suitable for transmission of higher bandwidth over long distances and yet has optimized effective area, cutoff wavelength and mode field diameter, herein after referred to as MFD, to achieve a high level of bend resistance for high bandwidth transmission, minimized non-linearities and low chromatic dispersion with a low .optical loss in the C-Band region is disclosed comprising a centre core, two side cores, a cladding region and a outer glass, wherein the first side core is provided onto the outer periphery of the center core, second side core is provided onto the outer periphery of the first side core and cladding region is provided onto the outer periphery of the second side core. According to the present invention the centre core, first side core, second side core and cladding region have ni, n2, n3 and n4 refractive index respectively and 2a, 2b1, 2b2 and 2b3 outer diameter respectively. The refractive index of outer glass is n5 and its diameter is selected to suit the requirement of desired fiber. The refractive indexes of said members are characterized by relationship n <n5<n3<n2<ni, and outer diameters' of each member are characterized by 5.1>2a>6.2 μm, 7>2bι>9 μm, 13>2b2>15 μm, 19>2b3>22 μm relationships.
In accordance to the preferred embodiment of the present invention the cladding region is depressed cladding region and the side cores have lower refractive index than the center core. The refractive index of centre core, two side cores are positive and refractive index of cladding region is negative with respect to the refractive index of outer glass.
The other preferred embodiments and the advantages of the present invention will be more apparent from the following description when it is read in conjunction with the accompanying figures which are not intended to limit the scope of the present invention.
Brief Description of the Figures
Figure 1a of figure 1 shows a cut-section of dispersion optimized fiber in accordance to the preferred embodiments of the present invention.
Figure 1 b of figure 1 shows the refractive index profile of dispersion optimized fiber in accordance to the preferred embodiments of the present invention.
Figure 2 shows the chromatic dispersion in the C-band region of dispersion optimized fiber in accordance to the preferred embodiments of the present invention.
Figure 3 shows the cut-off wavelength, using 2m-fiber as a reference length and measured on spectral analyzer, of the dispersion optimized fiber in accordance to the preferred embodiments of the present invention.
Figure 4 shows the intensity distribution along the diameter of the presently disclosed fiber for measuring the MFD of dispersion optimized fiber in accordance to the preferred embodiments of the present invention.
Figure 5 shows the attenuation spectra of dispersion optimized fiber in accordance to the preferred embodiments of the present invention. .
Detailed Description and Preferred Embodiments of Invention
Now referring to figure 1a showing a cut-section of dispersion optimized fiber in accordance to the preferred embodiments of the present invention, the dispersion optimized fiber T comprises of a centre core 2, two side cores 3 and 4, which are referred to as first side core 3 and second side core 4, a cladding region 5 and a outer glass 6, and in accordance to the present invention the first side core 3 is provided onto the outer periphery of the center core 2, second side core 4 is provided onto the outer periphery of the first side core 3, cladding region 5 is provided onto the outer periphery of the second side core 4 and outer glass 6 is provided onto the outer periphery of the cladding region 5.
Now referring to figure 1b, which shows the refractive index profile of dispersion optimized fiber in accordance to the preferred embodiments of the present invention, centre core 2 has refractive index ni, the first side core 3 has refractive index n2, the second side core 4 has refractive index n3, the cladding region 5 has refractive index n4 and the outer glass 6 has refractive index n5ι and the centre core 2 has outer diameter 2a, the first side core 3 has outer diameter 2bι, the second side core 4 has outer diameter 2b2, the cladding region 5 has outer diameter 2b3. The diameter of the outer glass 6 can be selected to suit the requirement of desired dispersion optimized fiber.
In accordance to the present invention the relative refractive index difference between center core 2 and outer glass 6 is Δ-i, the relative refractive index difference between first side core 3 and outer glass 6 is Δ2, the relative refractive index difference between second .side core 4 and outer glass 6 is Δ3 and the relative refractive index difference between cladding region 5 and outer glass 6 is Δ ) that is Δi = nι-n5, Δ2 = n2-n5,Δ3 = n3-n5, Δ4 = n -n5.
In accordance to one . of the preferred embodiments of the present invention the refractive index of center core 2, side cores 3 and 4, cladding region 5 and outer glass are characterized by the following relationship - n4 < n5 < n3 < n2 < n , which indicates that the refractive indexes n2, n3, and n4 of first side core 3, second side core 4 and cladding region 5 respectively are lower than the refractive index ni of the center core 2, and the refractive index n4 of cladding region 5 is also lower than the refractive index n5 of the outer glass 6. The refractive indexes n-i, n2 and n3 of center core 2, first side core 3 and second side core 4 respectively are positive, and refractive index n of cladding region 5 is negative with respect to the refractive index ns of outer glass 6, which is assigned zero value as reference.
In accordance to still another preferred embodiment of the present invention the cladding region 5 is depressed cladding region.
In accordance to another preferred embodiment of the present invention the relative refractive index differences Δi, Δ2, Δg and Δ4 between center core 2 and outer glass 6, between first side core 3 and outer glass 6, between second side core 4 and outer glass 6 and between cladding region 5 and outer glass 6 respectively are characterised by the following relationships :
0.009 > Δι > 0.0135
0.0009> Δ2 > 0.0019 0.0005> Δ3 > 0.0009 - 0.0001 > Δ4 > - 0.0006
and Δ1 , Δ2 and Δ3 are positive, and Δ-4 is negative with reference to outer glass 6:
In accordance to the preferred embodiment of the present invention the outer diameters of the centre core 2, first side core 3, second side core 4 and cladding region 5 are characterised by following relationships :
5.1 > 2a > 6.2 μm 7 > 2bι >_9 μm 13 > 2b2 >15 μm 19 > 2b3 >22 μm The ratio of radius 'bi'of first side core 3 and of radius 'a' of centre core 2 [b^a] is about 1.5 ± 0.2, the ratio of radius 'b2' of second side core 4 and of radius 'a' of centre core 2 [b2/a] is about 2.5 ± 0.2, the ratio of radius 'b3' of cladding region 5 and of radius 'a' of centre core 2 [bs/a] is about 3.7 ± 0.2.
The presently disclosed dispersion optimized fiber having the profile as described and disclosed herein above has attenuation less than or equal to about 0.22 dB/km at 1550 nm, mode field diameter about 8.4 to 9.4 micrometer at 1550 nm, the effective area between about 55 to 65 micron2 at 1550 nm, the cut-off wavelength less than about 1250 nm, the chromatic dispersion between about 2 to 8 ps/nm-km in 1530 - 1565 nm range, the polarized mode dispersion less than about 0.25 ps/km 5 and the microbending loss less than about 0.04 dB at 1550 nm. Further, the dispersion slope of the presently disclosed dispersion optimized fiber is about 0.060 ± 0.015 ps/nm2km over the predefined wavelength region and the zero chromatic dispersion lies in between about 1470 - 1510 nm wavelength region.
It is observed from the foregoing description that the dispersion optimized fiber as disclosed in the present invention has low dispersion and optical loss between 1530 to 1565 nm (C-band) transmissions and is suitable for transmission of higher bandwidth. over long distances.
The presently disclosed dispersion optimized fiber not only has optimized effective area, cut-off wave length and mode filed diameter but also has achieved a high level of bend resistance for high bandwidth transmission, minimized non- linearities and low chromatic dispersion with a low optical loss in the C-Band region.
In accordance to the preferred embodiment of the present invention, the center core 2 of the presently disclosed dispersion optimized fiber 1 is doped with germanium doped in Si02, the first, side core 3 is doped with germanium and fluorine doped in Si02, the second side core 4 is doped with germanium and fluorine doped in Si02 and the depressed cladding region 5 is doped with germanium'and fluorine doped in SiO≥. The doped dispersion optimized fiber' of the present invention can be manufactured in accordance to any known process.
However, in accordance to one of the preferred embodiments of the present invention the center core 2 of the presently disclosed dispersion optimized fiber 1 is doped with germanium doped in Si02 preferably at 55 to 166 SCCm (standard cubic centimeter) flow rate and preferably at 1920 to 1960°C temperature, the first side core 3 is doped with germanium and fluorine doped in Si02 preferably at 116 to 130 SCCm flow rate of germanium and preferably at 0.19 to 0.44 SCCm flow rate of fluorine and preferably at 1900 to 1916°C temperature, the second side core 4 is doped with germanium and fluorine doped in Si02 preferably at 105 to 115 SCCm flow rate of germanium and preferably at 0.19 to 0.78 SCCm flow rate of fluorine and preferably at 1860 to 1892°C temperature and the depressed cladding region 5 is doped with germanium and fluorine doped in Si02 preferably at 90.4 to 100.4 SCCm flow rate of germanium and preferably at 0.75 to 1.1 SCCm flow rate of fluorine and preferably at 1800 to 1844°C temperature.
The germanium dioxide (Ge02) is doped to quartz glass of the center core
2, first side core 3, and second side core 4 to increase the refractive index n1? n2) n3. However, when, the refractive index ni, n2 and n3 of the center core 2, first side core 3, and second side core 4 respectively is increased only by the doping of Ge02, Rayleigh scattering in the glass increases which in turn increases the attenuation of light transmission of the optical fiber. The solution of this problem has been achieved by fluorine doping in the outer cladding region 5. The doping of fluorine decreases the viscosity mismatch between center core 1 , first side core 3 and second side core 4 and at the same time increases the total refractive index difference between the core, comprising of center core 2, first side core 3, and second side core 4, and clad 5, that is, it reduces the attenuation by reducing the amount of Ge02 incorporation in the core. The dispersion optimized fiber design, as disclosed herein above has a unique profile which results in significantly less microbendiήg sensitivity.
Further, it has minimized non-linear effects, such as Four-Wave Mixing (FWM),
Self Phase Modulation (SPM), Cross Phase Modulation (XPM) etc. and hence does not cause degradation of signal during high power transmission.
The problems of the non-linearities at higher bandwidth transmission are overcome by the presently disclosed dispersion optimized fiber having above stated characteristics.
Figures 2 to 5 illustrate various characteristics of the presently disclosed dispersion optimized fiber. Figure 2 discloses the chromatic dispersion characteristics of dispersion optimized fiber in accordance with the present invention, particularly, it discloses low dispersion and low slope that have been achieved from the preferred combination of refractive indices ni, n2, n3) n4 and n5 and diameters 2a, 2bι, 2b2, 2b3 of the said members, as defined and described herein above, of the refractive index profile of the presently disclosed dispersion optimized fiber.
Figure 3 and figure 4 disclose the details regarding cut-off wavelength, for
2-meter reference length and mode field diameter characteristics of the presently disclosed dispersion optimized fiber in accordance with the present invention.
Figure 5 discloses spectral attenuation, characteristics of the presently disclosed dispersion optimized fiber in accordance with the present invention, particularly it discloses a combination of low loss in the previously defined C-band and low OH .peak, which has been created from the selection of flow rate of the dopants in accordance to the present invention.
The dispersion optimized fiber 1 according to the present invention is an optical fiber having a step index profile in case of first side core 3 and second side core 4 and trapezoidal profile in case of the center core 2. The profile volume of the presently disclosed dispersion optimized fiber can be defined as follows :
a bi b2 b3 Jλn(r)rdr + Jλn(r)rdr + jΔn(r)rdr + |Δn(r)rdr a
0 bi b2
where a, bi, b2, b3 are as defined herein above and are characterised by the relationships as described herein above. The calculated profile volume of the presently disclosed dispersion optimized fiber 1 is in the range of 8 %μm2 to 23 %μm2.
The refractive index profile of the presently disclosed dispersion optimized fiber 1 , as disclosed in figure 1 comprises of a germanium doped silica core, germanium and fluorine doped first and second side cores, germanium, fluorine doped depressed cladding and silica outer cladding, which is not intended to limit the scope of the present invention.

Claims

Claims
1. Dispersion optimized fiber 1 with low dispersion and optical loss comprising a centre core 2, two side cores 3 and 4, a cladding region 5 and a outer glass 6, wherein said centre core 2 has refractive index n-i, the first side core 3 has refractive index n2, the second side core 4 has refractive index n3, said cladding region 5 has refractive index n4 and said outer glass 6 has refractive index n5 and said centre core 2 has outer diameter 2a, said first side core 3 has outer diameter 2b-ι, said second side core 4 has outer diameter 2b2, said cladding region 5 has outer diameter
2b3 and the relative refractive index difference between said center core 2 and said outer glass 6 is Δi, the relative refractive index difference between said first side core 3 and said outer glass 6 is Δ2, the relative refractive index difference between said second side core 4 and said outer glass 6 is Δ3 and the relative refractive index difference between said cladding region 5 and said outer glass 6 is Δ4, wherein the refractive indexes n-i, n2j n3, n4 and n5 of said members 2, 3, 4, 5 and 6 respectively are characterized by the following relationship :-
Figure imgf000014_0001
the relative refractive index differences Δi, Δ2ι Δ3 and Δ4 between said members 2, 3, 4, 5 and 6 are characterized by the following relationships :
Figure imgf000014_0002
0.0009> Δ2 > 0.0019 0.0005> Δ3 > 0.0009 - 0.0001 > Δ4 > - 0.0006 and the relationship between said relative refractive index differences Δ-ι, Δ2, Δ3 and Δ4 between said members 2, 3, 4, 5 and 6, and said refractive indexes ni, n2) n3j n4 and n5 of said members 2, 3, 4, 5 and 6 respectively are characterized by the following relationships :
Figure imgf000014_0003
Δ2 = n2-n5 Δ3 = n3-n5 and
Figure imgf000015_0001
and the outer diameters 2a, 2^, 2b2 and 2b3 of said members 2, 3, 4 and 5 respectively are characterized by the following relationships : 5.1 > 2a > 6.2 μm
7 > 2bι >_9 μm 13 > 2b2 >15 μm 19 > 2b3 >22 μm
2. Dispersion optimized fiber according to claim 1 , wherein said first side core 3 is provided onto the outer periphery of said center core 2, and said second side core 4 is provided onto the outer periphery of said first side core 3, and said cladding region 5 is provided onto the outer periphery of said second side core 4.
3. Dispersion optimized fiber according to claims 1 and 2, wherein said cladding region 5 is depressed cladding region.
4. Dispersion optimized fiber according to claims 1 to 3, wherein the ratio of radius 'bi' of said first side core 3 and of radius 'a' of said centre core 2 [bi/a] is about 1.5 ± 0.2, the ratio of radius 'b2' of said second side core 4 and of radius 'a' of said centre core 2 [b2/a] is about 2.5 ± 0.2, the ratio of radius 'b3' of said cladding region 5 and of radius 'a' of said centre core 2 [bji/a] is about 3.7 ± 0.2.
5. Dispersion optimized fiber according to claims 1 to 4, wherein Δi, Δ2 and Δ3 are positive, but Δ-4 is negative with reference to said outer glass 6.
6. Dispersion optimized fiber according to claims 1 to 5, wherein the attenuation of said fiber 1 at 1550 nm is less than or equal to about 0.22 dB/km, and mode field diameter of said fiber 1 at 1550 nm.is about 8.4 to 9.4 micrometer, and effective area of said fiber 1 at 1550 nm is between about 55 to 65 micron2, and the cut-off wavelength of said fiber 1 is less than about 1250 nm, and the polarization mode dispersion of said fiber 1 is less than about 0.25 ps/km α5.
7. Dispersion optimized fiber according to claims 1 to 5, wherein the chromatic dispersion of said fiber 1 in 1530 - 1565 nm range is about 2 to 8 ps/nm-km, and the mierobending loss of said fiber 1 is less than about 0.04 dB at 1550 nm.
8. Dispersion optimized fiber according to claims 1 to 5, wherein the dispersion slope of said fiber 1 is about 0.060 ± 0.015 ps/nm2km over the predefined wavelength region, and the zero chromatic dispersion of said fiber 1 lies in between about 1470 - 1510 nm wavelength region. •
9. Dispersion optimized fiber according to claims 1 to 8, wherein said side . cores 3 & 4 have a step index profile and said center core 2 has trapezoidal profile.
10. Dispersion optimized fiber according to claims 1 to 9, wherein said fiber 1 has calculated profile volume in the range of 8 %μm2 to 23 %μm2.
11. Dispersion optimized fiber according to claims 1 to 10, wherein said center core 2 of said fiber 1 is doped with germanium doped in Si02, and said first side core 3 of said fiber 1 is doped with germanium and fluorine doped in
Si02, said second side core 4 of said fiber 1 is doped with germanium and fluorine doped in Si02, said depressed cladding region 5 of said fiber 1 is doped with germanium and fluorine doped in Si02.
12. Dispersion optimized fiber according to claim 11 , wherein said center core 2 is doped preferably at 55 to 166 SCCm flow rate and preferably at 1920 to 1960°C temperature, and said first side core 3 is doped preferably at • 116 to 130 SCCm flow rate of germanium and preferably at 0.19 to 0.44 SCCm flow rate of fluorine and preferably at 1900 to 1916°C temperature, and, said second side core 4 is doped preferably at 105 to 115 SCCm flow rate of germanium and preferably at 0.19 to, 0.78 SCCm flow rate of fluorine and preferably at 1860 to 1892°C temperature and said depressed cladding region 5 is preferably at .90.4 to 100.4 SCCm flow rate of germanium and preferably at 0.75 to 1.1 SCCm flow rate of fluorine and preferably at 1800 to 1844°C temperature.
13. Dispersion optimized fiber as claimed and described herein above with the help of the accompanying figures.
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EP1610161A1 (en) * 2004-06-23 2005-12-28 Furukawa Electric North America Inc. Optical fiber with reduced splice loss and method of making the same
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US10295733B2 (en) 2013-12-20 2019-05-21 Draka Comteq B.V. Single mode fibre with a trapezoid core, showing reduced losses
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US20170031089A1 (en) * 2013-12-20 2017-02-02 Draka Comteq B.V. Single Mode Fibre with a Trapezoid Core, Showing Reduced Losses
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WO2019122943A1 (en) * 2017-12-21 2019-06-27 Draka Comteq France Bending-loss insensitve single mode fibre, with a shallow trench, and corresponding optical system
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US10962708B2 (en) 2017-12-21 2021-03-30 Draka Comteq France Bending-loss insensitive single mode fibre, with a shallow trench, and corresponding optical system
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