CA1248386A - Quadruple-clad optical fiberguide - Google Patents
Quadruple-clad optical fiberguideInfo
- Publication number
- CA1248386A CA1248386A CA000420280A CA420280A CA1248386A CA 1248386 A CA1248386 A CA 1248386A CA 000420280 A CA000420280 A CA 000420280A CA 420280 A CA420280 A CA 420280A CA 1248386 A CA1248386 A CA 1248386A
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- Prior art keywords
- fiber
- cladding
- wavelengths
- dispersion
- optical fiber
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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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
- G02B6/02214—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
- G02B6/02223—Dual window fibres, i.e. characterised by dispersion properties around 1550 nm and in at least another wavelength window, e.g. 1310 nm
-
- 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
- G02B6/02233—Dispersion flattened fibres, i.e. having a low dispersion variation over an extended wavelength range having at least two dispersion zero wavelengths
-
- 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
- G02B6/036—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
- G02B6/03666—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 arranged - + - +
Landscapes
- Chemical & Material Sciences (AREA)
- Dispersion Chemistry (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Glass Compositions (AREA)
- Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)
- Waveguides (AREA)
- Surface Treatment Of Glass Fibres Or Filaments (AREA)
- Optical Communication System (AREA)
Abstract
QUADRUPLE-CLAD OPTICAL FIBERGUIDE
Abstract To broaden the range of wavelengths over which an optical fiber has low loss and low chromatic dispersion, four optically active cladding layers are employed. The relative refractive indices and radii of the core and claddings are advantageously selected such that the chromatic dispersion curve has three zero crossings.
Abstract To broaden the range of wavelengths over which an optical fiber has low loss and low chromatic dispersion, four optically active cladding layers are employed. The relative refractive indices and radii of the core and claddings are advantageously selected such that the chromatic dispersion curve has three zero crossings.
Description
- ,~
QUADRUPLE-CLAD OPTICAL FIBERGUIDE
( Technical Field -This invention relates to optical ibers and, in particular, to low-loss, low-dispersion fibers.
Background of the Invention In copending Canadian Patent Application Serial No.
410,323 filed Au~ust 27, 1982 in the name Gf L.G. Cohen, et al, there is disclosed a double-clad, single-mode optical fiber comprising a core region surrounded by a thin inner cladding and a thicker outer cladding. By the suitable selection of radii and refractive indices, low chromatic dispersion can be realized over the range of wavelengths between 1.3 and 1.55 ~m. However, as the wavelength increases, losses due to radiation through the cladding layers become signficiant. In particular, in the vicinity of the fundamental mode cut-off wavelength, a small change in signal wavelength causes the fundamental mode to change from a guided wave to a leaky wave that radiates through the claddings. The result is high loss at the upper end of the low dispersion range.
Summary of the Invention ______________________ _ In accordance with an aspect of the invention there is provided an optical fiber which comprises a core region having a refractive index nc and a radius Rc, surrounded by ~our cladding layers having refractive indices and radii (nl, Rl), (n2, R2), (n3, R3), and (n4, R4), respectively, total dispersion for the optical fiber is zero for at least one wavelength in a predetermined range of wavelengths, wherein ~ R4>R3>R2>
and nc>n2>n4>n3>nl and wherein (R~ - RC2) l + (R3 - R2)~3 > 1, RC2~C + (R22 - Rl2)~2 .- ~
- . .' : ::
, :, . :
: - :`', : : .
~ 6 - la -- where n~ - n n4 Q ¦
n4 n4--n3 n4 Ac = ~
In accordance with the present invention, the above-described loss mechanism is displaced away from the desired wavelength region of low chromatic dispersion and, in addition, the low dispersion band is broadened. This is accomplished in a lightguide comprising a core region surrounded by four cladding layers. Designating the refractive indices of the core and the successive cladding layers as nc, nl, n2, n3, and n~, respectively, :~ the indices are advantageously proportioned such that : nc>n2~n4>n3>nl~
By the appropriate selection of indices and radii, the chromatic dispersion curve can be made to have three zero crossings, as compared to the two possible :
, :
: . ,~: .
:. ~ , . ~ , ....
~4~3~
crossings for the prior art double-clad fiber, and to cover the desired range of wavelengths which includes 1~3 and 1.55 ~m.
Brief Description of the Drawing FIG. 1 shows a prior art double-clad (DC) optical fiber;
FIG. 2 shows a typical chro~atic dispersion curve for a double~clad fiber;
FIG. 3 shows a quadruple-clad (QC) fiber in accordance with the present invention;
FIG. 4 shows the variations in the group index in DC and QC fibers; and FIG. 5 shows chromatic dispersion curves for quadruple-clad fibers of different sizes; and FIG. 6 shows dispersion curves for single, double and quadruple clad fibers.
Detailed Description Referring to the drawing, FIG. 1 shows a cross section of a prior art double-clad (DC) optical fiber 10 comprising a core region 11 surrounded by a relatively thin first inner cladding 12 and a thicker, second outer cladding 13. Designating the refractive index of the outer cladding as nO, the refractive index nc of the core is equal to nO(l~c), and the refractive index nl of the inner cladding is equal to nO(l+Ql), where ac and ~1 are the fractional differences between the refractive indices of the core and outer cladding, and between the inner and the outer claddings. The index profile of such a fiber is the so-called "W-profile~', also illustrated in FIG. 1, wherein the several indices are shown as a func~ion of the fiber radius normalized with respect to the inner cladding radius a-For a fiber composed of a germaniu~-doped silica core, a fluorine-doped inner cladding, and a pure silica outer cladding, Rc is advantageously about 0~7, and the ratio~l/4c is advantageously e~ual to 2. For such a fiber, the total chromatic dispersion is low over the ~ : :
~ . ~ . .
:, -~ , .
desired wavelength region between 1.3 ~m and 1.55 ~m.
FIG. 2, included for purposes of explanation, shows a set of typical dispersion curves for a DC fiber including a material dispersion curve 15, a wavelength dispersion curve 16, and the resulting total chromatic dispersion curve 17, obtained by summing curves 15 and 16.
In general, the total dispersion curve for a DC fiber can have two zero crossings at wavelengths ~1 and ~2. For this particular illustrative fiber these occur at ~1 = 1.35 ~m and A2 = 1.63 ~m. Because of the large material dispersion at the longer wavelength, the ~2 zero crossing is associated with a correspondingly large waveguide dispersion that occurs near the fundamental mode cut-off wavelength ~co~ approximately equal to 1.7 ~m. This is the wavelength at which the effective refractive index becomes less than nO. At this wavelength, the signal wave is no longer guided by the fiber but, instead, radiates through the claddings and is lost.
In order to insure low-loss operation, ~co should be more than 0.1 ~m larger than the longest wavelength of interest. Based upon this criteria, the total chromatic dispersion characteristics obtainable with currently available double-clad fibers designed to have low dispersion over the range between 1.3 and 1.55 ~m are only marginally acceptable for operation near 1.55 ~m.
To avoid the above-described limitations and disadvantages of the prior art double-clad fiber, two additional claddings are added, in accordance with the pre~sent invention, to form the quadruple-clad fiber 20 illustrated in FIG. 3. This fiber comprises a core region 21 surrounded by four cladding layers 22, 23, 24 and 25, where layer 22 is the first, innermost cladding~ and layer 25 is the fourth, outermost cladding. Designating the refractive index n4 of the outermost cladding 25 as nO, the refractive indices of the core nc, and the indices nl, n2 and n3 of the respective claddings 22, 23 and 24 are given by nC = nO (l+~C) nl = nO (1-~1) n2 = nO (1-~2) and n3 = nO (1 ~3) 5 where c, ~1, A2 and ~3 are the fractional differences between the indices of the respective portions of the fiber and that of the outermost cladding.
The index profile for the QC fiber is shown in FIG. 3 as a function of the fiber radius normalized with respect to the radius Rl of the innermost cladding 22. As can be seen, the relative magnitudes of the indices are such that nc>n2>n4>n3>nl -As explained hereinabove, in the vicinity of the fundamental mode cut-off, a small change in wavelength causes the signal to change from a guided mode into a leaky mode that radiates into the second cladding~ The reason for this can be explained with reference to FIG. 4 which shows the effective group index, ng, as a function of wavelength, A-, for both the DC and QC fibers. At the shorter wavelengths, the signal is primarily guided by an inner lightguide formed by the core 21 and the first cladding 22. Accordingly, the effective group index at the shorter wavelengths, given by curve portion 43, is shown to be larger than the core ~index, given by curve 40. At the longer wavelengths, more of the signal field extends into the first cladding and beyond. The effect is to decrease the effective group index. In the DC fiber, the group index eventually becomes less than the outermost (i.e., second cladding) and the guide becomes cut-off. This is indicated by curve portion 44 which approaches cut-off at ~co ; By contrast, in the QC~fiber, the wave energy that radiates out of the fiber core is trapped in an outer ~z~
lightguide formed by the second cladding 23 and the surrounding first and third claddings 22 and 24~ The light thus trapped is not lost through radiation but continues to be guided, albeit in a different portion of the fiber. The effective group index, given by curve portion 45, is seen to change from a value greater than nc to a value that approaches that of the second cladding given by curve 41.
As can be seen, the resulting index curve for the QC fiber has three turning points at wavelengths Al, ~2 and ~3.
Inasmuch as the total chromatic dispersion characteristic is proportional to the slope of the group index curve, the chromatic dispersion can have three zero points, at wavelengths ~l' X~2 and ~3, as illustrated in FIG. 5.
In the design of a QC fiber, there are nine independent parameters ~c~ 2~ ~3~ Rc~ Rl~ R2~ R3 and a. The radius of the outermost cladding is not critical and, typically, is made relatively large for reasons to be explained hereinbelow. A generalized method for calculating the total chromatic dispersion characteristic for any arbitrary index profile is described in a paper by L. G. Cohen et al., entitled "Correlation Between Numerical Predictions and Measurements of Single-Mode Fiber Dispersion Characteristics," published in the June 15, 1980 issue of Applied Optics, Vol. 19, pp. 2007-2010. Using this method for the QC fiber, the illustrative series of curves shown in FIG. 5 are obtained. These particular curves are calculated for the four different values of 2a shown, and ~c 0-3% Rc = 0-7 ~1 = 0.6% R - l 0 ~2 = 0~06% R2 = 1.7 ~3 = 0.12~ R3 = 2Ø
A comparison with the dispersion curve for the DC fiber, shown in FIG. 2, illustrates that low dispersion for the QC
~iber occurs over a much broader band of wavelengths. In ' , particular, the inclusion of the two additional claddings has the effect of a~ding an additional zero crossing at the high wavelength end of the curves, thus significantly increasing the low dispersion interval. The improvement in the loss characteristic is also evident~ For the DC fiber, cut-off occurs at about 1.7 ~m whereas cut-off for the QC
fiber (indicated by the ends of the dispersion curves~
occurs above 1.9 ~m. Finally, the curves illustrate that the dispersion characteristics are relatively stable with respect to changes in fiber parameters. Compare, for example, the curves for 2a equal to 13.1, and 2a equal to 13.9.
The invention is of particular interest in connection with single mode fibers and dual mode fibers.
(See Chapter 3 of Optical Fiber Telecommunications edited by S. E. Miller and A. G. Chynoweth, Academic Press, 1979, and the article by L. G. Cohen, et al., entitled "Propagation Characteristics of Double-Mode Fibers,"
published in the July-August issue of the Bell System Technical Journal, Vol. 59, No. 6, pp. 1061-1072 for discussions of such fibers.) Therefore, the requirements of such fibers must also be taken into consideration in the design of a QC fiber. For example, if either ~2 or R2-R
is made too large, the fiber will not remain single-mode.
If ~3 or R3-R2 is too small, the dispersion curve at the longer wavelengths will not turn around enough to obtain the desired zero crossing at the high end of the band. In this regard one can define a function (Rl - RC)~l ~ (R3 R2)~3 ~ 1 ~ RC~c + (R2 Rl~ 2 :
which~must be greater than unity if a zero at the longer wavelength is to be obtained.
~An additional advantage of the invention is that bending losses in a QC fiber are less than in a DC fiber.
:~: : :
; ' "
, , Fibers, in accordance with the present invention, can be drawn from preforms manufactured by many of the well known techniques such as, for example, the modified chemical vapor deposition (MCVD) process. Similarly, any appropriate index-modifying dopants, or combination of dopants can be used. Exemplary dopants are F (fluorine), Ge (germanium) and P (phosphorous). In preferred embodiments, the outermost cladding consists of silica (SiO2) with the core and second cladding being silica that is lightly doped with an index-increasing dopant (i.e., germanium, and/or phosphorous in those cases where it is desired to move the first zero crossing to a shorter wavelength) and the first and third cladding being silica that is lightly doped with an index-decreasing dopant (i.e~, fluorine).
In addition to the four active, waveguiding cladding layers, there may be additional layers of material which are by-products of the method of manufacture, or are included for reasons unrelated to the waveguiding function of the fiber. Unlike the four optically active claddings, which are designed to have very low losses at the wavelengths of interest, such additional layers may be lossy at these wavelengths. For example, if the MCVD
process is employed, the outermost cladding will be surrounded by the preform starting tube which, while made of silica, typically has high losses. Other layers may include a barrier layer to prevent migration of OH-radicals into the core region. However, by making the fourth cladding layer thick enough, these additional claddings do not affect the lightguide characteristics of the fiber and can be ignored for the purposes of the present invention.
In summary, to broaden the range of wavelengths over which an opt;cal fiber has low chromatic dispersion (less than 5 ps/km-nm) and low loss ~less than 1 dB/km), four optically active cladding layers are employed.
principle advantage of the in~vention is that low dispersion and low loss are obtained over a range which includes 1.3 `'` ~
, 31~ki and 1.55 ~m. FIG. 6, included for purposes of comparison, shows the dispersion c~rves 60, 61 and 62 for a representative step-index single mode fiber, a typical double-clad fiber, and a quadruple-clad fiber. As can be readily seen, the low dispersion bandwid~h of the QC fiber is considerably broader than that of the other fibers.
:~ ;
:
QUADRUPLE-CLAD OPTICAL FIBERGUIDE
( Technical Field -This invention relates to optical ibers and, in particular, to low-loss, low-dispersion fibers.
Background of the Invention In copending Canadian Patent Application Serial No.
410,323 filed Au~ust 27, 1982 in the name Gf L.G. Cohen, et al, there is disclosed a double-clad, single-mode optical fiber comprising a core region surrounded by a thin inner cladding and a thicker outer cladding. By the suitable selection of radii and refractive indices, low chromatic dispersion can be realized over the range of wavelengths between 1.3 and 1.55 ~m. However, as the wavelength increases, losses due to radiation through the cladding layers become signficiant. In particular, in the vicinity of the fundamental mode cut-off wavelength, a small change in signal wavelength causes the fundamental mode to change from a guided wave to a leaky wave that radiates through the claddings. The result is high loss at the upper end of the low dispersion range.
Summary of the Invention ______________________ _ In accordance with an aspect of the invention there is provided an optical fiber which comprises a core region having a refractive index nc and a radius Rc, surrounded by ~our cladding layers having refractive indices and radii (nl, Rl), (n2, R2), (n3, R3), and (n4, R4), respectively, total dispersion for the optical fiber is zero for at least one wavelength in a predetermined range of wavelengths, wherein ~ R4>R3>R2>
and nc>n2>n4>n3>nl and wherein (R~ - RC2) l + (R3 - R2)~3 > 1, RC2~C + (R22 - Rl2)~2 .- ~
- . .' : ::
, :, . :
: - :`', : : .
~ 6 - la -- where n~ - n n4 Q ¦
n4 n4--n3 n4 Ac = ~
In accordance with the present invention, the above-described loss mechanism is displaced away from the desired wavelength region of low chromatic dispersion and, in addition, the low dispersion band is broadened. This is accomplished in a lightguide comprising a core region surrounded by four cladding layers. Designating the refractive indices of the core and the successive cladding layers as nc, nl, n2, n3, and n~, respectively, :~ the indices are advantageously proportioned such that : nc>n2~n4>n3>nl~
By the appropriate selection of indices and radii, the chromatic dispersion curve can be made to have three zero crossings, as compared to the two possible :
, :
: . ,~: .
:. ~ , . ~ , ....
~4~3~
crossings for the prior art double-clad fiber, and to cover the desired range of wavelengths which includes 1~3 and 1.55 ~m.
Brief Description of the Drawing FIG. 1 shows a prior art double-clad (DC) optical fiber;
FIG. 2 shows a typical chro~atic dispersion curve for a double~clad fiber;
FIG. 3 shows a quadruple-clad (QC) fiber in accordance with the present invention;
FIG. 4 shows the variations in the group index in DC and QC fibers; and FIG. 5 shows chromatic dispersion curves for quadruple-clad fibers of different sizes; and FIG. 6 shows dispersion curves for single, double and quadruple clad fibers.
Detailed Description Referring to the drawing, FIG. 1 shows a cross section of a prior art double-clad (DC) optical fiber 10 comprising a core region 11 surrounded by a relatively thin first inner cladding 12 and a thicker, second outer cladding 13. Designating the refractive index of the outer cladding as nO, the refractive index nc of the core is equal to nO(l~c), and the refractive index nl of the inner cladding is equal to nO(l+Ql), where ac and ~1 are the fractional differences between the refractive indices of the core and outer cladding, and between the inner and the outer claddings. The index profile of such a fiber is the so-called "W-profile~', also illustrated in FIG. 1, wherein the several indices are shown as a func~ion of the fiber radius normalized with respect to the inner cladding radius a-For a fiber composed of a germaniu~-doped silica core, a fluorine-doped inner cladding, and a pure silica outer cladding, Rc is advantageously about 0~7, and the ratio~l/4c is advantageously e~ual to 2. For such a fiber, the total chromatic dispersion is low over the ~ : :
~ . ~ . .
:, -~ , .
desired wavelength region between 1.3 ~m and 1.55 ~m.
FIG. 2, included for purposes of explanation, shows a set of typical dispersion curves for a DC fiber including a material dispersion curve 15, a wavelength dispersion curve 16, and the resulting total chromatic dispersion curve 17, obtained by summing curves 15 and 16.
In general, the total dispersion curve for a DC fiber can have two zero crossings at wavelengths ~1 and ~2. For this particular illustrative fiber these occur at ~1 = 1.35 ~m and A2 = 1.63 ~m. Because of the large material dispersion at the longer wavelength, the ~2 zero crossing is associated with a correspondingly large waveguide dispersion that occurs near the fundamental mode cut-off wavelength ~co~ approximately equal to 1.7 ~m. This is the wavelength at which the effective refractive index becomes less than nO. At this wavelength, the signal wave is no longer guided by the fiber but, instead, radiates through the claddings and is lost.
In order to insure low-loss operation, ~co should be more than 0.1 ~m larger than the longest wavelength of interest. Based upon this criteria, the total chromatic dispersion characteristics obtainable with currently available double-clad fibers designed to have low dispersion over the range between 1.3 and 1.55 ~m are only marginally acceptable for operation near 1.55 ~m.
To avoid the above-described limitations and disadvantages of the prior art double-clad fiber, two additional claddings are added, in accordance with the pre~sent invention, to form the quadruple-clad fiber 20 illustrated in FIG. 3. This fiber comprises a core region 21 surrounded by four cladding layers 22, 23, 24 and 25, where layer 22 is the first, innermost cladding~ and layer 25 is the fourth, outermost cladding. Designating the refractive index n4 of the outermost cladding 25 as nO, the refractive indices of the core nc, and the indices nl, n2 and n3 of the respective claddings 22, 23 and 24 are given by nC = nO (l+~C) nl = nO (1-~1) n2 = nO (1-~2) and n3 = nO (1 ~3) 5 where c, ~1, A2 and ~3 are the fractional differences between the indices of the respective portions of the fiber and that of the outermost cladding.
The index profile for the QC fiber is shown in FIG. 3 as a function of the fiber radius normalized with respect to the radius Rl of the innermost cladding 22. As can be seen, the relative magnitudes of the indices are such that nc>n2>n4>n3>nl -As explained hereinabove, in the vicinity of the fundamental mode cut-off, a small change in wavelength causes the signal to change from a guided mode into a leaky mode that radiates into the second cladding~ The reason for this can be explained with reference to FIG. 4 which shows the effective group index, ng, as a function of wavelength, A-, for both the DC and QC fibers. At the shorter wavelengths, the signal is primarily guided by an inner lightguide formed by the core 21 and the first cladding 22. Accordingly, the effective group index at the shorter wavelengths, given by curve portion 43, is shown to be larger than the core ~index, given by curve 40. At the longer wavelengths, more of the signal field extends into the first cladding and beyond. The effect is to decrease the effective group index. In the DC fiber, the group index eventually becomes less than the outermost (i.e., second cladding) and the guide becomes cut-off. This is indicated by curve portion 44 which approaches cut-off at ~co ; By contrast, in the QC~fiber, the wave energy that radiates out of the fiber core is trapped in an outer ~z~
lightguide formed by the second cladding 23 and the surrounding first and third claddings 22 and 24~ The light thus trapped is not lost through radiation but continues to be guided, albeit in a different portion of the fiber. The effective group index, given by curve portion 45, is seen to change from a value greater than nc to a value that approaches that of the second cladding given by curve 41.
As can be seen, the resulting index curve for the QC fiber has three turning points at wavelengths Al, ~2 and ~3.
Inasmuch as the total chromatic dispersion characteristic is proportional to the slope of the group index curve, the chromatic dispersion can have three zero points, at wavelengths ~l' X~2 and ~3, as illustrated in FIG. 5.
In the design of a QC fiber, there are nine independent parameters ~c~ 2~ ~3~ Rc~ Rl~ R2~ R3 and a. The radius of the outermost cladding is not critical and, typically, is made relatively large for reasons to be explained hereinbelow. A generalized method for calculating the total chromatic dispersion characteristic for any arbitrary index profile is described in a paper by L. G. Cohen et al., entitled "Correlation Between Numerical Predictions and Measurements of Single-Mode Fiber Dispersion Characteristics," published in the June 15, 1980 issue of Applied Optics, Vol. 19, pp. 2007-2010. Using this method for the QC fiber, the illustrative series of curves shown in FIG. 5 are obtained. These particular curves are calculated for the four different values of 2a shown, and ~c 0-3% Rc = 0-7 ~1 = 0.6% R - l 0 ~2 = 0~06% R2 = 1.7 ~3 = 0.12~ R3 = 2Ø
A comparison with the dispersion curve for the DC fiber, shown in FIG. 2, illustrates that low dispersion for the QC
~iber occurs over a much broader band of wavelengths. In ' , particular, the inclusion of the two additional claddings has the effect of a~ding an additional zero crossing at the high wavelength end of the curves, thus significantly increasing the low dispersion interval. The improvement in the loss characteristic is also evident~ For the DC fiber, cut-off occurs at about 1.7 ~m whereas cut-off for the QC
fiber (indicated by the ends of the dispersion curves~
occurs above 1.9 ~m. Finally, the curves illustrate that the dispersion characteristics are relatively stable with respect to changes in fiber parameters. Compare, for example, the curves for 2a equal to 13.1, and 2a equal to 13.9.
The invention is of particular interest in connection with single mode fibers and dual mode fibers.
(See Chapter 3 of Optical Fiber Telecommunications edited by S. E. Miller and A. G. Chynoweth, Academic Press, 1979, and the article by L. G. Cohen, et al., entitled "Propagation Characteristics of Double-Mode Fibers,"
published in the July-August issue of the Bell System Technical Journal, Vol. 59, No. 6, pp. 1061-1072 for discussions of such fibers.) Therefore, the requirements of such fibers must also be taken into consideration in the design of a QC fiber. For example, if either ~2 or R2-R
is made too large, the fiber will not remain single-mode.
If ~3 or R3-R2 is too small, the dispersion curve at the longer wavelengths will not turn around enough to obtain the desired zero crossing at the high end of the band. In this regard one can define a function (Rl - RC)~l ~ (R3 R2)~3 ~ 1 ~ RC~c + (R2 Rl~ 2 :
which~must be greater than unity if a zero at the longer wavelength is to be obtained.
~An additional advantage of the invention is that bending losses in a QC fiber are less than in a DC fiber.
:~: : :
; ' "
, , Fibers, in accordance with the present invention, can be drawn from preforms manufactured by many of the well known techniques such as, for example, the modified chemical vapor deposition (MCVD) process. Similarly, any appropriate index-modifying dopants, or combination of dopants can be used. Exemplary dopants are F (fluorine), Ge (germanium) and P (phosphorous). In preferred embodiments, the outermost cladding consists of silica (SiO2) with the core and second cladding being silica that is lightly doped with an index-increasing dopant (i.e., germanium, and/or phosphorous in those cases where it is desired to move the first zero crossing to a shorter wavelength) and the first and third cladding being silica that is lightly doped with an index-decreasing dopant (i.e~, fluorine).
In addition to the four active, waveguiding cladding layers, there may be additional layers of material which are by-products of the method of manufacture, or are included for reasons unrelated to the waveguiding function of the fiber. Unlike the four optically active claddings, which are designed to have very low losses at the wavelengths of interest, such additional layers may be lossy at these wavelengths. For example, if the MCVD
process is employed, the outermost cladding will be surrounded by the preform starting tube which, while made of silica, typically has high losses. Other layers may include a barrier layer to prevent migration of OH-radicals into the core region. However, by making the fourth cladding layer thick enough, these additional claddings do not affect the lightguide characteristics of the fiber and can be ignored for the purposes of the present invention.
In summary, to broaden the range of wavelengths over which an opt;cal fiber has low chromatic dispersion (less than 5 ps/km-nm) and low loss ~less than 1 dB/km), four optically active cladding layers are employed.
principle advantage of the in~vention is that low dispersion and low loss are obtained over a range which includes 1.3 `'` ~
, 31~ki and 1.55 ~m. FIG. 6, included for purposes of comparison, shows the dispersion c~rves 60, 61 and 62 for a representative step-index single mode fiber, a typical double-clad fiber, and a quadruple-clad fiber. As can be readily seen, the low dispersion bandwid~h of the QC fiber is considerably broader than that of the other fibers.
:~ ;
:
Claims (5)
1. An optical fiber which comprises a core region having a refractive index nc and a radius Rc, surrounded by four cladding layers having refractive indices and radii (n1, R1), (n2, R2), (n3, R3), and (n4, R4), respectively, total dispersion for the optical fiber is zero for at least one wavelength in a predetermined range of wavelengths, wherein R4 >R3 >R2 >R1 and nc>n2>n4>n3>n1 and wherein where
2. An optical fiber according to claim 1, wherein the total dispersion for the optical fiber is substantially close to zero over a portion of the predetermined range of wavelengths.
3. An optical fiber according to claim 1 or 2, wherein the predetermined range of wavelengths is between 1.3µm and 1.55,um, inclusively.
4. An optical fiber according to claim 1 or 2, wherein the predetermined range of wavelengths is between 1.4µm and 1.7µm, inclusively.
5. An optical fiber according to claim 1 or 2, wherein the total dispersion for the optical fiber is between +5.0 ps/km-nm and -5.0 ps/km-nm over the portion of the predetermined range of wavelengths.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US35705382A | 1982-03-11 | 1982-03-11 | |
| US357,053 | 1982-03-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1248386A true CA1248386A (en) | 1989-01-10 |
Family
ID=23404110
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000420280A Expired CA1248386A (en) | 1982-03-11 | 1983-01-26 | Quadruple-clad optical fiberguide |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS58168004A (en) |
| CA (1) | CA1248386A (en) |
| DE (1) | DE3307874A1 (en) |
| FR (1) | FR2523316B1 (en) |
| GB (1) | GB2116744B (en) |
| NL (1) | NL8300880A (en) |
Families Citing this family (21)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IL71644A (en) * | 1983-05-20 | 1987-11-30 | Corning Glass Works | Low dispersion,low-loss single-mode optical waveguide |
| US4641917A (en) * | 1985-02-08 | 1987-02-10 | At&T Bell Laboratories | Single mode optical fiber |
| NL8502625A (en) * | 1985-09-26 | 1987-04-16 | Philips Nv | OPTICAL TRANSMISSION SYSTEM CONTAINING A RADIATION SOURCE AND A MULTIPLY COATED MONOMODE OPTICAL TRANSMISSION FIBER WITH A NEGATIVE STEP IN THE FRACTION INDEX PROFILE. |
| DE3812140A1 (en) * | 1988-04-12 | 1989-11-02 | Schott Glaswerke | MONOMODE LIGHT FIBER |
| US5067793A (en) * | 1989-08-16 | 1991-11-26 | U.S. Philips Corporation | Polarization-maintaining single-mode optical fibre and method of making same |
| US5361319A (en) * | 1992-02-04 | 1994-11-01 | Corning Incorporated | Dispersion compensating devices and systems |
| US5553185A (en) * | 1994-12-27 | 1996-09-03 | Corning Incorporated | Controlled dispersion optical waveguide |
| FR2736440B1 (en) * | 1995-07-07 | 1997-08-01 | Alcatel Submarcom | SINGLE-MODE OPTICAL GUIDE WITH OFFSET DISPERSION AND LARGE EFFECTIVE MODE SURFACE |
| US5878182A (en) * | 1997-06-05 | 1999-03-02 | Lucent Technologies Inc. | Optical fiber having a low-dispersion slope in the erbium amplifier region |
| GB9814526D0 (en) | 1998-07-03 | 1998-09-02 | Univ Southampton | Optical fibre and optical fibre device |
| FR2782391A1 (en) | 1998-08-13 | 2000-02-18 | Alsthom Cge Alcatel | Shifted dispersion single mode fibre optic index doping technique; has central triangular, rectangular or trapezoidal profile and outer sheath region with specific inner doped region and higher doped outer region sections |
| TW451088B (en) | 1999-04-16 | 2001-08-21 | Sumitomo Electric Industries | Optical fiber and optical transmission line including the same |
| CA2367821A1 (en) | 1999-04-23 | 2000-11-02 | Massachusetts Institute Of Technology | All-dielectric coaxial waveguide |
| US6317549B1 (en) | 1999-05-24 | 2001-11-13 | Lucent Technologies Inc. | Optical fiber having negative dispersion and low slope in the Erbium amplifier region |
| EP1111414A3 (en) * | 1999-12-13 | 2007-08-08 | Sumitomo Electric Industries, Ltd. | Optical fiber and optical transmission system |
| JP4206623B2 (en) * | 2000-09-01 | 2009-01-14 | 住友電気工業株式会社 | Negative dispersion optical fiber and optical transmission line |
| US6856744B2 (en) | 2002-02-13 | 2005-02-15 | The Furukawa Electric Co., Ltd. | Optical fiber and optical transmission line and optical communication system including such optical fiber |
| JP2005031581A (en) * | 2003-07-11 | 2005-02-03 | Sumitomo Electric Ind Ltd | Optical fiber, optical fiber transmission line and optical transmission system |
| WO2005082801A2 (en) | 2004-02-20 | 2005-09-09 | Corning Incorporated | Optical fiber and method for making such fiber |
| US7203407B2 (en) * | 2004-10-21 | 2007-04-10 | Corning Incorporated | Rare earth doped single polarization double clad optical fiber and a method for making such fiber |
| JP4953097B2 (en) * | 2008-06-12 | 2012-06-13 | 市光工業株式会社 | Vehicle lighting |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU504423B2 (en) * | 1975-11-14 | 1979-10-11 | International Standard Electric Corporation | Optical fibre |
| GB1602052A (en) * | 1977-06-20 | 1981-11-04 | Int Standard Electric Corp | Optical fibre manufacture |
| US4179187A (en) * | 1977-08-12 | 1979-12-18 | Corning Glass Works | Multiple mode waveguide having cylindrical perturbations |
| US4183621A (en) * | 1977-12-29 | 1980-01-15 | International Telephone And Telegraph Corporation | Water resistant high strength fibers |
| GB2067781B (en) * | 1979-10-29 | 1983-09-01 | Standard Telephones Cables Ltd | Optical fibres |
| DE3064002D1 (en) * | 1980-02-12 | 1983-08-11 | Post Office | A glass optical fibre and a method of coating a plastic coated glass fibre with metal |
| US4418984A (en) * | 1980-11-03 | 1983-12-06 | Hughes Aircraft Company | Multiply coated metallic clad fiber optical waveguide |
| JPS6014321B2 (en) * | 1981-08-18 | 1985-04-12 | 日立電線株式会社 | Constant polarization optical fiber |
| AU531893B2 (en) * | 1981-08-19 | 1983-09-08 | Hitachi Cable Ltd. | d |
| CA1205307A (en) * | 1981-12-07 | 1986-06-03 | Venkata A. Bhagavatula | Low dispersion, low-loss single-mode optical waveguide |
-
1983
- 1983-01-26 CA CA000420280A patent/CA1248386A/en not_active Expired
- 1983-03-05 DE DE19833307874 patent/DE3307874A1/en active Granted
- 1983-03-07 FR FR8303686A patent/FR2523316B1/en not_active Expired
- 1983-03-09 GB GB08306443A patent/GB2116744B/en not_active Expired
- 1983-03-10 NL NL8300880A patent/NL8300880A/en not_active Application Discontinuation
- 1983-03-11 JP JP58039343A patent/JPS58168004A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| NL8300880A (en) | 1983-10-03 |
| JPS6237361B2 (en) | 1987-08-12 |
| FR2523316B1 (en) | 1987-11-27 |
| FR2523316A1 (en) | 1983-09-16 |
| GB2116744B (en) | 1987-01-21 |
| GB2116744A (en) | 1983-09-28 |
| GB8306443D0 (en) | 1983-04-13 |
| DE3307874C2 (en) | 1991-01-10 |
| JPS58168004A (en) | 1983-10-04 |
| DE3307874A1 (en) | 1983-09-22 |
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