CN103645539B - A kind of bend insensitive fiber - Google Patents
A kind of bend insensitive fiber Download PDFInfo
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- CN103645539B CN103645539B CN201310692614.6A CN201310692614A CN103645539B CN 103645539 B CN103645539 B CN 103645539B CN 201310692614 A CN201310692614 A CN 201310692614A CN 103645539 B CN103645539 B CN 103645539B
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Abstract
The present invention discloses a kind of bend insensitive fiber, by interior fibre core, outer fibre core and covering totally three parts form, and between its refractive index meet: n
core1aMP.AMp.Amp gt; n
core2aMP.AMp.Amp gt; n
clad, wherein, n
core1, n
core2, n
cladthe refractive index of fibre core, outer fibre core and covering in representing respectively.The cutoff wavelength (namely occurring wavelength during high-order mode) of optical fiber is greater than 1.26 μm, is namely a kind of non-single-mode fiber.This optical fiber has extremely low bending loss, its mode distributions and general single mode fiber and matches, and the optical fiber telecommunications system be made up of this optical fiber and general single mode fiber can realize the single mode transport of wide wavelength coverage.
Description
Technical field
The present invention relates to fiber optic communication field, particularly relate to the optical fiber with low bend loss characteristic.
Background technology
In the short distance optical communication systems such as fiber to the home, require that optical fiber still can normally can use under small-bend radius, this optical fiber is called bend insensitive fiber.Bend insensitive fiber can help structured optical fiber etc. to realize [K.Himeno by reducing the core size of standard single-mode fiber, the cladding structure introducing band groove and employing hole, S.Matsuo, N.Guan, andA.Wada, " Low-Bending-LossSingle-ModeFibersforFiber-to-the-Home; " JournalofLightwaveTechnology, 2005,23 (11): 3494-3499.].Such as, adopt the cladding structure of band groove, bending loss when bending radius can be made to be 10mm is less than 0.01dB/ circle, and is less than 0.16dB with the junction loss of ordinary optic fibre.
The difficulty that bend insensitive fiber realizes is, optical fiber must meet single mode transport (namely optical fiber is generally single-mode fiber) simultaneously, has low bend loss and have the requirement of low junction loss with general single mode fiber.If allow optical fiber to be non-single-mode fiber, remove high-order mode wherein by certain method, then optical fiber still can realize single mode transport simultaneously, because the fibre core of bend insensitive fiber and covering can have higher refringence, therefore, its bending loss can be lower.In order to realize the optical transport of low bend loss, ensure that optical fiber has the mode field area mated with general single mode fiber simultaneously, dual mode optical fiber [M.-Y.Chen can be adopted, Y.-R.Li, Y.Zhang, Y.-F.Zhu, Y.-K.Zhang, andJ.Zhou, " Designofdual-modeopticalfibresfortheFTTHapplications, " JournalofOptics, 2011, 13 (1): 015402. Chen Ming sun, Tong Yanqun, Zhang Yin, Li Yurong, Sun Bing, Fu Xiaoxia, Zhang Yongkang, a kind of dual mode optical fiber and communication system thereof, Chinese patent, 201010589018.1, 2010.12], allow Optical Fiber Transmission high-order mode, thus increase fibre core and clad refractive rate variance, the object realizing low bend loss and be connected with single-mode fiber low-loss.The communication system be made up of this optical fiber, all connects single-mode fiber in dual mode optical fiber both sides, the orthogonality between Land use models, suppresses the generation of high-order mode in dual mode optical fiber and the impact on signal transmission, realizes the single mode transport of equivalence.But adopt the dual mode optical fiber of step structure due to fiber core and covering refringence comparatively greatly, its mode distributions and single-mode fiber matching poor, when such optical fiber is connected with general single mode fiber, its basic mode junction loss cannot reduce.In fact, even if the mode field diameter of two kinds of optical fiber is equal, if the mode distributions of the pattern in two kinds of optical fiber is different, also junction loss can be caused.Therefore, junction loss be reduced, also need the mode distributions of consideration pattern.
Summary of the invention
For above deficiency, the object of the invention is to propose the insensitive optical fiber of a kind of Novel bending, its mode field area and mode distributions are all similar to standard single-mode fiber, thus the junction loss that can effectively reduce between itself and standard single-mode fiber, meanwhile, the optical transport of ultralow bending loss can also be realized.
Technical scheme of the present invention is: a kind of bend insensitive fiber, by interior fibre core, outer fibre core and covering totally three parts form, and between its refractive index meet: n
core1>n
core2>n
clad, wherein, n
core1, n
core2, n
cladthe refractive index of fibre core, outer fibre core and covering in representing respectively; Described interior fiber core radius a meets: 3 μm≤a≤6.5 μm, and interior fibre core and outer fiber core refractive index difference meet: 0.003≤n
core1-n
core2≤ 0.0065; Outer fibre core width h meets: 1 μm≤h≤10 μm, and outer fibre core and clad refractive rate variance meet: 0.002≤n
core2-n
clad≤ 0.015.When wavelength is 1.31 μm, the mode field diameter of optical fiber basic mode is 8.6 ~ 9.5 μm; Wherein, the ring width of the outer fibre core of outer fibre core width finger ring shape, the i.e. difference of the external radius of outer fibre core and the radius of interior fibre core.
As a kind of prioritization scheme, require that the outer fibre core width h of bend insensitive fiber meets 3 μm≤h≤6.5 μm, outer fibre core and clad refractive rate variance meet 0.003≤n
core2-n
clad≤ 0.006.At 1.55 mum wavelength places, the bending loss when bending radius of described optical fiber is 5mm is less than 0.1dB/m.
Beneficial effect of the present invention: utilize the feature between the interior fibre core of optical fiber of the present invention and covering with high index-contrast, realizes the transmission of ultralow bending loss; Simultaneously because fiber core radius is enough large, optical fiber is made to have large mode field diameter.The refringence of the refringence of interior fibre core and outer fibre core and the fibre core of general single mode fiber and covering is close, and light is mainly limited in transmitting in interior fibre core, therefore, basic mode in this bend insensitive fiber distributes very similar to the fundamental mode field of general single mode fiber, thus can realize being connected with the low-loss of general single mode fiber.And the existence of outer fibre core, make the specific refractivity of interior fibre core and covering enough large, thus ensure low bend loss transmission.The basic mode of optical fiber of the present invention can still have extremely low bending loss when bending radius is 5mm, and its structure is simple, and the fiber making processes of existing maturation can be adopted to realize.
Accompanying drawing explanation
The cross-sectional structure schematic diagram of Fig. 1 optical fiber of the present invention;
The junction loss of Fig. 2 index fiber of the present invention and general single mode fiber is with the change curve of outer fibre core width;
The basic mode of Fig. 3 optical fiber of the present invention energy proportion in core region is with the change curve of outer fibre core width.
Embodiment
For standard single-mode fiber, its cutoff wavelength (namely occurring wavelength during high-order mode) should be less than 1.26 μm.Namely optical fiber all can keep single mode transport 1.31,1.55 μm of equiwavelengths, thus can realize broadband, jumbo information transmission.For common step type single mode optical fiber, to reduce its bending loss, the most direct method is the refringence increasing its fibre core and covering.But due to covering constraint ability grow, the reduction of its foundational model field area also can be caused.And just cause the junction loss of the optical fiber after improving and general single mode fiber to increase like this.For this reason, just need to increase core diameter, to increase the mode field area of optical fiber.So just must cause its normalized frequency
vthe increase of value, thus there is high-order mode.
The bend insensitive fiber that the present invention proposes adopts double-deck core structure, while keeping the mode distributions of optical fiber basic mode similar to standard single-mode fiber, increase the refringence of fibre core and covering, thus effectively overcome the shortcoming that general single mode fiber cannot obtain high index-contrast.Exist although this optical fiber has high-order mode, the method similar to document [2] can be adopted, namely by the method at optical fiber two ends connection standard single-mode fiber, the single mode transport of equivalence can be realized.
Optical fiber structure as shown in Figure 1.This bend insensitive fiber that the present invention proposes can be understood like this.Suppose that the fiber core radius of general single mode fiber is a
0, fibre core and clad refractive rate variance are Δ
0.Then, the refringence should getting fibre core and outer fibre core in optical fiber is Δ
0, and get the radius a=a of interior fibre core
0.Like this, when the radius of outer fibre core is identical with cladding radius, namely reality now optical fiber be general single mode fiber.Now, optical fiber mates completely with the mould field of general single mode fiber, and both junction losss are minimum.
And when the radius of the outer fibre core of optical fiber of the present invention is identical with interior fibre core, when namely outer fibre core width is 0, namely optical fiber be a step index fiber.Obviously now fibre core and clad refractive rate variance greatly, and fiber core radius is minimum, the bending resistance of optical fiber is the strongest.But because fibre core and cladding index are comparatively large, its mode distributions differs comparatively large with general single mode fiber, cause both junction losss larger.
In sum, the width of outer fibre core can not be too large, otherwise its bend loss properties cannot meet the demands.Meanwhile, outer fibre core should have certain width, otherwise the junction loss of itself and general single mode fiber can be larger.The refringence of outer fibre core and covering is larger, is more conducive to the bending loss reducing optical fiber; But then, the refringence of interior fibre core and covering is also made to increase.And this just causes the difference that this optical fiber and general single mode fiber are larger on fiber core refractive index.Difference on fiber core refractive index also can cause the increase of loss of fibre-optical connection.Analysis shows: outer fibre core and clad refractive rate variance meet: 0.003≤n
core2-n
cladwhen≤0.006, can be implemented between low bend loss and low junction loss and obtain balance preferably.
Therefore, namely this optical fiber with double-deck fibre core that the present invention proposes be the intermediateness of above two kinds of extreme cases.For common step optical fiber, optical fiber basic mode is from core centre outwards in class Gaussian rolloff, and in clad region, exponentially type decays.For the bend insensitive fiber that the present invention proposes, because outer fibre core and interior fibre core exist refringence, therefore, outer fibre core also can play the effect of constraint light.The amplitude of its optical fiber basic mode outside fibre core also presents the feature of exponential decay.Therefore, select suitable parameters, can make the overwhelming majority basic mode concentration of energy in interior fibre core and outer core region, thus make its basic mode and general single mode fiber basic mode similarity degree very high, thus making the mould field matching degree of optical fiber of the present invention and general single mode fiber high, junction loss is little.
Therefore, when getting suitable outer core parameters, its mode distributions and general single mode fiber can be made very close, thus make both have low junction loss.Meanwhile, interior fibre core and covering have large refringence, make optical fiber basic mode have low bend loss.
In order to realize low-loss connection with general single mode fiber, require that the mode field diameter of the basic mode of few mould gradient index fibre differs less with single-mode fiber.The junction loss of the optical fiber that the mode field area due to two kinds of optical fiber is different and cause can be obtained by formula below:
Wherein
w sMF with
w dMF be respectively the mode field diameter of single-mode fiber and few mould step optical fiber.Obviously, when the mode field diameter of few mould step optical fiber is close with single-mode fiber, its junction loss can be less.Therefore, according to the mode field diameter feature of general single mode fiber (as the mode field diameter M of G652 optical fiber when 1310nm wavelength requires to be 8.6 ~ 9.5 μm), require when 1310nm wavelength, the span of the mode field diameter M of gradient index fibre is also between 8.6 ~ 9.5 μm.
As seen from Figure 2, when outer fibre core width increases, the junction loss of itself and single-mode fiber exponentially type reduces.When outer fibre core width is 0, when being a step optical fiber, junction loss is maximum.And outer fibre core width is more than 3 μm, junction loss can be made to be less than 0.03dB.
As seen from Figure 3, when outer fibre core width reaches more than 2.5 μm, optical fiber basic mode just can reach more than 90% at the energy proportion of core region (interior fibre core and outer fibre core).Therefore, the basic mode of optical fiber is similar to general single mode fiber height, thus easily realizes low junction loss.
In addition, owing to there is outer core region, high-order mode energy more easily appears at outer core region, thus makes the effective refractive index of high-order mode lower, and like this, the difference of optical fiber basic mode and high-order mode is larger, thus more difficult generation Energy Coupling.
Embodiment one:
The interior fiber core radius a=4.35 μm of optical fiber, interior fibre core and outer fiber core refractive index difference n
core1-n
core2=0.005, outer fibre core and clad refractive rate variance n
core2-n
clad=0.0035, outer fibre core width h=4 μm.When 1.31 micron wave length, its mode field diameter is 9 microns, is less than 0.03dB with the junction loss of general single mode fiber.When the bending radius of optical fiber is 5mm, its bending loss is less than 0.05dB/m.
Embodiment two:
The interior fiber core radius a=4.35 μm of optical fiber, interior fibre core and outer fiber core refractive index difference n
core1-n
core2=0.005, outer fibre core and clad refractive rate variance n
core2-n
clad=0.005, outer fibre core width h=5 μm.When 1.31 micron wave length, its mode field diameter is 9 microns.0.03dB is less than with the junction loss of general single mode fiber.When the bending radius of optical fiber is 5mm, its bending loss is less than 0.01dB/m.
Embodiment three:
The interior fiber core radius a=4 μm of optical fiber, interior fibre core and outer fiber core refractive index difference n
core1-n
core2=0.0044, outer fibre core and clad refractive rate variance n
core2-n
clad=0.004, outer fibre core width h=4.5 μm.When 1.31 micron wave length, its mode field diameter is 8.9 microns.0.03dB is less than with the junction loss of general single mode fiber.When the bending radius of optical fiber is 5mm, its bending loss is less than 0.01dB/m.
Above optical fiber all can adopt the manufacture craft identical with general single mode fiber to realize.
Above-mentioned accompanying drawing is only explanatory view, does not form restriction to protection scope of the present invention.Should be understood that these embodiments just in order to demonstrate the invention, but not limit the scope of the invention by any way.
Claims (3)
1. a bend insensitive fiber, is made up of interior fibre core, outer fibre core and covering, it is characterized in that, described interior fibre core, outer fibre core and covering are arranged in order from inside to outside; Described interior fibre core, between outer fibre core and the refractive index of covering meet: n
core1>n
core2>n
clad, wherein, n
core1, n
core2, n
cladthe refractive index of fibre core, outer fibre core and covering in representing respectively; Described interior fiber core radius a meets: 3 μm≤a≤6.5 μm, and described interior fibre core and outer fiber core refractive index difference meet: 0.003≤n
core1-n
core2≤ 0.0065; Described outer fibre core width h meets: 1 μm≤h≤10 μm, and described outer fibre core and clad refractive rate variance meet: 0.002≤n
core2-n
clad≤ 0.015, the ring width of the outer fibre core of described outer fibre core width finger ring shape, the i.e. difference of the external radius of outer fibre core and the radius of interior fibre core; At 1.55 mum wavelength places, the bending loss when bending radius of described optical fiber is 5mm is less than 0.1dB/m.
2. a kind of bend insensitive fiber according to claim 1, is characterized in that, described outer fibre core width h meets: 3 μm≤h≤6.5 μm, and outer fibre core and clad refractive rate variance meet: 0.003≤n
core2-n
clad≤ 0.006.
3. a kind of bend insensitive fiber according to claim 1, is characterized in that, the mode field diameter of described optical fiber basic mode is 8.6 ~ 9.5 μm.
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|---|---|---|---|---|
| KR100342711B1 (en) * | 1998-12-17 | 2002-10-25 | 엘지전선 주식회사 | Dispersion shifted fiber with triple clad |
| US6771865B2 (en) * | 2002-03-20 | 2004-08-03 | Corning Incorporated | Low bend loss optical fiber and components made therefrom |
| CN102122991B (en) * | 2010-12-15 | 2013-10-23 | 江苏大学 | Dual-mode optical fiber and communication system thereof |
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Address after: 212114 Zhenjiang, Zhejiang Province, Dantu high capital street, Xiangshan Road, No. 1 Patentee after: Jiangsu Univ. Address before: Lishui Economic Development Zone, Nanjing City, Jiangsu province 211215 zhe Ning Road No. 368 Patentee before: Jiangsu Univ. |