A kind of optical fibre mode converter
Technical field
The present invention relates to fiber optic communication field, be specifically related to have the optical fibre mode converter of changing between the implementation pattern.
Background technology
Because single-mode fiber can be avoided the multimode optical fiber intermode dispersion problem in when transmission, therefore extensively most widely used in fields such as communication, sensings at present is single-mode fiber.In recent years, people have also proposed many novel optical fiber structures.As adopting the Bragg optical fiber of photon band gap principle, the pattern that its loss is minimum is not the LP of general single mode fiber
01Mould, but TE
01Mould [Optics Express, 2001,9 (13), 748].In addition, people also propose to adopt high-order mode to realize dispersion compensation technology [Journal of Lightwave Technology, 2005,23 (11), 3426] and with basic mode light be converted to high-order mode [OpticsLetters, 2006,31 (12), 1797], thus realize big mould field, low-loss optically transmission or the like.
When above several optical fibre devices are connected with other conventional fiber, just need realize LP by mode converter
01Conversion between mould and other pattern.Optical fibre mode converter is a kind of device of changing between the different mode field in the optical fiber realized.
People have proposed several devices that are applicable to mould field conversion between optical fiber, the wherein modal mode converter [Journal of Lightwave Technology, 2005,23 (11), 3426] that is based on fiber grating.As adopt fiber grating that the basic mode of optical fiber is converted to high-order mode, and realize opposite function.But when adopting fiber grating, high-order mode after basic mode light and the conversion is all transmitted in same optical fiber, therefore, if fiber grating can not be realized basic mode light absolutely is converted to high-order mode, then in optical fiber, will there be remaining basic mode light in optical fiber, to transmit.Owing in above several optical fibre devices, all require only to have a pattern in the optical fiber, thereby realize the single mode transport on the another kind of meaning, therefore, these dump energies will be disturbed the light signal generating of transmission, thereby influence the performance of optical fibre device.
Summary of the invention
At the prior art deficiency, the technical problem to be solved in the present invention is to propose a kind of mode converter based on the double-core photonic crystal fiber structure.
The technical scheme that the present invention is adopted for the technical solution problem is: a kind of optical fibre mode converter, it is double-core photonic crystal fiber, comprise covering and fibre core that host material and airport are formed, it is characterized in that, said fibre core is two fibre cores that differ in size, its medium and small fibre core is used to transmit basic mode, and big fibre core is used to transmit high-order mode; The effective refractive index of the basic mode effective refractive index of little fibre core and the big corresponding high-order mode of fibre core equates in the operation wavelength position.
Described operation wavelength promptly needs to carry out the light wavelength of mode switch.Because coupling effect, after the light of this wavelength entered arbitrary fibre core of optical fiber, the energy in two fibre cores was with the transfer of generating period.If promptly input basic mode light from little fibre core then passes through coupling, basic mode light will be converted to the high-order mode that is complementary on effective refractive index with it in the big fibre core.If fiber lengths is taken as both coupling lengths or the integral multiple of coupling length, can realize basic mode light is converted to high-order mode fully.Therefore, above-mentioned said optical fibre mode converter, its fiber lengths preferably are taken as the coupling length of two-mode or the integral multiple of coupling length.Even because there are the relation of error etc. in error of making such as fiber lengths, can not realize changing completely, as previously mentioned, the basic mode energy is to be present in the little fibre core, and the high-order mode energy is to output to go in other optical fiber from big fibre core, thereby the portion of energy that does not transform fully can not mix mutually with the pattern after transforming, thereby can not influence the optical signal transmission quality.Therefore, this structure can allow fiber lengths to have certain error, and this error only can cause the reduction of mode switch efficient, and can not cause the mixing of two patterns, thus the not influence of quality to changing the back pattern.
Adopt identical double-core photonic crystal fiber structure, high-order mode is imported from big fibre core, then can be at the basic mode after the other end obtains conversion.Adopt this method the light signal that transmits with the high-order mode form can be converted to basic mode signal in the single-mode fiber in some optical fiber.
In above-mentioned said optical fibre mode converter, be filled with the dielectric rod of low-refraction in the little fibre core, big fibre core is made up of seven airports that lack on the regular grid structure.
In above-mentioned said optical fibre mode converter, regular grid is triangle or square structure.
The material of said optical fiber all is conventional among the present invention, and for example said host material can be pure quartz, also can be doped with fluorine or B
2O
3, GeO
2Or P
2O
5Deng quartz material, also can adopt polymeric material such as polystyrene etc.
Optical fibre mode converter of the present invention, utilize the coupling of the energy between the basic mode and high-order mode in two fibre cores, realize the conversion between basic mode and the high-order mode, because basic mode light is to transmit in two different fibre cores with high-order mode, thereby, even can not realize between basic mode light and the high-order mode changing completely, energy remaining still can not be coupled in the corresponding optical fiber and go, thereby makes the pattern of conversion reach purer.Simultaneously,, on manufacturing technology, there is not special requirement, and realizes the production of mass easily owing to adopt the double-core photonic crystal fiber structure, thus more competitive than adopting fiber grating.
Description of drawings
Fig. 1 is the cross sectional representation of a kind of embodiment of the present invention
Wherein, 1-host material, 2-airport, the little fibre core of 3-, the big fibre core of 4-.
Fig. 2 is the LP of the medium and small fibre core of structure shown in Figure 1
01LP in mould and the big fibre core
02The effective refractive index of mould and wavelength concern synoptic diagram
Fig. 3 is respectively 0 for light signal transmission range in optical fiber shown in Figure 1, L/3, and 2/3L, the field distribution synoptic diagram during L, L are the optical fiber physical length, its value is 12.7mm.
Embodiment
Below in conjunction with description of drawings the preferred embodiments of the present invention.Present embodiment is realized basic mode LP
01Mould and LP
02Conversion between the mould.
Embodiment one:
As shown in Figure 1, the host material 1 of double-core photonic crystal fiber is pure quartz, and the diameter d of airport 2 is 2.28 μ m, and pitch of holes is taken as Λ=4.56 μ m.Little fibre core 3 is made up of the quartz that mixes, and it is than the refractive index low 0.004 of pure quartz.Big fibre core 4 is made up of 7 airports of disappearance.Operation wavelength is 1.55 μ m, and fiber lengths is 12.7mm.Fig. 2 is the LP of the medium and small fibre core of structure shown in Figure 1
01LP in mould and the big fibre core
02The effective refractive index of mould and wavelength concern synoptic diagram.Article two, curve intersects at this 1.55 μ m place, therefore, and at the LP of this little fibre core in wavelength place
01LP in mould and the big fibre core
02Mould is with the energy coupling of generating period.Fiber lengths is taken as both coupling length, i.e. 12.7mm, purpose that just can the implementation pattern conversion.Adopt different optical fiber structure parameters, can realize the LP of little fibre core
01Conversion between other pattern in mould and the big fibre core.In the present embodiment, the LP in the little fibre core
01The mode field area of mould and loss are respectively 27 μ m
2And 0.05dB/m.And the LP in the big fibre core
02Corresponding mode field area and loss are respectively 75 μ m
2With 1 * 10
-4DB/m.Its mode field area is bigger, and loss is low.And optical fiber is polarization correlated little, and the Polarization Dependent Loss of the bandwidth range inner fiber of its 14nm is less than 0.14dB.Fig. 3 is in the little fibre core behind the input optical signal, the light field variation diagram in the optical fiber, and as can be seen, conversion efficiency is very high.
Above-mentioned accompanying drawing only is an explanatory view, protection scope of the present invention is not formed restriction.Should be understood that these embodiment just in order to demonstrate the invention, but not limit the scope of the invention by any way.