CN100465674C - Optical fiber - Google Patents

Abstract

Optical fiber mainly involves optical fiber communications technology. The invention includes first - and second-beam unit, the second unit distributes in the first's outside field, and was surrounded by the first unit stomata. The beneficial effect of invention is having a great unit length of dispersion compensation, and flexible design of the slope of the dispersion compensation. PCF clad special structure can be changed by the designers cladding air holes parameters of the structure to have the flexibility to change the refractive index of optical fiber cross-sectional distribution, designed to have different dispersion nature fiber.

Description

Light transmitting fiber

Technical field

The present invention relates to Fibre Optical Communication Technology.

Background technology

In optical fiber communication, there is chromatic dispersion problem in various degree.Chromatic dispersion is meant the optical pulse broadening phenomenon that the differential group delay of light wave in optical fiber of different frequency or different mode causes.Because the optical fiber and digital communications is a series of light pulse sign indicating numbers, when light pulse during along Optical Fiber Transmission, chromatic dispersion makes the optical signal pulses broadening, some is overlapped to cause the pulse that closes on, thereby cause system's error code thereby make two adjacent pulses can not be accepted the correct identification of device, influence communication quality.In order to limit intersymbol interference, the pulse strenching that chromatic dispersion is caused limits within limits, the broadening of the optical signal pulses that causes when chromatic dispersion is during greater than 0.3 times input pulsewidth, makes just that optical receiver sensitivity sharply descends, balanced difficulty, the bit error rate increase.Therefore want to guarantee the necessary intensity code spacing of communication quality, this just has to pay the cost that reduces bit rate, reduces message capacity.

Chromatic dispersion also must reduce repeater span to guarantee the quality of communication along with the increase of optical pulse propagation distance will be more and more serious in addition, and visible fine chromatic dispersion all has important restriction to unrepeatered transmission distance, transfer rate and the transmission capacity of communication system., at present more than one hundred million kilometers telecommunication optical fiber laying of the whole world is most of is standard single-mode fiber G.652, comprises the main fiber communication link of China's " Eight Verticals and Eight Horizontals ".G.652 optical fiber has very low loss at the 1550nm place, but its zero dispersion point is positioned near the 1310nm, and the chromatic dispersion of the 17ps/km/nm that has an appointment at the 1550nm place, obviously G.652 the CHROMATIC DISPERSION IN FIBER OPTICS problem has become the major obstacle that existing optical fiber telecommunications system is upgraded, and how solving G.652, the CHROMATIC DISPERSION IN FIBER OPTICS compensation problem has also just become important research project.In addition, grow Distance Transmission even if adopt novel non-zero dispersion displacement optical fiber, if single-channel transfer rate improves constantly, when distance surpasses certain-length, since the chromatic dispersion cumulative effect, also the performance of possibility restriction system also should adopt and treat the G.652 similar approach of fibre-optic transmission system (FOTS) at this moment, suitably carries out dispersion compensation.

At present, proposed some technical schemes for the CHROMATIC DISPERSION IN FIBER OPTICS problem and solved, as dispersion compensating fiber (DCF) method, laser prechirp method, mid-span-spectral-inversion method, dispersion management transmission method and chirped fiber grating method [26] etc.In these technical schemes that proposed, dispersion compensating fiber (DCF) penalty method is because it has convenient and flexible installation, good reliability, stable performance and becomes most popular technology on the most ripe at present, the engineering with numerous advantages such as conventional fiber compatibility.Its ultimate principle is as follows, if G.652 the flashlight of operating wave strong point transmits the big or small D of being of the chromatic dispersion that will accumulate behind the certain distance in the optical fiber in routine _Transmission, and the chromatic dispersion size D that the transmission back will accumulate in the DCF of certain-length _Compensation, the total dispersion of flashlight size D so _TotalRepresent with regard to available following formula.

D _total＝D _transmission+D _compensation (1)

This shows, if DCF operating wave strong point tool very big with the routine abbe number of optical fiber opposite in sign G.652, come the G.652 chromatic dispersion that optical fiber produces of the long routine of compensate for slower with regard to available one section very short DCF so, make total chromatic dispersion minimum, thereby the light signal that guarantees the operating wave strong point can be by the correct reception in undistorted ground.If the light wave to a plurality of wavelength compensates, then, so just require DCF that the suitable dispersion slope coefficient is arranged because the light wave of different wave length through different chromatic dispersion accumulation is arranged after the Transmission Fibers, make the chromatic dispersion of all wavelengths all minimum.

Although dispersion compensating fiber (DCF) penalty method has above-mentioned advantage, should be noted that simultaneously DCF unit length compensation rate is low, general every kilometer dispersion compensation value of DCF is about the magnitude of hundreds of ps/nm.DCF insertion loss is bigger in addition, needs behind the dispersion compensation to carry out loss balancing with image intensifer, and cost increases.Be exactly that DCF compares with standard fiber in addition, core diameter is thinner, and refringence is also bigger, so difficulty is more made also in the bad control of index distribution.In order to give full play to the advantage of compensating optical fiber, overcome the current DCF deficiency of optical fiber by way of compensation, seeking a kind of novel optical fiber that can realize dispersion compensation can become one of direction of effort.

Below to briefly introducing with the photonic crystal fiber technology of reference required for the present invention.Photonic crystal fiber (photonic crystal fiber, PCF, this optical fiber claim " porous optical fiber " or " microstructured optical fibers ", hereinafter referred to as " photonic crystal fiber " again).

To be that E.Yablonovitch in 1987 and S.John are independent separately respectively propose the notion of photonic crystal.In fact photonic crystal is exactly that the medium of differing dielectric constant is arranged a kind of artificial crystal that forms by some cycles in the space, and its arrangement cycle is the magnitude of optical wavelength.The space structure of photonic crystal can be divided into three types, as shown in Figure 1.The topmost characteristic of photonic crystal is exactly that transmission to the light of different frequency has selectivity.If it is compatible that photon energy and photonic crystal can be with, then photonic crystal is conduction, and photon can see through photonic crystal and blaze abroad, otherwise photon can not see through photonic crystal, forms forbidden photon band.The reason that this phenomenon forms is as follows: in dielectric material, according to the Classical Electromagnetic Field theory, electromagnetic field satisfies following equation:

$\tilde{N}\×(\frac{1}{\mathrm{\ϵ}\left(\stackrel{\→}{r}\right)}\tilde{N}\×\stackrel{\→}{H}\left(\stackrel{\→}{r}\right))={\left(\frac{\mathrm{\ω}}{c}\right)}^2\stackrel{\→}{H}\left(\stackrel{\→}{r}\right)---\left(2\right)$

When the periodically variable ratio of specific inductive capacity is enough big, and the space periodic that changes is when close with optical wavelength, and calculating shows that for specific frequencies omega, equation (2) nothing is separated, that is to say exist photon band gap (photonic band gap, PBG).Because photonic crystal can freely be controlled light propagation therein, and photon has the incomparable advantage of many electronics, the prospect so it is widely used, caused and paid attention to widely and study that the U.S. " Science " magazine is classified photonic crystal one of as 1999 ten big sciences progress.

Principle according to photonic crystal, people such as J.C.Russell proposed the notion of " photonic crystal fiber (PCF) " in 1992, and drew successfully first PCF in the world in Southampton, Britain university in 1996, this optical fiber evenly arranged along the axial airport, from fiber end face, the two-dimensional structure that has one-period, if one of them hole is destroyed, then defective can appear, light can be propagated in this defective, PCF and traditional fiber structurally have basic difference, and many important feature are arranged, such as unusual chromatic dispersion, variable on a large scale characteristic such as non-linear, high birefringence, unlimited unimodular property etc.Its appearance has caused the great interest of various countries research institutions.PCF has the mechanism of two kinds of leaded lights, be respectively total internal reflection (Total internal reflection, TIR) mechanism and photon band gap (Photonic band gap, PBG) mechanism, studies show that, the PCF (TIR-PCF) of TIR mechanism leaded light does not also rely on the periodicity of the airport in the covering, even the airport of stochastic distribution can be limited in light in the scope of fibre core in the covering, and this provides great dirigibility for the optical fiber designs that satisfies various performances.On the contrary, the PCF (PBG-PCF) of PBG mechanism leaded light requires very high to the periodicity that airport distributes.The structure of the xsect of two kinds of leaded light mechanism PCF all has a variety of, and Fig. 2 has shown the sem photograph of several PCF cross-sectional structures.

Summary of the invention

Technical matters to be solved by this invention is that a kind of optical fiber with good dispersion compensation effect is provided.

The technical scheme that the present invention solve the technical problem employing is, light transmitting fiber is characterized in that, includes first optical guide unit and second optical guide unit, second optical guide unit is distributed in the zone, outfield of first optical guide unit, and is the pore encirclement of first optical guide unit.

The described second optical guide unit structure is arranged according to the photonic crystal fiber mode.And first optical guide unit and second optical guide unit are all the photonic crystals optical fiber structure of solid leaded light.

Further, first light element and second light element are all the regular polygon structure, and the hole diameter of first light element and circumcircle diameter are greater than second light element.Has two-layer pore at least in the zone, outfield of first light element and second light element.

Further, described first light element comprises the center light waveguide region and is uniformly distributed in center light waveguide region multilayer pore on every side in the regular polygon mode that its part holes is that second optical guide unit replaces.

In the structure that the present invention proposes, the diameter difference of fibre core (light element), and it is also different to surround their diameter of airport, and a fibre core is at the center of whole optical fiber, and another fibre core distributes prejudicially.

Outstanding advantage of the present invention is to have very big unit length chromatic dispersion compensation quantity and dispersion compensation slope design flexibly.The dispersion characteristics of PCF have at home and abroad been carried out than extensive studies, but for traditional DCF, theory and practice all shows, want to improve the chromatic dispersion compensation quantity of traditional DCF unit length, to reduce the diameter of fibre core on the one hand, to improve refractive index poor of fibre core and covering on the other hand, but the difference of traditional fiber center core layer and cladding index can not be very big, this difference because of sandwich layer and cladding index is to realize by doped with rare-earth elements in sandwich layer, do not cause than the lossy problem but can bring like this owing to material matches, therefore limited the difference of sandwich layer and cladding index, and photonic crystal fiber is made of the same material, need not to mix does not exist the material mismatch problems, and therefore the difference of sandwich layer and cladding index can not be restricted.The difference size of refractive index is only relevant with size, the structure of fibre cladding pore, because the refringence of pore and quartz is bigger, so PCF can have very big negative dispersion coefficient.The special construction of PCF covering can make the deviser can change the index distribution of cross section of optic fibre neatly by the structure parameter (for example diameter of airport and airport spacing) that changes the covering airport, thereby design optical fiber, as dispersion shifted optical fiber, super smooth dispersive optical fiber etc. with different chromatic dispersion character.

Description of drawings

Fig. 1 is one dimension, two and three dimensions photonic crystal space structure synoptic diagram.

Fig. 2 is several PCF cross-sectional structure sem photographs of prior art.

Fig. 3 is the synoptic diagram of embodiments of the invention 1.

Fig. 4 is the area dividing synoptic diagram of the embodiment of the invention.

Fig. 5 is an algorithm flow chart of the present invention.

Fig. 6 is a kind of PCF cross-sectional structure and the covering equivalent process synoptic diagram that the present invention relates to.

Fig. 7 is that the mould effective refractive index is with wavelength variations situation synoptic diagram.

Fig. 8 is that abbe number is with wavelength variations situation synoptic diagram.

Fig. 9 is that Electric Field Distribution is with wavelength variations situation synoptic diagram.

Embodiment

The main chromatic dispersion that exists in the optical fiber is material dispersion and two kinds of waveguide dispersions (section chromatic dispersion and polarization mode dispersion are ignored here, because the former numerical value is very little, the latter then compensation mechanism is different with method, need to discuss specially).Material dispersion be since the group index n of material with the caused dispersion characteristics of wavelength variations, in other words by the caused chromatic dispersion of n=n (ω).

Waveguide dispersion (claiming the structure chromatic dispersion again) is by the chromatic dispersion of forming structures shape of optical fiber, and wherein the cross-sectional area shape and the index distribution of optical fiber play a major role.According to the definition of chromatic dispersion, the total dispersion of traditional fiber can be determined by following formula.

$D=\frac{\mathrm{d\&tau;}}{\mathrm{d\&lambda;}}=\frac{1}{c}\left(\frac{{\mathrm{<figure-callout\; id="2"\; label="dkn"\; filenames="C200710049019E00181.png"\; state="\{\{state\}\}">dkn</figure-callout>}}_2}{\mathrm{d\&lambda;}}\right)[1+\mathrm{\&Delta;}\frac{d\left(\mathrm{bV}\right)}{\mathrm{dV}}]+\frac{{\mathrm{kn}}_2}{c}\mathrm{\&Delta;}\left(\frac{d^2\left(\mathrm{bV}\right)}{{\mathrm{dV}}^2}\right)\left(\frac{\mathrm{dV}}{\mathrm{d\&lambda;}}\right)=D_m+D_w$

$D_m=\frac{1}{c}\left(\frac{{\mathrm{<figure-callout\; id="2"\; label="dkn"\; filenames="C200710049019E00181.png"\; state="\{\{state\}\}">dkn</figure-callout>}}_2}{\mathrm{d\&lambda;}}\right)[1+\mathrm{\&Delta;}\frac{d\left(\mathrm{bV}\right)}{\mathrm{dV}}]\&ap;-\frac{\mathrm{\&lambda;}}{c}\frac{d^2{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="C200710049019E00181.png"\; state="\{\{state\}\}">n</figure-callout>}}_2}{{\mathrm{d\&lambda;}}^2}[1+\mathrm{\&Delta;}\frac{d\left(\mathrm{bV}\right)}{\mathrm{dV}}]$

$D_w=\frac{{\mathrm{kn}}_2}{c}\mathrm{\&Delta;}\left(\frac{d^2\left(\mathrm{bV}\right)}{{\mathrm{dV}}^2}\right)(\frac{\mathrm{dV}}{\mathrm{d\&lambda;}}\&ap;-\frac{{\mathrm{kn}}_2}{c})\left(\frac{\mathrm{\&Delta;}}{\mathrm{\&lambda;}}\right)V\frac{d^2\left(\mathrm{bV}\right)}{{\mathrm{<figure-callout\; id="2"\; label="dV"\; filenames="C200710049019E00181.png"\; state="\{\{state\}\}">dV</figure-callout>}}^2}$

Wherein, first D _mBe exactly material dispersion, second D _wBe waveguide dispersion.

τ, λ, c, , b, k, n ₂Be respectively refringence, normalization propagation constant, wave vector, cladding index and the normalized frequency of group delay, optical wavelength, the light velocity, fibre core and covering with V.The chromatic dispersion of material is by the attribute decision of material, in case the material of optical fiber is selected, its dispersion properties has just been determined.The available Sellmeier formula fitting estimation of the refractive index (decision chromatic dispersion) of fiber optic materials at present.So, controlled chromatic dispersion has just been fallen in the guided wave chromatic dispersion, by preceding formula as seen, has big negative dispersion coefficient in order to make optical fiber, must strengthen , but still to keep single mode transport just must reduce fiber core radius simultaneously, so just increased the difficulty of the processing and the manufacturing of traditional fiber.And photonic crystal fiber is made of the same material, it is very big that the difference of sandwich layer and cladding index can be done, its refractive index distribution character on xsect mainly relies on its airport geometric configuration, size, the spacing in hole and the arrangement of airport to change, so can be by designing the single-mode fiber that different degree of freedom manufacturings has different dispersion characteristics.As for chromatic dispersion gradient, it only is the derivative of chromatic dispersion to wavelength, and the essence of design does not change, and just will increase one degree of freedom when optimizing concrete ATC-PCF parameter.

Be the ultimate principle that ATC-PCF that example discussion the present invention proposes can realize project objective with covering equivalent refractive index method more below.

At first simply introduce the equivalent refractive index model of PCF.It is that the core district of r and the diameter arranged according to triangular shaped periods on quartz substrate are that d, spacing are that photonic crystal fiber shown in Fig. 6 (a), its xsect can be divided into the radius that is made of pure quartz column The clad region that constitutes of airport.The basic thought of equivalent refractive index model is that the covering equivalence that will have the regular periodicity airport is n for refractive index _ClQuartz, so for the analysis of photonic crystal fiber, just can utilize the analytical approach and the analysis result of traditional step change type optical fiber.The key of equivalent refractive index model is to obtain basic space fill pattern (Fundamental Space-Filling Mode, transmission β FSM) _FSM, like this, the equivalent refractive index of photonic crystal fiber clad region is for being calculated as follows:

n _eff＝β _FSM/k ₀ (3)

k ₀＝2π/λ ₀ (4)

Wherein, k ₀And λ ₀Be respectively the wave number and the wavelength of free space.In order to obtain β _FSM, the photonic crystal fiber covering can be approximately infinitely great periodic structure, a unit in the covering, shown in Fig. 6 (b), when the airport diameter d was not very big, its regular hexagon border can be approximately radius was r _EffCircle, shown in Fig. 6 (c).In such one-period unit, adopt cylindrical coordinates to find the solution the scalar wave equation of covering, under the condition of basic mode transmission, can get in conjunction with the continuity boundary condition of quartz-air interface in cellular periodic boundary condition and the cellular:

$\frac{{\mathrm{UI}}_0\left(W\right)}{{\mathrm{WI}}_1\left(W\right)}=\frac{J_1(U\&CenterDot;r_{\mathrm{eff}}/a)N_0\left(U\right)-J_0\left(U\right)N_1(U\&CenterDot;r_{\mathrm{eff}}/a)}{J_1\left(U\right)N_1(U\&CenterDot;r_{\mathrm{eff}}/a)-J_1(U\&CenterDot;r_{\mathrm{eff}}/a)N_1\left(U\right)}---\left(5\right)$

A=d/2 wherein, the field of the implication of all the other each symbols and traditional fiber is separated identical, repeats no more here.The maximum root of this secular equation is exactly β _FSMThereby (3) formula of utilization can obtain photonic crystal fiber covering equivalent refractive index n _ClThe equivalent refractive index n that clad region has been arranged _Cl, just can utilize the theory of step optical fiber to study the guided mode characteristic of photonic crystal fiber.

The covering equivalent refraction rate theory of the analysis photonic crystal fiber of introducing according to the front, the cross-sectional structure that the present invention proposes ATC-PCF as shown in Figure 3 can be regarded the photonic crystal fiber with two parallel fibre cores as, one of them fibre core 1 is made of the A district, and another fibre core 2 is made of the C district.By adjusting its structural parameters, make two fibre cores support single mode transport independently of one another respectively, according to super model (Supermodes) theory, this structured optical fiber is supported an even super model and a strange super model so, and their propagation constant and Electric Field Distribution are determined by the following formula eigenvalue equation:

$\{{\&dtri;}_{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="C200710049019E00181.png"\; state="\{\{state\}\}">t</figure-callout>}}^2+{{\mathrm{<figure-callout\; id="0"\; label="k"\; filenames="C200710049019E00184.png"\; state="\{\{state\}\}">k</figure-callout>}}_0}^2{n}^2(x,y)-{\mathrm{\&beta;}}_{\&PlusMinus;}^2\}{\mathrm{\&psi;}}_{\&PlusMinus;}(x,y)=0---\left(6\right)$

Wherein, β _±And ψ _±Be respectively the propagation constant and the Electric Field Distribution of idol, strange super model,

Be the two dimensions Laplace operator, n (x, y) be the index distribution of cross section of optic fibre, here we see, the propagation constant of light wave fields is (according to definition, chromatic dispersion and chromatic dispersion gradient are by this parameter decision) and Electric Field Distribution (according to definition, effective core area is by this parameter decision) complete index distribution n by cross section of optic fibre (x, y) decision.By appropriate parameter setting, can make two super models have identical propagation constant at a certain wavelength place, this wavelength is called phase matching wavelengths (Phase-Matching Wavelength, PMW), away from the effective refractive index curve of these two super models of PMW place very near two fibre cores effective refractive index curve of institute's communication mode separately, so when the wavelength of light wave during less than PMW, the even super model of all light is limited in the A district fibre core 1 tightly, the area that causes effectively overlapping is less, when the wavelength of light wave increases to above PMW, the energy of light wave is diffused in the C district fibre core 2 gradually, and the area that causes effectively overlapping increases.In like manner, because the mode profile of propagation constant and electric field is determined that by same eigen[value (6) when the distribution of electric field changed, its propagation constant also must change (because have only two super models, not having the situation of degeneracy).Fig. 7～Fig. 9 be we according to above analysis, the PRELIMINARY RESULTS that adopts the calculation of parameter of a kind of ATC-PCF that estimates by rule of thumb to obtain.As seen, the variation of effective refractive index, chromatic dispersion, Electric Field Distribution and useful area all coincide with above-mentioned analysis.

Manufacturing problem about optical fiber proposed by the invention, for the traditional fiber manufacturing, twin-core fiber is had relatively high expectations to process conditions, the higher twin-core fiber of workmanship is difficulty very, process is quite loaded down with trivial details, generally after processing, cleaning, put into sleeve pipe together and place then on the glass work lathe, burn till through negative pressure, thermal-flame by two common single mode optical fibres prefabricated rods.The main problem that exists is that the optical fiber parameter that designs in advance is difficult for guaranteeing that be easy to generate bubble in the prefabricated rods, sleeve pipe combines bad with assembly, and shank is easy to generate stress, thereby occurs bursting phenomenon often, and prefabricated rods is scrapped, and yield rate is low.

For photonic crystal fiber, the making of double-core photonic crystal fiber is more much easier than the making of common double core fibre.The drawing process process years of development of photonic crystal fiber, the comparative maturity that has developed at present, common manufacturing process has three kinds: kapillary boundling (the pipe rod is piled up wire drawing) method, sol-gal process and extrusion.What wherein be used widely is kapillary boundling method, in the manufacturing process quartz capillary is piled up according to the periodic structure of desired design, replaces quartz capillary to form fibre core in the position of optical fiber fuse with quartz pushrod, adds sleeve pipe then and makes prefabricated rods; At last prefabricated rods is drawn into optical fiber on fiber drawing tower.The outstanding advantage of kapillary boundling method is can make to have very complicated cross-sectional geometry, because can realize the design of various photonic crystal fibers by the adjusting to quartz pushrod and number capillaceous, position, spacing and size.Just successfully drawn out double-core photonic crystal fiber as far back as calendar year 2001 G.Kakarantzas etc.As seen drawing ATC-PCF that the application proposes does not exist and is difficult to the difficulty that overcomes on the technological essence.

Embodiment 1:

With reference to the photonic crystals optical fiber structure of solid leaded light, it is to be made of quartz in the covering and airport, can be considered as the quartz that airport surrounds the center.Given this, the present invention is called optical guide unit with such structure, and the solid portion of central authorities is called the center light waveguide region, and peripheral airport and near zone thereof are called the zone, outfield.As shown in Figure 4, be the center light waveguide region in the middle annulus, the outside leachy zone that distributes is the zone, outfield.

Referring to Fig. 3.Present embodiment includes first optical guide unit and second optical guide unit, and second optical guide unit is distributed in the zone, outfield of first optical guide unit, and is the pore encirclement of first optical guide unit.The first and second optical guide unit structures are arranged according to the photonic crystal fiber mode,, are all the arrangement mode of " pore encirclement solid " that is.First light element comprises the center light waveguide region and is uniformly distributed in center light waveguide region multilayer pore on every side in the regular hexagon mode that its part holes is that second optical guide unit replaces.With Fig. 4 is example, and the solid of two-layer pore in the B district and central authorities thereof promptly constitutes second optical guide unit, and its position that occupies just is being the position of a pore of first optical guide unit.

First and second optical guide units of present embodiment are the regular hexagon structure, and promptly each layer pore constitutes a regular hexagon.It only is an embodiment, adopts other polygon can realize equally.

The size of first optical guide unit of present embodiment makes second optical guide unit be in the zone, outfield of first optical guide unit greater than second optical guide unit.That is, the hole diameter of first light element and circumcircle diameter are all greater than second light element.

Present embodiment comprise one first light element and one second light element.As other embodiment, a plurality of second light elements can be arranged also.The present invention can control than the realization chromatic dispersion by the useful area of first light element and second light element, and is also insensitive for the quantity of light element.

Referring to Fig. 5.Parameter L 1, d1, D1, λ and the Λ of present embodiment can determine by particle cluster algorithm.Be specially:

Suppose to form a group by m particle in the target search space of a D dimension, wherein i particle position can be expressed as the vector x that a D ties up _i=(x _I1, x _I2, L, x _ID), i=1,2, L, m, x _iPotential separating of the problem of asking exactly.With x _iObjective function of substitution just can calculate its adaptive value, weighs x according to the size of adaptive value _iQuality." circling in the air " speed of i particle also is a D dimensional vector, is designated as v _i(vi ₁, v _I2, L, v _ID).Remember that the optimal location that i particle searches up to now is p _i=(p _I1, p _I2, L, p _ID), the optimal location that whole population searches up to now is p _g=(p _G1, p _G2, L, p _GD), then the computing formula of particle swarm optimization algorithm is:

v _i＝wv _id+c ₁r ₁(p _id-x _id)+c ₂r ₂(p _gd-x _id) (7)

x _id＝x _id+v _id (8)

Wherein, d=1,2, L, D, w are non-negative constants, are called inertial factor, c ₁, c ₂Be non-negative constant, be called the study factor, r ₁, r ₂∈ [0,1] is a random number, in the application of reality, if the bounded problem generally also has following constraint condition:

v _Id∈ [v _Dmin, v _Dmax], x _Id∈ [x _Dmin, x _Dmax] v wherein _Dmin, v _Dmax, x _DminAnd x _DmaxFor predefined constant, work as v _IdOr (with) x _IdWhen exceeding predetermined border, v _IdOr (with) x _IdJust equal the corresponding edge dividing value.The general optimization step of particle cluster algorithm is:

1) all particle position of random initializtion and speed;

2) according to the adaptive value of each particulate of known target function calculation;

3) for each particulate, if the adaptive value of current location adaptive value and historical desired positions relatively is current location adaptive value optimum then upgrade p _i

4) adaptive value of more current all particle desired positions and the best adaptive value of all particle positions in history if current desired positions is more excellent, are then upgraded p _g

5) judge end condition, then withdraw from, do not satisfy then forwarding the operation of the 2nd step to if satisfy.

In the present embodiment, can go out the adaptive value of particle desired positions, comprise the diameter D1 of big airport according to above-mentioned algorithm computation, the diameter d 1 of little airport, the space of big airport is apart from Λ, and the space of little airport is apart from λ, the centre distance L1 of fibre core 1 district A and fibre core 2 district C.Should be noted in the discussion above that herein L1, d1 and D1 have concrete physical significance, with L, d and D in the particle cluster algorithm formula be diverse.

In the present embodiment, can go out the adaptive value of particle desired positions, comprise the diameter D1 of big airport according to above-mentioned algorithm computation, the diameter d 1 of little airport, the space of big airport is apart from Λ, and the space of little airport is apart from λ, the centre distance L1 of fibre core 1 district A and fibre core 2 district C.

Claims (9)

1, light transmitting fiber, include first light element and second light element, second light element is distributed in the zone, outfield of first light element, and surrounded by the pore of first light element, it is characterized in that the hole diameter of first light element and center light waveguide region circumcircle diameter are greater than the hole diameter and the center light waveguide region circumcircle diameter of second light element.

2, light transmitting fiber as claimed in claim 1 is characterized in that, the described second light element structure is arranged according to the photonic crystal fiber mode of solid leaded light.

3, light transmitting fiber as claimed in claim 1 is characterized in that, described first light element and second light element are all the photonic crystals optical fiber structure of solid leaded light.

4, light transmitting fiber as claimed in claim 1 is characterized in that, described first light element and second light element are all the regular polygon structure.

5, light transmitting fiber as claimed in claim 4 is characterized in that, described first light element and second light element are all the regular hexagon structure.

6, light transmitting fiber as claimed in claim 1 is characterized in that, has two-layer pore at least in the zone, outfield of described first light element and second light element.

7, light transmitting fiber as claimed in claim 1 is characterized in that, described first light element comprises the center light waveguide region and be uniformly distributed in center light waveguide region multilayer pore on every side in the regular polygon mode that its part holes is replaced by second light element.

8, light transmitting fiber as claimed in claim 1 is characterized in that, the pore of first light element and/or second light element is circle, triangle, rectangle or hexagon pore.

9, light transmitting fiber as claimed in claim 1 is characterized in that, first light element is positioned at the center of whole optical fiber, the second light element decentered distribution.

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