CN106443885A - Method of realizing low-loss welding of pohotonic crystal fiber and solid fiber - Google Patents
Method of realizing low-loss welding of pohotonic crystal fiber and solid fiber Download PDFInfo
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- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/255—Splicing of light guides, e.g. by fusion or bonding
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Abstract
The present invention belongs to an optical design technology, and relates to a method of realizing the low-loss welding of a pohotonic crystal fiber and a solid fiber. According to the present invention, by establishing a temperature field distribution model and an air hole stress model in the welding state of the pohotonic crystal fiber and the solid fiber, the numerical relationship between the air hole collapse degree and a carbon dioxide laser discharge parameter is deduced, and by establishing the numerical relationship of a pohotonic crystal fiber end face structure and an effective mode field area, a loss model of the welding of the pohotonic crystal fiber and the solid fiber is obtained, and further the carbon dioxide laser discharge parameter realizing the low-loss welding is calculated accurately. According to the present invention, by calculating the carbon dioxide laser discharge parameter accurately, an air hole structure of the pohotonic crystal fiber can be controlled, so that an effective mode field when the pohotonic crystal fiber and the general solid fiber are in a welding state can reach an optimal matching state, and further the welding loss is reduced.
Description
Technical field
The invention belongs to optical design techniques, are related to a kind of photonic crystal fiber of realizing with solid core fibres low loss welding
Method.
Background technology
Photonic crystal fiber (Photonic Crystal Fiber, PCF) or referred to as microstructured optical fibers (Micro-
Structure Fiber, MSF), it is a kind of novel optical fiber of appearance of nearly more than ten years, has significant difference with conventional tubeless optical fiber
New special optical fiber.The optical fiber of this structure is regularly dispersed with many airports along light axial direction, changes airport
Size and arrangement mode, it will change the characteristic of output light, this distinctive feature makes it be expected to develop various novelties
Opto-electronic device, special optical fiber, therefore photonic crystal fiber will be widely used in optic communication and optoelectronic areas.
But in these applications of developmental research, the interconnection technique of photonic crystal fiber is directed to, can be lived by optical fiber at present
Movement connector, arc discharge welding mode, carbon dioxide laser welding mode carry out photonic crystal fiber and solid plain light
Connection between fibre.And carbon dioxide laser welding mode is with its high-absorbility (wavelength 10.6um), the shape of laser and energy
Amount is controlled, but the advantage such as dye and residue becomes the preferred manner of photonic crystal fiber and solid plain fused fiber splice.
But on the one hand as photonic crystal fiber is all had differences with solid plain optical fiber structure, physical parameter, while
The presence of the special air pore structure that photonic crystal fiber is present, to, in carbon dioxide laser electric discharge heating process, going out
Now inconsistent with solid plain optical fiber temperature rise, profiling temperatures, melting situation phenomena impair splice loss, splice attenuation；On the other hand can
Reduce splice loss, splice attenuation with solid plain optical fiber mode fields by mating photonic crystal fiber, and the effective mould field face of photonic crystal fiber
Product is depending on the photonic crystal fiber air pore structure after the completion of welding.Therefore, it is necessary to by the temperature to discharging in heating process
Degree field distribution numerical analysis and emulation, the method for working out a set of control photonic crystal fiber air pore structure parameter, accurate real
While existing both sides fiber fuse, the control photonic crystal fiber airport degree of subsiding makes the effective mould field of two kinds of optical fiber reach most preferably
Coupling, so that splice loss, splice attenuation is reduced to minimum.
Content of the invention
The purpose of the present invention：There is provided a kind of subsided degree by control photonic crystal airport, realize photonic crystal fiber
Method with solid core fibres low loss welding.
Technical scheme：A kind of method for realizing photonic crystal fiber and solid core fibres low loss welding, which leads to
The thermo parameters method model and airport stress model that sets up under photonic crystal fiber and solid plain fiber fuse state is crossed,
Both sides fiber optic temperature situation of change and air hole wall stressing conditions in simulation discharge process, and then derive that airport subsides journey
Numerical relation between degree and carbon dioxide laser discharge parameter, then have with which by setting up photonic crystal fiber end face structure
The numerical relation of effect mode field area, obtains the loss model of photonic crystal fiber and solid core fibres welding, and then accurately calculates
Realize the carbon dioxide laser discharge parameter of low loss welding.
Carbon dioxide laser discharge parameter includes discharge centers position, discharge time, discharge capacity.
The described method for realizing photonic crystal fiber and solid core fibres low loss welding, which comprises the following steps that：
Step 1：Set up two optical fiber effective core area and splice loss, splice attenuation model
The high birefringence characteristic of photonic crystal fiber is formed by the geometry of its two great circle of immediate vicinity, according to
The electromagnetic theory of light is calculated, when light is bound in fiber optic hub, the electric field intensity at electric-field intensity distribution photonic crystal fiber center
Distribution E1；While calculating Electric Field Distribution E2 in solid plain fiber core；
When high birefringence type photonic crystal fiber and panda protecting polarized light fiber coupling, in abrupt interface, emergence pattern is changed,
A portion and the patterns match of waveguide, will continue to propagate in the waveguide；Another part is mismatched with the pattern of waveguide, is become
Become radiation mode and lose, this portion of energy for losing becomes coupling mismatch loss, calculated by the pattern match of two waveguides
Coupling efficiency, and then the model of two optical fiber effective core area and splice loss, splice attenuation can be set up；
Step 2：Photonic crystal fiber thermal conduction characteristic is analyzed
The thermal conduction characteristic that photonic crystal fiber is heated is analyzed, is obtained under different carbon dioxide laser discharge parameters
Photonic crystal fiber thermo parameters method model；
Step 3：Photonic crystal fiber is analyzed with thermal conduction characteristic during solid plain fused fiber splice
In conjunction with step 2 photonic crystal fiber thermo parameters method model, photonic crystal fiber is carried out with solid plain optical fiber welding
Thermal conduction characteristic analysis when connecing, and then set up the thermo parameters method mould of two optical fiber under different carbon dioxide laser discharge parameters
Type；
Step 4：Photonic crystal fiber and mechanical characteristic analysis during solid plain fused fiber splice
In conjunction with the both sides fiber optic temperature field distribution model under step 3 difference carbon dioxide laser discharge parameter, set up molten
Melt relation and the photonic crystal fiber flow equation of photonic crystal fiber viscosity coefficient and temperature under state, according to photonic crystal light
The flow process at gas-liquid two-phase interface in fibre, is carried out to its quartz-Air Interface using the Level Set Method in biphase gas and liquid flow
Follow the trail of, quartzy liquid surface equation of motion under surface tension is obtained, and then sets up different carbon dioxide laser discharge parameters
Lower photonic crystal fiber air micro pore structure；
Step 5：Set up the numerical model of carbon dioxide laser discharge parameter and splice loss, splice attenuation
In conjunction with photonic crystal fiber air micro pore structure under step 4 difference carbon dioxide laser discharge parameter, and
Step 1 photonic crystal fiber and solid plain optical fiber effective core area and loss model, set up carbon dioxide laser electric discharge
The numerical relation of parameter and splice loss, splice attenuation；
Step 6：Low loss welding parameter determination
In conjunction with the numerical model of step 5 carbon dioxide laser discharge parameter and splice loss, splice attenuation, minimum molten in order to obtain
Loss is connect, that is, is needed the best match of both sides optical fiber mode fields is realized, photonic crystal fiber air pore structure under molten condition is tried to achieve,
And then the carbon dioxide laser discharge parameter that will obtain said structure needs can be derived：Discharge capacity, discharge time, electric discharge
Center.
When determining discharge time, discharge centers position delta can be drawn by formula (1)
Z=-419.6delta2-0.945delta+7.943×10-5(7)
Wherein, Z is fiber end face axial coordinate.
Discharge capacity is under discharge time is determined, by z=0 position, temperature is determined with the relation curve of discharge time.
Under discharge time is determined, at z=0 position, the relation curve of temperature and discharge time, by as shown in formula (8)
Silicon dioxide viscosity coefficient μ determines
Wherein, T is the temperature related to discharge time.
The degree of subsiding of photonic crystal fiber airport affects the area that subsides, and so as to affect optical fiber to couple, two optical fiber exist
Optical coupling efficiency when emergence pattern is mated by abrupt interface, is determined by formula (5),
Wherein, E1(x, y) and E2(x, y) is respectively two mode distributions of two optical fiber in abrupt interface.
The advantages of the present invention are：By setting up under photonic crystal fiber and solid plain fiber fuse state
Thermo parameters method model and airport stress model, simulation discharge process in both sides fiber optic temperature situation of change and air
Hole wall stressing conditions, and then derive that subside degree and carbon dioxide laser discharge parameter of airport (discharge centers position, is put
Electric time, discharge capacity) between numerical relation, derived by the numerical model of two optical fiber effective core area and splice loss, splice attenuation
Go out the effective mode field diameter of photonic crystal fiber after cooling, and then accurately calculate the discharge parameter (electric discharge of carbon dioxide laser
Center, discharge time, discharge capacity).So on the one hand can accurately calculate before fusing operation is implemented to make two sidelights
Fibre reaches molten condition simultaneously, and maximum temperature point occurs in the carbon dioxide laser discharge parameter of interface, it is to avoid concrete
The loss that during production operation, operation failure brings, minimizing is done over again；On the other hand can be by putting to carbon dioxide laser
The accurate calculating of electrical quantity, can control photonic crystal fiber air pore structure, make photonic crystal fiber with solid plain optical fiber
Effective mould field in molten condition reaches best match state, so after making cooling splice loss, splice attenuation be down to minimum.
Description of the drawings
Fig. 1 is the isogram of photonic crystal fiber electric field effective model；
Fig. 2 is that carbon dioxide laser heating is melt optical fiber schematic diagram；
Fig. 3 is carbon oxide laser device heating photonic crystal fiber schematic diagram；
Fig. 4 is the temperature distribution history of two optical fiber of t=300ms；
Fig. 5 is at temperature and surface tension effects, cause airport to subside photonic crystal end view；
Fig. 6 is the relation curve of viscosity and temperature；
Fig. 7 end face temperature and time curve；
The contraction situation of airport during Fig. 8 0.5s；
Before and after Fig. 9 shrinks, model is contrasted；
Photonic crystal fiber pattern after Figure 10 contraction.
Specific embodiment
The present invention is further illustrated below in conjunction with the accompanying drawings：
The present invention realizes photonic crystal fiber with the method for solid core fibres low loss welding by setting up photonic crystal fiber
With thermo parameters method model under solid plain fiber fuse state and airport stress model, both sides in simulation discharge process
Fiber optic temperature situation of change and air hole wall stressing conditions, and then derive that airport subsides degree and carbon dioxide laser
Numerical relation between discharge parameter.Closed with the numerical value of its effective core area by setting up photonic crystal fiber end face structure again
System, obtains the loss model of photonic crystal fiber and solid core fibres welding, and then accurately calculates and realize the two of low loss welding
Carbon oxide laser device discharge parameter.
Detailed process comprises the steps：
Step 1：Set up two optical fiber effective core area and splice loss, splice attenuation model
The guiding property of photonic crystal fiber is to determine, its high birefringence characteristic is by several layer of air holes of immediate vicinity
Formed by the geometry of its two great circle of immediate vicinity.According to the electromagnetic theory of light, using the method for finite element, by following formula
Based on can analyze the pattern of photonic crystal fiber.
εr=(n-jk)2(3)
Wherein, E is electric field intensity, k0For wave number in vacuum, εrFor relative dielectric constant, it is refraction that β is propagation constant, n
Rate.(1) formula be Helmholtz equation, (2) formula be that the z-component of electric field is separated, (3) formula be refractive index with relative dielectric constant and
The relation of wave number.According to (2) formula, (1) formula can be converted into x, the electric field equation on y plane.According to (3) formula, (1) formula can be turned
Turn to the equation related to refractive index.
Light is when optical fiber is entered, and comprising many patterns, each pattern is corresponding with corresponding effective refractive index.Due to optical fiber
The restriction of structure, only specific pattern there may be.Therefore, using Finite Element Method to photonic crystal fiber Refractive Index of Material
Neighbouring effective refractive index is screened, you can obtain the pattern that can propagate in fibre core, electric field of the communication mode on end face
It is distributed as E1(x, y), as shown in Figure 1.
For panda type single-mode polarization maintaining fiber, light intensity is distributed as Gaussian in cross section, if mode field diameter be
(in 1/e2Light strength), the mode distributions of Gaussian beam are expressed as：
When high birefringence type photonic crystal fiber and panda protecting polarized light fiber coupling, in abrupt interface, emergence pattern is changed,
A portion and the patterns match of waveguide, will continue to propagate in the waveguide；Another part is mismatched with the pattern of waveguide, is become
Become radiation mode and lose, this portion of energy for losing becomes coupling mismatch loss, its coupling efficiency η is therefore obtained is：
Step 2：Photonic crystal fiber thermal conduction characteristic is analyzed
Laser has the characteristics that high monochromaticity, high coherence, high directivity and high brightness, and it is a kind of preferable heat, light
The energy.The wavelength of carbon dioxide laser is 10.6um, and its photon energy is 0.176eV, much smaller than the ionization energy of compound, it is impossible to
Directly result in compound and chemical reaction occurs.
The mode of operation of carbon dioxide laser is TEM00, and it is circle, laser irradiation region that light beam is Gauss distribution, hot spot
Relative position schematic diagram is as shown in Figure 2 between optical fiber.
Laser radiation rate is
Wherein, PtotalFor general power, Wy, WzRespectively carbon dioxide laser light beam irradiates circular light spot y, the z to be formed
The radius of field.
As the material of solid PCF is silicon dioxide, its fusing point is that (1700 ± 5) K, welding photonic crystal fiber was both required
The temperature of welding area can reach fusing point, again can not be too high, in order to avoid subsiding for airport is caused, and in order to obtain welding
The preferable photonic crystal fiber of quality, needs fibre core and covering while reaching fusing point.From heat transfer theory, as long as cross section
Covering is less than 1% with the temperature difference of fibre core, it is possible to think that they have reached unified temperature.Further, since laser energy is in light
Fine length direction is in Gauss distribution, carries out three-dimensional artificial to fiber optic temperature field, studies the effect of airport in photonic crystal fiber
With the control to welding condition.
Accompanying drawing 3 show the experimental provision schematic diagram for heating photonic crystal fiber using carbon dioxide laser, in figure z=
0 position is the center that the left side of photonic crystal fiber is located at laser irradiation region.
Using parameter shown in accompanying drawing 3 and photonic crystal fiber One-dimensional Heat Conduction Equation as boundary condition, set up and dioxy
Change the photonic crystal fiber distribution of three-dimensional temperature model of carbon laser discharge parameter correlation.
Step 3：Photonic crystal fiber is analyzed with thermal conduction characteristic during solid core fibres welding
Based on the numerical value emulation method of step 2, the laser power required for solid PCF and PM fused fiber splice to be calculated and put
The electric time, the side-play amount for needing the center for calculating laser irradiation region domain first to offset to solid PCF direction.The determining of side-play amount
Justice is：During welding, two end centre of optic fibre positions are to move side-play amount zero point, to PM optical fiber direction, and side-play amount is for just；To photon
Crystal optical fibre direction is moved, and side-play amount is negative.The value of side-play amount is laser irradiation region center to (x=0, y=0, z=0)
The distance of point.
During due to having two controlled splicing parameters, i.e. laser power P and electric discharge when carbon dioxide is used for fused fiber splice
Between t, meanwhile, for particularity during solid PCF and PM fused fiber splice, also there is the 3rd splicing parameter is in laser irradiation region
The position delta of the heart.Needing exist for calculating can make two kinds of optical fibre interface positions (i.e. position of z=0) for being entirely heated area
The thermal self-restraint stress in domain, the heated center position delta of carbon dioxide laser, and two optical fibre interface positions be (i.e. z=0's
Position) place temperature curve and laser instrument heating power P, the relation of t heat time heating time.To power P under different time in table 1, swash
The value of photoirradiation district center position delta is emulated.
1 simulated conditions parameter list of table
Can obtain determining under heat time heating time, during corresponding different capacity P and different heating center z, solid PCF and PM optical fiber
On temperature distribution history.
Simulation numerical result under the determination time is analyzed, the position delta of thermal self-restraint stress is only in heated center z
Position relevant, unrelated with heating power, therefore the position delta of heated center z and thermal self-restraint stress can be carried out secondary
Item fitting, as a result as shown in formula (5).
Z=-419.6delta2-0.945delta+7.943×10-5(7)
Heated center position when can occur in two optical fibre interfaces in the hope of the position of thermal self-restraint stress, i.e. during z=0
Delta is as shown in table 2.
Table 2 corresponds to the numerical result of different heating time heated center position
| Sequence number | Carbon dioxide laser T heat time heating time (ms) | Heated center position delta (um) | Thermal self-restraint stress position Z (um) |
| 1 | 300 | 113.68 | 0 |
| 2 | 350 | 90.22 | 0 |
| 3 | 400 | 88.42 | 0 |
| 4 | 450 | 86.5 | 0 |
| 5 | 500 | 81.1 | 0 |
Followed by heating power P and temperature maximum T linear fit, two optical fibre interface position (i.e. z can be obtained
=0 position) place temperature curve and laser instrument heating power P, the relational model of t heat time heating time.It is t=as shown in Figure 4
300ms, different side-play amount delta of correspondence, under different heating power, the temperature curve distribution of two optical fiber.
Step 4：Photonic crystal fiber and mechanical characteristic analysis during solid plain fused fiber splice
It is quartzy liquid after photonic crystal fiber melted by heating, the interface of quartzy liquid-to-air is in micro molecule power
Under effect, macroscopic view forms surface tension, and surface tension shrinks the airport in quartzy liquid, and shrinking law meets hydrodynamics
Theoretical.Due to viscosity, the density much smaller than quartzy liquid of air, therefore, this incompressible fluid of quartzy liquid is only studied
Flow field under surface tension effects.
Meanwhile, according to the both sides fiber optic temperature field distribution model under step 3 difference carbon dioxide laser discharge parameter, push away
Derive under quartzy photonic crystal fiber molten condition, thermo parameters method and viscosity coefficient model, and then set up light under molten condition
Photonic crystal fiber flow equation, as shown in formula (8) (9), (10).
U=0 (10)
Wherein, FstFor surface tension, it is to study the density at point that U is flow field velocity, ρ, and it is the time that I is unit matrix, t, μ
For viscosity.Formula (9), (10) derive from the Navier-Stokes equation of flow of fluid.
In formula (9), the surface tension for acting on gas-liquid two-phase interface is relevant with coefficient of surface tension, curvature, thus builds
The Surface Tension Equation of vertical (10).
Fst=σ κ δ n (11)
In formula (11), σ is coefficient of surface tension, and it (is 1, at which for Dirac function at gas-liquid interface that κ is curvature, δ
His position is 0), n is the normal unit vector of interface.
In formula (7), viscosity, mu is the function of end face temperature, and with the raising of end face temperature, viscosity value diminishes.By step
Three can obtain, and end face temperature is the function of carbon dioxide laser heat time heating time, heating location and heating power.Ignore quartzy liquefaction
The change that Shi Midu and latent heat of liquefaction cause, it is known that the contraction of photonic crystal fiber end face airport is added with carbon dioxide laser
Hot time, heating location are relevant with heating power.Gravity item is not included in formula (8), as surface tension is much larger than gravity, therefore not
The impact that consideration gravity is shunk to photonic crystal fiber.
According to the flow process at gas-liquid two-phase interface in photonic crystal fiber, using the Level Set Method in biphase gas and liquid flow
Its quartz-Air Interface is tracked, and quartzy liquid surface is obtained under surface tension shown in the equation of motion such as formula (11).
In formula, γ is initiation parameter again, and ε is that interfacial thickness parameter, φ represents the material ratio at two fluid interface
Example, ρ ' is the equivalent density of intersection, and μ ' is the equivalent viscosity of intersection, ρ1For quartzy fluid density, ρ2Close for air gas
Degree, μ1For quartzy liquid viscosity, μ2For air gas viscosity.According to the physical significance of φ, it is quartzy liquid when defining φ ＜ 0.5,
It is air fluid during φ ＞ 0.5.
Under conditions of atmospheric density and viscosity is ignored, according to (9) formula analyze quartzy liquid under surface tension effects in
The flow field velocity distribution in portion, analyzes the Interface Moving of quartzy liquid outer boundary according to (12) formula.Convolution (9) and formula (12), according to
By finite element analyses means, the position of the point by calculating φ=0.5, you can follow the trail of quartzy liquid surface and transport under surface tension
Dynamic process, and then set up photonic crystal fiber air micro pore structure under different carbon dioxide laser discharge parameters.Accompanying drawing 5
The heating showing through carbon dioxide laser, airport subside after surface texture schematic diagram.
Step 5：Set up the numerical model of carbon dioxide laser discharge parameter and splice loss, splice attenuation
According to the mould field loss model of step 1, and in practical application photonic crystal fiber and solid plain optical fiber knot
Structure parameter calculate meet lowest loss requirement, two optical fiber coupling effective core area, and then try to achieve be heated subside after photon
The end face structure of crystal optical fibre.
The position that both sides interface (i.e. z=0) will be reached under the different discharge times that step 3 is tried to achieve is thermal self-restraint stress
Corresponding heated center position, and during difference discharge time t, discharge power P, the position of (i.e. z=0) at the optical fibre interface of both sides
Temperature curve is used as the simulated conditions of step 4, and then simulation calculation goes out to obtain photonic crystal fiber during final mould field coupling
End face structure, discharge parameter (discharge time t, the discharge centers position delta, and electric discharge of the carbon dioxide laser of needs
Power P).
Embodiment 1
The present invention is proposed a kind of being subsided by control photonic crystal fiber airport and realizes which with solid core fibres low-loss
The method of welding.It is below specific embodiment.
In the present embodiment, following four steps are divided to be calculated：
(1) according to the analysis of step 3, when high double-refraction photon crystal fiber and panda protecting polarized light fiber welding, optical fiber axial direction
Maximum temperature position is unrelated with carbon dioxide laser heating power, relevant with heat time heating time, heating location.Therefore, may specify
Heat time heating time and heating location so as to temperature highest at two kinds of optical fiber interfaces, can then change carbon dioxide laser and add
Thermal power, tries to achieve appropriate photonic crystal fiber end face structure so that splice loss, splice attenuation minimum.This example selects a carbon dioxide
Laser instrument heating power, is determining heat time heating time, is determining under heating location, calculating splice loss, splice attenuation.
(2) under above-mentioned selected carbon dioxide laser heating power, heat time heating time, heating location, two kinds of light are calculated
Fine Axial Temperature Distribution.By the relation of two kinds of optical fiber intersection temperature and times with Polynomial curve-fit, obtain temperature when
Between function：
T=T (t) (13)
(3) in the mechanical model described in step 4, using temperature T=T (t) as input, change viscosity with temperature, meter
The airport that calculates under viscosity B coefficent shrinks.After contraction terminates, according to amount of contraction and its effective model of position calculation in hole.To have
Electric field intensity output under effect pattern.
(4) according to the electric field intensity under photonic crystal fiber effective model, with the theory of step 1, computed losses.
Before starting to calculate, the physical dimension for providing solid photonic crystal fiber first is as shown in table 3, in calculating process
Required physical parameter is as shown in table 4.
The solid PCF airport physical dimension table of table 3
| Sequence number | Title | Length (um) |
| 1 | Fibre cladding external diameter | 80 |
| 2 | Core diameter (x) | 4.09 |
| 3 | Core diameter (y) | 8.18 |
| 4 | Pitch of holes | 5.75 |
| 5 | Diameter macropores | 7.21 |
| 6 | Hole diameter | 3.9 |
4 physical parameter table of table
| Symbol | Definition | Value | Unit |
| CSiO2 | Quartzy specific heat capacity | 1345 | J.Kg-1.K-1 |
| Cair | Air specific heat capacity | 1010 | J.Kg-1.K-1 |
| D | Fibre diameter | 80 | um |
| R | Fiber radius | 40 | um |
| I | Carbon dioxide laser irradiance | See formula (1) | W.m-2 |
| Ptotal | The output of laser instrument | Undetermined | W |
| q | Heat flow density | See formula (8) | W.m-3 |
| Qabs | Absorptance | 3E-5 | Dimensionless |
| t | Time | Undetermined | ms |
| T | Melt temperature | 1700 | K |
| Wy, Wz | The beam width in y, z direction | 1.5 | mm |
| Wabs | S. E. A. | / | W |
| SiO2 | Quartzy density | 2200 | Kg.m-3 |
| air | Atmospheric density | 0.93 | Kg.m-3 |
| kSiO2 | Quartzy pyroconductivity | 2.68 | W.m-1.K-1 |
| Kair | Air pyroconductivity | 0.032 | W.m-1.K-1 |
With reference to the accompanying drawings 2, it is 0mm that definition optical fiber axial direction is the scope in z direction, photonic crystal fiber z direction<z<3mm, panda
The scope in optical fiber z direction is -3mm<z<0mm, the scope of carbon dioxide laser heating is -1.5mm<z<1.5mm.Select heating
Time is 500ms, and selected heating power is 1.7W.
For obtaining under selected heat time heating time, the carbon dioxide laser heated center of two optical fiber intersection maximum temperatures is made
Side-play amount, selected carbon dioxide laser heated center position is delta=0 in the skew of z-axis negative sense:30um:300um.I.e.
From the beginning of being 0 from side-play amount, select an offset point to be calculated every 30um, terminate for 300um to side-play amount.Inclined according to each
The maximum temperature position function for moving point fits side-play amount of the maximum temperature in two optical fiber intersections.Thermal source scope after skew
For -1.5mm-delta<z<1.5mm-delta, under with upper boundary conditions, with finite element analyses as means, is calculated selected
Heat time heating time is 500ms, and selected heating power is that 1.7W, the maximum temperature position under each side-play amount is as shown in table 5.
Maximum temperature and position under each side-play amount of table 5
| delta(um) | Position (um) | Maximum temperature (K) |
| 0 | 81 | 1922.331 |
| 30 | 42 | 1917.443 |
| 60 | 27 | 1912.583 |
| 90 | -6 | 1907.861 |
| 120 | -36 | 1902.986 |
| 150 | -72 | 1898.256 |
| 180 | -111 | 1893.655 |
| 210 | -138 | 1889.204 |
| 240 | -171 | 1885.176 |
| 270 | -207 | 1881.061 |
| 300 | -240 | 1877.102 |
Maximum value position z and side-play amount delta are made fitting of a polynomial, is obtained：
Z=-419.6delta2-0.945delta+7.943×10-5(14)
Z=0 is made, and side-play amount is tried to achieve for delta=81.13um.I.e. under heat time heating time is for 500ms so that two optical fiber are handed over
Interface temperature highest carbon dioxide laser center offset is 81.13um.Observation maximum temperature, is 1900K or so, here
At a temperature of quartzy liquid viscosity very big, be unfavorable for the contraction (will be specifically described later) of photonic crystal fiber airport.By
Unrelated with its heating power in carbon dioxide laser center offset, so after improving heating power, carbon dioxide laser
Center offset is still 81.13um.
By heating power with 1.8W as starting, take a bit every 0.1W, terminate to 2.5W, try to achieve under each power most
Big temperature is as shown in table 6：
Maximum temperature under 6 different heating power of table
| Power (W) | 1.8 | 1.9 | 2.0 | 2.1 | 2.2 | 2.3 | 2.4 | 2.5 |
| Maximum temperature (K) | 2006 | 2101 | 2197 | 2292 | 2388 | 2483 | 2579 | 2675 |
The boiling point of quartzy liquid is about 2600K, when selecting heating power, should ensure that the maximum temperature under this heating power is little
In 2600K.In the case of mode field diameter is unmatched, certain temperature should be selected to make the viscosity of quartzy liquid meet contraction will
Ask, and then make the amount of contraction of airport certain so as to which the mould field for being formed after contraction meets use requirement.
As shown in Figure 6, viscosity number reduces index decreased with temperature to the relation of the viscosity and temperature of quartz, and airport shrinks
Speed is also accelerated therewith.According to calculating (being obtained by the contraction process of hereinafter airport), the photonic crystal fiber in the present invention
It is 10 in viscosity value5When (corresponding temperature 2100K or so), contraction speed is about 0.7um/s.
In this example is calculated, according to temperature and the relation of quartzy liquid viscosity, carbon dioxide laser heating power is selected
For 2.2W.It is that under 2.2W, the temperature in 0～0.5s time is as shown in Figure 7 in carbon dioxide laser power.
The curve being fitted with quadratic polynomial in Fig. 8, the relation for obtaining temperature and time is：
Thus the relation of viscosity and time, i.e. μ=μ (T (t)) can be set up.
According to the theory analysis of step 4, the contraction situation in 0～0.5s airport is calculated.Gained amount of contraction such as Fig. 8 institute
Show, can obtain from the numerical value of amount of contraction, the shape after photonic crystal fiber airport shrinks is approximately circular, the shape of airport arrangement
Formula is still that triangle, whole airports still constitute approximate regular hexagon.
Photonic crystals optical fiber structure after contraction is as shown in table 7 with the comparison of primary photon crystal optical fibre structure：
Before and after 7 photonic crystal fiber of table shrinks, parameter compares
| Sequence number | Title | Before contraction (um) | After contraction (um) |
| 1 | Fibre cladding external diameter | 80 | 76.62 |
| 2 | Pitch of holes | 5.75 | 5.00 |
| 3 | Diameter macropores | 7.21 | 5.18 |
| 4 | Hole diameter | 3.9 | 2.65 |
The modeling of photonic crystal fiber end face is carried out according to upper table, to carry out the calculating of effective model.Model before and after contraction
Contrast as shown in Figure 9.
Under model after shrinking, according to the theory of step 1, communication mode of the light in photonic crystal fiber can be tried to achieve such as
Shown in accompanying drawing 10.
Meanwhile, the mode electric field distribution of panda optic fibre can be represented with equation below：
Wherein, ω=3.2um, removes A=1.,
Coupling efficiency can be calculated for η=0.9493 by formula (5).Therefore in this example, photonic crystal fiber with common
The splice loss, splice attenuation of solid core fibres is：
Claims (8)
1. a kind of method for realizing photonic crystal fiber and solid core fibres low loss welding, it is characterised in that by setting up photon
Thermo parameters method model and airport stress model under crystal optical fibre and solid plain fiber fuse state, simulation was discharged
Both sides fiber optic temperature situation of change and air hole wall stressing conditions in journey, and then derive that airport subsides degree and titanium dioxide
Numerical relation between carbon laser discharge parameter, then by setting up photonic crystal fiber end face structure with its effective core area
Numerical relation, obtain the loss model of photonic crystal fiber and solid core fibres welding, and then accurately calculate and realize low-loss
The carbon dioxide laser discharge parameter of welding.
2. the method for realizing photonic crystal fiber and solid core fibres low loss welding according to claim 1, its feature exists
In carbon dioxide laser discharge parameter includes discharge centers position, discharge time, discharge capacity.
3. the method for realizing photonic crystal fiber and solid core fibres low loss welding according to claim 2, its feature exists
In comprising the following steps that：
Step 1：Set up two optical fiber effective core area and splice loss, splice attenuation model
The high birefringence characteristic of photonic crystal fiber is formed by the geometry of its two great circle of immediate vicinity, according to light
Electromagnetic theory is calculated, when light is bound in fiber optic hub, the electric-field intensity distribution at electric-field intensity distribution photonic crystal fiber center
E1；While calculating Electric Field Distribution E2 in solid plain fiber core；
When high birefringence type photonic crystal fiber and panda protecting polarized light fiber coupling, in abrupt interface, emergence pattern is changed, wherein
A part and the patterns match of waveguide, will continue to propagate in the waveguide；Another part is mismatched with the pattern of waveguide, becomes spoke
Penetrate mould and lose, this portion of energy for losing becomes coupling mismatch loss, coupling is calculated by the pattern match of two waveguides
Efficiency, and then the model of two optical fiber effective core area and splice loss, splice attenuation can be set up；
Step 2：Photonic crystal fiber thermal conduction characteristic is analyzed
The thermal conduction characteristic that photonic crystal fiber is heated is analyzed, obtains photon under different carbon dioxide laser discharge parameters
Crystal optical fibre thermo parameters method model；
Step 3：Photonic crystal fiber is analyzed with thermal conduction characteristic during solid plain fused fiber splice
In conjunction with step 2 photonic crystal fiber thermo parameters method model, when carrying out photonic crystal fiber with solid plain fused fiber splice
Thermal conduction characteristic analysis, and then set up the thermo parameters method model of two optical fiber under different carbon dioxide laser discharge parameters；
Step 4：Photonic crystal fiber and mechanical characteristic analysis during solid plain fused fiber splice
In conjunction with the both sides fiber optic temperature field distribution model under step 3 difference carbon dioxide laser discharge parameter, molten is set up
Relation and the photonic crystal fiber flow equation of photonic crystal fiber viscosity coefficient and temperature under state, according in photonic crystal fiber
The flow process at gas-liquid two-phase interface, is tracked to its quartz-Air Interface using the Level Set Method in biphase gas and liquid flow,
Quartzy liquid surface equation of motion under surface tension is obtained, and then sets up photon under different carbon dioxide laser discharge parameters
Crystal optical fibre air micro pore structure；
Step 5：Set up the numerical model of carbon dioxide laser discharge parameter and splice loss, splice attenuation
In conjunction with photonic crystal fiber air micro pore structure under step 4 difference carbon dioxide laser discharge parameter, and step 1
Photonic crystal fiber and solid plain optical fiber effective core area and loss model, set up carbon dioxide laser discharge parameter with
The numerical relation of splice loss, splice attenuation；
Step 6：Low loss welding parameter determination
In conjunction with step 5 carbon dioxide laser discharge parameter and the numerical model of splice loss, splice attenuation, damage to obtain minimum welding
Consumption, that is, need to realize the best match of both sides optical fiber mode fields, try to achieve photonic crystal fiber air pore structure under molten condition, and then
Derive the carbon dioxide laser discharge parameter that will obtain said structure needs：Discharge capacity, discharge time, discharge centers position
Put.
4. the method for realizing photonic crystal fiber and solid core fibres low loss welding according to claim 3, its feature exists
In when determining discharge time, discharge centers position delta can be drawn by formula (1)
Z=-419.6delta2-0.945delta+7.943×10-5(7)
Wherein, Z is fiber end face axial coordinate.
5. the method for realizing photonic crystal fiber and solid core fibres low loss welding according to claim 3, its feature exists
In discharge capacity is under discharge time is determined, by z=0 position, temperature is determined with the relation curve of discharge time.
6. the method for realizing photonic crystal fiber and solid core fibres low loss welding according to claim 3, its feature exists
In, under discharge time is determined, at z=0 position, the relation curve of temperature and discharge time, by the titanium dioxide as shown in formula (8)
Silicon viscosity coefficient μ determines
Wherein, T is the temperature related to discharge time.
7. the method for realizing photonic crystal fiber and solid core fibres low loss welding according to claim 3, its feature exists
In, under discharge time is determined, under molten condition, silicon dioxide viscosity coefficient is by the photonic crystal fiber airport for needing to realize
Subside degree determination.
8. the method for realizing photonic crystal fiber and solid core fibres low loss welding according to claim 3, its feature exists
In the degree of subsiding of photonic crystal fiber airport affects the area that subsides, and so as to affect optical fiber to couple, two optical fiber are on mutation circle
Optical coupling efficiency when emergence pattern is mated by face, is determined by formula (5),
Wherein, E1(x, y) and E2(x, y) is respectively two mode distributions of two optical fiber in abrupt interface.
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