CN106443885A - Method of realizing low-loss welding of pohotonic crystal fiber and solid fiber - Google Patents

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

A kind of method for realizing photonic crystal fiber and solid core fibres low loss welding

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.

ε_r=(n-jk)²(3)

Wherein, E is electric field intensity, k₀For wave number in vacuum, ε_rFor 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, P_totalFor general power, W_y, W_zRespectively 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, F_stFor 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).

F_st=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

$\mathrm{\&mu;}=e^{240.2656-0.3055429T+1.41874\&times;{10}^{-4}{T}^2-2.293621\&times;{10}^{-8}{T}^3---\left(8\right)}$

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),

$\mathrm{\&eta;}=\frac{|\&Integral;E_1(x,y)\&CenterDot;E_2^{*}(x,y)dxdy{|}^2}{\&Integral;|E_1(x,y){|}^{2}dxdy\&CenterDot;\&Integral;|E_2(x,y){|}^{2}dxdy}---\left(5\right)$

Wherein, E₁(x, y) and E₂(x, y) is respectively two mode distributions of two optical fiber in abrupt interface.