CN1853124A - Fusion splicing of optical fibres having mismatched mode field diameters - Google Patents

Abstract

A method and arrangement for achieving low splice-losses when connecting Highly Rare-Earth-Doped (HRED) optical fibers and dissimilar optical fibers having a large Mode Field Diameter (MFD) mismatch. Warm images are taken during a pre-fusion process to capture thermal light emissions and determine an arc-center position. The end-surfaces of the fibers are abutted and longitudinally offset from the arc-center, based on the light propagation direction and the MFD-mismatch. The fibers are then asymmetrically heated with different fusion temperatures during the main fusion processes. An MFD-match is achieved with well-defined fusion currents and fusion time. To maintain the same offset distance in a sequence of splices, the main-fusion arc-center position is determined by a process of direct arc-recentering. Variations of fusion temperature caused by changes of electrode conditions and the operating environment are monitored in real-time, and an arc-check process is invoked to compensate for the large variations of fusion temperature.

Description

Welding with optical fiber of mismatched mode field diameters

Technical field

The present invention relates to communication system.Specifically and without limitation, the present invention relates to engage high rear-earth-doped (HRED) optical fiber and method and apparatus with dissimilar fiber optic of big mode field diameter (MFD) mismatch.

Background technology

In recent years, developed the HRED optical fiber of more number more to be used for the specialized application of optical communication system.These examples comprise Erbium-Doped Fiber Amplifier (EDFA) (EDFA), amplifying type spontaneous radiation (ASE) light source, fiber laser etc.HRED optical fiber mainly is very attractive because its optical fiber with extremely short length just can obtain excellent performance.For instance, sentence the high Er-doped fiber (EDF) of the peak absorbance of 40dB/m, required fiber lengths can be reduced 5-10 doubly, can also realize the identical performance that traditional fiber obtains as characteristic by using in operation wavelength.EDF has high power density output, wide and smooth gain profiles, and low nonlinear effects.Thereby HRED optical fiber makes it possible to develop compacter and more economical worthwhile communication system.

The main obstruction that adopts HRED optical fiber to face is the high splice-losses that produces when engaging with dissimilar fiber optic.The main cause that its high splice-losses of HRED optical fiber produces is because initial MFD mismatch.Because the common requirements that exists in the system design, HRED optical fiber often are fused and at MFD marked difference are arranged but do not have on the dissimilar fiber optic of rare-earth dopant.The exemplary of this type optical fiber is healthy and free from worry (Corning) SMF28 ^TM, its MFD approximately is the twice of HRED optical fiber.

In the past, proposed and developed several different methods and reduced MFD mismatch in the fusion process.These methods mainly are included in the docking section of the optical fiber (for example EDF) with less relatively MFD and implement extra thermal treatment.For making heat treated principle so-called " thermal diffusion expansion core (TEC) optical fiber (Thermlly-diffused Expanded Core (TEC)) " that optical fiber components develops (referring to people such as K.Shigihara; J.Appl.Phys., the 60th volume, the 4293rd page, 1986; With people such as K.Shiraishi; J.LightwaveTechnol., the 8th volume, the 1151st page, 1990).

The TEC method that engages dissimilar fiber optic is disclosed among the U.S. Patent Publication US2002/0197027.After two kinds of optical fiber of welding, immediately the abutment is reorientated, so that extra discharge can be applied on the butted part of the optical fiber with relatively little MFD.Adopt the similar approach of TEC technology also to be disclosed among U.S. Patent Publication US2002/0157424 and the US2002/0176673.These methods are utilized following process: engage the end face of two kinds of optical fiber, rather than move the optical fiber that engages; By on the docking section that heating unit (being electrode) is moved to fiber optic splicing or, carry out extra thermal treatment being installed near the auxiliary of the heating plate fiber alignment portion down by heat the abutment asymmetricly.

The applicant discovers, the previous method that adopts the TEC technology can work effectively to the optical fiber that does not have rare-earth dopant and/or have a low doping concentration, and ineffective to HRED optical fiber.Have been found that the optical fiber for HRED, except that the problem of initial MFD mismatch, the main cause that high splice-losses produces is also owing to the rapid diffusion of the core alloy that occurs in the fusion process.If the initial MFD mismatch of two kinds of optical fiber is less relatively, the MFD of these two kinds of optical fiber coupling can be achieved when the beginning just of the main melting process that is used for forming common joint so.Therefore, this additional heat treatment that adopts in the previous method can not obtain the MFD coupling, on the contrary, may cause reverse MFD mismatch (the HRED optical fiber that promptly has less MFD usually but obtained to be far longer than connect effective MFD of optical fiber MFD).Therefore, under the situation that light injects from HRED optical fiber, cladding mode is easy to be excited, and through the splice-losses of regular meeting's appearance up to 0.2-0.5dB.

Observed another problem is the inconsistent splice-losses result who occurs in a series of joints in the TEC process.This problem is mainly produced by usually said " electric arc moves (arc-walk) " phenomenon.Electric arc moves the change when referring to the arc center position from arc discharge to arc discharge next time, and this mainly is that dynamic change by deposited particles/layer on the electrode causes." electric arc moves " changed the relative position of heat distribution in the fiber alignment portion significantly, this so that changed splice-losses again.

The problem that electric arc moves can overcome with " electric arc recentralizing (the arc-recentering) " method that discloses in the International Patent Application WO 01/86331.Make in this way, in fusion process, take warm image (warm image).The heat radiation and the gas discharge that send from the optical fiber heating part are evaluated, to determine the position of arc center.Thereby the docking section of optical fiber can be reorientated with respect to arc center.This method depends on collected historical data in series engages, thereby the degree of accuracy of this method can reduce with the minimizing of numbers of splices.Therefore, this method and be not suitable for the frequent application that changes of combination of fiber type.

Improving one's methods of a kind of definite arc center is disclosed among the U.S. Patent Publication application US2003/0002827.Make in this way, also fiber orientation is not being produced preliminary arc discharge during at arc discharge area between electrode.Though this method can be used for the position of estimation of arc, the error of estimation of arc position may be quite big, for example greatly to 20 μ m.This error mainly self is caused by preliminary arc discharge, because preliminary arc discharge is along with electricity cleaning (electric cleaning) process is carried out, this so changed the state that is deposited on the particle on the electrode again, thereby cause that other electric arc moves, influence fusion process subsequently.In addition, have been found that the heat distribution of inserting in the effective coverage with arc discharge when not inserting optical fiber compares, surface/solid plasma that the boundary of heat distribution (confinement) also may be caused by energy deposition on the optical fiber excite change.Thereby the precision of this method may continue owing to the variation of heat distribution to descend.

Therefore, need to develop a kind of method and apparatus that can eliminate these defectives of prior art in the art, so that can obtain the low splice-losses of HRED optical fiber.

Summary of the invention

The invention provides a kind of method and apparatus that when the dissimilar fiber optic that connects high rear-earth-doped (HRED) optical fiber and have very big mode field diameter (MFD) mismatch, is used to obtain low splice-losses.During pre-fusion process, take warm image.Analysis comes from the hot light emission of atmospherical discharges and optical fiber, and the position of definite arc center.By the direction of consideration light propagation and the degree of MFD mismatch, orientate the end face of HRED optical fiber and dissimilar fiber optic as relative arc center wittingly and have relatively large vertical misalignment.Then, during main melting process, heat the docking section of two kinds of optical fiber with different melt temperatures asymmetricly.Therefore, can control the MFD expansion of the HRED optical fiber that the rapid diffusion owing to alloy in the HRED fiber core causes, and obtain MFD with fusion current that provides and melting time and mate.In order in a series of joint, to keep identical offset distance, accurately determine the arc center position of main fusion with direct-arc recentralizing process.Therefore, for each joint, can both obtain the splice-losses of consistent results.For the stable engagement process, monitor the change of the melt temperature that the variation by electrode state and working environment causes in real time, and call the very big change that arc-check process compensates melt temperature.

Thereby, in one aspect, the present invention relates to a kind of method that engages dissimilar fiber optic.This method is by analyzing the hot light emission of capturing in the warm image of low-power electric arc, determine the arc center position during the pre-fusion process, this low-power electric arc is used to clean micro mist dirt particle from the end face of the end face of first optical fiber and second dissimilar fiber optic, this first optical fiber and the second optical fiber ground located adjacent one another longitudinal register.This method is further comprising the steps of: determine apart from the vertical misalignment distance of described arc center position; Dock described two end faces; At described two the butt joint end faces of the described offset distance place of distance arc center position longitudinal register; And heat described butt joint end face of reorientating with the high power electric arc of center in described arc center position asymmetricly, fuse described two kinds of dissimilar fiber optics thus.This method can also comprise step: monitor the change of melt temperature in real time; With call arc-check process and regulate described high power electric arc, the change of the melt temperature that detects with compensation.

On the other hand, the present invention relates to a kind of method that engages dissimilar fiber optic, may further comprise the steps: the end face of longitudinal register first optical fiber is adjacent with the end face of second dissimilar fiber optic, between two end faces, to form the gap, wherein said end face is positioned in the contact maker, makes the center and the contact maker electrode alignment in described gap; The low-power electric arc that produces with the contact maker electrode cleans micro mist dirt particle from both ends of the surface; During cleaning, capture the warm image in described two end faces and described gap; By analyzing the hot light emission of in described warm image, capturing, determine pre-fusion arc center position.This method also comprises step: the degree of mode field diameter (MFD) mismatch is determined apart from the offset distance of described pre-fusion arc center position between direction of propagating based on light and the described dissimilar fiber optic; Dock described two end faces; By offset distance, longitudinally reorientate the end face of described two butt joints with respect to described pre-fusion arc center position; And heat described butt joint end face of reorientating with the high power electric arc that the contact maker electrode produces asymmetricly, engage described two dissimilar fiber optics thus.

In yet another aspect, the present invention relates to a kind of equipment that engages dissimilar fiber optic.This equipment comprises: be used in contact maker the device with the end face ground located adjacent one another longitudinal register of the end face of first optical fiber and second dissimilar fiber optic; Be used for applying low-power electric arc to clean the device of micro mist dirt particle from two fiber end faces to the end face of described vicinity; Camera is used for capturing the hot photoemissive warm image that sends from low-power electric arc and optical fiber during described cleaning micro mist dirt particle; Be used for determining the device of pre-fusion arc center position by analyzing the hot light emission of in described warm image, capturing.This equipment also comprises: the device that is used for the vertical misalignment distance of the described pre-fusion of definite distance arc center position; Be used for docking the devices of described two end faces and described two the butt joint end faces of longitudinal register at the offset distance place of the described pre-fusion of distance arc center position; And be used for heating described butt joint end face of reorientating asymmetricly, and fusing the device of described two dissimilar fiber optics thus with the high power electric arc of center in described arc center position.

Description of drawings

In the part, will the present invention be described below referring to the exemplary embodiment shown in the accompanying drawing, in the accompanying drawings:

Figure 1A-1D illustrates the process according to first embodiment of the present invention, offset splice HRED optical fiber and non-rear-earth-doped (NRED) optical fiber;

Fig. 2 A-2D illustrates the process according to second embodiment of the present invention, offset splice HRED optical fiber and NRED optical fiber;

Fig. 3 is the reconstructed chart of the warm image of two kinds of optical fiber taking during pre-fusion process;

Fig. 4 is the reconstructed chart of the warm image of two kinds of optical fiber taking during main melting process;

Fig. 5 illustrates process flow diagram instruction, each step of offset splice process according to the present invention.

Embodiment

According to instruction of the present invention, a kind of improved method is provided, be used for when various application, connection all types of different (dissimilar) optical fiber, reducing splice-losses.That describes herein exemplifies among the embodiment, the dissimilar fiber optic that this method is used to connect HRED optical fiber and has very big MFD mismatch.

First process that the present invention was appreciated that is offset splice (offset splicing) process.When with the electric arc heating optical fiber, the temperature at melting zone center may be above 2000 ℃.Under such high temperature, heat is delivered to fibre core effectively from covering, even the thermal conductivity of silica-based optical fibers is on duty mutually.When the temperature of inside of optical fibre reached the fusion point (promptly 1800 ℃) of silicon dioxide, the mobility of rare-earth dopant increased sharply with the growth of temperature in the fibre core.The rapid diffusion of alloy from the fibre core to the covering (for example, less than 0.3 second) in the very short time takes place.The result who spreads forms effective MFD of xsect greatly, and effective MFD is with the increase continuation expansion of melting time.For dissimilar HRED optical fiber, realize that the melting time of MFD coupling may be significantly different, this depends primarily on the concentration of alloy in the fiber core, initial MFD mismatch, and used fusion parameters in the main melting process, for example fusion current etc.

Compare non-rear-earth-doped (NRED) optical fiber (SMF28 of Corning Incorporated for example with HRED optical fiber ^TM, PureMode ^TMHI1060 etc.) a little less than the alloy diffusion quite.The time that enlarging markedly MFD (for example increasing about 30%) needs may need to reach the time of a few minutes.Because HRED and the NRED optical fiber significant difference on the diffusion time yardstick, so the diffusion process in its fibre core of HRED optical fiber has just determined to obtain final MFD and has mated the desired melting time in main melting process.

When the optical fiber of welding dissimilar types, splice-losses depends primarily on the direction that light is propagated.This direction of splice-losses relies on phenomenon can be by adopting the transition loss theory of propagating flux of light method to be explained (referring to people's such as K.Shiraishi J.Lightwave Technol., the 11st volume, the 1584th page, 1993).According to this theory, if the phase front of the light wave of propagating does not keep after light wave passes the abutment fully, the directional dependence of splice-losses can not be ignored.In the applicant's test, find two kinds of situations, promptly big MFD expansion (for example expanding about 2 times) of heat heating (for example greater than 5mm) and two kinds of optical fiber can provide the ripple that propagates into junction point to keep the basal conditions of phase front on a large scale.Yet unfortunately, commercial available contact maker only can be implemented the heat heating of short scope on the market, is generally 200-300 μ m.When this short scope heat heats, be difficult to keep the phase front of propagation wave, and when light passes the abutment, can excite cladding mode usually.As a result, very high splice-losses appears.

The applicant's test shows that also splice-losses depends primarily on the degree of MFD expansion in the HRED fiber core, and the section of the MFD of place of fiber alignment portion.Minimum splice-losses obtains under the state that is called " the accurate coupling of MFD " usually.The state of this " MFD accurate coupling " is meant: (1) if light injects from HRED optical fiber side, then when the MFD of the relative NRED optical fiber of final MFD of HRED optical fiber hour, obtain minimum splice-losses; (2) if light injects from NRED optical fiber side, then the MFD with NRED optical fiber compares, and needs the MFD section of relatively large and conical in shape at the place, docking section of HRED optical fiber.

This in order to obtain when engaging the optical fiber of dissimilar types " the accurate coupling of MFD " state proposes a kind of process that adopts vertical misalignment to engage.The basic thought that vertical misalignment engages is the docking section of heating dissimilar fiber optic in melting process with different melt temperatures asymmetricly.In order to contain the various application of optical communication system, when providing optical fiber combination and optical propagation direction, determine four kinds of typical situations.These four kinds of situations are:

Situation 1: light injects from HRED optical fiber, and the initial MFD mismatch of two kinds of optical fiber is less relatively.Typical example has Liekki LF2400 ^TM(HRED optical fiber, peak absorbance is about 40dB/m, corresponding M FD is about 6 μ m@1550nm) and Corning Puremode ^TMThe optical fiber combination of HI1060 (NRED optical fiber, MFD are about 8.5 μ m@1550nm).This combination provides the initial MFD mismatch of about 2.5 μ m.

Situation 2: light injects from NRED optical fiber, and the initial MFD mismatch of two kinds of optical fiber is less relatively.A typical example is to describe identical optical fiber combination with situation 1.

Situation 3: light injects from HRED optical fiber, and the initial MFD mismatch of two kinds of optical fiber is relatively large.A typical example is Liekki LF2400 ^TMWith Corning SMF28 ^TMThe optical fiber combination of (MFD is about the NRED optical fiber of 10.5 μ m@1550nm).This combination provides the initial MFD mismatch of about 4.5 μ m.

Situation 4: light injects from NRED optical fiber, and the initial MFD mismatch of two kinds of optical fiber is relatively large.A typical example is to describe identical optical fiber combination with situation 3.

In order to understand the process of offset splice, situation 1 is studied as an example.In situation 1, light is from HRED LF2400 ^TMOptical fiber injects.According to " the accurate coupling of MFD " theory, LF2400 ^TMThe final MFD expansion of optical fiber should be equal to or less than LF2400 ^TMOptical fiber and NRED Puremode ^TMInitial MFD between the HI1060 optical fiber poor (μ m promptly≤2.5).For melting process expansion LF2400 with standard ^TMThe MFD of optical fiber is to obtain " the accurate coupling of MFD ", and the applicant has been found that and must adopt the very short melting time, is about 0.5 second.Yet, in the short like this time, the joint of the very low poor like this quality of intensity often appears.This is because also liquefied completely at given melting time inner fiber butted part.Thereby, in order to obtain high-quality joint, must significantly increase the melting time.

When offset splice, HRED LF2400 ^TMThe docking section of optical fiber is positioned at the big like this offset distance place of 40 μ m with respect to arc center.Thereby, LF2400 ^TMThe docking section of optical fiber can be heated with low relatively melt temperature.Thus, assembling is enough to the required time of the isoionic energy of excitation fiber internal solid and significantly increases, this so that significantly delayed melting process again.The applicant has been found that the melting time of about 2-3 second is suitable.The remarkable increase of melting time makes to optimize becomes possibility such as fusion parameters such as offset distance, fusion current, melting time, overlap distances.Therefore, after optimizing, just can obtain very low splice-losses.

Figure 1A-1D illustrates the process according to first embodiment of the invention offset splice HRED optical fiber and NRED optical fiber.Especially, be offset splice Liekki LF2400 shown in these accompanying drawings ^TM Optical fiber 11 and CorningPuremode ^TMThe process of HI1060 optical fiber 12 this optical fiber combination.After optical fiber is put into contact maker, optical fiber is carried out cold image (cold-image) take, determine the relative position of fiber end face.This for example can utilize digital imaging system built-in in the contact maker to finish.Shown in Figure 1A, by the end face of the clearance distance 13 ground close to each other moving fibers that provide.This clearance distance is made as the half-breadth that equals the arc discharge effective coverage, typically is 100-150 μ m.During optical fiber moves, the center in this gap will with electrode (not shown) lateral alignment, electrode is positioned at the center in gap along vertical black line.

In Figure 1B, apply short arc discharge 14 and carry out pre-fusion process.The purpose of pre-fusion process is to remain in after removing optical fiber preparation the micro mist dirt particle on the optical fiber surface.In pre-fusion process, must adopt the low melt electric current I _PreWith short melting time t _PreI _PreAnd t _PreShould be set and make that micro mist dirt particle can be removed effectively, but can prevent LF2400 ^TMRapid diffusion in the optical fiber 11.Exemplary setting is I _Pre≤ 7mA, t _Pre≤ 0.2 second.During pre-fusion process, take warm image and extract arc-distribution information, particularly 15 places, arc center position.Utilize the digital imagery analytical technology, accurately determine the relative position of arc center, and derive the distance 16 of " electric arc moves ".

In Fig. 1 C, utilize arc-distribution information longitudinally to reorientate the end face of optical fiber, so that produce big skew 17 with respect to arc center.Offset distance is set like this, promptly makes HRED LF2400 ^TM Optical fiber 11 is positioned in the relative temperature range in arc-distribution zone.Here, determine offset distance by the relative distance between center, docking section and the arc-distribution center.Then, in Fig. 1 D, carry out the melting process of standard, obtain offset splice 18.

Fig. 2 A-2D illustrates the process according to second embodiment of the invention offset splice HRED optical fiber and NRED optical fiber.Especially, shown in these accompanying drawings is the process of offset splice situation 4 the sort of optical fiber combination, i.e. NRED Corning SMF28 ^TM Optical fiber 21 and HRED Liekki LF2400 ^TMOptical fiber 11.In situation 4, light is from SMF28 ^TMOptical fiber injects, shown in Fig. 2 A.After optical fiber is put into contact maker, optical fiber is taken cold image, determine the relative position of fiber end face.This for example can finish by utilizing the embedded digital imaging system in the contact maker.Shown in Fig. 2 A, by the clearance distance 13 ground close to each other moving fiber end faces that provide.This clearance distance is set at the half-breadth that equals the arc discharge effective coverage, typically is 100-150 μ m.During optical fiber moves, the center in gap will with electrode (not shown) lateral alignment, electrode is positioned at the center in gap along vertical black line.

In Fig. 2 B, apply short arc discharge 14 and carry out pre-fusion process.Be similar to said circumstances 1, the purpose of pre-fusion process is to remain in after removing optical fiber preparation the little dust granule on the optical fiber surface.

In order to obtain " the accurate coupling of MFD ", HRED Liekki LF2400 ^TMThe required MFD expansion of optical fiber should be equal to or greater than initially poor (the μ m promptly 〉=4.5) of MFD between two kinds of optical fiber, and LF2400 ^TMOptical fiber should be tapered in the shape of the MFD at place, docking section.In Fig. 2 C, LF2400 ^TMThe vertical misalignment of fiber alignment portion is set at the reverse direction of situation 1, thereby makes LF2400 ^TMThe docking section of optical fiber is heated in the relative higher temperature scope in arc-distribution zone wittingly.In fact, LF2400 ^TMThis unique phenomenon of alloy rapid diffusion that occurs in the optical fiber is used to quicken the expansion of MFD, so that obtain " MFD is accurate to be mated " this state in the used time window of standard melting process (for example 2-3 second).Then, in Fig. 2 D, carry out the melting process of standard, obtain offset splice 18.

Setting is mainly determined by the direction that light beam is gone into respect to the direction of the skew of arc center.The optimum distance of skew should be in considering initial MFD mismatch and HRED fiber core be determined by experiment on the basis of rate of propagation.For example, in situation 1 and situation 2, adopt the offset distance of 40 μ m to realize the lowest splice losses that this particular fiber makes up.For situation 3, adopt this different offset distance of 20 μ m to obtain minimum splice-losses, and, adopt the offset distance of 40 μ m for situation 4.

Being used to understand another process of the present invention is direct-arc recentralizing (direct arcrecentering) process.When electrode applies high voltage, the huge difference of potential energy and kinetic energy can cause that the particle and/or the layer that are deposited on loose combination (loose-banded) on the electrode produce injection (ejection) between the electrode.On the other hand, in the effective coverage of arc discharge, the high melting temperature that surpasses 1800 ℃ can evaporate some materials, and these materials mainly come from the silica dioxide granule of optical fiber.When arc discharge cut off, these materials just condensed and are deposited on the electrode.The dynamic change of particle deposition finally causes " electric arc moves " on the kind electrode.Electric arc moves the arc center position when having changed arc discharge to arc discharge next time.In various melting process, the electric arc displacement of 10-30 μ m often appears reaching.

The longitudinal profile of arc discharge can be represented with Gaussian distribution.Because the section of Gaussian distribution is quite flat near the heart therein, therefore moving (for example, in the scope with respect to electrode+/-20 μ m) relative to little electric arc causes the variation that melt temperature is very little usually, typically＜15%.For the melting process of standard, the abutment is positioned at the electrode centers place.Thereby because the very little variation of melt temperature, splice-losses can not be subjected to the strong influence of relative small arc displacement.Yet for offset splice, this process is extremely sensitive to be moved in electric arc, especially when engaging HRED optical fiber.This is that the abutment is positioned at the position away from electrode centers because in the situation of offset splice.In fact, the abutment is located in the steep slope scope of Gaussian distribution.Thereby the electric arc displacement of 20-30 μ m is easy to cause the change of melt temperature 30-50%, and this often can cause the variation of an order of magnitude of splice-losses.Therefore,, just must accurately determine the position of arc center, so that arc center is set at identical value with relative distance between the abutment in order in a series of joint, to keep best melt temperature.In order to reach this target, the present invention adopts " direct-arc recentralizing " process.

When electric arc was opened, the plasma in the melting zone in the residual air was excited, and produced high temperature.Under this high temperature, the solid plasma in the optical fiber also is excited.As the result of excitation of plasma, not only residual air but also optical fiber are all owing to light is sent in heat radiation.This light can be engaged the charge-coupled device (CCD) camera observes that comprises in the device imaging system and arrive.Because it is directly related with the intensity distributions of arc discharge that the light intensity that sends from residual air and optical fiber distributes, the information that therefore relevant arc space moves can be by anatomizing radiative intensity distributions derivation.

In the applicant's test, have been found that time delay common between the excitation of plasma of residual air and the fiber core internal solid excitation of plasma about 0.3 second, is 0.2 second and optical fiber is carried out effective electricity required common time of cleaning.Therefore, can utilize pre-fusion process to come detection of arc-distribution, and can not cause the diffusion of alloy in the HRED optical fiber.

Fig. 3 is the reconstructed chart of the warm image of two kinds of optical fiber 31 photographing during pre-fusion process and 32.Light intensity distribution from residual air extracts by being positioned at rectangular area 33 on the optical fiber and the rectangular area 34 that is positioned under the optical fiber.Its intensity distributions is Gaussian distribution on vertical and horizontal.In order accurately to determine the position of arc center, can utilize the method that is called light intensity distributions " center of gravity ".If supposition rectangular area, top can use coordinate (x1, y1), (x2, y1), (x2, y2), (x1, y2) } definite, then for the rectangular area, top, the center X of arc-distribution _{Arc, up}35 can be calculated by following formula:

$X_{\mathrm{arc},\mathrm{up}}=\frac{\underset{y1}{\overset{y2}{\∫}}\underset{x1}{\overset{x2}{\∫}}x{L}_{\mathrm{up}}(x,y)\mathrm{dxdy}}{\underset{y1}{\overset{y2}{\∫}}\underset{x1}{\overset{x2}{\∫}}{L}_{\mathrm{up}}(x,y)\mathrm{dxdy}}---\left(1\right)$

L _up(x，y)＝max[L _min，L(x，y)-L _BG] (2)

Wherein, (x y) is coordinate (x, the light intensity of y) locating to L; L _BGBe the mean intensity of bias light, it depends on the setting of imaging system; L _MinIt is the predetermined minimum value that to avoid the light intensity that the integration of definition in the equation (1) disperses.L _MinValue be set on the occasion of, can be by test or by valid supposition acquisition.

Thereby for the pre-fusion at upper-side area place, the initial distance that electric arc moves Δ (up, 0) can be calculated by following formula:

Δ(up，0)＝X _arc，up-X _center (3)

Wherein, X _CenterBe the position of electrode, determine by the Machine Design of contact maker.If for the rectangular area, bottom, define a similar function L _Down(X, Y)=max[L _Min, L (X, Y)-L _BG], then can adopt the above-mentioned center that the identical step in rectangular area, top is calculated arc-distribution 36 in the rectangular area, bottom, electric arc moves Δ (down, 0)=X _{Arc, down}-X _CenterTherefore, can estimate electric arc displacement Δ (arc-walk, 0) initial in the pre-fusion process by following formula:

Δ(arc-walk，0)＝1/2[Δ(up，0)+Δ(down，0)]. (4)

Can suppose that offset distance used in the offset splice process is defined by Δ (offset), (be X with reference to zero position by the position of electrode _Center=0) defines.Therefore, be used for defining center X main melting process abutment, between two kinds of fiber alignment portions _SpliceCan be set at:

X _spliec＝Δ(arc-walk，0)+Δ(offset). (5)

For normal engaging process, offset distance is set at 0 (that is, setting Δ (offset)=0) usually.Therefore, before main melting process, the abutment is reorientated, and aim at the prediction arc center of deriving and (that is, set X from pre-fusion process _Splice=Δ (arc-walk, 0)).This process is exactly so-called " direct-arc recentralizing " process.

Although direct-arc recentralizing process is verified for eliminating influence that electric arc moves and all be very effective for keeping the fiber alignment portion best melt temperature in place in test, the direct-arc recentralizing can not be handled the great changes of electrode situation on separately.Very big and electric arc at random moves and shows that significant wearing and tearing have appearred in electrode during main melting process.Therefore, the electric arc that not only needs to survey in the pre-fusion process moves, but also needs the electric arc during the main melting process of monitoring to move, preferably in real time.

Fig. 4 is the reconstructed chart of the warm image of two kinds of optical fiber photographing during main melting process.Compare with the pre-fusion process of Fig. 3, atmospherical discharges sends light intensity and is suppressed significantly in Fig. 4.This variation is to have a mind to carry out by the setting of regulating the CCD camera, is used for some special application, for example extracts the information of relevant fibre core and comes loss estimation.In this case, be used to extract that the rectangular area, top 41 of electric arc mobile message and rectangular area, bottom 42 are limited at the inside of optical fiber 43 rather than as shown in Figure 3 in the outside of optical fiber.

Move in order during main melting process, to monitor electric arc in real time, to take warm image the cycling time of for example 100ms periodically.These images are used referring to the same procedure of Fig. 3 explanation and are analyzed.Suppose electric arc as the function of time move variation can use Δ (arc-walk, i); I=1,2...n represent that then the bigger change of electrode state can be moved by reference initial measurement electric arc and be introduced the predetermined threshold δ that electric arc moves _Th(δ for example _Th=30 μ m) define.Also promptly:

δ _l＝|Δ(arc-walk，i)-Δ(arc-walk，0)|≥δ _th (6)

Wherein, δ ₁It is the relative variation of electric arc displacement.In control procedure,, then provide alerting signal, thereby stop main melting process if satisfy the condition of equation 6 expressions.In addition, call the processing that is called " arc-check process ", compensate these variations and recover optimum melt temperature.

Know that the melt temperature in the contact maker can change owing to the marked change (for example, highly (A), external temperature (T), the variation of humidity (H) etc.) of working environment.Even in the working environment that provides, melt temperature still may be because the variation of electrode state (for example, the wearing and tearing of electrode and/or be deposited on the dynamic change of the silicon dioxide layer on the electrode) and change.In addition, even for fusion parameters such as the fusion current and melting time of identical setting, limited tolerance also may cause the different melt temperature of contact maker of same type in the contact maker manufacturing process.Result as melt temperature in specific contact maker and/or the several contact makers at same type changes will obtain for example by the determined inconsistent joint effect of splice-losses, bond strength and loss evaluation.

The present invention utilizes arc-check process to overcome the problem of melt temperature change and recover melt temperature best in the various melting process together with the offset splice process.This also makes the present invention can stably obtain low splice-losses.Arc-check process is to supply with to electrode in fusion current is used to heat fiber optic splicing with generation the optical fibre cleaving device of electric arc, is used for calibrating the method for melt temperature.Temperature, the humidity of fusion current outside when implementing calibration and highly compensating.When with the electric arc heating optical fiber, the temperature at melting zone center is above 2000 ℃.Under such high temperature, the optical fiber in the melting zone is liquefied.Owing to the increase of the viscosity with temperature of liquid reduces, the temperature that therefore generates viscosity profile in melting zone relies on, thereby near covering and/or form tangential force at inside of optical fibre.As a result, during the melting time that prolongs, the diameter that is positioned at the covering at arc center place reduces.Based on the real-time detection that reduces, determine melt temperature to the cladding diameter of the warm optical fiber that is positioned at arc center place.The melt temperature of determining is used to calculate replace expects the required new electric current of fusion current value in the various engaging processes.

In order to keep best melt temperature, the criterion that provides except that equation (6) is δ _i〉=δ _ThIn the offset splice process, also adopt other criterion to call arc-check process outward.They are:

ΔT＝|T _j+1-T _j|≥T _th；T _j+1and?T _j∈{T _min，T _max} (7)

ΔH＝|H _j+1-H _j|≥H _th；H _j+1and?H _j∈{H _min，H _max} (8)

ΔA＝|A _j+1-A _j|≥A _th；A _j+1and?A _j∈{A _min，A _max} (9)

j＝0，1，2，....m

Δ T wherein, Δ H and Δ A are respectively external temperatures, the marked change amount of humidity and height.These variable quantities are that the measured value by more current joint draws with the measured value that last time engaged.These measured values can obtain with sensor built-in in the contact maker.T _Th, H _ThAnd A _ThBe respectively temperature, the threshold value of humidity and height, typical value is 10 ℃, 20%RH and 200 meters.T _Min, T _Max, H _Min, H _Max, A _MinAnd A _MaxThe working range of definition contact maker.The sequence number of contact maker is represented with j.

Considering because during the compensation of height, for example, the auxiliary height that records down based on built-in height meter in contact maker, adopt following formula (10) to regulate fusion current:

$I_j^{*}=h_1{I}_j+{(h_{2}H+h_3{I}_j+h_4)}^2+h_5---\left(10\right)$

Wherein H is a height, I _j(j=1 2...) is the preceding fusion current of compensation, I ^* _j(j=1 2...) is offset current used in the calibration process, h _k(k=1 2...5) is fitting parameter.After having set the initial position of arc center, reorientate optical fiber connector with respect to arc center.Then, open electric arc, heat the docking point of two kinds of optical fiber, and they are linked together, form joint with main fusion current.Measure the initial cladding diameter of warm optical fiber, and with target current (I _{C, 1}) alternative main fusion current.

Then, total (t heat time heating time of estimation _{C, 1}), the beginning calibration process.Estimate heat time heating time with following decaying exponential function:

t＝c ₁e-c ₂I (11)

C wherein ₁And c ₂It is fitting constant.By means of equation (11), the change of the melt temperature that calibration is caused by the variation of working environment, electrode state and mechanical tolerance.With target current (I _{C, 1}) heat docking point continuously, and measure reducing of warm fibre cladding diameter, till its diameter reaches predetermined threshold.Subsequently, stop electric arc, calculate the used total melting time (t of calibration process ₂).Then, derive corresponding electric current (I with equation (11) _{C, 2}).

Then, calculate required fusion current amount (the Δ I of compensation _c=I _{C, 1}- _{Ic, 2}) and correction factor δ i, this correction factor is used for compensating the difference between current between target current of using and the electric current of using in various engaging processes in calibration process.Correction factor can calculate with following formula:

δ _i＝1-0.5(I _c，1-I _i)/I _c，1 (12)

Then, calculate with following formula and be used for replacing the required new electric current of expecting at various engaging processes of fusion current value:

$I_{\mathrm{NEW},i}=I_j^{*}+{\mathrm{\δ}}_i{\mathrm{\ΔI}}_c.---\left(13\right)$

Other explanation of the arc-check process of relevant calibration melt temperature can be referring to the open WO03/096088 of the international pct application that the applicant owns together.

Fig. 5 is the process flow diagram that each step of the offset splice process of instructing according to the present invention is shown.This process starts from step 51, in step 52, determines whether the variation (Δ T) of (1) external temperature is greater than or equal to the threshold value (T of temperature _Th), and/or whether the variation of (2) outside humidity (Δ H) is greater than or equal to the threshold value (H of humidity _Th), and/or whether the variation (Δ A) of (3) external height be greater than or equal to the threshold value (A of height _Th).If any in these conditions satisfied, then process moves to step 53, in step 53, provides alarm, and stops main melting process, and calls arc-check process.Yet if these conditions all are not met at step 52 place, process moves to step 54, in step 54, fiber end face is taken cold image, and calculates the distance between the end face.

In step 55, with the end face of predetermined gap positioning optical waveguides, and with the center and the electrode alignment in gap.In step 56, the beginning pre-fusion process, and survey initial arc displacement Δ (arc-walk, 0).In step 57, obtain the value Δ (offset) of offset distance, use X _SpliceReorientate the end face of optical fiber, and begin main melting process.In step 58, the end face of optical fiber is taken warm image, calculate electric arc displacement Δ (arc-walk, i).

In step 59, determine the relative variation (δ of electric arc displacement _t) whether be greater than or equal to the predetermined threshold (δ that electric arc moves _Th).If, the step 53 that this process moves, the place provides alarm in step 53, and stops main melting process, and calls arc-check process.Yet, if the relative variation (δ of electric arc displacement _t) predetermined threshold (δ that moves less than electric arc _Th), then this process moves to step 60, determines at step 60 place whether main melting process is finished.If no, then this process turns back to step 58, and repeating step 58-60, till main melting process is finished.At this moment, this process finishes in step 61.

Will be familiar with as those skilled in the art, the innovation concept that the application describes can improve in wideer range of application and change.Therefore, the scope of patented subject matter should not be limited to above-mentioned any concrete exemplary teachings, and should be limited by appended claims.

Claims (27)

1. method that engages dissimilar fiber optic comprises:

Be adjacent to the end face of end face longitudinal register first optical fiber of second dissimilar fiber optic, to form the gap between two end faces, wherein said end face is positioned in the contact maker, makes the center and the contact maker electrode alignment in described gap;

The low-power electric arc that produces with the contact maker electrode cleans micro mist dirt particle from both ends of the surface;

During cleaning, capture the warm image in described two end faces and described gap;

By analyzing the hot light emission of in described warm image, capturing, determine pre-fusion arc center position;

The degree of mode field diameter (MFD) mismatch is determined the offset distance of the described pre-fusion of distance arc center position between direction of propagating based on light and the described dissimilar fiber optic;

Dock described two end faces;

By offset distance, longitudinally reorientate the end face of described two butt joints with respect to described pre-fusion arc center position;

The high power electric arc that produces with the contact maker electrode heats described butt joint end face of reorientating asymmetricly, thus described two dissimilar fiber optics of welding.

2. the method for claim 1, wherein described first optical fiber is high rear-earth-doped (HRED) optical fiber, and described second optical fiber is non-rear-earth-doped (NRED) optical fiber that has with very big mode field diameter (MFD) mismatch of described HRED optical fiber.

3. method as claimed in claim 2, wherein, the direction that light is propagated is to NRED optical fiber from HRED optical fiber, and vertically reorientate the direction that the step of described two butt joint end faces is included in HRED optical fiber with described offset distance and vertically reorientate described two butt joint end faces, so that when carrying out described asymmetric heating steps, in described HRED optical fiber, produce lower melt temperature.

4. method as claimed in claim 2, wherein, the direction that light is propagated is to HRED optical fiber from NRED optical fiber, and vertically reorientate the direction that the step of described two butt joint end faces is included in NRED optical fiber with described offset distance and vertically reorientate described two butt joint end faces, so that when carrying out described asymmetric heating steps, in described NRED optical fiber, produce lower melt temperature.

5. the method for claim 1, wherein repeatedly engage, and in described repeatedly joint, all repeat described method for each joint, so that all calculate new offset distance for each joint.

6. method as claimed in claim 5 also comprises:

During described asymmetric heating steps, capture the warm image of described two butt joint end faces; With

Determine main fusion arc center position by analyzing the hot light emission of capturing in the described warm image.

7. method as claimed in claim 6 wherein, during the step of the warm image of capturing described two butt joint end faces during the described asymmetric heating steps is included in described asymmetric heating steps, is captured a plurality of warm images by capturing warm image periodically.

8. method as claimed in claim 7, wherein, described step of capturing warm image is periodically approximately captured once warm image every 100ms during being included in described asymmetric heating steps.

9. method as claimed in claim 8 also comprises:

For a plurality of warm images of during described asymmetric heating steps, capturing each, determine main fusion arc center position;

For described definite main fusion arc center position each, determine poor between described main fusion arc center position and the described pre-fusion arc center position;

Poor with more described each arc center that determines of difference limen; And

If the arc center that determines difference surpasses described difference limen, then stop described asymmetric heating steps.

10. method as claimed in claim 9 comprises that also calling arc-check process compensates the very big change of melt temperature.

11. method as claimed in claim 6 wherein, describedly determines that by analyzing the hot light emission of capturing in the warm image step of main fusion arc center position comprises:

Definition rectangular area, top in the top of described optical fiber, rectangular area, described top connects longitudinal extension on the part that is incorporated in each described optical fiber across described, rectangular area, described top by coordinate (x1, y1), (x2, y1), (x2, y2), (x1, y2) } define;

Utilize the light intensity distributions in the rectangular area, the described top of described warm graphical analysis, described analytical procedure comprises:

Utilize following formula to calculate the position X of top arc center _{Arc, up}:

$X_{\mathrm{arc},\mathrm{up}}=\frac{\underset{y1}{\overset{y2}{\∫}}\underset{x1}{\overset{x2}{\∫}}x{L}_{\mathrm{up}}(x,y)\mathrm{dxdy}}{\underset{y1}{\overset{y2}{\∫}}\underset{x1}{\overset{x2}{\∫}}{L}_{\mathrm{up}}(x,y)\mathrm{dxdy}}---\left(1\right)$

With

L _Up(x, y)=max[L _Min, L (x, y)-L _BG] (2) wherein, (x y) is coordinate (x, the light intensity of y) locating to L; L _BGBe the mean intensity of bias light, it depends on the setting of imaging system; L _MinIt is the predetermined minimum value that to avoid the light intensity that the integration of definition in the equation (1) disperses; And

For the rectangular area, bottom in the described optical fiber bottom, repeat described definition and analytical procedure, rectangular area, described bottom connects longitudinal extension on the part that is incorporated in described each optical fiber across described, calculates the position X of bottom arc center thus _{Arc, down}

12. method as claimed in claim 11 also comprises:

Utilize following formula to determine electric arc displacement Δ (up, 0) in the rectangular area, described top:

Δ (up, 0)=X _{Arc, up}-X _CenterWherein, X _CenterIt is position with described electrode alignment;

Utilize following formula to determine electric arc displacement Δ (down, 0) in the rectangular area, described bottom:

Δ(down，0)＝X _arc，down-X _center

And

Utilize following formula to calculate initial average arc displacement Δ (acr-walk, 0):

Δ(arc-walk，0)＝1/2[Δ(up，0)+Δ(down，0)]。

13. the method for claim 1, wherein describedly determine that by analyzing the hot light emission of capturing in the warm image step of pre-fusion arc center position comprises:

On described optical fiber and described gap the definition rectangular area, top, rectangular area, described top across described gap and on the part of each described optical fiber longitudinal extension, rectangular area, described top by coordinate (x1, y1), (x2, y1), (x2, y2), (x1, y2) } definition;

Utilize the light intensity distributions in the rectangular area, the described top of described warm graphical analysis, described analytical procedure comprises:

Utilize following formula to calculate the position X of top arc center _{Arc, up}:

$X_{\mathrm{arc},\mathrm{up}}=\frac{\underset{y1}{\overset{y2}{\∫}}\underset{x1}{\overset{x2}{\∫}}x{L}_{\mathrm{up}}(x,y)\mathrm{dxdy}}{\underset{y1}{\overset{y2}{\∫}}\underset{x1}{\overset{x2}{\∫}}{L}_{\mathrm{up}}(x,y)\mathrm{dxdy}}---\left(1\right)$

With

L _Up(x, y)=max[L _Min, L (x, y)-L _BG] (2) wherein, (x y) is coordinate (x, the light intensity of y) locating to L; L _BGBe the mean intensity of bias light, it depends on the setting of imaging system; L _MinIt is the predetermined minimum value that to avoid the light intensity that the integration of definition in the equation (1) disperses; And

For the rectangular area, bottom that is positioned under described optical fiber and the described gap, repeat described definition and analytical procedure, rectangular area, described bottom across described gap and under the described part of described each optical fiber longitudinal extension, calculate the position X of bottom arc center thus _{Arc, down}

14. method as claimed in claim 13 also comprises:

Utilize following formula to determine electric arc displacement Δ (up, 0) in the rectangular area, described top:

Δ (up, 0)=X _{Arc, up}-X _CenterWherein, X _CenterIt is position with described electrode alignment;

Utilize following formula to determine electric arc displacement Δ (down, 0) in the rectangular area, described bottom:

Δ(down，0)＝X _arc，down-X _center

And

Utilize following formula to calculate initial average arc displacement Δ (acr-walk, 0):

Δ(arc-walk，0)＝1/2[Δ(up，0)+Δ(down，0)]。

15. a method that engages dissimilar fiber optic comprises:

During pre-fusion process, determine the arc center position by analyzing the hot light emission of in the warm image of low-power electric arc, capturing, described low-power electric arc is used to clean micro mist dirt particle from the end face of the end face of first optical fiber and second dissimilar fiber optic, wherein said two end face ground located adjacent one another longitudinal registers;

Determine apart from the vertical misalignment distance of described arc center position;

Dock described two end faces;

At described two the butt joint end faces of the described offset distance place of distance arc center position longitudinal register; And

Heat described butt joint end face of reorientating with the high power electric arc of center, thus the described two kinds of dissimilar fiber optics of welding in described arc center position asymmetricly.

16. method as claimed in claim 15, wherein, the step of the vertical misalignment distance of the described arc center of definite distance position comprises based on the degree of mode field diameter (MFD) mismatch between the direction of light propagation and the described dissimilar fiber optic determines the vertical misalignment distance.

17. method as claimed in claim 16, wherein, described first optical fiber is high rear-earth-doped (HRED) optical fiber, and described second optical fiber is non-rear-earth-doped (NRED) optical fiber that has with very big mode field diameter (MFD) mismatch of described HRED optical fiber.

18. method as claimed in claim 17, wherein, the direction that light is propagated is to NRED optical fiber from HRED optical fiber, and vertically reorientate described two butt joint end faces in the direction that the step of described two the butt joint end faces of described offset distance place longitudinal register is included in HRED optical fiber, so that when carrying out described asymmetric heating steps, in described HRED optical fiber, produce lower melt temperature.

19. method as claimed in claim 15 also comprises:

Monitor the change of melt temperature in real time; With

Call arc-check process and regulate described high power electric arc, the change of the melt temperature that detects with compensation.

20. an equipment that engages dissimilar fiber optic comprises:

Be used in contact maker device with the end face ground located adjacent one another longitudinal register of the end face of first optical fiber and second dissimilar fiber optic;

Be used for applying low-power electric arc to clean the device of micro mist dirt particle from two fiber end faces to the end face of described vicinity;

Camera is used for capturing the hot photoemissive warm image that sends from low-power electric arc and optical fiber during described cleaning micro mist dirt particle;

Be used for determining the device of pre-fusion arc center position by analyzing the hot light emission of in described warm image, capturing;

The device that is used for the vertical misalignment distance of the described pre-fusion of definite distance arc center position;

The device that is used to dock described two end faces and described two butt joint end faces is longitudinal positioning of the offset distance place of the described pre-fusion of distance arc center position;

Be used for heating described butt joint end face of reorientating, and the device of described two dissimilar fiber optics of welding thus with the high power electric arc of center in described arc center position asymmetricly.

21. equipment as claimed in claim 20, wherein, described camera also is suitable for capturing the warm images of described two butt joint end faces during described asymmetric heating steps, the described device that is used for determining pre-fusion arc center position also is adapted to pass through hot light emission that analysis captures and determines main fusion arc center position between the described asymmetric period of heating.

22. equipment as claimed in claim 21, wherein, described camera is suitable for capturing a plurality of warm images by capturing warm image periodically during described asymmetric heating steps.

23. equipment as claimed in claim 22, wherein, described camera is suitable for during described asymmetric heating steps every approximately 100ms and once captures warm image.

24. equipment as claimed in claim 23 also comprises:

Be used in described a plurality of warm images of during described asymmetric heating steps, capturing each to determine the device of main fusion arc center position;

Be used to the main fusion of described definite each arc center position to determine the device of difference between main fusion arc center position and the pre-fusion arc center position;

Be used for described definite each arc center's difference and difference limen device relatively;

Be used for when arc center's difference of determining surpasses described difference limen, stopping the device of described asymmetric heating steps;

Be used to call the device of arc-check process with the very big change of compensation melt temperature.

25. equipment as claimed in claim 20 also comprises:

Be used for monitoring in real time the device that main melt temperature changes; With

Be used to regulate the device of the change of the main melt temperature that described high power electric arc detects with compensation.

26. a method of determining the arc center position of the electric arc that forms between the top electrode of contact maker and bottom electrode, described contact maker is used to fiber optic splicing, and described method comprises:

Be adjacent to the end face of end face longitudinal register first optical fiber of second optical fiber, to form the gap between two end faces, wherein said end face is positioned in the contact maker, makes the center and the contact maker electrode alignment in described gap;

The low-power electric arc that produces with the contact maker electrode cleans micro mist dirt particle from both ends of the surface;

Utilize during the cleaning imaging system capture on the end of described gap, described two optical fiber and described gap and the described end and under the warm image in zone;

Define the rectangular area, top on described optical fiber and the described gap, rectangular area, described top across described gap and on the part of each described optical fiber longitudinal extension, rectangular area, described top by coordinate (x1, y1), (x2, y1), (x2, y2), (x1, y2) } definition;

Utilize the light intensity distributions in the rectangular area, the described top of described warm graphical analysis, described analytical procedure comprises:

Utilize following formula to calculate the position X of top arc center _{Arc, up}:

$X_{\mathrm{arc},\mathrm{up}}=\frac{\underset{y1}{\overset{y2}{\∫}}\underset{x1}{\overset{x2}{\∫}}x{L}_{\mathrm{up}}(x,y)\mathrm{dxdy}}{\underset{y1}{\overset{y2}{\∫}}\underset{x1}{\overset{x2}{\∫}}{L}_{\mathrm{up}}(x,y)\mathrm{dxdy}}---\left(1\right)$

With

L _Up(x, y)=max[L _Min, L (x, y)-L _BG] (2) wherein, (x y) is coordinate (x, the light intensity of y) locating to L; L _BGBe the mean intensity of bias light, it depends on the setting of imaging system; L _MinIt is the predetermined minimum value that to avoid the light intensity that the integration of definition in the equation (1) disperses; And

For the rectangular area, bottom that is positioned under described optical fiber and the described gap, repeat described definition and analytical procedure, rectangular area, described bottom across described gap and under the described part of described each optical fiber longitudinal extension, calculate the position X of bottom arc center thus _{Arc, down}

27. method as claimed in claim 26 also comprises:

Utilize following formula to determine electric arc displacement Δ (up, 0) in the rectangular area, described top:

Δ (up, 0)=X _{Arc, up}-X _CenterWherein, X _CenterIt is position with described electrode alignment;

Utilize following formula to determine electric arc displacement Δ (down, 0) in the rectangular area, described bottom:

Δ(down，0)＝X _arc，down-X _center

And

Utilize following formula to calculate initial average arc displacement Δ (acr-walk, 0):

Δ(arc-walk，0)＝1/2[Δ(up，0)+Δ(down，0)]。

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