Adjustable optical tapping element of passive full optical fibre
Technical field
The present invention relates to a kind of Adjustable optical tapping element of passive full optical fibre, be applicable to optical fiber telecommunications system and network.
Background technology
Optical branching device is to use one of optics very widely in the optical transmission system.Optical branching device is also referred to as beam splitter, luminous-power distributor sometimes, is that light with the input optical fibre port is divided into many parts by a certain percentage respectively from the device a kind of commonly used of a plurality of output optical fibre ports outputs.Optical branching device is widely used in optical communication system and the network as a kind of shunt device of light signal, as light broadcasting, multicast, protection, optical monitoring signal etc.Conventional optical branching device adopts fiber fuse to draw awl (Fused Biconical Taper-FBT) technology to realize usually, the shunt that forms is fixing in the power division ratio of each output port, uncontrollable, when the different distribution ratio of needs, have only the replacing shunt.
At present and the corresponding tunable optical shunt of optical branching device, though also there are some application technologies to be seen in report, generally speaking less to its research.Existing tunable optical shunt mostly is the adjusting that utilizes some distinctive optical effects realization allocation proportions, as electric light, acousto-optic, magneto-optic and thermo-optic effect etc.These the design since based on the principle difference, performance respectively has difference, but their common feature is can dynamic-configuration, product 1 * 2 solid-state Variable Fiber Optic Splitter (1 * 2 solid-state variable optical fiber optical branching device) usable level as agiltron company is directly regulated, and what it adopted is patented technology all-solid-state crystal (all solid state crystal) design of agiltron company.Yet owing to will utilizing these optical effects, they have to introduce extra optics, simultaneously because the difficulty of its technology own is bigger, so the cost of these technology is difficult to reduce.Consider from the angle of technical market, EPON (PON) and cable television network fields such as (CATV) at the widespread use optical branching device, the cost and price of tunable optical shunt is the key factor that can this device of decision be adopted in a large number, simultaneously, guarantee the passive realization of device for the maintenance and management of simplifying these networks, reduce network cost and have great importance.So research and develop a kind of cheap, superior performance, but do not require that the passive tunable optical shunt of dynamic-configuration complied with the demand in current techniques and market just.
Implementation method to existing tunable optical shunt studies show that, existing realization technology major part all is based on hot light, electric light, acousto-optic or the design of polarisation of light handling principle.The adjustable beam splitter that Chinese patent 0215003.7 is introduced uses thermo-optic effect to regulate the adjusting that the Fiber Bragg Grating Filter Structures realizes light reflection and transmission ratio.The Mach-Zehnder interferometric method that adopts in integrated opto-electronic also is one of common method that realizes by the tunable optical shunt, as the patent CA2258353 Optical Variable-ratio Power Splitter (variable proportion optical power divider) on EUROPEAN PATENT OFFICE's searching database (ep.espacenet.com), the change of phase of light wave difference when it need interfere the light path of arm to realize interfering by the electrode change.These devices are because its design concept limits, so complex structure, technical difficulty is big, the cost height.If use these control methods of hot light, electric light and acousto-optic, unavoidably adopt active mode, can't passively realize that this is unfavorable for the enforcement of networks such as PON very much.Wuhan Guangxun Science and Technology Co., Ltd has issued an adjustable optical power distributor in October, 2003, and it has adopted the polarized light disposal route.This method need be introduced the additional light device equally, and cost also is difficult to reduce.In addition, because these extra opticses, as the polarization manipulation parts, slab guide etc. unavoidably can bring extra insertion loss, chromatic dispersion and polarization correlated.
Therefore need a kind of simple passive tunable optical shunt of development, make it to have adaptability widely.
Investigation to prior art is told us, if can be by regulating the beyond doubt technology of low, the superior performance of cost of change that traditional FBT shunt realizes the light allocation proportion.Wavelength flat cure (T.A.Birks, C.D.Hussey, Electronics Letters, 1989,25, pp.407-408 that the early 1990s C.D.Hussey research group has studied the bending of FBT coupling mechanism coupled zone and reversed; N.M.O ' Sullivan, T.A.Birks, C.D.Hussey, Electronics Letters, 1992,28, pp.1485-1486).These studies show that the deformation of regulating the FBT coupled zone can change the luminous power distribution ratio of FBT on a large scale.
Shanghai Univ. of Science ﹠ Technology utilized the method for reversing the FBT shunt to study a kind of adjustable optic fibre beam splitting technology in 1992.Existing experiment shows, when changing the distribution ratio of a certain wavelength light when the FBT shunt reverses, has also changed the wavelength at maximum branch rate place.That is to say, reverse the change meeting difference to the distribution ratio of different wavelengths of light, this will cause the allocation proportion difference of different wave length very big, and be difficult to control, this obviously is not suitable for network applications such as PON and CATV, and the different wave length of getting it right in advance of luminous power should be identical usually in the network.On the contrary, if just there is not this problem in employing in the method for optical fiber plane inner bending FBT shunt, the distribution ratio of each wavelength variation ratio is consistent substantially during curved fiber, and the wavelength at maximum branch rate place also has only small variation.On the other hand, twisted fiber is very easy to cause the fracture of optical fiber, is difficult for making practical device, and the compression stress that produces because its bending that can bear of force rate is changeed in the distortion that optical fiber can bear is much smaller.From practical angle, bending is compared and is reversed also control easily.
Show through these investigations,, with regard to practicability, also need to carry out a large amount of work, still be not in the news up to now based on the practical devices of the passive tunable optical shunt of this principle though report is also arranged based on the research of FBT tunable optical shunt.
Summary of the invention
The objective of the invention is at the deficiencies in the prior art, propose the full optical-fibre adjustable optical branching device of a kind of novel passive, it realizes simple, and technology is reliable, and is with low cost, is applicable to optical fiber telecommunications system and network.
For realizing such purpose, the Adjustable optical tapping element of passive full optical fibre of the present invention's design, draw awl (FBT) technology based on fiber fuse,, realize the adjusting of luminous power in the allocation proportion of each output port by regulating the bending curvature of fused biconical taper optical fiber in the optical fiber plane of conventional fixed distribution ratio.The elasto-optical effect theory of optical fiber points out that the stress that exists can cause the refraction index changing of optical fiber in optical fiber when fibre-optical bending, thereby cause the propagation constant difference of light in two optical fiber of coupled zone, can make the light distribution ratio change so change bending curvature.
Adjustable optical tapping element of passive full optical fibre of the present invention comprises a fused biconical taper optical fiber and a device for precisely regulating of regulating fibre-optical bending curvature.Device for precisely regulating makes the awl coupled zone of drawing of fused biconical taper optical fiber can change the bending curvature of fused biconical taper optical fiber at the optical fiber plane inner bending, and keeps this crooked state up to regulate next time.
Fused biconical taper optical fiber fixedly is embedded on the flexure strip of regulating device, and its coupled zone is near the central authorities of flexure strip.The two ends of flexure strip embed respectively in the pickup groove and sliding tray at shell two ends.Pickup groove and flexure strip one end close-fitting, flexure strip can not slide in groove.Sliding tray and flexure strip other end pine are joined, and the flexure strip end in groove can be free to slide in groove.Respectively having a hole at the shell two ends is the optical fiber fairlead.In the vertical direction of flexure strip central authorities the microgroove screw rod is housed and is pressed on the flexure strip, the hole that the microgroove screw rod passes the shell upper end is fixed on the shell.In the direction relative with screw rod, promptly the another side of flexure strip is provided with a spring and withstands on the flexure strip, and the other end of spring links to each other with outer casing bottom.Can change the case of bending of flexure strip, and then change the bending curvature that fused biconical taper optical fiber draws the awl coupled zone externally by manual adjustments or electric type of drive rotation microgroove screw rod, realize the adjusting of luminous power in the allocation proportion of each output port.
Fused biconical taper optical fiber is drawn by multifiber and forms, and fiber count is more than or equal to two.Each optical fiber forms coupling regime near being stretched by fused biconical taper technology, forms the deformation-free fused biconical taper optical fiber in back and has a luminous power distribution ratio of determining at each output port.Drawing of fused biconical taper optical fiber bored the coupled zone when the optical fiber plane inner bending, can change the luminous power distribution ratio of each output port.The optical fiber plane is meant the plane of drawing the many optical fiber in awl coupled zone to form.
Tunable optical shunt of the present invention, light path part only is made of fused biconical taper optical fiber, does not introduce other discrete and integrated optical device.Effects such as electric light, acousto-optic, hot light, magneto-optic are not adopted in the adjusting of luminous power distribution ratio, do not need the processing procedure of polarization state, but regulate the bending curvature of optical fiber, can complete passive realization.Curved fiber is basic identical to the adjusting ratio of each Wavelength Assignment ratio, helps the enforcement in real network.Along the fused biconical taper technology and the feature of holding traditional fixed light shunt, can utilize the fiber fuse of present comparative maturity to draw the awl technology.Therefore device has the good characteristic of fused biconical taper optical branching device, as polarization correlated little, uses bandwidth, and realizes that easily the broadband of device is smooth etc.Simultaneously, very littler owing to regulating and distributing than the curvature of required bending, can not cause bending loss, so the insertion loss is also very little.Tunable optical shunt of the present invention does not need additional optics, is full optical fibre device, and simple in structure, volume is little, and cost is low, realizes that easily very high degree of regulation is arranged.
The most typical application of tunable optical shunt of the present invention is to make shunt device in various optical transport networks, such as, in the Optical CATV network, need a large amount of different optical branching devices of beam split ratio.If there is a kind of splitting ratio that simple and adjustable cheaply optical splitter is set, bring great convenience will for the construction of network.Other application in optical-fiber network of tunable optical shunt comprises: can directly be used as adjustable optical attenuator, because the luminous power of arbitrary output terminal of tunable optical shunt is adjustable, promptly output terminal is adjustable to input end's insertion loss (decay).For another example, the tunable optical shunt can be used as the light use of opening the light.Make the luminous power of adjustable shunt output port have only 0 and two states of maximal value, then this tunable optical shunt has had the function of photoswitch.The application of this device is for the dirigibility that realizes optical communication networks such as PON and CATV and easily extendability is significant.
Description of drawings
Fig. 1 is a tunable optical shunt structural representation of the present invention.
Among Fig. 1,1 is fused biconical taper optical fiber, and 2 is flexure strip, and 3 is shell, and 5 is pickup groove, and 6 is sliding tray, and 7,8 is the optical fiber fairlead, and 9 is the microgroove screw rod, and 10 is spring.
Fig. 2 is a flexure strip schematic cross-section of having inlayed fused biconical taper optical fiber.
Among Fig. 2,1 is fused biconical taper optical fiber, and 2 is flexure strip.
Fig. 3 is a fused biconical taper optical fiber coupled zone synoptic diagram.
Fig. 4 is a fused biconical taper fibre-optical bending synoptic diagram.
Among Fig. 4, L is a curved fiber length, and θ is crooked angle.
Embodiment
Below in conjunction with drawings and Examples technical scheme of the present invention is further described.
Shown in Figure 1 is one 1 * 2 passive tunable optical shunt example structure synoptic diagram of the present invention.As shown in Figure 1, fused biconical taper optical fiber 1 fixedly is embedded on the flexure strip 2, and its coupled zone is near the central authorities of flexure strip 2.The two ends of flexure strip 2 embed respectively in two grooves at shell 3 two ends, wherein pickup groove 5 and flexure strip 2 one end close-fittings, and flexure strip can not slide in groove, and sliding tray 6 is joined with flexure strip 2 other end pines, and the flexure strip end in groove can be free to slide in groove.Respectively there are an optical fiber fairlead 7 and 8 in the shell two ends.Vertical direction in flexure strip 2 central authorities has microgroove screw rod 9 to be pressed on the flexure strip 2, and the hole that microgroove screw rod 9 passes shell 3 upper ends is fixed on the shell 3.In the direction relative with microgroove screw rod 9, promptly the another side of flexure strip 2 is provided with a spring 10 and withstands on the flexure strip 2, and the other end of spring 10 links to each other with shell 3 bottoms.
Fig. 2 is a schematic cross-section of having inlayed the flexure strip 2 of fused biconical taper optical fiber 1.As shown in Figure 2, fused biconical taper optical fiber 1 fixedly is embedded on the flexure strip 2, and fused biconical taper optical fiber 1 can adopt resilient glue such as silica gel to fix after being placed in the groove of flexure strip 2.The plane that two optical fiber form during installation should can guarantee that like this optical fiber plane overlaps with plane of bending as far as possible perpendicular to the flexure strip plane.For keeping vertical flexure strip surface, optical fiber plane, the width of groove is processed into and only is a bit larger tham the optical fiber width.The elasticity of flexure strip 2 is in the elastic deformation state when guaranteeing to regulate the flexure strip bending curvature, material can adopt the plastic sheet of metal spring sheet or good springiness.
But flexure strip 2 compound bending under the acting in conjunction of microgroove screw rod 9 and spring 10 also can be guaranteed the repeatability that deformation is regulated, microgroove screw rod 9 and 2 one unique positions of spring 10 common decision flexure strips.Externally by manual adjustments or electric type of drive rotation microgroove screw rod 9,9 elongations of microgroove screw rod and shortening cause that flexure strip 2 case of bendings change, and are elongated to solid line position as Fig. 1 microgroove screw rod 9 from dotted line, and corresponding flexure strip 2 moves to solid line position from dotted line position.Because flexure strip 2 case of bendings change, it also can correspondingly slide at an end of loose slot 6.Flexure strip 2 bendings cause that fused biconical taper optical fiber 1 bending curvature that is embedded in wherein changes, thereby have changed the luminous power allocation proportion of fused biconical taper optical fiber 1.
A simple calculating can show the degree of regulation of this device of the present invention.Suppose that flexure strip 2 length are 50mm, coupled zone length 10mm, if angle of bend be 6 ° (concerning the light allocation proportion is regulated, 6 ° is a bigger value), microgroove screw rod 9 needs the about 3mm of elongation, a fine setting screw rod can be accurate to 0.01mm, can accurately be adjusted to 300 values in this distribution ratio range of adjustment, and degree of regulation can satisfy the network implementation needs fully.
Tunable optical shunt of the present invention inlet number is decided by the inlet number of the fused biconical taper optical fiber 1 that adopted, and present embodiment be that example is two outbound ports of an inbound port with 1 * 2 only.Fig. 3 is the coupled zone synoptic diagram of the fused biconical taper optical fiber that forms of two optical fiber, and its workspace is made up of three parts: the waist coupled zone, go into to hold cone and go out to hold cone.Fused biconical taper technology is eradicated two and is gone the optical fiber of coat to draw close in a certain way, and fusion mutually under flame or well heater high temperature stretches to both sides simultaneously, finally at the special Wave guide structure that forms the bicone form in the heating zone, realizes the luminous power coupling.For the coupled zone of improving optical fiber susceptibility, to make each optical fiber parallel close when making fused biconical taper optical fiber in the present invention to crooked deformation as far as possible.Light enters the coupled zone by the inlet of going into to hold cone of fused biconical taper optical fiber, exports from each output port by going out to hold cone with certain distribution ratio by the coupled zone luminous power.
Analyze Principles of Regulation from the angle of bending change optical fiber maximum allocated ratio below.Crooked influence to allocation proportion mainly is because the crooked two optical fibre refractivity differences that cause cause.As the bending of Fig. 4 owing to fused biconical taper optical fiber, cause two optical fiber one velamen compressions of coupled zone, another velamen stretches, their refractive index generation respective change, suppose to cause that the propagation constant difference in two optical fiber is Δ β, (Maximum Splitting Ratio MSR) can be expressed as according to asymmetric waveguides coupled wave theory maximum allocated ratio
Wherein K is the coupling coefficient of two coupled fibers.β is proportional to optical fiber curvature according to the theory of fiber Δ, i.e. Δ β=α ε, α be scale-up factor it by the self-characteristic decision of optical fiber, ε=θ/L is the curvature of curved fiber, L is a curved fiber length, θ is crooked angle.Just can reach the purpose that changes MSR by the size that changes θ.
Utilize the present invention to realize the tunable optical shunt in low-cost no seedbed, obviously it also can be used to realize adjustable attenuator and photoswitch.