DE19701908A1 - Optical network measuring method - Google Patents

Abstract

At least two groups of optical waveguide branches are connected to a main optical waveguide. Various couplers can be used to join the waveguides, such as multi-clad couplers, planar couplers, and wavelength division multiplex (WDM) couplers. Measurement light of at least two different wavelengths is coupled into the waveguides. Each wavelength is associated with a filter symbol by a filter to reconstruct a back-scattering profile. The number of different measurement wavelengths of the measurement light is equal to the number of groups of branch optical waveguides to be selectively measured. The measurement wavelengths are in the region of 1520 nm.

Description

The invention relates to a method for measuring on a optical network that has at least one common light has waveguide at which at a junction at least two groups of branching optical fibers are connected, being in the common light waves conductor measuring light of at least two different measuring waves coupled in lengths and at the junction on the Is divided into groups.

In an optical network with fiber optic branches In practice, it is difficult to get information about the ever because of the transmission status of the connected groups of Branch fiber optic selectively and spatially resolved to get along their length.

EP 0 447 439 B1 describes a method for detecting a possible loss in the branch lines of a fiber network works known, which are connected to a main line. For this purpose is inside, preferably at the end of the branch lines each provided a reflector, d. H. the reflectors are at different, usually far from each other th places. In particular, an impulse in the Main line of the branch lines coupled, which then proportionately into the branch lines up to the respective propagates and is reflected by this reflector. With the help of an OTDR measuring device ("optical time domain reflectometry ") at the entrance end of the main line thereupon only those reflexes that are caused by the Insertion locations of the reflectors come in a single, recorded sum signal for any weakening supervised. The same procedure is followed if Different frequency pulses in the main line be coupled. What is critical for the evaluation is  that especially with small damping on the respective Branch line and / or many connected branch lines the single reflex in the sum signal "disappears", i. H. yourself no longer significant compared to the overlay level of the Reflexes stand out from the other branch lines. With this known measuring method can also only the branch line route be monitored in front of the respective reflector and only roughly whether there is a malfunction or not. Would a point of very high damping such. B. a fiber break in one of the branch lines occurred, so would of their Reflector no reflex at all back to the main line come, d. H. it would be one of the reflections in the sum signal absence. This only allows the interpretation that in the affected There is damage to the branch line, but not a local area correct the fault location. In addition, statements are about the transmission status of the respective branch line behind whose reflector (when looking from the main line in the respective branch line in) is not available. Self if a variety of reflectors in each branch line is inserted, which is very complex, can only make a yes / no decision about whether a Error on the section from one reflector to the next There is a reflector. Where a possible error such. B. a Fiber break actually in the respective branch line before Reflector is not easy or not at all noticeable. The resolution is also dependent on the distance given by two successive reflectors and by the number of practically insertable reflectors per branch line limited, the effort is higher, depending greater the requirements for the desired spatial resolution will. A spatially resolved monitoring of the entire route the respective branch line is with this known measuring thus proceed too imprecisely and also not practicable. This The greater the problem, the worse the problem becomes Number of branch lines to be measured.

The invention has for its object to provide a way like a branched optical network of branching optical fibers in the simplest possible Way along their longitudinal extent as well can be measured selectively.

According to the invention, this object is achieved in a method of the type mentioned in that each Start of each group with at least one filter mark at least one filter element wavelengths acted specifically on backscatter signals of the measuring light is that of the transmission path of the respective Ver branching optical fiber behind the filter element stem from the fact that the common optical fiber at the Measuring wavelengths each have a superposition of this back scatter signals from the groups is measured, and that from these overlays of the backscattered measuring light under With the help of the measurement wavelengths assigned Filter indicator the time distribution of the return scattering characteristics of the respective group to be measured behind the filter element inserted is determined selectively.

By inserting at least one filter element Beginning, d. H. at the beginning of each group is certain posed that backscatter signals coming from the respective group are scattered back into the common optical fiber, even before entering the common optical fiber for the measuring wavelengths wavelength-specific with at least affects a filter indicator, d. H. be marked. On this is an effective and unambiguous, i.e. H. selective reconstruction of the temporal distribution of the Backscatter characteristics of each group to be measured from the recorded overlays of backscatter signals and thus a location-selective query of the transmission path of the enables each group. Furthermore, conclusions can be drawn on the specific, d. H. individual transmission state the connected group of one  Network location can be obtained from. For example, the Groups of branching optical fibers from one be monitored remotely from the central head-end station.

Because the respective filter element at the beginning of each Group, d. H. in the area of the respective branch point, is provided, information can advantageously about the transmission state of the respective branch Optical fiber in particular continuously over its full Length across, d. H. spatially resolved from its beginning to its end.

In particular, it is sufficient to simply filter elements to be inserted in at most as many different places as There are branches in the optical network.

The invention further relates to a measuring device for a optical network that has at least one common light has waveguide on which at least two groups of Branch fiber optic cables are connected, whereby the common optical fiber a transmitter can be coupled, the coupling of measuring light at least two different measuring wavelengths in the common Optical fiber is used, which is characterized is that the transmission device is designed such that at least one wavelength-specific filter indicator at least one filter element can be measured and / or held is that at the beginning of each group in this is inserted, and that to the common optical fiber a receiving device can be coupled, which the Rückge Scattered measuring light, each from the transmission path of the respective branching optical waveguide behind the added filter element and comes to the junction runs back, at the measuring wavelengths as an overlay recorded and from it with the aid of the measuring wavelengths assigned filter indicator the temporal distribution of the Backscatter characteristics of the group to be measured  selectively behind the inserted filter element certainly.

The invention also relates to an optical network at least one common optical fiber on which a branch at least two groups of ver Branch optical fibers are connected, which is characterized in that at the beginning of each group, at least one filter element is inserted that wavelength-specific with at least one filter indicator acts on backscatter signals from longitudinal locations of Ver pointing optical fiber behind the inserted Filter element.

Other developments of the invention are in the Unteran sayings reproduced.

The invention and its developments are as follows explained in more detail with reference to drawings.

Show it:

Fig. 1 is a schematic overview representation of a partial section of an inventive optical rule network, in which a measuring device is coupled for implementing the method according to the invention,

Fig. 2, 3 each a modification of the optical network according to the invention according to Fig. 1, and

Fig. 4, 5 each in a schematic overview representation another, compared to Fig. 1 modified optical network for performing the inventive method.

Elements with the same function and mode of operation are hen in FIG. 1 with 5 each with the same reference numerals.

Fig. 1 shows a schematic overview of a partial section of a first embodiment of an inventive optical network ON1 with network branches. This optical network ON1 has at least one common optical waveguide to which at least two groups of branching optical waveguides are connected in common. The respective group is preferably formed by at least one branching optical waveguide, ie one or more branching optical waveguides. In Fig. 1 are in the right half of the example three individual branching optical fibers LW1, LW2, LW3 with their associated, input-side ends ES1, ES2, ES3 at a splitting or branching point SP1 with the output-side end AG of the common Optical fiber GL firmly connected. The common optical waveguide GL is thus divided at the branching point SP1 into three groups G1, G2, G3, each of a single branching optical waveguide LW1, LW2, LW3. The longitudinal extent of the common optical waveguide GL and the branching optical waveguides LW1, LW2, LW3 are each indicated symbolically by a circle in FIG. 1. The branching of the common optical waveguide GL at the branching point SP1 into a multiplicity of individual branching optical waveguides can preferably be effected with the aid of a branching device. As such a branching device, for example, a so-called optical splitter or coupler can be attached or attached to the end at the output end AG of the common Lichtwellenlei age GL. With three branching optical fibers to be connected, e.g. B. LW1 with LW3 a 1 X 3 coupler or splitter is preferably used. So-called multiclad couplers, fusible couplers, planar couplers, WDM ("wavelength demultiplexers") couplers, etc. are particularly suitable for network branching.

All branching optical fibers such. B. LW1 with LW3, the the common optical fiber such. B. GL assigned are, so open into this common optical fiber GL at the same time and are AG at its output end permanently coupled. This can also be done if necessary be accomplished that the branching optical fiber LW1 with LW3 with their front ends on the input side the output end face of the common light waves conductor GL are spliced tight. In particular, the ends ES1 on the input side with ES3 of the branching light wel lenleiter LW1 mit LW3 with the output end AG of the common optical fiber GL be fusion welded. At the branch point SP1 is thus a leased line between between the branching optical fibers LW1 with LW3 and the common optical fiber GL permanently provided, d. H. the branching optical fibers remain in constant Contact with the common fiber optic cable GL. It is thus enables simultaneous, that is, simultaneous messaging tens signals NS over all connected branch light to send and / or receive waveguide LW1 with LW3. On in this way the branch point SP1 provides a network node ten, of which a network branch in the form of a multitude starts from branching optical fibers in a star shape.

The branching point SP1 opposite the input end EG of the common optical fiber GL is preferably guided to a so-called head station of the optical network ON1. There, a measuring device or device can be coupled to the input-side end EG of the common optical waveguide GL, as is indicated in FIG. 1 by a dash-dotted frame in FIG. 1 and provided with the reference symbol OTD. The measuring device OTD has a transmission device SE which can be coupled to the input end EG of the common Lichtwellenlei conductor GL with the aid of a coupling device USE. This coupling device USE is only symbolically indicated in FIG. 1 with the aid of a switch which, in its switch position PS, connects the transmitting device SE to the common optical fiber GL. In practice, a bending coupler or another optical coupling element can be provided as the coupling device USE, for example. In the same way, it may also be appropriate to feed the transmitter device directly into the front end KE of the common optical waveguide GL via a separate feed optical waveguide. The transmitting device SE is designed such that with its measuring light MSi (t) different ones, here in FIG. 1 in particular three measuring wavelengths λi with i = 1, 2, 3, ie λ1, λ2 and λ3, preferably one after the other in time common optical fiber GL can be coupled. This is illustrated in FIG. 1 in that a separate transmitter unit is shown in the transmitter device SE for the respective measuring wavelength. In Fig. 1, three transmitter units SE1 with SE3 are shown one below the other for clarity. The respective transmitter unit can be formed, for example, by a laser diode, which generates measuring light only of a certain measuring wavelength. In detail, the transmitter unit SE1 for transmitting measuring light MS1 (t) at the measuring wavelength λ1, the transmitting unit SE2 for transmitting measuring light MS2 (t) at the measuring wavelength λ2, and the transmitting unit SE3 for transmitting measuring light MS3 (t) the measuring wavelength λ3 responsible. With the help of a switching device US, in particular a switch or coupler, the transmitter unit SE1 is in its position S1, the transmitter unit SE2 is in its position S2, and the transmitter unit SE3 is coupled to a feed-in optical waveguide ELS in its position S3, via which the respective measuring light MS1 (t), MS2 (t), MS3 (t) can be coupled into the common optical waveguide GL with the aid of the coupling device USE. In this way, at three different measuring wavelengths λ1 ≠ λ2 ≠ λ3, measuring light MS1 (t), MS2 (t), MS3 (t) is preferably fed into the input-side end EG of the common optical waveguide GL one after the other and in each case at the splitting point SP1 into the Groups G1, G2, G3 ver distributed. For example, the first measuring wavelength λ1 is approximately equal to 1520 nm (nanometers), the second measuring wavelength λ2 approximately equal to 1522 nm, and the third measuring wavelength λ3 approximately equal to 1524 nm, while the actual message traffic is unaffected by this in the separately assigned wavelength range between 1530 nm and 1560 nm can be performed.

Generally speaking, the measurement wavelengths are preferred different from the transmission wavelengths of the actual Lichen NS message signals selected. That way despite the measurements on the network impairments or faults the regular message traffic in the optical fibers largely avoided the optical network, d. H. it can be measured and communicated at the same time. The measuring world The length range is particularly different from the transfer wavelength range selected. The bandwidth for that each measuring light is preferably smaller than that Bandwidth of the respective message signal selected. The following wavelength range assignments are in practice expedient:

The wavelength range around 1300 nm (= lower transmission band of common optical fibers), especially between 1380 and 1450 is used for the measurements during the Message traffic in the wavelength range around 1530 nm (= upper transmission band of common optical fibers), esp between 1500 and 1600 nm. It is the wavelength range between 1530 and 1560 for the night Directional transmission particularly useful, because in this waves optical fiber amplifiers ("optical fiber amplifier "), especially so-called" erbium-doped fiber amplifier "with their gain band. Before preferably, news opti over the optical network signals with carrier wavelengths between 1530 and 1560 µm, ins especially between 1540 and 1560 µm. Farther it may also be appropriate if the above  To swap transmission band allocation, d. H. the measurements in the upper transmission band at 1500 nm as well as the actual one Message signal transmission in the lower transmission band at 1300 nm. Furthermore, it can also be useful be the respective, such as B. the upper transmission band 1500 nm to divide yourself. In particular, the message signal NS, for example, the preferred transmission Wavelength range between 1530 and 1560 nm, the measuring light signals, however, the wavelength range between 1450 and 1530 nm or between 1560 and 1650 nm.

Furthermore, it may also be appropriate if Transmitting device only to provide a laser that over preferably over a predeterminable measuring wavelength range continuously or in particular finely tunable is. As a result, measuring light can be generated which is related to its measuring wavelength within a predeterminable measuring wave length band can be changed continuously. It can be on this way, measurement light with difference in time union measuring wavelengths in the common optical fiber be coupled. In particular, such is modifi graced transmitter, for example, over a wavelength range between 1450 and 1530 nm or preferably between 1560 and 1650 nm tunable. Two successive measuring Wavelengths preferably have a channel spacing between 0.5 and 10 nm, in particular between 1 and 5 nm of each other on.

In order to achieve that from a head-end station with the help of the measuring device OTD by measuring only on the common optical fiber GL conclusions about the respective transmission state of each connected branching optical fiber lenleiters such as LW1 with LW3 can be obtained selectively, is at least one filter element inserted at the beginning, ie at the beginning of the branching optical waveguide to be measured in each case, or attached to its front end. In Fig. 1, the filter element F1 is additionally used in the input-side end section ES1, ie (when looking from the branching point SP1 into the respective branching optical waveguide) at the beginning of the branching optical waveguide LW1, the filter element F2 in the input-side end section ES2 of the branching optical waveguide LW2 interposed and the filter element F3 additionally attached in the input-side end section ES3 of the branching optical waveguide LW3. The filter elements F1 with F3 preferably remain permanently in the respectively assigned branching optical waveguide LW1 with LW3.

In other words, that means (in the execution direction HR, i.e. when looking from the branch point SP1 in the respective branching optical fibers) on each Start of the branching optical fiber, i.e. H. in the area the branching point each have at least one filter element is inserted into the respective group. Preferably that sits respective filter element directly behind the splitter or in Coupler of the branching point at the input end or in the input-side end section of the respective branch Optical fiber.

It may be particularly expedient to insert the respective filter element itself at the branching point. This can preferably be done with the aid of a wavelength-selective coupler of known design such as e.g. B. directional coupler, grating coupler, grating chromatograph or the like, which is used as a splitter with 1 input and a plurality of outputs in the branching point. The branching optical fibers are connected to the outputs of such a wavelength-selective coupler. A cascade of 2X2 couplers connected in series is particularly suitable, each of which has a selective effect for two different measuring wavelengths. The specially provided filter elements such as B. F1 with F3 in FIG. 1 can then be omitted, since their filter function is automatically taken over by the wavelength-selective splitter or coupler at the branching point.

The fact that the filter elements directly on the respective Junction itself or immediately behind it in the input-side end sections of the connected Ver Branch optical fibers are provided, their Insertion points concentrated in the immediate vicinity, d. H. in the same area of the network and are not spatial widely separated. You can, for example, in a common splice cassette or splice sleeve be brought. You can therefore easily access them Concentration points of the network by a fitter at Neu installation of the network or retrospectively for one already installed optical network at the input ends of the Branch fiber optic spliced, plugged in, clamped or attached in any other way or in their input end sections are spliced. In front in part, there are at most so many different ones Insertion locations required, such as branching points in the opti network are available.

The filter element inserted in the respective branching optical waveguide is designed such that it specifically assigns at least one filter identifier to the respective measuring wavelength of the measuring light. Specifically, in FIG. 1, the filter element F1 specifically assigns measuring light portions which have entered the branching optical waveguide LW1 to its filter code K11 for the measuring wavelength λ1, its filter code K21 for the measuring wavelength λ2 and its filter code K31 for the measuring wavelength λ3 . Analogously, the filter element F2 of the second branching optical waveguide LW2 acts specifically on measurement light components of the measurement wavelength λ1 with its filter identifier K12, on measurement light components of the measurement wavelength λ2 with its filter identifier K22 and on measurement light components of the measurement wavelength λ3 with its filter identifier K23. According to the same assignment principle, the filter element F3 in the third branching optical waveguide LW3 specifically assigns its filter identifier K13 measuring light to the measuring wavelength λ1, its filter identifier K23 measuring light to the measuring wavelength λ2, and its filter identifier K33 to the measuring wavelength λ3. In other words, the filter element F1 speaks with its filter identifier K11, the filter element F2 with its filter identifier K12 and the filter element F3 with its filter identifier K13 at the measuring shaft length λ1. At the measuring wavelength λ2, the filter element F1 acts with its filter code K21, the filter element F2 with its filter code K22 and the filter element F3 with its filter code K23. Finally, at the measuring shaft length λ3, the filter element F1 with its filter code K31, the filter element F2 with its filter code K23 and the filter element F3 with its filter code K33 are effective. This assignment of the filter characteristics of each filter element to the measuring lengths used is illustrated in FIG. 1 in that the filter characteristics such as, for. B. K11, K21, K31 each filter element such. B. F1 are drawn in a column with each other, so that a pictorial assignment to the signed drawing units for the measuring wavelengths λ1, λ2, λ3 arises.

If, for example, the measuring light MS1 (t) of the measuring wavelength λ1 is fed in the common optical waveguide GL in the direction HR to the branching point SP1 and there divided up to the individual branching optical waveguides LW1, LW2 and LW3, then the respective branching optical waveguide LW1 with LW3 (in the direction of travel from the splitting point SP1 into the respective optical waveguide) from its longitudinal locations after the associated filter element F1 with F3 in each case a time-dependent backscatter signal SR1 (t), SR2 (t) and SR3 (t) in the opposite direction GR. These backscatter signals SR1 (t), SR2 (t) and SR3 (t) are generated in particular due to the so-called Rayleigh scattering in the respective branching optical waveguide. The parameter t identifies the time over which measurements are made. The measurement is effected in particular by the fact that a short pulse of light at the carrier measuring wavelength λ1 is applied to the common optical waveguide GL with the transmitting device SE. This transmission pulse is also shown symbolically in FIG. 1 in the form of a rectangle in the transmission device SE. It preferably triggers Rayleigh backscatter signals from longitudinal locations along the total longitudinal extent of the branching optical waveguides, the measuring light components each pass through the entire transmission path of the respective branching optical waveguide behind the filter element or its filter elements inserted on the input side. Appropriately, the common optical waveguide for the respective measuring wavelength is measured over such a long period of time that backscatter signals are recorded as superimposition, which originate from longitudinal locations along the entire longitudinal extent of the respective branching optical waveguide behind its filter element. In other words, this means that the entire transmission path of the respective branching optical waveguide behind its input-side filter element is continuously “scanned” with measuring light, that is to say it can be monitored locally. A selective, time-dependent backscatter signal can thus be received in the common optical fiber from each longitudinal location behind the input-side filter element of the respective branching light optical waveguide, which influences wavelength-specific by at least one filter indicator before entering the common optical fiber and thus marks it has been. In this way, the backscattered measuring light from the branching optical waveguide LW1, ie its backscattering signal SR1 (t) of the measuring wavelength λ1 with the filter identifier K11, the backscattered measuring light SR2 (t) of the measuring wavelength λ1 from the branching optical waveguide LW2 with the filter identifier K12 and the backscattered measuring light SR3 (t) of the measuring wavelength λ1 from the branching optical waveguide LW3 with the filter identifier K13 and thus specifically influenced. Considered in the spectral range, a backscattering spectrum R1 (S) results from the measurement wavelength λ1 in the common optical waveguide GL, which is the result of a superposition or superposition of the individual backscattering spectra SR1 (S), SR2 (S), each marked with a filter SR3 (S) the temporal distribution of the backscatter signals SR1 (t), SR2 (t), SR3 (t) is composed. S denotes the frequency. For the backscattered overlay spectrum R1 (S) in the common optical fiber GL, the following therefore applies in the spectral range at the measurement wavelength λ1:

R1 (S) = K11 SR1 (S) + K12 SR2 (S) + K13 SR3 (S),

where S denotes the frequency.

If the measuring light MS2 (t) is used for the measurement in an analogous manner wavelength λ2 in particular with the same temporal light impulse, d. H. a light pulse of the same shape and the same Intensity like the measuring light MS1 (t) in the common light waveguide GL fed, this results in a return scattered beat signal R2 (t) in the common light wave lenleiter GL, which in turn is considered in the spectral range from a combination of the selective single backscatter spectra SR1 (S), SR2 (S), SR2 (S) of the connected branch Optical fiber LW1 is combined with LW3. This return Scattering spectra, namely SR1 (S), SR2 (S) and SR3 (S) are now with the specific filter codes K21, K22 and K23 influenced, d. H. marked or characterized. For the back scattered overlay spectrum R2 (S) in common light waveguide GL at the measuring wavelength λ2 therefore applies:

R2 (S) = K21 SR1 (S) + K22 SR2 (S) + K23 SR3 (S).

Finally, a light is generated by means of the transmitting device SE pulse at the measuring wavelength λ3 in an analogous manner to  the measuring wavelengths λ1, λ2 on the common light waves given GL in the direction of HR, so in the branch supply optical fibers LW1 with LW3 each in turn selective backscatter signal generated on the spectral considered rich in the fiber optic cable LW1 with the filter characteristic Sign K31, in the fiber optic cable LW2 with the filter code Chen K23 and in the fiber optic cable LW3 with the filter code character K33 is specifically influenced. Known this recorded single backscatter spectra K31 · SR1 (S) from the Optical fiber LW1, K23 · SR2 (S) from the optical fiber LW2 and K33 · SR3 (S) from the optical fiber LW3 at the branch point SP1 in the common optical fiber ter GL merged and a backscattered overlay signal R3 (S) formed, for which the following applies:

R3 (S) = K31 * SR1 (S) + K23 * SR2 (S) + K33 * SR3 (S).

This allows for the backscattered overlay spectra R1 (S), R2 (S) and R3 (S) following system of equations (1) in Set up matrix notation:

It is particularly expedient for the backscatter produced signal such as B. RS1 (t), RS2 (t), RS3 (t) to be measured in each case the branching optical fiber such. B. LW1 with LW3 the measuring wavelengths such as B. λ1, λ2, λ3 with the help of leaky filter elements such. B. F1 with F3 as a filter indicator each assign a wavelength-specific transmission nen. The filter indicators such as B. K11, K21, K31 of each leaky filter elements such. B. F1 before each shows transmission coefficients. Such (transmission) Filter elements that have a specific measuring wavelength can have specific transmission coefficients preferably be formed in that the refractive index in respective branching optical fibers on a short  Part of the other actual transfer length is changed. This can preferably be done by a accordingly changed doping of the optical waveguide core be made. The transmission coefficients are preferably between 0% and 100%, in particular between 0.1% and 100% chosen. Are suitable as transmission filters preferably grating spectrometers, in particular so-called Bragg gratings, phased arrays, fusion couplers, evaporated Filters, etc. . . .

It can be particularly expedient to insert a filter element for assigning a speci fi cally assigned transmission coefficient on the input side into the respectively connected branching optical waveguide for each individual measuring shaft length. For three measuring wavelengths λ1 with λ3 as in the measuring arrangement according to FIG. 1, three filter elements are then preferably inserted one after the other into the input-side end section, ie at the beginning of the respective branching optical waveguide, instead of the filter element F1, each of the three filter elements then only with a single filter characteristic, in particular transmission coefficients, which influences the measuring light at the measuring wavelengths λ1, λ2, λ3. For this purpose, the respective branching light waveguide is expediently doped in successive sections in such a way that each measuring wave length can be assigned a specifically assignable transmission coefficient per section of the branching optical waveguide. In Fig. 1 this is exemplified for the branching optical waveguide LW1, in the input-side end section three such filter elements F11, F12 and F13 are shown in dash-dot lines one behind the other.

Additionally or independently of transmission filter elements it may be appropriate, in the respective ver Branch fiber for each measuring wave used length at least one additional attenuator each  add that a speci only for one of the measuring wavelengths fish damping of the measuring light causes. In the three measuring world lenlengths λ1, λ2, λ3 is like in the respective optical fiber e.g. B. LW1 thus preferably vorese a first attenuator hen that a specific only at the measurement wavelength λ1 assigned damping exerts on the measuring light. A second Attenuator ensures that only with the measuring shafts length λ2 a specifically assigned damping to the measurement light works. Finally, a third attenuator is used to the fact that only measuring light of measuring wavelength λ3 with a specifically associated damping is affected. As a damper Machunghnder interfero are preferred meters, Bragg grating, transmission grating, Fabry-Perot filter in evaporated form or with a gap, etc. . . .

Are the filter elements in particular designed such that in the respective branching optical waveguide open backscatter signal at the measuring wavelengths each specific transmission or damping is assigned, so the above system of equations also applies in the time domain:

where t is time designated.

In particular, the filter marks represent the product the transmission coefficient of the respective filter element for the forward and reverse direction HR, GR.

In order to be able to record and evaluate the time distribution of the backscattered overlay signals R1 (t), R2 (t) and R3 (t) from the common optical waveguide GL at a head-end station of the optical network ON1, the measuring device OTD of FIG. 1 has one Receiving device EE, which can be coupled with the aid of the coupling device USE preferably to the one end EG of the common optical waveguide GL, ie where the transmitting device SE is also positioned. To z. B. to be able to detect the superimposed backscatter signal R1 (t) at the input end EG of the common light waveguide GL with the receiving device EE, the symbolized by a switch coupler device USE from its first coupling or switch position PS to its second switch position PE moved to connect the receiving device EE. This switchover from the transmitting device SE to the receiving device EE is preferably carried out immediately after a measuring light pulse MS1 (t) of the measuring wavelength λ1 has been applied to the common optical fiber GL in the direction HR. The receiving device EE then detects the time distribution of the backscatter signal R1 (t) for the measuring wavelength λ1. To measure at the measuring wavelength λ2, the Ankoppelein direction USE preferably switches back to the PS position, ie to the transmitter SE, so that a measuring light pulse MS2 (t) of the measuring wavelength λ2 can be applied to the common optical fiber GL. Then the coupling device USE preferably immediately switches back to the receiving device EE, so that the reaction to this measuring light MS2 (t) of the measuring wavelength λ2 from the individual branching optical waveguides LW1 with LW3, that is to say the temporal superimposition of their selected backscatter signals SR1 ( t) can be detected with SR3 (t) as a superposition signal R2 (t). Finally, measurement light MS3 (t) of wavelength λ3 is coupled into the position PS of the switch of the coupling device USE in the common optical waveguide GL. The caused by this measuring light of the measuring wavelength λ3 in each individual branching light waveguide LW1, LW2 and LW3 backscattered light overlays in the common optical fiber GL as a backscatter signal R3 (t) in the opposite direction GR. To record the time distribution of this backscattered beat signal R3 (t), the coupling device USE is brought back into its position PE, so that the receiving device EE is actively coupled to the common optical fiber GL.

The transmitting device SE and / or the receiving device EE of FIG. 1 are particularly preferably part of a so-called multi-OTDR measuring device ("Optical time domain reflectometer") which works with at least two, ie two or more than two measuring wavelengths. It is particularly expedient to use an OTDR measuring device with a spectrally narrow band by tunable laser. The monitoring spectrum for such a tunable laser is expediently designed so that the regular transmission operation of news tens signals on the network is not disturbed as possible. For this purpose, the respective filter element with its filter characteristics in the branching optical waveguide responds only to measuring light of this monitoring spectrum for a specifically assigned measuring wavelength. In contrast, the filter elements have as little effect as possible on message signals in the message transmission spectral range. Of course, it is also possible to work with measuring light whose measuring wavelength corresponds to the transmission light wavelength of the message signals. A check of the branching optical waveguide is then only possible in the restricted transmission mode of the optical network. In particular, it is then expedient to briefly stop the message traffic on the optical network for the message branch to be checked.

The sequential acquisition of the temporal distribution of the three backscattered superposition signals R1 (t), R2 (t), R3 (t) for the three associated, different measuring wavelengths λ1 ≠ λ2 ≠ λ3 is illustrated in FIG. 1 by the measuring device OTD that in the receiving device EE each measuring wavelength λ1, λ2 and λ3 is assigned its own separate receiving unit EE1, EE2, EE3. The respective receiving unit can be formed, for example, by a light-sensitive element, in particular a photodiode, which is only sensitive to measuring light of a specific, specifically assigned measuring wavelength. Specifically, the receiving unit EE1 for receiving the backscatter light R1 (t) at the measuring wavelength λ1, the receiving unit EE2 for receiving the backscattering light R2 (t) at the measuring wavelength λ2, and the receiving unit EE3 for receiving the backscattering light R3 (t) at the measuring world length λ3 responsible. With the help of a switching device UE, in particular a switch or coupler, the receiving unit EE1 can be coupled in its position E1, the receiving unit EE2 in its position E2, and the receiving unit EE3 in its position S3 can be coupled to a coupling-out optical waveguide ALE, into which the respective backscattered overlay light R1 (t), R2 (t), R3 (t) is coupled out of the common optical fiber GL with the aid of the coupling device USE. In this way, at three different measuring wavelengths λ1 ≠ λ2 ≠ λ3, backscattered light R1 (t), R2 (t), R3 (t) from the input end EG of the common optical waveguide GL - in particular in the corresponding sequence of these measuring wavelengths λ1, λ2 and λ3 - recorded. The respective receiving unit EE1, EE2, EE3 preferably converts the received superposition signals R1 (t) with R3 (t) into electrical signals and feeds them separately via data lines L1 to L3 to an evaluation device AE, which is assigned to the receiving device EE . The evaluation device AE is used in particular to store the time distribution of the respectively received backscatter signal R1 (t), R2 (t) and R3 (t). It preferably has a processor unit CP. With their help, the temporal distribution of the backscattering characteristic of each individual connected branching optical waveguide LW1 with LW3 is determined selectively from the superimposed signals R1 (t) with R3 (t), i.e. the temporal distribution of the backscatter signals SR1 (t), SR2 (t) and SR3 (t) of the connected optical fiber LW1 with LW3 individually reconstructed. The time-wise selective distribution of the backscatter signals for the branching optical waveguide can then be subsequently recovered via separate data lines U1 to U3 to a display device ANZ, in particular a display. There the time distributions of the selective backscatter signals SR1 (t), SR2 (t), SR3 (t) can be shown together. Of course, it can also be expedient to only visualize a selective backscattering signal of interest, such as SR1 (t), individually using the display device ANZ. In particular, the selectively recovered backscatter signals SR1 (t), SR2 (t), SR3 (t) can be read out from the evaluation device AE in any order in time and can be displayed in any combination on the display device ANZ.

The measurement on the common optical waveguide GL from FIG. 1 therefore takes place in summary, preferably in the following order:

First of all, measuring light MS1 (t) emits measuring wavelength λ1 the transmitter unit SE1 in the position S1 of the switching device US via the feed-in optical fiber ELS and the coupling device USE in the switch position PS in the common Optical fiber GL in the direction of HR on the branch Optical fiber LW1 coupled to LW3. This measurement light MS1 (t) of the measuring wavelength λ1 is at the division place SP1 on the connected individual branch Optical fiber LW1 divided with LW3. Proportions of this measurement light pass through in the respective optical waveguide such as Example LW1 the filter element there in the execution and are in the actual transmission path below of the respective branching optical waveguide. The backscatter signal such as SR1 (t) in each Branch optical fibers such. B. LW1 runs like around the filter element F1 there in the input part section of the branching optical fiber. The from the connected branching optical fibers LW1 with LW3 incoming single backscatter signals SR1 (t), SR2 (t) and SR3 (t) are in each case by the in their input part cut inserted filter element F1 with F3 through  Predefinable filter indicator specifically marked or marked. These are marked in the opposite direction GR current, time-dependent backscatter signals overlap in the common optical fiber GL for the measuring wavelength λ1. The backscattered beat signal R1 (t) for the measurement Wavelength λ1 is common at the input end KE of the seed optical fiber GL with the help of the coupling device USE in the PE position in the connecting optical fiber ALE decoupled and with the help of the switching device UE in the position E1 to the receiving unit EE1 for the measurement wavelength λ1 forwarded. In an analogous manner, the Switch position S2 of the switch device US measuring light MS2 (t) of the measuring wavelength λ2 from the second transmitter unit SE2 via the connection optical fiber ELS in position PS the coupling device USE in the common light waves head GL coupled in the direction of HR. It comes again to overlap with the help of the filter elements F1 F3 marked single backscatter signals SR1 (t), SR2 (t) and SR3 (t) from the branching optical fibers in the common fiber optic cable GL. This backscattered Superposition signal R2 (t) for the measuring wavelength λ2 is in the position PE of the coupling device USE in the connection Optical fiber ALE from the input end KE of the common optical fiber GL uncoupled. In the Switch position E2 of the switch device UE becomes this backscattered beat signal R2 (t) of the second Receiver unit EE2 for the measuring wavelength λ2 Received device EE. In position S3 the Switch device US for the transmitter SE is finally measuring light MS3 (t) of measuring wavelength λ3 from the third transmitter unit SE3 over the connection light waves head of ELS using the coupling device USE in the scarf creation PS in the common fiber optic cable GL coupled. The in the connected branch Optical fibers LW1, LW2 and LW3 individually caused Backscatter signals SR1 (t), SR2 (t) and SR3 (t) are each when leaving the respective branching optical waveguide  marked with the help of the filter element F1 with F3. This specifically marked individual backscatter signals are in the common optical fiber GL at the splitting point SP1 concentrated merged so that a beat signal R3 (t) is formed for the measuring wavelength λ3. To this about To be able to detect position signal R3 (t), the coupling USE device in position PE for coupling the Receiver EE switched. In position E3 the Switch device UE then becomes this beat signal R3 (t) via the connection optical fiber ALE in the third receiving unit EE3 performed for the measuring wavelength λ3.

Instead of this time sequence when sending and receiving conditions of measurement light in the order of the measurement wavelengths λ1, λ2 and λ3, it can be particularly expedient to couple measurement light at the measurement wavelengths λ1, λ2 and λ3 simultaneously, that is to say simultaneously and simultaneously into the common optical fiber GL to recieve. For the measurement carried out simultaneously at the measurement wavelengths λ1, λ2 and λ3, in particular the switch device US for the transmitter device SE and the switch device UE for the receiver device EE of FIG. 1 can be omitted. A so-called WDM filter element is expediently connected upstream as a wavelength demultiplexer to the receiver device in order to transmit the backscattered overlay signals such as, for. B. Ri (t) with i = 1 with 3 for each measuring wavelength λi separately.

If necessary, it may also be sufficient for the Emp catching device EE only one large area to use photosensitive element which is the inclusion of Measuring light allowed for all measuring wavelengths used. Ins special is such a light-sensitive element such. B. with an InGaAs detector area in the wavelength range between 1 and 1.6 µm, in particular between 1.3 and 1.58 µm Designed to accommodate measuring light. Such a common one Photosensitive element in particular is already off sufficient if one after the other at the measuring wavelengths  λi measuring light MSi (t) into the common optical fiber is fed.

To the backscatter characteristics of e.g. B. three connected Branching optical fibers LW1, LW2, LW3 selectively single Lich by measurement on the common fiber optic cable GL be To be able to vote, measurement light is three different Measuring wavelengths in the common optical fiber GL coupled and the reaction in the branching light world lenleitern then as a beat signal in the common Optical fiber measured. This is how you get it linear system of equations (1) and (2). To this linear System of equations according to the individual backscatter signals such as B. Make SR1 (t), SR2 (t) and SR3 (t) uniquely resolvable , the measurement wavelengths λ1, λ2 and λ3 are added arranged filter indicators such as B. K11, K21, K31 of each only filter elements such as F1 tet linear regardless of the filter characteristics such. B. K12, K22, K23, K13, K23, K33 of the filter elements F2, F3, in the other groups specified or selected. The filter characteristics characters in the transfer matrix of the linear equation systems (1) are chosen such that the determinant this transfer matrix is not equal to 0. In this way can the single backscatter signals SR1 (t) with SR3 (t) Branching optical fiber LW1 with LW3 in unique Be selectively reconstructed. That way is one individual monitoring of each connected ver branch optical fiber from the head-end station on end of the common optical fiber GL on the aisle side enables. The individual network branches can therefore the temporal distribution of their backscatter signals held on and identified.

The statements that were made about the optical network ON1 of FIG. 1 with a triple branching are of course also advantageously transferable to any number of branching optical waveguides that are connected to a common optical waveguide.

Are z. B. to the common optical fiber GL only two branch optical fibers connected as for Example LW1, LW2 (the third optical waveguide is then LW3 omitted), it is already sufficient with help the transmitter SE only measuring light of two different ones ner measuring wavelengths such as λ1 ≠ λ2 in the common men to couple fiber optic cable GL. In each branch optical fiber LW1, LW2 with at least one, filter element inserted there the resulting Single backscatter signals a filter indicator wavelengths specifically, d. H. for the respective measuring wavelength net. It therefore comes for the measuring wavelength λ1 as well as for the Measurement wavelength λ2 to a beat signal in the common Fiber optic cable GL, each consisting of two superimposed, but wavelength-specific backscattered signals put together.

Generally expressed with n2 connected branch supply optical fibers preferably measuring light with n ver different measuring wavelengths in the common light waves conductor coupled in. In every branch optical fiber at least one filter element is assigned, which each of the n Measuring wavelengths of the measuring light each have at least one filter characteristic, in particular a transmission coefficient assigns specifically. So the number of different those measuring wavelengths of the measuring light preferably equal to Number of groups of branching Optical fibers selected. This is more advantageous Way a clear relationship between the backscattered Measuring light in the common optical fiber and the selective Backscatter signals from the connected groups are provided.

For n branching optical fibers to be measured, therefore with n measuring wavelengths λi (with i = 1 to n) n superimposition spec  tren Ri (t) (with i = 1 to n) as a function of time t and saved. All n temporal overlay signals Ri (t) contain an overlay of the single backscatter signals from all n connected branching light waves conductors. In particular, is not in any of the branches the wavelength-selective element is another wavelength gene-dependent component or element, so the selective depend Backscatter signals SRi (t) (with i = 1 to n) not from the measuring world len length λi.

The backscattered beat signals Ri (t), in particular Rayleigh backscatter signals thus result as overload the selective backscatter signals SRi (t) from the individual branching optical fibers LWi according to:

The coefficient Kÿ preferably denotes the trans Mission coefficients of the wavelength selective filter element ment in branch j at the wavelength λi. This linear slide system with n equations for n measuring wavelengths λi and with n variables for the branches SRj (t) has in particular one clear solution if the determinant of the coefficients matrix Kÿ ≠ 0.

For the measuring method according to the invention, in particular, always assumed that the optical network itself, i. H. without the inserted filter elements, at the measuring wavelengths largely independent of wavelength. Only that in the input-side end of the respective blurring light waveguide inserted, d. H. at the beginning of the transmission stretch of the respective branching optical waveguide brought filter element thus represents a wavelength dependent Otherwise, this is expediently by a corresponding adaptation or modification of the filter coefficient considered.  

Is the respective filter element in particular as a reflector element formed, d. H. it causes a wavelength dependency usual reflection for that in the respective branching light world measuring light, the filter elements can be Easily identify elements in the optical network from the head-end station certify. Because at each of the measuring wavelengths of transmission direction, especially when tuning the wavelength of the OTDR measuring devices such. B. OTD, gives the respective Filterele ment a clear backscatter signal so that its specific location, the specific transmission or Reflection coefficient and its respective reflection Wavelength at which the measuring light is influenced, current can be determined.

Furthermore, it may also be appropriate to use Help at least one filter element per under branching optical fiber looking for the measuring waves length in the spectral range to act on the measuring light ken that the backscatter signal in the respective branch Fiber optic a predeterminable phase for the respective Measuring wavelength can be specifically assigned. A reconstruction of the individual backscatter signals of the branching light waves leader is especially through so-called coherent reception the beat signals from the common optical fiber ter enables.

It may be particularly expedient if the number n of the different measuring wavelengths of the measuring light is greater than the number m <n of the selectively measured groups of ange closed branching optical fibers to choose from in this way to get an overdetermined system of equations, that is particularly cheap and computationally accurate according to the selections ven backscatter signals is resolvable. In particular, the Minimum number of different measuring wavelengths of the measuring light least 2, preferably between 3 and 10 times larger than that  Number of groups of branching Optical fibers can be selected.

Generally speaking, with n measuring wavelengths for m Groups of branching optical fibers to be measured fol system of equations in the spectral range:

Are the filter elements in particular designed such that in the respective branching optical waveguide open backscatter signal at the measuring wavelengths each specific transmission or damping can be assigned can, the above system of equations also applies in the time domain (= Extension of equation (2)).

This system of equations can still work even then selectively for at least some of the individual backscatter signals be resolved when the number n of the various measuring wel lenlengths of the measuring light in particular smaller than the number m (m <n) of the selectively measured groups of branch Optical fibers is selected. For this purpose, in the transfer supply matrix expediently the largest possible size Trix searched for either square or taller than wide is trained. Their filter indicators are more appropriate chosen so that the determinant of this sub-matrix becomes zero if possible. As a result, individual statements are still available specific backscatter characteristics at least for one Subset of the connected branching optical fibers  enables. In other words, that means the equation system can also be partially resolvable for the case m) n. However, it is then no longer all connected ver Identify branch optical fibers individually.

A clear reconstruction or identification of the one cell backscatter signals of the connected branch Optical waveguides can also be used in particular, for example by selecting the filter indicator:

1. z. B. with only two connected optical fibers and measuring light at two measuring wavelengths λ1, λ2:

Only two branching optical fibers LW1, LW2 are connected to the common optical fiber GL in FIG. 1 (LW3 has then been omitted) with the aid of a 1 X 2 coupler. For the filter element F1 in the optical waveguide LW1, its filter characteristics are selected equal to 1 (K11 = K21 = 1; K31 = 0), i.e. this filter element allows all measuring wavelengths to pass through unimpeded, which is equivalent to no filter element in the branching optical waveguide LW1. The filter element F2 is formed in the branching light wave guide LW2 in such a way that it blocks or absorbs measuring light of the measuring wave length λ2 as completely as possible (K21 = 0), the measuring light of the measuring wavelength λ1, on the other hand, lets it pass through unhindered (K11 = 1). In the common optical fiber GL of Fig. 1 can then be connected with only two connected optical fibers such. B. LW1, LW2 measure the following backscatter signals:

R1 (t) = 1SR1 (t) + 1SR2 (t)
R2 (t) = 1 * SR1 (t) + 0 * SR2 (t).

From these measured backscatter signals, the Single backscatter signals SR1 (t), SR2 (t) of the two closed branching fiber optic clearly teln:

SR1l (t) = R2 (t)
SR2 (t) = R1 (t) -R2 (t).

Obviously one obtains when the measuring wavelength is irradiated λ2, in which the filter element F2 essentially the measuring light completely absorbed, information R2 (t) = SR1 (t) from the first branching optical waveguide LW1. When irradiating the other measuring wavelength λ2 ≠ λ1 can then be Subtraction of the measured light R1 (t) for the measuring wavelength λ1 of the light R2 (t) measured at the measuring wavelength λ2 also the time distribution SR2 (t) of the backscattering characteristics selectively in the second branching optical waveguide LW2 determine.

2. with three branching optical fibers connected LW1 with LW3 and measuring light at three measuring wavelengths λ1, λ2, λ2:

Are - as in Fig. 1 - z. B. with the help of a 1 X 3 coupler three branching optical fibers LW1 with LW3 connected to the common optical fiber GL, in one of the branching optical fibers such. B. LW1 but the filter element such. B. F1 omitted, a clear reconstruction of the individual temporal distributions SR1 (t), SR2 (t), SR3 (t) of the backscattering characteristics of the branching optical waveguides LW1, LW2, LW3 is still possible. The omission of the filter element F1 is in the sense of the inven tion synonymous with a filter element whose filter characteristics are selected equal to 1, ie this filter element such. B. F1 then allows measurement light to pass through unhindered at all measurement wavelengths. The following applies to filter element F1: K11 = K21 = K31 = 1. The following backscatter signals R1 (t) with R3 (t) can thus be measured on the common optical fiber GL, for which the following applies:

R1 (t) = 1SR1 (t) + 1SR2 (t) + 1SR2 (t)
R2 (t) = k21 SR1 (t) + k22 SR2 (t) + k23 SR2 (t)
R3 (t) = k31 * SR1 (t) + k32 * SR2 (t) + k33 * SR2 (t).

From these measured backscatter signals R1 (t), R2 (t), R3 (t) the backscatter signals SR1 (t), SR2 (t), SR3 (t) single branching optical fiber LW1 with LW3 selek ascertain:

Generally speaking, only n-1 filter elements are therefore required for n branching optical waveguides to be measured, since total transmission 1 is also a filter in the sense of the definition used here. In particular, if there are nk filter elements in k branches, the n-k + 1 branches can still be kept apart. Assign so z. B. of n branching light wave lenleitern two optical fibers on no filter element, the two branches can not be separated without a filter, ie indistinguishable, the n-1 other very well.

The general system of equations (4) has in particular one clear solution for the selective backscatter signals SR1 (t) with SRm (t) for n = m, if the determinant of the transfer supply matrix of the filter code K11 with Knm not equal to zero is chosen. In other words, that means that the measurement wavelength-assigned filter indicator of the respective Filter elements are considered linearly independent of the filter indicator of the filter elements in the rest of the group  pen to be given a clear resolution of this general system of equations (4) after the selective return to allow stray signals.

From the system of equations (4), for example for the selective backscatter signals of the three connected branching optical waveguides at the branching point SP1 of FIG. 1, the following solution in matrix notation (in the time domain) results:

The general case for the 1 × 3 coupler is as follows Equations:

k11Z1 (t) + k12Z2 (t) + k13Z3 (t) = R1 (t)
k21Z1 (t) + k22Z2 (t) + k23Z3 (t) = R2 (t)
k31Z1 (t) + k32Z2 (t) + k33Z3 (t) = R3 (t).

With the solution (in matrix notation):

In particular for the special case that all diagonal elements Kii in the respective transmission matrix of the filter elements are selected identically, that is to say, for example, Kii = K = constant, and all other filter characteristics outside the diagonals are also selected identically, but unequal to the diagonal elements Kii, ie where Kÿ = T ≠ K, the following solution for the selective backscatter signals SRi (t) advantageously results:
(6) SRi (t) =

As long as T ≠ K, the determinant is ≠ 0 and it exists a clear solution for the selective backscatter signals SRi (t) of the individual branching optical fibers.

In particular, in the event that Kii = K, Kÿ = T, z. B. for three connected branching optical fibers as in Fig. 1, the system of equations

R1 (t) = KSR1 (t) + TSR2 (t) + TSR3 (t)
R2 (t) = TSR1 (t) + KSR2 (t) + TSR3 (t)
R3 (t) = TSR1 (t) + TSR2 (t) + KSR3 (t)

with the solution:

It can be particularly expedient to use the respective filter element on measuring light to exert at least one of the measuring wavelengths a blocking effect and at the same time to exert a transmitting effect in the respective branching optical waveguide for measuring light at least one of the measuring wavelengths. Such modified filter elements F1 * with F3 * instead of the previous filter elements F1 with F3 of Fig. 1 shows Fig. 2 in a schematic overview representation in the branching optical waveguides of another optical network ON1 *. This optical network ON1 * has in each branching lightwave conductor a filter element which only allows measuring light of a specifically assigned measuring wavelength, blocks it against measuring light of the other measuring wavelengths. In detail, the filter element F1 * of the optical waveguide LW1 has a filter identifier K11 ≠ 0 only for the measuring wavelength λ1, that is, it only allows for the measuring wavelength λ1 measuring light in the transmission path of the branching optical waveguide LW1. For the other two measuring wavelengths λ2, λ3, the associated filter characteristics are selected at least approximately K21 = 0, K31 = 0, so that the measuring light is blocked at the measuring wavelengths λ2, λ3, that is, it is not let into the optical waveguide LW1. For this blocking effect, the filter element F1 * is preferably designed as a reflection element which completely reflects the measuring light of the measuring wavelengths λ2, λ3 back into the common Lichtwellenlei ter GL, but does not let it into the branching optical waveguide LW1 to be checked. In the same way, it may be appropriate to design the filter element F1 * as a sump or absorption element that fades out the measuring light of the measuring wavelengths λ2, λ3 and does not allow it to reach the branching optical waveguide LW1. Analogous to the filter element F1 *, the filter element F2 * for the second branching optical waveguide LW2 is designed in such a way that only measuring light of the specifically assigned measuring wavelength λ2 is transmitted, but measuring light of the other two measuring wavelengths λ1, λ3 is blocked or hidden. The filter element F2 * thus preferably has a filter identifier K22 ≠ 0 for the measuring wavelength λ2, while the filter identifier K12 = 0 for the measuring wavelength λ1 and the filter identifier K31 = 0 for the measuring wavelength λ3 is selected. The filter element F2 * can preferably be formed for the measuring shaft lengths λ1 and λ3 as a reflection element or absorption element, the measuring light of these measuring wavelengths λ1, λ3 does not let into the branching optical waveguide LW2. Analogously, the filter element F3 * only has a transmitting effect at the specifically assigned measuring wavelength λ3, while it has a blocking effect on the measuring light at the other two measuring wavelengths λ1, λ2. Specifically, the filter is characteristic, in particular the transmission coefficient K13 for the measurement wavelength λ1 is chosen to be zero if possible. The same applies to the filter code K23 for the measuring shaft length λ2. For the filter code K33 applies to the measuring wavelength λ3 K33 ≠ 0, i.e. measuring light of this measuring wavelength λ3 is passed into the branching optical waveguide LW3 and can therefore pass the filter element F3 * in the opposite direction and in the opposite direction HR, GR largely unaffected.

The filter indicators of the filter elements F1 *, F2 * and F3 * are chosen in matrix notation such that applies Kii = K and Kÿ = 0 for all i ≠ j. This way, in each branching optical waveguide is only one measuring light single measuring wavelength transmitted while measuring light the other measuring wavelengths blocked, in particular reflec is tiert. It is particularly useful to choose Kii = 1, so that measuring light of measuring wavelength λ1 is as low-attenuation as possible through the filter element F1 *, measuring light of the measuring wavelength λ2 through the filter element F2 * and measuring light of the measuring wavelength λ3 through the filter element F3 * with as little attenuation as possible is let through. The filter elements are expediently elements F1 * with F3 * only active in one spectral range, that of the transmission waveband of the optical network ON1 * is different. In this way, the branching Optical waveguide even during the ongoing operation of the optical Network ON1 * can be measured. Impairments or malfunctions against the message signals are largely avoided.

If measuring light of the measuring wavelength λ1 is now coupled into the common optical waveguide GL with the aid of the transmitting device SE, this measuring light MS1 (t) only gets into the branching optical waveguide LW1. In the case of the other branching optical fibers LW2, LW3, however, it cannot occur, since it is blocked by the filter elements F2 *, F3 *. The measuring light MS1 (t) of the measuring wavelength λ1 is backscattered in the transmission path of the optical waveguide LW1. The temporal distribution of this backscatter signal SR1 * (t) runs back into the common optical waveguide GL and can therefore be measured there directly at the input end without any superposition. The switchover between the transmitting device SE and the receiving device EE is indicated in FIG. 2 by a switch USE * between the transmitting device SE and the receiving device EE. This selective backscatter signal R1 * (t) = SR1 * (t) is transmitted directly to the evaluation device AE via a line L1 and can be depicted with the aid of the display device ANZ. Analogously, you get for the measuring light MS2 (t) of the measuring wavelength λ2 only a single backscatter signal SR2 * (t), which runs from the branching light wave guide LW2 back into the common optical fiber GL and directly, that is, without superimposition with the aid of the measuring device EE can be measured. The same applies to the backscatter signal SR3 * (t), which is caused by the measuring light MS3 (t) in the third branching optical waveguide LW3. The temporal distribution of this backscatter signal SR3 * (t) can also be measured directly without superposition at the input of the common optical fiber GL without superposition.

For the direct single shot of the selective back beam characteristic of the respective connected branch Optical waveguide, it is expedient, a predetermined light baren measuring wavelength such. B. λ1 in the common Lichtwel supply line conductor GL and then immediately the measure backscatter signal. Only then is the measuring light a second, different measuring wavelength such. B. λ2 ≠ λ1 coupled into the common optical fiber GL and that associated backscatter signal R2 * (t) measured selectively. Close Lich the same measurement process for the measurement light of the third Measurement wavelength λ3 carried out by the measurement wavelengths λ1, λ2 is different. It is preferably successive, i. H.  Measuring light in succession with different measuring waves lengths fed into the common optical fiber and the reaction to it from the individual branching light waveguides on the common optical fiber via a measured according to the duration.

This optical transmission network ON1 * according to the invention is mainly characterized by the fact that the respective transmission status of the respectively connected Branch fiber optic individually, that is, selek tiv only by measurements on the common optical fiber ter GL can be included.

Fig. 3 shows a schematic overview of another optical network ON1 **, which has modified filter elements in the branching optical fibers compared to FIGS . 1, 2. In particular, a filter element F1 ** is inserted in the branching light waveguide LW1, which only has a blocking effect on the measuring light MS1 (t) of the measuring wavelength λ1, while measuring light MS2 (t), MS3 (t) of the other two measuring wavelengths λ2, λ3 is let through. In the second branching optical waveguide LW2, a filter element F2 ** is inserted, with which only measuring light MS2 (t) of measuring wavelength λ2 is blocked, while measuring light MS1 (t) for measuring wavelength λ1 and measuring light MS3 (t ) for the measuring wavelength λ3. At the beginning of the third branching optical waveguide LW3, a filter element F33 ** is provided in the area of the distribution point SP1, which only blocks the measuring light MS3 (t) of the measuring wavelength λ3, while the measuring light MS1 (t) of the measuring wavelength λ1 and the measuring light MS2 (t ) the measuring wavelength λ2 is transmitted. The filter characteristics or filter coefficients of the filter element F1 ** thus result in: K11 = 0, K21 ≠ 0 and K31 ≠ 0. The filter element F2 ** in the second branching optical waveguide LW2 is characterized by the following filter characteristics: K12 ≠ 0, K22 = 0, K32 ≠ 0. The filter element F3 ** in the third branching optical fiber LW3 has the following filter characteristics:

K13 ≠ 0, K23 ≠ 0 and K33 = 0.

The respective filter element can preferably be wave-length gene-selective reflector. Are suitable for this especially fiber grids such as Bragg grids. Ins The filter coefficients can be particularly useful Kÿ with i ≠ j, i.e. K21, K31, K12, K32, K13, K23 = 1 to choose. The measuring wavelength range is preferred different from the signal transmission wavelength range chosen. This allows the actual signal transmission from remain largely unaffected during the measurement.

With the transmitter SE the measuring light of the measuring waves given length λ1 on the common optical fiber GL, so this measuring light MS1 (t) at its entry into the actual Liche transmission path of the branching optical fiber LW1 prevented by the filter element F1 **. The meas light MS1 (t), on the other hand, can branch into the other two branches optical fiber LW2, LW3 enter and there cause a backscatter signal SR2 ** (t) and SR3 ** (t). in the common fiber optic cable GL thus occurs Superposition of the single backscatter signals SR2 ** (t) from the second branching optical waveguide LW2 and SR3 ** (t) the third branch optical fiber LW3. When measuring Wavelength λ1 is therefore a with the receiving device EE backscattered beat signal R1 ** (t) on the input side measured towards the end of the common optical fiber GL, the from the individual backscatter signals SR2 (t), SR3 (t) two other connected optical fibers ter LW2, LW3 consists of:

R1 ** (t) = K12 * SR2 ** (t) + K13 * SR3 ** (t).

The filter indicators represent transmis in particular tion coefficients.  

If the measuring light MS2 (t) of the measuring wavelength λ2 in the common seeds are fed into the fiber optic cable GL, so there are shares of this measurement light MS2 (t) only in the first branch Optical fiber LW1 and in the third branch Optical fiber LW3. The filter element F2 ** acts on the This measuring light MS2 (t), however, blocks and does not leave it into the actual transmission path of the second branch supply fiber LW2. In this way first branching optical waveguide the backscatter signal SR1 ** (t) the filter code K21 ≠ 0 for the measuring wavelength assigned λ2 and the backscatter signal SR3 ** (t) in the third LW3 branching fiber with the help of the filter element F3 ** the filter code K23 ≠ 0. The spec fish backscattered for the measuring wavelength λ2 signals SR1 ** (t) and SR3 ** (t) run on the branch reset SP1 and are in the common optical fiber GL overlaid. It thus results as a backscattered over position signal R2 ** (t) for the measuring wavelength λ2:

R2 ** (t) = K21 · SR1 ** (t) + K23 · SR3 ** (t).

Finally, the measuring light MS3 (t) of the measuring wavelength λ3 in fed the common optical fiber GL, so get Measuring light portions thereof only in the first branch Optical fiber LW1 and in the second branch Optical fiber LW2, while it from the third branch optical fiber is locked out. It is in first branching optical waveguide the backscatter signal SR1 ** (t) the filter code K31 and the backscatter signal SR2 ** (t) in the second branch optical fiber Filter indicator K32 specifically assigned. In common Optical waveguides GL are labeled as such selective backscatter signals SR1 ** (t), SR2 ** (t) superimposed, see above that for the third measured, backscattered overlay signal R3 ** (t) applies:

R3 ** (t) = K31 * SR1 ** (t) + K32 * SR32 ** (t).

With the help of the evaluation device AE, measurements can be made from these backscattered superposition signals R1 ** (t) with R3 ** (t) the temporal distribution of the individual backscatter signals SR1 ** (t) with SR3 ** (t) the branching optical waveguide LW1 can be determined selectively with LW3.

The following functional relationship applies in particular:

A measurement method modified in this way is particularly noteworthy the other characterized in that

• - the associated system of equations resolves stably leaves,
• - a disruptive influence on the spectra of the actual Message signals is largely avoided
• - An explicit solution for n measuring wavelengths at n branches to be measured.

FIG. 4 shows a schematic overview representation of an optical network ON2, which is expanded by 3 compared to the optical network according to FIG. 1. In this optical network ON2, groups are also connected to the common optical fiber GL, which have two or more branching optical fibers. For example, the individual branching optical waveguide LW1 after the filter element F1 is replaced by a group G11 of three branching optical waveguides LW11, LW12 and LW13. In other words, this means that the transmission path after the filter element F1 at a branch point SP11 is further divided into further, here three branching optical fibers LW11, LW12 and LW13. To the third group G3 of the optical network ON1 according to FIG. 1, a further group G31 of several, in particular three branching optical waveguides LW31 with LW33 is connected to a branching point SP31 in FIG. 4. With the aid of the measuring method according to the invention, it is then possible to be able to monitor or check the branches G11 and G31 at least in groups. According to the method according to the invention, a selective backscatter signal SRG1 (t) as a whole as well as a backscatter signal SRG3 (t) for group G31 overall can be selectively obtained, so that at least group monitoring is possible.

Fig. 5 shows a schematic overview of an optical network ON3 with several network branches. The optical network ON3 has, for example, three head stations KS1, KS2 and KS3, each of which is connected to a control center SZ via an optical waveguide ZL1, ZL2 and ZL3. For example, three network branches GL11, GL12 and GL13 hang on the head station KS1. The respective network branch is formed in each case by a common optical waveguide to which at least one group of at least one branching optical waveguide is connected. On the common optical fiber GL11, for example, four individual branching optical fibers LW111 with LW114 are firmly connected to the splitting point SP11. At the output end of the respective branching optical waveguide LW111 with LW114, end devices EG111 with EG114 such as telephones, faxes, PCs, televisions, multimedia terminals, etc. can be connected. Correspondingly, the second common optical fiber GL12 is connected to the distribution point SP12 with a plurality of branching optical fibers, such as LW121 to LW123, to which terminals EG121 to EG123 can be assigned. Analogously, a plurality of branching optical waveguides LW131 and LW134 are brought together at the distribution point SP13 at the output end of the third common optical waveguide GL13. This branching optical waveguide can also end in a terminal or be guided to further groups of branching optical waveguides. At least one, in particular several, network branches emanate from the head station KS1, each of which can be constructed and constructed with 4 in accordance with FIG . In this case (when looking from the respective branching point into the branching optical waveguide connected there) in each branching optical waveguide to be measured for selective monitoring, at least one filter element according to the invention is inserted on the input side, ie at the beginning of the respective transmission path. The filter elements can be particularly advantageously provided at the respective branch point itself. In detail, these are the filter elements F111 with F114 for the optical fibers LW111 with LW114, the filter elements F121 with F123 for the branching optical fibers LW121 with LW123 and the filter elements F131 with F134 for the branching optical fibers. From the head station KS1, the individual branching optical waveguides can thus be selectively monitored only by measurements on the respective common optical waveguides GL11, GL12 and GL13 according to the measuring principle according to the invention. In general terms, selective monitoring of each individual branch of the optical network ON3 is made possible in particular by

• - That preferably immediately behind the respective Distribution point in each branch optical fiber at least one filter element is used,
• - That in the common fiber optic a Netzver Branch measuring light with at least as many measuring wavelengths is coupled, as on the common optical fiber Ver branch optical fiber hang,
• - And that the respective filter element the measuring light at the different measuring wavelengths each assigned wavelength-specific filter indicator.

This makes it possible, according to the invention, to return conclude on the selective transmission behavior of everyone individual connected branching optical fiber or group of several optical fibers.

For this reason, at least one filter element additionally in the beginning of the respective branch Optical fiber of the network branch inserted by the Head station KS2 goes out. At the head station KS2 hang in individual the three common optical fibers GL21, GL22 as well as GL23, which are located at their ends on a split place SP21, SP22 and SP23 in a variety of split individual branching optical fibers. in the single is the common fiber optic GL21 with three Branch optical fibers LW211 with LW213 fixed connected, being in every single branching light a filter element F211 on the input side is inserted with F213. At the ends of the branching light Waveguides LW211 with LW213 can each use EG211 devices hang with EG213. Similarly, the common branch Optical fiber GL22 at its output end a splitting point SP22 into four individual branch Optical fiber LW221 with LW224 on. In every one Branch fiber is at the beginning of its over transmission line with an inventive filter element F221 F224 used. Again, the branching light waveguide LW221 with LW224 each to a terminal device EG221 with EG224. Also the common fiber optic cable GL23 branches at its output end SP23 in a star shape into several individual LW231 branching optical fibers LW236, on which end devices EG231 each have EG236 can hang. Every single branch light waveguide LW231 with LW236 is an inventive Filter element F231 with F236 assigned on the input side. On this way it is possible according to the invention Moves every connected branching light wave  to be able to selectively measure conductors from the head station KS2. The head stations KS1 and KS2 can be activated each preferably from the control center SZ via the Feed optical fibers ZL1 or ZL2 can be made.

From the control center SZ to the respective terminal, the optical network ON3 according to FIG. 5 preferably has a signal run length between 10 and 300 km, in particular between 20 and 50 km. The respective filter element is preferably inserted at the beginning of the respective branching optical waveguide immediately behind the distribution point of the common optical waveguide. In this way, it is made possible to capture essentially the entire transmission path of the respective branching optical waveguide in terms of its backscattering characteristic in terms of time and thus locally. Of course, it is also possible to use the respective filter element in the respective branching light waveguide only at the location from which end-side monitoring is desired. <; P 07178 00070 552 001000280000000200012000285910706700040 0002019701908 00004 07059AR <A further, third head-end station KS3 is connected to the control center SZ via a feed-light waveguide ZL3. A common fiber optic cable GL31 hangs from this head station KS3, which branches at the branch point SP31 into three individual fiber optic cables LW311 with LW313. No filter elements according to the principle of the invention have now been inserted into these three branching lightwave conductors LW311 with LW313. Would one now starting from the head station KS3 according to the so-called single OTDR measuring method ("optical time domain reflectome try") only measuring light of a single, certain measuring wavelength in the common optical waveguide GL31 and via the branch point SP31 in the connected branching optical waveguide Coupling LW311 with LW313, the backscatter signals from the individual branching optical fibers LW3I1 would overlap with LW313 without characteristic, wavelength-specific labeling in the common optical fiber GL31. A reconstruction of the individual selective backscatter signals would then no longer be possible. For a selective measurement of the backscatter characteristic of the respectively connected optical waveguide, it would therefore be necessary, for example, to measure extra on site, ie on the respective Ver branching optical waveguide itself with an OTDR measuring device to be connected there. Such a multiple measurement on site is very complex or even impossible in practice. For example, the respective branching optical waveguide can be laid underground or otherwise inaccessible. Personnel would have to be sent out specifically to connect a measuring device for each branch light waveguide to be examined, but this would disrupt or even interrupt the message transmission on this branch. Otherwise, it would be necessary for a permanently installed remote measuring operation from a head station to connect a measuring device to each branch optical fiber to be measured and to return the recorded measurement information via an extra return channel to the head station, which is very expensive and complex.

In contrast to this, it is only in particular that this enables inventions Invention measuring principle z. B. that

• - The network already through a one-time modification, d. H. by installing the filter elements on one Longitudinal location, especially the respective branch point of the network can be monitored selectively; as a result of that the filter elements in the area of the branching points of the Optical network are provided are advantageous Thus, at most as many insertion locations are required as There are branches in the optical network,
• - All branches are monitored from a single location can,
• - An error analysis even while the network is running drive can be performed so that even "creeping" errors can be detected,  
• - Analyzes any branch trees or ring structures can be
• - only passive, reliable components in the network are installed.

This location-selective measurement on an optical network, the has at least one common optical waveguide that at a branch point at least two groups of Branch optical fibers are connected, wherein in the common optical fiber measuring light at least two different measuring wavelengths coupled and at the ver branch is divided into groups, is in advantageously achieved by the following procedure:

At the beginning of each group, at least a filter indicator of at least one filter element wavelength-specific to backscatter signals of the measuring light acted on by the transmission path of each Branching fiber behind the filter element come from. At the common fiber optic cable Measuring wavelengths each have an overlay of this backscatter signals from the groups measured. From these overlays the backscattered measuring light is finally assisted took the filter indicator assigned to the measuring wavelengths the temporal distribution of the backscatter characteristic of the group to be measured behind the inserted group Filter element selectively determined.

It can be particularly advantageous to use the filter element the branch itself on the backscatter signals of the to influence the respective group in a wavelength-specific manner.

It is particularly useful on the common optical fiber a superposition of Ray at the measuring wavelengths leigh backscatter signals to measure when looking from the branch point into the groups of connected  Branch optical fibers in from their transmission caused behind the filter elements will.

Expediently for the common optical fiber the respective measuring wavelength over such a long period of time measured that backscatter signals as superimposition are recorded by longitudinal locations along the entire Longitudinal extension of the respective branching light waves Lead behind the filter element. With others Words that means that the entire transmission path of the respective branching optical fiber behind its filter element on the input side with measuring light "scanned", i.e. H. can be monitored locally. It can be on the common optical fiber from any longitudinal location behind the input filter element of the respective Branch fiber optic a selective, timed pending backscatter signal in the common optical fiber be received before entering the common Fiber-optic cable into the specific wavelength affects at least one filter indicator, and thus has been marked.

In particular, the method according to the invention enables for each of the fibers involved in a branched network their associated Rayleigh backscatter curve of a normal OTDR To reconstruct measuring device and thus also small damping to be able to localize changes in each fiber. It can a normal OTDR signal after the reconstruction in particular up to that longitudinal point of the respective Branch optical fiber reconstructed and displayed be at which a high damping such. B. a fiber break occurs. This is the exact longitudinal location where the person concerned ne branching optical fiber experiences its attenuation, from the known speed of light propagation in the light waveguide and the measured measuring light runtime be  tunable. This can be done with the usual spatial resolution OTDR measuring device, d. H. down to about 10 m spatial resolution and still below that.

Claims (23)

1. Method for measuring on an optical network (ON1), which has at least one common optical waveguide (GL), on which at a branching point (SP1) at least two groups (such as G1 with G3) of branching optical waveguides ( LW1 with LW3) are connected, with at least two different measuring wavelengths (λi, e.g. i = 1 with 3) in the common optical fiber (GL) measuring light (MSi (t), e.g. i = 1 with 3) is coupled in and divided at the branching point (SP1) between the groups (G1, G2, G3), characterized in that
that at the beginning of each group (G1 with G3) with at least one filter identifier (K11, K21, K31; K12, K22, K32; K13, K23, K33) at least one filter element (F1 with F3) wavelength-specific for backscatter signals (SR1 (t ) with SR3 (t)) of the measuring light (MSi (t), e.g. i = 1 with 3) acting on the transmission path of the respective branching optical fiber (LW1 with LW3) behind the filter element (F1 with F3) come from,
that at the common optical waveguide (GL) at the measuring wavelengths (λi, e.g. i = 1 with 3) there is a superposition (Ri (t)) of these backscatter signals (SRi (t), e.g. i = 1 with 3) is measured from the groups (G1 with G3) and that from these superimpositions of the backscattered measuring light (Ri (t)) with the aid of the filter indicators (K11, K21, K31; K12, K22, K32; assigned to the measuring wavelengths (λ1 with λ3); K13, K23, K33) the temporal distribution of the backscatter characteristic (SR1 (t) with SR3 (t)) of the respective group to be measured (G1, G2) behind the respective inserted filter element (such as F1) is selectively determined. 2. The method according to claim 1, characterized, that with the filter element (F1 with F3) at the branch  supply point (SP1) itself to the backscatter signals (SRi (t), e.g. B. i = 1 with 3) of the respective group (G1 with G3) length-specific. 3. The method according to any one of the preceding claims, characterized, that an overlap on the common optical fiber (GL) of Rayleigh backscatter signals (Ri (t)) is measured, the when looking from the junction (SP1) into the Groups of connected branching optical fibers (LW1 with LW3) from their transmission links behind the filter elements (F1 with F3). 4. The method according to any one of the preceding claims, characterized, that the number (n) of the different measuring wavelengths (λi with i = 1, 2, 3,. . .n) of the measuring light (MSi (t) with i = 1, 2, 3,... n) equal to the number (m) (m = n) of the groups to be measured selectively of branching optical fibers (e.g. for m = 3: LW1, LW2, LW3) is selected. 5. The method according to any one of claims 1 to 3, characterized, that the number (n) of the different measuring wavelengths (λi with i = 1, 2, 3,. . . n) of the measuring light (MSi (t) with i = 1, 2, 3,... n greater than the number (m) (m <n) of those to be measured selectively Groups of branching optical fibers (such as for m = 3: LW1, LW2, LW3) is selected. 6. The method according to any one of claims 1 to 3, characterized, that the number (n) of the different measuring wavelengths (λi with i = 1, 2, 3,. . .n) of the measuring light (MSi (t) with i = 1, 2, 3,... n) less than the number (m) (m <n) of those to be measured selectively Groups of branching optical fibers (such as for m = 3: LW1, LW2, LW3) is selected.   7. The method according to any one of the preceding claims, characterized, that the respective group (such as G1, G2, G3) by at least one branch optical fiber (such as LW1, LW2, LW3) is formed. 8. The method according to any one of the preceding claims, characterized, that the assigned to the measuring wavelengths (such as λ1, λ2, λ3) th filter identifier (such as K11, K21, K31) of the respective Filter element (such as F1) of one of the groups to be measured (such as G1) viewed vectorially linearly regardless of Filter indicator (such as K12, K22, K23; K13, K23, K33) the Filter elements (such as F2, F3) in the other groups (such as e.g. B. G2, G3) can be selected. 9. The method according to any one of the preceding claims, characterized, that the respective measuring wavelength (such as λ1) of the measuring light (such as MS1 (t)) with the help of the respective filter element (such as F1) as a filter identifier (K11) one wavelength specific transmission is assigned. 10. The method according to any one of the preceding claims, characterized, that using the respective filter element (such as F1) for Measuring light (such as MSi (t) with i = 2, 3) at least one of the Measuring wavelengths (such as λ2, λ3) a blocking effect and at the same time for measuring light (such as MSi (t) with i = 1) at least one of the measuring wavelengths (λ1) exerts a transmission effect becomes. 11. The method according to any one of the preceding claims, characterized, that with the filter element (such as F1) to the respective measuring group (such as G1) only on a measuring light specifically assigned measuring wavelength (such as λ1) blocking  is acted on, and that with this filter element (F1) Measuring light of the other measuring wavelengths (such as λ2, λ3) is left. 12. The method according to any one of claims 1 to 10, characterized thereby that with the filter element (such as F1) to be measured send group (such as G1) only measuring light of a speci fish-associated measuring wavelength (such as λ1) passed and that with this filter element (F1) on measuring light the other measuring wavelengths (such as λ2, λ3) have a blocking effect becomes. 13. The method according to any one of the preceding claims, characterized, that message through the respective filter element (such as F1) tens signals (NS) in the execution (HR) and / or opposite direction (GR) can be let through largely unaffected. 14. The method according to any one of the preceding claims, characterized, that using the respective filter element (such as F1) for Measuring light of at least one of the measuring wavelengths (such as λ1) at least a partial reflection is effected. 15. The method according to any one of the preceding claims, characterized, that on the common optical fiber (GL) for each Measuring wavelength (λi, e.g. i = 1 with 3) over such a long Time is measured that as a superposition (Ri (t)) in each case Backscatter signals (SRi (t)) are recorded by Longitudinal locations along the entire length of the respective branching optical fiber (LW1 with LW3) behind the filter element (F1 with F3). 16. Measuring device for an optical network (ON1), which has at least one common optical fiber (GL), at least two groups (such as G1 with G3) of branching optical fibers (such as LW1 with LW3) are connected, a transmitter (SE) can be coupled to the common optical fiber (GL), which is used to couple measuring light (such as MSi (t) with i = 1 with 3) of at least two different measuring wavelengths (such as B. λ1 with λ3) into the common optical waveguide (GL), in particular according to one of the preceding claims, characterized in that
that the transmitting device (SE) is designed such that at least one wavelength-specific filter identifier (F1 with F3) at least one filter element (F1 with F3) can be measured and / or held, which at the beginning of each group (G1 with G3) in this is inserted
and that to the common optical fiber (GL) a receiving device (EE) can be coupled, the backscattered measuring light (such as Ri (t) with i = 1 with 3), each of the transmission path of the respective branching optical fiber (LW1 with LW3) comes behind the inserted filter element (F1 with F3) and runs back to the branching point (SP1), at the measuring wavelengths (such as λ1 with λ3) each recorded as a superimposition and with the help of the measuring wavelengths (λ1 with λ3) assigned filter indicators (such as K11, K21) the temporal distribution of the backscatter characteristic (such as SR1 (t) with SR3 (t)) of the respective group to be measured (G1 with G3) behind the respective selectively inserted filter element (F1 with F3). 17. Measuring device according to claim 16, characterized, that the transmitting device (SE) and / or the receiving device device (EE) is part of an OTDR measuring device. 18. Measuring device according to one of claims 16 or 17, characterized,  that the transmitting device (SE) and the receiving device (EE) at the input end of the common Optical fiber (GL) can be coupled. 19. Optical network (ON1) with at least one common Optical fiber (GL), at a junction (SP1) at least two groups of branching light waveguides (such as G1 with G3) are connected, in particular according to one of the preceding claims, characterized, that at the beginning of each group (G1) at least a filter element (F1) is inserted with at least a filter indicator (K11, K21, K31) wavelengths acts specifically on backscatter signals (SR1 (t) with SR3 (t)), that of longitudinal locations of the branching optical waveguide (LW1 with LW3) behind the inserted filter element (F1) come from. 20. Optical network according to claim 19, characterized, that the respective group (G1, G2, G3) by at least one Branch optical waveguide (LW1, LW2, LW3) is formed. 21. Optical network according to one of claims 19 or 20, characterized, that the groups (G1, G2, G3) of branching light waves conductors (LW1, LW2, LW3) each firmly with the common Optical fiber (GL) at the junction (SP1) are connected. 22. Optical network according to one of claims 19 to 21, characterized, that the respective filter element (F1 with F3) on the Branch point (SP1) itself is inserted. 23. Optical network according to one of claims 19 to 22, characterized,  that filter elements (F1 with F3) have at most as many different places are inserted, such as Branch points (SP1) are present in the optical network.