DE19835681A1 - Optical communications system for transmitting signals via light conductors, has mode coupler or mixer for reducing dispersion at or after mode transition and before transmission path - Google Patents

Abstract

The system has a LED or laser (1) on the input side from which light is fed into a monomode fiber (3). A multi mode fiber (7) forms the transmission path (17). A transition from the monomode fiber to the multi mode fiber is arranged before the transmission path. The light wave transmission is based on an analogue data transmission. A mode coupler or a mixer (13) for reducing dispersion, especially mode dispersions, is arranged at the transition, or after it, and before the transmission path.

Description

The invention relates to an optical transmission system according to the preamble of claim 1.

Basically, data transmission is general and in computer technology especially in local but also electrical cabling used in external networks. A particularly high level of interference immunity even with extreme Transmission speeds and long cable lengths too reach, however, offer fiber optic transmission networks on.

When transmitting via fiber optics, however various special features are taken into account.

As especially in the pre-published magazine DE-c't Magazin für Computertechnik, issue 13 of 22. June 1998, pages 222 to 223 is highlighted, that is for example generated by an LED or a laser and  light fed into an optical fiber to several Modes distributed, which according to radiation theory means that the light reflects on the surface differently often is tiert and thus different distances back sets. This leads to different terms of the Signals (associated with signal distortion), this Effect is called dispersion.

The dispersion effects in turn depend on which optical fibers are used.

A distinction is made between three glasses fiber types, the so-called step index optical fiber (Multimode), the gradient index optical fiber (Multi mode) and the step index optical fiber (monomode). All three fibers consist of a cylindrical glass fa serkern (core) made of quartz glass, which in a so-called Cladding is embedded, which also made of glass with a different refractive index than the core glass consists. There is a be around the cladding glass Layering made of plastic (coating), which the glass fiber as Protection serves and careful handling.

With the multimode step index fiber optic is the Refractive index in the core glass and in the entire cross-section the same, however lower in the cladding glass. The rays are moving therefore by the refraction at the transition to the cladding glass zigzag through the optical fiber and lay un different ways back. When transferring from digital signals this leads to a broadening of the  Output pulse compared to the transmit pulse.

With a multimode optical fiber in the gradient index pro fil, the refractive index in the core glass falls continuously off the edges. One through the optical fiber by moving light beam moves due to the externally continuously changing refractive index curved webs instead of a zigzag web, as in the Step index optical fiber. Although the rays here if the distances are different, this leads however with less different terms, because in outer area of the core glass has a lower refractive index is given, whereby the speed of propagation there increases.

However, the most technically high quality are the so-called Single-mode fiber optic, the structure is principally correspond to the step index optical fiber, however a much smaller diameter in the core glass area have (instead of, for example, ≦ 200 µm, in this Case have a diameter of ≦ 10 µm).

An ideal optical transmission is therefore monomode and dispersion-free and influences the signal quality Lich noise, intermodulation or pulse shapes with off Do not take the damping, because in contrast with the optical transmission using multimode company change depending on the fiber type (gradient index or levels index) form several to many fashions that differ quickly on the optical transmission link (fiber)  spread out and lead to the undesired mode dispersion ren. In addition, the power distribution and phase relationship of the excited modes with multimode fibers variable and leads to the undesirable mode noise. With others Words using the propagation of signals a deterioration of multimode optical fibers Result in signal quality.

In digital technology, d. H. digital data transmission on fiber optics is also the principle of Fashions mix known. When using so-called modes mixer or mode coupler it is possible to certain ver to generate relationships in the mode excitation, whereby the Signal transmission is improved. It is in the Digi valley technology using multimode fiber optic cables also known as "offset launching", at which signal input side is a single-mode light wave conductor coupled to a multimode optical fiber using two on the front side Focusing trained towards the ends of the optical fibers lenses. The coupling from the single-mode optical fiber in the multimode optical fiber is done except middle (offset), whereby higher modes are stimulated and the dis persistence effects are reduced and thus the signal over wear is improved.

In contrast, analog technology is completely different conditions.

In analog technology, i.e. when transmitting analog  signals on fiber optic cables, multimode company not be used because of the explained fashions dispersion in analog technology such high intermodules tion distortions cause an as unlikely as possible fake signal transmission is made impossible.

In practice, two starting conditions therefore arise:

• - In the past, multimode fibers were made out of costs are relocated and are therefore exposed to many lights met waveguide routes. Nowadays Almost exclusively laid single-mode fibers. On multi Mode fibers can, however, with regard to the above Execution only digital transmission technology is used arrive because with analog technology no satisfactory Results regarding signal transmission achievable are.
• - If the customer uses the analog data Carrying on optical systems over long distances desired, this requires (according to the current State of the art) the laying of single-mode company to ensure adequate signal transmission ratios guarantee. Otherwise there is an analogue transfer engineering technology out of the question.

The object of the present invention is an optical Transmission system for analog data transmission too create, in which also for transmissions over large  Distances (in the kilometer range) as unlikely as possible fake data transmission is made possible.

The task is according to the invention in accordance with solved claim 1 specified features. Advantageous Ausge Events of the invention are set out in the dependent claims give.

It must be described as extremely surprising that with the optical technology based on analog technology support system a detailed below significant improvement was possible. This is at optical transmission systems for analog data transmission unpredictable.

Because although an increasing mode excitation (e.g. of sturgeon with increasing length of the transmission path) and an exchange of services, as well as constantly changing phases draws between the fashions are observed, whereby the variation of the electrical output level and the Reduction of the signal-to-noise ratio is necessary now shown according to the invention that the use of Mo mixer or mode couplers at the entrance of the transfer a balanced mode distribution also in the Analog technology enables. The better statistical ver division of the excited modes leads to the reduction of the Fluctuation. In other words, by using Mode mixers or mode couplers both the output level stabilized, as well as improving system noise the.  

The mode mixers or mode couplers can be found under be trained differently.

In a preferred embodiment of the invention for this purpose, the optical fiber mechanically on the input side Compressed fiber optic wires that are used to generate a me chanic stress can also be poured onto the fiber can. In a modified preferred embodiment is a mode coupler / mode mixer under integration so-called Selfoc lenses possible.

In a particularly preferred embodiment, however uses the principle of eccentric coupling at which has a very thin core diameter Single mode fiber eccentric to the core center one after following multimode fiber is arranged.

As mentioned, the invention is particularly suitable for Transmission of analog data on narrowband systems such as B. Cellular GSM, DCS.

The invention is explained below with reference to exemplary embodiments play explained in more detail. The individual shows:

Figure 1 is a schematic representation of a first embodiment of the invention using a mode coupler.

Fig. 1a is an enlarged detail view of a first exemplary embodiment of a mode coupler shown in Fig. 1;

Fig. 1b an example modified to Fig. 1a execution;

Fig. 1c another modified game Ausführungsbei to Fig. 1a and 1b;

Fig. 2 is a modified to Figure 1 execution example;

. Fig. 3 a to Figures 1 and 2 again abgewandel tes embodiment using a Zentrierverfahrens and dung and USAGE of four versions, and under Ver application of Selfoc lenses;

Fig. 3a shows a modified embodiment of Figure 3 using only two sockets;

Fig. 4 is a schematic representation of the eccentric arrangement of the fiber to be coupled without taper;

FIG. 5 shows a representation corresponding to FIG. 4 using a taper; FIG.

Fig. 6 shows an example of an eccentric arrangement using a Zentrierverfahrens with four frames and using Selfoc lens according to the Dar position shown in FIG. 3;

. Fig. 6a to Fig 6 modified example un ter use of only two versions;

Fig. 7 shows another embodiment of the invention;

Fig. 7a, 7b show two enlarged detail views of FIG. 7; and

Fig. 8 shows a repeater as an example of an application to the above-mentioned Glasfa serverbindungen in analog technology.

In Fig. 1 a first embodiment of a gear-side one, the transmission in the analog technique significantly improving mode coupler shown.

The optical system for the transmission of data in analog technology then comprises a laser 1 arranged on the input side, the generated modulated light beam of which is radiated into an optical waveguide (LWL) 3 in the form of a single-mode fiber.

In the exemplary embodiment shown, the optical waveguide 3 is wound several times into a ring and is connected via a so-called splice 5 to a subsequent, that is to say to a subsequent optical waveguide 7 in multimode fiber design using a splice technique.

A so-called mode coupler or mode mixer 13 is arranged downstream in the transmission direction 9 , as a result of which a balanced mode distribution, in particular a statistically better distribution of the excited modes with a significant reduction in the fluctuation in the transmission bandwidth that would otherwise occur, can be generated in order to significantly improve the signal transmission, in other words to be able to receive a significantly improved analog signal at the input side 15 of the transmission path 17 lying between the output 14 and the input 15 .

The mode coupler / mode mixer 13 can be constructed differently, as is shown only for example on the basis of the simplified longitudinal sectional illustration according to FIGS. 1a to 1c.

In the embodiment according to FIG. 1a, the light waveguide 7 is guided several times over deflection elements 19 in the form of needles, rollers or balls 19 a, 19 b or 19 c and bent several times in opposite directions, the bending radius being preferred values between 8 mm and 10 mm assumes and 8 to 15 turns result in a statistically better distribution of the excited modes.

The mode coupler / mode mixer 13 preferably consists of two (substantially along a division plane) GE divided halves 29 , in which the deflection elements 19 in the laying direction of the optical waveguide 7 are offset to each other, in both halves 29 offset from each other. From each of the exposed sections of the deflection elements 19 , the optical waveguide 7 is then guided around in a curved manner, with recesses 31 formed or being provided in the opposite half.

After the final laying of the optical fiber 7 , the two halves or plates 29 are positively connected with each other, for example also by means of a covering 30 z. B. a potting compound that surrounds, for example, the two halves 29 with the sandwiched between ordered and meandering Lichtwellenlei ter 7 .

In the modified embodiment according to FIG. 1c, two halves or plates 29 with different surface structure 33 are non-positively connected to one another, so that the optical waveguide 7 laid therein is also, if again, laid several times curved, for example cast in.

Due to the mechanically generated stress on the light waves head, d. H. the multimode optical fiber certain higher fashions with similar propagation speeds stimulated and thus favorable propagation conditions created conditions that lead to an improved Lead signal-to-noise ratio.  

In the embodiment shown in FIG. 2, a mode coupler 13 is used, which is provided from a body with multiple meandering tracks 37 . This mode coupler / mode mixer can be formed in two parts, for example have a lower half or shell, in which the tracks 37 are formed, and in which the multimode optical waveguide 7 can be inserted. Subsequently, a cover can be applied to the base body 31 , which comprises the webs 37 , and the entire unit can be firmly closed and connected. In general, however, after inserting the optical waveguide 7 in the webs or channels 37, these webs or channels 37 are shed, so that a one-piece manageable mode coupler 13 is generated, on which the multimode fiber 7 in a feeder side 41 in the mode coupler ler / mode mixer 13 introduced, in this multiple ge curved through meandering and passed out at its outlet side 43 out again.

In the embodiment according to FIGS. 3 and 6, a mode coupler / mode mixer 13 is compared with the Selbstjustierein device 44 is used.

This mode coupler / mode mixer 13 is used instead of the splice connection 5 used in the previous figures at the transition from an optical waveguide in the form of a single mode fiber 3 to a subsequent optical waveguide in the form of a multimode fiber 7 , in particular in the form of a gradient index fiber. The mode coupler is only indicated schematically, the end of the optical waveguide 3 being shown in the form of a monomode fiber, the end of which is guided and held in a socket 45 d, on the input side (that is to say without a laser connected in front of this embodiment).

For the sake of better representation, the single-mode light waveguide 3 is shown in cross section only with its core glass 47 , generally with a diameter of less than or equal to 10 μm, and the cladding glass 49 surrounding it, which usually has an outer diameter of 125 μm.

Downstream in the transmission direction, the multimode light waveguide 7 is shown with its cladding glass 49 (in the case of the gradient index fiber with the same outer diameter as the outer diameter of the cladding glass 49 of the single-mode optical waveguide 3 ), but in contrast with a significantly thicker core glass 47 , which has a diameter of, for example ≦ 100 microns, for example 50 microns can be. The beginning of the multimode optical waveguide 7 with its core glass 47 and its cladding glass 49 is held in an there version 45 c, anchored and ju stiert.

As can also be seen from FIG. 3, two further versions 45 a and 45 b are provided between the version 45 d for the single-mode optical waveguide 3 and the version 45 c for the multimode optical waveguide 7 following in the transmission direction, the version 45 a a multimode fiber 46 (also surrounded by a corresponding Man telglas), as well as centered and the subsequent subsequent version 45 b encompasses two Selfoc lenses 48 , anchored and holds. Furthermore, self-centering devices 44 are formed in the coupling direction between the socket 45 a and the socket 45 b, for example in the form of an embossed ring 53 which tapers conically in cross section in the coupling direction, with a corresponding annular recess on the counterpart, that is to say on the socket 45 a 55 can be introduced. This consisting of a projecting ring and a ring recess in the second fitting part self-centering device 44 is formed around the multimode fiber 46 or the selfoc lenses 48 around. However, different self-centering devices 44 can be provided.

In addition, in the area of self-centering 44 , ie the ring 53 on the mount 45 b and in the area of the ring recess 55 on the mount 45 a, various ne Selfoc lenses with a collimating and focusing design can also be formed.

The embodiment of FIG. 3a corresponds to that of FIG. 3, but deviating from Fig. 3, however, the Fas solution 45 a with the socket 45 d is formed as a uniform integrating socket 45 a, which with the socket 45 b using self-centering 44 are connected. The socket 45 c is thus also integrated in the socket 45 b in this embodiment.

In the embodiment according to FIG. 4 is a exzen-symmetrical arrangement of the fibers is shown without taper.

The central axis 56 of the core glass 47 of the sen-sided single-mode optical waveguide 3 with Seitenver set X to the central axis 57 of the core glass 47 of the optical fiber 7 following in the transmission direction is arranged in a step index fiber or preferably in a gradient index fiber or generally a multimode fiber. In this exemplary embodiment, the interface 59 is of flat design.

In the exemplary embodiment according to FIG. 5, in deviation from FIG. 4, a taper 61 is formed at least on the exit side of the single-mode optical waveguide 3 . But also in this embodiment, the two central axes 56 , 57 of the two optical fibers 3 , 7 are arranged eccentrically to each other.

Referring to FIG. 6 and 6a there is shown an eccentric arrangement, the construction in principle corresponds to that of FIG. 3 and 3a, respectively.

The frames are shown in FIG. 6 45 a, 45 b, 45 c and 45 d or FIG. 6a only 45 a and 45 b are used to ensure a pre-defined association with one another.

Here, too, the lateral offset X between the central axes 56 and 57 of the single-mode fiber and the multimode fiber represents the measure of the eccentric coupling.

Such an eccentric coupling of the monomode fiber into a multimode fiber (with or without additionally integrated multimode fiber 46 or integrated Selfoc lenses 48 ) is not only very inexpensive to manufacture, but also offers, in particular using correspondingly manufactured frames 45 a, 45 b, 45 c, 45 d or only 45 a and 45 b, due to a high precision mechanical processing of the eccentricity and the diameter, a high reproducibility and aging resistance. An eccentric offset X of ± 0.5 µm can be achieved.

Such a design of a mode coupler / mode mixer leads to the excitation of certain higher modes, and it will low signal level fluctuations with minimal attenuation achieved by the fashion mixer itself.

In order to select certain modes depending on the application and needs can already produce different ones from the manufacturer Versions for creating different eccentrici X values for the initiation of the coming from the monomode fiber be prepared for the light in the multimode fiber. Consequently can therefore many mode mix ratios through the Use of different dimensions of the eccentricities on the Enable and keep the single-mode fiber side ready.

A practical example of implementation of the invention is finally given with reference to FIGS. 7 and 7a and 7b.

In the exemplary embodiment according to FIG. 7, the monomode optical waveguide 3 is firmly connected on the laser side, that is to say on the transmitter side, to a plug 65 as an end plug. On the input side of the subsequent multimode optical waveguide 7 , an optical waveguide 67 is also provided, which in principle can be of the same design (at least from its outer dimensions and its shapes, such as the connector 65 ).

Both plugs 65 and 67 can finally be mechanically firmly connected via an interposed coupling 69 , with the design of the plugs 65 , 67 and the coupling 69 producing a clear, ie mechanically clearly reproducible, fixed connection for producing a continuous optical fiber strand, in which, however, an exact desired eccentricity can be reproduced in accordance with the plug 65 used with the integrated axial offset X in a predetermined size.

By using different plugs that correspond according to the different eccentricity values designed in different colors or in any other way can be labeled, according to the ge different transfer conditions tricities can also be easily produced on site.

The eccentric assignment of the optical waveguide cables in the middle of the coupling 69 is shown on the basis of the enlarged illustration according to FIGS. 7a and 7b.

In Fig. 8, an application for the above-explained fiber optic connections is now shown, namely for the application of two modified repeaters.

The repeater shown in FIG. 8 comprises two modified repeaters with a fiber optic connection between the two, namely a repeater 75 which is antenna-bound at the base station and a repeater 79 which is optically connected (usually channel-selective) via the fiber optic connection 77 on the transmission path 17 .

The repeater 75 bound to the base station is generally connected to its input 81 with a base station antenna 83 , although in principle a transmission cable can also be connected here.

As a rule, a cable (coax cable) leads from the antenna to a weatherproof housing of the base station repeater 75 . The electrical signals are then via a duplex soft 87 , that is, to the upper band (downlink), the band filter 85 includes a preamplifier 89 and then subsequently an optical transmitter 91 , which converts the electrical signal into an optically amplified one (here too usually uses an LED or laser). An integrated mode coupler / mode mixer 13 in or outside the optical transmitter according to one of the exemplary embodiments shown in FIGS . 1 to 7 is arranged downstream of the optical transmitter 91 . Before the transmission path 17 , the optical fiber cable is usually inserted into a splice box and guided via an optical fiber cable in the form of an earth cable to a receiver-side next splice box. The fiber optic cable from the splice box leads an optically connected, e.g. B. channel-selective repeater 79 , which in turn comprises an optical receiver for converting the opti's into electrical signals 93 ', a downstream amplifier 95 ' and a further duplexer 87 'with a bandpass filter 85 ' in the upper band, via which the electrical signals then over downstream cable (coax cable) transmits from the weatherproof housing of the optically connected repeater 79 to an antenna 83 ', from which the signals can be transmitted to a mobile station, for example a car.

The transmission path of the radio signals, especially telephone Radio signals from a mobile station (for example Car) to the base station takes place in reverse order in the so-called subband (in the so-called uplink) in reverse, what the corresponding modules are intended for.

In summary it can be said that at this embodiment of an antenna-based (or wired) repeater to the base station with an optical connection unit to a fiber optic cable Go splice box. Earth cables run from there to the next Splice box. From this go fiber optic cables an optically connected repeater that receives the Signals then to the mobile station of a car, for example transmits, with the reverse transmission path corresponding accordingly in a so-called subband (uplink).  

Such repeaters with a fiber optic connection between two modified repeaters it is possible to send range of C networks, GSM900 systems (D network) and GSM1800 system (DCS network or E network) to expand and To fill reception gaps caused by buildings, tunnels or topographic locations (e.g. shadowing) are necessary.

Claims (14)

1. Optical transmission system for transmitting signals via optical waveguides ( 3 , 7 ), in which light is introduced into a monomode fiber ( 3 ) on the input side via an LED or a laser ( 1 ), the transmission path ( 17 ) being through a multimode fiber ( 7 ) is formed, characterized by the following features

• - Before the transmission link ( 17 ), a transition from a single mode fiber ( 3 ) to a multimode fiber ( 7 ) is provided,
• - The light wave transmission is based on an analog data transmission, and
• - At the transition from the single mode to the multimode fiber ( 3 , 7 ) or subsequently, a mode coupler or mixer ( 13 ) for reducing dispersions, in particular the mode dispersion, is provided in front of the transmission link ( 17 ).

2. Optical transmission system according to claim 1, characterized in that the receiver side in the transmission direction ( 9 ) after the transmission path ( 17 ) filters ( 85 , 85 ') are provided. 3. Optical transmission system according to claim 1 or 2, characterized in that the optical system for over analog data in the mobile radio frequency range sets is. 4. Optical transmission system according to one of claims 1 to 3, characterized in that the mode coupler or -mi shear ( 13 ) means for generating a multiple curved course for the optical waveguide ( 7 ) for generating stress on the optical waveguide ( 7 ) Excitation of certain modes and thus to reduce the dispersion effects. 5. Optical transmission system according to one of claims 1 to 4, characterized in that the mode coupler or -mi shear ( 13 ) is constructed such that the central longitudinal axis ( 56 ) of the single-mode fiber ( 3 ) at the transition to the multimode fa ser ( 7 ) is arranged eccentrically, ie with a lateral offset to the central longitudinal axis ( 57 ) of the multimode fiber ( 7 ). 6. Optical transmission system according to claim 5, characterized in that a taper ( 61 ) is provided on the front exit side of the monomode fiber. 7. Optical transmission system according to one of claims 4 to 6, characterized in that at the transition area from the monomode to the multimode fiber ( 3 , 7 ) sockets ( 45 a, 45 b, 45 c, 45 d; 45 a, 45 b ) are provided with a self-centering device ( 44 ) which are formed from mutually interlocking projections / recesses ( 53 , 55 ). 8. Optical transmission system according to claim 7, characterized in that two sockets ( 45 a, 45 b) are provided with a self-centering ( 44 ) between them in the coupling direction, the one socket ( 45 a) in the transmission direction a single-mode fiber ( 3 ) and a following multimode fiber ( 46 ) with a predefined length and the adjoining it in the transmission direction two th socket ( 45 b) at least the multimode optical waveguide ( 7 ) and holds in a defined position. 9. Optical transmission system according to claim 8, characterized in that the second frame ( 45 b) further comprises two Selfoc lenses ( 48 ) and holds in a defined position. 10. Optical transmission system according to claim 8, characterized in that at least four sockets ( 45 a, 45 b, 45 c, 45 d) are provided, the socket ( 45 d) comprising the end of the single-mode fiber ( 3 ) and in a defined Holds position and that the subsequent version ( 45 a) holds a multimode fiber ( 46 ) in a predefined length in a defined position and that a version ( 45 b) following in the direction of transmission comprises two Selfoc lenses ( 48 ) and holds them in a defined position , wherein the version ( 45 b) with the previous version ( 45 a) on the self-centering device ( 44 ) to each other in a defined position and that in the transmission direction from the output side to the Selfoc lenses ( 48 ) a version ( 45 c) defined position of the outgoing multimode Lichtwel lenleiters ( 7 ) is provided. 11. Optical transmission system according to one of claims 4 to 10, characterized in that two mutually coordinated plugs ( 65 , 67 ) are provided at the transition area from the monomode to the multimode fiber ( 3 , 7 ), where through the monomode fiber ( 3 ) are held in relation to the multimode fiber ( 7 ) at the transition and coupling area in a predefined eccentric position. 12. Optical transmission system according to one of claims 4 to 11, characterized in that for generating ver different mode mixing ratios by realizing un different values for the lateral or eccentric offset (X) of the monomode fiber ( 3 ) compared to the multimode fiber ( 7 ) Different plugs ( 65 , 67 ) with differently generated eccentric displacements are provided. 13. Optical transmission system according to one of claims 4 to 12, characterized in that a connector ( 65 , 67 ) is provided in the transition and coupling area at the ends of the monomode and the multimode fiber ( 3 , 7 ) to be coupled Can be releasably connected to one another by means of a coupling device ( 69 ) which is firmly mechanically connected to one another. 14. Optical transmission system according to one of claims 1 to 13, characterized in that this part of a modified repeater with an antenna-based or line-bound repeater ( 75 ) at a base station and an optical link via fiber optic connections ( 77 ) to a transmission path ( 17 ) , preferably channel-selective repeater ( 79 ).