DE19835681C2 - Optical transmission system - Google Patents

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, there are fiber optic transmission networks on.

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

As is emphasized in particular in the previously published magazine DE-c't Magazin für Computertechnik, issue 13 from June 22, 1998, pages 222 to 223, the light generated, for example, via an LED or a laser and fed into an optical waveguide is distributed over several modes , which, according to radiation theory, means that the light is reflected at the surface different times and therefore covers different distances. This leads to different transit times of the signal (combined with signal distortion), this effect being referred to as 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 due to the refraction at the transition to the cladding glass zigzag through the optical fiber and lay un different ways back. When transferring digital signals this leads to a broadening of the Output impulses compared to the transmission pulse.

With a multimode optical fiber in the gradient index  Profile, the refractive index in the core glass drops 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 waveguide. Although the rays here if the distances are different, this leads however with less different terms, because in lower core 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 with regard to noise, intermodulation or pulse shapes Exception of the damping not, 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 and lead to the undesirable 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 it is possible to use certain ratios at the coupler To generate mode excitation, thereby signal transmission is improved. Here is in digital technology Use of multimode optical fibers also so known "offset launching" known at which signal a single-mode optical waveguide with a Multimode optical fiber is coupled, namely under Use two at the front ends of the light waveguide trained focusing lenses. The Einkopp from the single-mode optical fiber to the multimode Optical fiber is made off-center (offset), where higher modes are excited and the dispersion effects be reduced and thus the signal transmission verbes sert.

In contrast, there are completely different ones in analog technology 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 distortion causes an as 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 monomode fibers laid. On multi Mode fibers can, however, with regard to the above. exporting 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 monomode Fibers to ensure adequate signal transmission ratios guarantee. Otherwise there is an analogue transfer engineering technology out of the question.

From the generic state of the art according to US 5 416 862 is an optical transmission system for over Carrying signals known, which on the input side Single mode fiber and a transition from a single mode fiber on a multimode fiber. At this transition is a corresponding single-mode decoupler is provided.

However, such an optical transmission system is only intended and suitable for digital transmission, such as is executed above.

An optical transmission system for analog signal transmission can be found in the prior publication "Hoss, RJ: Fiber Optic Communications Design Handbook. Englewood Cliffs, New Jersey, Prentice Hall, 1990, ISBN 0-13-308586-4, page 189". Such an analog signal transmission system is used when the cost or complexity of digital coding make digital transmission appear less advantageous. According to this prior publication, only two alternatives can be identified as possible:

• - either there is a digital optical transmission system (according to the preamble of claim 1), then an optical transmission system in the sense of citation ( 2 ) will not have to be interpreted for an analog signal transmission (because the problems of signal transmission are then rather larger than would get smaller), or
• - The optical transmission system is through the analog Signal transmission designed because of the cost and the Complexity of digital coding a digital Transfer in fact as less beneficial let it shine, but only for example only if, for example, single-mode fibers are present - or misplaced - are!

Finally, WO 97/33390 is only one Multimode communication system to see what after if there is an eccentric offset between the coupled Fibers is described.

The object of the present invention is an optical Transmission system for analog data transmission too create, in which also with transfers 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 has to 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. The invention So there are obvious advantages realize that - although the lightwave transmission based on an analog data transmission - the analog one Data transmission to transmit the signals digitally mod takes place.

Because although an increasing mode excitation (e.g. to sturgeon with increasing length of the transmission path) and an exchange of services, as well as constantly changing phases draws between the fashions can be 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 Mode couplers at the entrance of the transmission link one balanced mode distribution also in analog technology allows. The better statistical distribution of the ang excited modes leads to a reduction in fluctuation. With in other words, by using mode couplers both the output level stabilized, as well as the system roughness be improved.

The mode couplers can do this in different ways  be trained.

In a preferred embodiment of the invention for this purpose, the optical fiber mechanically on the input side pressed fiber optic wires that are used to generate a mechanical stress can also be poured onto the fiber can. In a modified preferred embodiment is a fashion coupler integrating 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 following show in detail:

Fig. 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 embodiment modified to Fig. 1a;

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

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

Fig. 3 is a modified to Figures 1 and 2 again tes embodiment using a centering method and using four versions and using Ver using 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 centering method with four frames and using Selfoc lenses corresponding to the position shown in FIG. 3;

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

Fig. 7 shows a further 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 monomode fiber.

In the exemplary embodiment shown, the optical waveguide 3 is wound up several times to form 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.

In the transmission direction 9 , a so-called mode coupler 13 is subsequently arranged, as a result of which a balanced mode distribution, in particular a statistically better distribution of the excited modes while significantly reducing the otherwise occurring fluctuation in the transmission bandwidth, 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 13 can be constructed differently, as is shown only by way of 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 deflecting 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 preferably being 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 13 preferably consists of two halves 29 (essentially along a division plane), in which the deflecting elements 19 lie offset from one another in the direction in which the optical waveguide 7 is laid , in each case in both halves 29 offset from one another. Around the respectively exposed portions of the deflection elements 19 , the optical waveguide 7 is then guided around in a curved manner, recesses 31 being formed or being provided in the opposite half.

After final laying of the optical waveguide 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 signal Lead noise ratio.

In the exemplary embodiment according to FIG. 2, a mode coupler 13 is used, which is provided from one body with multiple meandering tracks 37 . This mode coupler can also 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. At closing, a cover can be applied to the base body 31 comprising the webs 37 and the entire unit can be firmly closed and connected. In general, however, after inserting the Lichtwellenlei age 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 13 is introduced, is guided through it in a multi-curved manner and runs out again at its outlet side 43 .

In the exemplary embodiment according to FIGS. 3 and 6, a mode coupler 13 with the self- adjusting device 44 is used.

This mode coupler 13 is used instead of the splice connection 5 used in the previous figures at the transition from an optical fiber in the form of a single-mode fiber 3 to a subsequent optical fiber 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 switched laser shown in this exemplary embodiment).

For the sake of better representation, the single-mode optical 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 optical 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, anchored and jus tiert in a version there 45 c.

As can also be seen from FIG. 3, two further sockets 45 a and 45 b are provided between the socket 45 d for the single-mode optical waveguide 3 and the socket 45 c for the multimode optical waveguide 7 following in the transmission direction, the socket 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, anchors and holds two Selfoc lenses 48 . 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, ie on the socket 45 a 55 can be introduced. These consist of a projecting ring and an annular recess in the second fitting part 44 is Selbstzentrier existing or formed extending to the multimode fiber 46 at the Selfoc lens 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 according to Fig. 3a corresponds to that shown in FIG. 3, wherein deviating from Fig. 3, however, the Fas solution 45 a is formed with the socket 45 d as a unitary integrated de socket 45 a, b with the socket 45 using the self- 44 are connected.

The socket 45 c is 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 single-sided single-mode optical fiber 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 planar.

In the embodiment shown in Fig. 5 is in contrast to FIG. 4 formed at least on the exit side of the single-mode optical waveguide 3, a taper 61st 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 45a and 45b used in order 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 45a and 45b, 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 fashion coupler leads to Excitation of certain higher modes, and it will be low Signal level fluctuations with minimal attenuation of the mode mixer achieved itself.

In order to select certain modes depending on usage and needs can already produce different ones from the manufacturer Versions for generating different eccentricity Values X to initiate that come 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 there is also an optical waveguide 67 , which in principle can be of the same design (at least from its external dimensions and its shape, 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 wanted different conditions of transmission 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 glass fiber 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 glass fiber connection 77 on the transmission link 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 switch 87 , that is, to a band belonging to the upper band (downlink), the band filter 85, a preamplifier 89 and then subsequently to an optical transmitter 91 which converts the electrical signal into an optically amplified one (this is described in usually uses an LED or laser). An integrated mode coupler 13 in or outside the optical transmitter's according to one of the exemplary embodiments shown in FIGS . 1 to 7 is arranged downstream of the optical transmitter 91 . Before the transmission link 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 out of the splice box te fiber optic cable leads an optically connected NEN, z. B. channel-selective repeater 79 , which in turn comprises an optical receiver for converting the optical 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 are then connected via a downstream cable (Coax cable) 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. From this go optical fiber cables an optically connected repeater that receives the Signals then to the mobile station of a car, for example transmits, where the reverse transmission path corresponds 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 fibers ( 3 , 7 ), with the following features

• a monomode fiber ( 3 ) is provided on the input side, into which light can be introduced on the input side via an LED or a laser ( 1 ),
• - The transmission path ( 17 ) is formed by a multimode fiber ( 7 ),
• - Before the transmission link ( 17 ) a transition from a single mode fiber ( 3 ) to a multimode fiber ( 7 ) is provided,
• - At the transition from the single mode to the multimode fiber ( 3 , 7 ) or subsequently, a mode coupler ( 13 ) for reducing dispersions, in particular the mode dispersion, is provided in front of the transmission link ( 17 ),

characterized by the following further features

• - The light wave transmission is based on an analog data transmission and
• - The analog data transmission is digitally modulated for the transmission of signals.

2. Optical transmission system according to claim 1, characterized in that electrical band filters ( 85 , 85 ') are provided on the receiver side in the transmission direction ( 9 ) after the transmission path ( 17 ). 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 ( 13 ) means for generating a multiple curved course for the optical waveguide ( 7 ) for generating stress on the optical waveguide ( 7 ) to excite certain modes and thus includes to reduce dispersion effects. 5. Optical transmission system according to one of claims 1 to 4, characterized in that the mode coupler ( 13 ) is constructed such that the central longitudinal axis ( 56 ) of the monomode fiber ( 3 ) at the transition to the multimode fiber ( 7 ) eccentrically, ie is arranged 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 / depressions ( 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 second mount ( 45 b) in the direction of transmission comprises at least the multimode optical waveguide ( 7 ) and holds it in a defined position. 9. Optical transmission system according to spoke 8, characterized in that the second version ( 45 b) also includes two Selfoc lenses ( 48 ) and holds this multimode optical waveguide 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 one socket ( 45 d) comprising the end of the single-mode fiber ( 3 ) and this in a position defined holds that the following it, Fas solution (45 a) a multimode fiber (46) keeps in a predefined length in a defined position, and that a subsequent in the transmission direction frame (45 b) two Selfoc lens comprises (48) and this Holds multimode fiber in a defined position, the holder ( 45 b) with the previous holder ( 45 a) being held in a defined position relative to one another via the self-centering device ( 44 ), and that in the direction of transmission on the output side to the Selfoc lenses ( 48 ) Version ( 45 c) is provided for bringing about a defined position of the outgoing multimode optical fiber ( 7 ). 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 to one another. 12. Optical transmission system according to one of claims 4 to 11, characterized in that for generating ver different mode mixing ratios by realizing different values for the lateral or eccentric offset (X) of the single-mode fiber ( 3 ) compared to the multi-mode 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 multimode fibers ( 3 , 7 ) to be coupled, which can be releasably connected to one another via a coupling device ( 69 ) which is firmly mechanically connected to one another. 14. Use of an optical transmission system according to one of claims 1 to 13 for a modified repeater, which has an antenna-based or line-based repeater ( 75 ) at a base station and an optically linked, preferably channel-selective repeater ( 77 ) via glass fiber connections ( 77 ) on a transmission path. 29 ) includes.