WO2008119625A1

WO2008119625A1 - Method for determining the mode group mixture matrix of a multimode optical fiber, and optical transmission systems

Info

Publication number: WO2008119625A1
Application number: PCT/EP2008/052894
Authority: WO
Inventors: Sebastian Randel; Harald Rohde
Original assignee: Siemens Aktiengesellschaft
Priority date: 2007-03-29
Filing date: 2008-03-12
Publication date: 2008-10-09
Also published as: DE102007015225A1

Abstract

The invention relates to a method for determining a mode group mixture matrix, which describes a mixture of mode groups of a mode group multiplexed light signal in a multimodal optical fiber in which, for each mode group, a single frequency pilot signal is transmitted. In addition, the invention relates to a method in which, for each mode group, a monochromatic pilot signal is transmitted. In addition, the invention relates to optical transmission systems suitable therefor.

Description

description

Method for determining a mode group mixture matrix of a multimode optical waveguide and optical transmission systems

The invention is in the technical field of optical transmission systems and relates to methods of detecting a mode group mixture matrix describing mode mixing in a multimodal optical fiber. Furthermore, it relates to optical transmission systems which are suitable for carrying out the method.

In optical transmission systems, so-called mode group division multiplexing is frequently used as the transmission method. This is an optical transmission method in which multiple optical mode groups of a multimodal optical fiber (transmission fiber) are used to transmit information. The various groups of modes are coupled into the transmission fiber at different angles to the fiber core at the same time. The purpose of mode group multiplexing is to increase the transmission capacity, whereby the amount of data transferable in the same optical waveguide multiplies according to the number of simultaneously used mode groups. At the end of the transmission path, the optical mode groups are selectively detected and the transmitted data recovered.

The known method of mode group multiplexing will be explained in more detail with reference to FIG. FIG. 4 schematically shows a multimodal optical waveguide 102 in the form of a stepped fiber, which comprises a fiber core 108 and a fiber cladding surrounding the fiber core, which is not shown in greater detail in FIG. 4. The fiber core

108 has a larger optical refractive index than the fiber cladding. At an end face 109 of the optical waveguide 102, two different models are shown by way of example. dengruppen 103, 104 coupled into the optical waveguide 102.

A first mode group 103 is coupled in parallel to the fiber core and propagates without reflection within the

Optical fiber 102 continues. A second mode group 104 is coupled in at an angle θ _in to the first mode group 103 or fiber core and is reflected several times (totally) within the optical waveguide 102 on the fiber cladding. Each mode group 103, 104 generally comprises a plurality of different, simultaneously excited modes due to the inaccuracies in the coupling (for example angular inaccuracy) that can not be avoided in practice.

At a front end face 110 of the optical waveguide 102, which faces the end face 109 for coupling the mode groups, the two mode groups 103, 104 emerge from the optical waveguide 102, wherein the first mode group 103 exits parallel to the fiber core and forms a circular spot 105, while the second mode group 104 emerges at an angle θ _out to the first mode group 103 and forms a light spot 106 annularly surrounding the spot 106. The two light spots 105, 106 are spatially separated from each other by a non-illuminated area 107, so that the two mode groups 103, 104 can be evaluated individually.

While in a straight (not curved) optical waveguide the coupled mode groups can be transmitted with virtually no interference, in a curved optical waveguide the transmitted mode groups are weakly coupled, resulting in a mixing (coupling) of the mode groups. In FIG. 4, this mode group mixture would lead to a "smearing" of the light spots 105, 106. The light exchange due to mode group mixing is usually so small that at the end of the transmission path the transmitted information of all groups of modes can be reconstructed using appropriate signal processing techniques.

In order to reconstruct the mode groups, the influence of the mode group mixture on the signal transmission is computed:

Let S ₁₁₁₁ S _n n be electrical signals which, after electro-optical conversion, are simultaneously multiplexed in a multimodal optical waveguide as n different groups of modes in the multiplexing process. Then the m electrical received signals, which are obtained after transmission of the n mode groups via the optical waveguide and subsequent optoelectronic conversion, given by the matrix equation E = H * S, where E is the vector of the received signals, S the vector of the input signals and H a so-called Modengruppenmixing matrix is.

With n electrical input signals S ₁ ... S _n and m electrical received signals E ₁₁₁₁ E _1n , H is an mxn matrix, so that the corresponding matrix equation is:

If the received signals E ₁₁₁₁ E _{1n are} multiplied by the inverse mode group mixing matrix H ^"1 , then ideally the transmitted signals S ₁₁₁₁ S _{n can be} reproduced.

The problem here is the determination of the mode group mixture matrix H, which for each multimodal

Optical fiber is different, since it depends on the specific conditions (such as fiber curvatures). In addition, the optical fibers are also temporarily exposed during operation. ren fluctuations, such as fiber vibrations, fiber contacts or temperature fluctuations.

So far, the mode group mixture matrix was H H _{1 ^ 1} ... H _m _ established by iterative tive trying out the matrix coefficients _n, where the matrix coefficients reconstructed in dependence of the signal quality from the received signals E ₁₁₁₁ E _1n input signals S ₁₁₁₁ S _n, with be compared to the actual input signals S ₁₁₁₁ S _n .

Fig. 5 schematically illustrates the structure of an optical transmission system for detecting the mode group mixture matrix H. The optical transmission system, generally designated by reference numeral 101, comprises a multimode optical fiber 102 (transmission fiber)

Transmission of a plurality of multiplexed light modes, as already explained in connection with FIG. 4.

The optical waveguide 102 is coupled to a multiplexer 111 at its one end face and to a demultiplexer 115 at its other end face. The multiplexer 111 is provided with n multiplexer signal inputs 113 at which the electrical input signals S ₁₁₁₁ S _{n are} supplied. The multiplexer 111 further comprises a plurality n of electro-optical converters 112 which are each assigned to the multiplexer signal inputs 113 and serve to convert the electrical signals S ₁₁₁₁ S _n into corresponding optical signals. As electro-optical converters 112, for example, single-mode semiconductor lasers can be used.

The optical signals generated by the electro-optical converters 112 are supplied to a coupling-in device 114, which couples the various modes or groups of modes into the optical waveguide 102.

The coupled mode groups are transmitted via the optical waveguide 102 and coupled out of the optical waveguide 102 by the demultiplexer 115. The demultiplexer 115 is provided for this purpose with a decoupling device 116, which is followed by a plurality m optoelectronic converter 117. In the optoelectronic converters 117, which are embodied, for example, as photodiodes, the decoupled mode groups are respectively converted into corresponding electrical signals E ₁₁₁₁ E _1n , which are fed to demultiplexer signal outputs 118 of the demultiplexer 115. The natural numbers n, m may be the same or different from each other.

The electrical received signals E ₁₁₁₁ E _1n are then fed to a signal processing device 119. In the signal processing device 119, the electrical signals E ₁₁₁₁ E _{1n are processed} after analog-to-digital conversion, whereby a mode group mixing matrix H is created. At the signal processing device signal outputs 120, output signals S ₁₁₁₁ S _1n generated by applying the inverse mode group mixture matrix to the received signals are provided: S = H ^"1 * E.

The determination of the matrix coefficients of the mode group mixing matrix H so far by iteratively Try matrix of coefficient values to the generated output signals S ₁₁₁₁ S _1n the original input signals S ₁₁₁₁ S _n within the framework of a desired tolerance range correspond. For example, the input signals S ₁₁₁₁ S _{n have been} stored in the signal processing device 119 or generated by the signal processing device 119 for this purpose.

However, since modulated data is transmitted on all signals S ₁₁₁₁ S _n , unambiguous discrimination and thus direct reconstruction of the signals S ₁₁₁₁ S _n by applying the inverted mode group mixture matrix H is not possible. In addition, the creation of the mode group mixture matrix H is time consuming for a higher number of coupled-in mode groups, so that an adaptation of the mode group mixture matrix H at changed transmission conditions in practice is difficult to carry out.

In contrast, the object of the present invention is to provide a method for determining the mode group mixture matrix, which describes a mode group mixture when transmitting a plurality of multiplexed mode groups through a multimodal optical transmission fiber.

In order to achieve the object, a first method for determining a mode group mixture matrix, which describes a mixture of mode groups of a mode group-multiplexed light signal in a multimodal optical waveguide, is shown in accordance with the invention.

The first method comprises the steps:

Generating a plurality of data-modulated light signals on the basis of a plurality of electrical input signals, wherein the electrical input signals each comprise at least one monofrequent electrical pilot signal, wherein the pilot signals associated with the different input signals have mutually different frequencies,

Coupling the plurality of light signals in the form of a modulo-multiplexed light signal into the optical waveguide,

Mode group demultiplexing of the transmitted light signal for generating mode group-specific light signals and optoelectronic conversion of the mode group-specific light signals for generating a plurality of mode group-specific electrical reception signals,

Detecting signal intensities of the pilot signals in each of the receive electrical signals and calculating the matrix coefficients of the mode group mix matrix from the signal intensities of the pilot signals.

Hereby, the mode group mix matrix can be created with high accuracy. Because in general due to the in the Practice unavoidable inaccuracies in the coupling of the light signals a plurality of modes are excited, here and in the following the (more precise) term "mode group" is used instead of mode. Nevertheless, a group of modes within the meaning of the invention may also contain only a single mode.

In an advantageous embodiment of the first method according to the invention, the signal intensities of the pilot signals are determined by means of Fourier transformation of the mode group-specific electrical received signals. This shows the advantage of a simple implementation.

In an alternative advantageous embodiment of the method according to the invention, the signal intensities of the pilot signals are determined by means of electrical frequency filtering of the mode group-specific electrical received signals and subsequent signal intensity measurement of the filtered received signals. This makes it very easy to reconstruct the electrical input signals.

The invention further extends to a first optical transmission system which is suitable for carrying out the first method described above. It comprises: a multimodal optical waveguide, - a multiplexer connected to the multimodal optical waveguide for generating data-modulated light signals by means of electro-optical transducers based on electrical input signals and for coupling a mode group-multiplexed light signal into the optical waveguide, - a demultiplexer connected to the multimodal optical waveguide for decoupling mode groups demultiplexed light signals from the optical waveguide and for generating mode group-specific electrical output signals, an electrically coupled to the demultiplexer signal processing means for reconstructing the multiplexer supplied electrical input signals from the mode group specific electrical output signals of the demultiplexer. The first optical transmission system is essentially characterized in that a transducer signal input of each electro-optical converter is electrically coupled, for example via an adder, to an oscillator for generating monofrequency pilot signals. Here, the oscillators are set up so that the frequencies of different pilot signals are different from each other. As a result, the electrical input signals can be reconstructed well.

In an advantageous embodiment of the first optical transmission system according to the invention, each demultiplexer signal output of the demultiplexer is electrically connected to a frequency filter bank, each frequency filter bank comprising frequency filters set to the frequencies of the pilot signals. In this case, each frequency filter of the frequency filter bank is electrically connected to a signal intensity detection device for detecting the signal intensity of the pilot signals. This achieves an improvement in the reconstruction of the electrical input signals.

The invention further extends to a machine-readable program code for a signal processing device of such a first optical transmission system, which contains control commands that cause the signal processing device to carry out a first method as described above.

Furthermore, the invention extends to an electronic signal processing device of such a first optical transmission system, which is provided with such a machine-readable program code.

In order to achieve the object, a second method for determining a mode group mixture matrix, which describes a mixture of mode groups of a mode group-multiplexed light signal in a multimodal optical waveguide, is furthermore shown according to the invention. The method comprises the steps:

Generating a plurality of data-modulated light signals based on a plurality of data-modulated electrical input signals,

Generating monochromatic optical pilot signals having different wavelengths and adding a pilot signal to each of the data-modulated light signals for generating sum-light signals, injecting the sum-light signals in the form of a mode-group-multiplexed light signal into the optical waveguide,

Mode group demultiplexing of the transmitted light signal to generate mode group specific light signals,

Optically filtering the pilot signals from each of the mode-group specific light signals, detecting the respective ones

Signal intensities of the pilot signals and calculating the matrix coefficients of the mode group mixture matrix from the signal intensities of the pilot signals.

Hereby, the mode group mix matrix can be created with high accuracy.

The invention further extends to a second optical transmission system which is suitable for carrying out the second method described above. It comprises: a multimodal optical waveguide, a multiplexer connected to the multimodal optical waveguide for generating modulated light signals by means of electro-optical transducers on the basis of electrical input signals and for coupling a mode group multiplexed

Light signal in the optical waveguide by means of a coupling device, a demultiplexer connected to the multimodal optical waveguide for coupling mode group-demultiplexed light signals from the optical waveguide by means of a decoupling device and for generating mode group-specific electrical lektrischer output signals, a signal processing device for reconstructing the electrical input signals supplied to the multiplexer from the mode group-specific output signals of the demultiplexer.

The second optical transmission system is essentially distinguished by the fact that each coupling-in signal input of the coupling device of the multiplexer is optically coupled to a light source for generating a monochromatic optical pilot signal, and that each coupling-out signal output of the coupling device of the demultiplexer is optically coupled to an optical filter bank is. Here, each optical filter bank comprises optical filters set to the wavelengths of the pilot signals. In addition, each optical filter of the optical filter bank is optically coupled to a signal intensity detector for detecting the signal intensity of the monochromatic pilot signals. As a result, the electrical input signals can be reconstructed well.

The invention further extends to a machine-readable program code for a signal processing device of such a second optical transmission system, which contains control commands that cause the signal processing device to carry out a second method as described above.

Furthermore, the invention extends to an electronic signal processing device of such a second optical transmission system, which is provided with such a machine-readable program code.

The invention will now be explained in more detail by means of exemplary embodiments, reference being made to the attached drawings. The same or equivalent components are designated in the figures with the same reference numerals. Show it: 1 shows schematically an embodiment of the first optical transmission system according to the invention;

FIG. 2 schematically shows a further embodiment of the first optical transmission system according to the invention; FIG.

3 shows schematically an embodiment of the second optical transmission system according to the invention;

FIG. 4 is a schematic illustration for illustrating mode group multiplexing known in the prior art; FIG.

Fig. 5 shows schematically an optical transmission system known in the prior art.

In Fig. 1, a first embodiment of the first optical transmission system according to the invention is shown in a schematic manner.

The optical transmission system 1 comprises a multimodal optical waveguide 2 (transmission fiber) for data transmission, which may be, for example, a step or gradient fiber of, for example, glass or a polymer material. The optical waveguide 2 is suitable for transmitting a plurality of optical modes or groups of modes.

At its one end face, the optical waveguide 2 is optically coupled to a multiplexer 3 and to a demultiplexer 12 at its other end face.

The multiplexer 3 is provided with a plurality n multiplexer signal inputs 4, through which a plurality of electrical signals S ₁₁₁₁ S _n can be supplied, each of which according to an information to be transmitted (data) data modulated (for example, frequency, amplitude or phase modulated). The multiplexer signal inputs 4 are each electrically coupled to e / o converter signal inputs 29 of electro-optical converters 5, for example single-mode semiconductor lasers, through which the inputs to the multiplexer signal inputs 4 of the multiplexer 3 electrical signals S ₁₁₁₁ S _n be converted into correspondingly data-modulated optical signals.

In the multiplexer 3, an adder 8 is connected upstream of each electro-optical converter 5. For this purpose, each adder 8 is electrically coupled to the associated multiplexer signal input 4 of the multiplexer 3, the e / o converter signal input 29 of the associated electro-optical converter 5 and an oscillator 9 for generating a monofrequency electrical signal of selectable oscillation frequency. Each adder 8 adds the data-modulated electrical signal supplied to the multiplexer signal input 4 of the multiplexer 3 to a monofrequency electrical signal generated by the oscillator 9, which is then supplied as an electrical sum signal to the electro-optical converter 5 electrically coupled to the adder 8.

The optical signals generated by the electro-optical converters 5 are provided at respective e / o converter signal outputs 6 and fed via an optical connection Einkoppeleinrichtung signal inputs 30 of a coupling device 7, which the various optical signals in mode group-multiplexed form in the optical waveguide coupled.

The exact structure of a coupling device 7 for coupling multiplexed optical signals in the optical waveguide 2 is not essential to the understanding of the invention and otherwise known to the expert, so that it need not be explained here. The multiplexer 3 is used for generating and multiplexing coupling of optical signals in the optical waveguide 2, which are based on sum signals resulting from the electrical input signals S ₁₁₁₁ S _n and the monofrequency electrical signals generated by the oscillators 8.

The coupled via the coupling device 7 in the optical waveguide 2 mode groups are transmitted via the optical waveguide 2 and decoupled via the demultiplexer 12 from the light waveguide 2 and converted into corresponding electrical signals.

The demultiplexer 12 is provided for this purpose with a decoupling device 10 which decouples the transmitted light signal modengruppe specific and provides the respective groups of mode corresponding light signals to m Auskoppeleinrichtung signal outputs 28.

The decoupling signal outputs 28 of the decoupling device 10 are each optically conductively connected to optoelectronic transducers 11. In the optoelectronic converters 11, which may be embodied, for example, as photodiodes, the mode group-specifically coupled-out light signals are each converted into electrical signals E ₁₁₁₁ E _1n , which are connected via electrical connecting lines to m demultiplexers.

Signal outputs 13 of the demultiplexer 12 are provided. The natural numbers n, m may be the same or different from each other.

Subsequently, the m electrical signals E ₁₁₁₁ E _{1n are} supplied to a digital signal processing device 14 via electrical connection lines connected to the demultiplexer signal outputs 13 of the demultiplexer 12. In the signal processing device 14, the analog electrical signals E ₁₁₁₁ E _{1n are} first converted into digital signals by means of respective analog / digital converters. Subsequently, from the electrical signals E ₁₁₁₁ E _1n, by means of an inverted mode group mixture matrix H are applied the matrix equation S = H ^{~ 1} * E reconstructed electrical input signals S ₁₁₁₁ S _1n generated and provided to signal processing device signal outputs 15 of the signal processing device 14.

The transmission of the light signals through the optical waveguide 2 can take place, for example, with a wavelength of 650 nm. Any other wavelength suitable for transmission in optical fiber 2 may be used. The light signals can be modulated for data transmission, for example, with a modulation frequency in the range of 0 to 1 GHz, in particular 0 to 200 MHz. Any other modulation frequency suitable for data transmission can be used. Frequency modulation of the light signal takes place on the basis of the modulation frequencies of the electrical input signals S ₁₁₁₁ S _n in

Multiplexer 3.

For determining a mode group mixing matrix H specific for the optical waveguide 2, which in inverted form (H ^"1 ) for determining the reconstructed input signals

S ₁₁₁₁ S _{1n is used} in the signal processing device 14, each of the multiplexer 3 supplied input signals S ₁₁₁ -S _{n is} a generated by the oscillator 8 monofrequentes pilot signal ("pilot tone") added with relatively small signal amplitude. The frequencies E ₁ ... F _{n of} the pilot tones are different from one another and chosen such that they lie outside the signal bandwidth (modulation frequencies) used for the data transmission of the signals S ₁₁₁₁ S _n used for the data transmission, in order to thereby disturb the data transmission avoid.

If, for example, modulation frequencies in the range from 0 to 1 GHz are used for the modulation of the light signals for data transmission, then frequencies in the range of 3 GHz can be used for the pilot tones, for example. For modulation of the light signals for data transmission, for example, modulation frequencies in the range of zero used up to 200 MHz, for example, frequencies in the range of 1 GHz can be used for the pilot tones. For example, the frequencies of the different pilot tones may differ by 0.1 GHz.

In the signal processing device 14, a (fast) Fourier transformation of the digital electrical signals E ₁₁₁₁ E _1n generated on the basis of the received mode groups is performed. From the Fourier coefficients or the signal intensities of the frequencies assigned to the pilot tones, the matrix coefficients of the mode group mixture matrix H can be calculated in a simple and direct manner. The mode group mixture matrix H generated in this way is applied in inverted form to the electrical signals E ₁₁₁₁ E _{1n in} order to determine the reconstructed input signals S ₁₁₁₁ S _1n .

Fig. 2 shows schematically a further embodiment of the first optical transmission system according to the invention, which represents a variant of the embodiment illustrated in Fig. 1. In order to avoid unnecessary repetition, only the differences from the embodiment shown in FIG. 1 are explained, and otherwise reference is made in full to the statements made with reference to FIG. 1.

In the embodiment of the optical transmission system according to the invention shown in FIG. 2, each demultiplexer signal output 13 of the demultiplexer 12 associated with a mode group is electrically conductively connected to an electrical filter bank 17 via an electrical coupler 16. Each filter bank 17 comprises a plurality m of electric filters 19. The electrical filters 19 of each filter bank 17 are set to be transparent only to the monotone frequencies of the pilot tones and thus to filter the various pilot tones. Furthermore, each filter 19 of each filter bank 17 is followed by a power measuring device 20 of a power measuring bench 18, which is connected for each the received signals E ₁₁₁₁ E _{1n determines} the signal intensity of the associated pilot tone. From the amplitudes of the pilot tones, the matrix coefficients of the mode group mixture matrix H can be easily and directly calculated. The group mode mixing matrix thus generated H ₁₁₁₁ E _1n applied in inverted form to the electrical signals E, to calculate the reconstructed input signals S ₁₁₁₁ S _1n.

In Fig. 3, an embodiment of the second optical transmission system according to the invention is shown in a schematic manner.

The transmission system 1 comprises a multimodal optical waveguide 2 (transmission fiber) for data transmission, which may be, for example, a stepped or gradient fiber of, for example, glass or a polymer material. The optical waveguide 2 is suitable for transmitting a plurality of optical modes or groups of optical modes. The optical waveguide 2 is connected to a multiplexer 3 at its one end face and to a demultiplexer 12 at its other end face.

The multiplexer 3 is provided with a plurality n multiplexer signal inputs 4, through which a plurality of electrical signals S ₁₁₁₁ S _n can be supplied, which are each data-modulated according to an information to be transmitted. The multiplexer signal inputs 4 are each electrically conductive with e / o converter signal inputs 29 of electro-optical converters 5, for example single-mode converters.

Semiconductor laser connected by which the signals supplied to the multiplexer x 4 signal inputs S ₁₁₁₁ S _{n are converted} into correspondingly modulated optical signals.

The optical generated by the electro-optical converters 5

Signals are then fed via an optical connection to a coupling-in device 7, which detects the various NEN modes or groups of modes coupled in a multiplexed form in the optical waveguide 2.

In the multiplexer 3, coupling device signal inputs 30 of the coupling device 7 are optically coupled via optical couplers 26 to a light source (eg laser, photodiode) for generating a monochromatic optical signal. In addition, each optical coupler 26 is optically coupled to an e / o converter signal output 6 of the electro-optical converter 5 belonging to the coupling-in signal input 30 of the coupling device 7. Each optical coupler 26 adds the optical signal supplied by the electro-optical converter 5 to a monochromatic optical signal generated by the light source 27, which is then supplied to the coupling device 7 as an optical sum signal. The coupling device 7 couples the plurality of optical sum signals in mode group-multiplexed form into the optical waveguide 2.

The coupled via the coupling device 7 in a multiplexed form light signal is transmitted via the optical waveguide 2 and decoupled via the demultiplexer 12 from the optical waveguide 2 mode groups-demultiplexed and converted into corresponding electrical signals. The demultiplexer 12 is provided for this purpose with a decoupling device 10, which provides the transmitted light signal modengruppe specific to Auskoppeleinrichtung signal outputs 28. The decoupling signal outputs 28 of the decoupling device are each optically conductively connected to optoelectronic transducers 11. In the optoelectronic converters 11, which may be embodied, for example, as photodiodes, the decoupled light signals are modenegroup-specifically converted into corresponding electrical signals E ₁₁₁₁ E _1n , which are provided via electrical connection lines to m demultiplexer signal outputs 13 of the demultiplexer 12. The natural numbers n, m may be the same or different from each other. For determining a mode group mixing matrix which is specific for the optical waveguide 2 and which is used in inverted form for determining the reconstructed input signals S ₁₁₁₁ S _1n in the

Signal evaluation device 14 is used, each of the optical signals generated from the electrical input signals S ₁₁₁₁ S _n in the electro-optical converters 5 added a generated by the light source 27 monochromatic pilot signal. The wavelengths A ₁ ... A _{n of} the pilot signals are different from one another and chosen so that they are different from the wavelength (s) used for data transmission, in order thus to avoid disturbance of the data transmission.

If, for example, a wavelength of 650 nm is used for the data transmission, then the pilot signals can have wavelengths in the range from 660 nm to 700 nm, for example. The wavelengths of the various pilot signals may differ, for example, by 5 nm from each other.

In the exemplary embodiment of the optical transmission system according to the invention shown in FIG. 3, each decoupling device signal output 28 of the decoupling device 12 which is optically conductively connected to an optoelectronic converter 11 is optically conductively connected via an optical coupler 21 to an optical filter bank 22. Each optical filter bank 22 includes a plurality of m optical filters 24. The optical filters 24 of each optical filter bank 22 are set to be transmissive only to the wavelengths A ₁ ... A _{n of} the pilot signals, thus filtering the pilot wavelengths. Furthermore, each optical filter 24 of each optical filter bank 22 is followed by a photodiode 25 of a photodiode bank 23, which determines the amplitude (signal intensity) for each pilot signal.

From the relative signal intensities of the pilot signals, the matrix coefficients of the mode group mixture matrix can be easily calculated. Subsequently, in the Signal processing device 14 from the electrical signals E ₁₁₁₁ E _1n based on the inverted Modengruppenmischungs- matrix H generates the reconstructed electrical input signals S ₁ ... S _m : S = H ^{~ 1} * E.

The illustrated methods according to the invention enable a robust mode group multiplex transmission over a multimode fiber, which can be adapted quickly and easily to changed transmission conditions, as occur, for example, by contact or fiber vibrations.

Claims

claims

A method of determining a mode group mixture matrix (H) describing a mixture of mode groups of a mode group multiplexed light signal in a multimodal optical fiber (2), comprising the steps of: generating a plurality of data modulated light signals based on a plurality of electrical input signals (S ₁₁₁₁ S _n ), the electrical input signals each comprising at least one monofrequency electrical pilot signal, the pilot signals associated with the input signals having mutually different frequencies,

Coupling the plurality of data-modulated light signals in the form of a mode-group-multiplexed light signal into the optical waveguide (2),

Mode group demultiplexing of the transmitted light signal for generating mode-group-specific light signals and optoelectronic conversion of the mode-group-specific light signals for generating a plurality of mode-group-specific electrical reception signals (E ₁₁₁₁ E _1n ),

Detecting signal intensities of the pilot signals in each of the received electrical signals and calculating the matrix coefficients of the mode group mixture matrix (H) from the signal intensities of the pilot signals.

2. Method according to claim 1, characterized in that the signal intensities of the pilot signals are determined by means of Fourier transform of the mode group-specific electrical received signals (E ₁₁₁₁ E _1n ).

3. The method according to any one of claims 1 to 2, characterized in that the signal intensities of the pilot signals by means of electrical frequency filtering of the modengruppenspei- fischen electrical received signals (E ₁₁₁₁ E _1n ) and subsequently Bender signal intensity measurement of the filtered received signals are determined.

4. A method for determining a mode group mixture matrix (H) which describes a mixture of mode groups of a mode group multiplexed light signal in a multimodal optical waveguide (2) comprising the steps of: generating a plurality of data modulated light signals based on a plurality of data modulated ones electrical input signals (S ₁₁₁₁ S _n ),

Generating monochromatic optical pilot signals of different wavelengths and adding a pilot signal to each of the data-modulated light signals to generate sum-light signals,

Coupling the sum light signals in the form of a mode-group-multiplexed light signal into the optical waveguide (2), - mode group demultiplexing of the transmitted light signal to generate mode-group-specific light signals,

Optically filtering the pilot signals from each of the mode group specific light signals, detecting the respective signal intensities of the pilot signals, and calculating the matrix coefficients of the mode group mixture matrix (H) from the signal intensities of the pilot signals.

5. An optical transmission system which comprises: a multimodal optical waveguide (2), a multiplexer (3) connected to the multimodal optical waveguide (2) for generating data-modulated light signals by means of electro-optical converters (5) based on electrical input signals (S ₁₁₁₁ S _n ) and coupling a mode group-multiplexed light signal in the optical waveguide (2), a demultiplexer (12) connected to the multimodal optical waveguide (2) for coupling mode group demultiplexed light signals from the optical waveguide (2) and generating modenegroup specific electrical Ausgangssigna- Ie (E ₁ . ..E _m ), a signal processing device (14) connected to the demultiplexer for generating reconstructed electrical input signals (S ₁₁₁₁ S _1n ) from the mode group-specific see electrical output signals (E ₁₁₁₁ E _1n ) of the demultiplexer, characterized in that the e / o converter signal input (29) of each electro-optical converter (5) with an oscillator (9) for generating monofrequenter pilot signals electrically coupled is.

6. Optical transmission system according to claim 5, characterized in that each demultiplexer signal output (13) of the demultiplexer (12) is electrically coupled to a frequency filter bank (17), each frequency filter bank (17) being tuned to the frequencies of the pilot signals. 19), and wherein each frequency filter (19) of the frequency filter bank (17) is electrically coupled to a signal intensity detection means (20) for detecting the signal intensity of the pilot signals.

7. Optical transmission system which comprises: a multimodal optical waveguide (2), - a multiplexer (3) connected to the multimodal optical waveguide (2) for generating modulated light signals by means of electro-optical converters (5) based on electrical input signals (S ₁₁₁₁ S _n ) and coupling a mode group-multiplexed light signal in the optical waveguide by means of a coupling device (7), a demultiplexer (12) connected to the multimodal optical waveguide (2) for coupling mode group demultiplexed light signals from the optical waveguide by means of a decoupling device (10) and generating modengruppespecific electrical output signals (E ₁₁₁₁ E _1n ), a signal processing device (14) for generating reconstructed electrical input signals (S ₁₁₁₁ S _1n ) from the mode group specific output signals (E ₁₁₁₁ E _1n ) of the demultiplexer, characterized in that each Einkoppeleinrichtung- signal input (30) of the Einkop peleinrichtung (7) of the multiplexer with a light source (27) for generating a monochromatic optical pilot signal optically conductively connected and in that each decoupler signal output (28) of the decoupling device (10) of the demultiplexer (12) is optically conductively connected to an optical filter bank (22), each optical filter bank (22) having optical filters (24) set to the wavelengths of the pilot signals ), and each optical filter (24) of the optical filter bank (22) is optically conductively connected to a signal intensity detector (25) for detecting the signal intensity of the monochromatic pilot signals.

8. Machine-readable program code for a signal processing device of an optical transmission system according to claim 5, which contains control commands which cause the signal processing device to carry out a method according to one of claims 1 to 3.

9. Machine-readable program code for a signal processing device of an optical transmission system according to claim 7, which contains control commands which cause the signal processing device to carry out a method according to claim 4.

10. Storage medium with a machine-readable program code stored thereon according to one of claims 8 or 9.

11. An electronic signal processing device of an optical transmission system, which is provided with a machine-readable program code according to one of claims 8 or 9.