WO2005032023A1

WO2005032023A1 - Optical multi-channel demultiplexer comprising an individual optical circuit

Info

Publication number: WO2005032023A1
Application number: PCT/DE2004/002096
Authority: WO
Inventors: Christof BÖRNER; Jörn BERGER
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2003-09-21
Filing date: 2004-09-18
Publication date: 2005-04-07
Also published as: DE10344314A1

Abstract

A known art multi-channel demultiplexer for a data rate of 40 Gbit/s based on an electro-absorbing modulator uses the bidirectionality thereof to simultaneously demultiplex two data channels. Reflection signals thus occurring can lead to influences. The inventive multi-channel demultiplexer (MKD) uses the unidirectional path through the optical circuit (OS, EAM) and distinguishes two data channels (A/B; C/D) by means of the polarisation state thereof. As a result, a double refraction element (DBE) is used to produce two orthogonal polarisation data signals which are to be demultiplexed. Said signals are temporally superimposed in the double refraction element (DBE, HiBi-F) in relation to the data channels (A/B; C/D) which are to be demultiplexed and subsequently synchronised on the circuit window of the optical circuit (OS, EAM). Four data channels (A, B, C, D) can be simultaneously demultiplexed, when both flow directions pass through the optical circuit (OS, EAM) and they are used simultaneously. All four data channels (A, B, C, D) are temporally superimposed and are synchronised on the circuit window. Data clock recovery can be simultaneously achieved according to the differential principle by using four visibly different data signals in the optical circuit (OS, EAM). Several data channels can be correspondingly simultaneously demulitplexed, even with a predetermined maximum data clock rate, by a cascade connection.

Description

applicant

Fraunhofer Society for the Promotion of Applied Research

OPTICAL MULTI-CHANNEL DEMULTIPLEXER WITH A SINGLE OPTICAL SWITCH

description

The invention relates to an optical multi-channel demultiplexer based on a single optical switch for receiving-side, simultaneous deinterleaving of at least two data channels time-nested in the time-division multiplexing in a digital transmission system in the data signal with a predetermined data clock, and to an application thereof.

The OTDM demultiplexer is a central component in optical time division multiplexing (OTDM). It unleashes the data channels combined in time multiplex. Most OTDM demultiplexers implemented so far, however, switch only a single data channel from the multiplexed data stream. Furthermore, these OTDM demultiplexers are usually made up of two units, an optical switch and a clock recovery. The simultaneous demultiplexing of several OTDM channels without clock recovery has so far been achieved primarily through the use of optically nonlinear effects. With the help of linearly chirped control pulses, the time-division multiplex signals are converted into wavelength-division multiplex signals and then separated with optical filters. The effects used for this are four-wave mixing, cross-phase modulation in an interferometer and cross-phase modulation with local chirp compensation. In addition to the separate realization of clock recovery and demultiplexer, there are already some approaches for the simultaneous realization of both components by means of a common electro absorption modulator (EAM) as an optical switch. Publication I by ID Phillips et al .: "Simultaneous demultiplexing and clock recovery using a single electroabsorption modulator in a novel bi-directional configuration" (Optics Communications (150 (1998) pp 101-105) describes a bidirectionally operated demultiplexer from a data signal at 40 Gbit / s to a data channel at 10 Gbit / s, in which one beam direction is used by the EAM for clock recovery and the other beam direction is used for demultiplexing the one data channel, also in publication II of ES: Awad et al .: "All-optical timing extraction with simultaneous Optical demultiplexing using time-dependent loss Saturation in Electro-Absorption Modulator" (Proc. CLEO 2002, paper CPDB9), the method works at 40 Gbit / s and bidirectionally. For the Clock recovery, both irradiation directions are evaluated with the help of a balanced photodetector of the two clock recovery channels. Demultiplexing a single data channel from 160 Gbit / s with alternating polarization to 40 Gbit / s is described in publication III by E. Lach et al .: “Advanced 160 Gbit / s OTDM System based on wavelength transparent 4x40 Gbit / s ETDM transmitters on receivers "(OFC 2002, paper TuA2), whereby the EAM only works as a demultiplexer for the data channel and the clock recovery is implemented electronically. In other concepts, multiple EAMs are used for the simultaneous recovery of the data clock and deinterleaving of a data channel, compare for example the publication IV of J.-L. Auge et al .: "Single Channel 160 GB / s OTDM propagation over 480 km of Standard fiber using a 40 GHz semiconductor mode-locked laser pulse source" (OFC 2002, paper TuA3)). In publication V by V. Kaman et al .: "Simultaneous OTDM Demultiplexing and Detection using an Electroabsorption Modulator" (IEEE Photonics Technology Letters, Vol.12, No.6, June 2000, pp 711-713) is for a single data channel the simultaneous use of an EAM as a demultiplexer and described because of its transparency as a detector for an optoelectric conversion. A polarization controller used here is used to set a single polarization of the data signal at the input of the EAM.

Furthermore, from publication VI by C. Börner et al .: "160 Gbit / s Clock Recovery with Electro-Optical PLL Using a bidirectionally operated Electroabsorption Modulator as Phase Comparator" (Proc. OFC 2003, Atlanta, USA, paper FF3) real differential reception-side clock recovery with an optoelectric phase-locked loop is known, in which two identical data signals are initially delayed and then unidirectionally or bidirectionally directed to an EAM as a phase comparator with a switching function, which enables a mathematically very closely approximated differential phase evaluation Dependencies on power fluctuations, the signal-to-noise ratio, the pulse shape and the transmitted bit pattern are largely eliminated and the long-term stability of the clock recovery is significantly improved (see also German patent application DE 103 100 15.6, filing date February 28, 2003).

The prior art on which the invention is based is disclosed in WO 99/05812. For a mean data cycle of 40 Gbit / s, a simultaneous demultiplexer for a maximum of two data channels is described, which is based on the bidirectional operation of a single EAM as a fast optical switch. A data channel is separated in each direction of the EAM. Another embodiment shows the use of a single EAM in bidirectional operation simultaneously for demultiplexing a single data channel and for clock recovery with purely optical control. However, reflections returning from the ends of the EAM are problematic in bidirectional operation. However, their influence can be minimized if they are aligned orthogonally to the data signal using a polarization setting. The data signal itself has only a single polarization level. Unidirectional operation is not provided in the known multi-channel demultiplexer. The object of the invention is therefore to be seen in specifying an optical multi-channel demultiplexer of the type described in the introduction on the basis of a single optical switch, in which the unidirectional operation by the optical switch can also be used for demultiplexing two data channels. In addition, it should be possible in terms of design, but also in application, to be able to demultiplex more than two data channels simultaneously. The integration of a clock recovery in the individual optical switch should also be possible. Demultiplexing should also be possible with data signals with high and highest data clocks. As a solution to this problem, a generic multi-channel demultiplexer provides according to the invention that a birefringent element is arranged in front of the optical switch, which divides the data signal symmetrically into two orthogonally polarized data signals and, due to its selected delay, these data channels are to be deinterleaved temporally superimposed, and that the superimposed orthogonally polarized data signals with respect to the data channels to be deinterleaved are then synchronized with the switching window of the optical switch and unidirectionally guided through the optical switch to a polarization beam splitter which assigns the switched through orthogonally polarized data signals to the two deinterleaved data channels.

In the multi-channel demultiplexer according to the invention based on a single optical switch, two orthogonal polarization planes are used for demultiplexing two data channels. The data signals of different data channels can thus be identified by their polarization state. Since the optical switch used has no influence on the polarization state of the data signals, this is retained behind the optical switch with its simple gate function. In order to divide both data channels to be deinterleaved into orthogonal polarization planes, a birefringent element is used which, due to its refractive properties, also has a propagation delay of the two orthogonally polarized data signals. The optical length of the birefringent element can be changed, for example, or a delay element can be provided in order to set this delay in time. The setting is made so that the delay time is one or multiple of the distance between two adjacent data pulses (channel spacing) in the data signal, so that two data channels are shifted in time. By selecting the delay in the birefringent element, the data channels to be deinterleaved can be selected and prepared accordingly by shifting them over time. The next step is to feed the data of the data channels to be deinterleaved to the optical switch in such a way that they lie in its switching window and are let through at the same time, whereas the data of the other, temporally offset data channels are blocked. Various options for this synchronization are shown below. Both orthogonally polarized data signals pass through the optical switch in the same direction (unidirectional). Reflections that occur at the ends of the EAM cannot interfere with the signals. Behind the optical switch, the orthogonally polarized signals are distributed to two fibers according to their polarization plane using a polarization beam splitter and are available for further processing.

Thus, the invention provides a two-channel demultiplexer that is alternative to the prior art in its basic form on the basis of a single optical switch for the simultaneous demultiplexing of two data channels, which does not operate in a bidirectional manner like the known two-channel demultiplexer is based, but on a unidirectional operation of two ideally power-equal data signals with orthogonal polarization planes. Based on this basic form, however, the multi-channel demultiplexer according to the invention can advantageously also be developed in such a way that simultaneous demultiplexing of four data channels is possible. For this purpose, the invention continues that behind the birefringent element, an optical coupler is arranged, which decouples the orthogonally polarized data signals onto a second parallel optical path, that a delay element is arranged in the first or second optical path for the temporal superimposition of the data channels already superimposed in pairs, and that subsequently the superimposed two pairs of orthogonally polarized Data signals relating to the data channels to be deinterleaved are synchronized with the switching window of the optical switch and are guided bidirectionally through the optical switch onto two polarization beam splitters which assign the switched through orthogonally polarized data signals to four deinterleaved data channels. This is the first time that a multi-channel demultiplexer for simultaneous demultiplexing of four data channels is presented, which is based on a single optical switch using both the unidirectional and the bidirectional direction of passage through the optical switch. Known multi-channel multiplexers already require a cascade, for example from EAM (see WO 99/05812). The invention thus provides an inexpensive variant that can be implemented with a minimal expenditure of material. Both possible polarization planes and the bidirectional passage through the optical switch are used for this. Two orthogonally polarized data channels which are shifted one above the other by a corresponding time delay are conducted in both directions of passage. All four data channels are then synchronized together to the switching window of the one optical switch, so that when the switch is open, the data from four different data channels are simultaneously passed through, which can be clearly distinguished from one another due to their direction of passage and their polarization. Behind the optical switch, the two pairs of orthogonally polarized data signals are divided by two polarization beam splitters and assigned to the four deinterleaved data channels. However, more than four data channels cannot be demultiplexed with a single optical switch at the same time, since this means that the relevant distinguishing features polarization and Direction of passage of data signals are exploited by an optical switch.

For exact demultiplexing, the optical switch must be loaded with the exact data clock in order to be able to generate data-synchronous switching windows. In the simplest but most complex case, the data clock can be transmitted on its own data channel. However, a recovery of the data clock at the receiving end is preferred, for which purpose various circuitry options are known from the prior art. According to a next preferred embodiment of the invention, it can advantageously be provided that the data clock on the receiving side is recovered with a differentially operating, optoelectronic phase-locked loop on the basis of a further optical switch, an optical coupler being arranged in front of the birefringent element for the partial decoupling of the data signal and for bidirectional Guidance of the two data signals by the optical switch, a further delay element is provided for the time delay of one of the two data signals or, for unidirectional guidance, a further birefringent element is also provided for splitting the decoupled data signal into two orthogonally polarized and mutually delayed data signals. The differential principle of data clock recovery is known in particular from publication VI and is intended to be protected by German patent application DE 103 100 15.6. The advantage of this differential recovery is its stable working point in the middle of the working area and thus its excellent locking stability while avoiding channel jumps with regard to the recovered subharmonic data clock. Data clock recovery and demultiplexing can be carried out in separate units with two optical switches, in which case two delay elements are also required. Since an optical switch, in particular in the embodiment of an EAM, can also be the central element in the clock recovery described, it can also be advantageously provided according to a next invention continuation that the further optical switches are used simultaneously as individual optical switches for deinterleaving one or two data channels, the different functions being implemented by the optical switch in the bidirectional passage of the data signal pairs passing through each unidirectionally. This enables particularly efficient material and cost savings to be achieved, which is of particular interest because the combination of data clock recovery with a data channel to be demultiplexed is frequently used (compare publications I and II and WO 99/05812). This can be done for reasons of data distribution technology, the stable data clock recovery in any case reducing the error rate. Seen overall, many mixed and cascading forms with different numbers of optical switches are possible to implement synchronous channel demultiplexing from one to almost any number of data channels with or without data clock recovery. In order to avoid repetition, reference is made to the special embodiment for further explanations of embodiments of the invention.

The birefringent element can be designed differently. For example, two parallel optical fibers can be arranged between a polarization beam splitter and a polarization beam combiner, which are acted upon by the two orthogonally polarized data signals. There is an optical delay element in one optical fiber, so that different lead times result for the two orthogonally polarized data signals. Polarization adjusters in the feed line to the first polarization beam splitter and in both parallel lines ensure the setting of the desired polarization state in each signal. Alternatively, polarization beam splitters and converters can also be implemented using symmetrical couplers (3 dB couplers). However, it is simpler, since it is compactly combined in one component, if, according to another embodiment of the invention, the birefringent element is designed as a birefringent optical fiber with two orthogonal main planes, with one upstream polarization controller the incoming data signal is set to a polarization level in a range of 45 ° to the main levels. A birefringent optical fiber (high birefringent fiber, HiBi fiber) is a commercially available element that can be obtained easily and inexpensively. The birefringence is caused by an elliptical cross section of the fiber core. The two main axes of the ellipse correspond to the main orthogonal planes of the birefringent element. The incidence of the polarization of the data signal at an angle of approximately 45 ° to the main planes ensures that the signal power is divided as equally as possible on both polarization planes. A differently strong absorption of both polarization directions along the birefringent fiber and data (sub) channels with different intensities can be compensated for by a deviation from the angle of incidence of 45 °. The delay time between the two orthogonally polarized data signals can be set in a simple manner by the selectable length dimensioning of the birefringent optical fiber. Furthermore, the optical switches for demultiplexing and data clock recovery from different elements can be implemented. Both switches can be implemented with the same or different elements if there are two in the structure. Possible optical switches can be used as interferometric switches (for example MZI, UNI, SLALOM (see publication VII by T. Yamamoto et al. "Clock recovery from 160 Gbit / s data signals using phase-locked loop with interferometric optical switch based on semiconductor optical amplifier" (Electronics Letters, 2001, Vol. 37, No. 8, pp. 509-510)), as a switch with a four-wave mixture (for example FWM), as a Kerr switch or as an electro-absorbing modulator EAM According to the invention, the individual and / or further optical switches are therefore designed as SLALOM, MZI, Kerr switches or as electro-absorbing modulators. The EAM in particular is currently the subject of diverse investigations and is used for different tasks. It can be controlled electronically or optically and allows the exact setting of a switching window even for high data cycles, for example 160 Gbit / s. With this data clock, four data channels with 40 Gbit / s each can be deinterleaved. The switching window of the optical switch preferably has a full width at half maximum of approximately 5 ps with a channel spacing of 6.25 ps. However, other division ratios with different data clocks or other data channel numbers are also possible, in particular when using other optical switches.

Also important for the correct demultiplexing of several data channels at the same time is the respective synchronous appearance of associated data signals in the relatively narrow switching window of the optical switch. For this purpose, the opening time of the switching window is matched to the occurrence of the data signals to be demultiplexed. For this purpose, an electrical or optical delay line can be used, which are commercially available in mechanically and electrically controllable designs. The cheapest place of use of the delay line depends on the particular version of the multi-channel demultiplexer. At best, it can be chosen so that all data channels move uniformly relative to the switching window clock. Alternatively, it can also be provided that a further delay element for synchronizing the data channels to be recovered to the switching window of the optical switch is provided according to a next invention. This can be, for example, a free beam retarder in which the delay time can be set manually or electrically by the length of a free path for the optical signals with a different refractive index than the optical fiber and thus with a different running speed.

A data clock of 160 Gbit / s to be demultiplexed with a division ratio of 1: 4 was mentioned above as an example. For signals with this data clock, for example, the EAM can provide a sufficient switching window. The maximum achievable with an EAM With sinusoidal control, however, the division ratio is also 1: 4. The width of the sine-shaped switching window in the EAM is permanently linked to the data clock. In the case of higher-rate data signals, the switching window must be reduced accordingly to ensure a clean switching function. For this purpose, it is possible to control the optical switch directly with short optical pulses, the repetition rate of which can be selected independently of the switching window width achieved. According to another embodiment of the invention, narrower switching windows can also be achieved in that, with an n-fold data clock cycle, n further optical switches are connected in series to the individual optical switch for n-fold division of the switching window. By connecting two EAMs in series, the width of the switching window can be halved, for example. In cascaded systems for demultiplexing more than four data channels, additional optical switches can thus be assigned in series to the individual optical switch, depending on the data cycle. A cascaded system results from the use of an optical multi-channel demultiplexer on the basis of a single optical switch for simultaneous deinterleaving of at least two data channels superimposed in a digital transmission system on the transmission side in time division multiplexing, in particular in one or more data signals with a predetermined data clock rate Embodiments explained above, in a cascade supplied with the data signal via additional optical couplers behind the birefringent element in the first multi-channel demultiplexer with further multi-channel demultiplexers for simultaneous deinterleaving of more than four data channels. Thus, by connecting the demultiplexer according to the invention in parallel and in series, virtually any number of data channels can be demultiplexed at the same time, four data channels always being demultiplexed via a common optical switch. The cost of materials and thus the cost can be minimized. Further details can be found in the special description section. Forms of embodiment of the invention are explained in more detail below with reference to the schematic figures for their further understanding. It shows:

1 shows the circuit structure of a four-channel demultiplexer, FIG. 2 shows a concept for combining a two-channel demultiplexer with data clock recovery, FIG. 3 shows a concept for combining a four-channel demultiplexer with data clock recovery, FIG. 4 shows a circuit structure for implementing the Concept according to Figure 2 and

Figure 5 shows an embodiment for the replacement of the birefringent element.

FIG. 1 shows an optical multi-channel demultiplexer MKD with which two data channels can be deinterleaved with a suitable delay by using both directions of irradiation into an optical switch OS (bidirectional operation) and two orthogonal polarization planes. The length of the selected delay corresponds to the distance between two adjacent data pulses of the high-rate data signal (channel spacing) or integral multiples thereof. At the input of the optical multi-channel demultiplexer MKD, the direction of polarization of the incoming high-rate (160 Gbit / s in the exemplary embodiment) data signal is kept constant with an automatic polarization controller POL. For generalization, the data clock of the incoming data signal is given as 4 xn Gbit / s, which indicates the maximum four-channel demultiplexing (per data channel with n Gbit / s) with a single optical switch OS. The number n can assume functionally realizable and in particular also known and frequently used values, such as 40, so that an OTDM data signal rate of 160 Gbit / s results. After the polarization controller POL, the data signal passes through a birefringent element DBE; in the selected exemplary embodiment, it is a highly birefringent HiBi-F optical fiber. The polarization of the incoming data signal is selected at approximately 45 ° to the two main axes of the birefringent HiBi-F optical fiber. The data signal propagates at different speeds along the two main axes and is thus divided into two mutually polarized data signals with approximately the same power level. Both orthogonally polarized data signals receive a delay from one another, which in the selected exemplary embodiment can be set by the length of the birefringent optical fiber HiBi-F. Behind this, the two signals are evenly divided into two optical paths OP1, OP2 with a 3-dB coupler 3dB-K and via circulators C1, C2 from both sides, that is to say bidirectionally through the optical switch OS, in the selected embodiment in training of an electro-absorbing modulator EAM. In the one optical path OP 1 behind the 3 dB coupler 3dB-K there is an optical delay element VE, which enables the delay of the bidirectional components in the electro-absorbing modulator EAM to be set.

All delays (the length of the birefringent HiBi-F optical fiber and the optical delay element VE) are set so that the resulting four data signals pass through the electro-absorbing modulator EAM at the correct time. This means that at the point in time at which the electro-absorbing modulator EAM opens a switching window (maximum transmission), the data information of all four data channels to be deinterleaved is simultaneously in the electro-absorbing modulator EAM. This can be achieved, for example, in that the delay due to the birefringent optical fiber HiBi-F corresponds to the distance between two adjacent data pulses of the high-rate data signal and the delay due to the optical delay element (delay line) corresponds to twice the distance between two adjacent data pulses of the high-rate data signal Data signal corresponds. After the polarized data signals have passed through the electro-absorbing modulator EAM, the demultiplexed, bidirectional, orthogonally polarized data signals pass through the circulators C1, C2 to polarization beam splitters PST1, PST2, which separate signal components that are polarized perpendicular to each other. In this way, the multi-channel demultiplexer MKD completely demultiplexes a high-rate OTDM signal into four data channels. The main advantage of the invention is a greatly reduced number of components required and thus a significant cost saving.

As variants to the circuit structure described, it can also be provided that the circulators C1, C2 shown in the embodiment are replaced in whole or in part by 3 dB couplers. In addition, it can be provided that the birefringent element DBE is not in front of the 3 dB coupler 3dB-K but in a double version in both arms behind the 3 dB coupler 3dB-K. It should also be noted that the presented embodiment shows a maximum demultiplexing of four data channels. A reduction of the demultiplexing to two or even one or three data channels is easily possible if necessary by omitting the corresponding components or ignoring further signals.

FIG. 2 shows a concept for combining a two-channel demultiplexer with data clock recovery for a data clock of 160 Gbit / s. The concept comprises two units, each unit using its own optical switch, in particular an electro-absorbing modulator. The two-channel demultiplexer can be operated in unidirectional, but also in bidirectional flow. The optical switch of the clock recovery is also used simultaneously for the deinterleaving of two further data channels, so that with the entire concept in turn, four data channels can be deinterleaved in both units. Data clock recovery can also be combined with only one data channel to be deinterleaved or without demultiplexing. The combination of data clock recovery with the deinterleaving of two data channels takes place in the manner described above, in which both the polarization splitting and the bidirectional direction of passage of the optical switch are used. The two-channel demultiplexer is then also controlled with the recovered data clock. At this point it should be noted that a four-channel demultiplexer can also be used, so that a total of six data channels can be demultiplexed at the same time. However, whether this makes sense depends on the selected data clock and the switching capacity of the optical switches used.

FIG. 3 shows a concept for combining a four-channel demultiplexer with data clock recovery, which in turn is made up of two units, each with an optical switch, in particular an electro-absorbing modulator. With this concept, all four ways of the demultiplexer are used for the simultaneous deinterleaving of four data channels. The second unit is used exclusively for data clock recovery. The recovered data clock is in turn fed to the demultiplexing unit.

Both concepts can in turn be implemented in different versions. The concept according to FIG. 3 can be implemented in a simple manner by arranging an asymmetrical coupler, for example with a division 9: 1, in front of the birefringent element DBE and behind the automatic polarization controller POL in a circuit construction according to FIG. 1 for simultaneous demultiplexing of four data channels, which decouples the data signal with a weak power component of 10% and leads to a circuit for data clock recovery using a single optical switch, as is known, for example, from publication VI. With this data clock recovery with a locked phase-locked loop, the electro-absorbing switch functions as a fast electro-optical phase comparator. For both polarization states the Optical power, which is transmitted by the electroabsorbing switch, is determined by the phase difference between the respective optical signal and the electrical control signal of the electroabsorbing switch. As a result, two downstream photo diodes generate two phase-dependent electrical signals whose difference is proportional to the phase difference between the optical signal and the electrical control signal. This electrical difference signal serves as a control signal for a voltage-controlled oscillator. The difference formation, which comes very close to the real first derivative, minimizes the influence of power fluctuations of the optical input signal on the clock recovery.

FIG. 4 shows a circuit structure for implementing the concept according to FIG. 2. The data signal (160 Gbit / s) is split into two parallel optical paths OP1, OP2 via an asymmetrical coupler AK (division ratio 9: 1) behind an automatic polarization controller POL. The data clock recovery only requires the weak signal, whereas the demultiplexing should receive a data signal that is as strong as possible. The upper optical path OP1 is used for data clock recovery. The data signals in this optical path OP1 are first passed via a first manual polarization controller PS1 and via a first birefringent optical fiber HiBi-F1 and then via a circulator C1 to an electro-absorbing modulator EAM1, where they are correlated as described above. The comparison signals, which are coupled out via a second circulator C2, are fed to a polarization beam splitter PST and are fed to two optoelectric detectors OD with the correct polarization, which are connected to the two inputs of a differential amplifier DA. The difference signal formed is then fed via a low-pass filter LPF to a voltage-controlled oscillator VCO and an operator element OE (here multiplier x4). The electroabsorbing modulator EAM1 is then controlled with the recovered data clock rate. Furthermore can the data clock are still made available externally and are still routed to a second electro-absorbing modulator EAM2 (see below).

A manual second polarization controller PS2 and a second birefringent optical fiber HiBi-F2 are also arranged in the second optical path P2. The data signal for demultiplexing is passed bidirectionally to the data signals for data clock recovery through the first electro-absorbing modulator EAM1. For synchronization with the switching window, a pair of the orthogonally polarized signals are passed via an optical delay element VE (the delay element VE can also be arranged in an analog position in the first optical path P1). The division takes place via a first polarization beam splitter PST1, behind which two duplexed channels A and B are then available.

A symmetrical 3dB coupler 3db-K (50%) is arranged behind the second birefringent optical fiber HiBi-F2 in the second path P2, half of which couples out the strong (90% of the data signal) orthogonally polarized data signals and a further delay element VE2 for switching window synchronization feeds the subsequent second electroabsorbing modulator EAM2, which is driven electrically with the data clock recovered from the first electroabsorbing modulator EAM1. Two further demultiplexed data channels C and D are then available behind a second polarization beam splitter PST2. With such an arrangement, cascades can also be constructed with a large number of electro-optical switches for the simultaneous demultiplexing of more than four data channels. Simultaneous data clock recovery and demultiplexing of two data channels with a single optical switch can be obtained if the circuit part described last, including the 3 dB coupler 3dB-K, is omitted. A data clock recovery with demultiplexing of only one data channel is achieved if in the remaining circuit structure the second double breaking HiBi-F2 optical fiber is not required. The first polarization beam splitter PST1 is then also omitted.

Another embodiment is shown in FIG. 5 as a replacement for a birefringent element DBE. Instead of a HiBi-F birefringent optical fiber, another element for orthogonal polarization splitting and delay can also be used. As in the exemplary embodiment shown, this can consist of a polarization beam splitter PST and a polarization beam combiner PV (which can also be implemented by 3dB couplers), which are connected to one another via two optical fibers LF1, LF2. A suitable delay element VE is integrated in an optical fiber LF1. Various polarization adjusters PS are used to set the desired polarization.

The present invention shows the use of a single optical switch with a unidirectional and / or bidirectional direction of travel using the orthogonal polarization splitting of the optical data signals to be switched. This means that four data signals that have passed through can be clearly distinguished from one another. This newly developed possibility is used in the invention for multi-channel demultiplexing with or without a combination with data clock recovery. In principle, however, other signal processing operations, such as add-drop functions and data clock synchronization, can also be implemented in a suitable manner with such a concept. LIST OF REFERENCE NUMBERS

A, B, C, D data channel AK asymmetrical coupler

C circulator

DA differential amplifier

DBE birefringent element

EAM electro-absorbing modulator HiBi-F birefringent optical fiber

LF optical fiber

LPF low pass filter

MKD multi-channel demultiplexer

OD optoelectric detector OE operator element

OP optical path

OS optical switch

POL automatic polarization controller

PS polarization controller PST polarization beam splitter

PV polarization beam combiner

VCO voltage controlled oscillator

VE delay element

3dB-K 3 dB coupler (balanced)

Claims

claims

1. Optical multi-channel demultiplexer based on a single optical switch for receiving-side, simultaneous deinterleaving of at least two time-division multiplexed data channels in a digital transmission system in the data signal with the given data clock, characterized in that in front of the optical switch (OS) A birefringent element (DBE) is arranged, which divides the data signal symmetrically into two orthogonally polarized data signals and, due to its selected delay, overlays them temporally with respect to two data channels to be deinterleaved, and that the superimposed orthogonally polarized data signals with respect to the data channels to be deinterleaved then with the switching window of the optical switch (OS) are synchronized and unidirectionally through the optical switch (OS) on a polarization beam splitter (PST), which the switched through orthogonally polarized data signal assigned to the two deinterleaved data channels.

2. Optical multi-channel demultiplexer according to claim 1, characterized in that an optical coupler (3dB-K) is arranged behind the birefringent element (DBE), which couples the orthogonally polarized data signals onto a second parallel optical path (OP2), that a delay element (VE) is arranged in the first or second optical path (OP1, OP2) for the temporal superimposition of the data channels already superimposed in pairs, and that subsequently the superimposed two pairs of orthogonally polarized data signals with respect to the data channels to be deinterleaved with the switching window of the optical switch ( OS) synchronized and bidirectionally through the optical switch (OS) on two polarization beam splitters (PST1, PST2), which are switched through orthogonally Assign polarized data signals to four deinterleaved data channels (A, B, C, D).

3. Optical multi-channel demultiplexer according to claim 1 or 2, characterized in that the data clock on the receiving side with a differentially operating, optoelektro ^¬ African phase locked loop is recovered on the basis of a further optical switch (OS), an optical coupler (AK) is arranged in front of the birefringent element (DBE2) for the partial decoupling of the data signal and for a bidirectional routing of the two data signals by the optical switch (OS) a further delay element is provided for the time delay of one of the two data signals or another birefringent for a unidirectional guidance Element (DBE1) is provided for splitting the decoupled data signal into two orthogonally polarized and mutually delayed data signals.

4. Optical multi-channel demultiplexer according to claim 3, characterized in that the further optical switch (OS) is used simultaneously as a single optical switch (OS) for deinterleaving one or two data channels, the different functions in the bidirectional run of the unidirectional continuous data signal pairs are implemented by the optical switch (OS).

5. Optical multi-channel demultiplexer according to one of claims 1 to 4, characterized in that the birefringent element (DBE) is designed as a birefringent optical fiber (HiBi- F) with two orthogonal main planes, with the upstream pole positioner (POL) incoming data signal is set to a polarization level in a range of 45 ° to the main planes.

6. Optical multi-channel demultiplexer according to one of claims 1 to 5, characterized in that the individual and / or further optical switches (OS) are designed as SLALOM, MZI, Kerr switches or as electro-absorbing modulators (EAM).

7. Optical multi-channel demultiplexer according to one of claims 1 to 5, characterized in that a further delay element (VE2) is provided for the synchronization of the data channels to be recovered on the switching window of the optical switch (OS).

8. Optical multi-channel demultiplexer according to one of claims 1 to 7, characterized in that with an n-fold data clock n further optical switches (OS) the individual optical switch (OS) for n-fold division of the switching window connected in series become.

9. Application of an optical multi-channel demultiplexer (MKD) on the basis of a single optical switch (OS) for reception-side, simultaneous deinterleaving of at least two data channels superimposed on the transmission side in time division multiplexing in the data signal with a predetermined data clock rate, in particular according to one of the Claims 1 to 8, in a cascade supplied with the data signal with additional multi-channel demultiplexers (MKD) for simultaneous deinterleaving of more than four data channels in an optical coupler behind the birefringent element (DBE) in the first multi-channel demultiplexer ,