Device for compensating dispersion of the polarization modes

 

The invention relates to a device for compensation modes of polarization. The technical result consists in increasing the reliability of the detector, can be used to identify large value of differential group delay. The device includes a mode Converter polarization (PPMS), photodiode (PD), the first solver (RU), band-pass filters or low pass filters (f) (1, 2, 3), power meter (1, 2, 3), controller (MP). In another embodiment uses one f switchable or custom boundary frequency or a center frequency F. is also Provided a second PN, which will come out of the auxiliary data signal. The output signals of the first and second PN are compared to obtain the error signal used by the regulator (MP) for control of the RAP. 2 C. and 8 C. p. F.-ly, 5 Il.

The invention relates to a device for compensating the dispersion of the modes of polarization of the optical data signal according to the generic concept of paragraph 1 of the claims.

In the technique of optical transmission used transmission channels on the optical waveguides great length. Optical waveguides, due to the technology of their production, are not absolutely izotropnoe-dependent conversion of polarization, called dispersion modes of polarization (SLE) or polarization dispersion. This results, due to changes in polarization of the optical signals in the function of the optical frequency and the associated different depending on the frequency of values of time passing, to the expansion of the transmitted pulses, resulting in intake decreases the possibility of their recognition and, therefore, limited data transfer rate.

The problem is compounded by the fact that, due to temperature changes or mechanical stresses, the transmission mode of the channel and thereby SLE varies. Therefore, use of adaptive compensators SLE. introduced in the transmission channel. To manage in the optical receiver, it is necessary to measure the distortion associated with SLE. The compensator can thus be optimally adjusted, for example, using a gradient algorithm.

Known bandpass filter for filtering a data signal for which you want to define DMP (see Electronic Letters, 17.02.1994, V. 30, 4. pp. 348-349). The power detector at the output of the filter outputs a signal, which is greater, the less the distortion caused by SLE.

The disadvantage is that if you have a large SLE of the first order this signal varies shall be clearly defined signal.

Know of any other way in which to evaluate the power of the differential signal between the output of the decision making unit and the input of the decision making unit (see Proceedings OEC 94. 14-12, pp. 258-259, Makuhari Messe, Japan 1994).

This signal, however, has a lower sensitivity to distortions due to SLE than the corresponding bandpass filter. Especially when strong distortions caused by SLE, in which DGUS exceeds the duration of the bit can be taken the wrong decision, so that the received signal in such cases is an unsuitable criterion for determining the existence of distortions caused by SLE.

The objective of the invention is to create a reliable detector can be used to determine the large value of the differential group delay. In addition, the task of the invention is to provide a corresponding device for compensating the dispersion of the modes of polarization and for the optimal configuration of such a detector.

This task is solved by a device for compensating the dispersion of the modes of polarization according to paragraph 1 of the claims.

In the independent claim 7 of the formula of the invention described variant of this solution.

Preferred embodiments of the invention shown in zawiya monotonically changing output voltages of the set of filters used in the main range and greater steepness, it is impossible to achieve using a single bandpass filter or a single lowpass filter. This causes significantly more accurate compensation.

The use of bandpass filters is compared with the use of low-pass filters, the advantage of greater slope of the output voltage filter, compared to the existing function of the differential group delay. Thereby, it is possible to perform more accurate and fast payment.

Instead of a set of band-pass filters or low-pass filters can also be used switched/controlled band-pass filter or switched/controlled lowpass filter.

The compensation device may be supplemented with other management criteria. Especially preferred are devices that assess the required image generated frequency errors auxiliary data signal, which is obtained from a received optical signal. A particularly simple scheme can be implemented by means of an adjustable threshold sampling in the evaluation of the data signal.

Examples of carrying out the invention is described below with reference to the drawings, in to the, 2 - an example embodiment of the invention with three bandpass filters.

Fig.3 is another embodiment with a single controllable bandpass filter.

Fig. 4 is another exemplary embodiment, additional evaluation of the auxiliary data signal.

Fig.5 is another variation of this example run.

In Fig. 1 presents the normalized characteristic output voltage from U1 to U3 three bandpass filters, the average frequency of which are 0,125/T 0,25/T and 0.5/T, where T is the bit duration of the transmitted data signal. In addition, the graph shows the output voltage U (LPF) low pass filter with a break frequency 0,125/T depending on the normalized differential group delay DGVS/T upon excitation of both principal polarizations of equal level. (As the basic state of polarization (BSA) further identified those orthogonal to each other by two polarization that when you change the optical frequency in a first approximation do not change. In the polarization-preserving optical waveguides of the main States of polarization coincide with the main axes that are horizontal and vertical. In General, the main polarization States are all orthogonal mi delay times, the difference is further defined as "differential group delay" - DGUS. If the transmitted optical signal with the main polarization, the first-order approximation no expansion pulse. If it is transmitted with the polarization, which upon decomposition on both the main polarization corresponds to equal constituent power, that is the maximum extension of the pulse, because the two are equal in magnitude pulse overlap with the difference in propagation time equal to DGUS.

If the main polarization change in the function of optical frequency, when applied to the inlet of main polarization, which corresponds to a particular frequency, the output polarization changes as a function of frequency, but even of a higher order than the first order. This phenomenon is defined as the dispersion of the modes of polarization (SLE) of a higher order. In the General case appears SLE higher order, but the influence of the SLE of the first order is dominant, and therefore it is the preferred way should be compensated.) It is obvious that the output signal U3 provides accurate determination of SLE only up to a certain value DGUS equal to 1T, so as to znacheniya filters and to a lesser extent for output voltages low-pass filters.

In Fig.2 shows the application of the device to determine SLE in the compensator. The optical transmitter PD transmits the optical signal OS optical waveguide S to the optical receiver PC. The latter contains a photodiode PD for converting the optical signal into an electrical signal. Included next solver RU produces output O the transmitted data signal SD.

Before the photodiode included Converter mod polarization (RAP) to compensate for the dispersion of the modes of polarization, input I which corresponds to the input of the receiver.

The criterion for the regulation of the transformer mod polarization TDM receive a signal from the base band of the URS from the output of the photodiode. This signal is fed to the multiple filters F1-F3, the outputs of which are respectively included power meters DET-DET. Through the use of smoothing capacitors or other similar devices, these power meters also implement a smoothing function or the function of a lowpass filter. Bandpass filters preferably have a center frequency equal to 0,125/T 0,25/T and 0.5/So-widths of the bands are from 0.0001 times to 0.2 times the value matching the s power DE-DET but essentially you can avoid anti-aliasing. Additional components, such as amplifiers, for reasons of clarity, the drawing is not shown.

To explain graphically the configuration of the joints, it is best to proceed from the fact that initially has a large value of differential group delay. First, to optimize the settings of the compensator applies the output voltage U1 of the band pass filter F1 (measured by the power meter) with the lowest center frequency 0,125/T output, used as a control microprocessor MP (analog-to-digital (AC) and digital to analog (CA) Converter). As soon as this signal passes through the threshold value SO, to optimize begins to apply the output signal of bandpass filter F2 with the next largest center frequency of 0.25/So as soon As this filter will emit a powerful output signal exceeding the aforementioned threshold value (or another threshold value that is selected in accordance with this variant of execution of the device), perform switching to a band-pass filter with the highest Central frequency of 0.5/So Although this filter has the smallest area of monotonicity of the output signal, however, through a joint evaluation of the output signals of the other �//img.russianpatents.com/chr/8804.gif">DGUSSo Therefore its very high sensitivity to compensate for distortion due to SLE, you can use a particularly advantageous way. Used area of monotonicity is shown in Fig.1 in the form of key values.

In order to achieve the optimal error values in bits, you can also use non-linear or linear combination of the output signals of the bandpass filters or, respectively, output signals enabled them measuring instruments (detectors) power. To do this, instead of the signal filter. selected as a function of output signals of a low frequency bandpass filters, share the output signal or output signals, which is the lower frequency, namely, until the output signal of the power meter GET not exceeded its threshold only applies this signal. If the threshold is exceeded, then there is also the output signal of the power meter DET. If, finally, and this threshold is exceeded, then adds the output signal of the power meter DET.

For the purposes of the measurements on the outputs of the detectors DET-DET can be connected directly to the measuring instruments, of which Fig.2 shows one - SPW.

In Fig. 3 shows a variant maintained/managed bandpass filter POOF. The operation of the compensator remains the same. Used as a controller microprocessor MP remembers the previous output voltage, so that allows unambiguous mapping of key values (region monotonicity) filter with a higher Central frequencies. Adjusting the filter is provided with the control signal SIMP.

In Fig.4 shows another variant of the claimed device, in which a second solver PY2, which is also fed the signal to base band by ESD. In this embodiment, the threshold of this casting device is controlled via the device settings of the UNIVERSITY in such a range that this is a crucial device generates auxiliary data signal IRR, when the first solver RU still produces the data signal SD, essentially without error. The output signals are compared in a logic "EXCLUSIVE OR", and the resulting error signal WITH also used by the microprocessor MP to control the mode Converter polarization of the RAP. Due to the shift of the threshold of the second casting device is continuously generated a measure of how udovletvoritel what about the data signal when the shift of the threshold relative to the optimal value, the better the signal quality. In a first approximation, the maximum output voltage is switched/controlled filter POOF and minimum error rate consistent with each other. A more accurate estimate, which leads to a lower error rate in bits casting device ROUX, it turns out, in contrast, when applying the error signal. Because of the stochastic deviations of the auxiliary data signal IRR relative to the data signal DM, it requires a relatively large time measurement or determination of the error signal, to obtain a good signal-to-noise ratio and thus the optimal compensation. Obtained using the second deciding device additional information is used to optimize the filter POOF, i.e., to change its transfer characteristic. This adaptive mode of operation is particularly favorable with regard to technological tolerances to temperature fluctuations, the manifestation of nonlinear effects, and so on, a Great advantage of this form of execution is that the output signal of the filter is already possible fast payment, and to fine tune and modify the transfer function of the filter remains compositely RAP, you may, however, use only the error signal, so as shown in Fig.4, the filter POOF and power meter (detector) DET can be omitted.

When using multiple bandpass filters, as shown in Fig.5, the transfer function of the filter or weight of the individual output signals of the filter can be modified in such a way as to manifest the minimum distortion associated with the dispersion of the modes of polarization. As it can be slow, while the output signals of filters and their combinations available quickly, this adaptive form of execution provides the same advantages as the embodiment according to Fig.4.

In principle, the management mode Converter polarization can be carried out using the error signal.

Claims

1. Device for compensating the dispersion of the modes of polarization of the optical data signal in which the criterion of regulation is obtained from the signal of the base band from the output of the photodiode, before which enabled mode Converter polarization to compensate for the dispersion of the modes of polarization, the input of which corresponds to the receiver input, and the output signal from the photodiode is fed to a band-s filter, measured by the power meter, is used to control the mode Converter polarization from the output of the regulator, characterized in that provided at least one additional filter connected to a power meter, the output voltage which is also applied to inverter mode polarization from the output of the controller.

2. The device under item 1, characterized in that measured only the monotony of the output voltages of bandpass filters between the values of the differential group delay time from minimum 0 to maximum value of differential group delay time corresponding to the change of sign of the slope of the output voltage.

3. The device according to p. 2, characterized in that when the output signal of bandpass filter with the lowest center frequency lying below the upper threshold, this output signal is evaluated individually, and if exceeded, the output signal of the threshold is estimated filter output signal with the next higher center frequency individually or advanced, and is the corresponding estimate for additional bandpass filters with higher centeraustria, based on the Central frequency corresponding to approximately one-half the clock frequency bits successively two times lower.

5. The device according to p. 4, characterized in that it uses three bandpass filter.

6. Device according to any one of paragraphs.1-5, characterized in that by means of the regulator is controlled transfer function of the filter or weights of the output signals of the respective power meters.

7. Device according to any one of paragraphs.1-6, characterized in that when explicitly deterioration of the signal to be enabled after the first diode crucial device that outputs the output signal of the data provided by the measurement device for measuring the error rate in bits containing the second crucial device to which is also fed the signal of the base band from the output of the photodiode, and the threshold of the second casting device is controlled by using the device settings in such a range that the second solver generates auxiliary data signal when the first crucial device still produces a signal having no error, the output data signals of the first and second computing devices are compared, and the resulting error signal through the regulator is olarization optical data signal, in which the criterion of regulation is obtained from the signal of the base band from the output of the photodiode, before which enabled mode Converter polarization to compensate for the dispersion of the modes of polarization, the input of which corresponds to the receiver input, and the output signal from the photodiode is fed to a bandpass filter or a lowpass filter, the output of which is connected to the power meter, the output voltage of the filter, as measured by the power meter, is used to control the mode Converter polarization from the output of the regulator, wherein the cutoff frequency or center frequency of the filter is switchable or adjustable, are evaluated only the monotonicity of the output voltage of the filter, located between the values of the differential group delay time from minimum 0 to maximum value of differential group delay time corresponding to the change of sign of the slope of the output voltage, and takes into account the previous filter settings.

9. The device under item 8, characterized in that the cutoff frequency or center frequency of the filter is switched in three stages.

10. The device under item 8 or 9, characterized in that when explicit about who expressed a data signal, provided by the measurement device for measuring the error rate in bits containing the second crucial device to which is also fed the signal of the base band from the output of the photodiode, and the threshold of the second casting device is controlled by using the device settings in such a range that the second solver generates auxiliary data signal when the first crucial device still produces a signal having no error, the output data signals of the first and second computing devices are compared, and the resulting error signal through the controller additionally controls the mode Converter polarization.

 

Same patents:

FIELD: fiber-optics.

SUBSTANCE: fiber has core and cover. Fiber is made in such a way, that in case of change of radiuses of beds with different refraction coefficients, at least one optical property of core, for example, effective section of core Aeff and slant of dispersion curve, reach appropriate limit values in given range of deflections from base radius. Length of cut wave equals 1450 nm or less. Optical fibers have practically constant optical properties and allow to vary chromatic dispersion in certain limits.

EFFECT: higher efficiency.

2 cl, 14 dwg

FIELD: optical transmitting systems.

SUBSTANCE: modulated optical signals S1, S2 being transmitted are synchronized with respect to one another or shaped so that phase difference for NRZ-modulated signals is at least about 0 deg. and for RZ-modulated ones, at least about 180 deg. They can be also shaped by means of various synchronizing devices.

EFFECT: reduced permanent degradation of polarization-multiplexed signal without limiting throughput transfer capacity.

15 cl, 8 dwg

FIELD: radio engineering.

SUBSTANCE: in accordance to the method, at transmitting side binary signals (A, B, C, D) are transformed to two optical signals (QPS1, QPS2), which are combined in form of signal (PMS) multiplexed by polarization and then transmitted. At receiving side, division is conducted onto two orthogonally polarized signal components (PS1, PS2), which are linearly transformed to orthogonal electric components (I1, Q1; I2, Q2) and injected into multidimensional filter. Aforementioned filter replaces polarization regulator and again restores values of signals (I11+jQ11; I12+Q12), which correspond to optical signals (QPS1, QPS2) of transmitting side. Additionally it is used to compensate distortions in signals.

EFFECT: increased traffic capacity of signal transmissions and reduced costs.

15 cl, 9 dwg

Photodetector // 2342792

FIELD: physics, communication.

SUBSTANCE: invention concerns optical communication, in particular to photodetectors and can be used at making of fiber-optical systems of transmission of the numeral information inconvertible against action of the various destabilising factors leading to fluctuation of level of an optical signal and magnification of its dynamic range. The essence of the invention consists that a photodetector contains a photodetector, the amplifier, a refactor, the integrator, the solving threshold device, the block of allocation of clock frequency, a synchronizer, the local generator, the optical amplifier, an adjustable radiant of a rating, the block of measuring of the peak value of a signal, the block of evaluation of the optimum relation a signal/noise, the block of guidance of a threshold of the solving threshold device, joined definitely among themselves for achievement of the specified technical effect.

EFFECT: pinch of noise stability of fiber-optical system of transmission.

2 dwg

Up!