JP2003087198A - Automatic equalizer filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compensate for waveform deterioration by polarization dispersion. SOLUTION: This automatic equalizer filter has an equalizer filter 10 for generating a plurality of signals having different phases and amplitudes based on an input signal and a feedback signal to a plurality of amplitude adjustment ports and outputting the sum of the generated signals as the output signals, and a feedback signal generation means 20 for inputting a plurality of amplitude signals according to a signal waveform obtained by sampling the output signal of the equalizer filter 10 to the respective amplitude adjustment ports of the equalizer filter 10 as the feedback signals. The feedback signal generation means 20 sends an amplitude signal at an hourly new timing out of the output signals of the equalization filter 10 to a port concerning waveform generation of small phase delay out of the plurality of amplitude adjustment ports, and sends an amplitude signal at an hourly old timing out of the output signals to a port concerning waveform generation of large phase delay out of the plurality of amplitude adjustment ports.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed digital signal control technique, and more particularly to an automatic equalization filter for compensating for signal waveform deterioration due to polarization dispersion, which has become apparent in digital optical communication systems as its speed increases. is there.

[0002]

2. Description of the Related Art FIG. 4 shows a mechanism of waveform deterioration due to polarization dispersion, which is a problem in an optical transmission system. Waveform deterioration caused by the polarization of the optical signal being broken during transmission through the optical transmission line 1 such as an optical fiber and the propagation speed of each polarization being different,
In particular, it has become apparent as the bit rate of transmission data increases. In FIG. 4, a state in which a clean rectangular wave is formed before entering the optical transmission line 1 and the optical signal waveform is disturbed on the emission side of the optical transmission line 1 is shown. Reference numerals 2a and 2b are polarization axes, and a phase difference is generated between the polarization axes 2a and 2b on the output side, resulting in waveform deterioration.

[0003]

Conventionally, although light wave processing is often used to compensate for this, sufficient characteristics have not been obtained yet. The main reason is that the characteristic time scale of polarization dispersion is about μs, and the method generally used in light wave processing cannot catch up with this in terms of speed.

An object of the present invention is to provide an automatic equalization filter capable of compensating for the above-mentioned waveform deterioration due to polarization dispersion with a time margin.

[0005]

According to a first aspect of the invention for solving the above problems, a plurality of signals having different phases and amplitudes are generated based on an input signal and a feedback signal to a plurality of amplitude adjusting ports. Then, an equalization filter that outputs the sum of the generated signals as an output signal, and a plurality of amplitude signals corresponding to a signal waveform obtained by sampling the output signal of the equalization filter are output from the equalization filter. The automatic equalization filter is characterized by comprising feedback signal generation means for inputting to each amplitude adjustment port as the feedback signal.

According to a second aspect of the present invention, in the first aspect of the invention, the feedback signal generating means outputs the amplitude signal at a timely new timing of the output signal of the equalization filter in the equalization filter. A phase delay with a small phase delay among the plurality of amplitude adjustment ports is sent to the amplitude adjustment port, and an amplitude signal at a time old timing of the output signals is output with a phase delay of the plurality of amplitude adjustment ports. The automatic equalization filter is characterized in that it is sent to the amplitude adjustment port for generating a large waveform.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of the principle of the present invention. In FIG. 1, the waveform shown as f (t) is a typical waveform generated by polarization dispersion. This waveform f (t)
Has a shape in which two rectangular signals whose phases are different from each other are added. In the present invention, it is not always necessary to specify this deteriorated waveform f (t) for signal equalization. The gist of the present invention is to add a waveform f (at) that is time-reversed to the deteriorated waveform f (t), for example, to obtain a waveform that is temporally symmetric and has a pulse width of about a. To obtain "f (t) + f (at)". Here, a indicates a signal period corresponding to the bit rate of the transmission data.
The concept of signal equalization is not given a clear definition, at least in a practical sense, but it can be said to be effective if it is defined as a function of outputting a set of a certain series of initial waveforms as relatively identical waveforms. The waveform shaping process described above embodies waveform equalization in this sense.

Regarding how to realize the waveform equalization function, the present invention uses the sampling signal of the output signal as a feedback signal (tap signal) to the equalization filter including a transversal filter or the like. And this is what we do. The input and output signals of the equalization filter are Is represented as Here, Sout represents an output signal and Sin represents an input signal. a _i represents a weight called a tap coefficient, and δt represents a unit delay for each tap. Here, i shall run from 1 to n. That is,
The equalization filter is composed of n constitutional units, and in each constitutional unit, a phase delay δt is given to the input signal, and in the i-th constitutional unit, the signal is amplified or attenuated by the weight a _i times and output. However, the circuit is for generating the sum of the output signals of these constituent units. Here, by using the feedback signal (output signal before that) as the weight a _i , the equalization filter changes its response according to the output signal. By using a signal that correlates with the time-reversed output signal waveform as this feedback signal,
The above-mentioned automation can be realized.

FIG. 2 is a block diagram showing the structure of the automatic equalization filter. Reference numeral 10 is an equalization filter including a transversal filter, and 20 is an equalization filter 1 based on the output signal.
It is a feedback signal generating means for generating a feedback signal to be returned to each port of 0. The equalization filter 10 has n constituent units 1
0 ₁ comprises a to 10 _n, i-th unit of the structure 10 _i amplifies or attenuates the weight a _i by a factor signal by the feedback signal to the port with providing a phase lag δt to the signal as described above. The construction units 10 ₁ to 10 _n is the phase delay δt in each stage
Is given, the total phase delay increases by Δt in this order. Then, each of the structural units 10 ₁ to
The sum of the 10 _n output signals is the final output signal.

The feedback signal generating means 20 is an equalizing filter 10.
Of the output signal of the constituent unit 10 ₁ to
By dividing the number n of 10 _n in time, the signal amplitude value in each time slot is obtained by sampling,
Weighting a ₁ ~a of this port of the respective structural units 10 ₁ to 10 _{n
Let n} be the feedback signals b _{n to} b ₁ . The time of about μs, which is too fast for the light wave processing, can be said to be sufficiently slow for such sampling processing, and can be processed with a large margin.

In the feedback signal generating means 20, the sampling value of the n-th time slot (the last part of the pulse width a of the output signal) of the output signal, which is newest in time, is used as the feedback signal b _n having the weight a _1. The total delay of the digitizing filter 10 is δt
Return to the port of the structural unit 10 ₁ (with the smallest delay). Further, the total delay of the equalization filter 10 is nδt (the largest value), where the sampling value of the earliest time slot (leading portion in the pulse width a of the output signal) is used as the feedback signal b ₁ of the weight a _n. It is returned to the port of the (delay) constituent unit 10 _n . Generally, the feedback signal b _i is weighted to the port of the structural unit 10 _{n + 1-i} , _{where i} is an arbitrary integer of _{1 to n.
It} returns as _{n + 1-i} . By doing so, it is possible to realize an automatic waveform equalization process that constantly gives an output that effectively converges on the correlation between the original signal and its time-reversed waveform signal.

FIG. 3 is a characteristic diagram showing the result of numerical calculation emulating the characteristic of the present invention. What is indicated by the dotted line in the figure is the input signal. In order to simulate the deterioration waveform due to polarization dispersion, the following It is in the form of. Where the function r (t) is a finite rise /
It is a rectangular signal having a fall time, and τ corresponds to the phase difference caused by the waveform dispersion. Further, δ represents the amplitude ratio of the superimposed waveform. In FIG. 3, several different values are prepared for this phase difference τ, and the response output of the automatic equalization filter for each phase difference τ is shown as a solid line waveform.
Specifically, assuming that the signal repetition period is 100, τ = 5
There were 5 steps from ˜30 and δ = 0.7 was given. Effectively, a sufficient equalized waveform has been obtained.

The feedback signal to the port described above is not limited to the use of the time-reversed waveform of the output signal, but any form that realizes effective equalization processing may be used. it can.

[0014]

As described above, according to the present invention, it is possible to compensate the waveform deterioration caused by the polarization dispersion, which has become apparent in the high-speed optical transmission system. At this time, since the high-speed feedback signal generation means by electric control is used, it is possible to compensate for the waveform deterioration due to the time scale of the polarization dispersion of the order of μs, which is impossible by the light wave processing, with a time margin.

[Brief description of drawings]

FIG. 1 is a waveform diagram for explaining the principle of the present invention.

FIG. 2 is a block diagram of an automatic equalization filter according to the embodiment of the present invention.

FIG. 3 is an input / output waveform diagram by a simulation of an automatic equalization filter.

FIG. 4 is an explanatory diagram of polarization dispersion.

[Explanation of symbols]

1: an optical transmission path 2a, 2b: Henhajiku 10: equalizing filter, 10 ₁ to 10 _n: Configuration Unit 20: feedback signal generating means a ₁ ~a _n: weight b ₁ ~b _n: feedback signal

Claims (2)

[Claims] 1. An equalization filter for generating a plurality of signals having different phases and amplitudes based on an input signal and feedback signals to a plurality of amplitude adjusting ports, and outputting the sum of the generated signals as an output signal. Feedback signal generating means for inputting a plurality of amplitude signals corresponding to a signal waveform obtained by sampling the output signal of the equalization filter to the respective amplitude adjustment ports of the equalization filter as the feedback signals. An automatic equalization filter characterized by: 2. The automatic equalization filter according to claim 1, wherein the feedback signal generating means outputs a plurality of amplitude signals in the equalization filter at a timely new timing among the output signals of the equalization filter. A waveform with a small phase delay in the amplitude adjustment port is sent to the amplitude adjustment port related to generation, and an amplitude signal at a time old timing in the output signal is a waveform with a large phase delay in the plurality of amplitude adjustment ports. An automatic equalization filter characterized by being sent to an amplitude adjustment port for generation.