JP2002296146A - Method and system of time response measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize measurement of time response in such a condition that the rate of mark is close to that (i.e., 1/2) in actual mode. SOLUTION: An amplitude modulated light signal, in which a pseudo random pattern synchronized with a clock is used as modulation data, is received as a signal to be measured. A sample clock generating means 2 outputs a sampling clock 2a that can vary in the relation of timing to a clock 1b from a clock supply means 1. A short pulse generator 3 and a PRBS pattern generator 4 output a short pulse train 3a synchronized with the sampling clock 2a and a pseudo random pattern 4a with a pattern identical to the above pseudo random pattern respectively. The signal to be measured 1a, the short pulse train 3a and the pseudo random pattern 4a are multiplied by a multiplying means 5, averaged by a averaging means 8, and corrected by a means for correcting time response 9. The time response 9a is calculated on the basis of a value of correlation 8b obtained by varying the relation of timing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for evaluating the quality of an optical signal intensity-modulated by a digital signal.
The present invention relates to an apparatus for measuring a time response of an intensity.

[0002]

2. Description of the Related Art In general, when evaluating the quality of an optical signal, a method of converting an optical signal into an electric signal by a photodetector and measuring a voltage waveform by a sampling oscilloscope is used. In the case of a high-speed modulated signal, an optical sampling oscilloscope that directly samples an optical signal may be used. Both are based on a technique of sampling the signal under measurement at regular time intervals, except for the difference between the electrical signal and the optical signal and the difference in performance. Hereinafter, they are collectively referred to as sampling oscilloscopes.

When a signal modulated with actual random data is measured by a sampling oscilloscope, an eye pattern is obtained. Although the eye pattern is suitable for comprehensive evaluation of the modulated signal, it is difficult to observe details such as the tail of the time response since noise is superimposed and a large number of waveforms are displayed in an overlapping manner.

Therefore, as shown in FIG. 10A), when a modulation signal is used in which only one bit is "1" and the other n-1 bits are "0" in a cycle of n bits, the overlapping of the waveforms in the sampling oscilloscope is used. No time response can be measured.
An ideal waveform is a rectangular pulse shown in FIG. 10B), but an actual transmission signal has a deformed waveform as shown in FIG. 10C). Here, if the tail of a pulse overlaps the tail of an adjacent pulse, it cannot be distinguished, so the repetition period nT needs to be set longer than the width of the time response.

FIG. 9 shows an example of the configuration of a time response measurement using a sampling oscilloscope. The clock reproducing unit 1 generates a clock 1b having a repetition frequency (1 / nT) of the signal under measurement 1a or a frequency that is a fraction thereof. The variable delay unit 2 generates a sampling clock 2a by giving a delay to the clock 1b. The short pulse generator 3 generates a short pulse train 3a having a width shorter than the pulse width of the signal under measurement in synchronization with the sampling clock 2a. The multiplication means 6 comprises a signal under test 1a and a short pulse train 3a.
And outputs a multiplied signal 6a proportional to the multiplied value of. Detection means 7
Outputs a peak value of the multiplication signal 6a or a detection signal 7a proportional thereto. The averaging means 8 outputs a time response 8a by averaging the detected signal 7a with time.

The operation of the sampling oscilloscope having the above configuration will be described below. When the delay time of the variable delay unit 2 is 0, the short pulse train 3a is as shown in FIG. 10D). The multiplication signal 6a is the signal under measurement
The center of the pulse of 1a is sampled, and the detection signal 7a becomes a voltage corresponding to the center of the pulse of the signal under measurement 1a (FIG. 10E)). Next, the delay time of the variable delay 2 is T / 2
In this case, the short pulse train 3a is as shown in FIG. 10F). Multiplier signal
6a is obtained by sampling the right end of the pulse of the signal under measurement 1a, and the detection signal 7a is a voltage corresponding to the right end of the pulse of the signal under measurement 1a (FIG. 10G)). When noise is superimposed on the signal under measurement, noise is also superimposed on the detected signal. However, when the averaging means 8 averages the time, the noise is reduced. When measurement is performed while sweeping the delay time, a time response waveform is obtained as shown in FIG. 10H).

[0007]

However, the time response measurement using the sampling oscilloscope shown in FIG. 9 has the following problems. That is, as shown in FIG. 10, the mark ratio of the modulation data is 1 / n. The mark rate in the actual use state is usually 1/2, but it is necessary to make n sufficiently large to observe the tail of the time response and the like, and the mark rate becomes smaller than that in the actual use state. When the mark ratio is small, the average power of light is low, and the quality in the actual use state cannot be correctly evaluated. The present invention has been made in view of such circumstances, and uses a signal modulated by a pseudo random pattern as a signal to be measured, and measures the time response in a state where the mark ratio is close to 1/2 and close to actual use. The purpose is to realize.

[0008]

According to a first aspect of the present invention, there is provided a time response measuring method comprising the steps of: receiving an optical signal which is intensity-modulated using a pseudo random pattern synchronized with a clock as modulation data; A time response measuring method for receiving a measurement signal and measuring a time response of the signal under measurement, comprising: a short pulse train synchronized with a sampling clock whose temporal positional relationship with the clock is variable; Generating a signal of a product of the pseudo-random pattern signal having the same pattern as the pseudo-random pattern and the signal under measurement, and averaging the product signals to obtain a correlation value corresponding to the temporal positional relationship; Determining a correlation value corresponding to each of the plurality of temporal positional relationships obtained by the change of the temporal positional relationship. Characterized in that said obtaining the time response of the signal under measurement based on the correlation value al.

A time response measuring method according to a second aspect of the present invention is a method of measuring a time response of a signal under measurement by receiving an intensity-modulated optical signal as a signal under measurement using a pseudo-random pattern synchronized with a clock as modulation data. Is a product of a sampling clock whose temporal positional relationship with the clock is variable and a pseudo random pattern signal synchronized with the sampling clock and having the same pattern as the pseudo random pattern. Generating a signal of a product of these signals from the short pulse train and the signal under test that are compressed pulse trains, and averaging the signal of the product to obtain a correlation value corresponding to the temporal positional relationship, A correlation value corresponding to each of the plurality of temporal positional relationships obtained by the change in the temporal positional relationship is obtained, and based on the correlation values, Characterized in that to obtain the time response of the signal to be measured Te.

The time response measuring method according to a third aspect of the present invention is the time response measuring method according to any one of the first and second aspects, wherein the sampling having a frequency that is a natural number of a natural number of the clock frequency. The temporal positional relationship is made variable by delaying a clock by a variable predetermined time.

According to a fourth aspect of the present invention, there is provided the time response measuring method according to any one of the first and second aspects, wherein the sampling clock has a frequency that is a natural number of a frequency of the clock. The temporal positional relationship is made variable using sampling clocks having slightly different frequencies.

A time response measuring apparatus according to a fifth aspect of the present invention receives a light signal, which is intensity-modulated using a pseudo random pattern synchronized with a clock as modulation data, as a signal to be measured, and responds to the time response of the signal to be measured. A clock response means for supplying the clock, and receiving the clock supplied by the clock supply means, the clock response means having a frequency that is a natural number of a natural number of the clock. Sampling clock generating means for outputting a sampling clock whose temporal positional relationship is variable;
Upon receiving the sampling clock, a short pulse train synchronized with the sampling clock and a pseudo random pattern signal having the same pattern as the signal under measurement synchronized with the sampling clock are generated, and receiving the signal under measurement, Product signal generating means for generating a product signal of the signal under test, the short pulse train and the pseudo random pattern signal, and averaging for receiving and averaging the product signal and outputting a correlation signal corresponding to the temporal positional relationship Means for obtaining a correlation value corresponding to each temporal positional relationship of the temporal positional relationship that changes, and obtaining a time response of the signal under measurement based on the correlation values.

A time response measuring apparatus according to a sixth aspect of the present invention receives a light signal, which is intensity-modulated using a pseudo random pattern synchronized with a clock as modulation data, as a signal to be measured, and responds to the time response of the signal to be measured. A clock supply means for supplying the clock, and a sampling clock for receiving the clock supplied by the clock supply means and outputting a sampling clock having a variable temporal positional relationship with the clock. Generating means, receives the sampling clock, generates an optical pulse train synchronized with the sampling clock, and modulates the optical pulse train with a pseudo random pattern signal having the same pattern as the signal under measurement, synchronized with the sampling clock; After compression to generate a pseudo-random optical short pulse train,
A product signal generating means for receiving the signal to be measured and generating a signal of the product of the signal to be measured and the pseudo random short pulse train; receiving and averaging the signal of the product to correspond to the temporal positional relationship; Averaging means for outputting a correlation signal, obtaining a correlation value corresponding to each temporal positional relationship of the temporal positional relationship that changes, and obtaining a time response of the signal under measurement based on the correlation values. Features.

[0014]

FIG. 1 shows a basic configuration of a time response measuring apparatus according to the present invention. The signal under test 1a is a signal modulated with a pseudo random pattern (PRBS pattern). The clock supply means 1 calculates the data clock frequency of the signal under measurement 1a.
A clock 1b having a frequency of (1 / T) or a fraction thereof is generated. The sampling clock generating means 2 generates a clock
The sampling clock 2a is generated by giving a delay to 1b.
The short pulse generator 3 generates a short pulse train 3a having a width shorter than the pulse width of the signal under measurement 1a in synchronization with the sampling clock 2a. The PRBS pattern generator 4 synchronizes with the sampling clock 2a and synchronizes it with the signal under measurement 1a or converts it to an integer.
A PRBS pattern 4a thinned to 1 is generated. The short pulse generator 3 and the PRBS pattern generator 4 constitute a short pulse / PRBS pattern generating means 51. The multiplication means 5 outputs a multiplication signal 6b as a signal of a product proportional to a multiplication value of the signal under measurement 1a, the short pulse train 3a, and the PRBS pattern 4a. The short pulse / PRBS pattern generating means 51 and the multiplying means 5 constitute a product signal generating means 50. The averaging means 8 outputs a correlation signal 8b by time-averaging the multiplied signal 6b. Time response correction means
9 performs a correction operation as needed and outputs a time response 9a.

FIG. 2 shows a waveform example of each signal of the time response measuring device of the present invention. FIG. 2A) is a signal modulated with a pseudo random pattern having a period of 15 bits. FIG. 2B) shows a clock 1b having the same frequency as the data clock of the signal under measurement 1a. FIG. 2C) shows a short pulse train 3a when the delay time of the sampling clock 2a with respect to the clock 1b is 0. Figure 2
D) is the PRBS pattern 4a when the delay time of the sampling clock 2a with respect to the clock 1b is 0. Short pulse train 3a
If the short pulse is positioned near the center of each bit of the PRBS pattern 4a, even if the rising / falling portion of the waveform of the PRBS pattern 4a is deformed, there is no influence on the measurement. If the delay time is 0, the signal under test 1a and the data pattern of the PRBS pattern 4a match, so the signal under test
The product of 1a, short pulse train 3a and PRBS pattern 4a is as shown in FIG. 2E). By averaging the multiplied signal 6b, a correlation signal 8b shown in FIG. 2F) is obtained.

When the delay time is T / 2, FIG. 2 G), H),
As shown in I) and J), the value of the time at which the data of the signal under measurement 1a changes is reflected. When the delay time is T, the correlation signal 8b becomes a small value because the data of the signal under test 1a and the data of the PRBS pattern 4a are shifted as shown in FIG. 2 K), L), M), N). Becomes When the measurement is performed while sweeping the delay time, a correlation signal 8b as shown in FIG. 2O) is obtained, and the time response becomes as shown in FIG. 2P).

FIG. 3 shows a case where the frequency of the clock 1b is halved. FIG. 3A) is a signal modulated with a pseudo random pattern having a period of 15 bits. Figure 3B) shows the measured signal.
This is a clock 1b having a half frequency of the data clock 1a. FIG. 3C) shows a short pulse train 3a having a repetition cycle that is half the data clock of the signal under measurement 1a. FIG. 3D) shows a PRBS pattern 4a in which the pseudo random pattern of the signal under measurement is halved. Where there is a short pulse, the signal under test 1a
And the data pattern of the PRBS pattern 4a match, the product of the signal under test 1a, the short pulse train 3a and the PRBS pattern 4a is as shown in FIG. 3E). When the multiplied signal 6b is time-averaged twice as long as the PRBS cycle, the correlation signal 8b shown in FIG. 3F) is obtained.
When the delay time of the sampling clock 2a with respect to the clock 1b is T, it becomes as shown in FIG. 3 G), H), I), J).
The same correlation signal 8b as in the case of FIG. 2 is obtained.

As described above, even when the clock 1b having a frequency that is an integer fraction of the data clock of the signal under measurement 1a is used, the condition is such that the pseudo-random pattern decimated to the integral fraction makes one cycle. For example, the same result can be obtained as when using clocks of the same frequency. The averaging time is longer, but the clock frequency is lower, which makes the hardware easier. In the above description, the frequency of the clock 1b is halved, but if the frequency of the sampling clock 2a is halved even if the frequency of the clock 1b is the same as the data clock of the signal under measurement 1a, FIG. 3C) The following is the same.

In the present invention, the signal under test 1a and the short pulse train 3a
And the PRBS pattern 4a. Short pulse train
1 bit period T of signal under test 1a by multiplying by 3a
Has the effect of sampling a specific part of the PRBS pattern and the effect of multiplying by the PRBS pattern 4a to increase the correlation of only one bit within the period of the PRBS pattern.
The same effect as sampling the received waveform when only bits are transmitted as "1" can be obtained. It is conventionally known that the autocorrelation function of a PRBS pattern becomes impulse-like, but simply by correlating the signal under test 1a with the PRBS pattern 4a does not provide a time response with a resolution of 1 bit period or less. . Only by combining the correlation of the PRBS pattern and the sampling effect by the short pulse can the time response waveform be measured. The averaging also has the effect of reducing the effect of noise superimposed on the signal under measurement 1a. The effect of reducing noise increases as the averaging time increases.

The operation will be described below using mathematical expressions. Time response is g (t), PRBS data is Pi = {0, 1} (i: integer),
The clock period is T, the period (time) of the PRBS pattern is Tp,
The period (number of bits) of the PRBS pattern is Bp. Signal under test x (t) modulated with PRBS data, short pulse train s (t) with period T, P
The RBS pattern p (t) is as follows.

[0021]

(Equation 1)

[0022]

(Equation 2)

[0023]

(Equation 3)

Sampling clock for clock 1b
Assuming that the delay time of 2a is to, the multiplied signal 6b is

[0025]

(Equation 4)

## EQU1 ## Correlation signal when time averaged during Tp
r (to) is obtained.

[0027]

(Equation 5)

Here, it is assumed that the width of the time response g (t) is shorter than Tp, and a function in which g (t) repeats with a period Tp is defined as g ′ (t). And

[0029]

(Equation 6)

[0030]

(Equation 7)

In other words, the correlation value r (to) is

[0032]

(Equation 8)

## EQU1 ## Here, since the multiplication in one phenomenon is performed using the data of {0, 1} for both the signal under test 1a and the PRBS pattern 4a, the correlation signal 8b does not become zero even in the portion where the time response becomes zero. (8) In order to eliminate the second term,
The following correction operation is performed.

[0034]

(Equation 9)

When this is multiplied by a constant, a time response g '(to) is obtained.

[0036]

(Equation 10)

On the other hand, the pseudo random pattern of the signal under test 1a is {0, 1}, the pseudo random pattern of the PRBS pattern 4a is {-1, 1}, and the multiplication of the two phenomena results in a correlation value.
r (to) is

[0038]

[Equation 11]

## EQU2 ## Since a time response can be obtained directly, no correction operation is required.

The basic configuration and operation of the time response measuring device of the present invention have been described above. Next, an embodiment of the time response measuring method of the present invention will be described.
In the time response measurement method of the present invention, an optical signal that is intensity-modulated using a pseudo-random pattern synchronized with a clock as modulation data is used as a signal to be measured. Then, a short pulse train synchronized with the sampling clock whose temporal positional relationship with the clock is variable, a pseudo-random pattern signal synchronized with the sampling clock and having the same pattern as the pseudo-random pattern, and those signals from the signal under measurement. Generates a signal of the product of Next, the signal of the product is averaged to obtain a correlation value corresponding to the temporal positional relationship. As the correlation value, a correlation value corresponding to each of the temporal positional relationships having different temporal positional relationships is obtained. A time response of the signal under measurement is obtained based on the correlation values.

Even if the sampling clock has the same frequency as the clock, it is １ ／ of the frequency of the clock,
It may be 1/3, etc., as long as it has a frequency that is 1 / natural number of the clock frequency. The temporal positional relationship between the clock and the sampling clock is changed by delaying the sampling clock by a predetermined variable time with respect to the clock. By changing the delay time, the required number of temporal positional relationships is obtained. The frequency of the sampling clock may be slightly different from the frequency of a natural number of the clock, and the temporal positional relationship may be gradually changed over time.

Further, in order to generate a product signal, a sampling clock having a variable temporal positional relationship with the clock and a pseudo random pattern signal synchronized with the sampling clock and having the same pattern as the pseudo random pattern are used. A pulse train that is the product of these may be generated, and a signal of the product of those signals may be generated from the short pulse train obtained by compressing the pulse train and the signal under measurement. Even in this case, as a result, multiplication of the signal under measurement 1a, the short pulse train 3a, and the PRBS pattern 4a is performed. The third and fifth embodiments of the apparatus described later rely on this method.

FIG. 4 shows a first embodiment of the time response measuring apparatus according to the present invention. The first embodiment uses a clock recovery unit 1 as the clock supply unit 1 and a variable delay unit 2 as the sampling clock generation unit 2 in the basic configuration shown in FIG. 1, and the short pulse / PRBS pattern generation unit 51 generates a short pulse. A PR 3, comprising a PRBS pattern generator 4 and a multiplier 10, and multiplying a short pulse train 3a by a PRBS pattern 4a.
This is an example in which the BS short pulse train 10a is sent to the multiplication means 5.

Clock recovery unit as clock supply means
1, a variable delay device as a sampling clock generating means 2,
The short pulse generator 3, the PRBS pattern generator 4, the averaging unit 8, and the time response correction unit 9 have the same reference numerals as those in FIG. The signal under test 1a is an optical signal modulated with a pseudo random pattern (PRBS pattern). The multiplier 10 includes the short pulse train 3a and the PR
The PRBS short pulse train 10a is output as the product of the BS pattern 4a. The PRBS short pulse train 10a is a signal in which a short pulse exists when the PRBS data is "1" and does not exist when the PRBS data is "0". The multiplication means 5 includes an optical modulator 11 and a photodetector 12. The optical modulator 11 converts the signal under test 1a which is an optical signal
The signal is modulated by the PRBS short pulse train 10a and a multiplied optical signal 11a is output. The multiplied optical signal 11a is composed of the signal under test 1a and the short pulse train 3a.
This is an optical signal proportional to the product of the PRBS pattern 4a. When this is converted into an electric signal by the photodetector 12, a multiplied electric signal 12a corresponding to the multiplied signal 6b in FIG. 1 is obtained. Thereafter, by performing averaging and time response correction in the same manner as in FIG. 1, a time response 9a is obtained. In the present embodiment, the short pulse train 3a, PR
Since both BS patterns 4a are {0, 1} signals, the multiplier
10 can be realized by a digital switch.

FIG. 5 shows a second embodiment. The second embodiment uses a clock recovery unit 1 as the clock supply unit 1 and a frequency synthesis unit 2 as the sampling clock generation unit 2 in the basic configuration shown in FIG.
Set the PRBS pattern generator 4 of the BS pattern generator 51 to bipolar
This is an example in which a PRBS pattern generator 4 is used, and a multiplying means 5 is composed of an optical modulator 13, a photodetector 14, and a multiplier 15. The band limiting section 8 is used as the averaging means 8.

The clock recovery unit 1 and the short pulse generator 3
This is the same as the first embodiment (FIG. 4), and the same reference numerals are given. The signal under test 1a is an optical signal modulated with a pseudo random pattern. The frequency synthesizer 2 uses a clock
A sampling clock 2b having a frequency slightly different from the frequency of 1b is generated. This has the same effect as continuously increasing or decreasing the delay amount of the variable delay device 2 of the first embodiment, and a time response can be obtained continuously. The optical modulator 13 modulates the optical signal 1a with the short pulse train 3a and outputs a sampling optical signal 13a. The photodetector 14 converts the sampling optical signal 13a into an electrical signal and
Is output. This sampling signal 14a is
a is a signal sampled by the short pulse train 3a, which is the same as that of the conventional sampling oscilloscope. The bipolar PRBS pattern generator 4 is a {-1, 1} bipolar PRBS pattern.
Generate 4b. The multiplier 15 outputs the product of the sampling signal 14a and the bipolar PRBS pattern 4b. Since the sampling signal 14a is unipolar and the PRBS pattern 4b is bipolar,
Multiplication of two phenomena is necessary. The band limiter 8 is a low-pass filter having a cutoff frequency lower than the repetition frequency of the short pulse train 3a, and has an effect of continuously averaging the multiplied signal 15a.

In this embodiment, since the multiplier 15 performs multiplication of two phenomena using a bipolar PRBS pattern, the output of the band limiting section 8 becomes a time response 9a, and no correction operation is required. Since the signal after sampling is input to the multiplier 15, the multiplier 15 only needs to operate at the frequency of the clock 1b and does not need to pass the harmonic component of the short pulse train. As shown in FIG. 3, since the frequency of the clock 1b can be set to an integer fraction of the data clock of the signal under measurement 1a, a multiplier that is lower in speed than that of the first embodiment is used. I can do it. The sampling signal 14a is the same as the measurement result of the conventional sampling oscilloscope. An eye pattern can be obtained by measuring a signal under measurement modulated by a pseudo-random pattern with a sampling oscilloscope, so that the eye pattern and the time response can be measured simultaneously.

FIG. 6 shows a third embodiment. The third embodiment uses a clock recovery unit 1 as the clock supply unit 1 and a variable delay unit 2 as the sampling clock generation unit 2 in the basic configuration shown in FIG.
The pattern generator 51 emits an optical pulse train 21a synchronized with the sampling clock 2a, a light source 21, a PRBS pattern generator 4, an optical modulator 22 for modulating the optical pulse train 21a with a PRBS pattern 4a, and an optical modulator 22. PRBS optical pulse train
An example in which an optical pulse compression unit 23 that receives and compresses 22a and outputs a PRBS optical short pulse train 23a is configured, and a multiplication unit 5 that receives the PRBS optical short pulse train 23a is configured by a nonlinear optical crystal 26 and a photodetector 27. It is.

The clock recovery unit 1, variable delay unit 2, PRBS pattern generator 4, averaging unit 8, and time response correction unit 9 are the same as those in the first embodiment, and are denoted by the same reference numerals. The light source 21 outputs an optical pulse train 21a intensity-modulated by the sampling clock 2a. The optical modulator 22 includes an optical pulse train 21a
Is modulated by the PRBS pattern 4a, and a PRBS optical pulse train 22a is output. The optical pulse compression unit 23 compresses the pulse width of light using nonlinear phenomena such as dispersion-reducing fiber, and
An optical short pulse train 23a is output. The optical amplifiers 24 and 25 amplify the PRBS short optical pulse train 23a and the signal under measurement 1a, respectively, and set the optical power to such an extent that a nonlinear phenomenon occurs in the nonlinear optical crystal 26. The nonlinear optical crystal 26 generates a sum frequency light 26a having a frequency equal to the sum of the optical frequencies of both input lights due to a nonlinear phenomenon. Here, the intensity of the sum frequency light 26a is proportional to the product of the intensity of both input lights. The photodetector 27 is a photoelectric converter that responds only to the light wavelength of the sum frequency light 26a, and the signal under test 1a and the PR
A multiplication signal 27a, which is an electric signal proportional to the product of the BS short optical pulse train 23a, is output. The multiplication signal 27a is the multiplication signal 6b of FIG.
The time response 9a is obtained by averaging and correcting the time response in the same manner as in FIG.

In the present embodiment, the technique of the optical sampling oscilloscope is used. When the optical pulse width is compressed by the dispersion reducing fiber, a pulse width shorter than a short pulse of a general electric signal is obtained, and the multiplication by the nonlinear optical crystal has no band limitation of the optical modulator. For this reason, there is a feature that the time resolution can be made higher than in the first embodiment.

FIG. 7 shows a fourth embodiment. The fourth embodiment uses a clock recovery unit 1 as the clock supply unit 1 and a frequency synthesis unit 2 as the sampling clock generation unit 2 in the basic configuration shown in FIG.
The short pulse generator 3 of the BS pattern generating means 51 is turned on by the light source 30 for emitting the CW light 30a, the CW light 30a and the sampling clock 2b.
And an optical modulator 31 for outputting an optical pulse train 31a synchronized with the sampling clock 2b, and receiving and compressing the optical pulse train 31a emitted from the optical modulator 31 to produce an optical short pulse train.
An optical short pulse generator 3 having an optical pulse compression unit 32 that outputs 32a, a PRBS pattern generator 4 as an ambipolar PRBS pattern generator 4, and a multiplier 5 as a nonlinear optical crystal 34, a photodetector 35, and a multiplier. This is an example composed of 15 and 15. Averaging means 8
The band limiting unit 8 is used as the control unit.

Clock recovery unit 1, frequency synthesis unit 2, bipolar
The PRBS pattern generator 4, multiplier 15, and band limiting unit 8
This embodiment is the same as the embodiment (FIG. 5), and is denoted by the same reference numerals. The light source 30 outputs CW light 30a having a constant intensity. The optical modulator 31 converts the CW light 30a into a sampling clock 2b.
And generates an optical pulse train 31a synchronized with the sampling clock 2b. The optical pulse compression unit 32 compresses the pulse width of light by using a nonlinear phenomenon such as a dispersion reducing fiber, and outputs an optical short pulse train 32a. Optical amplifier 33, 25
Amplifies the optical short pulse train 32a and the signal under measurement 1a, respectively,
The optical power is set to such an extent that a nonlinear phenomenon occurs in the nonlinear optical crystal. The nonlinear optical crystal 34 has a sum frequency light 34a which is the sum of the optical frequencies of both input lights due to the nonlinear phenomenon.
Occurs. Here, the intensity of the sum frequency light 34a is proportional to the product of the intensity of both input lights. The photodetector 35 is a photoelectric converter that responds only to the light wavelength of the sum frequency light 34a, and outputs a sampling signal 35a, which is an electric signal proportional to the product of the signal under measurement 1a and the optical short pulse train 32a. This sampling signal 35a
Is a signal obtained by sampling the signal under measurement 1a with the optical short pulse train 32a, which is the same as that of the conventional optical sampling oscilloscope. Thereafter, as in the second embodiment, the bipolar PRBS pattern generator 4 outputs the bipolar PRBS pattern of {-1, 1}.
4b, and the multiplier 15 outputs the sampling signal 35a and the PRBS
The multiplication signal 15a, which is the product of the pattern 4b, is output. The band limiting section 8 is a low-pass filter having a cutoff frequency lower than the repetition frequency of the optical short pulse train 32a, and has an effect of continuously averaging the multiplied signal 15a. In the present embodiment, since the multiplication of the two phenomena is performed, the band limiting unit 8
Output becomes the time response 9a.

In this embodiment, the configuration of the second embodiment is realized by using the technology of the optical sampling oscilloscope. For this reason, it has both the features of the second embodiment, in which a correction operation is unnecessary, a low-speed multiplier can be used, and an eye pattern and a time response can be measured simultaneously, and high time resolution by optical sampling.

FIG. 8 shows a fifth embodiment. In the fifth embodiment, a DC generator 41 and a PRBS pattern generator 4 are added to the short pulse / PRBS pattern generator 51 of the third embodiment.
Between the output signal 41a of the DC generator 41 and the PRBS pattern 4a from the PRBS pattern generator 4 as a modulation signal.
An optical short pulse / PRBS optical short pulse generating section 40 to which a first switch 42 is added for outputting to the output section, and further, after the time response correcting section 9, the output of the multiplying means 5 and the averaging section 8 and the time response correcting section This is an example in which a second switch 43 that outputs one of the outputs via the unit 9 is added.

Clock recovery unit 1, variable delay unit 2, optical amplifier 2
4, 25, the nonlinear optical crystal 26, the photodetector 27, the averaging unit 8, and the time response correction unit 9 are the same as in the third embodiment, and are denoted by the same reference numerals. Optical short pulse / PRBS The optical short pulse generator 40 switches and outputs an optical short pulse train synchronized with the sampling clock 2a and a PRBS optical short pulse train similar to the one 23a in the third embodiment. Then, the output 27a of the photodetector 27
And a switch 43 for switching the output 9a of the time response corrector 9. Optical short pulse / PRBS PR in optical short pulse generator 40
When the BS optical short pulse train is output and the switch 43 is set to the time response 9a side, the output 43a can obtain the same time response as in the third embodiment. Optical short pulse / PRBS The optical short pulse train is output in the optical short pulse generator 40 and the switch 43 is multiplied by a signal 27a.
When it is set to the side, the configuration is the same as that of the conventional optical sampling oscilloscope. When the signal under measurement 1a is a signal modulated by the PRBS pattern, the eye pattern can be observed.

Optical Short Pulse / PRBS The optical short pulse generator 40
For example, the configuration is as follows. PRBS pattern generator 4,
The light source 21, the optical modulator 22, and the optical pulse compression unit 23 are the same as those in the third embodiment, and are denoted by the same reference numerals. A DC generator 41 for generating a DC voltage corresponding to the "1" level of the PRBS pattern generator 4, a PRBS pattern 4a and a DC voltage 41a
And a switch 42 for switching the output of the switch 42.
Is input to the optical modulator 22. Switch 42 to PRBS pattern
When set to 4a, the configuration is the same as that of the third embodiment.
A PRBS optical short pulse train is output. Switch 42 to DC voltage
When it is set to the 41a side, the input 42a of the optical modulator 22 becomes a direct current and is not modulated by the optical modulator 22, so that the optical pulse train 21a at a constant interval is output as it is. Optical pulse compression unit 23
In order to compress the pulse width of the optical pulse train, an optical short pulse train at a constant interval is output. As described above, the time response measuring device and the optical sampling oscilloscope can be switched with a slight addition to the third embodiment.

As described above, in the embodiment, the clock reproducing means is used as the clock supplying means. However, instead of reproducing the clock from the signal under measurement, an external clock signal is received at the terminal and supplied. Is also good. Also,
As the sampling pulse generating means 2, both the variable delay device and the frequency synthesizer can be applied to any of the embodiments.

When a frequency synthesizing unit is used as the sampling clock generating means 2, the effect is the same as continuously increasing or decreasing the delay amount of the variable delay device. Naturally, a method of continuously obtaining a time response by performing averaging is used. In the embodiment using the above-described frequency synthesizer, a band limiter is used.
However, as the averaging means, both the averaging unit and the band limiting unit can be applied to any of the embodiments.

[0059]

According to the time response measuring method of the present invention, an optical signal whose intensity is modulated as a modulated data using a pseudo random pattern synchronized with a clock is received as a signal to be measured, and the temporal positional relationship with the clock is variable. A short pulse train synchronized with the sampling clock, a pseudo random pattern signal synchronized with the sampling clock and having the same pattern as the pseudo random pattern, and a signal of a product of those signals are generated from the signal under measurement, and a signal of the product is generated. Average to obtain a correlation value corresponding to the temporal positional relationship, and based on the correlation values, determine correlation values corresponding to a plurality of temporal positional relationships obtained by changing the temporal positional relationship. The time response of the signal under measurement was obtained.

Further, the time response measuring device of the present invention receives an optical signal whose intensity is modulated using a pseudo random pattern synchronized with a clock as modulation data as a signal to be measured, and measures the time response of the signal to be measured. Clock supply means for supplying the clock, and a sampling clock which receives the clock supplied by the clock supply means, has a frequency which is a natural number of a natural number of the clock, and has a variable temporal positional relationship with the clock. Receiving the sampling clock, generating a short pulse train synchronized with the sampling clock and a pseudo-random pattern signal having the same pattern as the signal under measurement, synchronized with the sampling clock, and Receiving the signal under test, the signal under test, the short pulse train and the A product signal generating means for generating a signal of a product of pseudo-random pattern signal, and a further comprising an averaging means for outputting a correlation signal corresponding to the averaged the temporal positional relationship upon receiving a signal integrating. As described above, the measurement of the time response in a state where the mark ratio is close to 1/2 and close to actual use can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of the present invention.

FIG. 2 is a diagram showing waveforms of respective parts of the present invention.

FIG. 3 is a diagram showing a waveform when the frequency of a clock 1b is half the clock frequency of a signal under measurement in the present invention.

FIG. 4 is a block diagram showing a first embodiment of the present invention.

FIG. 5 is a block diagram showing a second embodiment of the present invention.

FIG. 6 is a block diagram showing a third embodiment of the present invention.

FIG. 7 is a block diagram showing a fourth embodiment of the present invention.

FIG. 8 is a block diagram showing a fifth embodiment of the present invention.

FIG. 9 is a block diagram showing a time response measurement by a conventional sampling oscilloscope.

FIG. 10 is a diagram showing waveforms of respective units in a conventional time response measurement using a sampling oscilloscope.

[Explanation of symbols]

1 Clock supply means (Clock regeneration unit) 1a Signal under test 1b Clock 2 Sampling clock generation means (Variable delay unit, frequency synthesis unit) 2a Sampling clock 2b Sampling clock 3 Short pulse generator (Optical short pulse generator) 3a Short pulse train 4 PRBS pattern generator (bipolar PRBS pattern generator) 4a PRBS pattern (pseudo random pattern signal) 4b Bipolar PRBS pattern 5 Multiplication means 6 Multiplication means 6a Multiplication signal 6b Multiplication signal (product signal) 7 Detection means 7a Detection Signal 8 Averaging unit (averaging unit, band limiting unit) 8a Time response 8b Correlation signal 9 Time response correcting unit (time response correcting unit) 9a Time response 10 Multiplier 10a PRBS short pulse train 11 Optical modulator 11a Multiplied optical signal 12 Photodetector 12a Multiplied electrical signal (product signal) 13 Optical modulator 13a Sampling optical signal 14 Photodetector 14a Sampling signal 15 Multiplier 15a Multiplied signal 21 Light source 21a Optical pulse train 22 Optical modulator 22a PRBS RZ optical signal 23 Optical pulse compression unit 23a PRBS optical short pulse train 24 Optical amplifier 25 Optical amplifier 26 Nonlinear optical crystal 26a Sum frequency light 27 Photodetector 27a Multiplied signal ( 30 light source 30a CW light 31 optical modulator 31a optical pulse train 32 optical pulse compressor 32a optical short pulse train 33 optical amplifier 34 nonlinear optical crystal 34a sum frequency light 35 photodetector 35a sampling signal 40 optical short pulse / PRBS light Short pulse generator 40a Optical short pulse train or PRBS optical short pulse train 41 DC generator 41a DC voltage 42 switch 42a PRBS pattern or DC voltage 43 switch 43a Time response or sampling signal 50 Product signal generation means 51 Short pulse / PRBS pattern generation means

Claims (6)

[Claims] 1. A time response measuring method for receiving a light signal, which is intensity-modulated using a pseudo random pattern synchronized with a clock as modulation data, as a signal to be measured and measuring a time response of the signal to be measured, A short pulse train synchronized with a sampling clock whose temporal positional relationship is variable, a pseudo random pattern signal synchronized with the sampling clock and having the same pattern as the pseudo random pattern, and a signal of a product of those signals from the signal under measurement And averaging the signal of the product to obtain a correlation value corresponding to the temporal positional relationship, corresponding to a plurality of temporal positional relationships obtained by changing the temporal positional relationship. A time response measurement method for obtaining a time response of the signal under measurement based on the correlation values obtained. . 2. A time response measuring method for receiving an optical signal intensity-modulated using a pseudo-random pattern synchronized with a clock as modulation data as a signal to be measured and measuring a time response of the signal to be measured, A short pulse train which is a product of a sampling clock whose temporal position relationship is variable and a pseudo random pattern signal synchronized with the sampling clock and having the same pattern as the pseudo random pattern, Generating a signal of a product of the signals; and averaging the signal of the product to obtain a correlation value corresponding to the temporal positional relationship, wherein a plurality of each obtained by the change of the temporal positional relationship are included. Obtaining a correlation value corresponding to a temporal positional relationship, and obtaining a time response of the signal under measurement based on the correlation value. Time response measurement method. 3. A method according to claim 1, wherein said sampling clock having a frequency which is 1 / natural number of said clock frequency is delayed by a variable predetermined time to make said temporal positional relationship variable. The time response measurement method described in Crab. 4. The temporal position relationship is variable by using a sampling clock having a frequency slightly different from a frequency of a natural number of a frequency of the clock as the sampling clock. The time response measurement method according to any one of the above. 5. A time response measuring device for receiving an optical signal intensity-modulated using a pseudo random pattern synchronized with a clock as modulation data as a signal to be measured and measuring a time response of the signal to be measured, wherein the clock Receiving a clock (1b) supplied by the clock supplying means, and having a frequency that is a natural number of a natural number of the clock and having a variable temporal positional relationship with the clock. Sampling clock generating means for outputting a sampling clock (2)
Receiving the sampling clock, generating a short pulse train synchronized with the sampling clock and a pseudo-random pattern signal synchronized with the sampling clock and having the same pattern as the signal under measurement, and receiving the signal under measurement. A product signal generating means (50) for generating a signal (6b) of the product of the signal to be measured, the short pulse train and the pseudo random pattern signal, and receiving and averaging the product signal to correspond to the temporal positional relationship And an averaging means (8) for outputting a correlation signal (8b) that changes, and obtains a correlation value corresponding to each temporal positional relationship of the temporal positional relationship that changes, and calculates the correlation value based on the correlation values. A time response measuring device for obtaining a time response of a signal. 6. A time response measuring apparatus for receiving a light signal, which is intensity-modulated using a pseudo random pattern synchronized with a clock as modulation data, as a signal to be measured and measuring a time response of the signal to be measured, Clock supply means (1) for supplying a clock signal; sampling clock generation means (2) for receiving a clock (1b) supplied by the clock supply means and outputting a sampling clock having a variable temporal positional relationship with the clock; Receiving the sampling clock, generating an optical pulse train synchronized with the sampling clock, modulating the optical pulse train with a pseudo random pattern signal having the same pattern as the signal under measurement, synchronized with the sampling clock, and post-compressing A pseudo random optical short pulse train is generated, and the measured signal and the measured signal are received in response to the measured signal. And a product signal generating means (50) for generating a product signal (27a) of the pseudo random optical short pulse train, and receiving and averaging the product signal to output a correlation signal (8b) corresponding to the temporal positional relationship. Averaging means (8) for obtaining a correlation value corresponding to each temporal positional relationship of the changing temporal positional relationship, and obtaining a time response of the signal under measurement based on the correlation values. Time response measuring device.