JP2001349805A - Light characteristics measurement device, method and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for making the frequency of signal for modulation of light source match the frequency of signal for phase detection. SOLUTION: The device comprises a power source 14 for modulation, producing a signal for modulation for giving a frequency fa for modulation used for light modulation, a power source for a frequency direction 26 producing a signal for phase detection, for giving frequency of signal to detect the phase of transmission light, a band-pass filter 16a with a pass range of a specific range from the frequency fa of the signal for modulation, where the signal for phase detection is input, a measurement part 16b for measuring the amplitude of the output results of the band-pass filter 16a, and a frequency adjusting part 18, which makes a frequency fb with the maximum amplitude of the signal for phase detection the frequency fa of the signal for modulation, based on the measurement results of the measurement part 16b. With the frequency adjustment part 18, the frequency fb of the signal for phase detection and the frequency fa of the signal for modulation of the power source can be made to match.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an optical fiber and the like.
The present invention relates to measurement of a wavelength dispersion characteristic of a DUT (Device Under Test).

[0002]

2. Description of the Related Art FIG. 5 shows the configuration of a measurement system for measuring the wavelength dispersion characteristics of a device under test (DUT) such as an optical fiber.
As shown in FIG. 5, the measurement system is divided into a light source system 10 and a characteristic measurement system 20. The variable wavelength light source 12 of the light source system 10 changes the wavelength λx to generate light.
This light is modulated by the optical modulator 15 at the frequency fa of the modulation signal generated by the modulation power supply 14 and is incident on the DUT 30.

The light transmitted through the DUT 30 is transmitted to a photoelectric converter 22.
Is converted into an electric signal. The phase of this electric signal is detected by the phase comparator 24. From this phase, DUT3
The group delay and chromatic dispersion of 0 can be obtained.

Here, the electric signal output from the photoelectric converter 22 has a maximum amplitude at a frequency fa as shown in FIG. 6, but the amplitude does not always become zero at other frequencies. Therefore, a band-pass filter is provided in the phase comparator 24 so as to extract only components near the frequency fa. Here, the width Δf of the frequency at which the band-pass filter allows transmission is constant. On the other hand, the center of the frequency that allows transmission is given from the outside. Therefore, the frequency indicating power supply 26 of the characteristic measuring system 20 is switched to the frequency fb
Is supplied to the band-pass filter.
That is, the frequency fb is the center of the frequency that allows transmission. Note that fb is set to be equal to fa. In FIG. 6, the hatched area indicates
It is outside the pass band of the band pass filter.

[0005]

However, strictly speaking, fb and fa have a frequency difference. For example, f
Even if b = fa = 3 GHz, there is a frequency difference of about 10 KHz. Then, as shown in FIG. 7, fa is not included in the band of the frequency at which the band-pass filter allows transmission. In particular, when the band of the frequency that allows transmission is narrow, fa is often not included. Then, the component of the frequency fa is excessively attenuated, and the signal sensitivity is reduced. If the frequency band allowing transmission is widened, the component of the frequency fa can be prevented from being excessively attenuated.
/ N ratio (signal to noise ratio) becomes worse. In addition, since the reference frequency differs for the group delay characteristic and the distance measurement, the measured values differ, and individual differences between devices occur.

Accordingly, an object of the present invention is to provide an apparatus or the like for matching the frequency of a modulation signal of a light source with the frequency of a phase detection signal.

[0007]

According to a first aspect of the present invention, there is provided an apparatus for measuring characteristics of an object to be measured which transmits light, and generates a modulation signal for providing a modulation frequency used for modulation. Modulation signal generation means, optical modulation means for supplying incident light obtained by modulating variable wavelength light at a modulation frequency to a device under test, and phase detection for generating a phase detection signal for providing a frequency of a signal whose phase is to be detected Signal generation means, phase detection means for detecting the phase of the frequency component of the signal whose phase is to be detected, of the transmitted light whose incident light has passed through the device under test, and within a predetermined range from the frequency of the modulation signal. Amplitude measuring means for measuring the amplitude of the phase detection signal at a frequency of the frequency, and frequency adjusting means for setting the frequency at which the amplitude of the phase detection signal is maximum to the frequency of the modulation signal based on the measurement result of the amplitude measurement means And the phase Hazuki configured to measure a property of the object to be measured.

[0008] According to the optical characteristic measuring device configured as described above, the frequency of the phase detection signal and the frequency of the modulation signal can be matched by the frequency matching means.

According to a second aspect of the present invention, in the first aspect, the amplitude measuring means sets a pass band within a predetermined range from the frequency of the modulation signal, and receives the phase detection signal. And a measuring means for measuring the amplitude of the output result of the band-pass filter.

The invention according to claim 3 is the invention according to claim 1 or 2, wherein the modulation signal generating means is configured to be able to change the frequency of the modulation signal.

The invention according to claim 4 is the invention according to claim 3, wherein the variation width of the frequency of the modulation signal is equal to or greater than the difference between the frequency of the modulation signal and the frequency of the phase detection signal. Is configured to be

According to a fifth aspect of the present invention, there is provided a method for measuring characteristics of an object to be measured which transmits light, the method comprising a step of generating a modulation signal for providing a modulation frequency to be used for modulation. An optical modulation step of supplying incident light obtained by modulating the variable wavelength light with a modulation frequency to the device under test, and a phase detection signal generation step of generating a phase detection signal that gives the frequency of the signal whose phase is to be detected, A phase detecting step of detecting a phase of a frequency component of a signal whose phase is to be detected, of a transmitted light in which the incident light has transmitted through the device under test; Based on the measurement result of the amplitude measurement step for measuring the amplitude of the
A frequency adjustment step of setting the frequency at which the amplitude of the phase detection signal is maximized to the frequency of the modulation signal, so as to measure the characteristics of the device under test based on the phase.

According to a sixth aspect of the present invention, there is provided a computer-readable recording medium having recorded thereon a program for causing a computer to execute a process of measuring characteristics of an object through which light passes, and which is used for modulation. Signal generation processing for generating a modulation signal that provides a modulation frequency to be modulated, optical modulation processing for supplying incident light obtained by modulating variable wavelength light with the modulation frequency to the device under test, and processing of a signal whose phase is to be detected. Phase detection signal generation processing for generating a phase detection signal for giving a frequency, and phase detection processing for detecting the phase of the frequency component of the signal whose phase is to be detected in the transmitted light whose incident light has passed through the device under test An amplitude measurement process for measuring the amplitude of the phase detection signal at a frequency within a predetermined range from the frequency of the modulation signal, and an amplitude of the phase detection signal based on the measurement result of the amplitude measurement process. The frequency at which the large, and a frequency adjustment process of the frequency of the modulation signal, a recording medium for measuring the characteristics of the object to be measured based on the phase.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of an optical characteristic measuring device according to an embodiment of the present invention. The optical characteristic measuring device according to the embodiment of the present invention includes a light source system 10 connected to one end of the DUT 30 and a characteristic measuring system 20 connected to the other end of the DUT 30. DUT30
Is a device that transmits light, and is, for example, an optical fiber.

The light source system 10 includes a variable wavelength light source 12,
A power supply for modulation 14, an optical modulator 15, an amplitude measuring unit 16, and a frequency adjusting unit 18 are provided. The variable wavelength light source 12 generates variable wavelength light whose wavelength can be changed. Variable wavelength light source 1
2, the wavelength λx of the variable wavelength light can be swept. The modulation power supply 14 supplies the optical modulator 15 with a modulation signal having a frequency (modulation frequency) fa at which the variable wavelength light is to be modulated. The modulation power supply 14 can sweep and change the modulation frequency fa. The optical modulator 15 modulates the variable wavelength light at the modulation frequency fa and makes the light enter the DUT 30. The optical modulator 15 includes a lithium niobate (L
N) is common, but LN need not be included as long as the light intensity can be modulated.

The amplitude measuring section 16 includes the band-pass filter 1
6a and a measuring unit 16b. The bandpass filter 16a has a passband within a predetermined range from the modulation frequency fa of the modulation power supply 14, for example, ± Δf / 2. Generally, the pass band of the band-pass filter 16a is set to ± Δf / 2 from the center frequency, and the center frequency can be strictly matched with the modulation frequency fa. Note that the frequency of the input signal is the modulation frequency f
If a exceeds a predetermined range from a, the output signal is greatly attenuated. The bandpass filter 16a receives an electric signal output from a power supply 26 for frequency instruction, which will be described later. The band-pass filter 16a mainly outputs the frequency components in the pass band among the electric signals output from the frequency indicating power supply 26. The measuring unit 16b measures the maximum value of the electric signal output from the bandpass filter 16a and the frequency at which the electric signal takes the maximum value, and outputs the measured value to the frequency matching unit 18.

The frequency adjusting section 18 adjusts the modulation frequency fa of the modulation power supply 14 to a frequency at which the amplitude of the electric signal (phase detection signal) output from the frequency indicating power supply 26 becomes maximum.
To match. The frequency indicating power supply 26 generates a phase detection signal having a frequency fb of a signal whose phase is to be detected. However, as shown in FIG. 3A, electric signals of other frequency components are input to the band-pass filter 16a in a mixed form. Here, the amplitude of the phase detection signal generated by the frequency indicating power supply 26 becomes maximum at the frequency fb. Therefore, the frequency matching unit 18 determines the frequency fb
Then, the modulation frequency fa of the modulation power supply 14 is adjusted.

Light incident on the DUT 30 passes through the DUT 30. Light transmitted through the DUT 30 is called transmitted light.

The characteristic measuring system 20 includes the photoelectric converter 2
2. It has a phase detector 24 and a power supply 26 for frequency indication.

The photoelectric converter 22 converts the transmitted light into an electric signal. The phase detector 24 includes a band-pass filter 24a
And a phase comparator 24b. The pass band of the band-pass filter 24a is within a predetermined range, for example, ± Δf / 2 from the frequency fb of the phase detection signal generated by the frequency indicating power supply 26. If the frequency of the input signal exceeds a predetermined range from the frequency fb, the output signal is greatly attenuated. An electric signal output from the photoelectric converter 22 is input to the bandpass filter 24a. The band-pass filter 24a mainly outputs the frequency components in the pass band among the electric signals output from the photoelectric converter 22. The phase comparator 24b compares the phase of the electric signal output from the bandpass filter 24a with the phase of the reference electric signal,
The phase difference between them is detected. The reference electric signal is
For example, the transmission light when the light having the wavelength with the minimum chromatic dispersion is incident on the DUT 30 is photoelectrically converted. The frequency indicating power supply 26 is connected to the bandpass filter 16.
a and a band-pass filter 24a are supplied with a phase detection signal having a frequency fb.

Next, the operation of the embodiment of the present invention will be described with reference to the flowchart of FIG.

The variable wavelength light source 12 of the light source system 10 changes the wavelength to generate light. This light is modulated by the optical modulator 15 at the modulation frequency fa of the modulation signal generated by the power supply 14.
And is incident on the DUT 30.

The light transmitted through the DUT 30 is transmitted to the photoelectric converter 22
Is converted into an electric signal. This electric signal is input to the band-pass filter 24a, and the power
Only the components near the frequency fb of the phase detection signal generated by are extracted. Then, by the phase comparator 24b,
The phase difference between the output signal of the bandpass filter 24a and the reference electric signal is measured. Therefore, if fa and fb match, the phase difference measurement by the phase comparator 24b becomes accurate. Since the group delay, chromatic dispersion, and the like of the DUT 30 are obtained from the phase difference, if fa and fb match, the chromatic dispersion of the DUT 30 can be accurately obtained.

Here, a procedure for matching fa and fb will be described. First, the frequency fb of the phase detection signal generated by the frequency indicating power supply 26 is fixed and input to the band-pass filter 16a of the amplitude measuring unit 16 (S1).
0). The waveform of the electric signal input to the band-pass filter 16a is, as shown in FIG.
Although the maximum value Amax is obtained at the frequency fb of the phase detection signal generated by No. 6, frequency components other than the frequency fb are also included.

Next, it is assumed that the modulation frequency fa of the modulation signal generated by the modulation power supply 14 is swept, and it is determined whether the sweep is completed (S12). If the sweep has not been completed (S12, No), the modulation frequency fa is swept (S12).
14). In the sweeping of the modulation frequency fa, the modulation frequency fa is increased as shown in FIG. Here, it is assumed that a lower limit (initial value f0) and an upper limit (final value f1) for sweeping the modulation fa are determined. In addition,
The sweep method is not limited to monotonic increase as in the present embodiment,
It is arbitrary such as monotonically decreasing or combining decreasing and increasing. Further, the width f1-f0 of the change in the frequency of the modulation signal generated by the modulation power supply 14 is slightly larger than the difference between fa and fb. For example, if fa and fb are 1GH
If it is set to z, f1−f0 = about 30 kHz. Further, since the bandpass filter 16a has a passband of ± Δf / 2 from the modulation frequency fa that exactly matches the center frequency, if the modulation frequency fa is swept, the passband of the bandpass filter 16a also changes. . Note that the hatched region in FIG. 3B is outside the pass band of the bandpass filter 16a.

Then, the measuring section 16b performs the operation of the band-pass filter 16a in the pass band of the band-pass filter 16a.
Then, the maximum value of the amplitude of the output signal and the frequency at which the amplitude takes the maximum value are measured (S16). FIG. 3 (a) and FIG.
FIG. 3C is obtained by superimposing (b). FIG.
In the case shown in (c), the amplitude becomes maximum when the frequency is fa + Δf / 2 in the pass band. Note that fa
Becomes sufficiently larger than fb, the frequency becomes fa−Δf
At / 2, the amplitude becomes maximum. Also, as shown in FIG. 3D, if fa becomes substantially equal to fb, the frequency becomes f
The amplitude becomes maximum at b.

The measuring section 16b records in the frequency matching section 18 the maximum value of the amplitude of the output signal of the band-pass filter 16a in the pass band of the band-pass filter 16a. The format of the recording is shown in FIG. The modulation frequency fa is swept from the initial value f0 to the final value f1, and during the sweep, f
Take the neighborhood f ′ of b. When fa = f0, f0 + Δf
/ 2 takes the maximum value. When fa = f1, f1−Δ
It takes the maximum value at f / 2. When fa = f ', the maximum value Amax is taken at fb.

Returning to FIG. 2, the measured maximum value and the like are recorded in the frequency matching unit 18. Then, the process returns to the determination of the completion of the sweep (S12).

When the sweep is completed (S12, Yes), the frequency adjusting unit 18 sets the modulation frequency f
In the entire region (from f0 to f1) where a has been swept,
Frequency fa at which the amplitude of the band-pass filter 16a becomes maximum
_max is obtained (S18). As shown in FIG. 4, since the maximum value of the amplitude when sweeping fa is recorded in the frequency matching unit 18, the frequency at which the maximum value Amax among the maximum values of the amplitude is taken is fa_max. It is.

Then, the frequency adjusting unit 18 sets fa to fa.
_max (S20). Since fa_max is fb,
fa and fb match.

The modulation frequency fa of the modulation power supply 14
Is the frequency fa_m at which the amplitude of the band-pass filter 16a becomes maximum in the entire area (from f0 to f1) where
As long as ax can be obtained, another method may be used. For example, the differential value of the amplitude when the modulation frequency fa is swept is obtained, and the frequency when the amplitude becomes 0 is calculated.
It may be fa_max.

According to this embodiment, fa and fb can be matched. Therefore, the bandpass filter 16
a, a bandpass filter having a narrow pass band, for example, 1 Hz
It is possible to use those of the order, and it is possible to reduce measurement errors such as a phase difference and a group delay. In addition, since the reference frequencies for the group delay characteristics and the distance measurement can be matched, the measured values match, and individual differences between devices are eliminated.

The above embodiment can be realized as follows. The CPU, hard disk, and media (floppy (registered trademark) disk, CD-ROM, etc.) having a reader for reading a medium having a program for realizing the above parts are read by a media reader of a computer equipped with the reader and installed on the hard disk. I do. Even with such a method, the above function can be realized.

[0035]

According to the present invention, the modulation frequency of the light source,
By the frequency matching means, the frequency of the phase detection signal,
The frequency of the modulation signal can be matched.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an optical characteristic measuring device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing the operation of the embodiment of the present invention.

FIG. 3 shows an input signal to the band-pass filter 16a (FIG. 3)
(A)), the pass band of the band-pass filter 16a (FIG. 3)
FIG. 3B is a diagram illustrating filtering by the bandpass filter 16a (FIGS. 3C and 3D).

FIG. 4 shows a bandpass filter 16 in a pass band of a bandpass filter 16a recorded in a frequency matching unit 18.
FIG. 6 is a diagram illustrating a recording format such as a maximum value of the amplitude of the output signal of FIG.

FIG. 5 shows an object to be measured (DU) such as an optical fiber in the prior art.
It is a block diagram which shows the structure of the measurement system when measuring the wavelength dispersion characteristic of T).

FIG. 6 is a diagram showing an electric signal output by a photoelectric converter 22 according to the related art.

FIG. 7 is a diagram illustrating a difference between a modulation frequency and a band of a frequency in which a band-pass filter according to the related art allows transmission.

[Explanation of symbols]

 Reference Signs List 10 light source system 12 variable wavelength light source 14 power supply for modulation 15 optical modulator 16 amplitude measuring unit 18 frequency matching unit 20 characteristic measuring system 22 photoelectric converter 24 phase detector 26 power supply for frequency indication 30 DUT

Claims (6)

[Claims] 1. An apparatus for measuring characteristics of an object to be measured which transmits light, comprising: a modulation signal generating means for generating a modulation signal for providing a modulation frequency to be used for modulation; Optical modulation means for supplying incident light modulated at a frequency for use to the device under test; phase detection signal generating means for generating a phase detection signal for providing a frequency of a signal whose phase is to be detected; and Of the transmitted light transmitted through the device under test, phase detection means for detecting the phase of the frequency component of the signal whose phase is to be detected, and a frequency within a predetermined range from the frequency of the modulation signal,
Amplitude measuring means for measuring the amplitude of the signal for phase detection; and frequency matching means for setting the frequency at which the amplitude of the signal for phase detection becomes maximum to the frequency of the signal for modulation based on the measurement result of the amplitude measuring means. And an optical characteristic measuring device for measuring characteristics of the device under test based on the phase. 2. A band-pass filter to which a pass range is set within a predetermined range from the frequency of the modulation signal, wherein the amplitude detection means receives the phase detection signal, and an amplitude of an output result of the band-pass filter. The optical characteristic measuring apparatus according to claim 1, further comprising: a measuring unit configured to measure the optical characteristic. 3. The modulation signal generating means can change the frequency of the modulation signal.
The optical characteristic measuring device according to 1. 4. The optical characteristic measuring apparatus according to claim 3, wherein a variation width of the frequency of the modulation signal is equal to or larger than a difference between the frequency of the modulation signal and the frequency of the phase detection signal. 5. A method for measuring characteristics of an object to be measured which transmits light, comprising: a modulation signal generating step of generating a modulation signal for providing a modulation frequency used for modulation; A light modulation step of supplying incident light modulated at a frequency for use to the device under test, a phase detection signal generating step of generating a phase detection signal for providing a frequency of a signal whose phase is to be detected, Of the transmitted light transmitted through the device under test, a phase detection step of detecting the phase of the frequency component of the signal whose phase is to be detected, and a frequency within a predetermined range from the frequency of the modulation signal,
An amplitude measuring step of measuring the amplitude of the phase detection signal; and a frequency matching step of setting a frequency at which the amplitude of the phase detection signal is maximum to a frequency of the modulation signal based on the measurement result of the amplitude measurement step. And an optical characteristic measuring method for measuring characteristics of the device under test based on the phase. 6. A computer-readable recording medium having recorded thereon a program for causing a computer to execute a process of measuring characteristics of an object to be measured that transmits light, wherein the modulation is for providing a modulation frequency to be used for modulation. Signal generation processing for generating an optical signal, optical modulation processing for supplying incident light obtained by modulating variable wavelength light with the modulation frequency to the device under test, and phase detection for providing the frequency of a signal whose phase is to be detected Phase detection signal generation processing for generating a signal for use, phase detection processing for detecting the phase of the frequency component of the signal whose phase is to be detected, of the transmitted light in which the incident light has passed through the device under test, Of a frequency within a predetermined range from the frequency of the modulation signal,
An amplitude measurement process for measuring the amplitude of the phase detection signal; and a frequency matching process for setting a frequency at which the amplitude of the phase detection signal is maximum to a frequency of the modulation signal based on a measurement result of the amplitude measurement process. And a recording medium for measuring characteristics of the device under test based on the phase.