JP2017032466A - Optical reflectometry device and optical reflectometry method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a long distance measurement in optical reflectometry, and to enable high spatial resolving power therein.SOLUTION: A device measuring an optical reflectometry distribution of a measured device 7 is configured to: branch light emitted from an optical frequency com light source 1 into two light with one as probe light and the other as reference light; impart a phase modulation at prescribed timing based on a variable delay and prescribed signal with respect to the probe light; make the probe light incident upon the measured device 7 via a circulator 6; impart a phase modulation at timing delayed by τfurther than the prescribed timing based on the prescribed signal with respect to the reference light; multiplex the reference light and rear scattering light obtained via the circulator 6 and from the measured device 7; detect multiplexed light; acquire an interference signal; and obtain optical reflectance at a desired position in a long-side direction of the measured device 7 on the basis of the interference signal.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a light reflection measurement device and a light reflection measurement method.

  Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3 have been reported for the light reflection measurement technique.

Non-Patent Document 1 is composed of a low coherence light source and an interferometer in which one arm has a variable delay amount, and realizes reflection measurement as follows. The light emitted from the low coherence light source is input to the interferometer and branched into two. Of the two branched lights, one is incident as a probe light on the device under measurement, and the other is incident as a reference light on the arm with variable delay amount. At a certain point of the device under measurement, the probe light is backscattered, and the backscattered light travels back and forth through the device under measurement, and is subjected to a delay of τ _DUT . On the other hand, the reference light incident on the variable delay amount arm is delayed by τ _Ref . The backscattered light and the reference light are combined and their interference signal (correlation) is measured. Because of the low coherence, the interference signal represents the intensity of backscattered light from τ _DUT that matches τ _Ref, and a high spatial resolution measurement of about several tens of μm can be realized. And by changing (tau) _Ref , position decomposition can be performed and the backscattered light intensity distribution of a to-be-measured device can be measured.

で表される。 Non-Patent Document 2 realizes reflection measurement using a pulse light source as follows. Pulse light E _Probe (t) emitted from the pulse light source is incident on the device under measurement as probe light. The probe light is backscattered according to the reflectance R (τ) at each delay of the device under measurement. The backscattered light is the response of the device under test to the probe light, and the convolution integral of E _Probe (t) and R (τ)

It is represented by

（空間分解能はパルス幅程度）となり、後方散乱光の時間変化は各遅延における反射率Ｒ（τ）を表し、後方散乱光強度を測定することで各遅延における反射率を測定する。 Since probe light is pulsed light,

(The spatial resolution is about the pulse width), the time change of the backscattered light represents the reflectivity R (τ) at each delay, and the reflectivity at each delay is measured by measuring the backscattered light intensity.

  Non-Patent Document 3 includes a frequency sweep light source and an interferometer, and realizes reflection measurement as follows. The frequency sweep light emitted from the frequency sweep light source having the frequency sweep speed g is input to the interferometer and branched into two. Of the two branched lights, one is used as the probe light and is incident on the device to be measured, and the other is used as the reference light. Since the optical frequency of the backscattered light from each delay τ of the device under test is shifted by the gτ frequency with respect to the optical frequency of the reference light, the backscattered light and the reference light are caused to interfere and the beat signal is subjected to frequency analysis. Then, the reflectance distribution of the device under measurement is measured.

However, in Non-Patent Document 1, the delay amount variable range of τ _Ref is the measurable range. The delay is typically given by a movable mirror, but the maximum delay amount is several ns (several tens of centimeters in terms of length), and a long device cannot be evaluated. Therefore, Non-Patent Document 1 realizes reflection measurement with a short distance and high spatial resolution. In Non-Patent Document 2, a receiving system having a wider band than the probe light band (about the reciprocal of the pulse width) is required. Since widening the reception system deteriorates reception sensitivity, the pulse width (spatial resolution) of the probe light and the measurement distance are in a trade-off relationship. In Non-Patent Document 3, a measurement distance of several kilometers is realized with a spatial resolution of several millimeters. As described above, in the light reflection measurement technique, there is no measurement technique capable of measuring a long distance and having a high spatial resolution.

R. C. Youngquist, S.M. Carr, and D.C. E. N. Davies, “Optical coherence-domain reflexometry: a new optical evaluation technique,” Opt. Lett. , Vol. 12, no. 3, 1987. M.M. P. Gold, "Design of a Long-Range Single-Mode OTDR," J. Lighttw. Technol. , Vol. LT-3, No. 1, 1985. D. K. Gifford, M .; E. Froggatt, M.M. S. Wolfe, S.M. T. T. Kreger, and B.B. J. et al. Soller, “Millimeter Resolution Reflection Over Two Kilometers,” in Proc. 33rd ECOC, Tu. 3.6.1, 2007.

  The present invention has been made in view of the above-described problems of the prior art, and has an object to enable long distance measurement and high spatial resolution in light reflection measurement.

In order to achieve the above object, the present invention provides an apparatus for measuring the light reflectance distribution of a device under test, wherein the light emitted from the optical frequency comb light source is branched into two, one as the probe light and the other as the reference light. A variable delay and a phase modulation at a predetermined timing by a predetermined signal are given to the probe light, the probe light is made incident on the device under measurement via the circulator, and delayed by τ ₁ from the predetermined timing by the predetermined signal with respect to the reference light The reference light and the backscattered light from the device under measurement obtained via the circulator are combined, the combined light is detected to obtain an interference signal, Based on the interference signal, the light reflectance at a desired position in the longitudinal direction of the device under measurement is obtained.

Specifically, the light reflection measuring apparatus according to the present invention is:
An apparatus for measuring the light reflectance of a device under test,
An optical frequency comb light source;
An optical branching unit that splits the light emitted from the optical frequency comb light source into two;
An optical delay unit that generates a delay difference in the light branched by the optical branch unit;
A first optical phase modulation unit that phase-modulates one of the lights branched by the optical branching unit with an arbitrary signal waveform;
A second optical phase modulation unit that phase-modulates the other light branched by the optical branching unit with the arbitrary signal waveform;
A trigger controller for controlling timing of phase modulation in the first optical phase modulator and the second optical phase modulator;
A circulator that enters the device under measurement as the one light phase-modulated by the first optical phase modulation unit as probe light, and guides backscattered light scattered by the device under measurement; ,
An optical multiplexing unit configured to combine the reference light and the backscattered light with the other light phase-modulated by the second optical phase modulation unit as a reference light;
A light receiver for detecting an interference signal between the reference light and the backscattered light combined by the optical multiplexing unit;
Using the autocorrelation function of the phase-modulated signal included in the interference signal output from the light receiving unit, a data acquisition unit for obtaining a light reflectance at an arbitrary position in the longitudinal direction of the device under measurement;
With
The trigger control unit includes the first optical phase modulation unit and the first optical phase modulation unit so that the probe light reflected at an arbitrary position in the longitudinal direction of the device to be measured is combined with the reference light by the optical multiplexing unit. The timing of phase modulation in the second optical phase modulator is controlled.

In the light reflection measuring apparatus according to the present invention,
A first trigger source that outputs a first trigger signal for controlling the timing at which the first optical phase modulation section performs phase modulation;
A second trigger source that outputs a second trigger signal for controlling the timing of phase modulation by the second optical phase modulator;
Generation of a first arbitrary signal that generates a modulation signal having an arbitrary signal waveform at a timing when the first trigger signal is input from the first trigger source, and causes the first optical phase modulation unit to perform phase modulation with the modulation signal. And
A second arbitrary signal that generates a modulation signal having the arbitrary signal waveform at a timing when the second trigger signal is input from the second trigger source, and causes the second optical phase modulation unit to perform phase modulation with the modulation signal. Generating part,
Further comprising
The optical delay unit changes the delay amount of the light branched by the optical branching unit so as to sweep the autocorrelation function of the optical frequency comb branched by the optical branching unit,
The trigger control unit provides a delay in the output time of the first trigger signal and the second trigger signal according to the position in the longitudinal direction of the device under test for measuring the reflectance,
The data acquisition unit outputs from the light receiving unit using a delay difference generated by the optical delay unit and a delay amount between times when the first trigger source and the second trigger source output a trigger signal. The position of the device under measurement in the longitudinal direction may be specified from the interference signal thus obtained.

In the light reflection measuring apparatus according to the present invention, when the repetition frequency of the optical frequency comb light source is f _rep , the trigger control unit may select any one of the autocorrelation functions of the optical frequency comb that appears at a period of 1 / f _rep. A delay may be provided in the output times of the first trigger signal and the second trigger signal so as to select the autocorrelation function.

In the light reflection measuring apparatus according to the present invention, the sample rate f _sam of the arbitrary signal waveform output from the first arbitrary signal generator and the second arbitrary signal generator is a repetition frequency of the optical frequency comb light source. It may be larger than f _rep .

Specifically, the light reflection measurement method according to the present invention is:
A light reflection measurement method executed by an apparatus for measuring light reflectance of a device under test,
An optical branching procedure in which the optical branching unit splits the light emitted from the optical frequency comb light source into two;
An optical delay unit, an optical frequency comb delay generation procedure for generating a delay difference in the light branched by the optical branch unit;
The first optical phase modulation unit phase-modulates one light branched by the optical branching unit with an arbitrary signal waveform, and the second optical phase modulation unit converts the other light branched by the optical branching unit. , A phase modulation procedure for phase modulation with the arbitrary signal waveform;
A circulator is incident on the device under measurement as the one light phase-modulated by the first optical phase modulation unit as probe light, and the probe light guides backscattered light scattered by the device under measurement. And an optical multiplexing unit that uses the other light phase-modulated by the second optical phase modulation unit as reference light, and combines the reference light and the backscattered light,
A data acquisition procedure in which the data acquisition unit obtains the light reflectance at an arbitrary position in the longitudinal direction of the device under test using the autocorrelation function of the phase-modulated signal included in the interference signal output from the light receiving unit. When,
Have
In the phase modulation procedure, the trigger control unit is configured so that the probe light reflected at an arbitrary position in the longitudinal direction of the device under measurement is combined with the reference light by the optical multiplexing unit. The timing of phase modulation in the optical phase modulator and the second optical phase modulator is controlled.

In the light reflection measurement method according to the present invention,
The light reflection measuring device is:
A first trigger source that outputs a first trigger signal for controlling the timing at which the first optical phase modulation section performs phase modulation;
A second trigger source that outputs a second trigger signal for controlling the timing of phase modulation by the second optical phase modulator;
Generation of a first arbitrary signal that generates a modulation signal having an arbitrary signal waveform at a timing when the first trigger signal is input from the first trigger source, and causes the first optical phase modulation unit to perform phase modulation with the modulation signal. And
A second arbitrary signal that generates a modulation signal having the arbitrary signal waveform at a timing when the second trigger signal is input from the second trigger source, and causes the second optical phase modulation unit to perform phase modulation with the modulation signal. Generating part;
Further comprising
In the optical delay procedure, the optical delay unit changes the delay amount of the light bifurcated by the optical branching unit so as to sweep the autocorrelation function of the optical frequency comb bifurcated by the optical branching unit,
In the phase modulation procedure, the trigger control unit provides a delay in the output time of the first trigger signal and the second trigger signal according to the position in the longitudinal direction of the device under test for measuring reflectance. ,
In the data acquisition procedure, the data acquisition unit uses a delay difference generated by the optical delay unit and a delay amount between times when the first trigger source and the second trigger source output a trigger signal. The position of the device under measurement in the longitudinal direction may be specified.

In the light reflection measurement method according to the present invention, when the repetition frequency of the optical frequency comb light source is f _rep , in the phase modulation procedure, the trigger control unit performs the self-measurement of the optical frequency comb that appears at a period of 1 / f _rep. A delay may be provided in the output times of the first trigger signal and the second trigger signal so as to select an arbitrary autocorrelation function among the correlation functions.

In the light reflection measurement method according to the present invention, in the phase modulation procedure, the sample rate f _sam of the arbitrary signal waveform output from the first arbitrary signal generator and the second arbitrary signal generator is the light It may be greater than the repetition frequency f _rep of the frequency comb light source.

  According to the present invention, long distance measurement is possible and high spatial resolution is possible in light reflection measurement.

An example of the light reflection measuring apparatus which concerns on embodiment is shown. An example of the behavior of the coefficient C _XT with respect to the amplitude of the modulation signal f (t) is shown. An example of the autocorrelation of the modulation signal f (t) and the optical frequency comb is shown.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to embodiment shown below. These embodiments are merely examples, and the present invention can be implemented in various modifications and improvements based on the knowledge of those skilled in the art. In the present specification and drawings, the same reference numerals denote the same components.

  An embodiment of a light reflection measuring apparatus according to the present invention is shown in FIG. Here, 1 is an optical frequency comb light source, 2 is an optical branching unit, 3 is an optical delay unit, 4-1 and 4-2 are optical phase modulation units, 5-1 and 5-2 are arbitrary signal generation units, and 6 is An optical circulator, 7 is a device to be measured, 8-1 and 8-2 are trigger sources, 9 is a trigger source control unit, 10 is an optical multiplexing unit, 11 is a balanced light receiver, and 12 is a data acquisition unit. The optical phase modulation unit 4-1 functions as a first optical phase modulation unit, and the optical phase modulation unit 4-2 functions as a second optical phase modulation unit. The arbitrary signal generator 5-1 functions as a first arbitrary signal generator, and the arbitrary signal generator 5-2 functions as a second arbitrary signal generator. The trigger source 8-1 functions as a first trigger source, and the trigger source 8-2 functions as a second trigger source.

The light reflection measurement method according to this embodiment is:
A light reflection measurement method executed by an apparatus for measuring the light reflectance of a device under measurement, comprising: an optical branching procedure, an optical frequency comb delay generation procedure, a phase modulation procedure, a multiplexing procedure, a data acquisition procedure, Have Before and after the optical frequency comb delay generation procedure and the phase modulation procedure are arbitrary. For example, the optical frequency comb delay generation procedure may be performed after the phase modulation procedure.

In the optical branching procedure, the optical branching unit 2 splits the light emitted from the optical frequency comb light source into two.
In the optical frequency comb delay generation procedure, the optical delay unit 3 generates a delay difference in the light branched by the optical branching unit 2. At this time, the optical delay unit 3 changes the delay amount of the light branched by the optical branching unit 2 so as to sweep the autocorrelation function of the optical frequency comb branched by the optical branching unit 2.

  In the phase modulation procedure, the optical phase modulation unit 4-1 phase-modulates one of the lights branched by the optical branching unit 2 with an arbitrary signal waveform to generate probe light, and the optical phase modulation unit 4-2 The other light branched by the branching unit 2 is phase-modulated with an arbitrary signal waveform to generate reference light. At this time, the trigger source control unit 9 provides a delay in the time at which the trigger sources 8-1 and 8-2 output the trigger signal according to the position in the longitudinal direction of the device under measurement 7 for measuring the reflectance. Thereby, the trigger source control unit 9 causes the optical phase modulation unit 4-1 so that the probe light reflected at an arbitrary position in the longitudinal direction of the device under measurement 7 is combined with the reference light by the optical multiplexing unit 10. And 4-2 control the timing of phase modulation.

  In the multiplexing procedure, the circulator 6 enters the probe light into the device under measurement 7, the probe light guides the backscattered light scattered by the device under measurement 7, and the optical multiplexing unit 10 transmits the reference light and the backscattered light. Are combined.

  In the data acquisition procedure, the data acquisition unit 12 uses the autocorrelation function of the phase-modulated signal included in the interference signal output from the light receiving unit, and the light reflectance at an arbitrary position in the longitudinal direction of the device under measurement 7. Ask for. At this time, the data acquisition unit 12 uses the delay difference generated by the optical delay unit 3 and the delay amount between the times when the trigger sources 8-1 and 8-2 output the trigger signal. Specify the position of the direction.

  1 shows that the light reflection measuring apparatus according to the present embodiment can measure long distances and can realize high spatial resolution with the configuration of FIG.

The optical frequency comb light source 1 emits an optical frequency comb which is light having a broadband and comb-like spectrum. A complex electric field amplitude E (t) of light emitted from the optical frequency comb light source 1 is expressed by the following equation.

ここで、ｎは整数である。 Here, A (t) represents the amplitude waveform of the light emitted from the optical frequency comb light source 1, ν represents the center frequency, and θ (t) represents the phase noise. If the repetition frequency of the optical frequency comb light source 1 is f _rep , the amplitude waveform A (t) of the optical frequency comb is a periodic function with a period of 1 / f _rep . That is, the amplitude waveform A (t) of the optical frequency comb has a peak every 1 / f _rep .

Here, n is an integer.

Since the amplitude waveform A (t) is a periodic function represented by the equation (2), the autocorrelation function r _AA (τ) is obtained by integrating in a time sufficiently longer than the reciprocal of the band of the amplitude waveform A (t). Is also a periodic function.

  The light is branched into two by the optical branching unit 2, and one is sent to the optical phase modulation unit 4-1, and the other is sent to the optical phase modulation unit 4-2. The light transmitted to the optical phase modulation unit 4-1 is phase-modulated with the modulation signal output from the arbitrary signal generation unit 5-1 and becomes probe light.

Here, the time when the light is phase-modulated is the time when the arbitrary signal generator 5-1 receives the trigger signal from the trigger source 8-1. Assuming that the modulation signal output from the arbitrary signal generator 5-1 is f (t), the complex electric field amplitude of the probe light modulated by the optical phase modulator 4-1 is expressed by the following equation.

ここで、τ_ｍａｘは被測定デバイス７が与える最大の遅延量である。 The probe light generated by the optical phase modulation unit 4-1 enters the device under measurement 7 via the optical circulator 6 and is backscattered inside the device under measurement 7. When the reflectance at the delay τ of the device under measurement 7 is R (τ), the backscattered light E _sig (t) is expressed by the convolution integral of the reflectance R (τ) and the probe light.

Here, τ _max is the maximum delay amount given by the device under measurement 7.

  The backscattered light is sent to the optical multiplexing unit 10 via the optical circulator 6.

Next, consider the light sent by the optical branching unit 2 to the optical phase modulation unit 4-2. The optical phase modulation unit 4-2 is phase-modulated with the modulation signal output from the arbitrary signal generation unit 5-2 and becomes reference light. Here, the time when the optical phase modulation unit 4-2 performs phase modulation on the light is the time when the arbitrary signal generation unit 5-2 receives the trigger signal from the trigger source 8-2. When the modulation signal output from the arbitrary signal generator 5-2 is g (t), the complex electric field amplitude E _Lo (t) of the reference light modulated by the optical phase modulator 4-2 is expressed by the following equation. .

  The reference light is sent to the optical multiplexing unit 10.

The optical multiplexing unit 10 _{combines the} backscattered light E _sig (t) and the reference light E _Lo (t). The balance type light receiver 11 detects an interference component of the combined light intensity. The interference component detected by the balanced photoreceiver 11 is output as a photocurrent I (τ) and AD converted by the data acquisition unit 12. Assuming that the integration time of the balanced photoreceiver 11 is T, I (τ) is expressed by the following equation.

Here, if the coherence time τ _c of the optical frequency comb light source 1 is sufficiently longer than τ, the phase noise θ (t) of the optical frequency comb light source 1 satisfies the following equation.

となる。 From equations (7) and (8), the photocurrent I (τ) is

It becomes.

  Since the autocorrelation function of the optical frequency comb light source 1 is a periodic function as expressed by the equation (3), the sum of the reflectances R (τ) corresponding to the periodic function is measured as the photocurrent I (τ). The The arbitrary signal generator 5-2 selects the reflectance R (τ) at an arbitrary position from the sum of the reflectances R (τ).

The modulation signal g (t) output from the arbitrary signal generation unit 5-2 has the same waveform as the modulation signal f (t) output from the arbitrary signal generation unit 5-1. Furthermore, the trigger source controller 9 delays the time when the arbitrary signal generator 5-2 is driven by τ _{1 with} respect to the time when the arbitrary signal generator 5-1 is driven. Thereby, the optical phase modulation unit 4-1 and the optical phase modulation unit 4-4 are combined so that the probe light reflected at an arbitrary position in the longitudinal direction of the device under measurement 7 is combined with the reference light by the optical multiplexing unit 10. 2 can control the timing of phase modulation. At this time, the modulation signal g (t) is expressed by the following equation.

From the equations (9) and (10), the photocurrent I (τ) is expressed by the following equation.

Here, the coefficient C _XT is given by the following equation.

In the equation (11), the first item is a term representing the reflectance R (τ) at the delay τ ₁ which is a desired position, and the second item is a crosstalk from the delay τ ≠ τ ₁ which is another position. . If C _XT << 1 is satisfied, the reflectance R (τ) at the delay τ ₁ that is a desired position can be measured. The coefficient C _XT depends on the waveform of the modulation signal f (t) and its amplitude. Effect of A (t) A (t- τ) has on the result of the integration is intended to determine the magnitude of the coefficients C _XT, does not determine the behavior of the coefficients C _XT.

For the sake of simplicity, the amplitude waveform A (t) of the optical frequency comb is constant, the phase offset 2πντ is zero, and the amplitude of the modulation signal f (t) when the modulation signal f (t) is uniformly distributed white noise. The behavior of the coefficient C _XT is shown in FIG. Here, since the modulation signal is white noise, the standard deviation of noise is used as the amplitude. From FIG. 2, when the modulation signal f (t) has a certain amplitude value, the coefficient C _XT has a minimum value. This local minimum is constant regardless of the phase offset 2πντ. Therefore, as shown in FIG. 2, by designing the modulation signal f (t) with an amplitude value that gives a minimum value to the coefficient _CXT , the second term in the expression (12) is expressed as The influence of the appearing coefficient C _XT can be eliminated.

For example, as shown in FIG. 2, when the standard deviation of the noise waveform is about 1.8 rad, C _xT becomes minimum, so that the modulated signal f (t) is uniformly distributed white noise with a standard deviation of 1.8 rad / 2π. This can be realized by setting the waveform to 2π multiplied by 2π. However, even if it is a noise waveform, f (t) and g (t) need to be the same waveform with a delay difference from the equation (10), so that the arbitrary signal generators 5-1 and 5-2 Rather than generating noise separately, the same noise waveform must be shared by both signal generators and transmitted. Therefore, the reflectance R (τ) at a desired position can be measured by using the modulation signal f (t) having such an amplitude value that the coefficient C _XT becomes a minimum value.

By sweeping the position of the autocorrelation function of the optical frequency comb by the optical delay unit 3 and changing the time at which the arbitrary signal generators 5-1 and 5-2 are driven by the trigger source control unit 9, the period of the optical frequency comb is changed. An arbitrary autocorrelation function is selected from typical autocorrelation functions, and the reflectance R (τ) at an arbitrary position of the device under measurement 7 can be measured. The optical delay unit 3 can be _replaced by changing the repetition frequency f _rep (frequency interval of the optical frequency comb) of the optical frequency comb.

  As represented by the equation (13), in the measurement method according to the present embodiment, one correlation peak can be selected from the periodic autocorrelation function of the optical frequency comb. It is as follows.

If the sample rate of the modulation signal f (t) is f _sam , the autocorrelation has a width of 2 / f _sam . On the other hand, the autocorrelation function of the optical frequency comb is a periodic function of 1 / f _rep as expressed by equation (3). In this case, as shown in FIG. 3, in order to select one correlation peak from the periodic autocorrelation function of the optical frequency comb, since the correlation peak adjacent to the selected correlation peak is not included, the following equation is satisfied. There is a need.

  Further, the resolution of the measurement method according to the present embodiment is determined by the width of the autocorrelation function of the optical frequency comb. From Wiener Hinchin's theorem, the autocorrelation function is given by the Fourier transform of the spectrum of the optical frequency comb. In the case of an optical frequency comb having a band of 1 THz, the width of the autocorrelation function is about 1 ps (100 μm). Therefore, by using an optical frequency comb having a 1 THz band, the reflectance R (τ) at a desired position can be measured with a resolution of about 1 ps (100 μm).

As described above, in the invention according to the present embodiment, the optical frequency comb light source 1 is branched into two, one is the probe light, the other is the reference light, and the time for modulating each light using the trigger source control unit 9 Between the probe light and the reference light that are back-scattered from the inside of the device under measurement 7 with a delay τ ₁ between them and phase modulation with the same waveform in the optical phase modulators 4-1 and 4-2. This is a technique for measuring the light reflection of the device under measurement 7 by taking The trigger source control unit 9 is used to control the time when the probe light and the reference light are modulated, and the optical delay comb 3 is used to provide a delay between the two optical frequency combs. The autocorrelation function between the optical frequency combs can be swept, and the backscattering position of the device under measurement 7 can be resolved.

Note that the measurement distance is determined by the coherence time τ _c of the optical frequency comb light source 1, and light reflection measurement can be performed as long as Expression (8) is satisfied. For this reason, long distance measurement can be realized by using a high coherence light source such as a fiber laser as the seed light of the optical frequency comb light source 1. Therefore, the light reflection measuring apparatus according to the present embodiment realizes a long-distance high-spatial-resolution reflection measurement technique having a performance of several tens of kilometers and a spatial resolution of 100 μm that could not be reached in Non-Patent Documents 1 to 3. can do.

The present invention is not limited to the configuration shown in FIG.
For example, the optical delay unit 3 can employ any configuration that generates a delay difference in the light branched by the optical branch unit 2. For example, the optical phase modulator 4-1 and the optical circulator 6 may be disposed. The optical delay unit 3 is arranged between the optical branching unit 2 and the optical phase modulation unit 4-2 or between the optical phase modulation unit 4-2 and the optical multiplexing unit 10, and delays the reference light. Good.
Further, the trigger signal of the trigger source 8-1 may be delayed from the trigger signal of the trigger source 8-2.

  The present invention can be applied to the information communication industry.

1: Optical frequency comb light source 2: Optical branching unit 3: Optical delay unit 4-1, 4-2: Optical phase modulation unit 5-1, 5-2: Arbitrary signal generation unit 6: Optical circulator 7: Device under test 8 -1, 8-2: Trigger source 9: Trigger source control unit 10: Optical multiplexing unit 11: Balanced light receiver 12: Data acquisition unit

Claims (8)

An apparatus for measuring the light reflectance of a device under test,
An optical frequency comb light source;
An optical branching unit that splits the light emitted from the optical frequency comb light source into two;
An optical delay unit that generates a delay difference in the light branched by the optical branch unit;
A first optical phase modulation unit that phase-modulates one of the lights branched by the optical branching unit with an arbitrary signal waveform;
A second optical phase modulation unit that phase-modulates the other light branched by the optical branching unit with the arbitrary signal waveform;
A trigger controller for controlling timing of phase modulation in the first optical phase modulator and the second optical phase modulator;
A circulator that enters the device under measurement as the one light phase-modulated by the first optical phase modulation unit as probe light, and guides backscattered light scattered by the device under measurement; ,
An optical multiplexing unit configured to combine the reference light and the backscattered light with the other light phase-modulated by the second optical phase modulation unit as a reference light;
A light receiver for detecting an interference signal between the reference light and the backscattered light combined by the optical multiplexing unit;
Using the autocorrelation function of the phase-modulated signal included in the interference signal output from the light receiving unit, a data acquisition unit for obtaining a light reflectance at an arbitrary position in the longitudinal direction of the device under measurement;
With
The trigger control unit includes the first optical phase modulation unit and the first optical phase modulation unit so that the probe light reflected at an arbitrary position in the longitudinal direction of the device to be measured is combined with the reference light by the optical multiplexing unit. Controlling the timing of phase modulation in the second optical phase modulator;
Light reflection measuring device. A first trigger source that outputs a first trigger signal for controlling the timing at which the first optical phase modulation section performs phase modulation;
A second trigger source that outputs a second trigger signal for controlling the timing of phase modulation by the second optical phase modulator;
Generation of a first arbitrary signal that generates a modulation signal having an arbitrary signal waveform at a timing when the first trigger signal is input from the first trigger source, and causes the first optical phase modulation unit to perform phase modulation with the modulation signal. And
A second arbitrary signal that generates a modulation signal having the arbitrary signal waveform at a timing when the second trigger signal is input from the second trigger source, and causes the second optical phase modulation unit to perform phase modulation with the modulation signal. Generating part,
Further comprising
The optical delay unit changes the delay amount of the light branched by the optical branching unit so as to sweep the autocorrelation function of the optical frequency comb branched by the optical branching unit,
The trigger control unit provides a delay in the output time of the first trigger signal and the second trigger signal according to the position in the longitudinal direction of the device under test for measuring the reflectance,
The data acquisition unit outputs from the light receiving unit using a delay difference generated by the optical delay unit and a delay amount between times when the first trigger source and the second trigger source output a trigger signal. Identifying the position in the longitudinal direction of the device under test from the interference signal
The light reflection measuring apparatus according to claim 1. When the repetition frequency of the optical frequency comb light source is f _rep ,
The trigger control unit outputs an output time of the first trigger signal and the second trigger signal so as to select an arbitrary autocorrelation function among the autocorrelation functions of the optical frequency comb that appears at a period of 1 / f _rep. A delay in the
The light reflection measuring apparatus according to claim 2. A sample rate f _sam of the arbitrary signal waveform output from the first arbitrary signal generator and the second arbitrary signal generator is greater than a repetition frequency f _rep of the optical frequency comb light source;
The light reflection measuring apparatus according to claim 3. A light reflection measurement method executed by an apparatus for measuring light reflectance of a device under test,
An optical branching procedure in which the optical branching unit splits the light emitted from the optical frequency comb light source into two;
An optical delay unit, an optical frequency comb delay generation procedure for generating a delay difference in the light branched by the optical branch unit;
The first optical phase modulation unit phase-modulates one light branched by the optical branching unit with an arbitrary signal waveform, and the second optical phase modulation unit converts the other light branched by the optical branching unit. , A phase modulation procedure for phase modulation with the arbitrary signal waveform;
A circulator is incident on the device under measurement as the one light phase-modulated by the first optical phase modulation unit as probe light, and the probe light guides backscattered light scattered by the device under measurement. And an optical multiplexing unit that uses the other light phase-modulated by the second optical phase modulation unit as reference light, and combines the reference light and the backscattered light,
A data acquisition procedure in which the data acquisition unit obtains the light reflectance at an arbitrary position in the longitudinal direction of the device under test using the autocorrelation function of the phase-modulated signal included in the interference signal output from the light receiving unit. When,
Have
In the phase modulation procedure, the trigger control unit is configured so that the probe light reflected at an arbitrary position in the longitudinal direction of the device under measurement is combined with the reference light by the optical multiplexing unit. Controlling the timing of phase modulation in the optical phase modulator and the second optical phase modulator,
Light reflection measurement method. The light reflection measuring device is:
A first trigger source that outputs a first trigger signal for controlling the timing at which the first optical phase modulation section performs phase modulation;
A second trigger source that outputs a second trigger signal for controlling the timing of phase modulation by the second optical phase modulator;
Generation of a first arbitrary signal that generates a modulation signal having an arbitrary signal waveform at a timing when the first trigger signal is input from the first trigger source, and causes the first optical phase modulation unit to perform phase modulation with the modulation signal. And
A second arbitrary signal that generates a modulation signal having the arbitrary signal waveform at a timing when the second trigger signal is input from the second trigger source, and causes the second optical phase modulation unit to perform phase modulation with the modulation signal. Generating part;
Further comprising
In the optical delay procedure, the optical delay unit changes the delay amount of the light bifurcated by the optical branching unit so as to sweep the autocorrelation function of the optical frequency comb bifurcated by the optical branching unit,
In the phase modulation procedure, the trigger control unit provides a delay in the output time of the first trigger signal and the second trigger signal according to the position in the longitudinal direction of the device under test for measuring reflectance. ,
In the data acquisition procedure, the data acquisition unit uses a delay difference generated by the optical delay unit and a delay amount between times when the first trigger source and the second trigger source output a trigger signal. Identifying the position in the longitudinal direction of the device under test,
The light reflection measuring method according to claim 5. When the repetition frequency of the optical frequency comb light source is f _rep ,
In the phase modulation procedure, the trigger control unit selects the first trigger signal and the second trigger signal so as to select an arbitrary autocorrelation function among the autocorrelation functions of the optical frequency comb that appears at a period of 1 / f _rep . Provide a delay in the output time of the trigger signal
The light reflection measuring method according to claim 6. In the phase modulation procedure, the sample rate f _sam of the arbitrary signal waveform output from the first arbitrary signal generator and the second arbitrary signal generator is higher than the repetition frequency f _rep of the optical frequency comb light source. large,
The light reflection measuring method according to claim 7.

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