JP6729737B1 - Optical coherent sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove phase noise of a continuous light source by using an active noise canceller technology. An interference signal generation unit, a phase fluctuation signal generation unit, and a signal processing unit are configured. The interference signal generation unit generates continuous light, splits the continuous light into two beams, a probe light and a reference light, splits the reference light into a first reference light and a second reference light, and measures the probe light. An interference signal is generated by coherently detecting the scattered light scattered by the object and the first reference light. The phase fluctuation signal generation unit generates a phase fluctuation signal indicating the phase fluctuation of the second reference light. The signal processing unit detects the phase change of the scattered light by canceling the phase noise of the continuous light from the interference signal and the phase fluctuation signal using the active noise canceller technique. [Selection diagram] Figure 1

Description

The present invention relates to an optical coherent sensor.

Phase noise is superimposed on lasers used in optical communication and optical sensing.

For example, in the case of optical coherent communication using a phase modulation signal, demodulation performance deteriorates in proportion to the magnitude of phase noise of signal light and local light. Therefore, it is desirable to use a light source with low phase noise as the laser light source.

The same phenomenon applies to an optical sensor that uses the coherence of light (hereinafter, also referred to as an optical coherent sensor). As an optical coherent sensor, for example, there is a laser Doppler vibrometer (see, for example, Patent Document 1).

A conventional example of a laser Doppler vibrometer will be described with reference to FIG. FIG. 4 is a schematic diagram for explaining a conventional example of a laser Doppler vibrometer.

The linearly polarized continuous light output from the continuous light source (laser light source) 10 is split into two linearly polarized probe light and reference light by the first polarization beam splitter (PBS) 21. The polarization directions of the probe light and the reference light are orthogonal to each other. The probe light is sent to the λ/4 plate 30 via the second PBS 22. The probe light is converted from linearly polarized light into circularly polarized light at the λ/4 plate 30. The probe light converted into circularly polarized light is applied to the measurement target.

The scattered light obtained by scattering the probe light on the measurement target is incident on the λ/4 plate 30. The scattered light is converted from circularly polarized light into linearly polarized light at the λ/4 plate 30. Here, the polarization direction of the probe light input to the λ/4 plate 30 and the polarization direction of the scattered light output from the λ/4 plate 30 are orthogonal to each other. The scattered light converted into the linearly polarized light is sent to the third PBS 23 via the second PBS 22.

The reference light is reflected by the mirror 40 and is sent to the frequency shifter 50 while maintaining the polarization state. The reference light undergoes a frequency shift of the oscillation frequency Δf by the frequency shifter 50 using the oscillation signal generated by the oscillator 310, and is then sent to the third PBS 23.

In the third PBS 23, the scattered light and the reference light interfere with each other in the same polarization state to generate interference light. The interference light is converted into an interference electric signal by the photoelectric converter 60. The interference electric signal is amplified to a predetermined level by the amplifier 70, and then converted to an instantaneous differential value of the phase, that is, an instantaneous frequency, by the frequency discriminator 80. The frequency shift due to the Doppler shift is detected from this instantaneous frequency, and the velocity of the measurement object is obtained.

JP-A-4-218731

https://www.ljmu.ac.uk/~/media/files/ljmu/about-us /faculties-and-schools/tae/geri/onedimensionalphaseunwrapping_finalpdf http://www.cs.cmu.edu/~aarti/pubs/ANC.pdf

Here, in the laser Doppler vibrometer, the larger the distance to the measurement object, the larger the time difference between the scattered light and the reference light until they interfere with each other. Therefore, if a laser light source with large phase noise is used as the continuous light source, it becomes difficult to detect the phase information from the interference signal.

Therefore, the laser light source used in the laser Doppler vibrometer is required to have a narrow line width and high coherence.

However, such a narrow linewidth light source is generally very expensive, which is one of the reasons why the optical system of the laser Doppler vibrometer is expensive.

In view of the above-mentioned problems, the inventors of the present invention have made earnest studies, and by using the technology of the active noise canceller, by removing the phase noise of the laser light source, it becomes unnecessary to use a narrow linewidth light source. I found it.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical coherent sensor capable of removing the phase noise of a continuous light source by using the technology of an active noise canceller. Especially.

In order to achieve the above-mentioned object, the optical coherent sensor of the present invention includes an interference signal generation unit, a phase fluctuation signal generation unit, and a signal processing unit. The interference signal generation unit generates continuous light, splits the continuous light into two beams, a probe light and a reference light, splits the reference light into a first reference light and a second reference light, and measures the probe light. An interference signal is generated by coherently detecting the scattered light scattered by the object and the first reference light. The phase fluctuation signal generation unit generates a phase fluctuation signal indicating the phase fluctuation of the second reference light. The signal processing unit detects the phase change of the scattered light by canceling the phase noise of the continuous light from the interference signal and the phase fluctuation signal using the technique of the active noise canceller.

According to the optical coherent sensor of the present invention, the phase noise of the continuous light source is removed by using the technique of the active noise canceller, so that the costly narrow linewidth light source is not required.

It is a schematic diagram for demonstrating the optical coherent sensor of this invention. It is a schematic diagram for explaining a phase fluctuation signal generation unit included in the optical coherent sensor. It is a schematic diagram for explaining a signal processing unit included in the optical coherent sensor. It is a schematic diagram for demonstrating the prior art example of a laser Doppler vibrometer.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the shapes, sizes, and positional relationships of the respective constituents are merely schematically illustrated to the extent that the present invention can be understood. Further, although a preferred configuration example of the present invention will be described below, this is merely a preferred example. Therefore, the present invention is not limited to the following embodiments, and many changes or modifications that can achieve the effects of the present invention can be made without departing from the scope of the configuration of the present invention.

An optical coherent sensor according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic diagram for explaining the optical coherent sensor of the present invention. FIG. 2 is a schematic diagram for explaining the phase fluctuation signal generator included in the optical coherent sensor. FIG. 3 is a schematic diagram for explaining a signal processing unit included in the optical coherent sensor.

Here, a laser Doppler vibrometer will be described as a configuration example of the optical coherent sensor.

The laser Doppler vibrometer includes an interference signal generation unit 100, a phase fluctuation signal generation unit 200, an oscillation signal generation unit 300, and a signal processing unit 400.

The interference signal generation unit 100 includes a continuous light source 110, first to third polarization beam splitters (PBS) 121 to 123, a λ/4 plate 130, a mirror 140, a frequency shifter 150, a photoelectric converter 160, and a first band. A pass filter (BPF) 170 and a first analog-to-digital converter (ADC) 180 are provided.

The continuous-wave light source 110 is composed of, for example, any suitable conventional well-known laser light source capable of generating coherent light. The continuous light source 110 generates continuous light that is in a linearly polarized state. The continuous light generated by the continuous light source 110 is sent to the first PBS 121.

The first PBS 121 has an input end, a first output end, and a second output end. The first PBS 121 splits the continuous light input through the input end into two lights in two orthogonal linear polarization states. One of the two branches is output from the first output end and sent to the second PBS 122 as probe light. The other of the two branches is output from the second output end as reference light.

The second PBS 122 has an input end, an input/output end, and an output end. The second PBS 122 outputs the probe light input via the input end from the input/output end. The probe light output from the input/output terminal is sent to the λ/4 plate 130.

The λ/4 plate 130 converts the linearly polarized probe light received from the second PBS 122 into a circularly polarized state. The measurement light is irradiated with the probe light converted into the circularly polarized state. Further, the λ/4 plate 130 converts the scattered light in the circularly polarized state received from the measurement object into the linearly polarized state. The scattered light converted into the linearly polarized state is sent to the second PBS 122. Here, the probe light in the linearly polarized state passes through the λ/4 plate 130 twice to become scattered light in the linearly polarized state. For this reason, the polarization directions of the linearly polarized probe light input to the λ/4 plate 130 and the linearly polarized scattered light output from the λ/4 plate 130 are orthogonal to each other.

The second PBS 122 outputs the scattered light input from the input/output end from the output end. The scattered light output from the output end is sent to the third PBS 123.

The reference light output from the second output end of the first PBS 121 is split into a first reference light and a second reference light. The first reference light is sent to the mirror 140, and the second reference light is sent to the phase fluctuation signal generation unit 200.

The first reference light sent to the mirror 140 is reflected while maintaining its polarization state, and is sent to the frequency shifter 150. The frequency shifter 150 is composed of, for example, an AOM (Acoustic Opti Modulator). The frequency shifter 150 gives a frequency shift of the frequency Δf to the light propagating through the frequency shifter 150 by using the oscillation signal of the frequency Δf generated by the oscillation signal generation unit 300. The first reference light that has been frequency-shifted by the frequency Δf by the frequency shifter 150 is sent to the third PBS 123.

The third PBS 123 has a first input end, a second input end, and an output end. The scattered light sent from the second PBS 122 is input to the first input end of the third PBS 123. Further, the first reference light sent from the frequency shifter 150 is input to the second input end of the third PBS 123.

The third PBS 123 causes the scattered light having the same polarization state and the first reference light, which are input via the first input end and the second input end, to interfere with each other to generate interference light. The interference light is sent to the photoelectric converter 160.

The photoelectric converter 160 is composed of, for example, a photodiode (PD). The photoelectric converter 160 converts the interference light into an interference electric signal. The interference electric signal is a beat signal centered on the frequency Δf. The interference electrical signal includes a phase modulation component due to Doppler shift near the frequency Δf.

The interfering electrical signal is sent to the first BPF 170. The first BPF 170 functions as an anti-aliasing filter. The first BPF 170 extracts a frequency component near Δf including a phase modulation component due to Doppler shift of the interference electric signal. The interference electrical signal including the frequency component extracted by the first BPF 170 is sent to the first ADC 180.

The first ADC 180 converts the interference electrical signal sent from the first BPF 170 into a digital signal to obtain an interference signal. The interference signal, which is this digital signal, is sent to the signal processing unit 400.

The phase fluctuation signal generator will be described with reference to FIG. The phase fluctuation signal generation unit generates a phase fluctuation signal indicating the phase fluctuation of the second reference light.

The phase fluctuation signal generation unit 200 includes a branching unit 210, a frequency shifter 230, a delay unit 240, a multiplexing unit 250, a photoelectric converter 260, a second BPF 270, and a second ADC 280.

The branching unit 210 splits the second reference light into two light beams, a first light path and a second light path.

The frequency shifter 230 is provided in the first optical path. The frequency shifter 230 is composed of, for example, an AOM. The frequency shifter 230 gives a frequency shift of the oscillation frequency Δf to the light propagating through the frequency shifter 230 by using the oscillation signal of the frequency Δf generated by the oscillation signal generation unit 300. The light subjected to the frequency shift of the oscillation frequency Δf by the frequency shifter 230 is sent to the multiplexing unit 250.

The delay unit 240 is provided in the second optical path. The delay unit 240 gives a delay of time τ to the light propagating in the second optical path. The light delayed by the delay unit 240 is sent to the multiplexing unit 250.

The combining unit 250 combines lights propagating in the first optical path and the second optical path to generate combined light. An optical signal propagating in the first optical path and an optical signal propagating in the second optical path, which are incident on the multiplexing unit 250, are represented by the following equations (1) and (2), respectively.

Here, p ₁ and p ₂ are the powers of the optical signals propagating in the first and second optical paths, respectively. f ₀ is the frequency of continuous light, and φ _n is the phase noise of the second reference light, that is, continuous light.

The combined light is sent to the photoelectric converter 260. The photoelectric converter 260 is composed of, for example, a photodiode (PD). The electric signal output from the photoelectric converter 260 is represented by the following equations (3) and (4).

Here, p ₄ is the amplitude of the electric signal.

The electric signal output from the photoelectric converter 260 is sent to the second BPF 270. The second BPF 270 functions as an anti-aliasing filter. The second BPF 270 extracts a phase modulation component of the second reference light, that is, a frequency component near Δf including the phase noise of the continuous-wave light source 110 from the electric signal. The electric signal indicating the frequency component extracted by the second BPF 270 is sent to the second ADC 280.

The second ADC 280 converts the electric signal sent from the second BPF 270 into a digital signal to obtain a phase fluctuation signal. The phase fluctuation signal, which is this digital signal, is sent to the signal processing unit 400.

The oscillation signal generation unit 300 includes an oscillator 310, a third BPF 370, and a third ADC 380.

The oscillator 310 generates an oscillation signal which is a sine wave having a frequency Δf. The oscillation signal is branched into three and is sent to the interference signal generation unit 100, the phase fluctuation signal generation unit 200, and the third BPF 370, respectively.

The third BPF 370 functions as an anti-aliasing filter. The third BPF 370 extracts a frequency component near the oscillation frequency Δf. The electric signal indicating the frequency component extracted by the third BPF 370 is sent to the third ADC 380.

The third ADC 380 converts the electric signal sent from the third BPF 370 into a digital signal to obtain an oscillation frequency signal. The oscillation frequency signal, which is this digital signal, is sent to the signal processing unit 400.

The signal processing unit will be described with reference to FIG. The signal processing unit is a unit that processes a digital signal. In the signal processing unit, for example, a desired function is realized by the CPU executing software. The first to third ADCs described above are assumed to be synchronized. The signal processing unit detects the phase change of the scattered light by canceling the phase noise of the continuous light from the interference signal and the phase fluctuation signal using the technique of the active noise canceller.

The signal processing unit 400 includes a first phase extracting unit 410, a second phase extracting unit 420, a first differentiator 432, a variable filter 440, an adder 430, a second differentiator 434, a multiplier 460 and a third. The low pass filter (LPF) 470 and the speed detection unit 480 are included.

The first phase extraction unit 410 includes a first Hilbert transformer 412, a first mixer 414, a first LPF 416, and a first unwrapper 418. In addition, the second phase extraction unit 420 includes a second Hilbert transformer 422, a second mixer 424, a second LPF 426, and a second unwrapper 428.

The signal processing unit 400 further includes a third Hilbert transformer 482.

The interference signal has a frequency component of Δf, a phase component φ _d due to the Doppler shift, and a phase variation component of the first reference light, that is, a phase component φ _n due to the phase noise of the continuous light source. The interference signal is sent to the first phase extraction unit 410.

The phase fluctuation signal has a frequency component of Δf and a phase fluctuation component of the second reference light, that is, a phase component φ _n due to the phase noise of the continuous light source. The phase fluctuation signal is sent to the second phase extraction section 420.

The oscillation frequency signal has a frequency component of Δf. Here, the phase component of the oscillation frequency signal is 0. The oscillation frequency signal is sent to the third Hilbert transformer 482.

The first Hilbert transformer 412 converts the interference signal sent to the first phase extraction unit 410 into a first complex number signal which is a complex number signal. The second Hilbert transformer 422 converts the phase fluctuation signal sent to the second phase extraction unit 420 into a second complex number signal which is a complex number signal. The third Hilbert transformer 482 converts the oscillation frequency signal into a third complex number signal which is a complex number signal. These first to third Hilbert transformers have a function of generating orthogonal components from a real number trigonometric function signal and converting the trigonometric function signal into a complex number signal.

The first complex number signal and the third complex number signal are sent to the first mixer 414 and multiplied with each other. The signal multiplied by the first mixer 414 includes a frequency component of 2Δf and a DC component. The output of the first mixer 414 is sent to the first LPF 416.

The second complex number signal and the third complex number signal are sent to the second mixer 424 and multiplied with each other. The signal multiplied by the second mixer 424 includes a frequency component of 2Δf and a DC component. The output of the second mixer 424 is sent to the second LPF 426.

The first LPF 416 removes the frequency component near 2Δf from the output of the first mixer 414 and outputs the near DC component. The output of the first LPF 416 is sent to the first unwrapper 418.

Similarly, the second LPF 426 removes the frequency component near 2Δf from the output of the second mixer 424, and outputs the near DC component. The output of the second LPF 426 is sent to the second unwrapper 428.

The first unwrapper 418 extracts a phase component from the output of the first LPF 416 and outputs it as a first phase signal. The first phase signal includes the phase component of scattered light and the phase component of first reference light. The second unwrapper 428 extracts the phase component from the output of the second LPF 426 and outputs it as the second phase signal. The second phase signal includes the phase component of the second reference light. The phase components of the first reference light and the second reference light are both caused by the phase noise of the continuous-wave light source 110. Here, the unwrapper has a function of extracting a phase component from the complex signal. The first unwrapper 418 and the second unwrapper 428 can have a conventionally known configuration (see Non-Patent Document 1, for example).

In this way, the first phase extraction unit 410 extracts the phase component of the scattered light and the phase component of the first reference light from the interference signal to generate the first phase signal. Further, the second phase extraction section 420 extracts the phase component of the second reference light from the phase fluctuation signal to generate the second phase signal.

The first phase signal is represented by the following equations (5) and (6).

Here, k and p are integers, and equations (5) and (6) are functions of time. Note that k in parentheses indicates how many times the sampling period is. Further, p indicates the time difference between the scattered light and the reference light. Here, it is assumed that the sampling period is sufficiently small, and all times can be approximated to the nearest integer multiple of the sampling frequency.

Further, g _k is an impulse response when φ _n (k) is input and n(k) is regarded as an output.

The first phase signal is sent to adder 430.

The second phase signal is represented by the following equation (7).

Here, m and q are integers, and Expression (7) is a function of time. Note that m in parentheses indicates how many times the sampling cycle is. Further, q indicates the delay in the delay unit 240. Here, it is assumed that the sampling period is sufficiently small, and all times can be approximated to the nearest integer multiple of the sampling frequency. μ is a constant corresponding to 2πf ₀ τ in the above equation (3), and more accurately is a remainder obtained by dividing 2πf ₀ τ by an integral multiple of 2π radians.

m is not the same as k, but is a delayed amount with respect to k. Therefore, m can be represented by m=k−Δ using k and the integer Δ.

The second phase signal is sent to the first differentiator 432. The first differentiator 432 has a function of delaying the input second phase signal by one sampling period and obtaining the difference from the second phase signal input next. The first differential signal which is the output of the first differentiator 432 is represented by the following equation (8), and μ is canceled by this first differential signal.

Here, _{s m} as an input to φ _{n (m),} is the impulse response when regarded as outputs _y 3 (m).

Further, the relationship between y ₃ (k) and y ₃ (m) is expressed by the following equation (9).

Here, d _k is an impulse response when y ₃ (k) is input and y ₃ (m) is regarded as output.

The first differential signal is sent to the adder 430 via the variable filter 440.

The adder 430 takes the difference between the first phase signal and the first differential signal to generate a difference signal e(k). The difference signal e(k) output from the adder 430 is expressed by the following equations (10) and (11).

Here, f _l,k is the impulse response of the variable filter 440.

The variable filter 440 refers to the variance of the difference signal e(k) and dynamically changes f _l,k so that the variance becomes small. As an algorithm for changing the f _l,k , any suitable conventionally known method, for example, the least squares method (LMS) can be used. Here, 1 indicates the number of iterations in the algorithm.

The impulse response f _l,k converged by this algorithm has a value that reduces the influence of g _k *φ _n (k). That is, the difference signal e(k) becomes a signal close to the phase φ _d (k) due to Doppler shift.

In this way, the signal processing unit operates similarly to a conventionally known active noise canceller (see, for example, Non-Patent Document 2).

As a result of using the technique of the active noise canceller, the differential signal e(k) which is the output of the variable filter 440 is expressed by the following equation (12).

Here, n ₀ (k) is the residual phase noise in the state where the phase noise is relaxed by the technique of the active noise canceller.

The difference signal e(k) is sent to the second differentiator 434. The second differentiator 434 has a function of delaying the input difference signal e(k) by one sampling period and obtaining the difference from the next input difference signal e(k−1). The second differential signal output from the second differentiator 434 is represented by the following equation (13).

The second differential signal is sent to the multiplier 460. The multiplier 460 divides the second differential signal by the sampling period. As a result, the time change rate of the phase component of the differential signal e(k-1) is obtained. From the first and second terms on the right side of the above equation (13), the time change rate of the phase due to the Doppler shift between the sampling periods can be obtained. Further, the time change rate of the phase noise between the sampling periods can be obtained from the third and fourth terms on the right side of the above equation (13). The time change rate of this phase noise increases as the frequency becomes higher. The output of the multiplier 460 is sent to the third LPF 470.

The third LPF 470 attenuates the phase noise that increases as the frequency becomes higher. As a result, the phase change of scattered light due to Doppler shift is emphasized. The output of the third LPF 470 is sent to the speed detector 480.

The velocity detector 480 detects the velocity of the object to be measured from the phase change of the scattered light due to the Doppler shift contained in the signal sent from the third LPF 470. The speed detection unit 480 can have any suitable conventionally known configuration.

According to this laser Doppler vibrometer, the phase noise of the continuous light source is removed by using the technology of the active noise canceller, so that the costly narrow linewidth light source is unnecessary.

Further, in the laser Doppler vibrometer, when the time difference until the scattered light and the reference light interfere with each other increases, the fluctuation of the phase noise also increases in proportion to this time difference. Therefore, the measurable distance between the laser Doppler vibrometer and the measurement target is limited. On the other hand, in this laser Doppler vibrometer, the phase noise can be reduced by using the technology of active noise canceller. That is, there is also a secondary effect that the measurable distance between the laser Doppler vibrometer and the measurement object can be increased.

Here, the example of the laser Doppler vibrometer has been described as the optical coherent sensor, but the invention is not limited to this. The above-described configuration can be used as an optical coherent sensor that can be used for optical communication and optical sensing.

10, 110 Continuous light source 21, 22, 23, 121, 122, 123 Polarizing beam splitter (PBS)
30, 130 λ/4 plate 40, 140 Mirror 50, 150, 230 Frequency shifter 60, 160, 260 Photoelectric converter 70 Amplifier 80 Frequency discriminator 100 Interference signal generation unit 170, 270, 370 Bandpass filter (BPF)
180, 280, 380 Analog-to-digital converter (ADC)
200 phase fluctuation signal generation unit 210 branching unit 240 delay unit 250 multiplexing unit 300 oscillation signal generation unit 310 oscillator 400 signal processing unit 410, 420 phase extraction unit 412, 422, 482 Hilbert converter 414, 424 mixer 416, 426, 470 Low pass filter (LPF)
418, 428 Unwrapper 430 Adder 432, 434 Differentiator 440 Variable filter 460 Multiplier 480 Speed detector

Claims (5)

Produces continuous light,
The continuous light is split into a probe light and a reference light,
The reference light is split into a first reference light and a second reference light, and
An interference signal generation unit that generates an interference signal by coherently detecting the scattered light in which the probe light is scattered by the measurement target and the first reference light,
A phase fluctuation signal generation unit that generates a phase fluctuation signal indicating the phase fluctuation of the second reference light;
From the interference signal and the phase fluctuation signal, using the technology of active noise canceller, by canceling the phase noise of the continuous light, a signal processing unit for detecting a phase change of the scattered light ,
The signal processing unit,
A first phase extraction unit,
A second phase extraction unit,
A first differentiator,
Variable filter,
An adder,
A second differentiator,
With a multiplier
With a low pass filter
Equipped with
The first phase extraction unit extracts a phase change of the scattered light and a phase component of the continuous light from the interference signal to generate a first phase signal,
The second phase extraction unit extracts a phase component of the continuous light from the phase fluctuation signal to generate a second phase signal,
The first differentiator acquires a time change of a phase component included in the second phase signal,
The output of the first differentiator is sent to the variable filter,
The adder outputs the difference between the first phase signal and the output of the variable filter as a difference signal,
The variable filter operates to reduce the variance of the differential signal,
The second differentiator and the multiplier obtain a time change rate of the phase component of the difference signal,
The low pass filter, optical coherent sensor characterized that you remove the phase component of the continuous light. An oscillation signal generation unit that generates an oscillation frequency signal having a frequency component of the oscillation frequency Δf is further provided ,
The first phase extraction unit,
A first Hilbert transformer for converting the interference signal into a first complex number signal which is a complex number signal;
A first mixer for multiplying the first complex number signal by a third complex number signal obtained by converting the oscillation frequency signal into a complex number signal;
A first low-pass filter for extracting a frequency component near DC from the output of the first mixer;
A first unwrapper for extracting a phase component of the output of the first low-pass filter;
Equipped with
The second phase extraction unit,
A second Hilbert transformer for converting the phase fluctuation signal into a second complex number signal which is a complex number signal;
A second mixer for multiplying the second complex signal by the third complex signal;
A second low-pass filter for extracting a frequency component near DC from the output of the second mixer;
A second unwrapper that extracts the phase component of the output of the second low-pass filter;
Optical coherent sensor according to claim 1, characterized in Rukoto equipped with. The oscillation signal generation unit,
An oscillator,
A bandpass filter,
With analog-digital converter,
The oscillator produces an oscillating signal, which is a sine wave of frequency Δf,
The oscillation signal is branched into three and sent to the interference signal generation unit, the phase fluctuation signal generation unit, and the bandpass filter of the oscillation signal generation unit,
The bandpass filter of the oscillation signal generation unit extracts a component near the oscillation frequency Δf of the oscillation signal,
The analog-to-digital converter of the oscillation signal generation unit, optical coherent sensor according to claim 2, characterized in that by converting the output of said bandpass filter into a digital signal to obtain the oscillation frequency signal. The interference signal generation unit,
Continuous light source,
First to third polarization beam splitters,
λ/4 plate,
Frequency shifter,
Photoelectric converter,
A bandpass filter,
With analog-digital converter,
The continuous light source generates the continuous light,
The first polarization beam splitter splits the continuous light into two beams, a probe light and a reference light,
The second polarization beam splitter sends the probe light to the measurement target through the λ/4 plate, receives scattered light from the measurement target through the λ/4 plate, and outputs the probe light to the measurement target. To the polarization beam splitter of
The frequency shifter applies a frequency shift of the oscillation frequency Δf to the first reference light, and then sends the first reference light to the third polarization beam splitter,
The third polarization beam splitter interferes with the scattered light and the first reference light subjected to frequency shift to generate interference light,
The photoelectric converter photoelectrically converts the interference light to generate an interference electrical signal,
The bandpass filter extracts a component in the vicinity of the oscillation frequency Δf of the interference electric signal,
Said analog-to-digital converter, optical coherent sensor according to claim 2 or 3, characterized in that by converting the output of said bandpass filter into a digital signal to obtain the interference signal. The phase fluctuation signal generation unit,
Branching part,
Frequency shifter,
Delay part,
With the multiplexing section,
Photoelectric converter,
A bandpass filter,
With analog-digital converter,
The branching unit splits the second reference light into a first optical path and a second optical path,
The frequency shifter of the phase fluctuation signal generation unit is provided in the first optical path, and gives a frequency shift of the oscillation frequency Δf to light propagating in the first optical path.
The delay unit is provided in the second optical path, delays light propagating in the second optical path,
The combining unit combines lights propagating in the first optical path and the second optical path to generate combined light,
The photoelectric converter of the phase fluctuation signal generation unit photoelectrically converts the combined light to generate an electric signal,
The bandpass filter of the phase fluctuation signal generation unit extracts a component near the oscillation frequency Δf of the electric signal,
Said analog-to-digital converter of the phase variation signal generating unit according to any one of claims 2-4, characterized in that to obtain a phase variation signal is converted into a digital signal output of the bandpass filter Optical coherent sensor.