JP4932378B2 - Coherent rider device - Google Patents

Description

  The present invention relates to a coherent rider apparatus that can obtain high detection performance.

  A coherent lidar device emits laser light into the atmosphere, collects scattered light from the atmosphere, clouds, and aerosol using a transmission / reception optical system such as a reflective telescope, performs detection processing, and measures its strength and Doppler velocity. Thus, the distribution of atmospheric trace components, water vapor, wind, temperature, aerosol, clouds, etc. is measured. According to this apparatus, since sufficient scattering intensity can be obtained particularly for aerosols in the atmosphere, wind speed and wind speed distribution can be measured even in fine weather. For this reason, coherent riders have been installed at airports or mounted on airplanes to detect obstacles such as turbulence.

  As a conventional coherent rider device, for example, there is one described in Non-Patent Document 1. As shown in FIG. 6, this apparatus includes a laser light source 101, a first optical coupler 102, an optical modulator 103, an optical fiber amplifier 104, an optical circulator 105, a transmission / reception optical system 106, a second optical coupler 107, and an optical receiver 108. The AD converter 109 and the signal processor 110 are included. Further, in connection of each part, the laser light source 101 and the first optical coupler 102, the first optical coupler 102 and the optical modulator 103, the optical modulator 103 and the optical fiber amplifier 104, the optical fiber amplifier 104 and the optical circulator 105, and the optical circulator 105. And optical transceiver 106, first optical coupler 102 and second optical coupler 107, optical circulator 105 and second optical coupler 107, and second optical coupler 107 and optical receiver 108 are all connected by optical fibers. Has been. Furthermore, the optical receiver 108 and the AD converter 109, and the AD converter 109 and the signal processor 110 are connected by an electric cable such as a coaxial cable.

Next, the operation will be described.
A CW (Continuous Wave) laser beam output from the laser light source 101 is branched into two in the first optical coupler 102. One of the branched laser lights is used as transmission light, and the other is used as local light in heterodyne detection. The optical modulator 103 modulates one of the branched laser beams. The modulated laser light is sent to the optical fiber amplifier 104 and amplified. The amplified modulated light is irradiated toward the target by the transmission / reception optical system 106 via the optical circulator 105. Thereafter, scattered light from the target is received by the transmission / reception optical system 106. At this time, the frequency of the received light undergoes a Doppler shift corresponding to the speed of the target. This received light is sent to the second optical coupler 107 by the optical circulator 105. In the second optical coupler 107, the received light and the other laser light (local light) branched by the first optical coupler 102 are multiplexed. The optical receiver 108 heterodyne-detects the combined light from the second optical coupler 107 and outputs a beat signal between the received light and the local light. Further, the AD converter 109 performs AD conversion on the beat signal, and the signal processing unit 110 performs signal processing analysis of the AD converted beat signal to derive desired information such as a Doppler frequency.

Asaka, et al. “Examination of all-optical fiber Doppler lidar on board”, Laser Research, Journal of Laser Society, Vol. 29, no. 6, 2001, p. 371-P. 376

  In the coherent lidar device having a monostatic configuration with one transmission / reception system as shown in FIG. 6, since the transmission light and the reception light are separated via the optical circulator 105, the reception light obtained by the optical receiver 108 is obtained. In addition to the scattered light component from the target including the desired signal component, the component mainly contains internally reflected light from the optical circulator 105. For example, the internal reflection light level in the case of using an inline type optical fiber circulator is about −60 dB with a commercially available product. On the other hand, the scattered light from the target is often at a level smaller than -60 dB. Therefore, when the shift amount of the Doppler shift due to the scattered light component is very small, it overlaps with the internally reflected light level, which causes a problem that the scattered light component cannot be detected. In addition, when detecting the scattered light component from the target that does not move, the Doppler shift is 0, so that it overlaps with the internally reflected light component and cannot be detected as described above. As will be described later, when weak vibrations such as voice are detected, FM modulation may be performed to remove noise components due to intensity fluctuations and to extract only desired frequency components. In this case, in addition to the above problem, As a result, the S / N ratio of the demodulated signal to white noise also deteriorates.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a coherent rider device that can obtain high detection performance.

  A coherent lidar device according to the present invention includes a light source that outputs CW laser light having a single frequency, a first optical coupler that branches the laser light output from the light source into two, and the first optical coupler branched. An optical amplifier that amplifies one of the laser beams, the laser beam amplified by the optical amplifier is input to the first port and output from the second port, and the scattered light of the received target is input to the second port Then, an optical circulator that outputs to the third port, a frequency shifter that transmits the output laser light of the optical circulator to the transmission side, and shifts only the scattered light from the received target by a desired frequency, and the frequency shifter The transmitted output laser beam is transmitted toward the target, and the other optical signal branched by the first optical coupler and the transmission / reception optical system for receiving the scattered light from the target A second optical coupler that combines the light and the scattered light of the frequency-shifted target output from the optical circulator, heterodyne detection of the light combined by the second optical coupler, and the other laser light and the target An optical receiver that extracts a beat signal from the scattered light and converts it into an electrical signal, a filter that passes only the beat signal component from the electrical signal converted by this optical receiver, and the beat signal component that has passed through this filter The apparatus includes a signal processing unit that performs signal processing analysis and derives information such as Doppler frequency.

  According to the present invention, there is an effect of improving the detection performance by increasing the blocking power of the internally reflected light leaking from the optical circulator to the second optical coupler side.

Embodiment 1 FIG.
1 is a block diagram showing a configuration of a coherent rider apparatus according to Embodiment 1 of the present invention.
This coherent rider device includes a light source 1, a first optical coupler 2, an optical amplifier 3, an optical circulator 4, a frequency shifter 5, a transmission / reception optical system 6, a second optical coupler 7, an optical receiver 8, a filter 9, and a signal processing unit 10. It has.
In the figure, a light source 1 is connected to a first optical coupler 2, and one of two output ports of the first optical coupler 2 is connected to an optical amplifier 3. The other output port is connected to the second optical coupler 7. The optical amplifier 3 is connected to the input port of the optical circulator 4. Of the two output ports of the optical circulator 4, the one that outputs light from the optical amplifier 3 is connected to the frequency shifter 5, and the one that outputs light from the frequency shifter 5 is connected to the second optical coupler 7. . The frequency shifter 5 is connected to the transmission / reception optical system 6. The second optical coupler 7 is connected to the optical receiver 8. Here, the light source 1 and the first optical coupler 2, the first optical coupler 2 and the optical amplifier 3, the optical amplifier 3 and the optical circulator 4, the optical circulator 4 and the frequency shifter 5, the frequency shifter 5 and the transmission / reception optical system 6, the first light For the connection between the coupler 2 and the second optical coupler 7, the optical circulator 4 and the second optical coupler 7, and the second optical coupler 7 and the optical receiver 8, an optical circuit such as an optical fiber is used.
The optical receiver 8 is connected to the filter 9. The filter 9 is connected to the signal processing unit 10. For these electrical connections, for example, a cable such as a coaxial cable is used.

  The light source 1 has a function of outputting a single frequency CW (Continuous Wave) laser beam. The first optical coupler 2 has a function of branching the CW laser light input from the light source 1 into two. The optical amplifier 3 has a function of amplifying one laser beam branched by the first optical coupler 2. The optical circulator 4 has a function of outputting the laser light amplified by the optical amplifier 3 to the frequency shifter 5 and outputting the scattered light of the target input from the frequency shifter 5 side to the second optical coupler 7. . The frequency shifter 5 has a function of transmitting the output laser light of the optical circulator 4 to the transmission side and shifting only the scattered light of the target received by the transmission / reception optical system 6 by a desired frequency. The transmission / reception optical system 6 has a function of transmitting the output laser light of the frequency shifter 5 toward the target and receiving scattered light from the target. The second optical coupler 7 has a function of combining the other laser light branched by the first optical coupler 2 and the scattered light of the frequency-shifted target output from the optical circulator 4. The optical receiver 8 has a function of performing heterodyne detection on the light combined by the second optical coupler 7 and converting the beat signal of the local light and the scattered light of the target into an electric signal. The filter 9 has a function of passing only the beat signal component from the electrical signal converted by the optical receiver 8. The signal processing unit 10 has a function of performing signal processing analysis on the beat signal component that has passed through the filter 9 and deriving information such as Doppler frequency.

Here, the frequency shifter 5 may be a reversible and shiftable one, for example, an AO modulator (ACO modulator) that shifts the frequency of the input light by applying ultrasonic waves to the acoustooptic device. . However, the frequency shifter according to the present invention does not necessarily need to be reversible and can be shifted. For example, even if the frequency shifter shifts only in one direction, the detection function of this apparatus is sufficiently satisfied in the other non-shifted direction. As long as it has a transmittance sufficient to do so.
In the present invention, if the shot noise limit is reached when performing heterodyne detection, further improvement in detection performance can be obtained.

Next, the operation of the coherent rider apparatus of FIG. 1 will be described.
When CW laser light having a single frequency is output from the light source 1, the laser light is branched into two by the first optical coupler 2. One laser beam branched by the first optical coupler 2 is amplified by the optical amplifier 3, passes through the optical circulator 4, is shifted by a desired frequency by the frequency shifter 5, and is transmitted toward the target by the transmission / reception optical system 6. Is done. The other laser beam branched by the first optical coupler 2 is output to the second optical coupler 7 as local light used in heterodyne detection described later.
Here, when the target is an aerosol contained in the atmosphere, for example, the transmission light transmitted toward the target is scattered by the aerosol, and the scattered light returns and is received by the transmission / reception optical system 6. The carrier frequency of the scattered light at this time is a value shifted by the Doppler frequency of the wind speed in the transmission direction with respect to the carrier frequency of the transmission light.

  In the frequency shifter 5, only the scattered light from the target received by the transmission / reception optical system 6 is shifted by a desired frequency. The frequency-shifted scattered light is output to the second optical coupler 7 by the optical circulator 4. In the second optical coupler 7, the other laser light (local light) branched by the first optical coupler 2 and the scattered light shifted by the frequency from the optical circulator 4 are combined and supplied to the optical receiver 8. In the optical receiver 8, the combined light is heterodyne detected to extract a beat signal, converted into an electrical signal, and output to the filter 9. In the filter 9, only the detection component, that is, the beat signal component due to the local light and the scattered light is passed from the electric signal of the optical receiver 8, and the internally reflected light component (DC signal) leaked from the optical circulator 4 to the second optical coupler 7. Component). The filter 9 used here may be any type of filter. However, as described above, since only the beat signal component of the local light and the scattered light is allowed to pass, it is preferable to have a characteristic capable of blocking the extra colored noise by narrowing the band as much as possible. Thereafter, the signal processing unit 10 performs signal processing analysis using spectrum analysis including FFT (Fast Fourier Transform) on the beat signal component extracted by the filter 9 to derive information such as Doppler frequency. .

Considering a coherent lidar apparatus having a monostatic configuration with a single transmission / reception optical system as shown in FIG. 1, transmission light and reception light are separated via an optical circulator 4, and thus can be obtained by an optical receiver 8. In addition to the scattered light component from the target including the desired signal component, the internally reflected light mainly from the optical circulator 4 is mixed in the received light component. For example, the internal reflection light level in the case of using an inline type optical fiber circulator is about −60 dB with a commercially available product. On the other hand, scattered light from the target is often at a level smaller than -60 dB. Therefore, when the shift amount of the Doppler shift due to the scattered light component is very small, it overlaps with the internally reflected light component, causing a problem that the scattered light component cannot be detected. In addition, when detecting the scattered light component from the target that does not move, the Doppler shift is 0, so that it overlaps with the internally reflected light component and cannot be detected as described above.
However, according to the first embodiment, the frequency shifter 5 is installed behind the optical circulator 4 and the frequency shift is performed only on the scattered light from the target. Since only the beat signal components of the local light and scattered light detected at 8 are allowed to pass, the internally reflected light component can be substantially blocked.
Therefore, the scattered light component having a Doppler shift frequency that is small enough to overlap with the internally reflected light component as described above and the scattered light component from the target that does not move can be detected using the configuration of FIG. .
Further, with the above configuration, it is possible to remove the internally reflected light component and the colored noise component of the power source in the apparatus.

Further, in the first embodiment, the connection between the respective parts from the light source 1 to the optical circulator 4, the connection between the respective parts from the first optical coupler 2 to the optical receiver 8, and between the optical circulator 4 and the second optical coupler 7. When an optical fiber is used for the connection, a reduction in size, high reliability, ease of handling, flexibility in arrangement, and the like can be obtained. This also applies to other embodiments described below.
When an optical fiber is also used for optical circuit connection between the optical circulator 4 and the frequency shifter 5 and between the frequency shifter 5 and the transmission / reception optical system 6, the laser beam shifted by the frequency shifter 5 It is conceivable that Fresnel reflection or Rayleigh scattering occurs inside the fiber, and these cannot be blocked by the filter 9. However, if the filter 9 can block the Fresnel reflected light component and the Rayleigh scattered light component, or if the reflected light component and scattered light component have little influence on the detection performance of the apparatus, an optical fiber is connected to these connections. You may use.

In general, when a fiber circulator is used as an optical circulator, Fresnel reflection caused by the difference in refractive index between air and the fiber medium and Rayleigh scattering occurring inside the fiber occur at the fiber end, and these are physically avoided. It is impossible to do. However, in the configuration of the first embodiment, even if a fiber circulator is used as the optical circulator 4, the internally reflected light can be substantially blocked, so that an optical fiber can be used for optical circuit connection.
Further, even when a spatial light circulator is used as the optical circulator 4, since the internal reflection light from the circulator exists, the internal reflection light can be blocked by using the configuration of the first embodiment, and the detection performance is improved. The effect is obtained.

In the configuration shown in FIG. 1, the frequency shifter 5 is provided between the optical circulator 4 and the transmission / reception optical system 6. Alternatively, a frequency shifter may be provided between the transmission / reception optical system 6 and the target. A similar effect can be expected.
Further, since the coherent rider apparatus of the first embodiment can detect the Doppler frequency generated by the movement and vibration of the target, it is other than measuring the wind speed and the wind speed distribution by irradiating the aerosol in the atmosphere with laser light. In addition, the present invention can be applied to various applications such as measuring the traveling speed by irradiating an automobile, and detecting the vibration displacement or vibration frequency by irradiating a minutely vibrating target.

Embodiment 2. FIG.
FIG. 2 is a block diagram showing a configuration of a coherent rider apparatus according to Embodiment 2 of the present invention. In the figure, the same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted in principle.
The second embodiment is different from the first embodiment in that a pulse modulator 21 is newly provided between the first optical coupler 2 and the optical amplifier 3 configured as shown in FIG. The first optical coupler 2 and the pulse modulator 21 and the pulse modulator 21 and the optical amplifier 3 are connected by an optical circuit, for example, an optical fiber. The pulse modulator 21 has a function of modulating one of the laser beams branched by the first optical coupler 2 into pulsed light.
Of the two laser beams branched by the first optical coupler 2, the laser beam to be transmitted to the target is modulated into pulse light by the pulse modulator 21, and the modulated pulse light is amplified by the optical amplifier 3. It is given to the optical circulator 4. The subsequent operation of each part is the same as in FIG.

  In the case of the coherent lidar device shown in FIG. 2, the pulse light is modulated by the pulse modulator 21 and then amplified by the optical amplifier 3, so that the output light from the pulse modulator 21 is the same CW light as the average power. The peak power at the time of pulsing becomes larger than the optical power when amplified. Therefore, by adjusting the reception timing at the time of heterodyne detection in the optical receiver 8 in advance near the peak of the reception pulse signal using a trigger signal or the like, higher reception power can be obtained compared to the case of CW optical amplification. The detection performance can be improved, for example, by extending the measurement limit distance.

  Here, when the transmission light propagates the round-trip distance to the target longer than the pulse width time, the timing of reception by the optical receiver 8 is as follows. The scattered light component is received. Therefore, even a conventional pulse output coherent lidar device can separate the internally reflected light component and the scattered light component from the target. On the other hand, when the transmission light propagates through the round-trip distance to the target is shorter than the pulse width time, the scattered light component from the target is included in the pulse that is the internally reflected light component. Therefore, in the conventional pulse output coherent lidar apparatus, it is impossible to separate the internally reflected light component and the scattered light component from the target. However, according to the second embodiment, the internally reflected light can be substantially blocked in the same manner as described in the first embodiment, so that the scattered light component from the target can be detected.

Embodiment 3 FIG.
FIG. 3 is a block diagram showing a configuration of a coherent rider apparatus according to Embodiment 3 of the present invention. In the figure, the same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted in principle.
In the third embodiment, the second optical coupler 7 branches and outputs the combined light into two, and a balanced receiver 31 is provided in place of the optical receiver 8. This is different from the configuration of the first embodiment. The second optical coupler 7 and the balanced receiver 31 are connected by an optical circuit, for example, an optical fiber. The balanced receiver 31 and the filter 9 are connected by electrical connection, for example, an electric cable. The balanced receiver 31 performs heterodyne detection using the two output lights combined by the second optical coupler 7 and extracts the beat signal between the other laser light from the first optical coupler 2 and the scattered light of the target. It has the function of converting it into an electrical signal and outputting it.

  The operation until the local light from the first optical coupler 2 and the scattered light from the optical circulator 4 are combined by the second optical coupler 7 is the same as in FIG. Thereafter, the two output lights from the second optical coupler 7 are heterodyne detected by the balanced receiver 31. In this case, the beat signal components included in the two output lights from the second optical coupler 7 are output with their phases inverted. On the other hand, the intensity noise component from the light source 1 included in the two output lights from the second optical coupler 7 is output in the same phase. Therefore, when the difference signal between the two laser beams input to the balanced receiver 31 is extracted, the beat signal component is doubled and output, whereas the intensity noise component from the light source 1 is canceled out. Become. The operation principle of the balanced receiver is described in, for example, Japanese Patent Laid-Open No. 9-93206. The subsequent operation of each part is the same as in FIG.

In order to further improve the removal of intensity noise of the light source 1, the lengths of the two optical paths from the second optical coupler 7 to the balanced receiver 31 in the configuration of FIG. In addition to this, if the two optical powers input to the balanced receiver 31 are made equal by setting the branching ratio of the output light by the second optical coupler 7 to 1: 1, the intensity noise of the light source 1 is reduced. It can be substantially removed.
As described above, according to the third embodiment, since the heterodyne detection is performed using the balanced receiver, the intensity noise component from the light source is removed in addition to the effect of the first embodiment. be able to.

Embodiment 4 FIG.
As an application of the coherent rider apparatus, for example, a case is assumed in which the target is a window glass and the transmission light is irradiated to the window glass that is vibrated weakly by sound or the like. In this case, the transmitted light emitted from the coherent lidar device is voice-modulated by the vibration of the window glass, but the reflected light (scattered light) of the window glass has a very large intensity fluctuation in addition to its frequency modulation component. The noise component by etc. is included. In this case, it is necessary to extract only a desired frequency component. The fourth embodiment provides a configuration for that purpose.
4 is a block diagram showing a configuration of a coherent rider apparatus according to Embodiment 4 of the present invention. In the figure, the same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted in principle. The fourth embodiment is different from the first embodiment in that an FM demodulator 41 is newly provided between the filter 9 having the configuration shown in FIG. The filter 9 and the FM demodulator 41 and the FM demodulator 41 and the signal processing unit 10 are connected by an electrical connection, for example, a cable such as a coaxial cable. The FM demodulator 41 has a function of demodulating a desired frequency modulation component included in the beat signal component that has passed through the filter 9.

  The operation until only the beat signal component of the local light and the scattered light is passed using the filter 9 is the same as that of the first embodiment, but here, the beat demodulated by the FM demodulator 41 is further passed through the filter 9. A frequency modulation component that is a minute vibration included in the signal is demodulated. The demodulated frequency modulation component is given to the signal processing unit 10 and processed in the same manner as in the first embodiment.

ここで、Ｓはヘテロダイン検波信号におけるターゲットからの散乱光成分、Ｓ_i は内部反射光成分、Ｎは白色雑音成分を意味している。（１）式の右辺において、主信号成分は第１項のみであり、他の項は雑音成分となる。雑音成分の内、第２項、第３項は散乱光および内部反射光の周波数に依存する有色的な雑音、第４項〜第６項は白色的な雑音である。 There are many FM demodulation methods, and a case where one of them, the quadrature method, will be described. The quadrature FM demodulator has a configuration as shown in FIG. A main signal in the IF frequency band is divided into two by a distributor 411, one of them is shifted in phase by a phase shifter 413, and a value obtained by multiplying both signals by a mixer 412 is integrated by an integrator 414 to be frequency-modulated. Demodulate the signal. In this case, the demodulated signal of the FM demodulator circuit is schematically represented as the expression (1) by multiplication of the signals.

Here, S means a scattered light component from the target in the heterodyne detection signal, S _i means an internally reflected light component, and N means a white noise component. In the right side of equation (1), the main signal component is only the first term, and the other terms are noise components. Among the noise components, the second and third terms are colored noises depending on the frequencies of the scattered light and the internally reflected light, and the fourth to sixth terms are white noises.

ここで、Ｓ_L、Ｓ_iL、Ｎ_Lはそれぞれターゲットからの散乱光成分電力、内部反射光成分電力、白色雑音電力である。
（２）式より、内部反射光成分電力が支配的な場合、有色雑音が大きくなるだけではなく、白色雑音に関しても散乱光成分電力と内部反射光成分電力の比に比例してＳ／Ｎ比劣化が生じる。したがって、この方式では内部反射光レベルを散乱光レベルに対して十分低減する必要があるが、そのため、ＦＭ復調器を、図４の構成のようにこの発明のコヒーレントライダ装置に適用することで、内部反射光を実質的に遮断できるので特に有効である。 When the S / N ratio (SNR) of the demodulated signal with respect to white noise is obtained based on the equation (1), it is expressed as equation (2).

Here, S _L , S _iL , and N _L are scattered light component power from the target, internally reflected light component power, and white noise power, respectively.
From the equation (2), when the internal reflected light component power is dominant, not only the colored noise is increased, but also the white noise is proportional to the ratio of the scattered light component power to the internal reflected light component power. Deterioration occurs. Therefore, in this method, it is necessary to sufficiently reduce the internally reflected light level with respect to the scattered light level. Therefore, by applying the FM demodulator to the coherent lidar apparatus of the present invention as shown in FIG. This is particularly effective because the internally reflected light can be substantially blocked.

  As described above, according to the fourth embodiment, a desired frequency modulation component is demodulated between the filter of the configuration of the first embodiment and the signal processing unit in order to detect minute vibrations such as sound vibration. Since an FM demodulator is provided, a noise component due to an intensity fluctuation that is much larger than a desired frequency modulation component included in the beat signal obtained by the optical receiver, that is, an internally reflected light component can be substantially blocked. There is an effect of improving the detection accuracy of minute vibration which is a frequency modulation component.

It is a block diagram which shows the structure of the coherent rider apparatus by Embodiment 1 of this invention. It is a block diagram which shows the structure of the coherent rider apparatus by Embodiment 2 of this invention. It is a block diagram which shows the structure of the coherent rider apparatus by Embodiment 3 of this invention. It is a block diagram which shows the structure of the coherent rider apparatus by Embodiment 4 of this invention. It is a block diagram which shows the basic composition of the FM demodulator of the quadrature system which concerns on Embodiment 4 of this invention. It is a block diagram which shows the structure of the conventional coherent rider apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source, 2 1st optical coupler, 3 Optical amplifier, 4 Optical circulator, 5 Frequency shifter, 6 Transmission / reception optical system, 7 2nd optical coupler, 8 Optical receiver, 9 Filter, 10 Signal processing part, 21 Pulse modulator, 31 Balanced receiver, 41 FM demodulator.

Claims (9)

A light source that outputs CW laser light of a single frequency;
A first optical coupler for branching the laser beam output from the light source into two;
An optical amplifier for amplifying one of the laser beams branched by the first optical coupler;
An optical circulator for inputting the laser light amplified by the optical amplifier to the first port and outputting it from the second port, and inputting the received scattered light of the target to the second port and outputting it to the third port. When,
A frequency shifter that transmits the output laser light of the optical circulator to the transmission side and shifts only the scattered light from the received target by a desired frequency;
A transmission / reception optical system that transmits the output laser light transmitted from the frequency shifter toward the target, and receives scattered light from the target, and
A second optical coupler for combining the other laser beam branched by the first optical coupler and the scattered light of the frequency-shifted target output from the optical circulator;
An optical receiver that heterodyne-detects the light combined by the second optical coupler, extracts a beat signal between the other laser light and the scattered light of the target, and converts it into an electrical signal;
A filter that passes only the beat signal component from the electrical signal converted by the optical receiver;
A coherent rider apparatus comprising a signal processing unit that performs signal processing analysis on a beat signal component that has passed through the filter and derives information such as a Doppler frequency.   2. The coherent rider device according to claim 1, wherein a frequency shifter is provided between the transmission / reception optical system and the target instead of being provided between the optical circulator and the transmission / reception optical system.   3. The coherent rider device according to claim 1, wherein a pulse modulator for modulating one of the branched laser beams into pulsed light is provided between the optical coupler and the optical amplifier. The second optical coupler splits the combined light into two and outputs it,
Heterodyne detection is performed using the two output lights combined by the second optical coupler, and the beat signal of the other laser light from the first optical coupler and the scattered light of the target is converted into an electrical signal and output. The coherent rider device according to any one of claims 1 to 3, further comprising: an optical receiver instead of the optical receiver.   5. The coherent rider device according to claim 4, wherein the lengths of the two optical paths from the second optical coupler to the balanced receiver are set equal.   6. The coherent rider device according to claim 4, wherein a branching ratio of output light by the second optical coupler is set to 1: 1.   When a desired frequency modulation component is included in the beat signal that has passed through the filter, an FM demodulator that demodulates the frequency modulation component is provided between the filter and the signal processing unit. The coherent rider device according to any one of claims 1 to 6.   2. The branching ratio of the first optical coupler is set to a value that allows the other laser beam to reach the shot noise limit when performing heterodyne detection with an optical receiver or a balanced receiver. The coherent rider device according to claim 7. An optical fiber was used for connection between each part from the light source to the optical circulator, between each part from the first optical coupler to the optical receiver or the balanced receiver, and between the optical circulator and the second optical coupler. The coherent rider device according to any one of claims 1 to 8, wherein the coherent rider device is provided.

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