Patent Description:
A laser radar device called a light detection and ranging (LiDAR) device has been used for a long time in the fields of geology and meteorology, and in recent years, attracts attention also, for example, in the field of automatic driving of an automobile.

An operation principle of the laser radar device is to obtain information on a distance to a target and a speed of the target by irradiating the target with laser light and analyzing the light that has hit the target and bounced back. As indicated by the name, the laser radar device may be considered as a radar device using laser light. When it is desired to obtain a distance to the target, it is possible to obtain the distance by measuring time (time of flight, hereinafter referred to as "TOF") from when the laser light is emitted to when the laser light is reflected and returned, and multiplying a speed of the laser light by the TOF. When it is desired to obtain a speed of the target, it is possible to obtain the speed by analyzing a frequency of the reflected light, obtaining a Doppler frequency, and using a relationship between the frequency of the emitted laser light and the Doppler frequency.

In a case of an application of simultaneously obtaining the distance to the target and the speed of the target, the TOF and the Doppler frequency are to be simultaneously obtained as described above. In order to directly obtain these, the laser radar device needs a sensor corresponding to two states of time and frequency. Regarding this, a technique for converting TOF into information on frequency using a frequency modulated continuous wave (hereinafter, referred to as "FMCW") is disclosed. In particular, Non-Patent Literature <NUM> discloses a technique in which a frequency difference between transmitted light and received light caused by a distance to a target and a frequency difference between the transmitted light and the received light caused by a speed of the target are separately obtained by combining an up-chirp FMCW and a down-chirp FMCW (<FIG> of Non-Patent Literature <NUM>). <CIT> discloses a method of frequency modulation for interference free optical time of flight systems. <CIT> discloses a device and a method for measuring a distance to a reflective object. <CIT> discloses a laser detecting and ranging apparatus.

In the technique disclosed in Non-Patent Literature <NUM>, the frequency of transmitted light constantly changes, and information on up-chirp and down-chirp is used for analysis. Non-Patent Literature <NUM> discloses the technique as an application of navigation of a lunar surface exploration mobile body, and a problem does not occur for such a target at a certain distance (referred to as a hard target).

However, in a case of wind measurement, usually, there is aerosol at a plurality of places in an irradiation direction of laser light, and light scattered by the aerosol at the plurality of places is received in an overlapping manner. Therefore, a waveform of received light is complicated. In an application of wind measurement, the laser radar device is required to have a mechanism for separating frequency information resulting from a distance to a target and frequency information resulting from a speed of the target by a simpler method.

An object of the present disclosed technique is to solve the above problem, and to provide a laser radar device including a mechanism for separating frequency information resulting from a distance to a target and frequency information resulting from a speed of the target by a simple method.

In order to solve the above problem, the present invention provides a laser radar device according to claim <NUM>, and a wind measurement method according to claim <NUM>.

Since the laser radar device according to the present disclosed technique has the above configuration, the frequency of emitted laser light has discrete values at intervals of the frequency difference F. Therefore, TOF corresponding to a distance to a target appears in units of the frequency difference F for each time T, and a Doppler frequency corresponding to a speed of the target appears as a finer change than the frequency difference F. As described above, the present disclosed technique provides a laser radar device including a mechanism for separating frequency information resulting from a distance to a target and frequency information resulting from a speed of the target by a simple method.

Embodiments according to the present disclosed technique will be apparent by the following description with reference to the drawings.

<FIG> is a configuration diagram illustrating a configuration of a laser radar device according to a first embodiment. The laser radar device according to the first embodiment includes a Light source <NUM>, a frequency modulator <NUM> or a phase modulator 20B, a first beam splitter <NUM>, an amplifier <NUM>, a circulator <NUM>, a transmitting and receiving optics system <NUM>, a second beam splitter <NUM>, a balanced detector <NUM>, a control signal circuit <NUM>, and a receiving circuit <NUM>.

As the Light source <NUM>, a laser light source having a narrow line width is used. A light source at a wavelength band of <NUM> is preferable from the viewpoint of eye safety. Note that there is no problem if the Light source <NUM> is in other wavelength bands. The narrower the line width of the laser light is, the better it is. However, the narrower the line width of the laser light is, the more expensive the laser light tends to be. The line width of the laser light is appropriately determined by design. The Light source <NUM> is preferably a light source in a continuous-wave manner, that is, a continuous wave (CW) light source, but may be a light source in a quasi-continuous-wave manner, that is, a quasi-CW (QCW)-operated light source in consideration of a case where an intermittent operation is performed due to a safety problem and the like.

Either the frequency modulator <NUM> or the phase modulator 20B may be used, but in this case, frequency modulation is applied to laser light emitted by the Light source <NUM>. For the sake of simplicity, the description of the first embodiment will be given on the premise of using the frequency modulator <NUM>. In addition, the frequency modulator <NUM> is controlled by the control signal circuit <NUM>. Note that a reason why either the frequency modulator <NUM> or the phase modulator 20B may be used is that a relational formula represented by the following mathematical formula (<NUM>) is established. <MAT> in which θ represents a phase, f represents a frequency, π represents the circular constant, and t represents time.

The first beam splitter <NUM> splits the laser light modulated by the frequency modulator <NUM> into transmission light and local oscillator light. Usually, a beam splitter having an asymmetric branching ratio such as <NUM> : <NUM> is often used because the local oscillator light does not require so strong power. Note that the first beam splitter <NUM> may be a <NUM> : <NUM> beam splitter. In general, an optical fiber may be used as a beam splitter used in a laser radar device, and the constituent member may be referred to as another name such as an optical fiber coupler.

The amplifier <NUM> amplifies the transmission light out of the laser light split by the first beam splitter <NUM>. The amplifier <NUM> may have a one-stage configuration or a multistage configuration. A fiber amplifier is often used for the amplifier <NUM>, but an optical amplifier other than the fiber amplifier may be used. In a case of the multistage configuration, a fiber amplifier and an optical amplifier other than the fiber amplifier may be combined. In addition, in the case of the multistage configuration, a filter or an isolator for preventing return light may be inserted between an amplifier and an amplifier in order to remove amplified spontaneous emission (hereinafter, referred to as "ASE").

The transmission light amplified by the amplifier <NUM> is sent to the transmitting and receiving optics system <NUM> via the circulator <NUM>. In general, a circulator refers to a device that transmits light input from an optical path A to an optical path B, but outputs light input from the optical path B not from the optical path A but from another optical path C. In addition, a circulator in a narrow sense refers to a circulator using a Faraday rotator, but the circulator <NUM> may be simply a combination of a polarization beam splitter and a <NUM>/<NUM> wavelength plate.

The transmitting and receiving optics system <NUM> adjusts a beam diameter of the transmission light, emits the transmission light into the atmosphere, and collects received light scattered by and returned from aerosol in the atmosphere. The transmitting and receiving optics system <NUM> includes a telescope and a beam expander. In addition, the transmitting and receiving optics system <NUM> may use a scanner in order to be able to observe a plurality of lines of sight.

The second beam splitter <NUM> interferes with the received light collected by the transmitting and receiving optics system <NUM> and the local oscillator light, and transmits two beams of interference light obtained by the interference to the balanced detector <NUM>.

The balanced detector <NUM> includes two light receiving units, converts beams of light incident on the respective light receiving units into electrical signals, and outputs a difference between the two converted electrical signals. The balanced detector <NUM> may be an integrated light receiving element or may separately include a circuit that obtains a difference between photocurrents obtained from two photodiodes. The balanced detector <NUM> functions as a receiver, and therefore may be simply referred to as a receiver.

A role of the second beam splitter <NUM> is to obtain a frequency difference obtained by subtracting the frequency of the received light from the frequency of the local oscillator light. That is, this configuration utilizes a property that a beat of a difference between frequencies of two beams of light occurs as amplitude modulation when two beams of light having close frequencies interfere with each other. The balanced detector <NUM> is used to remove a DC component. Here, there is no problem if the frequency difference obtained by subtracting the frequency of the received light from the frequency of the local oscillator light is obtained by obtaining frequency components of the local oscillator light and the received light and then obtaining the frequency difference. In addition, since the frequency of the local oscillator light at each time is known, the frequency difference may be calculated simply by obtaining the frequency component of the received light in a time window in which the frequency of the local oscillator light is constant.

Note that the following paragraphs are based on the premise that the second beam splitter <NUM> and the balanced detector <NUM> are included.

The receiving circuit <NUM> processes the electrical signal converted by the balanced detector <NUM>, and calculates distance information and speed information of a target. More specifically, the receiving circuit <NUM> processes the difference signal output from the balanced detector <NUM> and calculates wind speed information for each distance. The receiving circuit <NUM> includes an electric filter, an amplifier, an analog-digital converter, a computer, and the like.

<FIG> is a configuration example of the receiving circuit <NUM>. The receiving circuit <NUM> includes a pre-filter <NUM>, an amplifier <NUM>, a frequency filter <NUM>, receivers <NUM> to <NUM>, and a computer <NUM>. Note that an electric amplifier may be used as the amplifier <NUM>.

An unnecessary frequency of the difference signal output from balanced detector <NUM> is removed by the pre-filter <NUM>, and then amplified by the amplifier <NUM>. The amplified signal is distributed for each frequency domain by the frequency filter <NUM> and transmitted to the receivers <NUM> to <NUM> depending on the frequency domain. In general, since an amplifier has band characteristics, the amplifier <NUM> may also function as the pre-filter <NUM>. In addition, since a band is limited after the frequency filter <NUM>, the amplifier <NUM> may be disposed after the frequency filter <NUM>. In this case, a common filter may be used as the pre-filter <NUM> and the frequency filter <NUM>, and the same number of amplifiers as the number of receivers are required. In the configuration example illustrated in <FIG>, three receivers are illustrated, but the number of receivers is appropriately determined by design. The receivers <NUM> to <NUM> are specifically analog-to-digital converters. The receivers <NUM> to <NUM> each transmit a reception signal to the computer <NUM>. The computer <NUM> performs signal processing such as Fourier transform on the signals transmitted from the receivers <NUM> to <NUM>, and calculates information regarding a distance and a wind condition. When performing signal processing, the computer <NUM> receives a timing signal and the like from the control signal circuit <NUM> as necessary and uses the timing signal and the like. The computer <NUM> may be a general-purpose computer such as a so-called personal computer, or may be a dedicated integrated circuit such as an application specific integrated circuit (ASIC). In addition, the computer <NUM> may be a combination of a plurality of types of computers.

An operation of the laser radar device and a wind measurement method according to the first embodiment will be clarified by the following description with reference to <FIG>.

<FIG> is a graph illustrating frequency modulation applied to transmission light by the frequency modulator <NUM>. That is, the frequency modulation applied by the frequency modulator <NUM> is modulation in which a stepwise change in which a frequency increases or decreases by a frequency difference F for each time width T is performed for at least one step. As a result, transmission light of the laser radar device according to the present disclosed technique has stepwise frequency characteristics illustrated in <FIG>.

The frequency difference F in the stepwise change is sufficiently larger than the Doppler frequency due to movement of aerosol in the air. The Doppler frequency fd due to movement of aerosol in the air is represented by the following mathematical formula (<NUM>), in which the frequency of light is represented by v<NUM>, the Doppler frequency is represented by fd, the wind speed is represented by V, and the light speed is represented by c.

Note that, as for the distance, a direction in which it goes away from the laser radar device serving as an origin is defined as a positive direction. In this case, also as for the speed, a direction in which it goes away from the laser radar device is considered as a positive speed. In this case, the wind speed has a positive value at the time of a tailwind, and has a negative value at the time of a headwind. The Doppler frequency fd may have either a positive value or a negative value corresponding to this. For example, when the frequency of light is <NUM> [THz] (≈ wavelength <NUM> [µm]), the Doppler frequency fd is -<NUM> [MHz] per <NUM> [m/s] of wind speed. Therefore, it can be said that the Doppler frequency fd when the frequency difference F is <NUM> [MHz] as illustrated in <FIG> is sufficiently larger than the Doppler frequency fd in a general wind condition. Note that the frequency difference F is not limited to <NUM> [MHz], and may be a smaller frequency or a larger frequency. For example, in weather terms, wind having a speed of more than <NUM>/s is defined as "furious wind" by the Japan Meteorological Agency, but a wind condition having a speed of more than <NUM>/s does not often occur on the ground. Even if it occurs, a storm occurs, and therefore it is often difficult to perform lidar measurement due to an influence of rain grains and dust. Therefore, even if the frequency difference F is set to <NUM> [MHz], which corresponds to distinguishing between a wind speed of about + <NUM> [m/s] and a wind speed of about -<NUM> [m/s], there is no practical problem.

<FIG> illustrates the properties of the transmission light of the laser radar device according to the present disclosed technique in terms of frequency, but can also illustrate the properties of the transmission light in terms of phase using formulas (<NUM>) and (<NUM>). <FIG> is a graph illustrating the frequency modulation illustrated in <FIG> as phase modulation. Note that, in general, a phase modulator cannot apply infinitely large phase modulation, and a phase is folded back at 2π in many cases, but this does not cause a problem. Controlling the phase modulator 20B by the control signal circuit <NUM> and applying the phase modulation as illustrated in <FIG> is substantially the same as the frequency modulation in the present disclosed technique. The graph of <FIG> is constituted by a polygonal line, and it can be seen that the phase continuously changes. Information on a phase cannot be read at a time when the frequency is switched from the graph of <FIG>, but in the frequency modulation, the phase changes continuously as illustrated in <FIG>.

An effect of the present disclosed technique will be clarified by the following specific example.

Transmission light of the laser radar device having the frequency characteristics illustrated in <FIG> is scattered by aerosol in the atmosphere and measured as received light. The received light is subjected to a Doppler shift corresponding to the speed of aerosol that is a wind condition of the atmosphere, and is received after a lapse of time τ that is TOF corresponding to the position of the scattered aerosol.

<FIG> is a graph illustrating local oscillator light and received light in the laser radar device according to the present disclosed technique in comparison with each other as a time change in frequency for the following specific example.

For example, light scattered from aerosol at a position of <NUM> [m] from the laser radar device is received after a lapse of <NUM> [µs], which is time during which the light flies for a distance of <NUM> [m] in going and returning ways. This is because the light speed is <NUM>,<NUM> kilometers per second. The local oscillator light and the received light received by the balanced detector <NUM> have frequency characteristics illustrated in <FIG>. In this specific example, the frequency modulator <NUM> applies a frequency modulation in which a stepwise change is performed by a frequency difference F of <NUM> [MHz] for a time width T of <NUM> [µs].

Here, the light scattered from the aerosol at the position of <NUM> [m] is received in a time-shifted manner after a lapse of TOF of <NUM> [µs]. Since the laser radar device according to the present disclosed technique uses stepwise frequency modulation, the information on the TOF is converted into information of a frequency difference that the frequency of the received light is lower than that of the local oscillator light by <NUM> [MHz]. Furthermore, since the received light is influenced by a Doppler shift, a relationship between the frequency of the received light and the frequency of the local oscillator light can be represented by the following mathematical formula (<NUM>).

The influence of the Doppler shift will be described by the following specific example. When the frequency of light is <NUM> [THz] (≈ wavelength <NUM> [µm]), the Doppler frequency fd is -<NUM> [MHz] per <NUM> [m/s] of wind speed. Therefore, when the frequency of the received light is lower than that of the local oscillator light by <NUM> [MHz], it can be seen that a wind condition at the distance of <NUM> [m] is + <NUM> [m/s], that is, <NUM> [m/s] of a tailwind.

As described above, the laser radar device according to the present disclosed technique divides the frequency difference between the local oscillator light and the received light by the frequency difference F, and determines a frequency difference corresponding to a remainder as the Doppler frequency fd. In the specific example described above, the present disclosed technique divides the frequency difference <NUM> [MHz] between the local oscillator light and the received light by the frequency difference F = <NUM> [MHz], and determines <NUM> [MHz] corresponding to a remainder as the Doppler frequency fd.

When the frequency difference between the received light and the local oscillator light is <NUM> [MHz], a remainder obtained by dividing the frequency difference by the frequency difference F = <NUM> [MHz] is not considered as <NUM> [MHz]. A reference frequency is considered as <NUM> [MHz] close to <NUM> [MHz], that is, it is considered that the frequency is <NUM> [MHz] short, and it is considered that a wind condition at the distance of <NUM> [m] is -<NUM> [m/s], that is, <NUM> [m/s] of a headwind.

<FIG> illustrates an example in which TOF = <NUM> [µs] is exactly an integral multiple of a time width T = <NUM> [µs]. When the TOF is an integral multiple of the time width T, the stepwise frequency of the local oscillator light changes at the same timing as the stepwise frequency of the received light. That is, when the received light is observed at a timing when the frequency of the local oscillator light is constant, for example, when the received light is observed in a time window of <NUM> [µs] to <NUM> [µs] in which the frequency of the local oscillator light is <NUM> [MHz], the frequency of the received light is a constant value of <NUM> [MHz] in the entire section.

In the present disclosed technique, there is no particular problem even if the TOF is not exactly an integral multiple of the time width T. The following specific example clarifies a way of thinking when the TOF is not exactly an integral multiple of the time width T.

Consider a case where the TOF is <NUM> [µs]. Similarly, when the received light is observed in a time window of <NUM> [µs] to <NUM> [µs] in which the frequency of the local oscillator light is <NUM> [MHz], the frequency of the received light is <NUM> [MHz] in a section of <NUM> [µs] to <NUM> [µs], and <NUM> [MHz] in a section of <NUM> [µs] to <NUM> [µs]. That is, the frequency difference F is <NUM> [MHz] in a section of <NUM> [µs] to <NUM> [µs], and <NUM> [MHz] in a section of <NUM> [µs] to <NUM> [µs].

Also consider a case where the TOF is <NUM> [µs]. Similarly, when the received light is observed in a time window of <NUM> [µs] to <NUM> [µs] in which the frequency of the local oscillator light is <NUM> [MHz], the frequency of the received light is <NUM> [MHz] in a section of <NUM> [µs] to <NUM> [µs], and <NUM> [MHz] in a section of <NUM> [µs] to <NUM> [µs]. That is, the frequency difference F is <NUM> [MHz] in a section of <NUM> [µs] to <NUM> [µs], and <NUM> [MHz] in a section of <NUM> [µs] to <NUM> [µs].

As described above, according to the present disclosed technique, the received light is observed in a time window in which the frequency of the local oscillator light is constant, and the TOF can be obtained from information on the two frequencies of the observed received light and information on a timing at which the frequency of the received light is switched. The information on the frequency of the received light is obtained by Fourier transform by the computer <NUM>.

The laser radar device may obtain a wind condition for each certain distance range (hereinafter, referred to as "range"). In the first embodiment, the frequency filter <NUM> and the receivers <NUM> to <NUM> correspond thereto.

The following is a specific example of the frequency filter <NUM> according to the first embodiment. For example, the frequency filter <NUM> includes three types of band pass filters. Specifically, the frequency filter <NUM> includes a band pass filter of <NUM> to <NUM> [MHz], a band pass filter of <NUM> to <NUM> [MHz], and a band pass filter of <NUM> to <NUM> [MHz]. In addition, the frequency filter <NUM> is disposed so as to send frequency components of <NUM> to <NUM> to the receiver <NUM>, frequency components of <NUM> to <NUM> to the receiver <NUM>, and frequency components of <NUM> to <NUM> to the receiver <NUM>.

When the frequency filter <NUM> and the receivers <NUM> to <NUM> are included as described above, information on a wind condition near a distance of <NUM> [m] can be measured by the receiver <NUM>, information on a wind condition near a distance of <NUM> [m] can be measured by the receiver <NUM>, and information on a wind condition near a distance of <NUM> [m] can be measured by the receiver <NUM>. The computer <NUM> can calculate a wind condition in each range by performing Fourier transform on an electrical signal measured by each of the receivers and obtaining a peak frequency.

<FIG> illustrates a configuration in which signals are separated by the frequency filter <NUM> in the receiving circuit <NUM> and then Fourier transform is performed on each of the signals, but it is not limited thereto. The laser radar device according to the present disclosed technique may convert a signal into a digital signal by performing AD conversion with one receiver without using the frequency filter <NUM>, and then may perform Fourier transform and range decomposition on the digital signal.

A signal including a frequency component of <NUM> or less corresponding to a distance of zero includes a signal generated by reception of light scattered by the optical system until the light is emitted into the atmosphere from the circulator <NUM> through the transmitting and receiving optics system <NUM> by the balanced detector <NUM>. Such scattered light generated inside the device is generally stronger than scattered light generated by aerosol in the atmosphere. In order to solve this problem, by inclusion of the pre-filter <NUM> that prevents saturation of the amplifier <NUM>, scattered light generated inside the device can be removed. As a result, SN in the receiving circuit <NUM> can be improved.

The laser radar device according to the first embodiment has the above configuration, and therefore includes a mechanism for separating frequency information resulting from a distance to a target and frequency information resulting from a speed of the target by a simple method.

In the first embodiment, the configuration in which frequency modulation is performed on laser light and then the laser light is split into transmission light and local oscillator light has been described, but the present disclosed technique is not limited to this configuration. A laser radar device according to a second embodiment splits laser light into transmission light and local oscillator light and then performs frequency modulation or phase modulation. The same reference signs are used for components common to those in the first embodiment, and redundant description is omitted.

<FIG> is a configuration diagram illustrating a configuration of the laser radar device according to the second embodiment. The laser radar device according to the second embodiment does not include the frequency modulator <NUM> or the phase modulator 20B at a former stage of the first beam splitter <NUM>. Instead, the laser radar device according to the second embodiment includes a first frequency modulator <NUM> and a second frequency modulator <NUM> in parallel at a later stage of the first beam splitter <NUM>.

Laser light emitted from a Light source <NUM> is split into transmission light and local oscillator light by the first beam splitter <NUM>. The transmission light is transmitted to the first frequency modulator <NUM>, and the local oscillator light is transmitted to the second frequency modulator <NUM>, and frequency modulation is applied to each of the transmission light and the local oscillator light. Although description has been given in the first embodiment, a phase modulator may be used instead of the frequency modulator. That is, phase modulation may be applied to the transmission light and the local oscillator light by a first phase modulator 21B and a second phase modulator 22B, respectively. Both the first frequency modulator <NUM> and the second frequency modulator <NUM> are controlled by a control signal circuit <NUM>, and perform modulation in synchronization. When the first phase modulator 21B and the second phase modulator 22B are used, similarly, the first phase modulator 21B and the second phase modulator 22B perform modulation in synchronization.

Advantages of using separate modulators for the transmission light and the local oscillator light will be clarified by the following specific example. As a specific example, the first phase modulator 21B and the second phase modulator 22B are used. Phase modulation applied by the first phase modulator 21B is represented by θ(t), and phase modulation applied by the second phase modulator 22B is represented by φ(t). If the same phase modulation is applied to the transmission light and the local oscillator light as in the first embodiment, θ(t) and φ(t) satisfy the following mathematical formula (<NUM>).

The laser radar device according to the second embodiment applies modulation in which time is shifted between the phase modulation θ(t) of the transmission light and the phase modulation φ(t) of the local oscillator light. A relationship between θ(t) and φ(t) satisfies the following mathematical formula (<NUM>).

Formula (<NUM>) means that the phase modulation θ of the transmission light is delayed by time t<NUM> as compared with the phase modulation φ of the local oscillator light.

Here, it is assumed that the phase modulation θ of the transmission light is phase modulation corresponding to frequency modulation as illustrated in <FIG>. In addition, it is assumed that the phase modulation θ of the transmission light has a time delay of t<NUM> = <NUM> [µs]. In this case, when TOF is <NUM> [µs], a response of received light is the same as that in <FIG>.

Similarly to the first embodiment, the frequency filter <NUM> includes a band pass filter of <NUM> to <NUM> [MHz], a band pass filter of <NUM> to <NUM> [MHz], and a band pass filter of <NUM> to <NUM> [MHz]. In addition, the band pass filters are arranged so as to send frequency components of <NUM> to <NUM> to a receiver <NUM>, frequency components of <NUM> to <NUM> to a receiver <NUM>, and frequency components of <NUM> to <NUM> to a receiver <NUM>. As a result, information on a wind condition near a distance of <NUM> [m] can be measured by the receiver <NUM>, information on a wind condition near a distance of <NUM> [m] can be measured by the receiver <NUM>, and information on a wind condition near a distance of <NUM> [m] can be measured by the receiver <NUM>.

It is difficult to observe a range including a distance of zero because noise is large due to scattered light generated inside the device as described above. However, according to the laser radar device according to the second embodiment, a wind condition in a range close to a distance of zero can also be measured. The laser radar device according to the second embodiment exhibits the above effect in addition to the effect described in the first embodiment. Note that the positions of the first frequency modulator <NUM> and the second frequency modulator <NUM> are not limited to the positions illustrated in <FIG>. The positions of the first frequency modulator <NUM> and the second frequency modulator <NUM> only need to satisfy the relationship represented by the mathematical formula (<NUM>). For example, the first frequency modulator <NUM> may be between the Light source <NUM> and the first beam splitter <NUM>.

A configuration of a laser radar device according to a third embodiment is similar to that of the second embodiment except for a receiving circuit <NUM>. The same reference signs are used for components common to those in the first or second embodiment, and redundant description is omitted.

<FIG> is a configuration diagram illustrating a configuration example of the receiving circuit <NUM> of the laser radar device according to the third embodiment. The laser radar device according to the third embodiment includes one receiver <NUM>, and measures only a frequency range selected by a pre-filter <NUM>. The pre-filter <NUM> removes a frequency corresponding to a distance of zero and transmits a frequency corresponding to a certain range. The pre-filter <NUM> may be constituted by one filter or may be constituted by combining two or more types of filters. In the laser radar device according to the third embodiment, an amplifier may also serve as a filter by using frequency characteristics of an amplifier <NUM>.

An operation of the laser radar device according to the third embodiment will be clarified by the following specific example. A second phase modulator 22B included in the laser radar device according to the third embodiment applies phase modulation φ(t) represented by the following formula (<NUM>).

Note that formula (<NUM>) is different from formula (<NUM>) of the second embodiment in positive and negative of the shift time. Formula (<NUM>) means that the phase modulation θ of the transmission light advances by time t<NUM> as compared with the phase modulation φ of the local oscillator light.

Here, it is also assumed that the phase modulation θ of the transmission light is phase modulation corresponding to frequency modulation as illustrated in <FIG>. In addition, it is assumed that the phase modulation θ of the transmission light has a time advance of t2 = <NUM> [µs]. In this case, when TOF is <NUM> [µs], a response of received light is the same as that in <FIG>.

The pre-filter <NUM> of the laser radar device according to the third embodiment is a band pass filter of <NUM> to <NUM> [MHz], and the receiver <NUM> is included at a later stage of the pre-filter <NUM>. In this specific example, the receiver <NUM> can measure a range of <NUM> [m]. A range to be measured can be changed by changing t2. The laser radar device according to the third embodiment intensively measures one variable range.

In <FIG>, it can be seen that when up-chirp modulation is selected as the frequency modulation, the frequency of the local oscillator light is shifted to a side higher than the frequency of delayed received light. Meanwhile, in this specific example, a response of received light corresponding to a distance of zero is on a side where the frequency of the received light is <NUM> higher by the time advance of t2 = <NUM> [µs].

In general, in light interference, a negative frequency and a positive frequency are measured as the same frequency whose phases are reversed in a processing system in which an interference fringe is measured by a balanced detector and an electrical signal is processed. Therefore, strong scattered light having a distance of zero is mixed in information on a range desired to be measured. In order to prevent this, by applying an offset to a frequency added to the local oscillator light or the received light, it is possible to prevent mixing of information on another range due to folding back of a negative frequency as described above. That is, by obtaining the following formula (<NUM>) by adding a term of an offset frequency to the left side of formula (<NUM>), it is possible to prevent a negative frequency from being folded back. <MAT> in which fo represents an offset frequency. Applying an offset to the frequency is none other than movement of a plot of the local oscillator light or a plot of the received light in the vertical axis direction in <FIG>.

With the above configuration, the laser radar device according to the third embodiment can measure a plurality of ranges by switching a delay time of a modulation frequency with one receiver. In addition, as a range has a longer distance, measurement at a higher frequency is necessary, and with such a configuration, the laser radar device according to the third embodiment can also be expected to lower the measurement frequency. In general, design of a circuit is more difficult as a frequency is higher, but the present disclosed technique can perform similar measurement by lowering the frequency, and can be expected to reduce cost.

The specific examples described in the first to third embodiments have clarified a detection principle of wind conditions at the points of <NUM> [m], which is a half of a distance for which light moves with a time width T = <NUM> [µs], and <NUM> [m], <NUM> [m],. , which are multiples of the distance. A laser radar device according to a fourth embodiment can easily obtain not only wind conditions at points of discrete distances determined by the time width T but also a wind condition at a point between the points of the discrete distances.

A problem to be solved by the laser radar device according to the fourth embodiment will be clarified by the following description with the same time width T = <NUM> [µs] as the specific examples described in the above embodiments. In the frequency modulation, up-chirp signals are adopted as illustrated in <FIG>, and the frequency difference F is <NUM> [MHz]. For example, light scattered from aerosol at a distance of <NUM> [m] is received <NUM> [µs] after emission from the device. Here, a period during which the frequency of the local oscillator light is constant is used as an observation window, and information on the frequency of the received light is observed. For example, an observation window of <NUM> [µs] to <NUM> [µs], in which the frequency of the local oscillator light is constant at <NUM> [MHz], is considered. The frequency of the received light is about <NUM> [MHz] in a first half time of the observation window, and the Doppler frequency is added. The frequency of the received light is about <NUM> [MHz] in a second half time of the observation window, and the Doppler frequency is added. That is, as for the frequency of the received light, time during which the frequency is about <NUM> [MHz] lower than the frequency of the local oscillator light and time during which the frequency is about <NUM> [MHz] lower than the frequency of the local oscillator light are mixed. As described above, when a signal whose frequency is switched halfway is subjected to Fourier transform in a wide time window of one cycle or more, a peak is generated at an intermediate frequency. Therefore, with only the configurations described in the first to third embodiments, it is difficult to distinguish between the position information and the speed information for the observation target.

An object of the laser radar device according to the fourth embodiment is to systematically obtain a wind condition at a point close to a boundary between a range and a range.

In order to solve the above problem, the laser radar device according to the fourth embodiment includes two discrete modulation lidar systems, and applies inverse frequency modulations to the respective two systems. Beams of laser light of the two systems are emitted to the atmosphere, and the beams of received light reflected by aerosol are mixed by a receiving circuit of the laser radar device.

<FIG> is a configuration diagram illustrating a configuration of the laser radar device according to the fourth embodiment. As illustrated in <FIG>, the laser radar device according to the fourth embodiment includes a first Light source <NUM>, a second Light source <NUM>, a first frequency modulator <NUM>, a second frequency modulator <NUM>, a first beam splitter <NUM>, a second beam splitter <NUM>, an amplifier <NUM>, a circulator <NUM>, a transmitting and receiving optics system <NUM>, a third beam splitter <NUM>, a fourth beam splitter <NUM>, a first balanced detector <NUM>, a second balanced detector <NUM>, a channel multiplexer <NUM>, a channel demultiplexer <NUM>, a control signal circuit <NUM>, and a receiving circuit <NUM>.

Note that, in the description of the technique according to the fourth embodiment, the same reference signs are used as much as possible for components common to those in the above embodiments, and redundant description is omitted appropriately.

The first Light source <NUM> is the same as the Light source <NUM> in the laser radar devices according to the first to third embodiments. The second Light source <NUM> is a Light source having a wavelength different from that of the first Light source <NUM>. A reason why the wavelength of the second Light source <NUM> is different from that of the first Light source <NUM> is to easily couple respective beams of laser light to each other and to easily split the respective beams of laser light from each other. The second Light source <NUM> may have a different mode by performing different polarization instead of having a different wavelength from that of the first Light source <NUM>.

The first frequency modulator <NUM> and the second frequency modulator <NUM> function in the same manner as the frequency modulator <NUM> of the laser radar devices according to the first to third embodiments. The first frequency modulator <NUM> and the second frequency modulator <NUM> may be replaced with a first phase modulator 23B and a second phase modulator 24B, respectively. Synchronism is important for modulation added by the first frequency modulator <NUM> and the second frequency modulator <NUM>. Therefore, the laser radar device according to the fourth embodiment includes the control signal circuit <NUM>, and the control signal circuit <NUM> controls the first frequency modulator <NUM> and the second frequency modulator <NUM>.

The first beam splitter <NUM> and the second beam splitter <NUM> function in the same manner as the first beam splitter <NUM> of the laser radar devices according to the first to third embodiments. Beams of laser light output from the first Light source <NUM> and the second Light source <NUM> are modulated by the first frequency modulator <NUM> and the second frequency modulator <NUM>, respectively, and are split into transmission light and local oscillator light by the first beam splitter <NUM> and the second beam splitter <NUM>, respectively. Branching ratios of the first beam splitter <NUM> and the second beam splitter <NUM> are determined by design.

The transmission light split by the first beam splitter <NUM> and the transmission light split by the second beam splitter <NUM> are multiplexed by the channel multiplexer <NUM>. When the second Light source <NUM> emits laser light having a wavelength different from that of the first Light source <NUM>, the channel multiplexer <NUM> only needs to be formed by a wavelength filter that transmits the wavelength of the first Light source <NUM> and reflects the wavelength of the second Light source <NUM>. In general, a wavelength filter formed of an optical fiber may be referred to as a WDM coupler. When polarization of the second Light source <NUM> is different from that of the first Light source <NUM>, the channel multiplexer <NUM> may be a polarization beam splitter. In addition, the polarization beam splitter may be referred to as a polarization coupler or a polarization combiner.

The transmission light multiplexed by the channel multiplexer <NUM> is amplified by the amplifier <NUM>. The amplifier <NUM> is similar to those of the laser radar devices according to the first to third embodiments. In the configuration example illustrated in <FIG>, the two channels are multiplexed in a former stage of the amplifier <NUM>, and a common optical path is used after the amplifier <NUM>, thus simplifying the structure. The laser radar device according to the present disclosed technique is not limited thereto, and the amplifiers <NUM> may be prepared for two channels so as to be included for the respective channels. Since an upper limit of output of the amplifier <NUM> is limited by a non-linear effect, it is possible to amplify light intensity per channel with higher intensity by inclusion of amplifiers for the number of channels. When the amplifier <NUM> has a multistage configuration, the channel multiplexer <NUM> may be disposed between the first-stage amplifier <NUM> and the second-stage amplifier <NUM>.

Output from the amplifier <NUM> is transmitted to the transmitting and receiving optics system <NUM> through the circulator <NUM>. This operation is the same as those of the laser radar devices according to the first to third embodiments. It should be noted that, when beams of laser light having different wavelengths are used between the first Light source <NUM> and the second Light source <NUM>, the transmitting and receiving optics system <NUM> is an optical system in which chromatic aberration is reduced.

The laser light emitted to the atmosphere is reflected by aerosol in the atmosphere, and is incident on the transmitting and receiving optics system <NUM> as received light. The incident received light is separated from the transmission light by the circulator <NUM> and is incident on the channel demultiplexer <NUM>. The channel demultiplexer <NUM> is a component that functions inversely with the channel multiplexer <NUM>. That is, the channel demultiplexer <NUM> emits, of the received light, a component corresponding to the wavelength of the first Light source <NUM> to the third beam splitter <NUM>, and emits a component corresponding to the wavelength of the second Light source <NUM> to the fourth beam splitter <NUM>. Note that there is no problem even if the wavelength of the second Light source <NUM> is mixed in the third beam splitter <NUM> or the wavelength of the first Light source <NUM> is mixed in the fourth beam splitter <NUM>. The channel demultiplexer <NUM> may be constituted by a beam splitter. Note that, when the channel demultiplexer <NUM> is constituted by a beam splitter, light intensity is lost by <NUM> [db].

The component corresponding to the wavelength of the first Light source <NUM> emitted from the channel demultiplexer <NUM> and the local oscillator light split by the first beam splitter <NUM> interfere with each other in the third beam splitter <NUM>. The two beams of interference light obtained in the third beam splitter <NUM> are emitted to the first balanced detector <NUM>. Note that the same applies to the system from the second Light source <NUM>, and thus description thereof is omitted here.

The receiving circuit <NUM> processes the signals obtained from the first balanced detector <NUM> and the second balanced detector <NUM> and calculates wind speed information for each distance. The receiving circuit <NUM> includes an electric filter, an amplifier, an analog-digital converter, and a computer. <FIG> is a configuration diagram illustrating a configuration of the receiving circuit <NUM>. As illustrated in <FIG>, the receiving circuit <NUM> includes a first pre-filter <NUM>, a second pre-filter <NUM>, a first amplifier <NUM>, a second amplifier <NUM>, a first frequency filter <NUM>, a second frequency filter <NUM>, a first mixer <NUM>, a second mixer <NUM>, a third mixer <NUM>, receivers <NUM> (<NUM>, <NUM>, and <NUM>), and a computer <NUM>.

A processing flow of the receiving circuit <NUM> of the laser radar device according to the fourth embodiment is the same as that of the first embodiment up to the first pre-filter <NUM>, the first amplifier <NUM>, and the first frequency filter <NUM>. The receiving circuit <NUM> also includes the second pre-filter <NUM>, the second amplifier <NUM>, and the second frequency filter <NUM> in parallel in order to process a signal from the second balanced detector <NUM>. The first frequency filter <NUM> distributes and emits signals emitted from the first amplifier <NUM> to the first mixer <NUM>, the second mixer <NUM>, and the third mixer <NUM> for each frequency. <FIG> illustrates the configuration including the three mixers, but it is not limited thereto, and any number of mixers may be arranged. Similarly, the second frequency filter <NUM> distributes and outputs signals output from the second amplifier <NUM> to the first mixer <NUM>, the second mixer <NUM>, and the third mixer <NUM> for each frequency.

The first mixer <NUM>, the second mixer <NUM>, and the third mixer <NUM> output a signal having a sum frequency or a difference frequency to the receivers <NUM> (<NUM>, <NUM>, and <NUM>) by multiplying the received signals by each other. In general, whether a sum frequency signal or a difference frequency signal is obtained by a mixer depends on phases of two input signals. Therefore, each of the first mixer <NUM>, the second mixer <NUM>, and the third mixer <NUM> may include a phase adjustment mechanism. A processing flow from the receivers <NUM> (<NUM>, <NUM>, and <NUM>) to the computer <NUM> is the same as that in the first embodiment.

An operation principle of the laser radar device according to the fourth embodiment will be clarified by the following specific example with reference to the drawings. <FIG> is a graph illustrating frequency modulation applied by each of the first frequency modulator <NUM> and the second frequency modulator <NUM> of the laser radar device according to the fourth embodiment. Note that as described in the above embodiments, the first frequency modulator <NUM> and the second frequency modulator <NUM> may be replaced with a first phase modulator 23B and a second phase modulator 24B, respectively.

Each frequency modulation applied by the first frequency modulator <NUM> and the second frequency modulator <NUM> is modulation in which a stepwise change in which a frequency increases or decreases by a frequency difference F for each time width T is performed for at least one step. The transmission light of the laser radar device according to the fourth embodiment has stepwise frequency characteristics as illustrated in <FIG>. The example of <FIG> illustrates stepwise frequency modulation of five steps with a time width T = <NUM> [µs] and a frequency difference F = <NUM> [MHz]. The first frequency modulator <NUM> adopts up-chirp stepwise frequency modulation, and the second frequency modulator <NUM> adopts down-chirp stepwise frequency modulation. In the present disclosed technique, the frequency difference F is sufficiently larger than a Doppler shift frequency.

The laser radar device according to the fourth embodiment is characterized in that two systems of beams of transmission light are generated, one of the systems is up-chirp, and the other of the systems is down-chirp. Each of the two systems of beams of transmission light is emitted to the atmosphere, scattered by aerosol in the atmosphere, and measured as received light. The received light interferes with the local oscillator light and is received by the balanced detector.

An effect of the laser radar device according to the fourth embodiment will be clarified by the following specific example. As a specific example, consider that there is aerosol at a point having a distance of <NUM> [m]. In this specific example, the received light is delayed by <NUM> [µs] as compared with the local oscillator light. The received light corresponding to the up-chirp stepwise local oscillator light has a frequency of -<NUM> [MHz] + Doppler frequency fd as compared with the frequency of the local oscillator light. Conversely, the received light corresponding to the down-chirp stepwise local oscillator light has a frequency of +<NUM> [MHz] + Doppler frequency fd as compared with the frequency of the local oscillator light.

The laser radar device according to the fourth embodiment includes the first frequency filter <NUM> and the second frequency filter <NUM> so as to perform processing for the two systems. The first frequency filter <NUM> and the second frequency filter <NUM> output frequency components from <NUM> [MHz] to <NUM> [MHz] to the first mixer <NUM>, frequency components from <NUM> [MHz] to <NUM> [MHz] to the second mixer <NUM>, and frequency components from <NUM> [MHz] to <NUM> [MHz] to the third mixer <NUM>. As a result, also in the laser radar device according to the fourth embodiment, information on a wind condition near a distance of <NUM> [m] is intended to be measured by the receiver <NUM>, information on a wind condition near a distance of <NUM> [m] is intended to be measured by the receiver <NUM>, and information on a wind condition near a distance of <NUM> [m] is intended to be measured by the receiver <NUM>.

The mixers <NUM> (<NUM>, <NUM>, and <NUM>) aim to obtain a sum frequency by multiplying two input signals by each other. In a specific example of aerosol at a point having a distance of <NUM> [m], a signal of "-<NUM> [MHz] + Doppler frequency fd" and a signal of "<NUM> [MHz] + Doppler frequency fd" are input to the second mixer <NUM>. The second mixer <NUM> outputs a signal of a sum frequency having a frequency twice the Doppler frequency fd to the receiver <NUM>.

Next, a specific example of aerosol at a point having a distance of <NUM> [m], to be solved by the laser radar device of the fourth embodiment, will be considered. Received light of an up-chirp system is observed as "-<NUM> [MHz] + Doppler frequency fd" in the first half of the observation window and "-<NUM> [MHz] + Doppler frequency fd" in the second half of the observation window. Received light of a down-chirp system is observed as "+<NUM> [MHz] + Doppler frequency fd" in the first half of the observation window and "+<NUM> [MHz] + Doppler frequency fd" in the second half of the observation window. Also in this specific example, the mixers <NUM> (<NUM>, <NUM>, and <NUM>) each output a signal of a sum frequency having a frequency twice the Doppler frequency fd.

<FIG> is a configuration diagram illustrating a modified configuration example of the laser radar device according to the fourth embodiment. As illustrated in <FIG>, a local oscillator light frequency modulator <NUM> may be inserted into any one of the two systems. The following specific example will clarify an effect of inserting the local oscillator light frequency modulator <NUM>. For example, it is assumed that the local oscillator light frequency modulator <NUM> reduces the frequency of first local oscillator light by <NUM> [MHz]. Light scattered from aerosol at a distance of <NUM> [m] is received <NUM> [µs] after emission from the device. A reception signal of the first system becomes "-<NUM> [MHz] + Doppler frequency fd" in the first half of the observation window and becomes "-<NUM> + fd frequency" in the second half of the observation window. Meanwhile, a reception signal of the second system becomes "+<NUM> [MHz] + Doppler frequency fd" in the first half of the observation window and becomes "+<NUM> + fd frequency" in the second half of the observation window.

In this case, the mixer <NUM> (<NUM>, <NUM>, <NUM>) each output a value obtained by adding a value obtained by multiplying the Doppler frequency fd by <NUM> to -<NUM>. In this manner, with the configuration of the modified example illustrated in <FIG>, the Doppler signal can be prevented from coming near a DC component with large noise, and improvement of SN can be expected. Here, the local oscillator light frequency modulator <NUM> may be replaced with a local oscillator light phase modulator 25B. In addition, the local oscillator light frequency modulator <NUM> may use an acousto-optic modulator (AOM) as a frequency shifter. In addition, the local oscillator light frequency modulator <NUM> may be inserted on a side of second local oscillator light, or may shift the frequency of first signal light by being inserted between the first beam splitter <NUM> and the channel multiplexer <NUM>. Alternatively, the local oscillator light frequency modulator <NUM> may shift the frequency of second signal light.

In other words, the laser radar device according to the fourth embodiment is a laser radar device including: the first balanced detector <NUM> that receives received light and first local oscillator light and converts each of the received light and the first local oscillator light into a first electrical signal; the second balanced detector <NUM> that receives received light and second local oscillator light and converts each of the received light and the second local oscillator light into a second electrical signal; and a receiving circuit that processes the first electrical signal and the second electrical signal converted by the first balanced detector <NUM> and the second balanced detector <NUM> and calculates distance information and speed information of a target, in which the frequency modulation applied by the first frequency modulator <NUM> is modulation in which a stepwise change in which a frequency increases or decreases by a frequency difference F for each time width T is performed for at least one step, the frequency modulation applied by the second frequency modulator <NUM> is modulation in which a frequency decreases or increases by the frequency difference F for each time width T, the modulation being reverse to that performed by the first frequency modulator <NUM>, and a Doppler frequency fd is obtained by mixing the frequency of the received light for the first transmission light and the frequency of the received light for the second transmission light.

With the above configuration, the laser radar device according to the fourth embodiment can accurately measure a wind condition at any position regardless of how the range is taken in addition to exhibiting the effects of the laser radar devices according to the above embodiments.

A laser radar device according to a fifth embodiment is obtained by adding a new configuration to the configuration of the laser radar device according to the fourth embodiment. The laser radar device according to the fifth embodiment uses a first Light source <NUM> in accordance with a gas absorption line. Here, the gas refers to a gas in the atmosphere, an exhaust gas from a factory, a gas leaked from a pipe, or the like. In the description of the technique according to the fifth embodiment, the same reference signs are used as much as possible for components common to those in the above embodiments, and redundant description is omitted appropriately.

<FIG> is a configuration diagram illustrating a configuration of the laser radar device according to the fifth embodiment. As illustrated in <FIG>, the laser radar device according to the fifth embodiment includes a control device <NUM> that controls the first Light source <NUM>. The control device <NUM> locks the first Light source <NUM> to a gas absorption line. The laser radar device according to the fifth embodiment can measure a concentration distribution of a gas in the atmosphere by setting a wavelength a second Light source <NUM> to a wavelength at which the gas is less absorbed. When the first Light source <NUM> is a laser diode, a wavelength thereof can be finely adjusted by a temperature or a current value. In general, since a gas absorption line is narrow, feedback control using a gas cell can be considered as control performed by the control device <NUM>. When the gas absorption line is relatively broad, the control device <NUM> can control a temperature or a current value of the first Light source <NUM> in an open loop and can lock the wavelength of the first Light source <NUM> to the gas absorption line.

<FIG> is a configuration diagram illustrating a configuration example of a receiving circuit <NUM> of the laser radar device according to the fifth embodiment. As illustrated in <FIG>, the receiving circuit <NUM> includes a first frequency filter <NUM> and a second frequency filter <NUM>. Signals distributed by the first frequency filter <NUM> and the second frequency filter <NUM> for each frequency are divided into two systems by a first signal splitter <NUM> and a second signal splitter <NUM>, respectively. Note that only the first signal splitter <NUM> and the second signal splitter <NUM> are illustrated in <FIG> for easy viewing, but signal splitters <NUM> are required for the number of distance ranges. Signals divided by the signal splitters <NUM> (<NUM> and <NUM>) are measured by a first gas concentration measurement receiver <NUM> and a second gas concentration measurement receiver <NUM>, respectively. A signal intensity measured by the first gas concentration measurement receiver <NUM> is relatively weaker than a signal intensity measured by the second gas concentration measurement receiver <NUM> due to absorption by a gas. The laser radar device according to the fifth embodiment measures a gas concentration distribution from the signal intensity ratio.

In other words, in the laser radar device according to the fifth embodiment, the first Light source <NUM> emits first laser light having a wavelength controlled to match an absorption line of a gas component to be measured, the second Light source <NUM> emits second laser light having a wavelength different from that of the first Light source <NUM>, and the laser radar device further includes: the first gas concentration measurement receiver <NUM> that receives a component corresponding to the first laser light in the received light; and the second gas concentration measurement receiver <NUM> that receives a component corresponding to the second laser light in the received light, and can measure the concentration of the gas component in the atmosphere by decomposing the concentration for each distance.

The laser radar device according to the fifth embodiment can measure a wind condition by combination with the method described in the fourth embodiment. In the measurement of the wind condition, signals divided by the first signal splitter <NUM> and the second signal splitter <NUM> are input to a first mixer <NUM>. The first mixer <NUM> can output a sum frequency to the receiver <NUM> and can calculate a Doppler frequency fd.

The laser radar device according to the fifth embodiment has the above configuration, and therefore can simultaneously measure a gas distribution in the atmosphere and a wind condition.

The laser radar device according to the present disclosed technique can be used for a device that measures a wind condition and a gas distribution in the atmosphere.

Claim 1:
A laser radar device comprising:
a Light source (<NUM>) to oscillate laser light in a continuous-wave manner or a quasi-continuous-wave manner;
a frequency modulator (<NUM>) to apply frequency modulation to the laser light oscillated by the Light source (<NUM>);
a beam splitter (<NUM>) to split the laser light modulated by the frequency modulator (<NUM>) into transmission light and local oscillator light;
a transmitting and receiving optics system (<NUM>) to transmit the transmission light and to receive light reflected from a target;
a receiver (<NUM>) to receive the received light and the local oscillator light received by the transmitting and receiving optics system (<NUM>) and to convert each of the received light and the local oscillator light into an electrical signal; and
a receiving circuit (<NUM>) to process the electrical signal converted by the receiver and to calculate distance information and speed information of the target, wherein
the frequency modulation applied by the frequency modulator (<NUM>) is modulation in which a stepwise change in which a frequency increases or decreases by a frequency difference F for each time width T is performed for at least one step,
characterized in that:
the frequency of the local oscillator is constant in a given time window,
wherein the laser radar device includes a mechanism for separating frequency information resulting from a distance to a target and frequency information resulting from a speed of the target,
wherein the receiving circuit (<NUM>) divides a frequency difference between the local oscillator light and the received light by the frequency difference F, and determines a frequency difference corresponding to a remainder or a shortage as a Doppler frequency fd,
wherein the frequency difference F in the stepwise change is sufficiently larger than the Doppler frequency due to movement of aerosol in the air.