JP2689633B2 - Laser radar device - Google Patents

Description

The present invention relates to a laser radar device for measuring the distance and speed of a target.

[Conventional technology]

Fig. 7 shows, for example, the literature (Optical Engineering, Vol.27, N
o.1, pp. 011 to 015, 1988) is a functional block diagram of a conventional laser radar device. However, the block for the distance measurement function is based on a well-known example.

In the figure, (30) is a carbon dioxide laser light source that continuously oscillates, (31) is a distributor that divides the irradiation light from this laser light source into two, and (32) is one of the irradiation light from this distributor, and the carrier angle is An acousto-optic device that converts the frequency ω ₀ with an offset angular frequency ω _AC , (33) an optical switch that converts the irradiation light from this acousto-optic device into an optical pulse according to the pulse signal from the time counter (34), (8) is a polarizer that separates and transmits the horizontal linearly polarized light of the irradiation light from this optical switch and the vertical linearly polarized light of the reflected light from the quarter-wave plate (9), and (9) is the polarizer from this polarizer. The 1/4 wavelength plate that converts the horizontally linearly polarized irradiation light into circularly polarized light and the circularly polarized reflected light from the telephoto optical system (10) into vertically linearly polarized light, respectively (10)
A telescopic optical system that irradiates the target with the irradiation light from the / 4 wavelength plate and receives the reflected light from the target. (11) makes the other side (reference light) of the irradiation light from the distributor (31) enter the polarizer ( 8) Polarization controller that matches the polarization direction of the reflected light from the target that passed (8)
2) is a multiplexer that combines the reference light that has passed through this polarization controller and the reflected light from the target that has passed through the polarizer (8), and (13) is the light that is emitted from this multiplexer. A light receiving element that performs electrical conversion and frequency mixing, (14) an amplifier that amplifies the detection signal from this light receiving element, and (34) inputs the pulse signal from this amplifier again after sending the pulse signal to the optical switch (33). The time counter for observing the time t until calculating the distance signal, and (35) is the spectrum analyzer for observing the Doppler frequency shift ω _DP included in the pulse signal from the amplifier (14) and calculating the velocity signal. is there.

The above-mentioned conventional laser radar device includes a laser light source (30)
The laser light with a constant angular frequency ω ₀ is continuously oscillated by and is split into two by the distributor (31) into irradiation light and reference light. The irradiation light is converted into an angular frequency ω ₀ + ω _AC by the acousto-optic element (32), converted into an optical pulse by the optical switch (33), and incident on the polarizer (8). The horizontally linearly polarized irradiation light from the polarizer (8) is polarized into circularly polarized light by the 1/4 wavelength plate (9), and the telescopic optical system (10) irradiates the target. Then receiving the reflected light from the target Doppler frequency shift omega angular frequency received the _{DP ω 0 + ω AC + ω} DP by the relative speed of the target in the telephoto optical system (10), with 1/4-wave plate (9) Converts the circularly polarized reflected light into vertical linearly polarized light and uses it as a polarizer (8).
At 1, the linearly polarized light of the irradiation light is separated from the vertically linearly polarized light of the reflected light which is separated and transmitted, and is incident on one side of the multiplexer (12). On the other hand, the reference light is made incident on the other side of the multiplexer (12) by being aligned with the polarization direction of the reflected light passing through the polarizer (8) by the polarization controller (11). Further, the reflected light from the target of the irradiation light and the reference light are combined by a multiplexer (12), and light-electric conversion is performed by a light receiving element (13) to mix the frequencies. A pulse signal obtained by amplifying the detection output of the light receiving element (13) by the amplifier (14) is input to the time counter (34), and the pulse signal is sent to the optical switch (33) by the time counter (34) and then input again. And the distance R to the target is calculated from the following equation.

Here, c is the speed of light, or the pulsed signal obtained by amplifying the detection output of the light receiving element (13) by the amplifier (14) is input to the spectrum analyzer (35), and the electrical signal I is observed by the spectrum analyzer (35). The target relative velocity v _{γ is determined} by discriminating the Doppler frequency shift ω _DP.
Is calculated from the following formula.

v _γ = ω _DP · c / ω ₀ where c is the speed of light The above electric signal I is expressed by the following equation.

Here, η is the sensitivity I ₁ of the light receiving element (13) and φ ₁ is the light receiving element (13) of the reflected light from the target of the irradiation light.
Intensity and phase I ₂ and φ ₂ are intensity and phase at the light receiving element (13) of the reference light [Problems to be solved by the invention] In the conventional laser radar device as described above, in order to improve the distance resolution. When the pulse signal is narrowed, the average power for speed signal detection is lowered and the signal-to-noise ratio (S / N) is deteriorated. On the other hand, if the sweep time during speed measurement is shortened and the average power of the speed signal is increased, the distance resolution is sacrificed. Therefore, there are conflicting problems in simultaneously measuring the target distance and speed.

It is an object of the present invention to obtain a laser radar device that provides a target distance and velocity measuring method with high range resolution and good velocity detection S / N.

[Means for solving the problem]

The laser radar device of the present invention uses an M-sequence generator for generating an M-sequence binary signal having a period length of 2 ⁿ -1 (n: arbitrary integer) bits, and an M-sequence binary signal from the M-sequence generator. Accordingly, the first angular frequency ω ₁₀ and the second angular frequency ω ₁₁ (ω ₁₀ <ω ₁₁ )
An irradiation light source that frequency-modulates and oscillates, a bit delay unit that delays the M-sequence binary signal from the M-sequence generator on a bit-by-bit basis, and a third according to the bit-delayed M-sequence binary signal.
Reference light source that performs frequency modulation oscillation at angular frequency ω ₂₀ and fourth angular frequency ω ₂₁ (ω ₂₀ <ω ₂₁ ), angular frequency deviation ω ₁₁ −ω _{10 of} irradiation light from the irradiation light source, and reference from reference light The angular frequency deviations ω ₂₁ −ω ₂₀ of the light are matched, and the angular frequency intervals | ω ₁₀ −ω ₂₀ | and | ω ₁₁ −ω ₂₁ |
Frequency management means for controlling the frequencies ω ₂₀ and ω ₂₁ of the reference light source so as to match _IF , transmission / reception optical system means for irradiating the target with the irradiation light from the irradiation light source, and entering the reflected light from the target, and the transmission / reception optics A system that combines the reflected light from the target and the reference light from the reference light source that is incident on the system means and converts it into an electrical signal.
The light receiving means, a high-pass filter that passes only the electric signal in the vicinity of the angular frequency of the difference between the angular frequencies ω ₁₁ and ω ₁₀ of the irradiation light among the electrical signals from the multiplexing / light receiving means, and the high-pass filter. A delay amount control means for adjusting the delay amount of the bit delay means so as to minimize the electric signal output that has passed through the filter at a high speed, and calculating and outputting a target distance signal based on this delay amount, and a multiplexing / light receiving means. A bandpass filter for extracting a signal component in the vicinity of the intermediate angular frequency ω _IF of the electrical signal from
A frequency discriminating means for discriminating the Doppler frequency shift ω _DP from the signal component extracted by the band pass filter, and calculating and outputting a target traveling speed signal based on the result is provided.

[Action]

In the present invention, the M-sequence generator has a cycle length of 2 ⁿ -1.
An (n: arbitrary integer) bit M-sequence binary signal is generated, and the irradiation light source is responsive to the M-sequence binary signal from the M-sequence generator to generate a first angular frequency ω ₁₀ and a second angular frequency ω ₁₁ ( ω ₁₀ <ω ₁₁ )
Frequency modulation oscillation is performed with. Also, the bit delay means delays the M-sequence binary signal from the M-sequence generator in bit units,
The reference light source performs frequency modulation oscillation at the third angular frequency ω ₂₀ and the fourth angular frequency ω ₂₁ (ω ₂₀ <ω ₂₁ ) according to the bit-delayed M-sequence binary signal. Next, the frequency management means matches the angular frequency deviation ω ₁₁ −ω _{10 of the} irradiation light from the irradiation light source with the angular frequency deviation ω ₂₁ −ω ₂₀ of the reference light from the reference light, and the angular frequency interval between the two. The frequencies ω ₂₀ and ω ₂₁ of the reference light source are controlled so that | ω ₁₀ −ω ₂₀ | and | ω ₁₁ −ω ₂₁ | match the predetermined intermediate angular frequency ω _IF .

When the transmission / reception optical system unit irradiates the target with the irradiation light from the irradiation light source, and when the reflected light from the target is incident, the combining / light receiving unit causes the transmission / reception optical system unit to reflect the reflected light from the target and the reference from the reference light source. The light is combined and converted into an electrical signal, and the high-pass filter raises only the electrical signal in the vicinity of the angular frequency difference ω ₁₁ and ω ₁₀ of the irradiation light among the electrical signals from the combining / light receiving means. When the signal is passed through the band, the delay amount control means adjusts the delay amount of the bit delay means so as to minimize the electric signal output of the high pass filter of the high pass filter, and based on this delay amount, the target distance signal is adjusted. Calculate and output. The bandpass filter extracts the signal component in the vicinity of the intermediate angular frequency ω _IF of the electrical signal from the combining / light receiving means, and the frequency discriminating means extracts the Doppler frequency shift ω _DP from the signal component extracted by this bandpass filter. The target moving speed signal is calculated and output based on the result.

[Embodiment] FIG. 1 is a functional block diagram of a laser radar device showing an embodiment of the present invention.

In the figure, (1) is composed of, for example, an N-stage shift register and a logical circuit that feeds back a logical combination of a plurality of stages to the shift register input, and has a cycle length of 2 ⁿ -1 (n: any integer) bit M series. (One of symbol sequences) M sequence generator for generating a binary signal, (2) is a first angular frequency ω ₁₀ and a second angular frequency ω ₁₁ according to the M sequence binary signal from the M sequence generator. (Ω
A semiconductor laser irradiation light source that oscillates a frequency-modulated pulse at ₁₀ <ω ₁₁ ), (3) is an M-sequence 2 from the M-sequence generator (1)
A delay device for delaying the value signal in bit units, (4) is the third angular frequency ω ₂₀ and the fourth angular frequency ω ₂₁ (ω ₂₀ <ω ₂₁ ) according to the M-sequence binary signal bit-delayed by this delay device. , A semiconductor laser reference light source that oscillates a frequency-modulated pulse, (5) is a first distributor that divides the light emitted from the irradiation light source (2) into two,
(6) is a second that splits the light emitted from the reference light source (4) into two
The distributor (7) receives one of the irradiation light and the reference light from the first and second distributors (5) and (6), respectively, and receives the angular frequency shifts ω ₁₁ −ω _{10 of the} irradiation light and the reference light, respectively. A frequency controller that matches ω ₂₁ −ω ₂₀ and holds the angular frequency intervals | ω ₁₀ −ω ₂₀ | and | ω ₁₁ −ω ₂₁ | of the two at an intermediate angular frequency ω _IF with a constant difference,
(8) is a polarizer that separates and transmits the other horizontal linearly polarized light of the irradiation light from the first distributor (5) and the vertical linearly polarized light of the reflected light from the quarter-wave plate (9), Is a quarter-wave plate that converts the horizontally linearly polarized light from this polarizer into circularly polarized light, and the circularly polarized reflected light from the telescopic optical system (10) into vertically linearly polarized light. A telescopic optical system that irradiates a target with irradiation light from a four-wave plate and receives reflected light from the target. (11) enters the other reference light from the second distributor (6) and a polarizer (8) A polarization controller (12) that matches the polarization direction of the reflected light from the target that has passed through, and the reference light that has passed through this polarization controller and the reflected light from the target that has passed through the polarizer (8) are incident and combined. A first multiplexer, (13), which outputs the light emitted from the first multiplexer,
A first light-receiving element that electrically converts and mixes frequencies, (14) an amplifier that amplifies an electric signal from the first light-receiving element, (15)
Is an intermediate angular frequency ω _IF (ω _IF + ω) corresponding to the angular frequency interval between the irradiation light and the reference light in the signal from this amplifier.
_A first band-pass filter for band-passing only the _DP signal,
(16) is a high-pass filter that passes only the signals in the vicinity of the angular frequency deviation Δω of the irradiation light and the reference light among the signals from the amplifier (14), and (17) is the high-pass filter from this high-pass filter. Delay controller that changes the number of delay bits of the delay device (3) so as to minimize the output value of the delay signal and calculates the distance signal from the number of delay bits (18) is the first bandpass filter (15).
Is a first frequency discriminator that discriminates the Doppler frequency shift ω _DP of the signal from and calculates the velocity signal.

FIG. 2 is a functional block diagram of the frequency manager (7) of FIG. 1 showing the above embodiment.

In the figure, (20a) and (20b) are third and fourth distributors that divide the irradiation light from the first and second distributors (5) and (6) and the reference light into two, and (21a) and (21b) are One of the first and second ones, which receives one of the light beams emitted from the third and fourth distributors and sweeps the resonance angular frequency of each of them by changing the distance between the two opposing semitransparent mirrors with an electrostrictive element or the like. Fabry-Perot type resonator,
(22) is a driver for generating a triangular wave signal of a constant period for linearly changing the interval between the resonance angular frequencies of the first and second Fabry-Perot resonators with time, (23a) and (23a)
b) is the first and second farbly Perot type resonators (21a) (21a)
The second and third light receiving elements for photoelectrically converting each of the emitted lights from b), and (24) is a signal obtained by electrically converting the irradiation light and the reference light from the second and third light receiving elements, respectively. Transfer ω ₁₁ −
A displacement current controller that feeds back the displacement current set value to the reference light source (4) so that the times corresponding to ω ₁₀ and ω ₂₁ −ω ₂₀ coincide with each other, and (25) is the third and fourth distributors (20a) ( A second multiplexer for entering and combining the other of the emitted lights from 20b), (26) is a fourth light receiving element for optoelectrically converting the emitted light from the second multiplexer, (27) is The second band-pass filter (28) that band-passes only the signal in the vicinity of the angular frequency ω _IF (ω _IF ′) among the signals obtained by electrically converting the combined light of the irradiation light from the fourth light receiving element and the reference light is By discriminating the angular frequency ω _IF ′ of the signal from the second band-pass filter, the desired intermediate angle corresponding to the angular frequency intervals | ω ₁₀ −ω ₂₀ | and | ω ₁₁ −ω ₂₁ | It is a second frequency discriminator that feeds back the bias current setting value to the reference light source (4) so as to match the frequency ω _IF .

The laser radar device according to the above embodiment is the M-sequence generator (1).
, An M-sequence binary signal is repeatedly generated every 2 ⁿ −1 bits, the injection current is modulated by the irradiation light source (2) according to the M-sequence binary signal, and frequency modulation is performed at angular frequencies ω ₁₀ and ω _11. The emitted light is oscillated. Similarly, the reference light source (4) modulates the M-sequence binary signal by the delay device (3) according to the signal delayed by the bit unit with respect to the irradiation light source (2), and the angular frequencies ω ₂₀ and ω
₂₁ oscillates the reference light subjected to frequency modulation. First and second
The distributor (5) (6) splits the irradiation light and the reference light into two,
One of them is incident on the frequency controller (7). The third and fourth distributors (20a) and (20b) of the frequency controller (7) further divide the irradiation light and the reference light into two parts, and one of the first and second farbly-Perot type resonators ( 21a) (21b)
At, the resonance angular frequencies of the irradiation light and the reference light are swept at a cycle t ₀ by the driver (22) (see FIG. 3 (a)). Second and third
Light emitted from each resonator (21a) (21b) is photo-electrically converted by the light receiving elements (23a) (23b), and the angular frequency deviation ω _{11 of} each of the irradiation light and the reference light is converted by the displacement current controller (24). −ω ₁₀ and ω ₂₁ −ω
Make the time Δt and Δt 'corresponding to ₂₀ match (3rd
(See FIGS. 2B and 2C.) The displacement current setting value is fed back to the reference light source (4) to set ω ₁₁ −ω ₁₀ = ω ₂₁ −ω ₂₀ = Δω. On the other hand, the irradiation light divided into two parts by the third and fourth distributors (20a) (20b) and the other of the reference lights are combined by the second combiner (25) which is incident, and then combined by the fourth light receiving element (26). Of the signals that have undergone opto-electric conversion and frequency mixing, only the signals near the angular frequency ω _IF (ω _IF ′) are band-passed by the second band pass filter (27) and ω _IF ′ by the second frequency discriminator (28). angular frequency omega to the reference light source (4) so as to match the desired intermediate angular frequency omega _{IF 20} or omega ₂₁
The bias current setting value corresponding to is fed back, and | ω ₁₀ −ω ₂₀
Let | = | ω ₁₁ −ω ₂₁ | = ω _IF .

Also, the other of the irradiation light split in two by the first distributor (5) is made incident on the polarizer (8), and the horizontally linearly polarized irradiation light from the polarizer (8) is circularized by the 1/4 wave plate (9). It is converted into polarized light and the target is illuminated by the telescopic optical system (10). Next, the first and second angular frequencies ω ₁₀ + that have received the Doppler frequency shift ω _DP due to the target relative velocity
The reflected light from the target of ω _DP and ω ₁₁ + ω _DP is set to the telephoto optical system (1
(0) receives the light, and the quarter-wave plate (9) converts the circularly polarized reflected light from the telephoto optical system (10) into vertical linearly polarized light, and a polarizer (8)
The vertical linearly polarized light, which is separated from the horizontal linearly polarized light of the illuminating light and transmitted, is incident on one side of the first multiplexer (12).

On the other hand, the other side of the reference light split into two by the second splitter (6) is made to coincide with the polarization direction of the reflected light from the target that has passed through the polarizer (8) by the polarization controller (11), and the first multiplexer is provided. It is incident on the other side of (12). Further, the reflected light from the target of the irradiation light and the reference light are combined by the first combiner (12), photoelectrically converted by the first light receiving element (13), the frequencies are mixed, and synchronous detection is performed. If the time T ₁ for synchronously detecting the reflected light from the target of the irradiation light and the time T ₂ for bit-delaying the reference light do not match (when T ₁ ≠ T ₂ ), irradiation by the first light receiving element (13) is performed. The changes over time of the angular frequencies of the reflected light from the target and the reference light and the angular frequency components of the detection output signal are as shown in FIGS. 4 (a), (b) and (c), and the first light receiving element (13 ) Includes a signal spectrum (a spectrum near ω _IF and two spectra near Δω) having three angular frequency components as central angular frequencies.

At this time, the first light receiving element (13) amplified by the amplifier (14)
Of the detection output signal from, for example, the signal component near ω _IF (ω _IF + ω _DP ) of about 100 MHz is band-passed by the first band pass filter (15), and the signal component near Δω of, for example, about several GHz. (Δω ± (ω _IF + ω _DP )) passes through the high pass filter (16). If ω _IF = 100 MHz and Δω = several GHz, the Doppler frequency shift ω _DP of the reflected light from the moving target with a relative velocity of 100 Km / h is about 10 MHz.

On the other hand, when the delay amount controller (17) controls the number of delay bits of the delay device (3) to make T ₁ and T ₂ coincident (T ₁ = T
₂ o'clock), the changes over time in the angular frequencies of the reflected light from the target and the reference light of the irradiation light from the first light receiving element (13) and the angular frequency components of the detection output signal are as shown in FIGS. 5 (a) and (b). As shown in (c), the detection output of the first light receiving element (13) includes only a signal spectrum (a spectrum in the vicinity of ω _IF ) having one angular frequency component as the center frequency.

At this time, the first light receiving element (13) amplified by the amplifier (14)
Since the signal component near Δω has disappeared in the detection output signal from the high-pass filter (16), it becomes zero as shown in Fig. 6, and the delay amount controller (17) outputs a specific delay bit. The number K is detected and the distance R to the target is calculated from the following equation.

R = K · ΔR ΔR = C / 2B where ΔR is the distance resolution C is the speed of light B is the bit rate of the M-sequence binary signal (bps) For example, to set the distance resolution ΔR to 1 m, the bit rate is set.
A 150-Mbps M-sequence binary signal may be used.

At this time, the output of the first bandpass filter (15) at the same time when the distance is calculated concentrates on the signal component of ω _IF + ω _DP and becomes large. Therefore, the Doppler frequency deviation detected by the first frequency discriminator (18) is increased. The signal component of the shift ω _DP also becomes large, and the influence of the spread spectrum of the frequency modulation by the M-sequence binary signal is also eliminated, and the Doppler frequency shift ω _DP is discriminated with a good S / N, and the target relative velocity v _γ is calculated as follows. Calculate from the formula.

v _γ = ω _DP · C / ω where ω = ω ₁₀ = ω ₁₁ [Effect of the invention] The present invention is configured as described above, and each M series 2 that directly modulates the irradiation light source and the reference light source is used. Match the delay time between the value signals with the time to synchronously detect the reflected light from the target of the irradiation light, maximize the correlation between the reflected light from the target of the irradiation light and the reference light, and eliminate the high-frequency component of the synchronous detection output. By utilizing the characteristic of the target detection, the Doppler frequency shift component of the synchronous detection output can be detected at a high signal level, and at the same time, the distance to the target can be detected by the number of bit delays of the M-sequence binary signal. The S / N and distance information can be simultaneously measured with high resolution.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of a laser radar device showing an embodiment of the present invention, FIG. 2 is a functional block diagram of a frequency controller shown in FIG. 1, and FIG. 3 is a Fabry-Perot type resonator shown in FIG. Fig. 4 shows the resonance angular frequency of the light receiving element and changes over time in the output. Figs. 4 and 5 show the detection output of the light receiving element shown in Fig. ₁ when T ₁ ≠ T ₂ and T ₁ = T ₂ FIG. 6 is a diagram showing the angular frequency component and its change with time, FIG. 6 is a diagram showing the relationship between the output of the high-pass filter shown in FIG. 1 and the number of delay bits, and FIG. 7 is a function of the laser radar device of the conventional example. It is a block diagram. In the figure, (1) is an M-series generator, (2) is an irradiation light source,
(3) is a delay device, (4) is a reference light source, (5) is a first distributor, (6) is a second distributor, (7) is a frequency controller,
(8) is a polarizer, (9) is a quarter-wave plate, (10) is a telescopic optical system, (11) is a polarization controller, (12) is a multiplexer, (13) is a light receiving element, ( 14) is an amplifier, (15) is a band-pass filter, (16) is a high-pass filter, (17) is a delay controller, and (18) is a frequency discriminator.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-57-168179 (JP, A) JP-A-62-249089 (JP, A) JP-A-57-86071 (JP, A)

Claims (1)

(57) [Claims] 1. A laser radar device for measuring the distance and speed of a target by synchronously detecting the reflected light of the irradiation light from the target with a reference light, and an M having a cycle length of 2 ⁿ -1 (n: any integer) bits. An M-sequence generator for generating a sequence binary signal, and a first angular frequency ω ₁₀ and a second angular frequency ω ₁₀ according to the M-sequence binary signal from the M-sequence generator.
Irradiation light source that oscillates with frequency modulation at an angular frequency ω ₁₁ (ω ₁₀ <ω ₁₁ ), bit delay means for delaying the M-sequence binary signal from the M-sequence generator in bit units, and the bit-delayed M-sequence binary A reference light source that frequency-oscillates at a third angular frequency ω ₂₀ and a fourth angular frequency ω ₂₁ (ω ₂₀ <ω ₂₁ ) according to the signal, and an angular frequency shift ω ₁₁ −ω of the irradiation light from the irradiation light source.
₁₀ and the angular frequency deviation of the reference light from the reference light ω ₂₁ −ω ₂₀
And the angular frequency intervals | ω ₁₀ −ω ₂₀ | and | ω ₁₁ −ω ₂₁ | of both are matched with a predetermined intermediate angular frequency ω _IF , and the frequencies ω ₂₀ and ω ₂₁ of the reference light source are controlled. Frequency management means, irradiating the target with irradiation light from the irradiation light source,
Transmitting / receiving optical system means for inputting reflected light from a target, multiplexing / light receiving means for multiplexing reflected light from the target incident on the transmitting / receiving optical system means and reference light from the reference light source to convert into an electric signal, A high-pass filter that passes only an electric signal in the vicinity of the angular frequency of the difference between the angular frequencies ω ₁₁ and ω ₁₀ of the irradiation light among the electric signals from the combining / light-receiving means, and the high-pass of this high-pass filter. The delay amount of the bit delay means is adjusted so as to minimize the output of the passed electric signal, and the delay amount control means for calculating and outputting the target distance signal based on the delay amount, A bandpass filter for extracting a signal component in the vicinity of the intermediate angular frequency ω _{IF of the} electric signal, discriminating the Doppler frequency shift ω _DP from the signal component extracted by this bandpass filter, and the target moving speed based on the result. Calculate the signal The laser radar apparatus provided with a frequency discriminating means for outputting.