JPS5921516B2 - laser radar - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a laser radar using light from a laser light source.

Laser radar is used to measure the depth distribution and position of atmospheric pollutants, but for this purpose, it is necessary to use infrared light, for example, that is continuously emitted from a master laser in the light emitting section of the laser radar. It is necessary to perform appropriate intermittent or chopping on the light before radiating it to the outside space.

At the same time, a heterodyne detection method must be adopted to detect with high sensitivity the weak incident light that is scattered by aerosols in the atmosphere, attenuated, and returned to the laser radar's light receiving section. However, for this purpose, it is necessary to introduce light from another light source as locally oscillated light into the infrared detector that receives the above-mentioned incident light. FIG. 1 shows the configuration of a laser radar previously filed by the present inventors in Japanese Patent Application No. 57721/1983.

The light whose optical frequency ν is ν from the master laser ML that performs continuous oscillation is branched into two optical paths A and I by the first half mirror HMI, and the continuous light branched to the optical path A is sent to the optical switch means CH. Therefore, for example, lμs per lsec interval
It is intermittent to be emitted in a rectangular waveform having a pulse width of ec, is amplified by a well-known TEA amplifier TA, and is emitted to the outside space as shown by arrow 2. On the other hand, the branched light (ν=ν,) at the optical path entrance is transferred to an acousto-optic modulator (Acoust-optic modulator).
The o-Optic Modulator (hereinafter referred to as A10 modulator) is passed through the AO, bent by an angle θ240, and output along the optical path C. At the same time, it undergoes a frequency shift by the driving frequency Δν of the A10 modulator, and the optical frequency Optical heterodyne detection is performed by utilizing the light whose ν becomes ν1+△ν as local oscillation light and introducing it into the detector D along with the incident light along the arrow E through the half mirror HM2 of the light receiving section. It is something to tighten. Here 51 is A/
0 modulator drive power source, P is a polarizer, 1 and 2 are total reflection mirrors, and the value of the frequency Δν of the drive power P from the drive power source 51 is selected to be, for example, 50 MH2. Further, the arrow indicates a radiation optical path of an unnecessary light component outputted from the A10 modulator AO without suffering a frequency shift. The electrical output of the detector D based on the heterodyne detection is subjected to a frequency shift of Δν by the A10 modulator, and ν=ν
There is a frequency difference between the locally oscillated light of 3+Δν and the incident light of ν=ν, that is, a frequency of Δν, which is amplified by the intermediate frequency amplifier FA.

The optical switch means CH of the laser radar with the above configuration includes a polarizer P and an electro-optic modulator (ElectrO-ptic).
M0du1at0r (hereinafter referred to as EO modulator)), but it is necessary to apply a high voltage EI of, for example, 50 KV to the EO modulator EO, and the optical switch means CH switches on and off the light. In order to do this, drive power supply S
The high voltage EB outputted from 2 has a square waveform.

Therefore, the waveform of the light emitted to the external space is a square wave with a width of 1 μS, but since the rise and fall of this light waveform are steep, the emitted light contains harmonics that cannot be ignored. However, as a result, the sidebands of the radiation frequency are broadened, and the monochromaticity of the laser beam is impaired. On the other hand, the half mirror HM2 is
The locally oscillated light input to the oscillator is not only the optical component ν2ν1+Δν (hereinafter referred to as the first optical component) described above, but also the light whose optical frequency remains ν without undergoing a very slight frequency shift. component (hereinafter referred to as the second light component) is also included in reality.

If the local oscillation light contains the above first and second light components of ν = ν and ν = ν1 + Δν, the light receiving section mainly composed of detector D performs heterodyne detection with high detection ability. In order to do this, even when there is no incident light along optical path E, the detector D heterodyne detects the second light component (ν=ν1) as if it were incident light,
In the output of the detector D, an intermediate frequency output component due to such an effect appears at the output terminal 3. The intermediate frequency component caused by such an effect cannot be distinguished from the intermediate frequency component based on the original incident light, and therefore, there is a disadvantage that the light receiving resolution of the laser radar is reduced.

The present invention has been made in view of these problems, and provides a new configuration of a laser radar that can suppress sideband waves contained in light to be emitted to external space and does not reduce the receiving resolution. This will be described in detail using the drawings below.

FIG. 2 shows a preferred light emitting part of the laser radar according to the present invention,
It is a diagram showing the configuration of a light receiving section, and the same parts as in FIG. 1 are given the same reference numerals.

First, the continuous emitted light having the optical frequency ν1 from the master laser ML is branched into both the optical path A and the optical path exit by the first half mirror HMl, and the light component along the optical path entrance is divided into the total reflection mirrors 4, 5, and 6. The light is introduced into the second half mirror HM2 along the optical path via the light receiving section, and is used as local oscillation light in the light receiving section. Therefore, the monochromaticity of the locally oscillated light is maintained. On the other hand, the light output from the first half mirror HM along the optical path A is input to the A/0 modulator AO provided on the optical path A.

For example, Δν is supplied to the A/O modulator AO from the drive power source S1.
Since driving power having a frequency of =50 MHz is supplied, the light component given a frequency shift of Δν by the A/O modulator AO is directed to an optical path that forms an angle of θ with the optical path. This light component is output to the TEA amplifier TA.
If the light is amplified by
becomes ν1+Δν, which has been subjected to a frequency shift in advance. The light that is scattered in the external space and returns following the optical path E, that is, the incident light, is sent to the second half mirror HM.
2 to the detector D, the frequency of which is ν1
+△ν. Here, along the optical path, the half mirror HM
As mentioned above, the local oscillation light introduced into step 2 is the light from the master laser ML and does not contain frequencies other than ν1. Therefore, even when the weak incident light with the frequency ν1+Δν is heterodyne detected, , the light receiving resolution does not deteriorate. Incidentally, the light to the external space must be emitted intermittently in a pulsed manner, and for this purpose it is necessary to intermittent the driving power to the A/O modulator AO in a pulsed manner.

M in Fig. 2 is a modulator for intermittent driving power, and in this modulator, the rise and fall characteristics are not steep, but are sufficiently blunted, and the effective pulse width is (Half width) W is 1 μSec and generation interval T is 1 sec
A voltage with a waveform as shown in FIG. 3a is generated. If the driving power P, whose frequency is 50 MHz, generated in the driving power supply S1 is amplitude-modulated with this pulse voltage, the power supplied to the A/0 modulator AO will be as shown in FIG. 3b, as shown in FIG. 3a. The result is modulated power whose waveform has an envelope. Therefore, along the optical path A, the A/0 modulator AO
The continuous light from the master laser ML input to the A/0
At the same time as the frequency shift is fixed by the modulator AO, the third
It is interrupted by the waveform shown in Figure a. Since the rise and fall of the waveform shown in Figure 3a is not steep, the harmonic components contained in the intermittent light emitted to the external space are significantly reduced, and the sideband waves of the emitted light are therefore significantly suppressed. be done. In the laser radar configured according to the present invention as described above, there is no need to use a combination of a polarizer and an expensive EO modulator as an optical switching means, and therefore a high voltage EO modulator driving power source is not required. Great practical effects can be expected.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing the configuration of the laser radar that was previously filed, FIG. 2 is a system diagram of the laser radar according to the present invention, and FIG.
Figure a shows the waveform for amplitude modulating the drive power, Figure 3 b
is the waveform of driving power for the A/0 modulator which is the optical switch means of the laser radar.

Claims (1)

[Claims] 1. In a laser radar equipped with a light emitting part and a light receiving part, a predetermined frequency shift is given in advance to the light emitted from the laser included in the light emitting part by an acousto-optic modulator as an optical switch means, and the light is transmitted to the outside. Heterodyne detection is performed by mixing the frequency-shifted incident light that is emitted into space, scattered in the external space, and incident on the light receiving section with local oscillation light that is branched from the laser of the light projecting section and supplied. A laser radar characterized in that the laser radar is configured to perform the following functions.