JPS6151740B2 - - 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 apply appropriate intermittent or chopping to the beam before radiating it to the outside space.

At the same time, a heterodyne detection method must be adopted in order to detect with a high degree of attenuation the weak incident light that is scattered by aerosols in the atmosphere, attenuated, and returned to the laser radar receiver. 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.

Figure 1 was originally filed by the inventors in Japanese Patent Application No. 54-57721.
This is the configuration of the laser radar applied for in JP-A-55-14903. The light whose optical frequency ν is ν ₁ from the master laser ML that performs continuous oscillation is split into two optical paths A and B by the first half mirror HM ₁ , and the continuous light branched to the optical path A is sent to the optical switch means CH. For example, the light is emitted intermittently in a square waveform with a pulse width of 1 μsec per 1 sec interval, and then
It is amplified by the well-known TEA amplifier TA and radiated to the outside space as shown by arrow D. On the other hand, the light (ν=ν ₁ ) branched into the optical path B is passed through an acousto-optic modulator (hereinafter referred to as an A/O modulator) AO, and the optical path is bent by an angle θ〓4°. The corresponding A/O
The light that has undergone a frequency shift by the modulator drive frequency △ν and whose optical frequency ν becomes ν ₁ +△ν is used as local oscillation light, and is used as a half mirror in the light receiving section.
Optical heterodyne detection is performed by introducing the light into the detector D together with the light incident along the arrow H through _HM2 . Here S ₁ is A/O
A driving power source for the modulator, P is a polarizer, 1 and 2 are total reflection mirrors, and the value of the frequency Δν of the driving power P ₁ from the driving power source S ₁ is selected to be, for example, 50 MHz. Further, the arrow indicates a radiation optical path of an unnecessary light component outputted from the A/O modulator AO without suffering a frequency shift.

The electrical output of the detector D based on the above-mentioned heterodyne detection is subjected to a frequency shift of △ν by the above-mentioned A/O modulator, and the local oscillation light becomes ν=ν ₁ +△ν and ν=ν The frequency difference with the incident light that is ₁ , that is, △
It has a frequency ν, which is an intermediate frequency amplifier.
Amplified by IFA. The optical switching means CH of the laser radar with the above configuration consists of a polarizer P and an electro-optic modulator (hereinafter referred to as EO).
It consists of a combination with an EO (called a modulator).

By the way, the optical path C through the half mirror HM ₂
The local oscillation light input to is the above ν=ν ₁ +△ν
In addition to the light component (hereinafter referred to as the first light component) that does not suffer from a very slight (for example, 1/1000) frequency shift and whose optical frequency remains ν ₁ (hereinafter referred to as stray light or second light component) (called the light component) is also included in reality. During local oscillation light, ν=ν
₁ and ν=ν ₁ +△ν, the light receiving section mainly consisting of the detector D has a high detection ability in order to perform heterodyne detection. Even when there is no incident light along E, the detector D detects the second light component (ν=
ν ₁ ) is heterodyne detected as if it were incident light, and an intermediate frequency output component due to this effect appears at the output terminal 3 in the output of the detector D.

The intermediate frequency component resulting from 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 in which the light receiving resolution does not deteriorate.The present invention will be described in detail with reference to the drawings from FIG. 2 onwards.

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

First, the light from the master laser ML, which is branched along the optical path B and has a power of P ₂ and an optical frequency of ν ₁ , is input as local light to the detector D via the total reflection mirror 4 and the half mirror HM ₂ . be done. On the other hand, the light with a frequency of _ν1 emitted in the direction of the optical path A is interrupted by the optical switch means CH, and then passed through the TEA amplifier.
For example, it is amplified by 100,000 times with TA. Up to this point, there is no difference from conventional laser radar, but among the above-mentioned light that has been amplified by the above amplifier TA and radiated into the external space, the power along the optical path H increases to a value of P ₈ due to scattering. The attenuated and returned light with a frequency ν ₁ is transmitted to the A/O installed on the optical path H.
The optical path is bent by θ〓4° by the modulator AO and directed toward the optical path C. In that case, the A/O modulator suffers a frequency deviation by the driving frequency △ν from the driving high-frequency power source S ₁ , and the optical frequency ν is ν ₁ +
It becomes △ν. This light enters the photoreceiver D via the total reflection mirror 5 and the half mirror _HM2 , but is mixed with the local light whose optical frequency is _ν1 , which was previously introduced into the photoreceiver D. Performs heterodyne detection.

However, due to the A/O modulator, the light (optical frequency ν
= ν ₁ ) is absorbed by the light absorber DM.

By the way, among the first optical components with optical frequency ν=ν ₁ +△ν directed in the above-mentioned optical path C direction, there is also a first optical component whose optical frequency remains ν ₁ without undergoing a frequency shift as described above. A very small amount of light component 2, that is, stray light, is mixed in. The optical power of this light component is P ₅
If expressed as, the optical power of the optical component, that is, the stray light, is
P ₅ is about 1/1000 of the optical power P ₈ introduced into the detector D following the optical path H, and the light of the local light introduced into the detector D following the optical path B. This is even more negligible compared to the power _P2 . By the way, the actual value of the optical power introduced into the detector D following the optical path B is, for example, about 1 mW, and the power of the optical component following the optical path E is about 10 ^-6 mW. The optical power of the stray light mixed into the light following the optical path E is about 10 ^-9 mW.

In this way, the optical power of stray light P ₅ is the incident optical power P ₈
Even if the stray light is detected by detector D, the intermediate frequency amplifier
It has no effect on the output of the IFA and therefore does not impair the original functionality of the laser radar.

In the laser radar configured according to the present invention as described above, the A/O as the optical frequency shifting means is
A modulator A/O is arranged before the detector D which performs heterodyne detection, so that the input to the detector, which is subjected to a frequency shift by the A/O modulator, is included in the second Since the light component, that is, the stray light component, is extremely small compared to the first light component, the light receiving resolution of the laser radar does not deteriorate;
Therefore, an extremely large practical effect can be expected.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing the configuration of the laser radar previously filed, and FIG. 2 is a system diagram of the laser radar according to the present invention. A, B, H, D, H, H: Optical path, AO: A/O
Modulator, D: Detector, IFA: Intermediate frequency amplifier,
ML: master laser, TA: TEA amplifier, 3: output terminal, 4, 5: total reflection mirror.

Claims (1)

[Claims] 1 In a laser radar equipped with a light emitting part and a light receiving part, light is emitted from a laser included in the light emitting part to an external space, is scattered in the space, and enters the light receiving part. A predetermined frequency shift is applied by an acousto-optic modulator as a frequency shift means, and the light subjected to the frequency shift is mixed with local oscillation light branched from the laser of the light projecting section and supplied. A laser radar characterized by performing heterodyne detection.