JPS6190074A - Laser range finder - Google Patents

Abstract

PURPOSE:To improve an SN ratio and to reduce the number of sample points of microwave frequency by taking out only an AM frequency component from electric signals after light detection. CONSTITUTION:Low frequency AM modulation is applied to a microwave circuit 4 by a frequency synthesizer 11. A DC component which is not a signal is cut from a photoelectric converted current by an AC amplifier 12, and only the AM frequency component is amplified. Consequently, laser light modulation components due to stress at the time of incorporating a crystal in a light modulator 5 and other components other than signals are removed and amplified. Therefore, its S/N ratio is improved. After that, the current is converted to an effective value by an RMS meter, inputted to a signal processing controller 10, and signal processing is performed. When a distance is measured by setting microwave frequencies as parameters, the position where a signal becomes zero is found clearly, the number of parameters can be reduced, and its measurement can be made with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an IjIII distance device using laser light.

An outline of the conventional laser distance measuring device for this building will be explained with reference to FIG. FIG. 1 is a block diagram showing the configuration of a conventional distance measuring device. A straight beam 1hli outputted from a laser device 1 is sent to a Wollaston prism 3 using a reflecting mirror 2. incident at a certain angle.

The optical modulator 5 has a birefringent crystal inside, and the microwave circuits 4 and 1 are controlled by a signal processing controller 10 to be bounded at a certain standard microwave frequency ω0. . The beam emitted from the Wollaston prism 3 passes through this optical modulator 5, and is thus converted into the first (f) of the birefringent crystal.
ast) component and o-(slow) component, and the phase difference between the vertical and horizontal components is r (r=π・-V, ,-,
Vπ; Vπ: half-wavelength voltage of the crystal; Vm: microwave hairball) are generated and modulated at a frequency (υ0). This modulated beam passes through the optical system 6 and is used for distance measurement l-tai. It is reflected by the reflection optical system 7 placed at the target point, passes through the optical system 6 again, enters the optical modulator 5', is modulated again, and enters the Wollaston prism 3.Then, this time, the modulated light is In order to measure only the component that is transmitted, the component that is perpendicular to the polarization at the time of transmission is guided to the photodetection type 8 using the reflection mirror 2 and subjected to light weight conversion.The intensity of the signal beam incident here is I =I
Jo(2F..s pull”=””(1+c.S 9
) f-pゎ@n;boC1"Cψ, optical modulator 5
The beam exiting the optical system 7 is reflected by the reflective optical system 7, and has distance information based on the phase difference that occurs until it returns to the optical modulator 5.

The current emitted from the photoelectric transformer J is amplified by a current amplifier 9,
The signal is manually processed by the signal processing controller IO.

Next, the signal processing controller 10 controls and changes the microwave frequency of the microwave circuit 40 and the resonance frequency of the optical modulator 5 to 5 frequencies ω1. ω2. ... Measure each using ωn as a parameter, and calculate the distance from the relationship between frequency and signal strength.

However, in this method, since the signal manually input to the photodetector is a DC component, light that is not a signal, such as luminous intensity iJM il
! The bias component due to the stress applied when the crystal is incorporated into the roof is the same as the signal reflected by the optical system or the crystal surface (in + light ljX, or back + light, etc., is also photoelectrically converted and amplified.

The signal being processed and the (-) sufficient signal-to-noise ratio (S/N)
was obtained l-), and f'L was not obtained. Also, estimate the point where the signal becomes zero! The number of frequency samples was large. This situation is shown in FIG. 3(a).

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks, and to provide a laser distance measuring device that is capable of extracting only signal components, improving the LS/N and reducing the number of microwave frequency samples. be.

The present invention applies low frequency AM to the microwave applied to the optical modulator.
It modulates the DC component that becomes signal light, performs optical detection, extracts only the AM frequency component from the photoelectrically converted electrical signal, amplifies it, and performs signal processing.

Next, embodiments of the present invention will be described with reference to 21st gold.

The configurations indicated by reference numerals 1 to 7 are the same as those of the conventional device, but the microwave circuit 4 is subjected to low frequency AM modulation by a frequency synthesizer 11. The photodetector 8 in FIG. 2 is also the same photodetector as the conventional device. The photoelectrically converted current has DC components that are not signals cut off by an AC amplifier 12.
Only AM frequency components are amplified. This reduces laser light modulation components based on stress when the crystal is incorporated into the optical modulator.

Since components other than other signals are removed and amplified, the S/N ratio is improved. its (&, 18 meters 1 to R
3, the signal is converted into an effective value, and then manually inputted to the signal processing controller 10 similar to the conventional device to perform the conventional signal processing. When measuring distance using the microwave frequency as a parameter, the point where the signal becomes zero can be clearly seen, so the number of parameters can be reduced and measurements can be made with high accuracy. This situation is shown in FIG. 3(b).

As explained above, the present invention applies low-frequency AM modulation using microwaves applied to an optical modulator, modulates the DC component that becomes signal light, and extracts only the AM frequency component from the electrical signal after photodetection. Because it amplifies and processes the signal, components other than the signal can be removed, improving the S/N ratio1-, and the zero point can be clearly seen in measurements using the microwave frequency as a parameter.
This has the effect of reducing the number of parameters.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of a conventional laser distance measuring device, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 (
Figures a) and (b) are diagrams showing signal waveforms measured using a laser rangefinder with the microwave frequency applied to the optical modulator as a parameter, and (a) is the signal waveform of a conventional device. FIG. 3B is a waveform diagram of the Hagakura signal of the device fA of the present invention. 1...Laser% if, 2...Reflecting mirror, 3...Wollaston prism. 4... Microwave circuit, 5... Optical modulator, 6
...optical system, 7...reflective optical system, 8
...Photodetector, 9...DC amplifier, 1
0...A word processing η1 controller, 11...Frequency synthesizer, 12...AC i armor IA device, 13...IζM
S meter.

Claims (1)

[Claims] A laser beam modulated to a microwave frequency is transmitted using an optical modulator, and the light that is reflected from the distance measurement target point is passed through the same optical modulator that was used when transmitting the beam, and the polarization is perpendicular to the transmitted laser polarization. In a laser ranging device that measures distance by measuring the intensity of a component using a microwave frequency as a parameter, low-frequency AM modulation is applied to the microwave applied to the optical modulator, and only the signal component at the AM modulation frequency is extracted from the received light component. A laser distance measuring device characterized by comprising means for extracting an electrical signal.