SU1599652A1 - Laser light range finder - Google Patents

Abstract

The invention relates to geodetic instrumentation and improves the accuracy of measurements. To do this, in a laser range finder, containing a series-arranged and optically coupled laser light source 1, modulator 2, demodulator-converter 3, photoelectric receivers 4 and 5, intermediate-frequency selector amplifiers 6 and 7, phase meter 8, modulating frequency generator and the local oscillator, the modulating frequency generator is designed as a series of reference oscillator 9 and connected to its first output of frequency multiplier 10, the first output of the frequency multiplier is connected to the input of power amplifier 13, and erodin the form of sequentially arranged the amplitude modulator 12 and the power amplifier, the first input of an amplitude modulator is connected to the second output of the reference oscillator and the second input of the amplitude modulator - to the second output of the frequency multiplier. 1 il.

Description

sd

with

 a: cd

tsD

The reference oscillator 9 and the frequency multiplier 10 connected to its first output, the first output of the frequency multiplier is connected to the input of power amplifier 13, and the local oscillator is made of sequentially located amplitude modulator 12 and power amplifier, and the first input of amplitude modulator connected to the second output of the reference oscillator, and the second input of the amplitude modulator to the second output of the frequency multiplier. 1 il.

The invention relates to optical instrument making and can be applied in optical communication systems, locations, in geodetic instrument making for the construction of high-precision light-range-ranging meters for geodetic and special purposes.

The aim of the invention is to increase the sensitivity and accuracy of a phase light range finder by eliminating asynchronous frequency drifts of signals generated in the reference and remote channels.

The drawing shows a diagram of the device.

The range finder consists of post-locally positioned and optically coupled laser light source 1, modulator 2, demodulator converter 3, photodetectors 4 and 5, receiving signals from the output of demodulator converter 3, amplifiers-selectors of intermediate frequency b and 7, connected to the outputs of photoelectronic receivers 4 and 5, respectively, and the phase-equalizing device (phase meter) 8. The electrical input of the modulator 2 is connected to the output of the modulating frequency generator (including a highly stable reference (I specify 9) frequency generator Q; multiplier 10 frequency Q.) and the first power amplifier 11 frequency (Ohm. The electrical input of the deductor converter 3 is connected to the output of the local oscillator frequency Schm- | -C made in the form of consecutive amplitude module torus 12 and second power amplifier 13, the first input of the amplitude modulator connected to the second output of the reference oscillator 9, and the second input of the amplitude modulator connected to the second output of the frequency multiplier 10. Blocks 9-13 are the source of the modulating voltage or (cash figure is not indicated).

Modulator 2 and converter modulator 3 can be implemented as crystalline cells operating on the linear electro-optical Pockels effect or acousto-optical effect. Amplitude modulator provides a single-band amplitude-modulated signal.

The device works as follows.

Light signal from a laser source

1 is directed to a light modulator 2, on

the electrical input of which receives the frequency signal Ы from the power amplifier 11. After modulating with the frequency som, a portion of the light flux through the optical delay line 14 is short-circuited to the input of the modulator-converter 3, thereby forming the reference channel of the range finder. Another part of the modulated radiation of the modulator 3 is directed to the measured distance and, being reflected from the mirror reflector 15, is received at the demodulator-converter 3, thereby forming a remote (measuring) channel of the remote end transmitter.

The conversion mode of the reference and remote optical signals is carried out by applying from the power amplifier 13 to the demodulator-converter 3 a high-frequency electrical signal, the amplitude of which varies according to the law. (S) sincoMt. The output of the demodulator of the converter-3 is formed by two optical signals (reference and remote).

intermediate frequency. The light sirens of Qip frequency (reference and remote, containing information about the measured distance) are received by the photoreceivers 4 and 5, respectively, amplified in the amplifier x-selectors 6 and 7, and fed to the inputs of the phase-equalizer 8. Consider the features of the device. For the light beam passing the reference channel, the phase shifts, respectively, in modulator 2 and demodulator-converter 3 are determined by the formula

f, (() f01 + I- -COSOit,

ff

1/9,

at)

ф2 (1 |) ф02 (som -f and) ti,

0

where | (1) is the phase shift introduced by modulator 2;

ф2 (1 |) -phase shift introduced by demodulator-converter 3; five

/ C;

At - time of passage of the light flux on the reference channel with a length

optical path D: from the output of the light modulator 2 to the input of the photodetector 5. The intensity of the luminous flux at the output of the demodulator of the converter for the reference channel is represented as

  sin -i jIiiiMlii lo2

(2)

Substituting the terms (I) into (2) after decomposing into a Fourier series and a series of transformations for a variable part of the light intensity at the output of the converter (at the input of the photodetector 5), we obtain

, () a, () cos ((co. + Q) -a,) t +,

+

(3)

We assume that the recorded signal lies in the linear portion of the amplitude characteristic of the photodetector 5. Then the output current of the photodetector (ia) will repeat in shape the input light flux, and the expression for ia will differ from (3) by a constant coefficient B, having dimension A / lk;

i (t) c, n BU (i) BIJ, () a, (-) x

2a) MO,

X cos (((o "+ Q) - (ov)

(four)

Thus, at the output of the photodetector 5, there is a signal whose amplitude is proportional to the phase difference of the oscillation harmonics with the modulation frequencies o and the local oscillation + y and changes over time with the frequency O. The considered signal after amplification in the amplifier-selector 7 enters the input phase measuring device 8.

Similarly, for a remote signal passed through modulator 2, measured distance D2, demodulator converter 3, photodetector 4 and amplifier-selector 6, the signal at the output of photodetector 4 is represented as

1a) ds. VS, () 1, () С05 (BL +

+ Q) -CO.) T +

(five)

where D2 is the distance traveled by the light

remote channel. Thus, in each channel of the light range finder (namely, at the outputs of the selector amplifiers 6 and 7) there is one signal defined for the reference channel by the expression (4) and the signal of the remote channel defined by the expression (5) accordingly. A comparison on the phase meter 8 phase of these intermediate frequency signals determines information on the measured distance D D2-D |.

It is known that the instrumental accuracy of the phase-rangefinder based on frequency conversion is mainly determined by the noise immunity of the system, the stability of the intermediate frequency signals being compared, and the signal-to-noise ratio at the input of the phase measuring device.

In the proposed device, the execution of the modulating frequency generator in the form of successively located reference generator and power amplifier, and the local oscillator in the form of successively located amplitude modulator and power amplifier, ensures synchronism of frequency drifts in the circuit of the crystal demodulator-converter and, as a consequence, small the relative detuning level of the intermediate frequency signals, allowing a reduction in the passbands of the selector amplifiers and the noise level in the receiving chains. In addition, it is possible to optimize the process.

0 converting and obtaining the maximum amplitudes of the oscillations of the intermediate frequency with high stability, providing an increase in the accuracy of the phase indication during phase comparison.

35

Claims (1)

Invention Formula  A laser range finder containing a radiation source, a modulator, an optical delay line, a demodulator converter, two outputs of which are connected to photo receivers connected to the phase meter inputs and a source of modulating voltage, the first and second output terminals of which are connected to control inputs, respectively, of the modulator and demodulator of the converter transformer, characterized in that, in order to increase the accuracy, the source of the modulating voltage is made in the form of a series-connected highly stable reference A generator, a frequency multiplier and a first power amplifier connected to the first output terminal, and a series-connected amplitude modulator and a second power amplifier connected to the second output terminal, the first and second inputs of the amplitude modulator connected to the corresponding outputs of the highly stable reference generator and frequency multiplier.