JPH06123774A - Distance measuring device - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain high distance measurement resolution independent of the response speed of the optical modulator. By adjusting the voltage of the DC bias power source 5 and the signal amplitude of the modulation drive frequency from the signal generator 4, the optical modulator 2 adjusts the harmonic component n times the modulation drive frequency f. A modulated signal light having a frequency of × f is output. In addition, by adjusting the voltage of the DC bias power supply 12, the input frequency (f−Δf /
n) is a high frequency component n times as high as (n × f−Δf)
The effective optical demodulation signal of is generated in the optical modulator 9. Then, the optical modulator 9 outputs the optical signal of the frequency Δf having the phase information of the measured distance on the basis of the heterodyne detection principle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device suitable for construction, civil engineering, large-scale steel industry, earthquake prediction and the like.

[0002]

2. Description of the Related Art Conventionally, in a distance measuring device using an optical modulator, an optical signal having the same frequency as the modulation driving frequency of the modulating optical modulator is used as the distance measuring optical signal.

The demodulation drive frequency of the demodulation optical modulator is the same as the frequency of the effective optical demodulation signal.

Further, as a reference signal for detecting the phase having the distance measurement information, the signal of the modulation drive frequency of the modulator and the signal of the demodulation drive frequency of the demodulator are frequency-mixed, and the intermediate frequency obtained by this is mixed. (1F) signal was used.

[0005]

In the prior art of the above technique, the optical signal having the same frequency as the predetermined modulation drive frequency of the modulator is used as the optical signal for distance measurement.
Distance measurement resolution is limited by the modulation band of the optical modulator,
Only the distance measurement resolution with a modulation driving frequency below the response speed of the modulator could be obtained.

Further, in the above-mentioned prior art, the modulation drive frequency of the modulation optical modulator and the frequency of the distance measuring optical signal are the same, and the demodulation drive frequency of the demodulation optical modulator and the effective optical demodulation are the same. Since the frequency of the signal is the same, when performing heterodyne detection, the leaked electric field generated from the modulation and demodulation transmission lines distorts the detected signal, often causing an error in distance measurement. .

Furthermore, it is not possible to perform high resolution range measurements with low error using the reference signals generated by the above described prior art.

The present invention has been made in view of such a situation, and a first object thereof is to obtain a high distance measurement resolution independent of the response speed of the optical modulator.

A second object of the present invention is to eliminate noise due to a leakage electric field.

A third object of the present invention is to generate a reference signal for phase detection suitable for distance measurement with high resolution and high accuracy.

[0011]

A distance measuring device according to a first aspect of the present invention is (1) a light source for emitting continuous wave light (for example,
The semiconductor laser 1) of FIG. 1, (2) a modulation optical modulator for modulating the light emitted from the light source (for example, the Mach-Zehnder optical waveguide intensity modulator 2 of FIG. 1), and (3) the modulation light. First harmonic generation means (for example, the coupling circuit 3 and the DC bias power supply 5 in FIG. 1) that causes the optical modulator for modulation to output an optical signal for distance measurement of a harmonic component with respect to the modulation drive frequency of the modulator; 4) An optical modulator for demodulation (for example, a Mach-Zehnder type optical waveguide intensity modulator 9 in FIG. 1) that receives an optical signal for distance measurement reflected from an object to be measured, and (5) demodulation drive of the optical modulator for demodulation. An optical signal having a frequency that is the difference between the frequency of the effective optical demodulation signal and the frequency of the distance measurement optical signal is generated from the demodulation optical modulator by generating an effective optical demodulation signal of a harmonic component with respect to the frequency. Second harmonic generator that outputs (For example, the coupling circuit 10 and the DC bias power supply 12 in FIG. 1), the distance to the object to be measured is measured using a signal having a difference frequency output from the demodulating optical modulator. And

The distance measuring device according to claim 2 is (a)
A first electric signal generating means (for example, the signal generator 4 in FIG. 1) for generating a first electric signal having a modulation driving frequency of the modulation optical modulator; and (b) a demodulation driving frequency of the demodulation optical modulator. Two
The second electric signal generating means (for example, the signal generator 11 in FIG. 1) for generating an electric signal and (c) the first electric signal and the second electric signal are received, and the frequency is the difference between the frequencies of the two signals. Frequency mixing means for generating a third electric signal (for example, the frequency mixer 16 in FIG. 1), and (d) Frequency multiplying means for multiplying the frequency of the third electric signal and outputting the fourth electric signal (for example, FIG. 1). Frequency multiplier 17) and (e)
Photoelectric conversion means (for example, the light receiving element 13 and the amplifier 14 in FIG. 1) that converts an optical signal output from the demodulation optical modulator into an electric signal and outputs the electric signal as a fifth electric signal;
A phase meter (for example, the phase meter 15 in FIG. 1) that receives the fourth electric signal as a reference signal, the fifth electric signal as a distance measurement signal, and obtains the phase difference between the two signals is provided.

The distance measuring device according to claim 3 is (A)
A first electric signal generating means (for example, the signal generator 4 in FIG. 2) for generating a first electric signal having a modulation driving frequency of the modulation optical modulator; and (B) a first demodulation driving frequency of the demodulation optical modulator. Two
Second electric signal generating means for generating an electric signal (for example, the signal generator 11 of FIG. 2) and (C) the optical signal output from the optical modulator for demodulation is converted into an electric signal to obtain a fifth electric signal. Output photoelectric conversion means (for example, the light receiving element 13 in FIG. 2)
And an amplifier 14), (D) first frequency multiplying means for multiplying the frequency of the first electric signal and outputting a sixth electric signal (for example, the frequency multiplier 20 of FIG. 2), and (E) second electric signal. The second which multiplies the frequency of the signal and outputs the seventh electric signal
Frequency multiplication means (for example, frequency multiplier 22 in FIG. 2)
And (F) a frequency mixing means for receiving the sixth electric signal and the seventh electric signal and generating an eighth electric signal whose frequency is the difference between the frequencies of the two signals (for example, the frequency mixer 21 of FIG. 2)). And (G) a phase meter that receives the eighth electric signal as a reference signal and the fifth electric signal as a distance measurement signal and obtains the phase difference between the two signals (for example, the phase meter 1 in FIG. 2).
5) and are provided.

[0014]

According to another aspect of the distance measuring device of the present invention, the first harmonic generating means outputs the distance measuring optical signal of the harmonic component with respect to the modulation driving frequency of the modulating optical modulator from the modulating optical modulator. Then, the second harmonic generation means causes the demodulation optical modulator to generate an effective optical demodulation signal of a harmonic component with respect to the demodulation drive frequency of the demodulation optical modulator, and the demodulation optical modulator outputs the effective optical demodulation signal. An optical signal having a difference frequency between the signal frequency and the distance measuring optical signal is output. Therefore, since the frequency of the optical signal for distance measurement is the frequency of the harmonic component with respect to the modulation drive frequency of the optical modulator for modulation,
When the harmonic component is the nth order (n is an integer of 2 or more), the distance measurement resolution can be increased by n times. Further, the modulation drive frequency of the modulation optical modulator and the frequency of the distance measurement optical signal are different, and the demodulation drive frequency of the demodulation optical modulator and the frequency of the effective optical demodulation signal by the demodulation optical modulator are different. Therefore, the distance measurement error does not occur due to the leakage electric field generated from the modulation and demodulation transmission lines.

According to another aspect of the distance measuring device of the present invention, the frequency mixing means has a first electric signal of a modulation driving frequency of the modulation optical modulator and a second electric signal of a demodulation driving frequency of the demodulation optical modulator. In response to this, a third electric signal whose frequency is the difference between the two signals is generated, and the frequency multiplication means multiplies the frequency of the third electric signal and supplies it to the phase meter as a reference signal. Therefore, it is possible to obtain a reference signal suitable for the distance measurement optical signal equal to the frequency of the harmonic component of the modulation drive frequency of the modulation optical modulator, and to generate a reference signal suitable for high resolution and high accuracy distance measurement. can do.

According to another aspect of the distance measuring device of the present invention, the first frequency multiplication means multiplies the frequency of the first electric signal of the modulation driving frequency of the optical modulator for modulation to output the sixth electric signal, The second frequency multiplication means multiplies the frequency of the second electric signal of the demodulation drive frequency of the demodulation optical modulator to output the seventh electric signal, and the frequency mixing means, the sixth electric signal and the seventh electric signal. In response, the reference signal whose frequency is the difference between the frequencies of the two signals is output. Therefore, it is possible to obtain a reference signal suitable for the distance measurement optical signal equal to the frequency of the harmonic component of the modulation drive frequency of the modulation optical modulator, and to generate a reference signal suitable for high resolution and high accuracy distance measurement. can do.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of an embodiment of the distance measuring device of the present invention. The continuous wave light beam emitted from the semiconductor laser 1 which is the light source is input to the Mach-Zehnder type optical waveguide intensity modulator 2 and is modulated by the electric signal output from the coupling circuit 3 here. This electric signal is created by combining the electric signal of the frequency f output from the signal generator 4 into the power divider 4D and combining one of the two divided signals with the bias voltage of the DC bias power source 5. It By adjusting this DC bias voltage, the frequency of n × f, which is a harmonic component n times (n is an integer of 2 or more) the input frequency, that is, the modulation drive frequency f, is adjusted from the optical waveguide intensity modulator 2. The modulated signal light can be output.

The signal light having an n × f modulation frequency component output from the Mach-Zehnder type waveguide intensity modulator 2 is
After passing through the beam splitter 6, it is reflected by the reflector 7 and returns to the beam splitter 6 again. A part of the return light is reflected by the beam splitter 6, then further reflected by the reflection mirror 8, enters the Mach-Zehnder type optical waveguide intensity modulator 9, and is modulated by the electric signal output from the coupling circuit 10. . As for this electric signal, the electric signal of the frequency (f−Δf / n) output from the signal generator 11 is input to the power divider 11D, and one of the two divided signals and the bias voltage of the DC bias power supply 12 are input. It is created by combining with. By adjusting this DC bias voltage, an effective optical demodulation signal of (n × f−Δf), which is a high frequency component n times as high as the input frequency (f−Δf / n), is generated in the optical waveguide intensity modulator 9. Is generated in. Then, the optical waveguide intensity modulator 9 outputs the optical signal of the frequency Δf having the phase information of the measured distance on the basis of the heterodyne detection principle. The light receiving element 13 photoelectrically converts the optical signal of the frequency Δf output from the optical waveguide intensity modulator 9. The electric signal output from the light receiving element 13 is the amplifier 1
After being amplified at 4, it is supplied to one input terminal Sig of the phase meter 15 as a distance measurement signal of frequency Δf.

Of the electric signals output from the signal generator 4, the other electric signal branched by the power divider 4D is supplied to one input terminal of the reference frequency mixer 16. Further, of the electric signals output from the signal generator 11, the other electric signal branched by the power divider 11D is supplied to the other input terminal of the reference frequency mixer 16. The reference frequency mixer 16 frequency-mixes the two input signals and outputs a signal of frequency Δf / n. This signal is output by the frequency multiplier 17
A signal having a frequency Δf that is n times as large is supplied as a reference signal to the other input terminal Ref of the phase meter 15. Phase meter 15
Calculates the distance to the measurement object by calculating the phase difference between the supplied distance measurement signal and the reference signal.

In the embodiment of FIG. 1, the electric signal frequency, that is, the modulation drive frequency of the optical waveguide intensity modulator 2 is f,
Since the frequency of the optical signal for distance measurement is n × f, the distance to the object to be measured can be accurately obtained with the resolution corresponding to the modulation frequency n × f.

Further, since the frequencies of the electric signal and the optical signal for distance measurement are different, the influence of crosstalk, which is one of the error factors during distance measurement, can be eliminated.

FIG. 2 shows the configuration of another embodiment of the distance measuring device of the present invention. In the embodiment of FIG. 2, semiconductor laser 1, Mach-Zehnder type optical waveguide intensity modulators 2 and 9, coupling circuits 3 and 10, signal generators 4 and 11, power dividers 4D and 11D, DC bias power supplies 5 and 1
2, the light receiving element 13, the amplifier 14, and the phase meter 15 are
This is the same as the embodiment of FIG. The difference is that frequency multipliers 20 and 22 and a frequency mixer 21 are provided instead of the frequency mixer 16 and the frequency multiplier 17 of FIG.

That is, of the electric signals output from the signal generator 4, the other signal branched by the power divider 4D is input to the frequency multiplier 20, where the frequency is multiplied by n and the frequency is multiplied by n × f. It is supplied to one input terminal of the frequency mixer 21 for use. The other signal of the electric signals output from the signal generator 11 that is branched by the power divider 11D is input to the frequency multiplier 22, where the frequency is n times (n × f−Δf), It is supplied to the other input terminal of the reference frequency mixer 21. The reference frequency mixer 21 frequency-mixes the two input signals and outputs a signal of frequency Δf. This signal is used as a reference signal for the other input terminal Ref of the phase meter 15.
Is supplied to. The phase meter 15 obtains the distance to the measurement object by obtaining the phase difference between the supplied distance measurement signal and the reference signal.

In the embodiment of FIG. 2 as well, similar to the embodiment of FIG. 1, the electrical signal frequency, that is, the optical waveguide intensity modulator 2 is used.
Although the modulation driving frequency of is f, but the frequency of the optical signal for distance measurement is n × f, the distance to the measurement object can be accurately obtained with a resolution corresponding to the modulation frequency n × f.

Further, since the frequencies of the electric signal and the optical signal for distance measurement are different, the influence of crosstalk, which is one of the error factors at the time of distance measurement, can be eliminated.

Furthermore, since the IF signal after frequency mixing becomes the reference signal, the phase noise of the reference signal with respect to the distance measurement signal can be suppressed to an extremely low level, and an accurate distance can be obtained.

In the above embodiment, (1) by adjusting the bias point of the Mach-Zehnder type optical waveguide intensity modulator by the DC voltage, the optical signal of the harmonic component of the input modulation drive frequency to the modulator is obtained. Is occurring,
(2) By applying an appropriate bias point to the optical path length difference between the two optical paths of the modulator, or (3) applying a large-amplitude input electric field, the harmonic components of the input modulation drive frequency to the modulator can be An optical signal may be generated. Alternatively, (1),
Two or more of (2) and (3) may be combined.

Further, although the optical waveguide intensity modulator is used in the above embodiment, a bulk type optical modulator or an acousto-optic modulator (AOM) may be used.

[0029]

According to the distance measuring device of the first aspect, the first
Second harmonic generation means outputs the distance measuring optical signal of the harmonic component with respect to the modulation driving frequency of the modulation optical modulator from the modulation optical modulator, and the second harmonic generation means is the demodulation optical modulator. The effective optical demodulation signal of the harmonic component with respect to the demodulation drive frequency of is generated in the demodulation optical modulator, and the frequency of the difference between the frequency of the effective optical demodulation signal and the frequency of the distance measurement optical signal is output from the demodulation optical modulator. Since the optical signal is output, the frequency of the optical signal for distance measurement becomes the frequency of the harmonic component with respect to the modulation drive frequency of the optical modulator for modulation. The resolution can be increased by n times. In addition, the modulation drive frequency of the modulation optical modulator and the frequency of the distance measurement optical signal are different, and the demodulation drive frequency of the demodulation optical modulator and the frequency of the effective optical demodulation signal are different. The distance measurement error does not occur due to the influence of the leakage electric field generated from the transmission line, that is, the crosstalk.

According to the distance measuring device of the second aspect, the frequency mixing means receives the electric signal of the modulation drive frequency of the optical modulator for modulation and the electric signal of demodulation drive frequency of the optical modulator for demodulation, An electric signal whose frequency is the difference between the two signals is generated, and the frequency multiplication means multiplies the frequency of the electric signal output from the frequency mixing means and supplies it to the phase meter as a reference signal. It is possible to obtain a reference signal that is suitable for the distance measurement optical signal that is equal to the frequency of the harmonic component of the modulation drive frequency of the optical modulator for use, and with a simple configuration, a reference signal suitable for high resolution and high precision distance measurement can be obtained. Can be generated. Further, there is an effect that the signal frequency band required for the electric system components of the entire distance measuring device can be set to be equal to or less than the modulator drive signal frequency band.

According to the distance measuring device of the third aspect, the first frequency multiplying means outputs the electric signal obtained by multiplying the frequency of the electric signal of the modulation drive frequency of the optical modulator for modulation, and the second frequency multiplying means. , An electric signal obtained by multiplying the frequency of the electric signal of the demodulation drive frequency of the demodulation optical modulator is output, and the frequency mixing means receives the electric signals output from the first and second frequency multiplying means, and the frequencies are both Since the reference signal, which is the difference in the frequency of the signals, is output, it is possible to obtain the reference signal suitable for the distance measuring optical signal equal to the frequency of the harmonic component of the modulation driving frequency of the modulating optical modulator,
A reference signal suitable for distance measurement with high resolution and high accuracy can be generated. Further, since the IF signal is not frequency-multiplied, that is, there is no nonlinear element from the IF signal to the reference signal, the phase noise of the reference signal with respect to the distance measurement signal can be suppressed extremely low.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a distance measuring device of the present invention.

FIG. 2 is a block diagram showing the configuration of another embodiment of the distance measuring device of the present invention.

[Explanation of symbols]

 1 Semiconductor Laser 2,9 Mach-Zehnder Type Optical Waveguide Strength Modulator 3,10 Coupling Circuit 4,11 Signal Generator 4D, 11D Power Divider 5,12 DC Bias Power Supply 13 Photoreceptor 14 Amplifier 15 Phase Meter 16,21 Frequency Mixer 17 , 20, 22 Frequency multiplier

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Koichi Matsumoto 1-4-1 Umezono, Tsukuba-shi, Ibaraki Industrial Technology Institute of Metrology Institute (72) Katsuo Seta 1-4-1 Umezono, Tsukuba-shi, Ibaraki Industrial Technology Inside the Institute of Metrology (72) Inventor Ichiro Fujima 1-4 Umezono, Tsukuba, Ibaraki Industrial Technology Institute within the Institute (72) Hisa Yoshida 3 2-3 Marunouchi, Chiyoda-ku, Tokyo Stock company Inside Nikon (72) Inventor Michiaki Saito 3 2-3 Marunouchi, Chiyoda-ku, Tokyo Inside Nikon Corporation

Claims (3)

[Claims] 1. A light source that emits continuous wave light, a modulation optical modulator that modulates the light emitted from the light source, and a distance measurement light of a harmonic component with respect to a modulation drive frequency of the modulation optical modulator. First harmonic generating means for outputting a signal from the modulating optical modulator, a demodulating optical modulator for receiving the distance measuring optical signal reflected from the object to be measured, and demodulating of the demodulating optical modulator Generate an effective optical demodulation signal of a harmonic component with respect to the driving frequency in the demodulation optical modulator,
A second harmonic generation unit for outputting an optical signal having a frequency of a difference between the frequency of the effective optical demodulation signal and the frequency of the distance measurement optical signal from the demodulation optical modulator; A distance measuring device, characterized in that the distance to the object to be measured is measured using a signal having the frequency of the difference output from an optical modulator. 2. A first electric signal generating means for generating a first electric signal of a modulation driving frequency of the modulation optical modulator, and a second electric signal for generating a second electric signal of a demodulation driving frequency of the demodulation optical modulator. 2 electric signal generating means, frequency mixing means for receiving the first electric signal and the second electric signal and generating a third electric signal whose frequency is a difference between the frequencies of the two signals, and Frequency multiplying means for multiplying the frequency and outputting as a fourth electric signal; photoelectric converting means for converting an optical signal output from the demodulating optical modulator into an electric signal and outputting as a fifth electric signal; The distance measuring device according to claim 1, further comprising a phase meter that receives an electric signal as a reference signal, receives the fifth electric signal as a distance measuring signal, and obtains a phase difference between the two signals. 3. A first electric signal generating means for generating a first electric signal of a modulation driving frequency of the modulation optical modulator, and a second electric signal for generating a second electric signal of a demodulation driving frequency of the demodulation optical modulator. 2 electric signal generating means, photoelectric conversion means for converting the optical signal output from the demodulating optical modulator into an electric signal and outputting the electric signal as a fifth electric signal, and multiplying the frequency of the first electric signal by First frequency multiplying means for outputting a sixth electrical signal; second frequency multiplying means for multiplying the frequency of the second electrical signal and outputting a seventh electrical signal; and the sixth electrical signal and the seventh electrical signal And a frequency mixing means for generating an eighth electric signal having a frequency difference between the two signals, the eighth electric signal as a reference signal, the fifth electric signal as a distance measuring signal, and both signals The phase difference of The distance measuring device according to claim 1, further comprising a phase meter.