JPH07119568B2 - Absolute length measuring machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention makes it possible to perform highly accurate length measurement in units of wavelength by utilizing interference of laser light, and to provide an afsolute length measurement output. It is about the length measuring instrument that can be obtained.

<Prior Art> FIG. 3 is a block diagram showing an example of a conventional absolute length measuring instrument of this type, which utilizes Michelson's interference optical system.

In FIG. 3, reference numeral 1 is a laser light source for selectively generating a plurality of coherent lights (λ1 to λ4) having different wavelengths, and 2
Is a half mirror, 3 is an acousto-optic modulator that modulates the light on the reference side to detect the amount of phase delay of the light (hereinafter, simply referred to as AO modulator), 4 is an AO modulator with a constant frequency
The modulation signal sources 5 and 6 driven by fb are cube corners. The cube corner 5 is a cube corner on the length measuring side that moves according to the length measuring operation, and the cube corner 6 is a cube corner on the reference side fixed at a fixed distance. It is a cube corner. Reference numeral 7 is a photodetector, and 8 is a phase difference meter for detecting the amount of phase delay included in the output of the photodetector 7.

The laser light source 1 is composed of, for example, a light source 11 having a constant wavelength and a wavelength shifter 12 that shifts the wavelength by an arbitrary amount.
Light having an arbitrary wavelength is sequentially generated. The arithmetic circuit 9 determines the distance to the cube corner 5 from the relationship between the wavelength of light used for measurement and the amount of phase delay at that time.

In the length measuring device configured in this way, the angular frequency of light is ω, and the modulation angular frequency of the AO modulator 3 is ωb (= 2πf
b) and the amplitude V0 of the light emitted from the laser light source 1 is V0 = sin ω t ... The amplitude V1 of the light modulated by the AO modulator 3 is V1 = sin (ω + ωb) t. The amplitude V2 of the light returned via V2 becomes V2 = sin (ωt + φ). Note that φ is a phase delay amount that occurs corresponding to the difference in optical path length between the reference side optical path and the length measuring side optical path.

On the photodetector 7, since the two lights as shown in the above formula are superimposed, the amplitude of the incident light is V1 + V2 = sin (ω + ωb) t + sin (ωt + φ) = 2sin (ωt + ωbt / 2 + φ) .cs {( ωbt−φ) / 2} is the sum of V1 and V2. Here, the photo detector 7
Since the output of is proportional to the square of the amplitude of the incident light, theoretically it is (V1 + V2) ² = 4sin ² {(ω + ωb / 2) t + φ} ・ cos ² {(ωbt−φ) / 2}… However, since the photodetector 7 cannot respond to the frequency of light and shows an average value, its output Vp is Vp = 2 + 2cos (ωbt−φ).

Therefore, if the modulation angular frequency ωb in the AO modulator 3 is known, the phase delay amount can be calculated from the value of the output Vp of the photodetector 7.

Similarly, the distance to the object to be measured can be obtained by sequentially measuring the wavelengths having different amounts of phase delay correspondingly and solving these measurement results as simultaneous equations.

Further, FIG. 4 shows a configuration in which a plurality of laser light sources having different generation wavelengths are used to obtain a large wavelength difference and the output light of these laser light sources is selectively emitted.

According to such a configuration, the lights having different wavelengths emitted from the two laser light sources 10a and 10b are passed through the cube corners 5 and 6 in opposite directions, and the phase signal of one signal is set to the reference side (for example, The photodetector 7a) and the other phase difference signal are received by the length measuring side (photodetector 7b), and the distance is obtained from the phase difference of those phase difference signals.

<Problems to be Solved by the Invention> However, as shown in the example of the absolute length measuring device shown in the above-mentioned prior art, a plurality of lights having different wavelengths are required to perform an absolute length measurement. In order to obtain a large wavelength difference, a plurality of laser light sources having different generation wavelengths are used as shown in FIG. 4 to selectively emit the output light of these laser light sources. As shown in FIG. 3, a small wavelength difference is obtained by a wavelength shifter that shifts the wavelength by an arbitrary amount. Therefore, there is a problem that the configuration of the laser light source that generates another wavelength is complicated.

The present invention has been made in view of the above problems of the prior art, and uses a compound resonator type laser light source in which a laser light source is combined with a proximity external mirror, and a predetermined distance between the laser light source and the proximity external mirror. A laser light source capable of generating a plurality of wavelengths required for absolute length measurement with a simple configuration by changing the distance by using driving means to change the wavelength of the resonance mode depending on the distance. It is intended to provide an afsolute length measuring instrument equipped with.

<Means for Solving the Problems> The configuration of the present invention for solving the above problems is at least 2
By switching the laser light of two or more different wavelengths, the phase delay amount of light according to the distance to the measurement target is sequentially measured, and the distance to the measurement target is obtained from the relationship between these wavelengths and the phase delay amount. In the absolute length measuring instrument using Michelson's interference optical system as described above, a predetermined distance is provided between the laser light source and the proximity external mirror, and the distance is changed by using the driving means, thereby depending on the distance. It is characterized by changing the wavelength of the resonance mode.

<Operation> As described above, by using the composite resonator type laser light source using the proximity external mirror as the light source for length measurement, the configuration of the laser light source that generates a plurality of wavelengths required for absolute length measurement can be simplified. It can be done.

<Examples> Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an absolute length measuring device according to the present invention. In FIG. 1, the same elements as those in FIG. 3 are designated by the same reference numerals, and duplicate description will be omitted.

In FIG. 1, reference numeral 20 denotes a compound resonator type laser light source,
Reference numeral 21 denotes a double-sided laser light source, one end surface 21a of which is coated with an antireflection film. Reference numeral 22 denotes a close-up external mirror, and the surface 22a of the close-up external mirror 22 and one end surface 2 of the laser light source 21.
The laser light source 21 and the laser light source 21 are arranged in parallel with each other with a predetermined gap d therebetween, and the laser light source 21 has a composite resonator structure including an external reflecting mirror 22. Reference numeral 23 is a PZT actuator (hereinafter simply referred to as PZT) attached to the proximity external mirror 22, which can be changed in the arrow direction shown in the figure by applying a voltage by a high voltage driver 24.

In the above-mentioned configuration, the laser light emitted from the laser light source 21 to the proximity external mirror 22 and the surface 22a of the proximity external mirror 22 and the laser light source 2
Output light having a wavelength (or frequency) that resonates in the gap d with the one end face 21a of 1 and has a resonance mode depending on the gap d
It becomes Pout and is output from the laser light source 21. On the other hand, when a voltage is applied from the high voltage drier 24 to the PZT23, the PZT23 is displaced in the direction of the arrow shown in the figure, and the proximity external mirror 22 attached to the PZT23 is displaced, and the external cavity length (gap d) is increased. Displace. Therefore, the wavelength of the resonance mode changes depending on the gap d between the laser light source 21 and the proximity external mirror 22. That is, the compound resonator type laser light source controls the wavelength (or frequency) of the laser light by displacing the proximity external mirror 22 attached to the PZT 23, and the displacement is from the high voltage driver 24 applied to the PZT 23. It is done by voltage.

In such a configuration, the laser light Pout emitted from the composite resonator type laser light source 20 performs the same operation as the absolute length measuring device shown in the conventional example to obtain the distance to the measurement target (cube corner 5). is there.

Here, FIG. 2 is a diagram showing the oscillation wavelength of the compound resonator type laser light source 20. The gap d between the laser light source 21 and the external reflecting mirror 22
Is varied by the PZT 23 to which a voltage is applied by the high voltage driver 24, the oscillation wavelength thereof changes stepwise as shown in FIG. Further, the number of changing steps (maximum change amount Δf1) and the change amount Δf2 in one step change depending on the absolute value of the gap d and the reflectance of the antireflection film coded on the one end face 21a of the laser light source 21. Therefore, by setting the value of the gap d to an appropriate value, several THz order (for example,
It is possible to simultaneously obtain a frequency difference on the order of several tens GHz (for example, a wavelength difference between points C and D in the figure) and a wavelength difference between points A and B in the figure. Further, by changing the injection current of the laser light source 21, it is possible to obtain a frequency of several hundred MHz, so that it is possible to obtain a plurality of frequency differences required for absolute length measurement with one laser light source. .

<Effect of the Invention> As described above in detail with reference to the embodiments, according to the present invention, at least two or more laser lights having different wavelengths are switched to change the phase of light according to the distance to the measurement target. In the absolute length measuring device using Michelson's interferometric optical system, which measures the delay amount one after another and finds the distance to the measurement target from the relationship between these wavelengths and the phase delay amount, the laser light source and the proximity external A predetermined distance is provided between the mirrors, and the wavelength of the resonance mode depending on the distance is changed by changing the distance by using the driving means. Therefore, with a simple configuration (one laser light source) It is possible to realize an absolute length measuring instrument equipped with a laser light source capable of generating a plurality of wavelengths required for absolute length measurement.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an absolute length measuring device according to the present invention, FIG. 2 is a diagram showing an oscillation wavelength of a composite resonator type laser light source used in the apparatus of FIG. 1, FIG. FIG. 4 shows a conventional example. 2 ... Half mirror, 3 ... Acousto-optic modulator, 4 ... Modulation signal source, 5, 6 ... Cube corner, 7 ... Photo detector, 8 ... Phase difference meter, 9 ... Arithmetic circuit, 20 ... Composite Resonator type laser light source, 21 ... Laser light source, 22 ... Proximity external mirror, 23 ... PZT actuator, 24 ... High voltage driver, 21a ... One end face of laser light source 21, 22a ... Proximity external mirror surface.

Claims (1)

[Claims] 1. At least two or more laser lights having different wavelengths are switched to sequentially measure a phase delay amount of light according to a distance to a measurement object, and the measurement is performed based on the relationship between these wavelengths and the phase delay amount. In an absolute length measuring instrument using Michelson's interference optical system designed to obtain the distance to the object, a predetermined distance is provided between the laser light source and the proximity external mirror, and the distance is changed by using driving means. The absolute length measuring instrument is characterized in that the wavelength of the resonance mode depending on the distance is changed by.