JPH02287105A - Absolute length measuring instrument - Google Patents

Abstract

PURPOSE:To easily generate light with plural wavelengths required for absolute length measurement by using a composite resonance laser light source which uses a nearby external mirror as a light source for measurement. CONSTITUTION:The composite resonator type laser light source 20 constituted by arranging a laser light source 21 and a nearby external mirror 22 while a specific gap (d) is held is used as the light source 20 for length measurement. The gap (d) of this laser light source 20 is varied by a PZT actuator 23 which is applied with a high voltage by a high-voltage driver 24 to generate plural wavelengths. The laser light Pout emitted by the light source 20 is used to derive the distance to a corner cube 2 as an object of measurement through the same operation as before. Consequently, the light with the plural wavelengths required for the absolute length measurement is easily found by the simple constitution.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention makes it possible to perform high-precision length measurement in units of wavelength by utilizing laser light interference, and also to provide absolute length measurement output. This is about a length measuring device that can be obtained.

<Prior Art> FIG. 3 is a block diagram showing an example of a conventional Abflu 1 length measuring device of this type, which utilizes a Michelson interference optical system.

In FIG. 3, 1 is a laser light source that selectively generates a plurality of coherent lights (λ1 to λ4) with different wavelengths; 2
The half mirror 13 is an acousto-optic modulator (hereinafter simply referred to as an AO modulator) that modulates the light on the reference side in order to heterodyne detect the amount of phase delay of the light, and 4 is a modulator that drives the AO modulator at a constant frequency fb. The signal source 5.6 is a cube corner, the cube corner 5 is a cube corner on the length measurement side that moves according to the length measurement operation, and the cube corner 6 is a cube corner on the reference side that is fixed at a constant distance. 7 is a photodetector, and 8 is a phase difference meter that detects the amount of phase delay included in the output of the photodetector 7.

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

In a length measuring device configured in this way, the angular frequency of light is ω
, the modulation angular frequency in the AO modulator 3 is ωb (=2π
fb), and the amplitude vO of the light emitted from the laser light source 1 is
When VO=sinωt...■, the amplitude V1 of the light modulated by the AO modulator 3 is Vl = Sin (ω+ωb) t -■ The amplitude V2 of the light returning via the cube corner 5 is V2 = sin (ωt+φ)...■. Note that -φ is the amount of phase delay that occurs in response to the difference in optical path length between the optical paths on the reference side and the length measurement side.

On the photodetector 7, the two lights as shown in the above formulas 1 and 2 are superimposed, so the amplitude of the incident light is Vl + V2 = sin (ω + ωb) + 10 Sin (ωt + φ
)=2Sin(ωt ωbt/2+φ)・COS
((ωbt-φ)/2) ...Vl, V as in ■
It becomes the sum of 2. Here, since the output of the photodetector is proportional to the square of the amplitude of the incident light, theoretically (Vl +V2) 2 - 4sin 21. (ω1ωb/2) t+φ1・c
os2((ωbt-φ)/2)...■However, the photodetector 7 cannot respond to the frequency of light and shows the average value, so its output Vp is VD = 2+2cos (ωbt-φ )...■
becomes.

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

Similarly, by sequentially measuring the amount of phase delay corresponding to different wavelengths and solving these measurement results as simultaneous equations, the distance to the measurement target can be determined.

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

According to such a configuration, two laser light sources 10a, 10
Light beams of different wavelengths emitted from b are passed through the cube corner 5.6 in opposite directions, and the phase difference signal of one signal is used as a reference 1!1 (for example, photodetector 7a), and the phase difference signal of the other signal is measured. Light is received on the long side (photodetector 7b), and the distance is determined from the phase difference between these phase difference signals.

<Problem 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, in order to perform absolute length measurement, multiple lights of different wavelengths are required. In order to obtain a large wavelength difference, multiple laser light sources with different generation wavelengths are used as shown in Figure 4, and the output light of these laser light sources is selectively emitted. 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 in that the configuration of a laser light source that generates multiple wavelengths is complicated.

The present invention has been made based on the above-mentioned problems of the prior art, and has a configuration using a composite resonator type laser light source in which a laser light source is combined with a close-in external mirror, and allows absolute measurement with a simple configuration. The purpose of this invention is to provide an absolute length measuring device equipped with a laser light source that can generate multiple wavelengths necessary for measuring length.

Means for Solving the Problems> The configuration of the present invention for solving the above problems includes at least two
The amount of phase delay of the light is sequentially measured according to the distance to the measurement target by switching laser beams with different wavelengths, and the J11 described above is determined based on the relationship between these wavelengths and the phase delay.
This is an absolute length measuring device that uses Michelson's interference optical system to determine the distance to a target, and is characterized by the use of a complex resonator type laser light source using a close-up external mirror as the light source for length measurement. It is something to do.

In this way, by using a composite resonator laser light source using a close external mirror as a light source for length measurement, it is possible to easily configure the laser light source that generates the multiple wavelengths required for absolute length measurement. It can be made into something.

<Example> Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 is a configuration 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 denoted by the same reference numerals, and redundant explanations will be omitted.

In FIG. 1, 20 is a composite resonator type laser light source, 21 is a double-sided laser light source, and one end surface 2
1a is coated with an antireflection film. Reference numeral 22 denotes a proximal external mirror, and the surface 22a of the proximal external mirror 22 and one end surface 21a of the laser light source 21 are arranged parallel to each other with a predetermined gap d maintained. The composite resonator j7F, ′? i. 23 is a pz 'r' actuator (hereinafter simply referred to as PZ '1') attached to the proximal external mirror 22, which can be varied in the direction of the arrow shown in the figure by applying voltage with a high voltage driver 24. be.

In the above configuration, from the laser light source 21 to the close external mirror 22
The laser beam emitted resonates within the gap d between the surface 22a of the proximal external mirror 22 and one end surface 21a of the laser light source 21, and output light with a wavelength (or frequency) having a resonance mode depending on the distance of the gap d. The light becomes Pou1 and is output from the laser light source 21. On the other hand, P Z T from the high voltage driver 24
When a voltage is applied to 23, PZT 23 is displaced in the direction of the arrow shown in the figure, and the proximity external mirror 22 attached to PZ i' 23 is displaced, and the external resonator length (gap d)
is displaced. Therefore, the laser light source 21 and the close external mirror 22
The wavelength of the resonant mode will change depending on the gap d. In other words, the compound cavity type laser light source controls the wavelength (or frequency) of the laser beam by displacing the close external mirror 22 attached to the PZT 23, and the displacement is P
This is done by the voltage from the high voltage driver 24 applied to Z'T'23.

In such a configuration, the laser beam pout emitted from the composite resonator type laser light source 20 operates in the same manner as the Abflu 1-length measuring device shown in the conventional example to determine the distance to the measurement target (cube corner 5). It is something.

Here, FIG. 2 is a diagram showing the oscillation wavelength of the composite resonator type laser light source 20. A voltage is applied to the gap d between the laser light source 21 and the external reflecting mirror 22 by the high voltage driver 24.
By varying the ZT23, the oscillation wavelength changes stepwise as shown in FIG. In addition, the number of changing steps (maximum amount of change Δf1) and the amount of change per one step Δf2
varies depending on the absolute value of the gap d and the reflectance of the antireflection film coated on one end surface 21a of the laser light source 21. Therefore, by setting the value of the gap d to an appropriate value, the number '
It is possible to simultaneously obtain frequency differences on the order of I' Hz (for example, the wavelength difference between points A and B in the figure) and on the order of several tens of GHz (for example, the wavelength difference between points C and D in the figure).

Also, by varying the injection flow of the laser light source 21,
Since it is possible to obtain a frequency of several 100 MHz, it is possible to obtain all the multiple frequency differences necessary for absolute length measurement with one laser light source.

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the present invention, at least two laser beams with different wavelengths are switched, and the phase delay of the light is determined according to the distance to the measurement target. In an absolute length measuring device that uses Michelson's interference optical system, which sequentially measures the amount of light and determines the distance to the measurement target from the relationship between the wavelength and phase delay amount, a close-up light source is used as a light source for length measurement. By using a complex resonator laser light source using an external mirror, we have created a laser light source that can generate multiple wavelengths necessary for absolute length measurement with a simple configuration (one laser light source). It is possible to realize an absolute length measuring device equipped with the following functions.

[Brief explanation 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 the oscillation wavelength of a composite resonator type laser light source used in the device shown in FIG. 1, and FIG. FIG. 4 shows a conventional example. 2...Half mirror 13...Sound warning optical modulator, 4.
...Modulation signal source, 5.6...Cube corner, 7...
- First detector, 8... Phase difference meter, 9... Arithmetic circuit, 20... Complex resonator type laser light source, 21...
・Laser light source, 22... Proximity external mirror, 23... PZ
T actuator, 24...high voltage driver, 21a
. . . One end surface of the laser light source 21, 22a . . . Proximate external mirror surface. L

Claims (1)

[Claims] By switching at least two or more laser beams with different wavelengths, the amount of phase delay of the light is sequentially measured according to the distance to the measurement target, and the distance to the measurement target is determined from the relationship between these wavelengths and the amount of phase delay. An absolute length measuring device using a Michelson interference optical system designed to obtain the following: An absolute length measuring device characterized by using a composite resonator type laser light source using a close external mirror as a length measuring light source.