JP2992829B2 - Laser length gauge - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser length meter, and more particularly, to linearly couple interference light obtained by splitting light from a laser into a reference optical path and a length measuring optical path. After passing through a polarizing element that changes the state of polarization, the light is branched into two- or three-phase interference light optically shifted by 90 ° by a plurality of optical elements. The present invention relates to a laser length measuring device that measures a change in a measurement optical path length and / or a direction of the change based on the following formula:

[Conventional technology]

An interference fringe counting type laser length meter as shown in FIG. 6 is known as a laser length meter as described above.

In this laser length meter, linearly polarized light from a stabilized laser 1 is split by a beam splitter 2 into a reference optical path having a λ / 8 plate 3 and a fixed corner cube 4 and a length measuring optical path having a moving corner cube 5. The reference light branched to the optical path passes through the λ / 8 plate 3 twice to be converted into circularly polarized light. The circularly polarized light of the reference light and the linearly polarized light of the measuring light branched to the measuring optical path are combined again by the beam splitter 2. One of the two divisions is further divided by the polarization beam splitter 6 so that the measured light is separated into ± 45 ° directions with respect to the polarization plane by the polarization beam splitter 6. When the light passes through the filter 7 and the polarizing plate 8, respectively, the three types of interference light whose phases interfere with each other by the movement of the moving corner cube 5 in the direction of the arrow are sequentially shifted by 90 °. Re respectively incident on the detector 9
After being converted into three kinds of electric signals having a phase difference of 90 °, the three kinds of electric signals are respectively amplified by the amplifier 10 and then sequentially made into two sets, each of which is adjacent to each other and shifted by 90 ° in phase.
These two sets of electric signals are input to the subtracter 11 to obtain 90 ° out of phase sin θ and cos
θ (where θ = 2π (Lm−Lr) / λ, Lm...
Lr: Reference optical path length, λ: Wavelength), the change in the measured optical path length is obtained from at least one of the electrical signals that change, and the change direction is obtained from both.

In other words, this laser length meter uses the principle of polarization of laser light to obtain three types of interference fringe signals sequentially shifted in phase by 90 °, and determines the change in the measured optical path length and the change based on the difference between the sequentially adjacent signals. Since the signal that changes in the above-mentioned sin θ and cos θ used for measuring the direction is obtained, the influence of disturbances such as intensity fluctuation of the laser beam is canceled out, and the center of the signal level is always constant,
There is the advantage that the miscount of interference fringes is reduced and measurement with high accuracy is performed.

However, this conventional laser length meter not only requires the polarizing beam splitter 6 to be accurately arranged with respect to the beam splitter 2, but also makes the filter 7 and the polarizing plate 8 accurate for each of the three types of split optical paths. There is an annoyance that it must be arranged.

[Problems to be solved by the invention]

SUMMARY OF THE INVENTION It is a first object of the present invention to provide an interference fringe counting type laser length meter which can easily arrange a plurality of optical elements for optically splitting two-phase or three-phase interference light.

Further, in addition to the first object, a second object of the present invention is to provide a laser length measuring device which makes it easier to combine and arrange a plurality of optical elements.
The purpose of.

[Means for solving the problem]

According to the present invention, the interference light obtained by splitting the light from the laser into the reference optical path and the length measuring optical path is passed through a 45 ° optical rotation plate that changes the state of linearly polarized light, and then optically controlled by a plurality of optical elements. To change into two-phase or three-phase interference light whose phase is shifted by 90 °, and to measure the change and / or the direction of the change of the length measurement optical path length based on the detected electric signal of the branched interference light. All of the plurality of optical elements or some of the plurality of optical elements that divide into two-phase or three-phase interference light are brought into contact with each other next to each other, and integrated with the 45 ° optical rotation plate. The laser length measurement device is characterized in that the first object is achieved by this configuration.

Further, the plurality of optical elements optically split into two-phase interference light wavelength plate having a retardation of λ / 4 or more,
And, including a polarizing beam splitter adjacent to the downstream side of the wave plate, the wave plate or the polarizing beam splitter is provided rotatably adjustable around the optical axis,
The second object is achieved.

[Action]

That is, in the laser length measuring device of the present invention, all or some of the plurality of optical elements that branch the interference light are in contact with each other next to each other, and together with the 45 ° optical rotation plate,
Since they are integrally connected, the arrangement of the plurality of optical elements can be easily and accurately performed, and interference light having a phase shifted by 90 ° can be easily obtained. Further, a 45 ° optical rotation plate that changes the state of linearly polarized light is also integrated with an optical element in which all or some of the optical elements are integrally coupled. In other words, the interference light obtained by splitting the light from the laser into the reference optical path and the length measuring optical path is incident on the integrally coupled light in a linearly polarized state. Therefore, it is possible to change the optical path of the interference light by arranging a mirror on the upstream side of what is integrally coupled,
The degree of freedom in setting the arrangement position can be increased.

More specifically, when light is reflected by a mirror using a general metal reflecting mirror, the phase changes before and after the reflection.
Therefore, if the interference light reflected by the mirror is in a circularly polarized state, it becomes elliptically polarized due to a change in phase due to the reflection, which has a great adverse effect on measurement accuracy. Therefore, if the polarization state of the interference light obtained by combining the reference light and the measurement light is changed immediately, it is difficult to arrange a mirror after that, and the arrangement of the optical element that splits the interference light is limited. Come. On the other hand, if the interference light is linearly polarized and reflected by a mirror in parallel or perpendicular to the plane of incidence, the change in the phase will not affect the measurement path length change and / or the direction of the change. Has no effect. In this way, the mirror is arranged on the upstream side of the optical unit by making the interference light, in a state of being linearly polarized, incident on the one obtained by integrating all or some of the plurality of optical elements into one. Thus, the mirror can be arranged without being affected by the measurement accuracy, and the degree of freedom in setting the arrangement position can be increased.

In addition, a wavelength plate having a retardation of λ / 4 or more of the plurality of optical elements, or a polarizing beam splitter adjacent to the downstream side of the wavelength plate is provided so as to be adjustable and rotatable around the optical axis. The phase of the branched interference light can be made exactly 90 °, and the coupling arrangement of a plurality of optical elements is further facilitated.

〔Example〕

 Hereinafter, the present invention will be described with reference to FIGS.

1 and 2 are schematic diagrams showing examples of a laser length measuring device according to the present invention. FIG. 3 is a diagram showing a relationship between an interference light beam and a detector. FIG. 4 is a diagram showing a case where a phase difference is π / 2 radians. Lissajous figure of two kinds of interference fringe signals, FIG. 5 shows a phase difference of π / 2
It is a Lissajous figure when it deviates from radians by △ θ radians.

1 and 2, the same reference numerals as those in FIG. 6 indicate those having the same functions. And 12 is a λ / 4 plate, 12A
Is a wavelength plate such as a λ / 4 plate or more, for example, a λ / 2 plate, 13 is a 45 ° optical rotation plate, 14 is a 45 ° reflection plane, 15 is an imaging lens, and 16 is a reflection amplifier.

That is, the laser length measuring device shown in FIGS. 1 and 2 converts the linearly polarized beam of the stabilized laser 1 into circularly polarized light by the λ / 4 plate 12, and converts the circularly polarized light by the polarization beam splitter 6 into a reference light path of linearly polarized light orthogonal to each other. Since the reference light and the measurement light on the measurement optical path are divided and then combined, the reference light and the measurement light are similarly polarized by the polarization beam splitter 6 to obtain interference light. And that the light combined by the polarization beam splitter 6 is reflected at 45 ° mirror plane or total reflection plane. The difference from the laser length measuring device shown in FIG. 6 is that the degree of freedom in setting the arrangement position of the optical element that optically branches the interference light is increased by changing the optical path by reflecting the light on the plane 14. I have.

Further, the laser length measuring device shown in FIG.
45 ° optical rotation plate 1 of an optical element that obtains three-phase interference light shifted by 90 °
3, the beam splitter 2, the λ / 4 plate 12 and the polarizing beam splitter 6 for one of the split beams split by the beam splitter 2, and the polarizing beam splitter 6 for the other split beam split into two by the beam splitter 2. In addition, optical elements in the form of a flat plate or a triangular, quadrangular, or parallelogram prism having a 45 ° reflecting plane 14 for the light passing through the polarizing beam splitter 6 are integrated in a state of being adjacent to each other in the order of the optical path. ing. Then, the 45 ° optical rotation plate 13 causes the beam splitter 2 to use the polarization beam splitter 6 for obtaining the combined light of the reference light and the length measuring light.
And the side can be arranged in parallel. Therefore, the arrangement of a plurality of optical elements for optically obtaining three-phase interference light is extremely easily and accurately performed as compared with the laser length meter of FIG. 6, and the interference fringe phase is sequentially shifted by 90 °. Three-phase interference light can be easily obtained.

In addition, the laser length measuring device shown in FIG. 2 is one of two divisions performed by a 45 ° optical rotation plate 13, a beam splitter 2, and a beam splitter 2 of an optical element for obtaining two-phase interference light in which the interference fringe phase is shifted by 90 °. A wavelength plate 12A such as a λ / 4 plate for light, a polarizing beam splitter 6, and a beam splitter 2
An optical element having a 45 ° prism configuration of a flat plate, a triangle, a square, or a parallelogram having a polarization beam splitter 6 for the other split light is integrated in a state of being adjacent to each other and being in contact with each other in the order of the optical path. Therefore, as compared with the laser length measuring device shown in FIG. 1, since there is no optical element having the 45 ° reflection plane 14, it is easy to form an integrated optical element, and the arrangement of the imaging lens 15 and the detector 9 for the interference light. It is even easier to set up only two-phase interference light.

1 and 2, the interference light is imaged on the detector 9 by the imaging lens 15 in order to obtain a clear interference fringe signal. For this purpose, as shown in FIG. 3, the positions of the imaging lens 15 and the detector 9 are set with respect to the interference light so that the interference fringe portion 17A appearing in the interference light beam 17 is captured by the detector 9. is important. In this regard, the laser length measuring device shown in FIG. 1 must be provided with an imaging lens 15 and a detector 9 for each of the three-phase interference light, while the laser length measuring device shown in FIG. Since it is sufficient only for the interference light, it is easy for one phase.

If the two-phase interference light has an accurate phase difference of 90 °, the laser length measuring device shown in FIG. 2 uses the inverting amplifier 16 to generate an interference fringe signal having a 180 ° phase difference from the detection signal of the one-phase interference light. As a result, three-phase interference fringe signals whose phases are shifted by 90 ° can be obtained accurately.

As described above, the laser length measuring apparatus shown in FIGS. 1 and 2 can easily obtain the interference light having the phase sequentially shifted by 90 °, and therefore, the interference fringe signal that changes with sin θ and cos θ, that is, the Lissajous figure Is easy to obtain an interference fringe signal having a circle as shown in FIG. And such sinθ, cos
From the interference fringe signal of θ, a change between interference fringes on the length measuring optical path can be easily and accurately measured. However, it is also required that the optical element for obtaining the interference light by dividing the combined light of the reference light and the measurement light be accurately integrated. If the integration is not accurate, the phase difference of the obtained interference light will deviate from 90 °, so that the finally obtained two-phase interference fringe signal will also change with sinθ, cos (θ + △ θ) And the Lissajous figure becomes an ellipse as shown in FIG. Since a periodic error is generated from such an interference fringe signal of sin θ, cos (θ + △ θ), it is difficult to accurately measure the change between the interference fringes in the length measuring optical path.

Therefore, the optical element for optically splitting two-phase interference light in the laser length measuring device shown in FIG.
The wavelength plate 12A or the polarizing beam splitter 6 downstream of the wavelength plate 12A having the above-described retardation can be adjusted and rotated around the optical axis. The phase difference of the phase interference light can be made exactly 90 °. Therefore, in this example, an interference fringe signal that varies with sin θ and cos θ can be obtained more easily.

The present invention is not limited to the above-described example, and the optical element in the optical path up to obtaining the combined light of the reference light and the length measuring light may be the same as that in the conventional laser length measuring device. In the case of splitting the interference light of the phase, if the interference light is guided to the detector of the length measuring unit by an optical fiber or the like, electric noise is less likely to be introduced.
A signal that does not generate a phase interference fringe signal may be used.

〔The invention's effect〕

In the laser length measurement device of the present invention, all or some of the plurality of optical elements that branch the interference light,
Adjacent to each other and integrated with a 45 ° optical rotation plate that changes linear polarization, multiple optical elements can be easily and accurately arranged, and interference light whose phase is shifted by 90 ° can be easily adjusted. And the degree of freedom in setting the arrangement position can be increased.

[Brief description of the drawings]

1 and 2 are schematic diagrams showing examples of a laser length measuring device according to the present invention. FIG. 3 is a diagram showing a relationship between an interference light beam and a detector. FIG. 4 is a diagram showing a case where a phase difference is π / 2 radians. Lissajous figure of two kinds of interference fringe signals, FIG. 5 is a Lissajous figure when the phase difference is shifted from π / 2 radians by △ θ radians,
FIG. 6 is a schematic configuration diagram showing an example of a conventional interference fringe counting type length measuring instrument. DESCRIPTION OF SYMBOLS 1 ... Stabilized laser, 2 ... Beam splitter 3 ... λ / 8 plate, 4 ... Fixed corner cube 5 ... Moving corner cube 6 ... Polarized beam splitter 7 ... Filter, 8 ... Polarizer 9 ... ... Detector, 10 ... Amplifier 11 ... Subtractor, 12 ... λ / 4 plate 12A ... Wave plate with retardation of more than λ / 4 13 …… 45 ° optical rotation plate, 14 …… 45 ° reflection plane 15 …… imaging lens, 16 …… inverting amplifier 17 …… interference beam, 17A …… interference fringe part

Claims (2)

(57) [Claims] An interference light obtained by splitting light from a laser into a reference optical path and a length measuring optical path is passed through a 45 ° optical rotation plate that changes a state of linear polarization, and then optically converted by a plurality of optical elements. The two-phase or three-phase interference light whose phase is shifted by 90 ° is branched, and the change and / or the direction of the change of the length measurement optical path length is measured based on the electric signal detected from the branched interference light. And all or a part of the plurality of optical elements branched into two-phase or three-phase interference light are brought into contact with each other next to each other, and the 45 ° optical rotation plate and Laser length measuring instrument characterized by being integrally connected. 2. The optical device according to claim 1, wherein the plurality of optical elements include a wave plate optically branched into two-phase interference light and having a retardation of λ / 4 or more, and a polarizing beam splitter adjacent to a downstream side of the wave plate. 2. A laser length measuring instrument according to claim 1, wherein said wavelength plate or said polarizing beam splitter is provided so as to be adjustable and rotatable around an optical axis.