JPH06194116A - Laser length-measuring apparatus - Google Patents

Abstract

PURPOSE:To provide a laser length-measuring apparatus allowing the number of part items to be reduced so as to be optimum to attain compactness. CONSTITUTION:A laser beam emitted from a laser diode 1 is branched by a polarizing beam splitter 2. One vertical element beam is reflected on a plane mirror 11 through a quarter wavelength plate 9 and injected again to the polarizing beam splitter 2 through the quarter wavelength plate 9 so as to become the horizontal element beam. The other horizontal element beam is reflected on a plane mirror 12 through a quarter wavelength plate 10 and injected again to the polarizing beam splitter 2 through the quarter wavelength plate 10 so as to become the vertical element team. These two teams are joined and transmitted through a quarter wavelength plate 13 so as to become circularly polarized light. This circularly polarized light is passed through a polarizer 14 so as to generate two signals with 90 deg. phase difference, and these signals are detected by a bisectioned photodiode 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser length measuring device,
For example, the present invention relates to a laser length measuring device used for a position sensor such as a precision positioning table and utilizing Michelson's interference optical system.

[0002]

2. Description of the Related Art FIG. 4 is a diagram showing an example of a conventional laser length measuring device using laser light. In FIG. 4, the light P emitted from the laser diode 1 is divided into two lights a1 by the polarization beam splitter 2 at a ratio of 1: 1 (50%, 50%).
The light a1 is split into b1 and one of the lights a1 is reflected twice by the corner mirror 5 as transmitted light (object light) and enters the beam splitter 2 again as light a2. Here, 50% of the light a2 is further divided into a straight light a3 and a 90-degree-bent light a4. The other light b1 split by the beam splitter 2
Is transmitted through the ⅛ wavelength plate 3 as reflected light (reference light), is reflected twice by the corner mirror 4, and is transmitted through the ⅛ wavelength plate 3 again as reflected light b2 to enter the beam splitter 2. Then, the light b2 is converted into 9 by the beam splitter 2.
It is branched into a light b3 that is bent by 0 ° and a light b4 that goes straight.

The lights a3 and b3 return to the laser diode 1, but do not return to the laser diode 1 because the optical paths differ from each other. That is, the lights a1 and b1 incident on the corner mirrors 4 and 5 and the lights a2 and b2 reflected on the corner mirrors 4 and 5, respectively.
Since the optical path of the laser beam is different, it does not return to the laser diode 1.
Lights a4 and b4 split by the beam splitter 2
Is incident on the polarization beam splitter 6, and the light a4,
b4 interferes with each other and strengthens or weakens each other.

FIG. 5 is a diagram for explaining the interference of the lights a4 and b4 incident on the polarizing beam splitter shown in FIG. 4, and FIG. 6 is a diagram for explaining the vertical and horizontal components distributed by the polarizing beam splitter. FIG. 7 is a diagram for explaining the phase difference between the vertical component and the horizontal component.

As shown in FIGS. 5A and 5B, the light a4
If the phases of and b4 are the same, the light output is enhanced as shown in FIG. 5 (c), and if the phases are opposite, the light output is not produced as shown in FIG. 5 (d). If the incident light a4, b4 vibrates in a certain direction θ, the polarization beam splitter 6
As shown in FIG. 6, a vertical component S and a horizontal component P are distributed. The vertical component S is incident on the photodiode 8, and the horizontal component P is incident on the photodiode 7. That is,
The vertical component S and the horizontal component P have a phase difference of 90 ° as shown in FIG. 7, and a sine wave signal having a phase difference of 90 ° is output from the photodiodes 7 and 8.
The signals appearing at the outputs of the photodiodes 7 and 8 change as shown in FIG. 7 depending on whether the corner mirror 5 is moved forward or backward. Can be determined.

[0006]

However, in the conventional laser length-measuring device shown in FIG. 4, the ease of setting the corner mirror 5 and the condition that the reflected light does not return to the laser diode 1 are required. To meet these requirements, corner mirrors 4 and 5 must be used, and in addition to the beam splitter 2, a polarization beam splitter 6 and two photodiodes 7 and 8 must be used. It had the drawback of not being suitable.

Therefore, a main object of the present invention is to provide a laser length measuring device which can reduce the number of parts and which is optimum for miniaturization.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a laser length measuring instrument for guiding a laser beam emitted from a light emitting element to an interferometer and receiving light from the interferometer by a light receiving element to measure a distance. The laser light emitted from the light emitting element is incident on one surface of the light source, transmits the light, reflects it at 90 °, transmits the laser light incident from the surface opposite to the one surface, and reflects it at 90 °. A polarizing beam splitter, a first quarter-wave plate that transmits the incident light that has passed through the polarizing beam splitter, a first mirror that reflects the incident light that has passed through the first quarter-wave plate, and a polarization A second quarter-wave plate that transmits the incident light reflected by the beam splitter by 90 °, and reflects the incident light that has passed through the second quarter-wave plate toward the second quarter-wave plate. The second mirror and the first and The transmitting light combined by the reflected and the polarization beam splitter in the second mirror 3 1
It comprises a quarter wave plate and a polarizer for guiding the reflected light transmitted through the third quarter wave plate to the light receiving element.

More preferably, the first mirror is composed of a corner mirror, and a total reflection mirror is provided or a total reflection film is vapor-deposited on the incident surface of the polarization beam splitter on which the light reflected by the corner mirror enters. It

[0010]

In the laser length measuring instrument according to the present invention, the laser light emitted from the light emitting element is split by the beam splitter, one of which is transmitted through the quarter wavelength plate and then reflected by the first mirror,
The light is made incident on the beam splitter again, and the other branched light is transmitted through the second quarter-wave plate, reflected by the second mirror, combined by the beam splitter, and then the third quarter-wave plate. Since the light is transmitted and is guided to the light receiving element by the polarizer, it is not necessary to provide two corner mirrors or two light receiving elements, the number of parts can be reduced, and the size can be reduced.

[0011]

FIG. 1 is a diagram showing an embodiment of the present invention.
In FIG. 1, similarly to FIG. 4 described above, the laser light from the laser diode 1 is incident on the beam splitter 2 and split into two lights. The vertical component light (object light) passes through the beam splitter 2, passes through the first quarter-wave plate 9, is totally reflected by the plane mirror 11, and passes through the quarter-wave plate 9 again. As a result, the light of the vertical component is 1/4
It travels back and forth through the wave plate 9 to become horizontal component light, which is totally reflected by the polarization beam splitter 2.

On the other hand, the horizontal component light (reference light) split by the polarization beam splitter 2 passes through the second quarter wave plate 10, is totally reflected by the plane mirror 12, and is again returned to the quarter wave plate 10. Will pass through. Based on the same idea as described above, the horizontal component light becomes a vertical component light by going back and forth through the quarter-wave plate 10, all of which pass through the polarization beam splitter 2 and are combined with the object light. The combined light is the third
And enters the quarter-wave plate 13 to become circularly polarized light. By passing through the polarizer 14 in which the left half passes through 45 ° and the right half passes through 90 °, a phase difference of 90 ° is obtained.
Two signals are generated. These two signals are detected by one 2-division or 4-division photodiode 15.

With the configuration as described above, the return light to the laser diode 1 can be prevented and the optical path is one without using a corner mirror. Therefore, a small polarization beam splitter 2 can be used. . Further, the quarter-wave plates 9, 10 and 13 can be manufactured with a thickness of about 0.4 mm, and the plane mirrors 11 and 12 and the polarizer 14 can also be manufactured from thin films, so that the installation space can be reduced. Also, only one photodiode 15 is required,
The number of parts can be reduced.

FIG. 2 is a diagram showing an example in which the embodiment shown in FIG. 1 is integrated. Each configuration shown in FIG. 2 is the same as that of FIG. 1, and is compactly integrated for further miniaturization.

FIG. 3 is a diagram showing another embodiment of the present invention. In the embodiment shown in FIG. 3, the plane mirror 11 shown in FIG. 1 is replaced with a corner mirror 5, and a reflection mirror 16 is adhered to a part of one surface of the polarization beam splitter 2 to obtain a polarization beam. The laser beam split by the splitter 2 is transmitted through the quarter-wave plate 9 and the corner mirror 5
And the light reflected by the reflection mirror 16 is again transmitted through the quarter-wave plate 9 and the polarization beam splitter 2
Is to be incident on. The other configuration is the same as that of FIG. In such a configuration, the optical path difference is doubled as compared with the example shown in FIG. 1, and the resolution is doubled. Also, by adopting the corner mirror 5, the mirror setting becomes easy.

In the embodiment shown in FIG. 3, the reflection mirror 16 is adhered to the polarization beam splitter 2, but the present invention is not limited to this, and a part of one surface of the polarization beam splitter 2 is entirely covered. A reflective film may be vapor-deposited.

[0017]

As described above, according to the present invention, the interference optical system is composed of the polarization beam splitter, the three quarter-wave plates, the polarizer and the reflecting mirror.
The number of parts can be reduced, and it becomes possible to integrate in a small size.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example in which the embodiment shown in FIG. 1 is integrated.

FIG. 3 is a diagram showing another embodiment of the present invention.

FIG. 4 is a diagram showing an example of a conventional laser length measuring device using laser light.

5 is a diagram for explaining interference between lights a4 and b4 incident on the polarization beam splitter shown in FIG.

FIG. 6 is a diagram for explaining vertical components and horizontal components distributed by a polarization beam splitter.

FIG. 7 is a diagram for explaining a phase difference between a vertical component and a horizontal component.

[Explanation of Codes] 1 Laser diode 2 Polarization beam splitter 9, 10, 13 1/4 wave plate 11, 12 Plane mirror 14 Polarizer 15 Photodiode 16 Reflection mirror 5 Corner mirror

[Procedure amendment]

[Submission date] April 7, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

Claims (2)

[Claims] 1. A laser length measuring device that guides laser light emitted from a light emitting element to an interferometer and receives light from the interferometer by a light receiving element to measure a distance, wherein the interferometer has one surface thereof. The laser light emitted from the light emitting element is incident, and the light is transmitted and reflected by 90 °,
A polarization beam splitter that transmits the laser light incident from the surface opposite to the one surface and reflects the laser light by 90 °; a first quarter-wave plate that transmits the incident light transmitted through the polarization beam splitter; A first mirror for reflecting the incident light transmitted through the first quarter-wave plate toward the first quarter-wave plate, and a second mirror for transmitting the incident light reflected by 90 ° by the polarization beam splitter. Quarter-wave plate, a second mirror that reflects the incident light transmitted through the second quarter-wave plate toward the second quarter-wave plate, and is reflected by the first and second mirrors And a third 1 / which transmits the light that has been coupled and is multiplexed by the polarization beam splitter.
A laser length measuring instrument comprising a four-wave plate and a polarizer for guiding the reflected light transmitted through the third quarter-wave plate to the light receiving element. 2. The first mirror is a corner mirror, and a total reflection mirror is provided or a total reflection film is vapor-deposited on an incident surface of the polarization beam splitter on which the light reflected by the corner mirror is incident. The laser length measuring device according to claim 1, wherein the laser length measuring device is provided.