JPH0463305A - Polarizing beam splitter and laser interferometer - Google Patents

Abstract

PURPOSE:To offer a highly accurate parallel beam splitter and a laser interference measuring meter having high characteristics by projecting reflecting light and passing light on/through a polarizing beam split coat from the same end face of a triangular prism. CONSTITUTION:A polarizing beam splitter 1 is constituted of a parallel plate-like prism 2 and the triangular prism 3. The cross section of the prism 2 is trapezoidally formed and an approximately half face of an end face 2c is coated with the polarizing beam split coat 4. Since both the parallel end faces of the prism 2 can be comparatively easily and accurately worked and parallelism between a reflection face 3 and the coat 4 respectively formed on the parallel end faces of the prism 2 can be highly accurately formed, parallelism between incident light upon the coat 4 and reflected light from a reflection face 3 can be secured. When the polarizing beam splitter is used as the laser interference measuring meter to execute separation between reference light and measuring light and the synthesis of return light, parallelism between the reference light and the measuring light can be highly accurately obtained, so that the return light can be effectively synthesized and measurement based upon the parallel projection beams of incident beams from a light source can be executed.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to a polarizing beam splitter and a laser interferometer, and more specifically, to a polarizing beam splitter that is suitable for obtaining two lights separated by a polarizing beam splitter as parallel lights. The present invention relates to a beam splitter and a laser interferometric measuring needle using the polarizing beam splitter.

<Prior art> Laser interferometers use a gas laser, semiconductor laser, etc. as a light source, and after dividing the beam into reference light and measurement light, the light returned from the object to be measured is combined with the reference light again. , length measurement (displacement) information is obtained by observing interference fringes and beats.

The configuration of such a laser interferometric length measurement meter is based on a Michelson type interferometer as shown in FIG.

That is, the luminous flux from the light source 20 is polarized beam splitter 2
1, it is divided into a reference light and a length measurement light, and the length measurement light is reflected by a movable mirror 22 attached to the object to be measured, and is combined with the reference light reflected from a fixed mirror 23 by a polarizing beam splitter 21 to form an interference pattern. occurs. Here, depending on the length measurement information detection method,
This method uses an interference fringe counting method that counts the movement of interference fringes generated by returned light, beats using multiple coherent wavelengths, and takes advantage of the Doppler shift in the frequency of the measuring light depending on the speed of the measuring object. There is a heterodyne method that detects beat frequency changes (PRECIs).
l0NENG4NEERING Vol, 1. Nol
(1979) 85, PRECISION ENGI
NEERING Vol.5. No.3 (1983)
111 etc.).

By the way, when separating the reference light and length measurement light using a beam splitter as described above, the simplest method is to separate the reference light and length measurement light into mutually orthogonal directions using the beam splitter, as shown in Figure 5. Previously, they were separated and irradiated directly onto a fixed mirror and a movable mirror, but if it was desired to provide a substantially linear optical path, it would be necessary to emit the reference light and measurement light parallel to each other. In this case, for example, as shown in FIG. 6, a beam splitter and a reflector are combined to obtain mutually parallel reference light and length measurement light.

In FIG. 6, the polarized beam split surface 31 is provided at the joint surface of the triangular prisms 32 and 33, and the triangular prism 35 provided with the reflective surface (or total reflection surface) 34 is connected to the reflective surface 34 and the polarized light beam. The beam split surface 31 is arranged so as to be parallel to the beam split surface 31, and the light enters and exits the transmission surface of each prism 32, 33, and 35 at a right angle. For example, the light from the light source incident on the reference light as passing light,
The reflected light is divided into a length measuring light, and the length measuring light traveling in a direction perpendicular to the reference light is reflectively bent by the reflective surface 34 in a parallel direction in the same direction as the reference light.

Note that the φ mark and the ◎ mark in FIG. 6 indicate polarization directions perpendicular to each other.

<Problems to be Solved by the Invention> However, when the reference light and the length measurement light are made into parallel light beams as described above, even if the parallelism between the polarized beam splitting surface 31 and the reflecting surface 34 is not accurately obtained, However, if the apex angle accuracy of each triangular prism is poor and parallelism between the exit surface of the triangular prism 32 and the exit surface of the triangular prism 35 cannot be achieved with high precision, the reference light and the length measurement light will not be accurately parallel. Therefore, it becomes impossible to combine the returned light with high accuracy.

Furthermore, in the above configuration, even if the apex angle accuracy of the triangular prisms is good, it is necessary to position each of the optical elements consisting of the triangular prisms 32 and 33 and the optical element consisting of the triangular prisms 35 with high precision, and such positioning requires If there is any variation, the parallelism between the polarized beam splitting surface 31 and the reflecting surface 34 cannot be obtained with high precision, resulting in a decrease in the parallelism of the emitted light after separation.

In this regard, as shown in FIG. 7, if a prism 36 whose cross section is a parallelogram and a triangular prism 37 are used in combination, if the parallelism of the end faces is obtained at the manufacturing stage of the prism 36, polarized light will be generated. Is the parallelism between the beam splitter 31 and the reflecting surface 34 stable? Since the reflected light (measuring light) and the passing light (reference light) on the polarized beam splitting surface are emitted from different end faces of the prism, both end faces The parallelism of the prisms became a problem, and it was difficult to stably obtain separated beams that were parallel to each other due to variations in the parallelism of the joint surfaces and variations in the apex angle accuracy of the triangular prism.

The present invention was made in view of the above-mentioned problems, and uses a parallel plate-like prism, which can achieve parallelism accuracy relatively easily compared to the apex angle accuracy of a triangular prism. Two lights can be transmitted without requiring high apex angle accuracy or joining accuracy of the triangular prism.
It is an object of the present invention to provide a polarizing beam splitter that can produce highly accurate parallel beams, and to provide a laser interferometric length measuring meter that takes advantage of the characteristics of the polarizing beam splitter.

<Means for Solving the Problems> Therefore, in the polarizing beam splitter according to the present invention, a reflective surface is formed on one side of both end faces facing each other in parallel of a parallel plate-like prism, and a polarizing surface is formed on the - portion of the other surface. A beam split coat is applied, and a triangular prism is bonded to the end face on which the polarizing beam split coat is applied, and the reflected light from the polarizing beam splitter is reflected by the reflective surface to form a polarizing beam split coat on the other side. The polarizing beam split coat is configured such that the light passes through an uncoated transparent portion and enters the triangular prism, and the reflected light and the transmitted light from the polarizing beam split coat are configured to exit from the same end face of the triangular prism.

Further, the laser interferometric length measuring meter according to the present invention uses the polarizing beam splitter to separate the light beam from the light source into a mutually parallel reference beam and a length measuring beam, and also separates the reference beam reflected by a fixed mirror and the length measuring beam attached to the measuring object. The length measuring light reflected by the movable mirror is returned to the polarizing beam splitter and combined to obtain an emitted light parallel to the light beam of the light source.

<Function> According to the polarizing beam splitter having such a configuration, since the parallelism of both end faces of the parallel plate-shaped prism facing each other can be achieved relatively easily and with high precision, the polarizing beam splitting coat provided on each of the both end faces Parallelism with the reflecting surface can be obtained. Therefore, the light passing through the polarizing beam split coat and the reflected light enter the triangular prism in a parallel state with high accuracy, and since they exit from the same end face when exiting the triangular prism, the apex of the triangular prism The angular accuracy does not affect the parallelism between the reflected light and the passing light, and the light is emitted from the polarizing beam splitter while maintaining a highly accurate parallel state.

If such a polarizing beam splitter is used in a laser interferometric length measurement meter to separate the reference light and measurement light and combine the returned light, the parallelism of the reference light and measurement light can be adjusted with accuracy. Since the returned light is well-obtained, the returned light is well combined, and the length can be measured based on the emitted light that is parallel to the light beam from the light source.

<Example> The present invention will be explained in detail below.

In FIG. 1 showing an embodiment of the polarizing beam splitter according to the present invention, the polarizing beam splitter (2) is composed of a parallel plate prism 2 and a triangular prism 3.

The parallel plate-like prism 2 has a trapezoidal cross section, and has one end surface 2 of both end surfaces 2a and 2b that face each other in parallel.
Both side surfaces 2c and 2d are formed so as to form an included angle θ of 45° with respect to a.

A reflective surface (total reflection surface) 3 is formed on substantially the entire surface of the end surface 2b, and a polarizing beam split coat 4 is applied to approximately half of the end surface 2a on the end surface 2C side.

In this way, the triangular prism 5 is joined to the parallel plate prism 2 provided with the reflective surface 3 and the polarizing beam split coat 4. The bottom surface 5a, which is formed in a cross section and faces the vertical apex angle, and the end surface 2a of the parallel plate-like prism 2 are joined with an adhesive.

In the polarizing beam splitter 1 having such a configuration, the polarizing beam splitter coat 4 is arranged so that a light beam (for example, a laser beam) from a light source (not shown) enters the end surface 2c of the parallel plate prism 2 at a substantially right angle. Light is incident at an angle of incidence of 45°.

The light reflected by the polarized beam split coat 4 (hereinafter referred to as
It is simply called reflected light. ) is incident on the reflective surface 3 parallel to the polarized beam split coat 4 at an incident angle of 45° and is reflected, so the reflected light from the reflective surface 3 and the luminous flux from the light source become parallel rays, The light reflected by the reflective surface 3 passes through a transparent portion of the end surface 2a that is not coated with the polarizing beam split coating 4, and enters the triangular prism 5.

Here, since the parallel plate prism 2 and the triangular prism 5 are made of materials with the same refractive index, the light passing through the polarizing beam split coat 4 (hereinafter simply referred to as passing light) and the reflecting surface 3 When the reflected light enters the triangular prism 5, it is not refracted and travels straight in a parallel state to one of the end surfaces 5 of the triangular prism 5, which sandwich the apex angle.
The light is emitted from b.

In this configuration, both parallel end surfaces of the parallel plate prism 2 can be processed relatively easily and with high precision, and the reflecting surface 3 and the polarizing beam split coat 4 provided on the parallel end surfaces of the parallel plate prism 2, respectively, can be processed with high accuracy. Since the parallelism can be obtained with high precision, it is ensured that the incident light on the polarizing beam split coat 4 and the reflected light on the reflective surface 3 are parallel.

The incident light of such a polarized beam split coat 4,
Parallelism with the reflected light of the reflecting surface 3 remains unchanged even if the incident light from the light source is incident obliquely to the end surface 2c and refracted, so the accuracy of the included angle θ and the light source Even if there is variation in the positional accuracy, as long as the accuracy of the parallel surfaces of the parallel plate prism 2 and the flatness of each end surface are obtained, the transmitted light that passes through the polarizing beam split coat 4 and the polarizing beam split Parallelism with the reflected light reflected by the coat 4 and the reflective surface 3 can be maintained.

Furthermore, the reflected light and the transmitted light are connected to a polarizing beam splitter l.
When the light is emitted from the triangular beam, the same end face 5 of the rhythm 5
Since the light is emitted from b, it is possible to emit the light without disturbing the parallel state between the reflected light and the passing light, even if the accuracy of the apex angle of the triangular prism 5 or the joining precision of the triangular prism 5 and the parallel plate prism 2 is poor. . In other words, even if the end surface 5b is not perpendicular to the reflected light and the passing light, and the passing light and the reflected light are refracted at the end surface 5b, the two lights emitted from the same end surface 5b will have the flatness of the end surface 5b. This is because if the beams were held parallel, the beams would be refracted while remaining parallel.

According to the polarizing beam splitter 1 of this embodiment, if the flatness of each end surface (transmission surface) and the parallelism of both end surfaces of the parallel plate prism 2 are obtained, the apex angle of the triangular prism 3 is Even if there are variations in accuracy, positional accuracy between the light source and polarizing beam splitter 1, bonding accuracy, etc., the transmitted light and reflected light separated by the polarizing beam split coat 4 can be emitted as highly accurate parallel light. It is possible.

In the above embodiment, it is clear that parallelism of the passing light and reflected light can be obtained even if the included angle θ is set to 45° or other than this angle. It is also possible to construct a structure in which the light from the light source is inputted from the transmitting surface of the end surface 2b instead of having all the reflecting surfaces 3.

Note that the marks φ and ◎ in FIG. 1 indicate polarization directions perpendicular to each other.

FIG. 2 shows an example in which the polarizing beam splitter 1 shown in FIG. 1 is used in a laser interferometer.

Here, the polarizing beam splitter 1 generates laser light from a light source (not shown) or linearly polarized light with polarization planes perpendicular to each other.
and passes through the polarization beam split coat 4 by the polarization beam splitter 1 (the polarization direction is set to the second polarization direction).
The reference beam S is reflected by the polarized beam split coat 4 and the reflective surface 3 and is obtained as a ray parallel to the length measurement light P (the polarization direction is indicated by ◎ in Figure 2). ) and are separated into

reflected by the polarized beam split coat 4 and the reflective surface 3,
The reference beam S that passes through the transparent portion of the flat prism 2 that is not coated with the polarization beam split coat 4 and is emitted is a λ/2 phase plate (900 optical rotation After the polarization direction is converted to be orthogonal (into the matching direction in FIG. 2) by the plate II, it enters the corner cube prism 12. Polarized beam splitting surface 12 of the corner cube prism 12
a is orthogonal to the polarization direction shown in Figure 2◎
Since only the light in the polarization direction indicated by φ is allowed to pass through the polarization direction, the reference light S passes through the polarized beam split surface 12a as it is and then passes through the λ/4 phase plate 13. is converted into circularly polarized light.

The reference light S converted to circularly polarized light is reflected at a right angle by the fixed mirror 14, passes through the λ/4 phase plate 13 again, and is now reflected in the polarization direction by the polarized beam split surface 12a. It is converted to the polarization direction shown in ◎. Therefore, the reference light S returned from the fixed mirror 14 is reflected by the polarized beam splitting surface 12a and travels toward the fixed mirror 14 again by the reflecting surface (or total reflection surface) of the corner cube prism I2.

At this time, it is again converted into circularly polarized light by the λ/4 phase plate 13, reflected by the fixed mirror 14, and the reflected light, which is circularly polarized light, is changed to λ/4.
When passing back through the four-phase phase plate 13, the polarization direction is converted to the polarization direction indicated by Q, which is the passing polarization direction of the polarization beam splitting surface 12a. Therefore, the reference light S reflected twice by the fixed mirror 14 and returned to the corner cube prism 12 passes through the polarization beam splitter 12a as it is in a direction perpendicular to the output direction of the polarization beam splitter l. It is bent and reflected by the reflective surface (or total reflection surface) 15a of the triangular prism 15 in a direction parallel to the emission of the polarized beam splitter 1, and is returned to the polarized beam splitter 1 again.

The reference light S returned to the polarizing beam splitter 1 passes through the polarizing beam splitter coat 4, continues straight, and is emitted from the polarizing beam splitter 1 in parallel to the light beam from the light source.

On the other hand, the length measuring light P whose polarization direction is indicated by the middle passing through the polarized beam split coat 4 changes its direction at right angles at the triangular prism 15, passes through the polarized beam split surface 12a of the corner cube prism 12, and passes through the corner cube prism 12. It is reflected by the reflective surface of the prism 12.

The length measurement light P passes through the λ/4 phase plate 13, is converted into circularly polarized light, is reflected at right angles by a movable mirror 16 attached to the object to be measured, and passes through the λ/4 phase plate 13 again. Since it is converted to the polarization direction indicated by ◎ in the figure, it is reflected by the polarized beam split surface 12a,
Proceed again in the direction of the movable mirror 16.

At this time, it passes through the λ/4 phase plate 13 and is converted into circularly polarized light, or when it is returned from the movable mirror 16, it passes through the λ/4 phase plate 13 again, this time as shown by the middle in the figure. The polarized light is converted to the polarization direction, so it passes through the polarized beam splitting surface 12a of the corner cube prism 12, and is incident on the λ/2 phase plate (90° optical rotation plate) ll, where it is marked with ◎ in the figure. converted to the polarization direction shown.

Then, the parallel plate prism 2 of the polarizing beam splitter l
The reflected light passes through the transmitting part where the polarized beam split coat 4 is not applied and is reflected by the reflective surface 3, and the reflected light enters the polarized beam split coat 4, or it is reflected because the polarization direction is the reflective direction, and the reflected light is reflected by the reflective surface 3. It is combined with the reference light S and output from the polarizing beam splitter I, and enters a detector (not shown).

According to this configuration, since the parallelism of the reference light S and the length measurement light P separated by the polarizing beam splitter l can be obtained with high precision as described above, the parallelism of the returned light can also be maintained, and the returned light can be accurately combined. In addition, since the light from the light source and the light after length measurement are parallel, there is a large degree of freedom in setting the length measuring needle, which has the advantage of being easy to use. Also,
Polarizing beam splitter 1. corner cube prism 12
゜Fixed mirror 14. Since the constituent optical elements such as the movable mirror 16 can be arranged approximately in rows, the height in the vertical direction in the figure can be reduced, and each optical element can be made smaller, resulting in lighter weight.・Miniaturization becomes possible. Furthermore, since the optical path is shortened due to the miniaturization as described above, the influence of disturbances such as temperature changes is reduced, and the stability of length measurement is improved.

In addition, in FIG. 2, the optical path through which the light from the light source enters and the optical path through which the light after length measurement is emitted may be interchanged. Further, in the above configuration, the length measurement information may be detected by either an interference fringe counting method or a heterodyne method.

Figure 3 shows the laser interferometric length measuring meter shown in Figure 2, which has the same optical elements but with a different arrangement.
In the example shown in the figure, only the λ/2 phase plate (90° optical rotation plate) 11 is joined to the polarizing beam splitter 1, but in the example shown in Figure 3, a triangular prism 15 is also joined and integrated. . In this configuration, the separation and return of the reference light S and the length measurement light P are performed in the same manner as described above, except that the polarization beam splitter l, the λ/2 phase plate 11. triangular prism 1
If the element in which 5 is integrated is turned upside down and its orientation is changed by 90 degrees, it can be arranged as shown in Fig. 4 and perform the same action, so the optical path is changed as shown in Fig. 4. The polarizing beam splitter l, the λ/2 phase plate 11. If the element in which the triangular prism 15 is integrated can be selectively arranged at the position shown in FIG. 3 and the position shown in FIG. 4, it can be easily handled without adding a reflector or the like. It is something that can be done.

In addition, as mentioned above, the polarizing beam splitter 1. In the configuration in which the λ/2 phase plate ratio triangular prism 15 is integrated, the optical system is not limited to the joining positions shown in FIGS. 3 and 4, but the optical system can be similarly converted 90' at various combination positions. is possible.

<Effects of the Invention> As explained above, according to the polarizing beam splitter according to the present invention, the light reflected by the polarizing beam split coat and the light passing through the polarizing beam splitter can be separated depending on the apex angle accuracy and bonding accuracy of the triangular prism. Since it can be emitted as parallel light with high precision without any interference, when used in a laser interferometric length measurement meter, it becomes possible to accurately combine the returned light, and also to combine the light flux of the light source and the combined light after length measurement. Since the light is obtained as parallel light, the degree of freedom in setting the length measuring needle is improved, and the optical elements can be arranged substantially linearly, allowing for miniaturization.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an embodiment of a polarizing beam splitter according to the present invention, and FIG. 2 is a configuration showing the configuration and polarization characteristics of a laser interferometer according to the present invention using the polarizing beam splitter shown in FIG. 1. The schematic diagrams, FIGS. 3 and 4, are diagrams showing examples in which the optical element arrangement of the laser interferometric length meter shown in FIG. 2 has been changed, respectively. FIG. Each figure is a plan view showing an example of a conventional polarizing beam splitter. ■...Polarizing beam splitter 2...Parallel plate prism 3...Reflecting surface 4...Polarizing beam split coat 5...Triangular prism 11...
λ/2 phase plate 12...corner cube prism
13...λ/4 phase plate 14... Fixed mirror 1
5...Triangular prism 16...Movable mirror

Claims (2)

[Claims] (1) A reflective surface is formed on one of both parallel end faces of a parallel plate-like prism, and a portion of the other face is coated with a polarizing beam split coat, and the end face coated with the polarizing beam split coat is coated with a polarizing beam split coat. A triangular prism is joined to the polarizing beam splitter, and the reflected light from the polarizing beam splitter is reflected by the reflecting surface, passes through a transparent portion of the other surface that is not coated with a polarizing beam splitting coating, and enters the triangular prism. and a polarizing beam splitter configured such that reflected light and passing light on the polarizing beam split coat are emitted from the same end face of the triangular prism. (2) Using the polarizing beam splitter according to claim 1, the light beam from the light source is divided into a mutually parallel reference light and a length measurement light, and the reference light reflected by a fixed mirror and reflected by a movable mirror attached to a length measurement object. 1. A laser interferometric length measuring meter, characterized in that the length measuring light is returned to the polarizing beam splitter and combined to obtain an emitted light parallel to the luminous flux of the light source.