JPH01316629A - Measuring device for optical axis - Google Patents

Abstract

PURPOSE:To improve operability and to decide the direction of an optical axis with high accuracy by providing a monochromatic light source, a first and a second polarization elements. CONSTITUTION:A reference setting polarization element 18 is provided so as to make the side surface 11 and the bottom surface 19 thereof abut on an abutting means 16 and the surface 15 of a sample table and set to a quenching position where the polarization plane of a fixed polarization element 12 is orthogonal to that of the element 18 by rotating the sample table 14. Then, the angle of the sample table 14 at this time is read. After that, the element 18 is removed and a movable polarization element 22 is arranged at the quenching position where it is orthogonal to the element 12 by placing or rotating the movable polarization element 22. Next, an object 24 to be measured is arranged on the surface 15 of the sample table by making the reference surface 25 of the object 24 to be measured butt on the means 16 and making the plane surface 27 of the object 24 to be measured abut on the surface 15 of the sample table. Then, the angle of the sample table 14 is read by rotating the sample table 14 and setting it to the quenching position, that means, the matching position where the fixed polarization plane of light which is made incident on the object 24 to be measured and the optical axis 26 of the object 24 to be measured coincide each other.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a measuring device for determining the direction of an optical axis of a crystal or the like.

Recently, composite prisms of various shapes have been widely used as components of optical pickups in the field of optical disks and magneto-optical disks. The number of composite prisms that incorporate a 174-wave plate or a 1/2-wave plate made of uniaxial crystal quartz is increasing, and the reference plane of this wavelength plate is bonded so that the reference plane of the prism coincides with the reference plane of the prism. There is. In this case, in order to improve the precision of the composite prism, it is necessary to accurately bond the optical axis of the wave plate at a predetermined angle with respect to the reference surface of this prism. therefore.

There is a demand for highly accurate measurement of the inclination angle between the reference plane of the wave plate itself and the optical axis.

(Prior Art and Problems to be Solved by the Invention) The above-mentioned crystal has two orthogonal axes called optical axes, which are called a fast axis and a slow axis. Light passing along the fast axis travels faster than light passing along the slow axis.

Using this principle, by appropriately setting the thickness of the wave plate, it is possible to create a wave plate having an arbitrary phase difference in the directions of the two axes.

As shown in FIGS. 1(a) and 1(b), the actual wave plates 1 and 2 are set at certain angles with respect to their optical axes S and F with respect to the reference cut planes, that is, the reference planes 3 and 4. It is made in

Furthermore, the wave plates 1 and 2 are flat and have flat surfaces 5 and 6.

By using such a wave plate, it is possible to create an arbitrary elliptical polarization state for incident light. Therefore, the accuracy of this type of wave plate is determined by the processing accuracy when cutting out the reference surfaces 3 and 4 from the crystal. However, at present, there is no method for accurately and efficiently measuring the inclination angle between the reference surfaces 3, 4 and the optical axes F, S after cutting.

Conventionally, this tilt angle has been measured using a polarization spectrometer.

Measurements are performed using the principle that if polarized light with a plane of polarization perpendicular or parallel to the optical axis of the wave plate is incident on this wave plate, the polarized light that passes through the wave plate will remain in the same polarization state. was.

However, there has been no simple method or device for aligning the plane of the sample stage of this polarization spectrometer with the plane of polarization of the polarizer in advance. In other words, it was possible to match the optical axis and polarization plane relatively easily, but the adjustment was complicated and inefficient because the polarization plane of the polarizer was made parallel to the plane of the sample stage, that is, the reference plane of the wave plate. was doing.

Moreover, in order to match the optical axis and polarization plane.

The extinction point was determined by gradually rotating the polarizer and analyzer, and this process was repeated until the first angular difference was reached where the polarizer and analyzer were perpendicular to each other.

Therefore, in order to obtain measurement results with good reproducibility, it was necessary to repeat inefficient operations, and moreover required skill.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of such conventional methods and to provide a measuring device that can determine the direction of the optical axis with good workability and high precision.

(Principle and Examples) The principle and Examples of the present invention will be described with reference to the drawings.

FIG. 2 is a diagram showing the basic concept of this invention. The measuring device of the invention comprises a monochromatic light source 10 for providing an incident light beam.
and a first fixed polarized light disposed on the optical path of this incident light beam, fixed with respect to the optical axis 26, and for setting the polarization plane of the incident light beam to a certain plane (fixed polarization plane) parallel to the optical axis 26. a cable 12, disposed on the optical path of the incident beam;
a second movable polarizing element 22 rotatably or detachably fixed around the optical axis 26 for setting its plane of polarization to a certain plane parallel to the optical axis 26; and these two polarizing elements 12.2.
2 and has a surface 15 perpendicular to the optical axis 26 on which the object to be measured is placed.

A sample stage 14 capable of rotating an object to be measured 24 around an optical axis 26 and having means for reading the rotation angle and an aperture 28 through which an incident light beam can pass, and fixed on the sample stage. A surface, a line, or a point on which the reference surface 25 of the object to be measured 24 comes into contact.

Tsukishima part 1 in the plane parallel to the optical axis (abutment reference plane)
7, and a light receiving means 20 for detecting the intensity of light transmitted through the polarizing element 12 and the like.

Next, a measurement method using the apparatus of the present invention will be explained.

As shown in FIG. 2(a), the side surface 1 of the reference setting polarizing element
The reference setting polarizing element 18 is arranged so that the reference setting polarizing element 18 and the bottom surface 19 are in contact with the abutting means 16 and the sample stage surface 15, and the sample stage 14 is rotated so that the polarization planes of the fixed polarizing element 12 and the reference setting polarizing element 18 are perpendicular to each other. The angle of the sample stage 14 at this time is read. In FIG. 2(a), the light source 10
Although the fixed polarizing element 12 is arranged on the side, the fixed polarizing element 12 may be placed at the second position on the light receiving means 20 side.

In this case, the movable polarizing element 22 is placed at the first position on the light source 10 side.
will be placed. Further, although the movable polarizing element 22 is removed, it may be rotated so that it has a polarization plane in the same direction as the fixed polarization plane.

This stage is characterized by the use of a reference setting polarizing element 18,
This polarizing element 18 has a bottom surface 19 that contacts the sample stage surface 15.
This is a polarizing element having a side surface 11 for contacting the abutting step 16, and has a function of polarizing the incident light beam incident on the bottom surface 19 into a component perpendicular to the side surface 11.

By making the polarization plane of the reference setting polarizing element 18 perpendicular to the fixed polarization plane, the fixed polarization plane becomes parallel to the side surface of the reference setting polarizing element 18, that is, the surface of the protruding island portion 17. Therefore, the optical polarization plane of the fixed polarizing element 12 can be made to coincide with the structural plane of the protruding island portion 17.

Next, as shown in FIG. 2(b), the reference setting polarizing element 18
is removed, and the movable polarizing element 22 is placed or rotated and placed at an extinction position orthogonal to the fixed polarizing element 12. This stage is preparation for the next stage.

Next, as shown in FIG. 2(c), the reference surface 25 of the object to be measured 24 is brought into contact with the abutment step 16, and the flat surface 27 of the object to be measured is brought into contact with the sample table surface 15, so that the object to be measured 24 is placed on the sample. The sample table 14 is placed on the table surface 15, and the sample table 14 is set at the extinction position, that is, the matching position where the fixed polarization plane of the incident light on the object to be measured 24 and the optical axis of the object to be measured coincide. Read the angle of 14.

At this stage, it is utilized that a parallel beam having a polarization plane parallel or perpendicular to the optical axis does not change its polarization state, and the optical polarization plane of the fixed polarizing element 12 is
When aligned with the optical axis of the light receiving means, the transmitted light detected by the light receiving means becomes minimal.

The angular difference read in FIG. 2(a) and FIG. 2(Q) becomes the inclination angle between the optical axis of the object to be measured and the reference surface 25.

The reason why this angle of inclination is given is as shown in Fig. 2 (a).
This means that the reference plane of the object to be measured and the fixed polarization plane are made parallel through the protruding island portion 17, and the optical axis of the object to be measured and the fixed polarization plane are made parallel to each other in FIG. 2(c). This is because the angle at which the sample stage, that is, the object to be measured, is rotated between these two cases is the inclination angle between the optical axis of the object to be measured and the reference plane.

In addition, in continuous measurements, Fig. 2 (a) and (c)
These steps are not necessarily necessary. Figure 2 (a
) and keep the movable polarizing element 22 at the extinction position with respect to the fixed polarizing element 12 as shown in Fig. 2(b), then only the measurement operation shown in Fig. 2(c) is possible. The angle of inclination between the optical axis and the reference plane can be determined repeatedly for a large number of samples.

In addition, in FIG. 2(a), the protruding island portion is parallel to the fixed plane of polarization, but it can be made perpendicular or at other angles. However, in this case, the calculation results must be corrected by 90° or other angles.

FIG. 3 shows an embodiment of the measuring device of the present invention.

This shows the state before the sample is placed.

The monochromatic light source section 32 of this optical axis measuring device 30 consists of a laser light source 50, a slit 52, and a chopper 54. Although a GaAs semiconductor laser is used as the laser light source 50, a broadband light source, a bandpass filter, etc. may be used in place of the semiconductor laser 50 in combination. The slit 52 serves to narrow down the monochromatic light beam from the laser light source 5° and block stray light.
4 is driven by a motor 56 at a constant rotation speed around a shaft 53. The chopper 54 has unevenness (not shown) around its periphery 55, and the monochromatic light source 3
The output beam of the light source section 32 is intermittently interrupted, and the beam output of the light source section 32 is converted into a sawtooth wave or the like with a constant frequency.

, the collimator lens 6o converts the beam from the monochromatic light source 32 into a parallel beam, and the 1-reflection mirror 64 converts the traveling direction of the parallel beam from the horizontal direction to the vertical direction, and converts the beam from the monochromatic light source section 32 into the optical axis 66.
Proceed along. A filter 62 is arranged between the collimator lens 60 and the reflection mirror 64, and is used to adjust the intensity of the parallel beam.

The polarizer 70 directs the parallel beam from the monochromatic light source 32 to an axis 66.
It is a means for polarizing light within a predetermined plane along the
BS: I will explain the details later. ) is used.

The sample stage section 38 includes a sample stage 74, an abutment plate 76, an angle reading device 82, and a sample stage support section 87. The sample stage 74 is rotatably supported by a sample stage support part 87, and this rotation axis is parallel to the optical axis 66. Referring to FIGS. 4(a) and 4(b), a sample stage surface 75 on which the object to be measured is placed is processed into a flat surface, and the surface 75 is perpendicular to the optical axis 66. Further, the sample stage 74 has an aperture 80 that determines the aperture of the parallel measuring beam, and this cylindrical opening 80 extends downward from the sample stage surface 75. A rectangular parallelepiped abutment plate 76 is fixed at a position close to the opening 80 on the sample stage surface 75, and its side surface 77 on the side closer to the opening 80 is a flat surface. This side surface 77 is called an abutting reference surface 77, and is set in advance to be precisely orthogonal to the sample stage surface 75. Note that the object to be measured 24 is arranged as shown by the dotted line.

Referring again to FIG. 3, the sample stage 74 and its support 87
An angle encoding device 87 is provided on the outer periphery of the sample stage 74, and information regarding the rotation angle of the sample stage 74 can be obtained from the rotation direction and angle encoding signal. Note that the sample stage 74 is provided with a motor 83 in order to actively rotate the sample stage 74.

The parallel beam passing through the sample stage 74 advances to the analyzer section 40 , which is composed of an analyzer 84 , an analyzer jig 86 , and an analyzer support section 89 . Analyzer (PBS
) 84 is held by an analyzer jig 86 so that its lower surface is perpendicular to the optical axis 66. Further, the analyzer jig 86 has a rotation bearing (not shown) between it and the analyzer support part 9 for rotating the analyzer (PBS) 84 around the optical axis 66. Note that the analyzer jig 86 includes an analyzer 8
A motor 85 is provided to rotate 4. This analyzer can transmit only a specific polarized light component parallel to the optical axis 66 among the parallel beams that have passed through the polarizer and the object to be measured.

A condenser lens 88 is arranged directly above the analyzer section 40 so as to focus the parallel beam transmitted through the analyzer 84 onto a light receiving surface 92, which will be described below.

The light receiving section 44 is arranged on the condenser lens 88, and the photoelectric conversion element 94 of the silicon photodiode of the light receiving section 44 is disposed on the condenser lens 88.
An image of the light emitting part of the laser 50 is formed on the light receiving surface 92 of the laser 50 . The electrical output of the photoelectric conversion element 94 is amplified in synchronization with the cutoff frequency of the chopper 54 in order to remove noise components from an external light source. This noise removal method is well known to those skilled in the art. The amplified signal from this photoelectric conversion element 90 is input to a peak detection circuit 95.

The signal processing of this device will be explained according to the block diagram in FIG. First, the measurement and processing of the rotation angle of the sample stage 74 will be described.1 An instruction to start measurement is sent to the control circuit 100 from the display/input device 99. The control circuit 100 starts driving the motor 83 via the motor drive circuit B97. The sample stage 74 rotates around the optical axis 66, and during this rotation, the peak detection circuit 95 is activated and detects the minimum value of the amplified signal from the element 90. For example, when the polarization planes of the polarizer 70 and the reference setting polarizing element 18 on the sample stage 74 are perpendicular to each other, the above signal becomes extremely small and a trigger signal is generated from the detection circuit 95, and this trigger signal is transmitted to the control circuit 100 and the motor. The motor is stopped via drive circuit B. Incidentally, when the motor is rotating, the pulse output from the angle encoding device 82 is input to the angle reading circuit 98.

Converted to angle information. The control circuit 100 stores this angle information when the motor 83 rotates.

Further, if necessary, the angle of rotation of the sample stage 74 can be converted and displayed on the display device 99. When determining the extinction position, the control circuit can be provided with a function of determining a more accurate extinction angle by repeating a reciprocating rotational movement at the extinction position.

Second, the rotation of the analyzer 84 and its control will be described. In this case as well, the rotation is similar to the rotation of the first sample stage 74, but instead of the motor drive circuit B, the motor drive circuit A96 operates. Further, the output of the angle readout circuit 98 is not stored.

When it is desired to stop the analyzer 84 perpendicular to the polarizer 70, a peak detector 95 detects the minimum value of the signal from the element 94 and generates a trigger signal. Also, when it is desired to stop the analyzer 84 in a state parallel to the polarizer 70, the peak detector detects the maximum value of the signal from the element 94 and generates a trigger signal. These trigger signals stop the rotation of the motor 85.

Measurement using such a device is performed as follows.

(1) Before placing the object to be measured on the sample stage, the motor 85 performs a test until the polarization planes of the polarizer 70 and analyzer 84 become parallel and the output of the light receiving section 44 reaches its maximum value. Rotate photon 84. Or analyzer 84 instead of one revolution
is removed from the device 30.

(2) Place the reference setting polarizing element (indicated by reference numeral 18 in FIG. 2) so that its bottom surface touches the sample table surface 75, and place the side surface 11 of the reference setting polarizing element on the abutment reference surface 77. Let them come into contact with you.

(3) While the reference setting polarizing element is placed on the sample stage 74, the sample stage 74 is rotated by the motor 83 to find the extinction position where the polarization planes of the reference setting polarizing element 18 and the polarizer 70 are perpendicular to each other. It is stopped at a position where the output of the light receiving section 44 becomes minimum.

(4) The angle information of the sample stage 74 at this time is read out from the angle reading circuit and stored.

(5) Remove the reference setting polarizing element 18 from the sample stage 74.

(6) The analyzer 84 is rotated by the motor 85, and the polarizer 7
The analyzer 84 is moved by the motor 85 until it reaches the zero and extinction position, that is, until it detects that the output of the light receiving section 44 has reached its minimum value.
Rotate.

(7) Wave plate of the object to be measured on the sample table surface 75 (see Figure 1)
The wave plates 1 and 2 are placed with the planes 5 and 6 of the wave plates in contact with each other, and the reference plane 3.4 of the wave plate in contact with the abutting reference surface 77.

(8) While rotating the sample stage 74 by the motor 83, the rotation is stopped at a position where the polarization plane of the polarizer 7o and the optical axes F and S of the wavelength plate 1°2 are parallel to each other, that is, at the extinction position.

(9) The angle reading circuit 9 reads the angle information of the sample stage 74 at this time.
8 and stored in the read control circuit 100.

(10) The angle at which the sample stage moved is calculated from the difference between the angle information stored in (4) and the angle information stored in (9). This is the reference planes 3 and 4 of the wave plates 1 and 2 and the optical axis F,
The result is the tilt angle of S, and the result is output on the display/input device.

(1) to (4) correspond to Fig. 2(a), and (5) and (6)
) corresponds to FIG. 2(b), and (7) to (10) correspond to FIG. 2(c).

The control circuit 1 repeats the operations (1) to (10) above.
00 may be configured, but if measurements are to be made on a large number of wavelength plates at one time, settings (1) to (6) should be made in advance, and settings (7) to (1) should be made for each wave plate.
By configuring the control circuit 100 to repeat the operation 0), sufficient power training accuracy can be obtained.

In the embodiments described above, the polarizer 70 is fixed, but it may be made rotatable along the optical axis 66, in this case (1).

In operation (6), the polarizer 70 is rotated or detached instead of the analyzer 84.

Here, the reference setting polarizing element 18 used in the measurement of the present invention will be explained. Such a reference setting polarizing element may be a polarizing element made of calcite or the like whose side surface is processed with high precision, but the following will be described. By utilizing the optical characteristics and shape characteristics of PBS, measurement accuracy can be easily improved.

A PBS 107 is shown in FIG. 5(a). P.B.
S has a structure in which 45° and 90° triangular prisms 101 and 102 are bonded together with an adhesive 104, and a dielectric multi-JFiJ film 103 is applied to one of them.

FIG. 5(b) shows the polarization effect of PBS. When the incident light 110 is perpendicularly incident on the plane 106 of the PBS, the light 112 reflected by the multilayer film surface 108 becomes S-polarized light. Further, the transmitted light 114 travels straight and becomes P-polarized light having a polarization plane parallel to the bottom surface 105 of the PBS in the figure.

When PBS is used as a polarizer, it is possible to increase the processing accuracy, thereby reducing the optical path deflection angle, and furthermore, the side surface 11 whose outer surface, ridges, etc. are in contact with the abutting plate 16 Can be used as As a result, more accurate measurement results were obtained than measurements using calcite or the like.

In the above embodiment, the abutting plate 76 is illustrated as a plate-shaped material, but it may have a straight line portion substantially parallel to the sample stage surface 75 or be composed of two points to restrict movement on the sample stage 74. Preferably, the shape is arbitrary. Furthermore, it is also possible to give this abutting plate 76 a polarizing function, by enlarging the opening 80 of the sample stage 74 and fixing a PBS or the like so as to span this opening 80, one side of this PBS can be abutted. It can be used as a reference surface 77. As a result, base P! The effort of attaching and detaching the PBS as the setting polarizing element 18 can be saved.

Furthermore, a mirror or the like may be provided on the optical path of the device 30 to change the optical path. For example, if a glass plate or the like is used as a polarizing element, it is necessary to reflect the light at Bruce's polygon, resulting in a shape that is quite different from the above-mentioned device.

It goes without saying that many other variations are possible.

The first feature of using the above-mentioned measuring device is that the reference plane 25 of the object to be measured 24 and the polarization plane of the fixed polarizing element 12 can be easily determined by a very simple operation (see FIG. 2(a)). and secondly, a single operation (Figure 2 (C
)) allows the optical axis of the object to be measured 24 to match the polarization plane of the fixed polarizing element 12, and the inclination angle of the optical axis of the object to be measured 24 can be easily determined.

In addition to the above points, if the entire apparatus is made vertical, it is possible to easily measure flaky samples. Furthermore, the measuring device of the present invention is not limited to plate-shaped samples.
In other words, even in a cubic uniaxial crystal sample, by performing the above measurements from two directions, the three-dimensional arrangement of the optical axis can be easily determined.

[Brief explanation of the drawing]

Figures 1(a) and 1(b) are schematic diagrams showing flat wave plates machined with different reference planes relative to the optical axis, where the S axis represents the slow axis and the F axis represents the fast axis. It shows. FIGS. 2(a), (b), and (c) are conceptual diagrams of optical axis measurement using the device of the present invention, and each conceptual diagram (a), (b),
(c) briefly shows the main steps of the measurement. FIG. 3 is a schematic configuration diagram of an optical axis measuring device used for measurement according to the present invention. Figure 4 shows the main parts of the sample stage of the optical axis measuring device shown in Figure 3. Figure 4 (a) is a top plan view of the sample stage, and Figure 4 (b) is a top plan view of the sample stage. FIG. FIG. 5(a) is a cross-sectional view schematically showing the structure of the PBS, and FIG. 5(b) is a schematic perspective view showing the polarization function of the PBS. [Explanation of symbols of main parts] 1.2・・・・・・・・・・・・・・・・・・・
・・・・・・Wave plate 3.4・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・Reference surface 5.6・・・・
・・・・・・・・・・・・・・・・・・・・・・・・・Plane S・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・Low speed axis F・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・High speed axis 1
0・・・・・・・・・・・・・・・・・・・・・
・・・・Monochromatic light source 12.22・・・・・・・・・・・・
......Polarizing element 14...
・・・・・・・・・・・・・・・・・・・・・Sample stand 1
5・・・・・・・・・・・・・・・・・・・・・・・・
...Sample white surface 16...
......Abutment means 17...
・・・・・・・・・・・・・・・・・・Tsukishima part 1
8・・・・・・・・・・・・・・・・・・・Reference setting polarizing element 19・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・Bottom 20・・・・・・・・・
・・・・・・・・・・・・・・・・Light receiving means 24
・・・・・・・・・・・・・・・・・・Object to be measured (optical element) 26・・・・・・・・・・・・・・・・・・・・・
......Optical axis Figure 1 (d) (b> Figure 2 (α) (b) (C) 3rd
figure

Claims (1)

[Claims] 1. In order to measure the inclination angle between the optical axis of an optical element having two opposing parallel planes and a reference plane intersecting the planes and the reference plane, a monochromatic light source and the monochromatic light source are used. A first polarizing element arranged in order on the optical path from the light source, a sample stage for holding the optical element so that the plane is perpendicular to the optical axis of the optical path, and a second polarizing element. An optical axis measuring device, wherein the reference plane of the optical element is abutted within an abutment reference plane that is parallel to the optical axis and makes a predetermined angle with the polarization plane of the first or second polarizing element. an abutting means for positioning the optical element, a rotation means for rotating the positioned optical element around an optical axis, and an amount of rotation of the optical element until the optical axis and the plane of polarization coincide with each other; 1. An optical axis measuring device comprising: reading means for reading.