JPH0810175B2 - Method and apparatus for measuring tilt angle between optical element reference plane and optical axis - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for measuring a tilt angle between a reference plane and an optical axis of an optical element such as a crystal or a half-wave plate.

Recently, in the fields of optical disks and magneto-optical disks, composite prisms of various shapes have been widely used as components of optical pickups. Increasing numbers of compound prisms incorporate a quarter-wave plate or a half-wave plate of quartz, which is a uniaxial crystal, and bond them so that the reference surface of this wave plate and the reference surface of the prism match. Has been done. In this case, in order to improve the accuracy of the compound prism, it is necessary to accurately bond the optical axis of the wave plate to the reference surface of the prism at a predetermined angle. Therefore, there is a demand for measuring the tilt angle between the reference plane of the wave plate itself and the optical axis with high accuracy.

(Problems to be Solved by Prior Art and Invention) In the crystal as described above, there are two axes which are called an optical axis and which have an orthogonal relationship, and they are called a fast axis and a slow axis.
Light passing in the fast axis direction travels faster than light passing in the slow axis direction. Using this principle, a wave plate having an arbitrary phase difference in the biaxial directions can be produced by setting the thickness of the wave plate appropriately.

As shown in FIGS. 1 (a) and 1 (b), actual wave plates 1, 2
Are designed such that their optical axes S and F are set at a certain angle with respect to the reference cutting planes, that is, the reference planes 3 and 4. Further, the wave plates 1 and 2 are flat and have flat surfaces 5 and 6. By using such a wave plate, an arbitrary elliptically polarized state can be generated for incident light. Therefore, the accuracy of this type of wave plate is determined by the processing accuracy when the reference planes 3 and 4 are cut out from the crystal. However, the reference plane after cutting 3,
At present, there is no method for accurately and efficiently measuring the tilt angle between the 4 and the optical axes F and S.

Conventionally, this tilt angle has been measured using a polarization spectrometer. When polarized light having a plane of polarization perpendicular or parallel to the optical axis of the wave plate enters this wave plate, measurement is performed using the principle that the polarized light that has passed through the wave plate is kept in the same polarization state. Was there.

However, there has been no simple method and apparatus for preliminarily matching the plane of the sample stage of this polarization spectrometer with the plane of polarization of the polarizer. In other words, the optical axis and the plane of polarization could be matched relatively easily,
In order to make the polarization plane of the polarizer parallel to the plane of the sample table, that is, the reference plane of the wave plate, complicated and inefficient adjustment was performed.

Moreover, in order to match the optical axis with the plane of polarization, the extinction point was obtained while gradually rotating the polarizer and the analyzer, and this was repeated until the first angular difference between the polarizer and the analyzer was reached. For this reason, in order to obtain a measurement result with good reproducibility, it is necessary to repeat inefficient work, and moreover skill is required.

An object of the present invention is to eliminate the drawbacks of the conventional method and to provide a measuring apparatus which can determine the direction of the optical axis with good workability and high accuracy.

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

FIG. 2 is a diagram showing the basic concept of the present invention. The measuring device of the present invention comprises a monochromatic light source 10 for providing an incident light beam.
And a first fixed polarization that is arranged on the optical path of this incident light beam and is fixed with respect to the optical axis 26 and that sets the plane of polarization of the incident light beam to a plane parallel to the optical axis 26 (fixed polarization plane). The element 12 and the optical axis 26 arranged in the optical path of the incident beam.
Between the two movable polarization elements 12 and 22, and a second movable polarization element 22 for setting its polarization plane rotatably or detachably fixed around to a plane parallel to the optical axis 26, Having a surface 15 perpendicular to the optical axis 26 for mounting an object to be measured, the object to be measured 24 can be rotated around the optical axis 26, means for reading the rotation angle and the incident light beam. A sample table 14 having an opening 28 capable of transmitting
A protrusion which is fixed on the sample table and has a contact portion 17 which is a surface or a line or a point for contacting the reference surface 25 of the DUT 24 and which is in a surface (abutting surface) parallel to the optical axis. This means
16 and a light receiving means 20 for detecting the intensity of light passing through the polarizing element 12 and others.

Next, a measuring method using the apparatus of the present invention will be described.

As shown in FIG. 2 (a), the side surface of the reference setting polarizing element
The reference setting polarization element 18 is arranged so that the 11 and the bottom surface 19 contact the abutting means 16 and the sample table surface 15, and the sample table 14 is rotated to make the polarization planes of the fixed polarization element 12 and the reference setting polarization element 18 orthogonal to each other. The extinction position is set as described above, and the angle of the sample table 14 at this time is read. In FIG. 2A, the fixed polarizing element 12 is provided on the light source 10 side.
, But the fixed polarizing element 12 may be provided at the second position on the side of the light receiving means 20. In this case, the movable polarization element 22 is arranged at the first position on the light source 10 side. Although the movable polarization element 22 is removed, it may be rotationally arranged so as to have a polarization plane in the same direction as the fixed polarization plane.

This stage is characterized by the use of the standard setting polarization element 18,
The polarizing element 18 is a polarizing element having a bottom surface 19 that contacts the sample table surface 15 and a side surface 11 that contacts the abutting means 16, and makes the incident light beam incident on the bottom surface 19 into a component perpendicular to the side surface 11. It has a function of polarization.

By thus making the polarization plane of the reference setting polarization element 18 orthogonal to the fixed polarization plane, the fixed polarization plane becomes parallel to the side surface of the reference setting polarization element 18, that is, the surface of the abutting portion 17. Therefore, the optical polarization plane of the fixed polarizing element 12 is abutted with the abutting portion 17
Can be matched to the structural aspects of.

Next, as shown in FIG. 2B, the reference setting polarization element 18
Then, 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 a preparation for the next stage.

Then, as shown in FIG. 2 (c), the reference surface 25 of the object to be measured 24 is brought into contact with the abutting means 16 so that the flat surface 27 of the object to be measured is brought into contact with the sample base surface 15 to sample the object to be measured 24. The sample table 14 is placed on the table surface 15, and the sample table 14 is rotated to set the extinction position, that is, the alignment position where the fixed polarization plane of the incident light to the object to be measured 24 and the optical axis of the object to be measured match. Read 14 angles.

At this stage, the fact that a parallel beam having a plane of polarization parallel or perpendicular to the optical axis does not change its polarization state is utilized, and the optical plane of polarization of the fixed polarization element 12 is aligned with the optical axis of the DUT 24. In that case, the transmitted light detected by the light receiving means becomes minimum.

The angular difference read in FIGS. 2A and 2C is the tilt angle between the optical axis of the object to be measured and the reference plane 25.

The reason why this tilt angle is given is that the reference plane of the object to be measured and the fixed polarization plane are made parallel to each other via the abutting portion 17 in FIG. 2 (a), and in FIG. 2 (c), It means that the optical axis of the DUT and the fixed polarization plane are parallel.
This is because the angle at which the sample stage, that is, the measured object is rotated between the two cases is the tilt angle between the optical axis of the measured object and the reference surface.

Further, in the continuous measurement, the procedure of FIGS. 2 (a) and 2 (c) is not always necessary. Second in advance
If the angle of the sample stage is read in FIG. 2A and the movable polarization element 22 is left in the extinction position with respect to the fixed polarization element 12 in FIG. The tilt angle between the optical axis and the reference plane can be repeatedly determined for many samples only by the measurement operation.

Although the abutting portion is parallel to the fixed polarization plane in FIG. 2 (a), it may be vertical or at another angle. However, in this case, the calculation result must be corrected by 90 ° or another angle.

FIG. 3 shows an embodiment of the measuring apparatus of the present invention and shows a state before placing a sample.

The monochromatic light source unit 32 of the optical axis measuring device 30 is a laser light source.
50, slit 52, and chopper 54. Laser light source 50
Although a GaAs semiconductor laser is used as the semiconductor laser, a wide band light source and a bandpass filter or the like may be used in combination instead of the semiconductor laser 50. The slit 52 is for narrowing the monochromatic light beam from the laser light source 50 and blocking stray light. The chopper 54 is driven around the shaft 53 by a motor 56 at a constant rotation speed. The chopper 54 has irregularities (not shown) around its periphery 55, and the peripheral portion 55
Interrupts the output beam of the monochromatic light source unit 32 intermittently,
The beam output of the light source unit 32 is converted into a sawtooth wave having a constant frequency.

The collimator lens 60 converts the beam from the monochromatic light source unit 32 into a parallel beam, and the reflection mirror 64 converts the traveling direction of the parallel beam from the horizontal direction to the vertical direction and advances it along the optical axis 66. A filter 62 is arranged between the collimator lens 60 and the reflection mirror 64 to adjust the intensity of the parallel beam.

The polarizer 70 is a means for polarizing the parallel beam from the monochromatic light source unit 32 in a predetermined plane along the axis 66, and in this embodiment, a cube-type polarization beam splitter (PBS: will be described later in detail). ) Is used.

The sample table 38 includes a sample table 74, an abutting plate 76, and an angle reading device 82.
And a sample table supporting part 87. The sample table 74 is the sample table support
It is rotatably supported by 87, and its axis of rotation is parallel to the optical axis 66. Referring to FIGS. 4A and 4B, a sample table surface 75 on which an object to be measured is placed is processed into a flat surface, and the surface 75 is in a relationship perpendicular to the optical axis 66. Further, the sample table 74 has an opening 80 that determines the aperture of the parallel beam for measurement, and this cylindrical opening 80 is the surface of the sample table.
It extends downward from 75. A rectangular parallelepiped abutting plate 76 is fixed at a position close to the opening 80 on the sample table surface 75,
The side surface 77 near the opening 80 is a flat surface. This side
77 is called an abutting surface 77, and is preset so as to be orthogonal to the sample table surface 75 precisely. The DUT 24 is arranged as shown by the dotted line.

Referring again to FIG. 3, an angle encoding device 87 is provided on the outer circumference of the sample table 74 and its supporting portion 87, and information about the rotation angle of the sample table 74 is obtained from the rotation direction and the angle encoded signal. You can The sample table 74 is provided with a motor 83 for rotating the sample table 74.

The parallel beam that has passed through the sample table 74 advances to the analyzer unit 40.
The analyzer unit 40 is composed of an analyzer 84, an analyzer jig 86, and an analyzer support 89. The 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 is connected to the analyzer supporting portion 89.
And a rotary bearing (not shown) for rotating the analyzer (PBS) 84 around the optical axis 66. The analyzer jig 86 is provided with a motor 85 for rotating the analyzer 84. This analyzer can transmit only a specific polarization component parallel to the optical axis 66 of the parallel beams transmitted through the polarizer and the DUT.

Immediately above the analyzer unit 40, a condenser lens 88 is arranged so that the parallel beam transmitted through the analyzer 84 is focused on the light receiving surface 92 described below.

The light receiving section 44 is arranged above the condenser lens 88, and an image of the light emitting section of the laser 50 is formed on the light receiving surface 92 of the photoelectric conversion element 94 of the silicon photodiode of the light receiving section 44. 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 the noise component from the external light source. This denoising method is well known to those skilled in the art. The amplified signal from the photoelectric conversion element 94 is input to the peak detection circuit 95.

The signal processing of this device will be described with reference to the block diagram in FIG. First, the measurement and processing of the rotation angle of the sample table 74 will be described. An instruction to start measurement is sent from the display / input device 99 to the control circuit 100. The control circuit 100 starts driving the motor 83 via the motor drive circuit B97. The sample table 74 rotates around the optical axis 66, and during this rotation, the peak detection circuit
95 activates and detects a local minimum of the amplified signal from element 90. For example, when the polarization planes of the polarizer 70 and the reference setting polarization element 18 on the sample table 74 are orthogonal to each other, the above signal becomes a minimum and a trigger signal is generated from the detection circuit 95, and this trigger signal is generated by the control circuit 100 and the motor. The motor is stopped via the drive circuit B. When the motor rotates, the angle encoder 82
The pulse output from is input to the angle reading circuit 98 and converted into angle information. The control circuit 100 stores this angle information when the motor 83 rotates. If necessary, it can be converted into a rotated angle of the sample table 74 and displayed on the display device 99. When determining the extinction position, the control circuit can be provided with a function of obtaining a more accurate extinction angle by repeating the reciprocating rotary motion at the extinction position.

Secondly, the rotation of the analyzer 84 and its control will be described. Also in this case, the rotation is similar to the rotation of the first sample table 74, but the motor drive circuit A96 is operated instead of the motor drive circuit B. Further, the output of the angle reading circuit 98 is not stored. When it is desired to stop the analyzer 84 in a state orthogonal to the polarizer 70, the peak detector 95 detects the minimum value of the signal from the element 94 and generates a trigger signal. In addition, the analyzer is parallel to the polarizer 70.
When it is desired to turn off 84, the peak detector detects the local maximum of the signal from element 94 and generates a trigger signal. The rotation of the motor 85 is stopped by these trigger signals.

The measurement using such an apparatus is performed as follows.

(1) Before the object to be measured is placed on the sample stage, the polarizer 70 and the analyzer 84 are parallel to each other, and the motor 85 detects until the output of the light receiving unit 44 reaches the maximum value. Rotate photon 84. Alternatively, instead of rotating, the analyzer 84 is removed from the device 30.

(2) A standard setting polarizing element (denoted by reference numeral 18 in FIG. 2) is placed on the sample table surface 75 so that the bottom surface is in contact with the sample table surface 75,
The side surface 11 of the reference setting polarization element is brought into contact with the abutting surface 77.

(3) The extinction position where the polarization planes of the reference setting polarization element 18 and the polarizer 70 are orthogonal to each other while the reference setting polarization element is still mounted on the sample table 74 and the sample table 74 is rotated by the motor 83, that is, The light receiving unit 44 is stopped at a position where the output is minimal.

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

 (5) Remove the reference setting polarization element 18 from the sample table 74.

(6) The analyzer 84 is rotated by the motor 85, and the analyzer 84 is rotated by the motor 85 up to the extinction position with the polarizer 70, that is, until it is detected that the output of the light receiving unit 44 reaches the minimum value.

(7) Wave plate of the object to be measured on the sample table surface 75 (see Fig. 1)
Abutting the flat surfaces 5 and 6 of the wave plate, and the reference surface
And the wave plates 1 and 2 are mounted.

(8) While the sample table 74 is rotated by the motor 83, the rotation is stopped at the position where the polarization plane of the polarizer 70 and the optical axes F and S of the wave plates 1 and 2 are parallel, that is, the extinction position.

(9) The angle information of the sample table 74 at this time is read by the angle reading circuit 98.
It is stored in the read control circuit 100.

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

(1) to (4) correspond to FIG. 2 (a), and (5),
(6) corresponds to FIG. 2 (b), and (7) to (10) are the second.
It corresponds to FIG.

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

Although the polarizer 70 is fixed in the above-described embodiment, it may be rotatable along the optical axis 66.
In this case, in the operations (1) and (6), the polarizer 70 is rotated or detached instead of the analyzer 84.

Here, the reference setting polarization element 18 used for the measurement of the present invention will be described. As such a standard setting polarizing element, the side surface of the polarizing element such as calcite may be processed with high precision, but by using the optical characteristics and shape characteristics of PBS as described below, The measurement accuracy can be easily improved.

PBS 107 is shown in FIG. PBS has a structure in which 45 ° and 90 ° triangular prisms 101 and 102 are bonded together by an adhesive material 104, and one of them has a dielectric multilayer film 10
3 has been applied.

The polarization effect of PBS is shown in FIG. 5 (b). When the incident light 110 is vertically incident on the PBS plane 106, the multilayer film surface 108
The light 112 reflected by becomes S-polarized light. In addition, the transmitted light 114 travels straight and has a polarization plane parallel to the bottom surface 105 of the PBS in the figure.
It becomes polarized light.

When PBS is used as a polarizer, it is possible to increase the processing accuracy, thereby reducing the optical path deviation angle, and at the same time, the side surface 11 for the outer surface, the ridge, or the like to contact the abutting plate 16. Can be used as As a result, it is possible to obtain a measurement result with higher accuracy than the measurement using calcite or the like.

Although the abutting plate 76 is shown as a plate-shaped material in the above-described embodiment, it has a straight portion substantially parallel to the sample table surface 75 or is composed of two points to control the movement on the sample table 74. The shape is arbitrary if possible. Further, it is possible to make the abutting plate 76 have a polarization function, and by making the opening 80 of the sample stand 74 large and fixing PBS or the like so as to hang on the opening 80, one side surface of the PBS is abutted. It can be used as 77. This allows the standard setting polarization element 18
As a result, it is possible to save the trouble of attaching and detaching the PBS.

Further, 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 the polarizing element, it is necessary to reflect at a Brewster's angle, and the shape becomes considerably different from that of the above-mentioned device.

It goes without saying that many other modifications are possible.

The feature of using the measuring device as described above is that the first point is that the reference plane 25 of the DUT 24, the fixed polarization element 12 and the polarization plane are measured only by a very simple operation (FIG. 2 (a)). And the second point is a single operation (Fig. 2 (c)).
Thus, the optical axis of the DUT 24 can be matched with the polarization plane of the fixed polarization element 12, and the tilt angle of the optical axis of the DUT 24 can be easily determined.

In addition to the above points, if the entire apparatus is of a vertical type, it is possible to easily measure a flaky sample. further,
The measuring device of the present invention is not limited to a plate-shaped sample. That is, even in a cubic uniaxial crystal sample, the three-dimensional arrangement of the optical axes can be easily determined by performing the above measurement from two directions.

[Brief description of drawings]

1 (a) and 1 (b) are schematic views showing a flat plate-shaped wave plate processed with different reference planes with respect to the optical axis, where the S axis indicates a low speed axis and the F axis indicates a high speed axis. Is shown. 2 (a), (b), and (c) are conceptual diagrams of optical axis measurement using the device of the present invention, and conceptual diagrams (a) and (b), respectively.
(C) briefly shows the main steps of the measurement. FIG. 3 is a schematic configuration diagram of an optical axis measuring device used for the measurement of the present invention. FIG. 4 shows the main part of the sample table part of the optical axis measuring device of FIG. 3, FIG. 4 (a) is a top plan view of the sample table, and FIG. 4 (b) is the sample table. FIG. FIG. 5 (a) is a sectional view schematically showing the structure of PBS, and FIG. 5 (b) is a schematic perspective view showing the polarization function of PBS. [Explanation of symbols for main parts] 1,2 ...... Wave plate 3, 4 …… Reference plane 5, 6 …… Plane S …… Slow axis F …… Fast axis 10 …… Monochromatic light source 12, 22 …… Polarizing element 14 …… Sample stand 15 …… Sample stand surface 16 …… Abutting means 17 …… Abutting part 18 …… Reference setting polarization element 19 …… Bottom surface 20 …… Light receiving means 24 …… Measuring object (optical element) 26… …optical axis

Claims (6)

[Claims] 1. An apparatus for measuring an inclination angle between an optical axis of an optical element having two parallel planes facing each other and a reference plane intersecting the plane and the reference plane, comprising: a monochromatic light source; A first polarizing element sequentially arranged on an optical path of light emitted from a monochromatic light source; a sample table for holding the measured optical element such that the plane is perpendicular to the optical axis of the optical path; And a polarization element parallel to the optical axis and positioned at a predetermined angle with a polarization plane formed by one of the first and second polarization elements. An abutting means for abutting the reference surface of the optical element at the abutting surface to position the reference surface, and when mounted on a removable sample table on the sample table Side contacting the abutting surface of the abutting means And a polarization generating surface that determines a polarization direction that makes a predetermined angle with respect to the side surface, and the reference setting polarizing element is a sample before measuring the tilt angle of the optical element to be measured. A reference for positioning the abutting surface by rotating and adjusting the sample table so that the reference setting polarizing element is placed in a Nicol state orthogonal or parallel to the first or second polarizing element. Setting polarization element, rotating means for rotating the sample table around the optical axis, and rotating the sample table from the state where the optical element to be measured is positioned as described above until the optical axis of the optical element coincides with the polarization plane. A device for measuring the tilt angle between the optical axis and the reference plane of the optical element having a reading means for reading the rotation angle at the time. 2. The apparatus for measuring the tilt angle between the reference plane and the optical axis of the optical element according to claim 1, wherein the reference setting optical element is a polarization beam splitter. 3. The optical element according to claim 1, wherein the one polarizing element that forms the polarization plane is a first polarizing element, and the second polarizing element is removable. A device for measuring the tilt angle between the reference plane and the optical axis. 4. The one polarizing element for forming the polarization plane is a first polarizing element, and the second polarizing element is rotatable about the optical axis. An apparatus for measuring a tilt angle between a reference plane and an optical axis of the described optical element. 5. A monochromatic light source, a polarizing element which is arranged in an optical path of light emitted from the monochromatic light source, and which produces linearly polarized light having a plane of polarization in a predetermined direction parallel to a predetermined optical axis, and two parallel planes facing each other. And a reference surface intersecting the plane, which is a sample table for holding the optical element to be measured so that the plane is perpendicular to the optical axis, and the reference surface of the optical element is butted against The tilt angle between the reference plane and the optical axis of the optical element is measured using a device having an abutting surface parallel to the optical axis for positioning and a sample table rotatable about the optical axis. A polarization generating surface that is removable from the sample table and has a side surface that abuts against the abutting surface when mounted on the sample table and that determines a polarization direction that forms a predetermined angle with respect to the side surface. A standard setting polarizing element having And adjust the direction of the abutting surface by rotationally adjusting the sample table so that the reference setting polarizing element is in a crossed Nicol or parallel Nicol state with respect to the polarizing element, and remove the reference setting polarizing element. Mount the optical element to be measured on the sample table so that the reference surface of the optical element abuts against the abutting surface of the sample table, rotate the optical element around the optical axis, and set the optical axis of the optical element to be measured to the optical axis. A method for measuring a tilt angle between a reference plane of an optical element and an optical axis, which comprises measuring a rotation angle of an optical axis until the polarization planes coincide with each other. 6. A method for measuring an inclination angle between a reference plane and an optical axis of an optical element according to claim 5, wherein a polarization beam splitter is used as the reference setting optical element.