Testing device for optical test piece and method for testing optical test piece

Abstract

The method presented herein provides a test device for an optical test piece, where the test device includes a beam source for emitting a beam along an optical axis. Further, the test device comprises an optical element configured as a filter element for applying or filtering a specific polarization direction of light of the light beam or light reflected or transmitted from the test piece. The test device also includes a rotation unit configured to rotate the test piece located on the optical axis to a rotation angle relative to the filter element. Finally, the test device includes a detector unit configured to determine a polarization axis of the test piece, and a measure of eccentricity of the test piece, as a function of the angle of rotation and a beam of the light beam reflected from or transmitted through the test piece.

Description

Technical Field

[0001] The method proposed here provides a testing device for an optical test piece and a method for testing an optical test piece according to the main claims. Background Art

[0002] Some lenses have polarization-influencing properties because they either generate refractive forces on them (liquid crystal lenses) or are coated accordingly (polarization layers, quarter-wave layers, etc.). When installing such lenses, both their centering and the alignment of the polarization axis are important. However, in this case, a multi-step process is usually required to measure the centering of the polarization axis on the one hand and the alignment of the polarization axis on the other hand. However, in order to measure the centering of the polarization axis on the one hand and the alignment of the polarization axis on the other hand in different measurement process steps, the execution of such a multi-step process requires additional expenditure on the design of the test device. At the same time, such a test device requires increased installation space. Therefore, it is necessary to measure the centering and polarization sequentially with two different measuring heads. Therefore, the measurement technology requires significant installation space, and the two sequential measurement steps result in a long measurement period. Summary of the invention

[0003] In view of this background, it is an object of the present invention to provide an improved testing device for an optical test piece and an improved method for testing an optical test piece.

[0004] This object is achieved by the subject matter of the main claim.

[0005] The method proposed in this article provides a test device for an optical test piece for determining the eccentricity and polarization characteristics of the test piece, wherein the test device includes the following features:

[0006] - a radiation source for emitting a plurality of light beams along an optical axis;

[0007] - an optical element configured as a filter element in the optical axis for applying or filtering a specific polarization direction of the plurality of light beams or light reflected or transmitted from the test piece;

[0008] a rotation unit, which is configured to rotate a test piece at least located in the vicinity of the optical axis by a rotation angle relative to the measuring system and / or the test unit;

[0009] a detector unit configured to capture light reflected or transmitted from the test piece and to produce an at least approximately sharp image of the light source or reticle; and

[0010] an evaluation unit configured to determine a characteristic value of the centering of the optical test piece from the measured impact circle and to determine a polarization axis of the optical test piece from the rotation angle and an associated change in the signal intensity of a light beam of a plurality of light beams reflected from or transmitted through the optical test piece.

[0011] In addition, the method proposed in this article provides a testing device for an optical test piece, wherein the testing device includes the following features:

[0012] - a radiation source for emitting a plurality of light beams along an optical axis;

[0013] - an optical element for collimating the emitted multiple light beams;

[0014] an optical element configured as a polarization-influencing element for imparting a specific polarization direction to the plurality of light beams;

[0015] - an element for holding an optical test piece;

[0016] - an optical element for re-collimating the plurality of light beams focused by the optical test piece;

[0017] - an optical element configured as a polarization filter for filtering light transmitted from the optical test piece;

[0018] - an optical element for refocusing the light transmitted from the test piece onto the detection plane;

[0019] a rotation unit configured to rotate the optical test piece about a beam propagation axis and / or an optical axis on which the optical test piece is located, the rotation being relative to the test device and / or its individual components; and

[0020] A detector unit configured to simultaneously determine an eccentricity value and a polarization axis of the optical test piece based on a rotation angle of the optical test piece and a light beam of the plurality of light beams transmitted by the optical test piece.

[0021] For example, a beam source can be understood as a light source or a lamp that emits a corresponding light beam as a light beam along an optical axis. Alternatively, this can also be an illuminated reticle. A filter element can be understood as an optical element that applies a corresponding polarization direction to the incident light, for example. A rotation unit can be understood as a mechanical unit that rotates the test piece relative to the measuring device, for example, wherein this can be achieved by an active rotation of the test piece itself even when the filter element is stationary, or by a rotation of the measuring device when the test piece is stationary. For example, the rotation unit can be configured to rotate the measuring device or the test piece by a specific rotation angle, for example around the optical axis or around the axis of the light beam, by means of an electric drive. A detection unit can be understood as, for example, an optical sensor or a projection surface, on which the light reflected from the test piece or the light transmitted through the test piece is imaged and subsequently evaluated by a corresponding evaluation unit relative to the position of the polarization axis of the test piece.

[0022] The method proposed here is based on the recognition that the position of the polarization axis can be evaluated very simply by a rotation of the test piece relative to the filter element. This can be achieved, for example, by detecting and evaluating the brightness change during the rotation, utilizing the fact that when the polarization axis of the test piece or the surface of the test piece is in the same position with the adjusted polarization direction imposed by the filter element on the light beam, the maximum light intensity that can be received by the detector unit. In this way, a test device for an optical test piece can be produced in a technically very simple way, in which there is the possibility of detecting the polarization axis of the test piece and, at the same time, with the same measuring structure, there is also the possibility of being able to carry out a centering measurement, i.e. to measure the position of the optical center or optical axis of the test piece. The method proposed here thus offers the advantage of measuring several parameters of the test piece simultaneously or simultaneously by means of the proposed measuring structure, as a result of which further measuring structures can be omitted, so that construction space of the test device can be saved.

[0023] An embodiment of the method proposed here is advantageous in which the detector unit is configured to use the brightness of the light beam, the brightness pattern and / or the light intensity pattern in the light beam to determine the polarization axis of the test piece. This embodiment has the advantage that the brightness and / or brightness pattern reference or the intensity pattern can be detected in a technically very simple manner, so that the polarization axis of the test piece can be determined accurately.

[0024] Another embodiment of the method proposed here is advantageous in which the rotation unit is configured to rotate the test piece and / or the sensor unit about a beam axis and / or an optical axis. For example, such a beam axis can be the axis of the light beam in the light beam. This embodiment offers the advantage of a compact design of the test device.

[0025] According to another embodiment of the method proposed herein, the filter element can be configured to impose a circular or linear polarization direction on the light, and / or wherein the detector unit comprises an analyzer configured to allow circular or linear polarized light to pass through. This embodiment offers the advantage that, by means of the filter element, a very precise polarization direction can be imposed on the light of the light beam or evaluated in a simple manner, so that the identification of the polarization direction of the test piece can be realized technically simply.

[0026] Furthermore, an embodiment of the method proposed here is particularly advantageous in which the polarization element and the analyzer are arranged relative to one another such that a predetermined azimuth angle is set between the polarization direction defined by the shaping element and the polarization direction of the light passing through the analyzer defined by the analyzer. By setting the predetermined azimuth angle, a further increase in the accuracy of detecting the polarization axis of the test piece can be achieved, given that this angle is known, and the polarization axis of the birefringent optical element can also be determined.

[0027] An embodiment of the method proposed here is particularly advantageous in which the detection unit is configured to perform a centering measurement of the test piece. Such a centering measurement of the test piece can include, for example, the measurement of the optical axis, the optical center or another parameter of the test piece. This embodiment of the method proposed here offers the advantage that several parameters, such as the polarization axis and the centering value of the test piece, can be determined with the measuring structure, so that the test device only requires very little construction space and, on the other hand, the measurement can be performed without the test piece having to be expensively exchanged for different devices or different measurements on one device.

[0028] Furthermore, according to one embodiment of the method proposed here, the detection unit can be configured to use the detected diameter and / or radius of the impact circle as a measure for the centering measurement. By detecting such a diameter or radius, the centering measurement can be realized or performed technically very simply and quickly.

[0029] An embodiment of the method proposed here operates particularly efficiently in which the detection unit is designed to perform the determination of the polarization axis and the centering measurement in parallel and / or simultaneously, wherein, in addition to the radius and / or diameter, brightness changes are also detected in the impact circle image. With this embodiment, a test device can be provided which requires only a small amount of construction space and is easy to handle in operation.

[0030] Furthermore, according to another embodiment of the method proposed here, the beam source and the detector unit can be mounted in an autocollimator together with a polarization filter element in the optical axis, and wherein a beam splitter is provided to separate the light reflected from the test piece from a beam path parallel to the light irradiated from the beam source. This embodiment offers the advantage of a very compact design of the test device.

[0031] According to another embodiment, an additional rotation of the polarization element in the measurement system relative to the measurement system can be performed. This can be done mechanically or optically. The optical rotation of the polarization element can be achieved, for example, by a liquid crystal element or LCD element. In this case, the polarization axis is rotated by applying a voltage.

[0032] In embodiments in which the rotation of the polarization element takes place with 1.25 times the physical rotation, a particularly advantageous embodiment is obtained. When physically rotating by 360 degrees, the polarization element is correspondingly rotated an additional 90 degrees. In a subsequent second rotation, the additional rotation of the polarization element is increased to 180°, which corresponds optically to the starting configuration. Thus, for each point of the double impact circle, two intensity values ​​are obtained, which are associated with polarization directions that are perpendicular to each other and which produce different or opposite intensity curves accordingly. Therefore, additional high signal intensities are also obtained in areas of the impact circle where only very low signal intensities are present in other embodiments. Due to this complementary intensity curve, by adding the images, the eccentricity can be measured using a "complete" impact circle. Optionally, this advantageous signal reception can also be achieved in that the measuring system and the polarization element are mechanically movable relative to each other and rotate at different speeds.

[0033] According to a further embodiment of the method proposed here, a collimator with a upstream polarizer can be used as a filter element and a telescope with an analyzer can be arranged in the beam path between the auxiliary optics and / or the decollimating lens.

[0034] An embodiment of the method proposed here is also advantageous as a method for testing an optical test piece, wherein the method is carried out using a variant of the test device proposed here and comprises the following steps:

[0035] - transmitting light of the light beam from the light beam source to the test piece through the filter element, and receiving light of the light beam reflected or transmitted from the test piece in the detector unit;

[0036] - performing a relative rotational movement between the test piece and the measuring device; and

[0037] -Determine the polarization axis of the test piece based on the light reflected or transmitted from the test piece.

[0038] The above advantages can also be achieved quickly and effectively through such an implementation.

[0039] In a further embodiment of the method, the rotational movement of the centering measuring unit is performed at a rotational speed that is different from the rotational movement of the polarization element.

[0040] The method proposed here also provides a control device, which is configured to execute, control or implement the steps of the variant of the method proposed here in a corresponding device. Through the implementation variant of the present invention in the form of a control device, the task on which the present invention is based can also be solved quickly and efficiently.

[0041] For this purpose, the control device can have at least one computing unit for processing signals or data, at least one storage unit for storing signals or data, at least one interface for sensors or actuators for reading in sensor signals from sensors or for outputting control signals to actuators, and / or at least one communication interface for reading in or outputting data embedded in a communication protocol. The computing unit can be, for example, a signal processor, a microcontroller, etc., wherein the storage unit can be a flash memory or a magnetic storage unit. The communication interface can be configured to read or output data wirelessly and / or wired, wherein the communication interface capable of reading or outputting wired data can read or output these data, for example electrically or optically, from a corresponding data transmission line or output them to a corresponding data transmission line.

[0042] The control device can be understood as an electrical device that processes sensor signals and outputs control signals and / or data signals according to the sensor signals. The control device can have an interface, which can be constructed according to hardware and / or according to software. In the hardware-based construction scheme, the interface can be, for example, part of a so-called system ASIC that contains various functions of the control device. However, it is also possible that the interface is an integrated circuit of its own or is at least partially composed of discrete components. In the software-based design scheme, the interface can be a software module that, for example, exists on a microcontroller together with other software modules.

[0043] A computer program product or a computer program with a program code is also advantageous, which can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory and is used to execute, implement and / or control the steps of the method according to one of the above embodiments, in particular when the program product or the program is executed on a computer or a device. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Advantageous embodiments of the method proposed here are explained in more detail below with reference to the accompanying drawings. In the drawings:

[0045] Figure 1 A schematic diagram showing an embodiment of a test apparatus for testing an optical test piece;

[0046] Figure 2 Shows from Figure 1 Schematic diagram of an image of reflected light on a sensor corresponding to the arrangement of a test piece;

[0047] Figure 3 Schematic diagram showing signal curves of the detected light intensity without and with additional rotation of the polarization element;

[0048] Figure 4 A schematic diagram showing an embodiment of a test apparatus for testing an optical test piece in transmission; and

[0049] Figure 5 A flow chart of an embodiment of a method is shown. DETAILED DESCRIPTION

[0050] In the following figures, the same or similar elements are denoted by the same or similar reference numerals, and repeated description of these elements is omitted for clarity.

[0051] Figure 1 A schematic diagram of an embodiment of a test device 100 for testing an optical test piece 105 is shown. In this case, a light beam 115 is deflected from a beam source 145 in the form of a beam along an optical axis 117 to a beam splitter 120, after which the light beam 115 is incident on a filter element 125. The beam source can advantageously be combined with a crosshair (reticle). In this case, the filter element 125 can be configured as a polarizer or analyzer and impose a specific polarization direction on the light of the light beam 115, or only allow the light reflected by the test piece 105 to pass in a specific polarization direction. In addition, for example, a collimation and focusing unit 130 can be provided, which is arranged in the optical axis 117 and can focus the light 115 on the optical test piece 105. In this case, the collimation and focusing unit 130 can be arranged, for example, in two subunits 130a and 130b, each of which is located in front of or behind the filter element 125 in the direction of the beam. In this case, the optical element 130a is called a collimating lens and the optical element 130b is called a focusing lens or an auxiliary lens. Furthermore, a rotation unit 135 is provided, which is designed, for example, as an electric drive for rotating the test piece 105 by a rotation angle 140. Figure 1 In this case, the rotation unit 135 rotates the test piece 105 or the holder of the test piece 105 ( Figure 1 Alternatively or additionally, the rotation unit 135 can also be configured to rotate the entire measuring system 100 around a rotation angle 140. The rotation unit is controlled by a control unit 165.

[0052] The light of the light beam 115 is now reflected from the test piece 105, more precisely from its surface, whereby polarization effects occur, in particular high intensity light incident in the same polarization direction as the surface reflection of the test piece 105 is strongest is reflected. This reflected light then passes through the beam splitter 120 and is received by the sensor 110 of the detector unit 147. The detector unit 147 can be integrated with the sensor 110 or connected to the control device 150 as a component of the control device 150 via a suitable wired or wireless interface. The sensor 110 can be configured, for example, as a CMOS or CCD camera or a projection screen with a camera pointed thereto, in order to obtain an image of the center of curvature of the surface of the optical test piece 105 from the reflected light.

[0053] The device 100 can now be operated using the control device 150. Here, the output of light from the beam source 145 can be controlled by means of the output unit 155. The reflected light or a corresponding signal obtained corresponding to the controlled output of light at the sensor 110 can now be read in via the read-in interface 160. For example, if a rotation of the test piece 105 about a corresponding rotation angle 140 is now controlled, the position of the polarization axis of the test piece 105 and the image obtained by the sensor 110 can be determined from the reflected light from the test piece 105 by means of the determination unit 170.

[0054] At the same time, you can also use Figure 1 The illustrated arrangement performs a centered measurement, which can only be achieved by further evaluating the image of the light reflected from the test piece 105 detected by the sensor 110 .

[0055] Figure 2 A schematic diagram of an image 200 of light reflected from a test piece 105 to a sensor 110 is shown. Figure 2 The diagram shows the light reflected or incident on the sensor 110, which forms a corresponding light pattern 210 or intensity pattern, respectively. It can be seen here that the reflected light produces an image of the object (in the specific example of a cross), which forms an impact circle 220 due to the rotation of the test piece or the autocollimator. From the radius R of the impact circle, conclusions can be drawn about the eccentricity of the test piece 105. Depending on the rotational position of the test piece and its polarization influence properties relative to the filter element 125, the (light) signal intensity varies within the rotational movement. If all camera images are integrated through a 360° rotation of the filter element 125 or the test piece 105, a sinusoidal intensity distribution that varies with the azimuth angle is obtained instead of a circle with constant brightness. In Figure 2, this variation is represented by the intensity curve. The rotation angle at which the brightness is maximum can be understood as the angle at which the polarization axis of the test piece 105 is aligned. The variation in brightness with the rotation angle thus contains information about the alignment of the polarization axis of the test piece 105, while the diameter or radius R of the impact circle 220 represents a measure of the centering of the test piece 105. The rotational movement of the test piece 105 is therefore used to determine two measurement variables, which are advantageously measured in parallel.

[0056] Figure 3 A schematic diagram of the signal curve of the detected light intensity without and with an additional rotation of the polarization element is shown. In this case, the normalized intensity on the ordinate is plotted via the angle on the abscissa. The solid sinusoidal curve describes the signal curve detected when the test piece is rotated at a constant rotational speed relative to the measuring system without an additional rotation of the polarizer / analyzer. In the case of reflection measurements, this can be achieved by a rotation of the ACM or a rotation of the test piece. When the polarizer / analyzer is rotated mechanically or optically at an increased speed relative to the measuring system, a dashed or dotted sinusoidal curve appears. Thus, for each azimuthal position, a first signal (dashed line) and a second, inverse signal (dotted line) are detected. By adding the signal curves, the fully illuminated impact circle is obtained.

[0057] Therefore, when the dashed and dotted intensity curves are added together, a “complete” impact circle can be obtained, e.g. Figure 3 as shown in the lower part of .

[0058] Thus, during the measurement, the centering measurement can advantageously be coupled to the polarization measurement. Thus, the construction space remains compact and the measurement time is minimized. To achieve this, according to one embodiment, the centering measurement of the test piece rotation is performed in conjunction with the polarization beam path. Thus, the method proposed here allows an advantageous combination of centering measurement and polarization measurement, which enables a compact measurement structure and short measurement times.

[0059] Depending on the characteristics of the test piece, the filter element 125 or the polarizer and / or the analyzer may be designed for circularly polarized light instead of linearly polarized light, or the azimuth angle between the polarizer and the (separate) analyzer may be set.

[0060] A further technical embodiment of the variant of the test device proposed here is, for example:

[0061] A collimator with a pre-polarizer and a telescope with an analyzer are located in the beam path between the auxiliary optics and the "decollimator lens". Centering is measured in transmission.

[0062] Figure 4A schematic diagram of an embodiment of a test device 100 for testing an optical test piece 105 in transmission is shown, wherein the decentering and polarization change characteristics of the optical element in transmission are measured simultaneously. In this case, the decentering is likewise determined by the radius or diameter of the impact circle which is generated by the rotation of the test piece relative to the measuring system. In order to determine the polarization change characteristics of the test piece 105, a polarization element, such as the polarizer 125, is provided in the collimator 400, as well as a polarization filtering element, such as the analyzer 410, which has an auxiliary lens 430 and a focusing lens or "decollimator lens", Figure 4 The polarizer 125 in the collimator 400 is illuminated, for example, by an illumination reticle 435. The polarization elements can in turn be rotated optically or mechanically relative to the measurement system in order to obtain, for example, complementary signal curves, such as Figure 3 As shown and described above. The polarizer 125 and the analyzer 410 can be rotated independently of each other, or an additional quarter lambda plate can be rotated, which is advantageous, for example, when determining the Miller matrix of the test piece. In addition, the polarizer 125 and the analyzer 410 can have different optical properties. For example, the polarizer 125 can be designed as a delay plate, or can be combined or connected with a delay plate, so that the light beam after the collimator 400 has a circular polarization. The light beam is further focused in the test piece focus 440 in front of the auxiliary lens 430 or the analyzer 410. This variant is advantageous, for example, if the test piece 105 changes the polarization of the light beam, for example from circular to linear, which is the case, for example, in flat optics for AR / VR applications. Therefore, for this type of test piece 105, it is particularly advantageous to perform the measurement in transmission.

[0063] Figure 5 A flow chart of an embodiment of a method 500 for testing an optical test piece is shown, wherein the method 500 is performed using a test device corresponding to the variant proposed here and comprises a step 510 of emitting light of a light beam from a light beam source onto the test piece through a filter element and receiving light of the light beam reflected or transmitted by the test piece in a detector unit. Furthermore, the method 500 comprises a step 520 of rotating the test piece relative to the filter element and a step 530 of determining a polarization axis of the test piece from the light reflected or transmitted by the test piece.

Claims

1. A testing device for testing an optical sample, wherein: The test device includes the following elements: - a radiation source for emitting a plurality of light beams along an optical axis; - a polarization influencing or polarization filtering optical element, which is located on the optical axis and is configured to impose a polarization direction on the plurality of light beams for filtering light reflected from the optical sample; a rotation unit configured to rotate the optical sample relative to the testing device and / or a subassembly thereof about a beam axis and / or the optical axis on which the optical sample is located; and - a detection unit for simultaneously determining an eccentricity and a polarization axis of the optical sample based on a rotation angle and a reflected light beam from the plurality of light beams reflected by the optical sample.

2. The test device (100) for an optical test piece (105), wherein: The testing device (100) has the following features: - a beam source (145) for emitting a light beam (115) along an optical axis (117); - optical elements for collimating the emitted light beam; - an optical element configured as a polarization-influencing element for imparting a specific polarization direction to the light of the light beam (115); - an element for holding the optical test piece; - an optical element for re-collimating the light beam focused by the test piece; - an optical element configured as a polarization filter, the optical element being used to filter light transmitted from the test piece (105); - an optical element for refocusing said light transmitted from said test piece onto a detection plane; a rotation unit (135) configured to rotate the test piece (105) located on the optical axis (117) about a beam axis and / or the optical axis (117), the rotation being relative to the test device and / or its individual components; and A detector unit (147) configured to simultaneously determine the polarization axis of the test piece (105) and its eccentricity as a function of the rotation angle (140) and as a function of the light beam of the light beam (115) transmitted by the test piece (105).

3. The testing device (100) according to claim 1 or 2, characterized in that: The polarization-influencing element in the beam path can be rotated mechanically and / or optically.

4. The testing device (100) according to claim 1 or 2, characterized in that: The detector unit (147) is configured to determine the polarization axis of the test piece (105) using the brightness, brightness pattern and / or light intensity pattern (210) of a reflected or transmitted beam of the light beam (115).

5. The testing device (100) according to claim 1 or 2, characterized in that: The polarizer (125) is configured to impose a circular or linear polarization direction on the light, and wherein the detector unit (147) includes an analyzer configured to allow the circular or linear polarized light to pass.

6. The testing device (100) according to claim 5, characterized in that: The polarizer (125) and the analyzer are arranged relative to each other such that a predefined azimuth angle is provided between a polarization direction defined by the polarizer (125) and a polarization direction defined by the analyzer of light passing through the analyzer.

7. The testing device (100) according to claim 1 or 2, characterized in that: The detector unit (147) is configured to determine a measure of decentering from a detected impingement circle (220) of the brightness variation.

8. The testing device (100) according to claim 1 or 2, characterized in that: The beam source (145) and the sensor (110) are mounted in an autocollimator together with the polarizer (125) and / or the analyzer in the optical axis (117), and wherein a beam splitter (120) is arranged to separate light reflected from the test piece (105) from a beam path parallel to the light irradiated from the beam source (145).

9. A method (500) for testing an optical test piece (105), wherein: The method (500) is performed using a testing device (100) according to any one of the preceding claims 1 to 8, and comprises the following steps: - emitting (510) light of a light beam (115) from the light beam source (145) to the test piece (105), wherein polarization is first applied to the light beam, and receiving light of the light beam (115) reflected from or transmitted through the test piece (105) in the detector unit (147); - rotating (520) the test piece (105) relative to the test device (100) and / or individual components of the test device; and - simultaneously determining (530) the polarization axis and the eccentricity of the test piece (105) from the light reflected or transmitted from the test piece (105).

10. The method (500) according to claim 9, characterized in that: The polarization-influencing element is rotated relative to the test device and, for each azimuthal position of the test piece, a first intensity signal and a second intensity signal deviating from said signal are detected during at least two rotations.

11. The method (500) according to claim 10, characterized in that: The first intensity signal and the second intensity signal are added to obtain an impact circle having an intensity variation within a tolerance range for measuring eccentricity.

12. A control device (150) configured to execute and / or control the steps (510, 520, 530) of the method (500) according to any one of the preceding claims with respective units (155, 160, 170).

13. A computer program arranged to perform and / or control the steps (510, 520, 530) of the method (500) according to claim 11.

14. A machine-readable storage medium having stored thereon the computer program according to claim 13.

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