Testing apparatus for optical test pieces and methods for testing optical test pieces

Abstract

The method presented herein provides a testing apparatus (100) for an optical test piece (105), wherein the testing apparatus (100) includes a beam source (145) for emitting a beam (115) along an optical axis (117). Furthermore, the testing apparatus (100) includes an optical element configured as a filter element (125) for applying or filtering a specific polarization direction of light from or reflected from the test piece (105) or transmitted from the test piece (105). The testing apparatus (100) also includes a rotation unit (135) configured to rotate the test piece (105) located on the optical axis (117) relative to the filter element (125) by a rotation angle (140). Finally, the testing apparatus (100) includes a detector unit (147) configured to determine the polarization axis of the test piece (105) and a measure of the test piece's eccentricity based on the rotation angle (140) and the beam of light (115) reflected from or transmitted through the test piece (105).

Description

Test device for an optical test piece and method for testing an optical test piece The method presented here provides a test device for an optical test piece and a method for testing an optical test piece according to the main claim. Some lenses have polarization influencing properties, as either a refractive force is generated thereon (liquid crystal lens) or it is correspondingly coated (polarization layer, quarter-wave layer, etc.). When installing such a lens, both its 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 regarding the design of the test device. At the same time, such a test device requires increased installation space. Therefore, sequential measurements of centering and polarization are required with two different measuring heads. Therefore, the measuring technique requires significant installation space, and the two sequential measurement steps result in a long measurement time period. In view of this background, the object of the present invention is to provide an improved test device for an optical test piece and an improved method for testing an optical test piece. This object is achieved by the subject matter of the main claim. The method presented here provides a test device for an optical test piece for determining the eccentricity and polarization properties of the test piece, wherein the test device comprises the following features: - a radiation source for emitting a plurality of light beams along the optical axis; - an optical element configured as a filter element in the optical axis, the optical element being for applying or filtering a specific polarization direction of a plurality of light beams or light reflected or transmitted from the test piece; - a rotation unit configured to rotate at least the test piece located near the optical axis relative to the measurement system and / or the test unit by a rotation angle; - a detector unit configured to capture the light reflected or transmitted from the test piece and generate at least an approximately clear image of the light source or the reference line; and - an evaluation unit configured to determine a characteristic value of the centering of the optical test piece based on the measured impact circle, and to determine the polarization axis of the optical test piece based on the rotation angle and the associated change in the signal intensity of the light beams in the plurality of light beams reflected or transmitted through the optical test piece. In addition, the method proposed in this paper provides a test device for an optical test piece, wherein the test device includes the following features: - a radiation source for emitting a plurality of light beams along the optical axis; - an optical element for collimating the emitted plurality of light beams; - an optical element configured as a polarization influencing element for applying a specific polarization direction to the plurality of light beams; - an element for holding the optical test piece; - an optical element for re-collimating the plurality of light beams focused by the optical test piece; - an optical element configured as a polarization filter for filtering the light transmitted from the optical test piece; - an optical element for re-focusing the light transmitted from the test piece onto a detection plane; - a rotation unit configured to rotate the optical test piece around the beam propagation axis and / or the optical axis on which the optical test piece is located, the rotation being relative to the test device and / or its individual components; and - a detector unit configured to simultaneously determine the eccentricity value and the polarization axis of the optical test piece based on the rotation angle of the optical test piece and the light beams transmitted by the optical test piece among the plurality of light beams. For example, the light beam source can be understood as a light source or a lamp that emits corresponding light beams along the optical axis as light beams. Alternatively, this can also be an illumination marking line. The filtering element can be understood as an optical element that applies a corresponding polarization direction to the incident light, for example. The rotation unit can be understood as a mechanical unit that rotates the test piece relative to the measuring device, for example, which can be achieved by the active rotation of the test piece itself even when the filtering element is stationary, or by the 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 by means of an electric drive, for example, around the optical axis or around the axis of the light beam. The detector unit can be understood as an optical sensor or a projection surface on which the light reflected from the test piece or transmitted through the test piece is imaged, and subsequently evaluated by the corresponding evaluation unit with respect to the position of the polarization axis of the test piece. The method proposed here is based on the recognition that the position of the polarization axis can be very simply evaluated by rotating the test piece relative to the filter element. This can be achieved, for example, by detecting and evaluating the brightness change during rotation, taking advantage of the fact that when the polarization axis of the test piece or the surface of the test piece is in the same position, the detector unit can receive the maximum light intensity on the light of the beam with the adjusted polarization direction applied by the filter element to the beam. In this way, a test device for an optical test piece can be manufactured in a technically very simple way, where there is a possibility of detecting the polarization axis of the test piece, and at the same time, using the same measurement structure, there is also a possibility of being able to perform centering measurement, that is, measuring the position of the optical center or the optical axis of the test piece. Therefore, the method proposed here offers the advantage of measuring several parameters of the test piece simultaneously or concurrently through the proposed measurement structure, as a result of which further measurement structures can be omitted, thus saving the structural space of the test device. One embodiment of the method proposed here is advantageous, where the detector unit is configured to use the brightness, brightness pattern, and / or light intensity pattern of the beam in the beam to determine the polarization axis of the test piece. The advantage of this embodiment is the ability to detect the brightness and / or brightness pattern reference or intensity pattern in a technically very simple way, so as to be able to accurately determine the polarization axis of the test piece. Another embodiment of the method proposed here is advantageous, where the rotation unit is configured to rotate the test piece and / or the sensor unit about the beam axis and / or the optical axis. For example, such a beam axis can be the axis of the beam in the beam. This embodiment offers the advantage of a compact structural form of the test device. According to another embodiment of the method proposed herein, the filter element can be configured to apply a circular or linear polarization direction to the light, and / or wherein the detector unit includes an analyzer configured to allow circularly or linearly polarized light to pass through. The advantage provided by this embodiment is that, through the filter element, a very precise polarization direction can be simply applied to or evaluated on the light of the beam, so that the identification of the polarization direction of the test piece can be achieved technically simply. Furthermore, one embodiment of the method proposed here is particularly advantageous, where the polarization element and the analyzer are arranged relative to each other 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, with the knowledge of this angle, a further improvement in the accuracy of detecting the polarization axis of the test piece can be achieved, and the polarization axis of the birefringent optical element can also be determined. One embodiment of the method presented here is particularly advantageous, where the detection unit is configured to perform centering measurements on the test piece. Such centering measurements of the test piece can include, for example, measurements of the optical axis, optical center, or another parameter of the test piece. This embodiment of the method presented here provides the advantage that several parameters can be determined with the measurement structure, such as the polarization axis and centering value of the test piece, such that the test device requires only very little structural space, and on the other hand, measurements can be performed without the need to expensively replace the test piece to a different device or perform different measurements on one device. Furthermore, according to one embodiment of the method presented here, the detection unit can be configured to use the detected diameter and / or radius of the impact circle as a measure of the centering measurement. By detecting such diameter or radius, the centering measurement can be technically very simply and quickly implemented or performed. One embodiment of the method presented here operates particularly effectively, where the detection unit is configured to determine the polarization axis and perform the centering measurement in parallel and / or simultaneously, where, in addition to the radius and / or diameter, brightness variations are also detected in the impact circle image. Through this embodiment, a test device can be provided that requires only little structural space and is easy to operate in operation. Furthermore, according to another embodiment of the method presented here, the light beam source and the detector unit can be installed in a collimator together with a polarization filter element in the optical axis, and where a beam splitter is provided to separate the light reflected from the test piece from the beam path of the light irradiated from the light beam source. This embodiment provides the advantage of a very compact structural form of the test device. According to another embodiment, an additional rotation of the polarization element relative to the measurement system can be performed in the measurement system. 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 an LCD element. In this case, the polarization axis is rotated by applying a voltage. In an embodiment where the rotation of the polarization element occurs at 1.25 times the physical rotation, a particularly advantageous implementation is obtained. When the physical rotation is 360 degrees, the polarization element is additionally rotated by 90 degrees accordingly. In a subsequent second rotation, the additional rotation of the polarization element increases to 180°, which optically corresponds to the starting configuration. Thus, for each point of the double impact circle, two intensity values are obtained, which are associated with polarization directions perpendicular to each other and accordingly produce different or reverse intensity curves. Therefore, additional high signal intensities are also obtained in regions of the impact circle where there is only a very low signal intensity in other embodiments. Due to this complementary intensity curve, by adding the images, the eccentricity can be measured using the "complete" impact circle. Optionally, this advantageous signal reception can also be achieved by the measurement system and the polarization element being mechanically movable relative to each other and rotating at different speeds. According to another embodiment of the method presented here, a collimator with a front polarizer can be used as a filtering element, and a telescope with an analyzer can be arranged in the beam path between the auxiliary optics and / or the collimating lens. One embodiment of the method presented 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 presented here and comprises the following steps: - emitting light of a beam from a beam source through a filtering element to the test piece and receiving in a detector unit light of the beam reflected or transmitted by the test piece; - performing a relative rotational movement between the test piece and the measuring device; and - determining the polarization axis of the test piece based on the light reflected or transmitted by the test piece. The above advantages can also be achieved quickly and effectively by such an embodiment. In another embodiment of the method, the rotational movement of the centering measurement unit is carried out at a rotational speed different from the rotational speed of the polarization element. The method presented here also provides a control device which is configured to carry out, control or implement the steps of a variant of the method presented here in a corresponding device. By means of the implementation variant in the form of a control device of the present invention, the problem underlying the present invention can also be solved quickly and efficiently. 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 in or output data wirelessly and / or wired, wherein a communication interface capable of reading in or outputting wired data can read in or output these data, for example, electrically or optically, from a corresponding data transmission line into a corresponding data transmission line. The control device can here be understood as an electrical device which processes sensor signals and outputs control signals and / or data signals based on these sensor signals. The control device can have an interface which can be configured according to hardware and / or according to software. In the hardware-based configuration scenario, the interface can be, for example, part of a so-called system ASIC which contains various functions of the control device. However, it is also possible for the interface to be a self-contained integrated circuit or to consist at least partly of discrete components. In the software-based design scenario, the interface can be software modules which, for example, are present together with other software modules on a microcontroller. A computer program product or computer program having code that 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 perform, implement, and / or control the steps of a method according to one of the above-described embodiments, particularly when the program product or program is executed on a computer or device. In the following figures, identical or similar elements are denoted by identical or similar reference signs, and for the sake of clarity, repeated descriptions of these elements are omitted. FIG. 1 shows a schematic view of an embodiment of a test device 100 for testing an optical test piece 105. In this case, a light beam 115 is deflected from a light beam source 145 in the form of a light beam along an optical axis 117 to a beam splitter 120, after which the light beam 115 impinges on a filter element 125. The light beam source can advantageously be combined with a reticle (marking line). In this case, the filter element 125 can be configured as a polarizer or analyzer and apply a specific polarization direction to the light of the light beam 115, or only allow the light reflected by the test piece 105 to pass through in a specific polarization direction. Furthermore, 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 onto the optical test piece 105. In this case, the collimation and focusing unit 130 can, for example, be arranged in two sub-units 130a and 130b, each of the sub-units 130a and 130b being located in front of or behind the filter element 125 in the light beam direction. In this case, the optical element 130a is referred to as a collimating lens, and the optical element 130b is referred to as a focusing lens or an auxiliary lens. In addition, a rotation unit 135 is provided, which is, for example, configured as an electric drive for rotating the test piece 105 by a rotation angle 140. In FIG. 1, this rotation is shown in such a way that the rotation unit 135 rotates the test piece 105 or the holder of the test piece 105 (not shown in FIG. 1). Alternatively or additionally, the rotation unit 135 can also be configured to rotate the entire measurement system 100 by the rotation angle 140. The rotation unit is controlled by a control unit 165. The light of the light beam 115 is now reflected from the test piece 105, more precisely from its surface, whereby a polarization effect occurs, particularly high-intensity light incident in the same polarization direction as the strongest surface reflection of the test piece 105 is reflected. This reflected light then passes through the beam splitter 120 and is received by a sensor 110 of a detector unit 147. The detector unit 147 can be integrated with the sensor 110 or connected to a control device 150 via a suitable wired or wireless interface as a component of the control device 150. The sensor 110 can be configured, for example, as a CMOS or CCD camera or a projection screen having a camera directed 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. The control device 150 can now be used to operate the device 100. Here, the output of the light from the light source 145 can be controlled by means of the output unit 155. The reflected light or the corresponding signal obtained corresponding to the control output of the light at the sensor 110 can now be read in through the read-in interface 160. For example, if the rotation of the test piece 105 around the 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 light reflected from the test piece 105 by means of the determination unit 170. At the same time, centering measurement can also be carried out using the structure shown in FIG. 1, which can only be achieved by further evaluating the image of the light reflected from the test piece 105 detected by the sensor 110. FIG. 2 shows a schematic diagram of the image 200 of the light reflected from the test piece 105 to the sensor 110. The illustration in FIG. 2 shows the light reflected or incident on the sensor 110, which respectively forms the corresponding light pattern 210 or intensity pattern. It can be seen here that the reflected light produces an image of the object (in the specific example of the cross), and this image forms the impact circle 220 through the rotation of the test piece or the autocollimator. The eccentricity of the test piece 105 can be concluded from the radius R of the impact circle. According to the rotation position of the test piece and its polarization influence characteristics relative to the filter element 125, the (light) signal intensity changes within the rotational movement. If all the camera images are integrated by a 360° rotation of the filter element 125 or the test piece 105, a sinusoidal intensity distribution that changes with the azimuth angle is obtained, rather than a circle with a constant brightness. In FIG. 2, this change is represented by the intensity curve. The rotation angle with the maximum brightness can be understood as the angle at which the polarization axis of the test piece 105 is aligned. Therefore, the change in brightness with the rotation angle 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. Therefore, the rotational movement of the test piece 105 is used to determine two measurement variables, and these two measurement variables are advantageously measured in parallel. FIG. 3 shows a schematic diagram of the signal curves of the light intensities detected with and without additional rotation of the polarization element. In this case, the normalized intensity on the vertical axis is plotted against the angle on the horizontal axis. The solid sinusoidal curve describes the signal curve detected when the test piece rotates relative to the measurement system at a constant rotational speed without additional rotation of the polarizer / analyzer. In the case of reflection measurement, this can be achieved by the rotation of the ACM or the rotation of the test piece. When the polarizer / analyzer rotates mechanically or optically at an increasing speed relative to the measurement system, the dashed or dotted sinusoidal curves appear. Therefore, for each azimuth angle position, the first signal (dashed line) and the second reverse signal (dotted line) are detected. By adding the signal curves, a fully illuminated impact circle is obtained. Thus, when adding the dashed and dotted line intensity curves, a "complete" impact circle can be obtained, as shown in the lower part of Figure 3. Thus, during the measurement process, the centering measurement can be advantageously associated with the polarization measurement. As a result, the structural space remains compact and the measurement time is minimized. To achieve this, according to one embodiment, the centering measurement that rotates the test piece is associated with the polarization beam path. Thus, the method proposed here allows for an advantageous combination of centering measurement and polarization measurement, which enables a compact measurement structure and a short measurement time. Depending on the characteristics of the test piece, the filter element 125 or the polarizer and / or analyzer can be designed for circularly polarized light instead of linearly polarized light, or the azimuth angle between the polarizer and the (separate) analyzer can be set. A further technical implementation of the variant of the test device proposed here is, for example: A collimator with a front polarizer and a telescope with an analyzer, located in the beam path between the auxiliary optical system and the "de-collimating lens". The centering is measured in transmission. Figure 4 shows a schematic diagram of an embodiment of a test device 100 for testing an optical test piece 105 in transmission, where the eccentricity and polarization change characteristics of the optical element in transmission are measured simultaneously. In this case, the eccentricity is also determined by the radius or diameter of the impact circle, which is generated by the rotation of the test piece relative to the measurement system. To determine the polarization change characteristics of the test piece 105, a polarization element, such as a polarizer 125, is provided in the collimator 400 here, and a polarization filter element, such as an analyzer 410, is provided in the telescope 420, which has an auxiliary lens 430 and a focusing lens or "de-collimating lens", not explicitly shown in Figure 4. The polarizer 125 in the collimator 400 is illuminated, for example, by an illumination reticle 435. The polarization element can be rotated optically or mechanically relative to the measurement system in sequence to obtain, for example, complementary signal curves, as shown in Figure 3 and described above. The polarizer 125 and the analyzer 410 can be rotated independently of each other, or an additional quarter-wave plate can be rotated, which is advantageous, for example, when determining the Mueller matrix of the test piece. In addition, the polarizer 125 and the analyzer 410 can have different optical characteristics. For example, the polarizer 125 can be designed as a retarder plate, or can be combined or connected with a retarder plate such that the beam behind the collimator 400 has circular polarization. The beam is further focused in the test piece focus 440 in front of the auxiliary lens 430 or the analyzer 410. For example, if the test piece 105 changes the polarization of the beam, for example, from circular to linear, this variant is advantageous, such as in the case of flat optical devices for AR / VR applications. Therefore, for this type of test piece 105, it is particularly advantageous to perform the measurement in transmission. FIG. 5 shows a flowchart of an embodiment of a method 500 for testing an optical test piece, wherein the method 500 is performed using a test device corresponding to the variants proposed herein, and includes 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 the light of the light beam reflected or transmitted by the test piece in a detector unit. In addition, the method 500 includes a step 520 of rotating the test piece relative to the filter element and a step 530 of determining the polarization axis of the test piece from the light reflected or transmitted by the test piece. 100: Test device 105: Test piece 110: Sensor 115: Light beam 117: Optical axis 120: Beam splitter 125: Polarizer 130a: Sub-unit 130b: Sub-unit 135: Rotation unit 140: Rotation angle 145: Light beam source 147: Detector unit 150: Control device 155: Output unit 160: Read-in interface 165: Control unit 170: Determination unit The advantageous embodiments of the method proposed herein are explained in more detail below with reference to the accompanying drawings. In the drawings: [FIG. 1] shows a schematic diagram of an embodiment of a test device for testing an optical test piece; [FIG. 2] shows a schematic diagram of an image of the reflected light on the sensor corresponding to the arrangement of the test piece in FIG. 1; [FIG. 3] shows a schematic diagram of a signal curve of the detected light intensity with and without additional rotation of a polarization element; [FIG. 4] shows a schematic diagram of an embodiment of a test device for testing an optical test piece in transmission; and [FIG. 5] shows a flowchart of an embodiment of the method. 100: Test device 105: Test piece 110: Sensor 115: Light beam 117: Optical axis 120: Beam splitter 125: Polarizer 130a: Sub-unit 130b: Sub-unit 135: Rotation unit 140: Rotation angle 145: Light beam source 147: Detector unit 150: Control device 155: Output unit 160: Read-in interface 165: Control unit 170: Determination unit

Claims

1. A testing apparatus (100) for testing optical samples (105), wherein, The test apparatus (100) includes the following elements: - a radiation source (145) for emitting a beam of multiple beams (115) along an optical axis (117); - a filter element (125) configured as a polarizer (125) and an analyzer (125), the filter element being located on the optical axis (117), the polarizer (125) being configured to apply a polarization direction to the beam of the multiple beams (115), and the analyzer (125) filtering light reflected from the optical sample (105); - a rotation unit (135) configured to rotate the optical sample relative to the test apparatus and / or a sub-assembly of the test apparatus about the beam axis on which the optical sample (105) is located and / or the optical axis (117) of the optical sample; and - Detector unit (147) is used to simultaneously determine the eccentricity and polarization axis of the optical sample (105) based on the rotation angle and the image reflected by the optical sample (105) from the beam of the light beam (115).

2. The test apparatus (100) as described in claim 1, wherein, The polarizer (125) in the beam path can be rotated mechanically and / or optically.

3. The test apparatus (100) as described in claim 1, wherein, 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 the reflected beam of the beam of the beam (115).

4. The test apparatus (100) as described in claim 1, wherein, The detector unit (147) is configured to determine the angle of eccentricity from the drawn circle (220) of the detected brightness change.

5. The test apparatus (100) as described in claim 1, wherein, The radiation source (145) and sensor (110) are mounted together with the polarizer (125) and the analyzer (125) in the optical axis (117) in the autocollimator, and wherein, A beam splitter (120) is configured to separate the light reflected from the test piece (105) from a beam path parallel to the light irradiated from the radiation source (145).

6. A method (500) for testing an optical test piece (105), wherein, The method (500) is performed using a test apparatus (100) according to any one of claims 1 to 5, and includes the following steps: - emitting (510) light of a beam of light (115) from the radiation source (145) to the test piece (105), wherein polarization is first applied to the beam of light (115), and an image of the beam of light (115) reflected from and then filtered by the test piece (105) is received in the detector unit (147); - rotating (520) the test piece (105) relative to the test apparatus (100) and / or the various components of the test apparatus; and - simultaneously determining (530) the polarization axis and its eccentricity of the test piece (105) from the image of the light reflected from the test piece (105).

7. The method (500) as described in request item 6, wherein, The polarizer rotates relative to the test apparatus, and for each azimuth position of the test piece, a first intensity signal and a second intensity signal deviating from the signal are detected during at least two rotations.

8. The method (500) as described in request item 7, wherein, The first intensity signal and the second intensity signal are added together to obtain a drawn circle with intensity variation within the tolerance range used to measure eccentricity.

9. A control device (150) configured to execute and / or control the steps (510, 520, 530) of the method (500) according to any one of claims 6 to 8 with corresponding units (155, 160, 170).

10. A computer program configured to perform and / or control the steps (510, 520, 530) of the method (500) according to request 8.

11. A machine-readable storage medium on which the computer program according to claim 10 is stored.

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