DE102024115156A1 - Device for testing an optical test specimen exhibiting polarization properties and method for operating such a device - Google Patents

Abstract

A device (400) for testing an optical test specimen exhibiting polarization properties is presented. The device (400) comprises an illumination unit (100) with a light source, a first polarizer, and a first rotating device. The light source is configured to emit test light to the test specimen. The first polarizer is configured to polarize the test light. The first rotating device is connected to the first polarizer and is configured to rotate the first polarizer to adjust the polarization state of the polarized test light. The device (400) also comprises a detector unit (300) with a detection device, a second polarizer used as an analyzer, and a second rotating device. The second polarizer used as an analyzer is configured to transmit the result light coupled out from the test specimen according to its polarization state. The second rotating device is connected to the second polarizer used as an analyzer and is configured to rotate the second polarizer used as an analyzer to adjust the polarization axis of the detection unit. The detection device is designed to determine at least one optical property of the optical test specimen, taking into account its polarization properties.

Description

The invention relates to a device for testing an optical test object exhibiting polarization properties and a method for operating a device for testing an optical test object exhibiting polarization properties.

The polarization properties of light are becoming increasingly important, for example, in the production of VR (Virtual Reality) and AR (Augmented Reality) elements. Generally, such systems can also be described as transparent or opaque NEDs (Near-to-Eye Displays). For these types of optical elements or components, there is a particular need for a concept that not only allows the polarization state of the coupled light to be controlled, but also enables various optical measurements on such test specimens.

The US20200096817A1 This concerns an active alignment process for a head-mounted display (HMD) with a pancake lens. More precisely, the process can be used to align different components of a pancake lens relative to each other. The alignment parameter can be either the polarization state of the light transmitted through the system, measured by a Stokes polarimeter, or a double image measured by a camera in combination with an external light source or the HMD display.

The JP2019144237A This describes a setup for measuring the polarization characteristics of a polarizing element. The setup includes a light source, an aperture or diaphragm, a collimating lens, an analyzer, and a detector. During a measurement, the analyzer is rotated, and the polarization characteristics of the polarizer are determined from signals recorded by the detector.

Against this background, the approach presented here introduces an improved device for testing an optical test specimen exhibiting polarization properties and an improved method for operating such a device according to the main claims. Advantageous embodiments and further developments of the invention are described in the dependent claims.

According to embodiments, a system with rotatable linear polarizers or analyzers, connected to both the light source and the detector, can be used, for example, to control and measure changes in the polarization angle of a polarizing optical test object. In particular, the proposed concept can be used with a polarization of the light source and detector according to a test object design. According to embodiments, it is possible, for example, to control the polarization state of a light source used for testing and to measure changes in polarization due to the propagation of light through the test object.

Advantageously, this enables precise and simple polarization measurements, for example, for optical AR or VR components, or similar test objects. Furthermore, precise control of the optical parameters of the coupled light source can be achieved. In addition, the quality of measurements, such as those of a modulation transfer function (MTF), on optical AR or VR components can be improved with regard to multiple reflections and transmissions. More precisely, the device proposed here allows the polarizing properties of the test object to be correctly incorporated into the measurement of optical parameters, such as the MTF, thus preventing misinterpretation of the measured optical parameters.

• eine Beleuchtungseinheit mit einer Lichtquelle, einem ersten Polarisator und einer ersten Dreheinrichtung, wobei die Lichtquelle ausgebildet ist, um Prüflicht zu dem Prüfling auszugeben, wobei der erste Polarisator ausgebildet ist, um das Prüflicht zu polarisieren, wobei die erste Dreheinrichtung mit dem ersten Polarisator verbunden und ausgebildet ist, um den ersten Polarisator zu drehen, um einen Polarisationszustand des polarisierten Prüflichts und/oder die Polarisationsachse der Beleuchtungseinheit einzustellen;
• eine Prüflingseinheit, die eine Halteeinrichtung zum Halten des Prüflings aufweist; und eine Detektoreinheit mit einer Erfassungseinrichtung, einem als Analysator verwendeten zweiten Polarisator und einer zweiten Dreheinrichtung, wobei der als Analysator verwendete zweite Polarisator ausgebildet ist, um von dem Prüfling ansprechend auf das polarisierte Prüflicht ausgekoppeltes polarisiertes Ergebnislicht entsprechend des Polarisationszustandes des Ergebnislichtes zu transmittieren, wobei die zweite Dreheinrichtung mit dem als Analysator verwendeten zweiten Polarisator verbunden und ausgebildet ist, um den als Analysator verwendeten zweiten Polarisator zu drehen, um eine Polarisationsachse der Detektoreinheit einzustellen, wobei die Erfassungseinrichtung ausgebildet ist, um mindestens eine optische Eigenschaft des optischen Prüflings unter Berücksichtigung von dessen Polarisationseigenschaften zu bestimmen.

A device for testing an optical test specimen exhibiting polarization properties is presented, wherein the device has the following features:

• a lighting unit comprising a light source, a first polarizer and a first rotating device, wherein the light source is configured to emit test light to the test object, wherein the first polarizer is configured to polarize the test light, and wherein the first rotating device is connected to the first polarizer and configured to rotate the first polarizer to adjust a polarization state of the polarized test light and/or the polarization axis of the lighting unit;
• a test specimen unit comprising a holding device for holding the test specimen; and a detector unit comprising a detection device, a second polarizer used as an analyzer, and a second rotating device, wherein the second polarizer used as an analyzer is configured to transmit polarized result light coupled from the test specimen in response to the polarized test light, according to the polarization state of the result light, wherein the The second rotating device is connected to and configured with the second polarizer used as an analyzer to rotate the second polarizer used as an analyzer in order to set a polarization axis of the detector unit, wherein the detection device is configured to determine at least one optical property of the optical test specimen taking into account its polarization properties.

The test object can be designed as an element or component for AR or VR applications. For example, the test object can be a so-called pancake lens, pancake lens system, a catadioptric lens element operating via polarization, or the like. The optical test object can have at least one lens. The test object can have a polarizing coating. The test object can be designed to extract the test light coupled into it as the result light. The test object can be designed to change the polarization state of the extracted result light compared to the polarization state of the coupled test light. A polarization state can be a polarization direction, a polarization axis, a polarization angle, or the like.

According to one embodiment, the test specimen unit can have a further rotary device for rotating the holding device, which can be operated independently of the first rotary device and the second rotary device.

According to one embodiment, the first and second rotating devices can be operated to rotate the first polarizer and the second polarizer, used as an analyzer, independently of each other. Additionally or alternatively, the first and second rotating devices can be driven piezoelectrically or by a comparable electric or manual drive. Such an embodiment offers the advantage of enabling highly accurate and comprehensive testing of the optical test specimen.

The first polarizer can be configured as either a linear or a circular polarizer. The second polarizer, used as an analyzer, can also be configured as either a linear or a circular polarizer. Both the first and second polarizers can be pivoted into the beam path. This design offers the advantage that suitable components, particularly custom-designed ones, can be used depending on the required configuration.

Furthermore, the illumination unit can have a first displacement device, which can be configured to displace the light source along at least one axis. Additionally or alternatively, the illumination unit can have a diffuser and at least one reticle. Such an embodiment offers the advantage that suitable and versatile conditioning of the test light can be achieved easily.

Furthermore, the detector unit can include an optical system and, additionally or alternatively, an interchangeable aperture. Additionally or alternatively, the detector unit's detection device can include a camera. Such an embodiment offers the advantage of enabling reliable and accurate detection of the resulting light with minimal effort.

The detector unit can also include an evaluation unit connected to the detection device for data transmission. This evaluation unit can be configured to analyze the detected light in order to determine at least one optical property of the test object as a measurement result. Such an embodiment offers the advantage of enabling reliable and accurate testing of the optical test object with regard to its optical properties.

The at least one optical property of the test specimen can include a modulation transfer function, a principal beam angle, distortion, an effective focal length, an image plane tilt, relative illumination, transmission efficiency, an intensity dependent on the polarizer rotation angle, and/or at least one Stokes parameter. Additionally or alternatively, the evaluation device can be configured to determine the at least one optical property of the test specimen depending on different eye-box positions, field angles, focus positions, and/or interpupillary distance positions. The modulation transfer function can also be referred to as the contrast transfer function or modulation transfer function (MTF). Such an embodiment offers the advantage that relevant and important optical properties of the test specimen can be determined comprehensively and precisely.

The test specimen unit may have an additional rotary device for rotating the holding device, which can be operated independently of the first and second rotary devices. Additionally or alternatively, the test specimen unit may The device includes a further displacement mechanism for moving the holding device along at least one axis. The test specimen unit can be arranged between the illumination unit and the detector unit. Such an embodiment offers the advantage of enabling simple, precise, and complete testing of the test specimen.

• Antreiben der ersten Dreheinrichtung, um den ersten Polarisator zu drehen, um eine Polarisationsachse der Beleuchtungseinheit einzustellen, die mit einer Polarisationsachse des Prüflings übereinstimmt;
• Justieren der ersten Dreheinrichtung, um den ersten Polarisator zu drehen, um einen Polarisationszustand des polarisierten Prüflichts, bei dem eine erste maximale Effizienz des Ergebnislichts erhalten wird, als korrekten Polarisationszustand des in den Prüfling eingekoppelten polarisierten Lichts zu erfassen; und
• Bestimmen mindestens einer optischen Eigenschaft des Prüflings als Messergebnis unter Verwendung mindestens eines korrekt erfassten Polarisationszustandes.

A method for operating an embodiment of a device mentioned herein is also presented, the method comprising the following steps:

• Driving the first rotary device to rotate the first polarizer to adjust a polarization axis of the illumination unit that coincides with a polarization axis of the test object;
• Adjusting the first rotary device to rotate the first polarizer in order to detect a polarization state of the polarized test light at which a first maximum efficiency of the result light is obtained, as the correct polarization state of the polarized light coupled into the test specimen; and
• Determine at least one optical property of the test object as a measurement result using at least one correctly recorded polarization state.

The steps of the procedure can be performed using or with the aid of the device's evaluation unit. The set polarization axis of the illumination unit can approximately coincide with the polarization axis of the test specimen. "Approximately" means within a tolerance range.

• Antreiben der zweiten Dreheinrichtung, um den als Analysator verwendeten zweiten Polarisator zu drehen, um eine Polarisationsachse der Detektoreinheit einzustellen, die mit einer Polarisationsachse des Prüflings übereinstimmt; und
• Justieren der zweiten Dreheinrichtung, um den als Analysator verwendeten zweiten Polarisator zu drehen, bis eine zweite maximale Effizienz des Ergebnislichts erhalten wird, um einen korrekten Polarisationszustand des vom Prüfling ausgekoppelten polarisierten Lichts zu erfassen

According to one embodiment, the method may optionally include the following further steps:

• Driving the second rotary device to rotate the second polarizer used as an analyzer in order to set a polarization axis of the detector unit that coincides with a polarization axis of the test object; and
• Adjusting the second rotating device to rotate the second polarizer used as an analyzer until a second maximum efficiency of the result light is obtained in order to detect a correct polarization state of the polarized light coupled out from the test object.

According to one embodiment, the method can include a step of inducing a rotational movement of the first polarizer together with the test specimen into a changed angular orientation. At least the step of determining the changed angular orientation can be repeated. This enables a correct and complete measurement of at least one optical property of the test specimen.

• 1 eine schematische Darstellung einer Beleuchtungseinheit eines Ausführungsbeispiels einer Vorrichtung zum Prüfen eines Polarisationseigenschaften aufweisenden optischen Prüflings;
• 2 eine schematische Darstellung einer Prüflingseinheit eines Ausführungsbeispiels einer Vorrichtung zum Prüfen eines Polarisationseigenschaften aufweisenden optischen Prüflings;
• 3 eine schematische Darstellung einer Detektoreinheit eines Ausführungsbeispiels einer Vorrichtung zum Prüfen eines Polarisationseigenschaften aufweisenden optischen Prüflings;
• 4 eine schematische Darstellung eines Ausführungsbeispiels einer Vorrichtung zum Prüfen eines Polarisationseigenschaften aufweisenden optischen Prüflings; und
• 5 ein Ablaufdiagramm eines Ausführungsbeispiels eines Verfahrens zum Betreiben einer Vorrichtung zum Prüfen eines Polarisationseigenschaften aufweisenden optischen Prüflings.

An embodiment of the invention is shown purely schematically in the drawings and is described in more detail below. It shows

• 1 a schematic representation of a lighting unit of an embodiment of a device for testing an optical test object exhibiting polarization properties;
• 2 a schematic representation of a test specimen unit of an embodiment of a device for testing an optical test specimen exhibiting polarization properties;
• 3 a schematic representation of a detector unit of an embodiment of a device for testing an optical test object exhibiting polarization properties;
• 4 a schematic representation of an embodiment of a device for testing an optical test specimen exhibiting polarization properties; and
• 5 a flowchart of an exemplary embodiment of a method for operating a device for testing an optical test specimen exhibiting polarization properties.

In the following description of favorable embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the various figures and having a similar effect, without repeating these elements.

1 Figure 1 shows a schematic representation of an illumination unit 100 of an embodiment of a device for testing an optical test specimen exhibiting polarization properties. The test specimen, or polarizing optical test specimen, is designed, for example, as a so-called pancake lens, pancake lens system, or the like for AR or VR applications. An embodiment of the complete device for testing the optical test specimen exhibiting polarization properties is shown in Figure 1. 4 depicted.

The illumination unit 100 comprises a light source 101, a first rotating device 103, and a first polarizer 106. The light source 101 is configured to emit test light to the test object. The first polarizer 106 is configured to polarize the test light emitted by the light source 101. The first rotating device 103 and the first polarizer 106 are connected to each other. The two components are mechanically coupled. The first rotary device 103 is designed to rotate the first polarizer 106 in order to set a polarization state of the polarized test light.

Depending on the embodiment, the first polarizer 106 is configured as a linear polarizer or as a circular polarizer. For example, the first rotary device 103 is driven by a motor. According to one embodiment, the illumination unit 100 also includes a first displacement device 102. The first displacement device 102 is configured to displace at least the light source 101 along at least one axis. Additionally or alternatively, the illumination unit 100 includes a diffuser 105 and/or at least one reticle 107 or mask element.

In other words, the illumination unit 100, which can also be referred to as the illumination system, comprises, according to one embodiment, the light source 101 with the first polarizer 106, which can be linear, circular, etc., depending on the measurement task or customer requirements, and which is mounted on the first rotary device 103. It also includes a connection system 104 for the first polarizer 106, which enables control of the polarization state of the light or test light emitted by the light source 101, which is mounted on the first sliding device 102, allowing free movement or linear motion along the x/z axis. The illumination unit 100 also includes, for example, a diffuser 105 and various types of masks or reticles 107, such as a cross or ring reticle. Furthermore, it is optionally possible to introduce different reticles into the beam path of the light source 101 via an interchangeable mechanism.

2 Figure 1 shows a schematic representation of a test specimen unit 200 of an embodiment of a device for testing an optical test specimen exhibiting polarization properties. An embodiment of the complete device for testing the optical test specimen exhibiting polarization properties is shown in Figure 2. 4 depicted.

The test specimen unit 200 comprises a holding device 201 for holding the test specimen. The holding device 201 is designed to fix the test specimen in the device. The test specimen unit 200 also comprises a further rotary device 203, which can be operated independently of the first rotary device of the lighting unit and a second rotary device of a detector unit of the device, for rotating the holding device 201. For this purpose, the further rotary device 203 and the holding device 201 are connected or mechanically coupled to each other. Optionally, the test specimen unit 200 also comprises a further displacement device 202 for displacing the holding device 201 along at least one axis. Thus, the further displacement device 202 is designed to displace the holding device 201 along at least one axis.

In other words, according to one embodiment, the test specimen unit 200 comprises a holding device 201, also referred to as a test specimen seat, in an optionally customer-specific design. This holding device allows free movement of the test specimen along an x/z axis by means of the further displacement device 202 or several further displacement devices 202 for an x-axis and/or a y-axis and/or a z-axis, as well as rotation of the test specimen by means of the further rotary device 203. The rotary device 203 enables movement of the holding device 201 relative to a rotational movement of the polarizer of the lighting unit of the device, which is connected to the light source, in order to maintain the correct polarization angle or polarization state or polarization orientation required for measurements.

3 Figure 1 shows a schematic representation of a detector unit 300 of an embodiment of a device for testing an optical test piece exhibiting polarization properties. An embodiment of the complete device for testing the optical test piece exhibiting polarization properties is shown in Figure 2. 4 depicted.

The detector unit 300 comprises a detection device 304, a second rotary device 302, and a second polarizer 303 used as an analyzer. The second polarizer 303, used as an analyzer, is configured to transmit polarized result light coupled from the test object, depending on its polarization state, in response to the polarized test light coupled into the test object by the illumination unit of the device. In other words, the second polarizer 303, used as an analyzer, is configured to align the polarization axis of the detection beam path with the polarization axis of the test object. The second rotary device 302 and the second polarizer 303, used as an analyzer, are connected or mechanically coupled to each other. The second rotary device 302 is configured to rotate the second polarizer 303, used as an analyzer, to align the polarization axis of the detection beam path. The detection device 304 closes The lich is designed to detect the result light transmitted by the second polarizer 303 used as an analyzer.

Depending on the embodiment, the second polarizer 303, used as an analyzer, is configured as either a linear polarizer or a circular polarizer. The second rotary device 302 can, for example, be motorized. According to one embodiment, the detector unit 300 further comprises an optical system 301 and/or an interchangeable aperture 307. The detection device 304 includes, for example, a camera. The optical system 301 can be configured as a telescope or conoscope. Furthermore, the optical system 301 can generate a diffraction-limited image for certain field angles, e.g., up to a field angle (full-field of view) of 120°. The combination of the detection device 304 and the optical system 301 can thus include a camera with a telescope and, for example, also an adjustable focus.

Furthermore, according to one embodiment, the detector unit 300 comprises an evaluation unit 305. The evaluation unit 305 is capable of data transmission and can be connected to, or is already connected to, the acquisition unit 304. The evaluation unit 305 is configured to evaluate the result light acquired by the acquisition unit 304 in order to determine at least one optical property of the test object as a measurement result. Optionally, the evaluation unit 305 is additionally configured to determine the at least one optical property of the test object depending on different eye-box positions, angular resolutions, and/or interpupillary distance positions. Examples of the at least one optical property of the test object include a modulation transfer function, a principal beam angle, distortion, an effective focal length, image plane tilt, relative illumination, transmission efficiency, an intensity dependent on the polarizer rotation angle, and/or other parameters, such as a Stokes parameter or components of a Müller matrix.

In other words, the at least one optical property or measurement parameter includes a line spread function (LSF) or edge spread function (ESF) from which the mean time factor (MTF) is calculated; a computational distortion ratio (CRA) from which distortion parameters can be calculated; the effective focal length (EFL); the tilt of the image plane; the relative illumination; the virtual image distance (VID); additional measurements due to the setup include: transmission efficiency due to the set polarization angle or the polarizing properties of the device under test; and parameters dependent on the rotation of the integrated analyzer on the detector unit 300 include: the intensity plotted against the rotation angle of the polarizer; and Stokes parameters. The measurements are calculated, in particular, from the efficiency results measured during the rotation of the polarizer or analyzer.

In other words, the detector unit 300 comprises the optical system 301, the second rotary unit 302 with the second polarizer 303, which serves as an analyzer and is designed to be linear, circular, etc., depending on customer requirements, and a detection unit 304, for example a camera, for capturing the transmitted light or result light, which is connected to the evaluation unit 305, which is, for example, a computer with software for image processing and analysis of measurement results. The second rotary unit 302 with the second polarizer 303, which serves as an analyzer, moves independently of the rotary units of the test specimen unit and the illumination unit of the device, making it possible to measure the intensity across polarization angles as well as other image quality parameters. The optical system 301 optionally also includes the interchangeable aperture 307, which can be implemented as either a physical or virtual aperture.

4 Figure 1 shows a schematic representation of an embodiment of a device 400 for testing an optical test specimen exhibiting polarization properties. The device 400 comprises the illumination unit 100. 1 or a similar lighting unit and the detector unit 300 from 3 or a similar detector unit. Additionally, the device 400 also includes the test specimen unit 200. 2 or a similar test object unit. The test object unit 200 is arranged between the illumination unit 100 and the detector unit 300. The illumination unit 100, the test object unit 200, and the detection unit 300 are mechanically connected to each other and designed as a single, integrated measuring device.

According to one embodiment, the first rotary device of the illumination unit 100 and the second rotary device of the detector unit 300 can be operated to rotate the first polarizer of the illumination unit 100 and the second polarizer of the detector unit 300, which is used as an analyzer, independently of each other. Optionally, the further rotary device of the test specimen unit 200 can also be operated to rotate the holding device of the test specimen unit 200 independently of the polarizers of the illumination unit 100 and the detector unit 300.

5 Figure 500 shows a flowchart of an embodiment of method 500 for operating a device for testing an optical test specimen exhibiting polarization properties. Method 500 for operating the device can be carried out to... 4 or to operate a similar device to test an optical specimen exhibiting polarization properties or to determine its optical properties. The steps of method 500 for operation can be carried out using the light source, the rotating devices, the detection device, and the evaluation device of the apparatus.

The operating procedure 500 comprises a driving step 510, an adjusting step 520, and a determining step 530. Additionally, the operating procedure 500 includes a driving step for the light source to emit the test light.

In step 510 of the drive process, the first rotary device is driven to rotate the first polarizer to set a polarization state of the polarized test light that approximately matches a polarization state of the test object, and the second rotary device is driven to rotate the second polarizer, used as an analyzer, to set a polarization state of the beam path in the detector unit that approximately matches a polarization state of the test object. The result light, also polarized, can be acquired and evaluated for this purpose.

In step 520 of the adjustment process, the first rotary device is adjusted to rotate the first polarizer to set a polarization state of the polarized test light that achieves a first maximum efficiency of the light beams transmitted by the test object, i.e., the result light. The second rotary device is then adjusted to rotate the second polarizer, used as an analyzer, to achieve a second maximum efficiency of the light beams transmitted by the test object, i.e., the result light, with its correct polarization state, can then be captured and evaluated.

In step 530 of the determination process, at least one optical property of the test specimen is determined as a measurement result using at least one correctly recorded polarization state. For example, an MTF measurement is performed in step 530. For this purpose, the resulting light, which is polarized, is recorded and evaluated.

The steps of controlling and adjusting the second polarizer, used as an analyzer, can be optional. The analyzer is always relevant when measuring individual components of a pancake lens to account for their polarization behavior during the measurement. For measuring the image quality of a composite pancake optic, the analyzer on the detection side is not necessary, as the human eye is not sensitive to polarization.

According to one embodiment, the operating method 500 also includes a step 540 of causing a rotational movement of the polarizer together with the test specimen into a changed angular orientation. Then at least the step 530 of determining the changed angular orientation is repeated. This additional step is advantageous, for example, when measuring the chief ray angle (CRA).

The following is a slightly different description of the operation of method 500 according to an exemplary embodiment. The test specimen is placed in the system or device for testing. The polarization angle of the first polarizer is adjusted by rotation so that the polarization direction of the test light closely approximates the polarization axis of the test specimen. Similarly, if necessary, depending on whether a single component of a pancake lens or a complete pancake optic is to be measured, the polarization axis of the detector or the detection beam path behind the test specimen is rotated by rotating the analyzer or the second polarizer used as an analyzer, in order to also closely approximate the polarization axis of the test specimen. Then, the first polarizer is rotated at the light source to achieve an initial maximum efficiency of the light transmitted through the test specimen. The angle is recorded as the correct polarization axis of the coupled light or the test light. The same check is optionally performed with the analyzer on the detector side, whereby the position of the analyzer at which the light coupled out from the test object or the resulting light exhibits a second maximum efficiency is recorded as the correct polarization angle of the coupled light or the detection beam path. Then, for example, an MTF measurement is performed with the correct polarization angles. Subsequently, the first polarization angle is additionally or alternatively determined. The sator is rotated together with the test specimen during further measurements at the light source. This enables a correct and complete measurement of, for example, MTF and CRA of pancake lens systems or comparable optical systems.

The following section briefly describes, in other words and in summary, exemplary embodiments as well as the background and advantages of exemplary embodiments, with reference to the figures described above.

Optical AR and VR elements, which can be tested here, may have additional coatings that influence or alter the polarization properties or polarization direction of the light as it passes through the optical system, sometimes multiple times. This creates a folded beam path, enabling a very compact design for these optical systems and thus for the AR/VR systems as a whole. When measuring optical properties, such as the MTF, of such optics, also known as pancake lenses, it is therefore essential to ensure that the light meets the polarization requirements. If the polarizing properties of the pancake lenses are disregarded during testing, this leads to a misinterpretation of the measurement results, for example, that they are considered too positive or too negative. Against this background, the device proposed here offers a way to adjust the polarization properties of the light coupled into the test object when measuring optical parameters, as well as to adjust or tune the detection unit to a preferred polarization of the light coupled out from the test object. Examples of optical parameters to be measured include: MTF, CRA (Chief Ray Angle), absolute efficiency, distortion, polarization parameters such as Stokes parameters or components of a Müller matrix, etc.

The same method can also be used for the effective characterization of subcomponents of the pancake lens, such as individual lenses with applied polarizing elements, in order to test their quality and other optical properties under the polarization conditions used in the overall lens.

A precise measurement of the MTF of a pancake lens cannot be performed without correcting the polarization state of the coupled light that is to be transmitted through the optical system. Similarly, the coupled-out light will have a different polarization state than that of the coupled-in light. A pancake lens forms a folded imaging system with two or more lenses. The correct propagation of optical rays through the system depends on the polarization state of the incident light. Thus, unpolarized or incorrectly polarized light would lead to incorrect imaging by the test object and therefore to an incorrect interpretation of the measurement results and consequently to an incorrect conclusion regarding the imaging performance of the system. This can be remedied according to the exemplary embodiments.

Thus, according to the exemplary embodiments, unlike a standard measuring system with motorized polarization control, more than just the measurement of polarization is made possible. In other words, the measurement of the aforementioned optical parameters of a polarizing test specimen is enabled, taking into account the polarization of the coupled light.

This is achieved, according to exemplary embodiments, in particular by a special design: the detector unit 300 and illumination unit 100, also referred to as a telescope or conoscope and camera (where the camera can be focusable or non-focusable), each have a polarizer 106 and analyzer 303, respectively, connected to a rotating device 302 and 103. The illumination unit 100 can also have a focusable or non-focusable collimator. Generally speaking, the object to be imaged by the test specimen (usually a reticle) can be located at a finite or infinite optical distance from the test specimen. The polarizer 106 and analyzer 303 can be either linear or circular. In other words, a light source 101 is connected to, for example, a linear polarizer 106 and coupled to the first rotary device 103, which is used to control coupled or incident light. The analyzer 303 on the detector side makes it possible to measure polarization changes propagating through the test object or to filter the light incident on the detector. According to exemplary embodiments, polarization adjustments based on the integration of a rotary device, in particular a piezoelectrically or motor-driven one, as the first rotary device 103 in the illumination unit 100 or light source unit are thus made possible in order to control the polarization state of coupled or coupled or incident light and to detect the efficiency fluctuations caused by the test object. A fixed or rotatable linear polarizer can also be added to the detector unit 300 as an analyzer 303 in order to measure changes in the polarization angle after the light has passed through the test object. The possibility of controlling the polarization of According to exemplary embodiments, coupled light and the measurement of the resulting Stokes parameters on the detector side enable a holistic and completely correct evaluation of image quality parameters, such as MTF and/or efficiency.

Thus, exemplary embodiments also offer advantages because the polarization properties of light are becoming increasingly important in the production of VR and AR elements. Being able to precisely and comprehensively test and consequently utilize the optical properties of test specimens, taking into account their polarization properties, using the device 400 and/or the method 500, helps to make such elements smaller and more efficient by folding the propagation of light. Therefore, according to exemplary embodiments, a concept can be provided that makes it possible both to control the polarization state of the light source 101 and, for example, to correctly measure the resulting Stokes parameters and other optical parameters of the test specimens.

If an embodiment includes an “and/or” connection between a first feature and a second feature, this is to be read as meaning that the embodiment according to one embodiment has both the first feature and the second feature, and according to another embodiment either only the first feature or only the second feature.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• US 20200096817A1 [0003]
• JP 2019144237A [0004]

Claims (11)

Device (400) for testing an optical test specimen exhibiting polarization properties, the device (400) comprising: a lighting unit (100) with a light source (101), a first polarizer (106), and a first rotating device (103), wherein the light source (101) is configured to emit test light to the test specimen, wherein the first polarizer (106) is configured to polarize the test light, and wherein the first rotating device (103) is connected to the first polarizer (106) and configured to rotate the first polarizer (106) to adjust a polarization state of the polarized test light and/or the polarization axis of the lighting unit (100); a test specimen unit (200) comprising a holding device (201) for holding the test specimen; and a detector unit (300) comprising a detection device (304), a second polarizer (303) used as an analyzer, and a second rotating device (302), wherein the second polarizer (303) used as an analyzer is configured to transmit polarized result light coupled from the test object in response to the polarized test light according to the polarization state of the result light, wherein the second rotating device (302) is connected to the second polarizer (303) used as an analyzer and is configured to rotate the second polarizer (303) used as an analyzer in order to adjust a polarization axis of the detector unit (300), wherein the detection device (304) is configured to determine at least one optical property of the optical test object taking into account its polarization properties. Device (400) according to Claim 1 , wherein the first rotary device (103) and the second rotary device (302) are operable to rotate the first polarizer (106) and the second polarizer (303) used as an analyzer independently of each other, and/or wherein the first rotary device (103) and/or the second rotary device (302) are driven by a motor. Device (400) according to one of the preceding claims, wherein the first polarizer (106) is configured as a linear polarizer or as a circular polarizer, wherein the second polarizer (303) used as an analyzer is configured as a linear polarizer or as a circular polarizer. Device (400) according to one of the preceding claims, wherein the lighting unit (100) has a first displacement device (102) configured to displace the light source (101) along at least one axis, and/or wherein the lighting unit (100) has a diffuser (105) and/or at least one reticle (107). Device (400) according to one of the preceding claims, wherein the detector unit (300) has an optical system (301) and/or an interchangeable aperture (307) and/or wherein the detection device (304) has a focusable or non-focusable camera. Device (400) according to one of the preceding claims, wherein the detector unit (300) has an evaluation unit (305) connected to the detection device (304) in a data-transmitting manner, which is configured to evaluate the detected result light in order to determine at least one optical property of the test object as a measurement result. Device (400) according to Claim 6 , wherein the at least one optical property of the test specimen comprises a modulation transfer function, a principal beam angle, a distortion, a polarization angle, an effective focal length, an image plane tilt, a relative illumination, a transmission efficiency, an intensity dependent on the polarizer rotation angle and/or at least one Stokes parameter, and/or wherein the evaluation device (305) is configured to determine the at least one optical property of the test specimen depending on different eye-box positions, field angles and/or interpupillary distance positions. Device (400) according to one of the preceding claims, wherein the test object unit (200) has a further rotary device (203) for rotating the holding device (201) that can be operated independently of the first rotary device (103) and the second rotary device (302), and/or wherein the test object unit (200) has a further displacement device (202) for displacing the holding device (201) along at least one axis. Method (500) for operating a device (400) according to one of the preceding claims, wherein the method (500) comprises the following steps: driving (510) the first rotary device (103) to rotate the first polarizer (106) to set a polarization axis of the illumination unit (100) that approximately coincides with a polarization axis of the test object, adjusting (520) the first rotary device (103) to rotate the first polarizer (106) to a polarization state of the polarized test light in which a first maximum efficiency of the to determine the result light obtained as the correct polarization state of the polarized light coupled into the test specimen; and to determine (530) at least one optical property of the test specimen as a measurement result using at least one correctly determined polarization state. Procedure (500) according to Claim 9 , wherein the method (500) further comprises the following steps: driving the second rotary device (302) to rotate the second polarizer (303) used as an analyzer in order to set a polarization axis of the detector unit that approximately coincides with a polarization axis of the test object; and adjusting the second rotary device (302) to rotate the second polarizer (303) used as an analyzer until a second maximum efficiency of the result light is obtained in order to detect a correct polarization state of the polarized light coupled out from the test object Procedure (500) according to Claim 9 , with a step (540) of causing a rotational movement of the first polarizer (106) together with the test specimen into a changed angular orientation, wherein at least the step (530) of determining for the changed angular orientation is repeated.