Optical testing apparatus and method of operating optical testing apparatus

Abstract

The invention discloses an optical test device (100) having: a light source (105) for emitting a light beam (110); and a light beam shaping unit (115) having a diffractive optical element (DOE, 120) for shaping the light beam (110) and guiding it onto a coupling-in region (125) of the optical workpiece (130) in order to couple the shaped light into the optical workpiece (130) to be inspected. Furthermore, the optical testing device (100) has: a workpiece holding element (135) for holding the optical workpiece (130); and a detector (145) for evaluating the light (110) emitted from the outcoupling region (140) of the optical workpiece (130) in order to inspect an optical property of the workpiece (130).

Description

Technical Field

[0001] The invention presented herein provides an optical testing device and a method for operating an optical testing device. Background Art

[0002] In order to test an optical workpiece (i.e., a workpiece that is at least partially transparent to light), the workpiece can be illuminated with a light beam having a certain intensity distribution and / or wavelength, and then measured to see how this intensity distribution changes, or how light having a certain wavelength is attenuated, so that one or more corresponding parameters of the workpiece can be detected. Summary of the Invention

[0003] Against this background, the present invention aims to improve the inspection of optical workpieces.

[0004] This object is achieved by the subject-matter of the independent claims.

[0005] The method described herein produces an optical test device having the following characteristics:

[0006] - a light source for emitting a light beam;

[0007] a beam shaping unit having a diffractive optical element for shaping the light beam and directing it onto a coupling-in region of the optical workpiece in order to couple the shaped light into the optical workpiece to be inspected;

[0008] a workpiece holding element for holding an optical workpiece;

[0009] A detector for evaluating the light emerging from the coupling-out region of the optical workpiece in order to check the optical properties of the workpiece with respect to the properties to be checked.

[0010] A light source can be understood to mean, for example, a laser light source that emits a laser beam as a light beam. For example, a beam shaping unit can be understood to mean a unit that uses a diffractive optical element to shape a light beam, in particular a laser beam, and outputs it to an incoupling region of an optical workpiece. In particular, the diffraction effect serves to deflect light at a predetermined wavelength that strikes this optical element at a certain angle (e.g., normal incidence), thereby illuminating the incoupling region at a predetermined angle and / or a predetermined angular range, so that the shaped light propagates along a desired optical path in the optical workpiece and is coupled out again in an outcoupling region of the optical workpiece and can enter a detector. An optical workpiece can be understood here as a waveguide, light guide, or optical fiber designed to transmit light with desired physical properties. For example, such an optical workpiece can be used as part of data goggles, augmented reality (AR) or virtual reality (VR) display systems, a near-eye device (NED), or another optical element in which an optical function with high optical quality is to be implemented. This received light is then tested in the detector itself for the desired properties. Such characteristics to be detected may be, for example, MTF, PSF, LSF and / or ESF parameters or other parameters such as chief ray angle (CRA) or chromatic aberration, which can be used to assess the quality of the optical workpiece.

[0011] The detector may comprise one camera, at least two cameras, or a plurality of cameras, or a portion of a detector unit. The one or more cameras may in turn comprise one or more telescopes and may have a fixed or variable focal length. The one or more cameras may be implemented as electronic cameras, such as CCD or CMOS cameras. Additionally or alternatively, the camera may be implemented as a color camera. In other embodiments, the detector may be implemented as a conoscopic polarimeter, a spectrometer, or a spectrophotometer.

[0012] The method proposed herein is based on the recognition that by using diffractive optical elements in a beam shaping unit, a specific desired deflection or shaping of the light beam can be performed in a technically very simple and cost-effective manner, in particular with respect to the angle at which the sample under test is illuminated, wherein parameters that are highly relevant to the function of the optical workpiece can be tested simply and reliably. In the prior art, one or more illumination units are moved or rotated for illuminating the sample under test at multiple angles of incidence or field angles. Publication US 20220163423 outlines a measurement system for waveguides used in AR / VR devices. The system comprises a light engine comprising a light source 320 and a lens 310. In one embodiment, the light source and the lens can be rotated or tilted to adjust the angle of incidence on the device under test 100.

[0013] Particularly advantageous embodiments of the method presented herein are those in which the beam shaping unit is designed to actively change the optical properties of the diffractive optical element and / or to use another diffractive optical element to shape the light beam. For example, the diffractive optical element can change its shape or structure by applying or changing a voltage, so that when illuminated by light from the light source, the pattern or deflection of the light differs from that without applying or changing the voltage. It is also conceivable to provide several corresponding diffractive optical elements in the beam shaping unit, which are introduced into the beam path of the light source as required, so that the desired shape or deflection of the light beam emitted into the coupling-in region can be set by replacing the corresponding diffractive optical element. This allows the light to be quickly and easily modified according to the desired application.

[0014] A particularly advantageous embodiment of the method presented here is one in which the beam shaping unit is designed to project a light pattern, in particular a dot pattern, a cross pattern, or a ring pattern, onto the coupling-in region using a diffractive optical element. This embodiment of the method presented here offers the advantage that by defining a specific light pattern and illuminating the sample under test with it at a set of predetermined field angles, physical effects relevant to the property under investigation can be particularly well tested.

[0015] According to another embodiment of the method proposed herein, the light source and / or the beam-shaping unit are designed to be adjustable along at least one axis, in particular to be displaced and / or rotated about at least one axis. For example, the light source and / or the beam-shaping unit can be moved vertically or laterally, or can also be tilted or rotated about one or more axes. Such an embodiment offers the advantage that, due to the flexible movement of the light source and / or the beam-shaping unit, the light beam formed by the beam-shaping unit can be flexibly coupled into the coupling region of the workpiece.

[0016] Another advantageous embodiment of the method proposed herein is one in which the workpiece holding element is designed to be adjustable along at least one axis, in particular to be displaced and / or rotated about at least one axis. Such an embodiment also allows for flexible positioning of the workpiece, enabling the testing of certain properties and / or parameters of the workpiece using the testing device proposed herein.

[0017] Also advantageous are embodiments of the method presented herein in which the workpiece holding element is designed to hold a flat, optically transmissive and / or reflective workpiece, such as a waveguide. The optical workpiece to be tested comprises an incoupling region and an outcoupling region. Such an embodiment enables the installation and, therefore, the testing of frequently used optical components, allowing for flexible use of the testing apparatus presented herein.

[0018] Furthermore, according to another embodiment of the method proposed herein, the detector is designed to be adjustable along at least one axis, in particular, to be displaced and / or rotated about at least one axis. Such an embodiment also allows the detector to flexibly adapt to different beam angles of the light beam emerging from the decoupling region of the optical workpiece. This makes it particularly easy to detect certain characteristics or parameters of the workpiece when a beam or light pattern of a predetermined shape is coupled in.

[0019] In one embodiment of the method presented herein, the detector can include a camera comprising an image sensor and an imaging optical system, such as a telescope. The camera can have a fixed or variable focal length. Optionally, the camera can be implemented as a color camera with different spectral channels. In this way, the wavelength-dependent properties of the optical artifact under test can be studied.

[0020] Another advantageous embodiment of the method proposed herein is one in which the detector comprises at least two partial detector units or cameras, each of which is designed to receive light emitted from a different direction of the outcoupling region, in particular wherein the at least two partial detector units or cameras are arranged adjacent to one another. Such an embodiment enables the parallel measurement or recording of values ​​or properties of the workpiece at different angles relative to the optical axis, resulting in an overall reduction in the minimum measurement duration and / or the ability to perform a significantly wider range of measurements, which also include, for example, the measurement or recording of different parameters or properties.

[0021] According to another embodiment of the method proposed herein, the detector is adapted to be movable at least partially within a range of motion. For example, this movement can occur along the optical axis of the detector and in at least two directions perpendicular thereto, so that the detector is aligned with the decoupling region at different locations and in different directions. This embodiment of the method proposed herein offers the advantage of being able to capture light beams coupled out in different directions and to evaluate them accordingly in order to detect desired characteristics or corresponding parameters.

[0022] The advantages mentioned above can also be implemented in the form of a process method for operating an optical testing device according to the version proposed herein, the method comprising the following steps:

[0023] - outputting a light beam from the light source to the diffractive optical element of the beam shaping unit; and

[0024] - evaluating the light beam emitted from the outcoupling region of the optical workpiece to be tested in order to check the property to be checked of the workpiece.

[0025] After passing through the diffractive optical element, the light beam can be emitted into the coupling-in region and coupled into the workpiece. In the coupling-out region, the light beam propagating through the workpiece can be recorded by a detector, so that the light recorded there can be evaluated accordingly to detect desired parameters or desired properties.

[0026] The method proposed herein also includes a control device or a control unit, which is designed to execute, control or implement the steps of the variant of the method proposed herein in the corresponding unit or device. This embodiment of the invention in the form of a control device can also achieve the object of the invention quickly and efficiently.

[0027] To this end, the control device may include at least one computing unit for processing signals or data, at least one memory unit for storing signals or data, at least one interface to a sensor or actuator for reading sensor signals from the sensor or for outputting control signals to the actuator, and / or at least one communication interface embedded in a communication protocol for reading or outputting data. The computing unit may be, for example, a signal processor, a microcontroller, etc., wherein the memory unit may be a flash memory or a magnetic storage unit. The communication interface may be designed to read or output data wirelessly and / or by wire, wherein a communication interface capable of reading or outputting data by wire may, for example, read data electrically or optically from a corresponding data transmission line or input data into a corresponding data transmission line.

[0028] In the present context, a control device can be understood as an electrical device that processes sensor signals and outputs control and / or data signals based on these sensor signals. The control device may have interfaces that can be hardware-based and / or software-based. In a hardware design, the interface may, for example, be part of a so-called ASIC system that contains the various functions of the control device. However, the interface may also be a separate integrated circuit or at least partially composed of discrete components. In a software-based design, for example, these interfaces may be software modules that reside on a microcontroller along with other software modules.

[0029] Also advantageous is a computer program product or a computer program with a program code, which can be stored on a machine-readable carrier or storage medium, such as a semiconductor memory, hard disk memory or optical memory, and which is used, in particular, to execute, implement and / or control the steps of the method according to one of the embodiments described above when the program product or program is executed on a computer or device. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] At least one embodiment of the present invention is explained in more detail below with reference to the accompanying drawings. In the drawings:

[0031] Figure 1a A diagram showing an embodiment of an optical testing apparatus;

[0032] Figure 1b A diagram showing an illumination portion of an optical testing apparatus;

[0033] Figure 2 A schematic diagram illustrating an embodiment of an optical testing apparatus is shown;

[0034] Figure 3 shows a schematic diagram of a light source and a beam shaping unit as an illumination unit for an embodiment of the method described herein;

[0035] Figure 4 shows a schematic diagram of a workpiece holding element for use with an embodiment of the method described herein;

[0036] Figure 5 shows a schematic diagram of a detector for use with embodiments of the methods described herein;

[0037] Figure 6 a flow chart illustrating an example of an embodiment of a method of operating an optical testing apparatus; and

[0038] Figure 7 A block diagram showing an example of embodiment of a control unit for operating an optical testing device is shown. DETAILED DESCRIPTION

[0039] The same or similar elements are identified by the same or similar reference numerals in the following description, wherein repeated description of these elements is omitted.

[0040] Figure 1aA diagram shows an embodiment of an optical testing device 100, in which a light source 105, such as a laser light source in the form of a laser diode, is used. Light source 105 can be relatively flat and small, and therefore requires little installation space. A light beam 110 is emitted from light source 105 and then modified by a beam shaping unit 115. Light shaping unit 115 includes a diffractive optical element 120, which is designed to deflect the light of light beam 110 by diffraction and / or form a light pattern therefrom. This light is then coupled into an optical workpiece 130 at an incoupling region 125, which is, for example, placed or fixed on a workpiece holding element 135. The light of the now formed light beam 110 can then propagate in workpiece 130, for example, via total internal reflection, and be coupled out of workpiece 130 at an outcoupling region 140 and received or evaluated by a detector 145. This evaluation can be carried out, for example, in such a way that the light is received by one and / or more partial detectors or cameras 150 and evaluated with regard to its wavelength, intensity and / or light pattern, so that with the aid of this evaluation and the original parameter information of the light beam 110 before or after the beam shaping unit 115, the changes of this light of the light beam in the workpiece 130 can be inferred and thus the corresponding properties of the workpiece, in particular the corresponding parameters, can subsequently be detected or determined.

[0041] The partial detector 150 or individual sensors of the detector 145 can be arranged, for example, movably so as to be able to receive the light beam 110 emerging from the outcoupling region 140 in different directions, for example, so as to be able to infer the corresponding propagation behavior of the light in the workpiece 130, in particular optical properties (such as MTF) observed from different field positions or field angles. It is also conceivable that the sensors of the detector 145 or the partial detector 150 are designed to detect light of different wavelengths, so that, for example, color-related optical parameters of the workpiece 130, such as the color MTF, can also be evaluated.

[0042] It is also conceivable that the beam shaping unit 115 is designed to actively change or modify the diffractive optical element 120. This can be achieved, for example, by applying a voltage to the diffractive optical element 120 by means of the control unit 155, so that the diffraction properties of the diffractive optical element change, thereby providing a deflection property for the light beam 110 that is different from the original deflection property. It is also conceivable that the control unit introduces a further diffractive optical element 160 into the beam path of the light beam 110, which then has a deflection property that is different from that of the diffractive optical element 120. This can also lead to a change in the beam shaping of the beam shaping unit 115, thereby enabling different illumination scenarios for the optical workpiece under test.

[0043] These systems for testing optical workpieces are used to measure, for example, chromatic aberrations or MTF / PSF / LSF / ESF or other efficiency parameters. The illumination pattern as well as the angle can be easily adjusted according to the requirements of the sample.

[0044] DOE-collimators disclosed in the prior art are used to calibrate assembled camera systems. In these collimator-DOE combinations, only the use of dot patterns is disclosed. Measurement systems used to test AR / VR waveguides either utilize mechanical displacement to change the angle of incidence of light onto the DUT's entrance pupil or use multiple collimators. Mechanically pivoting the light source results in extended measurement times, and using multiple collimators limits the available angles of incidence. Most measurement systems for waveguides do not use a laser illumination source, and similarly, the source does not use a DOE to create a pattern for measuring different field positions.

[0045] Figure 1b A detailed illustration of the irradiation of the sample under test is provided. Figure 1b In the embodiment shown in FIG, light source 105 emits collimated laser light 110. Light source 105 may include one or more laser emitters. Collimated light 110 illuminates a diffractive optical element (DOE) 120 and is deflected or "fanned" at a predetermined deflection angle. Thus, the collimated light illuminates the sample under test at multiple field angles. In the embodiment described herein, illumination pattern 116 is a dot pattern. Other patterns, such as a cross pattern, a ring pattern, or a bow-tie pattern, may also be implemented.

[0046] Figure 2 A schematic diagram of an embodiment of an optical testing device 100 is shown, as has already been described, for example, in Figure 1a The schematic diagram briefly explains the Figure 1a Compared with the figure, now Figure 2 , for example, light source 105 is arranged together with beam shaping unit 115 on first holder 200, forming a corresponding holder mechanism 205 for vertically or horizontally displacing holder 200 or rotating it about different axes. Thus, for example, light source and beam shaping unit 115 can be moved or rotated so that light beam 110 is coupled into workpiece 130 in coupling-in region 125 at a desired position and / or at a certain angle and then exits workpiece 130 again in coupling-out region 140 to be captured by detector 145. Detector 145 is therefore also arranged on or attached to detector mechanism 210, which is, for example, designed similarly to holder mechanism 205 and thus also allows for vertical or horizontal displacement or rotation about different axes. In this way, light beam 110 emerging from decoupling region 140 can also be recorded by detector 145 and subsequently evaluated.

[0047] Figure 3 A schematic diagram of a light source 105 and a beam shaping unit 115 as an illumination unit 300 for an embodiment of the method described herein is shown. It can be seen that, in addition to the light source 105, a reticle unit 305 is also provided to enable measurement processes using different illumination patterns. DOE 120 follows reticle unit 305. Positioned in the beam path downstream of diffractive optical element 120 is an optical system 310, which, for example, includes one or more lenses and relays the light beam formed by diffractive optical element 120 via a variable or interchangeable aperture 315 toward the sample under test. Light source 105 is attached to a holder mechanism 205, which is designed to move light source 105 in several directions or along multiple axes, schematically illustrated here as the x-direction, the x-direction, and the z-direction. Correspondingly, axis 320, about which light source 105 can rotate, is also shown.

[0048] Figure 4 A schematic diagram of a workpiece holding element 135 for an embodiment of the method described herein is shown, comprising a holding element 400 for holding a workpiece 130. The holding element 400 can be rotated about an axis 405 and can also be moved, for example, in the x-direction and / or the y-direction, as shown in FIG. Figure 4 Schematically shown in .

[0049] Figure 5 A schematic diagram of a detector 145 for use in an embodiment of the methods described herein is shown, the detector being attached to a detector mechanism 210 that also allows the detector 145 to be moved in the x-, y-, and / or z-directions, wherein movement in the z-direction is not performed in the detector mechanism 210. Figure 5 . Detector mechanism 210 also allows detector 145 to be rotated about one or more axes 500, so that the optical system 510 of detector 145, along with aperture 515, can be flexibly moved. Movement of the detector allows, for example, scanning the eye box of a sample under test. Aperture 515 can also be variable or interchangeable. One or more partial detectors 150 can then be arranged in detector 145 itself to record or analyze and thus evaluate corresponding parameters of the received light.

[0050] Figure 6 A flow chart showing an example of an embodiment of a method 600 for operating an optical testing apparatus according to a previously described version is shown, the method 600 comprising a step 610 of outputting a light beam by a light source to a diffractive optical element (DOE) of a beam shaping unit, and a step 620 of evaluating light emitted from an outcoupling region to inspect a property to be inspected of a workpiece.

[0051] Figure 7A block diagram shows an example of an embodiment of a control unit 700 for operating an optical testing device according to the previously described version, wherein the control unit 700 comprises a unit 710 for outputting a light beam by a light source to a diffractive optical element of a beam shaping unit, and a unit 720 for evaluating the light emitted from the outcoupling region in order to check desired optical properties of a workpiece under test.

[0052] In summary, it may be noted that in this description an illumination setup with light (in particular a laser) and a diffractive optical element (DOE) may be included in a test setup to perform high-quality measurements of specific parameters of optical workpieces (in particular waveguides or light guides for AR / VR display systems or NEDs).

[0053] A key aspect of the proposed method is the use of a DOE together with a light source (i.e., a laser) to illuminate an optical workpiece (e.g., a waveguide sample) with TIR to measure parameters such as MTF / PSF. Illuminating the sample under test using the light source (i.e., a laser) can be performed at a wide angle to cover the entire field of view.

[0054] In contrast, existing systems for testing AV / VR optics use different types of light engines to generate images for testing the workpiece. Some of these use LBS projectors, which do not allow for accurate or complete measurement of different optical parameters using the light sources used in some systems currently on the market.

[0055] In this concept, it is proposed to replace the LED with a light source (especially a laser system) in combination with a diffractive optical element. The concept of using a combination of a light source (especially a laser) different from a camera and a DOE to illuminate the optical element is a novel approach. The image formation used in measuring the MTF, for example, as the parameter in question, is accomplished by a reticle placed in front of the laser light source. Alternatively, the aperture of a laser or optical fiber can be used as a reticle. The lens system and the DOE element are used to split a light beam into different beams, which are used to cover the entire field of view of the sample under test (i.e., the workpiece). For example, the lens system as part of the optical system is used to transmit the first-order image of the reticle and the second-order, third-order and higher-order diffraction images of the reticle.

[0056] As mentioned earlier, the system has 3 main parts:

[0057] 1. Irradiation part 300,

[0058] This is the main part of the proposed method. A laser is used as the light source 105, a reticle with a pattern, a cross, a ring (in the shape of a donut), a bow tie, etc., used in the measurement 305, a diffractive optical element 120, and an optical system 310 for directing the light from the laser output coupling (i.e., the light source 105) toward the DOE 120 and then toward the entrance pupil of the sample (i.e., the workpiece 130). The last part of the system is an interchangeable aperture 315 located in front of the entrance pupil of the sample. The system has a degree of freedom of movement that allows not only movement in the x / y / z axes, but also rotation through at least two rotation axes 320 to cover different fields of view.

[0059] 2. Sample arm,

[0060] The system includes a sample holder 400 (i.e., a workpiece holder 135), which includes a sample holder 400 that is, for example, customer-specific. The sample holder 400 allows different types of samples or workpieces 130 to be measured in the system. The sample holder 400 also has degrees of freedom of movement along the x / y / z axes and a rotational axis 405.

[0061] 3. Detector 145

[0062] The detector 145 can be any type of detector used in similar measurement systems, such as a monochromatic camera to a spectrometer or a photodiode. The same is true for the optical system 510 attached to the detector 145, which can include a monofocal camera with a 2-degree FoV to a conoscopic polarimeter (with a FoV of up to 120 degrees), covering the entire field of view in one measurement. The optical system 510 also includes an interchangeable aperture 515. The detector 145 and the optical system 510 can be fixed, with freedom of movement in the x / y / z axes via the detector mechanism 210, and include different rotation stages 500.

[0063] Using the optical testing apparatus 100 proposed herein, several parameters can be measured by the system, including for example MTF, CRA, focus sweep, overfocus measurement, relative efficiency, external environment measurement, as well as camera-dependent color coordinates, absolute brightness; and so on.

Claims

1. An optical testing device (100), the optical testing device having the following characteristics: - a light source (105) for emitting a light beam (110); a beam shaping unit (115) having a diffractive optical element (120) for shaping the light beam (110) and directing it onto a coupling-in region (125) of an optical workpiece (130) in order to couple the shaped light into the optical workpiece (130) to be inspected; - a workpiece holding element (135) for holding the optical workpiece (130); A detector (145) for evaluating the light (110) emerging from the outcoupling region (140) of the optical workpiece (130) in order to examine the optical properties of the workpiece (130).

2. The optical testing device (100) according to claim 1, wherein The beam shaping unit (115) is designed to modify the diffractive optical element (120) and / or use another diffractive optical element (160) to shape the light beam (110).

3. The optical testing device (100) according to claim 1 or 2, wherein: The beam shaping unit (115) is designed to project a light pattern onto the coupling-in region (125) by means of the diffractive optical element (120).

4. The optical testing device (100) according to claim 1 or 2, wherein: The light source (105) and the beam shaping unit (115) are designed to be adjusted on at least one axis (x, y, z, 320), in particular to be displaced and / or rotated around at least one axis (x, y, z, 320).

5. The optical testing device (100) according to claim 1 or 2, wherein: The workpiece holding element (135) is designed to be adjusted in at least one axis (x, y, z, 405), in particular to be displaced and / or rotated about at least one axis (x, y, z, 405).

6. The optical testing device (100) according to claim 1 or 2, wherein: The workpiece holding element (135) is designed to hold a plate-shaped or flat optically transmissive and / or reflective workpiece (130), in particular a waveguide, and comprises a coupling-in region (125) and a coupling-out region (140).

7. The optical testing device (100) according to claim 1 or 2, wherein: The detector (145) is designed to be adjusted in at least one axis (x, y, z, 500), in particular to be displaced and / or rotated about at least one axis (x, y, z, 500).

8. The optical testing device (100) according to claim 1 or 2, wherein: The detector (145) is designed to receive light emitted from the outcoupling region (140) in different directions and / or having different wavelengths.

9. The optical testing device (100) according to claim 1 or 2, wherein: The detector (145) comprises at least two partial detector units (150), each of which is designed to receive light emitted from the outcoupling region (140) in different directions, in particular, the at least two partial detector units (150) are arranged adjacent to each other.

10. The optical testing device (100) according to claim 1 or 2, wherein: The detector (145) or at least one component (150, 510) of the detector (145) is adapted to move at least partially within a range of motion.

11. A method (600) of operating an optical testing device (100) according to any one of the preceding claims, the method (600) comprising the following steps: - outputting (610) a light beam (110) from the light source (105) to the diffractive optical element (120) of the beam shaping unit (115); and - evaluating (620) the light beam emitted from the outcoupling region (140) to check the optical properties of the workpiece (130).

12. A control unit (155, 700) adapted to control and / or perform the steps (610, 620) of the method (600) according to claim 11 in a respective unit (710, 720).

13. A computer program comprising a program code adapted to control and / or perform the steps (610, 620) of the method (600) according to claim 11 when the computer program is executed on a control unit (155, 700).

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

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