TWI904831B - Alignment method for optical projection module - Google Patents

Abstract

The invention relates to an alignment method for an optical projection module. The optical projection module has an optical panel, a compensator and a prism assembly. The method includes the following steps: aligning a central position of the optical panel according to the prism assembly, moving to scan the optical panel on a vertical axis to compensate a position of the optical panel, and confirming whether the optical panel is aligned to a predetermined optimal position, if not, repeating the above two steps until the optical panel aligns to the predetermined optimal position. The steps of moving to scan refers to continuously capturing images during the process of moving the optical panel, which is used as a basis for compensating the position of the optical panel.

Description

Alignment method for optical projection modules

This invention relates to a method for aligning an optical projection module, and more particularly to a method for aligning an optical projection module used in an augmented reality device.

Augmented Reality (AR) glasses are display devices that utilize micro-projection technology. Liquid Crystal on Silicon (LCOS) panels are a common and crucial optical component in AR glasses. The basic principle of LCOS is to place tiny liquid crystal particles on a silicon substrate. These particles can have their optical properties altered by controlling voltage. When light passes through these tiny liquid crystal particles, their position and state affect the phase of the light, thus forming an image. Because LCOS technology uses a silicon substrate, it offers several advantages in manufacturing and integration.

In AR glasses, LCOS technology can be used to project virtual images or information into the user's field of vision. These images can be displayed transparently in the real world, creating an augmented reality effect. LCOS's high resolution and display quality make it an important optical element in AR glasses display technology.

On the other hand, in AR micro-projectors, the alignment accuracy of the LCOS, optical compensator, and prism assembly is crucial because it directly affects the sharpness of the projected image, image quality, and the user's visual experience. The alignment accuracy between these components needs to be extremely high to ensure that the virtual image accurately corresponds to the real world. If the LCOS, optical compensator, and prism assembly are misaligned in three-dimensional space during the production and assembly process, various problems may occur in the optical imaging system. For example, misalignment between the optical compensator and the prism assembly will lead to reduced brightness, while misalignment between the LCOS and the prism assembly will cause image blurring, image rotation, and so on. To overcome these problems, the industry urgently needs an innovative alignment method to improve the various imaging distortions and aberrations caused by conventional misalignment.

The main purpose of this invention is to provide an innovative active alignment method for optical projection modules to improve various imaging problems caused by misalignment in conventional optical projection modules, such as reduced brightness, poor sharpness, and blurred images.

To achieve the above objectives, the present invention provides an alignment method for an optical projection module. The optical projection module has an optical panel, a compensator, and a prism assembly. The alignment method for the optical projection module includes: aligning a center position of the optical panel relative to the prism assembly; moving and scanning the optical panel along a vertical axis to compensate for a position of the optical panel; and confirming whether the optical panel is aligned to a predetermined position. If not, the above two steps are repeated until the optical panel is aligned to the predetermined position. The moving scan refers to continuously capturing images during the movement of the optical panel to compensate for the position of the optical panel.

In one embodiment of the alignment method of the present invention, the step of continuous image acquisition includes: during the process of moving the optical panel, continuously acquiring multiple images for a test calibration image, and confirming whether the optical panel is aligned to the predetermined position based on the sharpness change of the images.

In one embodiment of the alignment method of the present invention, the sharpness change of the images is calculated by the modulation conversion function curve of the images.

In one embodiment of the alignment method of the present invention, the step of moving the scanning optical panel on the vertical axis involves moving a plurality of small steps within a predetermined distance on the vertical axis and acquiring an image in each of the small steps.

In one embodiment of the alignment method of the present invention, the test calibration images are crosshair calibration images.

In one embodiment of the alignment method of the present invention, the optical panel is a silicon-based liquid crystal panel.

In one embodiment of the alignment method of the present invention, the method further includes: rotating and scanning a bright field of the compensator on a rotating axis; rotating and scanning a dark field of the compensator on a rotating axis; and compensating for a position of the compensator and confirming whether the compensator is aligned to a predetermined position. If not, the above two steps are repeated until the compensator is aligned to the predetermined position. The rotating scan refers to continuous measurement during the rotation of the compensator to determine the position of the compensator.

In one embodiment of the alignment method of the present invention, the continuous measurement step includes: continuously measuring the contrast curves of the bright field and the dark field respectively by means of a photodetector while rotating the compensator; and confirming whether the compensator is aligned to the predetermined position according to the contrast curves.

In one embodiment of the alignment method of the present invention, the step of rotating the scanning compensator on the rotation axis involves rotating the axis within a predetermined angle by a plurality of small angles and measuring at each of those small angles.

In one embodiment of the alignment method of the present invention, the optical panel and the compensator are confirmed to be aligned to the predetermined position and then the optical projection module is UV cured.

The present invention further provides an alignment method for an optical projection module. The optical projection module has an optical panel, an insulator, and a prism assembly. The alignment method for the optical projection module includes: positioning and inspecting the optical panel; temporarily fixing the optical panel and the insulator to the prism assembly; actively aligning the optical panel to a predetermined position; actively aligning the insulator to the predetermined position; and permanently fixing the optical panel and the insulator to the prism assembly. Active alignment of the optical panel refers to continuous image acquisition during the process of moving and scanning the optical panel, and active alignment of the insulator refers to continuous measurement during the process of rotating and scanning the insulator to compensate for the positional discrepancies between the optical panel and the insulator.

In one embodiment of the alignment method of the present invention, the step of actively aligning the optical panel to a predetermined position involves moving and scanning the optical panel along a vertical axis to compensate for a position of the optical panel to the predetermined position.

In one embodiment of the alignment method of the present invention, the step of actively aligning the compensator to the predetermined position involves rotating and scanning a bright field and a dark field of the compensator on a rotating axis to compensate for one position of the compensator to the predetermined position.

After referring to the figures and the embodiments described thereafter, those skilled in the art will understand the other purposes of the invention, as well as the technical means and embodiments of the invention.

The present invention will be explained through embodiments below. These embodiments are not intended to limit the implementation of the invention to any specific environment, application, or particular method described in the embodiments. Therefore, the description of the embodiments is for illustrative purposes only and is not intended to limit the invention. It should be noted that in the following embodiments and drawings, components not directly related to the present invention have been omitted and are not shown, and the dimensional relationships between the components in the drawings are for ease of understanding only and are not intended to limit the actual scale.

Please refer to Figure 1, which shows an optical projection module used in an augmented reality micro-projection device. It includes an optical panel, an compensater, and a prism assembly. The optical panel, for example, can be a liquid crystal on silicon (LCOS) panel 10, which uses voltage to control the liquid crystal particles, changing their position and state to affect the phase of light and thus form an image. The compensater 20 functions to correct or compensate for distortions or other optical problems in the optical system to ensure that the final image or optical system performance achieves the expected results. Secondly, the prism assembly 30 can be, for example, a polarizing beam splitter (PBS). The prism assembly 30 uses the polarization characteristics of light to guide different optical paths, thereby achieving control and adjustment of the optical path. The active alignment method of the optical projection module disclosed in this invention is to precisely assemble the silicon-based liquid crystal panel 10 and the compensator 20 onto the prism assembly 30, or to first assemble the silicon-based liquid crystal panel 10 and the compensator 20 and then precisely assemble them onto the prism assembly 30, so as to avoid the problems of low brightness, poor sharpness, and blurred image caused by misalignment in the prior art.

The following embodiment mainly illustrates the method of precise active alignment of the present invention by assembling the silicon-based liquid crystal panel 10 and the compensator 20 in the optical projection module into the prism assembly 30. Please refer to Figure 2, which shows the flowchart for active alignment of the optical projection module. First, it should be noted that before assembling the optical projection module, the surface of the silicon-based liquid crystal panel 10 needs to be inspected for dust particles. If there is no dust contamination, the Automated Optical Inspection (AOI) visual positioning inspection in step 200 is performed. Secondly, positioning compensation is performed on the prism assembly 30, for example, but not limited to, six degrees of freedom (including: three vertical coordinate axes X, Y, and Z, one rotation axis R, and two tilt angles Tx and Ty). After the positioning compensation is completed, step 202 is performed, in which adhesive is applied to the mechanism of the prism assembly 30 so that the silicon-based liquid crystal panel 10 and the compensator 20 can be temporarily bonded to the prism assembly 30 in a non-curing manner. Next, in steps 204 and 206, two active alignment processes are performed on the silicon-based liquid crystal panel 10 and the compensator 20, respectively, to align the silicon-based liquid crystal panel 10 and the compensator 20 to a predetermined position, which refers to a predetermined optimal position. This active alignment process refers to moving and scanning the silicon-based liquid crystal panel 10 and rotating and scanning the compensator 20 to compensate for the positional reference of the silicon-based liquid crystal panel and the compensator. More precisely, active alignment of the optical panel refers to continuously capturing images during the moving and scanning process of the optical panel to compensate for the position of the optical panel. On the other hand, the active alignment compensator refers to continuous measurement during the rotation scanning process of the compensator to compensate for the position of the compensator. In step 208, after the active alignment process is completed, the positions of the silicon-based liquid crystal panel 10, the compensator 20 and the prism group 30 in the optical projection module are permanently fixed by, for example, but not limited to, ultraviolet (UV) irradiation curing, thus completing the process of precise active alignment of the optical projection module of the present invention.

The following will describe the active alignment process of the silicon liquid crystal panel 10, the compensator 20, and the prism assembly 30. Please refer to Figure 3, which shows a flowchart of the active alignment of the silicon liquid crystal panel 10 in the optical projection module. First, in step 300, the center position of the silicon liquid crystal panel is aligned visually, including the X and Y coordinates and the rotation axis R. Second, in step 302, the silicon liquid crystal panel is “through-focus scanning” on a vertical axis (i.e., the Z coordinate) to compensate for the position of the silicon liquid crystal panel relative to one of the prism assemblies, which includes its center position and at least one tilt angle (e.g., Tx, Ty). Next, in step 304, it is confirmed whether the silicon-based liquid crystal panel is aligned to a predetermined position, which refers to a predetermined optimal position. If not, steps 300 and 302 above are repeated until the silicon-based liquid crystal panel is aligned to the predetermined optimal position. The "moving scan" mentioned in step 302 specifically refers to "continuous image acquisition" during the moving of the silicon-based liquid crystal panel, serving as a benchmark for compensating for the position of the silicon-based liquid crystal panel.

It should be noted that the aforementioned "continuous image acquisition" refers to providing light through an optical projection module to project a test calibration image (not shown) onto a photosensor, allowing the photosensor to continuously acquire multiple images of the test calibration image. In one embodiment, this test calibration image may be a crosshair calibration image, but is not limited to this. Based on the sharpness changes of these images, it is confirmed whether the silicon-based liquid crystal panel is aligned to a predetermined optimal position. Moreover, calculating the sharpness changes of these images involves calculating the sharpness change curves of these images. Specifically, for example, a modulation transfer function (MTF) can be applied to calculate imaging performance indicators such as resolution and sharpness of the optical projection module. By capturing multiple images through continuous shooting, MTF curve data can be obtained. Furthermore, the MTF curve data is interpreted and used as a compensation benchmark for adjusting the position of the silicon-based liquid crystal panel, and to confirm whether the optical projection module has been accurately aligned to the predetermined optimal position to exhibit good sharpness. It is emphasized that, when applying this invention to the assembly process of the optical projection module, because it employs an active alignment method that simultaneously and continuously captures images during movement, the scanning and image acquisition time can be significantly reduced compared to the traditional method of stopping and then "fixing" the scan after movement, thus shortening the assembly time. In a specific embodiment, the traditional alignment process using the "move, stop, capture, move, stop, capture..." method takes approximately 45 seconds. In contrast, the active alignment method using the synchronous continuous image acquisition of this invention only takes 20 seconds, significantly reducing the time spent on alignment.

Furthermore, it is further explained that the "moving scan" step on the vertical axis of the silicon-based liquid crystal panel in step 302 refers to moving a plurality of small steps within a predetermined distance on the vertical axis and capturing images within each of those small steps to achieve the aforementioned continuous imaging effect. In a specific embodiment, the first preliminary moving scan on the vertical axis involves moving 0.02 mm within a predetermined distance of approximately ±0.12 mm on the Z-axis, and simultaneously capturing images within approximately 13 small steps to obtain the aforementioned MTF curve data. Furthermore, when performing a second fine-movement scan on the vertical axis, a small step size of 0.01 mm is made within a predetermined distance of approximately ±0.05 mm on the Z-axis. Simultaneous continuous image acquisition is performed within approximately 11 small steps to obtain the aforementioned MTF curve data.

The active alignment process of the compensator in the optical projection module will be explained below, as shown in Figure 4. First, in step 400, a "rotational scan" of the bright field of the compensator is performed on a rotation axis. Second, in step 402, a "rotational scan" of the dark field of the compensator is performed on the rotation axis. Next, in step 404, the position of the compensator is checked and it is confirmed whether the compensator is aligned to the predetermined optimal position. If not, steps 400 and 402 are repeated until the compensator is aligned to the predetermined optimal position. In the above steps 400 and 402, the "rotational scanning" specifically refers to the simultaneous "continuous measurement" during the rotation of the compensator to obtain a comparison curve as a reference for adjusting the position of the compensator.

It should be noted that the aforementioned "continuous measurement" refers to providing a light source and rotating the compensator, continuously measuring the contrast curves of the bright and dark fields using a photosensor, and identifying the position with the highest brightness based on the contrast curves to confirm whether the compensator is aligned to the predetermined optimal position and presents good contrast. Furthermore, it should be further explained that the aforementioned step of "rotating and scanning" the compensator on the rotation axis involves rotating the compensator within a predetermined angle on the rotation axis several small angles, and simultaneously measuring during each of those small angles. In a specific embodiment, the first preliminary rotary scan on the rotation axis involves rotating the axis within a predetermined angle of approximately ±3°, with small-angle rotations of 0.5°, for a total of approximately 13 small angles, and synchronous continuous measurements are performed to obtain contrast curve data. Furthermore, when performing the second fine-motion scan on the vertical axis, the rotation axis is rotated within a predetermined angle of approximately ±0.5°, with small-angle rotations of 0.1°, for a total of approximately 11 small angles, and synchronous continuous measurements are performed to obtain contrast curve data. After confirming the predetermined optimal position with the highest brightness, UV curing is then performed to complete the alignment and assembly process of the silicon-based liquid crystal panel and the compensator of the optical projection module.

In summary, the active alignment method of the optical projection module disclosed in this invention uses an active alignment method to precisely assemble the silicon-based liquid crystal panel and the compensator onto the prism assembly. During the moving or rotating scanning process, images are continuously captured synchronously to compensate and adjust the relative positions between the silicon-based liquid crystal panel, the compensator, and the prism assembly in real time. This overcomes various imaging problems caused by misalignment of the optical projection module, such as reduced brightness, poor sharpness, and blurred images.

The above embodiments are merely illustrative of the embodiments of the present invention and to explain the technical features of the present invention, and are not intended to limit the scope of protection of the present invention. Any modifications or equivalent arrangements that can be easily made by those skilled in the art are within the scope claimed by the present invention, and the scope of protection of the present invention shall be determined by the scope of the patent application.

10: Silicon-based LCD panel 20: Compensator 30: Prism assembly

Figure 1 is a schematic diagram of the optical projection module in the augmented reality micro-projection device of an embodiment of the present invention. Figure 2 is a flowchart of the active alignment of the optical projection module in an embodiment of the present invention. Figure 3 is a flowchart of the active alignment of the silicon-based liquid crystal panel of the optical projection module in an embodiment of the present invention. Figure 4 is a flowchart of the active alignment of the compensator of the optical projection module in an embodiment of the present invention.

10: Silicon-based LCD panel

20: Compensator

30: Prism Group

Claims (11)

An alignment method for an optical projection module, the optical projection module having an optical panel, an compensater, and a prism assembly, the alignment method comprising: aligning a center position of the optical panel relative to the prism assembly; and performing through-focus scanning along a vertical axis. The optical panel is scanned to compensate for a position of the optical panel. The scanning of the optical panel on the vertical axis involves moving the optical panel within a predetermined distance on the vertical axis by a plurality of small steps and acquiring an image in each of the small steps. The process also involves confirming whether the optical panel is aligned to a predetermined position. If not, the above two steps are repeated until the optical panel is aligned to the predetermined position. The scanning of the optical panel refers to continuously acquiring images during the movement of the optical panel to compensate for the position of the optical panel. The alignment method for an optical projection module as described in claim 1, wherein the continuous image acquisition step includes: during the movement of the optical panel, continuously acquiring multiple images for a test calibration image, and confirming whether the optical panel is aligned to the predetermined position based on the sharpness changes of the images. The alignment method for an optical projection module as described in claim 2, wherein the sharpness variation of the images is calculated by the modulation transfer function (MTF) curve of the images. The alignment method for an optical projection module as described in claim 2, wherein the test calibration images are crosshair calibration images. The alignment method for an optical projection module as described in claim 1, wherein the optical panel is a silicon-based liquid crystal panel. The alignment method for an optical projection module as described in claim 1 further includes: rotating and scanning a bright field of the compensator on a rotation axis; rotating and scanning a dark field of the compensator on the rotation axis; and compensating for a position of the compensator and confirming whether the compensator is aligned to the predetermined position. If not, the above two steps are repeated until the compensator is aligned to the predetermined position. The rotating scan refers to continuous measurement during the rotation of the compensator to compensate for the position of the compensator. The alignment method for an optical projection module as described in claim 6, wherein the continuous measurement step includes: continuously measuring the contrast curves of the bright field and the dark field respectively by means of a photosensor while rotating the compensator; and confirming, based on the contrast curves, whether the compensator is aligned to the predetermined position. The alignment method for an optical projection module as described in claim 6, wherein the step of rotating and scanning the compensator on the rotation axis involves rotating a plurality of small angles within a predetermined angle on the rotation axis and measuring at each of the small angles. The alignment method for an optical projection module as described in claim 6 further includes confirming that the optical panel and the compensator are aligned to the predetermined position and then UV curing the optical projection module. An alignment method for an optical projection module, the optical projection module having an optical panel, an compensater, and a prism assembly, the alignment method comprising: positioning and inspecting the optical panel; temporarily fixing the optical panel and the compensater to the prism assembly; actively aligning the optical panel to a predetermined position; and actively aligning the compensater to the predetermined position, wherein the active alignment of the compensater to the predetermined position is performed on a rotation axis respectively. The compensator is rotated and scanned in a bright field and a dark field to compensate for one position of the compensator to the predetermined position; and the optical panel and the compensator are permanently fixed to the prism assembly. The active alignment of the optical panel refers to continuous image acquisition during the process of moving and scanning the optical panel, and the active alignment of the compensator refers to continuous measurement during the process of rotating and scanning the compensator to compensate for the position of the optical panel and the compensator. The alignment method for an optical projection module as described in claim 10, wherein the step of actively aligning the optical panel to a predetermined position involves moving and scanning the optical panel along a vertical axis to compensate for a position of the optical panel to the predetermined position.