Rainbow artifacts are reduced or eliminated by implementing one or more angle-dependent filters with a waveguide display
(Nweon June 03, 2024) -- Most users and eyewear manufacturers are eager for AR glasses with a shape similar to sunglasses. As simple as this may sound, there's one issue that is often overlooked: stray light.
The more open the AR glasses, the more light from unwanted directions and light sources can enter the system. While AR displays generally cope well with ambient light from the front, light from the side or behind the user can cause serious problems. Regular glasses usually don't reflect much light, so it's not much of a problem. But AR displays have to reflect and bend light, so they are more susceptible to stray light. Diffractive waveguides are particularly affected by this, as light from the side appears on the display as rainbow artifacts. Reflective waveguides perform better, but they also have problems with this.
In a patent application titled "Rainbow reduction for waveguide displays", Microsoft proposes that rainbow artifacts can be reduced or eliminated by implementing one or more angle-dependent filters with waveguide displays. Angular correlation filters consist of one or more layers of nanoscale/subwavelength structures whose subwavelength magnitude allows the angular correlation filter to suppress the introduction of higher-order diffraction and correlation artifacts.
Layers of nanoscale/subwavelength structures can be arranged on top of any surface of any number of optical components to form angular correlation filters, which advantageously provide manufacturing flexibility and enable the use of a variety of manufacturing techniques. Nanoscale/subwavelength structures are configured to limit or minimize the transmission of real-world light into the system within a specific angular range, while allowing or maximizing the transmission of real-world light outside of a specific angular range.
As a result, such a construction can reduce or minimize rainbow artifacts while maintaining the perspective quality of the waveguide display system and does not require additional power, as angular correlation filters with subwavelength nanostructures are passive components.
The geometry, shape, layered structure, material composition, and/or other aspects of this nanoscale/subwavelength structure of the angle-dependent filter can be selected/modified to adjust the transmission and/or reflection of the incident light to achieve the desired angular transmission function. The angular transmission function describes the total combined light transmission as a function of the incident angle of the multi-surface angular correlation filter when the angular correlation filter includes nanoscale/subwavelength structured layers above multiple surfaces.
The nanoscale/subwavelength structure of the angular correlation filter can be achieved as a periodic structure, an aperiodic structure, or some combination of periodic and nonperiodic structures. For example, rainbow artifacts can be position-dependent, as the range of angles of incidence that cause rainbow artifacts can vary depending on the position on the waveguide display.
As a result, different regions of the angular correlation filter can have nanoscale/subwavelength structures with different properties. Such spatial variations can improve the perspective quality of the angular correlation filter without compromising the rainbow reduction performance.
Figure 1A shows the waveguide 102 of the display system of the headset. When the angle of incidence of the light is high enough, ambient light output by a high-intensity light source can cause rainbow artifacts to be visible to the user's eyes106. Figure 1B shows a light source 120 in the environment whose output reaches the waveguide 102 at a high angle of incidence (arrow 122).
When interacting with the grating structure 104 of the waveguide 102, the 0th order (undiffraction) travels through the waveguide 102 without reaching the user's eye 106 (arrow 124), while the first-order diffracted light is directed towards the user's eye (arrow 126) through the waveguide 102. This first-order diffracted light (arrow 126) can cause rainbow artifacts visible to the user's eye106. In order to reduce or eliminate the rainbow artifact visible to the user's eye 106, one or more angular correlation filters can be implemented with the waveguide 102 in the waveguide display system.
Figures 2A to 2C illustrate exemplary angular correlation filters for mitigating rainbow artifacts. The angle-dependent filter 202 includes at least one layer 204, and the layer 204 includes multiple nanostructures.
Figure 2B shows multiple nanostructures of layer 204 of the angle-dependent filter 202222. Figure 2B shows four nanostructures 210A, 210B, 210C, and 210D, arranged in periodic arrays with subwavelength periods 212.
In one embodiment, the subwavelength period of multiple nanostructures 210 prevents multiple nanostructures 210 from diffracting incident light in the visible spectrum, thereby preventing multiple nanoparticles 210 from exacerbating rainbow artifacts.
Figure 2C shows a specific nanostructure 210A in multiple nanostructures 210 of layer 204 of the angle-dependent filter 202. In the example in Figure 2C, the nanostructure 210A comprises a first material 220 set on a substrate 206 of an angle-dependent filter 202 and a second material 222 set above a first material 220.
The nanostructure 210A includes a raised part 224, and the first material 220 and the second material 222 have different refractive indices. Such features contribute to the angle-dependent optical transmission characteristics of the nanostructure 210A. The angle-related optical transmission characteristics of the nanostructure 210A (and multiple nanostructures 210) are also affected by other properties of the nanostructure 210A, such as period 212, the pitch of the protrusion 224 226, the material selected for the first material 220 or the second material 222, the base height of the first material 220 228, the convex height of the first material 220220 230, the base height of the second material 222222 232, the convex height of the second material 222 234, and so on.
Thus, the angle-dependent light transmission characteristics of nanostructure 210 can be altered by altering the properties of the nanostructure 210A (and/or other nanostructures of the angle-dependent filter 202).
As mentioned above, the angle-dependent filter 202 can have different angle-dependent light transmission characteristics for different spatial regions of the angle-dependent filter 202. This can be facilitated by the implementation of different nanostructural properties for different regions of the nanostructure of the angular correlation filter 202.
The angle-dependent optical transmission characteristics of the angle-dependent filter 202 can be represented by the angle-dependent transfer function, where the angle-dependent filter defines the optical transmission of the angle-dependent filter as a function of the angle of incidence. The angle-dependent optical transmission characteristics of the angle-dependent filter 202 can be different for different wavelengths and/or optical polarization.
Thus, the angular transmission function of the angular correlation filter 202 can include different components/functions for different wavelengths and/or optical polarization. For example, Figure 3 illustrates an exemplary angle transfer function for an exemplary angle-dependent filter. In particular, Figure 3 shows the angular transmission function of an angle-dependent filter, which shows angular transmission as a function of the incidence angles of s-polarized light and p-polarized light.
It is evident from Figure 3 that angular correlation filters can have different angular correlation transmission characteristics for different optical polarizations.
The angular correlation filter 202 can have multiple regions with different nanostructural properties, which can generate additional angular transmission functions (or sets of angular transmission functions) for a single angular correlation filter.
Angular correlation filters can be used in rainbow artifact mitigation systems in waveguide display systems to facilitate the reduction or elimination of rainbow artifacts.
Figure 4A shows an example waveguide display system 400, which includes a rainbow artifact mitigation system 410. The rainbow artifact mitigation system 410 includes a linear polarizer 412 and an angular correlation filter 414. The linear polarizer 412 is configured to receive ambient light and filter one polarization of light from ambient light.
In the example in Figure 4A, the linear polarizer 412 is suitable for filtering p-polarized light while allowing the s-polarized light to be transmitted through the linear polarizer 412. For example, Figure 4A depicts the light output in the environment by a light source 420, where the output light includes s-polarized light and p-polarized light (arrow 422). The linear polarizer 412 filters p-polarized light from the light output of the light source 420, causing the s-polarized light to be transmitted through the linear polarizer 412 (arrow 424).
The angular correlation light transmission characteristics of the angular correlation filter 414 can be defined by one or more angular transmission functions. The angular correlation filter 414 for the example in Figure 4A is specifically configured to be used in combination with a linear polarizer 412 to form a rainbow artifact mitigation system 410.
In particular, the angle-dependent filter 414 is configured to at least partially mitigate the transmission of s-polarized light (whose transmission passes through the linear polarizer 412) for high angles of incidence. Figure 4A shows the high angle of incidence s-polarized light transmitted through a linear polarizer (arrow 424) reflected, absorbed, and/or scattered by an angle-dependent filter 414 (arrow 426) to prevent the s-polarized light from reaching the grating structure 404 of waveguide 402 of the waveguide display system 400.
In view of the foregoing, the linear polarizer 412 and the angular correlation filter 414 may be operated in combination with each other as a rainbow artifact mitigation system 410 to prevent high incidence angle light from reaching the grating structure 404 of the waveguide display system 400, thereby reducing or mitigating rainbow artifacts.
While preventing high incidence angle light from reaching the grating structure, the Rainbow Artifact Mitigation System 410 transmits low incidence angle light to enable users to see their real-world environment.
For example, Figure 4B shows light propagating from an object 408 in the environment to the waveguide display system 400 (arrow 430), where the p-polarized light is filtered by a linear polarizer 412, thereby allowing the s-polarized light to be transmitted through the linear polarizer 412 (arrow 432) and through the angle correlation filter 414 (arrow 434) to reach the grating structure 404 of the waveguide 402, which allows the 0th order light to reach the user's eye 406 (arrow 436) through the waveguide 402, At the same time, the first order of light diffracted through the waveguide 402 is far away from the user's eye (arrow 438).
The example waveguide shown in Figure 5A shows that the 500 includes an alternative rainbow artifact mitigation system 510. In particular, the rainbow artifact mitigation system 510 in Figure 5A includes an angle-correlation filter 512 and a polarization rotator 514.
The angle-dependent light transmission characteristics of the angle-dependent filter 512 can be defined by one or more angular transmission functions. The angular correlation filter 512 for the example in Figure 5A is configured to at least partially mitigate the transmission of p-polarized light for high angles of incidence.
Figure 5A shows the output of light source 520 in the environment, where the output light includes s-polarized light and p-polarized light (arrow 522). The angular correlation filter 512 reflects, absorbs, and/or scatters at least some of the p-polarized parts of the light output by the light source 520 (arrow 524), while allowing at least some s-polarized light to be transmitted through the angle correlation filter 512 (arrow 526).
The transmitted s-polarized light at a high angle of incidence through the angle-dependent filter 512 (arrow 526) reaches the polarizing rotator 514, which is configured to rotate the polarization of the received s-polarized light to transmit the polarized light of the target (arrow 528). The target polarization is the polarization that only weakly or slightly interacts with the grating structure 504 of the waveguide 502 of the waveguide display system 500 in such a way that the grating structure 504 diffracts the polarized light of the target only slightly, if any.
The target polarization can be selected based on the diffraction characteristics of the grating structure 504, and a polarization rotator 514 can be selected/fabricated to rotate the s-polarized light into the target-polarized light. At this point, the grating structure 504 can be configured to exhibit minimal diffraction of the target polarized light through the waveguide 502 towards the user's eyes.
In view of the foregoing, the angle-dependent filter 512 and the polarization rotator 514 may be operated in combination with each other as a rainbow artifact mitigation system 510 to prevent, at least partially, the high-incidence angle light from diffracting through the grating structure of the waveguide display system 400 504 in a manner that would cause rainbow artifacts.
When performing such a function, the Rainbow Artifact Mitigation System 510 still allows light with a low angle of incidence to reach the grating structure 504 and waveguide 502 to enable the user to see their real-world environment.
For example, Figure 5B shows light propagating from an object 508 in the environment towards the waveguide display system 500 (arrow 530), where both p-polarized and s-polarized light are transmitted through an angle-dependent filter 512 (arrow 532), rotating p-polarized light and s-polarized light are transmitted through a polarizing rotator 514 (arrow 534), and the rotating p-polarized and s-polarized light reach the grating structure 504 of the waveguide 502, This allows the 0th order light (arrow 536) to be transmitted through the waveguide 502 towards the user's eye (not shown in Figure 5A) while the diffracted first-order light (arrow 538) passes through the wave guide 502 away from the user's eye.
The example waveguide shown in Figure 6A shows that the 600 includes another alternative rainbow artifact mitigation system 610. In particular, the rainbow artifact mitigation system 610 in Figure 6A includes an angular correlation filter 612A, a polarization rotator 614, and another angular correlation filter 614B.
The angular correlation filters 612A and 612B generally correspond to the angular correlation filter 202 described above. For example, the angle-dependent optical transmission characteristics of the angle-dependent filter 612A can be defined by one or more angular transfer functions, and the angle-dependent optical transmission characteristics of the angle-dependent filter 611B can be defined by one or more second angular transfer functions.
The angular correlation filters 612A and 612B for the example in Figure 6A are configured to at least partially mitigate the transmission of p-polarized light for high angles of incidence. Figure 6A shows the light output in the environment by the light source 620, where the output light includes s-polarized light and p-polarized light (arrow 622). The angle-dependent filter 612A reflects, absorbs, and/or scatters at least some of the high-incidence portion of the p-polarized portion of the light output by the light source 620 (arrow 624), while allowing at least some s-polarized light to be transmitted through the angle-dependent filter 61.2A (arrow 626).
The transmitted s-polarized light (arrow 626) with a high angle of incidence of the angle-dependent filter 612A reaches the polarized rotator 614, which is configured to rotate the polarization of the received s-polarized light to transmit the p-polarized light (arrow 628). In this regard, the polarizing rotator 614 can be implemented as a quarter waveplate.
As with the angle-dependent filter 612A, the angle-dependent filter 611B for the example in Figure 6A is configured to at least partially mitigate the transmission of p-polarized light for high angles of incidence. Thus, at least some of the high-incidence p-polarized light transmitted through the polarizing rotator 614 (arrow 628) is reflected, absorbed, and/or scattered by the angular correlation filter 612B (arrow 630).
Figure 6A further shows that the light reflected by the angle-correlated filter 612B (arrow 630) is again transmitted through the polarizing rotator 614 to form s-polarized light (arrow-632), which is transmitted into the environment through the angle-dependent filter 611 (arrow-634).
The angular correlation filters 612A and 612B and the polarization rotator 614 may be operated in combination with each other as rainbow artifact mitigation systems 610 to at least partially prevent high incidence angle light from reaching the grating structure 604 of the waveguide display system 600, thereby mitigating or eliminating the rainbow artifacts of the waveguide display system 600.
When performing such a function, the rainbow artifact mitigation system 610 still allows light with a low angle of incidence to reach the grating structure 604 and waveguide 602, allowing the user to see their real-world environment.
For example, Figure 6B shows light propagating from an object 608 in the environment to a waveguide display system 600 (arrow 636), where both p-polarized light and s-polarized light are transmitted through an angle-dependent filter 612A (arrow 638), and rotating p-polarized light and s-polarized light are transmitted through a polarizing rotator 614 (arrow 640 as seen by the user's eye.
Although Figures 6A and 6B focus on an example where the angular correlation filters 612A and 612B are configured to mitigate the transmission of p-polarized light at high angles of incidence, the angular correlation filters 611A and 612B can be configured alternatively to reduce the transmission of s-polarized light at high angles of incidence, and the polarization rotator can be configured to rotate p-polarized light into s-polarized light.
As mentioned above, the occurrence of rainbow artifacts in a waveguide display system can depend on the position of the incident light on the waveguide grating structure (relative to the user's eyes) on the waveguide grating structure. This can result in different rainbow artifact results for light of the same wavelength and the same angle of incidence reaching different locations in the grating structure.
For example, Figure 7 shows a waveguide 702 with a grating structure 704 that receives incident light of the same wavelength (e.g., blue) and has a different angle of incidence and position on the grating structure 704 relative to the user's eye 706. The incident light at the angle θ1 reaching position "A" (arrow 720) is diffracted by the grating structure 704 towards the user's eye 706, while the angle θ1 at the angle reaching position "B" (arrow 722) does not diffract towards the user's eyeball 706. However, the incident light at the angle θ2 reaching position "B" (arrow 724) is diffracted towards the user's eye 706.
The spatial dependence of the rainbow effect is different for different wavelengths of light, which can cause light of different wavelengths and different angles of incidence to reach the same spatial location on the grating structure, thus both causing rainbow artifacts (albeit at different angles of incidence).
For example, Figure 8 shows a waveguide 802 with a grating structure 804 that receives incident light at different wavelengths (e.g., blue and red). The blue incident light at the angle θ1 reaching position "A" (arrow 820) is diffracted by the grating structure 804 towards the user's eye 806, and the red incident light at the angular angle θ2 reaching position "A" (arrow 822) is also diffracted by the grating structure 806 towards the eye 806 of user-846 (albeit at a different angle of incidence).
To account for the spatial and/or wavelength dependence of the rainbow effect, an angular correlation filter can be associated with several different angular transmission functions to define light transmission as a function of different regions and/or different wavelengths of the angular correlation filter.
Thus, nanostructures in different regions of angular correlation filters can have at least partially different nanostructural properties.
Figure 9 shows an example angular correlation filter with different angular transmission characteristics associated with different spatial regions of the angular correlation filter 902. For example, the exemplary angular correlation filter 902 in Figure 9 includes four different regions for each user's eye, including region A, region B, region C, and region D.
In the example in Figure 9, different regions have different nanostructural properties, resulting in different angular transmission functions for each different region.
Figure 10 shows the curves of the angular transfer function for the different regions of the angle-dependent filter 902 in Figure 9. The dark part of the graph in Figure 10 corresponds to low transmission with different combinations of wavelengths and angles of incidence.
The desired angular transmission function for one or more regions of the angular correlation filter can be tuned to account for the spatial and/or wavelength dependence of rainbow artifacts. For example, the initial nanostructure configuration can be used as input using RCWA or FDTD techniques to simulate the angular transfer function of the initial nanostructure configuration. The band-end offset technique can be applied to one or more regions of the input nanostructure to facilitate the tuning/modification of the simulated angular transfer function and can include modifying the characteristics of the input nanostructure configuration.
Such a process can be iterated (for any number of nanostructured regions) to determine the nanostructure configuration that achieves one or more desired angular transmission functions.
相关专利：Microsoft Patent | Rainbow reduction for waveguide displays
https://patent.nweon.com/35080
The Microsoft patent application, titled "Rainbow reduction for waveguide displays", was originally filed in October 2022 and published by the USPTO a few days ago.
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Original link: https://news.nweon.com/121428