WO2025032201A1

WO2025032201A1 - Reducing impact of the zeroth diffraction order or other low-angle scattered light of a transmission profile in an optical system

Info

Publication number: WO2025032201A1
Application number: PCT/EP2024/072535
Authority: WO
Inventors: Ulrich Quaade; Ugur Meric GUR; Villads Egede JOHANSEN
Original assignee: Nil Technology Aps
Priority date: 2023-08-10
Filing date: 2024-08-08
Publication date: 2025-02-13

Abstract

The disclosure describes apparatus that include an optical system including a transmission side and a receiver side. The transmission side includes a light source operable to generate light, and a light projecting element arranged to project the light toward a scene, wherein an illumination profile of the light projected toward the scene contains increased intensity near a center of a field-of-view due to 0^th-diffraction order rays or other low-angle scattered light. The receiver side includes an image sensor, and at least one lens to focus light reflected by the scene toward the optical sensor. The optical system includes means for reducing impact of the 0th-diffraction order or other low-angle scattered light.

Description

REDUCING IMPACT OF THE ZEROTH DIFFRACTION ORDER OR OTHER LOW-ANGLE SCATTERED LIGHT OF A TRANSMISSION PROFILE IN AN OPTICAL SYSTEM

FIELD OF THE DISCLOSURE

[0001] The present disclosure relates to optical systems.

BACKGROUND

[0002] In some applications for active illumination, optical diffusers or other light projection elements are used, and the illuminated area is monitored with a receiver module in the form, for example, of a camera, time-of-flight sensor or other sensor. The active illumination is generated at the transmission (Tx) side, and optical signals are sensed and processed at the receiver (Rx) side. In some cases, the Rx sensor is less sensitive toward the edges of the field of view (FoV), which is referred to as relative illumination. A challenge when co-designing the Tx and Rx parts of the system is to tailor the illumination profile of the Tx side to compensate for the relative illumination so that, if the receiver is monitoring a scene with uniform reflectance, the intensity of light on the Rx sensor also will be substantially uniform. In this way, the system can have substantially uniform sensitivity over the full FoV.

[0003] Optical systems may include various types of optical elements. Diffractive optical elements (DOEs), such as meta optical elements (MOEs), employ a flat optic technology and can provide several potential advantages compared to refractive elements. For example, compared to refractive lenses, MOEs can have fewer surfaces and less performance degradation due to tolerances. Further, MOEs can be stacked with flat glass surfaces, can have low thermal impact and/or can be designed easily with high sensitivity (e.g., high numerical aperture) across the field (i.e., telecentric at the image plane).

[0004] A challenge, however, in using MOEs is suppression of unwanted diffraction orders. In a typical application, the 1 or -1 diffraction order is the desired diffraction order for imaging, and all other orders are considered to be unwanted or stray light. For diffusers, the higher diffraction orders are of less concern because they have little impact on the illumination. However, the O^th-diffraction order, which also may referred to as ballistic light, shows up in the central part of the field of illumination. In a diffuser, for example, this light is visible in the field of illumination as an additional dimmed Opdiffraction order contribution from the light source. If the light source is, for example, a collimated beam, the O^th-diffraction order shows up as a bright dot in the center of the FoV; if it is a diverging light source, the O^th-diffraction order shows up as an additional dimmed O^th-order contribution from the light source with a profile similar to the bare light source.

[0005] One problem is that if the illumination profile contains higher intensity near the center of the FoV due to the O^th-diffraction order or other low-angle scattering, that part of the image can be saturated, thereby decreasing dynamic range and sensitivity.

SUMMARY

[0006] The present disclosure describes techniques for reducing the impact of the 0^th- diffraction order or other low-angle scattered light of a transmission profile in an optical system.

[0007] For example, in one aspect, the present disclosure describes an apparatus that includes an optical system including a transmission side and a receiver side. The transmission side includes, a light source operable to generate light, and a light projecting element arranged to project the light toward a scene. An illumination profile of the light projected toward the scene contains increased intensity near a center of a field-of-view due to 0^th-diffraction order rays or other low-angle scattered light. The receiver side includes an image sensor, and at least one lens to focus light reflected by the scene toward the optical sensor. The optical system includes means for reducing impact of the O^th-diffraction order or other low-angle scattered light. [0008] Some implementations include one or more of the following features. For example, in some implementations, the means for reducing impact of the O^th-diffraction order or other low-angle scattered light includes a transmission filter having lateral varying transmission, wherein the transmission filter is disposed on the receiver side to reduce the increased intensity due to the O^th-diffraction order or other low-angle scattered light. The transmission filter can be configured, for example, to have a transmission coefficient that reduces the intensity of a light profile in a region where O^th-diffraction order rays or other low-angle scattered light are present. In some implementations, the transmission filter is disposed optically between the at least one lens and the image sensor. The transmission filter can be configured, in some instances, to allow no more than a specified amount of variation (e.g., 10% or 5%) in an offset profile light incident on the image sensor.

[0009] In some implementations, the image sensor is calibrated to have a shorter integration time in a region configured to acquire signals corresponding to the increased intensity due to the 0^th-diffraction order or other low-angle scattered light. The image sensor can be calibrated, for example, so that, under a condition where the light projected onto the scene is uniformly reflected by the scene to the at least one lens in the receiver side, a measured intensity remains substantially uniform across a light sensitive surface of the sensor.

[0010] In some implementations, the means for reducing impact of the O^th-diffraction order or other low-angle scattered light includes an angle-of-incidence (AOI) filter disposed optically in front of the at least one lens on the receiver side. The AOI filter can be configured, for example, to reduce an intensity of a light profile within a specified angle that defines an area about a center of the profile where the 0^th-diffraction order or other low-angle scattered light is present. In some implementations, the AOI filter is configured to compensate for 0^th-diffraction order-induced angular brightness profile so that, under a condition where the light projected onto the scene is uniformly reflected by the scene toward the at least one lens in the receiver side, light incident on the image sensor has a measured intensity that remains substantially uniform across a light sensitive surface of the sensor. The AOI filter can be configured, for example, to allow no more than a specified amount of variation (e.g., 10% or 5%) in an offset profile light incident on the image sensor.

[0011] In some implementations, the means for reducing impact of the O^th-diffraction order or other low-angle scattered light includes an angle-of-incidence (AOI) filter disposed optically after the light projecting element on the transmission side. The AOI filter can be configured, for example, to reduce an intensity of a light profile within a specified angle that defines an area about a center of the profile where the 0^th-diffraction order or other low-angle scattered light is present. In some implementations, the AOI filter is configured to compensate for the O^th-diffraction order or other low-angle scattered light induced angular brightness profile so that the light incident on the scene has a substantially uniform intensity profile. The AOI filter can be configured, for example, to allow no more than a specified amount of variation (e.g., 10% or 5%) in an offset profile light incident on the scene.

[0012] In some implementations, the at least one lens at the receiver side includes at least one meta-lens.

[0013] In some implementations, one or more of the following advantages can be achieved. For example, the impact of the 0^th-diffraction order or other low-angle scattered light of a transmission system can be reduced. In some implementations, the dynamic range of the receiver can be improved.

[0014] Other aspects, features and advantages will be readily apparent from the following detailed description, the accompany drawings and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 illustrates a first example for reducing the impact of the O^th-diffraction order or other low-angle scattered light of a transmission profile in an optical system. [0016] FIG. 2 illustrates a second example for reducing the impact of the O^th-diffraction order or other low-angle scattered light of a transmission profile in an optical system.

[0017] FIG. 3 illustrates a third example for reducing the impact of the 0^th-diffraction order or other low-angle scattered light of a transmission profile in an optical system.

[0018] FIG. 4 illustrates a fourth example for reducing the impact of the 0^th-diffraction order or other low-angle scattered light of a transmission profile in an optical system.

DETAILED DESCRIPTION

[0019] The present disclosure describes techniques for reducing the impact of the Oth- diffraction order of a transmission profile in an optical system.

[0020] The inventors of the present disclosure have determined that since the Opdiffraction order projection is an intrinsic feature of the diffuser design and the illumination source, it will illuminate the field of view (FoV) in substantially the same predictable, non-varying way, varying only slightly between devices as a result of manufacturing or other tolerances. Thus, the receiver optics can map each field point of the FoV to a predictable, non-varying position of the sensor such that the extra illumination from the 0^th-diffraction order gives a predictable, non-varying brightness profile on the sensor.

[0021] FIG. 1 illustrates a first implementation, in which a transmission filter having lateral varying transmission is provided optically in front of the optical sensor to compensate for the increased brightness from the 0^th-diffraction order so that a substantially uniform intensity on the sensor can be obtained. In this implementation, filtering is performed in the image space. [0022] As shown in FIG. 1, the optical system includes a transmission side (Tx) and a receiver side (Rx). The transmission side includes a light source 20 that is operable to emit electromagnetic radiation (e.g., light) 22 at a particular wavelength or range of wavelengths (e.g., infra-red, visible, or ultra-violet). The light source 20 can be implemented, for example, as a vertical cavity surface emitting laser (VCSEL), a light emitting diode (LED), a laser, or other appropriate light emitting device. Light 22 emitted by the light source 20 passes through a light projecting element 24 such as a diffractive diffuser or diffractive fan-out element. A diffuser, for example, spreads the light over wider viewing area, whereas a diffractive fan-out element splits a light beam into multiple beams propagating in different directions, which can be used to generate an array of focused spots with a focusing lens or an array of collimated beams using for example a collimator lens. After passing through the light projecting element 24, the light has an intensity profile 26 and is incident on a scene 29, which may include one or more objects. In this example, the light 26 incident on the scene includes 0^th-diffraction order rays 28, which increase the intensity profile at or near its center.

[0023] In operation, some of the light incident on the scene 29 is reflected back toward the receiver side of the optical system, which includes receiver optics 36 to focus incoming light toward an optical sensor 30 (e.g., a CMOS, CCD or SPAD image sensor). The receiver optics 36 can include, for example, one or more lenses (e.g., diffractive lenses, meta-lenses, and/or refractive lenses). Light transmitted through the receiver optics 36 is indicated by 38. Assuming proper alignment in the optical system, the Opdiffraction order in the image space mirrors that in the optics space. Thus, the illumination profile of the light 38 may contain higher intensity near its center 39 as a result of the 0^th-diffraction order rays 28 present in the light 26 projected onto the scene 29. The presence of the higher intensity can adversely impact the dynamic range of the receiver. Accordingly, in the implementation of FIG. 1, a position-dependent transmission filter 34 is provided optically between the receiver optics 36 and the image sensor 30 to reduce the impact of the 0^th-diffraction order. For example, the filter 34 can be configured to have a transmission coefficient that reduces, proportionately, the intensity of the light profile 38 near the center 39 where the 0^th-diffraction order rays are present. The transmission coefficient of the filter 34 can be tailored, for example, based on the specifications for the light source 20 and the receiver optics 36. As indicated in FIG. 1, by incorporating the position-dependent transmission filter 34, the light incident on the image sensor 30 can have a relatively uniform intensity profile 40 (assuming, e.g., the light projected onto the scene is uniformly reflected by the scene to the receiver optics). In some cases, the filter 34 is configured to allow, for example, up to 5-10% variation (e.g., 5% or 10% variation) in the offset profile 40 of the light incident on the sensor 30. In other cases, the filter 34 is configured to allow up to 50% or even 75% variation in the offset profile 40 of the light incident on the sensor 30.

[0024] FIG. 2 illustrates a second implementation in which the sensor 30 is calibrated to have shorter integration time(s) in region(s) where the brightness is higher due to the Opdiffraction order. The sensor 30 can be calibrated so that the effective measured intensity remains substantially uniform across the light sensitive surface of the sensor. As described in connection with FIG. 1, the illumination profile of the light 38 transmitted through the receiver optics 36 may contain higher intensity near its center 39 as a result of Oth-diffraction order rays 28 present in the light profile 26 projected onto the scene 29. In this implementation, the sensor 30 is calibrated to compensate for the presence of the Oth-diffraction order so that the output profile 42 of the sensor 30 is substantially uniform despite the greater brightness near the center of the profile (assuming, e.g., the light projected onto the scene is uniformly reflected by the scene to the receiver optics). In some cases, the sensor 30 is configured to allow, for example, up to 5-10% variation (e.g., 5% or 10% variation) in the offset profile of the sensor output 42. In some cases, the sensor 30 is configured to allow, for example, up to 50-75% variation (e.g., 50% or 75% variation) in the offset profile of the sensor output 42.

[0025] FIG. 3 illustrates a third implementation for reducing the impact of the Oth- diffraction order. As the extra projected brightness from the O^th-diffraction order is distributed in a predictable, non-varying position in position space, the same is applicable in angular space because the 0^th-diffraction order propagates radially. This means that the O^th-diffraction order also has a well-defined profile in angular space and can be compensated for by applying, for example, an angle-of-incidence (AOI) filter 44 in front of the Rx optics 36. The AOI filter 44 reduces, proportionately, the intensity of the light profile within a specified angle, which defines an area about the center of the profile where the Oth-diffraction order is present. That is, the AOI filter 44 compensates for the O^th-diffraction order-induced angular brightness profile so that the profile 46 of the light incident on the image sensor 30 has a relatively uniform intensity profile (assuming, e.g., the light projected onto the scene is uniformly reflected by the scene to the receiver optics). In some cases, the AOI filter 44 is configured to allow, for example, up to 5-10% variation (e.g., 5% or 10% variation) in the offset profile 46 of the light incident on the sensor 30. In some cases, the AOI filter 44 is configured to allow, for example, up to 50- 75% variation (e.g., 50% or 75% variation) in the offset profile 46 of the light incident on the sensor 30.

[0026] FIG. 4 illustrates a further implementation that includes an AOI filter arranged to reduce the impact of the Oth-diffraction order or other low-angle scattered light. In this case, the AOI filter is disposed on the transmission (Tx) side of the optical system. For example, an AOI filter 50 can be disposed in the light path after the light projecting element 24. The light 22, 25 projected toward the scene contains increased intensity near a center of a field-of-view due to 0^th-diffraction order rays or other low-angle scattered light. As the extra projected brightness from the O^th-diffraction order, for example, is distributed in a predictable, non-varying position in position space, the 0^th-diffraction order can be compensated for by the AOI filter 50. The AOI filter 50 reduces, proportionately, the intensity of the light profile within a specified angle that defines an area about the center of the profile where the Oth-diffraction order is present. That is, the AOI filter 50 compensates for the O^th-diffraction order induced angular brightness profile so that the light incident on the scene 29 has a relatively uniform intensity profile 26. In some cases, the AOI filter 50 is configured to allow, for example, up to 5-10% variation (e.g., 5% or 10% variation) in the offset profile of the light incident on the scene 29. In some cases, the AOI filter 50 is configured to allow, for example, up to 50-75% variation (e.g., 50% or 75% variation) in the offset profile of the light incident on the scene 29.

Reducing the intensity of the O^th-diffraction order at the transmission (Tx) side provides a corresponding reduction in the intensity of the Oth-diffraction order at the receiver (Rx) side, with the result that the light 48 incident on the Rx optics 36, as well as the light 48 incident on the image sensor 30, has a relatively uniform intensity profile (assuming, e.g., the light projected onto the scene is uniformly reflected by the scene to the receiver optics).

[0027] The optical systems described above can be integrated, for example, into compact electronic devices such as smart phones, laptops, televisions, or wearable devices, as well as larger devices or systems such as automotive vehicles.

[0028] While this specification contains many specifics, these should not be construed as limitations on the scope of the disclosure or of what may be claimed, but rather as descriptions of features specific to particular implementations. Certain features described in this specification in the context of separate implementations also may be combined in the same implementation. Conversely, various features described in the context of a single implementation also may be implemented in multiple implementations separately or in any suitable sub-combination. Various modifications can be made to the foregoing examples. Accordingly, other implementations also are within the scope of the claims.

Claims

What is claimed is:

1. An apparatus comprising: an optical system including a transmission side and a receiver side, wherein the transmission side includes: a light source operable to generate light; and a light projecting element arranged to project the light toward a scene, wherein an illumination profile of the light projected toward the scene contains increased intensity near a center of a field-of-view due to O^th-diffraction order rays or other low-angle scattered light, wherein the receiver side includes: an image sensor; and at least one lens to focus light reflected by the scene toward the optical sensor, and wherein the optical system includes means for reducing impact of the Opdiffraction order or other low-angle scattered light.

2. The apparatus of claim 1 wherein the means for reducing impact of the O^th-diffraction order or other low-angle scattered light includes a transmission filter having lateral varying transmission, wherein the transmission filter is disposed on the receiver side to reduce the increased intensity due to the O^th-diffraction order or other low-angle scattered light.

3. The apparatus of claim 2 wherein the transmission filter is configured to have a transmission coefficient that reduces the intensity of a light profile in a region where 0^th- diffraction order rays or other low-angle scattered light are present.

4. The apparatus of claim 2 wherein the transmission filter is disposed optically between the at least one lens and the image sensor.

5. The apparatus of claim 2 wherein the transmission filter is configured to allow no more than 10% variation in an offset profile light incident on the image sensor.

6. The apparatus of claim 2 wherein the transmission filter is configured to allow no more than 5% variation in an offset profile light incident on the image sensor.

7. The apparatus of claim 1 wherein the image sensor is calibrated to have a shorter integration time in a region configured to acquire signals corresponding to the increased intensity due to the 0^th-diffraction order or other low-angle scattered light.

8. The apparatus of claim 7 wherein the image sensor is calibrated so that, under a condition where the light projected onto the scene is uniformly reflected by the scene to the at least one lens in the receiver side, a measured intensity remains substantially uniform across a light sensitive surface of the sensor.

9. The apparatus of claim 1 wherein the means for reducing impact of the O^th-diffraction order or other low-angle scattered light includes an angle-of-incidence (AOI) filter disposed optically in front of the at least one lens on the receiver side.

10. The apparatus of claim 9 wherein the AOI filter is configured to reduce an intensity of a light profile within a specified angle that defines an area about a center of the profile where the O^th-diffraction order or other low-angle scattered light is present.

11. The apparatus of claim 10 wherein the AOI filter is configured to compensate for Opdiffraction order-induced angular brightness profile so that, under a condition where the light projected onto the scene is uniformly reflected by the scene toward the at least one lens in the receiver side, light incident on the image sensor has a measured intensity that remains substantially uniform across a light sensitive surface of the sensor.

12. The apparatus of claim 11 wherein the AOI filter is configured to allow no more than 10% variation in an offset profile light incident on the image sensor.

13. The apparatus of claim 11 wherein the AOI filter is configured to allow no more than 5% variation in an offset profile light incident on the image sensor.

14. The apparatus of claim 1 wherein the means for reducing impact of the O^th-diffraction order or other low-angle scattered light includes an angle-of-incidence (AOI) filter disposed optically after the light projecting element on the transmission side.

15. The apparatus of claim 14 the AOI filter is configured to reduce an intensity of a light profile within a specified angle that defines an area about a center of the profile where the O^th-diffraction order or other low-angle scattered light is present.

16. The apparatus of claim 15 wherein the AOI filter is configured to compensate for the O^th-diffraction order or other low-angle scattered light induced angular brightness profile so that the light incident on the scene has a substantially uniform intensity profile.

17. The apparatus of claim 16 wherein the AOI filter is configured to allow no more than 10% variation in an offset profile light incident on the scene.

18. The apparatus of claim 16 wherein the AOI filter is configured to allow no more than 5% variation in an offset profile light incident on the scene.

19. The apparatus of any one of claims 1-18 wherein the at least one lens at the receiver side includes at least one meta-lens.