Camera module using META-optical element

Abstract

A camera module includes a substrate having a first surface and a second surface opposite the first surface The camera module includes a sensor on the second surface of the substrate and a meta-structure optical element (MOE) on the first surface of the substrate. The MOE defines an aperture stop on the substrate. A system including the camera module can include a light source and an electronic circuit. The electronic circuit actuates the light source, determines a value associated with at least one detection signal of the sensor and calculates a distance of the camera module to an object based on each detected value.

Description

NIL Technology ApSF&R Ref. 47717-0074WO1 PCT Application CAMERA MODULE USING META-OPTICAL ELEMENTBACKGROUND

[0001] A meta-optical element (MOE) refers to an optical element having distributed small structures (e.g., meta-atoms) arranged to interact with light in a particular manner. For example, a MOE can include a surface with a distributed array of nanostructures. The nanostructures may, individually or collectively, interact with light waves. For example, the nanostructures or other meta-atoms may change a local amplitude, a local phase, or both, of an incoming light wave.SUMMARY

[0002] In general, in some aspects, this disclosure relates to camera modules, time-of-flight detectors that employ MOEs and also relates to applications which utilize low resolution cameras that employ MOEs. Sample additional applications include, for example, time-of-flight receivers, presence sensors, object detectors, and low light intensity sensors. The object can be located at any distance from the camera module from a finite distance (e.g., 1 cm, 1 m, 1 km) to an infinite distance, or any distance in between.

[0003] A camera module is described including a substrate having a first surface and a second surface opposite the first surface. Implementations of the camera may include one or more of the following features. A meta-structure optical element (MOE) may be located on the first surface of the substrate and may define an aperture stop on the substrate. A sensor may be located at a focal plane of the MOE on or near the second surface of the substrate.

[0004] In some implementations, the sensor is directly on the second surface of the substrate. The camera module may include a spacer layer between the sensor and the second surface of the substrate. The spacer layer can include an air gap. The spacer layer can include a solid transparent material. A bandpass filter can be located between the sensor and the second surface of the substrate. A bonding layer can be located between the bandpass filter and the sensor. The bandpass filter can have a transmission wavelength range from 380 nm to 1500 nm. The F-number of the camera module can be in the range F / 0.8 to F / 8.0. The total track length of the camera module can be in the range 0.1 mm to 4 mm. The substrate may include at least one of glass, sapphire, quartz, a polymer, titanium oxide (TiCh), and mixtures of the same. A maximum image circle diameter may be in the range 0.14 mm to 1.30 mm and a pixel edge length may be in the range 25 pm to 100 pm. An image circle may be understood to mean a circle having a diameter of the image formed by the lens on the sensor.NIL Technology ApSF&R Ref. 47717-0074WO1 PCT ApplicationThe MOE can direct light entering the MOE at a plurality of different angles of incidence to a plurality of locations on the sensor, respectively. The aperture stop can be further defined by mechanical stops.

[0005] A system including the camera module can include a light source and an electronic circuit. The electronic circuit may be configured to actuate the light source so as to cause the light source to emit light. The electronic circuit may be configured to determine a value associated with at least one detection signal of the sensor upon the sensor detecting the light reflected from an object. The electronic circuit may be configured to calculate a distance of the camera module to the object based on each detected value.

[0006] Other systems, devices, methods, features and advantages of the subject matter described herein will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the subject matter described herein, and be protected by the accompanying claims. In no way should the features of the example embodiments be construed as limiting the appended claims, absent express recitation of those features in the claims.BRIEF DESCRIPTION OF THE FIGURES

[0007] The details of the subject matter set forth herein, both as to its structure and operation, may be apparent by study of the accompanying figures, in which like reference numerals refer to like parts. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the subject matter.Moreover, all illustrations are intended to convey concepts, where relative sizes, shapes and other detailed attributes may be illustrated schematically rather than literally or precisely.

[0008] FIG. l is a schematic that illustrates an example of an imaging module.

[0009] FIG. 2 is a schematic that illustrates an example of a time-of-flight system including an imaging module.

[0010] FIG. 3 is a schematic that illustrates an example of different rays of light incident on the receiver of FIG. 1.

[0011] FIGS. 4A, 4B, 4C, and 4D are schematics that illustrate examples of different MOE phase profiles and phase slopes.

[0012] FIG. 5 A illustrates a modulation transfer function (MTF) for an example camera module receiver.NIL Technology ApSF&R Ref. 47717-0074WO1 PCT Application

[0013] FIG. 5B illustrates a modulation transfer function (MTF) for an example camera module receiver.

[0014] FIG. 6 is a plot that illustrates different locations of light incident on a sensor.

[0015] FIG. 7 illustrates plots depicting a spot diagram of the image plane on a sensor.

[0016] FIG. 8 is a plot that illustrates a relative illumination on an example sensor.DETAILED DESCRIPTION

[0017] Before the present subject matter is described in detail, it is to be understood that this disclosure is not limited to the particular embodiments described, as such may, of course, vary.

[0018] The present disclosure describes using meta optical elements (MOEs) as part of a camera module (e.g., a time-of-flight (TOF) detector, a presence detector, a low resolution camera, etc.) and system. MOEs have a metasurface that includes distributed small subwavelength structures (e.g., nanostructures or other meta-atoms) arranged to interact with light in a particular manner. The meta-atoms can, individually and / or collectively, interact with light waves to change a local amplitude, a local phase, or both, of an incoming light wave. In some instances the MOEs may be referred to as metalenses. In some cases, MOEs 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 surface tolerances. MOE can utilize fewer lens surfaces and at the same time have the same image quality as conventional refractive lens systems. An as-built optical system based on pure MOEs suffers less performance degradation compared with an as-built optical system using standard processes and optical elements. Examples of MOEs include diffraction and other gratings, beam splitters, beam shapers, collimators, diffractive diffusers, as well as other optical elements.

[0019] Conventional optical elements such as lenses inherently have several problems including aberration of the beam due to the curved nature of the conventional optical elements, additional reflections due to the need for air gaps between multiple curved surfaces of conventional lenses, and overall system complexity. In some cases, MOEs can provide several potential advantages compared to refractive elements. In the present disclosure, in some implementations, an advantage of employing MOEs is that they allow a reduction in the total track length (TTL) of an imaging receiver of a camera module (e.g., a receiver of a time-of-flight (TOF) detector or a TOF system) and thus permit more a compact sizing of theNIL Technology ApSF&R Ref. 47717-0074W01 PCT Applicationcamera module as a whole. The TTL is the distance between the front element and the sensor surface of the optical system (imaging module or receiver) and may further depend on the field of view (FOV) for a specific image circle. For an image circle of a given size, the TTL decreases as the FOV increases. The front element can be either the lens system (e.g., the MOE) or the aperture stop, but in this disclosure the MOE and the aperture stop are located together. Such a compact size can be advantageous for integration of a camera module into relatively small devices, such as mobile phones. An advantage of using MOEs as part of a camera module is that, compared to modules that use refractive lenses, an MOE-based camera module can be designed to have a higher light throughput with relatively fewer lens surfaces (e.g., a single MOE surface) while still providing good image quality. A camera module based on refractive lenses would require significantly more lens surfaces to achieve the same image quality. The MOE-based camera module may have a low F-number while still maintaining good image quality. Another advantage of using MOEs is that, in certain implementations, they allow a large FOV of the system while maintaining the compactness over a system using refractive optical elements. Additional advantages of using MOEs for a camera module can include, e.g., a reduction of aberrations in light collected, reduced reflections of light, since no air gap is needed between curved lenses since the MOE has a flat surface, and also wide field of view to enable collection of more light and thus higher sensitivity.

[0020] FIG. 1 is a schematic that illustrates an example of an imaging module 100. The imaging module may be part of a camera module or other device. The imaging module 100 may alternatively be used in, for example, a low resolution camera, a presence sensor, an object detector, or a low resolution light intensity sensor. The imaging module 100 includes a lens system 101 and an imaging sensor 110. The lens system includes a substrate 106 and a meta-optical element (MOE) 102. The lens system 101 may optionally include a filter 108. The substrate 106 has a first surface 106 S1 and a second surface 106 S2 opposite the first surface. The substrate 106 is optically transparent and can be composed of optically transparent material such as, for example, of glass, titanium oxide, or a polymer. In the context of the present application, optically transparent indicates that the material is optically transparent for a specified operational wavelength (e.g., in the infra-red, UV, or visible part of the spectrum). The substrate 106 can include at least one of glass, sapphire, quartz, titanium oxide, a polymer, or mixtures of these materials. In some implementations, an anti-NIL Technology ApSF&R Ref. 47717-0074WO1 PCT Applicationreflective coating (ARC) layer is provided on top of the substrate 106 and on top of the MOE 102.

[0021] The lens system 101 includes a meta-optical element (MOE) 102. MOEs have a metasurface that includes distributed small subwavelength structures (e.g., nanostructures or other meta-atoms) arranged to interact with light in a particular manner. The meta-atoms can, individually and / or collectively, interact with light waves to change a local amplitude, a local phase, or both, of an incoming light wave. In some implementations, the MOE 102 directs nearly parallel light rays incident on the MOE 102 onto a particular location on the sensor 110. In some implementations the MOE 102 focuses nearly parallel incident light rays onto the focal plane of the sensor 110. In some implementations the MOE 102 both focuses the incident light rays and also directs the nearly parallel light rays onto particular locations on the sensor 110. In some implementations the MOE 102 directs the nearly parallel light rays onto the same location on the sensor 110 so that light rays at each angle of incidence are directed to a particular location on the sensor 110. In an example, the MOE 102 directs nearly parallel light rays onto an active area of the sensor 110, for example, on a matrix of pixels.

[0022] The aperture stop is the surface which limits the light in the optical system or in the imaging module. In this disclosure, the front MOE acts as a lens and also acts as the aperture stop which limits the light passing through the optical system. Outside the MOE acting as a lens, a coating or processing of the surface of the substrate or of an anti -refl ection coating on the surface may block the surrounding light from entering. The area outside the MOE may include, for example, an absorptive material to reduce stray light from entering the optical path. The area outside the MOE may also include a mechanical stop. In an example, light rays that are being projected from different field angles or different positions in object space to a different position with a limited area along the MOE can be reduced. The positioning of the MOE as the aperture stop, rather than, say in front of the aperture stop, allows close-to normal -incidence of chief ray angles (CRAs) to be incident on the sensor 110.

[0023] In the present example, there is a single MOE 102 in the device that is provided on the first surface 106 S1 of the substrate 106. The MOE 102 is co-incident with an aperture stop of the imaging module 100. In some implementations, the MOE 102 itself is the aperture stop. In some implementations, the MOE 102 acts as a lens and also as the aperture stop. In some implementations, the MOE 102 is above the first surface 106 S1. For example, a spacer layer or an air gap may be between the MOE 102 and the first surface 106 S1. In some implementations, the first surface 106 S1 of the substrate has a recessed portion andNIL Technology ApSF&R Ref. 47717-0074W01 PCT Applicationthe MOE 102 is in the recessed portion of the front surface. In some implementations, the aperture stop may optionally include one or more mechanical stops 104 that define the boundary of the aperture stop around the MOE 102 but do not otherwise interfere with the imaging light. For example, the aperture stop can be defined by mechanical stops 104 which block incident light from being transmitted through the substrate 106 onto the sensor 110. In some implementations, opaque elements such as black chrome or resist may be used as the aperture stop or the front surface 106 S1 outside of the placement of the MOE 102 may be treated to form an opaque surface. The mechanical stops 104 can include any material opaque at the wavelengths of interest and which is thick enough to effectively block any stray light from entering the substrate 106. The outer sidewalls of the substrate, an anti -refl ection coating, can be blackened or at least partially blackened, e.g., with a layer of black chrome, resist, or other opaque material, to prevent or reduce stray light from entering the MOE 102. The mechanical stops 104 may also act as baffles to block unwanted stray light from entering the system. The total track length (TTL) is the distance from the front surface of the first element in an optical system to the sensor. In conventional optical systems, the front surface is often the front surface of a lens, which is placed in front of the aperture. In the present system, in contrast, the imaging module 100 has the MOE 102 (acting as a lens) defining the aperture stop. Thus, in some implementations, the TTL is the distance from the front surface of the MOE 102 to the sensor 110. The aperture stop operates to limit the solid angle of rays passing through the receiver from the target, and thus defines the cone of light reaching the image plane of the sensor 110.

[0024] The imaging module 100 further includes a sensor 110. The sensor 110 is provided at or near the second surface 106 S2 of substrate 106. The sensor 110 includes one or more light detecting elements, such as a phototransistor, a photoresistor, or other type of light sensor. In some implementations, the sensor 110 has electrical contacts 116 for communication with the controller 230, but is not limited thereto. The imaging module 100 may communicate with the controller 230 through other means, such as radio frequency transmission. The sensor 110 may optionally be placed on its own substrate 114 or its own packaging element. The sensor 110 may be a single sensor or may include an array of sensors. The sensors may be square or circular or other shapes. An array of sensors may be a rectangular array in which the sensors form a rectangular lattice, or the array of sensors may use another lattice. The sensor 110 may be packaged prior to integrating it with the substrate 106 and the other elements of the imaging module 100. The sensor may include a cover glassNIL Technology ApSF&R Ref. 47717-0074WO1 PCT Applicationor other protective cover. An example packaging element is a printed circuit board. In some implementations, the substrate 106 and the MOE 102 are fabricated separately from the sensor 110 and then the sensor 110 is attached to the substrate 110. In an example, the sensor 110 includes square pixels in, for example, a 5 by 5 array or a 10 by 10 array, but the number of pixels is not limited thereto.

[0025] The imaging module 100 may optionally include a filter 108 between the substrate 106 and the sensor 110 or between the substrate 106 and the sensor substrate 114. In some implementations, the filter 108 may include a bandpass filter. In some implementations, the filter 108 is placed directly on the second surface 106 S2 of the substrate 106. If the filter 108 is designed as a bandpass filter, the bandpass filter may permit transmission of a central transmission wavelength in the near-infra-red wavelength range, for example in the range of 800 nm and 1500 nm, while not transmitting light outside the wavelength range. Although a filter (e.g., a bandpass filter) can be placed optically between the MOE and the light sensitive surface of the sensor 110, in some implementations, the light path may intersect more than one MOE. Some, or all, of these other optical elements also may be disposed optically between the MOE 102 and the light sensitive surface of the sensor 110. In some implementations, there is a second surface spacer between the substrate 106 and the sensor 110 or between the substrate 106 and the filter 108 or between the filter 108 and the sensor 110. A second surface spacer can comprise, for example, an air gap or a transparent solid material. In an example, a cover glass over the sensor may act as a second surface spacer. In some implementations a second surface space can be included separate from a cover glass of the sensor. Multiple second surface spacers can also be used, for example, a solid transparent material between the substrate 106 and the filter 108 and an air gap between the filter 108 and the sensor 110. In some implementations, the stack of optical element(s), substrates and spacers forms a dense block of transparent material from the first surface to the sensor without any air gaps. In some implementations, the stack of optical element(s), substrates and spacers forms a dense block of transparent material from the first surface to and including the cover glass of the sensor and having an air gap between the cover glass and the sensor. In some implementations, the stack of optical element(s), substrates and spacers forms a dense block of transparent material from the first surface to the sensor except an air gap between the bottom of the stack and the sensor surface.

[0026] The total track length (TTL) is shown and is the distance from the aperture stop to the surface of the sensor 110. The imaging module 100 may optionally include a bondingNIL Technology ApSF&R Ref. 47717-0074WO1 PCT Applicationlayer or bonding layers between the various elements. For example, there may be a bonding layer between the substrate 106 and the sensor substrate 114, between the substrate 106 and the filter 108, between the substrate 106 and the sensor 110, between a bandpass filter 108 and the sensor 110, but the imaging module 100 is not limited thereto and may include bonding layers between other elements. The material for the bonding layer or the filter 108 can be substantially index matched optically to the substrate 106. In some implementation, an adhesive (e.g., bonding glue) can serve as the encapsulant material. In some implementations, the optical stack may include one or more additional optical elements, For example, in some instances, the optical stack includes an optical filter 108 (e.g., a band pass filter or an angle-of-incidence filter), which can be attached to the substrate 106 or to the sensor substrate 114 or to the sensor 110 by a bonding layer (e.g., bonding glue).

[0027] FIG. 2 is a schematic that illustrates an example of a time-of-flight system including an imaging module. The time-of-flight system 200 includes at least one light source 210, at least one imaging module 100 to detect light, and an electronic controller 230 configured to actuate the light source 210 so as to cause the light source 210 to emit light, to determine a value associated with the sensor 110 detecting the light reflected from an object 220, and to calculate a distance of the time-of-flight detector to the objected based on the detected value. The TOF system 200 includes an illumination module 210 for illuminating a target 220 and a imaging module 100 for receiving illumination light reflected by the target 220. In some implementations the illumination module 210 includes an emitter (e.g., a controllable light source) such as a light emitting diode (LED) or a laser, for example, a vertical cavity surface emitting laser (VCSEL). The illumination module 210 may emit light of a single wavelength (e.g., 940 nm) or may emit light with a relatively narrow bandwidth (e.g., 940 nm ± 2.5 nm), though other variations are possible (e.g., 940 nm ± 5 nm, 940 nm ± 10 nm, 940 nm ± 20 nm). Using light emitted with a narrow bandwidth helps to reduce color aberrations. The illumination module 210 may include other optical elements such as collimators or lenses. Light from the illumination module 210 is reflected from the target 220 and detected by the imaging module 100. The imaging module 100 can include a lens system 101 and a light sensor 110, e.g., a photodiode, a phototransistor, a photoresistor, or other type of light sensor. The lens system 101 can include an MOE 102 to perform various functions. The lens system 101 can include an MOE 102 acting as another optical element. The light sensor 110 can include a single detector or an array of detectors, e.g., arranged as a pixel array in which each pixel includes a corresponding detector.NIL Technology ApSF&R Ref. 47717-0074W01 PCT Application

[0028] The time-of-flight system 200 further includes a controller 230. The illumination module 210 and the imaging module 100 are in communication with and under the control of the controller 230. The controller 230 sends signals to and receives signals from the illumination module 210. For instance, the controller 230 sends a control signal to the illumination module 210 to control activation of the illumination module 210 so that the illumination module 210 emits light towards the target 220. The controller 230 sends signals to and receives signals from the imaging module 100. For example, the controller 230 may receive signals from one or more light sensors in the imaging module 100. The controller 230 controls overall operation of the TOF system 200.

[0029] FIG. 3 is a schematic that illustrates an example of how the MOE 102 of the imaging module can be used to modify light incident on the imaging module. In the example shown in FIG. 3, three different sets of light rays are depicted as being incident on the imaging module. A first set of light rays 202 is incident nearly perpendicularly with respect to an upper surface of the MOE 102. A second set of light rays 204 is incident onto the MOE 102 at an angle with respect to the upper surface of the MOE 102. A third set of light rays 206 is incident at an even greater angle of incidence than the second set of light rays onto the MOE 102. The first set of light rays 202 are nearly parallel with each other due to the target being far away. The second set of light rays 204 are also nearly parallel with each other as are the third set of light rays 206 for the same reason — a distant target. The meta-structures which form the MOE 102 can be configured to cause the different sets of light rays to be incident at different positions on the sensor 110. The first set of light rays 202 are directed to a first portion 110A of the sensor 110. The second set of light rays 204 are directed to a second portion 110B of the sensor 110. The third set of light rays 206 are directed to a third portion 110C of the sensor 110. The aberrated light 302 is illustrated for the second and the third sets of light rays since some portion of the second set of light rays 204 or the third set of light rays 206 are not all focused at the image plane. The first set of light rays is for an on-axis point OF. The second set of light rays is for a first off-axis point 0.8F. The third set of light rays is for a second off-axis point IF which is the full field (100%) corresponding to half the full field of view angle (FOV / 2). Thus, the MOE 102 may be configured to cause a shift in the location of incident light based on light’s angle of incidence. The MOE 102 is not limited to modifying light in the manner shown in FIG. 3 and may be designed to alter incident light in other ways such as focusing light onto the plane of the sensor 110.NIL Technology ApSF&R Ref. 47717-0074W01 PCT Application

[0030] The sensor 110 detects the incident light and transmits the results to the controller 230 by, for example, an electrical connection with the controller 230. As explained herein, the controller 230 can be configured to cause the illumination module 210 to emit light and to determine a time-of-flight based on detected light once it returns the imaging module, as illustrated in FIG. 2. In some implementations, the controller 230 can be configured to measure the phase difference between the emitted light and the received light to determine a time-of-flight of each of the light rays. In an example the first set of light rays 202 and the second set of light rays 204 are reflected from different locations on the target 220 and so have different angles of incidence on the imaging module 100. The first set of light rays 202 and the second set of light rays 204 may also have been emitted from the illumination module 210 at different times. The controller 230 receives a first signal from the sensor 110 indicating that the first light ray 202 was incident on the sensor 110 at position 110A as well as time information related to the detection of the first set of light rays 202. In an example, the light emitter 210 emits a periodic pulse and the imaging module 100 detects the time the pulse has taken to travel from the emitter 210 to the imaging module 100. The controller calculates the time difference between when the first light ray left the emitter 210 and when the first light ray was received by the imaging module 100. The distance to the target is half of this time multiplied by the speed of light with a slight modification to account for the angle of incidence of the light ray. In another example, a signal (e.g., a continuous sinusoidal wave) modifies the light emitted by the light emitter 210 and the phase difference between the emitted signal and the received signal is determined by the controller 230 to determine the distance. The controller 230 receives a second signal from the sensor 110 indicating that the second set of light rays 202 was incident on the sensor 110 at position 110B as well as time information related to the detection of the second set of light rays 204. Based on the positions at which light is detected in the sensor 110 and the time information of the emitted and received light rays, the controller 230 determines a distance to the target 220 from which the first and second sets of light rays 202, 204 have been reflected. In some implementations, the first set of light rays 202 and the second set of light rays 204 are emitted towards different locations on the target 220. In an example, the first set of light rays 202 may be incident on a portion of the target 220 which is closer to the time-of-flight system 200 and the second set of light rays may be incident on a portion of the target 220 which is further from the time-of-flight system 200. The imaging module 100 receives the first set of light rays 202 and the second set of light rays 204. Based on signals received by the sensor 110 at positions 110A and HOB, the controller determines that the set of first light rays 202 was received first soNIL Technology ApSF&R Ref. 47717-0074WO1 PCT Applicationthat the portion of the target 220 which reflected the first set of light rays 202 is closer than the portion of the target 220 which reflected the second set of light rays 204. In addition, the controller 230 determines the actual distances from the time-of-flight system 200 to the different portions of the target 220.

[0031] In some optical systems, for instance in a traditional imaging camera, the aperture stop is positioned in front of and spaced apart from the lens element(s) (e.g., further away from the sensor). Such placement increases the TTL, but also allows the imaging module to correct aberrations before the light enters the sensor. Such corrections as finding the optimal position of the aperture stop can be based on the stop shift relations. In other optical systems, the aperture stop can be placed between the lens element(s) and the sensor. Such placement may degrade image quality.

[0032] In contrast, in the present disclosure, the MOE is located at generally the same position as the aperture stop. For instance, in the examples described herein, the aperture stop is positioned on a surface of the MOE. By locating the MOE and aperture stop at generally the same position (e.g., effectively at the same plane), it is possible to shorten the TTL.Shortening the TTL in turn allows a more compact device to be designed. While this placement may eliminate the ability to correct for certain optical aberrations (since the device avoids the use of lens elements that are designed based on the stop-shift relations), such aberrations may be less problematic for low resolution sensors (e.g., TOF detectors, presence sensors, object detectors, and the like). In particular, as TOF detectors are not attempting to image objects, TOF detectors can accommodate greater optical aberrations than other imaging systems (e.g., regular image cameras) might. For this reason, low resolution detectors may also be designed with sensors having pixel areas that are larger relative to other imaging systems.

[0033] As another advantage, co-locating the aperture stop and the MOE allows, in certain implementations, the system to collect more light and have a large field of view. In some implementations, the camera module has a low F-number, such as F / 0.8, F / 0.9, F / 1.0, F / 1.2, F / 1.4, F / 2, F / 2.8, F / 4, F / 5.6, of F / 8. These are only examples and the F-number may be higher than F / 8 (e.g., F / 22). In some implementations, the MOE camera module has a field of view, for example, in the range of 45° to 80°. More specifically the FOV may be in the range of 50° to 70° or in the range 60° to 65°. In these examples, the incidence angle of light entering the detector is within the range listed from +22.5° and -22.5° (± 22.5°) , ± 25°, ± 30°, ± 32.5°, ± 35°, or ± 40°.NIL Technology ApSF&R Ref. 47717-0074W01 PCT Application

[0034] With a shortened TTL, a camera module using an MOE may be compact enough to be incorporated into, e.g., a proximity sensor or a three-dimensional mapping device. The camera module may be integrated into other systems, for example, mobile phones, laptops, television, wearable devices, or vehicles. The example camera module described above includes a single MOE 102 positioned at an upper surface 106 S1 of the substrate 106. In some implementations, additional MOEs may be used. For instance, in some implementations, an additional MOE may be located on the bottom surface 106 S2 of the substrate 106, e.g., in front of the sensor 110 and / or in front of a filter, such as a bandpass filter.

[0035] Example implementations of simulated camera modules that employ the imaging module described herein are discussed below. The simulated examples are time-of-flight (TOF) systems, specifically direct time-of-flight systems. Although the simulated example systems are direct time-of-flight (dTOF) systems, the concepts disclosed herein are also applicable to indirect time-of-flight (iTOF) systems as well as to other camera modules and other imaging systems more generally. Additionally the example simulations described below locate the object at a finite distance (1 meter) from the camera module, but the object can be located at any distance from the camera module. For example, a low resolution imaging module may be focused at an infinite distance rather than at a finite distance. The imaging module can be focused at any object distance and the simulations performed are only nonlimiting examples.

[0036] A first finite optical system (e.g., a first dTOF system) with an object distance at 1 meter was simulated to have a TTL of 1.16 mm. A second finite optical system (e.g., a second dTOF system) also with an object distance at 1 meter was simulated to have a TTL of 0.78 mm. Both example dTOF systems include an illumination module configured to emit monochromatic light having a wavelength of 940 nm ±10 nm. The first example dTOF system was designed to have an imaging module with an F-number of F / 1.2, a FOV of 65° (incident angle of ± 32.5°), and an image circle diameter of 0.91 mm. The second example dTOF system was designed to have an imaging module with an F-number of F / 0.8 and a FOV of 65° (incident angle of ± 32.5°) and the same image circle diameter. The modulation transfer function (MTF) was simulated for both systems were simulated for tangential and sagittal light as a function spatial frequency. The spatial frequency range was out to the Nyquist spatial cut-off frequency (~ 10 cc / mm in these examples). The first dTOF system simulation yielded an image contrast value of 0.70 for field point 0.8F at a spatial frequencyNIL Technology ApSF&R Ref. 47717-0074W01 PCT Applicationof 10 cc / mm. The second dTOF system simulation yielded an image contrast value of 0.45 for field point 0.8F at the same spatial frequency.

[0037] Such example dTOF systems can be used in daylight applications in, for example, mobile phones. Both example systems used a glass substrate, a bandpass filter, and a low resolution sensor array with a 13 by 13 array of pixels, in which each pixel is in the shape of a 50 pm by 50 pm square. The overall area of the example low resolution sensor is thus approximately 650 pm by 650 pm. Other low resolution sensors can, for example, have an overall size in a range from approximately 50 pm by 50 pm up to approximately 1000 pm by 1000 pm with a pixel edge length range of from approximately 25 pm to approximately 500 pm with the number of pixels being adjusted to meet the corresponding low resolution sensor’s overall size. The phase profile MOE bending was varied given the TTL and other constraints with a goal of maintaining the relative illumination above a minimum of 70%. The relative illumination in this instance is the ratio of the illumination at the edge of the sensor divided by illumination at the center of the sensor. The aperture stops of the example devices were co-located at the same plane as the plane of the MOE, where the MOE is positioned on the first surface of the substrate.

[0038] FIGS. 4A, 4B, 4C, and 4D are schematics that illustrate examples of different MOE phase profiles and phase slopes for the two example systems. An MOE phase profile shows the change in the phase of the light passing through that portion of the MOE. Plots 402, 404 (FIGS. 4A and 4C) depict surface phase whereas plots 412, 414 (FIGS. 4B and 4D) depict tangential phase slope. The MOE phase profile for the first example is shown in FIGS.4A and 4B and the MOE design for the second example is shown in FIGS. 4C and 4D. (The X-axis ranges are different in FIGS. 4C and 4D than in FIGS. 4 A and 4B.) The surface phase 402, 404 shows how the phase of an incident ray of light is changed by the MOE, depending on the position where the ray of light is incident on the MOE. At the center of the MOE (corresponding to x = 0 in the plots, black arrows), there is no phase change, but towards the edges of the MOE (further away from x = 0), the phase change is more substantial. In the first example, at position approximately +0.3 mm indicated by the hashed arrows, the surface phase 402 of a ray of light is retarded by approximately 60 radians and the tangential phase slope 412 is approximately -375 radians / mm. In the second example, the surface phase 404 at +0.3 mm is retarded by approximately 70 radians and the tangential phase slope 414 is approximately -550 radians / mm. The differences in the surface phase change between the example MOE for the first system 402 and the example MOE for the second system 412 areNIL Technology ApSF&R Ref. 47717-0074W01 PCT Applicationsubtle and difficult to observe. Therefore, the tangential phase slope plots 412, 414 (FIGS. 4B and 4D) are the slopes of the surface phases, to emphasize the distinctions. Note that the plots for the first example 402, 412 have a more negative value at the extrema positions than the plots for the second example 404, 414. The first example has a very linear slope of the tangential phase slope 412 with an abrupt change of direction at the center of the MOE. The second example has a curved slope of the tangential phase slope 414 in an attempt to minimize aberrations of the system, despite the shorter TTL. A single MOE with a cubic phase profile cannot fully correct the kinds of aberrations inherent in these systems.

[0039] FIGS. 5A and 5B illustrate the modulation transfer function (MTF) as simulated for different example camera modules. The MTF for both examples 502, 504 shows the decrease in the modulus of the OTF as the spatial frequency increases. The simulations were performed for a wavelength of 940 nm ± 10 nm. The first plot 502 (FIG. 5 A) shows the MTF for the first simulation with TTL = 1.16 mm. The second plot 504 (FIG. 5B) shows the MTF for the second simulation with TTL = 0.78 mm. The different lines represent different orientations of light waves: tangential (Tan) and sagittal (Sag). The range of the MTF for different orientations for the first system 512 is less than the range for the second system 514. For the second example dTOF system (TTL = 0.78 mm), there is a faster decrease in the MTF than for the first example system (TTL = 1.16 mm). The worst MTF for the second system 504 is approximately 0.25 at the Nyquist spatial cut-off frequency 520 whereas for the first system 502 the worst MTF is approximately 0.5 at that spatial frequency. These simulation results for the second system indicate that even the optimizing the design of the MOE does not completely counter-balance the decrease in MTF due to the shorter TTL. The relatively large pixels (13 x 13 array of square pixels 50 pm by 50 pm) of both example systems enable achieving a Nyquist spatial cut-off frequency 520 of ~10 cc / mm, shown by the dashed line. This Nyquist spatial cut-off frequency 520 in turn makes possible obtaining a short total track length of the optical system with the given FOV (65°) and the low F-number (F / 1.2).The size of pixels and of the sensor as a whole determine the sensitivity of these example dTOF systems. The Nyquist spatial cut-off frequency 520 applies to the MTF performance, where only low-resolution spatial frequencies below a certain value need be considered.

[0040] FIGs. 6 and 7 illustrate how camera modules function for light rays incident at different locations of the sensor for the simulated TTL = 0.78 mm dTOF system. FIG. 6 is a plot that illustrates different locations of light incident on the sensor 110. The locationNIL Technology ApSF&R Ref. 47717-0074W01 PCT Applicationlabelled “CENTER” corresponds to the center of the sensor and the location labelled “CORNER” corresponds to the furthest periphery of the sensor from the center (e.g., the corner in the exemplary square sensor). In the simulation illustrated (made for the TTL = 0.78 mm example), the square represents the shape of the actual sensor 110 having a size of 650 pm x 650 pm which is a 13 by 13 array of pixels. The distance from the center to the corner is approximately 460 pm. The distance from the center to the corner represents the largest radius of the image circle or the maximum image circle.

[0041] FIG. 7 illustrates plots depicting a spot diagram of the image plane on a sensor for the TTL = 0.78 mm simulated dTOF system. Rays of light incident upon the sensor at different angles are spread more broadly or less broadly apart, depending on the location of incidence on the sensor and also on the wavelength. The shapes of the points correspond to the wavelength of light. Crosses indicate the target wavelength (940 nm), squares indicate 930 nm, and triangles indicate 950 nm. The most oblique light rays enter the optical system at the largest angle of incidence into the aperture stop. Rays of light which are incident nearly perpendicular to the MOE and perpendicular to the sensor cluster near the center of the sensor, thus the center of the pixel array. These rays of light are shown in the plot labelled “CENTER.” Rays of light close to the 32.5° incident angle limit and which are directed to the corner of the sensor are aberrated more significantly than those at the center and are labelled “CORNER” in the plot. Rays of light close to the 32.5° incident angle limit incident near the edge of the sensor are spread out widely and may fall off the individual pixel meant to detect them or may fall outside of the sensor entirely. As one progresses from the center of the sensor towards the edge or towards the corner of the sensor, the rays of light spread out even more significantly at each of the intermediate locations. The crosses, squares, and triangles each form two elliptical outlines which represent an inner range and an outer range and so detail the maximum range of the aberration at each wavelength. Thus, at such high angles of incidence and towards the edge of the sensor, the example application dTOF system is less able to properly determine a distance to the target.

[0042] Each symbol in FIG. 7 is a sub-figure that depicts the aberrated point for certain perfect field point at the object (target). In the ideal case this point shall be imaged as a perfect point. Each field point can be defined as an incident angle to the imaging module which corresponds to a spatial field point at the sensor. The spot diagram shows that the spatial location at the sensor IMA 0.0 corresponds to the center of the sensor and IMA 0.460 mm corresponds to the comer of the sensor. The IMA 0.460 mm corresponds to an incidentNIL Technology ApSF&R Ref. 47717-0074WO1 PCT Applicationangle 65 / 2 = 32.5°, since the FOV is 65°. The FOV is then the diagonal field of view which corresponds to the sensor corner IMA 0.460 mm.

[0043] FIG. 8 illustrates the relative illumination for the longer TTL example dTOF system (TTL = 1.16 mm). The relative illumination is high at the center of the sensor and decreases at the comer of the sensor. In an example, at the corner of the sensor, the relative illumination has decreased to 88%. The relative illuminations for the TTL = 0.78 mm example dTOF system were slightly different, with a minimum value of 78%, and a comer value of 84%. Despite some loss in illumination from the short TTL, the relative illumination is above a threshold to be considered adequate for a dTOF detector.

[0044] It should be noted that all features, elements, components, functions, and steps described with respect to any embodiment provided herein are intended to be freely combinable and substitutable with those from any other embodiment. If a certain feature, element, component, function, or step is described with respect to only one embodiment, then it should be understood that that feature, element, component, function, or step can be used with every other embodiment described herein unless explicitly stated otherwise. This paragraph therefore serves as antecedent basis and written support for the introduction of claims, at any time, that combine features, elements, components, functions, and steps from different embodiments, or that substitute features, elements, components, functions, and steps from one embodiment with those of another, even if the following description does not explicitly state, in a particular instance, that such combinations or substitutions are possible. It is explicitly acknowledged that express recitation of every possible combination and substitution is overly burdensome, especially given that the permissibility of each and every such combination and substitution will be readily recognized by those of ordinary skill in the art.

[0045] As used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0046] While the embodiments are susceptible to various modifications and alternative forms, specific examples thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that these embodiments are not to be limited to the particular form disclosed, but to the contrary, these embodiments are to cover all modifications, equivalents, and alternatives falling within the spirit of the disclosure.Furthermore, any features, functions, steps, or elements of the embodiments may be recited inNIL Technology ApSF&R Ref. 47717-0074W01 PCT Applicationor added to the claims, as well as negative limitations that define the inventive scope of the claims by features, functions, steps, or elements that are not within that scope.

Claims

NIL Technology ApSF&R Ref. 47717-0074WO1 PCT Application CAMERA MODULE USING META-OPTICAL ELEMENTBACKGROUND[0001] A meta-optical element (MOE) refers to an optical element having distributed small structures (e.g., meta-atoms) arranged to interact with light in a particular manner. For example, a MOE can include a surface with a distributed array of nanostructures. The nanostructures may, individually or collectively, interact with light waves. For example, the nanostructures or other meta-atoms may change a local amplitude, a local phase, or both, of an incoming light wave.SUMMARY[0002] In general, in some aspects, this disclosure relates to camera modules, time-of-flight detectors that employ MOEs and also relates to applications which utilize low resolution cameras that employ MOEs. Sample additional applications include, for example, time-of-flight receivers, presence sensors, object detectors, and low light intensity sensors. The object can be located at any distance from the camera module from a finite distance (e.g., 1 cm, 1 m, 1 km) to an infinite distance, or any distance in between.[0003] A camera module is described including a substrate having a first surface and a second surface opposite the first surface. Implementations of the camera may include one or more of the following features. A meta-structure optical element (MOE) may be located on the first surface of the substrate and may define an aperture stop on the substrate. A sensor may be located at a focal plane of the MOE on or near the second surface of the substrate.[0004] In some implementations, the sensor is directly on the second surface of the substrate. The camera module may include a spacer layer between the sensor and the second surface of the substrate. The spacer layer can include an air gap. The spacer layer can include a solid transparent material. A bandpass filter can be located between the sensor and the second surface of the substrate. A bonding layer can be located between the bandpass filter and the sensor. The bandpass filter can have a transmission wavelength range from 380 nm to 1500 nm. The F-number of the camera module can be in the range F / 0.8 to F / 8.

0. The total track length of the camera module can be in the range 0.1 mm to 4 mm. The substrate may include at least one of glass, sapphire, quartz, a polymer, titanium oxide (TiCh), and mixtures of the same. A maximum image circle diameter may be in the range 0.14 mm to 1.30 mm and a pixel edge length may be in the range 25 pm to 100 pm. An image circle may be understood to mean a circle having a diameter of the image formed by the lens on the sensor.NIL Technology ApSF&R Ref. 47717-0074WO1 PCT ApplicationThe MOE can direct light entering the MOE at a plurality of different angles of incidence to a plurality of locations on the sensor, respectively. The aperture stop can be further defined by mechanical stops.[0005] A system including the camera module can include a light source and an electronic circuit. The electronic circuit may be configured to actuate the light source so as to cause the light source to emit light. The electronic circuit may be configured to determine a value associated with at least one detection signal of the sensor upon the sensor detecting the light reflected from an object. The electronic circuit may be configured to calculate a distance of the camera module to the object based on each detected value.[0006] Other systems, devices, methods, features and advantages of the subject matter described herein will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the subject matter described herein, and be protected by the accompanying claims. In no way should the features of the example embodiments be construed as limiting the appended claims, absent express recitation of those features in the claims.BRIEF DESCRIPTION OF THE FIGURES[0007] The details of the subject matter set forth herein, both as to its structure and operation, may be apparent by study of the accompanying figures, in which like reference numerals refer to like parts. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the subject matter.Moreover, all illustrations are intended to convey concepts, where relative sizes, shapes and other detailed attributes may be illustrated schematically rather than literally or precisely.[0008] FIG. l is a schematic that illustrates an example of an imaging module.[0009] FIG. 2 is a schematic that illustrates an example of a time-of-flight system including an imaging module.[0010] FIG. 3 is a schematic that illustrates an example of different rays of light incident on the receiver of FIG. 1.[0011] FIGS. 4A, 4B, 4C, and 4D are schematics that illustrate examples of different MOE phase profiles and phase slopes.[0012] FIG. 5 A illustrates a modulation transfer function (MTF) for an example camera module receiver.

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