TECHNICAL FIELD

The disclosure relates to a light pattern generating system for a depth estimation system for an electronic device.

BACKGROUND

Many current commercial mobile electronic devices require depth estimation systems in order to provide artificial reality (AR) and/or virtual reality (VR) functionality. The operating conditions for these functionalities evolve constantly in response to technical development.

In order to scan a whole room using some prior art solutions, the user needs wander around the room, such that the depth system can gather all necessary data, i.e. cover a wide field of view. In other prior art solutions, the electronic device comprises a plurality of sensors, such as cameras, in order to cover a wide field of view.

Furthermore, the depth system may be based on structured light, passive stereo, active stereo or time of flight principles. When applying the structured light principle, one projector and one camera are used. For the stereo principles, two cameras are used. The time of flight principle utilizes one camera and a laser source.

When using much hardware such as cameras, projectors, and laser sources, the depth estimation system not only takes up much of the volume available in a small mobile electronic device, but is also relatively expensive and consumes a lot of power.

Furthermore, the cameras have to be calibrated to function properly. Mobile electronic devices are subjected to a large amount of physical stress over the years, which can invalidate factory calibration. SUMMARY

It is an object to provide a light pattern generating system for a depth estimation system for an electronic device. The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description, and the figures.

According to a first aspect, there is provided a light pattern generating system comprising a light source and a diffraction system, rays of light emitted by the light source travelling through the diffraction system and generating a light pattern, the diffraction system comprising a collimator lens, a diffractive optical element, and an expansion lens, the collimator lens, diffractive optical element, and expansion lens sharing an optical axis, the diffractive optical element being arranged between the collimator lens and the expansion lens, incident rays of light entering the collimator lens at a plurality of angles relative the optical axis, such that the incident rays of light form a first diverging pattern having a first projection angle, emergent rays of light exiting the expansion lens at a plurality of angles relative the optical axis, such that the emergent rays of light form a second diverging pattern having a second projection angle, the second projection angle being larger than the first projection angle, the emergent rays of light projecting the light pattern onto an object.

Such a system facilitates a depth estimation system which is small, has low power consumption, yet still covers a very wide field of view. Furthermore, the light pattern can be designed to suit a particular depth estimation camera, e.g. by using equidistant pattern elements, varying distance pattern elements, radial or circular patterns etc. Also, the camera can be calibrated to the current light pattern.

In a possible implementation form of the first aspect, the second projection angle is approximately 2 to 3 times larger than the first projection angle, facilitating a wide angle output while still utilizing narrow angle input.

In a further possible implementation form of the first aspect, the second projection angle is between ±50 and ±100° relative the optical axis. In a further possible implementation form of the first aspect, the diffractive optical element redirects the rays of light such that the rays of light form a third diverging pattern having a third projection angle, the third projection angle being larger than the first projection angle and smaller than the second projection angle, the third diverging pattern comprising the light pattern. This allows the angle to increase, i.e. expanding the light pattern, while still maintaining good quality light collimation.

In a further possible implementation form of the first aspect, the light pattern is a dot pattern or a grid pattern.

In a further possible implementation form of the first aspect, the third projection angle is less than ±20° relative the optical axis.

In a further possible implementation form of the first aspect, the diffractive optical element comprises a grating or a reflective surface.

In a further possible implementation form of the first aspect, the collimator lens redirects the rays of light such that the rays of light form a first converging pattern having a fourth proj ection angle, facilitating maintaining a narrow angle.

In a further possible implementation form of the first aspect, the collimator lens is aspherical, making the rays of light converge in the direction towards the diffractive optical element.

In a further possible implementation form of the first aspect, the expansion lens comprises a concave surface and a flat surface extending perpendicular to the optical axis, the concave surface collimating the rays of light, and the emergent rays of light exiting the light pattern generating system through the flat surface. Such a solution simultaneously collimates the diffraction order beams and expand the field of view of the light pattern generating system.

In a further possible implementation form of the first aspect, the light source is a laser.

According to a second aspect, there is provided a depth estimation system for an electronic device, the depth estimation system comprising a camera, the light pattern generating system according to the above, and a computational arrangement, wherein the depth estimation system projects a light pattern onto an object, the camera registers the light pattern, and the computational arrangement generates a depth map by means of the light pattern. Such a system is small, has low power consumption, and covers a very wide field of view.

In a possible implementation form of the second aspect, an optical axis of the camera is offset from the optical axis of the light pattern generating system.

According to a third aspect, there is provided an electronic device comprising the depth estimation system according to the above.

This and other aspects will be apparent from the embodiments described below.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present disclosure, the aspects, embodiments and implementations will be explained in more detail with reference to the example embodiments shown in the drawings, in which:

Fig. 1 shows a schematic illustration of a depth estimation system in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION

The present invention relates to an electronic device such as a smartphone or tablet (not shown) comprising a depth estimation system.

As shown in Fig. 1, the depth estimation system comprises a camera 7, a computational arrangement, and a light pattern generating system 1 described in more detail further below.

The depth estimation system projects a light pattern onto an object, such as a fixed object or a human being. The camera 7 registers the light pattern, and the computational arrangement generates a depth map by means of the light pattern. The computational arrangement utilizes algorithms to define the depth map in accordance with the behavior of the light pattern. The camera 7 is arranged such that an optical axis 02 of the camera 7 is offset from, but preferably parallel with, an optical axis 01 of the light pattern generating system 1.

The light pattern generating system 1 comprises a light source 2 and a diffraction system 3. Rays of light emitted by the light source 2 travel through the diffraction system 3 and generate the above-mentioned light pattern. The light source 2 may be a laser.

The diffraction system 3 comprises a collimator lens 4, a diffractive optical element 5, and an expansion lens 6 sharing an optical axis 01. The diffractive optical element 5 is arranged between the collimator lens 4 and the expansion lens 6.

Incident rays of light, emitted by the light source 2, enter the diffraction system 3 at a plurality of angles relative the optical axis 01, such that the incident rays of light form a first diverging pattern having a first projection angle al. Emergent rays of light exit the diffraction system 3 at a plurality of angles relative the optical axis 01, such that the emergent rays of light form a second diverging pattern having a second projection angle a2. The second projection angle a2 is larger than the first projection angle al. In other words, the rays of light emitted by the light source 2 firstly pass through the collimator lens 4, secondly pass through the diffractive optical element 5, and thirdly pass through the expansion lens 6, at which point the rays of light exit the diffraction system 3 and generate the above-mentioned light pattern onto an object.

The above-mentioned incident rays of light, emitted by the light source 2, enter the collimator lens 4 at a plurality of angles relative the optical axis 01, such that the incident rays of light form the first diverging pattern having the first projection angle al. The collimator lens 4 may be aspherical.

The collimator lens 4 redirects the rays of light such that the rays of light form a first converging pattern having a fourth projection angle a4.

The diffractive optical element 5 redirects the rays of light such that the rays of light form a third diverging pattern having a third projection angle a3. The third projection angle a3 is larger than the first projection angle al and smaller than the second projection angle a2. The third diverging pattern comprises the light pattern, which may be any kind of pattern such as a dot pattern or a grid pattern. The third projection angle a3 may be less than ±20° relative the optical axis 01, i.e. cover a total area of up to 40°.

The above-mentioned emergent rays of light exit the expansion lens 6 at a plurality of angles relative the optical axis 01, such that the emergent rays of light form the second diverging pattern having the second projection angle a2. The emergent rays of light project the light pattern onto an object.

The second projection angle a2 is larger than the first projection angle al. In one embodiment, the second projection angle a2 is approximately 2 to 3 times larger than the first projection angle al. The second projection angle a2 may be between ±50 and ±100° relative the optical axis 01, i.e. cover a total area of between 100 and 200°.

The expansion lens 6 may comprise a concave surface 6a and a flat surface 6b extending perpendicular to the optical axis 01. The concave surface 6a collimates the rays of light, and the emergent rays of light exit the light pattern generating system 1 through the flat surface 6b. The expansion lens 6 radius, i.e. the radius of the concave surface 6a, is configured to match the diffractive optical element 5 diffraction orders, and the flat surface 6b expands the light pattern field of view.

A plurality of parameters can be adapted to generate the desired system layout. For example, the following parameters for the collimator lens 4 can be adapted: front and rear lens radius, thickness, 6 x aspherical coefficients, distance between light source 2 and diffractive optical element 5, and glass material. For the expansion lens 6, the radius, distance from the diffractive optical element 5, material, and thickness can be adapted. For the diffractive optical element 5, the field of view of the generated orders can be varied.

The diffractive optical element 5 is preferably designed using the industry standard method called IFTA (Iterative Fourier Transform Algorithm). The diffractive optical element 5 functions as a phase or amplitude element that adjusts the field hitting the DOE such that the output field will be a diffraction pattern some distance after the diffractive optical element 5, the so-called far field. The diffractive optical element 5 consists of a one-dimensional or two- dimensional periodic structure with a period d _.y in the x- and y- directions, respectively. The period will determine the separation of the diffraction orders as computed in Equation 1, shown below. In one embodiment, the diffractive optical element 5 comprises a two-dimensional grating or a one-dimensional reflective surface.

Equation 1: d = m/l/sin(0 _rn ). For example, m=+100th diffraction order; qioo=20°; l=900 nm resulting in d= 263 pm.

The desired pattern consists of a uniform intensity pattern for all diffraction orders in the target area. To ensure that one can design such a pattern, enough design freedom should be present. To ensure this, the feature size should be at least that as given by Equation 2, shown below, and preferably a bit smaller to ensure good uniformity.

Equation 2: feature size = d/2m. For example, feature size= 0,5 pm.

For the diffractive optical element 5 to be functional in practice, multiple periods in both the x and y directions should be illuminated. This is required to satisfy the interference conditions for those gratings, such that the designed diffraction pattern occurs some distance after the grating.

The various aspects and implementations have been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed subject-matter, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

The reference signs used in the claims shall not be construed as limiting the scope. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this disclosure. As used in the description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.