WO2023245545A1

WO2023245545A1 - Reflected light ray path imaging system and electronic apparatus comprising said imaging system

Info

Publication number: WO2023245545A1
Application number: PCT/CN2022/100753
Authority: WO
Inventors: Mikko Juhola; Qiuyuan ZHANG; Heng Wang
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2022-06-23
Filing date: 2022-06-23
Publication date: 2023-12-28

Abstract

An imaging system (9) comprising a first lens arrangement (10), an image sensor (11), and a reflecting element (1) comprising a main surface having an incident ray area (2), a transmitted ray area (3), and a total reflection ray area (4). A first reflective surface (5) extends at a first angle (α) to a normal (N) of the main surface and a second reflective surface (6) extends at a second angle (β) to the normal (N), β=α. A light ray path (7) travels through the first lens arrangement (10) and the incident ray area (2) into an interior of the reflecting element (1), is reflected by means of the first reflective surface (5), the reflected ray area (4), and the second reflective surface (6), and exits the reflecting element (1) through the transmitted ray area (3), reaching the image sensor (11).

Description

REFLECTED LIGHT RAY PATH IMAGING SYSTEM AND ELECTRONIC APPARATUS COMPRISING SAID IMAGING SYSTEM

TECHNICAL FIELD

The disclosure relates to a reflected light ray path imaging system comprising a lens arrangement, a reflecting element, and an image sensor.

BACKGROUND

There are several difficulties relating to optical and imaging systems for portable electronic apparatuses. Electronic apparatuses such as smartphones preferably have as small outer dimensions as possible, while optical systems require certain dimensions in order to provide sufficiently good image sharpness, spatial frequency, sensitivity etc.

One problem relates to how to provide an imaging system having a very long focal length, such as film equivalent focal lengths equivalent to a range of conventional 90 to 280 mm lens systems.

The larger the aperture diameter of the imaging system, the larger the light ray path width. However, a narrow field of view lens, i.e. aperture, provides a longer focal length than a wide field of view lens.

A narrow field of view and small aperture leads to unwanted optical properties. Firstly, the lens modulation transfer function (MTF) values, a measure of sharpness vs spatial frequency, will be limited due to diffraction from the aperture. The lower the values on the MTF curve, the more blurred the image will be and fewer high-frequency details will be visible in the image. Secondly, the sensitivity of the imaging system at low light will be insufficient, leading to longer exposure times, in turn resulting in poorer image quality since it’s not possible to capture moving objects well using long exposure times, the long exposure time allowing the shaking of hands to deteriorate image quality.

These issues may be avoided, or improved, by providing the imaging system with a larger entrance pupil aperture for this narrow field of view, reducing the diffraction and improving the sensitivity at low light. The larger the entrance pupil aperture, the better the performance of the imaging system, but the larger the light ray path width too.

In order to achieve a long focal length, while still having a larger aperture in a small apparatus, prior art solutions suggest folding of the light ray path. One such solution is the Cassegrain double reflection-based system. One Cassegrain embodiment comprises a parabolic primary mirror and a hyperbolic secondary mirror that reflects the light back down through a hole in the primary. By folding the light ray path, the design is made more compact.

However, the secondary mirror obscures a central portion of the entrance pupil aperture of the system, leaving only a ring-shaped entrance pupil aperture which has a significantly reduced performance compared to a design comprising a fully open entrance aperture. The larger the secondary mirror, the lower the MTF value becomes at lower spatial frequencies.

Hence, there is a need for an improved light ray path folding element as well as an improved imaging system.

SUMMARY

It is an object to provide an improved reflected light ray path imaging system which allows a larger aperture light ray path to enter the narrow field of view imaging system and with improved performance. 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 reflected light ray path imaging system comprising a first lens arrangement, an image sensor, and a light ray path reflecting element, the light ray path reflecting element comprising a main surface comprising an incident ray area, a transmitted ray area, and a reflection ray area overlapping the incident ray area and the transmitted ray area. The incident ray area, the transmitted ray area, and the reflection ray area extend in a main plane. A first reflective surface extends at a first angle to a normal of the main surface; and a second reflective surface extends at a second angle to the normal of the main surface, β=-α. The first lens arrangement is arranged adjacent the incident ray area of the reflecting element, the image sensor is arranged adjacent the transmitted ray area of the reflecting element, optical axes of the first lens arrangement and the image sensor extending perpendicular to the main surface of the reflecting element. The reflected light ray path imaging system is configured such that a light ray path travels through the first lens arrangement and the incident ray area of the reflecting element into an interior of the reflecting element, the light ray path being reflected sequentially within the interior of the reflecting element by means of the first reflective surface, the reflected ray area, and the second reflective surface, and the light ray path exiting the reflecting element through the transmitted ray area, reaching the image sensor.

Such a folding structure, i.e., a structure in which the light ray path is reflected allows a focal length that is longer than the actual outer dimensions of the reflecting structure. A reflecting structure providing a longer focal length, when used in an imaging system such as that of a camera, results in higher magnification and a narrower field of view. An electronic device comprising such an imaging system can have a thin form factor while still having a long focal length.

In a possible implementation form of the first aspect, the reflection ray area is configured to reflect light rays by means of total internal reflection, allowing the reflection ray area to overlap the incident ray area and the transmitted ray area, resulting in very small folding element.

In a further possible implementation form of the first aspect, the first angle is an acute angle, allowing a design that is in accordance with specific reflection requirements while still having as small outer dimensions as possible.

In a further possible implementation form of the first aspect, the first reflective surface and the second reflective surface each extend at a third angle to a further plane parallel with the main plane and the light ray path is reflected by the first reflective surface, the reflected ray area, the second reflective surface at a reflection angle that is equal to the third angle, allowing a compact, one-piece reflecting structure which is easy to mount into an imaging system and an electronic apparatus.

In a further possible implementation form of the first aspect the reflected light ray path imaging system further comprises a second lens arrangement, the second lens arrangement being arranged adjacent the transmitted ray area, between the folding element and the image sensor, the optical axis of the second lens arrangement being coaxial with the optical axis of the image sensor, facilitating an even more improved imaging system.

In a further possible implementation form of the first aspect, the first lens arrangement and the second lens arrangement each comprise at least one lens, providing the system with maximum flexibility.

In a further possible implementation form of the first aspect, the first lens arrangement comprises at least one tunable lens, facilitating integration of autofocus into the lens arrangement.

In a further possible implementation form of the first aspect, the optical axis of the second lens arrangement is parallel with the optical axis of the first lens arrangement, allowing an as compact and accurate imaging system as possible.

In a further possible implementation form of the first aspect, the light ray path travels through the first lens arrangement and the incident ray area along a first axis and the light ray path exits the reflecting element through the transmitted ray area along a second axis, and wherein, when the first axis is perpendicular to the main surface, the second axis is parallel with the first axis such that a ray of light entering the reflecting element in a first direction along the first axis exits the reflecting element in a second direction along the second axis, the second direction being directly opposite to the first direction, facilitating a long focal length as well as a thin form factor.

In a further possible implementation form of the first aspect, the first reflective surface and the second reflective surface are arranged such that a folding element apex is formed in a reflective surface intersection area, in which area the first reflective surface and the second reflective surface connect directly, or the first reflective surface and the second reflective surface are connected by a bridging area, the bridging area extending in parallel with the main surface, increasing the flexibility of the folding element as the size of different the segments can be adapted to current needs.

In a further possible implementation form of the first aspect, the intersection area is arranged opposite the reflection ray area, allowing the light ray path to be folded as few times as possible while still achieving a desired focal length.

In a further possible implementation form of the first aspect, the folding element further comprises a section extending in an interior of said reflecting element, from the intersection area towards the reflection ray area, the section being configured to ensure rays of light follow a desired light ray path.

In a further possible implementation form of the first aspect, the first axis intersects the incident ray area and the first reflective surface, and the second axis intersects the transmitted ray area and the second reflective surface, facilitating an as compact folding element as possible.

In a further possible implementation form of the first aspect, the first reflective surface and the second reflective surface comprise mirrors, facilitating a simple and reliable reflection solution.

In a further possible implementation form of the first aspect, the main surface, the first reflective surface, and the second reflective surface are separated by a material facilitating total internal reflection, facilitating a folding element with a small form factor. According to a second aspect, there is provided an electronic apparatus comprising the reflected light ray path imaging system according to the above and a housing comprising a light ray path entrance aperture arranged within a wall of the housing, a center axis of the entrance aperture extending perpendicular to the main surface of the light ray path folding element, allowing an electronic apparatus which has as small outer dimensions as possible while also having an imaging system with improved performance.

In a possible implementation form of the third aspect, the entrance aperture is circular and has an unobstructed inner diameter, allowing an as high MTF value, and hence as good performance, as possible.

These 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 an illustration of a reflected light ray path imaging system in accordance with an example of the embodiments of the disclosure;

Fig. 2 shows an illustration of a reflected light ray path imaging system in accordance with an example of the embodiments of the disclosure;

Fig. 3 shows an illustration of a reflected light ray path imaging system in accordance with an example of the embodiments of the disclosure;

Fig. 4 shows an illustration of a reflected light ray path imaging system in accordance with an example of the embodiments of the disclosure;

Fig. 5 shows an illustration of a reflected light ray path imaging system in accordance with an example of the embodiments of the disclosure.

DETAILED DESCRIPTION

Figs. 1 to 5 show examples of reflected light ray path imaging systems 9 comprising a first lens arrangement 10, an image sensor 11, and a light ray path reflecting element 1.

The light ray path reflecting element 1 comprises a main surface which, in turn, comprises an incident ray area 2, configured to receive incoming light and forward it into the folding element 1, a transmitted ray area 3 configured to allow light to be transmitted from the interior of the folding element 1 to the exterior, and a reflection ray area 4 at least partially overlapping the incident ray area 2 and the transmitted ray area 3. The reflection ray area 4 may be configured to reflect light rays by means of total internal reflection.

The incident ray area 2, the transmitted ray area 3, and the reflection ray area 4 extend in a main plane P1, i.e. they constitute different, yet somewhat overlapping, areas of one planar surface which is the main surface of the light ray path reflecting element 1. The main surface is the surface of the light ray path reflecting element 1 arranged closest to the first lens arrangement 10 and image sensor 11.

The first lens arrangement 10 is arranged adjacent the incident ray area 2 of the reflecting element 1, while the image sensor 11 is arranged adjacent the transmitted ray area 3 of the reflecting element 1. The optical axes of the first lens arrangement 10 and the image sensor 11 extend perpendicular to the main surface of the reflecting element 1.

The reflected light ray path imaging system 9 may also comprise a second lens arrangement 12 arranged adjacent the transmitted ray area 3, between the reflecting element 1 and the image sensor 11. The second lens arrangement 12 is arranged such that its optical axis is coaxial with the optical axis of the image sensor 11. The first lens arrangement 10 and the second lens arrangement 12 may be arranged such that the optical axis of the second lens arrangement 12 is parallel with the optical axis of the first lens arrangement 10.

The first lens arrangement 10 and the second lens arrangement 12 may each comprise at least one lens. A diffractive optical element may be included at the front of the first lens arrangement 10, to reduce the total number of lenses while still maintaining sufficient color correction. Furthermore, the first lens arrangement 10 may comprise a prism, e.g. a freeform prism, in order to improve and simplify the first lens arrangement 10.

The lenses of the second lens arrangement 12 may have any suitable cut such as I-cut or D-cut, which frees up space within the second lens arrangement 12.

The first lens arrangement 10 may comprise at least one tunable lens 14. One or several tunable lenses 14 may be used in order to integrate the autofocus function into the first lens arrangement 10. However, autofocus may also be executed e.g. by moving the first lens arrangement 10 along its optical axis; moving the first lens arrangement 10 as well as the second lens arrangement 12 relative the prism and image sensor 11; moving the prism along the optical axis of the first lens arrangement 10; moving the image sensor 11 along the optical axis of the second lens arrangement 12; tilting the prism surfaces, if comprising an optical liquid or a soft optical material; or by adding an optical element allowing variations in thickness, i.e. decreasing and increasing the optical path.

Furthermore, optical image stabilization (OIS) may be executed e.g. by moving the first lens arrangement 10 in a xy-plane, its optical axis being the z-axis; moving the first lens arrangement 10 as well as the second lens arrangement 12 relative the prism and image sensor 11; moving the image sensor 11 in a xy-plane; tilting the prism; tilting the prism surfaces, if comprising an optical liquid or a soft optical material; or by using one or several tunable lenses 14.

The Figs. show the incident ray area 2 to the far left and the transmitted ray area 3 to the far right. The reflection ray area 4 extends between the incident ray area 2 and the transmitted ray area 3 and at least partially overlaps both

areas

2, 3. As illustrated in the Figs. the light rays passing the incident ray area 2 farthest to the left are reflected in a section of the reflection ray area 4 which overlaps with the incident ray area 2. However, the light rays passing the incident ray area 2 farthest to the right are reflected in a section of the reflection ray area 4 which overlaps with the transmitted ray area 3.

The light ray path folding element 1 also comprises a first reflective surface 5 extending at a first angle α to a normal N of the main surface and a second reflective surface 6 extending at a second angle β to the normal N of the main surface. β =-α, i.e. the first reflective surface 5 extends at the same numerical angle as the second reflective surface 6 to the main surface and to the normal N, however, the first reflective surface 5 and the second reflective surface 6 extend on opposite sides of the normal N and are not parallel.

The first angle α may be an acute angle.

The first reflective surface 5 and the second reflective surface 6 each extend at a third angle γ to a further plane P2 that is parallel with the main plane P1, as illustrated in Fig. 2. The light ray path 7 may be reflected by the first reflective surface 5, the reflected ray area 4, and the second reflective surface 6 at a reflection angle that is equal to the third angle γ. It is well known in the area of optics that the reflection angle, as well as the incidence angle, is measured relative a normal to the reflective surface. An incoming ray traveling along the light ray path 7 hits the reflective surface at incidence angle γ relative to the surface normal and, correspondingly, leaves the reflective surface at the reflection angle γ relative to the surface normal, on the opposite side of the normal. In other words, when the reflection angle is γ, the angle between the incident light and the reflected light of the light ray path 7 is 2*γ, as illustrated in Fig. 5 as the light reflects off the first reflective surface 5 and the second reflective surface 6. Correspondingly, when the reflection angle is 2*γ, the angle between the incident light and the reflected light of the light ray path 7 is 4*γ, as illustrated in Fig. 5 as the light reflects off the reflected ray area 4.

The first reflective surface 5 and the second reflective surface 6 may comprise mirrors. The main surface, the first reflective surface 5, and the second reflective surface 6 may be separated by a material facilitating total internal reflection.

The light ray path reflecting element 1 is configured such that the light ray path 7 enters the reflecting element 1 through the incident ray area 2 along a first axis A1, the light ray path 7 thereafter being reflected, in sequence, by means of the first reflective surface 5, the reflection ray area 4, and the second reflective surface 6, i.e. the light ray path 7 is first reflected by the first reflective surface 5, thereafter by the reflection ray area 4, and lastly by the second reflective surface 6. Finally, the light ray path 7 exits the light ray path reflecting element 1 through the transmitted ray area 3 along a second axis A2.

The first axis A1 may intersect the incident ray area 2 and the first reflective surface 5, and the second axis A2 may intersect the transmitted ray area 3 and the second reflective surface 6. When a ray of light travels along a first axis A1 that is parallel with the normal N, as illustrated in the Figs., the same ray of light will also travel along a second axis A2 that is parallel with the first axis A1, i.e. a ray of light entering the reflecting element 1 in a first direction along the first axis exits the reflecting element 1 in a second direction along the second axis, the second direction being directly opposite to the first direction as illustrated in Fig. 2. Nevertheless, all light rays travel along different first axes A1 and second axes A2 which extend at different angles to the main surface, as illustrated via, e.g., the three groups of incident light rays and the three groups of transmitted light rays shown in Figs. 1, 3, and 4. Each ray of one group travels along its own first axis A1 and its own second axis A2.

The imaging system 9 is configured such that a light ray path 7 travels through the first lens arrangement 10 and the incident ray area 2 of the reflecting element 1 into an interior of the reflecting element 1. The light ray path 7 is thereafter reflected within the interior by means of the first reflective surface 5, the reflection ray area 4, and the second reflective surface 6 of the reflecting element 1, as described above and as illustrated in the Figs. The light ray path 7 exits the reflecting element 1 through the transmitted ray area 3 whereafter it reaches the image sensor 11.

The first reflective surface 5 and the second reflective surface 6 may be arranged such that a reflecting element apex is formed in a reflective surface intersection area 8, in which area the first reflective surface 5 and the second reflective surface 6 connect directly, as shown in Fig. 1. The first reflective surface 5 and the second reflective surface 6 may also be connected by a bridging area 8a, the bridging area 8a extending in parallel with the main surface as shown in Figs. 2 and 3.

The intersection area 8 may be arranged opposite the reflection ray area 4 and may be a smaller area than the area of the reflection ray area 4. The reflecting element 1 may comprise a section 9 extending from the intersection area 8 towards the reflection ray area 4, the section 9 being configured to prevent rays of light from deviating from a desired light ray path 7. The section 9 may comprise an optically black material or be an air volume. The section 9 may be made as a groove and the section 9 may be filled with optically black material or the surfaces of section 9 may be painted with index matched paint to minimize stray light. Furthermore, any suitable additional surfaces of the components of the imaging system 9 may be painted with such paint.

The present invention also relates to an electronic apparatus comprising the reflected light ray path imaging system 9 described above and a housing comprising a light ray path entrance aperture 13 arranged within a wall of the housing, a center axis of the entrance aperture 13 extending perpendicular to the main surface of the light ray path reflecting element 1. The center axis of the entrance aperture 13 may be coaxial with the optical axis of the first lens arrangement 10. The entrance aperture 13 may be circular and have an unobstructed inner diameter allowing all light entering the aperture to travel without obstructions to the light ray path reflecting element 1.

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. 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.

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.

Claims

A reflected light ray path imaging system (9) comprising a first lens arrangement (10) , an image sensor (11) , and a light ray path reflecting element (1) ,

said light ray path reflecting element (1) comprising:

- a main surface comprising an incident ray area (2) , a transmitted ray area (3) , and a total reflection ray area (4) overlapping said incident ray area (2) and said transmitted ray area (3) , said incident ray area (2) , said transmitted ray area (3) , and said total reflection ray area (4) extending in a main plane (P1) ;

- a first reflective surface (5) extending at a first angle (α) to a normal (N) of said main surface; and

- a second reflective surface (6) extending at a second angle (β) to said normal (N) of said main surface, β=-α;

said first lens arrangement (10) being arranged adjacent the incident ray area (2) of said reflecting element (1) , said image sensor (11) being arranged adjacent the transmitted ray area (3) of said reflecting element (1) , optical axes of said first lens arrangement (10) and said image sensor (11) extending perpendicular to the main surface of said reflecting element (1) ,

said reflected light ray path imaging system (9) being configured such that a light ray path (7) travels through said first lens arrangement (10) and said incident ray area (2) of said reflecting element (1) into an interior of said reflecting element (1) ,

said light ray path (7) being reflected sequentially within said interior of said reflecting element (1) by means of said first reflective surface (5) , said reflected ray area (4) , and said second reflective surface (6) , and

said light ray path (7) exiting said reflecting element (1) through said transmitted ray area (3) , reaching said image sensor (11) .
The reflected light ray path imaging system (9) according to claim 1, wherein said reflected ray area (4) is configured to reflect light rays by means of total internal reflection.
The reflected light ray path imaging system (9) according to claim 1 or 2, wherein said first angle (α) is an acute angle.
The reflected light ray path imaging system (9) according to any one of the previous claims, wherein said first reflective surface (5) and said second reflective surface (6) each extend at a third angle (γ) to a further plane (P2) parallel with said main plane (P1) ; and said light ray path (7) is reflected by said first reflective surface (5) , said reflected ray area (4) , and said second reflective surface (6) at a reflection angle that is equal to said third angle (γ) .
The reflected light ray path imaging system (9) according to any one of the previous claims, further comprising a second lens arrangement (12) , said second lens arrangement (12) being arranged adjacent said transmitted ray area (3) , between said reflecting element (1) and said image sensor (11) , an optical axis of said second lens arrangement (12) being coaxial with the optical axis of said image sensor (11) .
The reflected light ray path imaging system (9) according any one of the previous claims, wherein said first lens arrangement (10) and/or said second lens arrangement (12) each comprise at least one lens (13) .
The reflected light ray path imaging system (9) according to claim 6, wherein said first lens arrangement (10) comprises at least one tunable lens (14) .
The reflected light ray path imaging system (9) according to any one of claims 4 to 7, wherein said optical axis of said second lens arrangement (12) is parallel with the optical axis of said first lens arrangement (10) .
The reflected light ray path imaging system (9) according to any one of the previous claims, wherein said first reflective surface (5) and said second reflective surface (6) are arranged such that a reflecting element apex is formed in a reflective surface intersection area (8) , in which area said first reflective surface (5) and said second reflective surface (6) connect directly, or

said first reflective surface (5) and said second reflective surface (6) are connected by a bridging area (8a) , said bridging area (8a) extending in parallel with said main surface.
The reflected light ray path imaging system (9) according to claim 9, wherein said intersection area (8) is arranged opposite said reflection ray area (4) .
The reflected light ray path imaging system (9) according to any one of the previous claims, further comprising a section (9) extending in an interior of said reflecting element (1) , from said intersection area (8) towards said reflected ray area (4) , said section (9) being configured to absorb rays of light and/or redirect rays of light towards an exterior of said reflecting element (1) .
The reflected light ray path imaging system (9) according to any one of the previous claims, wherein said first axis (A1) intersects said incident ray area (2) and said first reflective surface (5) and said second axis (A2) intersects said transmitted ray area (3) and said second reflective surface (6) .
The reflected light ray path imaging system (9) according to any one of the previous claims, wherein said first reflective surface (5) and said second reflective surface (6) comprise mirrors.
The reflected light ray path imaging system (9) according to any one of the previous claims, wherein said main surface, said first reflective surface (5) , and said second reflective surface (6) are separated by a material facilitating total internal reflection.
An electronic apparatus comprising the reflected light ray path imaging system (9) according to any one of claims 1 to 14 and a housing comprising a light ray path entrance aperture (13) arranged within a wall of said housing, a center axis of said entrance aperture (13) extending perpendicular to the main surface of the light ray path reflecting element (1) .
The electronic apparatus according to claim 15, wherein said entrance aperture (13) is circular and has an unobstructed inner diameter.