Reflected light path imaging system and electronic device including same

Abstract

An imaging system (9) comprises a first lens arrangement (10), an image sensor (11) and a reflective element (1) comprising a major surface having an incident light region (2), a transmitted light region (3) and a total reflection light region (4). The first reflective surface (5) extends at a first angle (alpha) to a normal (N) of the main surface, and the second reflective surface (6) extends at a second angle (beta) to the normal (N), beta = alpha. A light path (7) passes through the first lens arrangement (10) and the incident light region (2) into the interior of the reflective element (1), is reflected by the first reflective surface (5), the reflected light region (4) and the second reflective surface (6), and exits the reflective element (1) through the transmitted light region (3) to the image sensor (11).

Description

TECHNICAL FIELD

[0001] The present invention relates to a reflected light path imaging system comprising a lens arrangement, a reflecting element and an image sensor. BACKGROUND

[0002] There are difficulties with optical systems and imaging systems for portable electronic devices. Electronic devices such as smartphones preferably have an external size that is as small as possible, while the optical system needs a certain size to provide a sufficiently good image sharpness, spatial frequency, sensitivity, etc.

[0003] One problem concerns how to provide an imaging system with an ultra-long focal length, e.g. a film equivalent focal length corresponding to the range of traditional 90-280 mm lens systems.

[0004] The larger the aperture of an imaging system, the larger the light path width. However, a narrow field lens, i.e. an aperture, provides a longer focal length than a wide field lens.

[0005] A narrow field and a small aperture can result in unwanted optical properties. First, the lens Modulation Transfer Function (MTF) values, i.e. a measure of sharpness versus spatial frequency, will be limited due to diffraction from the aperture. The lower the values on the MTF curve, the more blurred the image and the less high frequency details visible in the image. Second, the sensitivity of the imaging system at low light will be insufficient, resulting in longer exposure times and in turn a poorer image quality, since moving objects cannot be captured well using long exposure times, which will degrade the image quality due to hand shake.

[0006] These problems can be avoided or improved by providing the imaging system with a larger entrance pupil aperture for such a narrow field, reducing diffraction and increasing sensitivity at low light. The larger the entrance pupil aperture, the better the performance of the imaging system, but also the larger the light path width.

[0007] In order to achieve a long focal length while still having a large aperture in a small device, prior art solutions suggest folding the light path. One such solution is a system based on a Cassegrain double reflection. One Cassegrain embodiment comprises a parabolic primary mirror and a hyperbolic secondary mirror, which reflects the light back through a hole in the primary mirror. By folding the light path, the above design is more compact.

[0008] However, the secondary mirror blocks the central part of the entrance pupil aperture of the system, leaving only an annular entrance pupil aperture, which significantly reduces the performance compared to a design comprising a fully open entrance pupil aperture. The larger the secondary mirror, the lower the MTF values at lower spatial frequencies become.

[0009] There is therefore a need for an improved light path folding element and an improved imaging system. SUMMARY

[0010] It is an object to provide an improved reflected light ray path imaging system that admits a larger aperture light ray path into a narrow field of view imaging system and has improved performance. The above and other objects are achieved by the features of the independent claims. Further implementation forms are evident from the dependent claims, the description and the drawings.

[0011] 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 light ray region, a transmitted light ray region and a reflected light ray region overlapping the incident light ray region and the transmitted light ray region. The incident light ray region, the transmitted light ray region and the reflected light ray region extend in a main plane. A first reflecting surface extends at a first angle to a normal of the main surface; a second reflecting surface extends at a second angle to the normal of the main surface, β = -α. The first lens arrangement is arranged adjacent to the incident light ray region of the reflecting element, the image sensor is arranged adjacent to the transmitted light ray region of the reflecting element, the optical axes of the first lens arrangement and the image sensor extend perpendicular to the main surface of the reflecting element. The reflected light ray path imaging system is configured such that a light ray path enters the interior of the reflecting element through the first lens arrangement and the incident light ray region of the reflecting element, the light ray path is reflected in the interior of the reflecting element by the first reflecting surface, the reflected light ray region and the second reflecting surface in sequence, and the light ray path exits the reflecting element through the transmitted light ray region to the image sensor.

[0012] This folding structure, i.e. the structure in which the light ray path is reflected, makes the focal length longer than the actual outer dimensions of the reflecting structure. The reflecting structure provides a longer focal length when used in an imaging system, e.g. an imaging system of a camera, which results in a 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.

[0013] In a possible implementation form of the first aspect, the reflected light ray region is configured to reflect light rays by total internal reflection such that the reflected light ray region overlaps with the incident light ray region and the transmitted light ray region, resulting in a very small folding element.

[0014] In another possible implementation form of the first aspect, the first angle is an acute angle, making the design comply with certain reflection requirements while still having an outer dimension as small as possible.

[0015] In a further possible implementation form of the first aspect, the first reflective surface and the second reflective surface each extend with a third angle to a further plane parallel to the main plane, and the light ray path is reflected by the first reflective surface, the reflective light ray area, the second reflective surface with a reflection angle equal to the third angle, resulting in a compact monolithic reflective structure which is easy to install into imaging systems and electronic devices.

[0016] In a further possible implementation form of the first aspect, the reflective light ray path imaging system further comprises a second lens device arranged adjacent to the transmissive light ray area between the folding element and the image sensor, an optical axis of the second lens device being coaxial with an optical axis of the image sensor, thereby facilitating a further improved imaging system.

[0017] In a further possible implementation form of the first aspect, the first lens device and the second lens device each comprise at least one lens, thereby providing maximum flexibility for the system.

[0018] In a further possible implementation form of the first aspect, the first lens device comprises at least one tunable lens, thereby facilitating the incorporation of auto focus into the lens device.

[0019] In a further possible implementation form of the first aspect, an optical axis of the second lens device is parallel to an optical axis of the first lens device, thereby making the imaging system as compact and precise as possible.

[0020] In a further possible implementation form of the first aspect, the light ray path passes through the first lens device and the incident light ray area along a first axis, and the light ray path exits the reflective element through the transmissive light ray area along a second axis, and wherein, when the first axis is perpendicular to the main surface, the second axis is parallel to the first axis, such that a light ray entering the reflective element in a first direction along the first axis exits the reflective element in a second direction along the second axis, the second direction being exactly opposite to the first direction, thereby facilitating a long focal length as well as a thin form factor.

[0021] 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 vertex is formed in a reflective surface intersection area, in which the first reflective surface and the second reflective surface are directly connected, or the first reflective surface and the second reflective surface are connected by a bridging area, the bridging area extending parallel to the main surface, thereby increasing the flexibility of the folding element, as the size of the different segments can be adapted to the current needs.

[0022] In a further possible implementation form of the first aspect, the intersection region is arranged opposite the reflected light ray region, such that the light ray path is folded as little as possible while still achieving the desired focal length.

[0023] In a further possible implementation form of the first aspect, the folding element further comprises a section extending inside the reflecting element from the intersection region towards the reflected light ray region, the section being configured to ensure that the light ray follows the desired light ray path.

[0024] In a further possible implementation form of the first aspect, the first axis intersects the incident light ray region and the first reflecting surface, and the second axis intersects the transmitted light ray region and the second reflecting surface, such that the folding element is as compact as possible.

[0025] In a further possible implementation form of the first aspect, the first reflecting surface and the second reflecting surface comprise mirrors, such that a simple and reliable reflection solution is facilitated.

[0026] In a further possible implementation form of the first aspect, the main surface, the first reflecting surface and the second reflecting surface are separated by a material that facilitates total internal reflection, such that a folding element with a small form factor is facilitated.

[0027] According to a second aspect, there is provided an electronic device comprising a reflected light ray path imaging system according to the above and a housing comprising a light ray path entrance aperture arranged in a wall of the housing, a central axis of the entrance aperture extending perpendicular to a main surface of a light ray path folding element, such that the electronic device has as small external dimensions as possible while still having a performance improved imaging system.

[0028] In a possible implementation form of the third aspect, the entrance aperture is circular and has an unobstructed inner diameter, such that as high MTF values, and thus as good performance, as possible are achieved.

[0029] These and other aspects are apparent from the embodiments described below. BRIEF DESCRIPTION OF DRAWINGS

[0030] In the following detailed description of the application, reference is made to the exemplary embodiments illustrated in the drawings, in which:

[0031] Figure 1 Fig. 1 shows a schematic illustration of a reflected light ray path imaging system according to an example of embodiments of the application;

[0032] Figure 2 Fig. 2 shows a schematic illustration of a reflected light ray path imaging system according to an example of embodiments of the application;

[0033] Figure 3Fig. 1 shows a schematic of a reflective light ray path imaging system according to an example of embodiments of the application;

[0034] Figure 4 Fig. 1 shows a schematic of a reflective light ray path imaging system according to an example of embodiments of the application;

[0035] Figure 5 Fig. 1 shows a schematic of a reflective light ray path imaging system according to an example of embodiments of the application. DETAILED DESCRIPTION

[0036] Figures 1 to 5 Fig. 1 shows an example of a reflective light ray path imaging system 9, a reflective light ray path imaging system comprising a first lens device, an image sensor and a light ray path reflecting element, the light ray path reflecting element comprising: a main surface comprising an incident light ray region, a transmitted light ray region and a totally reflected light ray region, the totally reflected light ray region overlapping with the incident light ray region and the transmitted light ray region, the incident light ray region, the transmitted light ray region and the totally reflected light ray region extending in a main plane; a first reflecting surface extending at a first angle a with a normal of the main surface; a second reflecting surface extending at a second angle β with the normal of the main surface, β = a, the first reflecting surface and the second reflecting surface extending on opposite sides of the normal N and being non-parallel; the first lens device being arranged adjacent to the incident light ray region of the reflecting element, the image sensor being arranged adjacent to the transmitted light ray region of the reflecting element, the optical axis of the first lens device and the image sensor extending perpendicular to the main surface of the reflecting element, the reflective light ray path imaging system being configured such that a light ray path enters the interior of the reflecting element through the first lens device and the incident light ray region of the reflecting element, the light ray path being reflected in the interior of the reflecting element by the first reflecting surface, the reflected light ray region and the second reflecting surface in sequence, the light ray path leaving the reflecting element through the transmitted light ray region, reaching the image sensor. The reflective light ray path imaging system comprises

[0037] a first lens device 10, an image sensor 11 and a light ray path reflecting element 1.

[0038] The light ray path reflecting element 1 comprises a main surface, which in turn comprises: an incident light ray region 2 for receiving incident light and forwarding the incident light to the folding element 1; a transmitted light ray region 3 for transmitting light from the interior of the folding element 1 to the exterior; and a reflected light ray region 4, which at least partially overlaps with the incident light ray region 2 and the transmitted light ray region 3. The reflected light ray region 4 can be used for reflecting light rays by total internal reflection.

[0039] The incident light ray area 2, the transmitted light ray area 3 and the reflected light ray area 4 extend in the main plane PI, i.e. they constitute different, but slightly overlapping areas of one planar surface of 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 which is arranged closest to the first lens arrangement 10 and the image sensor 11.

[0040] The first lens arrangement 10 is arranged adjacent to the incident light ray area 2 of the reflecting element 1, while the image sensor 11 is arranged adjacent to the transmitted light ray area 3 of the reflecting element 1. The optical axis of the first lens arrangement 10 and the image sensor 11 extends perpendicular to the main surface of the reflecting element 1.

[0041] The reflected light ray path imaging system 9 can further comprise a second lens arrangement 12 arranged between the reflecting element 1 and the image sensor 11 adjacent to the transmitted light ray area 3. 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 can be arranged such that the optical axis of the second lens arrangement 12 is parallel to the optical axis of the first lens arrangement 10.

[0042] The first lens arrangement 10 and the second lens arrangement 12 can each comprise at least one lens. Diffractive optical elements can be included in 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 can comprise prisms, e.g. freeform prisms, in order to improve and simplify the first lens arrangement 10.

[0043] The lenses of the second lens arrangement 12 can have any suitable cut, e.g. an I-cut or a D-cut, which releases space within the second lens arrangement 12.

[0044] The first lens arrangement 10 can comprise at least one tunable lens 14. In order to incorporate an autofocus function into the first lens arrangement 10, one or more tunable lenses 14 can be used. However, autofocus can also be performed, e.g. by moving the first lens arrangement 10 along its optical axis; moving the first lens arrangement 10 and the second lens arrangement 12 relative to the prism and the 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 surface if an optical liquid or soft optical material is included; or adding optical elements which change the thickness, i.e. reduce and increase the optical path.

[0045] Further, optical image stabilization (OIS) can be performed, for example, by moving the first lens arrangement 10 in the xy-plane, whose optical axis is the z-axis; moving the first lens arrangement 10 and the second lens arrangement 12 relative to the prism and the image sensor 11; moving the image sensor 11 in the xy-plane; tilting the prism; tilting the prism surface, if an optical liquid or a soft optical material is included; or using one or more tunable lenses 14.

[0046] The leftmost incident light ray region 2 and the rightmost transmitted light ray region 3 are illustrated. The reflected light ray region 4 extends between the incident light ray region 2 and the transmitted light ray region 3 and at least partially overlaps with both regions 2, 3. As illustrated in the figure, light rays passing through the leftmost incident light ray region 2 are reflected in a section of the reflected light ray region 4 that overlaps with the incident light ray region 2. However, light rays passing through the rightmost incident light ray region 2 are reflected in a section of the reflected light ray region 4 that overlaps with the transmitted light ray region 3.

[0047] The light ray path folding element 1 further comprises a first reflective surface 5 extending at a first angle a with the normal N of the main surface and a second reflective surface 6 extending at a second angle b with the normal N of the main surface. b = - a, i.e. the first reflective surface 5 and the second reflective surface 6 extend at the same numerical angle with the main surface and 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.

[0048] The first angle a can be an acute angle.

[0049] The first reflective surface 5 and the second reflective surface 6 each extend at a third angle g with a further plane P2 that is parallel to the main plane PI, as illustrated in Figure 2 The light ray path 7 can be reflected by the first reflective surface 5, the reflected light ray region 4 and the second reflective surface 6 at a reflection angle that is equal to the third angle g. It is well known in the field of optics that the reflection angle, as well as the incidence angle, is measured with respect to the normal of the reflective surface. On the opposite side of the normal, an incident light ray propagating along the light ray path 7 hits the reflective surface at an incidence angle g with respect to the surface normal and exits the reflective surface accordingly at a reflection angle g with respect to the surface normal. In other words, when the reflection angle is g, the angle between the incident light and the reflected light of the light ray path 7 is 2*g when light is reflected from the first reflective surface 5 and the second reflective surface 6, as illustrated in Figure 5 Correspondingly, when the reflection angle is 2*g, the angle between the incident light and the reflected light of the light ray path 7 is 4*g when light is reflected from the reflected light ray region 4, as illustrated in Figure 5

[0050] The first reflective surface 5 and the second reflective surface 6 can comprise a mirror.

[0051] ​The main surface, the first reflective surface 5 and the second reflective surface 6 can be separated by a material that facilitates total internal reflection.

[0052] The light ray path reflecting element 1 is configured such that the light ray path 7 enters the reflecting element 1 through the entrance light ray area 2 along a first axis Al, after which the light ray path 7 is reflected in turn by the first reflective surface 5, the reflecting light 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, after which it is reflected by the reflecting light ray area 4 and finally by the second reflective surface 6. Finally, the light ray path 7 exits the light ray path reflecting element 1 through the transmission light ray area 3 along a second axis A2.

[0053] The first axis Al can intersect the entrance light ray area 2 and the first reflective surface 5, and the second axis A2 can intersect the transmission light ray area 3 and the second reflective surface 6. When the light rays propagate along the first axis Al parallel to the normal N as shown in the figures, the same light rays will also propagate along the second axis A2 parallel to the first axis Al, i.e. the light rays that enter the reflecting element 1 in a first direction along the first axis will exit the reflecting element 1 in a second direction along the second axis, the second direction being exactly opposite to the first direction, as shown in Figure 2 Although, all light rays propagate along different first and second axes Al, A2 that extend at different angles to the main surface, as shown by the three sets of entrance and transmission light rays shown in, for example, Figure 1 , 3 and 4. Each light ray in a set propagates along its own first axis Al and its own second axis A2.

[0054] The imaging system 9 is configured such that the light ray path 7 enters the interior of the reflecting element 1 through the entrance light ray area 2 of the first lens arrangement 10 and the reflecting element 1. Thereafter, the light ray path 7 is reflected inside the reflecting element 1 by the first reflective surface 5, the reflecting light ray area 4 and the second reflective surface 6 of the reflecting element 1, as described above and as shown in the figures. The light ray path 7 exits the reflecting element 1 through the transmission light ray area 3 and then reaches the image sensor 11.

[0055] The first reflective surface 5 and the second reflective surface 6 can be arranged such that a reflecting element vertex is formed in a reflective surface intersection area 8 in which the first reflective surface 5 and the second reflective surface 6 are directly connected, as shown in Figure 1 The first reflective surface 5 and the second reflective surface 6 can also be connected by a bridging area 8a that extends parallel to the main surface, as shown in Figure 2 and 3 .

[0056] The intersection area 8 can be arranged opposite the reflected light area 4 and can have a smaller area than the reflected light area 4. The reflective element 1 can comprise a section 90 extending from the intersection area 8 towards the reflected light area 4, the section 90 serving to prevent light rays from deviating from the desired light path 7. The section 90 can comprise an optically black material or can be an air volume. The section 90 can be made as a recess, the section 90 can be filled with an optically black material, or the surface of the section 90 can be coated with an index matching paint to minimize stray light. Furthermore, any suitable additional surface of components of the imaging system 9 can be coated with such a paint.

[0057] The present application also relates to an electronic device comprising the above described reflected light path imaging system 9 and a housing comprising a light path entrance aperture 13 arranged in a wall of the housing, the central axis of the entrance aperture 13 extending perpendicular to the main surface of the light path reflective element 1. The central axis of the entrance aperture 13 can be coaxial with the optical axis of the first lens arrangement 10. The entrance aperture 13 can be circular and have an unobstructed inner diameter such that all light entering the aperture propagates unobstructed to the light path reflective element 1.

[0058] Various aspects and implementations have been described herein in conjunction with various embodiments. However, other variations than those described are possible and within the scope of the claimed subject matter. In the claims, the word "comprising" does not exclude other elements or steps, and the word "one" does not exclude a plurality. In the claims, the term "consisting of means "including and excluding also anything that is not recited". In the claims, the term "consisting essentially of means that the claim does not exclude additional elements or steps as long as these additional elements or steps do not materially alter the basic and novel characteristics set forth in the claim.

[0059] Reference signs used in the claims should not be construed as limiting the scope. The drawings (e.g., cross-sectional views, component arrangements, scaling, degrees, etc.) are intended to be illustrative and not limiting. Unless otherwise specified, the drawings are to be read in conjunction with the specification and should be considered a portion of the written description of the application. As used in the description, the terms "horizontal", "vertical", "left", "right", "up", and "down", and their derivatives, such as "horizontally", "rightwardly", "upwardly", etc., are intended to refer to the orientation as then being viewed by an observer in the drawing figure. Similarly, the terms "inwardly" and "outwardly" are used to describe the orientation within components, as viewed by an observer outside the component, etc.

Claims

1. A reflected light path imaging system, characterized by, comprising a first lens device (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 light ray area (2), a transmitted light ray area (3) and a totally reflected light ray area (4) overlapping said incident light ray area (2) and said transmitted light ray area (3), said incident light ray area (2), said transmitted light ray area (3) and said totally reflected light ray area (4) extending in a main plane (P1); - a first reflecting surface (5) extending at a first angle a with the normal (N) of said main surface; - a second reflecting surface (6) extending at a second angle β with the normal (N) of said main surface, β = a, said first reflecting surface (5) and said second reflecting surface (6) extending on opposite sides of the normal N and being non-parallel; said first lens device (10) being arranged adjacent to said incident light ray area (2) of said reflecting element (1), said image sensor (11) being arranged adjacent to said transmitted light ray area (3) of said reflecting element (1), the optical axis of said first lens device (10) and of said image sensor (11) extending perpendicular to said main surface of said reflecting element (1), said reflected light ray path imaging system being configured such that a light ray path (7) enters said reflecting element (1) through said first lens device (10) and said incident light ray area (2) of said reflecting element (1), said light ray path (7) being reflected in said interior of said reflecting element (1) by said first reflecting surface (5), said reflected light ray area (4) and said second reflecting surface (6) in sequence, said light ray path (7) leaving said reflecting element (1) through said transmitted light ray area (3) to said image sensor (11).

2. The reflected light path imaging system of claim 1, wherein, said reflected light ray area (4) is for reflecting light rays by total internal reflection.

3. The reflected light path imaging system of claim 1, wherein, said first angle a is an acute angle.

4. The reflected ray path imaging system of any one of claims 1 to 3, wherein, said first reflecting surface (5) and said second reflecting surface (6) each extend at a third angle γ with a further plane (P2) parallel to said main plane (P1); said light ray path (7) is reflected by said first reflecting surface (5), said reflected light ray area (4) and said second reflecting surface (6) at a reflection angle equal to said third angle γ.

5. The reflected ray path imaging system according to any one of claims 1 to 3, wherein, further comprising a second lens device (12), said second lens device (12) being arranged between said reflecting element (1) and said image sensor (11) adjacent to said transmitted light ray area (3), the optical axis of said second lens device (12) being coaxial with the optical axis of said image sensor (11).

6. The reflected ray path imaging system according to any one of claims 1 to 3, wherein, said first lens device (10) and / or said second lens device (12) each comprise at least one lens (13).

7. The reflected light path imaging system of claim 6, wherein, said first lens device (10) comprises at least one tunable lens (14).

8. The reflected light path imaging system of claim 4, wherein, the optical axis of said second lens device (12) is parallel to the optical axis of said first lens device (10).

9. The reflected ray path imaging system according to any one of claims 1 to 3, wherein, said first reflecting surface (5) and the second reflective surface (6) is arranged such that a reflective element vertex is formed in a reflective surface intersection area (8) in which the first reflective surface (5) and the second reflective surface (6) are directly connected, or the first reflective surface (5) and the second reflective surface (6) are connected by a bridging area (8a) which extends parallel to the main surface.

10. The reflected light path imaging system of claim 9, wherein, the intersection area (8) is arranged opposite the reflected light ray area (4).

11. The reflected ray path imaging system according to any one of claims 1 to 3, wherein, a section extending from the intersection area (8) towards the reflected light ray area (4) inside the reflective element (1) is also included, the section serving to absorb light rays and / or to redirect light rays towards the outside of the reflective element (1).

12. The reflected ray path imaging system of claim 11, wherein, the section comprises an optically black material or air.

13. The reflected ray path imaging system of claim 11, wherein, the section is a groove.

14. The reflected ray path imaging system of any one of claims 1 to 3, wherein, a first axis (A1) intersects the incident light ray area (2) and the first reflective surface (5), and a second axis (A2) intersects the transmitted light ray area (3) and the second reflective surface (6).

15. The reflected ray path imaging system of any one of claims 1 to 3, wherein, the first reflective surface (5) and the second reflective surface (6) comprise mirrors.

16. The reflected ray path imaging system of any one of claims 1 to 3, wherein, the main surface, the first reflective surface (5) and the second reflective surface (6) are separated by a material which facilitates total internal reflection.

17. An electronic device, comprising: a reflected light ray path imaging system according to any one of claims 1 to 16 and a housing comprising a light ray path entrance aperture (13) arranged in a wall of the housing, a central axis of the entrance aperture (13) extending perpendicular to the main surface of the light ray path reflective element (1). 18.The electronic device of claim 17, wherein, the entrance aperture (13) is circular and has an unobstructed inner diameter.

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