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

[0001] This application is a divisional application of the original application with the application number 202290000899.5 and the original filing date of 23 June 2022, the entire content of the original application is incorporated herein by reference. TECHNICAL FIELD

[0002] The present invention relates to a reflective light path imaging system comprising a lens arrangement, a reflective element and an image sensor. BACKGROUND

[0003] There are some 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.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] However, the secondary mirror blocks the central part of the entrance pupil aperture of the system, leaving only a ring-shaped entrance pupil aperture, which significantly reduces the performance compared to a design that includes a fully open entrance pupil aperture. The larger the secondary mirror, the lower the MTF values become at lower spatial frequencies.

[0010] Therefore, there is a need for an improved light path folding element and an improved imaging system. Invention content

[0011] It is an object to provide an improved reflective light path imaging system that enables a larger aperture light 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 figures.

[0012] According to a first aspect, there is provided a reflective light path imaging system comprising a first lens arrangement, an image sensor and a light path reflecting element, the light path reflecting element comprising a main surface, the main surface comprising an entrance light region, a transmitted light region and a reflected light region overlapping the entrance light region and the transmitted light region. The entrance light region, the transmitted light region and the reflected light 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 entrance light region of the reflecting element, the image sensor is arranged adjacent to the transmitted light 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 reflective light path imaging system is configured such that a light path enters an interior of the reflecting element through the first lens arrangement and the entrance light region of the reflecting element, the light path is reflected in the interior of the reflecting element by the first reflecting surface, the reflected light region and the second reflecting surface in sequence, and the light path exits the reflecting element through the transmitted light region to the image sensor.

[0013] This folding structure, i.e. the structure in which the light 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.

[0014] In a possible implementation form of the first aspect, the reflected light region is configured to reflect light by total internal reflection such that the reflected light region overlaps with the entrance light region and the transmitted light region, resulting in a very small folding element.

[0015] In a further possible implementation form of the first aspect, the first angle is an acute angle, making the design comply with specific reflection requirements while still having as small external dimensions as possible.

[0016] 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.

[0017] In a further possible implementation form of the first aspect, the reflective light ray path imaging system further comprises a second lens arrangement arranged between the folding element and the image sensor adjacent to the transmissive light ray area, an optical axis of the second lens arrangement being coaxial with an optical axis of the image sensor, thereby facilitating a further improved imaging system.

[0018] 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, thereby providing maximum flexibility for the system.

[0019] In a further possible implementation form of the first aspect, the first lens arrangement comprises at least one tunable lens, thereby facilitating the incorporation of auto focus into the lens arrangement.

[0020] In a further possible implementation form of the first aspect, an optical axis of the second lens arrangement is parallel to an optical axis of the first lens arrangement, thereby making the imaging system as compact and precise as possible.

[0021] In a further possible implementation form of the first aspect, the light ray path passes through the first lens arrangement 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 light rays entering the reflective element in a first direction along the first axis exit 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.

[0022] 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 area 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, which extends 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.

[0023] In a further possible implementation form of the first aspect, the intersection area is arranged opposite to the reflected light area, thereby folding the light path as little as possible while still achieving the desired focal length.

[0024] In a further possible implementation form of the first aspect, the folding element further comprises a segment extending from the intersection area towards the reflected light area inside the reflective element, the segment being used to ensure that the light follows the desired light path.

[0025] In a further possible implementation form of the first aspect, a first axis intersects the incident light area and the first reflective surface, and a second axis intersects the transmitted light area and the second reflective surface, thereby making the folding element as compact as possible.

[0026] In a further possible implementation form of the first aspect, the first reflective surface and the second reflective surface comprise mirrors, thereby facilitating a simple and reliable reflection solution.

[0027] 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 that facilitates total internal reflection, thereby facilitating a folding element with a small form factor.

[0028] According to a second aspect, there is provided an electronic device comprising a reflected light path imaging system according to the above and a housing, the housing comprising a light 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 path folding element, thereby making the electronic device have as small external dimensions as possible while still having a performance improved imaging system.

[0029] In a possible implementation form of the third aspect, the entrance aperture is circular and has an unobstructed inner diameter, thereby resulting in as high MTF values as possible, and thus as good performance as possible.

[0030] These and other aspects are apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0031] In the following detailed description of the application, various aspects, embodiments and implementations of the application are explained with reference to the drawings, which are described as follows:

[0032] Figure 1 A diagram of a reflective light ray path imaging system is shown, according to an example of an embodiment of the application;

[0033] Figure 2 A diagram of a reflective light ray path imaging system is shown, according to an example of an embodiment of the application;

[0034] Figure 3 A diagram of a reflective light ray path imaging system is shown, according to an example of an embodiment of the application;

[0035] Figure 4 A diagram of a reflective light ray path imaging system is shown, according to an example of an embodiment of the application;

[0036] Figure 5 A diagram of a reflective light ray path imaging system is shown, according to an example of an embodiment of the application. DETAILED DESCRIPTION

[0037] Figures 1 to 5 An example of a reflective light ray path imaging system 9 is shown, a reflective light ray path imaging system 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 comprising:

[0038] a main surface comprising an incident light ray region 2, a transmitted light ray region 3 and a totally reflected light ray region 4, the incident light ray region 2, the transmitted light ray region 3 and the totally reflected light ray region 4 extending in a main plane P1;

[0039] a first reflective surface 5 at a first angle a with a normal N of the main surface;

[0040] a second reflective surface 6 at a second angle β with the normal N of the main surface, β = a, the first reflective surface 5 and the second reflective surface 6 being on opposite sides of the normal N and being non-parallel;

[0041] The first lens arrangement 10 is arranged adjacent to the entrance light ray region 2 of the reflective element 1 and the image sensor 11 is arranged adjacent to the transmission light ray region 3 of the reflective element 1. The optical axis of the first lens arrangement 10 and the image sensor 11 extends perpendicular to the main plane P1 of the reflective element 1. The reflected light ray path imaging system 9 is configured such that the light ray path 7 enters the interior of the reflective element 1 through the first lens arrangement 10 and the entrance light ray region 2 of the reflective element 1, the light ray path 7 is reflected in the interior of the reflective element 1 in sequence by the first reflective surface 5, the reflected light ray region 4 and the second reflective surface 6, the light ray path 7 leaves the reflective element 1 through the transmission light ray region 3 to the image sensor 11.

[0042] The light ray path reflective element 1 further comprises an intersection region 8, which is opposite to the reflected light ray region 4. From the intersection region 8 towards the reflected light ray region 4 a section 90 is formed, which is a groove.

[0043] The reflected light ray path imaging system comprises

[0044] The first lens arrangement 10, the image sensor 11 and the light ray path reflective element 1.

[0045] The light ray path reflective element 1 comprises a main surface, which in turn comprises an entrance light ray region 2 for receiving incoming light and forwarding the incoming light to the folding element 1, a transmission 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 entrance light ray region 2 and the transmission light ray region 3. The reflected light ray region 4 can be configured to reflect light rays by total internal reflection.

[0046] The entrance light ray region 2, the transmission light ray region 3 and the reflected light ray region 4 extend in the main plane P1, i.e. they constitute different, but slightly overlapping regions of one planar surface as the main surface of the light ray path reflective element 1. The main surface is the surface of the light ray path reflective element 1 which is arranged closest to the first lens arrangement 10 and the image sensor 11.

[0047] The first lens arrangement 10 is arranged adjacent to the entrance light ray region 2 of the reflective element 1 and the image sensor 11 is arranged adjacent to the transmission light ray region 3 of the reflective element 1. The optical axis of the first lens arrangement 10 and the image sensor 11 extends perpendicular to the main surface of the reflective element 1.

[0048] The reflected light path imaging system 9 can further comprise a second lens arrangement 12 arranged between the reflective element 1 and the image sensor 11 adjacent to the transmitted light region 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.

[0049] The first lens arrangement 10 and the second lens arrangement 12 can each comprise at least one lens. A diffractive optical element can be comprised 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 a prism, e.g. a freeform prism, in order to improve and simplify the first lens arrangement 10.

[0050] The lenses of the second lens arrangement 12 can have any suitable cut, e.g. an I-cut or a D-cut, which frees up space within the second lens arrangement 12.

[0051] 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 comprised; or adding optical elements that change the thickness, i.e. reduce and increase the optical path.

[0052] Furthermore, optical image stabilization (OIS) can be performed, e.g. by moving the first lens arrangement 10 in the xy-plane, the optical axis of the first lens arrangement being 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 soft optical material is comprised; or using one or more tunable lenses 14.

[0053] The leftmost incident light region 2 and the rightmost transmitted light region 3 are illustrated. The reflected light region 4 extends between the incident light region 2 and the transmitted light region 3 and at least partially overlaps with both regions 2, 3. As shown in the figure, light rays passing through the leftmost incident light region 2 are reflected in a section of the reflected light region 4 that overlaps with the incident light region 2. However, light rays passing through the rightmost incident light region 2 are reflected in a section of the reflected light region 4 that overlaps with the transmitted light region 3.

[0054] 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 β with the normal N of the main surface. β = - 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.

[0055] The first angle a can be an acute angle.

[0056] The first reflective surface 5 and the second reflective surface 6 each extend at a third angle γ with a further plane P2 parallel to the main plane PI, as shown in Figure 2 The light ray path 7 can be reflected by the first reflective surface 5, the reflective light ray area 4 and the second reflective surface 6 at a reflection angle equal to the third angle γ. It is well known in the field of optics that the reflection angle as well as the angle of incidence are measured with respect to the normal of the reflective surface. On the opposite side of the normal, the incident light ray propagating along the light ray path 7 hits the reflective surface at an angle of incidence γ with respect to the surface normal and accordingly leaves the reflective surface at a reflection angle γ with respect to the surface 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 when the light is reflected from the first reflective surface 5 and the second reflective surface 6, as shown in Figure 5 Accordingly, 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 when the light is reflected from the reflective light ray area 4, as shown in Figure 5

[0057] The first reflective surface 5 and the second reflective surface 6 can comprise mirrors.

[0058] 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.

[0059] The light ray path reflective element 1 is configured such that the light ray path 7 enters the reflective element 1 along a first axis Al through the incident light ray area 2, after which the light ray path 7 is reflected in sequence by the first reflective surface 5, the reflective 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, thereafter by the reflective light ray area 4 and finally by the second reflective surface 6. Finally, the light ray path 7 exits the light ray path reflective element 1 along a second axis A2 through the transmitted light ray area 3.

[0060] ​The first axis A1 can intersect the incident light ray area 2 and the first reflective surface 5, and the second axis A2 can intersect the transmitted light ray area 3 and the second reflective surface 6. When a light ray propagates along the first axis A1 parallel to the normal N as shown in the figure, the same light ray will also propagate along the second axis A2 parallel to the first axis A1, i.e. a light ray entering the reflective element 1 in a first direction along the first axis will exit the reflective element 1 in a second direction along the second axis, the second direction being exactly opposite to the first direction, as indicated in Figure 2 . Nevertheless, all light rays propagate along different first and second axes A1, A2 extending at different angles to the main surface, as indicated by the three sets of incident and transmitted light rays shown in, e.g. Figure 1 , 3 and 4. Each light ray in a set propagates along its own first axis A1 and its own second axis A2.

[0061] The imaging system 9 is configured such that the light ray path 7 enters the interior of the reflective element 1 through the first lens arrangement 10 and the incident light ray area 2 of the reflective element 1. Thereafter, the light ray path 7 is internally reflected by the first reflective surface 5, the reflected light ray area 4 and the second reflective surface 6 of the reflective element 1, as described above and as shown in the figure. The light ray path 7 exits the reflective element 1 through the transmitted light ray area 3 and then reaches the image sensor 11.

[0062] The first reflective surface 5 and the second reflective surface 6 can be arranged such that a reflective element vertex is formed in the reflective surface intersection area 8 in which the first reflective surface 5 and the second reflective surface 6 are directly connected, as indicated in Figure 1 . The first reflective surface 5 and the second reflective surface 6 can also be connected by a bridging area 8a extending parallel to the main surface, as indicated in Figure 2 and 3 .

[0063] The intersection area 8 can be arranged opposite the reflected light ray area 4 and can have a smaller area than the area of the reflected light ray area 4. The reflective element 1 can comprise a segment 90 extending from the intersection area 8 towards the reflected light ray area 4, the segment 90 serving to prevent light rays from deviating from the desired light ray path 7. The segment 90 can comprise an optically black material or can be an air volume. The segment 90 can be made as a groove, the segment 90 can be filled with an optically black material, or the surface of the segment 90 can be coated with an index-matching paint to minimize stray light. Furthermore, any suitable additional surface of a component of the imaging system 9 can be coated with such a paint.

[0064] The present invention also relates to an electronic device comprising the above described light ray path imaging system 9 and a housing comprising a light ray 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 ray path reflecting 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 ray path reflecting element 1.

[0065] Various aspects and implementations have been described herein in conjunction with various embodiments. However, other variations than those described are possible in light of the above teachings. It is thus to be understood that, within the scope of the claimed subject matter, that modifications and / or improvements can be made to the disclosed embodiments and that other implementations may

[0066] The use of the same reference symbols in different drawings indicates similar or identical items. Numbers in the claims do not limit any claimed embodiment. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. It is appreciated that some embodiments can comprise steps or features not specifically mentioned in the claims. The word "about" preceding a numerical value indicates that the value is up to ±10% of the stated value. The word "substantially" does not exclude the presence of something that is not claimed in the claims. The word "multiple" before the quantity of an element does not exclude the presence of only one such element. The word "plurality" before an element does not exclude the presence of only one such element. The word "single" before an element does not exclude the presence of more than one such element. The terms "left", "right", "front", "back", "top", "bottom", "over", "under", and the like in the description and in the claims, refer to the orientation of the figure in which the drawing is viewed.

Claims

1. A reflected light path imaging system (9) characterized by, comprising a first lens device (10), an image sensor (11) and a light path reflecting element (1), said light path reflecting element (1) comprising: - a main surface comprising an incident light region (2), a transmitted light region (3) and a totally reflected light region (4), said incident light region (2), said transmitted light region (3) and said totally reflected light region (4) extending in a main plane (PI); - a first reflecting surface (5) making a first angle a with a normal (N) to said main surface; - a second reflecting surface (6) making a second angle β, β = a, with said normal (N) to said main surface, said first reflecting surface (5) and said second reflecting surface (6) being on opposite sides of said normal (N) and not parallel; said first lens device (10) being arranged adjacent to said incident light region (2) of said reflecting element (1), said image sensor (11) being arranged adjacent to said transmitted light region (3) of said reflecting element (1), an optical axis of said first lens device (10) and of said image sensor (11) being perpendicular to said main plane (PI) of said reflecting element (1), said reflected light path imaging system (9) being configured so that a light path (7) enters an interior of said reflecting element (1) through said first lens device (10) and said incident light region (2) of said reflecting element (1), said light path (7) being reflected in said interior of said reflecting element (1) by said first reflecting surface (5), said totally reflected light region (4) and said second reflecting surface (6) in this order, said light path (7) exiting said reflecting element (1) by said transmitted light region (3) to reach said image sensor (11); said light path reflecting element (1) further comprising an intersection region (8) opposite said totally reflected light region (4), a section (90) being formed from said intersection region (8) towards said totally reflected light region (4), said section (90) being a groove.

2. The reflected light path imaging system (9) according to claim 1, characterized in that said totally reflected light region (4) is configured to reflect light by total internal reflection.

3. The reflected light path imaging system (9) according to claim 1, characterized in that said first angle a is an acute angle.

4. The reflected light path imaging system (9) according to claim 1, characterized in that said first reflecting surface (5) and said second reflecting surface (6) each make a third angle γ with another plane (P2) parallel to said main plane (PI); said light path (7) is reflected by said first reflecting surface (5), said totally reflected light region (4) and said second reflecting surface (6) at a reflection angle equal to said third angle γ.

5. The reflected light path imaging system (9) according to claim 1, characterized in that a second lens device (12) is further comprised, said second lens device (12) being arranged between said reflecting element (1) and said image sensor (11) adjacent to said transmitted light region (3), an optical axis of said second lens device (12) being coaxial with an optical axis of said image sensor (11).

6. The reflected light path imaging system (9) according to claim 5, characterized in that said first lens device (10) and / or said second lens device (12) each comprise at least one lens.

7. The reflected light path imaging system (9) according to claim 6, characterized in that The first lens device (10) comprises at least one tunable lens (14).

8. The reflected ray path imaging system (9) according to any one of claims 5 to 7, characterized in that The optical axis of the second lens device (12) is parallel to the optical axis of the first lens device (10).

9. The reflected ray path imaging system (9) according to any one of claims 1 to 7, characterized in that The first reflective surface (5) and the second reflective surface (6) are connected by a bridging area (8a) which is parallel to the main surface.

10. The reflected ray path imaging system (9) according to any one of claims 1 to 7, characterized in that The segment (90) comprises an optically black material or air within.

11. The reflected ray path imaging system (9) according to any one of claims 1 to 7, characterized in that A first axis (A1) intersects the incident ray area (2) and the first reflective surface (5) and a second axis (A2) intersects the transmitted ray area (3) and the second reflective surface (6).

12. The reflected ray path imaging system (9) according to any one of claims 1 to 7, characterized in that The first reflective surface (5) and the second reflective surface (6) comprise mirrors.

13. The reflected ray path imaging system (9) according to any one of claims 1 to 7, characterized in that The main surface, the first reflective surface (5) and the second reflective surface (6) are separated by a material which facilitates total internal reflection.

14. An electronic device, comprising: A housing comprising a reflected ray path imaging system (9) according to any of claims 1-13 and a ray path entrance aperture (13) arranged in a wall of the housing, a central axis of the entrance aperture (13) being perpendicular to the main surface of the ray path reflective element (1). 15.The electronic device of claim 14, wherein, The entrance aperture (13) is circular and has an unobstructed inner diameter.

Images