Optical system and a mobile unit including such an optical system

Abstract

The invention relates to an optical unit (10) and a mobile unit (1) comprising such an optical unit (10). The optical unit is a catadioptric optical unit comprising a primary lens (13), a primary mirror (14), and a secondary mirror (15) arranged in the centre of the primary lens (13). Further, the optical unit (10) comprises an inclined mirror (16) arranged to direct the light from the secondary mirror (15) to an image sensor (34). A lens holder (12) for holding the primary lens (13) and the secondary mirror (15) is provided, and an extension mechanism (23) is arranged for moving the lens holder (12), the primary lens (13), and the secondary mirror (15) between a retracted position and an extended position, in which the secondary mirror (15) is farther away from the primary mirror (14). In the extended position, incoming light will pass through the primary lens (13), via the primary mirror (14), the secondary mirror (15), and the inclined mirror (16) to the image sensor (34). An image stabilisation unit (17) is arranged and functions by adjusting the inclination of the inclined mirror (16).

Description

[0001] OPTICAL SYSTEM AND A MOBILE UNIT INCLUDING SUCH AN OPTICAL SYSTEM

[0002] TECHNICAL FIELD

[0003] Embodiments of invention relate to an optical system for a mobile unit and to a mobile unit including such an optical system. Specifically, embodiments of invention mat be implemented in a pop-up camera in a mobile unit.

[0004] BACKGROUND

[0005] In mobile units of today, such as mobile phones, smart phones and tablets, the equipment incorporated in the mobile units are getting more and more sophisticated. With respect to the cameras of such mobile units there are many different criteria to fulfil while at the same time keeping the size of the camera to a minimum to be able to provide a mobile unit of an attractive performance and design.

[0006] One challenge of such mobile units lies in the provision of an optical system with a long focal length adapted for operating on long ranges.

[0007] Catadioptric optical systems provide optimum optical capabilities for designing super-long focal length cameras with compact sizes and suitability for mobile units. A catadioptric optical system is one where refraction and reflection are combined in an optical system, usually via lenses (dioptrics) and curved mirrors (catoptrics). Catadioptric combinations has conventionally been used in focusing systems such as searchlights, headlamps, lighthouse focusing systems, optical telescopes, microscopes, and telephoto lenses.

[0008] The proper combination of lenses and mirrors allows for high magnification with excellent resolution while maintaining a portable and lightweight form factor, making it ideal for advanced mobile imaging applications

[0009] However, a catadioptric optical system requires a certain length between the mirrors to achieve the desired long range functionality of the optical system which provides challenges to make it functional inside the limited space of a mobile unit.

[0010] Also, for a catadioptric optical system, it is not evident how to provide an effective optical image stabilization function.

[0011] It would be desirable to use the advantages of a catadioptric optical system without the negative effects of conventional systems.

[0012] SUMMARY

[0013] An objective of embodiments of the invention is to provide an optical system with high magnification which may be integrated into the compact dimensions of a mobile unit such as a mobile smart phone device or a tablet.

[0014] According to a first aspect of the invention, the above mentioned and other objectives are achieved by an optical unit, typically a catadioptric optical unit that comprises a primary lens, a primary mirror, and a secondary mirror arranged in the centre of the primary lens.

[0015] Further, the optical unit comprises an inclined mirror arranged to direct the light from the secondary mirror to an image sensor.

[0016] A lens holder for holding the primary lens and the secondary mirror is provided, and an extension mechanism is arranged for moving the lens holder, the primary lens, and the secondary mirror between a retracted position and an extended position. In the extended position, the lens holder, the primary lens, and the secondary mirror are farther away from the primary mirror than they are in the retracted position.

[0017] Further, in the extended position, incoming light will pass through the primary lens, via the primary mirror, the secondary mirror, and the inclined mirror to the image sensor.

[0018] An image stabilisation unit is arranged and is configured to stabilise an image by adjustment of an inclination of the inclined mirror.

[0019] In view of the inherent space saving possibilities related to the use of a retractable catadioptric optical unit it is well adapted to be used in mobile units such as mobile telephones, smart phones and tablets.

[0020] Further, in view of the implementation of an image stabilisation unit that uses a mirror to stabilise the image further space saving is provided in a non-evident manner.

[0021] The arrangement with an inclined mirror minimizes the unwanted stray light and internal reflections as the image sensor is separated and positioned outside the catadioptric system such that it will not be affected by incoming light that does not pass the intended path via the mirrors.

[0022] In an implementation form of the optical unit the primary mirror has a concave shape and is configured to converge the incoming light towards the secondary mirror.

[0023] An advantage of this implementation form is that the concave form of the primary mirror allows for the secondary mirror to be arranged in the centre of the primary lens.

[0024] In an implementation form of the optical unit the secondary mirror has a convex shape and is configured to direct the light from the primary mirror towards the inclined mirror.

[0025] In an implementation form of the optical unit the inclined mirror is arranged in the centre of the primary mirror.

[0026] An advantage of this implementation form is that the image sensor need not be positioned in line with the primary lens and the primary and secondary mirror. Thereby, the height of the optical unit may be minimised.

[0027] In an implementation form of the optical unit the inclined mirror is arranged at an angle of between 40° and 50° with respect to a mean direction of the light reflected from the secondary mirror.

[0028] Thereby, the light is reflected by the inclined mirror at angle of about 90°, making it possible to position the image sensor beside the mirrors instead of in line with them, which increases the compactness of the optical unit, thereby providing a very compact the optical unit, especially in its collapsed retracted position.

[0029] Specifically, the image sensor may be positioned beside the primary mirror and be configured to receive the incoming light from the inclined mirror substantially orthogonally with respect to the light entering the primary lens. Thereby, the height of the optical unit may be minimised. In an implementation form of the optical unit the inclined mirror is pivotally arranged on a pivot joint to a support structure of the optical unit, the image stabilisation unit comprising a plurality of coils at the support structure and magnets on the inclined mirror configured to control the inclination of the inclined mirror by powering the coils.

[0030] In an implementation form of the optical unit the plurality of coils and magnets are arranged to also control a tilt orientation of the inclined mirror, orthogonal to the inclination of the inclined mirror.

[0031] In an implementation form of the optical unit the optical unit is only operational when the primary lens is positioned in the extended position.

[0032] An advantage of this implementation form is that in the retracted position, focus may be directed to achieve a robust construction.

[0033] In an implementation form of the optical unit the lens holder is configured and positioned to cover the image sensor from incoming light in the retracted position.

[0034] An advantage of this implementation form is that, in the retracted position, the image sensor will not be exposed to any light.

[0035] In an implementation form of the optical unit the extension mechanism includes a rotation motor arranged to drive a worm gear which is geared to move the lens holder between the extended position and the retracted position.

[0036] In an implementation form of the optical unit the image sensor is positioned beside the primary mirror configured to receive the incoming light from the inclined mirror.

[0037] As indicated above, this is advantageous in that provides a very compact optical unit especially in its collapsed retracted position where the height of the optical unit may be minimised.

[0038] According to a second aspect of the invention, the above mentioned and other objectives are achieved by means of a mobile unit comprising an optical unit as described above.

[0039] Specifically, in the retracted position, the primary lens of the optical unit is substantially flush with a shell of the mobile communication unit, and, in the extended position, the primary lens extends outside said shell.

[0040] Further applications and advantages of embodiments of the invention will be apparent from the following detailed description.

[0041] BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The appended drawings are intended to clarify and explain different embodiments of the invention, wherein:

[0043] - Fig. 1 shows a mobile unit according to embodiments of the invention,

[0044] - Fig. 2 shows the mobile unit in Fig. 1 with an optical unit in an extended position,

[0045] - Fig. 3 is a perspective view of an optical unit according to embodiments of the invention,

[0046] - Fig. 4 shows the optical unit from below,

[0047] - Fig. 5 is a cut perspective view of the optical unit in a retracted position,

[0048] - Fig. 6 is a cut perspective view of the optical unit in an extended position,

[0049] - Fig. 7 is a partly cut exploded view of the optical unit in the retracted position,

[0050] - Fig. 8 is a cut perspective view illustrating incoming light into the optical unit in the extended position, Fig. 9 shows an exemplary elevation mechanism for the optical unit,

[0051] Fig. 10 shows an image stabilisation unit of the optical unit with an inclined mirror, and

[0052] Fig. 11 shows the image stabilisation unit with the inclined mirror in a cut view.

[0053] DETAILED DESCRIPTION

[0054] The invention is based on the idea that a collapsible catadioptric system may be used to provide an optical system with a long focal point in a mobile unit, such as smartphone or a tablet.

[0055] Fig. 1 and 2 show a mobile unit 1 with an extendable optical unit 10 in accordance with embodiments of the invention. In Fig. 1 , the optical unit 10 is in a retracted position with the primary lens 13 flush with the shell 2 of the mobile unit 1 , and in Fig. 2, the optical unit 10 is in an extended position with the primary lens 13 extending outside of the shell 2 of the mobile unit 1.

[0056] Fig. 3 and 4 are perspective views of the optical unit 10 from above and below, respectively. The optical unit 10 comprises a housing 11 and a primary lens 13, which in its centre carries a secondary mirror 15 for reflecting the incoming light a second time, after having been reflected by a primary mirror 14 arranged inside the optical unit 10.

[0057] When positioned in a mobile unit 1 the housing 11 of the optical unit 10 the housing 11 may be hidden under the shell 2 of the mobile unit 1 , wherein only the primary lens 13 is visible from outside the shell 2 of the mobile unit 1.

[0058] The optical unit 10 further comprises connectors to electronic parts of the optical unit 10, which will be described below. Specifically, the optical unit 10 comprises a connector 20 to an image stabilisation unit 17, a connector 21 to an image sensor, and a connector 22 to an extension mechanism, arranged to move the primary lens 13 between its retracted and extended positions.

[0059] The primary mirror 14 and the image stabilisation unit 17 are preferably supported by the housing 11 of the optical unit 10.

[0060] Also visible in Fig. 3 is an image sensor package 18 comprising the image sensor for producing an image from the incoming light. The image sensor package 18 is placed in a vertical orientation (pixel area pointing to horizontal direction) on the side opening of external housing. Secondary supportive optics elements 19 are located in front of the image sensor package 18 inside a side opening space of the optical unit 10. In this aspect vertical is defined as the general direction of the incoming light.

[0061] Figs. 5 and 6 are cut perspective views of the optical unit 10 in a retracted and an extended position, respectively. In Fig. 7 the optical unit 10 is shown in an exploded view.

[0062] Typically, the height of the optical unit 10 in the extended position is about twice the height of the optical unit 10 in the retracted position.

[0063] As is visible in these views the optical unit 10 comprises a primary lens 13, a primary mirror 14, a secondary mirror 15 arranged in the centre of the primary lens 13, and an inclined mirror 16 arranged in the centre of the primary mirror 14.

[0064] As is illustrated in Fig. 8, the primary mirror 14 has a concave (parabolic) shape, configured to converge the incoming light towards the secondary mirror 15 and the secondary mirror 15 has a convex shape, configured to direct the light from the primary mirror 14 towards the inclined mirror 16. The inclined mirror 16 may have a flat surface. Preferably all mirrors have a circular shape. The inclined mirror 16 is arranged in the centre of the primary mirror 14 and is configured to reflect the light from the secondary mirror 15 to an image sensor 34 where an image is produced from the incoming light.

[0065] A lens holder 12 is arranged for holding the primary lens 13 and the secondary mirror 15, and an extension mechanism 23 is arranged for moving the lens holder 12 and to move the primary lens 13 and the secondary mirror 15 between a retracted position and an extended position farther away from the primary mirror 14.

[0066] In the extended position, incoming light 25 will pass through the primary lens 13, via the primary mirror 14, the secondary mirror 15, and the inclined mirror 16 to the image sensor 34. In the retracted position on the other hand, the optical unit 10 is not operable. The lens holder 12 may be configured and positioned to protect the image sensor 34 from incoming light in the retracted position.

[0067] When the camera is not used and is stored in the lower (retracted) height configuration inside smart device the optical elements are positioned close to each other and with little free space between them. The camera functionality is disabled in this mode.

[0068] In embodiments of the optical unit 10 an image stabilisation unit 17 is arranged to adjust the inclination of the inclined mirror 16. The image stabilisation unit 17 may be governed by information coming from a gyro (not shown) arranged in the mobile unit 1. Further, of course, the mobile unit 1 may include a processing unit arranged to process information from the gyro and from the image sensor in order to optimise the image stabilisation function.

[0069] The inclined mirror 16 is preferably arranged at angle of between 40° and 50° with respect to a mean direction of the light reflected from the secondary mirror 15.

[0070] As is illustrated in Fig. 11, the inclined mirror 16 may be pivotally arranged on a pivot joint 33 to a support structure 35 of the optical unit 10. The image stabilisation unit 17 may comprise a plurality of coils 27 at the support structure 35 and magnets 26 on the inclined mirror 16 arranged to control the inclination of the inclined mirror 16 by powering the coils 27.

[0071] The plurality of coils 27 and magnets 26 are arranged to also control a tilt orientation of the inclined mirror 16, orthogonal to the inclination of the inclined mirror 16. Thereby, the inclined mirror 16 may be adjusted in all directions about the pivot joint 33.

[0072] To achieve this adjustability of the inclined mirror 16 at least three coils 27 and magnets 26 should be arranged. in other words, the inclined mirror 16 is mounted onto electro-mechanical platform via the pivot joint 33. A suitable actuator e.g. voice coil actuator (but also shape memory alloy, piezo) is used to generate controlled angular displacements for it using magnets 16 on the tiltable side and set of electrical coils 27 on the static side. Resulting electromagnetic fields adjust the mirror turning angle along two mutually perpendicular axes. Thus, the mirror works for beam steering purposes and can re-direct the light correctly between the scenery and image sensor under conditions involving e.g. hand movements.

[0073] In specific embodiments of the optical unit 10, illustrated in Fig. 9, the extension mechanism 23 may include a rotation motor 26 arranged to drive a worm gear 30 which is geared to move the lens holder 12 between the extended position and the retracted position.

[0074] Specifically, the rotation motor 26 may be connected via a gear box 29 to the worm gear 30, which is arranged to rotate an outer gear wheel 31, which in turn is in meshing contact with an inner gear wheel 32, which comprises an outer thread or splines configured to mesh with a mating thread on the inside of the outer gear wheel 31. The gear box 29 is preferably arranged to gear down the rotation of the rotation motor 26.

[0075] The inner gear wheel 32 may form part of, or be rigidly connected to, the lens holder 12 such that the lens holder 12 will move with the inner gear wheel 32. The extension mechanism 23 can be used for optics extension purposes.

[0076] It should be noted that the extension movement can be either switchable (from one level to another) or continuous (between two levels). The latter option can contain some additional functions such as focusing or zooming operations, specifically by repositioning the lens holder 12, the primary lens 13, and the secondary mirror 15.

[0077] Finally, it should be understood that the invention is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.

Claims

CLAIMS1. An optical unit (10) for a mobile unit (1), the optical unit (10) comprising: a primary lens (13), a primary mirror (14), a secondary mirror (15) arranged in the centre of the primary lens (13), an inclined mirror (16), an image sensor (34), a lens holder (12) for holding the primary lens (13) and the secondary mirror (15), and an extension mechanism (23) for moving the lens holder (12), the primary lens (13), and the secondary mirror (15) between a retracted position and an extended position, wherein, in the extended position, the lens holder (12), the primary lens (13), and the secondary mirror (15) are farther away from the primary mirror (14) than in the retracted position, wherein, in the extended position, the optical unit ( 10) is configured to allow incoming light to pass through the primary lens (13), via the primary mirror (14), the secondary mirror (15), and the inclined mirror (16) to the image sensor (34), and wherein an image stabilisation unit (17) is arranged and is configured stabilise an image by adjustment of an inclination of the inclined mirror (16).

2. The optical unit (10) according to claim 1, wherein the primary mirror (14) has a concave shape and is configured to converge the incoming light towards the secondary mirror (15).

3. The optical unit (10) according to claim 1 or 2, wherein the secondary mirror (15) has a convex shape and is configured to direct the light from the primary mirror (14) towards the inclined mirror (16).

4. The optical unit (10) according to any one of the preceding claims, wherein the inclined mirror (16) is arranged in the centre of the primary mirror (14).

5. The optical unit (10) according to any one of the preceding claims, wherein the inclined mirror (16) is arranged at an angle of between 40° and 50° with respect to a mean direction of the light reflected from the secondary mirror (15).

6. The optical unit (10) according to any one of the preceding claims, wherein the inclined mirror (16) is pivotally arranged by a pivot joint (33) to a support structure (35) of the optical unit (10), the image stabilisation unit (17) comprising a plurality of coils (27) at the support structure (35) and magnets (26) on the inclined mirror (16) arranged to control the inclination of the inclined mirror (16) by powering the coils (27).

7. The optical unit (10) according to claim 6, wherein the plurality of coils (27) and magnets (26) are arranged to also control a tilt orientation of the inclined mirror (16), orthogonal to the inclination of the inclined mirror (16).

8. The optical unit (10) according to any one of the preceding claims, wherein the optical unit (10) is only operational when the primary lens (13) is positioned in the extended position.

9. The optical unit (10) according to any one of the preceding claims, wherein the lens holder (12) is configured and positioned to cover the image sensor (34) from incoming light in the retracted position.

710. The optical unit (10) according to any one of the preceding claims, wherein the extension mechanism (23) includes a rotation motor (26) arranged to drive a worm gear (30) which is geared to move the lens holder (12) between the extended position and the retracted position.

11. The optical unit (10) according to any one of the preceding claims, wherein the image sensor (34) is positioned beside the primary mirror (14) and configured to receive the incoming light from the inclined mirror (16).

12. A mobile communication unit ( 1 ) comprising an optical unit (10) according to any one of the preceding claims, wherein, in the retracted position, the primary lens (13) is substantially flush with a shell (2) of the mobile communication unit (1), and, in the extended position, the primary lens (13) extends outside said shell (2).

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