OPTICAL ARRANGEMENT FOR CAMERA MODULES, CAMERA MODULES WITH OPTICAL ARRANGEMENTS, AND METHOD OF MANUFACTURE

Abstract

An optical arrangement for a camera module with an image sensor is provided. The optical arrangement includes optical components having a transparent cover element; an infrared absorbing cut-off filter; and an optical lens. The optical components are arranged, along an incident optical beam path going through the optical components onto the image sensor, in a sequence through the transparent cover element, then the infrared absorbing cut-off filter, and then the optical lens.

Claims

1. An optical arrangement for a camera module with an image sensor, comprising a plurality of optical components having an incident optical beam path towards the image sensor, the plurality of optical components comprising a transparent cover element, an infrared absorbing cut-off filter, and an optical lens, the plurality of optical components being arranged, along the incident optical beam, in a sequence from the cover element to the cut-off filter, and then to the optical lens.

2. The optical arrangement according to claim 1, wherein the cover element is formed as a sheet made of a material selected from the group consisting of sapphire, chemically strengthened glass, spinel, aluminium oxynitride, moissanite, corundum, and quartz.

3. The optical arrangement according to claim 1, wherein the cut-off filter is formed as an infrared absorbing filter glass element.

4. The optical arrangement according to claim 3, wherein the infrared absorbing filter glass element comprises a filter glass sheet or substrate.

5. The optical arrangement according to claim 4, wherein the infrared absorbing filter glass element comprises blue glass or an infrared absorbing layer made of an organic ink or organic film.

6. The optical arrangement according to claim 1, wherein the cut-off filter and the cover element are combined to a protective IR filter.

7. The optical arrangement according to claim 6, wherein the protective IR filter is composed of a filter film on a rear face of the cover element.

8. The optical arrangement according to claim 7, wherein the filter film is a two-layered material formed as a laminate material or as a coated material.

9. The optical arrangement according to claim 6, wherein the protective IR filter comprises an IR reflecting layer.

10. The optical arrangement according to claim 9, wherein the IR reflecting layer is arranged on one face of the cover element or on one face of the cut-off filter.

11. The optical arrangement according to claim 6, wherein the protective IR filter comprises an antireflection layer arranged on one face of the cover element or on one face of the cut-off filter.

12. The optical arrangement according to claim 6, wherein the protective IR filter comprises a hybrid IR reflecting and antireflection layer arranged on one face of the cover element or on one face of the cut-off filter.

13. The optical arrangement according to claim 1, further comprising an antireflection layer coated on a front face and/or on a rear face of the cover element.

14. The optical arrangement according to claim 1, wherein the cut-off filter has a thickness of less than 0.3 mm.

15. The optical arrangement according to claim 1, wherein the cover element and the cut-off filter are cemented together.

16. A camera module comprising the optical arrangement according to claim 1.

17. The camera module according to claim 16, wherein the optical lens is an objective lens having a minimum back focal length of 3.6 mm.

18. A method of manufacturing an optical arrangement for a camera module with an image sensor, the method comprising: providing a transparent cover element made of a chemically strengthened glass or sapphire; producing a protective IR filter by adding an infrared absorbing cut-off filter to the cover element, the infrared absorbing cut-off filter covering a rear face of the cover element; providing a lens or lens assembly; and arranging, along an incident optical beam path going onto the image sensor, the lens assembly at a position between the protective IR filter and the image sensor, a front face of the cover element, which is opposed to the rear face, being exposed to the incident optical beam.

19. The method according to claim 18, wherein the step of producing the protective IR filter is performed by laminating or coating the cover element with the infrared absorbing cut-off filter.

20. The method according to claim 19, further comprising the step of producing the IR reflecting coating on a face of the cover element, before or after, laminating the cover element with the infrared absorbing cut-off filter.

21. The method according to claim 18, further comprising the step of producing an antireflection coating and/or an IR reflecting coating or a hybrid IR reflecting and antireflection coating on the front face of the cover element.

22. The method according to claim 18, further comprising the step of producing an antireflection coating or a hybrid IR reflecting and antireflection coating on the rear face of the infrared absorbing cut-off filter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The invention will now be described in more detail by way of exemplary embodiments and with reference to the accompanying drawings. In the drawings, the same reference numerals designate the same or corresponding elements. In the drawings,

[0047] FIG. 1 illustrates a prior art example,

[0048] FIG. 2 illustrates an optical arrangement for a camera module with an image sensor according to the invention,

[0049] FIG. 3a-3d illustrates protective IR filter embodiments with different arrangements of IR reflecting, antireflection and hybrid layers, and

[0050] FIG. 4 illustrates a camera module comprising the optical arrangement.

DETAILED DESCRIPTION

[0051] FIG. 1 shows a prior art example of a filter arrangement. Herein, the following optical components are arranged, along an incident optical beam path 20 going through the optical components onto an image sensor 16: First a transparent cover element 12.1, then a lens 14, and then an infrared absorbing cut-off filter 12.2.

[0052] In this example, a range 15 in which the lens 14 is allowed to displace for autofocus is limited by the cut-off filter 12.2. Above that, the cut-off filter 12.2 is not allowed to be thin, otherwise a desired level of IR absorption and mechanical filter strength cannot be ensured.

[0053] FIG. 2 shows an optical arrangement 10 according to the invention. The optical arrangement 10 is adapted for a camera module 22 (see FIG. 2) with an image sensor 16.

[0054] The optical arrangement 10 comprises a plurality of optical components. The optical components comprise: a) a transparent cover element 12.1, b) an infrared absorbing cut-off filter 12.2, and c) an objective lens 14 fixed in a holder 18. The optical components a), b), c) are arranged, along an incident optical beam path 20 going through the optical components 12.1, 12.2, 14 onto the image sensor 16, in a sequence a) to c).

[0055] When taking a picture of an object outside the camera module 22 with the camera module 22, the optical arrangement 10 is traversed by the incident optical beam path 20. The optical components 12.1, 12.2, 14 are aligned with the image sensor 16 in a manner that light directed to the image sensor 16 of the camera has to pass through the optical components 12.1, 12.2, 14 of the optical arrangement 10.

[0056] The infrared absorbing cut-off filter 12.2 and the cover element 12.1 are combined to a protective IR filter 12 composed of a filter film on a rear face of the cover element 12.1, the protective IR filter 12 being a two layered material formed as a laminate material. Preferably, the infrared absorbing cut-off filter 12.2 and the cover element 12.1 are cemented together. This way, the infrared absorbing cut-off filter 12.2 is effectively stabilized and a low step in refractive index is achieved at the interfaces of the elements facing each other.

[0057] As compared with the range 15 in which the lens 14 in a prior arrangement (FIG. 1) is allowed to displace for autofocus, the space 15 available for auto focus lens movement is substantially larger.

[0058] FIG. 3a-3d shows protective IR filter embodiments with different arrangements of IR reflecting, antireflection and hybrid layers. The embodiments comply each with one of the following structuring principles, wherein the protective IR filter 12 comprises:

[0059] an IR reflecting layer 12.3 which is arranged, or preferably formed as a coating, on one face of the cover element 12.1, or optionally on one face of the infrared absorbing cut-off filter 12.2, or an antireflection layer 12.4 which is arranged, or preferably formed as a coating, on one face of the cover element 12.1, or optionally on one face of the infrared absorbing cut-off filter 12.2, or a hybrid IR reflecting and antireflection layer 12.5 which is arranged, or preferably formed as a coating, on one face of the cover element 12.1, or optionally on one face of the infrared absorbing cut-off filter 12.2.

[0060] In FIG. 3a, the protective IR filter 12 comprises: an IR reflecting layer 12.3, which is arranged on the rear face of the cover element 12.1 by laminating the IR reflecting layer 12.3 with the cover element 12.1; an antireflection layer 12.4 which is arranged on the front face of the cover element 12.1 by laminating the antireflection layer 12.4 with the cover element 12.1, and an antireflection layer 12.4 which is arranged on the rear face of the infrared absorbing cut-off filter 12.2 by laminating the antireflection layer 12.4 with the antireflection layer 12.4.

[0061] In FIG. 3b, the protective IR filter 12 comprises: an antireflection layer 12.4 which is coated on the front face of the cover element 12.1, and an antireflection layer 12.4 which is coated on the rear face of the infrared absorbing cut-off filter 12.2.

[0062] In FIG. 3c, the protective IR filter 12 comprises: an IR reflecting layer 12.3, which is coated on the front face of the cover element 12.1; an antireflection layer 12.4 which is arranged on the front face of the cover element 12.1 by coating the cover element i) with the IR reflecting layer 12.3, and ii) then coating the same with the antireflection layer 12.4, and an antireflection layer 12.4 which is deposited on the rear face of the infrared absorbing cut-off filter 12.2.

[0063] In FIG. 3d, the protective IR filter 12 comprises: a hybrid IR reflecting and antireflection layer 12.5 which is coated on the front face of the cover element 12.1, and a hybrid IR reflecting and antireflection layer 12.5 which is coated on the rear face of the infrared absorbing cut-off filter 12.2.

[0064] As also shown in the exemplary embodiments of FIGS. 3a to 3d, both the cover element 12.1 and the infrared absorbing filter element 12.2 are preferably panes, or disks, respectively, having coplanar faces. Thus, the protective filter element 12 as a whole does not alter or influence the focal length of the optical assembly.

[0065] FIG. 4 shows a smart phone or tablet PC with a camera module 22, comprising the optical arrangement 10. An incident optical beam path 20 enters the optical arrangement 10 at the front face of the transparent cover element 12.1 (see also FIG. 1) and, after passing through the optical arrangement 10, it is directed to the image sensor 16 of the smartphone 22.

[0066] Manufacturing the optical arrangement 10 comprises: laminating an infrared absorbing cut-off filter 12.2 made of blue glass with a transparent cover element 12.1 made of sapphire to obtain a protective IR filter 12 with a mechanical strength which is improved as compared with the strength of a simple blue glass filter; performing antireflection (AR) and IR-cut coating, separately on both surfaces of the protective IR filter 12, thus i) improving IR-cutoff characteristics by making the IR-cutoff edge in the transmission spectrum steeper, and ii) saving costs for coating on the camera cover glass and for the holder gluing process; arranging the protective IR filter 12 in front of the lens assembly 14, thus increasing the space available for auto focus lens movement and/or decreasing the camera module 22 thickness.

[0067] Locating the protective IR filter 12 in front of the lens assembly 14 also improves the optical performance. As the distance of the filter to the image plane of the sensor is increased, defects on the filter surface are not mapped to the image plane and thus are not visible in the recorded image.

[0068] As compared with the arrangement of FIG. 2, in a prior arrangement such as that of FIG. 1, the IR-cut filter is positioned between the optical sensor and the lens assembly. Such a structure requires additional space for the IR-cut filter in the imaging system, thereby increasing the minimal back focal length. This in turn increases the thickness of the camera module 22. As well, defect on the surface of the IR-cut filter may be visible in the image, due to the spatial proximity of the IR-cut filter to the image sensor. Further, in such an assembly, the IR-cut filter can easily be broken during drop tests.

[0069] As an additional effect of the invention, the camera module may have a shorter minimum back focal length compared to state of the art camera modules used in smart phones or tablet PCs. This may be used to increase the zoom range of an objective lens being set up as a zoom objective lens. Further, the distance of the objective lens to the sensor may be smaller than in existing camera modules that employ infrared absorbing cut-off filters as a shorter back focal length may be chosen. Thus, according to one embodiment of the invention, the back focal length of the objective lens may be 3.6 mm or less. In other words, the back focal length of objective lens (minimum autofocus back focal length) can be designed shorter, for example to a range of 0.3 to 0.5 mm, which is less than a conventional range of 0.6 to 0.9 mm back focal length configured with a conventional arrangement, wherein the IR-cut filter is between objective lens and imaging sensor. In case of an objective lens having a variable back focal length, this value of 3.6 mm at the most refers to the minimum back focal length.

[0070] As compared with prior arrangements, the optical arrangement 10 of the invention has a multitude of benefits: Lower costs for coating since the optical assembly according to the invention has fewer surfaces as an assembly with the infrared filter positioned at a distance to the image sensor and between sensor and objective lens; Increased mechanical stability of the protective IR absorbing filter 12, as the filter element is supported by the cover element; Decreased thickness of the camera module 22, based on the increased room for manoeuvre for the back focal length in the objective lens design; Improved optical performance, since defects on the filter surface are not imaged to the sensor.

REFERENCE SIGNS

[0071] 10 optical arrangement [0072] 12 protective IR filter [0073] 12.1 cover element [0074] 12.2 infrared cut-off filter [0075] 12.3 IR reflecting layer [0076] 12.4 antireflection layer [0077] 12.5 hybrid antireflection and IR reflecting layer [0078] 14 objective lens [0079] 15 lens displacement range for autofocus [0080] 16 image sensor [0081] 18 lens assembly holder [0082] 20 incident optical beam path [0083] 22 camera module, smartphone