WO2016145590A1

WO2016145590A1 - Camera module comprising a nir-cut filter and method for producing the same

Info

Publication number: WO2016145590A1
Application number: PCT/CN2015/074277
Authority: WO
Inventors: Dengke HOU; Fan Chen; Ralf Biertuempfel
Original assignee: Schott Glass Technologies (Suzhou) Co., Ltd.
Priority date: 2015-03-16
Filing date: 2015-03-16
Publication date: 2016-09-22
Also published as: KR20170128347A; CN107615112A

Abstract

A camera module (1) is provided having a camera sensor (3) and an objective lens (2) for focusing light onto the camera sensor (3), the objective lens (2) comprising a composite lens (5) with a base (7) made from a filter glass (70) or a base (7) made from a glass with an infrared absorptive coating and a first lens section (9) attached to one side (71,72) of the base (7), the first lens section (9) having a curved refractive outer surface (74) and being formed from a material different to the filter glass (70), the filter glass (70) of the flat base (7) or the infrared absorbing coating absorbing near infrared radiation and thus functioning as a near infrared cut filter. It can improve camera modules with IR-cut filters so as to reduce the length of the module.

Description

Camera module comprising a NIR-cut filter and method for producing the same

Specification

Background of the invention

The invention generally concerns optical designs with IR-cutting properties. Specifically， the invention is related to optical arrangements with a NIR-filter that filters the transmitted light by absorption of infrared light.

Camera chips typically are sensitive also in the infrared spectral range. However， the materials of the optical components of camera modules such as standard glasses or plastic materials generally exhibit a certain amount of infrared transmission. If， however， infrared light reaches the chip， undesirable color and brightness distortions are caused.

For this reason， camera modules are typically equipped with infrared filters. The most common infrared filters are interference filters. For such filters， a multi-layered dielectric layer system is deposited on a substrate， typically a glass substrate. The multi-layered dielectric layer system， based on physical reasons， is designed to reflect infrared radiation， but to transmit visible light. Such filters are relatively inexpensive to produce， but have several drawbacks. Interference filters often impart a certain modulation to the transmission curve. This modulation has an effect similar to that of a comb filter and may affect individual colors.

Moreover， interference filters exhibit a much stronger dependency of the filter curve (transmission curve) from the light incident angle than optical filter glass which is also referred to as ″colored glass″or as absorption filter. Compact cameras typically have a full opening angle of up to 30° and often are not telecentrically aligned， i.e. the light rays impinge to the image sensor at a certain angle (with the full opening angle) .

US 2014/0043677 A1 discloses a lens module with an infrared-cut (IR-cut) filter that includes a substrate and an IR-cut film coated on the substrate. The IR-cut consists of thirty-two high-refractive layers and thirty-two low-refractive layers alternately stacked on the substrate， thus forming an interference filter as explained above. Transmissivity of the IR-cut film at wavelengths from about 400 nm to about 800 nm is greater than about 90％， while transmissivity of the IR-cut film at wavelengths from about 850 nmto about 1300 nm is less than about 1％.

US 2012/0261550 A 1 discloses an optical lens assembly with a filter member for image taking. Sequentially arranged from an object side to an image side along an optical axis， the assembly comprises: a filter member and a lens assembly. The lens assembly is set at the object side of the filter member. The lens assembly comprises at least three lens elements with refractive powers， wherein at least two lens elements are made of plastic， and have at least one aspheric object-side surface or image-side surface. By such arrangements， the optical lens assembly with a filter member for image taking can have good chromatic aberration correction and reduce the total length for applications to electronic products such as cameras and mobile phones requiring high resolution. An absorbing filter with a coating thereof is used to provide a good effect of absorbing lights at the infrared band to reduce the color shift effectively.

According to the above discussed prior art， the filter is a separate part within the lens assembly. However， there are several disadvantages coming along with these designs. The filter limits the focal length of adjacent lenses due to the space required for the filter. Furthermore， the filter may be fabricated from a material that is sensitive to environmental substances such as water. In this case， the filter may need to be sealed. This， e.g. ， is the case for phosphate or fluorophosphate filter glasses which corrode if subjected to water. Moreover， these glasses are quite frangible.

It is therefore an object of the invention to improve camera modules with IR-cut filters so as to reduce the length of the module. It is a further object to simplify sealing and mechanical stabilization for filters made from sensitive and/or fragile materials.

These objects are solved by the subject matter of the independent claims. Advantageous refinements and embodiments of the invention are defined in the dependent claims.

Summary of the invention

Accordingly， a camera module is provided having a camera sensor and an objective lens for focusing light onto the camera sensor. The objective lens comprises a composite lens， the composite lens being a composite with a base or substrate made from a filter glass and a first lens section attached to one side of the base. This base or substrate can also be glass with an infrared absorptive coating. The infrared absorptive coating may in particular be an organic layer and/or a layer with an organic dye. The first lens section has a curved refractive outer surface and is formed from a material different to the filter glass of the base. The filter glass of the base or the infrared absorptive coating absorbs near infrared radiation and transmits visible light and thus functions as a near infrared cut filter. The curved refractive outer surface may be spherical or aspherical， depending on the lens type.

Thus， the composite lens is formed from two elements， i.e. the lens section and the base.

The objective lens may also comprise more than one compound lens. For example， two of these lenses with the same or different filter glasses may be employed to tailor the NIR-cut properties.

In particular， the base may have two parallel sides so that it does not contribute to the optical refraction power of the composite lens. A base or substrate with no optical power is in particular achieved if the base is a flat substrate with plane parallel sides or a shell-shaped substrate. The surfaces of the shell-shaped substrate may in particular be curved in two directions so that the base is bowl-shaped. This way， the shell shape may approximately follow one or both of the refractive surfaces of the lens. This way， the base may be embedded even in comparably thin convex-concave shaped lenses. However， the most preferred embodiment of the invention utilizes a flat base made from filter glass. A flat base， i.e. a base in form of a pane is particularly simple to produce.

The thickness of the base is preferably in a range from 0.05 mm to 3 mm. Especially in mobile phones there is a strong trend to thinner designs of the whole system. Thus， according to a preferred refinement， the thickness of the base is in a range from 0.05 mm to 1 mm， particularly preferable in a range from 0.05 mm to 0.5 mm.

If the objective lens comprises two or more lenses， the composite lens may be any of the lenses within the subsequence of optical elements. Thus， the composite lens may be the foremost lens， the last lens or an intermediate lens of the lens stack forming the objective lens.

A preferred filter glass used for the flat base is a copper ions containing glass. Particularly suited are phosphate glasses. These glasses are phosphate glasses with phosphate being partly replaced by fluorine. Phosphate glasses are optical glasses in which P₂O₅ functions as a glass former and in which P₂O₅ is present in the glass composition as a major component. When replacing a portion of the phosphate in a phosphate glass by fluorine， fluorophosphate glasses are obtained.

Fluorophosphate glasses as a subcategory of phosphate glasses are suited as well for near infrared filtering. For the synthesis of fluorophosphate glasses， instead of oxide compounds such as Na02， the corresponding fluorides such as NaF are added to the glass batch.

The invention also concerns a method of producing the camera module. The method generally comprises -producing a composite lens of an objective lens for the camera module by providing a base made from a filter glass or a base made from a glass with an infrared absorptive coating， the base having two opposed sides， and producing a first lens section on one side of the base， the first lens section having a curved refractive outer surface， and being formed from a material different to the filter glass of the base， -assembling the objective lens comprising at least the composite lens and the camera sensor.

If a lens section is attached only to one side of a flat base， then， a lens with a curved and a plane surface， typically either a plano-convex or plano-concave lens is derived.

Lenses， however， with two curved refractive surfaces are preferred to gain overall refractive power particularly for small camera modules (such as camera modules for mobile phones， tablet PCs and laptops) . Thus， according to a preferred refinement of the invention， the composite lens has a second lens section attached to the side opposite to that side of said base to which the first lens section is attached. Accordingly， in this embodiment the flat base is embedded between two sections of other materials， the outer surfaces of both sections forming the refractive surfaces of the composite lens.

It is further preferred that the flat base is also optically neutral for light rays transmitting the lens with larger angles to the optical axis. To achieve this， the first lens section and the filter glass of the flat base have the same index of refraction or indices of refraction differing by an amount of 0.3， preferably 0.25， particularly preferably 0.1 at the most. Of course， the difference can be further reduced by a suitable choice of material pairings. Thus， the difference of the refractive indices may as well be 0.05 or less. Preferably， the condition of a small difference of the refractive indices also holds for a second lens section attached to the opposite side of the flat base. By using filter glasses and materials for the lens sections having the same or nearly the same refractive indices， only the outer surfaces of the composite lens are effective for refraction of the light. It is preferred to use the same material for the first and second lens sections.

Accordingly， the invention also generally concerns a composite lens for a camera module， the composite lens functioning as an infrared filter and comprising a base made from a filter glass or a base made from a glass with an infrared absorptive coating and a first lens section attached to one side of the base， the first lens section having a curved refractive outer surface and being formed from a material different to the filter glass， but has an index of refraction that differs from the index of refraction of the filter glass by 0.3 at the most， preferably 0.25 at the most， the filter glass of the base and/or the infrared absorbing coating absorbing near infrared radiation and transmitting visible light and thus imparts near infrared cutting filter properties to the lens.

Typically， an optical system for mobile phones has several lenses made from plastics. Their refractive index is very close to a NIR cut filter glass as it is used for the composite lens according to the invention. Thus， according to a preferred embodiment of the invention， the first section and/or the second section of the composite lens are made from plastics or resin， respectively.

Plastics or resin as a material for the lens sections with the curved outer refractive surfaces is also advantageous to facilitate the production of the composite lens. Specifically， the first lens section， and， if present， the second lens section attached to the opposite side of the base can be formed directly on the base by molding. Thus， according to one embodiment of the invention， the first lens section is molded to the base. Preferably， also a second lens section is molded onto the opposite side of the base. The molding process preferably also includes the step of forming the curved outer refractive surface of the lens. The flat base may be placed inside of a mold or may formapart of the mold. In the latter case， a further part of the mold comprises a curved surface to cast the curved refractive surface of the composite lens.

The refractive indices of the first and preferably also the second lens section of the compound lens preferably is in the range of 1， 49 to 1， 64. There are plastics materials available which cover the above given range of refractive indices and which are suitable to form lenses.

As regards the filter glass used for the base， the refractive index preferably lies within a range from 1.52 and 1.55. This means， the NIR-cut filter provided by the filter glass and the lens material have refractive indices close to each other， so that a small mismatch in refractive index， if any， will not have any significant effect in the compound lens design. Especially， when the filter component is just a plano-parallel plate with no curvature， then the optical effect will not be noticeable. Nevertheless an antireflection-coating on one both faces of the filter component， i.e. on the sides of the base may be advantageous to gain optimal optical performance.

According to one embodiment of the invention， the lens section (s) may be formed by molding， such as injection molding. Embossing is contemplated as another type of molding. If the lens section (s) are formed by embossing， the mold acts as a stamp.

According to a further embodiment， the lens section (s) are formed by a reflow of the material of the lens section (s) . In this case， a portion of the material for the respective lens section with a predefined shape is placed on the base. Then the portion is molten an reshapes due to its surface tension to form a lens section.

However， it is also possible to use prefabricated lens sections. The lens section is then cemented to the base to form the composite lens. This， inter alia， is helpful if materials are employed for the lens sections that are unsuited for molding.

The composite lens according to the invention is not only advantageous to enable a space saving， compact camera module. Furthermore， the arrangement with lens sections attached to a base is also particularly suited for cost-effective mass production. For this purpose， a multitude of lenses is fabricated on a flat filter glass substrate and the filter glass substrate is cut after forming the first lens sections to form the composite lenses.

Brief description of the drawings

Fig. 1 shows a camera module according to prior art.

Fig. 2 shows a camera module according to the invention.

Fig. 3 shows an embodiment of the composite lens comprising element cemented together.

Fig. 4 shows a mold for injection molding of a lens.

Fig. 5 shows a lens produced with the mold shown in Fig. 4.

Fig. 6 to Fig. 9 illustrate method steps for fabricating composite lenses of the camera module.

Fig. 10 shows a variant of Fig. 6.

Fig. 11 and Fig. 12 illustrate method steps to produce lens sections by reflow.

Fig. 13 shows an embodiment of a camera module with five lenses.

Fig. 14 shows a variant of the embodiment of Fig. 13， with a curved， shell shaped base.

Fig. 15 shows a variant of a base for a compound lens.

Detailed description of the preferred embodiments

Fig. 1 shows a typical camera module 1 as it is commonly used in mobile phones， tablet PCs， other handheld devices and notebooks. The camera module includes an objective lens 2 with

lenses

15， 16， 17， 18 anda camera sensor 3. Typically， plastics or resin is used as a material for the lenses.

Between the objective lens 2 and the camera sensor 3， a NIR-cut filter 4 is placed. This filter selectively absorbs and/or reflects light having a wavelength in the near infrared range to avoid color shifts or other unwanted optical effects. It is clear from Fig. 1 that the near-infrared cut filter 4 requires additional space. This limits miniaturization of camera modules. Furthermore， the NIR-cut filter 4 reduces light transmission of the objective lens 2 due to its reflecting surfaces.

Fig. 2 shows a camera module 1 as provided by the invention. The objective lens 2 of the camera module 1 comprises at least a first lens 15. It is preferred， however， to employ

further lenses

16， 17， 18 to correct for aberrations. So far， the optical set up is similar to the camera module 1 according to Fig. 1.

In difference to the embodiment of Fig. 1， however， the camera module 1 according to the invention lacks of a separate NIR-cut-filter 4.

Instead， lens 5 is a composite lens that includes the NIR-cut filter in form of a flat base 7 made of filter glass 70. A first lens section 9 is attached to side 71 of the flat base 7 and a second lens section 9 is attached to side 72 opposite to side 71.The outer surface of first lens section 9 is a curved refractive surface 74 which， depending on curvature focuses or defocuses light passing through the refractive surface. The second lens section 10 also has an outer refractive surface 75.

Thus， the composite lens 5 is formed from the flat base 7 and the first and

second lens sections

9， 10 in contact to the

sides

71， 72 of the flat base 7. The optical power of the first lens is determined by the

refractive surfaces

74， 75. The flat base 7 in contrast has no or nearly no influence to the optical power of the first lens 5 or the paths of the light rays passing through the objective lens 2. This is since the first and second lens sections and the filter glass 70 of the flat base 7 have the same refractive index or a refractive index difference of 0.3 at the most， particularly 0.25 at the most， preferably 0.1 at the most， particularly preferable 0.05 at the most. This way， a parallel shift of light rays passing through the flat base 7 under an angle to the optical axis is avoided. In Figs. 1 and 2， three

bundles

80， 81， 82 of light rays are shown which pass through the objective lens 2 under different angles to the optical axis. As can be seen from Fig. 2， the light rays are not refracted at the interfaces between the

sides

71， 72 and the attached

lens sections

9， 10.

As mentioned above， the first and

second lens sections

9， 10 preferably are made from plastics and have a refractive index in the range from 1.49 to 1.64. The filter glass 70 of the base 7， in particular a phosphate or florophosphate glass with copper ions preferably has a refractive index in the range from 1.52 to 1.55. Thus， by choosing appropriate pairs of plastics and filter glass， the difference in the refractive indices can be held below 0.3 so that the interfaces between the

lens sections

9， 10 and the base 7 are optically substantially neutral.

The following table lists various plastics suited to form first and

second lens sections

9， 10 and their corresponding refractive indices.

In the embodiments of Figs. 1， 2， the composite lens 5 is biconvex and thus has a positive focal length. This lens is followed by a lens 16 having a negative focal length. Preferably and as shown in the figures， lens 16 is bi-concave.

Such a doublet of subsequent lenses with a positive and a negative focal length may in particular form an achromatic lens system. In order to be effective as an achromatic lens system， the lens with negative focal length should have a smaller Abbe number than the first lens with positive focal length. The difference between the Abbe numbers of the first lens and the second lens is preferably at least 15. If the lens doublet is to have a focusing effect， the absolute value of the focal length of the second lens is smaller than the focal length of the first lens. This embodiment is preferred， especially to be able to realize short focal lengths.

Incidentally， some filter glasses are proven to be very suited for achromatic lens systems. US 2013/0265478 A1 describes a camera objective lens with an achromatic lens system. In this system comprising a focusing and a defocusing lens， the focusing lens is fabricated from a copper ion containing filter glass. The difference in the Abbe numbers of this lens system is at least 15.

In discrepancy to the invention， however， according to US 2013/0265478 A1 the entire focusing lens including its refractive surfaces is fabricated from the filter glass. According to the invention， only a part of the lens， i.e. the flat base is fabricated from a filter glass. This is advantageous in that the composite lens 5 is much easier to be fabricated. Moreover， since a flat filter glass member is employed， the thickness and hence the absorption characteristics of the NIR-cut filter does not vary in radial direction.

To provide achromatic characteristics for the lens system including the first lens 5 and the further lens 16， the material of the

lens sections

9， 10 should have an Abbe number sufficiently different to the Abbe number of lens 16.

Thus， according to an embodiment of the invention and without restriction to the specific embodiment shown in Fig. 2， the camera module 1 comprises an achromatic lens system with the composite lens 5 and a second lens 16， wherein the composite lens 5 has a positive focal length， and the second lens 16 has a negative focal length， and wherein the filter glass 70 of the base 7 of the composite lens 5 is a copper ions containing glass， and wherein the second lens 16 with negative focal length has an Abbe number that is smaller than that of first and

second lens sections

9， 10 of the first lens 5， and wherein the difference between the Abbe numbers of the first and

second lens sections

9， 10 of the composite lens 5 and the second lens 16 is at least 15.

As already explained above， there are various methods to produce the composite lens 5 according to the invention. Fig. 3 shows an embodiment where the first lens section 9 is cemented to the flat base 7 to form the composite lens 5. Accordingly， the first and

second lens sections

9， 10 are attached to the

respective sides

71， 72 of the flat base 7 by means of an optical cement 12. This embodiment is advantageous， inter alia， if the material used for the lens sections is difficult to be molded. For example， a first lens 5 as shown in Fig. 3 may comprise first and

second lens sections

9， 10 made of glass. This embodiment may for example be advantageous to fabricate a lens with particular high or low Abbe numbers for use in an achromatic lens system.

On the other hand， cementing together different parts of a lens may be difficult and less suited for mass production. In particular， plastic lenses are now common for consumer electronics products such as camera modules in mobile phones. Thus， according to another embodiment of the invention， the method step of producing first and

second lens sections

9， 10 on

sides

71， 72 of the flat base 7 comprises molding the

lens sections

9， 10.

Fig. 4 shows a mold 20 for producing the first lens 5. The mold 20 encloses a cavity 25 in which plastics is injected to form the lens. The flat base 7 made of filter glass 70 is placed within the cavity 25. To insert the flat base 7 and to extract the lens after molding， the mold of this embodiment comprises two

mold halves

21， 22 between which the cavity 25 is formed. After inserting the flat base and closing the mold， the plastics is injected via injection channels 24 to fill the cavity.

Fig. 5 shows the composite lens 5 after molding of the first and

second lens sections

9， 10 and extraction from the mold 20. As can be seen from Fig. 5， according to one embodiment of the invention， the base 7 made of filter glass 70 is embedded within plastics or resin. Thus， first and

second sections

9， 10 of the first lens 5 are sections of a plastics element that encloses the flat base 7. Preferably the base 7 is entirely enclosed by plastics. This way， the first and second lens sections are interconnected at the edge 77 of the flat base 7. The enclosure of the base 7 by a plastics element that also forms the

lens sections

9， 10 with their respective

refractive surfaces

74， 75 is advantageous to protect the filter glass 70， e.g. against corrosion.

To inject the plastics into the mold 20， the plastics may be melted. Then， the molten plastics solidifies as it cools down. According to a further embodiment of the invention， a resin is formed to a lens section (at least to the first lens section 9) in a mold and then the resin is hardened by curing. According to a refinement of this embodiment， the resin is radiation-curable and is cured and thus hardened by irradiation of light having a suitable wavelength. Preferably， a UV-curable resin is employed and hardened in the mold by irradiating UV-light. Generally， curing a resin is advantageous to create refractive surfaces of high contour accuracy as there is no shrinking induced by a cooling down of the molded material.

For example， in the embodiment shown in Fig. 4， a UV light source 27 may be used to irradiate resin inside of the cavity 25. In this embodiment， advantageously， a mold 20 that is transparent to the UV-light emitted by UV light source 27 is employed.

In the following， embodiments of the invention are described with the first lens section 9 and preferably also a second lens section 10 are formed by embossing the material of the lens section within a mold 20. Further， these embodiments are examples where a multitude of lenses is fabricated on a larger flat filter glass substrate and the filter glass substrate is cut after forming the first lens sections to form the first lenses.

Generally， without restriction to the specific embodiments as shown in the figures， the lenses of the objective lens may advantageously be provided with antireflection-coatings on their outer refractive surfaces. Thus， the embodiment of the composite lens 5 as shown in Fig. 5 has antireflection coatings 13 deposited onto its

refractive surfaces

74， 75.

Generally， although the refractive index deviation between the filter glass of the base 7 and the material of the

lens sections

9， 10 is preferably very small， an interference coating may be provided on at least one of the

sides

71， 72 of the base 7 to optimize the optical properties of the composite lens 5. Further， as it is also shown in Fig. 5， both

sides

71， 72 may have interference coatings 14 deposited thereon. For example， the interference coatings 14 may suppress reflection of near infrared spectral components if the refractive indices of the filter glass and the lens sections in this wavelength range is larger than in the visible spectral range. According to a further embodiment， the interference coating 14 may be a coating that blocks UV-light by reflection. As well， the coating may be a near-infrared reflecting coating to support the NIR-cutting function of the filter glass.

The interference coating 14 may also serve as a protective coating to prohibit corrosion of the glass due to humidity. According to a further embodiment， a protective coating may be provided on one or both

sides

71， 72 in addition to or instead of an antireflection coating 14.

Fig. 6 shows a flat filter glass substrate 6 with droplets 30 of resin 29 on one side 71 of the substrate. A mold 20 comprises cavities 25 complementary to the lens section to be formed.

Then， as shown in Fig. 7， the mold 20 is pressed onto the flat filter glass substrate 6， causing a reshape of the droplets 30 so that the cavities 25 are filled with the resin. Auxiliary cavities 26 may be provided in the mold 20 to receive excess material of the resin droplets 30.

The mold 20 is then irradiated with radiation of a suitable wavelength to cure the resin. For example， as shown in Fig. 7， a UV light source 27 may be employed whose UV-light is transmitted through mold 20. After curing， the mold can be removed as shown in Fig. 8 so that a flat filter glass 6 with a multitude of first lens sections 9 is obtained.

The procedure as described may then be repeated on the opposite side 72 of the flat filter glass substrate 6 to form second lens sections 10. The resulting processed flat filter glass substrate 6 is shown in Fig. 9. Composite lenses 5 of the camera module according to the invention may now be obtained by cutting the flat filter glass substrate 6 along predefined cutting lines 32. The sections diced from the filter glass substrate 6 then form the flat bases 7 of the composite lenses 5.

However， dicing may also be performed at a later time if assembly of the objective lens 2 and/or the camera module 1 is performed at wafer level. In this case， one or more wafers with optical components and/or a wafer with the camera sensors 3 may be stacked with the flat filter glass substrate 6 to form a compound wafer with a multitude of objective lenses 2 and/or camera modules 3.

Fig. 10 shows a variant of the embodiment of Fig. 6. According to this variant， a continuous layer 31 of resin 29 instead of separated droplets 30 is applied to side 71 of the flat filter glass substrate 6. For example， the layer 31 may be applied by spin coating. The first lens sections 9 may then formed in the same manner as already described with reference to Figs. 6 -8.

In the following， yet a further embodiment of forming the first lens sections 9 and preferably also second lens sections 10 is described with respect to Figs. 11， 12. This embodiment of the method according to the invention is based on forming the lens sections by a reflow of a portion of the lens material.

In a first step， as shown in Fig. 11， portions 34 of the material of the first lens sections 9 are placed on one side 71 of the flat filter glass substrate 6. The material of the portions 34 is then molten， e.g.， by means of a heater 36. Due to the surface tension of the material， the portions 34 reshape to form lens sections 9 as shown in Fig. 12.

The curvature of the lens sections 9 can be influenced by the shape of the portion 34. For example， the portion may be disc- cylinder-cone-or donut-shaped. All these different shapes result in different curvatures of the refractive surfaces 74 of the lens sections. For example， an elongated cylinder shaped portion placed on the flat filter glass substrate 6 with one of its end faces will produce a refractive surface with a stronger curvature in the centre， compared to a portion in the shape of a flat disc.

In the embodiment of Fig. 2， the composite lens 5 is the foremost lens of the objective lens 2. However， a composite lens 5 according to the invention may replace any other of the lenses within the objective lens 2. Fig. 13 shows an example of a camera module 1 with an objective lens 2 having five

lenses

5， 15， 16， 18， 19. Counted along the direction of the incoming light， the third lens of the objective lens is a composite lens 5 according to the invention. Furthermore， in the example of Fig. 13， the composite lens 5 is a concave-convex lens instead of a biconvex lens as in the other examples.

In all examples described so far， the base made of filter glass has the shape of a pane， i.e.， a flat substrate with plane parallel sides. Flat filter glass panes are particularly simple to produce. Moreover， the plane parallel sides 71， 72 of the base 7 will not contribute to the optical power of the composite lens 5. Thus， the refractive properties of the lens are only determined by its

refractive surfaces

74， 75. However， in some cases， it may be desirable to use a filter glass base that is shell-shaped or bowl-shaped， respectively. An example is shown in Fig. 14. The objective lens of the camera module 1 is designed similarly to the one shown in Fig. 13. However， in this case， the lens proximate to the sensor 3 is a compound lens according to the invention. The form of the

refractive surfaces

74， 75 and the thickness of the lens do not allow for embedding a flat base 7. Rather， a shell-shaped base 7 is used which in its shape approximately follows the

refractive surfaces

74， 75.

According to a further embodiment， more than one compound lens 5 with a filter glass base may be used in the objective lens. For example， the embodiments of Figs. 13 and 14 may be combined so that the third and fifth lenses of the objective lens are compound lenses according to the invention.

In the embodiments of Figs. 2 -5， the base 7 is made from a filter glass 70 that selectively absorbs near infrared light. This is a preferred type of a base to be used for the compound lens. However， alternatively， a base as schematically shown in Fig. 15 may be used. In this case， the base 7 is made from glass 76 having an infrared-absorbing coating 78 thereon. In the example of Fig. 15， the base 7 is coated on only one side 72. However， the coating 78 may as well applied to both

sides

71， 72 to increase near infrared absorption.

The invention has various advantages with respect to the prior art:

- The use of a hybrid or compound lens enables a much thinner design of the whole lens system， because the additional NIR cut filter is obsolete and the other lenses can be placed much closer to the sensor which could reduce their thickness.

- There is also one element less during assembly， although manufacture of the compound lens may be more complex.

- NIR cut filter materials are often sensitive to humidity， thus， a hybrid design adds an additional protection against humidity.

- The compound lens can be placed at different positions within the lens system.

- The shape accuracy of the filter inside the compound lens may be lower than for a single filter component. Especially， when the refractive index of the material of the lens is close to the refractive index of the filter， the shape of the volume filter has no optical effect.

- A compound lens of a filter glass and plastic lens sections has more ″thermal″stability. Shrinkage and thermal shift of the optical properties are reduced significantly. Thus， the design become more stable against temperature variations.

- Further， a compound lens has much higher mechanical strength against breakage than a single NIR-cut filter.

List of reference signs:

1 Camera module

2 Objective lens

3 Camera sensor

4 NIR-cut filter

5 composite lens

6 Filter glass substrate

7 Filter glass base

9 First lens section

10 Second lens section

12 Cement

13 Antireflex-coating

14 Interference coating

15， 16，

17， 18， 19 Lenses

20 Mold

21，22 Mold halves

24 Injection channel

25 Cavity

26 Auxiliary cavity

27 UV light source

29 Resin

30 Droplet

32 Cutting line

34 Portion of lens material

36 Heater

70 Filter glass

71， 72 Sides of filter glass base 7

74， 75 Refractive surface

76 Glass

77 Edge of 7

78 infrared absorptive coating

80， 81， 82 Light ray bundle

Claims

A camera module (1) having

-a camera sensor (3) and

-an objective lens (2) for focusing light onto said camera sensor (3) ， said objective lens (2) comprising - a composite lens (5) ， said composite lens (5) comprising a base (7) made from a filter glass (70) or a base (7) made from a glass with an infrared absorptive coating and a first lens section (9) attached to one side (71， 72) of said base (7) ， the first lens section (9) having a curved refractive outer surface (74) and being formed from a material different to said filter glass (70) ， said filter glass (70) of said flat base (7) or said infrared absorptive coating absorbing near infrared radiation and thus functioning as a near infrared cut filter.
The camera module according to claim 1， wherein said first lens (5) has a second lens section (10) attached to the side (72) opposite to the side (71) of said base (7) to which said first lens section (9) is attached.
The camera module (1) according to the preceding claim， wherein said first and second sections (9， 10) of said first lens (5) are sections of a plastics element that encloses said base (7) .
The camera module (1) according to claim 1， wherein said first lens section (9) and said filter glass of said base (7) have the same index of refraction or indices of refraction differing by an amount of 0.25 at the most.
The camera module according to claim 1， wherein said first lens section (9) is made from plastics.
The camera module according to the preceding claim， characterized in that said first lens section (9) is molded to said base (7) .
The camera module according to claim 1， wherein said first lens section (9) is cemented to said base (7) to form said first lens (5) .
The camera module according to claim 1， wherein said filter glass (50) is a phosphate glass or a fluorophosphate glass.
The camera module according to claim 1， wherein said filter glass (50) comprises copper ions.
The camera module according to claim 1， characterized in that said base (7) is a flat substrate with plane parallel sides or a shell-shaped substrate.
The camera module according to claim 1， comprising an achromatic lens system with said first lens (5) and a second lens (16) ， wherein the first lens (5) has a positive focal length， and the second lens (16) has a negative focal length， and wherein the second lens (16) with negative focal length has an Abbe number that is smaller than that of first and second lens sections (9， 10) of the first lens (5)， and wherein the difference between the Abbe numbers of the first and second lens sections (9， 10) of the first lens (5) and the second lens (16) is at least 15.
The camera module according to claim 1， characterized in that the thickness of said base (7) is in a range from 0.05 mm to 3 mm， preferably in a range from 0.05 mm to 1 mm， particularly preferred in a range from 0.05 mm to 0.5 mm.
A lens (5) for a camera module (1) ， the lens (5) functioning as an infrared filter and being a composite with a base (7) made from a filter glass (70) or a base (7) made from a glass (76) with an infrared absorptive coating (78) and a first lens section (5) attached to one side (71) of the base (7) ， the first lens section (5) having a curved refractive outer surface (74) and being formed fromamaterial different to the filter glass (70) ， but having an index of refraction that differs from the index of refraction of the filter glass (70) by 0.3 at the most， the filter glass (70) of the base (7) or the infrared absorptive coating (78) absorbing near infrared radiation and transmitting visible light and thus imparting near infrared cutting filter properties to the lens (5) .
The lens (5) according to the preceding claim， characterized in that said first lens section (9) has a refractive index in the range from 1.49 to 1.64 and said filter glass (70) of said base (7) has a refractive index in the range from 1.52 to 1.55.
The lens (5) according to claim 13， characterized in that an interference coating (14) is deposited on at least one side (71， 72) of said base (7) .
A method of producing a camera module (1) comprising - producing a composite lens (5) of an objective lens (2) for said camera module (1) by providing a base (7) made from a filter glass (70) or a base (7) made from a glass with an infrared absorptive coating and having two opposed sides (71， 72) ， and producing a first lens section (9) on one side (71， 72) of said base (7) ， the first lens section (9) having a curved refractive outer surface (74) ， and being formed from a material different to said glass (76) or filter glass (70) of said base (7) ，

-assembling the objective lens (2) comprising at least said composite lens (5) and said camera sensor (3) .
The method according to claim 16， wherein the step of producing a first lens section (9) on one side (71， 72) of said base (7) comprises molding said first lens section (9) with said curved outer refractive surface (74) .
The method according to claim 16， wherein the first lens section (9) is formed with a mold (20) .
The method according to the preceding claim， wherein the first lens section (9) is formed by injection molding or embossing.
The method according to claim 19， wherein a resin is formed to said first lens section (9) by amold (20) and then the resin is hardened by curing， in particular cured by irradiation of light.
The method according to claim 16， wherein said first lens section (9) is formed by a reflow of a portion of the material of the lens section (9) ， said portion being placed on the base (7) and being molten so that said portion reshapes due to its surface tension to form said lens section (9) .
The method according to claim 16， wherein a multitude of lenses is fabricated on a flat filter glass substrate and the filter glass substrate is cut after forming the first lens sections (9) to form the first lenses (5) .