WO2009096281A1 - Imaging lens, imaging device and mobile terminal - Google Patents

Abstract

This invention provides an imaging lens that prevents ghosting. For this purpose, the imaging lens comprises a lens block with a lens substrate and a lens extending from at least one of the substrate surfaces, either from the substrate surface on the object side or from the substrate surface on the imaging side and exhibiting positive power or negative power. The lens substrate comprises parallel flat plates with the substrate surfaces on the object side and on the image side of the lens substrate being flat planes. The lens block contains a lens or lenses comprising material different from that of the lens substrate and at least one of the boundaries from among the boundaries between the lens substrate and the lens or lenses comprising material which is different from that of the lens substrate is provided with an anti-reflection function.

Description

Imaging lens, imaging device, and portable terminal

The present invention relates to an imaging lens, an imaging device, and a mobile terminal.

Recently, a compact and thin imaging device is mounted on a portable terminal (for example, a mobile phone or a PDA (Personal Digital Assistant)) which is a compact and thin electronic device. Information such as audio information and image information is transmitted bidirectionally between such a portable terminal and, for example, a remote electronic device.

Examples of the imaging device used in an imaging device such as a portable terminal include solid-state imaging devices such as a CCD (Charge Coupled Device) type image sensor and a CMOS (Complementary Metal-Oxide Semiconductor) type image sensor. In recent years, resin lenses that can be mass-produced inexpensively are used as imaging lenses that form subject images on these imaging elements in order to reduce costs. In addition, when the lens is formed of resin, it can be processed easily and with high accuracy. For example, a lens having a desired aspheric surface is easily manufactured. Therefore, in the case of a high-performance imaging lens, such a resin lens has been particularly used.

Generally, an imaging lens employing an optical system including only a resin lens, and an imaging lens employing an optical system including a resin lens and a glass lens are known. However, it is difficult to achieve both ultra-compact and high productivity for these imaging lenses due to technical limitations.

As a countermeasure for overcoming such problems, the replica method is cited in Patent Document 1. The replica method is a method in which a large number of lenses (lens elements) are simultaneously formed on one lens substrate (wafer). A lens substrate (lens unit) including a plurality of lenses formed by this method is divided after being connected to a wafer-like imaging device (sensor wafer). In this way, in the divided lens unit, the imaging lens corresponding to the imaging device is called a wafer scale lens (lens block), and the module including the wafer scale lens and the imaging device is called a wafer scale camera module.

Patent Document 1 discloses an imaging lens including a wafer scale lens (an optical element having a lens connected to at least one substrate surface of a lens substrate) formed by a replica method. Similarly to Patent Document 1, Patent Document 2 discloses an imaging lens including a wafer scale lens.
JP 2006-323365 A Japanese Patent No. 3929479

However, in the imaging lenses described in Patent Documents 1 and 2, a ghost is generated due to the boundary surface between the lens and the lens substrate in the wafer scale lens. In particular, in the case of an imaging lens including a parallel plate, inter-surface reflection between the imaging element surface, cover glass, filter, and the like and the parallel plate greatly affects the imaging performance.

The present invention has been made in view of the above situation. And the objective of this invention is providing the imaging lens, imaging device, and portable terminal which prevented the ghost.

The imaging lens includes a lens block having a lens substrate and a lens that exhibits positive power or negative power connected to at least one of the object-side substrate surface and the image-side substrate surface of the lens substrate. The lens substrate is a parallel plate in which both the object-side substrate surface and the image-side substrate surface of the lens substrate are flat surfaces. In this imaging lens, the lens block includes a lens formed of a material different from that of the lens substrate, and at least one of the boundaries between the lens substrate and the lens has an antireflection function.

The boundary having an antireflection function means that, for example, an AR (Anti-Reflective) coat is coated on at least one of the lens substrate and the lens that form the boundary.

Also, the fact that the boundary has an antireflection function means that, for example, an AR (Anti-Reflective) film is interposed between the lens substrate and the lens forming the boundary.

Also, the fact that the boundary has an antireflection function means that, for example, a nano antireflection structure is interposed between the lens substrate and the lens forming the boundary.

Also, in the imaging lens, it is desirable that the following conditional expression (1) is satisfied.

| N [LS] -N [L] |> 0.01 (1)
However,
N [LS]: Refractive index of the lens substrate located on one side of the boundary having the antireflection function N [L]: Refractive index of the lens located on the other side of the boundary having the antireflection function.

In the imaging lens, it is desirable that the boundary located closest to the image side among all the boundaries between the lens substrate and the lens formed of a different material has an antireflection function.

In addition, it is desirable that the imaging lens includes at least two lens substrates.

In the imaging lens, it is desirable that the lens substrate is made of glass and the lens is made of resin.

Note that an imaging apparatus including the above imaging lens and an imaging element that captures an optical image formed by the imaging lens can also be said to be the present invention. A portable terminal including such an imaging apparatus can also be said to be the present invention.

Since the imaging lens of the present invention has an antireflection function at the boundary between the lens substrate and the lens included in the lens block, reflection of light that causes ghost is suppressed.

3 is an optical cross-sectional view of the imaging lens of Example 1. FIG. FIG. 6 is an optical cross-sectional view of the imaging lens of Example 2. 6 is an optical cross-sectional view of the imaging lens of Example 3. FIG. It is a block diagram of a portable terminal.

Explanation of symbols

BK1, BK2 Lens block L1, L2, L3, L4 Lens LS1, LS2 Lens substrate PT Parallel plane plate LN Imaging lens SR Imaging device IM Optical image (image plane)
SS light receiving surface AX optical axis LU imaging device CU portable terminal 1 signal processing unit 2 control unit 3 memory 4 operation unit 5 display unit

[Imaging device and portable terminal]
In general, the imaging lens is suitable for use in a digital device with an image input function (for example, a portable terminal). This is because a digital device including a combination of an imaging lens and an imaging element is an imaging device that optically captures an image of a subject and outputs it as an electrical signal.

The imaging device is a main component (optical device) of a camera that captures still images and moving images of a subject. For example, an imaging lens that forms an optical image of an object in order from the object (that is, subject) side, and the imaging lens And an image sensor that converts the optical image formed by the method into an electrical signal.

Examples of cameras include digital cameras, video cameras, surveillance cameras, in-vehicle cameras, and videophone cameras. Cameras are built into personal computers, mobile terminals (for example, compact and portable information device terminals such as mobile phones and mobile computers), peripheral devices (scanners, printers, etc.), and other digital devices. Or it may be externally attached.

As can be seen from these examples, not only a camera is configured by mounting an imaging apparatus, but also various devices having a camera function are configured by mounting the imaging apparatus. For example, a digital device with an image input function such as a mobile phone with a camera is configured.

FIG. 4 is a block diagram of a mobile terminal CU that is an example of a digital device with an image input function. The imaging device LU mounted on the portable terminal CU in this figure includes an imaging lens LN, a plane parallel plate PT, and an imaging element SR.

The imaging lens LN forms an optical image IM of the object. Specifically, the imaging lens LN includes, for example, a lens block BK (details will be described later), and forms an optical image IM on the light receiving surface SS of the imaging element SR. Note that the symbol IM may indicate an image plane on which an optical image is formed.

The optical image IM to be formed by the imaging lens LN passes, for example, an optical low-pass filter (parallel plane plate PT in FIG. 4) having a predetermined cutoff frequency characteristic determined by the pixel pitch of the imaging element SR. To do. By this passage, the spatial frequency characteristics are adjusted so that so-called aliasing noise that occurs when converted into an electrical signal is minimized.

And, by adjusting this spatial frequency characteristic, generation of color moire can be suppressed. However, if the performance around the resolution limit frequency is suppressed, no noise is generated even if an optical low-pass filter is not used. Further, when a user performs shooting or viewing using a display system (for example, a liquid crystal screen of a mobile phone) that is not very noticeable, an optical low-pass filter is not necessary.

The plane parallel plate PT is, for example, an optical filter such as an optical low-pass filter or an infrared cut filter disposed as necessary (the plane parallel plate PT corresponds to a cover glass or the like of the image sensor SR). There is also.)

The imaging element SR converts the optical image IM formed on the light receiving surface SS by the imaging lens LN into an electrical signal. For example, a CCD (Charge Coupled Device) type image sensor having a plurality of pixels and a CMOS (Complementary Metal-Oxide Semiconductor) type image sensor can be cited as the imaging element (solid imaging element). The imaging lens LN is positioned so as to form an optical image IM of the subject on the light receiving surface SS of the imaging element SR. Therefore, the optical image IM formed by the imaging lens LN is efficiently converted into an electrical signal by the imaging element SR.

In addition, when such an imaging device LU is mounted on a portable terminal CU with an image input function, the imaging device LU is usually arranged inside the body of the portable terminal CU. However, when the mobile terminal CU exhibits the camera function, the imaging device LU takes a form as necessary. For example, the unitized imaging device LU may be detachable or rotatable with respect to the main body of the mobile terminal CU.

Incidentally, the mobile terminal CU includes a signal processing unit 1, a control unit 2, a memory 3, an operation unit 4, and a display unit 5 in addition to the imaging device LU.

The signal processing unit 1 performs predetermined digital image processing, image compression processing, and the like on the signal generated by the image sensor SR as necessary. The processed signal is recorded as a digital video signal in the memory 3 (semiconductor memory, optical disc, etc.), or converted into an infrared signal via a cable and transmitted to another device.

The control unit 2 is a microcomputer and performs function control such as a photographing function and an image reproduction function, that is, control of a lens moving mechanism for focusing. For example, the control unit 2 controls the imaging device LU so as to perform at least one of still image shooting and moving image shooting of a subject.

The memory 3 stores, for example, a signal generated by the image sensor SR and processed by the signal processing unit 1.

The operation unit 4 is a part including operation members such as an operation button (for example, a release button) and an operation dial (for example, a shooting mode dial), and transmits information input by the operator to the control unit 2.

The display unit 5 includes a display such as a liquid crystal monitor, and displays an image using an image signal converted by the image sensor SR or image information recorded in the memory 3.

[About imaging lens]
Here, the imaging lens LN will be described in detail. The imaging lens LN includes a lens block BK in which a plurality of optical elements are connected (see FIGS. 1 to 3 described later). The lens block BK, for example, connects the lens L to at least one of the two surfaces (object-side substrate surface and image-side substrate surface) facing each other on the lens substrate LS (note that the lens L is Show positive or negative power).

Note that “continuous” means that the substrate surface of the lens substrate LS and the lens surface of the lens L are in a directly bonded state, or the substrate surface of the lens substrate LS and the lens surface of the lens L are interposed via separate members. It means in an indirect bonding state.

[Lens configuration related to imaging lens]
Next, the lens configuration related to the imaging lens LN of Examples 1 to 3 will be described using the optical cross-sectional views of FIGS. 1 to 3 corresponding to Examples 1 to 3, respectively. The following lens substrate is a parallel plate, and both the object-side substrate surface and the image-side substrate surface are flat. Nd is the refractive index of the medium with respect to the d-line (wavelength 587.56 nm), and νd is the Abbe number of the medium with respect to the d-line.

Also, the symbols in the optical cross-sectional view etc. are as follows.

Li: i-th lens L
LSi: i-th lens substrate LS
BKi: i-th lens block BK
Si: i-th lens surface or lens substrate surface i: number given to "Li", etc., in order from the object side to the image side in each member *: the lens surface The surface attached to the right side of the reference numeral is an aspherical surface.

AA: Position of a member having an antireflection function (It is preferable that an AR coat, an AR film, and a film including a nano antireflection structure, which will be described later, exist at the position indicated by AA.)
AX: optical axis [Example 1]
FIG. 1 shows one lens block BK in the imaging lens LN, more specifically, the first lens block BK1 positioned closest to the object side.

The first lens block BK1 includes a first lens substrate LS1. The first lens L1 is connected to the object side substrate surface of the first lens substrate LS1, and the second lens L2 is connected to the image side substrate surface of the first lens substrate LS1. Specifically, the first lens L1, the first lens substrate LS1, and the second lens L2 are as follows.

First lens L1: Plano-convex lens convex on the object side (nd = 1.52, νd = 57, the object-side surface s1 is aspherical, and the first lens L1 is made of resin)
First lens substrate LS1: Parallel flat plate (nd = 1.47, νd = 56. The first lens substrate LS1 is made of glass.)
Second lens L2: concave concave lens on the image side (nd = 1.52, νd = 57, the image side surface s6 is aspherical, and the second lens L2 is made of resin)
Note that the boundary between the first lens L1 and the first lens substrate LS1 and the boundary between the first lens substrate LS1 and the second lens L2 are positions of members having an antireflection function.

[Example 2]
FIG. 2 shows one lens block BK in the imaging lens LN, more specifically, the first lens block BK1 located closest to the object side as in FIG.

The first lens block BK1 includes a first lens substrate LS1. The first lens L1 is continuous only with the object side substrate surface of the first lens substrate LS1. Specifically, the first lens L1 and the first lens substrate LS1 are as follows.

First lens L1: Plano-convex lens convex on the object side (nd = 1.50, νd = 41, the object-side surface s1 is aspherical, and the first lens L1 is made of resin)
First lens substrate LS1: Parallel flat plate (nd = 1.84, νd = 43. The first lens substrate LS1 is made of glass.)
Note that the boundary between the first lens L1 and the first lens substrate LS1 is the position of a member having an antireflection function.

[Example 3]
FIG. 3 shows the first lens block BK1 and the second lens block BK2 that are the imaging lens LN, and further the imaging element SR. Note that the light-receiving surface (imaging surface) of the imaging element SR also has a surface code “ Add s13 "}.

The first lens block BK1 includes a first lens substrate LS1. The first lens L1 is connected to the object side substrate surface of the first lens substrate LS1, and the second lens L2 is connected to the image side substrate surface of the first lens substrate LS1. Specifically, the first lens L1, the first lens substrate LS1, and the second lens L2 are as follows.

First lens L1: Plano-convex lens convex on the object side (nd = 1.51, νd = 54, the object-side surface s1 is aspherical, and the first lens L1 is made of resin)
First lens substrate LS1: Parallel flat plate (nd = 1.65, νd = 30. The first lens substrate LS1 is made of glass.)
Second lens L2: Plano-concave lens that is concave on the image side (nd = 1.57, νd = 29, the image-side surface s6 is aspherical, and the second lens L2 is made of resin)
The first lens block BK1 does not include a member having an antireflection function.

The second lens block BK2 includes a second lens substrate LS2. The third lens L3 is connected to the object side substrate surface of the second lens substrate LS2, and the fourth lens L4 is connected to the image side substrate surface of the second lens substrate LS2. More specifically, the third lens L3, the second lens substrate LS2, and the fourth lens L4 are as follows.

Third lens L3: concave concave object side (nd = 1.51, νd = 54, the object side surface s7 is aspherical, and the third lens L3 is made of resin)
Second lens substrate LS2: parallel flat plate (nd = 1.65, νd = 30. The second lens substrate LS2 is made of glass).
Fourth lens L4: Plano-concave lens that is concave on the image side (nd = 1.51, νd = 54, the image-side surface s12 is aspherical, and the fourth lens L4 is made of resin)
Note that the boundary between the second lens substrate LS2 and the fourth lens L4 is the position of a member having an antireflection function.

[Details of imaging lens]
The imaging lens LN includes a lens block BK. The lens substrate LS and the lens L in the lens block BK are formed of different materials. In this case, the choice of materials increases, and for example, a material that can be easily processed or an inexpensive material can be selected, and the cost of the imaging lens LN is reduced.

However, at the boundary between the lens substrate LS and the lens L with different lens block materials (especially refractive index) (AA portion in the figure), reflection of ghost light is likely to occur. In particular, since the lens substrate LS uses a parallel plate substrate, a ghost is easily generated due to reflection on a plane. Therefore, at least one of the boundaries between the lens substrate LS and the lens in the imaging lens LN has an antireflection function. When the antireflection function is provided at the boundary in this way, even if there is a difference in refractive index at the boundary between the lens substrate LS and the lens L, reflection of light is effectively suppressed, and ghost is less likely to occur. As a result, the imaging lens LN has high performance.

In addition, as an example having an antireflection function, it is possible to coat an AR (Anti-Reflective) coat on at least one of the substrate surface of the lens substrate LS and the lens surface of the lens L that form a boundary (required) , An AR coating film is formed).

Such AR coating is performed using a coating technique that is normally performed on the lens L or the like. For example, vacuum deposition methods such as ion plating and sputtering are used. Therefore, no special device or the like is required to provide an antireflection function at the boundary between the lens substrate LS and the lens L in the lens block BK. Therefore, the cost (equipment investment etc.) for manufacturing such an imaging lens LN can be suppressed.

In addition to the AR coating, for example, an AR film may be interposed between the lens substrate LS and the lens L forming the boundary.

Such an AR film is produced in large quantities by, for example, a batch type film forming technique and a roll-to-roll type film forming technique. Therefore, if such an AR film is used, the cost of the imaging lens LN is reduced. In addition, the AR film can have not only an antireflection function but also other functions such as an anti-electricity prevention function. Therefore, the imaging lens LN using such a multifunctional AR film has a function of preventing adhesion of dust and the like and is multifunctional.

In addition, as an example of the above AR film, the film which carried out AR coating on the surface of a polyethylene terephthalate (PET) film is mentioned.

In addition to the AR coating and AR film, a nano antireflection structure may be interposed between the lens substrate forming the boundary and the lens.

The nano-reflective structure does not reflect incident light by continuously changing the refractive index in the thickness direction by regularly concentrating protrusions of the wavelength of transmitted light or less on the surface of the film or lens. For example, in the case of a moth-eye type non-reflective film that is an example of a film including a nano-reflection preventing structure, the amount of reflected light that can be suppressed by a general AR film can be further reduced to about 1/20. Therefore, even with such a nano-reflection preventing structure, ghost in the imaging lens LN is suppressed as in the AR coating and the AR film.

In the imaging lens LN, it is preferable that the following conditional expression (1) is satisfied. Conditional expression (1) defines the difference in absolute value between the refractive index of the lens substrate LS located on one side and the refractive index of the lens L located on the other side, with the boundary having the antireflection function as a boundary. .

| N [LS] -N [L] |> 0.01 (1)
However,
N [LS]: Refractive index of the lens substrate located on one side of the boundary having the antireflection function N [L]: Refractive index of the lens located on the other side of the boundary having the antireflection function.

If the value of the conditional expression (1) exceeds the lower limit value, optical elements (lens substrate LS / lens L) having a relatively large refractive index difference are arranged at the boundary having the antireflection function. Then, for example, chromatic aberration caused by the difference in wavelength of light passing through the lens substrate LS and the lens L is corrected using the refractive index difference. Therefore, such an imaging lens LN suppresses ghost while suppressing aberration.

Also, if the aberration can be efficiently corrected by the difference in refractive index between the optical elements, the number of other optical elements responsible for the aberration correction may be small. For this reason, the entire length of the imaging lens LN tends to be short. In order to satisfy this conditional expression (1), the entire length of the imaging lens LN can be suppressed if the lens substrate LS has a high refractive index. On the other hand, in order to satisfy the conditional expression (1), if the lens L has a high refractive index, the curvature of the lens L may be weakened, so the requirement for the surface accuracy of the lens L is low. . Therefore, processing of the lens L is simplified.

In particular, in the imaging lens LN, it is more preferable that the following conditional expression (1a) and further conditional expression (1b) are satisfied than conditional expression (1). With this configuration, the imaging lens LN is more likely to have a high aberration correction function.

| N [LS] -N [L] |> 0.1 (1a)
| N [LS] -N [L] |> 0.15 (1b)
The values of | N [LS] −N [L] | in Examples 1 to 3 are as follows. Therefore, the boundary between the following optical elements is a position having an antireflection function.

Example 1
Refractive index difference between the first lens L1 and the first substrate LS1: 0.05
Refractive index difference between the first lens substrate LS1 and the second lens L2: 0.05
Example 2
Refractive index difference between the first lens L1 and the first substrate LS1: 0.34
Example 3
Refractive index difference between the second lens substrate LS2 and the fourth lens L4: 0.14
By the way, it is desirable that the boundary having the antireflection function is located closest to the image side among all the boundaries in the imaging lens LN.

Normally, the light converges and reaches the image sensor SR. And if light reflects in the vicinity of this image pick-up element SR and reaches | attains an image pick-up element again, a ghost (a kind of flare) will be conspicuous. In particular, when the light is reflected by the parallel plate and the reflected light reaches the image pickup device, the light does not diverge and is conspicuous. Therefore, when the boundary having the antireflection function is the boundary facing the lens substrate LS located closest to the image side, that is, the most image side, the ghost in the imaging lens LN can be efficiently suppressed.

Further, there is a ghost that is generated by reflecting twice inside the imaging device LN. Such a ghost is likely to occur with a probability proportional to the factorial as the boundary surface of the optical element (for example, the boundary surface between the lens substrate LS and the lens L) increases. For example, the occurrence probability of a ghost in an imaging lens LN including two lens substrates LS is six times the probability of occurrence of a ghost in an imaging lens LN including only one lens substrate LS (actually, the lens L Since the reflection occurs between the lens substrate LS and the lens substrate LS, the ghost occurrence probability is further increased.

However, even if the imaging lens LN includes two or more lens substrates LS, the occurrence of ghost is suppressed if at least one boundary having an antireflection function is included. Conversely, it can be said that the ghost suppression effect brought about by the boundary having the antireflection function is more effective only in the imaging lens LN including two or more such lens substrates LS.

Further, the lens substrate LS in the imaging lens LN is a parallel plate having both the object side substrate surface and the image side substrate surface as planes.

In this case, the boundary surface between the lens substrate LS and the lens L does not have power. For this reason, for example, the surface accuracy of the lens substrate LS on the substrate surface hardly affects the focus position on the image surface of the imaging lens LN. Therefore, the imaging lens LN has high performance.

In addition, when the lens substrate LS is a parallel plate, not only processing for the lens substrate LS is simplified or unnecessary in the manufacturing process of the imaging lens LN, but also the lens L is easily formed on a flat surface. Therefore, the parallel flat lens substrate LS reduces the manufacturing burden of the imaging lens LN.

The lens substrate LS in the imaging lens LN is preferably made of glass, and the lens L is preferably made of resin.

The fact that the lens substrate is made of glass increases the choice of materials other than resin. Further, when the lens is formed of resin, the lens L having an aspherical lens surface is easily formed (for example, it is easily manufactured by molding or the like). Therefore, the manufacturing burden of the imaging lens LN is reduced, which leads to cost reduction of the imaging lens LN.

Also, examples of the resin include an ultraviolet curable resin and a thermosetting resin. And in the case of thermosetting resin, even if the lens L is comparatively thick, it is manufactured with high accuracy. In the case of an ultraviolet curable resin, the lens L is manufactured in a short time because it is cured in a relatively short time. That is, if it is resin, it can respond to various manufacturing methods.

Claims (10)

A lens block having a lens substrate and a lens that exhibits positive power or negative power connected to at least one of the object-side substrate surface and the image-side substrate surface of the lens substrate;
The lens substrate is a parallel plate in which both the object side substrate surface and the image side substrate surface of the lens substrate are planes,
The lens block includes the lens formed of a material different from the lens substrate,
An imaging lens in which at least one of the boundaries with the lens formed of a material different from that of the lens substrate has an antireflection function. The range 1 according to claim 1, wherein the boundary has an antireflection function is that at least one of the lens substrate and the lens forming the boundary is coated with an AR (Anti-Reflective) coat. The imaging lens described. 2. The imaging according to claim 1, wherein the boundary has an antireflection function is that an AR (Anti-Reflective) film is interposed between the lens substrate and the lens forming the boundary. lens. The imaging lens according to claim 1, wherein that the boundary has an antireflection function is that a nano antireflection structure is interposed between the lens substrate and the lens forming the boundary. The imaging lens according to any one of claims 1 to 4, wherein the following conditional expression (1) is satisfied.
| N [LS] -N [L] |> 0.01 (1)
However,
N [LS]: Refractive index of the lens substrate located on one side of the boundary having the antireflection function N [L]: Refractive index of the lens located on the other side of the boundary having the antireflection function The boundary located at the most image side among all the boundaries between the lens formed of a material different from that of the lens substrate has any one of the antireflection functions. The imaging lens described in 1. The imaging lens according to any one of claims 1 to 6, wherein at least two of the lens substrates are included. The lens substrate is formed of glass,
The imaging lens according to any one of claims 1 to 7, wherein the lens is formed of a resin. The imaging lens according to any one of claims 1 to 8,
An image sensor that captures an optical image formed by the imaging lens;
An imaging apparatus including: A portable terminal including the imaging device according to claim 9.

Images