KR100925614B1 - Liquid crystal lens having a aspherical optical properties - Google Patents

Abstract

A liquid crystal lens having aspherical optical characteristics is provided.

The present invention comprises a lower glass substrate laminated via an upper glass substrate and a spacer; A liquid crystal layer provided between the upper glass substrate and the lower glass substrate; Forming an alignment layer formed on an upper surface of the voltage driving transparent electrode layer provided on the upper surface of the lower glass substrate and an lower surface of the upper glass substrate, and an opaque electrode pattern printed by a metal material on the upper surface of the upper glass substrate; And a transparent electrode pattern formed in an opening having an internal diameter of a predetermined size formed in the opaque electrode pattern to generate a first phase difference generated when a voltage is applied in the opaque electrode pattern and a voltage in the transparent electrode pattern. By combining the second phase difference, the refractive indices in the optical axis center and the peripheral portion are formed differently.

According to the present invention, it is possible to implement an auto focusing optical system capable of miniaturization and high resolution.

Liquid crystal, liquid crystal lens, optical system, aspherical surface, auto focus, high resolution, miniaturization

Description

LIQUID CRYSTAL LENS HAVING A ASPHERICAL OPTICAL PROPERTIES}

The present invention relates to a liquid crystal lens having aspherical optical characteristics capable of realizing an auto focusing optical system capable of miniaturization and high resolution.

Generally, a camera has a plurality of lenses and is configured to adjust the optical focal length by moving each lens to change its relative distance. Recently, a mobile communication terminal equipped with a camera has been introduced to enable recording of still images and videos, and the performance of the camera is gradually being improved for high resolution and high quality shooting.

In particular, the development of a camera module for a mobile phone with various functions such as autofocus, zoom, flash, image stabilization, shutter, etc. is increasing. Among these functions, various technologies have been tried to implement autofocus and zoom functions. Currently, a voice coil actuator (VCA) or a piezo-actuator driving method is adopted as a conveying means for conveying a lens.

This driving method is a manual method, and is a method of changing the focal length between the variable lens and the image sensor by varying the position of the lens by the driving force. In contrast to this, there is an active method, and there is a method of using individual optical lenses whose focal lengths change as desired. For example, variable focus lenses using liquids and liquid crystals have been developed.

That is, in the case of the liquid crystal lens, as a variable focusing element whose focal length is changed by a change in refractive index of the liquid crystal according to voltage driving, an autofocus and zoom function may be performed in addition to the fixed focus lens module.

FIG. 1 is a schematic configuration diagram illustrating a general liquid crystal lens, in which a spacer 130 is disposed between two glass substrates 110 and 120 to form a chamber having a predetermined size, and the liquid crystal layer 113 in the chamber. It was provided.

An indium-tin oxide (ITO) transparent electrode layer 114 for voltage driving is formed on an upper surface of the lower glass substrate 120, and an upper surface of the transparent electrode layer 114 and a lower surface of the upper glass substrate 110 are formed. In the liquid crystal alignment, PI layers 115a and 115b are formed of polyimide, respectively, and an electrode pattern printed on a top surface of the upper glass substrate 110 is made of a metal material such as aluminum, chromium, and nickel. 116.

The electrode pattern 116 has an aperture area that transmits circular or elliptical light so as to serve as a stop for controlling the amount of light, and a driving voltage for driving the liquid crystal layer 113 is applied.

Accordingly, when the voltage is driven only in the range other than the aperture region through the electrode pattern 116, the potential difference P is formed to be gradient, and thus, the phase difference is generated while the orientation of the liquid crystal molecules of the liquid crystal layer 113 is controlled. It acts as a lens that collects light.

Due to the distribution of the potential difference P shown in FIG. 1, a phase difference of light occurs as shown in FIG. 2A, and the phase difference corresponds to an optical path phase difference of light, which is the same as the optical path difference of a general glass lens. You have a principle.

That is, the phase difference distribution value generated in the liquid crystal lens 100 having the liquid crystal layer 113 may correspond to a general lens shape as shown in FIG. Know the characteristics.

Here, FIG. 2 (a) is not limited to the values disclosed as data applied for explaining the operation of the liquid crystal lens, and FIG. 2 (b) is data obtained when the corresponding general lens is assumed to be a convex lens having a refractive index of 1.52. As shown in FIG. 2 (a), the liquid crystal lens having the phase difference distributed as shown in FIG. 2 (b) has the same optical characteristics as the convex spherical lens having a refractive index of 1.52 having a radius of curvature of -100 mm.

FIG. 3 is a lens layout view of an optical system in which a general liquid crystal lens is applied to a fixed focus lens module. The liquid crystal lens 100 having optical characteristics of a general spherical lens may be a fixed focus lens module to perform autofocus and zoom functions. 200) on the object side.

The thickness, size, and shape of the lens shown in FIG. 3 are exaggerated for explanation, and in particular, the shape of the liquid crystal lens shown in FIG. 3 is a state when the spherical lens corresponds to a general spherical lens. It is presented as an example only, and is not limited to this shape.

That is, the optical system includes a liquid crystal lens 100 and a fixed focus lens module 200 in which a phase difference distribution is formed in a liquid crystal layer included therein according to a voltage applied in sequence from an object side, and thus curvature changes. The fixed-focus lens module 200 includes a first lens L1 having both convex surfaces 3 and 4 convex, a negative refractive power, a flat surface of an object side surface 5, and a concave second surface 6. The lens L2 has a positive refractive power and the object side surface 7 is concave, the image side surface 8 has a convex third lens L3 and a negative refractive power, and the object side surface 9 is convex toward the object side, The image side surface 10 is provided with the concave fourth lens L4.

An aperture S for adjusting the amount of light is provided between the liquid crystal lens 100 and the fixed focus lens module 200, and an infrared filter, a cover glass, etc., between the third lens L4 and the image surface IP. An optical filter (OF) is provided, and the image surface (IP) is a photosensitive surface for receiving an image formed by a lens in a CCD sensor, a CMOS sensor, or the like.

In addition, the F number of the fixed focus lens module 200 of FIG. 3, which is presented as an example, is 2.6, the effective focal length of the optical system is 3.57 mm, the angle of view is 64 °, and the total optical system length is 4.66 mm.

Table 1 lists the values of the liquid crystal lens and the fixed focus lens module having the optical characteristics of the general spherical lens.

Here, r represents a radius of curvature of the lens surface, t represents a thickness of the lens or a distance between the lens surfaces, and n represents a refractive index. In addition, the unit of the value which shows a length is mm.

As shown in FIG. 3, when the liquid crystal lens having the optical characteristics of the general spherical lens is photographed with a 5 cm close-up of the optical system combined with the fixed focus lens caps, the MTF characteristic is as shown in FIG. 4.

Here, the MTF (Modulation Transfer Function) depends on the spatial frequency of the cycle per millimeter, and is a value defined by the following equation between the maximum intensity (Max) and the minimum intensity (Min) of light.

Here, MTF (Modulation Transfer Function) depends on the spatial frequency of the cycle per millimeter, and is a value defined by the following equation 1 between the maximum intensity (Max) and the minimum intensity (Min) of light.

In other words, when the MTF is 1, it is most ideal. The resolution decreases as the MTF value decreases.

Referring to Fig. 4, it shows the MTF change of spatial frequency per millimeter when the image height (distance from the center of the lens) is 0, and the MTF of spatial frequency per millimeter when 0.2 fields, 0.5 fields, 0.8 and 1.0 fields. Each change is shown. T represents a tangential MTF and R represents a MTF on a radiation source.

As shown in FIG. 4, the MTF characteristics measured in the optical system including the liquid crystal lens having the optical characteristics of the spherical lens are deteriorated. This is because the liquid crystal lens 100 is illustrated in FIG. 2 (b). Similarly, because of the optical characteristics of the spherical lens, aberrations are generated to lower the resolution. Accordingly, there is a problem in that it is difficult to implement an autofocus control optical system having a high pixel function by employing a liquid crystal lens having such a structure.

Accordingly, an object of the present invention is to provide a liquid crystal lens having aspherical optical characteristics capable of realizing an auto focusing optical system capable of miniaturization and high resolution.

As a specific means for achieving the above object, the present invention is a lower glass substrate laminated via an upper glass substrate and a spacer; A liquid crystal layer provided between the upper glass substrate and the lower glass substrate; Forming an alignment layer formed on an upper surface of the voltage driving transparent electrode layer provided on the upper surface of the lower glass substrate and an lower surface of the upper glass substrate, and an opaque electrode pattern printed by a metal material on the upper surface of the upper glass substrate; Including,

A first phase difference generated when a voltage is applied to the opaque electrode pattern and a second voltage generated when the voltage is applied to the transparent electrode pattern by having a transparent electrode pattern formed in an opening having a predetermined inner diameter formed on the opaque electrode pattern Provided is a liquid crystal lens having aspherical optical characteristics, characterized in that the refractive indices in the optical axis center and the peripheral portion are formed differently by synthesizing the phase difference.

Preferably, the transparent electrode pattern is provided in a disk-shaped pattern having an outer diameter size relatively smaller than the inner diameter size of the opening.

More preferably, the center of the opening coincides with the center of the transparent electrode pattern.

Preferably, different voltages are applied to the opaque electrode pattern and the transparent electrode pattern at a constant ratio.

As described above, according to the present invention, the liquid crystal lens employed in the auto focusing optical system has an aspherical optical characteristic, so that the whole optical system can be miniaturized and high resolution can be obtained. In particular, it can be applied to a micro camera module such as a camera phone.

In addition, an effect that can be applied to a camera module having a faster response speed and an optical zoom function than the conventional mechanical driving method is obtained.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

5 is a block diagram showing a liquid crystal lens having an aspherical optical characteristic according to the present invention.

According to the exemplary embodiment of the present invention, the liquid crystal lens 10 includes upper and lower glass substrates 1 and 2, a liquid crystal layer 3, an alignment layer 4a and 4b, a transparent electrode layer 5, and an opaque electrode pattern 6. And a transparent electrode pattern 7.

The upper glass substrate 1 and the lower glass substrate 2 are made of a transparent glass material having a thickness of a predetermined size, and they are stacked up and down through a spacer having a predetermined size of height.

Accordingly, a predetermined size internal space is formed between the upper and lower substrates 1 and 2 and the spacer, and the liquid crystal layer 3 having the liquid crystal molecules oriented in one direction is provided in the internal space.

In addition, a transparent electrode layer 5 made of ITO (Indium-Tin Oxide) is formed on the upper surface of the lower glass substrate 2 facing the liquid crystal layer 3 for voltage driving.

On the upper surface of the transparent electrode layer 5 and the lower surface of the upper glass substrate 110, alignment layers 4a and 4b made of polyimide are formed for liquid crystal alignment, respectively.

In addition, an upper surface of the upper glass substrate 1 is provided with an opaque electrode pattern 6 printed with metal materials such as aluminum, chromium and nickel, and the opaque electrode pattern 6 has an inner diameter of a predetermined size in a central area. In order to form an opening (6a) for exposing the upper surface of the upper glass substrate (1).

Accordingly, the opaque electrode pattern 6 serves as an aperture to remove unnecessary light while controlling the amount of light passing through the opening 6a.

On the other hand, in the opening 6a formed in the central region of the opaque electrode pattern 6, a transparent electrode pattern 7 made of indium tin oxide (ITO) is formed for voltage driving.

The transparent electrode pattern 7 is formed as a disc shaped pattern having an outer diameter size that is relatively smaller than the inner diameter size of the opening 6a, thereby forming a gap between the outer circumference of the transparent electrode pattern 7 and the inner circumference of the opening 6a. Done.

At this time, the centers of the openings 6a coincide with the centers of the transparent electrode patterns 7 that are pattern-printed in a disc shape, and the optical axis of the liquid crystal lens 1 should pass through the centers thereof.

In addition, the opaque electrode pattern 6 and the transparent electrode pattern 7 are provided on the upper surface of the upper transparent substrate 1 so that the pattern is printed to have the same height on the same plane.

In addition, the opaque electrode pattern 6 and the transparent electrode pattern 7 is preferably further provided with a transparent glass protective layer (not shown) to protect them from the external environment.

When a certain intensity voltage is applied to the opaque electrode pattern 6 and the transparent electrode layer 5 of the liquid crystal lens 1 having the above-described configuration, a voltage between the opaque electrode pattern 6 and the transparent electrode layer 6 is applied. As shown in 6 (b), it has a potential distribution having a first phase difference A, and it can be seen that this potential distribution is the same as the optical characteristic of the spherical lens generated in the structure of the conventional liquid crystal lens.

At the same time, when a voltage of a certain intensity is applied to the transparent electrode pattern 7 and the transparent electrode layer 5 from the voltage supply unit, the transparent electrode pattern 6 and the transparent electrode layer 6 are shown in FIG. 6 (b). As described above, the central portion has a potential distribution having a second phase difference A that forms a flat curve.

Accordingly, in the liquid crystal lens 1 of the present invention, the first phase difference A generated when the voltage of the opaque electrode pattern 6 is applied and the second phase difference B generated when the voltage of the opaque electrode pattern 7 is applied. As shown in FIG. 6 (a) by the synthesis of the above, it can be seen that the curvature at the optical axis center and the periphery has different aspherical optical characteristics.

In this case, the voltages applied to the opaque electrode pattern 6 and the transparent electrode pattern 7 should be supplied at a predetermined ratio with different voltage sizes.

On the other hand, the aspherical surface coefficient of the liquid crystal lens having the aspherical optical characteristics as shown in Fig. 6 (a) is the same as, but not limited to, the aspherical lens as shown in Table 2, the size of the opening and the transparent electrode pattern and the opaque electrode pattern and the transparent electrode The voltage may vary depending on the voltage applied to the pattern.

Equation 2 for the aspheric coefficient is as follows.

Z: Distance from the vertex of the lens to the optical axis direction

Y: distance in the direction perpendicular to the optical axis

c: Inverse of the radius of curvature at the vertex of the lens (1 / R)

K: Conic constant

A, B, C, D, E, F: Aspheric coefficient

In addition, the liquid crystal lens 1 having the aspherical optical characteristic is disposed in front of the object side of the fixed focus lens module 200 shown in FIG. MTF characteristics are as shown in FIG.

Here, in comparison with the MTF characteristic of FIG. 4 employing the conventional liquid crystal lens 100 having spherical optical characteristics, the MTF is most ideal when 1, and as the MTF value does not decrease, the resolution is excellent. It can be seen that the MTF characteristic of 7 shows more improved results, and thus high resolution and high quality images can be obtained.

As mentioned above, although this invention was demonstrated in detail using the preferable Example, the scope of the present invention is not limited to a specific Example and should be interpreted by the attached Claim. In addition, those skilled in the art should understand that many modifications and variations are possible without departing from the scope of the present invention.

1 is a schematic diagram illustrating a general liquid crystal lens.

2 (a) is a graph showing the optical characteristics of the liquid crystal lens.

2 (b) is a graph showing the optical characteristics of the spherical lens.

3 is a lens layout view of an imaging optical system in which a general liquid crystal lens is applied to a fixed focus lens module.

4 is a graph illustrating MTF characteristics of an optical system in which a general liquid crystal lens is applied to a fixed focus lens module.

5 is a block diagram showing a liquid crystal lens having an aspherical optical characteristic according to the present invention.

Fig. 6A is a graph showing the optical characteristics of the liquid crystal lens of the present invention.

6 (b) is a graph showing the optical characteristics formed by the opaque metal pattern and the transparent metal pattern.

FIG. 7 is a graph illustrating MTF characteristics of an imaging optical system to which a liquid crystal lens of the present invention is applied to a fixed focus lens module. FIG.

* Explanation of Signs of Major Parts of Drawings *

1: upper transparent board 2: lower transparent board

3: liquid crystal layer 5: transparent electrode layer

6: opaque metal pattern 6a: opening

7: transparent metal pattern P: potential difference

100: liquid crystal lens 200: fixed focus lens module

Claims (4)

A lower glass substrate laminated through the upper glass substrate and the spacer; A liquid crystal layer provided between the upper glass substrate and the lower glass substrate; An alignment layer formed on an upper surface of the voltage driving transparent electrode layer provided on an upper surface of the lower glass substrate and a lower surface of the upper glass substrate; An opaque electrode pattern printed on the upper surface of the upper glass substrate by a metal material; A first phase difference generated when a voltage is applied to the opaque electrode pattern and a second voltage generated when the voltage is applied to the transparent electrode pattern by having a transparent electrode pattern formed in an opening having a predetermined inner diameter formed on the opaque electrode pattern A liquid crystal lens having aspherical optical characteristics, characterized in that the refractive index is formed differently at the optical axis center and the peripheral portion by synthesizing the phase difference. The liquid crystal lens of claim 1, wherein the transparent electrode pattern has a disk-shaped pattern having an outer diameter that is relatively smaller than an inner diameter of the opening. The liquid crystal lens of claim 2, wherein the centers of the openings coincide with the centers of the transparent electrode patterns. The liquid crystal lens of claim 1, wherein different voltages are applied to the opaque electrode pattern and the transparent electrode pattern at a constant ratio.

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