Patent Description:
<CIT> disclose an optical system according to the preamble of claim <NUM>.

<CIT> discloses an optical imaging system including four lenses. The first lens has negative power, the second lens has positive power or negative power; the third lens has positive power or negative power, and the image side is concave. The fourth lens has positive power. The image side is concave.

<CIT> discloses an optical lens assembly, which includes four lens elements. The four lens elements are, in order from an outside to an inside, a first lens element, a second lens element, a third lens element and a fourth lens element. The first lens element has an outside surface being convex in a paraxial region thereof. The second lens element has an inside surface being convex in a paraxial region thereof. The fourth lens element has an inside surface being concave in a paraxial region thereof.

<CIT> discloses an optical lens assembly, which includes four lens elements.

<CIT> A discloses a camera lens which includes a first lens with positive refractive power, a second lens with negative refractive power; a third lens with positive refractive power, a fourth lens with negative refractive power, which are arranged sequentially from an object side.

<CIT> discloses an imaging lens, which includes in order from its object side, a stop and four single lenses. The imaging lens comprises, from its image side a first lens being positive and convex towards the object, a second lens being a negative meniscus being concave on the image side, a third lens being positive and convex on the image side and a fourth lens being negative and concave on the image side.

<CIT> discloses a method of generating a depth image in a 3D image acquisition apparatus.

<CIT> discloses an image capturing lens system, in order from an object side to an image side comprising: a first lens element with positive refractive power having a convex object-side surface and a concave image-side surface; a second lens element with positive refractive power; a third lens element with positive refractive power; and a fourth lens element with positive refractive power having a convex object-side surface, a concave at a paraxial region and convex at a peripheral region image-side surface.

<CIT> discloses a technology for obtaining a 3D image using a photographing device. The technology includes a first lens group including a first lens and a second lens, and a second lens group including a third to a fifth lens, which are sequentially arranged from an object side to an image side. The first lens has negative refractive power, the second lens has positive refractive power, and the third to fifth lenses have positive refractive power.

<CIT> discloses an optical photographing lens system comprising four lens elements, the four lens elements being, in order from an object side to an image side a first lens element with positive refractive power having an object-side surface being convex in a paraxial region thereof, a second lens element, a third lens element, and a fourth lens element with positive refractive power having an object-side surface being convex in a paraxial region thereof and an image-side surface being concave in a paraxial region thereof, the image-side surface of the fourth lens element having one convex critical point in an offaxial region thereof, both the object-side and the image-side surfaces thereof being aspheric.

Three-dimensional (3D) contents have been applied to not only games and cultural fields but also a variety of fields such as education, manufacturing, autonomous driving, and the like, and a depth map is necessary for obtaining 3D contents. The depth map is information indicating a distance on space and indicates perspective information of another point with respect to one point in a two-dimensional (2D) image.

As a method of obtaining the depth map, a method of projecting infrared (IR) structured light toward an object, a method using a stereo camera, a time of flight (ToF) method, and the like have been used. According to the ToF method, a distance to an object is calculated by measuring the time of flight, that is, the time taken for light to be emitted and returned by being reflected. The biggest advantage of the ToF method is that a distance information (map) on a 3D space is quickly provided in real time. In addition, an accurate distance information (map) may be obtained even when a user does not apply a separate algorithm or perform a hardware correction. In addition, an accurate depth map may be obtained even when measuring a subject that is very close or measuring a moving subject.

Meanwhile, as the technology of a portable terminal and a camera embedded therein is developed, there is an attempt to embed a camera module having a ToF function even in the portable terminal, but due to the restriction of design in the portable terminal, it is difficult to obtain high-resolution optical performance while satisfying a small thickness, low power consumption, and light weight.

The present invention is directed to providing an optical system and a camera module including the same.

The invention further refers to a camera module as defined in claim <NUM>.

According to an embodiment of the present invention, it is possible to provide an optical system and a camera module that can realize small size and high resolution even in a low-illuminance environment. The camera module according to the embodiment of the present invention can be applied to realize a time of flight (ToF) function.

The first and fifth embodiments are embodiments according to the claimed subject-matter, while the second, third and fourth embodiments are not embodiments according to the claimed subject-matter.

In addition, unless clearly and expressly defined herein, the terms (including technical and scientific terms) used in the embodiments of the present invention have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. It should be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the related art.

Further, the terms used in the embodiments of the present invention are provided only to describe embodiments of the present invention and not for purposes of limitation.

In the present specification, the singular forms include the plural forms unless the context clearly indicates otherwise, and the phrase "at least one element (or one or more elements) of an element A, an element B, and an element C," should be understood as including the meaning of at least one of all combinations being obtained by combining the element A, the element B, and the element C.

Further, in describing elements of the embodiments of the present invention, the terms such as first, second, A, B, (a), (b), and the like may be used.

These terms are merely for distinguishing one element from another element, and the property, order, sequence, and the like of corresponding elements are not limited by the terms.

In addition, it will be understood that when one element is referred to as being "connected" or "coupled" to another element, the element may not only be directly connected or coupled to another element but may also be connected or coupled to another element through the other element presented between one element and another element.

Further, when one element is referred to as being formed or disposed "on (above)" or "under (below)" another element, the terms "on (above)" or "under (below)" includes both of a case in which the two elements are in direct contact with each other or a case in which one or more elements are (indirectly) formed or disposed between the two elements. In addition, the term "on (above)" or "under (below)" includes a case in which another element is disposed in an upward direction or a downward direction with respect to one element.

An optical system according to the present invention includes a first lens, a second lens, a third lens, and a fourth lens that are sequentially arranged from an object side to an image side, and has an F value of <NUM> or less and a ratio (total top length (TTL)/F value) of a TTL to the F value of <NUM> to <NUM>. In addition, the first lens and the third lens each have a positive power, and the fourth lens has a negative power. The power of each lens may be represented by the reciprocal of a focal length of each lens. Such an optical system may have excellent imaging performance, may correct chromatic aberration, and may also correct distortion well, even in a low-illuminance environment.

Meanwhile, the optical system according to the embodiment of the present invention may have a ratio (F3/F <NUM>) of a focal length F3 of the third lens to a focal length F1 of the first lens of <NUM> to <NUM>. Accordingly, the optical system may be miniaturized, chromatic aberration may be well maintained, and distortion may be well corrected.

Further, in the optical system according to the embodiment of the present invention, among a first distance between an image-side surface of the first lens and an object-side surface of the second lens, a second distance between an image-side surface of the second lens and an object-side surface of the third lens, and a third distance between an image-side surface of the third lens and an object-side surface of the fourth lens, the third distance may be the shortest. The third distance is formed to be the shortest by designing the image-side surface of the third lens in a convex shape and the object-side surface of the fourth lens in a convex shape. Accordingly, the TTL of the optical system may be reduced and the resolution thereof may be improved. In addition, among a first refractive index of the first lens, a second refractive index of the second lens, a third refractive index of the third lens, and a fourth refractive index of the fourth lens, the third refractive index may be the highest. Accordingly, the sensitivity of the third lens may be reduced and thus the manufacturing tolerance may be increased when the third lens is manufactured.

<FIG> is a cross-sectional view of an optical system according to a first embodiment of the present invention. Table <NUM> illustrates optical characteristics of four lenses according to the first embodiment. In the first embodiment, a total effective focal length (EFL) is <NUM>, a TTL is <NUM>, and an F value is <NUM>. Tables <NUM> and <NUM> illustrate conic constants and aspheric coefficients for each lens constituting the optical system according to the first embodiment.

Referring to <FIG>, an optical system <NUM> includes a first lens <NUM>, a second lens <NUM>, a third lens <NUM>, and a fourth lens <NUM> that are sequentially arranged from an object side to an image side. A filter <NUM> may be disposed above an image sensor <NUM>, and the optical system <NUM> may be disposed above the filter <NUM>.

Light reflected from the object sequentially passes through the first to fourth lenses <NUM> to <NUM> of the optical system <NUM> and the filter <NUM> and is then received by the image sensor <NUM>.

The filter <NUM> may be an infrared (IR) filter. The filter <NUM> may filter out near-IR (NIR) light, for example, light with a wavelength of <NUM> to <NUM>, from light incident on the camera module. In addition, the image sensor <NUM> may be connected to a printed circuit board through wires.

The optical system <NUM> according to the first embodiment of the present invention has an F value of <NUM> or less, and has a ratio (TTL/F value) of a TTL to the F value of <NUM> to <NUM>. For example, the optical system <NUM> according to the first embodiment may have an F value of <NUM>, a TTL of <NUM>, and a ratio (TTL/F value) of <NUM>.

Here, the F value may refer to a ratio (F/D) of a focal length F of the lens to an effective diameter D of an aperture. Accordingly, the smaller the F value, the greater the diameter of the aperture and the diameter of the lens and the larger the amount of light collected. On the contrary, the greater the F value, the smaller the diameter of the aperture and the diameter of the lens and the smaller the amount of light collected.

The TTL refers to a distance from the image sensor <NUM> on which an image is formed to the first surface of the optical system <NUM>. Here, the TTL may refer to a distance from the image sensor <NUM> on which the image is formed to an object-side surface <NUM> of the first lens <NUM>.

When the ratio (TTL/F value) is less than <NUM>, the optical system may be difficult to configure or may be degraded in performance and thus may be difficult to apply in a low-illuminance environment, and when the ratio (TTL/F value) exceeds <NUM>, the optical system may be difficult to apply to a portable terminal due to an increase in size.

In the optical system <NUM> according to the first embodiment of the present invention, the first lens <NUM> has a positive (+) power. Accordingly, the first lens <NUM> may provide a part of the refractive power required by the optical system <NUM>. The object-side surface <NUM> of the first lens <NUM> is convex and an image-side surface <NUM> thereof is concave. That is, the first lens <NUM> may have a meniscus shape. Since the object-side surface <NUM> of the first lens <NUM> is convex, the refractive power of the first lens <NUM> may be enhanced. Since the image-side surface <NUM> of the first lens <NUM> is concave, the dispersion force of light may be increased to improve resolution.

In the optical system <NUM> according to the first embodiment of the present invention, the second lens <NUM> has a negative (-) power, an object-side surface <NUM> of the second lens <NUM> is concave, and an image-side surface <NUM> of the second lens <NUM> is concave.

As described above, the second lens <NUM> may have a biconcave shape.

In the optical system <NUM> according to the first embodiment of the present invention, the third lens <NUM> has a positive (+) power, an object-side surface <NUM> of the third lens <NUM> is concave, and an image-side surface <NUM> of the third lens <NUM> is convex. As described above, the third lens <NUM> may have a meniscus shape, and at least one of the object-side surface <NUM> and the image-side surface <NUM> of the third lens <NUM> may include at least one inflection point. Here, the thickness of the third lens <NUM> may be greater than the thickness of the second lens <NUM>.

In the optical system <NUM> according to the first embodiment of the present invention, the fourth lens <NUM> has a negative (-) power, an object-side surface <NUM> of the fourth lens <NUM> is convex, and an image-side surface <NUM> of the fourth lens <NUM> is concave. In addition, in the fourth lens <NUM>, the absolute value of a radius of curvature of the object-side surface <NUM> may be greater than the absolute value of a radius of curvature of the image-side surface <NUM>. Here, at least one of the object-side surface <NUM> and the image-side surface <NUM> of the fourth lens <NUM> may include at least one inflection point at a position other than the intersection with an optical axis. Here, the inflection point refers to a point on an aspherical surface in which a tangent plane of an aspherical vertex is perpendicular to an optical axis in a curve of a lens cross-sectional shape within an effective radius. Accordingly, the maximum emergence angle of key light received by the image sensor <NUM> may be adjusted so that a phenomenon in which a peripheral portion of a screen is darkened may be prevented.

At least one of the first to fourth lenses <NUM> to <NUM> may be made of a plastic material. Accordingly, the optical system that is lightweight and inexpensive to manufacture may be realized.

Meanwhile, an aperture (not shown) may be further disposed between the first lens <NUM> and the second lens <NUM>. The aperture is provided to control a focal length by selectively receiving incident light.

Here, a focal length F1 of the first lens <NUM> may be in a range of <NUM> to <NUM>. When the focal length F1 of the first lens <NUM> is less than <NUM>, it may be difficult to manufacture the lens due to the increased lens sensitivity, and when the focal length F1 of the first lens <NUM> exceeds <NUM>, it may be difficult to correct aberration due to lack of lens refractivity. In addition, the absolute value of a focal length of the third lens <NUM> may be greater than the absolute value of a focal length of the second lens <NUM>. When the absolute value of the focal length of the third lens <NUM> is equal to or less than the absolute value of the focal length of the second lens <NUM>, the ratio of lens refractivity may not be maintained, and thus it may be difficult to adjust resolution.

A ratio (F3/F1) of a focal length F3 of the third lens <NUM> to the focal length F1 of the first lens <NUM> may be in a range of <NUM> to <NUM>. For example, in the first embodiment, the ratio (F3/F1) of the focal length F3 of the third lens <NUM> to the focal length F1 of the first lens <NUM> may be <NUM>. When the ratio (F3/F1) of the focal length F3 of the third lens <NUM> to the focal length F1 of the first lens <NUM> is less than <NUM>, the overall size of the optical system <NUM> may be increased, and when the ratio (F3/F1) exceeds <NUM>, resolution may be lowered.

Further, when a distance between the image-side surface <NUM> of the first lens <NUM> and the object-side surface <NUM> of the second lens <NUM> is referred to as a first distance, when a distance between the image-side surface <NUM> of the second lens <NUM> and the object-side surface <NUM> of the third lens <NUM> is referred to as a second distance, and when a distance between the image-side surface <NUM> of the third lens <NUM> and the object-side surface <NUM> of the fourth lens <NUM> is referred to as a third distance, the third distance may be less than <NUM>, and the third distance among the first distance, the second distance, and the third distance may be the shortest. That is, referring to Table <NUM>, the third distance is <NUM> and may be less than the first distance and the second distance.

Further, among a first refractive index of the first lens <NUM>, a second refractive index of the second lens <NUM>, a third refractive index of the third lens <NUM>, and a fourth refractive index of the fourth lens <NUM>, the third refractive index may be the highest. That is, referring to Table <NUM>, it may be seen that an index constant of the third lens <NUM> is <NUM> and the third lens <NUM> has the highest refractive index together with the fourth lens <NUM>.

Here, the thickness (mm) represents the distance from each lens surface to a lens surface next to each lens surface. That is, the thickness described on the obj ect-side surface <NUM> of the first lens <NUM> represents the distance from the obj ect-side surface <NUM> to the image-side surface <NUM> of the first lens <NUM>. In addition, the thickness described on the image-side surface <NUM> of the first lens <NUM> represents the distance from the image-side surface <NUM> of the first lens <NUM> to the object-side surface <NUM> of the second lens <NUM>.

The index constant refers to the refractive index of the lens measured using a d-line.

<FIG> is a cross-sectional view of an optical system according to a second embodiment which is not an embodiment according to the claimed subject-matter. Table <NUM> illustrates optical characteristics of four lenses according to the second embodiment. In the second embodiment, a total EFL is <NUM>, a TTL is <NUM>, and an F value is <NUM>. Tables <NUM> and <NUM> illustrate conic constants and aspheric coefficients for each lens constituting the optical system according to the second embodiment. Duplicate descriptions of the same contents as those of the first embodiment described with reference to <FIG> will be omitted.

The optical system <NUM> according to the second embodiment may have an F value of <NUM>, a TTL of <NUM>, and a ratio (TTL/F value) of <NUM>.

In the optical system <NUM> according to the second embodiment of the present invention, the first lens <NUM> has a positive (+) power. Accordingly, the first lens <NUM> may provide a part of the refractive power required by the optical system <NUM>. An object-side surface <NUM> of the first lens <NUM> is convex and an image-side surface <NUM> thereof is concave. That is, the first lens <NUM> may have a meniscus shape. Since the object-side surface <NUM> of the first lens <NUM> is convex, the refractive power of the first lens <NUM> may be enhanced.

In the optical system <NUM> according to the second embodiment, the second lens <NUM> may have a positive (+) power, an object-side surface <NUM> of the second lens <NUM> may be convex, and an image-side surface <NUM> of the second lens <NUM> may be concave.

In the optical system <NUM> according to the second embodiment, the third lens <NUM> may have a positive (+) power, an object-side surface <NUM> of the third lens <NUM> is concave, and an image-side surface <NUM> of the third lens <NUM> is convex. As described above, the third lens <NUM> may have a meniscus shape, and at least one of the object-side surface <NUM> and the image-side surface <NUM> of the third lens <NUM> may include at least one inflection point. Here, the thickness of the third lens <NUM> may be greater than the thickness of the second lens <NUM>.

In the optical system <NUM> according to the second embodiment, the fourth lens <NUM> may have a negative (-) power, an object-side surface <NUM> of the fourth lens <NUM> is convex, and an image-side surface <NUM> of the fourth lens <NUM> is concave. In addition, in the fourth lens <NUM>, the absolute value of a radius of curvature of the object-side surface <NUM> may be greater than the absolute value of a radius of curvature of the image-side surface <NUM>. Here, at least one of the object-side surface <NUM> and the image-side surface <NUM> of the fourth lens <NUM> may include at least one inflection point at a position other than the intersection with an optical axis.

Here, a focal length F1 of the first lens <NUM> may be in a range of <NUM> to <NUM>, and the absolute value of a focal length of the third lens <NUM> may be greater than the absolute value of a focal length of the second lens <NUM>. In the second embodiment, a ratio (F3/F1) of a focal length F3 of the third lens <NUM> to the focal length F1 of the first lens <NUM> may be <NUM>.

Further, referring to Table <NUM>, a third distance may be less than or equal to <NUM>, for example, <NUM>, and may be less than a first distance and a second distance.

Further, referring to Table <NUM>, it may be seen that an index constant of the third lens <NUM> is <NUM> and the third lens <NUM> has the highest refractive index together with the fourth lens <NUM>.

<FIG> is a cross-sectional view of an optical system according to a third embodiment which is not an embodiment according to the claimed subject-matter. Table <NUM> illustrates optical characteristics of four lenses according to the third embodiment. In the third embodiment, a total EFL is <NUM>, a TTL is <NUM>, and an F value is <NUM>. Tables <NUM> and <NUM> illustrate conic constants and aspheric coefficients for each lens constituting the optical system according to the third embodiment. Duplicate descriptions of the same contents as those of the first embodiment described with reference to <FIG> will be omitted.

Light reflected from the object sequentially passes through the first to fourth lenses <NUM> to <NUM> of the optical system <NUM> and the filter <NUM> and is then received by the image sensor <NUM>.

The optical system <NUM> according to the third embodiment may have an F value of <NUM>, a TTL of <NUM>, and a ratio (TTL/F value) of <NUM>.

In the optical system <NUM> according to the third embodiment, the first lens <NUM> has a positive (+) power. Accordingly, the first lens <NUM> may provide a part of the refractive power required by the optical system <NUM>. An object-side surface <NUM> of the first lens <NUM> is convex and an image-side surface <NUM> thereof is concave. That is, the first lens <NUM> may have a meniscus shape. Since the object-side surface <NUM> of the first lens <NUM> is convex, the refractive power of the first lens <NUM> may be enhanced.

In the optical system <NUM> according to the third embodiment, the second lens <NUM> may have a positive (+) power, an object-side surface <NUM> of the second lens <NUM> may be convex, and an image-side surface <NUM> of the second lens <NUM> may be concave.

In the optical system <NUM> according to the third embodiment, the third lens <NUM> may have a positive (+) power, an object-side surface <NUM> of the third lens <NUM> is concave, and an image-side surface <NUM> of the third lens <NUM> is convex. As described above, the third lens <NUM> may have a meniscus shape, and at least one of the object-side surface <NUM> and the image-side surface <NUM> of the third lens <NUM> may include at least one inflection point. Here, the thickness of the third lens <NUM> may be greater than the thickness of the second lens <NUM>.

In the optical system <NUM> according to the third embodiment, the fourth lens <NUM> may have a negative (-) power, an object-side surface <NUM> of the fourth lens <NUM> is convex, and an image-side surface <NUM> of the fourth lens <NUM> is concave. In addition, in the fourth lens <NUM>, the absolute value of a radius of curvature of the object-side surface <NUM> may be greater than the absolute value of a radius of curvature of the image-side surface <NUM>. Here, at least one of the object-side surface <NUM> and the image-side surface <NUM> of the fourth lens <NUM> may include at least one inflection point at a position other than the intersection with an optical axis.

Here, a focal length F1 of the first lens <NUM> may be in a range of <NUM> to <NUM>, and the absolute value of a focal length of the third lens <NUM> may be greater than the absolute value of a focal length of the second lens <NUM>. In the third embodiment, a ratio (F3/F1) of a focal length F3 of the third lens <NUM> to the focal length F1 of the first lens <NUM> may be <NUM>.

<FIG> is a cross-sectional view of an optical system according to a fourth embodiment which is not an embodiment according to the claimed subject-matter. Table <NUM> illustrates optical characteristics of four lenses according to the fourth embodiment. In the fourth embodiment, a total EFL is <NUM>, a TTL is <NUM>, and an F value is <NUM>. Tables <NUM> and <NUM> illustrate conic constants and aspheric coefficients for each lens constituting the optical system according to the fourth embodiment. Duplicate descriptions of the same contents as those of the first embodiment described with reference to <FIG> will be omitted.

The optical system <NUM> according to the fourth embodiment, may have an F value of <NUM>, a TTL of <NUM>, and a ratio (TTL/F value) of <NUM>.

In the optical system <NUM> according to the fourth embodiment, the first lens <NUM> has a positive (+) power. Accordingly, the first lens <NUM> may provide a part of the refractive power required by the optical system <NUM>. An object-side surface <NUM> of the first lens <NUM> is convex and an image-side surface <NUM> thereof is concave. That is, the first lens <NUM> may have a meniscus shape. Since the object-side surface <NUM> of the first lens <NUM> is convex, the refractive power of the first lens <NUM> may be enhanced.

In the optical system <NUM> according to the fourth embodiment, the second lens <NUM> may have a negative (-) power, an object-side surface <NUM> of the second lens <NUM> may be concave, and an image-side surface <NUM> of the second lens <NUM> may be concave.

In the optical system <NUM> according to the fourth embodiment, the third lens <NUM> may have a positive (+) power, an object-side surface <NUM> of the third lens <NUM> is concave, and an image-side surface <NUM> of the third lens <NUM> is convex. As described above, the third lens <NUM> may have a meniscus shape, and at least one of the object-side surface <NUM> and the image-side surface <NUM> of the third lens <NUM> may include at least one inflection point. Here, the thickness of the third lens <NUM> may be greater than the thickness of the second lens <NUM>.

In the optical system <NUM> according to the fourth embodiment, the fourth lens <NUM> may have a negative (-) power, an object-side surface <NUM> of the fourth lens <NUM> is convex, and an image-side surface <NUM> of the fourth lens <NUM> is concave. In addition, in the fourth lens <NUM>, the absolute value of a radius of curvature of the object-side surface <NUM> may be greater than the absolute value of a radius of curvature of the image-side surface <NUM>. Here, at least one of the object-side surface <NUM> and the image-side surface <NUM> of the fourth lens <NUM> may include at least one inflection point at a position other than the intersection with an optical axis.

Here, a focal length F1 of the first lens <NUM> may be in a range of <NUM> to <NUM>, and the absolute value of a focal length of the third lens <NUM> may be greater than the absolute value of a focal length of the second lens <NUM>. In the fourth embodiment, a ratio (F3/F1) of a focal length F3 of the third lens <NUM> to the focal length F1 of the first lens <NUM> may be <NUM>.

Further, referring to Table <NUM>, a third distance may be less than or equal to <NUM>, for example, <NUM>, and may be equal to or less than a first distance and a second distance.

Further, referring to Table <NUM>, it may be seen that the index constant of the third lens <NUM> is <NUM> and the third lens <NUM> has the highest refractive index together with the first lens <NUM> and the second lens <NUM>.

<FIG> is a cross-sectional view of an optical system according to a fifth embodiment of the present invention. Table <NUM> illustrates optical characteristics of four lenses according to the fifth embodiment. In the fifth embodiment, a total EFL is <NUM>, a TTL is <NUM>, and an F value is <NUM>. Tables <NUM> and <NUM> illustrate conic constants and aspheric coefficients for each lens constituting the optical system according to the fifth embodiment. Duplicate descriptions of the same contents as those of the first embodiment described with reference to <FIG> will be omitted.

The optical system <NUM> according to the fifth embodiment of the present invention may have an F value of <NUM>, a TTL of <NUM>, and a ratio (TTL/F value) of <NUM>.

In the optical system <NUM> according to the fifth embodiment of the present invention, the first lens <NUM> has a positive (+) power. Accordingly, the first lens <NUM> may provide a part of the refractive power required by the optical system <NUM>. An object-side surface <NUM> of the first lens <NUM> is convex and an image-side surface <NUM> thereof is concave. That is, the first lens <NUM> may have a meniscus shape. Since the object-side surface <NUM> of the first lens <NUM> is convex, the refractive power of the first lens <NUM> may be enhanced.

In the optical system <NUM> according to the fifth embodiment of the present invention, the second lens <NUM> has a negative (-) power, an object-side surface <NUM> of the second lens <NUM> is concave, and an image-side surface <NUM> of the second lens <NUM> is convex.

In the optical system <NUM> according to the fifth embodiment of the present invention, the third lens <NUM> has a positive (+) power, an object-side surface <NUM> of the third lens <NUM> is concave, and an image-side surface <NUM> of the third lens <NUM> is convex. As described above, the third lens <NUM> may have a meniscus shape, and at least one of the object-side surface <NUM> and the image-side surface <NUM> of the third lens <NUM> may include at least one inflection point. Here, the thickness of the third lens <NUM> may be greater than the thickness of the second lens <NUM>.

In the optical system <NUM> according to the fifth embodiment of the present invention, the fourth lens <NUM> has a negative (-) power, an object-side surface <NUM> of the fourth lens <NUM> is convex, and an image-side surface <NUM> of the fourth lens <NUM> is concave. In addition, in the fourth lens <NUM>, the absolute value of a radius of curvature of the object-side surface <NUM> may be greater than the absolute value of a radius of curvature of the image-side surface <NUM>. Here, at least one of the object-side surface <NUM> and the image-side surface <NUM> of the fourth lens <NUM> may include at least one inflection point at a position other than the intersection with an optical axis.

Here, a focal length F1 of the first lens <NUM> may be in a range of <NUM> to <NUM>, and the absolute value of a focal length of the third lens <NUM> may be greater than the absolute value of a focal length of the second lens <NUM>. In the fifth embodiment, a ratio (F3/F1) of a focal length F3 of the third lens <NUM> to the focal length F1 of the first lens <NUM> may be <NUM>.

Further, referring to Table <NUM>, it may be seen that an index constant of the third lens <NUM> is <NUM> and the third lens 530has the highest refractive index together with the fourth lens <NUM>.

<FIG> are graphs each obtained by measuring longitudinal spherical aberration, astigmatic field curves, and distortion of each of the optical systems according to the first to fifth embodiments.

<FIG> is a graph obtained by measuring longitudinal spherical aberration for light having wavelengths of <NUM>, <NUM>, and <NUM> in the optical system according to the first embodiment, <FIG> is a graph obtained by measuring astigmatic field curves for the light having wavelengths of <NUM>, <NUM>, and <NUM> in the optical system according to the first embodiment, and <FIG> is a graph obtained by measuring distortion for the light having wavelengths of <NUM>, <NUM>, and <NUM> in the optical system according to the first embodiment.

<FIG> is a graph obtained by measuring longitudinal spherical aberration for light having wavelengths of <NUM>, <NUM>, and <NUM> in the optical system according to the second embodiment, <FIG> is a graph obtained by measuring astigmatic field curves for the light having wavelengths of <NUM>, <NUM>, and <NUM> in the optical system according to the second embodiment, and <FIG> is a graph obtained by measuring distortion for the light having wavelengths of <NUM>, <NUM>, and <NUM> in the optical system according to the second embodiment.

<FIG> is a graph obtained by measuring longitudinal spherical aberration for light having wavelengths of <NUM>, <NUM>, and <NUM> in the optical system according to the third embodiment, <FIG> is a graph obtained by measuring astigmatic field curves for the light having wavelengths of <NUM>, <NUM>, and <NUM> in the optical system according to the third embodiment, and <FIG> is a graph obtained by measuring distortion for the light having wavelengths of <NUM>, <NUM>, and <NUM> in the optical system according to the third embodiment.

<FIG> is a graph obtained by measuring longitudinal spherical aberration for light having wavelengths of <NUM>, <NUM>, and <NUM> in the optical system according to the fourth embodiment, <FIG> is a graph obtained by measuring astigmatic field curves for the light having wavelengths of <NUM>, <NUM>, and <NUM> in the optical system according to the fourth embodiment, and <FIG> is a graph obtained by measuring distortion for the light having wavelengths of <NUM>, <NUM>, and <NUM> in the optical system according to the fourth embodiment.

<FIG> is a graph obtained by measuring longitudinal spherical aberration for light having wavelengths of <NUM>, <NUM>, and <NUM> in the optical system according to the fifth embodiment, <FIG> is a graph obtained by measuring astigmatic field curves for the light having wavelengths of <NUM>, <NUM>, and <NUM> in the optical system according to the fifth embodiment, and <FIG> is a graph obtained by measuring distortion for the light having wavelengths of <NUM>, <NUM>, and <NUM> in the optical system according to the fifth embodiment.

The longitudinal spherical aberration shows longitudinal spherical aberration depending on each wavelength, the astigmatic field curve shows aberration characteristics of a tangential plane and a sagital plane according to an image surface height, and the distortion shows a degree of distortion according to the image surface height. Referring to <FIG>, it may be seen that the longitudinal spherical aberration is within a range of - <NUM> to <NUM> regardless of the wavelength, and the astigmatic field curves are within a range of -<NUM> to <NUM> regardless of the wavelength, and the distortion is within a range of -<NUM> % to <NUM> % regardless of the wavelength.

Accordingly, it may be seen that the optical system according to the embodiment of the present invention has excellent aberration characteristics.

Meanwhile, the optical system according to the embodiment of the present invention may be applied to a camera module. <FIG> is a cross-sectional view of a camera module to which the optical system according to one embodiment of the present invention is applied.

Referring to <FIG>, a camera module <NUM> includes a lens assembly <NUM>, an image sensor <NUM>, and a printed circuit board <NUM>. Here, the lens assembly <NUM> may include an optical system <NUM>, a lens barrel <NUM>, a lens holder <NUM>, and an IR filter <NUM>. The optical system <NUM> may correspond to the optical systems according to the embodiments of the present invention illustrated with reference to <FIG>, and the IR filter <NUM> may correspond to the filter <NUM> illustrated in <FIG>. The image sensor <NUM> may correspond to the image sensor <NUM> illustrated in <FIG>.

A plurality of lenses constituting the optical system <NUM> may be aligned with respect to a central axis. Here, the central axis may be the same as the optical axis of the optical system.

The lens barrel <NUM> is coupled to the lens holder <NUM> and may be provided with a space for accommodating the lenses therein. The lens barrel <NUM> may be rotationally coupled with the plurality of lenses constituting the optical system <NUM>, but this is exemplary and the lens barrel <NUM> may be coupled using another method such as a method using an adhesive (for example, an adhesive resin such as epoxy and the like).

The lens holder <NUM> may be coupled to the lens barrel <NUM> to support the lens barrel <NUM> and may be coupled to the printed circuit board <NUM> on which the image sensor <NUM> is mounted. A space in which the IR filter <NUM> may be attached to a lower part of the lens barrel <NUM> may be formed by the lens holder <NUM>. A spiral pattern may be formed on an inner circumferential surface of the lens holder <NUM>, and similarly, the lens holder <NUM> may be rotatably coupled to the lens barrel <NUM> having an outer circumferential surface on which a spiral pattern is formed. However, this is merely exemplary, and the lens holder <NUM> and the lens barrel <NUM> may be coupled to each other using an adhesive or may be integrally formed.

The lens holder <NUM> may be divided into an upper holder <NUM>-<NUM> coupled to the lens barrel <NUM> and a lower holder <NUM>-<NUM> coupled to the printed circuit board <NUM> on which the image sensor <NUM> is mounted, and the upper holder <NUM>-<NUM> and the lower holder <NUM>-<NUM> may be integrally formed, may be formed in a structure separated from each other and then fastened or coupled to each other, or may have a structure separated and spaced apart from each other. Here, the diameter of the upper holder <NUM>-<NUM> may be formed to be smaller than the diameter of the lower holder <NUM>-<NUM>.

Such a camera module may be a camera module that extracts a depth map.

<FIG> illustrates a block diagram of a camera module that extracts a depth map according to one embodiment of the present invention.

Referring to <FIG>, a camera module <NUM> includes a light output unit <NUM>, a lens unit <NUM>, an image sensor <NUM>, a tilting unit <NUM>, and an image processing unit <NUM>. The camera module <NUM> according to the embodiment of the present invention extracts a depth map using a time of flight (ToF) function and thus may be used interchangeably with a ToF camera device or a ToF camera module in the present specification.

The light output unit <NUM> generates an output light signal and irradiates the generated output light signal to an object. Here, the light output unit <NUM> may generate and output the output light signal in the form of a pulse wave or a continuous wave. The continuous wave may be in the form of a sine wave or a square wave. By generating the output light signal in the form of a pulse wave or a continuous wave, the camera module <NUM> may detect a phase difference between the output light signal output from the light output unit <NUM> and an input light signal input to the camera module <NUM> after being reflected from the object. In the present specification, output light may refer to light output from the light output unit <NUM> and incident on the object, and input light may refer to light which is output from the light output unit <NUM>, reaches the object, is reflected from the object, and then input to the camera device <NUM>. From the perspective of the object, the output light may be incident light and the input light may be reflected light.

The light output unit <NUM> irradiates the generated output light signal to the object for a predetermined exposure period. Here, the exposure period means one frame period. When a plurality of frames are generated, a preset exposure period is repeated. For example, when the camera device <NUM> captures an image of the object at <NUM> frames per second (FPS), the exposure period becomes <NUM>/<NUM> sec. Also, when <NUM> frames are generated, the exposure period may be repeated <NUM> times.

The light output unit <NUM> may generate a plurality of output light signals having different frequencies. The light output unit <NUM> may sequentially and repeatedly generate the plurality of output light signals having different frequencies. Alternatively, the light output unit <NUM> may simultaneously generate the plurality of output light signals having different frequencies.

To this end, the light output unit <NUM> may include a light source <NUM> configured to generate light and a light modulating unit <NUM> configured to modulate the light.

First, the light source <NUM> generates light. The light generated by the light source <NUM> may be an infrared light having a wavelength of <NUM> to <NUM> or may be a visible light having a wavelength of <NUM> to <NUM>. The light source <NUM> may use a light-emitting diode (LED), and may have a shape in which a plurality of light-emitting diodes are arranged in a predetermined pattern. In addition, the light source <NUM> may also include an organic light-emitting diode (OLED) or a laser diode (LD). Alternatively, the light source <NUM> may also include a vertical cavity surface emitting laser (VCSEL). The VCSEL is a type of laser diode that converts an electrical signal into a light signal and may use a wavelength of about <NUM> to <NUM>, for example, about <NUM> or about <NUM>.

The light source <NUM> is repeatedly turned on/off at a predetermined time interval to generate the output light signal in the form of a pulse wave or a continuous wave. The predetermined time interval may be the frequency of the output light signal. Turning the light source on/off may be controlled by the light modulating unit <NUM>.

The light modulating unit <NUM> controls turning the light source <NUM> on/off so that the light source <NUM> generates the output light signal in the form of a continuous wave or a pulse wave. The light modulating unit <NUM> may control the light source <NUM> to generate the output light signal in the form of a continuous wave or a pulse wave through frequency modulation, pulse modulation, or the like.

Meanwhile, the lens unit <NUM> collects the input light signal reflected from the object and transmits the collected light signal to the image sensor <NUM>. Here, the lens unit <NUM> may correspond to the lens assembly <NUM> illustrated in <FIG> and may include an optical system and an IR filter. Here, the optical system may be the optical systems according to the embodiments of the present invention illustrated with reference to <FIG>, and the IR filter may be the filter <NUM> illustrated in <FIG>.

The image sensor <NUM> generates an electrical signal using the input light signal collected by the lens unit <NUM>.

The image sensor <NUM> may be synchronized with a cycle of turning the light output unit <NUM> on/off to detect the input light signal. Specifically, the image sensor <NUM> may detect light in an in-phase and out-phase with the output light signal output from the light output unit <NUM>. That is, the image sensor <NUM> may repeatedly perform operations of absorbing the light input signal at the time at which the light source is turned on and absorbing the light input signal at the time at which the light source is turned off.

Next, the image sensor <NUM> may generate an electrical signal corresponding to each of a plurality of reference signals having different phase differences using the reference signals. A frequency of the reference signals may be set to be equal to a frequency of the output light signal output from the light output unit <NUM>. Accordingly, when the light output unit <NUM> generates the output light signals with a plurality of frequencies, the image sensor <NUM> generates electrical signals using the plurality of reference signals corresponding to the frequencies, respectively. The electrical signal may include information related to voltage or quantity of electric charge corresponding to each reference signal.

<FIG> is a view for describing a process of generating the electrical signals according to the embodiment of the present invention. As illustrated in <FIG>, according to the embodiment of the present invention, four reference signals C1 to C4 may be provided. The reference signals C1 to C4 have the same frequency as the output light signal, that is, an incident light signal from the perspective of the object, but may have a phase difference of <NUM>° from each other. One reference signal C1 of the four reference signals may have the same phase as the output light signal. The input light signal, that is, a reflected light signal from the perspective of the object, is phase-delayed by as much as the distance at which the output light signal is reflected and then returned after being incident on the object. The image sensor <NUM> mixes the input light signal and each of the reference signals. Then, the image sensor <NUM> may generate an electrical signal corresponding to a shaded portion in <FIG> for each reference signal.

As another embodiment, when output light signals are generated with a plurality of frequencies during an exposure time, the image sensor <NUM> absorbs input light signals having the plurality of frequencies. For example, it is assumed that the output light signals are generated with frequencies f1 and f2, and the plurality of reference signals have a phase difference of <NUM>° from each other. Then, the input light signals also have frequencies f1 and f2, and thus four electrical signals may be generated through an input light signal having a frequency of f1 and four reference signals corresponding to the input light signal. In addition, four electrical signals may be generated through an input light signal having a frequency of f2 and four reference signals corresponding to the input light signal. Accordingly, a total of eight electrical signals may be generated.

The image sensor <NUM> may have a structure in which a plurality of pixels are arranged in a grid shape. The image sensor <NUM> may be a complementary metal-oxide semiconductor (CMOS) image sensor or may be a charge-coupled device (CCD) image sensor. In addition, the image sensor <NUM> may include a ToF sensor that receives IR light reflected from a subject and measures a distance using a time or phase difference.

The image processing unit <NUM> calculates a phase difference between the output light and the input light using the electrical signal received from the image sensor <NUM> and calculates a distance between the object and the camera module <NUM> using the phase difference.

Specifically, the image processing unit <NUM> may calculate the phase difference between the output light and the input light using the information on the quantity of electric charge of the electrical signal.

As described above, four electrical signals may be generated for each frequency of the output light signal. Accordingly, the image processing unit <NUM> may calculate a phase difference td between the output light signal and the input light signal using Equation <NUM> below. <MAT> where Q<NUM> to Q<NUM> are quantities of electric charge of the four electrical signals, respectively. Q<NUM> is the quantity of electric charge of the electrical signal corresponding to the reference signal having the same phase as the output light signal. Q<NUM> is the quantity of electric charge of the electrical signal corresponding to the reference signal whose phase is delayed by <NUM>° from the output light signal. Q<NUM> is the quantity of electric charge of the electrical signal corresponding to the reference signal whose phase is delayed by <NUM>° from the output light signal. Q<NUM> is the quantity of electric charge of the electrical signal corresponding to the reference signal whose phase is delayed by <NUM>° degrees from the output light signal.

Then, the image processing unit <NUM> may calculate the distance between the object and the camera module <NUM> using the phase difference between the output light signal and the input light signal. At this point, the image processing unit <NUM> may calculate a distance d between the object and the camera module <NUM> using Equation <NUM> below. <MAT> where c is the speed of light, and f is the frequency of the output light.

<FIG> is a simplified view of an example of a method of obtaining a ToF-IR image or a depth image using four phase images.

Referring to <FIG>, a depth image <NUM> may be obtained by sequentially extracting a phase image <NUM> for phase <NUM>°, a phase image <NUM> for phase <NUM>°, a phase image <NUM> for phase <NUM>°, and a phase image <NUM> for phase <NUM>°, and a depth image <NUM> may be obtained by sequentially extracting a phase image <NUM> for phase <NUM>°, a phase image <NUM> for phase <NUM>°, a phase image <NUM> for phase <NUM>°, and a phase image <NUM> for phase <NUM>°.

Meanwhile, in order to increase the resolution of the depth images, the camera module according to the embodiment of the present invention may use a super resolution (SR) technique. The SR technique is a technique of obtaining a high-resolution image from a plurality of low-resolution images, and the mathematical model of the SR technique may be represented by Equation <NUM> below. <MAT> where <NUM>≤k≤p, p represents the number of the low-resolution images, yk represents the low-resolution image (=[yk,<NUM>, yk,<NUM>,. , yk,M]T; where M=N<NUM>*N<NUM>), Dk represents a downsampling matrix, Bk represents an optical blur matrix, Mk represents an image warping matrix, x represents the high-resolution image (=[x<NUM>, x<NUM>,. , xN]T; where N=L<NUM>N<NUM>*L<NUM>N<NUM>), and nk represents noise. That is, according to the SR technique, the inverse function of estimated resolution degradation elements is applied to yk to estimate x. The SR technique may be mainly divided into a statistical method and a multi-frame method, and the multi-frame method may be mainly divided into a space-division method and a time-division method.

In order to apply the SR technique to extract the depth map, the image processing unit <NUM> may generate a plurality of low-resolution subframes using the electrical signals received from the image sensor <NUM> and then extract a plurality of low-resolution depth maps using the plurality of low-resolution sub-frames. In addition, a high-resolution depth map may be extracted by rearranging pixel values of the plurality of low-resolution depth maps.

Here, the high resolution is a relative meaning that indicates a resolution higher than the low resolution.

Here, the subframe may refer to image data generated from the electrical signal corresponding to one exposure period and one reference signal. For example, when electrical signals are generated using eight reference signals in one image frame, i.e., a first exposure period, eight subframes may be generated and one start frame may be additionally generated. In the present specification, the term "subframe" may be used interchangeably with the terms such as "image data," "subframe image data," and the like.

Alternatively, in order to apply the SR technique according to the embodiment of the present invention to extract the depth map, the image processing unit <NUM> may generate a plurality of low-resolution subframes using the electrical signals received from the image sensor <NUM> and then rearrange pixel values of the low-resolution subframes to generate a plurality of high-resolution subframes. In addition, the high-resolution subframes may be used to extract a high-resolution depth map.

To this end, a pixel shift technique may be used. That is, data for multiple images shifted by as much as the subpixels is obtained per subframe using the pixel shift technique, and then the SR technique is applied to each subframe to obtain data for a plurality of high-resolution subframe images, and the data may be used to extract high-resolution depth images. For the pixel shift, the camera device <NUM> according to the embodiment of the present invention further includes the tilting unit <NUM>.

Referring to <FIG> again, the tilting unit <NUM> changes a light path for at least one of the output light signal and the input light signal in the unit of subpixels of the image sensor <NUM>. Here, the subpixel may be a unit greater than zero pixels and smaller than one pixel.

The tilting unit <NUM> changes a light path for at least one of the output light signal and the input light signal for each image frame. As described above, one image frame may be generated for each exposure period. Accordingly, when one exposure period ends, the tilting unit <NUM> changes the light path for at least one of the output light signal or the input light signal.

The tilting unit <NUM> changes the light path for at least one of the output light signal or the input light signal by as much as the subpixel unit on the basis of the image sensor <NUM>. Here, the tilting unit <NUM> changes the light path for at least one of the output light signal or the input light signal in one of upward, downward, leftward, and rightward directions on the basis of the current light path.

<FIG> is a view for describing the light path of the input light signal changed by the tilting unit, and <FIG> is a view for describing the interpolation of input light data by moving a pixel in the unit of subpixels in the image sensor.

In <FIG>, the portion indicated by a solid line represents a current light path of the input light signal, and the portion indicated by a dotted line represents a changed light path. When the exposure period corresponding to the current light path is ended, the tilting unit <NUM> may change the light path of the input light signal to be like the dotted line. The path of the input light signal is then shifted by as much as the subpixels from the current light path. For example, when the tilting unit <NUM> tilts the current light path <NUM>° to the right as shown in <FIG>, the input light signal incident on the image sensor <NUM> may move rightward by as much as the subpixels.

According to the embodiment of the present invention, the tilting unit <NUM> may change the light path of the input light signal in a clockwise direction from a reference position. For example, as illustrated in <FIG>, after a first exposure period is ended, in a second exposure period, the tilting unit <NUM> moves the light path of the input light signal in the rightward direction by as much as the subpixels on the basis of the image sensor <NUM>. In addition, in a third exposure period, the tilting unit <NUM> moves the light path of the input light signal in the rightward direction by as much as the subpixels on the basis of the image sensor <NUM>. In addition, in a fourth exposure period, the tilting unit <NUM> moves the light path of the input light signal in the rightward direction by as much as the subpixels on the basis of the image sensor <NUM>. In addition, in a fifth exposure period, the tilting unit <NUM> moves the light path of the input light signal in a downward direction by as much as the subpixels on the basis of the image sensor <NUM>. In this way, the tilting unit <NUM> may move the light path of the input light signal in the unit of subpixels with a plurality of exposure periods. This may be similarly applied to shifting the light path of the output light signal, and thus detailed description thereof will be omitted. In addition, the pattern in which the light path is changed in a clockwise direction is merely an example, and the light path may be changed in a counterclockwise direction. As described above, when the tilting unit <NUM> moves the light path of the input light signal in the unit of subpixels, the information may be interpolated in the unit of subpixels, and thus it is possible to maintain a high resolution even when four phase signals are simultaneously received within one period.

Here, as shown in <FIG>, according to one embodiment, the tilting unit <NUM> shifts the input light signal by controlling the slope of the IR filter and thus may obtain data shifted by as much as the subpixels. To this end, the tilting unit <NUM> may include an actuator connected directly or indirectly to the IR filter, and the actuator may include at least one of micro electro mechanical systems (MEMS), voice coil motor (VCM), and piezoelectric elements.

However, the present invention is not limited thereto, and the method of interpolating the input light data by moving the pixel in the unit of subpixels in the image sensor described in <FIG> may be realized as software.

The camera module according to the embodiment of the present invention may be embedded in a portable terminal such as a smartphone, a tablet personal computer (PC), a laptop computer, a personal digital assistant (PDA), and the like.

Claim 1:
An optical system (<NUM>) comprising:
a first lens (<NUM>), a second lens (<NUM>), a third lens (<NUM>), and a fourth lens (<NUM>) sequentially arranged from an object side to an image side;
wherein
the first lens (<NUM>) has a positive power, and includes a convex object-side surface (<NUM>) and a concave image-side surface (<NUM>),
the second lens (<NUM>) has a negative power, and includes a concave object-side surface (<NUM>, <NUM>) and an image-side surface (<NUM>, <NUM>) which is concave or convex,
the third lens (<NUM>) has a positive power, and includes a concave object-side surface (<NUM>) and a convex image-side surface (<NUM>),
the fourth lens (<NUM>) has a negative power, and includes a convex object-side surface (<NUM>) and a concave image-side surface (<NUM>),
characterized in that:
an F value is <NUM> or less;
a ratio (total top length (TTL)/F value) of a TTL to the F value is in a range of <NUM> to <NUM>.