Illumination optical system and endoscope

Abstract

To provide an illumination optical system which has a large light distribution angle and exhibits an excellent transmission efficiency in spite of being downsized, and an endoscope having the illumination optical system.SOLUTION: The illumination optical system is arranged in the top end of the light guide of an endoscope, and the illumination optical system has two lenses at a maximum as lenses and presents a negative refractive power as a whole. A first lens surface, which is the closest to the light guide, includes a recessed surface in the center part and a light diffusion surface located on the outer side in a radial direction than the recessed surface. The illumination optical system satisfies a predetermined conditional expression.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The technology of the present disclosure relates to an illumination optical system and an endoscope. [Background technology]

[0002] 2. Description of the Related Art Conventionally, illumination optical systems that are disposed at the tip of an insertion portion of an endoscope and that illuminate a subject are known, for example, from the illumination optical systems described in Patent Documents 1 to 3 listed below. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 57-097508 [Patent Document 2] Patent No. 3060245 [Patent Document 3] Japanese Patent Application Publication No. 5-142485 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been a demand for an illumination optical system that is compact, has a wide light distribution angle, and has good transmission efficiency.

[0005] The present disclosure provides an illumination optical system that is compact yet has a wide light distribution angle and good transmission efficiency, and an endoscope equipped with this illumination optical system. [Means for solving the problem]

[0006] A first illumination optical system of the present disclosure is an illumination optical system arranged at the tip of a light guide of an endoscope, comprising only two or less lenses as lenses, having a negative refractive power overall, a first lens surface closest to the light guide including a concave surface at the center and a light diffusing surface radially outward from the concave surface, wherein R is the absolute value of the paraxial radius of curvature of the concave surface, D is the distance on the optical axis from the exit end surface of the light guide to the first lens surface, and G is the diameter of the exit end surface of the light guide:

number

[0007] A second illumination optical system of the present disclosure is an illumination optical system arranged at the tip of a light guide of an endoscope, comprising only two or less lenses as lenses, having a negative refractive power overall, a first lens surface closest to the light guide including a concave surface at the center and a light diffusing surface radially outward from the concave surface, wherein R is the absolute value of the paraxial radius of curvature of the concave surface, D is the distance on the optical axis from the exit end surface of the light guide to the first lens surface, G is the diameter of the exit end surface of the light guide, and f is the focal length of the illumination optical system:

number

[0008] The illumination optical system of the present disclosure comprises: 0.2 <R / G<0.6 (3)

number

[0009] In the illumination optical system of the present disclosure, when the lens closest to the light guide has a core-clad structure in which the core is covered with clad, the diameter in the direction perpendicular to the optical axis of the core is defined as C, and when the lens closest to the light guide does not have a core-clad structure, the outer diameter of the first lens surface is defined as C. 0.8 <C / G<1.5 (5)

number

[0010] In the illumination optical system of the present disclosure, when the distance on the optical axis from the first lens surface to the surface closest to the object to be illuminated is L, the focal length of the illumination optical system is f, and when the lens closest to the light guide has a core-clad structure in which the core is covered with a clad, the refractive index of the core to the d-line is Nd1, and when the lens closest to the light guide does not have a core-clad structure, the refractive index of the lens closest to the light guide to the d-line is Nd1, -1 <L / (Nd1×f)<-0.22 (7) It is preferable to satisfy conditional expression (7) expressed as follows:

[0011] A first illumination optical system according to the present disclosure includes:

number

[0012] The second illumination optical system of the present disclosure includes:

number

[0013] The illumination optical system of the present disclosure comprises: 0.3 <R / G<0.5 (3-1)

number

[0014] The illumination optical system of the present disclosure comprises: 1.0 <C / G<1.4 (5-1)

number

[0015] The illumination optical system of the present disclosure comprises: -0.5 <L / (Nd1×f)<-0.21 (7-1) It is preferable to satisfy condition (7-1) expressed by the following formula:

[0016] The endoscope of the present disclosure includes the illumination optical system of the present disclosure.

[0017] In addition, in this specification, "consisting of" and "consisting of" are intended to mean that in addition to the listed components, the invention may also include lenses that have substantially no refractive power, as well as optical elements other than lenses, such as apertures, filters, and cover glasses, as well as lens flanges and lens barrels.

[0018] A "single lens" means a single lens that is not cemented. The number of lenses mentioned above refers to the number of lenses that are components. For example, the number of lenses in a cemented lens in which multiple single lenses made of different materials are cemented together is expressed as the number of single lenses that make up the cemented lens. However, a composite aspheric lens (i.e., a lens in which a lens (e.g., a spherical lens) and an aspheric film formed on the lens are integrally formed and function as a single aspheric lens as a whole) is not considered a cemented lens, but is treated as a single lens.

[0019] The sign of the refractive power of a lens including an aspheric surface, the radius of curvature of the lens surface, and the shape of the lens surface are considered in the paraxial region unless otherwise specified. The sign of the radius of curvature is positive for a surface with a convex surface facing the light guide side, and negative for a surface with a convex surface facing the irradiated object side.

[0020] The "focal length" used in the conditional expressions is the paraxial focal length. The "distance on the optical axis" used in the conditional expressions is the geometric distance unless otherwise specified. The values ​​used in the conditional expressions are based on the d-line (wavelength 587.56 nm (nanometers)). Effect of the Invention

[0021] According to the present disclosure, it is possible to provide an illumination optical system that is compact, yet has a wide light distribution angle and good transmission efficiency, and an endoscope equipped with this illumination optical system. [Brief description of the drawings]

[0022] [Figure 1] FIG. 2 is a cross-sectional view of the configuration of an illumination optical system according to one embodiment, corresponding to the illumination optical system of Example 1. [Diagram 2] FIG. 2 is a diagram for explaining a light diffusing surface. [Diagram 3] FIG. 2 is a diagram for explaining a light diffusing surface. [Figure 4] FIG. 13 is a diagram for explaining a comparative example that does not have a light diffusing surface. [Diagram 5] 1 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a first embodiment. [Figure 6] 1 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a first embodiment. [Figure 7] FIG. 11 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a second embodiment. [Figure 8] FIG. 11 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a second embodiment. [Figure 9] FIG. 11 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a third embodiment. [Figure 10]FIG. 11 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a third embodiment. [Figure 11] FIG. 11 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a fourth embodiment. [Figure 12] FIG. 11 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a fourth embodiment. [Figure 13] FIG. 11 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a fifth embodiment. [Figure 14] FIG. 11 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a fifth embodiment. [Figure 15] FIG. 13 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a sixth embodiment. [Figure 16] FIG. 13 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a sixth embodiment. [Figure 17] FIG. 13 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a seventh embodiment. [Figure 18] FIG. 13 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a seventh embodiment. [Figure 19] FIG. 13 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to an eighth embodiment. [Figure 20] FIG. 13 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to an eighth embodiment. [Figure 21] FIG. 13 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a ninth embodiment. [Figure 22] FIG. 13 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a ninth embodiment. [Diagram 23] 1 is a schematic configuration diagram of an endoscope according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. Fig. 1 is a cross-sectional view showing a configuration of an illumination optical system 10 according to an embodiment of the present disclosure. The illumination optical system 10 shown in Fig. 1 corresponds to Example 1 described later.

[0024] The illumination optical system 10 is an optical system arranged at the tip of a light guide 3 of an endoscope. The light guide 3 is made of a bundle fiber in which multiple optical fibers are bundled, and outputs light emitted from a light source (not shown) to the illumination optical system 10. That is, the light emitted from the light source enters the illumination optical system 10 via the light guide 3, and is emitted from the illumination optical system 10 to become illumination light. When the illumination optical system 10 is arranged at the tip of the insertion part of the endoscope, the illumination light illuminates an irradiated object (not shown) that is an observation target. FIG. 1 shows a cross-sectional view including the optical axis Z, with the left side being the light source side and the right side being the irradiated object side.

[0025] The illumination optical system 10 of the present disclosure includes only two or less lenses as lenses, and has a negative refractive power as a whole. Here, the two or less lenses included in the illumination optical system 10 may be a cemented lens in which two lenses are cemented together. By configuring the illumination optical system 10 to include two or less lenses and to have a negative refractive power as a whole, it is easy to widen the light distribution angle while achieving miniaturization. As an example, the illumination optical system 10 shown in FIG. 1 includes one negative lens L1. Note that the illumination optical system 10 may include an optical member that does not have a refractive power, such as a parallel plane plate.

[0026] In the illumination optical system 10, the first lens surface 20 closest to the light guide 3 includes a concave surface 20a at the center and a light diffusing surface 20b radially outward from the concave surface 20a. By making the center of the first lens surface 20 the concave surface 20a, it is easy to widen the light distribution angle while achieving miniaturization. By providing the light diffusing surface 20b radially outward from the concave surface 20a of the first lens surface 20, it is easy to improve the light transmission efficiency and maintain a wide light distribution angle (details will be described later). The light diffusing surface 20b is formed, for example, by polishing the surface of the lens.

[0027] In the illumination optical system 10, the lens closest to the light guide 3 may have a core-clad structure in which the core 22 is covered with the clad 24 (so-called single fiber). With the core-clad structure, light incident on the boundary surface between the core 22 and the clad 24, which have different refractive indices, is totally reflected and directed toward the periphery of the field of view on the opposite side. Therefore, even if the light is refracted by the concave surface 20a or diffused by the light diffusion surface 20b, it is possible to prevent the light from leaking from the outer periphery of the lens. In addition, if the lens surface opposite the concave surface 20a is chamfered, the light passing through the chamfered portion may be absorbed, but by utilizing the total reflection due to the core-clad structure, it is possible to prevent the light from passing through the chamfered portion. In other words, the lens closest to the light guide 3 has a core-clad structure, which improves the light transmission efficiency.

[0028] As an example, lens L1 shown in Fig. 1 has a core-clad structure including a core 22 and a clad 24. In Fig. 1, the boundary between the core 22 and the clad 24 is illustrated by a dotted line. In the first lens surface 20 closest to the light guide 3, a concave surface 20a is formed in the core 22. A light diffusing surface 20b is formed across the core 22 and the clad 24. Note that the light diffusing surface 20b may be formed only in the core 22, for example, and may not be formed in the clad 24.

[0029] The light diffusing surface 20b will be described in detail with reference to Figs. 2 to 4. Fig. 2 is a diagram showing the correspondence relationship between the radial positions of the exit end surface of the light guide 3 and the first lens surface 20. Fig. 2 also shows, as a comparative example, a lens surface 20X that is formed only of a concave surface and does not have a light diffusing surface. For the sake of explanation, Fig. 2 also shows that the exit end surface of the light guide 3 is divided into four equal areas 3a to 3d so that the areas are equal. That is, the amount of light emitted from each of the areas 3a to 3d is the same.

[0030] When the diameter of the concave surface is equal to or larger than the diameter of the exit end surface of the light guide 3, as in the case of lens surface 20X of the comparative example, the light emitted from an outer region of the exit end surface of the light guide 3 (e.g., region 3d) diverges as it passes through the concave surface, causing light leakage. Even if an attempt is made to suppress this light leakage using, for example, a core-clad structure, sufficient effects may not be obtained due to factors such as the spread angle of the light emitted from the light guide 3.

[0031] In addition, the concave surface has a larger area through which light passes, since the change in depth becomes steeper toward the periphery. For example, the area of ​​lens surface 20X through which light emitted from inner region 3a of the exit end surface of light guide 3 passes is larger than the area of ​​lens surface 20X through which light emitted from outer region 3d of the exit end surface of light guide 3 passes. Therefore, in the concave surface, the influence on the transmission efficiency due to light leakage and light absorption by the chamfered portion is larger in the outer peripheral portion (e.g., the portion shown by the thick line in FIG. 2) than in the central portion.

[0032] In the illumination optical system 10 according to this embodiment, a light diffusing surface 20b is formed on a plane extending radially outward from the concave surface 20a on the first lens surface 20 closest to the light guide 3. That is, by forming the light diffusing surface 20b on the outside of the outer periphery of the concave surface 20a, which is likely to be a cause of a decrease in the light transmission efficiency, the decrease in the light transmission efficiency can be suppressed.

[0033] Fig. 3 is a diagram showing a state of light rays emitted from the exit end surface of the light guide 3, incident on the light diffusion surface 20b of the illumination optical system 10 in Fig. 1, and emitted from the illumination optical system 10. Fig. 4 is a comparative example of Fig. 3, and shows a state of light rays in an illumination optical system 10X when the lens L1 of the illumination optical system 10 in Fig. 1 is replaced with a lens L1X that does not have the light diffusion surface 20b. In Figs. 3 and 4, light rays incident on the lens L1 or lens L1X from three points on the exit end surface of the light guide 3 are shown by straight lines, dashed lines, and dotted lines, respectively.

[0034] 3, the light rays that have passed through the light diffusion surface 20b are diffused and projected onto the object surface Obj in a state in which the light is widely spread. That is, as in the illumination optical system 10 according to this embodiment, by diffusing the light rays using the light diffusion surface 20b, it becomes easy to maintain a wide light distribution angle.

[0035] In addition, by diffusing the light beam, it is possible to suppress the image of the exit end surface of the light guide 3 from being formed on the object surface Obj by the illumination optical system 10. The exit end surface of the light guide 3 made of a bundle fiber includes dark and bright areas because the cladding that does not emit light, the gaps between the fibers, and the emitting cores are arranged on the same plane. When the image of the exit end surface of the light guide 3 is formed on the object surface Obj, a light and dark pattern (uneven light distribution) is projected on the object surface Obj, and if this projected image is clear, it causes an obstacle to observation of the object surface Obj (illuminated object). By diffusing the light beam by the light diffusion surface 20b as in this embodiment, it is possible to suppress the generation of a projected image of a light and dark pattern on the object surface Obj.

[0036] On the other hand, as shown in Fig. 4, in the lens L1X that does not have the light diffusion surface 20b, the degree of diffusion of light rays is weaker than in Fig. 3, and it is understood that the light is projected onto the object plane Obj in a state in which the spread of light is small. That is, in the lens L1X that does not have the light diffusion surface 20b, it is difficult to maintain a wide light distribution angle compared to the illumination optical system 10 according to this embodiment, and there is an increased possibility that a projected image of a light and dark pattern (uneven light distribution) will occur on the object plane Obj.

[0037] Next, preferred and possible configurations for the conditional expressions of the illumination optical system of the present disclosure will be described. In the following description of the conditional expressions, in order to avoid redundant explanations, the same symbols are used for elements with the same definitions, and some of the redundant explanations of the symbols will be omitted. In addition, in the following, in order to avoid redundant explanations, the "illumination optical system of the present disclosure" will also be simply referred to as the "illumination optical system."

[0038] It is preferable that the illumination optical system 10 satisfies the following conditional formula (1), where R is the absolute value of the paraxial radius of curvature of the concave surface 20a, D is the distance on the optical axis Z from the exit end surface of the light guide 3 to the first lens surface 20, and G is the diameter of the exit end surface of the light guide 3. That is, when the apex of the concave surface 20a is located on the optical axis Z, D means the distance on the optical axis Z from the exit end surface of the light guide 3 to the apex of the concave surface 20a. By making the corresponding value of the conditional formula (1) not equal to or less than the lower limit, the concave surface 20a does not become too small, so that the light distribution does not become too narrow, which is advantageous for widening the angle of the light distribution. By making the corresponding value of the conditional formula (1) not equal to or more than the upper limit, the concave surface 20a does not become too large, so that the transmission efficiency does not decrease too much, which is advantageous for improving the transmission efficiency. In order to obtain better characteristics, it is more preferable that the illumination optical system 10 satisfies the following conditional formula (1-1).

number

number

[0039] When the focal length of the illumination optical system 10 is f, it is preferable that the illumination optical system 10 satisfies the following conditional formula (2). By ensuring that the corresponding value of the conditional formula (2) is not equal to or less than the lower limit, the concave surface 20a does not become too small, so that the light distribution does not become too narrow, which is advantageous for widening the angle of the light distribution. By ensuring that the corresponding value of the conditional formula (1) is not equal to or more than the upper limit, the concave surface 20a does not become too large, so that the transmission efficiency does not decrease too much, which is advantageous for improving the transmission efficiency. In order to obtain better characteristics, it is more preferable that the illumination optical system 10 satisfies the following conditional formula (2-1).

number

number

[0040] It is preferable that the illumination optical system 10 satisfies the following conditional formula (3). By ensuring that the corresponding value of conditional formula (3) is not below the lower limit, the light does not diverge too much, which makes it possible to suppress leakage of light from the outer periphery and to suppress a decrease in transmission efficiency. By ensuring that the corresponding value of conditional formula (3) is not above the upper limit, the light distribution does not become too narrow, which is advantageous for widening the angle of light distribution. In order to obtain better characteristics, it is more preferable that the illumination optical system 10 satisfies the following conditional formula (3-1). 0.2 <R / G<0.6 (3) 0.3 <R / G<0.5 (3-1)

[0041] It is preferable that the illumination optical system 10 satisfies the following conditional formula (4). By making sure that the corresponding value of conditional formula (4) is not equal to or less than the lower limit, the light does not diverge too much, so that it is possible to suppress the light from leaking from the outer periphery and to suppress a decrease in the transmission efficiency. By making sure that the corresponding value of conditional formula (4) is not equal to or greater than the upper limit, the light distribution does not become too narrow, which is advantageous for widening the angle of the light distribution. In order to obtain better characteristics, it is more preferable that the illumination optical system 10 satisfies the following conditional formula (4-1).

number

number

[0042] It is preferable that the illumination optical system 10 satisfies the following conditional formula (5). In conditional formula (5) and conditional formula (6) described later, when the lens L1 closest to the light guide 3 has a core-clad structure, the diameter of the core 22 in the direction perpendicular to the optical axis Z is C. On the other hand, when the lens L1 closest to the light guide 3 does not have a core-clad structure, the outer diameter of the first lens surface 20 is C. By making the corresponding value of conditional formula (5) not equal to or less than the lower limit, the outer diameter of the lens L1 does not become too small, so that it is possible to suppress leakage from the outer periphery while allowing sufficient light to pass through, and thus suppress a decrease in transmission efficiency. By making the corresponding value of conditional formula (5) not equal to or more than the upper limit, the outer diameter of the lens L1 does not become too large, which is advantageous for miniaturization. In order to obtain better characteristics, it is more preferable that the illumination optical system 10 satisfies the following conditional formula (5-1). 0.8 <C / G<1.5 (5) 1.0 <C / G<1.4 (5-1)

[0043] It is preferable that the illumination optical system 10 satisfies the following conditional formula (6). By ensuring that the corresponding value of conditional formula (6) is not equal to or less than the lower limit, the outer diameter of the lens L1 does not become too large, which is advantageous for miniaturization. By ensuring that the corresponding value of conditional formula (6) is not equal to or greater than the upper limit, the outer diameter of the lens L1 does not become too small, which allows light to pass sufficiently while preventing leakage from the outer periphery, and prevents a decrease in transmission efficiency. In order to obtain better characteristics, it is more preferable that the illumination optical system 10 satisfies the following conditional formula (6-1).

number

number

[0044] In the illumination optical system 10, it is preferable to satisfy the following conditional formula (7), where L is the distance on the optical axis Z from the first lens surface 20 to the surface closest to the object to be illuminated, Nd1 is the refractive index of the core 22 at the d-line when the lens L1 closest to the light guide 3 has a core-clad structure, and Nd1 is the refractive index of the lens L1 closest to the light guide at the d-line when the lens L1 closest to the light guide 3 does not have a core-clad structure. That is, L means the thickness on the optical axis Z of the entire illumination optical system 10. By making the corresponding value of the conditional formula (7) not equal to or less than the lower limit, the central thickness of the illumination optical system 10 does not become too large, which is advantageous for miniaturization. By making the corresponding value of the conditional formula (7) not equal to or more than the upper limit, the central thickness of the illumination optical system 10 does not become too small, which makes the lens less likely to break. In order to obtain better characteristics, it is more preferable that the illumination optical system 10 satisfies the following conditional formula (7-1). -1 <L / (Nd1×f)<-0.22 (7) -0.5 <L / (Nd1×f)<-0.21 (7-1)

[0045] The above-mentioned preferable configurations and possible configurations, including the configurations relating to the conditional expressions, can be combined in any desired manner, and it is preferable that they are appropriately and selectively adopted according to the required specifications.

[0046] As an example, a preferred embodiment of the illumination optical system of the present disclosure is an illumination optical system arranged at the tip of a light guide of an endoscope, which includes only two or less lenses as lenses, has a negative refractive power overall, and a first lens surface closest to the light guide includes a concave surface at the center and a light diffusing surface radially outward from the concave surface, and satisfies the above conditional formula (1).

[0047] As another example, a preferred embodiment of the illumination optical system of the present disclosure is an illumination optical system arranged at the tip of a light guide of an endoscope, which includes only two or less lenses as lenses, has a negative refractive power overall, and a first lens surface closest to the light guide includes a concave surface at the center and a light diffusing surface radially outward from the concave surface, and satisfies the above conditional formula (2).

[0048] Next, examples of the illumination optical system of the present disclosure will be described with reference to the drawings. Note that the reference symbols attached to the lenses in the cross-sectional views of each example are used independently for each example to avoid complication of the explanation and drawings due to an increase in the number of digits of the reference symbols. Therefore, even if common reference symbols are attached in drawings of different examples, they do not necessarily have the same configuration.

[0049] [Example 1] A cross-sectional view of the configuration of the illumination optical system of Example 1 is shown in FIG. 1, and the method of illustration is as described above, so some overlapping explanations will be omitted here. The illumination optical system of Example 1 is composed of one negative lens L1. The first lens surface closest to the light guide 3 includes a concave surface at the center and a light diffusing surface radially outward from the concave surface. Lens L1 has a core-clad structure. The above is an overview of the illumination optical system of Example 1.

[0050] For the illumination optical system of Example 1, basic lens data is shown in Table 1 and specifications are shown in Table 2. The table of basic lens data is written as follows. The Sn column shows the surface number when the surface closest to the light guide is designated as the first surface and the numbers increase by one toward the illuminated object side. The R column shows the radius of curvature of each surface. The D column shows the surface distance on the optical axis between each surface and its adjacent surface on the illuminated object side. The Nd column shows the refractive index of each lens with respect to the d line. The νd column shows the Abbe number of each lens based on the d line. For lenses with a core-clad structure, the refractive index Nd and Abbe number νd are listed for each of the core and clad.

[0051] Table 2 shows the diameter H of the concave surface of the first lens surface, the diameter G of the exit end surface of the light guide, the diameter C of the core of lens L1 in the direction perpendicular to the optical axis Z, the maximum outer diameter Cm of the illumination optical system, and the focal length f of the illumination optical system, based on the d-line.

[0052] In the data in each table, millimeters are used as the unit of length, but since the optical system can be used with proportional enlargement or reduction, other appropriate units can be used. Also, in each table shown below, values ​​are rounded to a predetermined number of decimal places.

[0053] [Table 1]

[0054] [Table 2]

[0055] Figures 5 and 6 are cross-sectional views showing the configuration and optical paths of the illumination optical system of Example 1. The optical paths shown in Figures 5 and 6 are the optical paths of the light rays when a plurality of light rays emitted from a plurality of points on the exit end surface of the light guide 3 are made to enter the illumination optical system, and Figure 5 shows the optical path of the light rays incident on the concave surface, and Figure 6 shows the optical path of the light rays incident on the light diffusing surface. In Figures 5 and 6, the method of illustrating the cross-sectional views is the same as in Figure 1, so repeated explanations will be omitted here.

[0056] The symbols, meanings, description methods and illustration methods of each data item related to the above-mentioned Example 1 are the same in the following Examples unless otherwise specified, and therefore duplicated explanations will be omitted below.

[0057] [Example 2] 7 and 8 are cross-sectional views showing the configuration and optical path of the illumination optical system of Example 2. Fig. 7 shows the optical path of a light ray incident on a concave surface, and Fig. 8 shows the optical path of a light ray incident on a light diffusing surface. The illumination optical system of Example 2 has a configuration similar to the outline of the illumination optical system of Example 1. For the illumination optical system of Example 2, basic lens data is shown in Table 3, and specifications are shown in Table 4.

[0058] [Table 3]

[0059] [Table 4]

[0060] [Example 3] 9 and 10 are cross-sectional views showing the configuration and optical path of the illumination optical system of Example 3. Fig. 9 shows the optical path of a light beam incident on a concave surface, and Fig. 10 shows the optical path of a light beam incident on a light diffusing surface. The illumination optical system of Example 3 has a configuration similar to the outline of the illumination optical system of Example 1. Table 5 shows basic lens data and Table 6 shows specifications of the illumination optical system of Example 3.

[0061] [Table 5]

[0062] [Table 6]

[0063] [Example 4] 11 and 12 are cross-sectional views showing the configuration and optical path of the illumination optical system of Example 4. FIG. 11 shows the optical path of the light beam incident on the concave surface, and FIG. 12 shows the optical path of the light beam incident on the light diffusion surface. The illumination optical system of Example 4 is composed of a negative lens L1 and a plane-parallel plate PP having no refractive power, in that order from the light guide 3 side to the illuminated body side. The first lens surface closest to the light guide 3 includes a concave surface at the center and a light diffusion surface radially outward from the concave surface. The lens L1 has a core-clad structure. The basic lens data and the specifications of the illumination optical system of Example 4 are shown in Table 7 and Table 8, respectively. In Table 7, the row with Sn=3 lists data on the bonding agent that bonds the lens L1 and the plane-parallel plate PP.

[0064] [Table 7]

[0065] [Table 8]

[0066] [Example 5] 13 and 14 are cross-sectional views showing the configuration and optical path of the illumination optical system of Example 5. FIG. 13 shows the optical path of the light beam incident on the concave surface, and FIG. 14 shows the optical path of the light beam incident on the light diffusion surface. The illumination optical system of Example 5 is composed of a negative lens L1 and a negative lens L2 in this order from the light guide 3 side to the illuminated body side, and the lenses L1 and L2 are cemented together. The first lens surface closest to the light guide 3 includes a concave surface at the center and a light diffusion surface radially outward from the concave surface. The lens L1 has a core-clad structure. The lens L2 does not have a core-clad structure. Table 9 shows basic lens data and Table 10 shows specifications for the illumination optical system of Example 5. In Table 9, the row with Sn of 3 lists data on the cement that bonds the lenses L1 and L2.

[0067] [Table 9]

[0068] [Table 10]

[0069] [Example 6] 15 and 16 are cross-sectional views showing the configuration and optical path of the illumination optical system of Example 6. FIG. 15 shows the optical path of the light ray incident on the concave surface, and FIG. 16 shows the optical path of the light ray incident on the light diffusing surface. The illumination optical system of Example 6 is composed of one negative lens L1. The first lens surface closest to the light guide 3 includes an aspheric concave surface at the center and a light diffusing surface radially outward from the concave surface. For the illumination optical system of Example 6, basic lens data is shown in Table 11, specifications are shown in Table 12, and aspheric coefficients are shown in Table 13. In Example 6, lens L1 does not have a core-cladding structure, so the core diameter C is omitted in Table 12. The outer diameter Cn of the first lens surface is also added to Table 12.

[0070] In the basic lens data, the aspheric surface numbers are marked with an *, and the paraxial radius of curvature is listed in the aspheric radius of curvature column. In Table 13, the Sn row shows the aspheric surface numbers, and the KA and Am rows show the numerical values ​​of the aspheric coefficients for each aspheric surface. The numerical values ​​of the aspheric coefficients in Table 13, "E±n" (n: integer), are expressed as "×10 ±n " KA and Am (m = 4, 6, 8, ... 16) are aspheric coefficients in the aspheric formula expressed below. Zd = C × h 2 / {1+(1-KA×C 2 ×h 2 ) 1 / 2}+ΣAm×h m however, Zd: Aspheric depth (the length of the perpendicular line drawn from a point on the aspheric surface at height h to a plane perpendicular to the optical axis Z where the apex of the aspheric surface is in contact) h: Height (distance from optical axis Z to lens surface) C: Reciprocal of paraxial curvature radius KA, Am: Aspheric coefficients In the aspheric surface formula, Σ means the summation with respect to m.

[0071] [Table 11]

[0072] [Table 12]

[0073] [Table 13]

[0074] [Example 7] 17 and 18 are cross-sectional views showing the configuration and optical path of the illumination optical system of Example 7. Fig. 17 shows the optical path of a light ray incident on a concave surface, and Fig. 18 shows the optical path of a light ray incident on a light diffusing surface. The illumination optical system of Example 7 has a configuration similar to the outline of the illumination optical system of Example 1. Table 14 shows basic lens data and Table 15 shows specifications of the illumination optical system of Example 7.

[0075] [Table 14]

[0076] [Table 15]

[0077] [Example 8] 19 and 20 are cross-sectional views showing the configuration and optical path of the illumination optical system of Example 8. Fig. 19 shows the optical path of a light beam incident on a concave surface, and Fig. 20 shows the optical path of a light beam incident on a light diffusing surface. The illumination optical system of Example 8 has a configuration similar to the outline of the illumination optical system of Example 1. Table 16 shows basic lens data and Table 17 shows specifications of the illumination optical system of Example 8.

[0078] [Table 16]

[0079] [Table 17]

[0080] [Example 9] 21 and 22 are cross-sectional views showing the configuration and optical path of the illumination optical system of Example 9. Fig. 21 shows the optical path of a light beam incident on a concave surface, and Fig. 22 shows the optical path of a light beam incident on a light diffusing surface. The illumination optical system of Example 9 has a configuration similar to the outline of the illumination optical system of Example 1. Table 18 shows basic lens data and Table 19 shows specifications of the illumination optical system of Example 9.

[0081] [Table 18]

[0082] [Table 19]

[0083] Table 20 shows values ​​corresponding to conditional expressions (1) to (7) of the illumination optical systems of Examples 1 to 9. The corresponding values ​​of the Examples shown in Table 20 may be used as upper or lower limits to set preferred ranges for the conditional expressions.

[0084] [Table 20]

[0085] From the above data, it is evident that all of the illumination optical systems of Examples 1 to 9 have a wide light distribution angle and good transmission efficiency while being constructed to be compact.

[0086] Next, an endoscope according to an embodiment of the present disclosure will be described. FIG. 23 shows a schematic overall configuration diagram of an endoscope according to an embodiment of the present disclosure. The endoscope 100 shown in FIG. 23 mainly includes an operation section 102, an insertion section 104, and a universal cord 106 connected to a connector section (not shown). Most of the insertion section 104 is a flexible section 107 that bends in any direction along the insertion path, and a bending section 108 is connected to the tip of the flexible section 107, and a tip section 110 is connected to the tip of the bending section 108. The bending section 108 is provided to direct the tip section 110 in a desired direction, and bending operation is possible by rotating a bending operation knob 109 provided on the operation section 102.

[0087] An illumination optical system 10 according to an embodiment of the present disclosure is disposed at the inner tip of the tip portion 110. Fig. 23 shows a schematic diagram of the illumination optical system 10. Since the endoscope according to the present disclosure includes the illumination optical system according to an embodiment of the present disclosure, it is possible to perform observation using good wide-angle illumination light while miniaturizing the tip portion of the insertion section 104.

[0088] Although the technology of the present disclosure has been described above with reference to the embodiments and examples, the technology of the present disclosure is not limited to the above embodiments and examples, and various modifications are possible. For example, the radius of curvature, surface spacing, refractive index, Abbe number, aspheric coefficient, etc. of each lens are not limited to the values ​​shown in the above examples, and may take other values.

[0089] Regarding the above-mentioned embodiments and examples, the following supplementary notes are further disclosed. [Appendix 1] An illumination optical system disposed at a tip of a light guide of an endoscope, The lens is made up of two or less lenses and has a negative refractive power as a whole. the first lens surface closest to the light guide includes a concave surface at the center and a light diffusing surface radially outward from the concave surface, The absolute value of the paraxial radius of curvature of the concave surface is R, The distance on the optical axis from the exit end surface of the light guide to the first lens surface is D. If the diameter of the exit end face of the light guide is G,

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[0090] 3 Light Guide 3a~3d area 10, 10X illumination optics 20, 20X lens surface 20a concave 20b Diffusion surface 22 cores 24 Clad 100 Endoscope 102 Operation section 104 Insertion part 106 Universal Code 107 Soft part 108 Curved section 109 Curvature control knob 110 Tip C Core diameter D is the distance on the optical axis from the exit end of the light guide to the first lens surface. G Diameter of the light guide exit end L is the distance on the optical axis from the first lens surface to the surface closest to the object to be irradiated. L1, L1X, L2 Lenses Obj object plane PP parallel plane plate Z optical axis

Claims

1. An illumination optical system disposed at a tip of a light guide of an endoscope, The lens has only two or less lenses as lenses, and has a negative refractive power as a whole, the first lens surface closest to the light guide includes a concave surface at a center portion and a light diffusing surface radially outward from the concave surface, The absolute value of the paraxial radius of curvature of the concave surface is R, The distance on the optical axis from the exit end surface of the light guide to the first lens surface is D, If the diameter of the exit end surface of the light guide is G, [0010] An illumination optical system that satisfies conditional expression (1) expressed by:

2. 0.2<R / G<0.6 (3) [0025] 2. The illumination optical system according to claim 1, which satisfies conditional expressions (3) and (4) expressed by:

3. When the lens closest to the light guide has a core-clad structure in which a core is covered with a clad, the diameter of the core in a direction perpendicular to the optical axis is defined as C. When the lens closest to the light guide does not have the core-clad structure, the outer diameter of the first lens surface is defined as C. 0.8<C / G<1.5 (5) [0030] 2. The illumination optical system according to claim 1, which satisfies conditional expressions (5) and (6) expressed by:

4. The distance on the optical axis from the first lens surface to the surface closest to the object to be irradiated is L. The focal length of the illumination optical system is f, When the lens closest to the light guide has a core-clad structure in which a core is covered with a clad, the refractive index of the core to the d-line is Nd1. When the lens closest to the light guide does not have the core-clad structure, the refractive index of the lens closest to the light guide to the d-line is Nd1. -1<L / (Nd1×f)<-0.22 (7) 2. The illumination optical system according to claim 1, which satisfies conditional expression (7) expressed as follows: 【Request 5】 【Number 4】 2. The illumination optical system according to claim 1, which satisfies the conditional expression (1-1) expressed by:

6. 0.3<R / G<0.5 (3-1) [0050] 3. The illumination optical system according to claim 2, which satisfies at least one of conditional expressions (3-1) and (4-1) expressed by:

7. 1.0<C / G<1.4 (5-1) [006] 4. The illumination optical system according to claim 3, which satisfies at least one of conditional expressions (5-1) and (6-1) expressed by:

8. -0.5<L / (Nd1×f)<-0.21 (7-1) 5. The illumination optical system according to claim 4, which satisfies conditional expression (7-1) expressed by:

9. An illumination optical system disposed at a tip of a light guide of an endoscope, The lens has only two or less lenses as lenses, and has a negative refractive power as a whole, the first lens surface closest to the light guide includes a concave surface at a center portion and a light diffusing surface radially outward from the concave surface, The absolute value of the paraxial radius of curvature of the concave surface is R, The distance on the optical axis from the exit end surface of the light guide to the first lens surface is D, The diameter of the light guide at the exit end face is G, When the focal length of the illumination optical system is f, [0070] An illumination optical system that satisfies conditional expression (2) expressed by:

10. 0.2<R / G<0.6 (3) [0080] 10. The illumination optical system according to claim 9, which satisfies conditional expressions (3) and (4) expressed by the following formula:

11. When the lens closest to the light guide has a core-clad structure in which a core is covered with a clad, the diameter of the core in a direction perpendicular to the optical axis is defined as C. When the lens closest to the light guide does not have the core-clad structure, the outer diameter of the first lens surface is defined as C. 0.8<C / G<1.5 (5) [0097] 10. The illumination optical system according to claim 9, which satisfies conditional expressions (5) and (6) expressed by the following:

12. The distance on the optical axis from the first lens surface to the surface closest to the object to be irradiated is L. The focal length of the illumination optical system is f, When the lens closest to the light guide has a core-clad structure in which a core is covered with a clad, the refractive index of the core to the d-line is Nd1. When the lens closest to the light guide does not have the core-clad structure, the refractive index of the lens closest to the light guide to the d-line is Nd1. -1<L / (Nd1×f)<-0.22 (7) 10. The illumination optical system according to claim 9, which satisfies conditional expression (7) expressed as follows: 【Request 13】 【Number 10】 10. The illumination optical system according to claim 9, which satisfies conditional expression (2-1) expressed by:

14. 0.3<R / G<0.5 (3-1) ##EQU00011## 11. The illumination optical system according to claim 10, which satisfies at least one of conditional expressions (3-1) and (4-1) expressed by:

15. 1.0<C / G<1.4 (5-1) ##EQU00012## 12. The illumination optical system according to claim 11, which satisfies at least one of conditional expressions (5-1) and (6-1) expressed by:

16. -0.5<L / (Nd1×f)<-0.21 (7-1) 13. The illumination optical system according to claim 12, which satisfies conditional expression (7-1) expressed by:

17. An endoscope comprising the illumination optical system according to any one of claims 1 to 16.

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