Illumination optical system and endoscope

Abstract

To provide an illumination optical system which is compact, has wide light distribution, has little light distribution unevenness, and has excellent transmission efficiency, and to provide an endoscope equipped with the illumination optical system.SOLUTION: The illumination optical system is disposed on an emission side of a light guide of the endoscope. When a surface of the illumination optical system closest to the light guide is a first surface and a surface of the illumination optical system closest to the object to be irradiated is a second surface, an outer peripheral surface of the illumination optical system from the first surface to the second surface is a light reflecting surface on the first surface side and a light absorbing surface on the second surface side. A step surface, which is a surface perpendicular to the optical axis of the illumination optical system and constitutes a step at which an outer diameter dimension changes, is formed at a boundary between the light reflecting surface and the light absorbing surface. The first surface is provided in a small-diameter portion having a smaller diameter than an outermost diameter portion where an outer diameter of the illumination optical system is maximum, and has a plurality of first concave surface portions having the same curvature radius. 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 arranged at the tip of an insertion part of an endoscope and that illuminate a subject are known, for example, from the illumination optical systems described in Patent Documents 1 and 2 below. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-004927 [Patent Document 2] Japanese Patent Application Publication No. 62-287215 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, yet has a wide light distribution, little unevenness in light distribution, and good transmission efficiency.

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

[0006] One aspect of the technology of the present disclosure is an illumination optical system arranged on the exit side of a light guide of an endoscope, wherein when the surface of the illumination optical system closest to the light guide is defined as a first surface and the surface closest to an illuminated body is defined as a second surface, the outer peripheral surface of the illumination optical system from the first surface to the second surface is a light reflecting surface on the first surface side and a light absorbing surface on the second surface side, and a step surface that is perpendicular to the optical axis of the illumination optical system and constitutes a step where the outer diameter dimension changes is formed at the boundary between the light reflecting surface and the light absorbing surface, and the first surface is provided in a small diameter portion that is smaller in diameter than an outermost diameter portion where the outer diameter of the illumination optical system is maximum, and has a plurality of first concave surface portions with the same radius of curvature, 0.4 <C / H<0.95 (1) 0.45 <D / (D+E)<0.95 (2) 0.05 <R1 / H<0.5 (3) The conditional expressions (1), (2), and (3) expressed as follows are satisfied. Here, the radius of the small diameter portion is defined as C. The radius of the outermost diameter portion is defined as H. The distance in the direction of the optical axis from the position of the first surface closest to the light guide to the step surface is defined as D. The distance in the direction of the optical axis from the intersection of the second surface and the optical axis to the step surface is defined as E. The radius of curvature of the first concave surface portion is defined as R1.

[0007] The illumination optical system of the above aspect preferably satisfies at least one of the following conditional expressions (4) to (8): Here, the distance between the vertices of adjacent first concave surface portions in a plane perpendicular to the optical axis is defined as P. The radius of the light guide is defined as G. 0.8<(CP) / D<2 (4) 0.02<(2×R1-P) / C<0.25 (5)

number

[0008] In the illumination optical system of the above aspect, it is preferable that at least one first concave surface portion includes a light diffusing surface.

[0009] The first surface may be configured to have at least one second concave surface portion, the second concave surface portion having a radius of curvature larger than that of the first concave surface portion, located closer to the optical axis than the first concave surface portion. In this case, it is preferable that the illumination optical system of the above aspect satisfies the following conditional expression (9). Here, the radius of curvature of the second concave surface portion closest to the optical axis is R2. The distance in the optical axis direction from the intersection of the second concave surface portion closest to the optical axis and the optical axis to the second surface is T. 0.55 <R2 / T<1.3 (9)

[0010] Another aspect of the technique of the present disclosure is an endoscope including a light guide and the illumination optical system of the above aspect.

[0011] In this specification, the terms "consisting of" and "consisting of" are intended to mean that, in addition to the listed components, a lens having substantially no refractive power, optical elements other than lenses such as an aperture, a filter, and a cover glass, as well as a lens flange and a lens barrel, etc. may also be included.

[0012] In the description of this specification, "vertical" refers to not only completely vertical but also approximately vertical, which includes a tolerance that is generally acceptable in the technical field to which the technology of the present disclosure belongs. In the description of this specification, "flat" refers to not only completely flat but also approximately flat, which includes a tolerance that is generally acceptable in the technical field to which the technology of the present disclosure belongs. In the description of this specification, the "same" in "same radii of curvature" refers to not only completely identical but also approximately identical, which includes a tolerance that is generally acceptable in the technical field to which the technology of the present disclosure belongs. In the description of this specification, the "radius of curvature" is a positive value. [Effects of the Invention]

[0013] According to the present disclosure, it is possible to provide an illumination optical system that is compact, yet has a wide light distribution, little unevenness in light distribution, and good transmission efficiency, and an endoscope equipped with this illumination optical system. [Brief explanation of the drawings]

[0014] [Figure 1]1 is a cross-sectional view showing the configuration of an illumination optical system according to an embodiment, which corresponds to the illumination optical system of Example 1. FIG. [Figure 2] FIG. 2 is a plan view showing the configuration of the illumination optical system in FIG. [Figure 3] FIG. 2 is a side view showing the configuration of the illumination optical system of FIG. [Figure 4] 2 is a cross-sectional view showing the configuration and optical paths of the illumination optical system of FIG. 1. [Figure 5] FIG. 10 is a diagram for explaining a comparative example. [Figure 6] FIG. 10 is a diagram for explaining symbols in a conditional expression. [Figure 7] 4 is a graph showing the light distribution characteristics of the illumination optical system of Example 1. [Figure 8] FIG. 10 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a second embodiment. [Figure 9] FIG. 10 is a plan view showing the configuration of an illumination optical system according to a second embodiment. [Figure 10] 10 is a graph showing the light distribution characteristics of the illumination optical system of Example 2. [Figure 11] FIG. 10 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a third embodiment. [Figure 12] FIG. 10 is a plan view showing the configuration of an illumination optical system according to a third embodiment. [Figure 13] 10 is a graph showing the light distribution characteristics of the illumination optical system of Example 3. [Figure 14] FIG. 10 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a fourth embodiment. [Figure 15] FIG. 10 is a plan view showing the configuration of an illumination optical system according to a fourth embodiment. [Figure 16] 10 is a graph showing the light distribution characteristics of the illumination optical system of Example 4. [Figure 17] FIG. 11 is a cross-sectional view showing the configuration of an illumination optical system according to a modified example, which corresponds to the illumination optical system of Example 5. [Figure 18] FIG. 10 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a fifth embodiment. [Figure 19] FIG. 10 is a plan view showing the configuration of an illumination optical system according to a fifth embodiment. [Figure 20] 10 is a graph showing the light distribution characteristics of the illumination optical system of Example 5. [Figure 21] FIG. 10 is a cross-sectional view showing the configuration of an illumination optical system according to a sixth embodiment. [Figure 22] FIG. 10 is a cross-sectional view showing the configuration and optical paths of an illumination optical system according to a sixth embodiment. [Figure 23] FIG. 13 is a plan view showing the configuration of an illumination optical system according to a sixth embodiment. [Figure 24] 13 is a graph showing the light distribution characteristics of the illumination optical system of Example 6. [Figure 25] 1 is a schematic configuration diagram of an endoscope according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Fig. 1 shows the configuration of an illumination optical system 10 according to one embodiment of the present disclosure, taken along a cross section including an optical axis Z. The illumination optical system 10 shown in Fig. 1 corresponds to Example 1, which will be described later.

[0016] The illumination optical system 10 is an optical system disposed on the exit side of a light guide 50 of an endoscope. The end face of the illumination optical system 10 is disposed so as to be in close proximity to or in close proximity to the tip of the light guide 50. The light guide 50 is composed of a fiber bundle in which multiple optical fibers are bundled together, and emits 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 50 and is emitted from the illumination optical system 10 as illumination light. When the illumination optical system 10 is disposed at the tip of the insertion portion of the endoscope, the illumination light illuminates an illuminated object (not shown) that is the object of observation. FIG. 1 shows a cross-sectional view of the illumination optical system 10 including the optical axis Z, with the left side being the light source side and the right side being the illuminated object side.

[0017] As an example, the illumination optical system 10 shown in Fig. 1 is composed of a single optical element and has a rotationally symmetric configuration with the optical axis Z as the axis of rotation. Of the surfaces of the illumination optical system 10, a first surface 10a is the surface of the illumination optical system 10 closest to the light guide, and a second surface 10b is the surface of the illumination optical system 10 closest to the object to be illuminated. As an example, the second surface 10b in Fig. 1 is a flat surface.

[0018] The first surface 10a has multiple first concave surface portions 1 with the same radius of curvature. As an example, each of the first concave surface portions 1 in FIG. 1 is spherical. Each of the first concave surface portions 1 has a diverging effect on incident light like a concave lens. Forming multiple first concave surface portions 1 on the surface closest to the light guide is advantageous for achieving a wide light distribution while miniaturizing the illumination optical system 10, and also contributes to reducing unevenness in the light distribution. FIG. 2 shows the configuration of the illumination optical system 10 in a plane perpendicular to the optical axis Z as viewed from the light guide side. FIG. 3 shows the configuration of the illumination optical system 10 in a plane parallel to the optical axis Z.

[0019] As shown in FIG. 2, the first concave surface portion 1 of this example is configured as follows, for example. The outer shape of the first concave surface portion 1 in a plane perpendicular to the optical axis Z is a substantially regular hexagon. A plurality of first concave surface portions 1 of the same size and shape are arranged in a honeycomb pattern, with the spacing between adjacent first concave surface portions 1 being a predetermined interval. This configuration allows a plurality of first concave surface portions 1 to be arranged at a high density, which is also advantageous for reducing uneven light distribution.

[0020] The exit end surface of the light guide 50, which is made of a bundle fiber, contains dark and bright areas because the non-emitting cladding, gaps between fibers, and the emitting cores are arranged on the same plane. If an image of the exit end surface of this light guide 50 were to be formed on an illuminated object, a bright and dark pattern would be projected onto the illuminated object, resulting in significant unevenness in the light distribution. If the projected image of this bright and dark pattern were too clear, it could interfere with observation of the illuminated object. By forming multiple first concave portions 1 on the surface closest to the light guide, the projection of the bright and dark pattern onto the illuminated object can be suppressed.

[0021] In the technology disclosed herein, at least one first concave surface portion provided on the surface of the illumination optical system closest to the light guide may be configured to include a diffusing surface. By including a light diffusing surface in the first concave surface portion, the light emitted from the first concave surface portion can be spread more widely, thereby reducing uneven light distribution on the surface of the illuminated object. When the first concave surface portion is configured to include a light diffusing surface, the light diffusing surface can diffuse the light, thereby further suppressing the occurrence of a projected image of a light and dark pattern on the illuminated object.

[0022] The light diffusing surface may be a roughened surface having fine irregularities, for example, a surface that has been subjected to a graining treatment by polishing. The light diffusing surface may also be a surface provided with a layer containing a substance having a light diffusing function, such as glass beads. The surface roughness of the light diffusing surface having fine irregularities can typically be several μm or less in terms of arithmetic mean roughness Ra.

[0023] Next, we will explain the step structure and outer peripheral surface configuration of the illumination optical system 10. As shown in Figure 1, the illumination optical system 10 has a step structure including a large diameter section 12 located on the illuminated object side and a small diameter section 16 located on the light guide side and configured with a smaller diameter than the large diameter section 12. Between the small diameter section 16 and the large diameter section 12, a step surface 14 is formed, which is a plane perpendicular to the optical axis Z of the illumination optical system 10 and forms a step where the outer diameter dimension changes.

[0024] The large diameter portion 12 includes a chamfered portion 12a, an outermost diameter portion 12b, and a second surface 10b. The chamfered portion 12a has a curved surface connecting the step surface 14 and the surface of the outermost diameter portion 12b. The outermost diameter portion 12b is the portion where the outer diameter of the illumination optical system 10 is greatest.

[0025] The small diameter portion 16 includes a first surface 10a, a chamfered portion 16a, and a small diameter step portion 16b. The chamfered portion 16a has a curved surface connecting the first surface 10a and the surface of the small diameter step portion 16b. The small diameter step portion 16b is cylindrical with a generatrix parallel to the optical axis Z.

[0026] The outer peripheral surface of the illumination optical system 10 from the first surface 10a to the second surface 10b is configured so that the first surface side is a light reflecting surface and the second surface side is a light absorbing surface. A step surface 14 is formed at the boundary between the light reflecting surface on the first surface side and the light absorbing surface on the second surface side.

[0027] In this example, the outer peripheral surface of small diameter portion 16 is a light-reflecting surface, and the outer peripheral surface of large diameter portion 12 is a light-absorbing surface. In this example, the outer peripheral surface of small diameter portion 16 is roughly the outer peripheral surface of small diameter step portion 16b, which is a mirror surface like the surface of a lens. In Figure 1, the dashed line with an arrow indicates a light ray that is emitted from one end of light guide 50 and reflected by the surface of small diameter step portion 16b.

[0028] The light-reflecting surface on the first surface side has a reflectance of 80% or more for light rays traveling from the interior of the illumination optical system 10 toward the outer peripheral surface at an incident angle of 50 degrees or more. The incident angle is the angle between the normal to the incident surface and the incident light ray. When the illumination optical system 10 is made of glass, the interface between the glass and air can serve as the light-reflecting surface. The light-reflecting surface may further be coated with a mirror coating such as a vapor-deposited film of aluminum or silver to improve reflectance.

[0029] The light absorbing surface on the second surface side has a light absorption rate of 50% or more. The outer peripheral surface on the second surface side is often configured to have an adhesive applied to prevent parts from falling off, and this configuration makes it a light absorbing surface.

[0030] The reflectance and light absorptance values ​​are those at the wavelength of the light used. When visible light is used as the light, it is preferable that the reflectance and light absorptance values ​​are secured within a wavelength range of, for example, 400 to 700 nm.

[0031] As described above, by making the outer diameter of the small diameter portion 16 on the light guide side smaller than the diameter of the outermost diameter portion 12b and making the outer peripheral surface of the small diameter portion 16 a light reflecting surface, it is possible to reduce light loss at the outer peripheral surface of the large diameter portion 12, which is advantageous for good transmission efficiency.

[0032] Figure 4 shows the optical paths of the illumination optical system 10 of Figure 1 having the above configuration using solid lines and dashed dotted lines. Figure 4 shows the state of light rays when multiple light rays emitted from multiple points on the exit end surface of the light guide 50 are incident on the illumination optical system 10. As shown in Figure 4, the illumination optical system 10 of Figure 1 achieves a wide light distribution angle.

[0033] FIG. 5 shows a comparative example in which the illumination optical system 10 in FIG. 1 is replaced with a lens L1X. The lens L1X in FIG. 5 is a negative lens with only one concave surface formed on the light guide side. In the comparative example in FIG. 5, the divergence angle of light rays emitted from near the center of the light guide 50 is small, and the divergence angle of the light rays tends to increase as the emission position moves from the center toward the outer diameter. In this configuration, if the outer diameter of the lens L1X is reduced to achieve compactness, light rays with a large emission angle may be incident on the outer peripheral surface of the lens L1X, and may be blocked by the outer peripheral surface, making the lens unusable as illumination light. In the comparative example in FIG. 5, the outer diameter of the lens L1X needs to be increased to a certain extent so that the outer peripheral surface of the lens L1X does not block the light rays. In other words, it is difficult to achieve both compactness and wide light distribution in the comparative example in FIG. 5.

[0034] In contrast, in the example shown in Fig. 4, even if the light emerges from the light guide 50 at the outer diameter side, it is reflected by the outer peripheral surface of the small diameter portion 16 and can be used as illumination light. Furthermore, in the example shown in Fig. 4, even if the diameter of the small diameter portion 16 on the light guide side is smaller than that of the outermost diameter portion 12b, the light is not blocked by the outer peripheral surface of the small diameter portion 16 and can be used as illumination light. As described above, the example shown in Fig. 4 easily achieves both compactness and wide light distribution, and also has good transmission efficiency.

[0035] Next, preferred and possible configurations for the conditional expressions will be described. In the following description of the conditional expressions, in order to avoid redundant explanation, the same symbols are used for elements with the same definitions, and some duplicate explanations of the symbols will be omitted.

[0036] It is preferable that the illumination optical system 10 satisfy the following conditional formula (1). Here, the radius of the small diameter portion 16 is C. The radius of the outermost diameter portion 12b is H. FIG. 6 shows the light guide 50 and the illumination optical system 10 of FIG. 1, and shows the above-mentioned length radius C and radius H as an example. By ensuring that the corresponding value of conditional formula (1) is not equal to or less than the lower limit, the outermost diameter portion 12b can be prevented from becoming too large, which is advantageous for miniaturization. By ensuring that the corresponding value of conditional formula (1) is not equal to or greater than the upper limit, the amount of light absorption at the outer peripheral surface of the large diameter portion 12 can be reduced, which is advantageous for improving transmission efficiency. 0.4 <C / H<0.95 (1)

[0037] To obtain better characteristics, the lower limit of conditional expression (1) is more preferably set to 0.5, even more preferably to 0.6, and even more preferably to 0.68. To obtain even better characteristics, the upper limit of conditional expression (1) is more preferably set to 0.9, even more preferably to 0.85, and even more preferably to 0.83. For example, it is more preferable that the illumination optical system 10 satisfy at least one of the following conditional expressions (1-1), (1-2), and (1-3). 0.5 <C / H<0.9 (1-1) 0.6 <C / H<0.85 (1-2) 0.68 <C / H<0.83 (1-3)

[0038] 6, when the outer peripheral surface of small diameter portion 16 is roughly the outer peripheral surface of small diameter step portion 16b and small diameter step portion 16b is cylindrical with a generatrix parallel to optical axis Z, the radius of small diameter step portion 16b is constant, and therefore the radius of small diameter step portion 16b is taken as C. Unlike the example in FIG. 6, in an illumination optical system in which the radius of small diameter portion 16 from step surface 14 to chamfered portion 16a is not constant, the average value of the maximum and minimum radii of small diameter portion 16 in this range may be taken as C.

[0039] It is preferable that the illumination optical system 10 satisfy the following conditional expression (2). Here, D is the distance in the direction of the optical axis Z from the position of the first surface 10a closest to the light guide to the step surface 14. E is the distance in the direction of the optical axis Z from the intersection of the second surface 10b and the optical axis Z to the step surface 14. As an example, FIG. 6 shows the above distances D and E. By ensuring that the corresponding value of conditional expression (2) is not equal to or less than the lower limit, the amount of light absorption at the outer peripheral surface of the large diameter portion 12 can be suppressed, which is advantageous for improving the transmission efficiency. By ensuring that the corresponding value of conditional expression (2) is not equal to or greater than the upper limit, the illumination optical system 10 becomes less likely to break, which is advantageous for preventing damage. 0.45 <D / (D+E)<0.95 (2)

[0040] To obtain better characteristics, the lower limit of conditional expression (2) is more preferably set to 0.48, even more preferably to 0.51, and even more preferably to 0.55. To obtain even better characteristics, the upper limit of conditional expression (2) is more preferably set to 0.85, even more preferably to 0.75, and even more preferably to 0.65. For example, it is more preferable that the illumination optical system 10 satisfy at least one of the following conditional expressions (2-1), (2-2), and (2-3). 0.48 <D / (D+E)<0.85 (2-1) 0.51 <D / (D+E)<0.75 (2-2) 0.55 <D / (D+E)<0.65 (2-3)

[0041] When the radius of curvature of the first concave surface portion 1 is R1, it is preferable that the illumination optical system 10 satisfies the following conditional expression (3). As an example, the above radius of curvature R1 is shown in FIG. 6. By ensuring that the corresponding value of conditional expression (3) is not equal to or less than the lower limit, it is possible to prevent the outermost diameter portion 12b from becoming too large, which is advantageous for miniaturization. By ensuring that the corresponding value of conditional expression (3) is not equal to or greater than the upper limit, it is easier for the light to be spread by refraction at the first concave surface portion 1, which is advantageous for wide light distribution. 0.05 <R1 / H<0.5 (3)

[0042] To obtain better characteristics, the lower limit of conditional expression (3) is preferably set to 0.1, more preferably 0.12, and even more preferably 0.14. To obtain even better characteristics, the upper limit of conditional expression (3) is preferably set to 0.4, more preferably 0.3, and even more preferably 0.21. For example, it is more preferable that the illumination optical system 10 satisfy at least one of the following conditional expressions (3-1), (3-2), and (3-3). 0.1 <R1 / H<0.4 (3-1) 0.12 <R1 / H<0.3 (3-2) 0.14 <R1 / H<0.21 (3-3)

[0043] If the distance between the vertices of adjacent first concave surface portions 1 on a plane perpendicular to the optical axis Z is P, it is preferable that the illumination optical system 10 satisfy the following conditional expression (4). As an example, the above-mentioned distance P is shown in FIG. 6. By ensuring that the corresponding value of conditional expression (4) is not equal to or less than the lower limit, the values ​​of C and P do not become too close, making it easy to increase the number of first concave surface portions 1 formed on the first surface 10a, which is advantageous for wide light distribution. By ensuring that the corresponding value of conditional expression (4) is not equal to or greater than the upper limit, the amount of light absorption on the outer circumferential surface of the large diameter portion 12 can be suppressed, which is advantageous for improving transmission efficiency. 0.8<(CP) / D<2 (4)

[0044] In this specification, when the tangent plane of the first concave surface portion 1 at a certain point on the first concave surface portion is a plane perpendicular to the optical axis Z, the certain point is conveniently referred to as the "surface vertex" of the first concave surface portion 1. This concept of "surface vertex" can also be applied to the second concave surface portion described below. In FIG. 6, as an example, the tangent plane perpendicular to the optical axis Z is shown by a two-dot chain line. In the example of FIG. 6, the point on the first concave surface portion 1 closest to the object to be illuminated, i.e., the point at which the depth of the first concave surface portion 1 is greatest, is the surface vertex. Here, in this specification, the "depth of the first concave surface portion 1" refers to the distance in the direction of the optical axis Z from the point on the first concave surface portion 1 closest to the light guide to the point on the first concave surface portion 1 closest to the object to be illuminated.

[0045] To obtain better characteristics, the lower limit of conditional expression (4) should preferably be set to 0.82, more preferably 0.84, and even more preferably 0.85. To obtain better characteristics, the upper limit of conditional expression (4) should preferably be set to 1.7, more preferably 1.5, and even more preferably 1.3. For example, it is more preferable that the illumination optical system 10 satisfy at least one of the following conditional expressions (4-1), (4-2), and (4-3). 0.82<(CP) / D<1.7 (4-1) 0.84<(CP) / D<1.5 (4-2) 0.85<(CP) / D<1.3 (4-3)

[0046] It is preferable that the illumination optical system 10 satisfies the following conditional expression (5): By ensuring that the corresponding value of conditional expression (5) is not equal to or less than the lower limit, the gaps between the first concave surface portions 1 can be made smaller, making it easier to arrange the first concave surface portions 1 more densely, which is advantageous for wide light distribution. By ensuring that the corresponding value of conditional expression (5) is not equal to or greater than the upper limit, the depth of the first concave surface portions 1 can be made deeper, making it easier to spread the light rays more, which is advantageous for wide light distribution. 0.02<(2×R1-P) / C<0.25 (5)

[0047] To obtain better characteristics, the lower limit of conditional expression (5) is more preferably set to 0.03, even more preferably to 0.04, and even more preferably to 0.05. To obtain better characteristics, the upper limit of conditional expression (5) is more preferably set to 0.23, even more preferably to 0.21, and even more preferably to 0.2. For example, it is more preferable that the illumination optical system 10 satisfy at least one of the following conditional expressions (5-1), (5-2), and (5-3). 0.03<(2×R1-P) / C<0.23 (5-1) 0.04<(2×R1-P) / C<0.21 (5-2) 0.05<(2×R1-P) / C<0.2 (5-3)

[0048] It is preferable that the illumination optical system 10 satisfies the following conditional expression (6). By ensuring that the corresponding value of conditional expression (6) is not equal to or less than the lower limit, the depth of the first concave surface portion 1 can be made deeper, making it easier to spread the light rays, which is advantageous for wide light distribution. However, if the depth of the first concave surface portion 1 is too deep, the light rays will spread too much, making it easier for light absorption at the outer peripheral surface of the large diameter portion 12 to occur. Therefore, by ensuring that the corresponding value of conditional expression (6) is not equal to or greater than the upper limit, the depth of the first concave surface portion 1 can be prevented from becoming too deep, which reduces the amount of light absorption at the outer peripheral surface of the large diameter portion 12, which is advantageous for improving transmission efficiency.

[0049]

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[0050] To obtain better characteristics, the lower limit of conditional expression (6) is more preferably set to 0.05, even more preferably to 0.06, and even more preferably to 0.07. To obtain even better characteristics, the upper limit of conditional expression (6) is more preferably set to 0.25, even more preferably to 0.2, and even more preferably to 0.18. For example, it is more preferable that the illumination optical system 10 satisfy at least one of the following conditional expressions (6-1), (6-2), and (6-3).

[0051]

number

[0052]

number

[0053]

number

[0054] It is preferable that the illumination optical system 10 satisfies the following conditional expression (7): By ensuring that the corresponding value of conditional expression (7) is not equal to or less than the lower limit, the amount of light absorption on the outer peripheral surface of the large diameter portion 12 can be suppressed, which is advantageous for improving the transmission efficiency. By ensuring that the corresponding value of conditional expression (7) is not equal to or greater than the upper limit, the diameter of the outermost diameter portion 12b can be prevented from becoming too large, which is advantageous for miniaturization. 0.9 <H / (D+E)<1.5 (7)

[0055] To obtain better characteristics, the lower limit of conditional expression (7) should preferably be set to 0.93, more preferably to 0.96, and even more preferably to 1. To obtain better characteristics, the upper limit of conditional expression (7) should preferably be set to 1.4, more preferably to 1.35, and even more preferably to 1.3. For example, it is more preferable that the illumination optical system 10 satisfy at least one of the following conditional expressions (7-1), (7-2), and (7-3). 0.93 <H / (D+E)<1.4 (7-1) 0.96 <H / (D+E)<1.35 (7-2) 1 <H / (D+E)<1.3 (7-3)

[0056] When the radius of the light guide 50 is G, it is preferable that the illumination optical system 10 satisfies the following conditional expression (8). As an example, the radius G is shown in FIG. 6. If the diameter of the light guide 50 is not constant, the radius of the exit end surface of the light guide 50 is set to G. By ensuring that the corresponding value of conditional expression (8) is not equal to or less than the lower limit, the diameter of the first surface 10a can be made larger than the diameter of the light guide 50, thereby suppressing light leakage and advantageously improving transmission efficiency. By ensuring that the corresponding value of conditional expression (8) is not equal to or greater than the upper limit, the effect of light reflection on the outer peripheral surface of the small diameter portion 16 can be further improved. 1 <C / G<1.5 (8)

[0057] To obtain better characteristics, the lower limit of conditional expression (8) should preferably be set to 1.03, more preferably 1.04, and even more preferably 1.05. To obtain even better characteristics, the upper limit of conditional expression (8) should preferably be set to 1.4, more preferably 1.3, and even more preferably 1.2. For example, it is more preferable that the illumination optical system 10 satisfy at least one of the following conditional expressions (8-1), (8-2), and (8-3). 1.03 <C / G<1.4 (8-1) 1.04 <C / G<1.3 (8-2) 1.05 <C / G<1.2 (8-3)

[0058] Next, a modified example of the present disclosure will be described with reference to FIG. 17. FIG. 17 shows the configuration of an illumination optical system 510 in a cross section including the optical axis Z, as a modified example of the present disclosure. The illumination optical system 510 shown in FIG. 17 corresponds to Example 5, which will be described later. The illumination optical system 510 in FIG. 17 differs significantly from the illumination optical system 10 in FIG. 1 in that the surface closest to the light guide includes a second concave surface portion 502. The following description of the modified example will mainly focus on this difference, and components similar to those of the illumination optical system 10 in FIG. 1 will be assigned the same reference numerals and some overlapping description will be omitted.

[0059] The illumination optical system 510 has a step structure including a large diameter section 12 located on the side of the object to be illuminated and a small diameter section 516 located on the side of the light guide and configured to have a smaller diameter than the large diameter section 12. A step surface 14 is formed between the small diameter section 516 and the large diameter section 12, which is a plane perpendicular to the optical axis Z of the illumination optical system 510 and forms a step where the outer diameter dimension changes.

[0060] The small diameter portion 516 includes a first surface 510a, a chamfered portion 16a, and a small diameter step portion 516b. The first surface 510a is the surface of the illumination optical system 510 closest to the light guide. The chamfered portion 16a has a curved surface connecting the first surface 510a and the surface of the small diameter step portion 516b. The small diameter step portion 516b is cylindrical with a generatrix parallel to the optical axis Z.

[0061] The first surface 510a has a plurality of first concave surface portions 501K with the same radius of curvature, and at least one second concave surface portion 502. The second concave surface portion 502 is located closer to the optical axis Z than the first concave surface portion 501K and has a radius of curvature larger than that of the first concave surface portion 501K. The second concave surface portion 502 provides a diverging effect on incident light like a concave lens. As an example, FIG. 17 shows an example in which the first surface 510a has only one second concave surface portion 502, which is spherical, and the vertex of the second concave surface portion 502 is located on the optical axis.

[0062] The plurality of first concave surface portions 501K are arranged radially outward of the second concave surface portion 502 so as to surround the second concave surface portion 502. The first concave surface portion 501K is configured to have a light diffusing surface. In FIG. 17, the surface having the light diffusing surface is schematically shown as a surface with many small dots, and this illustration method is also used in the drawings of other embodiments described below. The first concave surface portion 501K has the same configuration as the first concave surface portion 1 in FIG. 1, except that it has a light diffusing surface.

[0063] During surgery using an endoscope, blood or other substances may adhere to the illumination window, which is located closer to the subject than the illumination optical system. If the intensity of the illumination light is too strong, the blood adhering to the illumination window may coagulate. In particular, the illumination light on and near the optical axis has a higher density of light rays and a higher intensity than the illumination light around the outer diameter. In this example, by positioning the second concave surface portion 502, which has a larger radius of curvature than the first concave surface portion 501K, closer to the optical axis Z than the first concave surface portion 501K, the density of light rays on and near the optical axis can be reduced. This makes it easier to prevent blood adhering to the illumination window from coagulating.

[0064] The illumination optical system 510 preferably satisfies the following conditional expression (9). Here, the radius of curvature of the second concave surface portion 502 is R2. The distance along the optical axis Z from the intersection of the second concave surface portion 502 and the optical axis Z to the second surface 10b is T. As an example, FIG. 17 shows the distance T. By ensuring that the corresponding value of conditional expression (9) is not equal to or less than the lower limit, the radius of curvature of the second concave surface portion 502 does not become too close to the radius of curvature of the first concave surface portion 501K, and the distance along the optical axis between the vertex of the second concave surface portion 502 and the vertex of the first concave surface portion 501K does not become too short, thereby reducing the concentration of light rays on and near the optical axis. This makes it easier to prevent blood adhering to the illumination window from coagulating. By ensuring that the corresponding value of conditional expression (9) is not equal to or greater than the upper limit, the thickness of the illumination optical system 510 on the optical axis can be increased, making the illumination optical system 510 less likely to crack, which is advantageous in preventing damage. 0.55 <R2 / T<1.3 (9)

[0065] To obtain better characteristics, the lower limit of conditional expression (9) is more preferably set to 0.6, even more preferably set to 0.65, and even more preferably set to 0.7. To obtain better characteristics, the upper limit of conditional expression (9) is more preferably set to 1.2, even more preferably set to 1.1, and even more preferably set to 1. For example, it is more preferable that the illumination optical system 510 satisfy at least one of the following conditional expressions (9-1), (9-2), and (9-3). 0.6 <R2 / T<1.2 (9-1) 0.65 <R2 / T<1.1 (9-2) 0.7 <R2 / T<1 (9-3)

[0066] 17, first surface 510a has only one second concave surface portion 502, but the technology of the present disclosure is not limited to this. The surface of the illumination optical system closest to the light guide side may have multiple second concave surface portions located closer to optical axis Z than the first concave surface portions and having a larger radius of curvature than the first concave surface portions. In this case, R2 above is the radius of curvature of the second concave surface portion closest to optical axis Z, and T above is the distance in the direction of optical axis Z from the intersection of the optical axis Z and the second concave surface portion closest to optical axis Z.

[0067] Moreover, it is preferable that the illumination optical system 510 according to the modified example satisfies at least one of the above-mentioned conditional expressions (1) to (8).

[0068] In the above modification, the first concave surface portion 501K has a light diffusing surface, but it is also possible to configure the first surface 510a to have the second concave surface portion 502, and the first concave surface portion 501K not to have a light diffusing surface.

[0069] The technology of the present disclosure is not necessarily limited to the examples shown in FIGS. 1 and 17, and various modifications are possible within the scope of the gist of the technology of the present disclosure.

[0070] 1 shows an example in which the illumination optical system 10 is made up of one optical element, but in the technology of the present disclosure, the illumination optical system may be made up of multiple optical elements. The small diameter section and the large diameter section may be made up of separate optical elements that are cemented together to form the illumination optical system.

[0071] Although FIG. 1 shows an example in which the first concave surface portion 1 is spherical, in the technology of the present disclosure, the first concave surface portion may be aspherical. When the first concave surface portion is aspherical, the paraxial radius of curvature of the first concave surface portion may be R1. Similarly, while FIG. 17 shows an example in which the second concave surface portion 502 is spherical, in the technology of the present disclosure, the second concave surface portion may be aspherical. When the second concave surface portion is aspherical, the paraxial radius of curvature of the second concave surface portion may be R2.

[0072] 1 shows an example in which the outer shape of the first concave surface portion 1 in a plane perpendicular to the optical axis Z is substantially hexagonal, but in the technology of the present disclosure, the outer shape of the first concave surface portion is not limited to this. Also, in Fig. 1, an example in which the first concave surface portions 1 are arranged in a honeycomb pattern is shown, but in the technology of the present disclosure, the method of arranging the first concave surface portions is not limited to this.

[0073] Although Fig. 1 shows an example in which there is only one step where the outer diameter dimension changes, the technology disclosed herein may have multiple steps where the outer diameter dimension changes. When there are multiple planar step surfaces that are perpendicular to the optical axis Z of the illumination optical system and that constitute steps where the outer diameter dimension changes, it is preferable that the step surface that forms the boundary between the light-reflecting surface and the light-absorbing surface be the step surface closest to the illuminated object. In this case, it is advantageous to widen the area of ​​the light-reflecting surface as much as possible and obtain higher transmission efficiency.

[0074] 1 shows a configuration in which the large diameter portion 12 and the small diameter portion 16 include chamfered portions 12a and 16a, respectively, but the technology of the present disclosure also allows for a configuration in which no chamfered portions are included. Also, while the example of FIG. 1 does not include a chamfered portion between the outermost diameter portion 12b and the second surface 10b, the technology of the present disclosure may include a chamfered portion in this portion.

[0075] The preferred and possible configurations described in the above embodiments and variants, including configurations relating to conditional expressions, can be combined in any manner within a range that does not result in contradictions, and it is preferable that they be selectively adopted as appropriate depending on the required specifications.

[0076] As an example, a preferred aspect of the illumination optical system of the present disclosure is an illumination optical system arranged on the exit side of a light guide of an endoscope, where the surface of the illumination optical system closest to the light guide is defined as the first surface and the surface closest to the illuminated body is defined as the second surface, and the outer peripheral surface of the illumination optical system from the first surface to the second surface is a light-reflecting surface on the first surface side and a light-absorbing surface on the second surface side, and a step surface is formed at the boundary between the light-reflecting surface and the light-absorbing surface, the step surface being a surface perpendicular to the optical axis of the illumination optical system and constituting a step where the outer diameter dimension changes, and the first surface is provided at a small diameter portion whose diameter is smaller than the outermost diameter portion where the outer diameter of the illumination optical system is maximum, and has a plurality of first concave surface portions with the same radius of curvature, and satisfies the above conditional expressions (1), (2), and (3).

[0077] Next, examples of the illumination optical system of the present disclosure will be described with reference to the drawings. All of Examples 1 to 6 shown below are made up of a single optical element and have a rotationally symmetric configuration with the optical axis Z as the axis of rotation.

[0078] [Example 1] The configuration of the illumination optical system 10 of Example 1 is shown in Figures 1, 2, and 3, and its optical path is shown in Figure 4. Since the configuration is as described above, some of the redundant explanation will be omitted here. In the illumination optical system 10, the first surface 10a, which is the surface closest to the light guide, has multiple first concave surface portions 1 with the same radius of curvature. The second surface 10b, which is the surface closest to the illuminated object, is flat. A step surface 14 perpendicular to the optical axis Z is formed at the boundary between the small diameter portion 16 on the light guide side and the large diameter portion 12 on the illuminated object side. The outer peripheral surface of the small diameter portion 16 is a light-reflecting surface, and the outer peripheral surface of the large diameter portion 12 is a light-absorbing surface.

[0079] Table 1 shows various data for the illumination optical system 10. In addition to the values ​​used in the above-mentioned conditional expressions, Table 1 also shows the following values: "Sag1" is the depth of the first concave surface 1. "Rb" is the radius of curvature of the second surface 10b. "Nd" is the refractive index at the d-line of the optical elements that make up the illumination optical system 10. "νd" is the Abbe number of the optical elements that make up the illumination optical system 10 based on the d-line. The wavelength of the d-line is treated as 587.56 nm (nanometers).

[0080] [Table 1]

[0081] Fig. 7 shows a graph of the light distribution characteristics of the illumination optical system 10 of Example 1. In Fig. 7, the horizontal axis represents the angle θ from the optical axis Z, and the vertical axis represents the radiant intensity. The half angles at half maximum of this graph are listed together with the values ​​of the other Examples in Table 7, which will be described later.

[0082] The symbols, meanings, notation and illustration methods of each data item related to the above-mentioned Example 1 are basically the same in the following Examples unless otherwise specified, and therefore, redundant explanations will be omitted below.

[0083] In the data in each table in this specification, millimeters are used as the unit of length and degrees as the unit of angle, but since the optical system can be used with proportional enlargement or reduction, other appropriate units can also be used. Also, the values ​​shown in the data in each table are rounded to a predetermined number of decimal places.

[0084] [Example 2] FIG. 8 shows the configuration and optical path of an illumination optical system 210 of the second embodiment in a cross section including the optical axis Z, and FIG. 9 shows the configuration in a plane perpendicular to the optical axis Z as viewed from the light guide side.

[0085] The first surface 210a of the illumination optical system 210, which is the surface closest to the light guide, has a plurality of first concave surface portions 201K with the same radius of curvature. On the first surface 210a, the portion inside a diameter of 0.76 mm (millimeters) is a light diffusing surface. The illumination optical system 210 differs from the illumination optical system 10 of Example 1 in that the first concave surface portion 201K has a light diffusing surface, but the other configurations are the same as those of the illumination optical system 10 of Example 1.

[0086] Various data of the illumination optical system 210 are shown in Table 2, and a graph of the light distribution characteristics is shown in FIG. [Table 2]

[0087] [Example 3] FIG. 11 shows the configuration and optical path of an illumination optical system 310 of Example 3 in a cross section including the optical axis Z, and FIG. 12 shows the configuration in a plane perpendicular to the optical axis Z as viewed from the light guide side.

[0088] The illumination optical system 310 has a configuration substantially similar to that of the illumination optical system 10 of Example 1, but is configured such that the radius of the small diameter portion is smaller and the radius of the outermost diameter portion is larger than that of the illumination optical system 10 of Example 1.

[0089] Various data of the illumination optical system 310 are shown in Table 3, and a graph of the light distribution characteristics is shown in FIG. [Table 3]

[0090] [Example 4] FIG. 14 shows the configuration and optical path of an illumination optical system 410 of Example 4 in a cross section including the optical axis Z, and FIG. 15 shows the configuration in a plane perpendicular to the optical axis Z as viewed from the light guide side.

[0091] The illumination optical system 410 has a configuration substantially similar to that of the illumination optical system 10 of Example 1, but is configured such that the radius of the small diameter portion is larger and the radius of the outermost diameter portion is smaller than that of the illumination optical system 10 of Example 1.

[0092] Various data of the illumination optical system 410 are shown in Table 4, and a graph of the light distribution characteristics is shown in FIG. [Table 4]

[0093] [Example 5] FIG. 17 shows the configuration of the illumination optical system 510 of Example 5 in a cross section including the optical axis Z, FIG. 18 shows the configuration and optical path in the cross section including the optical axis Z, and FIG. 19 shows the configuration in a plane perpendicular to the optical axis Z as viewed from the light guide side.

[0094] The illumination optical system 510 has the configuration of the above-described modified example. The configuration of the fifth embodiment is as described above in the description of the modified example, so some of the overlapping description will be omitted here. The illumination optical system 510 is significantly different from the illumination optical system 10 of the first embodiment in that the first surface 510a has the second concave surface portion 502 and the first concave surface portion 501K has a light diffusing surface, but the other configurations are substantially the same.

[0095] The first surface 510a, which is the surface closest to the light guide, has one second concave surface portion 502 and multiple first concave surface portions 501K with the same radius of curvature. The second concave surface portion 502 has a radius of curvature larger than that of the first concave surface portion 501K. The vertex of the second concave surface portion 502 is located on the optical axis. Multiple first concave surface portions 501K are arranged on the outer diameter side of the second concave surface portion 502. The second surface 10b, which is the surface closest to the object to be illuminated, is flat. A step surface 14 perpendicular to the optical axis Z is formed at the boundary between the small diameter portion 516 on the light guide side and the large diameter portion 12 on the object to be illuminated. The outer peripheral surface of the small diameter portion 516 is a light-reflecting surface, and the outer peripheral surface of the large diameter portion 12 is a light-absorbing surface.

[0096] Table 5 shows various data of the illumination optical system 510, and FIG. 20 shows a graph of the light distribution characteristics. "D+ET" in Table 5 is the distance in the direction of the optical axis Z from the point on the first surface 510a closest to the light guide to the vertex of the second concave surface portion 502. The diameter of the second concave surface portion 502 is 0.47 mm (millimeters). On the first surface 510a, the portion on the outer diameter side of the 0.47 mm (millimeters) is a light diffusing surface. In other words, the first concave surface portion 501K has a light diffusing surface.

[0097] [Table 5]

[0098] [Example 6] Figure 21 shows the configuration of the illumination optical system 610 of Example 6 in a cross section including the optical axis Z, Figure 22 shows the configuration and optical path in the cross section including the optical axis Z, and Figure 23 shows the configuration in a plane perpendicular to the optical axis Z as viewed from the light guide side.

[0099] The illumination optical system 610 of Example 6 has the configuration of the above-described modified example. The illumination optical system 610 of Example 6 is significantly different from the illumination optical system 510 of Example 5 in that it has a second concave surface portion 603, but the other configurations are substantially the same.

[0100] The illumination optical system 610 has a stepped structure including a large diameter section 12 located on the side of the object to be illuminated and a small diameter section 616 located on the side of the light guide and configured to have a smaller diameter than the large diameter section 12. A step surface 14 is formed between the small diameter section 616 and the large diameter section 12, which is a surface perpendicular to the optical axis Z of the illumination optical system 610 and forms a step where the outer diameter dimension changes.

[0101] The small diameter portion 616 includes a first surface 610a, a chamfered portion 16a, and a small diameter step portion 616b. The first surface 610a is the surface of the illumination optical system 610 closest to the light guide. The chamfered portion 16a has a curved surface connecting the first surface 610a and the surface of the small diameter step portion 616b. The small diameter step portion 616b is cylindrical with a generatrix parallel to the optical axis Z.

[0102] The first surface 610a, which is the surface closest to the light guide, has one second concave surface portion 602K, one second concave surface portion 603, and multiple first concave surface portions 601K with the same radius of curvature. The vertex of the second concave surface portion 602K is located on the optical axis. A substantially ring-shaped second concave surface portion 603 is arranged on the outer diameter side of the second concave surface portion 602K, and multiple first concave surface portions 601K are arranged on the outer diameter side of the second concave surface portion 603. The first concave surface portion 601K, the second concave surface portion 602K, and the second concave surface portion 603 have a diverging effect on incident light. The second surface 10b, which is the surface closest to the illuminated object, is flat. A step surface 14 perpendicular to the optical axis Z is formed at the boundary between the small diameter portion 616 on the light guide side and the large diameter portion 12 on the illuminated object side. The outer peripheral surface of the small diameter portion 616 is a light reflecting surface, and the outer peripheral surface of the large diameter portion 12 is a light absorbing surface.

[0103] Table 6 shows various data of the illumination optical system 610, and FIG. 24 shows a graph of the light distribution characteristics. In Table 6, "R2" is the radius of curvature of the second concave surface portion 602K. "T" is the distance from the vertex of the second concave surface portion 602K to the second surface 10b along the optical axis Z. "D+ET" is the distance from the point on the first surface 610a closest to the light guide to the vertex of the second concave surface portion 602K along the optical axis Z. "R3" is the radius of curvature of the second concave surface portion 603. The diameter of the second concave surface portion 602K is 0.35 mm (millimeters). The inner diameter of the second concave surface portion 603 is 0.35 mm (millimeters), and the outer diameter is 0.57 mm (millimeters). On the first surface 610a, the portion closer to the optical axis than the 0.35 mm diameter and the portion closer to the outer diameter than the 0.57 mm diameter are light diffusing surfaces. That is, the second concave surface portion 602K and the first concave surface portion 601K have a light diffusing surface.

[0104] The illumination optical system 610 has the second concave surface portion 603 in addition to the second concave surface portion 602K, which makes it more advantageous in preventing coagulation of blood adhering to the illumination window than the illumination optical system 510. Furthermore, the illumination optical system 610 has the advantage of wider light distribution than the illumination optical system 510 because the second concave surface portion 602K has a light diffusing surface.

[0105] [Table 6]

[0106] Table 7 shows the corresponding values ​​of conditional expressions (1) to (8) for the illumination optical systems of Examples 1 to 6, and the corresponding value of conditional expression (9) for the illumination optical systems of Examples 5 and 6. The "θHWHM" row in Table 7 also shows the half angles at half maximum for the graphs of the light distribution characteristics of each Example. The values ​​in Table 7 may be used as the upper or lower limit values ​​for the conditional expressions to set preferred ranges for the conditional expressions.

[0107] [Table 7]

[0108] As described above, all of the illumination optical systems of Examples 1 to 6 have a wide light distribution angle while being constructed to be compact.

[0109] Next, an endoscope according to an embodiment of the present disclosure will be described. Fig. 25 shows a schematic overall configuration diagram of an endoscope according to an embodiment of the present disclosure. The endoscope 100 shown in Fig. 25 mainly includes an operation unit 102, an insertion unit 104, and a universal cord 106 connected to a connector unit (not shown). The majority of the insertion unit 104 is a flexible section 107 that can bend in any direction along the insertion path. A bending section 108 is connected to the tip of the flexible section 107, and a tip unit 110 is connected to the tip of the bending section 108. The bending section 108 is provided to direct the tip unit 110 in a desired direction, and bending operation can be performed by turning a bending operation knob 109 provided on the operation unit 102.

[0110] An illumination optical system 10 according to an embodiment of the present disclosure is disposed at the inner tip of the tip portion 110. Furthermore, a light guide 50 is disposed inside the endoscope so that the tip of the light guide 50 faces the illumination optical system 10. Note that in Fig. 25, the illumination optical system 10 is illustrated schematically, and the light guide 50 is partially omitted from illustration.

[0111] Although the technology of the present disclosure has been described above using embodiments and examples, the technology of the present disclosure is not limited to the above embodiments and examples and can be modified in various ways. For example, the dimensions of each part, the radii of curvature of the first concave surface portion and the second concave surface portion, and the refractive index and Abbe number of the optical elements that make up the illumination optical system are not limited to the values ​​shown in the above examples and can take other values.

[0112] The following additional notes are provided regarding the above embodiments and examples. [Appendix 1] An illumination optical system disposed on the exit side of a light guide of an endoscope, In the illumination optical system, the surface closest to the light guide is designated as a first surface, and the surface closest to the object to be illuminated is designated as a second surface, an outer peripheral surface of the illumination optical system from the first surface to the second surface is a light reflecting surface on the first surface side and a light absorbing surface on the second surface side; a step surface that is perpendicular to the optical axis of the illumination optical system and that constitutes a step at which an outer diameter dimension changes is formed at the boundary between the light reflecting surface and the light absorbing surface, the first surface is provided at a small diameter portion having a diameter smaller than an outermost diameter portion where the outer diameter of the illumination optical system is maximum, and has a plurality of first concave surface portions having the same radius of curvature; The radius of the small diameter portion is C, The radius of the outermost diameter portion is H, The distance in the direction of the optical axis from the position of the first surface closest to the light guide to the step surface is D, The distance in the direction of the optical axis from the intersection point of the second surface and the optical axis to the step surface is E, When the radius of curvature of the first concave surface portion is R1, 0.4 <C / H<0.95 (1) 0.45 <D / (D+E)<0.95 (2) 0.05 <R1 / H<0.5 (3) An illumination optical system that satisfies conditional expressions (1), (2), and (3) expressed as follows: [Appendix 2] When the distance between the vertices of the adjacent first concave surface portions on the plane perpendicular to the optical axis is P, 0.8<(CP) / D<2 (4) 10. The illumination optical system according to claim 1, which satisfies conditional expression (4) expressed as follows: [Appendix 3] When the distance between the vertices of the adjacent first concave surface portions on the plane perpendicular to the optical axis is P, 0.02<(2×R1-P) / C<0.25 (5) 10. The illumination optical system according to claim 1, wherein the illumination optical system satisfies conditional expression (5) below. [Appendix 4] When the distance between the vertices of the adjacent first concave surface portions on the plane perpendicular to the optical axis is P,

number

[0113] 1, 201K, 501K, 601K 1st concave part 10, 210, 310, 410, 510, 610 Illumination optical system 10a, 210a, 510a, 610a Page 1 10b 2nd side 12 Large diameter section 12a Chamfered part 12b Outermost diameter part 14 Step surface 16, 516, 616 Small diameter section 16a Chamfer 16b, 516b, 616b Small diameter stepped section 50 Light Guide 100 Endoscope 102 Operation section 104 Insertion section 106 Universal Code 107 Soft part 108 Curved section 109 Curvature control knob 110 Tip 502, 602K, 603 2nd concave part C radius D distance E distance G radius H radius L1X Lens P interval R1 radius of curvature T distance Z optical axis

Claims

1. An illumination optical system disposed on the exit side of a light guide of an endoscope, In the illumination optical system, the surface closest to the light guide is designated as a first surface, and the surface closest to the object to be illuminated is designated as a second surface, an outer peripheral surface of the illumination optical system from the first surface to the second surface is a light reflecting surface on the first surface side and a light absorbing surface on the second surface side; a step surface that is perpendicular to the optical axis of the illumination optical system and that constitutes a step at which an outer diameter dimension changes is formed at the boundary between the light reflecting surface and the light absorbing surface, the first surface is provided at a small diameter portion having a diameter smaller than an outermost diameter portion where the outer diameter of the illumination optical system is maximum, and has a plurality of first concave surface portions having the same radius of curvature; The radius of the small diameter portion is C, The radius of the outermost diameter portion is H, The distance in the direction of the optical axis from the position of the first surface closest to the light guide to the step surface is D, The distance in the direction of the optical axis from the intersection point of the second surface and the optical axis to the step surface is E, When the radius of curvature of the first concave surface portion is R1, 0.4<C / H<0.95 (1) 0.45<D / (D+E)<0.95 (2) 0.05<R1 / H<0.5 (3) An illumination optical system that satisfies conditional expressions (1), (2), and (3) expressed by the following formulas.

2. When the distance between the vertices of the adjacent first concave surface portions on the plane perpendicular to the optical axis is P, 0.8<(CP) / D<2 (4) 2. The illumination optical system according to claim 1, which satisfies conditional expression (4) expressed as follows:

3. When the distance between the vertices of the adjacent first concave surface portions on the plane perpendicular to the optical axis is P, 0.02<(2×R1-P) / C<0.25 (5) 2. The illumination optical system according to claim 1, which satisfies conditional expression (5) expressed as follows:

4. When the distance between the vertices of the adjacent first concave surface portions on the plane perpendicular to the optical axis is P, [Equation 1] 2. The illumination optical system according to claim 1, which satisfies conditional expression (6) expressed as follows:

5. 0.9<H / (D+E)<1.5 (7) 2. The illumination optical system according to claim 1, which satisfies conditional expression (7) expressed as follows:

6. When the radius of the light guide is G, 1<C / G<1.5 (8) 2. The illumination optical system according to claim 1, which satisfies conditional expression (8) expressed as follows:

7. The illumination optical system of claim 1 , wherein at least one of the first concave portions includes a light diffusing surface.

8. the first surface has at least one second concave surface portion located closer to the optical axis than the first concave surface portion and having a larger radius of curvature than the radius of curvature of the first concave surface portion; The radius of curvature of the second concave surface portion closest to the optical axis is R2, When the distance in the optical axis direction from the intersection of the second concave surface portion closest to the optical axis and the optical axis to the second surface is T, 0.55<R2 / T<1.3 (9) 2. The illumination optical system according to claim 1, which satisfies conditional expression (9) expressed as follows:

9. A light guide and An endoscope comprising the illumination optical system according to any one of claims 1 to 8.

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