Illumination device and endoscope

1. An illumination device comprising:

a light-emitting part that has an emission end from which illumination light is emitted;

a diffusion optical member that is disposed around a predetermined axis in a circumferential direction, that is provided with an incident end disposed so as to be opposed to the emission end, that guides the illumination light entering from the incident end while diffusing the illumination light, and that emits the illumination light from a surface thereof; and

a reflective layer that is disposed adjacent to a radially inward surface of the diffusion optical member and that reflects the illumination light radially outward,

wherein the diffusion optical member is provided with a notch portion having a shape in which a part of a circumferential section of a cylinder is removed along an entire length thereof in a direction along the predetermined axis and is also provided with, at a section thereof close to the notch portion, an inclined surface having a shape with which a notch angle is increased as a distance from the incident end is increased in the direction along the predetermined axis.

2. The illumination device according to claim 1 , wherein the inclined surface is provided with a reflecting means that reflects the illumination light that has been guided inside the diffusion optical member toward the inside of the diffusion optical member.

3. The illumination device according to claim 1 , wherein the inclined surface is a flat surface.

4. The illumination device according to claim 3 , wherein an angle between the inclined surface and the predetermined axis is equal to or greater than 20 degrees and is equal to or less than 70 degrees.

5. The illumination device according to claim 1 , wherein the inclined surface has, at a section thereof close to the incident end, a surface whose angle with respect to the predetermined axis is less than the angle between the inclined surface and the axis.

6. The illumination device according to claim 1 , wherein at least a partial section of the emission end is disposed at a position of the incident end that overlaps with the inclined surface in the circumferential direction.

7. The illumination device according to claim 1 , wherein the notch angle is equal to or greater than 100 degrees and is equal to or less than 240 degrees at a position farthest from the incident end of the diffusion optical member in the direction along the predetermined axis.

8. The illumination device according to claim 1 , wherein the diffusion optical member has a substantially fan shape in transverse section perpendicular to the predetermined axis.

9. The illumination device according to claim 1 , further comprising:

a light-shielding region that limits an emission region for the illumination light in the diffusion optical member to a partial section around the predetermined axis in the circumferential direction,

wherein an angle of the light-shielding region around the predetermined axis is equal to or greater than 100 degrees and is equal to or less than 240 degrees at a position farthest from the incident end of the diffusion optical member in the direction along the predetermined axis.

10. The illumination device according to claim 9 , wherein the light-shielding region comprises the notch portion.

11. The illumination device according to claim 10 , wherein the diffusion optical member has a substantially fan shape in transverse section perpendicular to the predetermined axis.

12. An endoscope comprising:

the illumination device according to claim 1 ;

an imaging optical system that is disposed along an axis parallel to the predetermined axis; and

an air-supply or water-supply nozzle that is disposed at an opposite side from the emission region across the axis.

13. The endoscope according to claim 12 , wherein the axis is a central axis of the imaging optical system.