Illumination Unit for Endoscope

The invention relates to an illumination unit for an endoscope, and more particularly, to such unit of the type having a cover glass located within an illumination window and through which illuminating light transmitted through a light guide disposed within a flexible tube of an endoscope exits.

In the conventional arrangement of illumination unit for an endoscope of the type described, the cover glass is located forwardly of the end face of the light guide from which light exits. The said cover glass is disposed in a water-tight manner within an illumination window which is mounted at the distal end of the endoscope. The cover glass is often formed with a concave lens portion in order to increase the illumination angle of exiting light rays.

One example of such arrangement is illustrated in FIG. 1. Cover glass 1 is tightly fitted into illumination window 103 formed at the distal end 102 of an endoscope so as to form a water-tight seal with the window. Light guide member 104, which comprises a bundle of optical fibres, has its exposed end face 104a disposed centrally in the bottom of illumination window 103. Illuminating light is provided from an external source (typically located at the proximal end of the guide member 104). Light transmitted through light guide member 104 exits from the end face 104a and is directed into a coeloma through cover glass 101. The inner surface of cover glass 101, namely, the surface which is in direct opposition to end face 104a, is defined by concave lens 105 having a uniform radius of curvature. The concave lens 105 increases the area which can be illuminated by the light exiting the window 103 as a result of the refraction illustrated in FIG. 1 which occurs as the light passes through the cover glass. However, it will be seen from FIG. 1 that because concave lens 105 is formed as part of a spherical surface, rays b impinging on the central region of the lens will be refracted by an amount which is less than the refraction which rays impinging on the peripheral region of the lens experiences (illustrated by rays a). Thus, the exiting rays b from the central region cannot be spread as desired. Consequently, although satisfactory brightness is obtained in the central region of the field of sight of the endoscope, the conventional endoscopes of the prior art fail to achieve a uniform and sufficient brightness over the entire field.

It is an object of the invention to provide an illumination unit for an endoscope which is capable of providing uniform and sufficient brightness over the entire field of sight, by forming the concave lens of the cover glass with a plurality of coaxial concave lens portions having different radii of curvature.

In accordance with the invention all of the preferred embodiments have at least one lens surface formed of a plurality of concave lens portions having different radii of curvature formed in a cover glass which is disposed forwardly of a light exiting end face of light guide member which transmits the illuminating light. This arrangement permits a greater degree of refraction for rays passing through the central region to achieve a satisfactory diffusion so that the level of brightness of the peripheral region can be maintained at substantially the same level as the central region of the field of sight. In this manner, simple means can be used to facilitate an observation of the interior of a coeloma.

The aforesaid arrangement may be provided upon either the light entry or light exit surface of the cover glass or upon both the entry or exit surfaces. As a further alternative one of said entry or exit surfaces may have the novel concave lens configuration while the remaining surface may have a concave lens surface having a uniform radius of curvature.

FIG. 1 is an enlarged cross section of a cover glass of a conventional illumination unit;

FIG. 2 is a fragmentary cross section of the illumination unit according to one embodiment of the invention;

FIG. 3 is an enlarged cross section of the cover glass shown in FIG. 2; and

FIGS. 4 through 8 are enlarged cross sections of other preferred embodiments of the cover glass.

Referring to FIG. 2, there is shown endoscope 1 including flexible tube 2, the distal end 3 of which is adpated to be inserted into a coeloma. Illumination window 4 and observation window 5 are formed in the sidewall of the distal end and are adjacent to each other. Transparent cover glasses 6, 7 are fitted into the respective windows 4, 5 in a water-tight manner and are secured against movement.

Right-angled prism 8 is disposed below cover glass 7 and is in close contact with the bottom surface thereof. Objective lens system 10 is disposed between prism 8 and the distal end of an image guide member 9, which extends through flexible tube 2 of the endoscope. The member 9 comprises a bundle of optical fibres. A light image which is incident on observation window 5 is refracted by prism 8 and is focussed by objective lens system 10 onto the distal end face 9a of member 9. The focussed image can be observed through guide member 9 and a magnifying glass (not shown) which is disposed in the controller of the endoscope which is located outside of the coeloma.

Light guide member 11, which also comprises a bundle of optical fibres, extends through the flexible tube 2 and has its end face 11a exposed centrally in the bottom surface of illumination window 4. Illuminating light introduced into guide member 11 from an external source exits the end face 11a and passes through cover glass 6 to be directed toward a coeloma.

As shown in FIG. 3, the entry surface of cover glass 6 is provided with a plurality of coaxial concave lens portions, which are two in number in the present embodiment as indicated at 12 and 13, having different radii of curvature, the centers of the imaginary circles formed by said radii being located on a common axis A. The lens portions are formed in the entry surface of cover glass 6 which is disposed in direct opposition to end face 11a. The inner lens portion 12 has a radius of curvature which is less than that of the concentric outer concave lens portion 13 so that rays impinging on lens portion 12 experience a greater degree of refraction as they pass through cover glass 6.

As illustrated at b.sub.0, the exiting rays which pass through the flat exit surface of ground glass 6 will be sufficiently spread outside cover glass 6. Illuminating light impinging on the peripheral region of cover glass 6 will be refracted by the outer concave lens portion 13, the exiting rays a.sub.0 being also spread outside cover glass 6. As a consequence, the light which illuminates the coeloma exhibits an increased brightness in the peripheral region of the field of the sight even though the brightness in the central region will be slightly reduced as compared with the conventional arrangement, thereby achieving a uniform brightness over the entire field.

FIG. 4 shows the use of three coaxial concave lens portions 14, 15 and 16 on the entry surface of the ground glass said lens portions having the centers of their radii of curvature arranged on a common axis, with the innermost lens portion having a radius of curvature which is less than that of the concentric middle lens portion, and the outermost concentric lens portion having the largest radius of curvature.

Instead of forming the entry surface of the cover glass so as to define the concave lens portions, the outer, light exiting surface of cover glass 6 may be defined by concave lens portions 17, 18 having different radii of curvature as illustrated in FIG. 5. This achieves an effect upon exiting light rays which is similar to that of the embodiments shown in FIGS. 3 and 4.

FIG. 6 shows another preferred embodiment of the present invention in which the entry surface of cover glass 30 has a concave lens comprised of lens surface portions 21 and 22 substantially the same as the entry surface shown in FIG. 3. The exit surface is provided with a concave lens surface 20 having a single uniform radius of curvature. The center of the circle defining the curved surface 20 preferably lies on the same axis A as the centers of the imaginary circles defining the concave lens portions of entry surface 22. The spread angle of rays b1 entering concave lens portion 21 and leaving the cover glass in the central region of concave lens surface 20 is larger than the spread angle of rays b.sub.0 leaving the exit surface in the central region of the cover glass 6 of FIG. 3. This increased spread angle is due to the light refraction at concave central lens surface 21 along the entry surface of the cover glass and the light refraction at concave lens surface 20 along the exit surface 6 of the cover glass 30.

The cover glass embodiment 30' of FIG. 7 is basically identical to that shown in FIG. 6 except that the concave lens surfaces 20 and 21-22 are respectively arranged upon the entry and exit surfaces of the cover glass. The resulting spread angle of rays b.sub.2 entering lens surface 20 and exiting lens surface 21 is substantially the same as that obtained from the embodiment of FIG. 6 and provides a spread angle in the central region which is larger than that spread angle of the rays b.sub.0 passing through the concave surface 12 in the embodiment of FIG. 5.

FIG. 8 shows still another embodiment of cover glass 32 in which both the entry and exit surfaces of the cover glass are provided with coaxial concave lens surfaces of the type shown in FIG. 3. The spread angle of rays b.sub.3 entering concave surface portion 28 and leaving concave surface portion 26 is still further improved over the spread angles obtained in any of the previously described embodiments. The choice of embodiments described herein is thus dependent upon the size of the field of view over which more uniform brightness is desired.

It is to be understood that the concave surface of respective lens portions need not be part of a true spherical surface, but may be formed to be an approximation of part of a spherical surface. The centers of radii of curvature of the individual concave lens portions on either the same side or on opposite sides of the cover glass need not be in complete alignment, but may be offset from each other depending on the area of the field of sight of the endoscope. While the above described embodiments illustrate the use of the invention with an endoscope of lateral view type, it may be similarly applied to an endoscope of direct view type.

A latitude of modification, change and substitution is intended in the foregoing disclosure and, in some instances, some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly in a manner consistent with the spirit and scope of the invention herein.