JPH06230294A - Illuminating optical system for endoscope - Google Patents

Abstract

PURPOSE:To make illuminating light from a light guide or a light emitting element sufficiently a distributed light without the irregularity of a light quantity by including at least one optical device utilizing diffraction phenomena. CONSTITUTION:An optical device (a diffraction type optical device) 2 having a diffraction plane on the side of a light guide 1 and utilizing diffraction phenomena is arranged on the object side of the light guide 1. An illuminating light 4 transmitted from the light guide 1 is diverged by the diffraction plane of the optical device 2 and illuminates the object. The optical device 2 satisfies the condition: f<(D<2>+H<2>) {/(n=1).2D}. Here, (f) is the focal length of the optical device 2, D is the thickness of the optical device 2 and (n) is the refractive index of glass used for the optical device 2. By setting the pitch so as to give such a diffraction characteristic that gradually weakens the divergence power of a light flux as the flux approaches the periphery of the optical device 2, the insufficient light quantity on the periphery is avoided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illumination optical system for an endoscope.

[0002]

2. Description of the Related Art In recent years, endoscopes have been applied in various fields including medical treatment. Since an endoscope is often used in a narrow space such as a body cavity, it is necessary to reduce its diameter. Therefore, a technique for producing an endoscope having an extremely small diameter has been developed, and for example, an endoscope for blood vessels and the like has been produced and applied to surgery and the like. These endoscopes require illumination light for observation, illumination light guided from the outside of the endoscope by a light guide using a glass fiber, and illumination supplied by light emitting elements such as light emitting diodes and semiconductor lasers. Light is distributed by the illumination lens.

However, in a microscopic endoscope such as a blood vessel endoscope, it is difficult to process a minute illumination lens, and conventionally, illumination is performed by a light guide in which the end face of the fiber bundle is exposed without the illumination lens. I had to do it. Therefore, the required light distribution characteristics cannot be obtained.

Also in other endoscopes, it is desired to make the distal end portion of the endoscope as small as possible. For this reason, the illumination lens is limited in diameter and curvature, and necessary light distribution characteristics cannot be obtained. . For example, as shown in FIG. 24, when a concave lens is provided in an object example of a light guide to distribute illumination light, when the lens needs to be housed in a space of radius H and thickness D, the radius of curvature r of the lens surface is Is subject to the following restrictions:

R> (D ² + H ² ) / 2D (1) Here, when the refractive index of the lens is n and the focal length is f, the following equation (2) is established.

F = r / (n−1) (2) From (1) and (2), the following relationship (3) is established.

F> (D ² + H ² ) / (n−1) · 2D (3) When a light beam with a light beam height H parallel to the optical axis enters this lens, this light beam is refracted by the lens It is emitted at an angle of ω with respect to the axis. Where the angle ω
Is paraxially represented by the following equation (4).

Sin (ω) = H / f (4) The following relationship (5) is established from the expressions (3) and (4).

Sin (ω) <(n−1) · 2DH / (D ² + H ² ) (5) At this time, the illuminatable angle of view θ is twice the refraction angle and is as follows.

Θ = 2 sin ⁻¹ {(n−1) · 2DH / (D ² + H ² )} (6) For example, when n = 1.5 and D = H, θ is as follows.

Θ <60 ° As described above, when a normal lens is used, the light distribution angle is limited, and when performing wide-angle illumination, uneven light quantity occurs, and a practical light distribution is obtained. It is difficult.

Further, when light is distributed only by a general spherical lens, the light passing through the periphery is refracted more by the spherical aberration, and as a result, the amount of light in the periphery is insufficient as compared with that in the vicinity of the center and uneven light amount occurs. .

[0013]

DISCLOSURE OF THE INVENTION The present invention provides an endoscope illuminating device which makes the illumination light from the light guide or the light emitting element a good light distribution without unevenness of the light quantity.

[0014]

The endoscope illumination optical system of the present invention comprises a light guide for guiding illumination light or a light emitting element for emitting illumination light, and an optical element for distributing illumination light. However, at least one of the optical elements is an optical element utilizing a diffraction phenomenon. That is, the illumination optical system of the present invention has, for example, a configuration as shown in FIG.
An optical element using a diffraction phenomenon (hereinafter referred to as a diffractive optical element 2) 2 having a diffractive surface on the object side of the light guide or the light emitting element, that is, a diffractive optics element [Diffractive Optics Ele].
ments (DOE)] are arranged. The illumination light 4 emitted from the light guide is diverged by the diffractive surface of the diffractive optical element DOE and illuminates the object.

This diffractive optical element is described in detail in, for example, Chapters 6 and 7 of "Small Optical Element for Optical Designer" (published by Optronics), and its operation will be briefly described. It is as follows.

A normal optical glass refracts according to Snell's law represented by the following equation in FIG.

Nsin θ = n′sin θ ′ (7) where n is the refractive index of the incident side medium, n ′ is the refractive index of the exit side medium, θ is the incident angle of the light beam, and θ ′ is the outgoing angle of the light beam. is there.

On the other hand, in the diffraction phenomenon, light is refracted according to the law of diffraction represented by the following equation, as shown in FIG.

Sin θ−sin θ ′ = mλ / d (8) where m is the order of diffracted light, λ is the wavelength, and d is the lattice spacing.

An optical element that refracts a light beam according to the above equation (8) is a diffractive optical element. In this formula (8), d is changed according to the ray height, and the outgoing angle θ ′ of the primary light is changed according to the ray height so that the light is condensed at one point. An optical element (diffractive lens) can be made. However, as it is, it is generally called a Fresnel zone plate, and because it is shielded in a lattice shape and light of an order other than the first order is generated, a large amount of light is wasted. The cross-sectional shape called a kinoform as shown in (A) is serrated. As a result, the incident light is blazed and the first-order diffraction efficiency becomes 100%. Actually, it is difficult to form a perfect saw-tooth shape, and although it is approximated in a stepwise manner by etching as shown in FIG. 3B, the diffraction efficiency is still 90% or more.

Since this diffractive optical element can be produced by processing on the surface of glass or plastic,
For example, a surface forming a diffractive optical element can be formed on a plane-parallel plate. Therefore, there is no influence due to the restrictions on the diameter and the thickness of ordinary lenses. Further, since the processing for forming the diffractive optical element can be performed by etching or lithography by means of a technique, it is possible to process a minute element which is difficult to process with an ordinary lens.
Further, since the pitch d can be freely changed, a diffractive optical element having an aspherical effect and a diffractive optical element having a discontinuous pitch can be easily manufactured.

When a normal lens is used as an illuminating lens, the light ray is refracted by the equation (7). Therefore n
When <n ', the incident angle θ is limited as shown in the following (9).

-N / n '<sin (θ) <n / n' (9) A light ray having an incident angle outside the above range is totally reflected and is not distributed. On the other hand, when the diffractive optical element is used as the illumination lens, the light rays are distributed according to the equation (8), so that total reflection does not occur in principle. Therefore, in a normal lens, when a wide-angle light distribution is performed, a light amount is lost due to total reflection, but since the diffractive optical element does not totally reflect even in a wide-angle light distribution, a wide-angle light distribution is performed. Suitable for

The simplest designing method for such a diffractive optical element is an automatic designing program having a function capable of designing HOE, that is, Holographic Optics Elements, among commonly used automatic designing programs. Is to use. Ultra-high index lens (U
By assuming a lens called “ltra-High Index Lens” as a diffractive optical element, it can be designed even by using a normal lens automatic design program. This is described in SPIE 126, pp. 46-53 (1977). This refractive index n is n >>
In the ultra-high index lens having the value of 1, the relationship expressed by the following equation (10) is established.

(N-1) dz / dh = sin θ−sin θ ′ (10) where θ and θ ′ are the incident angle and the output of the light beam, and n and z
Are the refractive index and the wall thickness of the ultra-high index lens, respectively.

From equations (8) and (10), the following equation (1)
1) is obtained.

(N-1) dz / dh = mλ / d (11) Ultra-High Index If an aspherical surface is defined as a lens, it is expressed as follows.

Z = Cy ² / [1+ (1-C ² Py ² ) ^1/2 ] + By ² + Ey ⁴ + Fy ⁶ + Gy ⁸ + ... (12) However, as shown in FIG. 1, z is the optical axis ( The direction of the image is positive),
y is the coordinate axis in the meridional direction of the coordinate axes orthogonal to the z axis with the origin at the intersection of the surface and the z axis, C is the curvature of the reference surface,
P is a conic constant and is a value given by P = 1-e ² (e is an eccentricity), and B, E, F, G, ... Are secondary, quaternary, and 6 respectively.
Next-order, eighth-order, ... Aspherical coefficients.

From the expressions (11) and (12), the pitch d of the diffractive optical element at a certain ray height is expressed by the following expression (13).

Therefore, if the design is performed using the ultra-high index lens, the surface shape of the diffractive lens equivalent to the lens data can be obtained.

The data of the diffractive optical element used in the illumination optical system of the present invention is, for example, as shown in the data of Example 1 shown later. As in Example 1, in the data, for example, an ultra-high index lens having a thickness of 0 is joined to a plane-parallel plate made of a normal glass material. From the diffractive optical element of this example, 50
Relative light distribution intensity at each angle (hereinafter referred to as light distribution on a plane) when the intensity on the optical axis is 1 in a plane at a position separated by mm is shown in Table 1 below and illustrated in the figure. The thing is the graph of FIG. This light distribution is about 60 ° on one side
It has a sufficient amount of light up to the vicinity and is suitable for illumination of an endoscope with an angle of view of 70 to 120 °. The focal length is 1.

For example, the diffractive optical element used in Example 1 of the present invention has an outer diameter (radius) H of 1.74 and a thickness D of 0.
Since it is 99, in order to illuminate using a concave lens of the same size as this to obtain this light distribution, the focal length f becomes 2.29 or more from equation (3), and illumination is possible from equation (6). The maximum angle of view θ ₀ is 49 °. Further, it is possible to reduce the unevenness of the light amount by the aspherical effect of the diffractive optical element.
In other words, the uneven light quantity can be reduced by setting the pitch so as to have a diffraction characteristic so that the divergent power of the light beam is gradually weakened toward the periphery of the diffractive optical element and distributing the light so as not to cause insufficient light quantity in the periphery. . For example, when P = 0 and B = 0 in the equation (12), the unevenness of the light amount can be reduced by setting the pitch so as to satisfy the following condition (14).

C · E ≦ 0 (14) In the first embodiment, the curvature C and the fourth-order aspherical coefficient E are used.
The unevenness of the light amount is reduced by setting the product C · E = −0.691.

Next, the present invention (Example 1) will be compared with an illuminating device using a concave lens. The following values are the same as those in Example 1 among those shown in the tables of Examples 1 to 4 described later.

Lens outer diameter Thickness Illuminable concave lens can be illuminated CE (radius) HD D Angle of view θ Maximum angle of view θ ₀ × 10 ^-7 1.74 0.99 120 ° 99 ° -0.691 Above condition (14) Even when the above condition is not satisfied, the refractive index of the medium forming the illumination optical system is n ₁ in order from the light guide side,
When n ₂ , ... _Ni , _{ni + 1} , ..., P = 0,
If at least one of the aspherical coefficients A of the fourth or higher order satisfies the following condition in the equation (12) in which B = 0, spherical aberration can be reduced, and light distribution without unevenness in the amount of light becomes possible.

A · (n _{i + 1} −n _i ) <0 As described above, the diffractive optical element is an optical element having a focal length f as shown in the following formula (15), which is impossible with a normal lens. Therefore, even if the size is limited, there is no shortage of the amount of light in the surroundings when performing wide-angle illumination, and it is possible to perform illumination without unevenness in the amount of light.

F <(D ² + H ² ) / {(n−1) · 2D} (15) Therefore, it is suitable for an illumination optical system for an endoscope having a limited lens size.

[0038]

EXAMPLES Next, examples of the endoscope illumination optical system of the present invention will be described. The data of each example show the diffraction type optical element in the radius of curvature and the aspherical surface coefficient of an ultra-high index lens equivalent to this. Example 1 r ₁ = ∞ d ₁ = 0.0000 r ₂ = -1000.2929 (aspherical surface) d ₂ = 0.0000 n ₁ = 100
1.42 ν ₁ = -3.45 r ₃ = ∞ d ₃ = 0.9940 n ₂ = 1.8830
0 ν ₂ = 40.78 r ₄ = ∞ aspherical surface coefficient P = 0.0000, B = 0.0000, E = 0.69072 × 10 ⁻⁴ , F = 0.
16602 × 10 ^-9 G = 0.32690 × 10 ^-15 light guide bundle radius = 1.088, lens outer diameter (radius) = 1.7395 Example 2 r ₁ = ∞ d ₁ = 0.0000 r ₂ = -1000.3193 (aspherical surface) d ₂ = 0.0000 n ₁ = 100
1.42 ν ₁ = -3.45 r ₃ = ∞ d ₃ = 1.8708 n ₂ = 1.8830
0 ν ₂ = 40.78 r ₄ = ∞ aspherical coefficient P = 0.0000, B = 0.0000, E = 0.34964 × 10 ⁻⁴ , F = 0.
19950 × 10 ^-5 G = 0.17256 × 10 ^-11 Light guide bundle radius = 2.05, lens outer diameter (radius)
= 3.27 Example 3 r ₁ = ∞ d ₁ = 0.0000 r ₂ = -1001.9767 (aspherical surface) d ₂ = 0.0000 n ₁ = 100
1.42 ν ₁ = -3.45 r ₃ = ∞ d ₃ = 1.4822 n ₂ = 1.8830
0 ν ₂ = 40.78 r ₄ = ∞ Aspheric coefficient P = 0.0000, B = 0.0000, E = 0.45095 × 10 ^-4 , F =-
0.49260 × 10 ^-8 G = -0.45218 × 10 ^-6 Light guide bundle radius = 1.62, lens outer diameter (radius)
= 2.59 Example 4 r ₁ = ∞ d ₁ = 0.0000 r ₂ = -1000.7586 (aspherical surface) d ₂ = 0.0000 n ₁ = 100
1.42 ν ₁ = -3.45 r ₃ = ∞ d ₃ = 1.2330 n ₂ = 1.8830
0 ν ₂ = 40.78 r ₄ = ∞ Aspheric coefficient P = 0.0000, B = 0.0000, E = 0.19092 × 10 ^-3 , F =-
0.10383 × 10 ^-3 G = 0.19751 × 10 ^-4 Light guide bundle radius = 1.35, lens outer diameter (radius)
= 2.16 Example 5 (inside) r ₁ = ∞ d ₁ = 0.0000 r ₂ = -1000.7957 (aspherical surface) d ₂ = 0.0000 n ₁ = 100
1.42 ν ₁ = -3.45 r ₃ = ∞ d ₃ = 1.5060 n ₂ = 1.8830
0 ν ₂ = 40.78 r ₄ = ∞ aspherical surface coefficient P = 0.0000, B = 0.0000, E = 0.35616 × 10 ⁻⁴ , F = 0.
35910 × 10 ^-5 G = -0.82483 × 10 ^-6 light guide bundle radius = 1.649, lens outer diameter (radius) = 1.355 Example 5 (outer side) r ₁ = ∞ d ₁ = 0.0000 r ₂ = -775.7758 (aspherical surface) ) D ₂ = 0.0000 n ₁ = 10
01.42 ν ₁ = -3.45 r ₃ = ∞ d ₃ = 1.5060 n ₂ = 1.8830
0 ν ₂ = 40.78 r ₄ = ∞ aspherical surface coefficient P = 0.0000, B = 0.0000, E = 0.11919 × 10 ^-3 , F =-
0.17478 × 10 ⁻⁴ G = 0.11347 × 10 ⁻⁵ Light guide bundle radius = 1.649, lens outer diameter (radius) = 2.636 (outer) Lens outer diameter (radius) = 1.355 (inner) Example 6 r ₁ = ∞ d ₁ = 0.0000 r ₂ = -1000.4962 (aspherical surface) d ₂ = 0.0000 n ₁ = 100
1.42 ν ₁ = -3.45 r ₃ = ∞ d ₃ = 2.2698 n ₂ = 1.8830
0 ν ₂ = 40.78 r ₄ = ∞ Aspheric coefficient P = 0.0000, B = 0.0000, E = 0.66858 × 10 ^-3 , F =-
0.33658 × 10 ^-3 G = -0.19127 × 10 ^-10 Light guide bundle radius = 0.76 (outside) Light guide bundle radius = 0.488 (inside) Lens outer diameter (radius) = 0.76 (outside) Lens outer diameter (radius) = 0.488 (Inside) Example 7 r ₁ = ∞ d ₁ = 0.0000 r ₂ = -1000.2097 (aspherical surface) d ₂ = 0.0000 n ₁ = 100
1.42 ν ₁ = -3.45 r ₃ = ∞ d ₃ = 5.2031 n ₂ = 1.8830
0 ν ₂ = 40.78 r ₄ = ∞ Aspheric coefficient P = 0.0000, B = 0.0000, E = 0.91835 × 10 ^-4 , F =-
0.84065 × 10 ^-5 G = -0.80981 × 10 ^-13 Light guide bundle radius = 1.743 (outside) Light guide bundle radius = 1.119 (inside) Lens outer diameter (radius) = 1.743 (outside) Lens outer diameter (radius) = 1.119 (Inside) In this data, the light guide side is the first surface r ₁ ,
Further, the diffractive optical element is represented as a parallel plane plate made of a normal glass material and an ultra-high index lens having a thickness of 0 (d ₂ = 0) cemented thereto. Further, in the drawing, the light guide 1 and the diffractive optical element are separated from each other as shown in FIG. 1, but in the data, d ₁ = 0 and they are in close contact with each other.

Each of Examples 1 to 4 has a structure as shown in FIG. 1, and the lens outer diameter H, thickness D, and illuminatable angle of view θ are as follows. Also shown are values and the like obtained by the equation (6) for the maximum field angle θ ₀ that can be illuminated by a normal lens under the same outer diameter and thickness restrictions as those of the lenses of these examples.

Lens Outer Diameter Thickness Illumination Possible Concave Lens Illumination CE (radius) HD Field Angle θ Maximum Possible Field Angle θ ₀ × 10 ^-7 Example 1 1.74 0.99 120 ° 99 ° -0.691 Example 2 2.05 1.87 140 ° 123 ° -0.350 Example 3 2.59 1.48 140 ° 99 ° -0.450 Example 4 2.16 1.23 140 ° 99 ° -1.908 Further, the light distributions of Examples 1 to 7 are shown in Tables 1 to 7, respectively.
As shown in. Table 8 shows the light distribution only for the light guide.

In these embodiments, the focal length is standardized to 1.

Example 1 is as described above, and Example 2
Has a sufficient amount of light in the vicinity of 20 ° to 50 °, and one side 70
It has a sufficient amount of light up to around 140 °, and is suitable for illuminating an endoscope with an angle of view up to about 140 °.

The third embodiment has a sufficient amount of light up to about 70 ° on one side and is suitable for illuminating an endoscope with an angle of view up to about 140 °. Further, the plane light distribution amount around 0 ° to 25 ° is flat, which is suitable for illuminating a planar object.

The fourth embodiment has a sufficient amount of light up to about 70 ° on one side and is suitable for illuminating an endoscope with an angle of view of up to about 140 °. Further, the spherical light distribution around 0 ° to 25 ° is flat, and the light amount gradually decreases gradually at 25 ° or more, which is an illumination optical system particularly suitable for illuminating a spherical object.

As described above, the optical systems of Examples 1 to 4 are compact optical systems capable of obtaining a wide-angle light distribution and having no unevenness in the amount of light.

The fifth embodiment is an optical system suitable for illuminating a tubular object, and can illuminate up to a field angle of about 150 °. In order to illuminate the tubular object, a sufficient amount of peripheral light is required. Therefore, in Example 5, the pitch is discontinuously changed between the inside and the outside of the diffractive optical element to increase the amount of peripheral light. The uneven light quantity is reduced. With a normal lens, it is difficult to change the refractive index discontinuously between the inside and the outside,
Even if it could be realized, it would be very expensive. However, since the diffractive lens can be produced by an etching technique, a discontinuous pitch diffractive lens can be easily produced as in the case of producing a continuous pitch diffractive lens.

Examples 6 and 7 are illumination optics suitable for an ultra-fine endoscope mainly used for blood vessels and the like, particularly an endoscope in which a light guide for illumination is arranged around an objective lens for observation. It is a system.

When the light is distributed only by the light guide as in the illumination system used in the conventional ultrafine endoscope, the luminous intensity distribution in the lumen is as shown in FIG. That is, the amount of light is maximized in the vicinity of 35 ° on one side, and the amount of light changes greatly depending on the angle, and unevenness in the amount of light is likely to occur.

In the illumination optical systems of Examples 6 and 7, the diffractive optical element has a ring shape as shown in FIG. 4, and an observation objective lens can be arranged inside the ring 5. . The light distribution of these examples has a large amount of light in the periphery,
It is suitable for illuminating luminal objects such as blood vessels.

In the sixth embodiment, the luminous intensity distribution of the lumen is maximized in the vicinity of 40 ° on one side, the angular distribution of the luminous intensity is relatively flat, and it is suitable for illuminating an endoscope with an angle of view of up to about 100 °. ing.

The seventh embodiment is suitable for an endoscope in which the luminous intensity distribution of the lumen becomes maximum around 60 ° on one side and the angle of view is up to 130 °. By using a diffractive optical element in the illumination optical system of the ultra-thin endoscope, which has been difficult to achieve in the past, it is possible to realize illumination with a wider angle and less unevenness of light quantity than the conventional light distribution using only a light guide.

Example 8 is an example in which a diffraction characteristic is set so that a part of the surface of the diffractive optical element used for illumination is used for purposes other than illumination. As shown in FIG. 5, the inside of the diffractive optical element for illumination of Example 7 was used as an observation objective lens to form a surface 6 having a diffraction effect, and the diffractive optical element 2 for illumination and the diffractive optical element for observation were used. It is integrated with 6. Conventionally, a lens system has been required for illumination and observation, respectively.
This embodiment can be integrated, thereby reducing the number of lenses and cost.

In each of the embodiments described above, a plane-parallel plate that is processed to have the effect as a diffractive optical element is provided on the object side of the light guide. A diffractive optical element can also be obtained by subjecting it to processing that has the effect of a diffractive optical element. In that case, a compact illumination optical system can be formed as compared with a separate diffractive optical element, and the cost can be reduced.

Further, in each of the above embodiments, the surface having the effect as a diffractive optical element is provided near the end surface of the fiber handle. However, as shown in FIG. 6, the end surface has an effect as a diffractive optical element. It is also possible to arrange the single fiber 8 provided with the surface near the end surface of the fiber handle 1. This makes it possible to effectively use the light rays emitted around the lens, increase the amount of illumination light, and obtain a bright image.

Further, the diffractive optical element can be applied to a condensing optical system in the light source. For example, a light source for an endoscope includes a light collecting optical system for efficiently collecting light from a lamp and guiding the light to a light guide. Further, in many cases, an infrared cut filter is used in order to prevent the observation target and the light guide from being damaged by the infrared light emitted from the light source. By processing this infrared cut filter as a diffractive optical element and condensing it as a diffractive optical element, it is possible to reduce the number of lenses, make it compact and reduce cost. Become.

As described above, since the processing for forming the diffractive optical element can be performed by the etching technique, fine processing can be easily performed. Therefore, it is possible to easily make a microlens array in which a large number of minute diffractive optical elements are arranged so as to correspond to the individual optical fibers in the light guide.

As shown in FIGS. 7A and 7B, the microlens array 9 formed by the diffractive optical elements 2a, 2b, 2c, 2d ... Is used as an optical fiber 1 for illumination in a light guide.
a, 1b, 1c, 1d, ... Can be arranged so as to correspond to each of a, 1b, 1c, 1d, ..., Independently control the light rays from the optical fibers, and an illumination optical system with less uneven light quantity can be realized. Further, it is also possible to dispose the microlens array by the diffractive optical element so as to be eccentric with respect to the optical fiber as shown in FIG. 8, so that the light rays emitted from the individual optical fibers are aligned with the optical axis. The light is distributed with a certain exit angle. Then, the decentering amount of the microlens array by the diffractive optical element can be changed so that the exit angle of each light ray becomes a desired angle, and a practical light distribution can be performed. In this case, the spread angle of each light beam does not need to be so large, and the color unevenness can be reduced as compared with the case where only one diffractive optical element is used, thus enabling wide-angle illumination with less color unevenness. Become.

Further, as shown in FIG. 9, by providing a plurality of diffractive optical elements to perform multi-stage light collection, it is possible to obtain a uniform light distribution.

In the embodiment described above, only the diffractive optical element is arranged in the optical system without using the ordinary lens, but as shown in FIG. 10, the ordinary lens 3 and the diffractive optical element 2 are arranged.
A configuration in which and are arranged may be combined. Further, as shown in FIG. 11, the surface of the ordinary lens 3 may be processed 9 having an effect as a diffractive optical element to reduce the number of lenses, so that an endoscope optical element having a lower cost can be obtained.

In general, when illuminating an endoscope, since the light distribution of each wavelength is different, uneven color of the illumination may become a problem. For example, when light is distributed by a concave lens as shown in FIG. 12, the light passing through the periphery of the concave lens has a larger refraction angle, and color unevenness occurs according to the dispersion characteristics of the glass material of the lens, such as 4a and 4b. The diffractive optical element has the formula (7)
As can be seen from the above, it has a negative dispersion value, which is the opposite of the general glass material. Therefore, as shown in FIG. 13, color unevenness can be reduced by performing a process having a diffraction effect at a pitch such that the deviation of the light distribution angle due to the wavelength is reduced around the concave lens.

Further, FIG. 14 shows three zones of red (R), green (G) and blue (B) in the shape of a ring on the light guide side of the diffractive optical element.
A color filter 14 for each color is arranged, and light rays of three colors are incident on the diffractive optical element 13. In this case 3
The color light beam is bent and distributed in each ring-shaped portion of the diffractive optical element. That is, the light distribution angles can be set independently for each of the colors red, green, and blue. Here, if the pitch of the diffractive optical element is set so that the light distribution angles of the respective colors are equal, it is possible to eliminate the color unevenness.

As another method for removing color unevenness, there is a method using secondary light. That is, this is a method in which the surface of the diffractive optical element is shifted from the kinoform to intentionally generate secondary light. This secondary light is refracted according to the equation where m = 2 in equation (8). Here, as shown in FIG. 15, the pitch d of the diffractive optical element is adjusted so that the short-wavelength primary light 4c passing around the surface of the diffractive optical element and the long-wavelength secondary light 4d passing near the center are parallel to each other. Set to reduce color unevenness.

[0063]

In the endoscope optical system of the present invention, an optical element utilizing the reduction of diffraction is used to obtain a light distribution without unevenness in the amount of light.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of the present invention.

FIG. 2 is a diagram showing refraction and diffraction of light.

FIG. 3 is a diagram showing an example of a sectional shape of a diffraction grating.

FIG. 4 is a diagram showing a configuration of Examples 6 and 7 of the present invention.

FIG. 5 is a diagram showing a configuration of an eighth embodiment of the present invention.

FIG. 6 is a diagram showing an example in which a single fiber surface has a diffraction effect.

FIG. 7 is a diagram showing an example in which a microlens array is configured by a diffractive optical element.

FIG. 8 is a diagram showing an embodiment in which the microlens array is eccentric with respect to each fiber.

FIG. 9 is a diagram showing an embodiment in which a plurality of diffractive optical elements are arranged.

FIG. 10 is a diagram showing an embodiment in which a lens and a diffractive optical element are combined.

FIG. 11 is a diagram showing an example in which one surface of the lens is a surface having a diffraction effect.

FIG. 12 is a diagram showing a situation in which color unevenness is generated by a conventional illumination optical system.

FIG. 13 is a diagram showing an embodiment in which the peripheral portion of the concave lens is a surface having a diffraction effect.

FIG. 14 is a diagram showing an embodiment in which color filters are arranged to eliminate color unevenness.

FIG. 15 is a diagram showing an example in which color unevenness is removed by using secondary light.

16 is a diagram showing the light distribution characteristics of Example 1. FIG.

FIG. 17 is a diagram showing a light distribution characteristic of the second embodiment.

FIG. 18 is a diagram showing a light distribution characteristic of the third embodiment.

FIG. 19 is a diagram showing a light distribution characteristic of Example 4;

20 is a diagram showing the light distribution characteristics of Example 5. FIG.

FIG. 21 is a diagram showing a light distribution characteristic of Example 6;

FIG. 22 is a diagram showing the light distribution characteristics of Example 7.

FIG. 23 is a diagram showing a light distribution characteristic of only a light guide.

FIG. 24 is a diagram showing a configuration of a conventional endoscope illumination optical system.

[Explanation of symbols]

 1 Light guide 2 Diffractive optical element

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[Procedure amendment]

[Submission date] November 30, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 2

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0002

[Correction method] Change

[Correction content]

[0002]

2. Description of the Related Art In recent years, endoscopes have been applied in various fields including medical treatment. Since an endoscope is often used in a narrow space such as a body cavity, it is necessary to reduce its diameter. Therefore, a technique for producing an endoscope having an extremely small diameter has been developed, and for example, an endoscope for blood vessels and the like has been produced and applied to surgery and the like. These endoscopes require illumination light for observation, and illumination light guided from the outside of the endoscope by a light guide using a glass fiber or light-emitting elements such as light-emitting diodes and semiconductor lasers are supplied. The illumination light is distributed by the illumination lens.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

F <(D ² + H ² ) / {(n−1) · 2D} (3) When a light beam having a light beam height H parallel to the optical axis enters the lens, the light beam is refracted by the lens. And emitted at an angle of ω with respect to the optical axis. Where the angle ω
Is paraxially represented by the following equation (4).

[Procedure amendment 4]

[Document name to be corrected] Drawing

[Correction target item name] Figure 8

[Correction method] Change

[Correction content]

[Figure 8]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuya Ono 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd. (72) Inventor Yoshiharu Takasugi 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd. (72) Inventor Kimihiko Nishioka 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd.

Claims (5)

[Claims] 1. An endoscope illumination optical system having a light guide for guiding illumination light for illuminating an object or a light emitting element for illuminating an object, and an optical system for distributing the illumination light, wherein: An endoscopic illumination optical system characterized in that the system includes at least one optical element utilizing a diffraction phenomenon. 2. The endoscope illumination optical system according to claim 1, wherein the optical element satisfies the following condition. f <(D ² + H ² ) / (n−1) · 2D where f is the focal length of the optical element, D is the thickness of the optical element, H is the radius of the optical element, and n is used for the optical element. The refractive index of the glass material. 3. The endoscope illumination optical system according to claim 1, wherein the optical element has a diffraction characteristic that gradually weakens the diverging power of the light beam toward the periphery. 4. The endoscope illumination optical system according to claim 1, wherein the surface shape of the optical element satisfies the following condition. C · E ≦ 0 However, C and E represent the surface shape of the optical element by the following formulas, respectively, and are the curvature and the fourth-order aspherical surface coefficient when P = 0 and B = 0. ^{z = Cy 2 / [1+ (} 1-C 2 Py 2) 1/2] + By 2
+ Ey ⁴ + Fy ⁶ + Gy ⁸ + ... In the above equation, z is the optical axis (the object direction is the positive direction), and y is the coordinate axis orthogonal to the z axis when the origin is at the intersection of the surface and the z axis. Coordinate axis, C is curvature (C = 1 / R when radius of curvature is R), P is P = 1-e when eccentricity is e
^The values given by ² , B, E, F, G, ... are each 2
These are aspherical coefficients of the 4th, 4th, 6th, 8th, ... 5. The refractive index of the medium forming the endoscope illumination optical system is n ₁ , n in order from the light guide side or the light emitting element side.
_{2. The} endoscope illumination optical system according to claim 1, wherein at least one aspherical surface coefficient A satisfies the following condition, where ₂ , ... N _i , n _{i + 1} ,. A · (n _{i + 1} −n _i ) <0 where n _i is the refractive index of the medium representing the diffraction surface of the optical element, A is the surface shape of the optical element by the following equation, and P
It is an aspherical coefficient of 4th order or higher when = 0 and B = 0. ^{z = Cy 2 / [1+ (} 1-C 2 Py 2) 1/2] + By 2
+ Ey ⁴ + Fy ⁶ + Gy ⁸ + ... In the above equation, z is the optical axis (the object direction is the positive direction), and y is the coordinate axis orthogonal to the z axis when the origin is at the intersection of the surface and the z axis. Coordinate axis, C is curvature (C = 1 / R when radius of curvature is R), P is P = 1-e when eccentricity is e
^The values given by ² , B, E, F, G, ... are each 2
These are aspherical coefficients of the 4th, 4th, 6th, 8th, ...