JP4475912B2 - Condensing optical system, confocal optical system, and scanning confocal endoscope - Google Patents

Description

  The present invention relates to a side-viewing confocal optical system in a scanning confocal endoscope that can observe a tomographic image of a living tissue in a body cavity at a high magnification.

  Conventionally, a confocal probe employing a confocal microscope optical system capable of observing an image with a higher magnification and higher resolution than an image obtained by a normal endoscope optical system, and a scanning confocal using the probe Endoscopes are known. The confocal probe irradiates a living body tissue in a body cavity, which is an object to be examined, with laser light, and the light on the object-side focal plane of the objective optical system among reflected light from the living tissue or autofluorescence of the living tissue. It is characterized by extracting only. In general, probes are classified into a direct view type in which light is applied to the living tissue from the tip end surface of the probe and a side view type in which light is applied to the living tissue from the side surface of the probe. The optical system used for the probe has a different optical path to be ensured depending on whether it is a direct-view type or a side-view type. Therefore, it is necessary to configure a suitable optical system for each type.

An optical system that can be used for a side-viewing confocal probe is disclosed, for example, in Patent Document 1 below.
JP 2000-292703 A

  The configuration of the optical system disclosed in Patent Document 1 scans light on a living tissue by using a reflecting surface such as a mirror. For this reason, there is a problem that the distance between the light source and the objective lens is increased in order to secure a space for disposing the reflection surface, so that the objective lens is enlarged or it is difficult to ensure a wide scanning range. Furthermore, a space for driving the reflecting surface in a predetermined direction is also required at the place where it is arranged.

  Further, the configuration of the optical system disclosed in Patent Document 1 does not have a mechanism for changing the light collection position along the depth direction of the test object, in other words, along the optical axis direction of the objective lens. Therefore, there is a problem that the position of the test surface cannot be detected with high accuracy and a high-definition image cannot be observed.

  By the way, in recent years, an integrated scanning confocal endoscope (hereinafter referred to as an integrated scanning confocal endoscope) that combines a function of a conventional endoscope and a function of a side-viewing confocal probe in order to reduce a burden on an operation of an operator. What is simply called an integrated endoscope is desired. The integrated endoscope needs to be provided with an optical system for general endoscope observation (hereinafter referred to as normal observation) and an optical system for so-called confocal observation independently. Therefore, one of the most important issues is to reduce the size of each optical system, in particular, the optical system for confocal observation, and to reduce the diameter of the flexible tube. However, if the configuration disclosed in Patent Document 1 is employed in the optical system for confocal observation, the diameter and length of the flexible tube are undesirably large. Therefore, in order to enable the scanning of the widest possible range while reducing the size of the flexible tube, a point image of light is covered by shaking a point light source as disclosed in Patent Document 2 below. It is conceivable to use a configuration for scanning on the inspection surface in an optical system for confocal observation.

US Pat. No. 5,161,053

  However, it is suitable for the conventional optical system in a side-viewing confocal endoscope that employs a configuration in which the above point light source is shaken, that is, a condensing optical system that can satisfactorily suppress light loss and various aberrations. There has not been any examination or suggestion.

  Therefore, in view of the above circumstances, the present invention has a configuration suitable for a side-view type integrated endoscope having a configuration in which a point image of light is scanned on a surface to be measured by oscillating a point light source, and various aberrations. An object of the present invention is to provide a condensing optical system that can satisfactorily suppress the above. It is another object of the present invention to provide an optical system for confocal observation that is provided with the condensing optical system and is small in size and has a wide scanning range.

  In order to solve the above problem, the condensing optical system according to claim 1 observes the surface to be examined by moving a point light source that functions as a confocal pinhole and scanning a light beam from the point light source. A condensing optical system mounted in the scanning confocal optical system, in order from the point light source side, a first group having a positive power, a deflection group including at least one deflection member, and a first group having a positive power It has two groups and a cover glass, and at least the distance between the second group and the cover glass is changed to change the condensing position along the optical axis direction of the condensing optical system.

  By comprising as mentioned above, it becomes possible to irradiate the light beam from a point light source from the side surface of a flexible tube. Moreover, according to the said structure, a fixed distance can be ensured between the condensing position made in a test object and a test surface by making a cover glass contact | abut to a test surface. Therefore, by changing the distance between the second group and the cover glass by driving at least the second group in the optical axis direction, the condensing position is changed along the optical axis direction (that is, the thickness direction of the test object). Can do.

Further, in the condensing optical system according to claim 2, when the magnification is m and the numerical aperture on the test surface side is NA, the following conditional expression (1),
0.1 <| m × NA | <0.2 ... (1)
It is characterized by satisfying.

  Condition (1) is a condition that defines the relationship between the scanning range obtained by shaking the point light source and the numerical aperture on the surface to be examined. Specifically, in the condition (1), when the value falls below the lower limit, the numerical aperture NA is lowered, and sufficient resolution cannot be obtained. If the value exceeds the upper limit, the numerical aperture becomes too large, making it difficult to correct spherical aberration, and the magnification becomes small, making it difficult to ensure a sufficient scanning range. That is, the condensing optical system according to the fourth aspect is suitable for a configuration in which a point image of light is scanned on the surface to be measured by shaking the point light source inside the flexible tube that can ensure only a limited space.

  According to the invention described in claim 3, the first group of the condensing optical system includes, in order from the point light source side, the first A group having a positive power, and a single lens having a concave surface at least on the cover glass side. Alternatively, the first group B includes either one of a pair of cemented lenses, and the first C group having a positive power composed of a pair of cemented lenses and a single lens. In this description, for the sake of convenience, in the description of each optical member, it is assumed that the optical path of the condensing optical system is linearly extended unless otherwise noted.

  Specifically, the first group A converges the divergent light beam emitted from the point light source with positive power. That is, the first group mainly has a function as a condenser lens. The concave surface of the first group B is mainly intended to keep the Petzval sum small, thereby correcting the curvature of field. That is, the lens having the concave surface has a function as a so-called field flattener. Here, the first group B causes the luminous flux that tends to converge by passing through the first group A to diverge again. Accordingly, the first C group has a positive power so as not to diverge the light beam after passing through the first B group. By adopting such a configuration for the condensing optical system, the entire length of the system can be kept short.

In the condensing optical system having the above configuration, when the distance from the point light source to the first surface of the condensing optical system is d0, the combined focal length of the first group is f1, and the focal length of the first group A is f1A, the following conditions are satisfied. Formulas (2) and (3)
0.1 <d0 / f1A <0.5 (2)
0.2 <| f1A / f1 | <0.8 (3)
It is preferable to satisfy both (claim 4).

  The point light source is moving to scan the luminous flux. In addition, the light beam emitted from the point light source tends to diverge in the first place. That is, the light beam emitted from the point light source spreads (diverges) greatly as the distance from the point light source increases. The condensing optical system according to the present invention condenses the spreading light beam by the first group A arranged immediately after the point light source. Therefore, as the 1A group is arranged closer to the point light source, the diameter of the lens, that is, the entire condensing optical system can be reduced. However, if it is too close, the moving point light source and the lens of the 1A group can be reduced. Since there is a possibility of contact, it is not preferable. Condition (2) defines the positional relationship between such a point light source and the first group A and the miniaturization of the condensing optical system. When the upper limit of the condition (2) is exceeded, downsizing becomes difficult, while when the lower limit is exceeded, the point light source and the first group A come into contact.

  Further, as described above, the first group A has positive power to converge the divergent light beam emitted from the point light source. Condition (3) is a condition for appropriately setting the power of the first group A in consideration of the balance with the power of the entire system. If the lower limit of condition (3) is not reached, the power of the first group A will be too strong and distortion will occur. If the upper limit of the condition (3) is exceeded, the power of the first group A will be too weak, and the diameter of the lens constituting the lens will become large.

Further, according to the invention described in claim 5, the first group A may be composed of one single lens. However, when the first A group is composed of only a single lens, the Abbe number ν1A of the first A group is expressed by the following conditional expression (4):
ν1 <30 (4)
It is necessary to design to satisfy.

  In order to make the number of lenses of the condensing optical system as small as possible and to have a simple configuration, a single lens may be used as the first A group. Here, the cemented lenses (particularly the cemented surfaces) of the first C group and the second group mainly play a role of correcting axial chromatic aberration, but cannot correct chromatic aberration of magnification. Conditional expression (4) is a condition for giving appropriate chromatic aberration to the first group A and correcting chromatic aberrations on the axis and magnification in a comprehensive manner. When the first lens group is composed of a single lens, the chromatic aberration of magnification can be effectively suppressed by using a single lens having an Abbe number that satisfies the condition (4).

  According to the invention described in claim 6, it is desirable that the second group includes one set of positive and negative bonded lenses and at least one positive single lens. It is desirable that the second group having the function as the movable group has various aberrations corrected alone. Therefore, spherical aberration and coma are corrected by using a bonded lens. In addition, correction of axial chromatic aberration is also achieved by the bonding surface of the bonded lens.

  The second group preferably includes three positive single lenses. As described above, in the second group, by dividing the positive power into a plurality of single lenses, it is possible to suppress spherical aberration and coma aberration even if each lens is constituted by a spherical lens.

  Here, it is desirable that the condensing optical system is configured so that the light beam emitted from the deflection group and incident on the second group becomes a substantially parallel light beam. Thus, even if the second group is moved in the direction of the optical axis of the emitted light beam in order to change the light collection position by making the emitted light beam from the deflection group substantially parallel, the light is condensed. The magnification of the entire optical system does not change and various aberrations do not deteriorate.

In an optical system in which an optical path is deflected in the middle of the system, such as a condensing optical system according to the present invention, it is very difficult to maintain high assembly accuracy with respect to groups before and after the deflection group. Further, eccentricity due to individual differences (for example, processing errors) of the deflection group, more specifically, a phenomenon in which on-axis light of the first group travels straight out of the optical axis of the second group due to individual differences of the deflection group. Cheap. In order to suppress an assembly accuracy error and to suppress aberration due to decentration, it is necessary that not only the light beam incident on the second group is a substantially parallel light beam but also the light beam emitted from the first group is a substantially parallel light beam. Therefore, according to the condensing optical system of the ninth aspect, when the combined focal length of the first group is f1, and the combined focal length of the second group is f2, the first group and the second group satisfy the following conditions: Formula (5),
0.97 <f2 × m / f1 <1.03 (5)
It is desirable to satisfy. In the optical system satisfying the condition (5), it is desirable that the deflection group is composed of a prism or mirror made of only a plane so that the parallel light beam emitted from the first group is directly incident on the second group. ).

  In addition, when the interval occupied by the deflection group (equivalent air length) is increased, the off-axis light beam having a fixed angle with respect to the optical axis is incident on the second group, and there is a risk of being garbled. Therefore, according to the invention described in claim 11, a prism having an air conversion length shorter than that of the mirror is used as the deflection group. Then, the incident light beam is totally reflected by at least one surface of the prism to realize the deflection of the optical path. Thereby, the loss of the light quantity at the time of deflection can be minimized, and the light utilization efficiency can be increased.

  Here, assuming that the angle formed by the optical axis of the first group and the optical axis of the second group is θ, a triangular prism is used when the angle θ exceeds 60 °. For example, when the angle θ is 90 °, a right angle prism may be used. When the right-angle prism is used, the air conversion length can be shortened by designing the inclined surface as a total reflection surface. In addition, when the angle θ is 60 ° or less, a prism that deflects by two-time reflection (for example, a prism having a pentagonal cross section including an optical axis, hereinafter referred to as a two-time reflection prism) or the like shortens the air equivalent length. Is preferable. Each prism described above may be a single prism having the shape described above, or a plurality of polygonal prisms may be bonded together. Further, in the case of a two-time reflecting prism, if it is difficult to design the arrangement so that both surfaces are totally reflected, it is possible to apply a metal coat or the like on one surface.

Conditional expression (6) according to claim 11,
35 ° <θ <105 ° (6)
Is a condition for the deflection group to satisfy the total reflection condition. In conditional expression (6), if the value falls below the lower limit, the off-axis light flux that does not satisfy the total reflection condition of the two-time reflecting prism will occur. On the other hand, if the value exceeds the upper limit, an off-axis light beam that does not satisfy the total reflection condition of the triangular prism will be distorted.

  More preferably, the first group, the deflection group, and the cover glass are fixed inside the scanning confocal optical system (claim 12). That is, it is preferable that only the second group is movable, since the condensing optical system has a simple configuration.

  The confocal optical system according to claim 13 condenses a point light source functioning as a confocal pinhole and a light beam emitted from the point light source. By moving the optical optical system and the point light source at least on a plane substantially orthogonal to the optical axis of the condensing optical system, the distance between the scanning unit for scanning the light beam and at least the second group and the cover glass is changed. In this way, there is provided a condensing position moving means for moving the condensing position in the optical axis direction of the condensing optical system.

  According to the confocal optical system of the thirteenth aspect, three-dimensional scanning is possible by the scanning unit and the converging position moving unit, and not only the surface image of the living tissue in the body cavity but also the tomographic image is observed. It becomes possible. In addition, the scanning means does not scan the light beam using a mirror as in the prior art, but performs scanning by moving the point light source, so that the entire system can be reduced in size. Further, by mounting the above-described condensing optical system, it is possible to condense the light beam irradiated from the point light source moving by the scanning unit on the surface to be measured while suppressing loss of light amount and various aberrations. This enables observation with a brighter and clearer image over a wide range.

  In a so-called fiber scan type confocal optical system in which the exit end of a single mode optical fiber is used as a point light source and a confocal pinhole, the optical axis direction of the condensing optical system and the fiber arrangement direction (the length of the flexible tube) (Direction) is required to be substantially on the same straight line. Therefore, when the confocal optical system is used for a side view type integrated endoscope, it is extremely preferable to use the above-described condensing optical system. At this time, by disposing the condensing optical system so that the optical axis of the first group substantially coincides with the disposing direction of the fiber, the condensing optical system can be formed without increasing the size of the flexible tube. It can be stored in a flexible tube.

According to the confocal optical system according to claim 14, the substantially orthogonal plane is a curved surface having a center of curvature on the optical axis of the condensing optical system, and the combined focal point of the entire condensing optical system. The distance is f, and the distance between the intersection of the principal ray of the light beam emitted from the moving point light source and the optical axis of the condensing optical system and the front principal point of the condensing optical system is s (where, Assuming that the direction toward the test surface is +), the following conditional expression (7),
0.1 <-f / s <1.0 (7)
Meet.

  More specifically, the point light source is an exit end of one optical fiber disposed between the light emitting unit and the condensing optical system and along the optical axis of the condensing optical system. The point light source is moved on the curved surface by curving the vicinity of the emission end (claim 15).

  As described above, the diameter of the flexible tube can be reduced so that it can be applied to an integrated endoscope by moving the fiber exit end surface as a point light source by curving the light source side from the exit end of the optical fiber. The objective of obtaining a wide scanning range while maintaining can be achieved relatively easily.

  In addition, by curving the light source side from the optical fiber exit end as described above, the locus drawn by the fiber exit end surface is not a flat surface but strictly a curved surface. However, if the distance from the center of curvature of the fiber to the exit end is sufficiently long with respect to the scanning width of the fiber, it can be considered as a substantially flat surface. That is, substantially, the curved surface can be identified with a surface that is substantially orthogonal to the optical axis of the condensing optical system.

  In addition, when the light source side is curved from the exit end of the optical fiber, the exit end face is inclined according to the degree of the curvature, so that the angle formed between the principal ray of the irradiated light beam and the optical axis of the condensing optical system becomes large. . The condensing optical system is disposed so that the entrance pupil position is at a predetermined position where the extension of the principal ray of the light beam irradiated from the exit end surface and the optical axis of the condensing optical system intersect. The predetermined position is considered based on the principal ray of the light beam irradiated from the exit end surface when the position (X, Y) on the XY plane of the fiber exit end is the maximum, that is, the farthest from the optical axis. And easily obtained. By arranging in this way, the light beam emitted from the fiber can be taken into the condensing optical system without vignetting, and a sufficient amount of light can be ensured up to the periphery of the field of view.

  In the confocal optical system, the light beam from the fiber end face moved to a predetermined position must be guided to the fiber end face at a predetermined position after being reflected by the test surface. When scanning using the reflected light from the test surface in this way, it is effective to provide telecentricity on the test surface side of the optical system in order to return the reflected light to the condensing optical system more efficiently. It is. In terms of paraxiality, it is only necessary to have an entrance pupil at the front (fiber side) focal position of the condensing optical system. However, since the spherical aberration of the pupil increases outside the axis, the entrance pupil for the off-axis light beam is generally located at a position shifted from the paraxial calculation position. Condition (7) is a condition for ensuring the minimum necessary telecentricity even when the off-axis light beam has spherical aberration of the pupil. In other words, the telecentricity is remarkably lost and the amount of light in the peripheral portion is significantly reduced when either the upper limit or the lower limit of the condition (7) is exceeded.

  By using the confocal optical system as described above, the diameter of the flexible tube can be maintained, so that an integrated endoscope that can reduce the burden on the subject can be realized.

  As described above, according to the present invention, the condensing optical system that is suitable for a side-viewing optical system equipped with a confocal optical system that realizes three-dimensional scanning by oscillating a point light source and that suppresses various aberrations satisfactorily. A system is provided. A confocal optical system equipped with such a condensing optical system can ensure a wide scanning range without increasing its size even if it is a side view type. Further, by using such a confocal optical system, it is possible to realize an integrated endoscope including a flexible tube having a small diameter close to that of the direct view type even if it is a side view type.

  Embodiments of a condensing optical system according to the present invention and a confocal optical system including the condensing optical system will be described below. FIG. 1 is an enlarged view of the vicinity of the condensing optical system 10 in the confocal optical system 100. The confocal optical system 100 is provided in an integrated endoscope equipped with a side-viewing optical system in order to observe a living tissue OB in a body cavity at a high magnification (confocal observation). The integrated endoscope also includes a normal observation optical system (not shown) for normal observation of the living tissue OB. In addition, the integrated endoscope is electrically connected to a processor (not shown) including a light emitting unit that illuminates the living tissue OB, an image processing unit that performs predetermined image processing on an image of the living tissue OB captured by each optical system, and the like. And optically connected.

  The confocal optical system 100 includes a condensing optical system 10, a single mode optical fiber (hereinafter simply referred to as an optical fiber) 20, a cover glass 30, a fiber end driving unit 40, and a lens driving unit 50. The condensing optical system 10 includes a first group G1, a deflection group GD, and a second group G2 in order from the exit end 21 side of the optical fiber 20. The optical fiber 20, the fiber end drive unit 40, the first group G1, the deflection group GD, and the cover glass 30 are each fixed inside the system 100 (not shown). The second group G2 is held by the lens driving unit 50 so as to be slidable along the optical axis direction of the second group G2.

  In the following drawings including FIG. 1, the arrangement direction of the optical fiber 20 (the optical axis direction of the first group) is orthogonal to the Z direction, the Z direction, and the directions orthogonal to each other are the X direction and the Y direction, respectively. And That is, the X direction and the Y direction define a plane (XY plane) orthogonal to the Z direction. For convenience of explanation, the optical axis direction of the second group is referred to as AX2 direction.

  The optical fiber 20 is light guiding means disposed between the light emitting unit of the processor and the condensing optical system 10. The fiber end drive unit 40 includes two piezoelectric elements that are in the vicinity of the emission end 21 of the optical fiber 20 and are displaced in directions orthogonal to each other (that is, the X direction and the Y direction) in the XY plane. That is, by applying a voltage to each piezoelectric element, the fiber end driving unit 40 presses the vicinity of the emission end 21 in the X direction and the Y direction, and moves in that direction. When the vicinity of the emission end 21 is moved in the direction orthogonal to the Z direction by the fiber end drive unit 40, the light beam irradiated from the emission end 21 scans the surface of the living tissue OB two-dimensionally with the movement.

  Further, when the second group G2 moves along the AX2 direction by the lens driving unit 50, the condensing position of the light beam irradiated from the optical fiber 21 via the condensing optical system 10 is slightly shifted in the AX2 direction. That is, scanning in the AX2 direction is possible. Furthermore, the confocal optical system 100 can obtain a three-dimensional image composed of XY-AX2 related to the biological tissue OB by the action of the fiber end driving unit 40 and the lens driving unit 50.

  The optical fiber 20 guides the light beam from the light emitting unit of the processor into the system 100 and irradiates it from the emission end 21. That is, the exit end 21 of the optical fiber 20 functions as a secondary point light source. As described above, the emission end 21 moves on the XY plane by the fiber end driving unit 40. Strictly speaking, as shown in FIG. 1, the locus of the exit end 21 has a curvature at an intersection P between an extension line (thick dashed line) of the principal ray of the light beam emitted from the exit end 21 and the optical axis (dashed line). It becomes a curved surface (arrow dotted line) as the center. However, since the movement amount of the injection end 21 is very small, it is considered that the curved surface substantially coincides with the XY plane. As shown in FIG. 1, the intersection point P is located closer to the condensing optical system 10 than the curved center C of the exit end of the optical fiber 20 that is moved by the fiber end driving unit 40. The first group G1 of the condensing optical system 10 is arranged so that the entrance pupil is located at the intersection P.

The light beam irradiated from the exit end 21 is condensed by the living tissue OB via the condensing optical system 10 and the cover glass 30. The light reflected by the living tissue OB returns in the order of the cover glass 30, the condensing optical system 10, and the exit end 21. In other words, the confocal optical system 100 is configured such that the reflected light from the living tissue OB has telecentricity. Therefore, the condensing optical system 10 and the optical fiber 20 are arranged so that the exit end 21 is positioned at the front focal position of the condensing optical system 10. This ensures the telecentricity of the reflected light paraxially. Furthermore, the confocal optical system 100 satisfies the following condition (7) in order to ensure the telecentricity of the reflected light even off-axis.
0.1 <-f / s <1.0 (7)
However, f is the total focal length of the entire condensing optical system, and s is the distance between the intersection P and the front principal point H of the condensing optical system 10 (however, it is applied to the living tissue OB that is the test surface). The direction to go is +).

  Further, since the core diameter of the optical fiber 20 is extremely small, the emission end 21 functions not only as a point light source but also as a diaphragm. Therefore, by configuring so as to satisfy the condition (7), the emission end 21 at the predetermined position is irradiated from the emission end 21 at the predetermined position, and is a condensing point conjugate with the emission end 21 by the living tissue OB. Only the light reflected from the light enters.

  The reflected light incident on the exit end 21 is guided to the processor. Then, it is converted into a video signal in the processor. By outputting the video signal to a monitor or the like, a high-magnification image obtained by the confocal optical system can be obtained.

  The condensing optical system 10 mounted on the confocal optical system 100 as described above will be described in detail below. FIG. 2 is an example of a diagram illustrating a lens arrangement of the condensing optical system 10.

  In the condensing optical system 10, the first group G1 includes, in order from the exit end 21 side, that is, the left side in the drawing, the first A group having positive power and a single lens or a cemented lens having a concave surface at least on the cover glass 30 side. 1B group, and 1C group consisting of a pair of cemented lenses and a single lens.

The first group A can also be composed of a plurality of lenses. However, in order to reduce the number of lenses to reduce cost and weight, the first group A of this embodiment is composed of a single lens. The first group A having positive power has a function as a condenser lens that converges the divergent light beam emitted from the exit end 21. In order to give the single lens a function of correcting chromatic aberration of magnification, the single lens is given an Abbe number ν1A that satisfies the following condition (4).
ν1A <30 (4)

The condensing optical system 10 has a distance from the exit end 21 to the first surface r1 of the condensing optical system 10 as d0, a combined focal length of the first A group as f1, and a focal length of the first A group as f1A. Conditional expressions (2) and (3) below
0.1 <d0 / f1A <0.5 (2)
0.2 <| f1A / f1 | <0.8 (3)
It is configured to satisfy both.

  Conditions (2) and (3) are conditions for reducing the size of the condensing optical system 10. . By satisfying both the condition (2) and the condition (3), the condensing optical system 10 can satisfactorily suppress various aberrations including distortion while being downsized.

  The concave surface r4 on the cover glass 30 side of the first B group is provided to correct field curvature. However, the light beam emitted from the first group B diverges due to the concave surface. The first group C is given positive power in order to suppress the divergence of the luminous flux. Note that the bonding surface r6 of the first C group has an effect of correcting axial chromatic aberration.

  The second group G2 includes a biconcave lens, one cemented lens of the biconvex lens, and at least one positive single lens. The bonded lens has a negative power as a whole. The strong diverging surface r16 directed to the exit end 21 side of the cemented lens has an action of correcting spherical aberration and coma aberration. Further, the cemented surface r17 of the cemented lens contributes to correction of longitudinal chromatic aberration together with the surface r6 described above. As described above, in this embodiment, the axial chromatic aberration is corrected in each group by providing the axial chromatic aberration correction function to each of the first group G1 and the second group G2.

  As described above, the second group G2 slidably held by the lens driving unit 50 is in a state in which various aberrations are suppressed by using the bonded lens. In the second group G2 of the present embodiment, positive power is divided and applied to three single lenses. Thereby, spherical aberration and coma generated in each lens are kept small. Further, the two single lenses and the bonded lenses on the cover glass 30 side of the second group G2 have a retrofocus arrangement configuration. This ensures a sufficient working distance.

  Here, it is necessary to prevent variation in magnification and deterioration of aberration due to movement of the second group G2.

That is, first, in order to avoid the deterioration of aberration due to the movement of the second group, the condensing optical system 10 causes the light beam emitted from the deflection group GD and incident on the second group G2 to be a substantially parallel light beam. Composed. Further, in order to suppress the influence of the eccentricity of the deflection group GD to be small, an optical member composed only of a plane is used for the deflection group GD. However, if the deflection group GD is composed of an optical member having only a flat surface, in order to make the light beam incident on the second group G2 a parallel light beam, the light beam emitted from the first group G1 and incident on the deflection group GD. Need to be parallel light flux. That is, in the condensing optical system 10, if the combined focal length of the first group is f1, and the combined focal length of the second group is f2, the first group and the second group satisfy the following conditional expression (5). Configured as follows.
0.97 <f2 × m / f1 <1.03 (5)

  Conditional expression (5) is satisfied, that is, the light beams emitted from the first group G1 and incident on the deflection group GD and the light beams emitted from the deflection group GD and incident on the second group G2 are substantially parallel light beams. If configured, relative positioning with respect to each other becomes easy in the confocal optical system 100, and it is not necessary to maintain high assembly accuracy.

  Note that the deflection group GD of the present embodiment uses a prism that has a shorter air conversion length than the mirror. The prism is arranged so that the incident light beam is totally reflected on at least one surface of the prism. By utilizing the total reflection of the prism, the light quantity loss during deflection is suppressed. It is used depending on how much the optical path of the light beam is deflected in order to view the living tissue OB side-by-side, more specifically, how many angles θ between the optical axis of the first group G1 and the optical axis of the second group G2 are set. The types of prisms are also different. Specifically, when the angle θ is 60 ° or less, a two-time reflecting prism may be used (see Examples 1 and 3). If the angle θ exceeds 60 °, the triangular prism may be arranged so that the incident light beam is totally reflected on one surface of the prism (see Example 2).

In the condensing optical system 10, the angle θ is set within the range of the following conditional expression (6) so that the incident light beam satisfies the total reflection condition in the deflection group GD.
35 ° <θ <105 ° (6)

The condensing optical system 10 has the following conditional expression (1), where m is the magnification and NA is the numerical aperture on the surface to be measured.
0.1 <| m × NA | <0.2 ... (1)
Configured to meet. The condensing optical system 10 that satisfies the condition (1) irradiates the light beam irradiated from the exit end 21 while suppressing the occurrence of aberration while minimizing the loss of the light amount, and condenses it on the surface to be measured. Can do.

  Hereinafter, three specific examples of the condensing optical system 10 will be described.

  FIG. 2 is a diagram illustrating the lens arrangement of the condensing optical system 10 according to the first embodiment. Table 1 shows specific numerical configurations of the condensing optical system 10 of the first embodiment.

  In Table 1, No. Is the surface number, r is the radius of curvature of each lens surface (unit: mm), d is the lens thickness or lens interval (unit: mm), n is the refractive index at the d-line (588 nm), and ν is the Abbe at the d-line. Is a number. Remarks in Table 1 represent optical members indicated by the respective surface numbers. The same applies to the following tables.

  In the condensing optical system 10 of Example 1, the angle θ is set to 60 °. Therefore, two prisms are used for the deflection group GD. The light path of the light beam is deflected by reflecting twice.

  FIG. 3 is a diagram illustrating the lens arrangement of the condensing optical system 10 according to the second embodiment. Table 2 shows a specific numerical configuration of the condensing optical system 10 of the second embodiment.

  In the condensing optical system 10 of Example 2, the angle θ is set to 90 °. Therefore, a right angle prism is used for the deflection group GD. The incident light beam is totally reflected on the inclined surface of the right-angle prism, thereby realizing the deflection of the optical path.

  FIG. 4 is a diagram illustrating the lens arrangement of the condensing optical system 10 according to the third embodiment. Table 3 shows specific numerical configurations of the condensing optical system 10 of the third embodiment.

  In the condensing optical system 10 of Example 3, the angle θ is set to 45 °. Therefore, a single twice reflecting prism is used for the deflection group GD.

  As shown in FIGS. 2 to 4, in each of the first to third embodiments, the first group A includes a single lens in order to reduce the number of lenses and reduce the weight. Further, in the first and third embodiments, the first group B is configured by a single lens, whereas the second embodiment is configured as a cemented lens, thereby corresponding to a high NA of about 0.5. As described above, the second group G2 gives positive power divided into three single lenses. Thereby, spherical aberration and coma generated when a spherical lens is used for the second group G2 are satisfactorily suppressed.

  Table 4 shows numerical values necessary for the above conditions (1) to (7) in the condensing optical system 10 of each of Examples 1 to 3. In Table 4, H1 indicates the distance from the first surface to the front principal point. Table 5 shows values obtained when the numerical values shown in Table 4 are applied to the conditions (1) to (5).

  FIG. 5 to FIG. 7 are aberration diagrams showing various aberrations that occur in each condensing optical system 10 of Examples 1 to 3 in order. In each drawing, from the left, there are an aberration diagram, a lateral chromatic aberration diagram, an astigmatism diagram, and a distortion diagram showing spherical aberration and longitudinal chromatic aberration. In the aberration diagrams showing spherical aberration and axial chromatic aberration, the e-line is 546 nm and the F-line is 486 nm. In the astigmatism diagram, S is sagittal and M is meridional. Further, as shown in Table 5, all the examples satisfy all the conditions (1) to (7). Therefore, as shown in FIGS. 5 to 7, various aberrations are sufficiently suppressed in the condensing optical system 10 of any embodiment.

It is an enlarged view of the condensing optical system vicinity in the confocal optical system of embodiment of this invention. FIG. 3 is a diagram illustrating a lens arrangement of a condensing optical system according to Example 1. 6 is a diagram illustrating a lens arrangement of a condensing optical system according to Example 2. FIG. FIG. 6 is a diagram illustrating a lens arrangement of a condensing optical system according to Example 3. FIG. 6 is an aberration diagram illustrating various aberrations that occur in the condensing optical system of Example 1. FIG. 6 is an aberration diagram illustrating various aberrations that occur in the condensing optical system of Example 2. FIG. 6 is an aberration diagram illustrating various aberrations that occur in the condensing optical system of Example 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Condensing optical system 20 Single mode optical fiber 21 Outlet end G1 1st group G2 2nd group GD Deflection group OB Living tissue

Claims (15)

A condensing optical system mounted on a scanning confocal optical system for observing a test surface by moving a point light source that functions as a confocal pinhole and scanning a light beam from the point light source,
Sequentially from the point light source side, a first group having a positive power, a deflection unit comprising at least one deflection member, a second group having positive power, a cover glass, made of,
By changing at least the distance between the second group and the cover glass, the condensing position is changed along the optical axis direction of the condensing optical system ,
When the magnification is m and the numerical aperture on the surface to be tested is NA, the following conditional expression (1),
0.1 <| m × NA | <0.2 ... (1)
The condensing optical system characterized by satisfy | filling . The first group is sequentially from the point light source side,
A first group A having positive power;
A first group B consisting of either a single lens or a set of cemented lenses, with at least a concave surface facing the cover glass;
A first group C having positive power including a pair of cemented lenses and a single lens;
The condensing optical system according to claim 1, comprising: When the distance from the point light source to the first surface of the condensing optical system is d0, the combined focal length of the first group is f1, and the focal length of the first A group is f1A, the following conditional expression (2): And (3)
0.1 <d0 / f1A <0.5 (2)
0.2 <| f1A / f1 | <0.8 (3)
Condensing optical system according to claim 1 or claim 2, characterized in that meet together. In the condensing optical system in any one of Claims 1-3 ,
The first A group is composed of one single lens,
When the Abbe number of the first group A is ν1A, the following conditional expression (4):
ν1A <30 (4)
The condensing optical system characterized by satisfy | filling. In the condensing optical system in any one of Claims 1-4 ,
The condensing optical system, wherein the second group includes a pair of positive and negative bonded lenses and at least one positive single lens. In the condensing optical system according to any one of claims 1 to 5 ,
The condensing optical system, wherein the second group includes three positive single lenses. The light beam emitted from the deflection unit is incident on the second group is characterized by a substantially parallel light beam, the condensing optical system according to any one of claims 1 to 6. In the condensing optical system according to claim 7 ,
The first group and the second group have the following conditional expression (5), where f1 is the combined focal length of the first group and f2 is the combined focal length of the second group:
0.97 <f2 × m / f1 <1.03 (5)
The condensing optical system characterized by satisfy | filling. The condensing optical system according to claim 8 , wherein the deflection group is configured by an optical member including only a plane. In the light converging optical system according to claim 1, claim 9,
The deflection group includes a prism disposed so that an incident light beam is totally reflected by at least one surface;
The angle θ formed by the optical axis of the first group and the optical axis of the second group is expressed by the following conditional expression (6),
35 ° <θ <105 ° (6)
The condensing optical system characterized by satisfy | filling. The condensing according to any one of claims 1 to 10 , wherein the first group, the deflection group, and the cover glass are fixed inside the scanning confocal optical system. Optical system. A point light source that functions as a confocal pinhole;
The condensing optical system according to any one of claims 1 to 11, which collects a light beam emitted from a point light source;
Scanning means for scanning the luminous flux by moving the point light source at least on a plane substantially orthogonal to the optical axis of the condensing optical system;
A condensing position moving means for moving the condensing position in the optical axis direction of the condensing optical system by changing at least the distance between the second group and the cover glass;
A confocal optical system comprising: The confocal optical system according to claim 12 ,
The substantially orthogonal surface is a curved surface having a center of curvature on the optical axis of the condensing optical system,
The converging focal length of the entire system of the condensing optical system is f, the intersection point of the principal ray of the light beam emitted from the point light source in the moving state and the optical axis of the condensing optical system, and the condensing optical system When the distance from the front principal point of s is s (where the direction toward the test surface is +), the following conditional expression (7):
0.1 <-f / s <1.0 (7)
A confocal optical system characterized by satisfying The confocal optical system according to claim 13 .
The point light source is an exit end of one optical fiber disposed between the light emitting unit and the condensing optical system and disposed along the optical axis of the condensing optical system,
The confocal optical system characterized in that the scanning means moves the point light source on the curved surface by curving the light source side from the emission end. A scanning confocal endoscope comprising the confocal optical system according to any one of claims 12 to 14 .

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