JP2001281409A - Lens with antireflection film and endoscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lens capable of enhancing its IR cutting rate without increasing the number of interference filters. SOLUTION: The lens has an antireflection film having <=1% reflectance Rv in the wavelength region of 420-650 nm and >=40% reflectance Rir in the wavelength region of 920-1,100 nm to the incidence of light parallel to the optical axis of the lens. The antireflection film is a five- or six-layer film, the 1st layer on the substrate side consists of an intermediate refractive index material, a layer above the 1st layer consists of a low or high refractive index material, an upper layer consists of high and low refractive index materials alternately stacked toward the air side and the top layer on the air side consists of a low refractive index material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens provided with an antireflection film capable of reducing the transmittance of light of a specific wavelength and improving the transmittance of light of a specific wavelength, and an endoscope using the lens. About.

[0002]

2. Description of the Related Art Recently, among endoscopes, an image pickup device (CC)
A so-called videoscope incorporating D) in an objective optical system has been put to practical use. FIG. 31 shows this endoscope, in which an objective optical system 31 and an optical fiber 32 parallel to the objective optical system 31 are inserted into the endoscope main body 30. A light source 33 is connected to the proximal end of the optical fiber 32, while an illumination optical system 42 is provided at the distal end of the optical fiber 32.

In this endoscope, light emitted from a light source 33 is emitted from an illumination optical system 42 through an optical fiber 32 to illuminate a treatment section 39. Then, the observation image of the treatment section 39 is taken into the CCD 41 from the objective optical system 31. The captured observation image is subjected to image processing via the processor 34 and then observed by the monitor 35.

On the other hand, the treatment is performed by a laser probe 36 inserted in the endoscope body 30 in parallel with the observation objective optical system 31. That is, the treatment is performed by irradiating the treatment section 39 with the laser light 38 from the laser light source 37 via the laser probe 36. At this time, the laser light 38 applied to the treatment section 39 is reflected by the treatment section 39, and when the reflected light 40 enters the objective optical system 31, the observation image is disturbed.
It is necessary to prevent the light from being incident on.

FIG. 2 shows an objective optical system for preventing incidence of reflected light (corresponding to the objective optical system 31 in FIG. 31).
Is shown. This objective optical system includes a first objective lens group 51 composed of a compound lens, an infrared absorbing glass (color glass) 52, and a second objective lens group 54 having a multilayer filter 53. A cover glass 50 for protecting the CCD is disposed on the back side (right side) of the first objective lens group 51, and illustration of the cover glass 50 on the opposite side of the objective lens groups 51 and 54 is omitted. The CCD is bonded.

As the multilayer filter 53, for example, as described in Japanese Patent Application Laid-Open No. 4-133004, a multi-layer filter is formed after forming a zinc oxide thin film,
As described in JP-A-243935, a filter adapted to a laser beam to be cut is used, and a filter formed in a multilayer shape on a lens surface is used. Other lenses without the multilayer filter 53 are provided with a multilayer antireflection film as described in JP-A-57-112701 for the purpose of preventing ghost and flare during observation. It is formed.

This multilayer antireflection film is composed of about five layers in which low refractive index materials and high refractive index materials are alternately laminated from the substrate side to the air side, and the outermost layer is a low refractive index material. This prevents the reflection of visible light.
In this case, assuming that λ is approximately 520 nm of the center wavelength in the visible region, the total film thickness of the first to third layers from the substrate side is an optical film thickness of λ / 4 in terms of 1.65, the fourth layer is 入 / 2, The fifth layer is λ
It is configured to have an optical film thickness of / 4. In addition, 1 to
In three layers, the total film thickness is λ in terms of an intermediate refractive index of 1.65.
The film thickness of the high-refractive-index material and the low-refractive-index material is determined by the equivalent approximate film method so that the optical film thickness becomes / 4.

As a laser used for laser light therapy, for example, a YAG laser or a semiconductor laser has been used, but in recent years, semiconductor lasers have gradually shifted to semiconductor lasers which are less expensive than the YAG laser. For the objective optical system in such an endoscope, it is desired to shorten the rigid portion at the distal end of the endoscope chain in order to increase the degree of freedom of treatment and reduce the burden on doctors and patients. At the same time, with the improvement in the irradiation power of the laser in recent years, it has been desired to improve the efficiency of cutting the treatment laser light by the objective optical system. On the other hand, in order to shorten the hard part, it is necessary to reduce the thickness of the glass having the infrared absorption function (infrared absorption glass 52), but to improve the laser cut rate, it is used in treatment. It is necessary to increase the number of interference filters that cut off the laser light.

[0009]

The above-mentioned interference filter for cutting a laser beam is composed of a multilayer film, and it takes several hours to form one surface thereof, resulting in poor production efficiency. ing. Also, the yield in optical characteristics is worse than that of an antireflection film or the like composed of several layers. For these reasons, increasing the number of layers of the multilayer film of the interference filter for the purpose of cutting the laser is not advantageous because the productivity is reduced. Further, when the thickness of the infrared absorbing glass is reduced, the cut rate of infrared rays is deteriorated.

The present invention has been made in consideration of such conventional problems, and it is possible to improve the cut rate of infrared rays without increasing the number of interference filters and to reduce the thickness of infrared absorbing glass. Accordingly, an object of the present invention is to provide a lens with an antireflection film capable of shortening the rigid portion at the distal end of the endoscope and increasing the degree of freedom of the observation range, and an endoscope having the lens.

[0011]

Means for Solving the Problems To achieve the above object,
Therefore, the lens with an antireflection film according to the first aspect of the present invention
With respect to parallel light incidence, the wavelength region is 420 nm to 650.
nm reflectivity R_vIs R_v≦ 1%, wavelength region 920
nm to 1100 nm reflectivity R_irIs 40% ≦ R _irso
Lens having an antireflection film having certain reflectance characteristics formed
In the antireflection film, the first layer from the substrate side has an intermediate bending.
Layer of low refractive index material or high refractive index material.
Material, and the layer above it faces the air side.
It consists of alternating high and low index materials.
And the outermost layer on the air side has five or
It is characterized by having six layers.

According to the first aspect of the present invention, the antireflection film formed of five or six layers prevents reflection so as to be 1% or less in the visible wavelength region of 420 to 650 nm,
By increasing the reflection in the infrared wavelength region of 100 nm, the transmitted light of the YAG laser at around 1060 nm can be reduced. Therefore, the cut efficiency in the infrared region can be improved without depending only on the cut efficiency of the interference filter provided on the lens or the parallel plate in the objective optical system.

In the present invention, assuming that λ is approximately 520 nm of the center wavelength in the visible region where an antireflection effect is required, the air-side outermost layer is approximately λ / 2 and the air-side outermost layer is λ / 2 from the second and subsequent layers on the substrate side. While adjusting the optical film thickness so as to be / 4,
The thickness of the first layer on the substrate side is determined by adjusting the reflectance so as not to increase in the desired antireflection band.

Each refractive index material has a wavelength λ = 500 n
Those having a refractive index n at m in the following range are selected. Intermediate refractive index material: 1.550 ≦ n <1.900 High refractive index material: 1.900 ≦ n ≦ 2.300 Low refractive index material: 1.350 ≦ n ≦ 1.480

As the intermediate refractive index material in this range,
Al ₂ O ₃ , WO ₃ , CeF ₃ , MgO or a mixture thereof or a mixture of Al ₂ O ₃ and La can be arbitrarily selected. Examples of the low refractive index material include SiO ₂ ,
MgF ₂ , Na ₃ AlF ₆ , LiF, CaF ₂ or a mixture thereof can be selected. As the high refractive index material, ZrO ₂ , TiO ₂ , Ta ₂ O ₅ , Nb ₂ O
₅ or Y ₂ O ₃ or a mixture thereof can be selected.

The lens (substrate) provided with an antireflection film having an infrared reflection function is not particularly limited.
Any glass material having a refractive index in the range of 1.465 to 1.925 at d-line can be used, and infrared absorbing glass may be used. The method for forming the antireflection film is not particularly limited, such as a vacuum deposition method, an ion assist method, and a sputtering method.

[0017] Lens of a second invention, the incident of the light parallel to the optical axis, reflectance _{R v} of the wavelength region 420nm~530nm is _{R v} ≦ 1%, the wavelength region 720nm~
A lens on which an antireflection film having a reflectance characteristic of 920 nm with a reflectance R _ir of 40% ≦ R _ir is formed,
In the antireflection film, a first layer from the substrate side is made of an intermediate refractive index material, a layer thereover is made of a low refractive index material or a high refractive index material, and further layers are alternately turned toward the air side. It is characterized in that the outermost layer on the air side is composed of five or six layers made of a low-refractive-index material.

According to the second aspect of the present invention, the antireflection film composed of five layers or six layers prevents reflection so as to be 1% or less in the visible wavelength region of 420 to 530 nm.
By increasing the reflection in the infrared wavelength range from 0 to 920 nm, the transmitted light of the semiconductor laser near 800 nm can be reduced. Therefore, the cut efficiency in the infrared region can be improved without depending only on the cut efficiency of the interference filter provided on the lens or the parallel plate in the objective optical system.

According to the present invention, when the approximate center wavelength of 475 nm in the visible region where an antireflection effect is required is λ,
The film thickness except for the air-side outermost layer from the layer after the layer is adjusted to an optical film thickness such that the refractive index of each layer is approximately λ / 2, and the air-side outermost layer is approximately λ / 4. The thickness of the first layer is determined by adjusting so that partial reflection does not increase in a desired antireflection band.

[0020] Lens of the invention of claim 3, the incident of the light parallel to the optical axis, reflectance _{R v} of the wavelength region 420nm~530nm is _{R v} ≦ 1%, the wavelength region 720nm~
Reflectance _{R ir} of 920nm is 40% ≦ _{R ir} lens antireflection film is formed is, the antireflection film,
The first layer from the substrate side is made of a low-refractive-index material, and the upper layer is made of a high-refractive-index material and a low-refractive-index material alternately laminated toward the air side. It is characterized by five layers made of a material.

The five-layer antireflection film of the present invention is composed of two materials, a low-refractive-index material and a high-refractive-index material.
The reflection is prevented so as to be 1% or less, and 720 to 920 n
By increasing the reflection in the infrared wavelength region of m
It is possible to reduce the transmitted light of the semiconductor laser near nm.

In the present invention, the optical film thickness of the layers excluding the air-side outermost layer from the first and subsequent layers on the substrate side is approximately λ / 2, and the air-side outermost layer is approximately λ / 4. adjust.

According to a fourth aspect of the present invention, there is provided an endoscope wherein the lens with the antireflection film according to the first aspect is disposed in the objective optical system.

According to a fifth aspect of the present invention, there is provided an endoscope wherein the lens with the antireflection film according to the second aspect is disposed in the objective optical system.

According to a sixth aspect of the present invention, there is provided an endoscope wherein the lens with the antireflection film according to the third aspect is disposed in the objective optical system.

In the inventions of claims 4 to 6, each lens of the rigid portion at the tip of the objective optical system in the endoscope is provided with the corresponding antireflection film. The glass material of each lens is determined from the optical design, and the visible region antireflection film has a film thickness suitable for each glass material. According to these inventions, without depending on the cut efficiency of the interference filter,
Since the cutting efficiency in the infrared region can be improved, the thickness of the infrared absorbing glass can be reduced. For this reason, the rigid portion at the distal end of the endoscope can be shortened, and the degree of freedom of the observation range can be increased. The anti-reflection film can be formed on each lens by a vacuum deposition method, an ion assist method, a sputtering method, or the like.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments.

Embodiment 1 FIG. 2 shows an objective optical system using a lens with an antireflection film according to Embodiment 1 of the present invention. As shown in FIG. 2, a first objective lens group 51, an infrared absorbing glass 52, and a second objective lens group 54 are arranged from the cover lens 50 side. CCD is a cover lens 5
0 is bonded to the surface opposite to the objective lens. The lens surface of the first objective lens group 51 is divided into a first surface 51a, a second surface 51b, and an infrared absorbing lens 52 from the cover lens 50 side.
Are the third surface 52a and the fourth surface 52b, and the lens surfaces of the second objective lens group 54 are the fifth surface 54a and the sixth surface 54.
b, the seventh surface 54c and the eighth surface 54d. In this embodiment, the flat surface side (sixth surface 54c) in the lens of the second objective lens group 54 in which one surface is convex and the other surface is flat
Is provided with a multilayer filter 53.

The number of surfaces other than the surface on which the multilayer filter 53 is formed, including the two surfaces of the infrared absorbing glass 52, is seven in total, excluding the cover glass 50. The antireflection film A of the present embodiment is applied to these seven surfaces. This antireflection film A prevents reflection in the wavelength range of 420 to 650 nm and reduces transmission of light in the wavelength range around 1060 nm.

For forming the antireflection film, a vacuum evaporation apparatus shown in FIG. 1 is used. The vacuum evaporation apparatus includes a rotary pump 11 and a diffusion pump 12 as an exhaust system in the film forming chamber 10.
Having. In the film forming chamber 10, an electron gun 15 for forming a film forming material 13 made of MgF ₂ and a film forming material of Al ₂ O ₃ and ZrO ₂ filled in material crucibles 14a and 14b are exchanged. An electron gun 16 for forming a film is provided. Material exchange is performed by rotation of a vacuum motor 22 arranged below the material crucibles 14a and 14b.
In the film forming chamber 10, a shutter 17 corresponding to the film forming material 13 and a shutter 18 corresponding to the material crucibles 14a and 14b are provided.

A reflective optical film thickness monitor 19 is provided above the film forming chamber 10. The reflection type optical film thickness monitor 19 monitors the film thickness formed on the monitoring glass 20 based on the amount of change in the reflectance. Substrate 2 on which film is formed
Reference numeral 1 denotes a dome 23 which is set on the substrate holder 22 so that the film formation surface faces downward, and rotates at 15 rpm during film formation.
Is set to

In this embodiment, the rotary pump 1
After the inside of the film forming chamber 10 is evacuated to a degree of 2.6 × 10 ⁻³ pa by the diffusion pump 12 and the diffusion pump 12, the current value of the electron gun 16 is increased, and then the shutter 18 is opened to release Al ₂ O _3.
A film-forming material 14a made of is formed. When the film thickness reaches a predetermined film thickness as measured by the reflection type film thickness monitor 19, the shutter 18 is closed to block the film forming material, and the electron gun 1
6 is lowered.

Next, the vacuum motor 22 is rotated, and Zr
A film-forming material 14b made of O ₂ is set at a predetermined position,
After increasing the current value of the electron gun 16, the shutter 18 is opened to form a film. Also in this film formation, when a predetermined film thickness is reached by the measurement of the reflection type film thickness monitor 19, the shutter 18 is closed to block the film formation material, and the current value of the electron gun 16 is reduced.

Next, after increasing the current value of the electron gun 15, the shutter 17 is opened and the film forming material 1 made of MgF ₂ is opened.
3 is formed. When a predetermined film thickness is reached by the measurement of the reflection type film thickness monitor 19, the shutter 17 is closed to block the film forming material, and the current value of the electron gun 15 is reduced. The above operation is alternately repeated to form a six-layer antireflection film on the substrate 21.

By the above-described vacuum deposition method, the first layer of the antireflection film A of this embodiment is formed of A1 ₂ O ₃ , 2
Subsequent layers are composed of MgF ₂ / ZrO ₂ / MgF ₂ / ZrO ₂ /
It becomes a six-layer film made of MgF ₂ . Table 1 shows the film configuration of this embodiment. Table 1 shows the optical film thickness of each film. or,
In the same table, the type of the substrate and the refractive index thereof are also described.

[0036]

[Table 1]

On the other hand, on the sixth surface 54c, a multilayer filter 53 for cutting the YAG laser was formed.
This multilayer filter 53 is formed by converting SiO ₂ into L, TiO ₂
Is H, the optical film thickness (unit: nm) is: substrate / 2
This is a 32 layer YAG cut film having a configuration of 47H / (251L / 247H) × 15 / 128L / air. FIG. 5 shows the spectral transmittance characteristics of the multilayer filter 53.
Shown in This multilayer filter can reduce the transmittance of the YAG laser light having a wavelength of 1060 nm to 0.1% or less.

FIGS. 11 to 14 show the spectral reflectance characteristics of the antireflection film in this embodiment at normal incidence.
FIGS. 11A and 11B show spectral reflectance characteristics of third surfaces 52 a and 52 b which are both surfaces of the infrared absorbing glass 52.
12A and 12B show the spectral reflectance characteristics of the second surface 51b, and FIGS. 13A and 13B show the fifth surface 54a and the seventh surface 54.
c, Spectral reflectance characteristics of the eighth surface 54d, FIG. 14 (a)
(B) is a spectral reflectance characteristic of the first surface 51a. In each of these figures, (a) shows the reflectance in the visible and infrared regions, and (b) shows the reflectance in the visible region enlarged by reducing the measurement range measured in (a). It is. Hereinafter, (a) and (b) of FIGS. 15 to 29 described later show the same relationship.

FIG. 6 shows the spectral transmittance characteristics of the optical system. In measuring the spectral reflectance, in order to compare only the antireflection film, the infrared absorbing glass 52 was replaced with BSL7, and the multilayer filter 53 and the antireflection film were replaced with the surface 54a.
Except for the lens formed above, the others were formed on a flat plate made of the same glass material as the above-mentioned substrate, and the spectral transmittance of the substrate having an antireflection film A formed on a total of six surfaces was measured at the vertical incidence of the total substrate. When measuring, the spectral reflectance was measured using a lens reflectance measuring device USPM-RU manufactured by Olympus Optical Industrial Co., Ltd.
Spectral transmittance was measured by a self-recording spectrophotometer U-manufactured by Hitachi, Ltd.
4000 each were used.

The reflectance of each surface is 420 to 650, respectively.
0.96% or less, 920 to 1100 nm in a wavelength region of nm
Indicates 52% or more. Further, the spectral transmittance of the light transmitted through the six surfaces is 91% or more at 420 to 650 nm and 92% or more.
It shows 13.5% or less at 0 to 1100 nm. Thereby, without impairing the characteristics in the visible region, the transmittance in the infrared region is further increased by 86.
It can be reduced by 5%.

In this embodiment, the infrared absorbing glass 52
When the thickness was 0.4 mm, a necessary and sufficient cut rate was obtained, and the objective optical system could be shortened by 1.0 mm to the thickness of 1.4 mm in Comparative Example 1 described later.

The antireflection film according to such an embodiment has d
A glass glass material having a refractive index of 1.465 to 1.925 in the line can be used. There is no problem even if infrared absorbing glass is used for the substrate. That is, the film used for the first surface 51a is a substrate having a refractive index of 1.75 or more, and the second surface 51b, 5
The films used for the surfaces 54a, 54c, and 54d are substrates having a refractive index of 1.60 or more and less than 1.75,
The films used for a and the fourth surface 52b can be used for substrates having a refractive index of less than 1.60, respectively.

The method of forming the antireflection film is not limited to the vacuum evaporation method, but may be an ion assist method or a sputtering method.

As the film material, the refractive index at λ = 500 nm is as follows: Intermediate refractive index material layer: 1.550 ≦ n <1.900 High refractive index material layer: 1.900 ≦ n ≦ 2.300 Low refractive index There is no problem if the material layer is within the range of 1.350 ≦ n ≦ 1.480.

Further, Mg used as a low refractive index material
F₂A1 used as an intermediate refractive index material ₂O₃, High refraction
ZrO used as rate material₂Instead of other materials,
For example, in the case of a low refractive index material, SiO 2₂, Na₃AlF₆,
LiF, CaF₂Or MgF₂And mixtures thereof,
A1 for intermediate refractive index materials₂O₃, WO₃, CeF₃, M
gO or ZrO₂And a mixture thereof, or A1₂
O₃Of La and La, TiO in high refractive index material₂, Ta
₂O₅, Nb₂O₅, Y₂O₃, WO₃Or ZrO₂
And mixtures thereof.

Table 2 shows the dispersion of the optical film thickness when the antireflection film of this embodiment is formed repeatedly 10 times. If the variation between batches in the range of optical thickness in Table 2, the reflectance in the wavelength region 420nm~650nm _{R v}
Is the reflectance R in the range of 920 nm to 1100 nm, where R _v ≦ 1%
_ir can satisfy 40% ≦ R _ir . Thereby, an antireflection film having no problem in production can be obtained.

[0047]

[Table 2]

Comparative Example 1 In this comparative example, the same objective optical system as that of the first embodiment shown in FIG. 2 was used except that a multilayer filter 53 for cutting a YAG laser was formed.
An ordinary antireflection film in the visible region was formed on the surface. Table 3 shows the film configuration of the antireflection film of this comparative example in terms of optical film thickness.

[0049]

[Table 3]

FIGS. 15 to 18 show spectral reflectance characteristics of the antireflection film of this comparative example at normal incidence. FIG.
(A) and (b) are the three sides of the infrared absorbing glass 52.
FIG. 16 shows the spectral reflectance characteristics of the surfaces 52a and 52b.
(A), (b) is a spectral reflectance characteristic of the second surface 51b, FIG.
7 (a) and 7 (b) show the spectral reflectance characteristics of the fifth surface 54a, the seventh surface 54c, and the eighth surface 54d, and FIGS.
This is the spectral reflectance characteristic of the surface 51a.

The reflectance in this comparative example is 420 to 65
0.30% or less at 0 nm, and 920 nm to 1
In the wavelength range of 100 nm, 920 is at least 110
The curve is a gentle curve with the maximum at 0 nm, and the maximum reflectance is 12.5% or less.

FIG. 7 is similar to Embodiment 1, except that the lens provided with the multilayer filter 53 is excluded, the infrared absorbing lens 52 is changed to BSL7, and the others are formed on a flat plate made of the same glass material as the above substrate. This shows the spectral transmittance characteristics at normal incidence when films are formed on a total of six surfaces. The transmittance is 98% or more in the wavelength range of 420 to 650 nm, and the wavelength is 1060.
In the wavelength region of 920 to 1100 nm, the curve has a gentle decrease curve with the maximum at 920 nm and the minimum at 1100 nm, and the minimum transmittance is 53%. In this comparative example, the transmittance is as high as 55% in the wavelength range of the YAG laser, so that it does not significantly contribute to the cut rate. The height had to be 1.4 mm.

(Comparative Example 2) In this comparative example, using the optical system of Comparative Example 1, antireflection films in the visible region were formed on seven surfaces other than the surface on which the multilayer filter 53 for YAG laser cutting was formed. A film was formed in the same manner as in Comparative Example 1. Therefore, the antireflection film is the same as that in Table 3 described above, and the spectral reflectance characteristics at normal incidence are also shown in FIGS.

On the other hand, instead of the multilayer filter 53, S
When iO ₂ is L and TiO ₂ is H, the optical film thickness (unit: nm) is as follows: substrate / 245H / 256L / 200H /
(213L / 200H) x 13 / 244L / 210L /
A 32-layer semiconductor laser cut multilayer filter composed of 210H / 113L / air was used. FIG.
It is a spectral transmittance characteristic of this multilayer filter.

In this comparative example, the lens provided with a multilayer film filter for semiconductor laser cutting was excluded, the infrared absorbing lens 53 was changed to BSL7, and the others were formed on a flat plate made of the same glass material as the above-mentioned substrate. The spectral transmittance characteristics at normal incidence when the film is formed on the substrate are the same as in FIG.

In the optical system of this comparative example, the transmittance is 98% or more in the wavelength range of 420 to 650 nm and the transmittance is
84.1% at 0 nm, wavelength range 720 to 1100 n
m, a gentle decrease curve with 720 nm at the maximum and 920 nm at the minimum is obtained, and the wavelength range is 720 to 920.
The minimum transmittance in nm was 65.4% (920 nm). Accordingly, since the transmittance is as high as 84.1% in the wavelength region of the semiconductor laser, it does not significantly contribute to the cut rate. Therefore, in order to obtain a desired cut ratio in the wavelength range of the semiconductor laser, the thickness of the infrared absorption filter 52 needs to be 1.4 mm.

(Embodiment 2) FIG. 3 shows an objective optical system of Embodiment 2. The lens configuration in this embodiment is basically the same as the configuration shown in FIG. 2, except that the antireflection film A of the first embodiment is formed on the second surface 51b, the third surface 52a, and the fourth surface 52b. The first surface 51a, the fifth surface 54a,
The antireflection film B on the seventh surface 54c is formed. 8th surface of plane 5
On 4d, a semiconductor laser cut coat 55 of about 800 nm consisting of 32 layers of Comparative Example 2 was formed.
On b, a multilayer filter 53 for YAG cutting composed of 32 layers similar to that of the first embodiment is formed. Note that the same vacuum evaporation apparatus as that in Embodiment 1 was used for film formation.

The anti-reflection film A has the same film material and film configuration as in the first embodiment, and prevents reflection of light in the wavelength range of 420 to 650 nm and reduces transmission of light in the wavelength range around 1060 nm. It is. The anti-reflection film B is formed by forming a first layer of Al ₂ O ₃ and a second and subsequent layers of MgF ₂ / ZrO ₂ / MgF ₂ / ZrO ₂ / MgF ₂ from the substrate by vacuum evaporation. Constitute. This antireflection film B prevents reflection in the wavelength range of 420 to 530 nm,
It reflects light in the wavelength range around 0 nm. Table 4
The thicknesses of the antireflection films A and B are shown in FIG.

[0059]

[Table 4]

FIGS. 19 and 20 show the spectral reflectance characteristics of the antireflection film A at normal incidence, and FIGS. 21 and 22 show the spectral reflectance characteristics of the antireflection film B. FIG. 19 (a),
(B) shows both surfaces 52a, 52 of the infrared absorbing glass 52;
b, FIGS. 20 (a) and (b) show the second surface 51b, FIG.
(A), (b) is the fifth surface 54a, the seventh surface 54c, FIG.
(A) and (b) are spectral reflectance characteristics of the first surface 51a.

The reflectance of the antireflection film A is 0.90% or less in the wavelength range of 420 to 650 nm, 47% or more in the wavelength range of 920 to 1100 nm, and the maximum reflectance is 52 to 53 in the wavelength range of about 1010 nm. %showed that. The reflectance of the anti-reflection pus B is in each of the wavelength ranges 420 to 53 on each surface.
0.76% or less at 0 nm, 45% or more at a wavelength range of 720 to 920 nm, and a maximum reflectance of 52 to 800 nm at around 800 nm.
57%.

FIG. 9 shows the spectral transmittance characteristics of this embodiment. The measurement of the spectral transmittance is difficult with a lens, and only the antireflection film is compared.
2 was replaced with BSL7, and the others were formed on a flat plate of the same glass material as the above substrate, and the total spectral transmittance was measured. Where Y
Since the lens provided with the multilayer filter 53 for AG cut and the multilayer filter 55 for semiconductor laser cut is made of the same glass material, the lens is formed using both surfaces of one flat plate,
The spectral transmittance of substrates formed on six surfaces in total was used.

The transmittance of the light transmitted through the six surfaces is in the wavelength range 42
98% or more at 0 to 650 nm, 17 at 800 nm
%, 16% at a wavelength of 1060 nm, wavelength range 720 to 110
The minimum transmittance at 0 nm was 14% (931 nm).
The vicinity of 800 nm of the semiconductor laser and around 1060 nm of the YAG laser are cut by 83% and 84%, respectively, by the antireflection film of this embodiment. Therefore, by setting the thickness of the infrared absorbing glass to 0.5 mm,
A necessary and sufficient cut rate can be obtained. On the other hand, a wavelength of 800 nm
In the vicinity, the thickness of the infrared absorbing glass is 0.4 mm, and a necessary and sufficient cut ratio can be obtained. As a result, in this embodiment, the necessary and sufficient cut ratio can be obtained by setting the wavelength range of the semiconductor laser and the wavelength range of the YAG laser to 0.5 mm.

In this embodiment, the anti-reflection films A and B
Has a refractive index of 1.46 at d-line.
A glass material having a refractive index of 5 to 1.925 can be used. Further, an infrared absorbing glass may be used for the substrate.
That is, the film thickness of the antireflection film A with respect to the refractive index of the substrate is the same as that in the embodiment. When the antireflection film B is used for the first surface 51a, the substrate having a refractive index of 1.75 or more and the fifth surface 54a, When used for the seventh surface 54c, it can be applied to a substrate having a refractive index of 1.60 or more and less than 1.75. In the optical film thickness shown in Table 11,
It can be used for a substrate having a refractive index of less than 1.60.

[0065]

[Table 5]

Table 6 shows the variation of the optical film thickness when the antireflection films A and B of this embodiment were formed ten times each. If the variation between batches is within the range of the optical film thickness shown in Table 6, the antireflection film A has a wavelength range of 420 nm.
reflectance _{R v} of nm~650nm is _{R v} ≦ 1%, the wavelength range 9
The reflectance R _ir of 20 nm to 1100 nm is 40% ≦ R
satisfies the _ir, antireflection film B, the wavelength region 420nm~
The reflectance R _{v at} 530 nm is R _v ≦ 1%, and the wavelength range 720 n
Since the reflectance R _{ir of} m to 920 nm satisfies 40% ≦ R _ir , there is no problem in production.

[0067]

[Table 6]

As in the first embodiment, the method for forming the antireflection film is not limited to the vacuum deposition method, and the same effect can be obtained by the ion assist method or the sputtering method. As a film material used for film formation, λ = 5
The refractive index at 00 nm is as follows: Intermediate refractive index material layer: 1.550 ≦ n <1.900 High refractive index material layer: 1.900 ≦ n ≦ 2.300 Low refractive index material layer: 1.350 ≦ n ≦ 1 .480, there is no problem.

(Embodiment 3) In this embodiment, the third surface 52 of the objective optical system of Embodiment 2 shown in FIG.
a, an antireflection film C is provided in place of the antireflection film A provided on the infrared absorbing glass on the fourth surface 52b. The antireflection film C has a film configuration similar to that of the first embodiment, and has a wavelength range of 4
20-650 nm light is prevented from being reflected, and a wavelength range of 1060
It reduces the transmission of light in the vicinity of nm. This antireflection film C is obtained by depositing the first layer from the substrate by a vacuum deposition method.
₂ O ₃ , the second and subsequent layers are TiO ₂ / MgF ₂ / TiO ₂ /
It is formed by forming a total of five layers of MgF ₂ . Table 7 shows the film configuration of the antireflection film in terms of optical film thickness.

[0070]

[Table 7]

FIGS. 23 (a) and 23 (b) show the spectral reflectance characteristics of the antireflection film C at normal incidence. The reflectance is 0.66% or less in the wavelength range of 420 to 650 nm, and the wavelength range is 920 to 920.
At 1100 nm, the reflectance is 51% or more, and the maximum reflectance is 56% (wavelength around 1040 nm). That is, it has the same spectral characteristics as the antireflection film A used for the infrared absorbing glass 52 of the second embodiment. As a result, also in this embodiment, the same effects as those of the second embodiment can be obtained, and the configuration can be made with a small number of layers.

In the antireflection film C of this embodiment, a glass material having a refractive index of 1.465 to 1.580 at d-line can be used as a substrate.

Table 8 shows the dispersion of the optical film thickness when the antireflection film C was formed 10 times using a substrate having the above-mentioned refractive index range. If the variation between batches is within the range of the optical film thickness shown in Table 8, the wavelength region is from 420 nm to 650 n.
reflectance _{R v} m is _{R v} ≦ 1%, the wavelength range 920nm~11
The reflectance R _{ir of} 00 nm satisfies 40% ≦ R _ir, and there is no problem in production.

[0074]

[Table 8]

In the film formation of this embodiment, a vacuum evaporation method,
It can be performed by an ion assist method, a sputtering method, or the like. As a film material used for film formation, λ = 50
The refractive index at 0 nm is: Intermediate refractive index material layer: 1.550 ≦ n <1.900 High refractive index material layer: 1.900 ≦ n ≦ 2.300 Low refractive index material layer: 1.350 ≦ n ≦ 1 .480, there is no problem.

(Embodiment 4) FIG. 4 shows an objective optical system according to Embodiment 4. An infrared absorbing glass 56 and a first objective glass 59 are arranged from the cover glass 50 side. From the cover glass 50 side, both surfaces of the infrared absorbing lens 56 are the first surface 56a, the second surface 56b, and the respective surfaces of the first group of objective lenses are the third surface 57a, the fourth surface 57b, the fifth surface 58a,
The sixth side is 58b. In this embodiment, a multilayer filter 60 for a semiconductor laser having 32 layers similar to that of Comparative Example 2 is provided on a fourth surface 57b formed of a flat surface. Therefore, the number of surfaces other than the film on which the multilayer filter 60 is formed is
Except for the cover glass 50, there are a total of five surfaces.

The antireflection film D of this embodiment is formed on the five surfaces by a vacuum evaporation method. The antireflection film D prevents reflection of light in a wavelength range of 420 to 530 nm and reduces transmission of light near a wavelength of 800 nm. This antireflection film D is made of MgF as a low refractive index material.
_{2. As} a high refractive index material, a mixed material in which ZrO ₂ and Ta ₂ O ₅ were mixed at a weight ratio of 9: 1 was used. The first layer from the substrate is MgF ₂ , and the second layer is ZrO ₂ and Ta ₂ O ₅
Of the third layer and thereafter, MgF ₂ / ZrO ₂ and Ta ₂ O
₅ were alternately laminated, and the outermost layer on the air side was MgF ₂
And a total of five layers were formed. Table 9 shows the film configuration of the antireflection film D by optical film thickness.

[0078]

[Table 9]

FIGS. 24 to 26 show the spectral reflectance characteristics of the antireflection film D of this embodiment, and FIGS. 24 (a) and 24 (b).
Are first surfaces 56a, both surfaces of the infrared absorbing glass 56;
FIGS. 25A and 25B of the surface 56b are the first surface 58a,
26A and 26B of the second surface 58b are the third surface 57a.
Is the reflectance. The reflectance is 0.87% or less in the wavelength range of 420 to 530 nm, 47% or more in the wavelength range of 720 to 920 nm, and the maximum reflectance is 790 to 820n.
It is 51 to 58% around m.

FIG. 10 shows a case where the infrared absorbing glass 56 is replaced with BSL7 except for the lens provided with the multilayer filter 60.
Others are formed on a flat plate made of the same glass material as the above-mentioned substrate, and show the spectral transmittance characteristics when formed on a total of four surfaces. The spectral transmittance of light transmitted through the four surfaces is 97% or more in a wavelength range of 420 to 530 nm, 16% at a wavelength of 800 nm, and a wavelength range of 720 to 920 n.
m showed a minimum transmittance (824 nm) of 16%. Therefore, with the antireflection film of this embodiment, it can be further reduced by 84% in the vicinity of the semiconductor laser at 800 nm as compared with the case where only the semiconductor laser cut coat is used.

In this embodiment, in the wavelength range of the semiconductor laser, the necessary and sufficient cut rate can be obtained by setting the thickness L of the edge of the lens of the infrared absorbing glass 56 to 0.3 mm. The thickness L of Example 3 is 1.4 mm
In contrast, the objective optical system can be reduced by 1.1 mm.

In the antireflection film D of this embodiment, a glass material having a refractive index of 1.465 to 1.925 at d-line can be used as a substrate. There is no. That is, the third surface 57a
Can be used for a substrate having a refractive index of 1.80 or more, a substrate having a refractive index of less than 1.80 with a film configuration used for the first surface 56a, the second surface 56b, the fourth surface 58a, and the fifth surface 58b.

Table 10 shows the dispersion of the optical thickness when the formation of the antireflection film D was repeated 10 times. Variation between batches is within the range of the optical thickness of the table 10, the reflectance _{R v} in the wavelength range 420nm~530nm is R
_v ≦ 1%, reflectance R in a wavelength range of 720 nm to 920 nm
_ir satisfies 40% ≦ R _ir , and the antireflection film D has no problem in production.

[0084]

[Table 10]

The method for forming the antireflection film in this embodiment is not limited to the vacuum deposition method, and the same effect can be obtained by an ion assist method or a sputtering method. As a film material used for film formation, λ = 500 nm
The intermediate refractive index material layer: 1.550 ≦ n <1.900 The high refractive index material layer: 1.900 ≦ n ≦ 2.300 The low refractive index material layer: 1.350 ≦ n ≦ 1. There is no problem within the range of 480.

(Comparative Example 3) In Comparative Example 3, Embodiment 4
In the same manner as in the fourth embodiment, an anti-reflection film in the visible region is formed on five surfaces other than the surface on which the multilayer film filter 60 for semiconductor laser cutting is formed, using the optical system described in. The antireflection film of this comparative example is the same as the film configuration of comparative example 1, and its optical film thickness is shown in Table 11.

[0087]

[Table 11]

FIGS. 27 to 29 show the spectral reflectance characteristics of the antireflection film of this comparative example. FIGS. 27 (a) and 27 (b) show the first surface 56a and the second surface
FIGS. 28A and 28B show the reflectance of the first surface 58a, the reflectance of the second surface 58b, and FIGS. 29A and 29B show the reflectance of the third surface 57a. The reflectance is 0.50% or less in the wavelength range of 420 to 530 nm, and in the wavelength range of 720 to 920 nm, the curve has a gentle curve in which the wavelength 720 nm is minimum and the wavelength 920 nm is maximum, and the maximum reflectance is 9.7%.
It is as follows.

FIG. 30 shows a case where the infrared absorbing glass 56 is replaced with BSL7 except for the lens provided with the multilayer filter 60, and the other is formed on a flat plate made of the same material as that of the above-mentioned substrate. 4 shows spectral transmittance characteristics. The spectral transmittance of the light transmitted through the four surfaces is 97% in the wavelength range of 420 to 530 nm.
As described above, 82.9% at a wavelength of 800 nm and a wavelength range of 72
Of the wavelengths 0 to 720 nm, the wavelength 720 nm is the maximum, and the wavelength 9
The curve has a gentle decrease curve with a minimum value of 20 nm, and the minimum transmittance is 70.3%. As described above, since the transmittance is as high as 70.3% in the wavelength range of the YAG laser, it does not greatly contribute to the cut rate. To obtain a desired cut rate in the wavelength range of the semiconductor laser, the infrared absorbing glass 56 The thickness L of the edge of the lens is 1.
4 mm is required.

[0090]

According to the first aspect of the present invention, the transmitted light of the YAG laser can be reduced, and
The cut efficiency in the infrared region can be improved without depending only on the cut efficiency of the interference filter provided on the lens or the parallel plate.

According to the second and third aspects of the present invention, the transmitted light of the semiconductor laser can be reduced, and only the cut efficiency of the interference filter provided on the lens or the parallel plate in the objective optical system can be reduced. In addition, the cut efficiency in the infrared region can be improved.

According to the invention of claims 4 to 6, since the cut efficiency in the infrared region can be improved without depending on the cut efficiency of the interference filter, the thickness of the infrared absorbing glass can be reduced. In addition, the rigid portion at the endoscope end can be shortened, and the degree of freedom of the observation range can be increased.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a vacuum deposition apparatus used for film formation according to the present invention.

FIG. 2 is a side view of the objective optical system according to the first embodiment.

FIG. 3 is a side view of an objective optical system according to Embodiments 2 and 3.

FIG. 4 is a side view of an objective optical system according to a fourth embodiment.

FIG. 5 is a characteristic diagram of a spectral transmittance of a multilayer filter for YAG laser cutting.

FIG. 6 is a characteristic diagram of the spectral transmittance of the first embodiment.

FIG. 7 is a characteristic diagram of the spectral transmittance of Comparative Example 1.

FIG. 8 is a characteristic diagram of spectral transmittance of a multilayer filter for semiconductor laser cutting.

FIG. 9 is a characteristic diagram of a spectral transmittance according to the second embodiment.

FIG. 10 is a characteristic diagram of the spectral transmittance of the fourth embodiment.

FIG. 11 is a reflectance characteristic diagram of an antireflection film formed on the infrared absorbing glass according to the first embodiment.

FIG. 12 is a reflectance characteristic diagram of the antireflection film formed on the second surface according to the first embodiment.

FIG. 13 is a reflectance characteristic diagram of the antireflection film formed on the fifth, seventh, and eighth surfaces according to the first embodiment.

FIG. 14 is a reflectance characteristic diagram of the antireflection film formed on the first surface according to the first embodiment.

FIG. 15 is a reflectance characteristic diagram of an antireflection film formed on the infrared absorbing glass of Comparative Example 1.

FIG. 16 is a reflectance characteristic diagram of the antireflection film formed on the second surface of Comparative Example 1.

FIG. 17 is a reflectance characteristic diagram of the antireflection film formed on the fifth, seventh, and eighth surfaces of Comparative Example 1.

FIG. 18 is a reflectance characteristic diagram of the antireflection film formed on the first surface of Comparative Example 1.

FIG. 19 is a reflectance characteristic diagram of the antireflection film formed on the infrared absorbing glass according to the second embodiment.

FIG. 20 is a reflectance characteristic diagram of the antireflection film formed on the second surface according to the second embodiment.

FIG. 21 is a reflectance characteristic diagram of an antireflection film formed on the fifth, seventh, and eighth surfaces according to the second embodiment.

FIG. 22 is a reflectance characteristic diagram of the antireflection film formed on the first surface according to the second embodiment.

FIG. 23 is a reflectance characteristic diagram of the antireflection film formed on the infrared absorbing glass according to the third embodiment.

FIG. 24 is a reflectance characteristic diagram of the antireflection film formed on the infrared absorbing glass according to the fourth embodiment.

FIG. 25 is a reflectance characteristic diagram of the antireflection film formed on the fifth and sixth surfaces according to the fourth embodiment.

FIG. 26 is a reflectance characteristic diagram of an antireflection film formed on the third surface according to the fourth embodiment.

FIG. 27 is a reflectance characteristic diagram of an antireflection film formed on the first and second surfaces of Comparative Example 3.

FIG. 28 is a reflectance characteristic diagram of the antireflection films formed on the fifth and sixth surfaces in Comparative Example 3.

FIG. 29 is a reflectance characteristic diagram of the antireflection film formed on the third surface of Comparative Example 3.

FIG. 30 is a spectral transmittance characteristic diagram of Comparative Example 3.

FIG. 31 is a sectional view showing an endoscope.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H040 BA00 CA23 GA02 2K009 AA08 AA09 BB02 CC03 CC06 DD03 DD04 DD07 4C061 FF40 FF47

Claims (6)

[Claims] To 1. A incident light parallel to the optical axis, reflectance _{R v} wavelength region 420nm~650nm a is _{R v} ≦ 1%, the reflectance in the wavelength region 920Nm～1100nm R
A lens on which an antireflection film having a reflectance characteristic in which _ir is 40% ≦ R _ir is formed, wherein the first layer from the substrate side is made of an intermediate refractive index material, and It is made of a low-refractive-index material or a high-refractive-index material, and the upper layer is made of a high-refractive-index material and a low-refractive-index material alternately laminated toward the air side. 5. A lens provided with an antireflection film, comprising 5 or 6 layers comprising: 2. With respect to incidence of light parallel to the optical axis, the reflectance R _{v in the} wavelength region of 420 nm to 530 nm is R _v ≦ 1%, and the reflectance R _{ir in the} wavelength region of 720 nm to 920 nm.
Is a lens provided with an antireflection film having a reflectance characteristic of 40% ≦ R _ir , wherein the first layer of the antireflection film from the substrate side is made of an intermediate refractive index material, and the upper layer is low. It is made of a high-refractive-index material or a high-refractive-index material, and the upper layer is made of a high-refractive-index material and a low-refractive-index material alternately laminated toward the air side, and the outermost layer on the air side is made of a low-refractive-index material. A lens with an antireflection film, characterized by comprising 5 or 6 layers. To 3. An incident light parallel to the optical axis, reflectance _{R v} wavelength region 420nm~530nm a is _{R v} ≦ 1%, the reflectance in the wavelength region 720nm~920nm _{R ir}
Is a lens on which an antireflection film _satisfying 40% ≦ R _ir is formed, wherein the first layer of the antireflection film is made of a low refractive index material from the substrate side, and the layers above it alternately face the air side. A layer with a high refractive index material and a low refractive index material laminated thereon, and the outermost layer on the air side has five layers made of a low refractive index material. 4. An endoscope, wherein the lens with an anti-reflection film according to claim 1 is disposed in an objective optical system. 5. An endoscope, wherein the lens with an antireflection film according to claim 2 is arranged in an objective optical system. 6. An endoscope, wherein the lens with an antireflection film according to claim 3 is arranged in an objective optical system.