JP2008276059A - Optical element and optical system having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress generation of harmful light causing a flare and a ghost. <P>SOLUTION: An optical element 1 having a sub-wavelength structure formed on a lens surface 2a has the sub-wavelength structure formed on an edge part 3 and a film 4 formed on the sub-wavelength structure and opaque to light having a used wavelength region. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical element that suppresses generation of harmful light that causes flare, ghost, and the like.

Various optical devices such as lenses have been devised for the purpose of suppressing the generation of harmful light causing flare, ghosting, etc., and obtaining a high-quality and high-performance optical system. They can be broadly classified into the following two categories.
(1) A method of reducing reflection by improving light transmittance in a light beam effective portion (2) A method of reducing reflection by improving light absorption rate in a non-light beam effective portion Conventionally (1) As a method of the above, a method of providing a dielectric thin film on a light beam effective portion such as a lens surface by a vacuum deposition method or a sputtering method is widely used.

  In an antireflection film using a dielectric thin film, the refractive index and film thickness of each film are controlled, and reflected light generated at the surface and interface is made to interfere with each other to reduce the reflectance. Therefore, although a high-performance antireflection performance can be obtained at a specific wavelength and a specific incident angle, there is a problem that the performance is greatly deteriorated at other wavelengths and incident angles.

  On the other hand, as a method for replacing the dielectric thin film, an antireflection structure using a sub-wavelength structure (SWS) equal to or less than a used wavelength is also known.

  For example, Patent Document 1 discloses an example in which an antireflection portion having a fine periodic uneven structure formed at a pitch equal to or less than the wavelength of a light beam to be antireflection is provided on a curved surface forming a member.

  In the antireflection structure composed of a fine periodic concavo-convex structure with a wavelength equal to or less than that disclosed in Patent Document 1, since the space occupancy of the member continuously changes, the refractive index continues from the incident medium to the exit medium. Will change. Therefore, when the height of the fine periodic concavo-convex structure is not less than a certain level (for example, not less than one half of the wavelength used), antireflection performance excellent in wavelength band characteristics and incident angle characteristics can be obtained.

On the other hand, as the method (2), a method of forming a coating film containing coal tar, coal tar pitch, black pigment, black dye, carbon black or the like on the lens side end portion (so-called edge portion) is widely used. It has been.
Japanese Laid-Open Patent Publication No. 2006-053220

  In addition to light necessary for photographing or observation, light from various angles may enter an optical element such as a lens.

  An example in which a member disclosed in Patent Document 1 is used in an imaging optical system and an observation optical system will be described with reference to FIG. The light 11 incident on the member 1 at a large angle passes through the light effective portion (lens surface) 2a on which the fine periodic uneven structure is formed, and reaches the non-light effective portion (edge portion) 3. At this time, since the fine periodic concavo-convex structure is excellent in the incident angle characteristic of the reflectance, light is transmitted through the light beam effective portion 2a with a high transmittance even at a large incident angle.

  However, in the member 1 described in Patent Document 1, since the non-light effective portion 3 is not subjected to any processing, the light 11 is reflected by the non-light effective portion 3 to become unnecessary light 12, such as flare and ghost. Causes harmful light.

  An object of the present invention is to suppress the generation of harmful light that causes flare, ghost, and the like as much as possible.

  An optical element of the present invention is an optical element in which a sub-wavelength structure having a wavelength less than or equal to a use wavelength is formed in a light effective portion, and a sub-wavelength structure having a wavelength less than or equal to a use wavelength formed in a non-light effective portion and the sub-wavelength structure It is characterized by having an opaque film formed with respect to light in the used wavelength range.

  According to the present invention, generation of harmful light can be suppressed as compared with the case where a coating film is simply formed on the non-light-effective portion.

  Hereinafter, an optical element of the present invention and an optical system using the same will be described with reference to the drawings.

  The optical element of the present invention is an element in which the light beam effective portion (lens surface or the like) is provided with an antireflection portion having a sub-wavelength structure having a use wavelength or less in the in-plane direction. Further, a sub-wavelength structure having a wavelength less than or equal to the use wavelength is formed in the in-plane direction on the non-light effective portion (edge portion or the like), and a film that is substantially opaque to the light in the use wavelength region is further formed on the sub-wavelength structure. Formed.

  The sub-wavelength structure in the present invention may be produced by any method. For example, a method of forming a fine uneven structure by applying a solution containing aluminum on the surface of the optical element to form a film and treating the film with warm water can be used. In addition, a method may be used in which pores formed when anodizing aluminum or an aluminum alloy are formed on the mold surface, and a fine uneven shape is integrally formed with the optical element by injection molding using the pores. Good. If these methods are used, a sub-wavelength structure can be formed on a curved surface with a large area at low cost, which is preferable. In addition, it may be formed using photolithography, etching, nanoimprint technology, or the like.

  As the substantially opaque film, a coating film containing coal tar, coal tar pitch, black pigment, black dye, carbon black, or the like is preferable, but an absorption film that has high light absorption and can suppress reflection. If you want, you can use another one.

  In FIG. 8A, a lens inner surface antireflection coating (trade name: GT-7, manufactured by Canon Kasei Co., Ltd.) 81 is formed on a lens 80 formed of optical glass S-LAH65 (nd = 1.840) manufactured by OHARA INC. An example in which is applied. FIG. 8B is an enlarged view of an interface portion between the lens 80 and the antireflection paint 81, and FIG. 8C is a diagram showing a change in refractive index in a direction perpendicular to the interface. FIG. 8D shows the reflectance in the visible range (internal reflectance).

  By forming an opaque film at the working wavelength on the surface of the non-light effective portion, the reflectance is 0.6% or less in the entire visible range (here, the wavelength range of 400 nm to 700 nm). The reflectance is greatly reduced as compared with the reflectance when the coating film shown in the above is not formed. However, in the optical element having the sub-wavelength structure in the light effective portion, the incident angle characteristic of the antireflection effect is excellent as described above, so that more light is transmitted through the light effective portion, and the non-light effective The ratio of light reaching the part also increases compared to the conventional case. For this reason, it is not sufficient to simply form an opaque film on the non-light effective portion.

  Therefore, in the optical element of the present invention, a sub-wavelength structure having a wavelength shorter than the use wavelength is formed also in the non-light effective portion, and an opaque film is formed on the sub-wavelength structure.

  In FIG. 7A, a sub-wavelength structure 72 of a wavelength or less made of a material containing aluminum oxide is formed on a lens 70 formed of the same S-LAH 65 as in FIG. 8, and a lens inner surface antireflection coating (Canon) is formed on the subwavelength structure 72. The example which apply | coated Kasei Co., Ltd. brand name: GT-7) 71 is shown. Although the sub-wavelength structure 72 is conceptually represented by a sawtooth shape, it is not always necessary to have such a shape. FIG. 7B is an enlarged view of an interface portion between the lens 70 and the antireflection paint 71, and FIG. 7C is a diagram showing a change in refractive index in a direction perpendicular to the interface. FIG. 7D shows the reflectance (internal reflectance) in the visible range.

  By forming an opaque film on the sub-wavelength structure in this way, the reflectance is 0.1% or less over the entire visible range, which is significantly lower than the reflectance shown in FIG.

  This is due to the fact that the subwavelength structure was formed between the glass and the internal antireflection coating, and the refractive index gap at the interface was continuously changed, so that reflection was suppressed and light absorption efficiency was improved. .

  As a result, even in an optical element in which an anti-reflection part having a sub-wavelength structure is provided in the light beam effective part of the optical element, reflection of light at the non-light beam effective part is reduced, and harmful light that causes flare, ghost, etc. Occurrence can be greatly suppressed.

  The optical element of the present invention can be applied to lenses, prisms and the like. The optical element of the present invention can be used in various optical systems such as an imaging optical system and an observation optical system.

  FIG. 1 is a sectional view of an optical element according to Example 1 of the present invention.

  In FIG. 1, the optical element 1 is a concave meniscus lens. The light effective portions (lens surfaces) 2a and 2b are provided with subwavelength structures (shown by broken lines in the figure) made of a material containing aluminum oxide. The light 11 incident on the optical element 1 at a large angle passes through the light beam effective portion 2a having the sub-wavelength structure and reaches the non-light beam effective portion (edge portion) 3. The non-light effective portion 3 has a sub-wavelength structure and a coating film 4 made of a lens inner surface antireflection coating (manufactured by Canon Kasei Co., Ltd., trade name: GT-7). For this reason, the intensity | strength of the reflected light 12 reduces remarkably and generation | occurrence | production of the harmful light which causes a flare, a ghost, etc. can be suppressed.

  In the first embodiment, the case of a concave meniscus lens is shown as the optical element, but the optical element of the present embodiment is not limited to this. An optical element of any shape such as a biconvex lens, a biconcave lens, a planoconvex lens, a planoconcave lens, a convex meniscus lens, an aspherical lens, a free-form surface lens, or a prism may be used. This is the same in other embodiments described later.

  FIG. 2 is a sectional view of an optical element according to Example 2 of the present invention.

  In FIG. 2, the optical element 1 is a biconcave lens. The light effective portion (lens surface) 2a is provided with a sub-wavelength structure (indicated by a broken line in the figure) made of a material containing aluminum oxide. The second embodiment is different from the first embodiment in that the sub-wavelength structure is provided only on one lens surface as described above.

  The light 11 incident on the optical element 1 at a large angle passes through the light beam effective part 2 a having the sub-wavelength structure and reaches the non-light beam effective part 3. However, the non-light beam effective portion 3 has a lens inner surface antireflection coating (trade name) manufactured by Canon Kasei Co., Ltd. through a sub-wavelength structure (shown by a broken line in the figure) made of a material containing aluminum oxide, similar to the light beam effective portion. : The coating film 4 which consists of GT-7) is formed. Thereby, the intensity of the reflected light 12 is remarkably reduced, and the generation of harmful light that causes flare, ghost, and the like is suppressed.

  FIG. 3 is a sectional view of an optical element according to Example 3 of the present invention.

  In FIG. 3, the optical element 1 is a biconvex lens. The light effective part 2a and the non-light effective part 3 are provided with a sub-wavelength structure (shown by a broken line in the figure) made of a cycloolefin polymer (manufactured by Nippon Zeon Co., Ltd.) which is the same material as the optical element. The light 11 incident on the optical element 1 at a large angle passes through the light beam effective portion 2 a having the sub-wavelength structure and reaches the non-light beam effective portion 3. However, a coating film 4 made of a material containing a black pigment is formed on the sub-wavelength structure on the non-light effective portion 3. For this reason, the intensity of the reflected light 12 is remarkably reduced, and generation of harmful light that causes flare, ghost, and the like is suppressed.

  FIG. 4 is a sectional view of an optical element according to Example 4 of the present invention.

  In FIG. 4, the optical element 1 is a convex meniscus lens. The light beam effective portions 2a and 2b are provided with a sub-wavelength structure (indicated by a broken line in the figure) made of polycarbonate resin (manufactured by Teijin Chemicals Ltd.), which is the same material as the optical element. The light 11 incident on the optical element 1 at a large angle passes through the light beam effective portion 2 a having the sub-wavelength structure and reaches the non-light beam effective portion 3. However, the non-light effective portion 3 is formed with a coating film 4 made of a material containing a black pigment via a subwavelength structure. Therefore, the intensity of the reflected light 12 is remarkably reduced, and the generation of harmful light that causes flare, ghost, and the like is suppressed.

  FIG. 5 is a cross-sectional view of the imaging optical system of Example 5 of the present invention.

  In FIG. 5, the optical system 5 has an optical element 1 made of a concave meniscus lens, and the light effective portion 2b and the non-light effective portion 3 have a sub-wavelength structure made of a material containing aluminum oxide (shown by a broken line in the figure). ) Is provided. On the non-light effective portion 3, a coating film 4 made of a lens inner surface antireflection coating (manufactured by Canon Kasei Co., Ltd., trade name: GT-7) is formed on the sub-wavelength structure. For this reason, reflection at the non-light effective portion 3 is reduced, and generation of harmful light that causes flare, ghost, and the like is suppressed. Therefore, a high-quality and high-performance imaging optical system is realized.

  In the fifth embodiment, the antireflection portion having the sub-wavelength structure is provided only on the exit surface 2b of the first lens on the incident side. However, the present embodiment is not limited to this, and the entrance surface / exit of another lens is used. It may be provided on the surface.

  However, it is better not to provide an antireflection portion having a sub-wavelength structure on the entrance surface 2a of the first lens and the exit surface 2c of the final lens. This is because the sub-wavelength structure has extremely low mechanical strength and cannot be wiped off when dirt or the like adheres.

  FIG. 6 is a cross-sectional view of an observation optical system (finder optical system of a single-lens reflex camera) according to Example 6 of the present invention.

  In FIG. 6, an optical system 5 has optical elements 1a, 1b, and 1c made of a concave lens, a convex lens, and a concave meniscus lens, and a sub-wavelength structure (shown by a broken line in the figure) made of the same material as the optical element in the light beam effective portion. ) Is provided. A coating film 4 made of a material containing a black pigment is formed on the subwavelength structure in the non-light effective portion. For this reason, reflection of light reaching the non-light beam effective portion is reduced and generation of harmful light is suppressed, so that a high-quality and high-performance observation optical system is realized.

  In Example 6, the antireflection function having the sub-wavelength structure is not provided on the exit side (right side) surface of the optical element 1c. This is because the problem due to the mechanical strength of the sub-wavelength structure does not occur as in the fifth embodiment.

1 is a cross-sectional view of an optical element of Example 1. FIG. 6 is a cross-sectional view of an optical element according to Example 2. FIG. 6 is a cross-sectional view of an optical element according to Example 3. FIG. 6 is a sectional view of an optical element according to Example 4. FIG. 10 is a cross-sectional view of an imaging optical system according to Example 5. FIG. 10 is a cross-sectional view of an observation optical system in Example 6. FIG. It is a figure for demonstrating the outline of the optical element of this invention. It is a figure for demonstrating the outline of the optical element of a comparative example. It is a figure which shows the reflectance of the non-light-effective part of the optical element of a comparative example. It is a figure showing the conventional optical element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical element 2a, 2b Light beam effective part 3 Non-light beam effective part 4 Opaque film | membrane 5 Optical system 6 Shooting lens 7 Reflecting mirror 8 Prism

Claims (9)

  An optical element in which a sub-wavelength structure with a sub-wavelength less than the use wavelength is formed in the light effective portion, formed on the sub-wavelength structure with a sub-wavelength less than the use wavelength formed in the non-light effective portion An optical element having a film opaque to the light in the used wavelength range.   The optical element according to claim 1, wherein the optical element is a lens, and the non-light ray effective part is an edge part of the lens.   The optical element according to claim 1, wherein the opaque film is an absorption film that absorbs light having a wavelength to be used.   The optical element according to any one of claims 1 to 3, wherein the wavelength used is in a wavelength range of 400 nm to 700 nm.   The optical element according to claim 1, wherein the sub-wavelength structure is a structure containing aluminum or aluminum oxide.   The optical element according to claim 1, wherein the sub-wavelength structure is made of the same material as the optical element.   The optical element according to claim 1, wherein the opaque film contains at least one of coal tar and coal tar pitch.   The optical element according to claim 1, wherein the opaque film contains at least one of a black pigment and a black dye.   An optical system comprising the optical element according to claim 1.

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