JP2006162822A - Diffraction optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffraction optical element reducing a deterioration in performance due to the occurrence of flare of the diffraction optical element. <P>SOLUTION: In a blazed grating made by alternately arranging an inclined optical surface 11 and a wall surface 12, a light absorption part 13 for absorbing incident light Lb made incident on the wall surface 12 by means of the optical surface 11 after reflection by means of the wall surface 12 is provided. The light absorption part 13 on the optical surface 11 can be simply formed by applying a resist ink on a coating film 10a having oil repellent property and producing an ink puddle on a cross point 12a between the optical surface 11 and the wall surface 12. As compared to the case of performing antireflection by providing a thin film on the wall surface 12 or roughening the wall surface 12, occurrence of flare is effectively prevented at a lower cost. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a diffractive optical element applied to an optical system of an imaging device, an observation device, and other optical devices.

  A diffractive optical element used in an optical system such as an imaging apparatus is often used as a lens element. In particular, in a diffractive optical element having a blazed diffraction grating, there is a light beam that does not enter the relief pattern wall surface in parallel due to processing problems and restrictions on the arrangement of the optical system, and this light beam passes through the wall surface. It becomes flare light and reaches the image pickup surface, which degrades the optical performance of the diffractive optical element.

  For example, as shown in FIG. 5A, when the incident light L is parallel to the wall surface 112 of the diffraction grating 110, most of the light is incident on the optical surface 111, but there is no problem in optical performance. As shown in FIG. 5B, when the wall surface 112 is not parallel to the optical axis of the incident light L in order to improve the moldability for forming the relief pattern, or as shown in FIG. When the incident light L is incident obliquely with respect to the blazed diffraction grating, the amount of light incident on the wall surface 112 is increased, and in any case, the optical performance of the diffraction grating is degraded due to flare light. Various proposals have been made to solve this problem.

  For example, in Patent Document 1, the ratio between the total area of non-lens surfaces and the average value of projection surfaces onto a plane (wall surface) perpendicular to the optical axis of the diffractive surface included in the optical system is a predetermined value or less. An optical system having a diffraction grating in which flare on a non-lens surface is suppressed has been proposed.

  Further, in Patent Document 2, as shown in FIG. 6, a configuration in which a stepped portion 123 is provided on an edge portion (wall surface) 122 of a diffraction grating 120, or a micro uneven structure having a smaller wavelength than the used wavelength on the optical portion surface of the diffraction grating. Proposals have been made such as providing

Further, Patent Document 3 discloses a diffractive optical element having a light shielding unit 143 that shields light Lb incident on an edge portion (wall surface) 142 of a diffraction grating 140 and emitted to an optical substrate 130 as shown in FIG. Proposed and Patent Document 4 discloses a method of performing a matting process by ashing only on a vertical surface (wall surface) of a diffraction grating, and Patent Document 5 discloses a boundary between two optical members made of different materials. There has been proposed a diffractive optical element in which a thin film layer made of silicon dioxide, zinc sulfide, or aluminum oxide is formed on the boundary surface of an optical material having a relief pattern.
JP 2001-305323 A JP 2002-071925 A JP 2002-048906 A JP 2003-240931 A JP 2001-337214 A

  However, according to the above conventional techniques, there are unsolved problems such as insufficient suppression of flare and an increase in manufacturing cost.

  In the proposal of Patent Document 1, since the scattered light entering through the photographing lens is not blocked by a plane (wall surface portion) perpendicular to the optical axis, the occurrence of flare cannot be completely suppressed.

  Further, in the configuration disclosed in Patent Document 2, a slight incident light Lb cannot be blocked at the intersection 122a of the wall surface 122 having the optical surface 121 of the diffraction grating 120 and the stepped portion 123 of FIG. Is not perfect. In this proposal, there is a problem in the shape stability of the staircase portion in terms of releasability when forming a relief pattern.

  Furthermore, in the configuration of Patent Document 3, flare light can only be suppressed when incident / exit light including a flare factor follows the optical path in the direction of the arrow indicated by the broken line in FIG. Although it corresponds to the reflected light of the inclined wall surface (edge portion) 142, it is difficult to handle when the wall surface is parallel to the optical axis, and the formation of the light shielding portion is not easy, and the manufacturing process is complicated. It is expected to become.

  In the configuration of Patent Document 4, the matte processing on the vertical surface (wall surface) of the diffraction grating completely blocks the incident light on the vertical surface and the light emitted from the vertical surface, and can completely suppress flare light. However, the manufacture of this element has the problem that the matting process by ashing is complicated, the tact time is increased, and the manufacturing cost is increased. With the configuration of Patent Document 5, the wavelength dependency characteristic of diffraction efficiency is reduced, and unnecessary order light is emitted. Therefore, it is difficult to stably fix the thin film layer on the diffraction grating wall surface, and the cost of equipment and management space increases in the process of forming the thin film layer.

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and has excellent quality and productivity that can be manufactured at low cost by efficiently reducing flare light with a simple configuration. An object of the present invention is to provide a diffractive optical element.

  In order to achieve the above object, a diffractive optical element of the present invention includes a diffraction grating including a plurality of optical surfaces that perform light diffraction and a plurality of wall surfaces that separate the plurality of optical surfaces from each other. A light absorbing portion for absorbing incident light scattered by an adjacent wall surface is provided at a predetermined portion of the surface.

  Since the light reflected from the wall surface of the diffraction grating is absorbed by the optical surface, the occurrence of flare is prevented. Therefore, it is possible to effectively prevent the deterioration of the optical performance due to the flare light at a low cost.

  As shown in FIG. 1, among incident light La and Lb incident on the optical surface 11 and the wall surface 12 of the diffraction grating 10, the reflected light of the incident light Lb incident on the wall surface 12 is part of the optical surface 11. Absorption by the provided light absorber 13 reduces the occurrence of flare.

  The light absorbing portion 13 provided on the optical surface 11 of the diffraction grating 10 is disposed in the vicinity (intersection) of the intersection 12a between the optical surface 11 and the wall surface 12 so as not to greatly affect the light diffraction action of the optical surface 11. Constitute.

  For example, in a blazed diffraction grating, light that is reflected and scattered by the wall surface of the diffraction grating is blocked on the optical surface, so that a decrease in optical performance due to flare light can be prevented very effectively.

  With a simple configuration, flare light can be reliably absorbed, and it is easy to add a light absorption part to the optical surface in the process of forming a diffraction grating, so a high-performance diffractive optical element can be manufactured at low cost. realizable.

  FIG. 1 is a partial schematic cross-sectional view showing a part of the diffractive optical element according to the first embodiment. A resin-made diffraction grating (blazed diffraction grating) 10 is disposed on an optical base material 1 serving as a base, and its optical surface 11 and wall surface 12 are covered with a coating film 10a. A light absorber constituting the light absorbing portion 13 is attached in the vicinity of the intersection 12a of the wall 11 and the wall 11.

  Of the incident light La and Lb, the incident light La on the optical surface 11 is diffracted as emitted light Le to the optical substrate 1 side at a desired angle by the optical surface 11 which is a relief pattern transfer surface. However, the incident light Lb on the wall surface 12 is reflected and refracted on the wall surface 12 and then travels to the light absorption unit 13 and is thus absorbed on the optical surface 11. Therefore, it does not pass through the optical base material 1 and does not reach the imaging surface or the like as flare light. In this way, image quality deterioration due to flare light can be prevented.

  FIG. 2 is a process diagram showing a method of forming the light absorbing portion 13 near the intersection of the optical surface 11 and the wall surface 12. First, as shown in FIG. 2 (a), a photocuring reaction type monomer that is a resin material is used, and an optical pattern on the relief pattern transfer surface is formed on the optical substrate 1 using a stamper type and a light irradiation device (not shown). The diffraction grating 10 having the surface 11 and the wall surface 12 is replica-molded. As the resin material of the diffraction grating 10, a thermosetting resin or a photocuring / thermosetting combined resin is used.

  A coating film 10a containing a fluorine group is coated on the optical surface 11 and the wall surface 12 on the relief pattern transfer surface by spin coating. The coating film 10a used here is prepared by diluting an organic coating material containing fluorine in a fluorine-based solvent solution to 0.1 to 0.5 wt%. When a resist ink which is a light absorbent impregnated with a light absorbing material (opaque material) is dipped on the optical surface 11 and the wall surface 12 coated with the coating film 10a, the surface of the coating film 10a is extremely water and oil repellent. Due to the high fluorine group reaction, more resist ink tends to be fixed on the stabilization surface. This stabilization surface is fixed as a resist ink ink reservoir 13a centering on the lower position where the resist ink is most likely to gather, that is, in the vicinity of the intersection 12a of the optical surface 11 and the wall surface 12. It becomes the surface layer 13b of resist ink.

  Thereafter, an ashing process such as corona discharge is performed to activate the surface layer 13b of the resist ink having a thickness of 20 to 30 nm. As shown in FIG. 2B, the resist other than the ink reservoir 13a fixed on the stabilization surface is obtained. Remove ink.

  A predetermined amount of resist ink stays on the stabilization surface as an ink reservoir 13a as shown in FIG. 2C, and after confirming the stable state, as shown in FIG. The light absorbing portion 13 is formed by performing a curing process.

  In addition, although this light absorption part may form chromium oxide, a chromium plating film, etc. using techniques, such as an electronic mask and a photolithographic method, it will increase in cost by introduction of an expensive apparatus and a complicated process. there is a possibility. Further, even if a method such as printing or vapor deposition is used, there is a problem that the manufacturing process is complicated such as masking. Therefore, in order to improve the manufacturing efficiency and provide a stable quality optical element, FIG. The method shown is desirable.

  FIG. 3 is a partial schematic cross-sectional view showing a part of the diffractive optical element according to the second embodiment. This is a relief type in which the optical substrate 1 of Example 1 is applied as a convex spherical optical substrate, and the diffraction grating 30 on the optical substrate 20 which is a concave spherical optical substrate is laminated on the diffraction grating 10. It is a diffractive optical element, and light absorbing portions 13 and 33 are provided on optical surfaces 11 and 31 of the diffraction gratings 10 and 30, respectively.

  Incident light La reaches the optical surface 31 of the relief pattern transfer surface at a desired angle from the surface of the optical substrate 20 and is diffracted. The diffracted light between the optical surfaces 31 passes through the air gap between the two diffraction gratings 30 and 10 and is incident on the optical surface 11 of the relief pattern transfer surface of the diffraction grating 10 to be diffracted and output to the optical substrate 1 side. The light is emitted as light Le. However, since the incident light Lb passes through the optical substrate 20 and then travels toward the light absorbing portion 33 of the optical surface 31 of the diffraction grating 30, it is absorbed here and does not reach the wall surface 32 between the optical surfaces 31. Therefore, flare light is not generated due to wall surface reflection, and the image quality is not deteriorated.

  The optical substrate 1, the diffraction grating 10, the optical surface 11, the wall surface 12, and the light absorption unit 13 are the same as those in FIG.

  FIG. 4 shows a process of manufacturing the diffraction grating 30. A resist ink impregnated with a light-absorbing material from an opening 41a is used as a stamper mold for a stamper mold 40 for transfer-molding a relief pattern of the diffraction grating 30. A screen mask 41 for application on top is positioned. That is, the screen mask 41 is aligned with the diffraction grating forming tip 40a of the stamper mold 40, an organic release film 40b such as CYTOP is applied from the opening 41a, and then resist ink impregnated with a light absorbing material is stamped. It is applied onto the mold 40 and immediately cured with a predetermined temperature profile. In this way, the light absorbing agent 33a is coated on the diffraction grating forming tip 40a of the stamper mold 40.

  When the diffraction grating 30 having the relief pattern transfer surface is formed using the stamper mold 40, the light absorber 33a is transferred to the optical surface 31 that intersects the wall surface 32 and is adjacent thereto. Here, since the organic release film 40b is applied on the stamper mold 40, the transfer of the light absorber 33a from the stamper mold 40 is easy, and strict alignment accuracy is required for the alignment of the screen mask 41. Not. Therefore, there is no possibility that the manufacturing process becomes complicated.

  In addition, when it is more suitable to use the manufacturing method similar to Example 1, it is preferable to select it suitably.

  In the present embodiment, the surface other than the portion where the light absorbing portion 13 is formed of the optical surface 11 is covered without providing the coating film 10a of the first embodiment, and the portion corresponding to the light absorbing portion 13 is covered by sandblasting. The next processing is performed. Although the surface roughness by the blast treatment is Rmax 0.8 to 1.3 μm, it is preferably set appropriately according to the performance of the optical element, and is not limited to this range. Other points are the same as in the first embodiment.

  In the present embodiment, the coating film 10a of the first embodiment is not required, and the light absorbing portion 13 is formed on the satin transfer surface. As the transfer mold, a stamper-type diffraction grating molding tip similar to the stamper mold 40 of FIG. 4 is used, and a replica surface is processed with a resin material similar to that in Example 1 to obtain a transfer surface. The pear ground obtained here has an Ra of 1 to 3 μm and a semi-glossy appearance, but it is preferably set appropriately according to the performance of the optical element, and is not limited to this range. Other points are the same as in the first embodiment.

2 is a partial schematic cross-sectional view showing a configuration of Example 1. FIG. FIG. 3 is a process diagram illustrating the manufacturing method of Example 1. 3 is a partial schematic cross-sectional view showing a configuration of Example 2. FIG. 6 is a diagram illustrating a manufacturing process of Example 2. FIG. It is a figure explaining the relationship between the incident light of a diffraction grating, and a diffraction grating. It is a partial schematic cross section which shows one prior art example. It is a partial schematic cross section which shows another prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,20 Optical base material 10,30 Diffraction grating 10a Coating film 11,31 Optical surface 12,32 Wall surface 13,33 Light absorption part 40 Stamper type

Claims (4)

  Incident light that has a diffraction grating having a plurality of optical surfaces that perform light diffraction and a plurality of wall surfaces that separate the plurality of optical surfaces from each other, and is scattered by a predetermined wall surface of each optical surface by adjacent wall surfaces A diffractive optical element, wherein a light absorbing portion for absorbing the light is provided.   The diffractive optical element according to claim 1, wherein the light absorbing portion is formed by depositing an opaque light absorber on a predetermined portion of each optical surface.   The diffractive optical element according to claim 1, wherein the light absorbing portion is formed by roughening a predetermined portion of each optical surface.   The diffractive optical element according to any one of claims 1 to 3, wherein the light absorbing portion is disposed at an intersection between the optical surface and the wall surface.

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