JP2009175481A - Antireflection optical member and optical module - Google Patents

Abstract

Provided is an antireflection optical member that is excellent in reflection characteristics and can be easily manufactured when forming a periodic structure with fine irregularities, and an optical module using the antireflection optical member. To do.
An optical member having an antireflection surface formed by forming a fine concavo-convex structure with a sub-wavelength period on a surface 20 of a translucent substrate using a molding die, It is formed by a large number of fine frustum-shaped recesses 21 that are densely provided with a wavelength period. The frustum-shaped concave portion 21 has “0.35 <(W / P) <0.7” and “0” when the pitch is P, the bottom width is W, the depth is H, and the incident light wavelength is λ. .25 <(H / λ) <0.4 ”.
[Selection] Figure 1

Description

  The present invention relates to an antireflection member in which a fine concavo-convex structure for antireflection is formed on the surface of a translucent substrate, and an optical module using the antireflection member.

Recent advances in microfabrication technology have enabled the formation of concave and convex structures (several hundreds of nanometers) with sub-wavelength periods smaller than the wavelength used for optical members made of translucent substrates. It is known that surface reflection in an optical device can be suppressed using the structure.
For example, in Patent Document 1, as schematically shown in FIG. 9A, a light guide plate in which an uneven surface for preventing reflection composed of a conical fine continuous pattern is formed on a surface light source of a reflective liquid crystal device. Is disclosed.

  In this device, an illumination device 2 is arranged as a front light on the reflective liquid crystal means 1 side. The illuminating device 2 includes a linear light source 3 and a light guide plate 4, and an antireflection surface 5 including a fine uneven surface is formed on the back surface of the light guide plate 4 in order to improve visibility. The light incident from one end side of the light guide plate 4 is reflected by the reflecting surface 6 formed on the surface side of the light guide plate 4 and given to the reflective liquid crystal display means 1. Next, the light modulated and reflected by the reflective liquid crystal display means 1 is prevented from being reflected by the antireflection surface 5 on the back surface of the light guide plate 4 and is incident on the light guide plate 4 without being diffracted. , And is visible through the light-transmitting surface 7.

  As shown in FIG. 9B, the antireflection surface 5 has fine conical (quadrangular pyramidal) projections 8 formed continuously on the surface of the light guide plate 4 of the translucent substrate. The ratio (D / P) when the pattern pitch P and the height D of the protrusion 8 are taken as the aspect ratio. If this aspect ratio is smaller than “1”, the reflectance on the long wavelength side increases and the interference color of red due to reflection becomes stronger. If the aspect ratio is larger than “1”, the reflectance decreases and the interference color due to reflection is colorless. Is disclosed.

  Further, the light guide plate 4 having an uneven surface by the fine protrusions 8 is formed by molding a translucent resin material 9 with upper and lower molds 10 and 11 as shown in FIG. . The lower mold 11 is formed with a pattern for continuously forming the protrusions 8 of the antireflection surface 5. It is also disclosed that the reflectance increases when the pattern on the lower mold 11 side is not accurately transferred (the shape of the end portions of the protrusions 8 and the valleys is dull).

  Further, Patent Document 2 discloses an antireflection article used for window materials and the like of various display parts such as a liquid crystal display as shown in FIGS. 10 (A) and 10 (B). This antireflective article is formed by providing fine irregularities 13 on the surface of the substrate 12, where P is the period at the most convex portion 13 a of the fine irregularities 13, and P is the minimum wavelength of visible light to be used. ≦ λm. In addition, it is disclosed that the cross-sectional area in the horizontal plane of the substrate 12 is continuously increased gradually from the most convex portion 13a of the fine unevenness 13 to the most concave portion 13b.

In addition, in Patent Document 3, as shown in FIG. 11, the lower electrode of the light emitting element 14 is bonded and fixed to the first terminal 15a, and the upper electrode is connected to the second terminal 15b by wire bonding. A light emitting diode is disclosed in which the outside is sealed with a lens 16 made of a transparent resin, and an antireflection microstructure 16a is formed on a surface portion of a predetermined region of the lens 16. The antireflection microstructure 16a has a shape in which minute conical protrusions similar to those described in FIG. 9B are continuously formed.
JP 2003-279705 A JP 2003-240904 A Japanese Patent Laid-Open No. 2005-79244

  As shown in FIGS. 9 to 11 described above, by continuously forming conical projections with a sub-wavelength microstructure on the surface of the optical member, light having a wavelength that passes through the optical member is reflected. It is possible to prevent. However, the fine cone-shaped projections for preventing reflection are usually formed using a mold made of glass or a semiconductor substrate. As a mold for this purpose, as shown in FIGS. 12A and 12B, a conical recess 18 is formed in a predetermined region portion 17a of the mold base 17 by etching a fine pattern or the like. is doing.

  When the above-described mold is used and the transparent resin 19 is filled and the fine cone-shaped protrusions are densely continuously formed at a predetermined cycle, as shown in FIG. The air 18a remains in the deepest part of the fine cone-shaped recess 18 provided in the air, and the air 19 is blocked so that the resin 19 does not sufficiently flow, and the filling may remain incomplete. There is. For this reason, as disclosed in FIG. 9 (Cited document 1), the transfer rate from the mold is deteriorated, and predetermined reflection characteristics may not be obtained.

  The present invention has been made in view of the above-described circumstances, and provides an anti-reflection optical member that is excellent in reflection characteristics that can be easily transferred from a mold and can be easily manufactured when forming a periodic structure with fine irregularities. An object of the present invention is to provide an optical module using the antireflection optical member.

The antireflection optical member according to the present invention is an optical member that forms an antireflection surface by forming a fine concavo-convex structure with a sub-wavelength period on the surface of a translucent substrate using a molding die. The structure is formed by a large number of fine frustum-shaped recesses that are densely provided with a sub-wavelength period. The frustum-shaped concave portions have a pitch of P, a width of the bottom surface of W, a depth of H, and a wavelength of incident light of λ, “0.35 <(W / P) <0.7” and “0.3. It is preferable that 25 <(H / λ) <0.4 ”is satisfied.
The frustum shape is a polygonal frustum shape, preferably a quadrangular frustum shape, and may be a truncated cone shape.

  Further, the antireflection optical member can be provided with a light antireflection function by using it in an optical system path of an optical module on which an optical element such as a laser element is mounted. When the refractive index of the antireflection optical member is n and the incident light wavelength is λ, the pitch of the frustum-shaped recesses is set to be P ≦ λ / (1 + n) so as to suppress the generation of diffracted light. Also good.

  According to the present invention, when forming a fine concavo-convex structure with a sub-wavelength period on the surface of a substrate such as a translucent resin, a large number of frustum-shaped convex portions that are convex with respect to the reference surface on the mold side Since the bottom portions that are concave are in communication with each other on the reference surface of the mold, it is possible to prevent air from remaining on the bottom portions that are concave when the resin is molded. As a result, the fine concavo-convex structure of the mold can be transferred satisfactorily and the antireflection function can be improved.

Moreover, since the bottom part which becomes a concave is made into the frustum shape which cut off the front-end | tip part of a cone, since the sharp front-end | tip shape is lost in a metal mold | die and the height difference of a frustum shape can also be made small, handling is good. Note that it is easier to manufacture and reduce the cost of mold manufacture than forming a large number of fine frustum-shaped convex portions on the mold surface rather than forming a large number of fine frustum-shaped concave portions on the mold surface. be able to.
In addition, by using this irregular structure for reflection prevention in the optical system of the optical module, the optical characteristics can be improved and the manufacturing cost of the optical module can be reduced.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1A is a view showing an example of a concavo-convex structure on the surface of a light-transmitting substrate formed by molding according to the present invention, and FIG. 1B is a view showing an example of another concavo-convex structure. In the figure, 20 indicates the surface of the translucent substrate, 21 indicates a quadrangular pyramid-shaped recess, 21a indicates an upper end, 21b indicates a bottom, and 22 indicates a truncated cone-shaped recess.

  The antireflection optical member of the present invention is provided with a structure (hereinafter referred to as a concavo-convex periodic structure) in which a number of irregularities are continuously and densely formed on a translucent resin base material with a sub-wavelength period smaller than the use wavelength. Composed. In the present invention, in particular, the concave-convex periodic structure has a frustum shape (for example, a fine quadrangular frustum shape) from the surface 20 of the translucent substrate toward the inside of the substrate, as shown in FIG. ) Recesses 21 are formed to be periodically continuous in the X direction and the Y direction. Note that the arrangement pitch in the X direction of the recesses 21 is Px, the arrangement pitch in the Y direction is Py, and the depth of the recesses 21 is H.

  The arrangement pitch Px in the X direction and the arrangement pitch Py in the Y direction are set to be smaller than the minimum wavelength λmin of the wavelength region to be used. The arrangement pitch Px and the arrangement pitch Py may be the same or different as long as they are smaller than the minimum wavelength λmin in the wavelength region. Further, the concave portion 21 is formed in a frustum shape in which the concave section is gradually reduced from the substrate surface 20 toward the inside.

  The concrete frustum-shaped recess 21 can be easily realized by forming a quadrangular frustum shape as shown in FIG. 1A, but in addition, a triangular frustum shape, a hexagonal frustum shape, and the like. (Honeycomb shape) It can be formed in various polygonal frustum shapes such as a mixture of a pentagonal frustum shape and a hexagonal frustum shape. In addition, these polygonal frustum shapes do not need to maintain the exact polygonal frustum shape from the upper end 21a of the base material surface 20 to the bottom part 21b, and the shape is ensured at least by the base material surface 20 side. That's fine. Furthermore, it may be a truncated cone shape as shown in FIG.

  The periodic structure by the concave portion 21 has a shape (frustum shape) obtained by inverting the periodic structure of the convex portion as shown in FIG. Compared with the shape of the convex portion side with respect to the shape of both the concave and convex periodic structures, in FIG. 9B, the convex portion top portion is a pointed shape with a quadrangular pyramid apex, whereas in FIG. 1A of the present invention, A portion corresponding to the top of the convex portion is a linear ridgeline. However, by making the pitches (Px, Py, and P) that are continuously formed smaller than the minimum wavelength λmin in the wavelength region in which both are formed, it is possible to provide a similar antireflection function.

  FIG. 2 is a view for explaining an example of a mold and a resin molded body for molding the antireflection member according to the present invention. FIG. 2A shows a mold, and FIG. 2B shows a resin molded body. In the figure, 30 is a mold, 30a and 30b are V-grooves, 31 is a quadrangular pyramid, 31a is a trapezoidal top surface, 31b is a trapezoid base, 32 is a reference surface, and other symbols are used in FIG. The description will be omitted by using the same reference numerals.

  The concave / convex periodic structure including a large number of frustum-shaped concave portions described above is formed such that a large number of quadrangular frustums 31 protrude from the reference surface 32 of the mold 30 as shown in FIG. The quadrangular pyramid 31 includes a trapezoidal top surface 31 a in a state where the top portion of the quadrangular pyramid is cut off, and a trapezoidal base portion 31 b at substantially the same position as the reference surface 32. The quadrangular frustums 31 are arranged closely in a matrix, and have V-grooves 30 a and 30 b between adjacent quadrangular frustums 31.

  As shown in FIG. 2, the base material surface 20 of the resin molded body is transferred with the four-sided truncated pyramids 31 arranged in a matrix provided in the mold 30 as shown in FIG. A concave-convex periodic structure in which the quadrangular frustum-shaped concave portions 21 are arranged in a matrix is obtained. Note that the upper end 21 a of the recess 21 is formed by the V grooves 30 a and 30 b of the mold 30 so as to be a lattice line-shaped ridgeline, and the height position thereof coincides with the substrate surface 20. Further, the bottom 21 b of the recess 21 is formed flat by the trapezoidal top surface 31 a of the mold 30.

  In the present invention, as described above, since the fine uneven periodic structure for preventing reflection of the molded resin base material is a concave portion on the resin base side, the mold side for molding the convex structure is convex. The part can be formed. As a result, the base of the convex portion is located at the same position as the reference surface of the mold, so that air remains in the deepest portion of the concave portion as described in FIG. can do. As a result, the fine uneven periodic structure on the mold side can be accurately transferred to the resin base material side, and an optical member having good reflection characteristics can be obtained.

  Forming fine concave portions on the mold surface requires labor and cost such as etching with a fine pattern, but forming the fine frustum-shaped convex portions on the mold surface is the latest This can be done easily with precision machining techniques. For example, in the case where the fine quadrangular frustum 31 as shown in FIG. 2A is continuously formed densely in a matrix, after the surface of the mold is ground in the X direction, a plurality of minute V grooves 30a are formed. By forming a plurality of similar micro V-grooves 30b in the Y direction orthogonal to this, it is possible to easily form micro four-sided pyramids densely at a predetermined pitch. Thereafter, the apex portion of the quadrangular pyramid is ground in the Z direction as necessary. That is, as a mold for forming a concave-convex periodic structure, it is easier to form a convex portion than a concave portion on a wall surface, and the accuracy can be increased, and particularly a sub-wavelength. Therefore, it is possible to form a highly accurate mold at a low cost.

  FIG. 3 and FIG. 4 are diagrams showing the reflectivity of the frustum-shaped irregular periodic structure by contour lines. As shown in FIG. 3A and FIG. 4A, for example, the period (pitch) of the frustum-shaped concave portion is P, the depth is H, the bottom width is W, and the incident light wavelength is λ. Design parameters are used, and (W / P) and (H / λ) are representative parameters. 3B and 4B show the reflectance when the incident angle θx = θy = 0 when (W / P) is taken on the horizontal axis and (H / λ) is taken on the vertical axis. Are indicated by contour lines of 0.1% to 2.0%.

  FIG. 3 assumes that the transfer rate from the mold to the resin molding is 100% (ideal state), and shows that there are two regions where the reflectance is the smallest. One is in the vicinity of (W / P, H / λ) = (0.4, 0.7) indicated by point E, and the other is indicated by point F (W / P, H / λ) = (0 .55, 0.32). Considering that the transfer from the mold, which is the subject of the present invention, is good and easy manufacture is possible, it can be said that F having a small frustum-shaped depth H and a large bottom surface width W is optimal. Therefore, the shaded portion centering on this point F is in the range of “0.35 <(W / P) <0.7” and “0.25 <(H / λ) <0.4”. It is desirable to set each parameter.

  In addition, when the above-mentioned concave portion has a conical shape (a shape in which the tip portion is not cut), when estimated from the contour lines in FIG. 3 (equivalent to W / P = 0), it is about the same as the frustum shape of the present invention. In order to obtain a reflectivity of “(H / λ) ≧ 0.6”, it is necessary to satisfy the above condition. In the present invention, since “0.25 <(H / λ) <0.4” as described above, the depth H can be formed lower than the cone shape, and the productivity is also improved from this viewpoint. It can be said.

In FIG. 3 (B) above, it is assumed that the transfer rate of resin molding is performed at 100%. However, since it is difficult in practice, the transfer rate is about 80%. Verification was performed. Note that the transfer rate refers to a ratio with respect to the whole excluding a state in which the shape of the portion indicated by the dotted line (ridge line portion on the upper part of the molding resin) is missing or blunted as shown in FIG.
FIG. 4B shows the case where the transfer rate from the mold to the resin molding is 80%, and the region where the reflectance is the smallest is the point E ′ as in the case of FIG. And F ′ point.

  Also in this case, F ′ having a smaller frustum-shaped depth H and a larger bottom surface width W can be optimized. The shaded portion centered on the F ′ point substantially coincides with the shaded area in the figure. Therefore, “0.35 <(W / P) <0.7” and “0.25 <(H / λ) <0.4”, which are the optimum ranges when the transfer rate is 100%, are the transfer rates. This can also be applied to the case where the value is 80%.

FIG. 5 is a diagram comparing the reflection characteristics of the fine quadrangular pyramid-shaped concave-convex periodic structure of FIG. 1A and the reflection characteristics of the AR coat.
FIG. 5A is a diagram showing the wavelength dependency of the reflectance. The horizontal axis represents the incident light wavelength, the vertical axis represents the reflectance (%), and the incident angle of light (θx, θy in FIG. 1) is 0. This is a reflection characteristic showing the wavelength dependency when the wavelength of 1.31 μm used in the optical communication system is set to an optimum value. The thick line is the reflection characteristic due to the above-described uneven periodic structure according to the present invention, and the thin line is the reflection characteristic due to the AR coating.

  FIG. 5B shows the incident angle dependence of the reflectance. The horizontal axis represents the light incident angle (θx, θy in FIG. 1), and the vertical axis represents the reflectance (%). The characteristics when Px = Py = 0.4λ and the light wavelength is 1.31 μm are shown. As in FIG. 5A, the thick line is the reflection characteristic due to the above-described uneven periodic structure according to the present invention, and the thin line is the reflection characteristic due to the AR coating. The solid line shows the reflectivity by the TE mode having no electric field component in the z direction, and the dotted line shows the reflectivity by the TM mode having no magnetic field component in the z direction. According to FIG. 5B, in the present invention, there is no significant difference between the TE mode and the TM mode, and if the incident angle of light is 35 degrees or less, the reflectance can be suppressed to 0.2% or less. it can.

  As shown in the reflection characteristics of FIGS. 5 (A) and 5 (B), the uneven periodic structure according to the present invention has a wavelength dependency and an incident angle dependency that are as good as or better than an AR coat (Anti-Reflection Coat). Has excellent reflection characteristics. For this reason, by using the concave-convex periodic structure according to the present invention, the AR coating is unnecessary and the cost can be reduced.

  In addition, if the period of the fine uneven periodic structure is increased, diffracted light is generated in addition to transmitted light and reflected light, which is a cause of lowering optical characteristics. Therefore, when the refractive index of the resin on which the fine concavo-convex periodic structure is formed is n, the pitch P of the concavo-convex periodic structure (the pitches Px and Py of the recesses in FIG. 1) is less than “λ / (1 + n)”. Thus, it is desirable to suppress the generation of diffracted light.

  FIG. 6 is a diagram showing an example in which the fine concave-convex periodic structure composed of the frustum-shaped concave portions is formed into an optical module component using a mold to form a reflective surface. In the figure, 23 is an optical element, 24 is a circuit board, 33, 33a and 33b are upper molds, 34 is a frustum-shaped convex part, 35 is an inner wall surface, 36 is a duct for decompression, 37 is a lower mold, 38a , 38b indicate molding spaces.

  The optical module component includes, for example, an optical element 23 such as a light-emitting element or a light-receiving element mounted on a circuit board 24, which is sealed with a translucent resin base material and has a fine optical path on the resin surface. It is assumed that an antireflection surface is formed by a simple uneven periodic structure. For example, as shown in FIG. 6 (A), a mold for molding a translucent resin base material is composed of an upper mold 33 and a lower mold 37, and sandwiches a circuit board 24 from above and below. Molding spaces 38a and 38b filled with resin are formed between the molds 33 and 37. In addition, a molding resin injection port (not shown) and a decompression duct 36 are provided in any part of the upper and lower molds 33 and 37.

  On the inner wall surface 35 of the upper mold 33, frustum-shaped convex portions 34 for forming a fine concave-convex periodic structure for preventing reflection are formed at a predetermined pitch on a portion that becomes an optical system path of the optical member. It is densely formed continuously at a height. The convex portion 34 is formed so as to be convex with respect to the inner wall surface 35 of the upper mold 33. For example, as shown in FIG. It can be formed in a side-by-side shape. Then, when the molding spaces 38a and 38b of the upper and lower molds 33 and 37 are decompressed and filled with a translucent resin, the above-described fine quadrangular pyramid-shaped convex portions 34 are transferred to the molding resin as described above. As shown in FIG. 1 (A), a concave-convex periodic structure composed of fine quadrangular frustum-shaped concave portions is formed on the upper surface of the resin base material. In addition, after molding of the resin, the upper mold 33 is removed from the upper direction as indicated by an arrow.

  FIG. 6B shows another example of molding, in which the optical system path of the optical element 23 of the optical member is in the side surface direction. In this case, for example, the upper mold is configured by combining two molds, an upper mold 33a to be removed from the upper direction and an upper mold 33b to be removed from the lateral direction. As in the case of FIG. 6A, the upper mold 33b has a shape in which fine quadrangular pyramid-shaped projections are continuously arranged so that the convex portion 34 is convex with respect to the inner wall surface 35 thereof. Formed with. Thereby, the uneven | corrugated periodic structure which consists of a concave part of a fine quadrangular pyramid shape is formed in the side surface of the shape | molded translucent resin base material. After molding of the resin, the upper mold 33a is removed from the upper side as indicated by an arrow, and the upper mold 33b is removed from the lateral direction indicated by the arrow.

  FIG. 7 is a diagram illustrating an example in which the above-described fine uneven periodic structure for preventing reflection is applied to an optical module used for optical communication. In the figure, 25 is an optical device, 25a is a stem, 25b is a lead pin, 25c is a cap, 25d is a transparent window portion, 27 is a sleeve, 27a is a condensing lens, 27b is a fitting portion, 27c is a ferrule insertion portion, 28 Indicates a fiber ferrule. Description of other reference numerals is omitted by using the same reference numerals as those used in FIG.

  As shown in FIG. 7, the optical module is configured, for example, by attaching a sleeve 27 that forms a connection with an optical fiber to the optical device 25. The optical device 25 is formed of a coaxial CAN type package, and an optical element 23 such as a semiconductor light emitting element or a semiconductor light receiving element is mounted on a stem 25a provided with a lead pin 25b for connection to an external circuit. It is formed by covering with a cap 25c having a translucent window portion 25d.

  For example, the sleeve 27 forms an optical coupling between the fitting portion 27b coupled to the optical device 25, a ferrule insertion portion 27c that forms a connection with the optical fiber, and the optical element 23 and the fiber ferrule 28 in the optical device 25. It is assumed that the condenser lens 27a to be formed is integrally formed with a light-transmitting resin. Optical transmission of signal light is formed between the optical element 23 and the tip of the fiber ferrule 28, but an antireflection structure is formed on the lens surface so that signal light is not reflected on the surface of the condenser lens 27a. Is done.

  By using the fine uneven periodic structure described above for the antireflection structure of the condenser lens 27a, the reflection of the signal light can be efficiently reduced, and the optical module can be manufactured at low cost. The concave-convex periodic structure for preventing reflection periodically and continuously forms, for example, the fine quadrangular frustum-shaped concave portions 21 described in FIG. 1 from the lens surface in a predetermined region of the condenser lens 27a into the lens. Do it. In addition, the arrangement pitch and depth of the recesses 21 are formed at a pitch smaller than the wavelength used as the signal light in the optical element 23 as described with reference to FIG. By forming with a value, an antireflection function can be provided.

  FIG. 8 is a diagram showing an example in which the sleeve 27 shown in FIG. 7 is molded using a mold. In the figure, 39 is an upper mold, 39a is a base molding part, 39b is a cylindrical molding part, 39c is a lens molding part, 39d is a resin filling port, 39e is a decompression duct, 40 is a frustum-shaped convex part, 41 is A lower die, 41a is a cylindrical molding portion, and 42a to 42d are molding spaces.

  The mold for molding the sleeve is composed of an upper mold 39 and a lower mold 41 as described in FIG. The upper mold 39 includes a base molding portion 39a for molding the cylindrical base portion of the sleeve, a cylindrical molding portion 39b for molding the fitting portion 27b of the optical device, a lens molding portion 39c for molding the condenser lens 27a, and a light transmitting property. A resin filling port 39d for filling the resin base material, and a decompression duct 39e for evacuating and decompressing the inside of the mold. The lower mold 41 has a cylindrical forming part 41a for forming the ferrule insertion part 27c.

  On the surface of a predetermined region of the lens forming portion 39c of the upper mold 39, fine frustum-shaped convex portions 40 for forming a fine concave-convex periodic structure for antireflection are formed at a predetermined pitch and height. Is done. The convex portion 40 is formed so as to be convex with respect to the concave inner wall spherical surface of the upper mold 39. For example, as shown in FIG. It can be formed by periodically arranging them on the inner wall surface. In addition, since this fine frustum-shaped convex part 40 is formed along the concave spherical surface of the lens molding part 39c, on the peripheral side of the region, the molded concave part 21 is formed during die cutting after molding. It is necessary to consider the angle of the convex side surface so that the shape is not deformed.

  In the mold configured as described above, molding spaces 42 a to 42 d having shapes corresponding to the sleeve 27 are formed by closing the upper mold 39 and the lower mold 41. The air in the mold is decompressed by evacuating, and the light-transmitting resin base material is filled into the molding space from the resin filling port 39d. The fine frustum-shaped convex portion 40 is transferred to a molding resin, and a fine frustum-shaped concave portion 21 can be formed in a predetermined region of the condenser lens 27a as shown in FIG. Thereby, at the same time as the formation of the condenser lens 27a, the concave-convex periodic structure for antireflection can be formed on the lens surface, and the antireflection function can be provided by an inexpensive method. In addition, you may provide the antireflection function by the uneven | corrugated periodic structure of this invention in the surface which cross | intersects an optical axis like the inclined surface 27d in FIG. 7, and the cylindrical part bottom face 41b of the lower mold in FIG.

It is a figure explaining the outline of the reflection preventing optical member by this invention. It is a figure explaining an example of the metal mold | die and resin molding which shape | mold the antireflection member by this invention. It is the figure which represented the reflectance by the uneven | corrugated periodic structure (transfer rate 100%) of this invention with the contour line. It is the figure which represented the reflectance by the uneven | corrugated periodic structure (transfer rate 80%) of this invention with the contour line. It is the figure which compared and showed the reflection characteristic by the uneven | corrugated periodic structure of this invention, and the reflection characteristic by AR coating. It is a figure which shows the structural example of the metal mold | die which shape | molds the antireflection optical member by this invention. FIG. 3 is a diagram illustrating a configuration example in which the antireflection optical member according to the present invention is applied to an optical module. It is a figure which shows the example of shaping | molding of the reflection preventing optical member in FIG. It is a figure explaining a prior art. It is a figure explaining other prior art. It is a figure explaining other prior art. It is a figure explaining the problem of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... The surface of a translucent base material, 21 ... Recessed part of 4 pyramid shape, 21a ... Upper part, 21b ... Bottom part, 22 ... Recessed part of truncated cone shape, 23 ... Optical element, 24 ... Circuit board, 25 ... Optical device, 25a ... Stem, 25b ... Lead pin, 25c ... Cap, 25d ... Translucent window part, 27 ... Sleeve, 27a ... Condensing lens, 27b ... Fitting part, 27c ... Ferrule insertion part, 27d ... Inclined surface, 28 ... Fiber ferrule , 30 ... mold, 30a, 30b ... V groove, 31 ... quadrangular frustum, 31a ... trapezoid top surface, 31b ... trapezoid base, 32 ... reference plane, 33, 33a, 33b ... upper die, 34 ... frustum shape , 35 ... inner wall surface, 36 ... decompression duct, 37 ... lower mold, 38a, 38b ... molding space, 39 ... upper mold, 39a ... base molding part, 39b ... cylindrical molding part, 39c ... lens molding Part, 39d ... resin filling port, 3 e ... vacuum duct, 40 ... protruding portion of the frustum-shaped, 41 ... lower mold, 41a ... cylindrical molded part, 41b ... cylindrical portion bottom surface, 42 a to 42 d ... molding space.

Claims (7)

An optical member that uses a molding die to mold a fine concavo-convex structure with a sub-wavelength period on the surface of a translucent substrate to serve as an antireflection surface,
2. The antireflection optical member according to claim 1, wherein the concavo-convex structure is formed by a large number of fine frustum-shaped concave portions provided densely with a sub-wavelength period.   When the pitch of the frustum-shaped recesses is P, the width of the bottom surface is W, the depth is H, and the incident light wavelength is λ, “0.35 <(W / P) <0.7” and “0.3. An antireflection optical member, wherein 25 <(H / λ) <0.4 ”.   The antireflection optical member according to claim 1, wherein the frustum shape is a polygonal frustum shape.   The antireflection optical member according to claim 3, wherein the polygonal frustum shape is a quadrangular frustum shape.   The antireflection optical member according to claim 1, wherein the frustum shape is a frustum shape.   An optical module comprising the antireflection optical member according to any one of claims 1 to 5 disposed in an optical system path of an optical element.   The optical module according to claim 6, wherein when the refractive index of the antireflection optical member is n and the incident light wavelength is λ, the pitch P of the frustum-shaped recesses is P ≦ λ / (1 + n).

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