JP4246670B2 - Hologram element, semiconductor laser module, and optical pickup device - Google Patents

Description

  The present invention relates to a hologram element, a semiconductor laser module, and an optical pickup device.

  Optical discs to be optically picked up by optical pickup devices are diversified and their practicality is increased, and further downsizing and cost reduction of optical pickup devices are required.

  As an effective configuration for downsizing and cost reduction of an optical pickup device, an optical system using a hologram element is being put into practical use. The hologram element in this case is used to separate the optical path of light irradiated from the light source to the optical disk (outward path) and the optical path of return light from the optical disk (return path). Compared with the “beam splitter”, the size is small, which greatly contributes to the compactness of the optical pickup device. The light receiving part for signal detection can be arranged on the same surface as the light emitting part of the light source, and the design of the optical path is easy. This is also advantageous in terms of reducing the above.

  As such a hologram element, a polydiacetylene alignment film is formed on an optically isotropic substrate and a periodic grating is formed on this alignment film (Patent Document 1), or a periodic on an optically isotropic substrate. The one loaded with a birefringent film having a concavo-convex grating (Patent Document 2) has been proposed. The hologram elements described in Patent Documents 1 and 2 can be reduced in cost, the grating pitch can be narrowed, and the diffraction angle is large, so that the optical pickup device can be more effectively downsized.

By the way, paying attention to the diffraction efficiency of the hologram element, the incident light wavelength: λ ₀ , the diffraction grating depth: T, the refractive index of the material on which the diffraction grating is formed: n ₀ , and the grating period: Λ
Q = (2πλ ₀ T) / (n ₀ Λ ² ) (1)
When the value of “Q” defined in (1) is larger than 1, the “volume hologram effect” occurs, and the diffraction efficiency of the hologram element changes depending on the “incident angle”.

  In order to increase the diffraction angle in order to make the optical system of the optical pickup apparatus compact, it is necessary to reduce the pitch of the hologram element by reducing the grating period: Λ. ), The denominator of the right side becomes smaller and the value of “Q” increases, and generally becomes larger than 1.

  The inventor stated that “the surface of the optically transparent organic material layer formed on the transparent substrate has a substantially concave-convex periodic structure for diffraction with a substantially rectangular wave-like cross-sectional shape. Although research has been conducted on “hologram elements filled with optically transparent materials”, such hologram elements have been developed in the process of manufacturing “the collapse of the irregular periodic structure (the convex part in the irregular periodic structure is The phenomenon of tilting with respect to the normal direction) is likely to occur, and the tilt of the concavo-convex periodic structure causes a variation in the incident angle of the incident light, resulting in “non-uniformity of ± first-order diffracted light” for each hologram element. It has been found that there is a problem that it occurs and reduces the yield of hologram element manufacturing.

JP2000-221325A JP 2000-75130 A

  In view of the above-described circumstances, an object of the present invention is to realize a hologram element having a structure capable of effectively reducing or preventing the collapse of the concavo-convex periodic structure, an optical pick-up device using the hologram element, and a semiconductor laser module.

The hologram element of the present invention has “a concave / convex periodic structure having a substantially rectangular wave shape in cross section on the surface of an optically transparent organic material layer formed on a transparent substrate and having a minute concave / convex periodic structure for diffraction. Is filled with an optically transparent material, the wavelength used is λ ₀ , the depth of the recess is T, the refractive index of the organic material layer is n ₀ , and the grating period is Λ, Q = (2πλ ₀ T) / (N ₀ Λ ² ) (1)
The hologram element having a Q value defined by (1) larger than 1 has the following characteristics (claim 1).

That is, “connecting portions that connect adjacent convex portions” are formed at intervals of 100 μm order in the concave portion of the minute concave-convex periodic structure.
The “connecting portion” has a width substantially in the order of the wavelength used in the direction orthogonal to the surface of the transparent organic material layer. Further, the upper surface portion of the uneven periodic structure, the upper surface portion of the connecting portion, and the organic material layer surface portion where the uneven periodic structure is not formed are flush with each other.

The “upper surface portion” in the “upper surface portion of the concavo-convex periodic structure” and the “upper surface portion of the connecting portion” does not necessarily mean the upper surface in the spatial vertical relationship, and the concavo-convex formed on the surface of the organic material layer It means “a surface portion opposite to the transparent substrate” in the periodic structure.
[Connecting portion] may be formed in each concave portion of the concavo-convex periodic structure, or may be formed every other concave portion. It may be formed in such a way that the recesses that do not form the connecting portions are “one exists for a plurality of recesses”.

When the interval between the connecting portions formed in the same recess is as narrow as 10 μm, the presence of the connecting portion deteriorates the diffraction characteristics of the hologram element. Further, when the interval is in the order of several hundred μm, the effect of effectively preventing “falling of the uneven periodic structure” is insufficient. Therefore, the interval between the connecting portions formed in the same recess is preferably on the order of 100 μm, for example, about 100 to 300 μm.
Further, in order for the presence of the connecting portion not to affect the diffraction characteristics, the width of the connecting portion needs to be in the “use wavelength order”.

The hologram element according to claim 1, wherein “an optically transparent organic material layer formed on a transparent substrate” is formed into a film shape and “refracted in the direction of a fast axis and a slow axis that are orthogonal optical axes thereof. It is possible to use a material having optical anisotropy having different ratios.
In this case, the “refractive index of the organic material layer: n ₀ ” in claim 1 is the average value of the refractive indexes in the orthogonal optical axis direction.

  The hologram element according to claim 2, wherein “an optically transparent material that fills the concave portions of the concave and convex periodic structure” is “any one of the optical axis directions” in a film-like organic material having optical anisotropy. It is possible to adopt a configuration having substantially the same refractive index as that of the "refractive index".

  The hologram element according to claim 2 or 3, wherein a film-like organic material having optical anisotropy is "adhered to an optically isotropic transparent substrate with an adhesive material", and the adhesive material is It has the substantially same refractive index as that of the optically transparent material filled in the concave portion of the periodic structure.

  In the hologram element according to claim 1 or 2, “an optically isotropic substrate is bonded onto the optically transparent material filled in the concave portion of the concave-convex periodic structure using the transparent material as an adhesive material. It is preferable to use the “configuration” (claim 5).

  Similarly, in the hologram element according to claim 3 or 4, an optically isotropic substrate is formed by using this transparent material as an adhesive material on an optically transparent material filled in the concave portion of the concave-convex periodic structure. It is preferable to use “adhered configuration”.

  6. The hologram element according to claim 6, wherein a film-like organic material having optical anisotropy is adhered to an optically isotropic transparent substrate by an adhesive material, and the adhesive material is formed in the concave portion of the concavo-convex periodic structure. “A configuration in which the optically transparent material to be filled has substantially the same refractive index and the adhesive material is the same material as the optically transparent material filled in the concave portions of the concave-convex periodic structure”. (Claim 7).

The semiconductor laser module of the present invention is a “semiconductor laser module for an optical pickup device”, and includes a semiconductor laser, an optical path separation element, and a light receiving unit as a unit.
The “semiconductor laser” emits light for irradiating the optical disk as a light source.
The “optical path separation element” is an optical element that separates the optical path of the irradiation light from the semiconductor laser to the optical disk (outward path) and the optical path of the return light from the optical disk (return path).
The “light receiving unit” receives the return light whose optical path is separated by the optical path separation element, and generates a light reception signal for generating various signals.
The hologram element according to any one of claims 1 to 7 is used as the optical path separation element (claim 8).

  The optical pickup device of the present invention is defined as “an optical path separation element that separates an optical path (outward path) of irradiation light from a light source onto an optical disk and an optical path (return path) of return light from the optical disk”. 7. The hologram element according to any one of 7 is used (claim 9).

  9. The optical pickup device according to claim 9, wherein a semiconductor laser as a light source, a light receiving unit that receives return light from the optical disk, and the hologram element according to any one of claims 1 to 7, The semiconductor laser module can be unitized (claim 10).

  The hologram element of the present invention can be used as an optical path separation element in an optical pickup device as described above, but the application of the hologram element of the present invention is not limited to this, and various diffractive optical elements (incident light, Needless to say, it can be used as an optical element having a function of dispersing light into zero-order light (transmitted light), ± first-order light, ± second-order light, etc. at a constant ratio.

  In the hologram element of the present invention, as described above, “a connecting portion that connects adjacent convex portions” is formed in the concave portion of the minute concave and convex periodic structure, so that this connecting portion is “the collapse of the concave and convex periodic structure”. Is effectively reduced or prevented. Therefore, the hologram element of the present invention can reduce or prevent the non-uniformity of ± first-order diffracted light for each hologram element due to “variation” of the incident angle of the incident light, and the production yield is good. Since such a hologram element can be manufactured with a high yield, the manufacturing cost of the hologram element, and thus the manufacturing cost of the semiconductor laser module and the optical pickup device can be reduced.

  Hereinafter, the embodiment will be described with reference to specific examples.

FIG. 1 is a cross-sectional view of the hologram element according to the first embodiment.
As shown in FIG. 1, the hologram element is placed on a BK7 substrate (parallel plate) having a thickness of 1.0 mm as a transparent substrate 11 via an epoxy-based ultraviolet curable resin 12 (thickness: about 40 μm). The thickness of the diffraction grating 15 formed: a polyester-based organic birefringent film 13 having a thickness of about 100 μm is adhered, and the epoxy-based ultraviolet curable resin 14 ( (Thickness: about 40 μm) is formed.

  As shown in the figure, the diffraction grating 15 has a “substantially rectangular wave shape” cross section, a grating pitch of 1.9 μm, a duty of 0.5, and a grating depth of 2.7 μm. The refractive index of the organic birefringent film 13 as the “optically transparent organic material layer” is 1.58 and 1.67, respectively, in the directions of the fast axis and slow axis, which are orthogonal optical axes. In addition, the refractive index of the ultraviolet curable resins 12 and 14 which are “optically transparent materials” is 1.58. All of these refractive indexes are refractive indexes at a use wavelength: 660 nm.

Wavelength used: λ ₀ = 660 nm (= 0.66 μm), depth of recess: T = 2.7 μm, refractive index of organic material layer: n ₀ = 1.625 (= 1.58 and 1.67 average values) ), Lattice period: Λ = 1.9 μm and calculating the right side of equation (1),
(2πλ ₀ T) / (n ₀ Λ ² ) = 2 × 3.14 × 0.66 × 2.7 / (1.625 × 1.9 × 1.9) = 1.9077
Thus, the value of “Q” is larger than 1.

  Here, a method for producing the hologram element shown in FIG. 1 and a mechanism for causing the collapse of the irregular periodic structure will be described.

  Referring to FIG. 3, as shown in FIG. 3A, an organic birefringent film 13 is formed on a transparent substrate 11 made of a BK7 substrate via an adhesive (ultraviolet curable resin) 12. That is, the adhesive 12 is spin-coated on the transparent substrate 11, and the organic birefringent film 13 is placed on the coated adhesive 12 so as not to “mix air bubbles”. After mounting, the transparent substrate 11 is rotated to shake off the “excess adhesive”, the organic birefringent film 13 is flattened by centrifugal force, and finally the adhesive 12 is cured by irradiating ultraviolet rays, thereby strengthening the whole. Integrate.

Next, as shown in FIG. 3B, a diffraction grating 15 having an uneven periodic structure is formed.
An aluminum metal thin film is deposited on the free surface of the organic birefringent film 13, a photoresist layer is formed thereon, and etching having a pattern corresponding to the planar shape of the concavo-convex periodic structure is performed by a photolithography process and an etching process. A mask was obtained, and anisotropic dry etching with oxygen plasma was performed to invade the concave portion of the diffraction grating 15, and then the etching mask was removed to form the diffraction grating 15.

  Next, as illustrated in FIG. 3C, a layer of the ultraviolet curable resin 14 is formed so as to fill the concave portion of the diffraction grating 15. That is, the ultraviolet curable resin 14 is botted onto the diffraction grating 15, spin coating is performed, and after the spin coating, the ultraviolet curable resin 14 is cured by irradiating ultraviolet rays.

By the way, in general, those having the same structure as the hologram element of the present invention, including the hologram element being described, have a size of “about several millimeters in length and width”, and the hologram element as shown in FIG. Are not manufactured individually.
In general, an organic material layer is formed on a transparent substrate (wafer) having a size of 100 mm in length and width, and an array of several tens to several hundreds of diffraction gratings is formed on the formed large-sized organic material layer at a time. Then, a transparent material film is formed on the entire array surface of the formed diffraction grating. Then, after the whole is integrated, the individual diffraction gratings are separated by cutting with a dicing saw to obtain “individual hologram elements”. In Example 1 in the description, the size of the hologram element is 3 mm × 3 mm.

FIG. 4 illustrates the process of forming a “transparent material film” on a large organic material layer in the above manufacturing process.
A large number of diffraction grating portions are formed on the large-sized organic material layer 41 (formed on a circular transparent substrate having a diameter of 100 mm). In FIG. 3 shows three diffraction gratings. Of these diffraction gratings 42A, 42B, and 42C, the diffraction grating 42A indicates that formed in the vicinity of the center of the large-sized organic material layer 41, and the diffraction gratings 42B and 42C indicate the peripheral portions of the large-sized organic material layer 41. The one formed in the vicinity is shown.

In the example of FIG. 4, the layer of the transparent material 43 is formed by spin coating.
The state of FIG. 4A shows a state where a transparent material (ultraviolet curable resin) 43 is botted to the center of the large-sized organic material layer 41. When a large transparent substrate is rotated at a high speed in this state, the transparent material 43 is spread on the large organic material layer 43 by centrifugal force acting on the transparent material 43 (FIG. 4B). Finally, as shown in FIG. 4C, the material 43 is flattened and then cured by ultraviolet rays, and the concave portion of each diffraction grating is filled with the transparent material 43.

  In the process of spreading the transparent material 43 by rotation, centrifugal force acts on the transparent material 43 and the organic material film 41. The action of this centrifugal force is greater as it is closer to the periphery of the large-sized organic material layer 41. For this reason, in the peripheral portion of the large-sized organic material layer 41, as shown in FIG. 4C, the concave and convex periodic structure of the diffraction gratings 42B and 42C collapses due to the action of centrifugal force (the convexity in the concave and convex periodic structure). Part may be inclined with respect to the “normal direction of the transparent substrate (not shown) (vertical direction in the figure)”.

  Further, when the ultraviolet curable resin 43 is cured, the resin contracts, and depending on the “position of the diffraction grating” on the large-sized organic material layer, the concavo-convex periodic structure may be oriented in the direction of FIG. On the contrary, it may fall down to the center part side of a large-sized organic material layer.

  In this way, the collapse of the uneven periodic structure formed in the large-sized organic material layer 41 differs depending on the “positions of the individual uneven periodic structures” on the large-sized organic material layer 41. In particular, in the state where individual hologram elements are separated from each other, dozens to hundreds of hologram elements obtained from one wafer have various irregular periodic structures.

  In the hologram element of Example 1, since the Q value is about 1.97, which is larger than 1, a volume hologram effect is generated, and the tilting of the uneven periodic structure varies, so that the diffraction efficiency of ± first-order diffracted light is “approximately ± 3”. % Variation "occurs, and the variation is larger than the processing tolerance. For this reason, in order to increase the yield of holographic element manufacturing, the processing tolerances must be tightened, and the productivity is lowered.

  In order to solve such a problem, in the present invention, “connecting portions for connecting adjacent convex portions” are formed at intervals of 100 μm in the same concave portion in the concave portions of the minute concave and convex periodic structure. Part has “a width substantially in the order of the wavelength used in the direction orthogonal to the surface of the transparent organic material layer”, the upper surface part of the uneven periodic structure, the upper surface part of the connecting part, and the uneven periodic structure The organic material layer surface portion that is not formed is flush with the surface portion (Claim 1).

  FIG. 2A illustrates the planar shape of the hologlass element of Example 1 in an explanatory manner. The hologram element (having the structure shown in FIG. 1) has a square shape of 3 mm × 3 mm in plan view (the state shown in FIG. 1 as viewed from above in FIG. 1). A concave-convex periodic structure 21 (part indicated by reference numeral 15 in FIG. 1) is formed of three types of diffraction grating portions having different arrangement directions.

In FIG. 2 (a), the portion indicated by the symbol B is enlarged and schematically shown in FIG. 2 (b). In addition, the part indicated by the symbol C in FIG. 2A is enlarged and shown in FIG. The cross-sectional shape of the portion indicated by the symbol A in FIG. 2A is as shown in FIG.
In FIGS. 2B and 2C, a portion indicated by reference numeral 23 indicates a “convex portion” in the concavo-convex periodic structure, a reference numeral 24 indicates a “concave portion”, and a reference numeral 25 indicates a “connection portion”. The connection part 25 connects the adjacent convex parts 23, and is formed in the recessed part 24 of a minute uneven | corrugated shaped periodic structure.

  In the first embodiment, the connecting portions 25 formed in the same recess are formed at intervals of 100 μm in the recess (aligned in the vertical direction in FIGS. 2B and 2C). The width of the connecting portion 25 (the width in the vertical direction in FIGS. 2B and 2C) is 0.3 μm, and the wavelength used is smaller than 0.66 μm, but in the “used wavelength order”. Moreover, the upper surface part (upper surface part of the convex part 23) of the uneven | corrugated shaped periodic structure, the upper surface part of the connection part 25, and the organic material layer surface part 22 in which the uneven | corrugated shaped periodic structure is not formed are the same surface.

  The planar shape of the concavo-convex periodic structure shown in FIG. 2 is practically the same shape in a direction orthogonal to the drawing of FIG. 2 (direction of the depth of the concavo-convex recess). That is, the pattern of the concavo-convex periodic structure shown in FIG. 2 is the same as the “etching mask” pattern described above.

  Since the upper surface portion of the concavo-convex periodic structure, the upper surface portion of the connecting portion 25, and the organic material layer surface portion 22 where the concavo-convex periodic structure is not formed form the same surface, the concavo-convex periodic structure having the connecting portion is etched. The hologram element can be easily formed.

  Since the connecting portion 25 is formed in the concavo-convex periodic structure, the inclination of the convex portion due to the action of centrifugal force when spin-coating a transparent material is effectively reduced or prevented. A large number of good hologram elements without collapse of the periodic structure can be obtained, the yield of hologram element manufacture is good, and the cost of hologram element manufacture can be reduced.

The hologram element of Example 1 is used as an “optical path separation element” in an optical pickup for DVD.
When laser light from a light source (semiconductor laser) enters the hologram element of Example 1, diffracted light is generated. However, since a diffraction grating is formed on the organic birefringent film 13, the diffraction efficiency depends on the polarization direction of the laser light. Is different. The polarized light in the optical axis direction having a refractive index of 1.58 of the organic birefringent film 13 is the same as the refractive index of the resin 14 that is filled, so it is equivalent to the absence of a diffraction grating and has a low diffraction efficiency. Is transparent. It is filled with a polarization direction orthogonal to the direction of the optical axis (the return light is polarized in this direction by the action of a quarter-wave plate provided in the optical path between the hologram element and the DVD). Since there is a difference in refractive index from the resin, the return light is diffracted toward the light receiving unit with a diffraction efficiency of about 32%.

The structure of the hologram element of Example 2 is shown in FIG. In order to avoid complications, the same symbols as in FIG.
The hologram element shown in FIG. 5 has a diffraction grating 15 on a transparent substrate 11 made of a BK7 substrate (parallel plate) having a thickness of 1.0 mm via an epoxy-based ultraviolet curable resin 12 (thickness: about 40 μm). An epoxy UV curable resin 54 having a structure in which a polyester-based organic birefringent film 13 having a thickness of about 100 μm is bonded and a “concave portion of the diffraction grating 15” is embedded on the surface thereof is formed as an uneven periodic structure. (Thickness: about 40 μm) is formed, and an optically isotropic substrate 16 made of a BK7 substrate (parallel plate) having a thickness of 1.0 mm is further bonded thereon.

  The diffraction grating 15 has a rectangular wave cross section with a grating pitch of 1.9 μm, a duty of 0.5, and a grating depth of 2.7 μm, and the refractive index of the organic birefringent film 13 is in the direction of the optical axes perpendicular to each other. 1.58 and 1.67, and the refractive indexes of the ultraviolet curable resins 12 and 14 are 1.58 (both are used at a wavelength of 660 nm).

  The planar shape of the formed irregular periodic structure is as shown in FIG. That is, the hologram element of Example 2 is the same as that of Example 1 in terms of material and form, except for the optically isotropic substrate 16, and is defined by the right side of the expression (1). The value of “Q” is also 1.9077 as in the first embodiment. The method for manufacturing the diffraction grating 15 is the same as the method for manufacturing the hologram element of the first embodiment.

  That is, as shown in FIG. 6A, the organic birefringent film 13 is bonded to the transparent substrate 11 made of the BK7 substrate via the adhesive 12. That is, the adhesive 12 is spin-coated on the transparent substrate 11, and the organic birefringent film 13 is placed on the transparent substrate 11 so that “bubbles are not mixed”. The adhesive is shaken off, the organic refracting film is flattened by the action of centrifugal force, and the adhesive 12 is solidified by irradiation with ultraviolet rays.

  Next, as shown in FIG. 6B, the diffraction grating 15 is formed in the same manner as in the case of the first embodiment, and as shown in FIG. The resin 14 is added, and the optically isotropic substrate 16 made of the BK7 substrate is bonded by using the ultraviolet effect resin 14 as an adhesive material to integrate the whole.

In the second embodiment, the concave portions of the diffraction grating 15 are filled with the ultraviolet curable resin 14 and the optically isotropic substrate 16 is bonded as follows.
FIG. 7 is a schematic diagram showing the process of “filling the concave portion of the diffraction grating with the ultraviolet curable resin and bonding the optically isotropic substrate” in the above manufacturing process on a large transparent substrate (wafer) (not shown). The process performed with respect to the organic material layer 41 of a size is shown in explanatory drawing.
A large number of diffraction grating portions are formed on the large-sized organic material layer 41 (formed on a circular transparent substrate (wafer) having a diameter of 100 mm as in the case of Example 1). For the sake of simplicity, three diffraction gratings are shown. Of these diffraction gratings 42A, 42B, and 42C, the diffraction grating 42A indicates that formed in the vicinity of the center of the large-sized organic material layer 41, and the diffraction gratings 42B and 42C indicate the peripheral portions of the large-sized organic material layer 41. The one formed in the vicinity is shown.

  As shown in FIG. 7A, a transparent material (ultraviolet curable resin) 43 is botted at the center of a large-sized organic material layer 41 in which a large number of diffraction gratings are arranged, and from above, The optically isotropic substrate 46 is placed, and a pressing force is applied from above to control the layer thickness of the transparent material 43, and the concave portions of the diffraction gratings are embedded with the transparent material 43.

  A transparent material 43 is spread on the organic material layer 41 by applying a pressing force to the optically isotropic substrate 46. In this way, the transparent material 43 is spread to the periphery, and finally spreads uniformly over the entire surface of the wafer as shown in FIG. At this time, the gap between the organic material layer 41 and the optically isotropic substrate 46 is controlled to cure the ultraviolet curable resin that is the transparent material 43.

  Due to the pressing by the optically isotropic substrate 46, the convex portions of the diffraction gratings 42B and 42C may be inclined toward the wafer peripheral side as shown in FIG. 7C. Also, due to shrinkage during resin curing, the convex portion of the diffraction grating may be inclined toward the inside of the wafer, contrary to FIG. 7 (c).

  Also in the second embodiment, since the connecting portion similar to that of the first embodiment is formed in the concave portion of the diffraction grating, such a tilt of the diffraction grating, that is, the collapse of the concavo-convex periodic structure is effectively reduced or prevented.

In the hologram elements of Examples 1 and 2 described above, the cross-sectional shape is a substantially rectangular wave shape on the surface of the optically transparent organic material layer 13 formed on the transparent substrate 11, and a minute uneven period for diffraction. The concave portion of the concavo-convex periodic structure 15 is filled with an optically transparent material 14, used wavelength: λ ₀ , depth of the concave portion: T, refractive index of organic material layer: n ₀ , grating Period: By Λ Q = (2πλ ₀ T) / (n ₀ Λ ² )
Is a hologram element having a Q value (= 1.9077) defined by (1) greater than 1.

  And the connection part 25 which connects the adjacent convex parts 23 to the recessed part of the minute uneven | corrugated shaped periodic structure 15 is formed in 100 micrometer order space | interval in the same recessed part 24, and the connection part 25 is a transparent organic material layer. An organic material layer having a width in the order of wavelength used in a direction orthogonal to the surface of the surface, an upper surface portion of the uneven periodic structure 15, an upper surface portion of the connecting portion 25, and an uneven periodic structure not formed The surface portion 22 is flush with the surface portion (claim 1).

  Further, the optically transparent organic material layer 13 formed on the transparent substrate is a film-like material (a polyester organic birefringent film having a thickness of about 100 μm), and a phase advance which is an optical axis perpendicular thereto. It has optical anisotropy with different refractive indexes in the direction of the axis and the slow axis (claim 2).

  In addition, the optically transparent material 14 filling the concave portions of the concavo-convex periodic structure 15 is substantially the same as the refractive index (= 1.58) in the optical axis direction of any organic material having optical anisotropy. (Ref. 3) (= 1.58).

  The film-like organic material layer 13 having optical anisotropy is bonded to the optically isotropic transparent substrate 11 by the adhesive material 12, and the adhesive material 12 fills the concave portions of the concavo-convex periodic structure 15. The transparent material 14 has substantially the same refractive index (= 1.58) (claim 4).

  In the hologram element of Example 2, the optically isotropic substrate 16 is bonded to the optically transparent material 14 filled in the concave portions of the concave-convex periodic structure 15 using the transparent material as an adhesive material. (Claims 5 and 6).

  In both the hologram elements of Examples 1 and 2, the film-like organic material layer 13 having optical anisotropy is bonded to the optically isotropic transparent substrate 11 with the adhesive material 12, and the adhesive material 12 is An optically transparent material having substantially the same refractive index as that of the optically transparent material 14 filling the concave portions of the concave-convex periodic structure 15 and having the adhesive material 12 filled in the concave portions of the concave-convex periodic structure 15 14 (Claim 7).

  In the hologram elements of Examples 1 and 2, since the organic material layer is a birefringent material, polarization characteristics can be added to the hologram element, and the organic material layer can be used as a “film-like material”. The production cost can be reduced by reducing the amount. Further, the efficiency of polarization is improved by matching the refractive index of the material filled in the diffraction grating with “the refractive index of any of the orthogonal optical axes” of the organic birefringent film.

  Furthermore, by attaching the organic birefringent film 13 to the BK7 substrate (transparent substrate) 11, the flatness of the BK7 substrate surface is improved and the wavefront aberration characteristics are improved. As in the hologram element of Example 2, a BK7 substrate (optically isotropic substrate) is arranged on the surface side of the diffraction grating to flatten the surface of the transparent material 14, thereby “embedding by spin coating or the like. Wavefront aberration due to “surface waviness that may occur when performing the operation” is also improved.

  Since all the resins used for bonding are made of the same material, the refractive index between the upper and lower BK7 substrates can be made substantially the same, and the wavefront aberration due to the unevenness of the internal layer structure can also be reduced. .

  As Example 3, an embodiment of a “semiconductor laser module” for an optical pickup is shown in FIG.

  The semiconductor laser module of Example 3 includes a hologram element 81, a semiconductor laser 82, a light receiving element 83, a package 84, and a stem 85 for mounting the semiconductor laser and the light receiving element, and these are unitized.

  The semiconductor laser 82 has a wavelength of 660 nm. As the hologram element 81, those shown in the first and second embodiments can be used as appropriate. In this embodiment, the hologram element of the second embodiment is used.

  That is, the semiconductor laser module of Example 3 is a semiconductor laser module for an optical pickup device, and includes a semiconductor laser 82 as a light source, an optical path of light irradiated from the semiconductor laser 82 to an optical disk, and an optical disk. The optical path separating element 81 for separating the optical path of the return light from the optical path and the light receiving portion 83 for receiving the return light 87 separated by the optical path separating element 81 as a unit. This hologram element is used (claim 8).

FIG. 10 shows an embodiment of an optical pickup device as a fourth embodiment.
The optical pickup device uses the one of Example 3 as the semiconductor laser module 91 for optical pickup, and a configuration in which a collimator lens 92, a focus lens 93, and a quarter wavelength plate 96 are added to the semiconductor laser module 91. It has become. Of course, although there are other components in the actual optical pickup device, FIG. 9 shows a simplified configuration.

  Laser light (wavelength: 660 nm) emitted from the semiconductor laser module 91 passes through the collimating lens 92, the quarter wavelength plate 96, and the focus lens 93, and is irradiated onto the optical disk 94 that is a DVD. The laser light applied to the optical disc 94 is reflected by obtaining information on the optical disc 94, becomes return light, passes through the optical system again, and returns to the semiconductor laser module 91. Since the return light travels back and forth through the quarter-wave plate 96, it returns to the hologram element 81 of the semiconductor laser module 91 with the polarization direction rotated by 90 degrees, and the diffracted return light 87 is received by the light receiving unit 83 and received. A signal is emitted and used for generation of various signals.

  The optical pickup device of the fourth embodiment can be realized as an optical pickup device with high uniformity of characteristics because the hologram element 81 is a “hologram element with high uniformity of diffraction efficiency and transmittance”.

  That is, the optical pickup device of the fourth embodiment uses the hologram of the second embodiment as an optical path separation element 81 that separates the optical path of the light irradiated from the light source 82 onto the optical disk 94 and the optical path of the return light from the optical disk 94. The semiconductor laser 82 as a light source, the light receiving unit 83 for receiving the return light from the optical disk, and the hologram element 81 of the second embodiment are unitized as a semiconductor laser module. (Claim 10).

FIG. 3 is a diagram for explaining the hologram element of Example 1. It is a figure for demonstrating the uneven | corrugated periodic structure of a hologram element, and the connection part which connects convex parts. 6 is a diagram for explaining a manufacturing process of the hologram element of Example 1. FIG. 6 is a diagram for explaining the collapse of the concavo-convex periodic structure that occurs in the manufacturing process of the hologram element of Example 1. FIG. 6 is a diagram for explaining a hologram element of Example 2. FIG. 6 is a diagram for explaining a manufacturing process of the hologram element of Example 2. FIG. 6 is a diagram for explaining the collapse of the concavo-convex periodic structure that occurs in the manufacturing process of the hologram element of Example 2. FIG. FIG. 6 is a diagram for explaining a semiconductor laser module of Example 3. FIG. 6 is a diagram for explaining an optical pickup device according to a fourth embodiment.

Explanation of symbols

11 Transparent substrate 13 Organic material layer 14 Transparent material 15 Concave and convex periodic structure (diffraction grating)
22 Surface portion of the organic material layer where the irregular periodic structure is not formed 23 Convex portion of the irregular periodic structure 25 Connection portion

Claims (10)

On the surface of the optically transparent organic material layer formed on the transparent substrate, the cross-sectional shape is a substantially rectangular wave shape, and there is a fine concavo-convex periodic structure for diffraction. Filled with a transparent material, wavelength used: λ ₀ , depth of the recess: T, refractive index of organic material layer: n ₀ , lattice period: Λ Q = (2πλ ₀ T) / (n ₀ Λ ² )
In a hologram element having a Q value defined by
Connection portions that connect adjacent convex portions to the concave portions of the minute uneven periodic structure are formed at intervals of the order of 100 μm in the same concave portion,
The connecting portion has a width substantially in the order of the wavelength used over the direction orthogonal to the surface of the transparent organic material layer,
A hologram element, wherein an upper surface portion of the concavo-convex periodic structure, an upper surface portion of the coupling portion, and a surface portion of the organic material layer where the concavo-convex periodic structure is not formed are flush with each other. The hologram element according to claim 1, wherein
An optically transparent organic material layer formed on a transparent substrate is a film-like material and has optical anisotropy with different refractive indexes in the direction of the fast axis and the slow axis, which are orthogonal optical axes. A hologram element characterized by having. The hologram element according to claim 2, wherein
The optically transparent material filling the concave portions of the concavo-convex periodic structure has a refractive index substantially the same as the refractive index in the optical axis direction of any organic material having optical anisotropy, Hologram element. The hologram element according to claim 2 or 3,
A film-like organic material having optical anisotropy is bonded to an optically isotropic transparent substrate by an adhesive material, and the adhesive material is an optically transparent material that fills the concave portions of the concavo-convex periodic structure. A hologram element having substantially the same refractive index. The hologram element according to claim 1 or 2,
A hologram element characterized in that an optically isotropic substrate is bonded onto an optically transparent material filled in a concave portion of an uneven periodic structure using the transparent material as an adhesive material. The hologram element according to claim 3 or 4,
A hologram element characterized in that an optically isotropic substrate is bonded onto an optically transparent material filled in a concave portion of an uneven periodic structure using the transparent material as an adhesive material. The hologram element according to claim 6, wherein
A film-like organic material having optical anisotropy is bonded to an optically isotropic transparent substrate by an adhesive material, and the adhesive material is an optically transparent material that fills the concave portions of the concavo-convex periodic structure. A hologram element having substantially the same refractive index, and wherein the adhesive material is the same material as an optically transparent material filled in the concave portions of the concave-convex periodic structure. A semiconductor laser module for an optical pickup device,
A semiconductor laser as a light source;
An optical path separation element that separates the optical path of the light irradiated from the semiconductor laser onto the optical disk and the optical path of the return light from the optical disk;
A light receiving unit that receives return light separated by the optical path separation element as a unit, and the hologram element according to any one of claims 1 to 7 is used as the optical path separation element. Semiconductor laser module.   The hologram element according to any one of claims 1 to 7 is used as an optical path separation element for separating an optical path of light irradiated from a light source onto an optical disk and an optical path of return light from the optical disk. A characteristic optical pickup device. The optical pickup device according to claim 9, wherein
The semiconductor laser as the light source, the light receiving unit for receiving the return light from the optical disk, and the hologram element according to any one of claims 1 to 7 are unitized as the semiconductor laser module according to claim 8. An optical pickup device characterized by the above.

Images