WO2013031123A1

WO2013031123A1 - Compound lens, optical head device, optical disk device, and optical information device

Info

Publication number: WO2013031123A1
Application number: PCT/JP2012/005178
Authority: WO
Inventors: 金馬　慶明; 文朝山崎; 和博南
Original assignee: パナソニック株式会社
Priority date: 2011-08-30
Filing date: 2012-08-16
Publication date: 2013-03-07

Abstract

A compound objective lens is provided with a diffraction structure for diffracting light and a refraction surface for refracting light, the diffraction structure having a step-shaped cross-section with one cycle at an M level of M-1 (M being a natural number equal to or greater than 3) and a step (d1) adding an optical path difference longer than a wavelength 1 in relation to blue light and an optical path difference less than the wavelength 1 in relation to red light, each flat section of the diffraction structure being inclined upward.

Description

Compound lens, optical head device, optical disk device, and optical information device

The present invention relates to a compound lens that condenses light on an optical information medium such as an optical disk, an optical head device that records, reproduces, or erases information on the optical information medium, an optical disk device including the optical head device, and The present invention relates to an optical information device including an optical disk device.

In a compact disc (CD) that can be said to be a first generation optical disc, infrared light having a wavelength λ3 (wavelength λ3 is 780 nm to 820 nm) and an objective lens having a numerical aperture (NA) of 0.45 are used. The substrate thickness is 1.2 mm. In the second generation DVD, red light having a wavelength λ2 (wavelength λ2 is 630 nm to 680 nm) and an objective lens having an NA of 0.6 are used, and the substrate thickness of the optical disk is 0.6 mm. Furthermore, in the third generation optical disc, blue light having a wavelength λ1 (wavelength λ1 is 390 nm to 415 nm) and an objective lens having an NA of 0.85 are used, and the substrate thickness of the optical disc is 0.1 mm. .

In this specification, the substrate thickness (or base material thickness) refers to the thickness from the surface on which an optical beam (or optical information medium) is incident to the information recording surface on which information is recorded.

The substrate thickness of the high density optical disc is reduced. From the viewpoint of economy and space occupied by the apparatus, an optical information apparatus capable of recording or reproducing information on optical disks having different substrate thicknesses or recording densities is desired. For this purpose, an optical head device including a condensing optical system capable of condensing a light beam up to the diffraction limit on optical disks having different substrate thicknesses is required.

In addition, when recording or reproducing information on an optical disk having a thick base material, it is necessary to focus the light beam on an information recording surface located deeper than the surface of the optical disk. Therefore, it is desirable to make the focal length longer.

Conventionally, for the purpose of compatible reproduction or compatible recording between an optical disc corresponding to red light having a substrate thickness of 0.6 mm and a wavelength λ2 and an optical disc corresponding to blue light having a substrate thickness of 0.1 mm and a wavelength λ1. The structure to do is known.

As a first conventional example, a configuration in which a refractive objective lens and a diffraction element are combined is known. For example, in Patent Document 1, an optical head device that records or reproduces information on a high-density optical disk using an objective lens having a large NA has a stepped cross section for recording or reproducing information on a conventional optical disk such as a DVD. Includes a hologram with a grating having a shape. One step of the stepped cross-sectional shape is an integral multiple of the unit step, and the unit step gives an optical path difference of approximately 1.25 wavelengths to the first light beam having the wavelength λ1.

FIG. 27A is a cross-sectional view showing the basic shape of the grating in the first conventional example, and FIG. 27B shows the phase modulation amount for the blue light beam of wavelength λ1 in the grating shown in FIG. FIG. 27C is a diagram showing the amount of phase modulation with respect to the red light beam having the wavelength λ 2 in the grating shown in FIG. 27A.

The wavelength λ1 is 390 nm to 415 nm. As shown in FIG. 27A, one period of the grating is a stepped

shape having heights

0, 1, 2, and 3 times higher than the step d1 in order from the outer peripheral side of the diffraction element to the optical axis side. is there. As shown in FIG. 27B, the grating changes its phase in the same direction as the grating shape with respect to the blue light beam and exhibits a convex lens action. Further, as shown in FIG. 27C, the grating changes its phase in the direction opposite to the grating shape with respect to the red light beam and exhibits a concave lens action. For this reason, the chromatic aberration of the refractive lens can be corrected with respect to the blue light beam. In addition, the working distance (the distance between the surface of the objective lens and the surface of the optical disk) can be increased by the concave lens action for the red light beam.

As a second conventional example, by arranging a relay lens between a light source that emits infrared light having a wavelength λ3 (wavelength λ3 is 780 nm to 820 nm) and an objective lens, the infrared light and the NA are set to be 0.1. A configuration is also known in which 45 objective lenses are used and compatibility with a first generation optical disc having a substrate thickness of 1.2 mm is realized (see, for example, Patent Document 2).

As a third conventional example, the first conventional example is developed to improve the diffraction efficiency with respect to infrared light having a wavelength λ3 (wavelength λ3 is 780 nm to 820 nm). There is known a configuration that more easily realizes compatibility with a first generation optical disc (see, for example, Patent Document 3).

However, in the configurations of the first to third conventional examples, a method for dealing with a production error that occurs when a diffractive structure is actually produced is not sufficiently shown, and a higher diffraction efficiency is obtained. There was a problem that there was room for ingenuity.

JP 2004-071134 A JP 2004-281034 A International Publication No. 2009/016847

The present invention has been made to solve the above problems, and an object of the present invention is to provide a compound lens, an optical head device, an optical disk device, and an optical information device that can further improve the diffraction efficiency. .

A compound lens according to one aspect of the present invention includes a diffractive structure that diffracts light and a refracting surface that refracts the light, and the diffractive structure has (M−1) stages of M levels (M is 3). The step d1 of the diffractive structure adds an optical path difference longer than one wavelength to blue light and an optical path difference less than one wavelength to red light. The flat portions of the diffractive structure are inclined in the direction in which the stairs are raised.

According to this configuration, the diffractive structure diffracts light and the refracting surface refracts light. The diffractive structure has a step-like cross section in which one period is (M−1) steps and M levels (M is a natural number of 3 or more). The step d1 of the diffractive structure adds an optical path difference longer than one wavelength to blue light and adds an optical path difference less than one wavelength to red light. Each flat part of the diffractive structure is inclined in the direction in which the stairs are raised.

According to the present invention, each flat portion of the diffractive structure is inclined in the direction in which the staircase becomes higher or vice versa, so that the diffraction efficiency of the desired order diffracted light of the desired wavelength can be further improved. The generation of unnecessary orders of diffracted light can be suppressed.

The objects, features and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

It is sectional drawing which shows the structure of the compound objective lens in Embodiment 1 of this invention. It is the top view which looked at the compound objective lens shown in Drawing 1 from the upper part. (A) is a figure which shows the material shape of the diffraction structure formed on the base material in Embodiment 1 of this invention, (B) is with respect to blue light in Embodiment 1 of this invention. It is a figure which shows a phase modulation amount, (C) is a figure which shows the phase modulation amount with respect to red light in Embodiment 1 of this invention. It is a figure for demonstrating the manufacturing method of the metal mold | die for manufacturing the compound objective lens in Embodiment 1 of this invention. It is a figure for demonstrating the manufacturing method of the metal mold | die for manufacturing the compound objective lens in Embodiment 1 of this invention. It is a figure for demonstrating the manufacturing method of the metal mold | die for manufacturing the compound objective lens in Embodiment 1 of this invention. It is a figure for demonstrating the manufacturing method of the metal mold | die for manufacturing the compound objective lens in Embodiment 1 of this invention. It is a figure for demonstrating the manufacturing method of the metal mold | die for manufacturing the compound objective lens in Embodiment 1 of this invention. It is a figure which shows the diffraction structure in Embodiment 1 of this invention. It is a figure which shows the diffraction structure in the 1st modification of Embodiment 1 of this invention. It is a figure which shows the diffraction structure in the 2nd modification of Embodiment 1 of this invention. It is a figure which shows the diffraction structure in the 3rd modification of Embodiment 1 of this invention. It is a figure which shows the diffraction structure in the 4th modification of Embodiment 1 of this invention. It is a figure which shows the diffraction structure in the 5th modification of Embodiment 1 of this invention. It is a figure which shows the compound objective lens in the 6th modification of Embodiment 1 of this invention. (A) is a figure which shows the material shape of the diffraction structure formed on the base material in Embodiment 2 of this invention, (B) is with respect to blue light in Embodiment 2 of this invention. It is a figure which shows a phase modulation amount, (C) is a figure which shows the phase modulation amount with respect to red light in Embodiment 2 of this invention. In Embodiment 2 of this invention, it is a figure which shows the diffractive structure which has a step-shaped cross section with 5 steps 6 levels in 1 period. It is a figure which shows the relationship between the inclination width of the flat part of the diffraction structure shown in FIG. 17, and a diffraction efficiency calculation result. (A) is a figure which shows the material shape of the diffraction structure formed on the base material in the modification of Embodiment 2 of this invention, (B) is a deformation | transformation of Embodiment 2 of this invention. In the example, it is a figure which shows the phase modulation amount with respect to blue light, (C) is a figure which shows the phase modulation amount with respect to red light in the modification of Embodiment 2 of this invention. It is a figure which shows schematic structure of the optical head apparatus in Embodiment 3 of this invention. It is the figure which expanded the compound objective lens vicinity of the optical head apparatus in Embodiment 3 of this invention. It is a figure which shows schematic structure of the optical disk apparatus in Embodiment 4 of this invention. It is a figure which shows schematic structure of the computer in Embodiment 5 of this invention. It is a figure which shows schematic structure of the optical disk player in Embodiment 6 of this invention. It is a figure which shows schematic structure of the optical disk recorder in Embodiment 7 of this invention. It is a figure which shows schematic structure of the optical disk server in Embodiment 8 of this invention. (A) is sectional drawing which shows the basic shape of the grating | lattice in a 1st prior art example, (B) is a figure which shows the phase modulation amount with respect to the blue light beam of wavelength (lambda) 1 in the grating | lattice shown to FIG. 27 (A). FIG. 27C is a diagram showing the amount of phase modulation with respect to the red light beam having the wavelength λ2 in the grating shown in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments are examples embodying the present invention, and do not limit the technical scope of the present invention.

(Embodiment 1)
FIG. 1 is a cross-sectional view showing a configuration of a composite objective lens according to Embodiment 1 of the present invention.

FIG. 1 schematically shows a cross section of the composite objective lens 201. In FIG. 1, a diffractive structure 201 </ b> A is formed on one surface of a composite objective lens 201. The compound objective lens 201 includes a diffractive structure 201A that diffracts light and a refracting surface 201B that refracts light. The diffractive structure 201A is integrally formed on the refractive surface 201B. The compound objective lens 201 is divided into two

regions

202 and 203 on the inner and outer peripheral sides concentrically around the optical axis.

FIG. 2 is a plan view of the compound objective lens shown in FIG. 1 as viewed from above. The compound objective lens 201 includes a first region 202 formed on the inner peripheral side and a second region 203 formed on the outer peripheral side. The boundary 204A between the first region 202 and the second region 203 and the effective range 204D of light passing through the composite objective lens 201 are both virtual design boundaries.

The second region 203 converges blue light through a substrate of about 0.1 mm. As disclosed in Patent Documents 1 to 3, the second region 203 is formed with a diffractive structure having a sawtooth-shaped cross section or a diffractive structure having a stepped shape approximating the sawtooth shape. The second region 203 is designed so that the incident blue light converges through a substrate of about 0.1 mm. The second region 203 is a region dedicated to the first recording medium having a base of about 0.1 mm because it does not converge red light.

The first region 202 converges blue light on the recording surface of the first recording medium through a base of about 0.1 mm. The first region 202 converges the blue light at the same position as the blue light that has passed through the second region 203. The first region 202 also focuses red light through a substrate of about 0.6 mm. That is, the first area 202 is an area shared by the first recording medium and the second recording medium having a base of about 0.6 mm.

The numerical aperture at which the blue light having the wavelength λ1 is condensed through the base material having the thickness t1 is larger than the numerical aperture at which the red light having the wavelength λ2 is condensed through the base material having the thickness t2 larger than the thickness t1. large.

FIGS. 3A to 3C are diagrams for explaining the basic concept of the diffractive structure formed in the first region 202. FIG. FIG. 3A is a diagram showing a material shape of a diffractive structure formed on a substrate in Embodiment 1 of the present invention. FIG. 3B is a diagram showing a phase modulation amount for blue light in the first embodiment of the present invention. Note that the phase modulation amount for the blue light in the vertical direction shown in FIG. 3B is shown in units of one wavelength. FIG. 3C is a diagram showing the amount of phase modulation with respect to red light in the first embodiment of the present invention. Note that the phase modulation amount for the red light in the vertical direction shown in FIG. 3C is shown in units of one wavelength.

3 (A), the vertical direction indicates the thickness or height of the base material in the optical axis direction. The refractive index of the element material for the blue light beam is nb. For example, when the element material is BK7, the refractive index nb is 1.5302. When the element material is a polyolefin resin, the refractive index nb is about 1.522.

One step d1 is designed so that the optical path length difference is about 1.25 wavelengths with respect to the blue light beam, that is, the phase difference is about 2π + π / 2. For example, the unit level difference d1 is d1 = λ1 / (nb−1) × 1.25 = 0.96 μm when the base material is quartz. Further, the unit level difference d1 is d1 = 0.97 μm if the base material is resin.

FIG. 3 (A) shows that the optical path difference caused by the unit step d1 is 1.25 times the wavelength λ1 of the blue light. The optical path difference caused by the unit step d1 is represented by a step / (nb-1). Therefore, the value of 1.25 is a value obtained by dividing the step / (nb-1) by λ1. In FIG. 3B and FIG. 3C, they are simply expressed in the form of optical path difference / wavelength, but they have the same meaning except that the integer part is subtracted.

If the height (level) of the diffractive structure is an integral multiple of the level difference d1, the phase modulation amount for blue light due to the shape of the diffractive structure is 2π + π / 2 per step. In other words, the phase modulation amount given by each step is an integral multiple of 2π + π / 2. This substantially means that the phase modulation amount is π / 2 per stage as shown in FIG.

On the other hand, when the refractive index of the element material for the red light beam is nr, the refractive index nr is 1.5142 when the element material is, for example, BK7. When the element material is a polyolefin resin, the refractive index nr is about 1.505. The optical path length difference with respect to the red light beam caused by the step d1 is d1 × (nr−1) /λ2≈0.75 regardless of whether the base material is quartz or resin. That is, the optical path length difference is about 3/4 times the wavelength λ2, and the phase modulation amount is about −π / 2 per stage.

As shown in FIG. 3A, the height of the diffractive structure is made an integral multiple of one step d1, and the diffractive structure has a stepped cross section. In this case, when the stages of the diffractive structure are stacked one by one, as shown in FIG. 3B, the phase modulation amount changes substantially by π / 2 per stage with respect to the blue light beam. That is, the optical path length difference changes by +1/4 with respect to the wavelength λ1 for each stage. By forming four steps, the phase changes by 2π, and the diffraction efficiency of the + 1st order diffracted light generated from the diffraction structure of one period is calculated to be about 80% by scalar calculation. Therefore, the diffraction efficiency of the + 1st order diffracted light is the strongest among the diffraction orders.

For the red light beam, when the steps of the diffractive structure are stacked one by one, the amount of phase modulation changes substantially by −π / 2 per step as shown in FIG. That is, the optical path length difference changes by −1/4 with respect to the wavelength λ2 for each stage. When the four steps are formed, the phase changes by 2π, and the diffraction efficiency of the −1st order diffracted light generated from the diffraction structure of one period is calculated to be about 80% by scalar calculation. Therefore, the diffraction efficiency of the −1st order diffracted light is the strongest among the diffraction orders. Note that the fact that the diffraction order is negative means that light is bent in the opposite direction to the case where the diffraction order is positive.

As described above, the step d1 of the diffractive structure adds an optical path difference longer than one wavelength to blue light and an optical path difference less than one wavelength to red light. The wavefront converting action that the diffractive structure gives to red light is the opposite action compared to the wavefront converting action that the diffractive structure gives to blue light.

Further, the diffractive structure has at least two diffractive regions formed concentrically around the optical axis of the light incident on the compound objective lens. A diffraction structure having a stepped cross section is formed in the diffraction area that is not the outermost of the at least two diffraction areas. The step d1 of the diffractive structure gives an optical path difference of approximately 1.25 wavelengths to blue light. The diffractive structure is a three-step, four-level step-like cross section having a height of 0 times, 1 time, 2 times and 3 times the step d1 in order from the outer peripheral side of the diffractive structure to the optical axis side within one period. Have.

In such a diffractive structure, the order of diffraction of blue light is opposite to that of positive and negative with respect to red light. Accordingly, the minimum pitch of the diffractive structure necessary for exhibiting the aberration correction effect between wavelengths and the effect of moving the focal position can be widened, the diffractive structure can be easily manufactured, and the diffracted light quantity as calculated can be easily obtained. be able to. Further, when the diffractive structure acts as a convex lens with respect to the blue light beam, the chromatic dispersion of the diffractive action is in the opposite direction to the refractive action. Therefore, when the objective lens which is a refractive convex lens and the diffractive structure are combined, chromatic aberration with respect to a wavelength change within several nm can be canceled and reduced, and in particular, the wavelength dependence of the focal length can be canceled and reduced. In addition, the diffractive structure described above exhibits a concave lens action for red light, so that the working distance can be increased.

In FIG. 3A, the step width ratio is 1: 1: 1: 1. When the surrounding grid pitch is constant, the ratio of the staircase width is the ratio of the physical length as it is. However, when the surrounding grid pitch is changing rapidly, it is desirable to change the step width ratio in accordance with the change. Since the staircase width is a ratio to the lattice pitch, the same width change as the lattice pitch is necessary. When one step is formed each time the phase difference between the incident light and the diffracted light becomes ¼, the ratio of the step width is changed by changing the ratio of the step widths according to the change of the surrounding grating pitch. The ratio is 1: 1: 1: 1, and it can be said that the ratio of the lattice pitch is equal. In this application, such a ratio of the lattice pitch is simply referred to as a staircase width or a staircase width. The step width in one pitch is equal, and the phase modulation amount is changed by substantially the same amount per step. Thereby, the diffraction efficiency of the desired order with respect to a desired wavelength can be made higher. This also applies to the embodiments described later.

Such a diffractive structure is formed in the first region 202 shown in FIGS. As shown in FIG. 1, when a diffractive structure is formed on a curved surface that causes the refractive action of the compound objective lens, a staircase shape as shown in FIG. 3A is formed on the basis of the curved surface. The diffractive structure typically has a shape shown in the first region 202 of FIG.

A method for producing a mold for producing a composite objective lens having such a diffractive structure by molding will be described with reference to FIGS. 4 to 8 are diagrams for explaining a mold manufacturing method for manufacturing the composite objective lens according to Embodiment 1 of the present invention. The period of the diffraction grating (diffraction structure) that diffracts visible light is several microns to several tens of microns, and the depth of the unevenness of the diffraction structure is about submicron to several microns. In order to form a mold having such a structure, it is desirable to use a cutting tool made of a particularly hard material such as diamond.

However, even if the cutting tool is made of diamond, a cutting tool such as a thin needle may break when processing the mold. Therefore, as shown in FIG. 4, it is conceivable that the cutting tool 211 has a cross-sectional shape with the tip as thin as possible and the base side thickened. As described above, in a staircase-shaped diffraction structure, when an optical path difference of one wavelength or more of blue light occurs discontinuously at one step, an optical path length difference that is an integral multiple of the wavelength, that is, an integral multiple of 2π. We take advantage of the fact that there is no phase. Therefore, it is desirable to realize the shape of the step as much as possible. From this point of view, when emphasizing the realization of the shape of the step whose height gradually changes, as shown in FIG. 4, the step 212 is processed so that the surface of the cutting bit 211 is substantially parallel to the optical axis 213. It is desirable to do. The mold is rotated around the optical axis 213 to form concentric lattice grooves.

At this time, the surface facing the surface contacting the step 212 of the cutting bit 211 is inclined with respect to the optical axis 213. Therefore, as shown in FIG. 5, the step 214 sandwiched between the highest level and the lowest level of the staircase shape cannot be parallel to the optical axis 213. Before the tip of the cutting bit 211 reaches the most recessed portion of the mold, the inclined portion of the cutting bit 211 hits the most protruding portion of the mold. Therefore, if the position in the direction of the optical axis 213 is maintained as it is and the cutting tool 211 is moved to the optical axis 213 side, the die will be shaved excessively. When cutting is stopped at a position where the inclined portion of the cutting tool 211 hits the most protruding portion of the mold, the manufactured mold remains without the dotted line portion shown in FIG. 6 being cut. When an optical element is molded using the mold thus produced, the dotted line portion shown in FIG. 6 is reduced. As a result, the width of the flat portion of only the highest step-shaped portion formed on the surface of the optical element (composite objective lens) becomes narrow.

Here, it is designed so that the step widths constituting one period are all equal, and the phase modulation amount is changed by substantially the same amount per step, so that the diffraction efficiency of the desired order of the desired wavelength is obtained. Will be higher. In view of such a viewpoint, the inventors have invented that the most protruding portion of the mold is slightly cut as shown in FIG. As a result, as shown in FIG. 8, the width W4 of the flat portion at the highest level and the width W1 of the flat portion at the lowest level are both narrower than the widths W2, W3 of the other flat portions. In this case, as shown in FIG. 6, the symmetry is better than the case where only the width of a specific flat portion is narrowed in a stepped shape of one cycle, and the diffraction efficiency of a desired order at a desired wavelength is higher. Become. The diffractive structure in the first embodiment is a device for obtaining higher diffraction efficiency when the width of the flat portion becomes narrow for the convenience of the manufacturing method in the design in which all the step widths are the same. Therefore, as disclosed in Japanese Patent Application Laid-Open No. 5-232321, the method is completely different from the method of changing the diffraction efficiency by making the step widths constituting one period different from the step of designing the step shape.

3 is developed to improve the diffraction efficiency of infrared light having a wavelength λ3 (wavelength λ3 is 780 nm to 820 nm). Accordingly, in addition to the first recording medium and the second recording medium, the same structure as the above-described diffraction structure is used for compatibility with a first generation optical disc (third recording medium) having a substrate thickness of 1.2 mm. And can be realized with a simpler optical system configuration.

The diffractive structure has a stepped cross section. The refractive index of the element material of the compound objective lens is nb, nr, and ni for blue light with wavelength λ1, red light with wavelength λ2, and infrared light with wavelength λ3, respectively (J × λ1) / ( nb-1), (K × λ2) / (nr-1), and (L × λ3) / (ni-1) are substantially equal (J, K, and L are natural numbers, and J> M> K> L Is). The step d1 of the diffractive structure is (J × λ1) / (nb-1), (K × λ2) / (nr-1), and (L × λ3) / (ni-1), respectively (1 / M). It is a value within the range between the minimum value and the maximum value among the multiplied values.

When the refractive index nb, the refractive index nr, and the refractive index ni can be regarded as substantially equal, the average value of the refractive index nb, the refractive index nr, and the refractive index ni may be used as the refractive index nc. At this time, the refractive index nc of the element material of the composite objective lens is substantially the same for the blue light having the wavelength λ1, the red light having the wavelength λ2, and the infrared light having the wavelength λ3, and (J × λ1) and ( K × λ2) and (L × λ3) are substantially equal (J, K, and L are natural numbers, and J> M> K> L). The step d1 of the diffractive structure is (J × λ1) / (nc-1), (K × λ2) / (nc-1), and (L × λ3) / (nc-1), respectively (1 / M). It is a value within the range between the minimum value and the maximum value among the multiplied values.

The step d1 of the diffractive structure adds an optical path length difference of (J × λ1) / M to blue light having a wavelength λ1 and an optical path difference of (K × λ2) / M to red light having a wavelength λ2 (or (Also referred to as an optical path length difference), and an optical path length difference of (L × λ3) / M is added to infrared light of wavelength λ3.

FIG. 9 is a diagram showing a diffraction structure according to the first embodiment of the present invention. FIG. 9 shows a basic shape of a one-period diffraction structure based on (J, K, L, M) = (10, 6, 5, 8). Since J / M≈1.25, one step corresponds to an optical path difference of about 1.25 times the wavelength λ1 of blue light. The diffractive structure has a step-like cross section in which one period is seven steps and eight levels. The diffraction efficiencies of the blue light + 2nd order diffracted light, the red light −1st order diffracted light, and the infrared light −2nd order diffracted light are larger than the other orders of diffracted light at the respective wavelengths. Thereby, the diffraction efficiencies of blue light and red light can be increased to the same extent. When the diffractive structure is formed on the surface of the optical element (compound objective lens), the width W8 of the highest level flat portion and the width W1 of the lowest level flat portion of the staircase shape are both other flat portions. Narrower than the width W2 to W7.

FIG. 10 is a diagram showing a diffractive structure in the first modification of the first embodiment of the present invention. FIG. 10 shows a basic shape of a one-period diffraction structure based on (J, K, L, M) = (10, 6, 5, 7). Since J / M≈1.43, one step corresponds to an optical path difference of about 1.43 times the wavelength λ1 of blue light. The diffractive structure has a stepped cross section with one cycle having 6 steps and 7 levels. The diffraction efficiencies of the blue light + 3rd order diffracted light, the red light −1st order diffracted light, and the infrared light −2nd order diffracted light are larger than those of other orders of diffracted light at the respective wavelengths. In particular, in this configuration, the diffraction efficiency of infrared light can be increased. When the diffractive structure is formed on the surface of the optical element (compound objective lens), the width W7 of the highest level flat portion and the width W1 of the lowest level flat portion of the staircase shape are both other flat portions. Narrower than the width W2 to W6.

FIG. 11 is a diagram showing a diffraction structure in the second modification of the first embodiment of the present invention. FIG. 11 shows a basic shape of a one-period diffraction structure based on (J, K, L, M) = (10, 6, 5, 9). Since J / M≈1.11, one step corresponds to an optical path difference of about 1.11 times the wavelength λ1 of blue light. The diffractive structure has a step-like cross section in which one period is eight steps and nine levels. The diffraction efficiencies of the + 1st order diffracted light of blue light, the 3rd order diffracted light of red light, and the 4th order diffracted light of infrared light are larger than those of other orders of diffracted light at the respective wavelengths. In particular, in this configuration, the diffraction efficiency of blue light can be increased. When the diffractive structure is formed on the surface of the optical element (compound objective lens), the width W9 of the highest level flat portion and the width W1 of the lowest level flat portion of the staircase shape are both other flat portions. Narrower than the width W2 to W8.

FIG. 12 is a diagram showing a diffraction structure in the third modification of the first embodiment of the present invention. FIG. 12 shows a basic shape of a one-period diffraction structure based on (J, K, L, M) = (8, 5, 4, 7). Since J / M≈1.14, one step corresponds to an optical path difference of about 1.14 times the wavelength λ1 of blue light. The diffractive structure has a stepped cross section with one cycle having 6 steps and 7 levels. The diffraction efficiencies of the + 1st order diffracted light of blue light, the −2nd order diffracted light of red light, and the −3rd order diffracted light of infrared light are larger than those of other orders of diffracted light at the respective wavelengths. In particular, in this configuration, the diffraction efficiency of blue light can be increased. When the diffractive structure is formed on the surface of the optical element (compound objective lens), the width W7 of the highest level flat portion and the width W1 of the lowest level flat portion of the staircase shape are both other flat portions. Narrower than the width W2 to W6.

FIG. 13 is a diagram showing a diffractive structure in the fourth modification of the first embodiment of the present invention. FIG. 13 shows a basic shape of a one-period diffraction structure based on (J, K, L, M) = (8, 5, 4, 6). Since J / M≈1.33, one step corresponds to an optical path difference of about 1.33 times the wavelength λ1 of blue light. The diffractive structure has a step-like cross section in which one period is five steps and six levels. The diffraction efficiencies of the blue light + 2nd order diffracted light, the red light −1st order diffracted light, and the infrared light −2nd order diffracted light are larger than the other orders of diffracted light at the respective wavelengths. In particular, in this configuration, the diffraction efficiency of blue light can be increased. When the diffractive structure is formed on the surface of the optical element (compound objective lens), the width W6 of the highest level flat portion and the width W1 of the lowest level flat portion of the staircase shape are both other flat portions. Narrower than the width W2 to W5.

The wave analysis was performed on the diffractive structure having a stepped cross section with 5 steps and 6 levels, and the diffraction efficiency was calculated. The length of one period of the diffractive structure is about 20 μm. At this time, when only the width of the flat portion of the highest level of the staircase shape shown in FIG. 6 is made narrower than the width of the other flat portions, the diffraction efficiency of the + 2nd order diffracted light of the blue light is about 48.4%. It was. On the other hand, if the width of the highest level flat portion and the width of the lowest level flat portion of the staircase shape shown in FIG. 8 are both narrower than the width of the other flat portions, the + second order diffracted light of blue light The diffraction efficiency of was about 50.9%. Thus, the diffraction efficiency of blue light in the diffraction structure shown in FIG. 8 was higher than the diffraction efficiency of blue light in the diffraction structure shown in FIG.

Further, in the case of the diffraction structure shown in FIG. 6, the diffraction efficiency of the −1st order diffracted light of red light was about 59.3%. On the other hand, in the case of the diffractive structure shown in FIG. 8, the diffraction efficiency of the −1st order diffracted light of the red light was about 62.8%. Thus, the diffraction efficiency of red light in the diffraction structure shown in FIG. 8 was higher than the diffraction efficiency of red light in the diffraction structure shown in FIG.

Furthermore, in the case of the diffractive structure shown in FIG. 6, the diffraction efficiency of the infrared second-order diffracted light was about 40.5%. On the other hand, in the case of the diffractive structure shown in FIG. 8, the diffraction efficiency of the second-order diffracted light of infrared light was about 41.8%. As described above, the diffraction efficiency of infrared light in the diffraction structure shown in FIG. 8 was higher than the diffraction efficiency of infrared light in the diffraction structure shown in FIG. As described above, the effect of the diffractive structure in the first embodiment was confirmed by numerical analysis.

FIG. 14 is a diagram showing a diffractive structure in the fifth modification of the first embodiment of the present invention. FIG. 14 shows a basic shape of a one-period diffraction structure based on (J, K, L, M) = (6, 4, 3, 5). Since J / M≈1.2, one step corresponds to an optical path difference of about 1.2 times the wavelength λ1 of blue light. The diffractive structure has a step-like cross section in which one period has four steps and five levels. The diffraction efficiencies of the + 1st order diffracted light of blue light, the −1st order diffracted light of red light, and the −2nd order diffracted light of infrared light are larger than those of other orders of diffraction at each wavelength. In particular, in this configuration, since the number of levels is small, the change in diffraction efficiency when the wavelength deviates from the design wavelength can be particularly reduced. When the diffractive structure is formed on the surface of the optical element (compound objective lens), the width W5 of the highest level flat portion and the width W1 of the lowest level flat portion of the staircase shape are both other flat portions. Narrower than the width W2 to W4.

Thus, the diffractive structure has a step-like cross section in which one period is (M−1) steps and M levels (M is a natural number of 3 or more). When the width of each flat portion of the diffractive structure is W1, W2,..., W (M−1) and WM in order from the lowest to the highest, the width W1 and the width WM are the width W2. Narrower than width W (M-1). Further, the surface connecting the end of the highest flat portion in the diffraction structure in the first period and the end of the lowest flat portion in the diffraction structure in the second period following the first period is an optical It is inclined at a predetermined angle with respect to the axis. Thereby, it is possible to suppress a decrease in diffraction efficiency even with respect to processing errors and to obtain high diffraction efficiency.

FIG. 15 is a diagram showing a compound objective lens according to the sixth modification of the first embodiment of the present invention. The composite objective lens 221 shown in FIG. 15 is a diffraction that can realize compatibility with a first generation optical disc (third recording medium) having a substrate thickness of 1.2 mm in addition to the first recording medium and the second recording medium. Provide structure. FIG. 15 is a view of the compound objective lens 221 as viewed from the side on which the diffraction grating is formed. The boundary 221A, the boundary 221E, and the effective range 221D are virtual design boundary lines.

The compound objective lens 221 includes a first region 221C including the optical axis of light, a second region 221B formed in a direction farther from the optical axis than the first region 221C, and light more than the second region 221B. And a third region 221F formed in a direction away from the axis.

The third region 221F converges blue light on the recording surface of the first recording medium through the base material of about 0.1 mm. In the third region 221F, as disclosed in Patent Documents 1 to 3, a sawtooth-shaped diffractive structure or a diffractive structure in which the sawtooth shape is approximated by a staircase shape is formed. The diffractive structure formed in the third region 221F is designed to converge on the recording surface of the first recording medium through the base material of about 0.1 mm when blue light is incident. The third region 221F does not converge red light. Therefore, the third area 221F is a first recording medium dedicated area having a base of about 0.1 mm. The third region 221F is the same region as the second region 203 in FIG.

The second region 221B converges blue light on the recording surface of the first recording medium through the base material of about 0.1 mm. The second region 221B converges the blue light at the same position as the blue light that has passed through the third region 221F. In addition, the second region 221B converges red light on the recording surface of the second recording medium through the base material of about 0.6 mm. That is, the second area 221B is an area shared by the first recording medium and the second recording medium having a base material of about 0.6 mm. The second region 221B is the same region as the first region 202 in FIG.

The first region 221C converges blue light on the recording surface of the first recording medium through the base material of about 0.1 mm. The first region 221C converges the blue light at the same position as the blue light that has passed through the third region 221F and the second region 221B. The first region 221C converges red light on the recording surface of the second recording medium through the base material of about 0.6 mm. The first region 221C converges the red light at the same position as the red light that has passed through the second region 221B. The first region 221C converges infrared light on the recording surface of the third recording medium through the base material of about 1.2 mm. That is, the first area 221C is an area shared by the first recording medium, the second recording medium, and the third recording medium.

As described above, a diffraction structure having a stepped cross section is formed in the first region 221C. In the first region 221C, blue light is condensed on the recording surface of the optical disc through the base material having a thickness t1, and red light is condensed on the recording surface of the optical disc through a base material having a thickness t2 larger than the thickness t1. Infrared light is condensed on the recording surface of the optical disc through the base material having a thickness t3 larger than the thickness t2. In addition, the second region 221B condenses blue light on the recording surface of the optical disc through the base material having a thickness t1, and condenses red light on the recording surface of the optical disc through the base material of thickness t2. The third region 221F condenses blue light on the recording surface of the optical disc through the base material having a thickness t1.

The step d1 of the diffractive structure adds an optical path difference longer than one wavelength to blue light, adds an optical path difference of less than one wavelength to red light, and has one wavelength for infrared light having a wavelength λ3. Add less optical path difference. The wavefront conversion action that the diffractive structure gives to red light and infrared light is the opposite action compared to the wavefront conversion action that the diffractive structure gives to blue light.

In the above description, the diffraction structure is entirely formed on the surface of the composite objective lens 221, but the diffraction element having the diffraction structure may be combined with a refractive lens. That is, the diffractive structure 201A may be formed separately from the refractive surface 201B.

(Embodiment 2)
Patent Document 1 discloses a configuration that can maximize the diffraction efficiencies of both red light and blue light. Specifically, the number of levels of a diffractive structure having a stepped cross section and the height of a step (1 step) between each level can maximize the diffraction efficiency of both red light and blue light. Has been.

Further, Patent Document 3 discloses a configuration capable of maximizing the diffraction efficiency of light having three wavelengths of infrared light, red light, and blue light. Specifically, a configuration is shown in which the number of levels of a diffractive structure having a stepped cross section and the height of a step (one step) between each level can maximize the diffraction efficiency of light of three wavelengths.

In these conventional examples, a plurality of configurations are shown, and various combinations of diffraction efficiency of light of each wavelength are shown. By selecting a desired configuration from a plurality of configurations, it is possible to select a combination of diffraction efficiencies. However, in the conventional example, the diffraction efficiency is a maximum value with respect to the height of the step. For this reason, once the configuration is determined, diffraction efficiency higher than the maximum value cannot be obtained even if the height of the step is changed. In addition, since unnecessary diffracted light of orders other than the diffraction order to be used is generated, a method for reducing unnecessary diffracted light is desired. The second embodiment shows a configuration that can be further improved based on such a viewpoint.

FIGS. 16A to 16C are diagrams for explaining a diffractive structure having a step-shaped cross section in Embodiment 2 of the present invention. FIG. 16A is a diagram showing a material shape of a diffractive structure formed on a substrate in Embodiment 2 of the present invention. FIG. 16B is a diagram showing a phase modulation amount with respect to blue light in the second embodiment of the present invention. Note that the phase modulation amount for the blue light in the vertical direction shown in FIG. 16B is shown in units of one wavelength. FIG. 16C is a diagram showing the amount of phase modulation for red light in the second embodiment of the present invention. Note that the phase modulation amount for the red light in the vertical direction shown in FIG. 16C is shown in units of one wavelength.

FIG. 16B shows that blue light undergoes a phase change by an optical path difference of ¼ wavelength in one period of a three-stage four-level diffraction grating (diffraction structure). Then, a desired order of diffracted light generated by the sawtooth shape (blazed shape) represented by the slope shown by the dotted line in FIG. However, the difference between the dotted line and the solid line, in other words, the error that approximates the slope with a staircase shape, causes the diffraction efficiency of the diffracted light of the desired order to decrease and causes the unnecessary order of diffracted light to be generated. Become.

Therefore, in order to further improve the diffraction efficiency of the desired order diffracted light and suppress the generation of unnecessary order diffracted light, the inventors have changed the shape of the flat portion of the staircase-shaped diffraction structure to FIG. It was considered that it would be possible to approach the sawtooth-shaped slope indicated by the dotted line B). FIG. 16B shows the amount of phase modulation for blue light. Therefore, when the phase modulation amount shown in FIG. 16B is reflected in the material shape, the flat portion becomes the shape shown by the dotted line in FIG. As shown by the dotted line in FIG. 16A, the step-shaped flat portion is inclined, so that the diffraction efficiency of the diffracted light of the desired order of the blue light can be further improved beyond the conventional maximum value, Generation of unnecessary orders of diffracted light can be suppressed.

In the second embodiment, as shown by a dotted line in FIG. 16A, inclining the flat portion in the same direction as the direction in which the staircase becomes higher in the material shape is “inclining the flat portion in the forward direction”. It is defined as Furthermore, in the second embodiment, the amount of change in the height of the slope between both ends of a single level is defined as “inclination width”. As shown in FIG. 16A, the inclination width C1 represents a difference in height between both ends of the flat portion. However, the material shape in the second embodiment is a shape formed only by the diffraction grating, and the diffraction grating is used in combination with other optical elements, such as when the diffraction grating is formed on the lens surface. Is a shape obtained by subtracting the shape of another optical element such as the shape of the lens refracting surface.

Thus, the diffractive structure has a step-like cross section in which one period is (M−1) steps and M levels (M is a natural number of 3 or more). The step d1 of the diffractive structure adds an optical path difference longer than one wavelength to blue light and an optical path difference less than one wavelength to red light. The plurality of flat portions of the diffractive structure are higher toward the optical axis. Each flat portion is inclined so that the end near the optical axis is higher than the end far from the optical axis.

In the second embodiment, the diffraction efficiency of the diffracted light of the desired order of blue light can be increased beyond the maximum value, but the diffraction efficiency of light of other wavelengths is reduced. As shown by the dotted line in FIG. 16C, the phase or optical path difference of red light increases toward the left side of the drawing, but the inclination of the flat portion increases toward the right side of the drawing. Therefore, when red light is incident, the difference between the staircase shape and the sawtooth shape increases. As the difference between the staircase shape and the sawtooth shape increases, the diffraction efficiency of the desired order of red light decreases.

Up to this point, the diffraction structure having a stepped cross section with three steps and four levels in one cycle has been described with reference to FIGS. 16A to 16C. The same principle as in the second embodiment can be applied. FIG. 17 is a diagram showing a diffractive structure having a stepped cross section with one cycle having five steps and six levels in the second embodiment of the present invention. FIG. 17 shows the material shape of the diffractive structure formed on the substrate. As shown by the dotted line in FIG. 17, by tilting the flat portion of the staircase shape in the forward direction, the diffraction efficiency of the diffracted light of the desired order of blue light can be further improved beyond the conventional maximum value, which is unnecessary. The generation of diffracted light of a proper order can be suppressed.

FIG. 18 is a diagram showing the relationship between the inclination width of the flat portion of the diffraction structure shown in FIG. 17 and the diffraction efficiency calculation result. In FIG. 18, the vertical axis represents the diffraction efficiency, and the horizontal axis represents the inclination width C1. The unit of the horizontal axis is an optical path difference of one wavelength of the blue light wavelength λ1. When the unit length is converted into a physical shape, the value “1” on the horizontal axis is λ1 / (nb−1). Here, nb is the refractive index at the wavelength of blue light of the element material. The diffraction efficiency was calculated by vector calculation. As described in the first embodiment, the diffraction efficiency was calculated in consideration of the manufacturing error when manufacturing the mold. The grating pitch is about 0.2 mm. Reflection loss is not considered.

In FIG. 18, the solid line represents the diffraction efficiency of the + 2nd order diffracted light, which is the desired diffracted light of blue light. As the inclination width C1 increases from 0, the diffraction efficiency of the + 2nd order diffracted light of blue light increases. When the inclination width C1 becomes about 0.33, the diffraction efficiency becomes maximum, and then the diffraction efficiency decreases conversely. In FIG. 18, the dotted line represents the diffraction efficiency of the fourth-order diffracted light of blue light, that is, unnecessary diffracted light. As the inclination width C1 increases from 0, the diffraction efficiency of the fourth-order diffracted light of blue light decreases. When the inclination width C1 is about 0.33, the diffraction efficiency is minimized, and then the diffraction efficiency increases conversely.

The reason for this is as follows. When the inclination width C1 is 0.33, the difference between the height of the right edge of the flat portion inclined in FIG. 17 and the height of the left edge of the inclined flat portion right next to the flat portion is 1 for blue light. It becomes the wavelength. Since the phases of the light that is an integral multiple of the wavelength are equal to each other, the phase change caused by the slope is continuously connected, and the staircase shape is equivalent to the sawtooth shape. Therefore, the diffraction efficiency of the desired order diffracted light is maximized, and the diffraction efficiency of unnecessary diffracted light is minimized.

On the other hand, in FIG. 18, the two-dot chain line represents the diffraction efficiency of the −1st order diffracted light, which is the desired diffracted light of red light. In FIG. 18, the alternate long and short dash line represents the diffraction efficiency of the −2nd order diffracted light, which is the desired diffracted light of infrared light. In any case, as described with reference to FIGS. 16A to 16C, the diffraction efficiency decreases as the inclination width C1 increases. It can be seen from FIG. 18 that increasing the inclination width C1 to 0.33 or more reduces the diffraction efficiency of all three wavelengths and is not a good idea. The inclination width C1 is preferably between 0 and 0.33, and is preferably set to the most balanced value of the diffraction efficiency of the three wavelengths.

Here, since the diffractive structure having a stepped cross section with 5 steps and 6 levels has been described, the inclination width C1 is preferably in the range of 0 <C1 ≦ 0.33. However, the slope C1 can be generalized for diffractive structures with different number of levels. The upper limit value of the inclination width C1 is a value in which the difference between the height of the inclined flat portion on the right side of the paper surface and the height of the inclined left portion of the inclined flat portion on the right side of the flat portion corresponds to one wavelength of blue light. .

Accordingly, the step d1 of the diffractive structure having a stepped cross section in one cycle adds an optical path difference Cd1 × λ1 longer than one wavelength to blue light of wavelength λ1, and the stepped flat portion is inclined in the forward direction. The inclination width C1 of the flat portion may be set with the value obtained by subtracting 1 from the constant Cd1 as the upper limit. That is, the width C1 for inclining the flat portion may satisfy 0 <C1 ≦ (Cd1-1).

Note that the diffraction efficiency of desired diffracted light of red light or infrared light can be increased to a maximum value or more. A modification of the second embodiment will be described with reference to FIGS. 19A to 19C, taking as an example a diffraction structure having a stepped cross section with three steps and four levels.

FIG. 19 (A) is a diagram showing a material shape of a diffractive structure formed on a substrate in the modification of the second embodiment of the present invention. FIG. 19B is a diagram showing a phase modulation amount with respect to blue light in the modification of the second embodiment of the present invention. Note that the phase modulation amount for the blue light in the vertical direction shown in FIG. 19B is shown in units of one wavelength. FIG. 19C is a diagram showing a phase modulation amount with respect to red light in the modification of the second embodiment of the present invention. Note that the phase modulation amount for the red light in the vertical direction shown in FIG. 19C is shown in units of one wavelength.

A diffractive structure having a stepped cross-section with three steps and four levels in one cycle gives an optical path difference as shown by a solid line in FIG. 19C to red light of wavelength λ2. In order to improve the diffraction efficiency of red light, the cross-sectional shape may be brought close to a sawtooth shape as indicated by the dotted line in FIG. Accordingly, the material shape of the diffractive structure is the shape shown by the dotted line in FIG. As shown in FIG. 19A, the step-shaped flat portion is inclined, so that the diffraction efficiency of the desired order of red light can be further improved beyond the conventional maximum value, which is unnecessary. Generation of diffracted light of the order can be suppressed.

Thus, the diffractive structure has a step-like cross section in which one period is (M−1) steps and M levels (M is a natural number of 3 or more). The step d1 of the diffractive structure adds an optical path difference longer than one wavelength to blue light and an optical path difference less than one wavelength to red light. The plurality of flat portions of the diffractive structure are higher toward the optical axis. Each flat portion is inclined so that the end portion on the side close to the optical axis is lower than the end portion on the side far from the optical axis.

In Embodiment Mode 2, as shown by the dotted line in FIG. 19A, inclining the flat portion in the opposite direction to the direction in which the staircase becomes higher in the material shape is defined as “inclining the flat portion in the opposite direction”. To do. Further, as shown in FIG. 19A, the inclination width C2 represents a difference in height between both ends of the flat portion. Here, taking a diffraction structure having a stepped cross section of three steps and four levels as an example, it is described that the diffraction efficiency of a desired order of diffracted light of red light is further improved beyond the conventional maximum value. However, the same applies to infrared light in the case of using stages with 5 or more levels.

Further, the range of the inclination width C2 can be determined as follows based on the same consideration as in the case of blue light. In order to further improve the diffraction efficiency of the diffracted light of the desired order of red light beyond the conventional maximum value, the step d1 of the diffractive structure having a step-like cross section in one period is compared with the red light having the wavelength λ2. Thus, an optical path difference Cd2 × λ2 shorter than one wavelength is added, the step-shaped flat portion is inclined in the reverse direction, and the inclination width C2 of the flat portion may be set with the value obtained by subtracting the constant Cd2 from 1 as an upper limit. In other words, the width C2 for inclining the flat portion only needs to satisfy 0 <C2 ≦ (1-Cd2).

In order to further improve the diffraction efficiency of the diffracted light of the desired order of the infrared light beyond the conventional maximum value, the step d1 of the diffractive structure having one step having a step-like cross section is formed of red with a wavelength λ3. An optical path difference Cd3 × λ3 shorter than one wavelength is added to the outside light, the staircase-shaped flat part is inclined in the opposite direction, and the flat part inclination width C2 is set with the value obtained by subtracting the constant Cd3 from 1 as an upper limit. That's fine. That is, the width C2 for inclining the flat portion only needs to satisfy 0 <C2 ≦ (1−Cd3).

Thus, the composite objective lens includes a diffractive structure that diffracts light and a refracting surface that refracts light. The diffractive structure has a step-like cross section in which one period is (M−1) steps and M levels (M is a natural number of 3 or more). The step d1 of the diffractive structure adds an optical path difference longer than one wavelength to blue light and an optical path difference less than one wavelength to red light. And each flat part of a diffraction structure inclines in the direction where a staircase becomes high. That is, each flat portion of the diffractive structure is inclined at a predetermined angle with respect to a direction perpendicular to the optical axis.

As described above, the diffractive structure has been described separately in the first embodiment and the second embodiment. However, the first embodiment and the second embodiment can be used in combination. In addition, the compound objective lens in the second embodiment can apply the contents of the first embodiment also to the region division of the lens structure or the diffractive structure, and is combined with the region configuration shown in Patent Document 1 or Patent Document 3. Is possible.

(Embodiment 3)
FIG. 20 is a diagram showing a schematic configuration of the optical head device according to Embodiment 3 of the present invention. In FIG. 20, an optical head device 103 includes a laser light source 1, a three-beam grating 3, a beam splitter 4, a quarter wavelength plate 5, a condensing lens 6, a photodetector 7, a collimating lens 8, a rising mirror 12, and a composite. An objective lens 221, an actuator 15, a beam splitter 16, a two-wavelength laser light source 20, a three-beam grating 22, a detection diffraction element 31, a detection lens 32, and a photodetector 33 are provided.

The laser light source 1 emits blue light having a wavelength λ1 which is in a range of 390 nm to 415 nm and is typically 408 nm. The two-wavelength laser light source 20 is in the range of 630 nm to 680 nm, typically red light with a wavelength λ2 of 660 nm, and red with a wavelength λ3 of 770 nm to 810 nm, typically 780 nm. Emits external light. The collimating lens 8 converts light into parallel light. The rising mirror 12 bends the optical axis. The compound objective lens 221 is the compound objective lens described with reference to FIG.

The optical disc (first recording medium) 9 has a substrate thickness t1 of about 0.1 mm (a substrate thickness of 0.11 mm or less including manufacturing errors is called about 0.1 mm) or a substrate thickness thinner than 0.1 mm. Thus, the optical disc is a third generation optical disc such as a BD in which information is recorded or reproduced by a light beam having a wavelength λ1. The optical disc (second recording medium) 10 has a substrate thickness t2 of about 0.6 mm (a substrate thickness of 0.5 mm to 0.7 mm including manufacturing errors is called about 0.6 mm), and has a wavelength λ2. It is a second generation optical disc such as a DVD on which information is recorded or reproduced by a light beam. The optical disk (third recording medium) 11 has a substrate thickness t3 of about 1.2 mm (a substrate thickness of 0.8 mm to 1.5 mm including manufacturing errors is called about 1.2 mm), and has a wavelength λ3. It is a first generation optical disc such as a CD on which information is recorded or reproduced by a light beam.

The optical disc 9 and the optical disc 10 shown in FIG. 20 show only the base material from the light incident surface to the recording surface. Actually, in order to reinforce the mechanical strength and to make the outer shape 1.2 mm, which is the same as that of the CD (optical disk 11), the base material and the protective material are bonded together. In the optical disc 10, the base material is bonded to a protective material having a thickness of 0.6 mm. In the optical disc 9, the base material is bonded to a protective material having a thickness of 1.1 mm. Also in the optical disc 11, the base material is bonded to a thin protective material. In FIG. 20, the protective material is omitted for simplification.

20 shows a configuration in which the optical head device 103 includes a two-wavelength laser light source 20 that emits light of two wavelengths of wavelength λ2 and wavelength λ3. A configuration including a dichroic mirror that matches an optical path of light from the light source may be used. Further, when compatible reproduction of a CD (third recording medium) is not performed, a laser light source that emits only red light having a wavelength λ2 may be used instead of a laser light source that emits infrared light having a wavelength λ3. . In that case, the optical head device 103 desirably includes the composite objective lens 201 shown in FIGS. 1 and 2 instead of the composite objective lens 221.

The laser light source 1 and the two-wavelength laser light source 20 are preferably constituted by a semiconductor laser light source, so that the optical head device and the optical information device including the optical head device can be reduced in size, weight, and power consumption.

When recording or reproducing information on the optical disk 9 having the highest recording density, the blue light 61 having the wavelength λ 1 emitted from the laser light source 1 is reflected by the beam splitter 4 and converted into circularly polarized light by the quarter wavelength plate 5. The The quarter-wave plate 5 is designed so as to act as a quarter-wave plate for both the light with the wavelengths λ1 and λ2. The blue light 61 converted into circularly polarized light is converted into substantially parallel light by the collimating lens 8. The blue light 61 converted into substantially parallel light is bent by the rising mirror 12 and condensed by the composite objective lens 221 on the information recording surface through the transparent base material of the optical disk 9 having a thickness of about 0.1 mm.

Here, for convenience of drawing, the rising mirror 12 is described as bending the light beam upward in the drawing, but actually, the light beam is emitted from the drawing to the front (or back) in a direction perpendicular to the drawing. The shaft is bent. The quarter wavelength plate 5 may be disposed between the composite objective lens 221 and the rising mirror 12. The compound objective lens 221 is moved by the actuator 15 in the optical axis direction or the radial direction of the optical disk.

The blue light 61 reflected by the information recording surface of the optical disc 9 follows the original optical path in the reverse direction (return path) and is converted into linearly polarized light in a direction perpendicular to the forward path by the quarter wavelength plate 5, The light passes through the beam splitter 16 almost completely. The blue light 61 that has passed through the beam splitter 16 is diffracted by the detection diffraction element 31, further extended in focal length by the detection lens 32, and incident on the photodetector 33. By calculating the output of the photodetector 33, a servo signal used for focus control or tracking control and an information signal are obtained.

As described above, the beam splitter 4 includes the polarization separation film that totally reflects linearly polarized light in one direction and totally transmits linearly polarized light in a direction perpendicular to the blue light 61 having the wavelength λ1. As will be described later, the beam splitter 4 totally transmits the red light 62 or the infrared light 63 emitted from the two-wavelength laser light source 20 with respect to the red light 62 having the wavelength λ2 or the infrared light 63 having the wavelength λ3. . Thus, the beam splitter 4 is an optical path branching element having wavelength selectivity as well as polarization characteristics. The quarter wavelength plate 5 can be omitted by eliminating the polarization dependency from the beam splitter 4. A configuration in which the detection diffraction element 31 is omitted is also possible.

Next, when information is recorded on or reproduced from the optical disk 10, the substantially linearly polarized red light 62 having the wavelength λ2 emitted from the two-wavelength laser light source 20 is reflected by the beam splitter 16 and transmitted through the beam splitter 4. The light is converted into substantially parallel light by the collimating lens 8. The red light 62 converted into substantially parallel light is further bent by the rising mirror 12 and condensed by the composite objective lens 221 through the transparent base material of the optical disc 10 having a thickness of about 0.6 mm onto the information recording surface.

The red light 62 reflected by the information recording surface of the optical disk 10 traces the original optical path in the reverse direction (return path), passes through the beam splitter 4 almost entirely, and passes through the beam splitter 16. The red light 62 that has passed through the beam splitter 16 is diffracted by the detection diffraction element 31, is further extended in focal length by the detection lens 32, and enters the photodetector 33. By calculating the output of the photodetector 33, a servo signal used for focus control or tracking control and an information signal are obtained. As described above, in order to obtain servo signals of the optical disk 9 and the optical disk 10 from the photodetector 33 common to the blue light and the red light, the light emission point of the laser light source 1 and the red light emission of the two-wavelength laser light source 20 are obtained. The points are arranged so as to form an imaging relationship with respect to the optical axis direction with respect to the common position on the compound objective lens 221 side. By doing so, the number of photodetectors and the number of wirings can be reduced.

The beam splitter 16 has a polarization separation film that totally transmits linearly polarized light in one direction and totally reflects linearly polarized light in a direction perpendicular to the red light 62 having the wavelength λ2. In addition, the beam splitter 16 totally transmits the blue light 61 having the wavelength λ1. Thus, the beam splitter 16 is also an optical path branching element having wavelength selectivity as well as polarization characteristics. The quarter wavelength plate 5 can be omitted by eliminating the polarization dependency from the beam splitter 16. A configuration in which the positional relationship between the two-wavelength laser light source 20 and the photodetector 33 is switched is also possible.

The operation when the infrared light 63 is emitted from the two-wavelength laser light source 20 to record or reproduce information on the optical disk 11 is performed by emitting the red light 62 from the two-wavelength laser light source 20 to record or reproduce information on the optical disk 10. It is the same as the operation at the time.

Further, a configuration example that is additionally effective as the overall configuration of the optical head device will be described below. However, the important point of the present embodiment is the diffractive structure of the composite objective lens for realizing compatible reproduction or recording of the optical disc 9, the optical disc 10, and the optical disc 11. The configuration described in addition to the compound objective lens includes the following contents, and even in the configuration already described, the beam splitter, the detection lens, and the detection diffraction element are not essential configurations, but each has an effect as a preferable configuration. Configurations can also be used as appropriate.

In FIG. 20, the optical head device further includes a three-beam grating (diffraction element) 3 between the laser light source 1 and the beam splitter 4 so that the well-known differential push-pull (DPP) It is also possible to detect by the method.

The optical head device may further include a relay lens between the laser light source 1 and the beam splitter 4. Thereby, it is possible to make the numerical aperture of the blue light 61 on the collimating lens 8 side appropriate.

Further, the optical head device further includes a three-beam grating (diffraction element) 22 between the two-wavelength laser light source 20 and the beam splitter 16, so that the tracking error signal of the optical disk 10 can be well known differential push-pull (DPP). It is also possible to detect by the method.

It is also effective for the optical head device to change the parallelism of the light beam as shown in FIG. 21 by moving the collimating lens 8 in the optical axis direction (left-right direction in FIG. 20). FIG. 21 is an enlarged view of the vicinity of the composite objective lens of the optical head device according to Embodiment 3 of the present invention. When the substrate has a thickness error, or when the optical disc 9 is a two-layer disc, spherical aberration due to the interlayer thickness occurs. However, spherical aberration can be corrected by moving the collimating lens 8 in the optical axis direction in this way.

Thus, by moving the collimating lens 8, it is possible to correct a spherical aberration of about several hundred mλ when the NA of the condensed light with respect to the optical disk is 0.85, and a substrate thickness error of ± 30 μm can be corrected. It can also be corrected. Further, when information is reproduced on the optical disk 10 using the red light 62, the red light traveling toward the composite objective lens 221 is moved by moving the collimating lens 8 to the left side of FIG. 20, that is, the side closer to the two-wavelength laser light source 20. 62 is divergent light as shown in FIG. As a result, the condensing spot with respect to the optical disk 10 is further away from the composite objective lens 221, and a part of the aberration due to the thickness of the base material is corrected, and the aberration correction amount required for the diffractive structure is reduced to widen the diffraction pitch. Further, the composite objective lens 221 can be easily created.

Further, the beam splitter 4 transmits a part of the linearly polarized blue light emitted from the laser light source 1 (for example, about 10%), and the condenser lens 6 transmits the blue light transmitted through the beam splitter 4 to the photodetector 7. You may lead to. Then, a change in the amount of emitted light from the laser light source 1 is monitored using a signal obtained from the photodetector 7, and the change in the amount of emitted light emitted from the laser light source 1 is fed back to control to keep the emitted light amount of the laser light source 1 constant. it can.

Further, the beam splitter 4 reflects a part of linearly polarized red light or infrared light (for example, about 10%) emitted from the two-wavelength laser light source 20, and the condenser lens 6 reflects the red light reflected from the beam splitter 4. Light or infrared light may be guided to the photodetector 7. Then, a change in the amount of emitted light from the two-wavelength laser light source 20 is monitored using a signal obtained from the photodetector 7, and the change in the amount of emitted light emitted from the two-wavelength laser light source 20 is fed back to keep the emitted light amount from the two-wavelength laser light source 20 constant. Can also be done.

(Embodiment 4)
Furthermore, an optical disk device provided with the optical head device 103 according to Embodiment 3 of the present invention will be described. FIG. 22 is a diagram showing a schematic configuration of the optical disc apparatus according to Embodiment 4 of the present invention. The optical disc device 100 includes a drive device 101, an electric circuit 102, an optical head device 103, and a motor 104.

22, the optical disc 9 (or the optical disc 10 or the optical disc 11) is placed on the turntable 105, fixed between the turntable 105 and the clamper 106, and rotated by the motor 104. The optical head device 103 is the optical head device described in the third embodiment. The driving device 101 coarsely moves the optical head device 103 to the position of the track on the optical disk 9 where desired information exists.

The optical head device 103 sends a focus error (focus error) signal or a tracking error signal to the electric circuit 102 in accordance with the positional relationship with the optical disk 9. The electric circuit 102 sends a lens drive signal for finely moving the composite objective lens to the optical head device 103 in response to the focus error signal or the tracking error signal. The optical head device 103 performs focus control or tracking control on the optical disc 9 by a lens drive signal, reads information from the optical disc 9, writes information on the optical disc 9 (records), and receives information from the optical disc 9. Or erase.

The optical disc device 100 according to the fourth embodiment includes the optical head device 103 described above in the third embodiment. Therefore, it is possible to cope with a plurality of optical discs having different recording densities by a small, inexpensive and light optical head device configured by a single small number of parts.

(Embodiment 5)
The computer, the optical disc player, the optical disc recorder, and the like provided with the optical disc apparatus 100 according to the fourth embodiment can record or reproduce information stably on different types of optical discs, and thus have an effect that it can be used for a wide range of applications. . These devices that exchange light with a recording medium using light are collectively referred to as an optical information device. Hereinafter, specific examples of the optical information device will be described.

The fifth embodiment shows an embodiment of a computer provided with the optical disc device 100 of the fourth embodiment. FIG. 23 is a diagram showing a schematic configuration of a computer according to Embodiment 5 of the present invention. In FIG. 23, a computer 110 includes an optical disk device 100, an input device 112, a calculation device 111, and an output device 113.

The optical disc apparatus 100 is the optical disc apparatus described in the fourth embodiment. The input device 112 is configured with a keyboard, a mouse, a touch panel, or the like, and receives input of information. The arithmetic device 111 is composed of a central processing unit (CPU) or the like, and performs an operation based on information input from the input device 112 or information read from the optical disc device 100. The output device 113 is configured by a display device such as a CRT (Cathode Ray Tube) monitor or a liquid crystal display device, and displays information such as a result calculated by the calculation device 111. The output device 113 may be configured by a printer, and may print information such as a result calculated by the calculation device 111. The arithmetic device 111 processes information recorded on the optical disc device 100 and / or information reproduced from the optical disc device 100.

In the fifth embodiment, the computer 110 corresponds to an example of an optical information device, and the arithmetic device 111 corresponds to an example of an information processing unit.

(Embodiment 6)
The sixth embodiment shows an embodiment of an optical disc player including the optical disc device 100 of the fourth embodiment.

FIG. 24 is a diagram showing a schematic configuration of the optical disc player according to Embodiment 6 of the present invention. 24, the optical disc player 120 includes an optical disc device 100 and a decoder 121.

The optical disc apparatus 100 is the optical disc apparatus described in the fourth embodiment. The decoder 121 converts the information signal obtained from the optical disc apparatus 100 into image information. The decoder 121 processes information recorded on the optical disc apparatus 100 and / or information reproduced from the optical disc apparatus 100. Also, the optical disc player 120 having this configuration can be used as a car navigation system by combining with a GPS (Global Positioning System). Further, the optical disc player 120 may be configured to include a display device 122 for displaying information such as a liquid crystal display device.

In the sixth embodiment, the optical disc player 120 corresponds to an example of an optical information device, and the decoder 121 corresponds to an example of an information processing unit.

(Embodiment 7)
The seventh embodiment shows an embodiment of an optical disc recorder provided with the optical disc device 100 of the fourth embodiment.

The optical disk recorder according to the seventh embodiment will be described with reference to FIG. FIG. 25 is a diagram showing a schematic configuration of the optical disc recorder according to Embodiment 7 of the present invention. In FIG. 25, the optical disk recorder 130 includes an optical disk device 100 and an encoder 132.

The optical disc apparatus 100 is the optical disc apparatus described in the fourth embodiment. The encoder 132 converts the image information into an information signal to be recorded on the optical disc by the optical disc apparatus 100. The encoder 132 processes information recorded on the optical disc device 100 and / or information reproduced from the optical disc device 100. Desirably, the optical disk recorder 130 includes a decoder 121 that converts an information signal obtained from the optical disk device 100 into image information, so that information already recorded on the optical disk can be reproduced.

Further, the optical disk recorder 130 may include an output device 113 that outputs information. The output device 113 includes a display device such as a CRT monitor or a liquid crystal display device, and displays the image information converted by the decoder 121. The output device 113 may be configured with a printer.

In the seventh embodiment, the optical disk recorder 130 corresponds to an example of an optical information device, and the encoder 132 corresponds to an example of an information processing unit.

(Embodiment 8)
The eighth embodiment shows an embodiment of an optical disk server provided with the optical disk device 100 of the fourth embodiment.

The optical disk server according to the eighth embodiment will be described with reference to FIG. FIG. 26 is a diagram showing a schematic configuration of the optical disk server in the eighth embodiment of the present invention. In FIG. 26, the optical disk server 140 includes an optical disk device 100 and an input / output unit 141.

The optical disc apparatus 100 is the optical disc apparatus described in the fourth embodiment. The input / output unit 141 captures information to be recorded on the optical disc apparatus 100 and outputs information read by the optical disc apparatus 100 to the outside. The input / output unit 141 is connected to the network 142 by wire or wireless. The input / output unit 141 transmits / receives information to / from a plurality of devices such as a computer, a telephone, or a TV tuner via the network 142. Thereby, the optical disk server 140 can be used as an information server shared by the plurality of devices.

Since the optical disk server 140 can stably record or reproduce information on different types of optical disks, it has an effect that can be used for a wide range of purposes. The optical disk server 140 may include an output device 113 that outputs information. The output device 113 includes a display device such as a CRT monitor or a liquid crystal display device, and displays information. The output device 113 may be configured with a printer. The optical disk server 140 may include an input device 112 for inputting information such as a keyboard, a mouse, or a touch panel.

Furthermore, the optical disk server 140 may include a changer 143 for taking a plurality of optical disks into and out of the optical disk device 100. Thereby, a lot of information can be recorded and accumulated.

In the eighth embodiment, the optical disk server 140 corresponds to an example of an optical information device, and the input / output unit 141 corresponds to an example of an information processing unit.

In the above fifth to eighth embodiments, FIGS. 23 to 26 show the output device 113 and the display device 122. The computer 110, the optical disc player 120, the optical disc recorder 130, and the optical disc server 140 have output terminals, respectively. Needless to say, there may be a product form that includes the output device 113 or the display device 122. 24 and 25 do not illustrate an input device, the optical disc player 120 and the optical disc recorder 130 may include an input device for inputting information such as a keyboard, a touch panel, a mouse, or a remote control device. Good. Conversely, in Embodiments 5 to 8 described above, the computer 110, the optical disc player 120, the optical disc recorder 130, and the optical disc server 140 may be provided with only an input terminal without including an input device.

The specific embodiments described above mainly include inventions having the following configurations.

Accordingly, since each flat portion of the diffractive structure is inclined in the direction in which the stairs are raised, the diffraction efficiency of a desired order of diffracted light can be further improved, and generation of unnecessary order of diffracted light is suppressed. be able to.

In the above compound lens, the plurality of flat portions of the diffractive structure are higher toward the optical axis, and each flat portion has an end portion closer to the optical axis at a side farther from the optical axis. It is preferable to incline so that it may become higher than an edge part.

According to this configuration, the plurality of flat portions of the diffractive structure are higher toward the optical axis. Each flat portion is inclined so that the end near the optical axis is higher than the end far from the optical axis, so that the diffraction efficiency of diffracted light of a desired order is further improved with respect to blue light. And generation of unnecessary orders of diffracted light can be suppressed.

In the above compound lens, the optical path difference given by the step d1 to the blue light having the wavelength λ1 is a constant Cd1 × λ1, and the width C1 for inclining the flat portion is 0 <C1 ≦ (Cd1-1). ) Is preferably satisfied.

According to this configuration, by designing the width C1 for inclining the flat portion so as to satisfy 0 <C1 ≦ (Cd1-1), the diffraction efficiency of the diffracted light of a desired order with respect to the blue light having the wavelength λ1 is increased. The generation of diffracted light of an unnecessary order can be suppressed.

In the above compound lens, the plurality of flat portions of the diffractive structure are higher toward the optical axis, and each flat portion has an end portion closer to the optical axis at a side farther from the optical axis. It is preferable to incline so that it may become lower than an edge part.

According to this configuration, the plurality of flat portions of the diffractive structure are higher toward the optical axis. Each flat portion is inclined so that the end portion closer to the optical axis is lower than the end portion far from the optical axis, so that the diffraction efficiency of diffracted light of a desired order is further improved with respect to red light. And generation of unnecessary orders of diffracted light can be suppressed.

In the above compound lens, the optical path difference given by the step d1 to the red light having the wavelength λ2 is a constant Cd2 × λ2, and the width C2 for inclining the flat portion is 0 <C2 ≦ (1-Cd2). ) Is preferably satisfied.

According to this configuration, by designing the width C2 for inclining the flat portion so as to satisfy 0 <C2 ≦ (1-Cd2), the diffraction efficiency of the desired order diffracted light with respect to the red light having the wavelength λ2 is increased. The generation of diffracted light of an unnecessary order can be suppressed.

In the above compound lens, the optical path difference given by the step d1 to the infrared light having the wavelength λ3 is a constant Cd3 × λ3, and the width C2 for inclining the flat portion is 0 <C2 ≦ (1− It is preferable to satisfy Cd3).

According to this configuration, by designing the width C2 for inclining the flat portion so as to satisfy 0 <C2 ≦ (1-Cd3), the diffraction efficiency of the desired order diffracted light with respect to the infrared light having the wavelength λ3. Can be further improved, and generation of unnecessary orders of diffracted light can be suppressed.

A compound lens according to another aspect of the present invention includes a diffractive structure that diffracts light and a refracting surface that refracts the light, and the diffractive structure has (M−1) stages of M levels (M is a period). A natural number of 3 or more), and the width of each flat portion of the diffractive structure is W1, W2,..., W (M−1) and W1 in order from the lowest to the highest. When WM is defined, the width W1 and the width WM are narrower than the width W2 to the width W (M−1).

According to this configuration, the diffractive structure diffracts light and the refracting surface refracts light. The diffractive structure has a step-like cross section in which one period is (M−1) steps and M levels (M is a natural number of 3 or more). Then, when the width of each flat portion of the diffractive structure is W1, W2,..., W (M−1) and WM in order from the lowest to the highest, the width W1 and the width WM are: It is narrower than the width W2 to the width W (M-1).

Therefore, when the width of each flat portion of the diffractive structure is W1, W2,..., W (M−1) and WM in order from the lowest to the highest, the width W1 and the width WM are: Since it is narrower than the width W2 to the width W (M-1), the diffraction efficiency can be further improved in consideration of the shape of the cutting tool used for producing the mold.

In the above compound lens, the step d1 of the diffractive structure adds an optical path difference longer than one wavelength to blue light, and adds an optical path difference less than one wavelength to red light. It is preferable that the wavefront converting action given to the red light is a reverse action compared to the wavefront converting action given to the blue light by the diffractive structure.

According to this configuration, the wavefront converting action that the diffractive structure gives to the red light is the reverse of the wavefront converting action that the diffractive structure gives to the blue light. For example, the diffraction order of the blue light with respect to the red light When the positive and negative are opposite, the minimum pitch of the diffractive structure necessary for exhibiting the aberration correction effect between wavelengths and the effect of moving the focal position can be widened, and the diffractive structure can be easily manufactured.

In the above compound lens, the compound lens has at least two diffractive regions formed concentrically around the optical axis of light incident on the compound lens, and among the at least two diffractive regions, The diffractive structure having a stepped cross section is formed in a diffractive region other than the outermost diffractive region, and the step d1 of the diffractive structure gives an optical path difference of approximately 1.25 wavelengths to blue light, The diffractive structure is a three-step, four-level step-like shape having a height of 0, 1, 2, and 3 times the step d1 in order from the outer peripheral side of the diffractive structure to the optical axis side within one period. It preferably has a cross section.

According to this configuration, the composite lens has at least two diffraction regions formed concentrically around the optical axis of light incident on the composite lens. A diffraction structure having a stepped cross section is formed in a diffraction region other than the outermost diffraction region among the at least two diffraction regions. The step d1 of the diffractive structure gives an optical path difference of approximately 1.25 wavelengths to blue light. The diffractive structure is a three-step, four-level step-like cross section having a height of 0 times, 1 time, 2 times and 3 times the step d1 in order from the outer peripheral side of the diffractive structure to the optical axis side within one period. Have. In the above description, “1.25 wavelength” includes “substantially 1.25 wavelength”.

Therefore, the step d1 of the diffractive structure gives an optical path difference of approximately 1.25 wavelengths to the blue light, so that the phase modulation amount for the blue light changes substantially by π / 2 per step, and the optical path length The difference changes by +1/4 with respect to the wavelength of blue light for each stage. By forming four steps, the phase changes by 2π, so that the diffraction efficiency of the + 1st order diffracted light generated from a one-period diffraction structure can be maximized.

In the above compound lens, the numerical aperture at which the blue light having the wavelength λ1 is collected through the base material having the thickness t1 is set so that the red light having the wavelength λ2 is collected through the base material having the thickness t2 larger than the thickness t1. It is preferable that the numerical aperture is larger than the lighted numerical aperture.

According to this configuration, the numerical aperture at which the blue light having the wavelength λ1 is collected through the base material having the thickness t1 is such that the red light having the wavelength λ2 is condensed through the base material having the thickness t2 larger than the thickness t1. Since it is larger than the numerical aperture, it is possible to increase the recording density of a recording medium that records or reproduces information using blue light.

In the above compound lens, the step d1 of the diffractive structure adds an optical path difference longer than one wavelength to the blue light, adds an optical path difference less than one wavelength to the red light, and adds to the infrared light. On the other hand, the wavefront conversion effect that the diffraction structure gives to the red light and the infrared light by adding an optical path difference of less than one wavelength is the reverse of the wavefront conversion action that the diffraction structure gives to the blue light. Preferably there is.

According to this configuration, the wavefront converting action that the diffractive structure gives to red light and infrared light is the opposite action compared to the wavefront converting action that the diffractive structure gives to blue light. In contrast, when the positive and negative diffraction orders of blue light are opposite, the minimum pitch of the diffractive structure necessary to exhibit the aberration correction effect between wavelengths and the effect of moving the focal position can be widened, It can be easily manufactured.

In the above compound lens, the diffractive structure is integrally formed on the refracting surface, and the refractive index nc of the element material of the compound lens is blue light of wavelength λ1, red light of wavelength λ2, and wavelength λ3. It is substantially the same as infrared light, and (J × λ1), (K × λ2), and (L × λ3) are substantially equal (J, K, and L are natural numbers, and J> M> K > L), the step d1 of the diffractive structure preferably adds an optical path difference of (J × λ1) / M to the blue light having the wavelength λ1.

According to this configuration, the diffractive structure is integrally formed on the refractive surface. The refractive index nc of the element material of the compound lens is substantially the same for blue light having a wavelength λ1, red light having a wavelength λ2, and infrared light having a wavelength λ3. (J × λ1), (K × λ2), and (L × λ3) are substantially equal (J, K, and L are natural numbers, and J> M> K> L), and the step d1 of the diffractive structure is An optical path difference of (J × λ1) / M is added to blue light of wavelength λ1. In the above description, the case of “same” and “equal” includes the case of substantially the same and the case of being substantially equal.

Therefore, an optical path difference of (J × λ1) / M can be added to the blue light having the wavelength λ1 by the step d1 of the diffractive structure.

In the above compound lens, the diffractive structure is integrally formed on the refracting surface, and the refractive index nc of the element material of the compound lens is blue light of wavelength λ1, red light of wavelength λ2, and wavelength λ3. It is substantially the same as infrared light, and (J × λ1), (K × λ2), and (L × λ3) are substantially equal (J, K, and L are natural numbers, and J> M> K > L), the level difference d1 of the diffraction structure is (J × λ1) / (nc-1), (K × λ2) / (nc-1), and (L × λ3) / (nc-1). It is preferable that the value is in a range between the minimum value and the maximum value among the values obtained by multiplying (1 / M) by each.

According to this configuration, the diffractive structure is integrally formed on the refractive surface. The refractive index nc of the element material of the compound lens is substantially the same for blue light having a wavelength λ1, red light having a wavelength λ2, and infrared light having a wavelength λ3. (J × λ1), (K × λ2), and (L × λ3) are substantially equal (J, K, and L are natural numbers, and J> M> K> L), and the step d1 of the diffractive structure is (J × λ1) / (nc-1), (K × λ2) / (nc-1), and (L × λ3) / (nc-1) multiplied by (1 / M), respectively. A value in the range between the value and the maximum value. In the above description, the case of “same” and “equal” includes the case of substantially the same and the case of being substantially equal.

Therefore, the level difference d1 of the diffractive structure is (J × λ1) / (nc-1), (K × λ2) / (nc-1), and (L × λ3) / (nc-1), respectively (1 / M) A diffractive structure which is a value within the range between the minimum value and the maximum value among the multiplied values and is compatible with blue light of wavelength λ1, red light of wavelength λ2, and infrared light of wavelength λ3. Can be formed.

In the above compound lens, the diffractive structure is integrally formed on the refracting surface, and the refractive index of the element material of the compound lens is blue light of wavelength λ1, red light of wavelength λ2, and red light of wavelength λ3. For external light, they are nb, nr and ni, respectively (J × λ1) / (nb-1), (K × λ2) / (nr-1) and (L × λ3) / (ni-1 ) Is substantially equal (J, K, and L are natural numbers, J> M> K> L), and the step d1 of the diffractive structure is (J × λ1) / (nb−1) and (K × λ2) / (nr-1) and (L × λ3) / (ni-1) multiplied by (1 / M), and the value is within the range between the minimum value and the maximum value. Is preferred.

According to this configuration, the diffractive structure is integrally formed on the refractive surface. The refractive index of the element material of the compound lens is nb, nr, and ni for blue light of wavelength λ1, red light of wavelength λ2, and infrared light of wavelength λ3, respectively. (J × λ1) / (nb-1), (K × λ2) / (nr-1), and (L × λ3) / (ni-1) are substantially equal (J, K, and L are natural numbers, J> M> K> L), and the step d1 of the diffraction structure is (J × λ1) / (nb−1), (K × λ2) / (nr−1), and (L × λ3) / (ni -1) is a value within a range between the minimum value and the maximum value among the values obtained by multiplying each by (1 / M). In the above description, “equal” includes the case where it is substantially equal.

Therefore, the level difference d1 of the diffractive structure is (1 / x-1) / (nb-1), (Kxλ2) / (nr-1), and (Lxλ3) / (ni-1) (1 / M) A diffractive structure that is compatible with the blue light having the wavelength λ1, the red light having the wavelength λ2, and the infrared light having the wavelength λ3 because the value is within the range between the minimum value and the maximum value among the multiplied values. Can be formed.

In the above compound lens, the compound lens includes a first region including the optical axis of the light, a second region formed in a direction away from the optical axis than the first region, and the first lens. A third region formed in a direction away from the optical axis than the second region, the diffractive structure is formed in the first region, and the first region has a thickness of blue light. Condensing on the recording surface of the first recording medium through the base material having a thickness t1, condensing red light on the recording surface of the second recording medium through the base material having a thickness t2 larger than the thickness t1, Infrared light is condensed on the recording surface of the third recording medium through a base material having a thickness t3 larger than the thickness t2, and the second region is configured to transmit blue light through the base material having the thickness t1. The second recording is performed by focusing the red light on the recording surface of the first recording medium and passing the red light through the base material having the thickness t2. Is converged to the body of the recording surface, said third region preferably be condensed onto the recording surface of the first recording medium blue light through the substrate of the thickness t1.

According to this configuration, the compound lens includes the first region including the optical axis of light, the second region formed in a direction farther from the optical axis than the first region, and the light from the second region. And a third region formed in a direction away from the axis. A diffraction structure having a stepped cross section is formed in the first region. In the first region, blue light is condensed on the recording surface of the first recording medium through the base material having the thickness t1, and the red light is passed through the base material having the thickness t2 larger than the thickness t1. And the infrared light is condensed on the recording surface of the third recording medium through the base material having a thickness t3 larger than the thickness t2. The second region condenses blue light on the recording surface of the first recording medium through the base material having a thickness of t1, and records the red light through the base material of thickness t2 on the recording surface of the second recording medium. Focus it up. In the third region, blue light is condensed on the recording surface of the first recording medium through the base material having a thickness t1.

Therefore, the first region is shared by blue light, red light, and infrared light, the second region is shared by blue light and red light, and the third region is used only for blue light. Therefore, it is possible to realize compatibility of light of three wavelengths having different numerical apertures.

In the above compound lens, it is preferable that the diffractive structure is integrally formed on the refractive surface.

According to this configuration, since the diffractive structure is integrally formed on the refracting surface, the number of parts can be reduced and downsizing can be realized.

An optical head device according to another aspect of the present invention has a first light source that emits blue light, a second light source that emits red light, and a thickness t1 of blue light emitted from the first light source. The red light emitted from the second light source is condensed on the recording surface of the first recording medium through the base material of the first recording medium, and recorded on the second recording medium through the base material having a thickness t2 larger than the thickness t1. 11. The compound lens according to claim 1, which collects light on a surface, and the blue light reflected on the recording surface of the first recording medium or the reflection on the recording surface of the second recording medium. And a photodetector that receives the red light and outputs an electrical signal according to the amount of received light.

According to this configuration, the first light source emits blue light. The second light source emits red light. The compound lens condenses the blue light emitted from the first light source onto the recording surface of the first recording medium through the substrate having the thickness t1, and the red light emitted from the second light source has the thickness t1. Light is condensed on the recording surface of the second recording medium through the base material having a larger thickness t2. The photodetector receives blue light reflected on the recording surface of the first recording medium or red light reflected on the recording surface of the second recording medium, and outputs an electrical signal according to the amount of received light. Therefore, the above compound lens can be applied to an optical head device.

An optical head device according to another aspect of the present invention includes a first light source that emits blue light, a second light source that emits red light, a third light source that emits infrared light, and the first light source. The blue light emitted from the light source is condensed on the recording surface of the first recording medium through the substrate having the thickness t1, and the red light emitted from the second light source is thicker than the thickness t1. The third recording medium is focused on the recording surface of the second recording medium through the base material of t2, and the infrared light emitted from the third light source passes through the base material of thickness t3 larger than the thickness t2. The compound lens according to any one of claims 11 to 16, and the blue light reflected on the recording surface of the first recording medium, and the recording surface of the second recording medium. Receiving the red light reflected on the recording medium or the infrared light reflected on the recording surface of the third recording medium. Flip and a light detector for outputting an electrical signal.

According to this configuration, the first light source emits blue light. The second light source emits red light. The third light source emits infrared light. The compound lens condenses the blue light emitted from the first light source onto the recording surface of the first recording medium through the substrate having the thickness t1, and the red light emitted from the second light source has the thickness t1. The infrared light emitted from the third light source is condensed on the recording surface of the second recording medium through the base material having the larger thickness t2, and the third light passes through the base material having the thickness t3 larger than the thickness t2. Condensed on the recording surface of the recording medium. The photodetector is blue light reflected on the recording surface of the first recording medium, red light reflected on the recording surface of the second recording medium, or infrared light reflected on the recording surface of the third recording medium. Is received, and an electrical signal is output according to the amount of received light. Therefore, the above compound lens can be applied to an optical head device.

An optical disc apparatus according to another aspect of the present invention provides a control for controlling the motor and the optical head device based on an electric signal obtained from the optical head device, a motor for rotating the optical disc, and the optical head device. A part. According to this configuration, the above optical head device can be applied to an optical disk device.

An optical information device according to another aspect of the present invention includes the above-described optical disc device and an information processing unit that processes information recorded on the optical disc device and / or information reproduced from the optical disc device. According to this configuration, the optical disk device described above can be applied to an optical information device.

It should be noted that the specific embodiments or examples made in the section for carrying out the invention are merely to clarify the technical contents of the present invention, and are limited to such specific examples. The present invention should not be interpreted in a narrow sense, and various modifications can be made within the spirit and scope of the present invention.

The compound lens according to the present invention can further improve the diffraction efficiency, is useful as an objective lens used in an optical head device, and can be applied to uses such as a lens used in optical communication.

Claims

A diffractive structure that diffracts light;
A refracting surface for refracting the light,
The diffractive structure has a step-like cross section with one cycle of (M−1) steps and M levels (M is a natural number of 3 or more),
The step d1 of the diffractive structure adds an optical path difference longer than one wavelength to blue light, adds an optical path difference less than one wavelength to red light,
Each of the flat portions of the diffractive structure is inclined in the direction in which the stairs are raised.
The plurality of flat portions of the diffractive structure are higher toward the optical axis,
2. The compound lens according to claim 1, wherein each flat portion is inclined so that an end portion on a side close to the optical axis is higher than an end portion on a side far from the optical axis.
The optical path difference that the step d1 gives to the blue light having the wavelength λ1 is a constant Cd1 × λ1.
3. The compound lens according to claim 2, wherein a width C1 for inclining the flat portion satisfies 0 <C1 ≦ (Cd1-1).
The plurality of flat portions of the diffractive structure are higher toward the optical axis,
2. The compound lens according to claim 1, wherein each flat portion is inclined so that an end portion on a side close to the optical axis is lower than an end portion on a side far from the optical axis.
The optical path difference that the step d1 gives to the red light having the wavelength λ2 is a constant Cd2 × λ2.
5. The compound lens according to claim 4, wherein a width C2 for inclining the flat portion satisfies 0 <C2 ≦ (1-Cd2).
The optical path difference that the step d1 gives to the infrared light having the wavelength λ3 is a constant Cd3 × λ3.
6. The compound lens according to claim 4, wherein a width C2 for inclining the flat portion satisfies 0 <C2 ≦ (1-Cd3).
A diffractive structure that diffracts light;
A refracting surface for refracting the light,
The diffractive structure has a step-like cross section with one cycle of (M−1) steps and M levels (M is a natural number of 3 or more),
When the width of each flat portion of the diffractive structure is W1, W2,..., W (M-1) and WM in order from the lowest to the highest, the width W1 and the width WM are the widths. A compound lens characterized by being narrower than W2 to width W (M-1).
The step d1 of the diffractive structure adds an optical path difference longer than one wavelength to blue light, adds an optical path difference less than one wavelength to red light,
The wavefront converting action that the diffractive structure gives to the red light is an action opposite to the wavefront converting action that the diffractive structure gives to the blue light. Compound lens.
The compound lens has at least two diffraction regions formed concentrically around the optical axis of light incident on the compound lens;
Of the at least two diffractive regions, the diffractive region other than the outermost diffractive region is formed with the diffractive structure having a stepped cross section,
The step d1 of the diffractive structure gives an optical path difference of approximately 1.25 wavelengths to blue light,
The diffractive structure has a three-step, four-level staircase shape having a height of 0, 1, 2, and 3 times the step d1 in order from the outer peripheral side of the diffractive structure to the optical axis side in one cycle. The compound lens according to claim 1, having a cross section of:
The numerical aperture at which the blue light having the wavelength λ1 is collected through the base material having the thickness t1 is larger than the numerical aperture at which the red light having the wavelength λ2 is condensed through the base material having the thickness t2 larger than the thickness t1. The compound lens according to any one of claims 1 to 9, wherein:
The step d1 of the diffractive structure adds an optical path difference longer than one wavelength to blue light, adds an optical path difference less than one wavelength to red light, and less than one wavelength for infrared light having a wavelength λ3. The optical path difference of
11. The wavefront converting action that the diffractive structure gives to the red light and the infrared light is an action opposite to the wavefront converting action that the diffractive structure gives to the blue light. The compound lens in any one.
The diffractive structure is integrally formed on the refractive surface,
The refractive index nc of the element material of the compound lens is substantially the same for blue light having a wavelength λ1, red light having a wavelength λ2, and infrared light having a wavelength λ3.
(J × λ1), (K × λ2), and (L × λ3) are substantially equal (J, K, and L are natural numbers, and J>M>K> L),
12. The compound lens according to claim 1, wherein the step d1 of the diffractive structure adds an optical path difference of (J × λ1) / M to blue light having a wavelength λ1.
The diffractive structure is integrally formed on the refractive surface,
The refractive index nc of the element material of the compound lens is substantially the same for blue light having a wavelength λ1, red light having a wavelength λ2, and infrared light having a wavelength λ3.
(J × λ1), (K × λ2), and (L × λ3) are substantially equal (J, K, and L are natural numbers, and J>M>K> L),
The step d1 of the diffractive structure has (J × λ1) / (nc-1), (K × λ2) / (nc-1), and (L × λ3) / (nc-1), respectively (1 / M 13. The compound lens according to claim 1, wherein the compound lens has a value within a range between a minimum value and a maximum value among the multiplied values.
The diffractive structure is integrally formed on the refractive surface,
The refractive index of the element material of the compound lens is nb, nr and ni for blue light of wavelength λ1, red light of wavelength λ2 and infrared light of wavelength λ3, respectively.
(J × λ1) / (nb-1), (K × λ2) / (nr-1), and (L × λ3) / (ni-1) are substantially equal (J, K, and L are natural numbers, J>M>K> L),
The level difference d1 of the diffractive structure is (J × λ1) / (nb-1), (K × λ2) / (nr-1), and (L × λ3) / (ni-1), respectively (1 / M 12. The compound lens according to claim 1, wherein the compound lens has a value within a range between a minimum value and a maximum value among the multiplied values.
The compound lens includes a first region including an optical axis of the light, a second region formed in a direction farther from the optical axis than the first region, and the light from the second region. A third region formed in a direction away from the axis,
The diffractive structure is formed in the first region,
The first region collects blue light through the base material having a thickness of t1 onto the recording surface of the first recording medium, and causes the red light to pass through the base material having a thickness of t2 larger than the thickness t1. Condensing on the recording surface of the recording medium, and condensing infrared light onto the recording surface of the third recording medium through a base material having a thickness t3 larger than the thickness t2.
The second region condenses blue light through the base material having the thickness t1 onto the recording surface of the first recording medium, and red light passes through the base material having the thickness t2. Focus on the recording surface of
The compound lens according to any one of claims 11 to 14, wherein the third region condenses blue light on the recording surface of the first recording medium through the base material having the thickness t1. .
The compound lens according to claim 1, wherein the diffractive structure is integrally formed on the refractive surface.
A first light source that emits blue light;
A second light source that emits red light;
The blue light emitted from the first light source is condensed on the recording surface of the first recording medium through the substrate having the thickness t1, and the red light emitted from the second light source is collected from the thickness t1. The compound lens according to any one of claims 1 to 10, which collects light on a recording surface of the second recording medium through a base material having a large thickness t2.
A photodetector that receives the blue light reflected on the recording surface of the first recording medium or the red light reflected on the recording surface of the second recording medium, and outputs an electrical signal according to the amount of received light An optical head device comprising:
A first light source that emits blue light;
A second light source that emits red light;
A third light source that emits infrared light;
The blue light emitted from the first light source is condensed on the recording surface of the first recording medium through the substrate having the thickness t1, and the red light emitted from the second light source is collected from the thickness t1. The light is condensed on the recording surface of the second recording medium through the base material having the large thickness t2, and the infrared light emitted from the third light source is passed through the base material having the thickness t3 larger than the thickness t2. The compound lens according to any one of claims 11 to 16, which collects light on a recording surface of the recording medium of
The blue light reflected on the recording surface of the first recording medium, the red light reflected on the recording surface of the second recording medium, or the infrared light reflected on the recording surface of the third recording medium. An optical head device comprising: a photodetector that receives light and outputs an electrical signal according to the amount of received light.
The optical head device according to claim 17 or 18,
A motor for rotating the optical disc;
An optical disc apparatus comprising: a motor and a control unit that controls the optical head apparatus based on an electrical signal obtained from the optical head apparatus.
An optical disc device according to claim 19,
An optical information device comprising: an information processing unit that processes information recorded on the optical disc device and / or information reproduced from the optical disc device.