Objective optical element and optical pickup apparatus

This application is based on Japanese Patent Application Nos. 2004-154702 filed on May 25, 2004, and 2004-234297 filed on Aug. 11, 2004 in Japanese Patent Office, the entire content of which is hereby incorporated by reference.

The present invention relates to an objective optical element and an optical pickup apparatus, and in particular, to an optical pickup apparatus capable of coping with optical information recording media in different types and to an objective optical element used in the optical pickup apparatus.

There has been a rapid advance of research and development recently, for a high density optical disc system capable of conducting recording and reproducing of information by using a violet semiconductor laser having a wavelength of about 400 nm. As an example, on an optical disc conducting recording and reproducing of information under the specifications including NA 0.85 and light source wavelength 405 nm, namely, on the so-called Blu-ray Disc (BD), there can be recorded information of 20-30 GB per one side of the optical disc having a diameter of 12 cm that is the same in terms of size as DVD (whose specifications include NA 0.6, light source wavelength 650 nm and storage capacity 4.7 GB), and on an optical disc conducting recording and reproducing of information under the specifications including NA 0.65 and light source wavelength 405 nm, namely, on the so-called HD DVD, there can be recorded information of 15-20 GB per one side of the optical disc having a diameter of 12 cm. Hereafter, the optical disc of this kind is called “high density DVD” in the present specification.

Incidentally, if an optical pickup apparatus can only conduct recording and reproducing of information properly for the high density DVD of this kind, the commercial value of the optical pickup apparatus is not sufficient. When giving consideration to current realities where DVD and CD on which various pieces of information are recorded are on the market, it is not sufficient to be capable of conducting recording and reproducing of information properly for high density DVD only, and being capable of conducting recording and reproducing of information properly also for conventional DVD and CD owned by a user, for example, leads to enhancement of commercial value as an optical pickup apparatus of a compatibility type. From this background, an optical system used for the optical pickup apparatus of a compatibility type is required to obtain an excellent spot, for conducting recording and reproducing of information properly for any of high density DVD, and conventional DVD and CD. Though the optical pickup apparatus capable of conducting recording and/or reproducing of information on a compatibility basis for DVD and CD has been put to practical use, the apparatus is still demanded to be smaller in size, thinner in thickness and lower in cost.

When trying to conduct recording and/or reproducing of information for optical discs in different kinds in this case, there exists a problem that the aperture restriction corresponding to numerical aperture NA in the case of using each optical disc is needed. However, when trying to conduct the aperture restriction by using a mechanical shutter that makes an aperture diameter to be variable, the structure becomes complicated and cost increase is caused. For this problem, Patent Document 1 discloses a technology to place a glass flat plate covered by a wavelength selective film in front of an objective lens, and thereby to make the objective lens to have a function to regulate to the aperture corresponding to the wavelength of the light flux to be transmitted. Further, each of Patent Documents 2, 3 and 4 discloses a technology to cover directly the optical surface of the objective lens with a wavelength selective film, and thereby to give a function of aperture restriction to the objective lens.

(Patent Document 1) TOKKAIHEI No. 11-161997

(Patent Document 2) TOKKAI No. 2001-264533

(Patent Document 3) TOKKAI No. 2000-20998

(Patent Document 4) TOKKAI No. 2001-330770

However, in each of Patent Documents 1, 2 and 3, a function of aperture restriction is given selectively, concerning light fluxes respectively for DVD and CD in terms of wavelength. That is, there is neither disclosure nor suggestion, concerning the selective aperture restriction for a light flux with short wavelength of about 400 nm and for a light flux with wavelength other than the aforementioned wavelength. Further, the film described in Patent Document 4 does not transmit the light flux with short wavelength of about 400 nm, and it is difficult to use it for the aperture restriction concerning the light flux with short wavelength of about 400 nm.

The invention has been achieved, in view of the problems mentioned above, and its object is to provide an objective optical system capable of conducting aperture restriction properly even when using a light flux with a short wavelength and a light flux with a wavelength that is different from the foresaid wavelength, and to provide an optical pickup apparatus that uses the aforesaid objective optical system.

An objective optical element described in Item 1 is a structure for use in an optical pickup apparatus having: a first light source for emitting a first light flux with a wavelength λ 1 (380 nm≦λ 1 ≦420 nm); a second light source for emitting a second light flux with a wavelength λ 2 (λ 1 <λ 2 ); an objective optical element for converging the first light flux on an information recording surface of a first optical information recording medium and converging the second light flux on an information recording surface of a second information recording medium. The objective optical element includes: an optical surface including a common area and an exclusive area; and a wavelength selective film formed on at least one of the common area and the exclusive area for transmitting at least one of the first light flux and a light flux with a wavelength excluding the wavelength λ 1 selectively. The common area transmits the first light flux which is formed into a converged spot on the information recording surface of the first optical information recording medium, and transmits the second light flux which is formed into a converged spot on the information recording surface of the second optical information recording medium, and the exclusive area transmits the first light flux which is formed into a converged spot on the information recording surface of the first optical information recording medium, and transmits the second light flux which is not formed into a converged spot on the information recording surface of the second optical information recording medium. Thereby, when relatively large numerical aperture NA of, for example, BD or HD DVD is needed, a light-convergent spot can be narrowed down by causing the light flux emitted from the first light source to be used therefor to pass through the exclusive area and the common area, and when relatively small numerical aperture NA of DVD and CD, on the other hand, is needed, a diameter of a light-convergent spot can be made appropriate by preventing a light flux emitted from the second light source to be used therefor from passing through the exclusive area. Incidentally, the “wavelength selective film” means a film whose transmittance is low for the light flux with the wavelength that is within a prescribed range and is high for the light flux with the wavelength that is outside the prescribed range.

An objective optical system described in Item 13 representing another preferred embodiment of the invention is a structure for use in an optical pickup apparatus having: a first light source for emitting a first light flux with a wavelength λ 1 ; a second light source for emitting a second light flux with a wavelength λ 2 (λ 1 <λ 2 ); an objective optical element for converging the first light flux on an information recording surface of a first optical information recording medium and converging the second light flux on an information recording surface of a second information recording medium. The objective optical element includes; a plurality of optical surfaces including an optical surface S 2 with a curvature R 2 closest to the optical information recording medium and an optical surface S 1 with a curvature R 1 secondary closest to the optical information recording medium, a common area and an exclusive area arranged on at least one of the plurality of optical surfaces; and a film arranged at least one of the common area and the exclusive area. The objective optical element satisfies R 1 >R 2 . The first light flux passes whole area of an effective diameter of the optical surface S 1 and enters into a most outer periphery of an effective diameter of the optical surface S 1 at an incident angle equal to 60 degrees or more. The common area transmits the first light flux which is formed into a converged spot on the information recording surface of the first optical information recording medium, and transmits the second light flux which is formed into a converged spot on the information recording surface of the second optical information recording medium. The exclusive area transmits the first light flux which is formed into a converged spot on the information recording surface of the first optical information recording medium, and transmits the second light flux which is not formed into a converged spot on the information recording surface of the second optical information recording medium. The film transmits the second light flux going from the second light source to the second optical information recording medium when the second light flux enters into the optical surface S 1 at an angle less than a predetermined angle θ 2 , and does not transmit the second light flux going from the second light source to the second optical information recording medium when the second light flux enters into the optical surface S 1 at an incident angle equal to the predetermined angle θ 2 or more. The predetermined angle θ 2 satisfies 25 degrees≦θ 2 ≦50 degrees.

Incidentally, in the present specification, “an angle of incidence” or “an incident angle” means an angle that is formed between a ray of light within an effective diameter of the objective optical element and a normal line on the surface, and “an angle of emergence” or “an emergence angle” means an angle formed between a light of emergence within an effective diameter of the objective optical element and a normal line on the surface. Further, when “the objective optical element” is composed of plural elements, an optical surface closest to the light source on the element closest to the optical information recording medium is handled as S 1 , and an optical surface on the optical information recording medium side is handled as S 2 on the element closest to the optical information recording medium. Further, in the present specification, “an effective diameter” means a range of the optical surface which makes an incident light flux with working wavelength λ to be transmitted or converged so that wavefront aberration may be within 0.07 λrms.

The present structure is achieved by paying attention to that the maximum incident angle of the light flux with wavelength λ 1 and the maximum incident angle of the light flux with wavelength λ 2 are different each other, corresponding to aperture restriction. For example, when relatively large numerical aperture NA such as, for example, BD is required, the maximum incident angle of the light flux emitted from the first light source used therefor becomes 60° or mote, and therefore, the light flux having such maximum incident angle is made to be capable of narrowing down the light-converged spot by causing the light flux to pass through the exclusive area and the common area. On the other hand, when relatively small numerical aperture NA such as DVD and CD is required, an incident angle of the light flux emitted from the second light source used therefor becomes less than prescribed angle θ 2 (provided that 25°≦θ 2 ≦50°), and therefore, the light flux having such incident angle is prevented by the film stated above from passing through the exclusive area, thus, an appropriate light-convergent spot can be formed.

An objective optical element described in Item 27 representing another preferred embodiment of the invention is a structure for use in an optical pickup apparatus having: a first light source for emitting a first light flux with a wavelength λ 1 ; a second light source for emitting a second light flux with a wavelength λ 2 (λ 1 <λ 2 ); an objective optical element for converging the first light flux on an information recording surface of a first optical information recording medium and converging the second light flux on an information recording surface of a second information recording medium. The objective optical element includes; a plurality of optical surfaces including an optical surface S 2 with a curvature R 2 closest to the optical information recording medium and an optical surface S 1 with a curvature R 1 secondary closest to the optical information recording medium, a common area and an exclusive area arranged on at least one of the plurality of optical surfaces; and a film arranged at least one of the common area and the exclusive area. The objective optical element satisfies R 1 >R 2 . The first light flux passes whole area of an effective diameter of the optical surface S 2 and goes out of a most outer periphery of an effective diameter of the optical surface S 2 at an emergence angle equal to 55 degrees or more. The common area transmits the first light flux which is formed into a converged spot on the information recording surface of the first optical information recording medium, and transmits the second light flux which is formed into a converged spot on the information recording surface of the second optical information recording medium. The exclusive area transmits the first light flux which is formed into a converged spot on the information recording surface of the first optical information recording medium, and transmits the second light flux which is not formed into a converged spot on the information recording surface of the second optical information recording medium. The film transmits the second light flux going from the second light source to the second optical information recording medium when the second light flux goes out from the optical surface S 2 at an angle less than a predetermined angle θ 2 ′, and does not transmit the second light flux going from the second light source to the second optical information recording medium when the second light flux goes out from the optical surface S 2 at an angle equal to the predetermined angle θ 2 ′ or more. The predetermined angle θ 2 ′ satisfies 25 degrees≦θ 2 ′≦50 degrees.

The present structure is achieved by paying attention to that the maximum emergence angle of the light flux with wavelength λ 1 and the maximum emergence angle of the light flux with wavelength λ 2 are different each other, corresponding to aperture restriction. For example, when relatively large numerical aperture NA such as, for example, BD is required, the maximum emergence angle of the light flux emitted from the first light source used therefor becomes 55° or more, and therefore, the light flux having such maximum emergence angle is made to be capable of narrowing down the light-converged spot by causing the light flux to pass through the exclusive area and the common area. On the other hand, when relatively small numerical aperture NA such as DVD and CD is required, an angle of emergence of the light flux emitted from the second light source used therefore becomes to be less than the predetermined angle θ 2 ′ (provided that 25°≦θ 2 ′≦50°), and therefore, the light flux having such angle of emergence is prevented by the film stated above from passing through the exclusive area, thus, an appropriate light-convergent spot can be formed.

An objective optical element described in Item 41 representing another preferred embodiment of the invention is a structure for use in an optical pickup apparatus having: a first light source for emitting a first light flux with a wavelength λ 1 ; a second light source for emitting a second light flux with a wavelength λ 2 (λ 1 <λ 2 ); a third light source for emitting a third light flux with a wavelength λ 3 (λ 1 <λ 2 <λ 3 and 0.9<2×λ 1 /λ 3 <1.1); an objective optical element for converging the first light flux on an information recording surface of a first optical information recording medium, converging the second light flux on an information recording surface of a second information recording medium and, and converging the third light flux on an information recording surface of a third information recording medium. The objective optical element includes; a plurality of optical surfaces; an inner area arranged on an area from an optical axis to a first height of at least one of the plurality of optical surfaces, a middle area arranged on an area from the first height to a second height of at least one of the plurality of optical surfaces; an outer area arranged on an area outside of the second height of at least one of the plurality of optical surfaces; a film with a predefined optical property on at least one of the plurality of optical surfaces; and a diffractive structure on at least one of the plurality of optical surfaces. The film transmits the first light flux and the second light flux passing through the inner area, the middle area and the outer area, and does not transmit the third light flux passing through the middle area and the outer area. The diffractive structure makes the second light flux which has passed though the outer area into a flare light on the information recording surface of the second optical information recording medium. Thereby, it is possible to properly conduct recording and/or reproducing of information for an optical information recording medium by complementing characteristics such as, for example, wavelength-selectivity and an angle dependence by using diffracting characteristic of the diffractive structure and by using properly convergence and non-convergence of light fluxes respectively with different wavelengths on an information recording surface.

An objective optical element described in Item 53 representing another preferred embodiment of the invention is a structure for use in an optical pickup apparatus having: a first light source for emitting a first light flux with a wavelength λ 1 ; a second light source for emitting a second light flux with a wavelength λ 2 (λ 1 <λ 2 ); a third light source for emitting a third light flux with a wavelength λ 3 (λ 1 <λ 2 <λ 3 and 0.9<2×λ 1 /λ 3 <1.1); an objective optical element for converging the first light flux on an information recording surface of a first optical information recording medium, converging the second light flux on an information recording surface of a second information recording medium and, converging the third light flux on an information recording surface of a third information recording medium. The objective optical element includes; a plurality of optical surfaces, an inner area arranged on an area from an optical axis to a first height of at least one of the plurality of optical surfaces, a middle area arranged on an area from the first height to a second height of at least one of the plurality of optical surfaces, an outer area arranged on an area outside of the second height of at least one of the plurality of optical surfaces, a wavelength selective film on at least one of the plurality of optical surfaces; and a diffractive-structure on at least one of the plurality of optical surfaces. The wavelength selective film transmits the first light flux and the second light flux passing through the inner area, the middle area and the outer area, and does not transmit the third light flux passing through the middle area and the outer area, and the diffractive structure makes the first light flux which has passed though the outer area into a flare light on the information recording surface of the first optical information recording medium. Thereby, it is possible to properly conduct recording and/or reproducing of information for an optical information recording medium by complementing characteristics such as, for example, wavelength-selectivity and an angle dependence by using diffracting characteristic of the diffractive structure and by using properly convergence and non-convergence of light fluxes respectively with different wavelengths on an information recording surface.

An objective optical element described in Item 65 representing another preferred embodiment of the invention is a structure for use in an optical pickup apparatus having: a first light source for emitting a first light flux with a wavelength λ 1 ; a second light source for emitting a second light flux with a wavelength λ 2 (λ 1 <λ 2 ); a third light source for emitting a third light flux with a wavelength λ 3 (λ 1 <λ 2 <λ 3 and 0.9<2×λ 1 /λ 3 <1.1); an objective optical element for converging the first light flux on an information recording surface of a first optical information recording medium, converging the second light flux on an information recording surface of a second information recording medium and, converging the third light flux on an information recording surface of a third information recording medium. The objective optical element includes; a plurality of optical surfaces; an inner area arranged on an area from an optical axis to a first height of at least one of the plurality of optical surfaces; a middle area arranged on an area from the first height to a second height of at least one of the plurality of optical surfaces; an outer area arranged on an area outside of the second height of at least one of the plurality of optical surfaces; a third film arranged in the inner area; a second film arranged in the middle area; a third film arranged in the outer area. The third film transmits the first light flux, the second light flux, and the third light flux. The second film transmits the first light flux and the second light flux, and does not transmit the third light flux. The first film transmits the first light flux, and does not transmit the second light flux and the third light flux. Thereby, it is possible to properly conduct recording and/or reproducing of information for each optical information recording medium by changing, for example, the film thickness locally, and by using properly convergence and non-convergence of light fluxes respectively with three or more different wavelengths on an information recording surface, because only a light flux emitted from the first light source passes.

The invention makes it possible to provide an objective optical element for which an aperture restriction can be properly conducted even when using a light flux with a short wavelength or a light flux with a wavelength that is different from the short wavelength, and to provide an optical pickup apparatus employing the aforesaid objective optical element.

FIGS. 1( a ) and 1 ( b ) show a schematic cross section of an optical pickup apparatus capable of conducting recording and reproducing of information for an optical disc.

FIG. 2 shows a schematic cross section of objective lens OBJ- 1 in Example 1.

FIG. 3 is a diagram showing a transmittance of a film covering the objective lens OBJ- 1 for the wavelength.

FIG. 4 is a diagram showing a transmittance of a film covering the objective lens OBJ- 1 for the wavelength.

FIG. 5 is a diagram showing a transmittance of a film covering the objective lens OBJ- 1 for the wavelength.

FIG. 6 is a diagram showing a transmittance of a film covering the objective lens in Example 2 for the wavelength.

FIG. 7 is a diagram showing a transmittance of a film covering the objective lens in Example 3 for the wavelength.

FIG. 8 is a diagram showing a transmittance of a film covering the objective lens OBJ- 2 in Example 4 for the wavelength.

FIG. 9 is a diagram showing a transmittance of a film covering the objective lens OBJ- 2 in Example 4 for the wavelength.

FIG. 10 is a diagram showing a transmittance of a film covering the objective lens OBJ- 2 in Example 4 for the wavelength.

FIG. 11 shows a schematic cross section of objective lens OBJ- 3 in Example 5.

FIG. 12 is a diagram showing a transmittance of a film covering the objective lens OBJ- 3 in Example 5 for the wavelength.

FIG. 13 is a diagram showing a transmittance of a film covering the objective lens OBJ- 3 in Example 5 for the wavelength.

FIG. 14 is a diagram showing a transmittance of a film covering the objective lens OBJ- 3 in Example 5 for the wavelength.

FIG. 15 shows a schematic cross section of objective lens OBJ- 4 in Example 6.

FIG. 16 shows a schematic cross section of objective lens OBJ- 5 in Example 7.

FIG. 17 shows a schematic cross section of objective lens OBJ- 6 in Example 8.

FIG. 18 is a diagram showing a transmittance of a film covering the objective lens OBJ- 6 in Example 8 for the wavelength.

FIG. 19 is a diagram showing a transmittance of a film covering the objective lens OBJ- 6 in Example 8 for the wavelength.

FIG. 20 is a diagram showing a transmittance of a film covering the objective lens OBJ- 6 in Example 8 for the wavelength.

FIG. 21 shows a schematic cross section of objective lens OBJ- 7 in Example 9.

Preferred embodiments of the invention will be explained as follow.

In an objective optical element described in Item 2, it is preferable that the wavelength λ 2 satisfies 630 nm≦λ 2 ≦670 nm in the structure described in Item 1. It is therefore possible to conduct recording and/or reproducing of information on a compatible basis, for example, between BD and DVD or between HD DVD and DVD.

In an objective optical element described in Item 3, it is preferable that the optical pickup apparatus further has a third light source for emitting a third light flux with wavelength λ 3 (λ 1 <λ 2 <λ 3 ), the objective optical element converges the third light flux on an information recording surface of the third optical information recording medium, and the wavelength λ 3 satisfies 760 nm≦λ 3 ≦800 nm, in the structure described in Item 2. It is therefore possible to conduct recording and/or reproducing of information on a compatible basis, for example, for BD, DVD and CD, or for HD DVD, DVD and CD.

In an objective optical element described in Item 4, it is preferable that the objective optical element further includes a diffractive structure on an optical surface of the objective optical element for limiting a numerical aperture for the second light flux, in the structure described in Item 3. Therefore, it is possible to properly conduct recording and/or reproducing of information for an optical information recording medium by combining a wavelength selective film and a diffractive structure and thereby by using properly convergence and non-convergence of light fluxes respectively with three or more different wavelengths on an information recording surface.

In the present specification, “a diffractive structure for restricting an aperture” or “a diffractive structure for limiting a numerical aperture” means that light with a specific wavelength entering the diffractive structure is made to be a flare on an information recording surface. In the present specification, “flare component (flare light)” means a light flux with a numerical aperture that is not less than the prescribed numerical aperture that has been subjected to actions which do not contribute to formation of spots necessary for recording or reproducing on a prescribed information recording surface, and it means, for example, a light flux causing aberration with wavefront aberration of not less than 0.07 λrms (λ represents a wavelength in the case of using CD, in this case) for incident light flux corresponding to the numerical aperture of 0-0.43 necessary for conducting recording or reproducing for CD, or to the numerical aperture higher than 0.45, in the case of recording or reproducing for CD. “Making to be a flare” means that the incident light flux is made to be of characteristics to irradiate an information recording surface with a light flux that causes aberration.

In an objective optical element described in Item 5, it is preferable that the objective optical element further includes a diffractive structure on an optical surface of the objective optical element for limiting a numerical aperture for each of the first light flux and the third light flux, in the structure described in Item 3. Since λ 3 is about twice as long as λ 1 , there is an occasion that diffracting actions of the diffractive structure become common. It is therefore possible to use properly convergence and non-convergence of light fluxes respectively with three or more different wavelengths on an information recording surface.

In an objective optical element described in Item 6, it is preferable that the common area includes an optical axis and the exclusive area is arranged outside of the common area, in the structure described in any one of Items 1-5.

In an objective optical element described in Item 7, the wavelength selective film is formed of one type of film having a same layer construction within an optical surface including wavelength selective film of the objective optical element, in the structure described in any one of Items 1-6.

In an objective optical element described in Item 8, it is preferable that an optical surface including the wavelength selective film of the objective optical element is a plane surface, the wavelength selective film transmits the third light flux going toward the third optical information recording medium when the third light flux goes from the optical surface including the wavelength selective film to outside of the objective optical element at an angle less than a predetermined angle θ 3 e , and does not transmit the third light flux going toward the third optical information recording medium when the third light flux goes from the optical surface including the wavelength selective film to outside of the objective optical element at an angle equal to the predetermined angle θ 3 e or more, and the predetermined angle θ 3 e satisfies 25 degrees≦θ 3 e ≦35 degrees, in the structure described in any one of Items 3-7.

In an objective optical element described in Item 9, it is preferable that an optical surface including the wavelength selective film of the objective optical element is a plane surface, the wavelength selective film transmits the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the wavelength selective film at an angle less than a predetermined angle θ 3 f , and does not transmit the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the wavelength selective film at an angle equal to the predetermined angle θ 3 f or more, and the predetermined angle θ 3 f satisfies 25 degrees≦θ 3 f ≦35 degrees, in the structure described in any one of Items 3-8.

In an objective optical element described in Item 10, it is preferable that an optical surface including the wavelength selective film of the objective optical element is a curved surface, the wavelength selective film transmits the third light flux going toward the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the wavelength selective film at an angle less than a predetermined angle θ 3 g , and does not transmit the third light flux going toward the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the wavelength selective film at an angle equal to the predetermined angle θ 3 g or more, and the predetermined angle θ 3 g satisfies 40 degrees≦θ 3 g ≦50 degrees, in the structure described in any one of Items 3-9.

In an objective optical element described in Item 11, it is preferable that an optical surface including the wavelength selective film of the objective optical element is a curved surface, the wavelength selective film transmits the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux goes from the optical surface including the wavelength selective film to outside of the objective optical element at an angle less than a predetermined angle θ 3 h , and does not transmit the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux goes from the optical surface including the wavelength selective film to outside of the objective optical element at an angle equal to the predetermined angle θ 3 h or more, and the predetermined angle θ 3 h satisfies 40 degrees≦θ 3 h ≦50 degrees, in the structure described in any one of Items 3-10.

In an objective optical element described in Item 12, it is preferable that a circular polarized light flux enters the objective optical element, in the structure described in any one of Items 1-11.

In an objective optical element described in Item 14, it is preferable that the film mentioned above is arranged on the optical surface S 1 , in the structure described in Item 13.

In an objective optical element described in Item 15, it is preferable that the film mentioned above is arranged on the optical surface S 2 , in the structure described in Item 13. When curvature R 1 of the optical surface S 1 is greater than curvature R 2 of the optical surface S 2 , there is a merit that a uniform film can easily be made, when the film is formed on the optical surface S 1 through sputtering for example.

In an objective optical element described in Item 16, it is preferable that the second light flux enters into a most outer periphery of an effective diameter of the optical surface S 1 at an incident angle equal to 45 degrees or more, and less than 60 degrees, in the structure described in any one of Items 13-15. Accordingly, it is possible to conduct recording and/or reproducing of information on a compatible basis for BD and DVD, for example.

In an objective optical element described in Item 17, it is preferable that the optical pickup apparatus further has a third light source for emitting a third light flux with wavelength λ 3 (λ 1 l<λ 2 <λ 3 ), and the objective optical element converges the third light flux on an information recording surface of the third optical information recording medium, while, the third light flux enters into a most outer periphery of an effective diameter of the optical surface S 1 at an incident angle that is equal to 30 degrees or more, and is less than 50 degrees, in the structure described in any one of Items 13-16. It is therefore possible to conduct recording and/or reproducing of information on a compatible basis, for example, for BD, DVD and CD.

In an objective optical element described in Item 18, it is preferable that the objective optical element further includes a diffractive structure arranged on one of the plurality of optical surfaces for limiting a numerical aperture for the second light flux, in the structure described in Item 17. Therefore, it is possible to properly conduct recording and/or reproducing of information for an optical information recording medium by complementing characteristics of the wavelength selective film by using characteristics of the diffractive structure and by using properly convergence and non-convergence of light fluxes respectively with different wavelengths on an information recording surface.

In an objective optical element described in Item 19, it is preferable that the objective optical element further includes a diffractive structure arranged on one of the plurality of optical surfaces for limiting a numerical aperture for each of the first light flux and the third light flux, in the structure described in Item 17 or Item 18. Therefore, it is possible to properly conduct recording and/or reproducing of information for an optical information recording medium by complementing characteristics of the wavelength selective film by using characteristics of the diffractive structure and by using properly convergence and non-convergence of light fluxes respectively with different wavelengths on an information recording surface.

In an objective optical element described in Item 20, it is preferable that the common area includes an optical axis and the exclusive area is arranged outside of the common area, in the structure described in any one of Items 13-19.

In an objective optical element described in Item 21, the film is formed of one type of film having a same layer construction within an optical surface including the film of the objective optical element, in the structure described in any one of Items 13-20.

In an objective optical element described in Item 22, it is preferable that an optical surface including the film of the objective optical element is a plane surface, the film transmits the third light flux going toward the third optical information recording medium when the third light flux goes from the optical surface including the film to outside of the objective optical element at an angle less than a predetermined angle θ 3 e , and does not transmit the third light flux going to the third optical information recording medium when the third light flux goes from the optical surface including the film to outside of the objective optical element at an angle equal to the predetermined angle θ 3 e or more, and the predetermined angle θ 3 e satisfies 25 degrees≦θ 3 e ≦35 degrees, in the structure described in any one of Items 17-33.

In an objective optical element described in Item 23, it is preferable that an optical surface including the film of the objective optical element is a plane surface, the film transmits the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the wavelength selective film at an angle less than a predetermined angle θ 3 f , and does not transmit the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the wavelength selective film at an angle equal to the predetermined angle θ 3 f or more, and the predetermined angle θ 3 f satisfies 25 degrees≦θ 3 f ≦35 degrees, in the structure described in any one of Items 17-22.

In an objective optical element described in Item 24, it is preferable that an optical surface including the film of the objective optical element is a curved surface, the film transmits the third light flux going toward the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the wavelength selective film at an angle less than a predetermined angle θ 3 g , and does not transmit the third light flux going toward the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the wavelength selective film at an angle equal to the predetermined angle θ 3 g or more, and the predetermined angle θ 3 g satisfies 40 degrees≦θ 3 g ≦50 degrees, in the structure described in any one of Items 17-23.

In an objective optical element described in Item 25, it is preferable that an optical surface including the film of the objective optical element is a curved surface, the film transmits the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux goes from the optical surface including the wavelength selective film to outside of the objective optical element at an angle less than a predetermined angle θ 3 h , and does not transmit the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux goes from the optical surface including the wavelength selective film to outside of the objective optical element at an angle equal to the predetermined angle θ 3 h or more, and the predetermined angle θ 3 h satisfies 40 degrees≦θ 3 h ≦50 degrees, in the structure described in any one of Items 17-24.

In an objective optical element described in Item 26, it is preferable that a circular polarized light flux enters the objective optical element, in the structure described in any one of Items 13-25.

In an objective optical element described in Item 28, it is preferable that the film is arranged on the optical surface S 1 , in the structure described in Items 27.

In an objective optical element described in Item 29, it is preferable that the film is arranged on the optical surface S 2 , in the structure described in Items 27. When curvature R 1 of the optical surface S 1 is greater than curvature R 2 of the optical surface S 2 , there is a merit, for example, that a uniform film can easily be formed when forming the film on the optical surface S 1 through sputtering or the like.

In an objective optical element described in Item 30, it is preferable that the second light flux goes out of a most outer periphery of an effective diameter of the optical surface S 2 at an emergence angle equal to 35 degrees or more, and less than 60 degrees, in the structure described in any one of Items 27-29. It is therefore possible to conduct recording and/or reproducing of information for BD and DVD on a compatible basis.

In an objective optical element described in Item 31, it is preferable that the optical pickup apparatus further has a third light source for emitting a third light flux with wavelength λ 3 (λ 1 <λ 2 <λ 3 ), and the objective optical element converges the third light flux on an information recording surface of the third optical information recording medium, while, the third light flux goes out of a most outer periphery of an effective diameter of the optical surface S 2 at an emergence angle equal to 20 degrees or more, and less than 35 degrees, in the structure described in any one of Items 27-30. It is therefore possible to conduct recording and/or reproducing of information on a compatible basis, for example, for BD, DVD and CD.

In an objective optical element described in Item 32, it is preferable that the objective optical element further includes a diffractive structure arranged on one of the plurality of optical surfaces for limiting a numerical aperture for the second light flux, in the structure described in Item 31. Therefore, it is possible to properly conduct recording and/or reproducing of information for an optical information recording medium by complementing characteristics of the wavelength selective film by using characteristics of the diffractive structure and by using properly convergence and non-convergence of light fluxes respectively with different wavelengths on an information recording surface.

In an objective optical element described in Item 33, it is preferable that the objective optical element further comprising: a diffractive structure arranged on one of the plurality of optical surfaces for limiting a numerical aperture for each of the first light flux and the third light flux, in the structure described in Item 31 or Item 32. Therefore, it is possible to properly conduct recording and/or reproducing of information for an optical information recording medium by complementing characteristics of the wavelength selective film by using characteristics of the diffractive structure and by using properly convergence and non-convergence of light fluxes respectively with different wavelengths on an information recording surface.

In an objective optical element described in Item 34, it is preferable that the common area is provided within a range including an optical axis of the objective optical element, and the exclusive area is arranged outside the common area, in the structure described in any one of Items 27-33.

In an objective optical element described in Item 35, the film is formed of one type of film having a same layer construction within an optical surface including the film of the objective optical element, in the structure described in any one of Items 27-34.

In an objective optical element described in Item 36, it is preferable that an optical surface including the film of the objective optical element is a plane surface, the film transmits the third light flux going toward the third optical information recording medium when the third light flux goes from the optical surface including the film to outside of the objective optical element at an angle less than a predetermined angle θ 3 e , and does not transmit the third light flux going to the third optical information recording medium when the third light flux goes from the optical surface including the film to outside of the objective optical element at an angle equal to the predetermined angle θ 3 e or more, and the predetermined angle θ 3 e satisfies 25 degrees≦θ 3 e ≦35 degrees, in the structure described in any one of Items 31-34.

In an objective optical element described in Item 37, it is preferable that the optical surface including the film of the objective optical element is a plane surface, the film transmits the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the wavelength selective film at an angle less than a predetermined angle θ 3 f , and does not transmit the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the film at an angle equal to the predetermined angle θ 3 f or more, and the predetermined angle θ 3 f satisfies 25 degrees≦θ 3 f ≦35 degrees, in the structure described in any one of Items 31-34.

In an objective optical element described in Item 38, it is preferable that an optical surface including the film of the objective optical element is a curved surface, the film transmits the third light flux going toward the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the film at an angle less than a predetermined angle θ 3 g , and does not transmit the third light flux going toward the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the film at an angle equal to the predetermined angle θ 3 g or more, and the predetermined angle θ 3 g satisfies 40 degrees≦θ 3 g ≦50 degrees, in the structure described in any one of Items 31-37.

In an objective optical element described in Item 39, it is preferable that an optical surface including the film of the objective optical element is a curved surface, the film transmits the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux goes from the optical surface including the film to outside of the objective optical element at an angle less than a predetermined angle θ 3 h , and does not transmit the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux goes from the optical surface including the film to outside of the objective optical element at an angle equal to the predetermined angle θ 3 h or more, and the predetermined angle θ 3 h satisfies 40 degrees≦θ 3 h ≦50 degrees, in the structure described in any one of Items 31-38.

In an objective optical element described in Item 40, it is preferable that a circular polarized light flux enters the objective optical element, in the structure described in any one of Items 27-39.

In an objective optical element described in Item 42, it is preferable that the film has wavelength-selectivity so as to transmit at least one of the first and third fluxes, and the third light flux selectively, in the structure described in Item 41, which makes it possible to conduct aperture restriction properly when, for example, CD is used.

In an objective optical element described in Item 43, it is preferable that when an optical surface S 1 is one of the plurality of optical surfaces which is secondary closest to the optical information recording medium, the film transmits the third light flux going toward the third optical information recording medium when the third light flux enters from a light-source side of the objective optical element into the optical surface S 1 at an angle less than a predetermined angle θ 3 a , and does not transmit the third light flux going toward the third optical information recording medium when the third light flux enters from the light-source side into the optical surface S 1 at an angle equal to the predetermined angle θ 3 a or more, and the predetermined angle θ 3 a satisfies 40 degrees≦θ 3 a ≦50 degrees, in the structure described in Item 41 or Item 42. Thus, it is possible to restrict an aperture properly when CD is used by eliminating unwanted light in, for example, incident light.

In an objective optical element described in Item 44, it is preferable that when an optical surface S 2 is one of the plurality of optical surfaces which is closest to the optical information recording medium, the film transmits the third light flux going toward the third optical information recording medium when the third light flux goes out from the optical surface S 2 to an optical-information-recording-medium side of the objective element at an angle less than a predetermined angle θ 3 b , and does not transmit the third light flux going toward the third optical information recording medium when the third light flux goes out from the optical surface S 2 to an optical-information-recording-medium side of the objective element at an angle equal to the predetermined angle θ 3 b or more, and the predetermined angle θ 3 b satisfies 25 degrees≦θ 3 b ≦35 degrees in the structure described in any one of Items 41-43. Thus, it is possible to restrict an aperture properly when CD is used by eliminating unwanted light in, for example, incident light.

In an objective optical element described in Item 45, it is preferable that when an optical surface S 2 is one of the plurality of optical surfaces which is closest to the optical information recording medium, the film transmits the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux enters from an optical-information-recording-medium side of the objective element into the optical surface S 2 at an angle less than a predetermined angle θ 3 c , and does not transmit the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux enters from the optical-information-recording-medium side of the objective element into the optical surface S 2 at an angle equal to the predetermined angle θ 3 c or more, and the predetermined angle θ 3 c satisfies 25 degrees≦θ 3 c ≦35 degrees, in the structure described in Item 41 or Item 42. Thus, it is possible to improve the detecting accuracy of a photodetector by eliminating unwanted light in reflected light coming from, for example, the optical information recording medium.

In an objective optical element described in Item 46, it is preferable that when an optical surface S 1 is one of the plurality of optical surfaces which is secondary closest to the optical information recording medium, the film transmits the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux goes out from the optical surface S 1 to a light-source side of the objective element at an angle less than a predetermined angle θ 3 d , and does not transmit the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux goes out from the optical surface S 1 to a light source side of the objective element at an angle equal to the predetermined angle θ 3 d or more, and the predetermined angle θ 3 d satisfies 40 degrees≦θ 3 d ≦50 degrees, in the structure described in any one of Items 41, 42 and 45. Thus, it is possible to improve the detecting accuracy of a photodetector by eliminating unwanted light in reflected light coming from, for example, the optical information recording medium.

In an objective optical element described in Item 47, the film is formed of one type of film having a same layer construction within an optical surface including the film of the objective optical element, in the structure described in any one of Items 41-46.

In an objective optical element described in Item 48, it is preferable that an optical surface including the film of the objective optical element is a plane surface, the film transmits the third light flux going toward the third optical information recording medium when the third light flux goes from the optical surface including the film to outside of the objective optical element at an angle less than a predetermined angle θ 3 e , and does not transmit the third light flux going to the third optical information recording medium when the third light flux goes from the optical surface including the film to outside of the objective optical element at an angle equal to the predetermined angle θ3e or more, and the predetermined angle θ 3 e satisfies 25 degrees≦θ 3 e ≦35 degrees, in the structure described in any one of Items 41-47.

In an objective optical element described in Item 49, it is preferable that an optical surface including the film of the objective optical element is a plane surface, the film transmits the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the film at an angle less than a predetermined angle θ 3 f , and does not transmit the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the film at an angle equal to the predetermined angle θ 3 f or more, and the predetermined angle θ 3 f satisfies 25 degrees≦θ 3 f ≦35 degrees, in the structure described in any one of Items 41-48.

In an objective optical element described in Item 50, it is preferable that an optical surface including the film of the objective optical element is a curved surface, the film transmits the third light flux going toward the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the film at an angle less than a predetermined angle θ 3 g , and does not transmit the third light flux going toward the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the film at an angle equal to the predetermined angle θ 3 g or more, and the predetermined angle θ 3 g satisfies 40 degrees≦θ 3 g ≦50 degrees, in the structure described in any one of Items 41-49.

In an objective optical element described in Item 51, it is preferable that an optical surface including the film of the objective optical element is a curved surface, the film transmits the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux goes from the optical surface including the film to outside of the objective optical element at an angle less than a predetermined angle θ 3 h , and does not transmit the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux goes from the optical surface including the film to outside of the objective optical element at an angle equal to the predetermined angle θ 3 h or more, and the predetermined angle θ 3 h satisfies 40 degrees≦θ 3 h ≦50 degrees, in the structure described in any one of Items 41-50.

In an objective optical element described in Item 52, it is preferable that a circular polarized light flux enters the objective optical element, in the structure described in any one of Items 41-51.

In an objective optical element described in Item 54, it is preferable that the wavelength selective film has wavelength-selectivity that makes a first light flux, a second light flux and a third light flux to be transmitted selectively, in the structure described in Item 53, which makes it possible to conduct aperture restriction properly when, for example, CD is used.

In an objective optical element described in Item 55, it is preferable that when an optical surface S 1 is one of the plurality of optical surfaces which is secondary closest to the optical information recording medium, the wavelength selective film transmits the third light flux going toward the third optical information recording medium when the third light flux enters from a light-source side of the objective optical element into the optical surface S 1 at an angle less than a predetermined angle θ 3 a , and does not transmit the third light flux going toward the third optical information recording medium when the third light flux enters from the light-source side into the optical surface S 1 at an angle equal to the predetermined angle θ 3 a or more, and the predetermined angle θ 3 a satisfies 40 degrees≦θ 3 a ≦50 degrees, in the structure described in Item 53 or Item 54. Thus, it is possible to restrict an aperture properly when CD is used by eliminating unwanted light in, for example, incident light.

In an objective optical element described in Item 56, it is preferable that when an optical surface S 2 is one of the plurality of optical surfaces which is closest to the optical information recording medium, the wavelength selective film transmits the third light flux going toward the third optical information recording medium when the third light flux goes out from the optical surface S 2 to an optical-information-recording-medium side of the objective element at an angle less than a predetermined angle θ 3 b , and does not transmit the third light flux going toward the third optical information recording medium when the third light flux goes out from the optical surface S 2 to an optical-information-recording-medium side of the objective element at an angle equal to the predetermined angle θ 3 b or more, and the predetermined angle θ 3 b satisfies 25 degrees≦θ 3 b ≦35 degrees in the structure described in any one of Items 53-55. Thus, it is possible to restrict an aperture properly when CD is used by eliminating unwanted light in, for example, incident light.

In an objective optical element described in Item 57, it is preferable that when an optical surface S 2 is one of the plurality of optical surfaces which is closest to the optical information recording medium, the wavelength selective film transmits the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux enters from an optical-information-recording-medium side of the objective element into the optical surface S 2 at an angle less than a predetermined angle θ 3 c , and does not transmit the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux enters from the optical-information-recording-medium side of the objective element into the optical surface S 2 at an angle equal to the predetermined angle θ 3 c or more, and the predetermined angle. θ 3 c satisfies 25 degrees≦θ 3 c ≦35 degrees, in the structure described in Item 53 or Item 54. Thus, it is possible to improve the detecting accuracy of a photodetector by eliminating unwanted light in reflected light coming from, for example, the optical information recording medium.

In an objective optical element described in Item 58, it is preferable that when an optical surface S 1 is one of the plurality of optical surfaces which is secondary closest to the optical information recording medium, the wavelength selective film transmits the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux goes out from the optical surface S 1 to a light-source side of the objective element at an angle less than a predetermined angle θ3d, and does not transmit the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux goes out from the optical surface S 1 to a light source side of the objective element at an angle equal to the predetermined angle θ 3 d or more, and the predetermined angle θ 3 d satisfies 40 degrees≦θ 3 d ≦50 degrees, in the structure described in any one of Items 53, 54 and 57. Thus, it is possible to improve the detecting accuracy of a photodetector by eliminating unwanted light in reflected light coming from, for example, the optical information recording medium.

In an objective optical element described in Item 59, the wavelength selective film is formed of one type of film having a same layer construction within an optical surface including the wavelength selective film of the objective optical element, in the structure described in any one of Items 53-58.

In an objective optical element described in Item 60, it is preferable that an optical surface including the wavelength selective film is a plane surface, the wavelength selective film transmits the third light flux going toward the third optical information recording medium when the third light flux goes from the optical surface including the wavelength selective film to outside of the objective optical element at an angle less than a predetermined angle θ 3 e , and does not transmit the third light flux going toward the third optical information recording medium when the third light flux goes from the optical surface including the wavelength selective film to outside of the objective optical element at an angle equal to the predetermined angle θ 3 e or more, and the predetermined angle θ 3 e satisfies 25 degrees≦θ 3 e ≦35 degrees, in the structure described in any one of Items 53-59.

In an objective optical element described in Item 61, it is preferable that an optical surface including the wavelength selective film is a plane surface, the wavelength selective film transmits the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the wavelength selective film at an angle less than a predetermined angle θ 3 f , and does not transmit the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the wavelength selective film at an angle equal to the predetermined angle θ 3 f or more, and the predetermined angle θ 3 f satisfies 25 degrees≦θ 3 f ≦35 degrees, in the structure described in any one of Items 53-60.

In an objective optical element described in Item 62, it is preferable that an optical surface including the wavelength selective film is a curved surface, the wavelength selective film transmits the third light flux going toward the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the wavelength selective film at an angle less than a predetermined angle θ 3 g , and does not transmit the third light flux going toward the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the wavelength selective film at an angle equal to the predetermined angle θ 3 g or more, and the predetermined angle θ 3 g satisfies 40 degrees≦θ 3 g ≦50 degrees, in the structure described in any one of Items 53-61.

In an objective optical element described in Item 63, it is preferable that an optical surface including the wavelength selective film is a curved surface, the wavelength selective film transmits the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux goes from the optical surface including the wavelength selective film to outside of the objective optical element at an angle less than a predetermined angle θ 3 h , and does not transmit the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux goes from the optical surface including the wavelength selective film to outside of the objective optical element at an angle equal to the predetermined angle θ 3 h or more, and the predetermined angle θ 3 h satisfies 40 degrees≦θ 3 h ≦50 degrees, in the structure described in any one of Items 53-62.

In an objective optical element described in Item 64, it is preferable that a circular polarized light flux enters the objective optical element, in the structure described in any one of Items 53-62.

In an objective optical element described in Item 66, it is preferable that an optical surface including the first film is a plane surface, the first film transmits the second light flux going toward the second optical information recording medium when the second light flux goes from the optical surface including the first film to outside of the objective optical element at an angle less than θ 2 e , and does not transmit the second light flux going toward the second optical information recording medium when the second light flux goes from the optical surface including the first film to outside of the objective optical element at an angle equal to θ 2 e or more, and the θ 2 e satisfies 35 degrees≦θ 2 e ≦45 degrees, in the structure described in Item 65.

In an objective optical element described in Item 67, it is preferable that an optical surface including the first film is a plane surface, the first film transmits the second light flux reflected by the information recording surface of the second optical information recording medium when the second light flux enters from outside of the objective optical element into the optical surface including the first film at an angle less than θ 2 f , and does not transmit the second light flux reflected by the information recording surface of the second optical information recording medium when the second light flux enters from outside of the objective optical element into the optical surface including the first film at an angle equal to θ 2 f or more, and the θ 2 f satisfies 35 degrees≦θ 2 f ≦45 degrees, in the structure described in Item 65 or Item 66.

In an objective optical element described in Item 68, it is preferable that an optical surface including the second film is a plane surface, the second film transmits the third light flux going toward the third optical information recording medium when the third light flux goes from the optical surface including the second film to outside of the objective optical element at an angle less than a predetermined angle θ 3 k , and does not transmit the third light flux going toward the third optical information recording medium when the third light flux goes from the optical surface including the second film to outside of the objective optical element at an angle equal to the predetermined angle θ 3 k or more, and the predetermined angle θ 3 k satisfies 25 degrees≦θ 3 k ≦35 degrees, in the structure described in any one of Items 65-67.

In an objective optical element described in Item 69, it is preferable that an optical surface including the second film is a plane surface, the second film transmits the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the second film at an angle less than a predetermined angle θ 3 m , and does not transmit the third light flux reflected by the information recording surface of the third optical information recording medium when the third light flux enters from outside of the objective optical element into the optical surface including the second film at an angle equal to the predetermined angle θ 3 m or more, and the predetermined angle θ 3 m satisfies 25 degrees≦θ 3 m ≦35 degrees, in the structure described in any one of Items 65-68.

In an objective optical element described in Item 70, it is preferable that a circular polarized light flux enters the objective optical element, in the structure described in any one of Items 65-69.

In the objective optical element, it is preferable that the first-third films are formed at least two types of films having different layer constructions within the optical surface including the films of the objective optical element, and each film has a circular aperture having its center on the optical axis.

In the objective optical element, it is preferable that the film contains a low refractive index material whose refractive index n for light with λ=500 nm satisfies 1.3≦n≦1.55, and a high refractive index material whose refractive index n satisfies 1.7≦n≦2.5.

In the objective optical element, it is preferable that the low refractive index material is a material whose main component is MgF 2 or SiO 2 , and the high refractive index material is a material whose main component is TiO 2 , Ta 2 O 5 , Nb 2 O 3 , ZrO 2 , CeO 2 , HfO 2 , or CeF 3 in the structure.

In the present specification, “the main component” is one having the highest content among components constituting the material.

In the objective optical element, it is preferable that the objective optical element is made of plastic.

In the objective optical element, it is preferable that the objective optical element is made of glass.

In the objective optical element, it is preferable that the objective optical element is made of plastic and glass.

In the objective optical element, it is preferable that the objective optical element is composed of a single optical element.

In the objective optical element, it is preferable that the objective optical element is composed of a plurality of optical elements.

An optical pickup apparatus described in Item 71 has a first light source for emitting a first light flux with a wavelength λ 1 (380 nm≦λ 1 ≦420 nm); a second light source for emitting a second light flux with a wavelength λ 2 (λ 1 <λ 2 ); and the objective optical element described in any one of Items 1-12.

An optical pickup apparatus described in Item 72 has a first light source for emitting a first light flux with a wavelength λ 1 (380 nm≦λ 1 ≦420 nm); a second light source for emitting a second light flux with a wavelength λ 2 (λ 1 ≦λ 2 ); and the objective optical element of any one of Items 13-26.

An optical pickup apparatus described in Item 73 has a first light source for emitting a first light flux with a wavelength λ 1 ; a second light source for emitting a second light flux with a wavelength λ 2 (λ 1 <λ 2 ); and the objective optical element of any one of Items 27-40.

An optical pickup apparatus described in Item 74 has: a first light source for emitting a first light flux with a wavelength λ 1 ; a second light source for emitting a second light flux with a wavelength λ 2 (λ 1 <λ 2 ); a third light source for emitting a third light flux with a wavelength λ 3 (λ 1 <λ 2 <λ 3 and 0.9<2×λ1/λ3<1.1); and the objective optical element of any one of Items 41-52.

An optical pickup apparatus described in Item 75 has: a first light source for emitting a first light flux with a wavelength λ 1 ; a second light source for emitting a second light flux with a wavelength λ 2 (λ 1 <λ 2 ); a third light source for emitting a third light flux with a wavelength λ 3 (λ 1 <λ 2 <λ 3 and 0.9<2×λ1/λ3<1.1); and the objective optical element of any one of Items 53-64.

An optical pickup apparatus described in Item 76 has: a first light source for emitting a first light flux with a wavelength λ 1 ; a second light source for emitting a second light flux with a wavelength λ 2 (λ 1 <λ 2 ); a third light source for emitting a third light flux with a wavelength λ 3 (λ 1 <λ 2 <λ 3 and 0.9<2×λ1/λ3<1.1); and the objective optical element of any one of Items 65-70.

In the present specification, an expression of the objective optical element means, in a narrow sense, an optical element having a light-converging function arranged to be closest to an optical information recording medium (which is also called an optical disc) to face it under the condition that the optical information recording medium is inserted in an optical pickup apparatus, while, the objective optical element means, in a wide sense, an optical element that can be moved together with the aforementioned optical element by an actuator, at least in its optical axis direction. In the present specification, therefore, numerical aperture NA of an objective optical element on the optical information recording medium side (image side) means numerical aperture NA of the surface closest to an optical information recording medium on the objective optical element. Further, in the present specification, necessary numerical aperture NA is assumed to show a numerical aperture prescribed by the standard of each optical information recording medium, or a numerical aperture of an objective optical element having diffraction limit capacity which makes it possible to obtain a necessary spot for conducting recording or reproducing of information, corresponding to a wavelength of a light source to be used for each optical information recording medium.

FIG. 1( a ) is a diagram showing schematically the structure of optical pickup apparatus PU 1 that can conduct recording and reproducing of information properly for any of high density optical disc HD (including BD or HD DVD), DVD and CD, while, FIG. 1( b ) is a front view of a light source unit used for optical pickup apparatus PU 1 . Optical specifications of high density optical disc HD include wavelength λ 1 =408 nm, thickness t 1 of protective layer PL 1 that is 0.1 mm or 0.6 mm, and numerical aperture NA 1 that is 0.85 or 0.6-0.65, optical specifications of DVD include wavelength λ 2 =658 nm, thickness t 2 of protective layer PL 2 that is 0.6 mm, and numerical aperture NA 2 that is 0.65, and optical specifications of CD include wavelength λ 3 =785 nm, thickness t 3 of protective layer PL 3 that is 1.2 mm, and numerical aperture NA 3 that is 0.45. However, a combination of a wavelength, a thickness of a protective layer and a numerical aperture is not limited to the foregoing.

When conducting recording and reproducing of information for high density optical disc HD on the optical pickup apparatus PU 1 , negative lens E 1 is moved to a prescribed position (position P 1 in FIG. 1( a )) by uniaxial actuator AC 2 so that the first light flux may emerge from expander lens EXP in a form of a parallel light flux. After that, laser module LM representing a light source is operated to cause light-emitting point EP 1 to emit light. A divergent light flux emitted from the first light-emitting point EP 1 is reflected by prism PS, then, passes through collimator lens COL to turn into a parallel light flux, and its diameter is expanded by expander optical system EXP, then the light flux diameter is regulated by an unillustrated diaphragm STO, thus it becomes a spot that is formed on information recording surface RL 1 through the first protective layer PL 1 by objective optical element OBJ that is composed of two optical elements (or one optical element). The objective optical element OBJ conducts focusing and tracking with biaxial actuator AC 1 arranged on a periphery of the objective optical element OBJ. A reflected light flux modulated by information pits on the information recording surface RL 1 is transmitted again through the objective optical element OBJ and the expander optical system EXP, and is made to be a converged light flux by collimator lens COL to be converged on light-receiving section DS 1 after being reflected twice in prism PS. Thus, it is possible to read information recorded on high density optical disc HD by using output signals coming from the light-receiving section DS 1 .

In this case, spherical aberration of the spot formed on the information recording surface RL 1 of the high density optical disc HD is corrected by moving positive lens E 2 in the optical axis direction by uniaxial actuator AC 3 . Causes for generation of spherical aberration to be corrected by positional adjustment of positive lens E 2 include wavelength fluctuations caused by manufacturing errors for the first light source, for example, refractive index changes and refractive index distribution of the objective optical element OBJ caused by temperature changes, focus jump between information recording layers of a high density disc of a multi-layer-recording type such as a 2-layer disc and a 4-layer disc, and thickness fluctuations and thickness distribution caused by manufacturing errors for the protective layer PL 1 .

Since numerical aperture NA 1 of high density optical disc HD is large, if positional errors of positive lens E 2 in the optical axis direction is great when correcting spherical aberration, spherical aberration is caused by magnification errors of objective optical element OBJ, and spherical aberration of a spot formed on information recording surface RL 1 cannot be corrected accurately. Therefore, uniaxial actuator AC 3 that drives positive lens E 2 is required to have ability to control a position delicately. Further, since the rotating speed of high density optical disc HD in the case of conducting recording and reproducing of information is high compared with conventional optical discs such as DVD and CD, an actuator capable of responding quickly is demanded for conducting correction of spherical aberration, following rotation of the high density optical disc HD. On the other hand, since the numerical aperture NA 1 of high density optical disc HD is large, it is possible to generate relatively large spherical aberration only by moving positive lens E 2 slightly, uniaxial actuator AC 3 that drives positive lens E 2 is not requested to have so large range of movement. As an actuator having such characteristics, there is a voice coil actuator or an actuator utilizing a piezo-electric element. Incidentally, when replacing optical discs each having a different protective layer thickness, it is possible to determine the initial position of positive lens E 2 accurately and quickly by moving it roughly with uniaxial actuator AC 2 and by moving it finely with uniaxial actuator AC 3 , which is preferable.

When high density optical disc HD is replaced to BD in the case of conducting recording and reproducing of information for DVD in optical pickup apparatus PU 1 , negative lens E 1 is moved by uniaxial actuator AC 2 to the position (position P 2 in FIG. 1( a )) where the distance between negative lens E 1 and positive lens E 2 is made to be smaller than that in the case of conducting recording and reproducing of information for high density optical disc HD, so that spherical aberration caused by a difference between thickness t 1 of protective layer PL 1 and thickness t 2 of protective layer PL 2 may be corrected. After that, laser module LM is operated to drive the second light-emitting point EP 2 to emit light. A divergent light flux emitted from the second light-emitting point EP 2 is reflected, as its light path is drawn with dotted lines in FIG. 1( a ), by prism PS, then, it passes through collimator lens COL to be changed substantially into a parallel light flux, and is transmitted through expander optical system EXP to be changed into a divergent light flux, and is regulated by objective optical element OBJ in terms of a light flux diameter to be within an aperture limit required for DVD, to become a spot formed by the objective optical element OBJ on information recording surface RL 2 through the second protective layer PL 2 . Biaxial actuator AC 1 arranged on a periphery of the objective optical element OBJ makes it to conduct focusing and tracking. A reflected light flux modulated by information pits on the information recording surface RL 2 is transmitted again through the objective optical element OBJ and expander optical system EXP, and is made to be a converged light flux by collimator lens COL to be converged on light-receiving section DS 2 after being reflected twice in the prism PS. Thus, information recorded on DVD can be read by using output signals coming from the light-receiving section DS 2 .

When conducting recording and reproducing of information for CD in optical pickup apparatus PU 1 , negative lens E 1 is moved by uniaxial actuator AC 1 to the position (position P 3 in FIG. 1( a )) where the distance between negative lens E 1 and positive lens E 2 is made to be smaller than that in the case of conducting recording and reproducing of information for DVD, so that spherical aberration caused by a difference between thickness t 1 of protective layer PL 1 and thickness t 3 of protective layer PL 3 may be corrected. After that, laser module LM is operated to drive the third light-emitting point EP 3 to emit light. A divergent light flux emitted from the third light-emitting point EP 3 is reflected, as its light path is drawn with two-dot chain lines in FIG. 1( a ), by prism PS, then, it passes through collimator lens COL to be changed substantially into a parallel light flux, and is transmitted through expander optical system EXP to be changed into a divergent light flux, and is regulated by objective optical element OBJ in terms of a light flux diameter to be within an aperture limit required for CD, to become a spot formed by the objective optical element OBJ on information recording surface RL 3 through the third protective layer PL 3 . Biaxial actuator AC 1 arranged on a periphery of the objective optical element OBJ makes it to conduct focusing and tracking. A reflected light flux modulated by information pits on the information recording surface RL 3 is transmitted again through the objective optical element OBJ and expander optical system EXP, and is made to be a converged light flux by collimator lens COL to be converged on light-receiving section DS 3 after being reflected twice in the prism PS. Thus, information recorded on CD can be read by using output signals coming from the light-receiving section DS 3 .

Examples of the objective optical element suited for the aforementioned embodiment will be explained as follows. Incidentally, in the following examples, an area from the optical axis to the first position corresponding to the aperture restriction of the optical disc whose numerical aperture NA is minimum is assumed to be an inner area (or a common area), an area from this first position to the second position corresponding to the aperture restriction of the optical disc whose numerical aperture NA is the second smallest is assumed to be an intermediate area (or a common area), and an area existing outside this second position is assumed to be an outer area (or an exclusive area). Further, under the condition that R 1 represents a curvature of optical surface S 1 positioned to be closer to the light source and R 2 represents a curvature of optical surface S 2 positioned to be closer to the optical information recording medium, R 1 >R 2 is assumed be satisfied, in the following examples.