Optical head, optical device, and aberration correcting element

2 The optical head as set forth in claim 1,

• wherein when radius of beam spot of the beam converged onto the recording layer is assumed to be r, and variables different from each other are assumed to be A and B, the aberration correcting means allows the beam to generate phase distribution indicated by the following phase distribution formula
• A(−r4)−B(−r2).

3 The optical head as set forth in claim 2,

• wherein the converging means has numerical aperture of 0.65 or more.

4 The optical head as set forth in claim 2,

• wherein the aberration correcting means allows the variable A and the variable B in the phase distribution formula to be changed independently each other.

5 The optical head as set forth in claim 2,

• wherein when A and B in the phase distribution formula are used so that B/A=K is provided, and this phase distribution formula is represented as follows:
• 6 A ⁢ ( - r 4 ) - B ⁡ ( - r 2 ) = ⁢ A ⁢ { ( - r 4 ) - B / A ⁡ ( - r 2 ) } = ⁢ A ⁢ { ( - r 4 ) - K ⁢ ( - r 2 ) }
• value of K is set to value which cancels deviation of the optimum value of focus bias produced when spherical aberration quantity given to the beam is changed so that change quantity of focus bias value becomes minimum.

6 The optical head as set forth in claim 5,

• wherein value of K is more than 1.

7 The optical head as set forth in claim 2,

• wherein at least one of recording and reproduction of the information signal is carried out with respect to an optical recording medium in which at least two recording layers or more are provided.

8 The optical head as set forth in claim 7,

• wherein when A and B in the phase distribution formula are used so that B/A=K is provided, and this phase distribution formula is represented as follows:
• 7 A ⁢ ( - r 4 ) - B ⁡ ( - r 2 ) = ⁢ A ⁢ { ( - r 4 ) - B / A ⁡ ( - r 2 ) } = ⁢ A ⁢ { ( - r 4 ) - K ⁢ ( - r 2 ) }
• value of K is caused to be value which cancels change of the optimum value of focus bias produced by switching of selection of recording layer of two recording layers or more in the optical recording medium.

9 The optical head as set forth in claim 7,

• wherein when A and B in the phase distribution formula are used so that B/A=K is provided, and this phase distribution formula is represented as follows:
• 8 A ⁢ ( - r 4 ) - B ⁡ ( - r 2 ) = ⁢ A ⁢ { ( - r 4 ) - B / A ⁡ ( - r 2 ) } = ⁢ A ⁢ { ( - r 4 ) - K ⁢ ( - r 2 ) }
• plural values are set in advance in correspondence with two recording layers or more in the optical recording medium as value of K, and value of K corresponding to a selected recording layer is selected and is used.

10 The optical head as set forth in claim 2,

• wherein the aberration correcting means is caused to be of the configuration comprising refractive index adjustable means in which refractive index is changed on the basis of applied voltage, and an electrode for applying voltage to this refarctive index adjustable means.

11 The optical head as set forth in claim 10,

• wherein the aberration correcting means is comprised of liquid crystal element.

12 The optical head as set forth in claim 10,

• wherein voltage value applied by the electrode has a concentrical distribution with respect to the transmitted beam.

13 The optical head as set forth in claim 10,

• wherein the aberration correcting means is caused to be of the configuration in which electrodes which make a pair are provided at both sides of the refractive index adjustable means, and generates phase distribution corresponding to [A(−r4)] term in the phase distribution formula by one electrode and generates phase distribution corresponding to [B(−r2)] term in the phase distribution formula by the other electrode.

14 The optical head as set forth in claim 10,

• wherein the aberration correcting means is caused to be of the configuration in which electrodes which make a pair are provided at both sides of the refractive index adjustable means, and
• wherein in the case where B=B1+B2 is assumed in the phase distribution formula, phase distribution corresponding to [A(−r4)−B1(−r2)] term is generated by one electrode and phase distribution corresponding to [B2(−r2)] term in the phase distribution formula is generated by the other electrode.

15 The optical head as set forth in claim 10,

• wherein the aberration correcting means is caused to be of the configuration in which electrodes which make a pair are provided at both sides of the refractive index adjustable means, and
• wherein in the case where A=A1+A2 is assumed in the phase distribution formula, phase distribution corresponding to [A1(−r4)−B1(−r2)] term is generated by one electrode and phase distribution corresponding to [−A2(−r4)] term in the phase distribution formula is generated by the other electrode.

16 The optical head as set forth in claim 10,

• wherein the aberration correcting means is caused to be of the configuration in which electrodes which make a pair are provided at both sides of the refractive index adjustable means, and
• wherein in the case where A=A1+A2 and B=B1+B2 are assumed in the phase distribution formula, phase distribution corresponding to [A1(−r4)−B1(−r2)] term is generated by one electrode and phase distribution corresponding to [−A2(−r4)+B2(−r2)] term in the phase distribution formula is generated by the other electrode.

20 The optical apparatus as set forth in claim 19,

• wherein when radius of beam spot of the beam converged onto the recording layer is assumed to be r, and variables different from each other are assumed to be A and B, the aberration correcting means allows the beam to generate phase distribution indicated by the following phase distribution formula:
• A(−r4)−B(−r2).

21 The optical apparatus as set forth in claim 20,

• wherein the converging means has numerical aperture of 0.65 or more.

22 The optical apparatus as set forth in claim 20,

• wherein the aberration correcting means includes means for changing the variables A and B in the phase distribution formula independently each other.

23 The optical apparatus as set forth in claim 20,

• wherein when A and B in the phase distribution formula are used so that B/A=K is provided, and this phase distribution formula is represented as follows:
• 11 A ⁡ ( - r 4 ) - B ⁡ ( - r 2 ) = A ⁢ { ( - r 4 ) - B / A ⁡ ( - r 2 ) } = A ⁢ { ( - r 4 ) - K ⁡ ( - r 2 ) }
• value of K is set to value which cancels deviation of the optimum value of focus bias produced when spherical aberration quantity given to the beam is changed so that change quantity of focus bias value becomes minimum.

24 The optical apparatus as set forth in claim 23,

• wherein value of K is more than 1.

25 The optical apparatus as set forth in claim 20,

• wherein at least one of recording and reproduction of an information signal is carried out with respect to an optical recording medium where at least two recording layers or more are provided.

26 The optical apparatus as set forth in claim 20,

• wherein when A and B in the phase distribution formula are used so that B/A=K is provided, and this phase distribution formula is represented as follows:
• 12 A ⁡ ( - r 4 ) - B ⁡ ( - r 2 ) = A ⁢ { ( - r 4 ) - B / A ⁡ ( - r 2 ) } = A ⁢ { ( - r 4 ) - K ⁡ ( - r 2 ) }
• value of K is caused to be value which cancels change of the optimum value of focus bias produced by switching of selection of recording layer of two recording layers or more in the optical recording medium.

27 The optical apparatus as set forth in claim 20,

• wherein when A and B in the phase distribution formula are used so that B/A=K is provided, and this phase distribution is represented as follows:
• 13 A ⁡ ( - r 4 ) - B ⁡ ( - r 2 ) = A ⁢ { ( - r 4 ) - B / A ⁡ ( - r 2 ) } = A ⁢ { ( - r 4 ) - K ⁡ ( - r 2 ) }
• plural values are set in advance in correspondence with two recording layers or more in the optical recording medium as value of K, and value of K corresponding to a selected recording layer is selected and is used.

28 The optical apparatus as set forth in claim 20,

• wherein the aberration correcting means is caused to be of the configuration comprising refractive index adjustable means in which refractive index is changed on the basis of applied voltage, and an electrode for applying voltage to this refractive index adjustable means.

29 The optical apparatus as set forth in claim 28,

• wherein the aberration correcting means is comprised of liquid crystal element.

30 The optical apparatus as set forth in claim 28,

• wherein voltage value applied by the electrode has a concentrical distribution with respect to the transmitted beam.

31 The optical apparatus as set forth in claim 28,

• wherein the aberration correcting means is caused to be of the configuration in which electrodes which make a pair are provided at both sides of the refractive index adjustable means, and generates phase distribution corresponding to [A(−r4)] term in the phase distribution formula by one electrode and generates phase distribution corresponding to [B(−r2)] term in the phase distribution formula by the other electrode.

32 The optical apparatus as set forth in claim 28,

• wherein the aberration correcting means is caused to be of the configuration in which electrodes which make a pair are provided at both sides of the refractive index adjustable means, and
• wherein in the case where B=B1+B2 is assumed in the phase distribution formula, phase distribution corresponding to [A(−r4)−B1(−r2)] term is generated by one electrode, and phase distribution corresponding to [B2(−r2)] term in the phase distribution formula is generated by the other electrode.

33 The optical apparatus as set forth in claim 28,

• wherein the aberration correcting means is caused to be of the configuration in which electrodes which make a pair are provided at both sides of the refractive index adjustable means, and
• wherein in the case where A=A1+A2 is assumed in the phase distribution formula, phase distribution corresponding to [A1(−r4)−B(−r2)] term is generated by one electrode, and phase distribution corresponding to [−A2(−r4)] term in the phase distribution formula is generated by the other electrode.

34 The optical apparatus as set forth in claim 28,

• wherein the aberration correcting means is caused to be of the configuration in which electrodes which make a pair are provided at both sides of the refractive index adjustable means, and
• wherein in the case where A=A1+A2 and B=B1+B2 are assumed in the phase distribution formula, phase distribution corresponding to [A1(−r4)−B1(−r2)] term is generated by one electrode and phase distribution corresponding to [−A2(−r4)+B2(−r2)] term in the phase distribution formula is generated by the other electrode.

37 An aberration correcting element which can be disposed on an optical path within an optical head for carrying out at least one of recording and reproduction of an information signal with respect to an optical recording medium including a light transmission layer on a recording layer where the information signal is recorded,

• wherein when radius of beam spot of a beam converged onto the recording layer is assumed to be r, and variables different from each other are assumed to be A and B,
• a transmitted beam is caused to generate phase distribution represented by the following phase distribution formula
• A(−r4)−B(−r2).

38 The aberration correcting element as set forth in claim 37,

• wherein the aberration correcting element is caused to be of the configuration comprising refractive index adjustable means in which refractive index is changed on the basis of applied voltage, and an electrode for applying voltage to this refractive index adjustable means.

39 The aberration correcting element as set forth in claim 38,

• wherein the aberration correcting means is comprised of liquid crystal element.

40 The aberration correcting element as set forth in claim 38,

• wherein voltage value applied by the electrode has a concentrical distribution with respect to the transmitted beam.

41 The aberration correcting element as set forth in claim 37,

• which includes means for changing variables A and B in the phase distribution formula independently each other.

42 The aberration correcting element as set forth in claim 38,

• wherein the aberration correcting element is caused to be of the configuration in which electrodes which make a pair are provided at both sides of the refractive index adjustable means, and wherein phase distribution corresponding to [A(−r4)] term in the phase distribution formula is generated by one electrode, and phase distribution corresponding to [B(−r2)] term in the phase distribution formula is generated by the other electrode.

43 The aberration correcting element as set forth in claim 38,

• wherein the aberration correcting element is caused to be of the configuration in which electrodes which make a pair are provided at both sides of the refractive index adjustable means, and
• wherein in the case where B=B1+B2 is assumed in the phase distribution formula, phase distribution corresponding to [A(−r4)−B1(−r2)] term is generated by one electrode, and phase distribution corresponding to [B2(−r2)] term in the phase distribution formula is generated by the other electrode.

44 The aberration correcting element as set forth in claim 38,

• wherein the aberration correcting means is caused to be of the configuration in which electrodes which make a pair are provided at both sides of the refractive index adjustable means, and
• wherein in the case where A=A1+A2 is assumed in the phase distribution formula, phase distribution corresponding to [A1(−r4)−B(−r2)] term is generated by one electrode, and phase distribution corresponding to [−A2(−r4)] term in the phase distribution formula is generated by the other electrode.

45 The aberration correcting element as set forth in claim 38,

• wherein the aberration correcting means is caused to be of the configuration in which electrodes which make a pair are provided at both sides of the refractive index adjustable means, and
• wherein in the case where A=A1+A2 and B=B1+B2 are assumed in the phase distribution formula, phase distribution corresponding to [A1(−r4)−B1(−r2)] term is generated by one electrode, and phase distribution corresponding to [−A2 (−r4)+B2(−r2)] term in the phase distribution formula is generated by the other electrode.