Objective lens, optical pickup device and information recording regeneration method

[0158] (Example 1)

[0159] This embodiment is related to the above-mentioned first embodiment, and is about using DVD as the first optical information recording medium of high recording density and CD as the second optical information recording medium of low recording density, and information can be performed on them respectively. Examples of recording or reproducing objectives.

[0160] In DVD, the thickness of the transparent substrate of the optical information recording medium is 0.6 mm, the necessary numerical aperture NA1 = 0.60, and the light source wavelength λ 1 =655nm, in CD, the thickness of the transparent substrate of the optical information recording medium is 1.2mm, the necessary numerical aperture NA2 = 0.45, the light source wavelength λ 2 =785nm.

[0161] Both surfaces of the objective lens are aspherical surfaces represented by [Formula 1]. Here, Z is the axis in the optical axis direction, h is the axis in the direction perpendicular to the optical axis, r is the paraxial radius of curvature, κ is the conic coefficient, A is the aspheric coefficient, and P is the power of the aspheric surface.

[0162] 〖Formula 1〗

[0163] Z = h 2 / R 0 1 + 1 - ( 1 + κ ) ( h / R 0 ) 2 + Σ i = 1 ∞ A i h Pi

[0164] Furthermore, a diffractive structure is formed on the entire surface of the aspheric surface on the light source side of the objective lens. The diffraction structure phase difference function Фb is in radians, and is represented by [Formula 2]. This quadratic coefficient represents the paraxial ability of the diffractive part. In addition, the spherical aberration can be controlled with a coefficient other than the second order, for example, a fourth order or a sixth order coefficient. The so-called controllable here means that the spherical aberration of the refraction part has an inverse characteristic spherical aberration in the diffractive part to correct the spherical aberration as a whole, and the spherical aberration of the diffractive part is manipulated so that the total spherical aberration becomes the desired spot amount . At this time, the spherical aberration at the time of temperature change can also be considered to be the sum of the temperature change of the spherical aberration of the refracting part and the spherical aberration of the diffractive part.

[0165] 〖Formula 2〗

[0166] Φ b = Σ i = 1 ∞ b 2 i h 2 i

[0167]Diffraction structures with different purposes are formed in the outer optical function region on the outer side of the distance h from the optical axis and the inner optical function region on the inner side thereof. The diffractive structure of the inner optically functional area corrects spherical aberration for the light beam passing through the area in the respective use states of DVD and CD. Since the inner optical functional region is used for both DVD and CD, it is most desirable to use the same order of diffraction from the viewpoint of light utilization efficiency, and in this embodiment, the first-order diffracted light is used as the diffraction order.

[0168] On the other hand, since the light beam passing through the outer optical functional area is only used for DVD, spherical aberration is corrected when DVD is used, but it is a prefocal spot when CD is used. Here, in the outer optical function region, for example, the light of the second diffraction order is used, so that the diffraction efficiency of the light of the wavelength used by CD is lower than that of the wavelength used by DVD. as by Image 6 As can be understood, if the manufacturing wavelength is set to the wavelength used for DVD, the diffraction efficiency of the wavelength used for CD decreases when a higher order diffraction order is used.

[0169] The lens data of the objective lens used in this example is shown in [Table 2], and the spherical aberration graph is shown in Figure 7. Figure 8 When simulating the defocus signal of the objective lens when actually using the CD, the same diffraction order is used for the inner optical functional area, the diffraction order of the outer optical functional area is designed with 2 orders (a), and the outer optical function area is designed with 1 order. Comparison result of the case (b) of the diffraction order of the optical functional region. Figure 8 Among them, the vertical axis is the signal value of the photodetector, and the horizontal axis is the movement amount of the objective lens (hereinafter, the same in the same figure). As is clear from this figure, in the outer optical function region, the noise signal during defocusing in the CD-use state can be reduced by making it flare and utilizing the high-order diffraction order when the CD is used.

[0170] [Table 2]

[0171] Example 1 Lens data

[0172]

[0173] Aspheric data

[0174] 2nd side (0

[0175] Aspheric coefficient

[0176] κ-4.8740×E-1

[0177] A1-2.6458×E-3 P1 4.0

[0178] A2+1.8535×E-4 P2 6.0

[0179] A3-5.2811×E-4 P3 8.0

[0180] A4+2.2666×E-4 P4 10.0

[0181] A5-4.7529×E-5 P5 12.0

[0182] A6+4.0351×E-6 P6 14.0

[0183] Optical path difference function (coefficient of optical path difference function: reference wavelength 720nm)

[0184] B2-5.2503×E-0

[0185] B4-1.2037×E-0

[0186] B6+2.3295×E-2

[0187] B8-2.5110×E-2

[0188] B10+4.2122×E-3

[0189] 2' side (1.77653mm

[0190] Aspheric coefficient

[0191] κ-8.2230×E-1

[0192] A1+1.1653×E-2 P1 4.0

[0193] A2-7.0244×E-3 P2 6.0

[0194] A3+2.0291×E-3 P3 8.0

[0195] A4-2.8510×E-4 P4 10.0

[0196] A5+1.5360×E-5 P5 12.0

[0197] A6-6.0691×E-8 P6 14.0

[0198] Optical path difference function (coefficient of optical path difference function: reference wavelength 655nm)

[0199] B2+4.7541×E-0

[0200] B4-3.8635×E-0

[0201] B6+1.5428×E-0

[0202] B8-3.1025×E-1

[0203] B10+2.1616×E-2

[0204] 3rd face aspheric coefficient

[0205] κ-1.90222×E-0

[0206] A1+2.23498×E-2 P1 4.0

[0207] A2-1.11325×E-2 P2 6.0

[0208] A3+5.18333×E-3 P3 8.0

[0209] A4-1.48863×E-3 P4 10.0

[0210] A5+2.17667×E-4 P5 12.0

[0211] A6-1.25321×E-5 P6 14.0

[0212] In addition, the objective lens is made of a plastic material with a limited magnification, and the required numerical aperture of the optical information recording medium is 0.6. Furthermore, the amount of change in spherical aberration when there is a temperature change (including the laser light source excitation wavelength shift) is also a good 0.039λ. 1 rms.

[0213] (Example 2)

[0214] This embodiment is related to the above-mentioned second embodiment, and is about using DVD as the first optical information recording medium with high recording density, and using CD as the second optical information recording medium with low recording density, and information can be separately performed on them. Examples of recording or reproducing objectives. Here, the description of the overlapped part with that of Embodiment 1 is omitted.

[0215] The present embodiment is characterized in that by setting the manufacturing wavelength (wavelength used for the shape design of the diffractive structure) in the diffractive structure of the outer optical function region to a wavelength shorter than that of the DVD, it is possible to ease the passage of time when the CD is used. Noise caused by beams in the outer region.

[0216] [Table 3] The lens data of the objective lens of this example is given, and the spherical aberration diagram is shown in Figure 9. Figure 10 When simulating the objective lens defocus signal when actually using CD, the manufacturing wavelength of the diffraction structure of the outer optical function region is set to 525 nm, which is shorter than the wavelength used for DVD (655 nm) (a) and make it consistent. Comparison results for the case (b) of the wavelength used for DVD. As is clear from this figure, in the outer optical function region, by setting the manufacturing wavelength of the diffractive structure to a wavelength shorter than the wavelength used for DVD, the noise signal at the time of defocusing when CD is used can be reduced.

[0217] [table 3]

[0218] Example 2 Lens Data

[0219]

[0220] Aspheric data

[0221] 2nd side (0

[0222] Aspheric coefficient

[0223] κ-4.8740×E-1

[0224] A1-2.6458×E-3 P1 4.0

[0225] A2+1.8535×E-4 P2 6.0

[0226] A3-5.2811×E-4 P3 8.0

[0227] A4+2.2666×E-4 P4 10.0

[0228] A5-4.7529×E-5 P5 12.0

[0229] A6+4.0351×E-6 P6 14.0

[0230] Optical path difference function (coefficient of optical path difference function: reference wavelength 720nm)

[0231] B2-5.2503×E-0

[0232] B4-1.2037×E-0

[0233] B6+2.3295×E-2

[0234] B8-2.5110×E-2

[0235] B10+4.2122×E-3

[0236] 2' side (1.77653mm

[0237] Aspheric coefficient

[0238] κ-8.2230×E-1

[0239] A1+1.1653×E-2 P1 4.0

[0240] A2-7.0244×E-3 P2 6.0

[0241] A3+2.0291×E-3 P3 8.0

[0242] A4-2.8510×E-4 P4 10.0

[0243] A5+1.5360×E-5 P5 12.0

[0244] A6-6.0691×E-8 P6 14.0

[0245] Optical path difference function (coefficient of optical path difference function: reference wavelength 525nm)

[0246] B2+4.7541×E-0

[0247] B4-3.8635×E-0

[0248] B6+1.5428×E-0

[0249] B8-3.1025×E-1

[0250] B10+2.1616×E-2

[0251] 3rd face aspheric coefficient

[0252] κ-1.90222×E-0

[0253] A1+2.23498×E-2 P1 4.0

[0254] A2-1.11325×E-2 P2 6.0

[0255] A3+5.18333×E-3 P3 8.0

[0256] A4-1.48863×E-3 P4 10.0

[0257] A5+2.17667×E-4 P5 12.0

[0258] A6-1.25321×E-5 P6 14.0

[0259] In addition, the objective lens is made of a plastic material with a limited magnification, and the required numerical aperture of the optical information recording medium is 0.6. Furthermore, the amount of change in spherical aberration when there is a temperature change (including the laser light source excitation wavelength shift) is also a good 0.039λ. 1 rms.

[0260] (Example 3)

[0261] This embodiment is related to the above-mentioned third embodiment, and is about using DVD as the first optical information recording medium with high recording density, and using CD as the second optical information recording medium with low recording density, and information can be performed on them respectively. Examples of recording or reproducing objectives.

[0262] In DVD, the thickness of the transparent substrate of the optical information recording medium is 0.6 mm, the necessary numerical aperture NA1 = 0.60, and the light source wavelength λ 1 =655nm, in CD, the thickness of the transparent substrate of the optical information recording medium is 1.2mm, the necessary numerical aperture NA2 = 0.45, the light source wavelength λ 2 =785nm.

[0263] The objective lens is aspherical on both sides, and the surface on the light source side consists of three optical functional areas, which are used for different purposes. like figure 2 As shown in (b), diffractive structures are integrally formed on the aspheric surfaces of the inner optical function region within the distance h1 from the optical axis and the aspheric surface of the outer optical function region outside the distance h2. Here too, diffractive structures are provided in the intermediate optically functional region located in between them.

[0264] Here, the diffractive structure of the inner optical function region within h1 corrects spherical aberration for the light beam passing through the region in the respective usage states of DVD and CD. Since the inner optical functional region is used in common with DVDs and CDs, it is most desirable to use the same order of diffraction from the viewpoint of light utilization efficiency, and in this embodiment, the first-order diffracted light is used as the diffraction order.

[0265] The light beam passing through the outer optical function region other than the distance h2 is similar to the above-mentioned embodiment, and the CD light beam is spotted and the spherical aberration region of the DVD light beam is corrected. The used diffraction order of DVD/CD is the first-order diffracted light, and the production wavelength is set to be the same as that of DVD.

[0266] The diffractive structure of the middle optical functional area corrects the spherical aberration when using DVD, but forms a light spot when using CD, this is the same as the diffractive structure of the outer optical functional area, but the amount of light spot is designed more (here is the deviation from the main spot). [Table 4] gives the lens data of the objective lens of this example, Figure 11 A spherical aberration diagram is given.

[0267] [Table 4]

[0268] Example 3 Lens Data

[0269]

[0270] Aspheric data

[0271] 2nd side (0

[0272] Aspheric coefficient

[0273] κ+1.9482×E-0

[0274] A1-7.8168×E-3 P1 4.0

[0275] A2-2.6336×E-3 P2 6.0

[0276] A3+6.5161×E-4 P3 8.0

[0277] A4-4.5809×E-4 P4 10.0

[0278] A5+1.3052×E-4 P5 12.0

[0279] A6-1.7981×E-5 P6 14.0

[0280] Optical path difference function (coefficient of optical path difference function: reference wavelength 720nm)

[0281] B4-6.8480×E-1

[0282] B6-3.4672×E-1

[0283] B8+9.4038×E-2

[0284] B10-1.0037×E-2

[0285] 2' side (1.757mm

[0286] Aspheric coefficient

[0287] κ-7.5473×E-1

[0288] A1+1.3248×E-2 P1 4.0

[0289] A2-7.5434×E-3 P2 6.0

[0290] A3+1.9491×E-3 P3 8.0

[0291] A4-2.6331×E-4 P4 10.0

[0292] A5+1.8217×E-5 P5 12.0

[0293] A6-5.1106×E-7 P6 14.0

[0294] Optical path difference function (coefficient of optical path difference function: reference wavelength 655nm)

[0295] B2+8.3505×E-0

[0296] B4-6.7131×E-0

[0297] B6+1.4679×E-0

[0298] B8-2.2767×E-1

[0299] B10+1.6721×E-2

[0300] 2" side (1.952mm

[0301] Aspheric coefficient

[0302] κ-6.7190×E-1

[0303] A1+1.4186×E-2 P1 4.0

[0304] A2-7.4834×E-3 P2 6.0

[0305] A3+1.9399×E-3 P3 8.0

[0306] A4-2.6720×E-4 P4 10.0

[0307] A5+1.7809×E-5 P5 12.0

[0308] A6-4.5775×E-7 P6 14.0

[0309] Optical path difference function (coefficient of optical path difference function: reference wavelength 655nm)

[0310] B2+1.9429×E-0

[0311] B4-4.1994×E-0

[0312] B6+1.4300×E-0

[0313] B8-2.6371×E-1

[0314] B10+1.7489×E-2

[0315] 3rd face aspheric coefficient

[0316]κ-1.63569×E+1

[0317] A1+1.02626×E-2 P1 4.0

[0318] A2-9.93228×E-2 P2 6.0

[0319] A3+5.40235×E-3 P3 8.0

[0320] A4-1.52935×E-3 P4 10.0

[0321] A5+2.13329×E-4 P5 12.0

[0322] A6-1.17997×E-5 P6 14.0

[0323] Figure 12 The result (a) of simulating the defocus signal of the objective lens when the intermediate optical functional area is formed with a diffractive surface different from that of the outer optical functional area of ​​the present embodiment, and the simulation of forming the intermediate optical functional area with the same diffractive surface as the outer optical functional area are given. Results (b) in the optical functional area. also, Figure 13 shown corresponds to Figure 12 (b) The cross-sectional view of the light spot on the optical information recording surface when the CD is optimally defocused, Figure 14 shown corresponds to Figure 12 (a) Cross-sectional view of a light spot on the optical information recording surface of CD with optimal defocusing. As is clear from comparing these figures, since the amount of light incident on the photodetector in the spot light can be reduced by increasing the interval between the main spot and the spot, the noise signal when the objective lens is defocused in the CD state can be reduced.

[0324] In addition, the objective lens is made of a plastic material with limited magnification, and the required numerical aperture of the optical information recording medium is 0.6. Furthermore, the amount of change in spherical aberration when there is a temperature change (including the shift in the excitation wavelength of the laser light source) is also a good 0.041λ. 1 rms.