# US 7,613,096 B2 · Converging optical element and optical pickup apparatus

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- Number: US 7,613,096 B2
- Document ID: US7613096B2
- Status: Granted
- Kind: B2
- Application number: 11/153,391
- Filed: 2005-06-16
- Published: 2005-12-22
- Granted: 2009-11-03
- Earliest claimed: 2004-06-22
- Assignees: Konica Minolta Opto, Inc.
- Inventors: Mika Wachi
- Web page: https://patentgrep.com/patent/US7613096B2

## CPC

- G11B 7/1353: Diffractive elements, e.g. holograms or gratings {(diffraction gratings per se G02B5/18; holograms per se G02B5/32; grating systems G02B27/44)}
- G11B 7/1374: Objective lenses {(optical objectives per se G02B9/00)}
- G11B 7/1392: Means for controlling the beam wavefront, e.g. for correction of aberration {(optical systems for aberration correction per se G02B27/00)}
- G11B 7/13922: {passive}
- G11B 2007/0006: {adapted for scanning different types of carrier, e.g. CD & DVD}
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)

## Abstract

A converging optical element for use in an optical pickup apparatus reproducing and/or recording information on a first optical disc using a first light flux with a wavelength λ1 emitted by a first light source, reproducing and/or recording information on a second optical disc using a second light flux with a wavelength λ2 emitted by a second light source, and reproducing and/or recording information on a third optical disc using a third light flux with a wavelength λ3 emitted by a third light source, the converting optical element includes: a phase structure arranged on at least one surface of the converging optical element, wherein when f3 is a focal length of the converging optical element for the third light flux, the focal length f3 satisfies a predefined condition.

## Claims

### Claim 1

A converging optical element for use in an optical pickup apparatus reproducing and/or recording information on a first optical disc having a protective substrate with a thickness t1 (mm) using a first light flux with a wavelength λI (nm) emitted by a first light source, reproducing and/or recording information on a second optical disc having a protective substrate with a thickness t2 (mm) using a second light flux with a wavelength λ2 (nm) emitted by a second light source, and reproducing and/or recording information on a third optical disc having a protective substrate with a thickness t3 (mm) using a third light flux with a wavelength λ3 (nm) emitted by a third light source, the converting optical element comprising:
a phase structure arranged on at least one surface of the converging optical element, wherein
the thicknesses t1, t2 and t3 satisfy t1 ≦t2 <t3,
when m3 is an optical system magnification of the converging optical element for an effective light flux which is necessary for recording or reproducing information on the third disc and f3 is a focal length of the converging optical element for the third light flux, the focal length f3 satisfies
0.01<|m3|×(t3−t1)/f3<0.03, and
the converging optical element satisfies
0.03<|SC max|/f<0.05
where SCmax is an amount of an offence against sine condition on an edge of an effective diameter of the converging optical element when the pickup apparatus reproduces or records information on the third disc using a finite coniugated system, and f is a focal length of the converging optical system for a light flux emitted by one of the first to third light sources and passing through a position which is on a principal plane of the converging optical element and is located away from the optical axis by a distance H in a perpendicular direction to the optical axis.

### Claim 2 (depends on 1)

The converging optical element of claim 1, wherein the converging optical element satisfies
0.05≦|SC1 max/SC3 max|≦0.25
where u is an angle between an optical axis and a light flux emitted by one of the first-third light sources and passing through a position which is on a principal plane of the converging optical element and is located away from the optical axis by a distance H in a perpendicular direction to the optical axis,
U is an angle between the optical axis and the light flux emitted from an optical surface facing an optical-disc side of the converging optical element,
n is a refractive index of an object-side area of the converging optical element,
n′ is a refractive index of an image-side area of the converging optical element,
m is an optical system magnification of the converging optical system for the light flux,
f is a focal length of the converging optical system for the light flux,
SC is an amount of an offence against sine condition and satisfies the following expressions,
SC=n×H/n′×sin U−f for m=0, and
SC=f(1−1/m)(sin u/sin U−m) for m≠0,
SC1max is a maximum value of the offence against sine condition for converging the first light flux on the first optical disc, and
SC3max is a maximum value of the offence against sine condition for converging the third light flux on the first optical disc.

### Claim 3 (depends on 2)

The converging optical element of claim 2, wherein the converging optical element satisfies the following expressions:
0.5≦NA1≦0.7,
0.4≦NA3≦0.64,
where NA1 is a numerical aperture of an image side of the converging optical element for the first light flux, and
NA3 is a numerical aperture of an image side of the converging optical element for the third light flux.

### Claim 4 (depends on 1)

The converging optical element of claim 1, wherein
each of an optical surface facing a light-source side and an optical surface facing an optical-disc side of the converging optical element is divided into a plurality of areas which are arranged concentrically around the optical axis,
the plurality of areas include
a first area being on the optical surface facing the light-source side and including an optical axis,
a second area arranged outside of the first area,
a third area being on the optical surface facing the optical-disc side and including an optical axis, and
a fourth area arranged outside of the third area,
the first area and the third area transmit the first to third light fluxes for reproducing or recording information on the first to third optical discs respectively,
the second area and the fourth area transmit the first and second light fluxes for reproducing or recording information on the first and second optical discs respectively, and
the converging optical element satisfies
0.5<(1Rr2−2Rr2)/(1Rr1−2Rr1)<1.5,
where 1Rr1 is a curvature radius of the first area, 1Rr2 is a curvature radius of the second area, 2Rr1 is a curvature radius of the third area, and 2Rr2 is a curvature radius of the fourth area.

### Claim 5 (depends on 4)

The converging optical element of claim 4, wherein a height h of the first area from the optical axis is a height of an effective light flux diameter which is necessary for forming a converged spot on an information recording surface on the third optical disc.

### Claim 6 (depends on 1)

The converging optical element of claim 1, wherein the converging optical element is formed of a single lens.

### Claim 7 (depends on 1)

The converging optical element of claim 1,
wherein the converging optical element satisfies 1.8≦f≦2.3,
wherein f (mm) is a focal length of the converging optical element for a light flux emitted by one of the first to third light sources.

### Claim 8 (depends on 7)

The converging optical element of claim 7, wherein the converging optical element satisfies 1.8≦f≦2.0.

### Claim 9 (depends on 1)

The converging optical element of claim 1, wherein the converging optical element satisfies 0.035≦|m3|≦0.066.

### Claim 10 (depends on 1)

The converging optical element of claim 1, wherein the converging optical element satisfies the following expressions:
1.5×λ1≦λ2≦1.7×λ1,
1.8×λ1≦λ3≦2.2×λ1.

### Claim 11 (depends on 1)

The converging optical element of claim 1, wherein the converging optical element satisfies the following expressions:
0.9×t1≦t2≦1.1×t1,
1.9×t1≦t3≦2.1×t1.

### Claim 12

An optical pickup apparatus for information recording and/or reproducing comprising:
a first light source for emitting a first light flux with a wavelength λ1 (nm) for recording and/or reproducing information on a first optical disc having a protective substrate with a thickness t1 (mm);
a second light source for emitting a second light flux with a wavelength λ2 (nm) for recording and/or reproducing information on a second optical disc having a protective substrate with a thickness t2 (mm);
a third light source for emitting a third light flux with a wavelength λ3 (nm) for recording and/or reproducing information on a third optical disc having a protective substrate with a thickness t3 (mm); and
a converging optical element having a phase structure arranged on at least one surface of the converging optical element, for converging the first light flux, the second light flux and the third light flux on the first disc, the second disc and the third disc, respectively, wherein
the thicknesses t1, t2 and t3 satisfy t1≦t2<t3,
when m3 is an optical system magnification of the converging optical element for an effective light flux which is necessary for recording or reproducing information on the third disc and f3 is a focal length of the converging optical element for the third light flux, the focal length f3 satisfies
0.01<|m3|×(t3−t1)/f3<0.03, and
the optical pickup apparatus satisfies
0.03<|SC max|/f<0.05
where SCmax is an amount of an offence against sine condition on an edge of an effective diameter of the converging optical element when the pickup apparatus reproduces or records information on the third disc using a finite coniugated system, and f is a focal length of the converging optical system for a light flux emitted by one of the first to third light sources and passing through a position which is on a principal plane of the converging optical element and is located away from the optical axis by a distance H in a perpendicular direction to the optical axis.

### Claim 13 (depends on 12)

The optical pickup apparatus of claim 12, wherein the optical pickup apparatus satisfies
0.05<|SC1 max/SC3 max|<0.25
where u is an angle between an optical axis and a light flux emitted by one of the first third light sources and passing through a position which is on a principal plane of the converging optical element and is located away from the optical axis by a distance H in a perpendicular direction to the optical axis,
U is an angle between the optical axis and the light flux emitted from an optical surface facing an optical-disc side of the converging optical element,
n is a refractive index of an object-side area of the converging optical element,
n′ is a refractive index of an image-side area of the converging optical element,
m is an optical system magnification of the converging optical system for the light flux,
f is a focal length of the converging optical system for the light flux,
SC is an amount of an offence against sine condition and satisfies the following expressions,
SC=n×H/n′×sin U−f for m=0, and
SC=f(1−1/m)(sin u/sin U−m) for m≠0,
SC1max is a maximum value of the offence against sine condition for converging the first light flux on the first optical disc, and
SC3max is a maximum value of the offence against sine condition for converging the third light flux on the first optical disc.

### Claim 14 (depends on 13)

The optical pickup apparatus of claim 13, wherein the optical pickup apparatus satisfies the following expressions:
0.5≦NA1≦0.7,
0.4≦NA3≦0.64,
where NA1 is a numerical aperture of an image side of the converging optical element for the first light flux, and
NA3 is a numerical aperture of an image side of the converging optical element for the third light flux.

### Claim 15 (depends on 12)

The optical pickup apparatus of claim 12, wherein
each of an optical surface facing a light-source side and an optical surface facing an optical-disc side of the converging optical element is divided into a plurality of areas which are arranged concentrically around the optical axis,
the plurality of areas include
a first area being on the optical surface facing the light-source side and including an optical axis,
a second area arranged outside of the first area,
a third area being on the optical surface facing the optical-disc side and including an optical axis, and
a fourth area arranged outside of the third area,
the first area and the third area transmit the first to third light fluxes for reproducing or recording information on the first to third optical discs respectively,
the second area and the fourth area transmit the first and second light fluxes for reproducing or recording information on the first and second optical discs respectively, and
the converging optical element satisfies
0.5<(1Rr2−2Rr2)/(1Rr1−2Rr1)<1.5,
where 1Rr1 is a curvature radius of the first area, 1Rr2 is a curvature radius of the second area, 2Rr1 is a curvature radius of the third area, and 2Rr2 is a curvature radius of the fourth area.

### Claim 16 (depends on 15)

The optical pickup apparatus of claim 15, wherein a height h of the first area of the converging optical element from the optical axis is a height of an effective light flux diameter which is necessary for forming a converged spot on an information recording surface on the third optical disc.

### Claim 17 (depends on 12)

The optical pickup apparatus of claim 12, wherein the converging optical element is formed of a single lens.

### Claim 18 (depends on 12)

The optical pickup apparatus of claim 12,
wherein the optical pickup apparatus satisfies 1.8≦f≦2.3,
wherein f (mm) is a focal length of the converging optical element for a light flux emitted by one of the first to third light sources.

### Claim 19 (depends on 12)

The converging optical element of claim 12, wherein the optical pickup apparatus satisfies 1.8≦f≦2.0.

### Claim 20 (depends on 12)

The optical pickup apparatus of claim 12, wherein the optical pickup apparatus satisfies 0.03≦|m3|0.066.

### Claim 21 (depends on 12)

The optical pickup apparatus of claim 12, wherein the optical pickup apparatus satisfies the following expressions:
1.5×λ1≦λ2≦1.7×λ1,
1.8×λ1≦λ3≦2.2×λ1.

### Claim 22 (depends on 12)

The converging optical element of claim 12, wherein the optical pickup apparatus satisfies the following expressions:
0.9×t1≦t2≦1.1×t1,
1.9×t1≦t3≦2.1×t1.