United States Patent
`Komma et a].
`
`[19]
`
`[54] COMPOUND OBJECTIVE LENS HAVING
`TWO FOCAL POINTS
`
`[75] Inventors:
`
`Yoshiaki Komma, Kyoto; Sadao
`Mizuno; Seji Nishino, both of Osaka,
`all of Japan
`
`[73] Assignee:
`
`Matsushita Electric Industrial Co.,
`Ltd., Osaka, Japan
`
`[21] Appl. No.: 190,520
`
`[22] Filed:
`
`Feb. 1, 1994
`
`[30]
`
`Foreign Application Priority Data
`
`Feb. 1, 1993 [JP] Japan .................................. 5-014432
`Aug. 4, 1993 [JP] Japan .................................. 5-193353
`
`[51] Int. 0..6 ........................... G02B 5/32; GlIB 7/00
`[52] U.S. Cl .................................... 359/19, 369/44.23;
`369/94; 369/103; 369/112
`[58] Field of Search ............... 359/15, 16, 19; 369/94,
`369/103, 109, 1 I2, 44.23
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,999,009 12/1976 Bouwthuis ............................ 369/94
`4,441,179 4/1984 Slaten .................................... 369/94
`4,450,553 5/1984 Holster et al ......................... 369/94
`4,731,772 3/1988 Lee.
`4,733,065 3/1988 Hoshi et aL .
`4,733,943 3/1988 Suzuki et aL .
`4,757,197 7/1988 Lee.
`4,758,062 7/1988 Sunagawa et aL .
`4,876,680 10/1989 Misawa et aL .
`(List continued on next page.)
`
`FOREIGN PATENT DOCUMENTS
`0341743 11/1989 European Pat. Off..
`0357780 3/1990 European Pat. Off. ¯
`0367878 5/1990 European Pat. Off..
`0457553 11/1991 European Pat. Off..
`0470807 2/1992 European Pat. Off..
`61-131245 6/1986 Japan.
`61-189504 8/1986 Japan.
`(List continued on next page.)
`
`I lllllMlllllllllMIIIIlllllllmHIllllIHlllllllllllllllllll
`
`US005446565A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,446,565
`Aug. 29, 1995
`
`OTHER PUBLICATIONS
`
`Applied Optics, vol. 29, No. 7, 1 Mar. 1990, New York,
`US, pp. 994-997, XP000101359, Ojeda-Castaneda &
`Berriel-Valdos ’Zone plate for arbitrarily high focal
`depth’.
`"Apo-Tele Lenses With Kinoform Elements" by M. A.
`Gan et al; Spie vol. 1507 Holographic Optics III: Princi-
`ples and Applications (1991); pp., 116-125.
`"Design of Some Achromatic Imaging Hybrid Diffrac-
`tive-Refractive Lenses" by P. Twardowski et al Spie
`(List continued on next page.)
`
`Primary Examiner--Martin Lerner
`Attorney, Agent, or Firm--Lowe, Price, Leblanc &
`Becker
`
`[57] " ABSTRACT
`A compound objective lens is composed of a hologram
`lens for transmitting a part of incident light without any
`diffraction to form a beam of transmitted light and dif-
`fracting a remaining part of the incident light to form a
`beam of first-order diffracted light, and an objective
`lens for converging the transmitted light to form a fh-st
`converging spot on a front surface of a thin type of first
`information medium and converging the diffracted light
`to form a second converging spot on a front surface of
`a thick type of second information medium. Because the
`hologram !ens selectively functions as a concave lens
`for the diffracted light, a curvature of the transmitted
`light differs from that of the diffracted light. Therefore,
`even though the first and second information mediums
`have different thicknesses, the transmitted light incident
`on a rear surface of the fwst information medium is
`converged on the its front surface, and the diffracted
`light incident on a rear surface of the second informa-
`tion medium is converged on the its front surface. That
`is, the compound objective lens has two focal points.
`
`34 Claims, 43 Drawing Sheets
`
`LG Electronics, Inc. et al.
`EXHIBIT 1006
`IPR Petition for
`U.S. Patent No. RE43,106
`
`

`
`5,446,565
`
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`4,945,529 7/1990 Ono et al..
`5,062,098 10/1991 Hori et al..
`5,!34,604 7/1992 Nagashima et al ................. 369/112
`5,202,875 4/1993 Rosen et al ........................... 369/94
`5,243,590 9/1993 Aratani ................................ 369/109
`5,245,596 9/1993 Gupta et al ......................... 369/112
`5,251,198 10/1993 Striclder .............................. 369/112
`!/1994 Russell ................................ 369/109
`5,278,816
`5,303,224 4/1994 ChLkuma et al ..................... 369/112
`
`FOREIGN PATENT DOCUMENTS
`
`62-073429 4/1987 Japan.
`63-241735 10/1988 Japan.
`222452 5/1990 Japan.
`2185722 7/1990 Japan.
`
`4212730 8/1992 Japan .
`5205282 8/1993 Japan .
`OTHER PUBLICATIONS
`vol. 1507 Holographic Optics Ill: Principles and Appli-
`cations (1991); pp., 55-65.
`"Optical Design With Diffractive Lenses" by D. Faklis
`et al; Designer’s Handbook; Photonics Spectra, Nov.,
`1991; pp., 205-208.
`"Diffractive Lenses in Broadband Optical System De-
`sign" by D. Faklis et a!; Designer’s Hanbook; Photonies
`Spectra, Dec., 1991; pp., 131-134.
`"Sherical Granting Objective Lenses for Optical Disk
`Pick-Ups" by K. Goto et al; Proc. Int. Syrup. On Opti-
`cal Memory, 1987; Japanese Journal of Applied Phys-
`ics, vol. 26 (1987) Supplement 26-4; pp., 135-140.
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 1 of 43
`
`5,446,565
`
`FIG. 1
`PRIOR A R T
`
`FIS. 2,4
`PRIOR A R T
`
`15
`
`16
`
`1/,
`
`1_1
`
`I ,I )
`
`13
`
`C
`
`1’/
`
`I
`
`FIG. 2B
`PR!OR APT
`
`|e ’41,1
`
`¯
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 2 of 43
`
`5,446,565
`
`FIG. 3
`
`PRIOR A RT
`
`iii
`pp.
`
`i=.
`
`Iii
`m_
`
`0.9
`
`0.8
`
`0.7
`
`0.6
`
`0.4 0.8 1.2
`THICKNESS OF AN OPTICAL
`DISK [M]
`
`1.6
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 3 of 43
`
`5,446,565
`
`S1 23
`
`T1
`lr
`
`r’
`
`I
`
`22
`21 /
`<l
`~ 27.~,
`
`29LL~<
`26y
`
`(
`
`1.3
`.,5
`
`Fig. 4.B
`/
`S2 25 T2
`
`24,
`
`A ’Sl/’
`
`T,,..7.C __.~26j
`26A
`
`)L3
`
`FIG. 5
`
`26
`
`26B
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 4 of 43
`
`5,446,565
`
`FIG. 5
`
`26
`
`TOP PORTION
`BOTTOM PORTION
`
`28
`,rv
`
`I I
`I
`I I
`
`BLOCK BLOCK
`
`26A
`
`FIG. 7
`
`F--
`-v-
`
`Lt.
`
`>-
`
`z
`
`z
`
`OPTICAL AXIS
`
`K 1
`
`PRIMARY MAXIMUM
`(MAIN LOBE)
`
`SECONDARY MAXIMA
`(SIDE LOBES)
`
`POSITION ON THE INFORMATION
`MEDIUM 23 OR 25
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 5 of 43
`
`5,446,565
`
`FIG. 8,4
`
`FIG. 8B
`BLOCK
`
`I
`I
`
`~.
`
`110’
`
`-- -.I-~_. no
`
`o
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 6 of 43
`
`5,446,565
`
`21M
`
`29H{ 27
`
`FIG. 9B
`25
`
`23 T1
`
`"- L5 ~;28
`"t
`
`L~
`28
`
`~ J
`
`T2
`
`21M
`
`27 } 29H
`
`26H
`
`L3
`
`FIG. 10A
`
`F/G. 10B
`s~ 2s ~2
`
`,
`
`~" 32~ 28
`
`27
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 7 of 43
`
`5,446,565
`
`FIS. 11
`
`U~V
`o::
`
`=z=cD
`(D i--~
`
`I.UU_
`:~:: U.J
`
`POSITION ON PATTERN REGION 32A
`
`I
`!
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet S of 43
`
`5,446,565
`
`~1 =
`
`BLOCK
`
`"4
`
`~ H1 WI>W2
`
`W1 W2 W28z W1
`
`W1 W2 W2 WI
`
`I
`
`I
`
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`
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`
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`
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`,
`
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`
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`
`FIG. 12,4
`
`FIG. 12B
`
`FIG. 12C
`
`FIG. 12D
`
`FIG. 12E
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 9 of 43
`
`5,446,565
`
`FIG. 72A
`OPTICAL
`S AXIS
`
`/
`
`1,2.
`
`>-
`!,,--
`1,,-,,I
`o~
`
`I.tJ
`I--
`z¸
`
`FIG. 13/3
`OPTICAL
`
`~ AXIS
`
`i
`
`i
`
`I.L
`
`z
`
`I--
`z
`
`POSITION ON FAR FIELD
`
`POSITION ON FAR FIELD
`
`II
`.-r. (D
`i,..4
`
`I.i_
`
`I--
`I--.I
`(.0
`z
`M-
`
`I.-,I
`
`FI6. 7Z, A
`~OPTICAL AXIS
`
`FIRST-ORDER
`DIFFRACTED LIGHT
`
`IGHT
`
`~
`
`o
`DISTANCE FROM OPTICAL
`AXIS
`
`.-,-,-,Ill,,
`
`FIG. 1Z, B
`jOPTICAL AXIS
`’
`FIRST-ORDER
`I
`DIFFRACTED
`(cid:128)LIGHT
`
`/
`
`.|
`I
`I
`I
`i
`
`FIS. lZ, C
`~.,..OPTICAL AXIS
`
`~ T~NSMIrrED
`
`LIGHT
`
`I
`I
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 10 of 43
`
`5,446,565
`
`15,4
`
`33
`
`330
`
`33A
`
`32A
`
`33B
`
`33C
`
`22
`
`L5
`
`15B
`23 T1
`
`28
`
`L3
`
`FIG. 15C
`
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`)
`\
`
`l
`
`(
`r~27
`’~’~~ .rL~
`6-
`
`(
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 11 of 43
`
`5,446,565
`
`FiS. 15,4
`23
`
`$5
`
`T1
`
`FI6. 15B
`
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`!
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`!
`
`POSITION ON PATTERN
`REOION 42A
`
`I~
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 12 of 43
`
`5,446,565
`
`FIG. 18A
`
`6OPTICAL AXIS
`
`I
`I
`
`18B
`
`OPTICAL AXIS
`
`I
`
`IA.
`0
`>-
`t,-
`t,,,e
`
`Z
`t,-,
`Z
`p,W
`
`0
`DISTANCE FROM OPTIOAL
`AXIS
`
`FIG. 18C
`
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`
`I
`
`FIG. 19B
`
`FIG. 19,4
`2?
`
`26, 32, OR 42
`
`26.32, OR 42
`
`FIG. 20~7
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 13 of 43
`
`5,446,565
`
`FI6. 21
`
`T1
`
`$2 1 ~21J30R25
`
`L5
`L~,
`
`I’ 27
`
`26. 26M. 32.j~
`33 OR /,2
`
`I
`I
`i
`I
`
`L3
`
`52
`
`--Z
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 14 of 43
`
`5,446,565
`
`FIG. 22
`56
`
`~56b
`
`56
`
`Y
`
`t;x
`
`Z
`
`/=/6. 23
`
`55
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`
`L~57
`
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`
`Y
`
`=-Z
`
`L8
`
`%.
`
`%
`
`" " ""-"- FP2
`----...~
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 15 of 43
`
`5,446,565
`
`L9 SB
`
`L12 $9 57
`
`FIG. 2/+
`
`60a J"
`
`59 -.
`SE1--
`SE2 -
`SE3
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`
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`I ~_J ~SE6
`
`25B
`
`25C
`
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`
`J Y
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 16 of 43
`
`5,446,565
`
`FIG. 26
`
`5~ .56b
`
`/ / ,z,--5g ,,,A ’ /-,- 5g
`,, ....
`/"’ x..,.60d
`z..,.60b
`
`Y
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`
`26, 26M, 32
`33 ORI,2
`
`61
`
`63
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`
`52
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 17 of 43
`
`5,446,565
`
`FIG. 28
`
`SE9
`
`63
`
`FIG. 29,4
`
`.... i
`
`SEIO
`
`SEB
`
`FiG. 29B
`SE9 ~ --
`
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`
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`
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`
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`PIT
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`
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`
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`
`Dr" Dt
`
`""|
`
`Ot
`
`TANGENTIAL
`DIRECTION
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 18 of 43
`
`5,446,565
`
`FIG. 30
`
`.
`
`L4R OR LSR
`
`63
`
`3
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 19 of 43
`
`5,446,565
`
`RG. 31
`
`23 OR 25
`
`I L5R
`
`69
`
`55 66
`L&R OR LSR
`
`63
`
`I L4, L~R
`
`58
`
`26.26M.
`33 OR ~2
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 20 of 43
`
`5,446,565
`
`FIG. 32
`
`

`
`U.S, Patent
`
`Aug. 29, 1995
`
`Sheet 21 of 43
`
`5,446,565
`
`FIG. 33
`23 OR 25
`
`I
`L5, L5R
`27
`
`71
`
`55
`
`66
`L&R OR L5R
`
`63
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`33 OR ~2
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`53
`
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`
`52
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 22 of 43
`
`5,446,565
`
`FIG. 34.
`
`!.13
`
`61+ SlO
`
`L13
`
`63
`
`73
`$11
`
`[~52
`
`$8 $9
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 23 of 43
`
`5,446,565
`
`OBJECTIVE LENS 27
`APPROACHES FIRST
`INFORMATION MEDIUM 23
`
`OBJECTIVE LENS 27
`GOES AWAY FROM FIRST
`INFORMATION MEDIUM 23
`
`FEI
`
`THRESHOLD
`VALUE
`
`FE2
`
`UNNECESSARY FOCUS
`ERROR SIGNALS
`
`t--~O
`
`W~
`¢Y- er-
`i._. e,,.
`(.wOW
`
`__THRESHOLD
`VALUE
`
`JUST-FOCUS
`POINT
`
`FIG. 35B
`
`OBJECTIVE LENS 27
`APPROACHES SECOND
`INFORMATION MEDIUM 25
`
`OBJECTIVE LENS 27
`GOES AWAY FROM SECOND
`INFORMATION MEDIUM 25
`
`FE4
`
`FE3
`
`/~
`_....J \
`
`,.r~_ THRESHOLD
`-7-F--VALU~
`
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`
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`
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`wO
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`
`f.,OUJ
`
`~JUST-FOCUS
`UNNECESSARY FOCUS POINT
`ERROR SIGNALS
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 24 of 43
`
`5,446,565
`
`F/G 36,4
`
`OBJECTIVE LENS 27
`APPROACHES
`
`OBJECTIVE LENS 27
`GOES AWAY
`
`FE6
`
`THRESHOLD
`VALUE
`
`c~
`
`,?
`
`Z
`
`JUST-FOCUS
`POINT
`
`36B
`
`OBJECTIVE LENS 27
`APPROACHES
`
`OBJECTIVE LENS 27
`GOES AWAY
`
`r
`
`FE7
`
`u.,~
`
`-’r" p-.l
`
`Zn,-
`IJU,O
`l-- n"
`(.0 I.U
`
`~_~LRuESFHOL~.
`
`JUST-FOCUS
`POINT
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 25 of 43
`
`5,446,565
`
`$2
`
`T2
`
`T1
`
`OR 25
`
`26, 32 OR 33
`5/,
`
`I
`I
`
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`27
`
`91
`
`55 92
`
`93 L4R 63
`
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`
`57
`
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`
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`
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`
`I
`
`52
`
`/"I~
`
`93c
`
`93b
`
`XI=
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 26 of 43
`
`5,446,565
`
`F16. 40,4
`
`$1
`
`T1
`
`L4., L4.R ,,," 7
`
`26,32 OR 33 J
`
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`?s3
`
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`
`×1
`
`X
`
`I .z
`
`Y
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 27 of 43
`
`5,446,565
`
`FIG. 40B
`
`$2
`
`26, 32
`OR 33
`
`FIG 41
`
`I03a
`
`102
`
`103b
`
`103b
`
`102a
`
`Y1
`
`T
`
`X1°
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 28 of 43
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`5,446,565
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`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 29 of 43
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`5,446,565
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`FIG. /+3
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`T1 $6
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`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 30 of 43
`
`5,446,565
`
`FIG. 1+4
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`53
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`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 31 of 43
`
`5,446,565
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`FIG. /+5
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`INFORMATION
`SIGNAL
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`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 32 of 43
`
`5,446,565
`
`FIG. /-,6
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`135
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`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 33 of 43
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`5,446,565
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`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 34 of 43
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`5,446,565
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`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 35 of 43
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`5,446,565
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`
`U.S. Patent
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`Aug. 29, 1995
`
`Sheet 36 of 43
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`5,446,565
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`FIG. 50
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`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 37 of 43
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`5,446,565
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`FIG. 51
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`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 38 of 43
`
`5,446,565
`
`FIG. 53
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`172 173
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`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 39 of 43
`
`5,446,565
`
`FIG. 55
`
`176
`
`\
`
`FIG. 55
`
`AN OPTICAL HEAD APPARATUS IS MOVED UNDER AN
`INNERMOST RECORDING TRACK OF AN OPTICAL DISK
`(cid:128)
`I A FOCUS CONTROL IS PERFORMED TO CONVERGE
`DIFFRACTED LIGHT ON THE INNERMOST RECORDING TRACK
`
`~211
`212
`
`I A TRACKING CONTROL IS PERFORMED TO DETECT A PIECE ~213
`
`±
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`ORMATION ~ YES
`A PIECE OF ~
`DISTINGU!SHING / I
`"-..~ORMATION?~ I
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`I NO
`[
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`ANOTHER FOCUS CONTROL IS
`PERFORMED TO CONVERGE
`TRANSMITTED LIGHT ON A HIGH
`DENSITY OPTICAL DISK
`
`THE FOCUS CONTROL AND THE TRACKING CONTROL IS
`CONTINUED TO CONVERGE THE DIFFRACTED LIGHT ON
`A CONVENTIONAL OPTICAL DISK
`
`1216
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 40 of 43
`
`5,446,565
`
`FIG. 57
`
`CONVENTIONAL OPTICAL DISK
`
`182 OR 25 182
`/v /’v
`ROTATING MEANS
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`OPTICAL HEAD APPARATUS ¢101,111,121,151 OR 16!
`t
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`
`FIG. 58
`
`AN OPTICAL HEAD APPARATUS IS MOVED UNDER AN
`INNERMOST RECORDING TRACK OF AN OPTICAL DISK
`
`A FOCUS CONTROL IS PERFORMED TO CONVERGE
`DIFFRACTED LIGHT ON THE INNERMOST RECORDING TRACK
`
`A TRACKING CONTROL IS PERFORMED TO DETECT A PIECE
`OF INFORMATION
`
`I
`I
`
`224
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`~J
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`/ INTENSITY OF AN
`/ INFORMATION SIGNAL ~ NO
`EXPRESSING THE INFORMATION ..%,,
`~MORE THAN A ~
`~THRESHOLD ~
`~VALUE ?/
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`ANOTHER FOCUS CONTROL IS
`PERFORMED TO CONVERGE
`TRANSMITTED LIGHT ON A HIGH
`DENSITY OPTICAL DISK
`
`THE FOCUS CONTROL AND THE TRACKING CONTROL IS
`
`I~226
`
`CONTINUED TO CONVERGE THE DIFFRACTED LIGHT ON r
`
`A CONVENTIONAl OPTICAL DISK
`
`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 41 of 43
`
`5,446,565
`
`FIG 59
`
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`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 42 of 43
`
`5,446,565
`
`FIG. 60
`
`1%
`
`195
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`193
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`OR /+2
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`SP2 SP1
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`

`
`U.S. Patent
`
`Aug. 29, 1995
`
`Sheet 43 of 43
`
`5,446,565
`
`ILl
`
`m
`oct
`
`m
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`

`
`1
`
`5,446,565
`
`2
`optical head apparatus proposed in Japanese Patent
`Application No. 46630 of 1991 which is applied by
`inventors of the present invention.
`
`COMPOUND OBJECTIVE LENS HAVING TWO
`FOCAL POINTS
`
`BACKGROUND OFTHEINVENTION
`
`1. Field of the Invention
`The present invention relates to a compound objec-
`tive lens composed of an objective lens and a hologram
`lens which has two focal points, an imaging optical
`system for converging light on two converging spots
`placed at different depths of an information medium
`with the compound objective lens, an optical head ap-
`paratus for recording, reproducing or erasing informa-
`tion on or from an information medium such as an opti-
`cal medium or a magneto-optical medium like an optical
`disk or an optical card with the imaging optical system,
`an optical disk in which a series of high density record-
`ing pits and a series of comparatively low density re-
`cording pits are provided, an optical disk apparatus for
`recording or reproducing information on or from the
`optical disk with the compound objective lens, a binary
`focus microscope having two focal points in which two
`types of images drawn at different depths are simulta~
`neousty observed, and an alignment apparatus for align-
`ing two types of images drawn at different depths with
`the binary focus microscope.
`
`2. Description of the Related Art
`
`An optical memory technique has been put to practi-
`cal use to manufacture an optical disk in which a pit
`pattern formed of a series of pits is drawn to record
`information. The optical disk is utilized as a high density
`and large capacity of information medium. For exam-
`ple, the optical disk is utilized for a digital audio disk, a
`video disk, a document fde disk, and a data file disk. To
`record information on the optical disk and to reproduce
`the information from the optical disk, a light beam radi-
`ated from a light source is minutely converged in an
`imaging optical system, and the light beam minutely
`converged is radiated to the optical disk through the
`imaging optical system. Therefore, the light beam is
`required to be reliably controlled in the imaging optical
`system with high accuracy.
`
`The imaging optical system is utilized for an optical
`head apparatus in which a u~L~,~a~ ~y~,e,~, ,o ,,dd,~,o~~
`ally provided to detect the intensity of the light beam
`reflected from the optical disk. Fundamental functions
`of the optical head apparatus are classified into a con-
`verging performance for minutely converging a light
`beam to form a diffraction-limited micro-spot of the
`light beam radiated on the optical disk, a focus control
`in a foens servo system, a tracking control in a tracking
`serve system, and the detection of pit signals (or infor-
`mation signals) obtained by radiating the light beam on
`a pit pattern of the optical disk. The fundamental func-
`tion of the optical head apparatus is determined by the
`combination of optical sub-systems and a photoelectric
`transfer detecting process according to a purpose and a
`use. Specifically, an optical head apparatus in which a
`holographic optical element (or hologram) is utilized to
`minimize and thin the optical head apparatus has been
`recently proposed.
`
`PREVIOUSLY PROPOSED ART
`
`FIG. 1 is a constitutional view of a conventional
`
`5 As shown in FIG. 1, a conventional optical head
`apparatus 11 for recording or reproducing information
`on or from an information medium 12 such as an optical
`disk is provided with a light beam source 13 such as a
`semiconductor laser, a transmission type of blazed holo-
`10 gram 14 for transmitting a light beam L1 radiated from
`the light beam source 12 without any diffraction in an
`outgoing optical path and diffracting a light beam L2
`reflected on the information medium 12 in a returning
`optical path, an objective lens 15 for converging the
`15 fight beam L1 transmitting through the hologram 13 on
`the information medium 14 to read the information, an
`actuator 16 for integrally moving the objective lens 15
`with the blazed hologram 13 to focus the light beam L1
`on the information medium 12 with the objective lens
`20 15, and a photo detector 17 for detecting the intensity of
`the light beam L2 reflected on the information medium
`12 to reproduce the information.
`
`As shown in FIG. 2A, a relative position between the
`blazed hologram 14 and the objective lens 15 is fixed by
`25 a fixing means 18. Or, as shown in FIG. 2B, a blazed
`
`pattern is formed on a side of the objective lens 15 to
`integrally form the blazed hologram 14 with the objec-
`tive lens 15.
`
`30 In the above configuration, a light beam L1 (or a laser
`beam) radiated f~om the light beam source 13 is radiated
`to the blazed hologram 14, and the light beam L1
`mainly transmits through the blazed hologram 14 with-
`out any diffraction in an outgoing optical path. The
`35 light beam L1 transmitting through the blazed holo-
`gram 14 is called zero-order diffracted light. Thereafter,
`the zero-order diffracted light L1 is converged on the
`information medium 12 by the objective lens 15. In the
`information medium 12, information indicated by a
`40 series of patterned pits is recorded and read by the
`zero-order diffracted light L1. Thereafter, a beam light
`L2 having the information is reflected toward the ob-
`jective lens 15 in a returning optical path and is incident
`to the blazed hologram 14. In the blazed hologram 14,
`45 the light L2 is mainly diffracted. The light L2 diffracted
`is called first-order diffracted light. Thereafter, the
`first-order diffracted light L2 is received in the photo
`detector 17.
`
`In the photo detector 17, the intensity distribution of
`50 the first-order diffracted light L2 is detected. Therefore,
`a servo signal for adjusting the position of the objective
`lens 15 by the action of the actuator 16 is obtained. Also,
`the intensity of the fLrst-order diffracted light L2 is
`detected in the photo detector 17. Because the informa-
`55 tion medium 12 is rotated at high speed, the patterned
`pits radiated by the light 17 are changed so that the
`intensity of the first-order diffracted light L2 detected is
`changed. Therefore, an information signal indicating
`the information recorded in the information medium 12
`60 is obtained by detecting the change in intensity of the
`first-order diffracted light L2.
`
`65
`
`In the above operation, a part of the light beam L1 is
`necessarily diffracted in the blazed hologram 14 when
`the light beam LI is radiated to the blazed hologram 14
`in the outgoing optical path. Therefore, unnecessary
`diffracted light such as first-order diffracted light and
`minus first-order diffracted light necessarily occurs. In
`
`

`
`5,446,565
`
`eases where the hologram 14 is not blazed, the unneces-
`sary diffracted light in the outgoing optical path also
`reads the information recorded in the information me-
`dium 12, and the unnecessary fight is undesirably re-
`ceived in the photo detector 17. To prevent the unnec-
`essary fight from transmitting to the information me-
`dium 12, the blazed hologram 14 is manufactured to
`form a blazed hologram pattern on the surface thereof,
`so that the intensity of the unnecessary light received in
`the photo detector 17 is decreased.
`Also, because an objective lens of a conventional
`microscope has only a focal point, images placed within
`a focal depth ofthe objective lens can be only observed
`with the conventional microscope.
`Also, a minute circuit is formed on a semiconductor
`such as a group III-V compound semiconductor to
`form a microwave circuit, an opto-eleetronic detector
`or a solid state laser. In this ease, a photo-sensitive mate-
`rial is coated on a sample made of the semiconductor.
`Thereafter, a relative position between the sample and a
`photo mask covering the sample is adjusted by utilizing
`an alignment apparatus, and the photo-sensitive sensi-
`tive material is exposed by a beam of exposure fight
`through the photo mask to transfer a circuit pattern
`drawn on the photo mask to the photo-sensitive mate-
`rial in an exposure process by utilizing an exposure
`apparatus. For example, an alignment pattern is drawn
`on a reverse side of the sample, and a relative position
`between the sample and the photo mask is adjusted with
`high accuracy while simultaneously observing the
`alignment pattern of the sample and the circuit pattern
`of the photo mask with the conventional microscope.
`Thereafter, the circuit pattern of the photo mask is
`transferred to a front side of the sample.
`In this case, because images placed within a focal
`depth of an objective lens utilized in the conventional
`microscope can be only observed with the conventional
`microscope, it is required to utilize the conventional
`microscope having a deep focal depth in the alignment
`apparatus in eases where the alignment pattern and the
`circuit pattern are simultaneously observed with the
`conventional microscope. Therefore, the magnification
`of the conventional microscope having a deep focal
`depth is lowered.
`
`PROBLEMS TO BE SOLVED BY THE
`
`An optical disk having a high density memory capac-
`ity has been recently developed because of the improve-
`ment in a design technique of an optical system and the
`shortening of the wavelength of light radiated from a
`semiconductor laser. For example, a numerical aperture
`at an optical disk side of an imaging optical system in
`which a light beam converged on an optical disk is
`minutely narrowed in diameter is enlarged to obtain the
`optical disk having a high density memory capacity. In
`this case, the degree of aberration occurring in the im-
`aging optical system is increased because an optical axis
`of the system tilts from a normal fine of the optical disk.
`As the numerical aperture is increased, the degree of the
`aberration is enlarged. To prevent the increase of the
`numerical aperture, it is effective to thin the thickness of
`the optical disk. The thickness of the optical disk de-
`notes a distance from a surface of the optical disk (or an
`information medium) radiated by a light beam to an
`information recording plane on which a series of pat-
`terned pits are formed.
`
`FIG. 3 shows a relationship between the thickness of
`the optical disk and the numerical aperture on condition
`that the tilt of the optical axis is constant.
`As shown in FIG. 3, because the numerical aperture
`5 is 0.5 when the thickness of the optical disk is 1.2 ram, it
`is effective to thin the optical disk to 0.6 mm in thickness
`when the numerical aperture is increased to 0.6. In this
`case, even though the numerical aperture is increased
`on condition that the tilt of the optical axis is not
`10 changed, the degree of the aberration is not increased.
`Therefore, it is preferred that the thickness of the opti-
`cal disk be thinned to obtain the optical disk having a
`high density memory capacity.
`Accordingly, it is expected that the thickness of a
`15 prospective optical disk having a high density memory
`capacity becomes thinner than that of a present optical
`disk such as a compact disk appearing on the market
`now. For example, the thickness of the compact disk is
`about 1.2 rnrn~ and the thickness of the prospective
`20 optical disk is expected to range from 0.4 ram to 0.8 ram.
`In this ease, it is required to record or reproduce infor-
`mation on or from an optical disk with an optical head
`system regardless of whether the optical disk is the
`present optical disk or the prospective optical disk hay-
`25 ing a high density memory capacity. That is, an optical
`head apparatus having an imaging optical system in
`which a light beam is converged on an optical.disk
`within the diffraction limit regardless of whether the
`optical disk is thick or thin is required.
`30 However, in .a conventional optical head apparatus, a
`piece of information is only recorded or reproduced on
`or from an optical disk having a fixed thickness. For
`example, in eases where the thickness of the information
`medium 12 is off a regular range by about __+0.1 mm or
`35 more, an aberration such as a spherical aberration oc-
`curs when the optical head apparatus 11 is operated.
`Therefore, the recording or the reproduction of the
`information is impossible. Accordingly, there is a draw-
`back that an optical head apparatus in which a piece of
`40 information is recorded or reproduced on or from an
`optical .disk regardless of whether the optical disk is the
`present optical disk or the prospective optical disk hav-
`ing a high density memory capacity cannot be manufac-
`tured in a conventional technique.
`45 Also, there is a problem in the conventional micro-
`scope. That is, because an objective lens of the conven-
`f!on~ mJeroseope 1~ .... ly ~ focal point *,and images
`placed within a focal depth of the objective lens can be
`only observed with the conventional microscope, the
`50 magnification of the conventional microscope and an
`observed range in an optical axis direction are in a
`trade-off relationship. Therefore, there is a drawback
`that it is impossible to observe the images over a wide
`observed range in the optical axis direction at high
`55 magnification
`Also, there is a problem in the alignment apparatus.
`That is, when a circuit pattern drawn on the photo mask
`is transferred to the front side of the sample after an
`alignment pattern is drawn on the reverse side of the
`60 sample, the alignment of the photomask and the sample
`is performed by simultaneously observing the circuit
`pattern of the photo mask and the alignment pattern of
`the sample with the conventional microscope having a
`deep focal depth and a low magnification. Therefore,
`65 because the conventional microscope has a low magnifi-
`cation, there is a drawback that it is impossible to align
`the photo mask with the sample at a high accuracy
`ranging within 5/~m.
`
`

`
`5,446,565
`
`6
`and converged by the lens means, so that the transmit-
`ted light is focused on a fast converging spot positioned
`at a first focal point.
`In contrast, a remaining part of incident light is dif-
`5 fracted by the hologram means. Therefore, a beam of
`diffracted light such as a beam of first-order diffracted
`light which is diverged from the hologram lens or con-
`verges is formed. Thereafter, the diffracted light is re.
`fracted and converged by the lens means, so that the
`10 diffracted light is focused on a second converging spot
`positioned at a second focal point.
`In this case, because a propagation direction of the
`transmitted light differs from that of the diffracted light,
`the first focal point of the compound objective lens for
`15 the transmitted light differs from the second focal point
`of the compound objective lens for the diffracted light.
`Therefore, the compound objective lens has two focal
`points, and the incident light transmitting through the
`compound objective lens are converged on two con-
`20 verging points.
`
`25
`
`Accordingly, the incident light transmitting through
`the compound objective lens can be reliably converged
`on an information medium regardless whether the infor-
`mation medium has a fast thickness or a second thick-
`hess.
`It is preferred that a grating pattern be drawn in the
`hologram means in a concentric circle shape, the grat-
`ing pattern of the hologram means be formed in relief to
`30 concentrically form alternating rows of bottom portions
`and top portions, a height H of relief in the grating
`pattern be set to H<k/(n(k)--l) where a symbol ~.
`denotes a wavelength of the incident light and a symbol
`n(k) denotes a refractive index of the hologram means
`35 made of a glass material for the incident light having the
`wavelength k, and a difference in phase modulation
`degree between the incident light transmitting through
`a bottom portion of the grating pattern and the incident
`light transmitting through a top portion of the grating
`
`40 pattern be lower than 2~r radians to set a diffraction
`efficiency of the hologram means to a value lower than
`100%.
`In the above configuration, because the height of the
`relief in the grating pattern is lower than a value
`
`S~RY OF THE INVENTION
`A first object of the present invention is to provide,
`with due consideration to the drawbacks of such a con-
`ventional objective lens having a focal point, a com-
`pound objective lens having two focal points.
`A second object of the present invention is to provide
`an imaging optical system having the compound objec-
`tive lens in which fight transmitting through the com-
`pound objective lens is converged at a diffraction limit
`on two converging spots placed at different depths of an
`information medium.
`A third object of the present invention is to provide
`an optical head apparatus having the imaging optical
`system in which information is recorded, reproduced or
`erased on or from one of the converging spots of the
`information medium at which light is converged by the
`action of the imaging optical system.
`A fourth object of the present invention is to provide
`a high density optical disk in which a series of first
`recording pits is formed to record pieces of information
`at high density on a thin substrate.
`A f