(19) United States
`(12) Reissued Patent
`Yoo et al.
`
`I Illll IMI Ill Illll IM Ill IIll M Illll Ill Illll IIIIII Ill Jill Illl
`
`US00RE43106E
`
`(lO) Patent Number:
`US RE43,106 E
`(45) Date of Reissued Patent:
`Jan. 17, 2012
`
`(54) OPTICAL PICKUP COMPATIBLE WITH A
`DIGITAL VERSATILE DISK AND A
`RECORDABLE COMPACT DISK USING A
`HOLOGRAPHIC RING LENS
`
`(75)
`
`Inventors: Jang-Hoon Yoo, Seoul (KR); Chul-Woo
`Lee, Kyunggi-Do (KR)
`
`(73) Assignee: Samsung Electronics Co., Ltd.,
`Suwon-si (KR)
`
`(21) Appl. No.: 11/849,609
`
`(22) Filed:
`
`Sep. 4, 2007
`
`Related U.S. Patent Documents
`
`Reissue of:
`
`(64) Patent No.:
`Issued:
`Appl. No.:
`Filed:
`
`7,046,611
`May 16, 2006
`09/930,964
`Aug. 17, 2001
`
`(56)
`
`References Cited
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`
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`
`(Continued)
`
`Primary Examiner -- Muhammad N Edun
`(74) Attorney, Agent, or Firm -- NSIP Law
`
`U.S. Applications:
`Continuation of application No. 09/419,792, filed on
`
`(63)
`
`Oct. 18, 1999, now Pat. No. 6,304,540, which is a
`continuation of application No. 09/049,988, filed on
`Mar. 30, 1998, now Pat. No. 6,043,912.
`
`(3o)
`
`Foreign Application Priority Data
`
`Mar. 28,1997 (KR) ..................................... 97-11297
`
`(51) Int. CI.
`GllB 7/00
`
`(2006.01)
`(52) U.S. CI ............ 369/112.08; 369/112.1; 369/112.13;
`369/112.23; 369/44.23
`(58) Field of Classification Search ........................ None
`See application file for complete search history.
`
`ABSTRACT
`(57)
`An optical pickup apparatus compatible with at least two
`types of optical recording media, using light beams having
`respective different wavelengths for recording and reading
`information, the optical pickup apparatus including two laser
`light sources to emit light beams having the different wave-
`lengths, a holographic lens including a holographic ring to
`transmit the light beams incident in an imler region of the
`holographic ring, and to difliact a specific light beam among
`the light beams emitted ~om the laser light sources incident in
`an outer region relative to the inner region, an objective lens
`to focus the light beams passed through the holographic ring
`lens on the respective information recording surfaces of the
`two types of the optical recording media, optical elements to
`alter optical paths of the light beams reflected from the infor-
`mation recording surfaces of the optical recording media to
`corresponding photodetectors.
`
`62 Claims, 5 Drawing Sheets
`
`[--]
`
`I !
`
`41L__ j
`
`37
`
`LG Electronics, Inc. et al.
`EXHIBIT 1001
`IPR Petition for
`U.S. Patent No. RE43,106
`
`

`
`U.S. PATENT
`
`DOCUMENTS
`
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`
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`
`US RE43,106 E
`Page 2
`
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`
`FOREIGN PATENT DOCUMENTS
`
`EP
`EP
`EP
`EP
`GB
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`WO
`
`0 587 297
`0 747 893
`0 803 867
`0 838 812
`508448
`62-73429
`2-118508
`3-244450
`4-178931
`5-81698
`5-242520
`6-96466
`6-259804
`7-65407
`7-98431
`7-302437
`7-311969
`8-55363
`8-62493
`8-240718
`WO 98/19303
`
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`9/1994
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`11/1995
`11/1995
`2/1996
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`9/1996
`5/1998
`
`OTHER PUBLICATIONS
`
`Tagaki et al., "DVD/CD Compatible Pick-up with Liquid Crystal
`Shutter," IEEE (1997).
`M. Shinoda, et al., "Two-Element Objective Lenses and Spherical
`Aberration Correction for DVR," ]EEE Transactions on Consumer
`Electronics, vol. 42, No. 3, pp. 808-813 (Aug. 1996).
`
`

`
`U.S. Patent
`
`Jan. 17, 2012 Sheet 1 of 5
`
`US RE43,106 E
`
`FIG, I
`
`2 ,-14- 1
`
`9 r----=_ , .~..~- , ~ ......
`~’" ""
`,~25
`r 5 17
`1
`~_~.~_ .. _ _
`
`!
`
`J
`
`18
`
`E ! \ I 1
`
`13 ~ 16
`, _,, 24-
`
`% i
`\ t
`
`FIG. 2
`(PRIOR ART)
`
`REGION 2
`
`REGION 1
`
`REGION 2
`
`IIIIII
`IIIII~
`IIIIII
`
`"rTT~
`,lllltl
`III1111
`
`NA=0.4-5
`NA=O,6
`
`

`
`U.S. Patent
`
`Jan. 17, 2012 Sheet 2 of 5
`
`US RE43,106 E
`
`FIG, 3
`
`3
`
`!
`I
`
`~ ~ J
`
`~37
`
`43
`
`~
`35
`42
`
`FIG. 4A
`
`r--]
`
`37
`
`

`
`U.S. Patent
`
`Jan. 17, 2012 Sheet 3 of 5
`
`US RE43,106 E
`
`FIG, 4B
`
`I
`
`FIG, 5A
`
`E
`
`C
`
`I
`
`I
`
`FLA==0.3
`NA=0.5
`
`351 "----..
`
`

`
`U.S. Patent
`
`Jan. 17, 2012 Sheet 4 of 5
`
`US RE43,106 E
`
`FIG, 5B
`
`T’’-~
`I
`
`!
`
`I
`|
`I
`
`1200
`
`1000
`
`800
`
`600
`
`400
`
`200
`
`o
`0 200 400 600 800 10001200
`
`FIG,, 6
`
`0 1 2 3 # 5 t
`
`

`
`U.S. Patent
`
`Jan. 17, 2012 Sheet 5 of 5
`
`US RE43,106 E
`
`FIG. 7
`
`

`
`US RE43,106 E
`
`1
`OPTICAL PICKUP COMPATIBLE WITH A
`DIGITAL VERSATILE DISK AND A
`RECORDABLE COMPACT DISK USING A
`HOLOGRAPItlC RING LENS
`
`Matter enclosed in heavy brackets [ ] appears in the
`original patent but forms no part of this reissue specifica-
`tion; matter printed in italics indicates the additions
`made by reissue.
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`20
`
`2
`Light having the 635 run wavelength emitted from a first
`laser light source 11 is incident to a first collimating lens 12,
`in which the light is shown in a solid line. The first collimating
`lens 12 collimates the incident light beam to be in a parallel
`5 light beam. The light beam passing through the first collimat-
`ing lens 12 is reflected by a beam splitter 13 and then goes to
`an interference filter prism 14.
`Light having the 780 nm wavelength emitted from a second
`laser light source 21 passes through a second collimating lens
`10 22, a beam splitter 23 and a converging lens 24, and then goes
`to the interference filter prism 14, in which the fight is shown
`in a dotted line. Here, the light beam of the 780 nm wave-
`length is converged by the interference filter prism 14. An
`optical system having such a structure is called a "finite
`optical system." The interference filter prism 14 totally trans-
`mits the light beam of the 635 nm wavelength reflected from
`the beam splitter 13, and totally reflects the light beam of the
`780 nm wavelength converged by the converging lens 24. As
`a result, the light beam outgoing t?om the first laser light
`source 11 is incident to a quarter-wave plate 15 in the form of
`a parallel beam by the collimating lens 12, while the light
`beam from the second laser light source 21 is incident to the
`quarter-wave plate 15 in the form of a divergent beam by the
`converging lens 24 and the interference filter prism 14. The
`25 light transmitted through the quarter-wave plate 15 passes
`fltrough a variable aperture 16 having a thin film structure and
`then is incident to an objective lens 17.
`The light beam of the 635 nm wavelength emitted from the
`first laser light source 11 is focused by the objective lens 17 on
`30 an information recording surface in the DVD 18 having a
`thickness of 0.6 man. Therefore, the light reflected from the
`information recording surface of the DVD 18 contains infor-
`mation recorded on the information recording surface. The
`reflected light is transmitted by the beam splitter 13, and is
`35 then incident to a photodetector tbr detecting optical inibr-
`marion.
`If the finite optical system described above is not used,
`when the light beam of the 780 mn wavelength emitted from
`the second laser light source 21 is focused on an information
`40 recording surface in the CD-R 25 having a thickness of 1.2
`mm using the above described objective lens 17, spherical
`aberration is generated due to a difference in thickness
`between the DVD 18 and the CD-R 25. The spherical aber-
`ration is due to the fact that the distance between the infor-
`45 marion recording surface of the CD-R 25 and the objective
`lens 17 is farther than that between the information recording
`surface of the DVD 18 and the objective lens 17, along an
`optical axis. To reduce such a spherical aberration, a construc-
`tion of a finite optical system including the converging lens 24
`50 is required. By using the variable aperture 16 to be described
`later with reference to FIG. 2, the light beam of the 780 nm
`wavelength lbrms an optimized beam spot on the information
`recording surface of the CD-R 25. The light beam of the 780
`nm wavelength reflected t~om the CD-R 25 is reflected by the
`55 beam splitter 23, and then detected in a photodetector 26.
`The thin-film type variable aperture 16 of FIG. I, as shown
`in FIG. 2, has a structure which can selectively transmit the
`light beams incident to the regions whose numerical aperture
`(NA) is less than or equal to 0.6, which coincides with the
`6o diameter of the objective lens 17. That is, the variable aperture
`16 is partitioned into two regions based on the numerical
`aperture (NA) of 0.45 with respect to an optical axis. Among
`the two regions, a first region 1 transmits both light beanas of
`635 nm wavelength and 780 nm wavelength. A second region
`65 2 totally transmits the light beam of the 635 nm wavelength
`and totally reflects the light beam of the 780 nm wavelength.
`The region 1 is a region having a numerical aperture less than
`
`This application claims the benefit of Korean Application 15
`No. 97-11297, filed Mar. 28, 1997, oald is a continuation of
`U.S. patent application Ser. No. 09/419,792 filed in the U.S.
`Patent and Trademark Office on Oct. 18, 1999 and which
`issued as U.S. Pat. No. 6,304,540 which is a continuation of
`U.S. patent application Ser. No. 09/049,988 filed Mar. 30,
`1998, which issued as U.S. Pat. No. 6,043,912, the disclo-
`sures of which are incorporated herein by reference.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention relates to an optical pickup apparatus
`compatible with a digital video disk (DVD) and a recordable
`compact disk (CD-R), and more particularly, to an optical
`pickup apparatus which can compatibly record information
`on and read information from a digital video disk (DVD) and
`a recordable compact disk (CD-R), respectively, using a holo-
`graphic lens.
`2. Description of the Related Art
`An optical pickup apparatus records and reads the infor-
`mation such as video, audio or data at a high density, and
`various types of recording media are a disk, a card and a tape.
`Among them, the disk type is primarily used. Recently, in the
`field of the optical disk apparatus, a laser disk (LD), a com-
`pact disk (CD) and a digital video disk (DVD) have been
`developed. Such an optical disk includes a plastic or glass
`medium having a certain thickness along an axial direction to
`which light is incident, and a signal recording surface on
`which information is recorded and located on the plastic or
`glass mediuna.
`So far, a high-density optical disk system enlarges a
`numerical aperture of an objective lens to increase a recording
`density, and uses a short wavelength light source of 635 nm or
`650 nm, Accordingly, the high-density optical disk system
`can record or read signals on or from a digital video disk, and
`can also read signals fl’om a CD. However, to be compatible
`with a recent type ofa CD, that is, a recordable CD (CD-R),
`light having a wavelength of 780 nm should be used, due to
`the recording characteristic of the CD-R recording medium.
`As a result, using the light beam wavelengths of 780 nm and
`635 (or 650) mn in a single optical pickup becomes very
`important for compatibility of the DVD and the CD-R. A
`conventional optical pickup which is compatible with the
`DVD and the CD-R will be described below with reference to
`FIG. 1.
`FIG. I shows an optical pickup using two laser light diodes
`as light sources for a DVD and a CD-R and a single objective
`lens. The FIG. 1 optical pickup uses laser light having a
`wavelength of 635 mn when reproducing a 1)VD, and uses
`laser light having a wavelength of 780 nm when recording and
`reproducing a CD-R.
`
`

`
`US RE43,106 E
`
`3
`or equal to 0.45, and the region 2 is an outer region relative to
`the region 1 in which a dielectric thin film is coated. The
`region I is comprised of a quartz (51!)2) thin film to remove
`any optical aberration generated by the dielectric thin film
`coated region 2.
`By using the variable aperture 16, the 780 nm wavelength
`light transmitted through the region I having the 0.45 NA or
`below forms a beam spot appropriate to the CD-R 25 on the
`information recording surface thereof. Thus, the FIG. 1 opti-
`cal pickup uses an optimum beam spot when a disk mode is
`changed from the DVD 18 to the CD-R 25. Accordingly, the
`FIG. 1 optical pickup is compatible for use with the CD-R.
`However, the optical pickup shown in FIG. 1 and as
`described above should form a "finite optical system" with
`respect to the 780 run wavelength light in order to remove any
`spherical aberration generated when changing a DVD com-
`patibly with a CD-R. Also, due to the optical thin film, that is,
`tile dielectric thin film, wtfich is formed in the region 2 of the
`variable aperture 16 having the NA of 0.45 or above, an
`optical path difference between the light transmitted through
`the region 1 having the NA of 0.45 or below and that trans-
`mitted through the region 2 having the NA of 0.45 or above,
`is generated. To eradicate this difference, it is necessary to
`form an optical thin film in the region 1. Due to this reason, a
`quartz coating (SiOa) is fbmled in the region 1 and a multi-
`layer thin fihn is formed in the region 2. However, such a
`fabricating process does not only become complicated but
`also adjustment of the thickness of the thin fihn should be
`performed precisely in units of"pm". Thus, it has been diffi-
`cult to mass-produce the optical pickup.
`
`SUMMARY OF THE INVENTION
`
`An object of the present invention is to provide an optical
`pickup apparatus which is compatible with a digital video
`disk (DVD) and a recordable compact disk (CD-R), by adopt-
`ing an infinite optical system and using a holographic lens to
`remove a spherical aberration generated due to a difference in
`thickness between optical disks.
`Additional objects and advamages of the invention will be
`set forth in part in the description which follows and, in part,
`will be obvious ti-om the description, or may be leamed by
`practice of the invention.
`To accomplish the above and other objects of the present
`invention, there is provided an optical pickup apparatus com-
`patible with at least two types of optical recording media,
`using light beams having respective different wavelengths for
`recording and reading information, the optical pickup appa-
`ratus including two laser light sources to emit light beams
`having different wavelengths, respectively, a holographic
`lens, including a holographic ring, for transmitting both of the
`light beams emitted from the two laser light sources in an
`inner region of the holographic ring, and diffracting a specific
`light beam among the light beams emitted from the laser light
`sources in an outer region of the holographic ring, an objec-
`tive lens to focus the light beams passed through the holo-
`graphic ring lens on the respective information recording
`surfaces of the two types of the optical recording media,
`optical elements to alter optical paths of the light beams
`reflected from the information recording surfaces of the opti-
`cal recording media, and two photodetectors to individually
`detect optical information from the light beams incident from
`the optical elements.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`These and other objects and advantages of the invention
`will become apparent and more readily appreciated from the
`
`5
`
`4
`following description of the preferred embodiments, taken in
`conjunction with the accompanying drawings of which:
`FIG. I is a view showing the construction of a conventional
`optical pickup;
`FIG. 2 is a view for explaining the structure of a conven-
`tional variable aperture shown in FIG. 1
`FIG. 3 is a view showing an optical system of an optical
`pickup according to an embodiment of the prcsent invention;
`FIG. 4A is a view showing a positional relationship
`between a holographic ring lens and an obj ective lens accord-
`ing to the embodiment of the present invention, and
`FIG. 4B is a view showing the plane surface of the holo-
`graphic ring lens;
`FIG. 5A is a view showing the plane surface of the holo-
`graphic ring lens, and FIG. 5B is a graphical view showing
`that part of the FIG. 5A region which is enlarged;
`FIG. 6 is a graphical view showing transmissive efficiency
`according to the groove depth of the holographic ring lens
`x0 with regard to two wavelengths; and
`FIG. 7 is a view showing that the holographic ring lens and
`the objective lens are integrally incorporated.
`
`10
`
`55
`
`DETAILED DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`25
`
`Reference will now be made in detail to the present pre-
`ferred embodiments of the present invention, examples of
`which are illustrated in the accompanying drawings, wherein
`3o like reference numerals refer to the like elements throughout.
`The embodiments are described below in order to explain the
`present invention by referring to the figures.
`FIG. 3 shows an optical system of an optical pickup accord-
`ing to an embodiment of the present invention. Referring to
`35 FIG. 3, the optical pickup apparatus includes two laser light
`sources 31 and 39 for emitting light beams having different
`wavelengths, respectively, two holographic beam splitters 32
`and 40 for altering optical paths of the light beams reflected
`from information recording surfaces of first and second types
`4o of optical disks, a beam splitter 33 for totally transmitting or
`reflecting the incident light beam according to the light wave-
`length, a collimating lens 34 for collimating the incident light
`beam to be in a parallel form, a holographic ring lens 35 for
`diffracting the incident light beam according to its wave-
`45 length, and an objective lens 36 for focusing the light beams
`on the respective information recording surfaces of optical
`disks 37 and 41. Two photodetectors 38 and 42 which detect
`the light beams reflected from the respective information
`recording surfaces of the optical disks 37 and 41 and the laser
`5o light sources 31 and 39 are integrally incorporated into single
`modules to form units 30 and 43, respectively. The operation
`of the optical pickup constructed above will be described
`below, in which a DVD and a CD-R are described as optical
`recording media.
`First, when recording and/or reading information on a
`DVI), a light beam having the 650 nm (or 635 nm) wave-
`length is enfitted from the first laser light source 31 and is
`incident to the holographic beam splitter 32, in whichthe light
`is shown as a solid line. The incident light beam passes
`60 through the holographic beam splitter 32 and proceeds to tile
`beam splitter 33. When recording and/or reading intbmmtion
`about a CD-R, a light beam having the 780 lml wavelength is
`emitted from the second laser light source 39 and is incident
`to the holographic beam splitter 40, in which the light is
`65 shown as a dotted line. The incident light beam passes
`through the holographic beam splitter 40 and proceeds to the
`beam splitter 33.
`
`55
`
`

`
`US RE43,106 E
`
`5
`The beam splitter 33 totally transmits the incident light
`beam of the 650 nm wavelength and totally reflects the inci-
`dent light beam of the 780 mn wavelength. The totally trans-
`mitted or reflected light beam goes to the holographic ring
`lens 35 in the lbrm of a parallel beam after passing through the
`collimating lens 34. The holographic ring lens 35 selectively
`diffracts the incident light beana according to the wavelength
`thereot, to prevent the generation of spherical aberration with
`regard to the light beams focused on the information record-
`ing surfaces of the optical disks 37 and 41.
`FIG. 4A is a view showing a positional relationship
`between the holographic ring lens 35 and an optical surface of
`the holographic ring lens 35. As shown in FIG. 4A, the objec-
`tive lens 36 is partitioned into regions A and B. The region A,
`being closer to an optical axis of the objective lens 36, has
`little effect on a spherical aberration and the region B, being
`farther from the optical axis, has a large effect on the spherical
`aberration. Also, the objective lens 36 is most appropriate for
`a disk having a thin thickness such as a DVD. Thus, when a
`DVD is exchanged with a thick disk such as a CD-R to operate
`the optical pickup, the holographic ring lens 35 is required. If
`the holographic ring lens 35 is not used when recording
`and/or reading information on the CD-R, the spherical aber-
`ration in the beam spot formed on the information recording
`surface of the disk becomes large, in which the size is more
`than 1.7 pan. Generally, the size of the beam spot formed on
`the information recording surface of the CD-R is 1.41 pan.
`The holograplfic ring tens 35 diffracts the 780 nm wavelength
`light beam passed through the region F of the holographic
`ring lens 35 so as to prevent the generation of spherical
`aberration, for which a hologram depicted with clots ha FIG.
`4B is disposed on the region F of the holographic ring lens 35.
`Accordingly, the light beam which is incident to the region A
`of the holographic ring lens 35, passes through the objective
`lens 36 without any diffraction by the holographic ring lens
`35, and then is directly focused on the disk. The region F of
`the light beam which is incident to the holographic ring lens
`35, is wavelength-selectively diffracted by the holographic
`ring lens 35 and then proceeds to the objective lens 36. The
`diffracted light beam of 780 nm wavelength passing through
`the objective lens 36 makes the size of the beam spot focused
`on the disk smaller, and no spherical aberration is generated.
`A focal plane on which the diffracted 780 mn wavelength
`light beam passing through the region F is focused should
`coincide with an optimizxxt surface of the disk on which the
`780 nrn wavelength light beam passing through the region A
`is focused. By using the holographic ring lens 35, a working
`distance from the surface of the objective lens 36 to the
`information recording surfaces of the disks becomes shorter
`in the CD-R 41 rather than in the DVD 37.
`FIG. 5A is a view showing the structure of the holographic
`ring lens 35. The holographic ring lens 35 has an ilmer region
`351 including an optical center of the holographic ring lens
`35, a holographic ring 353 centering at the optical center of
`the holographic ring lens 35 and surrounding the inner region
`351, and an outer region 355 surrounding the holographic
`ring 353. In connection with FIG. 4A, the hmer region 351
`coincides with the region A, the holographic ring 353 coin-
`cides with the region F, and the outer region 355 coincides
`with the region B except the region F. A region D shown in
`FIG. 5B below where the hologram in the holographic ring
`lens 35 shown in FIG. 5A is provided on the holographic ring
`353, corresponds to the numerical aperture of 0.3-0.5 which is
`intended to be appropriate to the CD-R. In FIG. 5A, a symbol
`E indicates the diameter of the objective lens for a DVD
`whose numerical aperture (NA) is 0.6. Also, the holographic
`ring lens 35 used in the present invention can selectively
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`6
`adjust the numerical aperture (NA) of the objective lens
`according to the wavelengths of the light beam, and requires
`no separate variable aperture. The holographic ring lens 35
`has the same function as a general spherical lens which trans-
`5 mits a light beam in the convergent or divergent form. Further,
`
`the holographic ring lens 35 has a positive optical power and
`uses a phase shift hologram as a hologram formed in the
`holographic ring 353. An optimized depth of the grooves the
`hologram should be determined so that the holographic ring
`10 353 selectively diffracts the incident light beam according to
`
`the wavelength thereof. The holographic ring lens 35 is con-
`stmcted so that the light beam of the 650 nm wavelength has
`transmissive efficiency close to 100% and the light beam of
`the 780 mn wavelength has a zero-order transmissive effi-
`25 ciency 0% with respect to non-diffi’acted light beam. For that,
`
`in case that the holographic ring 52 has grooves of a constant
`depth the phase variation by the groove depth of the holo-
`graphic ring should be about 360° with respect to the 650 nm
`wavelength light. Since the phase variation is generated by
`2o 360o, the holographic ring lens 35 transmits most of the 650
`mn wavelength light. The phase variation by the holographic
`ring 353 should be optimized with respect to the 780 nm
`wavelength light, by which the 780 nm wavelength light is all
`diffracted as first-order light. As a result, the holographic ring
`25 353 is designed to hardly diffract the 650 wavelength light,
`
`but to diffract the 780 nm wavelength light as a first-order
`diffracted light. An optimized surface groove depth d of the
`holographic ring 353 for selectively diffracting 650 ran and
`780 nm wavelength light beams is detemfined by the follow-
`30 ing equations (1) and (2).
`
`35
`
`2rrd
`--~- (n - 1) = 2nm
`
`2rid ,
`--~7-(n - 1) = (2m’ + 1),I.
`
`(1)
`
`(2)
`
`Here, ~. is the 650 nm wavelength, ~’ is the 780 nna wave-
`4o length, and n and n’ denote a reflective index (1.514520) in the
`650 nm wavelength and a reflective index (1.511183) in the
`780 nm wavelength, respectively. In the above equations (1)
`and (2), if m-3 and m’ 2, the depth d becomes about 3.8 pm.
`FIG. 5B is a graphical view showing an enlarged view of
`45 the hologram region 1) shown in FIG. 5A. The hologram
`which is formed in the holographic ring 353 has grooves of a
`constant depth by etching or can be manufactured by mold-
`ing. Further, grooves of the hologram can be formed step-
`wisely, together with a ring pattern. The grooves of the holo-
`50 gram can also be tbrmed in a blazed type so as to maximize
`the diffraction efficiency on a non-zeroth order diffracted
`light.
`FIG. 6 is a graphical view showing zero-order transmissive
`efficiency of the holographic ring according to the wave-
`55 lengths of incident lights. When the surface groove depth d is
`3.8 grn, the 650 nm wavelength light is transmitted via the
`holographic ring 353 by 100% as shown in a solid line over-
`lapped with the symbol "++", and the 780 nm wavelength
`light is transmitted via the holographic ring 353 by 0% as
`6o shown by a solid line overlapped with a circle. At this time,
`the holographic ring 353 diffracts the 780 ran wavelength
`light as the first-order light, in which diffraction efficiency
`thereof is 40%.
`All of the 650 um wavelength light incident to the holo-
`65 graphic ring lens 35 having the above characteristics is trans-
`mitted and then proceeds to the objective lens 36. The inci-
`dent light beam passes through the objective lens 36 and
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`

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`US RE43,106 E
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`7
`forms a beam spot on the information recording surface of the
`DVD 37. The light beam reflected from the information
`recording surface of the DVD 37 is incident to the holo-
`graphic ring lens 35. After passing through the holographic
`ring lens 35, the reflected light beam is incident to the colli-
`mating lens 34, the beam splitter 33 and then to the holo-
`graphic beam splitter 32, wherein the holographic beam split-
`ter 32 directs the reflected light beam to the photodetector 38.
`The 780 nm wavelength light incident to the holographic ring
`lens 35 is transmitted in the holographic lens 353 and then
`proceeds to the objective lens 36 as shown in FIG. 4A, but is
`diffracted in the region A and then proceeds to the objective
`lens 36. Therefore, the light beam passing through the objec-
`tive lens 36 forms an optimized beam spot on the information
`recording surface of the CD-R 41. The light beam reflected
`from the information recording surface of the CD-R 41 is
`incident to the beam splitter 33 and then reflected. The
`reflected light proceeds to the holographic beam splitter 40
`and then is incident to the photodetector 42 by altering the
`optical path.
`The holographic ring lens 35 having the above functions
`may be manufactured integrally with an objective lens by
`being etched or molded to a constant depth inwards from one
`optical surthce of the objective lens. The integrally incorpo-
`rated holographic ring lens has the same function as the
`holographic ring lens 35. FIG. 7 is a view showing that the
`holographic ring lens and the objective lens are integrally
`incorporated.
`As described above, the optical pickup apparatus accord-
`ing to the present invention is used compatibly with a DVD
`and a CD-R, by using a holographic ring lens to eliminate a
`spherical aberration generated in response to a disk being
`changed Io another disk having a differenl lhickness, in which
`a working distance is shorter in the case of the CD-R than the
`DVD. Also, the optical pickup apparatus provides advantages
`which include ease in construction of a holographic ring lens
`and good mass-production capabilities.
`While only certain embodiments of the invention have
`been specifically described herein, it will be apparent that
`numerous modifications may be made thereto without depart-
`ing from the spirit and scope of the invention.
`What is claimed is:
`1. An objective lens to form beam spots using light beams
`of respectively diflbrent wavelengths, the objective lens com-
`prising:
`an inner region including an optical center of the objective
`lens;
`a holographic region surrounding said inner region and
`comprising a plurality of steps disposed on a lens surface
`of the objective lens; and
`an outer region surrounding said holographic region,
`wherein
`said inner region transmits the light beams,
`said holographic region diffracts a second one of the
`light beams, and
`the outer region transmits a first one of the light beams.
`2. The objective lens according to claim 1, wherein a first
`focal plane on which a first portion of the second light beam
`incident on said holographic region is focused coincides with
`a second focal plane on which a second portion of the second
`light beam incident on said inner region is focused.
`