WO2006033501A1 - Random vibration wave retardation plate and optical film and/or optical pickup device has them - Google Patents

Random vibration wave retardation plate and optical film and/or optical pickup device has them Download PDF

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Publication number
WO2006033501A1
WO2006033501A1 PCT/KR2004/002963 KR2004002963W WO2006033501A1 WO 2006033501 A1 WO2006033501 A1 WO 2006033501A1 KR 2004002963 W KR2004002963 W KR 2004002963W WO 2006033501 A1 WO2006033501 A1 WO 2006033501A1
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Prior art keywords
retardation plate
optical
light
angle
optical axis
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PCT/KR2004/002963
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French (fr)
Inventor
Woo-Joo Lah
Yong-Shig Shim
Sung-Min Cho
Soon-Ryong Park
Jae-Wan Jeong
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Lgs Corporation Ltd.
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Publication of WO2006033501A1 publication Critical patent/WO2006033501A1/en

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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
    • G11B7/127—Lasers; Multiple laser arrays
    • G11B7/1275—Two or more lasers having different wavelengths
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1365—Separate or integrated refractive elements, e.g. wave plates
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
    • G11B2007/0006—Recording, reproducing or erasing systems characterised by the structure or type of the carrier adapted for scanning different types of carrier, e.g. CD & DVD

Definitions

  • phase retardation plate 101 In the structure of the phase retardation plate 101, two retardation plates I l ia and 111b, which are made of a thin organic film with birefringence, overlap with optical axes thereof intersecting each other between a pair of transparent substrates 110a and HOb.
  • the transparent substrates HOa and HOb and the retardation plates I l ia and 111b are fixed to one another with an adhesive.
  • a retardation value of the retardation plate 11 Ia on which laser light is firstly incident is larger than that of the retardation plate 11 Ib on which the laser light is secondly incident.
  • the ratio of the retardation values of both the retardation plates I l ia and 111b is in a range of 1.8 to 2.2. It makes it possible to convert laser light of a relatively wide wavelength band (broadband) from a linearly polarized light to a circularly polarized light.
  • both retardation plates are bonded to each other so that the optical axes thereof intersect each other at a predetermined angle.
  • an ellipticity value depends on an error in the angles of optical axes, it is required to reduce the error in the angles of optical axes.
  • the two retardation plates are bonded to each other with the error in the angles of optical axes exceeding tolerance, there is no method capable of correct the error since the conventional phase retardation plate employs only two retardation plates. Thus, there are problems of a high deviation in quality and a high percent defective of products.
  • So M( ⁇ 3 , ⁇ )M( ⁇ 2 , ⁇ )M( ⁇ i, P)Si
  • ⁇ i is the angle of optical axis of the first retardation plate
  • ⁇ 2 is the angle of optical axis of the second retardation plate
  • ⁇ 3 is the angle of optical axis of the third retardation plate.
  • Fig. 6 is a view schematically showing a configuration of an optical pickup device with the broadband phase retardation plate of Fig. 5.
  • Phase retardation plate 10a, 10b Transparent substrate
  • E x (t) iE Ox ( ' t)cos (kx - ⁇ t) + ⁇ x (t) (1)
  • E(t) E ⁇ [(t) + ⁇ E v (t) .
  • the polarization state of the laser light can be represented by four terms (i.e., Stokes vector), as can be seen from Table 1.
  • the polarization state of the laser light may have various angles and states and be obtained as the Stokes vector value from Equations 3 and 4.
  • Equation 7 a transfer function of the Muller matrix associated with birefringence is defined by the following Equation 7:
  • This combination of the phase retardation values and the angles of optical axes is a combination for converting incident light in a linear polarization state into emitted light in a circular polarization state.
  • This is an example of a combination capable of converting incident linear light of any wavelength belong to a wavelength band of about 600 to 800 nm into circularly polarized light and emitting the circularly polarized light.
  • the first to third retardation plates 21 , 22 and 23 are bonded to one another with the relevant angles of optical axes thereof. In the bonding process, when one retardation plate is bonded to another retardation plate with a wrong angle of optical axis thereof, the wrong bonding can be corrected upon bonding of the remaining one.
  • optical pickup device 60' laser light from a light source 61', which generated light of two different wavelengths (X 1 and ⁇ 2 ), is focused and induced onto an optical disc 5' such as DVD or CD via an optical element A', a collimating lens 64' and an objective lens 65', wherein the optical element A' has diffraction lattices 62', a hologram layer 63', and phase retardation plates Ib and Ic.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Head (AREA)
  • Polarising Elements (AREA)

Abstract

The present invention relates to a broadband phase retardation plate for converting a polarization state of incident light and emitting the converted light. The broadband phase retardation plate comprises at least three retardation plates with the same phase retardation value, wherein the retardation plates convert the polarization state of the incident light in at least one wavelength band using a combination of adjusted angles of optical axes (θ) of the respective retardation plates. According to the present invention, there is provided a broadband phase retardation plate, and an optical element and/or an optical pickup device having the phase retardation plate, which can minimize a deviation in quality of products and reduce a percent defective by correcting an error in the angle of optical axis, and can be easily manufactured and produced.

Description

RANDOM VIBRATION WAVE RETARDATION PLATE AND OPTICAL FILM AND/OR OPTICAL PICKUP DEVICE HAS THEM
TECHNICAL FIELD
The present invention relates to a broadband phase retardation plate, and an optical element and/or an optical pickup device having the same.
BACKGROUND ART A phase retardation plate converts a polarization direction of incident light into a desired polarization direction. The phase retardation plate is used to convert the polarization state of laser light in an optical pickup device that reads or records information from or in an optical disc such as a compact disc (CD) or a digital versatile disc (DVD). As shown in Fig. 1 , a typical optical pickup device 200 reads information stored in an optical disc 250, by focusing and inducing laser light from a light source 210 onto the optical disc 250 via a beam splitter 220, a collimating lens 230 and an objective lens 240 and by receiving reflected light from the optical disc 250 using an optical detector 260. The laser light in a linear polarization state is directed from the light source 210 to the optical disc 250. The laser light in the linear polarization state should be converted into circularly polarized light and the circularly polarized light should be irradiated onto the optical disc 250, and the circularly polarized light reflected by the optical disc 250 should be converted back to the linearly polarized light and be then delivered to the optical detector 260 so that information is read from the optical disc 250. To perform conversion between the polarization states of the laser light, a phase retardation plate A is disposed on a light path between the light source 210 and the optical disc 250.
Meanwhile, in recent years, a CD and DVD compatible optical pickup device is being widely used to record or reproduce information in or from both optical discs of CD and DVD. Generally, in such a CD and DVD compatible optical pickup device, laser light of λi belong to a 650 run wavelength band is used for a DVD type optical disc, and laser light of λ2 belong to a 790 nm wavelength band is used for a CD type optical disc. Thus, there is a need for a phase retardation plate capable of performing conversion between polarization states for two different wavelengths (λi and λ2). To implement this, different phase retardation plates can be used for respective wavelengths. However, this causes a problem in that the size of the optical pickup device and production costs increase.
Accordingly, a single, phase retardation plate 101 capable of converting the polarization state of laser light of two different wavelengths (λj and λ2) is being used recently. This technique is disclosed in Korean Patent Laid-Open Publication No. 2001-0089321, as shown in Fig. 2.
In the structure of the phase retardation plate 101, two retardation plates I l ia and 111b, which are made of a thin organic film with birefringence, overlap with optical axes thereof intersecting each other between a pair of transparent substrates 110a and HOb. The transparent substrates HOa and HOb and the retardation plates I l ia and 111b are fixed to one another with an adhesive.
At this time, a retardation value of the retardation plate 11 Ia on which laser light is firstly incident is larger than that of the retardation plate 11 Ib on which the laser light is secondly incident. Further, the ratio of the retardation values of both the retardation plates I l ia and 111b is in a range of 1.8 to 2.2. It makes it possible to convert laser light of a relatively wide wavelength band (broadband) from a linearly polarized light to a circularly polarized light.
However, to convert light of two different wavelengths from linearly polarized light to circularly polarized light in this conventional phase retardation plate, both retardation plates are bonded to each other so that the optical axes thereof intersect each other at a predetermined angle. At this time, since an ellipticity value depends on an error in the angles of optical axes, it is required to reduce the error in the angles of optical axes. However, if the two retardation plates are bonded to each other with the error in the angles of optical axes exceeding tolerance, there is no method capable of correct the error since the conventional phase retardation plate employs only two retardation plates. Thus, there are problems of a high deviation in quality and a high percent defective of products.
Further, as well known in the optical element manufacturing field, the ellipticity value of a phase retardation plate is rapidly reduced even though the angle of optical axis of the retardation plate is changed by about 0.5°. Further, it is impossible to bond a pair of retardation plates to each other such that an error in the angles of optical axes is not out of 0.5°. Therefore, the conventional phase retardation plate has a problem in that it is veiy difficult to manufacture and produce.
DISCLOSURE OF INVENTION
TECHNICAL PROBLEM
Accordingly, an object of the present invention is to provide a broadband phase retardation plate, and an optical element and/or an optical pickup device having the phase retardation plate, which can minimize a deviation in quality of products and reduce a percent defective by correcting an error in the angle of optical axis, and can be easily manufactured and produced.
TECHNICAL SOLUTION
The object of the present invention is achieved by a broadband phase retardation plate for converting a polarization state of incident light and emitting the converted light, according to an aspect of the present invention. The broadband phase retardation plate comprises at least three retardation plates with the same phase retardation value. The retardation plates convert the polarization state of the incident light in at least one wavelength band using a combination of adjusted angles of optical axes (θ) of the respective retardation plates.
Preferably, the retardation plates comprise first to third retardation plates, the combination of the angles of optical axes (θ) of the respective retardation plates is derived based on a Stokes vector value (Si) of the incident light, an expected Stokes vector value (So) of the emitted light and the phase retardation value (β), and is represented by the following equation:
So=M(θ3, β)M(θ2, β)M(θi, P)Si where θi is the angle of optical axis of the first retardation plate, θ2 is the angle of optical axis of the second retardation plate, and θ3 is the angle of optical axis of the third retardation plate.
At this time, the angle of optical axis of the first retardation plate may be in a range of 10 to 20°, the angle of optical axis of the second retardation plate may be in a range of 10 to 20°, and the angle of optical axis of the third retardation plate may be in a range of 70 to 80°.
Alternatively, the angle of optical axis of the first retardation plate may be in a range of 115 to 125°, the angle of optical axis of the second retardation plate may be in a range of 10 to 20°, and the angle of optical axis of the third retardation plate may be in a range of 70 to 80°. Alternatively, the angle of optical axis of the first retardation plate may be in a range of 10 to 20°, the angle of optical axis of the second retardation plate may be in a range of 45 to 55°, and the angle of optical axis of the third retardation plate may be in a range of 70 to 80°.
The object of the present invention is achieved by an optical pickup device including a light source for emitting light in at least one wavelength band, an objective lens for focusing the light onto an optical recording medium, and an optical detector for detecting light reflected by the optical recording medium, according to another aspect of the present invention. In the optical pickup device, the broadband phase retardation plate is disposed on a light path between the light source and the objective lens. The object of the present invention is achieved by an optical element including diffraction lattices for diffracting incident light in at least one wavelength band and a hologram layer, according to a further aspect of the present invention. In the optical element, the broadband phase retardation plate is disposed on an incidence side of the incident light. The object of the present invention is achieved by an optical pickup device including a light source for emitting light in at least one wavelength band, an objective lens for focusing the light onto an optical recording medium, and an optical detector for detecting light reflected by the optical recording medium, according to a still further aspect of the present invention. In the optical pickup device, the optical element is disposed on a light path between the light source and the objective lens.
ADVANTAGEOUS EFFECTS
The present invention provides a broadband phase retardation plate, and an optical element and/or an optical pickup device having the phase retardation plate, which can minimize a deviation in quality of products and simultaneously reduce a percent defective by correcting an error in the angle of optical axis, and can be easily manufactured and produced.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. l is a view schematically showing a configuration of a typical optical pickup device.
Fig. 2 is a sectional view of a conventional broadband phase retardation plate. Fig. 3 is a sectional view of a broadband phase retardation plate according to the present invention.
Fig. 4 is a view showing an arrangement of the angles of optical axes of retardation plates constituting the phase retardation plate of Fig. 3.
Fig. 5 is a view showing an arrangement of the angles of optical axes of retardation plates in a broadband phase retardation plate according to a first embodiment of the present invention.
Fig. 6 is a view schematically showing a configuration of an optical pickup device with the broadband phase retardation plate of Fig. 5.
Figs. 7 and 8 are views showing arrangements of the angles of optical axes of retardation plates in a broadband phase retardation plate according to a second embodiment of the present invention.
Fig. 9 is a view schematically showing a configuration of an optical pickup device with one of the broadband phase retardation plates of Figs. 7 and 8.
Figs. 10 and 1 1 are sectional views of an optical element including the retardation plate according to the present invention.
Fig. 12 is a view schematically showing a configuration of an optical pickup device with the optical element of Figs. 10 and 11.
<Explanation of reference numerals for designating main components in the drawings>
1: Phase retardation plate 10a, 10b: Transparent substrate
11, 12, 13: Retardation plate 15 : Adhesive material
50: Optical element
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
Fig. 3 is a sectional view of a broadband phase retardation plate according to an embodiment of the present invention, and Fig. 4 is a view showing an exemplary arrangement of the angles of optical axes of retardation plates 11, 12 and 13 constituting the phase retardation plate of Fig. 3. As shown in these figures, the broadband phase retardation plate according to the present invention has a structure in which at least three retardation plates 1 1, 12 and 13 are stacked between a pair of transparent substrates 1 Oa and 10b using an adhesive material 15.
These retardation plates 1 1, 12 and 13 are manufactured in the form of a film using a thin organic film with birefringence. The thin organic film may be made to have a phase retardation function by imparting birefringence to any one of polycarbonate, polyimide, polyarylate, polyethersulfone, (alicyclic) polyolefin, poly(metha)crylate, and polyetherimide, or a polymer thereof.
These retardation plates 11, 12 and 13 properly convert a polarization state of laser light of a wide wavelength band into a desired polarization state, wherein the retardation plates 11, 12 and 13 are caused to have the same phase retardation value β and are then arranged at the predetermined angles of optical axes θ obtained through calculation using Stokes parameters and a Muller matrix to be described later.
That is, the polarization state of the laser light can be converted using a relationship between the same phase retardation value β of the at least three retardation plates 11, 12 and 13 and the angles of optical axes θ thereof. The relationship can be defined by the following equations.
The polarization state of the laser light can be generally described using four positive terms. First, the polarization state of the laser light can be represented by the following equations 1 and 2:
Ex (t) = iEOx( 't)cos (kx - ωt) + εx (t) (1)
Figure imgf000015_0001
where, E(t) = E~[(t) + ~Ev(t) .
By using Equations 1 and 2 as they are, Stokes parameters for the laser light can be represented by the following equations:
Figure imgf000015_0002
S2 =< 2EoxEoγcos(ε) > (5) S3 =< 2EoxEoysin(ε) > (6)
Based on Equations 3 to 6, respective representative polarization states of the laser light are represented by Stokes vectors as shown in the following Table 1.
Table 1
Figure imgf000015_0003
That is, the polarization state of the laser light can be represented by four terms (i.e., Stokes vector), as can be seen from Table 1. Here, the polarization state of the laser light may have various angles and states and be obtained as the Stokes vector value from Equations 3 and 4.
Accordingly, to obtain emitted laser light in a desired polarization state, it suffices to convert a Stokes vector of relevant incident laser light to a Stokes vector that correspond to the desired polarization state of the emitted light.
For example, in Table 1 , in order to cause laser light in a horizontal polarization state incident on the phase retardation plate 1 to be converted into light of the left-rotated, circular polarization state and to be emitted, it suffices to convert the Stokes vector [1 1 0 O]1 of the incident laser light into the Stokes vector [1 0 0 -1]' that corresponds to the left- rotated, circular polarization state.
The Stokes vector has an attribute that it is applicable to both polarized light and partially polarized light. By using this Stokes vector and a Muller matrix, the polarization state of the emitted laser light dependent on the relationship between the angles of optical axes θ and the phase retardation values β of the respective retardation plates 11, 12 and 13 can be represented by the following Equations 7 and 8.
First, a transfer function of the Muller matrix associated with birefringence is defined by the following Equation 7:
1 0 0 0
0 cos2 2Q + cos$sin2 2Q (l - cos$)sin2Qcos2Q snφsw2θ
M(θ,β) = (7)
0 Q. ~ cόs$)sw2θcos2θ sin22Q + cos$cos22Q -sinβcos2θ
0 — sin$sin2Q sin$cos2Q cosfi
For example, if the transfer function of Equation 7 is used and the retardation plates include the three retardation plates 11, 12 and 13 as shown in Figs. 3 and 4, a relationship between the angles of optical axes θi, θ2 and θ3 and the phase retardation values βi, β2 and β3 of the respective retardation plates 11, 12 and 13 can be calculated by the following Equation 8: So=M(G3, β3)M(θ2, β2)M(θ,, βi)Si (8)
where, Si is a Stokes vector corresponding to a polarization state of incident light, and So is a Stokes vector corresponding to a polarization state of emitted light.
That is, as shown in Fig. 4, it is possible to obtain a desired polarization state So of emitted light from any polarization state Si of incident light, by substituting and adjusting the angles of optical axes θi, θ2 and θ3 and the phase retardation values βi, β2 and β3 of the respective retardation plates 11, 12 and 13 into and in Equation 8. Here, it will be apparent that application of the transfer function to Equation 8 makes it possible to manufacture a phase retardation plate 1 including more than three retardation plates.
According to the present invention, such configurations and theories become a basis in manufacturing the broadband phase retardation plate 1. A representative example includes a phase retardation plate that converts incident light in a linear polarization state into emitted light in a circular polarization state using the three retardation plates 11, 12 and 13, and a phase retardation plate that converts incident light in a linear polarization state into linearly polarized light in a deflected state.
Embodiment 1
According to this embodiment, a phase retardation plate Ia, as shown in Fig. 5, comprises first to third retardation plates 21, 22 and 23 between a pair of transparent substrates 10a and 10b, wherein the first to third retardation plates have the same phase retardation value (βi=β2=β3) and the angles of optical axes θi, θ2 and θ3 thereof are θi=l 5°, Θ2=l 5° and Θ3=75°, respectively. The first to third retardation plates 21 , 22 and 23 are fixed to one another by the adhesive material 15, as shown in Fig. 3.
This combination of the phase retardation values and the angles of optical axes is a combination for converting incident light in a linear polarization state into emitted light in a circular polarization state. This is an example of a combination capable of converting incident linear light of any wavelength belong to a wavelength band of about 600 to 800 nm into circularly polarized light and emitting the circularly polarized light. At this time, the first to third retardation plates 21 , 22 and 23 are bonded to one another with the relevant angles of optical axes thereof. In the bonding process, when one retardation plate is bonded to another retardation plate with a wrong angle of optical axis thereof, the wrong bonding can be corrected upon bonding of the remaining one.
Meanwhile, the optimal performance of the phase retardation plate Ia, which converts the linearly polarized light into the circularly polarized light, is achieved when the emitted light polarization state is a substantially circular state where the ellipticity of the emitted light is close to 1 and when a change in the ellipticity value dependent on an error in the angle of optical axis of any retardation plate 21, 22 or 23 is minimized. Here, "ellipticity" refers to a ratio of a major axis to a minor axis of a circularly polarized light that is the emitted light.
From comparison between an ellipticity property of the broadband phase retardation plate Ia according to this embodiment and an ellipticity property of the conventional broadband phase retardation plate Ia shown in Fig. 2, the results of the following Graphs Ia and Ib can be obtained:
Graph Ia
_
Figure imgf000018_0001
Wavelength band X (nm)
From Graph Ia, it can be found that, when the broadband phase retardation plate Ia according to the present invention converts incident linear light of any wavelength belong to a wavelength band of 600 to 800 nm into circularly polarized light and emits the circularly polarized light, a change in the ellipticity falls within a range of l±O.l even though the angle of optical axis of the third retardation plate 23 has a value with an error in a range of 75°±2° (i.e., 73° to 77°). Here, the ellipticity of 1 means perfectly circularly polarized light and the ellipticity of l±O.l means a substantially perfect circle.
Graph Ib
Figure imgf000019_0002
Figure imgf000019_0001
Wavclongth tiand λ (rm\
From Graph Ib, it can be found that, when the conventional broadband phase retardation plate Ia converts incident linear light of any wavelength belong to a wavelength band of 600 to 800 mil into circularly polarized light and emits the circularly polarized light, a change in the ellipticity is out of a range of l±O.l in a case where the angle of optical axis θ2 of a retardation plate 11 Ib has a value with an error in a range of 75°±2° (i.e., 73° to 77°).
Further, according to this embodiment, when the broadband phase retardation plate Ia receives linearly polarized light of two different incident wavelengths (λi and λ2) belong to 790 nm and 650 nm wavelength bands for use in the CD and DVD compatible optical pickup device, the broadband phase retardation plate Ia emits the circularly polarized light with certain density distribution in which the ellipticity is close to substantially 1 , as can be seen from Graph 2 below.
Accordingly, it can be seen that the phase retardation plate Ia according to this embodiment is very suitable for the CD and DVD compatible optical pickup device. Graph 2
Figure imgf000020_0001
<Wavelength=650 nm, Ellipticity=1.08>
Figure imgf000020_0002
<Wavelength=790 nm, Ellipticity=0.99>
A type of CD and DVD compatible optical pickup device having such a phase retardation plate Ia is shown in Fig. 6. The optical pickup device 60 has a DVD type light source 61a and a CD type light source 61b for generating laser light of two different wavelengths. The laser light generated from the light sources 61a and 61b is split into three beams at diffraction lattices 62a and 62b that in turn are focused and induced onto an optical disc 5 via beam splitters 63a and 63b, a collimating lens 64 and an objective lens 65. Reflected light from the optical disc 5 is received by an optical detector 66 via the objective lens 65, the collimating lens 64 and the beam splitter 63b. Accordingly, information stored in the optical disc 5 is read.
At this time, the aforementioned phase retardation plate Ia disposed on a light path (e.g., between the beam splitter 63b and the collimating lens 64 in Fig. 6) converts the linearly polarized light of the two different wavelengths (λi and λ2), which is generated by the DVD type light source 61a and the CD type light source 61b, into the circularly polarized light.
As such, it is confirmed that the broadband phase retardation plate 1 a according to this embodiment can also smoothly convert the linearly polarized light of a wide wavelength band into the circularly polarized light, as well as convert the linearly polarized light into the circularly polarized light with a minimum change in the ellipticity value in the wide wavelength band, even though the retardation plates 21, 22 and 23 have large errors in the angles of optical axes thereof. Further, it is confirmed that the phase retardation plate Ia according to this embodiment is very suitable for the CD and DVD compatible optical pickup device.
As a result, it is possible to effectively reduce a deviation in quality and a percent defective of products by setting a wide error range of the angle of optical axis, and to improve productivity by simplifying manufacture of the products.
Further, as described above, if the first to third retardation plates 21, 22 and 23 have the same phase retardation value (βi=β2 =β3), it is possible to save material costs since only a raw material film having a single retardation value can be employed upon manufacture of the phase retardation plate 1 a.
Embodiment 2
According to this embodiment, as shown in Fig. 7, the phase retardation plate Ib comprises first to third retardation plates 31, 32 and 33 between a pair of transparent substrates 10a and 10b, wherein the first to third retardation plates have the same phase retardation value (βi=β2~β3) and the angles of optical axes θi, G2 and θ3 thereof are 0^120°, Θ2=15° and Θ3=75°, respectively. The first to third retardation plates 21, 22 and 23 are fixed to one another by the adhesive material 15, as shown in Fig. 3.
This combination of the phase retardation values and the angles of optical axes is a combination for converting incident light in a linear polarization state to emitted light in a circular polarization state that is deflected in a substantially horizontal direction. This is an example of a combination capable of converting incident linear light of any wavelength belong to a wavelength band of about 600 to 800 nm into circularly polarized light and emitting the circularly polarized light.
Even in this embodiment, even though one retardation plate is bonded to another retardation plate with a wrong angle of optical axis, the wrong bonding can be corrected upon bonding of the remaining one.
Further, according to this embodiment, when the broadband phase retardation plate Ia with such a combination of the angles of optical axes O1, O2 and O3 receives linearly polarized light of two different wavelengths (I1 and λ2) belong to 790 nm and 650 nm wavelength bands, which is incident in the same direction, for use in the CD and DVD compatible optical pickup device, the broadband phase retardation plate Ia converts the linearly polarized light into linearly polarized light that is deflected at different deflection angles and then emits the deflected, linearly polarized light, as can be seen from Graph 3 below.
Graph 3
Figure imgf000022_0001
< Wavelength^ 50 nm, Deflection angle= -15°>
Figure imgf000023_0001
<Wavelength=790 nm, Deflection angle= -8°>
Meanwhile, Fig. 8 illustrates a combination for the phase retardation plate Ic that converts incident linear light of any wavelength belong to a wavelength band of about 600 to 800 nm into emitted light in a linear polarization state that is deflected in a substantially vertical direction, wherein first to third retardation plates 41, 42 and 43 have the same phase retardation value (P1=P2=P3) and the angles of optical axes O1, O2 and O3 thereof are O1=IS0, 02=51° and 03=75°, respectively. The converted, vertically polarized light of two wavelengths exhibits a difference in deflection angles, as shown in Graph 4.
Graph 4
Figure imgf000023_0002
<Wavelength=650 nm, Deflection angle=105 ° >
Figure imgf000024_0002
Figure imgf000024_0001
nm, Deflection angle=98°>
As can be seen from Graphs 3 and 4, with other phase retardation plates Ib and Ic according to this embodiment, when laser light of two different wavelengths is incident as horizontal, linearly polarized light in the same direction, it is possible to convert the incident laser light to horizontal or vertical, linearly polarized light of which respective light of the wavelengths is deflected at different angles, by properly adjusting a combination of the angles of optical axes G1, θ2, and θ3 of the respective retardation plates 31, 32 and 33 or 41, 42 and 43. The deflected, linearly polarized light exhibits a significant difference in deflection angles, as can be seen from Graphs 3 and 4. The phase , retardation plates Ib and Ic according to this embodiment are applicable to an optical pickup device shown in Fig. 9.
In the optical pickup device 60', laser light from a light source 61', which generated light of two different wavelengths (X1 and λ2), is focused and induced onto an optical disc 5' such as DVD or CD via an optical element A', a collimating lens 64' and an objective lens 65', wherein the optical element A' has diffraction lattices 62', a hologram layer 63', and phase retardation plates Ib and Ic.
At this time, each of the phase retardation plates Ib and Ic converts linearly polarized light of one of the two different wavelengths into deflected, linearly polarized light. A selected one of both the deflected, linearly polarized light is transferred to the relevant optical disc 5'. Here, since the deflection angles of the light of the two wavelengths have a significant difference therebetween as described above, selectivity of polarization of the optical pickup device 60' is improved.
The reflected light from the optical disc 5' is received by an optical detector 66' via the objective lens 65', the collimating lens 64' and the optical element, so that information stored in the optical disc 5' is read. At this time, the hologram layer 63' formed in the optical element A' deflects a progress direction of the light of the selected wavelength so that the light is received at the optical detector 6&. The hologram layer 63' is widely used for a compact optical pickup device without an additional beam splitter.
The optical pickup device 60' should have a difference between the deflection angles of the two-wavelength light. This enables any light selected by the hologram layer 63' to be received by the optical detector 66' through adjustment of the position of the optical detector 66'.
According to this embodiment, since the phase retardation plates Ib and Ic have significantly different deflection angles for the two wavelengths, they are very suitable for such a type of optical pickup device 60'.
Meanwhile, according to the present invention, it is possible to manufacture an optical element 50 with a structure in which diffraction lattices 55 and at least three retardation plates 51, 52 and 53 are stacked between a pair of transparent substrates 10a and 10b by an adhesive material, as shown in Figs. 10 and 11. Such an optical element 50 is one of those widely used in a recent CD and DVD compatible optical pickup device and functions to selectively diffract light of any wavelength (X1 in the Fig. 10) of two different wavelengths (X1 and λ2) of incident light.
The light to be diffracted, which has the wavelength selected among the wavelengths (λ\ and λ2), is converted such that its polarization state matches with a diffraction condition while passing through the retardation plates, and is then transmitted through the diffraction lattices 55. At this time, since the transmitted two-wavelength light passing through the retardation plates 51, 52 and 53 according to the present invention has significantly different deflection angles, accurate selective diffraction for the incident light can be achieved. The diffraction lattices 55 may be single-layer diffraction lattices 55 as shown in the figures, or multi-layer diffraction lattices comprising a plurality of layers. A type of CD and DVD compatible optical pickup device employing such an optical element 50 is shown in Fig. 12. This optical pickup device 60" has a DVD type light source 61a" and a CD type light source 61b", which generate laser light of two different wavelengths. The laser light generated by the respective light sources 61a" and 61b" is focused and induced onto an optical disc 5" via beam splitters 63a" and 63b", a collimating lens 64", and an objective lens 65".
Reflected light from the optical disc 5" is received by an optical detector 66" via the objective lens 65", the collimating lens 64", and the beam splitter 63b," so that the information stored in the optical disc 5" is read. At this time, the aforementioned optical element 50, which is disposed on a light path (e.g., between both the beam splitters 63a" and 63b" in Fig. 12), converts linearly polarized light of two different wavelengths (I1 and λ2) generated by the DVD type light source 61a" and the CD type light source 61b" into circularly polarized light, and diffracts light of a selected one of the two wavelengths into three light beams. In this optical pickup device 60", since the respective emitted light of the two wavelengths passing through the retardation plates 51, 52 and 53 of the optical element 50 has significantly different deflection angles, accurate selective diffraction for the incident light is achieved.
As described above, the phase retardation plate, and the optical element and/or the optical pickup device having the phase retardation plate according to the present invention comprise at least three retardation plates with the same phase retardation value, which constitute the phase retardation plate. The angles of optical axes of the respective retardation plates are adjusted such that the polarization state of the incident light can be adjusted. Accordingly, incident light in at least one wavelength band can be converted from linearly polarized light into circularly polarized light or from the linearly polarized light into deflected, linearly polarized light, if necessary.
Further, even though one of the retardation plates is bonded to another retardation plate with a wrong angle of optical axis, the wrong bonding can be corrected upon bonding of the remaining one. Further, by using at least three retardation plates, it is possible to prevent the ellipticity value from being degraded by widening an error range of the angle of optical axis. Accordingly, it is possible to significantly reduce a deviation in quality and a percent defective of products and to ensure relatively easy manufacture and production of the products.
Although the present invention has been described in conjunction with the three retardation plates constituting the phase retardation plate and the incident light in two wavelength bands, it will be apparent that the phase retardation plate may include more than three retardation plates so far as the thickness of the phase retardation plate is available, and the incident light in more than two wavelength bands may be subjected to conversion of its polarization state into a desired polarization state. Further, the phase retardation plate according to the present invention is not limited to the applications to the optical element and the optical pickup device previously described in the embodiments and shown in the drawings, but is applicable to various optical elements and optical pickup devices that require phase retardation by the phase retardation plate according to the present invention.
INDUSTRIAL APPLICABILITY
As described above, according to the present invention, there is provided a broadband phase retardation plate, and an optical element and/or an optical pickup device having the phase retardation plate, which can minimize a deviation in quality of products and reduce a percent defective by correcting an error in the angle of optical axis, and can be easily manufactured and produced.

Claims

1. A broadband phase retardation plate for converting a polarization state of incident light and emitting the converted light, comprising: at least three retardation plates with the same phase retardation value, wherein the retardation plates convert the polarization state of the incident light in at least one wavelength band using a combination of adjusted angles of optical axes (θ) of the respective retardation plates.
2. The plate as claimed in claim 1, wherein the retardation plates comprise first to third retardation plates, the combination of the angles of optical axes (θ) of the respective retardation plates is derived based on a Stokes vector value (Si) of the incident light, an expected Stokes vector value (So) of the emitted light and the phase retardation value (β), and is represented by the following equation: So=M(θ3, β)M(θ2, β)M(θb β)Si where G1 is the angle of optical axis of the first retardation plate, G2 is the angle of optical axis of the second retardation plate, and θ3 is the angle of optical axis of the third retardation plate.
3. The plate as claimed in claim 2, wherein the angle of optical axis of the first retardation plate is in a range of 10 to 20°, the angle of optical axis of the second retardation plate is in a range of 10 to 20°, and the angle of optical axis of the third retardation plate is in a range of 70 to 80°.
4. The plate as claimed in claim 2, wherein the angle of optical axis of the first retardation plate is in a range of 115 to 125°, the angle of optical axis of the second retardation plate is in a range of 10 to 20°, and the angle of optical axis of the third retardation plate is in a range of 70 to 80°.
5. The plate as claimed in claim 2, wherein the angle of optical axis of the first retardation plate is in a range of 10 to 20°, the angle of optical axis of the second retardation plate is in a range of 45 to 55°, and the angle of optical axis of the third retardation plate is in a range of 70 to 80°.
6. An optical pickup device including a light source for emitting light in at least one wavelength band, an objective lens for focusing the light onto an optical recording medium, and an optical detector for detecting light reflected by the optical recording medium, wherein: the broadband phase retardation plate according to any one of claims 1 to 5 is disposed on a light path between the light source and the objective lens.
7. An optical element including diffraction lattices for diffracting incident light in at least one wavelength band and a hologram layer, wherein: the broadband phase retardation plate according to any one of claims 1 to 5 is disposed on an incidence side of the incident light.
8. An optical pickup device including a light source for emitting light in at least one wavelength band, an objective lens for focusing the light onto an optical recording medium, and an optical detector for detecting light reflected by the optical recording medium, wherein: the optical element according to claim 7 is disposed on a light path between the light source and the objective lens.
PCT/KR2004/002963 2004-09-20 2004-11-16 Random vibration wave retardation plate and optical film and/or optical pickup device has them WO2006033501A1 (en)

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Cited By (1)

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Publication number Priority date Publication date Assignee Title
EP2037457A2 (en) * 2007-09-13 2009-03-18 Samsung Electronics Co., Ltd. Optical pickup

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Publication number Priority date Publication date Assignee Title
JP2024057839A (en) * 2022-10-13 2024-04-25 日東電工株式会社 Optical laminate

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JPH07239471A (en) * 1994-02-28 1995-09-12 Hitachi Ltd Reflection type liquid crystal display device
JPH1152133A (en) * 1997-07-31 1999-02-26 Nitto Denko Corp Elliptic polarizing element
EP0916989A2 (en) * 1997-11-14 1999-05-19 Nitto Denko Corporation Laminated wavelength plate, circular polarizing plate and liquid crystal display
EP1126291A1 (en) * 1999-08-26 2001-08-22 Asahi Glass Company Ltd. Phase shifter and optical head device mounted with the same

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH07239471A (en) * 1994-02-28 1995-09-12 Hitachi Ltd Reflection type liquid crystal display device
JPH1152133A (en) * 1997-07-31 1999-02-26 Nitto Denko Corp Elliptic polarizing element
EP0916989A2 (en) * 1997-11-14 1999-05-19 Nitto Denko Corporation Laminated wavelength plate, circular polarizing plate and liquid crystal display
EP1126291A1 (en) * 1999-08-26 2001-08-22 Asahi Glass Company Ltd. Phase shifter and optical head device mounted with the same

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2037457A2 (en) * 2007-09-13 2009-03-18 Samsung Electronics Co., Ltd. Optical pickup
EP2037457A3 (en) * 2007-09-13 2009-07-29 Samsung Electronics Co., Ltd. Optical pickup

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