WO2008069031A1 - 光学素子および光ピックアップ装置 - Google Patents
光学素子および光ピックアップ装置 Download PDFInfo
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- WO2008069031A1 WO2008069031A1 PCT/JP2007/072723 JP2007072723W WO2008069031A1 WO 2008069031 A1 WO2008069031 A1 WO 2008069031A1 JP 2007072723 W JP2007072723 W JP 2007072723W WO 2008069031 A1 WO2008069031 A1 WO 2008069031A1
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- refractive index
- optical
- lens
- multilayer film
- index layer
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
- G02B1/10—Optical coatings produced by application to, or surface treatment of, optical elements
- G02B1/11—Anti-reflection coatings
- G02B1/113—Anti-reflection coatings using inorganic layer materials only
- G02B1/115—Multilayers
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
- G02B1/10—Optical coatings produced by application to, or surface treatment of, optical elements
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/0025—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical correction, e.g. distorsion, aberration
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/30—Polarising elements
- G02B5/3083—Birefringent or phase retarding elements
-
- 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
- G11B7/1372—Lenses
- G11B7/1374—Objective lenses
-
- 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
- G11B7/1392—Means for controlling the beam wavefront, e.g. for correction of aberration
- G11B7/13922—Means for controlling the beam wavefront, e.g. for correction of aberration passive
-
- 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
- the present invention relates to an optical element having a lens surface coated.
- the present invention also relates to an optical pickup device on which the optical element is mounted.
- an optical pickup device is equipped with an objective lens (optical element) that condenses light from a laser diode and guides it to an optical disk.
- an objective lens optical element
- Such an objective lens is molded from a plastic material or a glass material!
- the molded objective lens causes various aberrations (wavefront aberration) in the emitted light due to various factors, for example, tolerance of the lens surface and non-uniformity of the refractive index distribution in the lens. These aberrations make the shape of the spot diameter focused on the optical disc different from the desired shape. For this reason, a shape error occurs between the spot diameter deformed in this way and the spot diameter of the desired shape, and the phenomenon that data cannot be stably recorded on the optical disk and the data read from the optical disk force cannot be reproduced accurately. A phenomenon occurs.
- An objective lens for a blue laser (wavelength near 405 nm) that requires high accuracy is required to have a wavefront aberration of 10 m ⁇ rms or less, for example!
- One of the causes for making the refractive index distribution in the lens non-uniform is glass molding.
- the objective lens OL is manufactured by glass molding, as shown in FIG. 4, the molten glass base material GM is press-molded into a mold ⁇ ( ⁇ 1 ⁇ 2) having a predetermined curved surface. For this reason, a relatively large pressure is applied to the outer edge of the objective lens OL, which causes stress distortion inside the objective lens OL, resulting in birefringence (see FIG. The number of arrows in 4 indicates the pressure distribution).
- Such birefringence is generated in a lens having a large numerical aperture (for example, a numerical aperture of 0.6 or more) having a large thickness difference between the center and the outer edge of the lens.
- Patent Document 1 As one measure for preventing the above phenomenon, for example, there is a method disclosed in Patent Document 1. According to this method, first, assuming that the internal refractive index distribution is uniform, the optical An initial design value of the element is obtained. Next, an optical element is formed based on this initial set value, and the refractive index distribution of the molded product (initial product) is actually measured.
- Patent Document 1 JP 2005-283783 A
- the present invention has been made to solve the above problems.
- the object is to provide an optical element that can easily suppress various aberrations of the emitted light (for example, astigmatism component of wavefront aberration) and an optical pickup equipped with the optical element. It is in.
- the present invention is an optical element having an optical multilayer film on the lens surface.
- the lens has birefringence, the astigmatism component of the wavefront aberration caused by the lens is 10 m rms or more, and the optical multilayer film generates a phase difference between the P-polarized light and the S-polarized light.
- the astigmatism component of wavefront aberration by the optical element is reduced to 5m rms or less.
- phase difference of the optical multilayer film substantially monotonically increases from the center of the lens toward the outer edge.
- An example of the monotonous change is a linear change.
- the optical multilayer film is an antireflection film, and in the optical thin film included in the optical multilayer film,
- Condition (1) The astigmatism component in the wavefront aberration of the lens is 20 m rms or more.
- the optical multilayer film is an antireflection film, and in the optical thin film included in the optical multilayer film,
- the astigmatism component in the wavefront aberration of the lens is 10 m ⁇ rms or more and
- the optical multilayer film has a low refractive index layer, an intermediate refractive index layer, and a high refractive index layer, and has a total of 7 or more layers.
- the optical multilayer film is an antireflection film, and in the optical thin film included in the optical multilayer film,
- Condition (5) The astigmatism component in the wavefront aberration of the lens is 20 m rms or more.
- the optical multilayer film is an antireflection film, and in the optical thin film included in the optical multilayer film,
- the optical multilayer film includes a total of five or more optical films, and includes a repeating structure in which low refractive index layers and high refractive index layers are alternately laminated.
- the lens is formed by molding.
- the numerical aperture of the lens is 0.6 or more.
- the birefringence occurs radially with respect to the lens axis center of the lens, and increases with the amount S of birefringence and the force from the lens axis center to the outer edge of the lens.
- the optical multilayer film is a dielectric multilayer film in which dielectric films for antireflection are laminated. desirable.
- optical pickup device including the above-described optical element can also be said to be the present invention.
- the lens has birefringence, and the optical multilayer film generates a phase difference between the P-polarized light and the S-polarized light to cancel the birefringence. Therefore, an optical element that reduces the astigmatism component of the wavefront aberration generated in the lens to half or less can also be said to be the present invention.
- the optical multilayer film reduce the astigmatism component of wavefront aberration generated in the lens to 1/5 or less! /.
- the optical multilayer film formed on the optical element can easily suppress various aberrations of the emitted light (for example, astigmatism component of wavefront aberration).
- FIG. 1 is an enlarged view of the objective lens in FIG. 2 described later.
- FIG. 2 is a configuration diagram of an optical pickup device.
- FIG. 3A is a perspective view of a confirmation device for confirming birefringence.
- FIG. 3B is a plan view of a lens surface seen by the confirmation device.
- FIG. 3C is a plan view of the lens surface when the objective lens is rotated.
- FIG. 3D is a plan view of the lens surface when the polarizing plate in the confirmation apparatus is rotated.
- FIG. 4 is a configuration diagram showing a molding die for an objective lens and a glass base material.
- FIG. 5 is a reflection characteristic diagram showing reflection characteristics of the dielectric multilayer film of Example 1.
- FIG. 6 is a phase difference characteristic diagram showing the phase difference characteristics of the dielectric multilayer film of Example 1 at a wavelength of 405 nm.
- FIG. 7 is a phase difference characteristic diagram showing the phase difference characteristics of the dielectric multilayer film of Example 1 at a wavelength of 660 nm.
- FIG. 8 is a phase difference characteristic diagram showing the phase difference characteristic of the dielectric multilayer film of Example 1 at a wavelength of 785 nm.
- FIG. 9 is a reflection characteristic diagram showing the reflection characteristics of the dielectric multilayer film of Example 2.
- FIG. 10 shows the retardation characteristics of the dielectric multilayer film of Example 2 at a wavelength of 405 nm. It is a phase difference characteristic view.
- FIG. 13 is a reflection characteristic diagram showing the reflection characteristics of the dielectric multilayer film of Example 3.
- 14] A phase difference characteristic diagram showing the phase difference characteristic of the dielectric multilayer film of Example 3 at a wavelength of 405 nm.
- FIG. 17 is a reflection characteristic diagram showing the reflection characteristics of the dielectric multilayer film of Example 4.
- 18] A phase difference characteristic diagram showing the phase difference characteristic of the dielectric multilayer film of Example 4 at a wavelength of 405 nm.
- FIG. 19 is a phase difference characteristic diagram showing the phase difference characteristic of the dielectric multilayer film of Example 4 at a wavelength of 660 nm.
- FIG. 20 is a phase difference characteristic diagram showing the phase difference characteristics of the dielectric multilayer film of Example 4 at a wavelength of 785 nm.
- FIG. 21 is a reflection characteristic diagram showing the reflection characteristics of the dielectric multilayer film of Example 5.
- FIG. 22 is a phase difference characteristic diagram showing the phase difference characteristics of the dielectric multilayer film of Example 5 at a wavelength of 405 nm.
- FIG. 23 is a phase difference characteristic diagram showing the phase difference characteristics of the dielectric multilayer film of Example 5 at a wavelength of 660 nm.
- FIG. 24 is a phase difference characteristic diagram showing the phase difference characteristics of the dielectric multilayer film of Example 5 at a wavelength of 785 nm.
- FIG. 25 is a reflection characteristic diagram showing the reflection characteristics of the dielectric multilayer film of Example 6.
- FIG. 26 shows retardation characteristics of the dielectric multilayer film of Example 6 at a wavelength of 405 nm. It is a phase difference characteristic view.
- FIG. 27 is a phase difference characteristic diagram showing the phase difference characteristics of the dielectric multilayer film of Example 6 at a wavelength of 660 nm.
- FIG. 28 is a phase difference characteristic diagram showing the phase difference characteristic of the dielectric multilayer film of Example 6 at a wavelength of 785 mn.
- FIG. 29 is a reflection characteristic diagram showing the reflection characteristic of the dielectric multilayer film of the comparative example.
- FIG. 30 is a phase difference characteristic diagram showing the phase difference characteristics of the dielectric multilayer film of the comparative example at a wavelength of 405 nm.
- FIG. 31 is a phase difference characteristic diagram showing a phase difference characteristic of a dielectric multilayer film of a comparative example at a wavelength of 660 mn.
- FIG. 32 is a phase difference characteristic diagram showing a phase difference characteristic of a dielectric multilayer film of a comparative example at a wavelength of 785 nm.
- FIG. 33 is a block diagram of a Twiman Green interferometer.
- FIG. 2 is a configuration diagram showing a schematic configuration of the optical pickup device 59.
- the optical pick-up device 59 includes a first laser unit 21, a second laser unit 31, a dichroic prism 41, a rising mirror 42, a quarter-wave plate 43, and a coating objective lens COL. .
- the optical disc 44 is also shown for convenience.
- the light incident on the optical disk 44 is referred to as “irradiation light”, and the light reflected from the optical disk 44 is referred to as “signal light” (the light is illustrated by a broken line).
- the first laser unit 21 will be described.
- the first laser unit 21 is a first laser unit 21
- LD Laser diode
- PBS polarization beam splitter
- PD photodiode
- the first LD 22 emits laser light (blue laser) having a wavelength of 405 nm toward the first PBS 23.
- the first LD 22 is one of the next generation DVDs (Digital Versatile Discs).
- BD Luray Disc
- the first PBS 23 transmits linearly polarized laser light (eg, P-polarized light) emitted from the first LD 22 and guides it to the first collimator lens 24.
- the first PBS 23 reflects the signal light (for example, S-polarized light) traveling through the first collimator lens 24 and guides it to the first PD 25.
- the first collimator lens 24 converts the laser light incident through the first PBS 23 into parallel light and guides it to the dichroic prism 41. On the other hand, the first collimator lens 24 guides the signal light traveling through the dichroic prism 41 to the first PBS 23.
- the first PD 25 receives the signal light incident through the first PBS 23.
- the light received by the first PD25 detects servo signals (focus error signals, tracking error signals), information signals, aberration signals, etc. during recording / playback on Blu-ray discs.
- the second laser unit 31 will be described.
- the second laser unit 31
- the second LD 32 emits laser light having a wavelength of 660 nm and laser light having a wavelength of 785 nm toward the second PBS 33. That is, the second LD 32 is a light source that emits laser light of two wavelengths, and corresponds to DVD and CD (Compact Disc).
- the second PBS 33 transmits linearly polarized laser light (eg, P-polarized light) emitted from the second LD 32 and guides it to the second collimator lens 34.
- the second PBS 33 reflects the signal light (for example, S-polarized light) traveling through the second collimator lens 34 and guides it to the second PD 35.
- the second collimator lens 34 converts the laser light incident through the second PBS 33 into parallel light and guides it to the dichroic prism 41.
- the second collimator lens 34 guides the signal light traveling through the dichroic prism 41 to the second PBS 33.
- the second PD 35 receives the signal light incident through the second PBS 33.
- the light received by the first PD 25 detects a servo signal (focus error signal, tracking error signal), information signal, aberration signal, etc. during recording / reproducing on a DVD or CD.
- the dichroic prism 41 that reflects the power reflects and directs the laser beam supplied from the first laser unit 21 to the rising mirror 42 and transmits the laser beam supplied from the second laser unit 31 to transmit the laser beam. Lead to Ra 42.
- the dichroic prism 41 is an optical path conversion element that emits the laser light incident from different directions with the same traveling direction.
- the dichroic prism 41 guides the signal light traveling through the rising mirror 42 to the first laser unit 21 or the second laser unit 31. Specifically, the signal light of the laser light emitted from the first LD 22 is reflected after being incident on the dichroic prism 41 and guided to the first collimator lens 24 of the first laser unit 21. Further, the signal light of the laser beam from which the second LD 32 force is also emitted is transmitted after being incident on the dichroic prism 41 and guided to the second collimator lens 34 of the second laser unit 31.
- the rising mirror 42 is emitted from the dichroic prism 41 and directed to the optical disk 44 to bend the optical path of the laser beam and guide it to the coating objective lens COL.
- the force and the raising mirror 42 are arranged in the optical path between the first LD22 ′ second LD32 and the optical disc 44, more specifically between the dichroic prism 41 and the coated object lens COL. .
- the raising mirror 42 bends the optical path of the signal light traveling through the coating objective lens COL and guides it to the dichroic prism 41.
- the quarter-wave plate 43 converts linearly polarized light (for example, P-polarized light) reflected by the rising mirror 42 into circularly polarized light.
- the quarter-wave plate 43 converts the signal light (circularly polarized light) from the optical disk 44 into linearly polarized light (for example, S-polarized light).
- the coated object lens COL is reflected by the rising mirror 42 and collects the light (irradiation light) obtained through the quarter-wave plate 43 on the optical disk 44.
- the coating objective lens COL guides light (signal light) reflected from the optical disk 44 to the quarter-wave plate 43.
- the coated objective lens COL is provided with a dielectric multilayer film MLR which is an antireflection film ⁇ AR (Anti Reflection) film ⁇ ! (Details will be described later).
- the material of the objective lens OL in the coating objective lens COL is not particularly limited. However, it can be said that glass having high weather resistance against ultraviolet light is desirable. For example, the following glass molded lens is mentioned as an example.
- NA 0.85 Lens outline (diameter): 5mm
- the standard values of the numerical aperture of the coating objective lens COL used for BD, DVD, and CD are 0.85, 0.65, and 0.5, respectively.
- the objective lens OL formed by glass molding has radiation birefringence centered on the lens axis, and the birefringence amount increases as it approaches the outer edge of the objective lens OL. Yes.
- the birefringence of the objective lens OL is distributed radially from the lens axis, that is, axisymmetrically distributed! /, So the optical axis of birefringence (the fast axis is! / Is the slow axis) Exists in the radial and circumferential directions of the lens.
- the light (marginal ray) incident on the outer edge of the objective lens OL is greatly affected by birefringence and generates wavefront aberration.
- the coating objective COL includes a plurality of dielectric films Li for antireflection treatment (AR treatment). It is. Then, as shown in FIG. 1, for example, when parallel light is incident on the dielectric film Li, the incident angle ⁇ gradually increases as it approaches the outer edge of the coating objective lens COL (note that the dotted line in FIG. And shows the normal at the incident point in the dielectric film Li).
- the incident angle ⁇ changes, the light traveling in the dielectric film Li is polarized (oscillating in parallel to the incident surface) and S-polarized light (perpendicular to the incident surface). The phase difference between and the polarization changes.
- the phase difference between the P-polarized light and the S-polarized light ⁇ more specifically, the phase difference of the transmitted light passing through the plurality of dielectric films Li (dielectric multilayer film MLR); the transmission phase difference D ⁇ and the birefringence
- the phase difference (birefringence phase difference) between P-polarized light and S-polarized light have opposite polarities. This is because the birefringence phase difference is canceled out by the transmission phase difference D caused by the dielectric film Li.
- the astigmatism component in the wavefront aberration is reduced due to the cancellation of the birefringence phase difference.
- the transmission phase difference D due to the dielectric film Li increases substantially monotonically as it goes from the lens center to the outer edge.
- the birefringence of the objective lens OL is directed toward the outer edge and sea urchin. This is because it can be canceled by the transmission phase difference D.
- a substantially monotonic increase means that the transmission phase difference D increases toward the outer edge and, as a whole, increases as a whole, even if the transmission phase difference D slightly decreases near the outermost edge. It can be said that it is increasing monotonically.
- the object lens OL has birefringence, the polarization state of the emitted light is changed.
- the signal light is directed to the first PBS 23 and the second PBS 33, and includes components other than S-polarized light.
- so-called return light that passes through the PBSs 23 and 33 and reaches the LD is generated.
- the return light must be eliminated as much as possible to destabilize the LD oscillation.
- the dielectric multilayer film (optical multilayer film) MLR constituting the antireflection film will be described in detail.
- a plurality of dielectric films Li are formed on the coating objective lens COL.
- the reflectivity of the dielectric multilayer film MLR is defined as follows.
- the thickness of each dielectric film Li and the refractive index of each dielectric film Li are expressed by the following Fresnel equations for each boundary surface ("dielectric material"). It is obtained by applying the number of films of Li film (number of layers) ").
- the dielectric multilayer films MLR in Examples to be described later;! To 6 are designed to generate a transmission phase difference D (phase difference between P-polarized light and S-polarized light) not only for antireflection.
- the principle of adjusting the transmission phase difference D is as follows. [0055] Normally, when light passes through a medium having a different refractive index (refractive index n> refractive index n), the refractive index n
- phase ⁇ of the light passing through the medium (the phase ⁇ 'of the P-polarized light ⁇ '
- phase difference phase ⁇ -phase ⁇
- refractive index ⁇ refractive index
- phase difference between P-polarized light and S-polarized light (phase ⁇ — phase ⁇ ) is different.
- the transmission phase difference D can be set appropriately using the refractive index difference (refractive index difference) and the distance in the medium (film thickness) as parameters.
- Table 16 shows the construction data of six types (Examples;! To 6) of dielectric multilayer MLR considering the transmission phase difference D.
- Table 7 shows the construction data of one type of dielectric multilayer MLR that does not take the transmission phase difference D into consideration as a comparative example.
- the construction data of Example 16 is a value derived from commercially available film configuration design software with the antireflection characteristic and the desired phase difference as target values.
- the construction data of the comparative example is a value of an antireflection film that is generally used conventionally.
- the refractive index (nd) corresponds to the d-line (wavelength 587/6 nm), and the Abbe number (i> d) of the glass corresponding to the d-line is 5 6.88.
- the material of the dielectric film Li is indicated by a compound formula in the case of a single compound and indicated by a product name in the case of a mixture (see below).
- H4 is a mixture of TiO and La 2 O (lanthanum oxide)
- M3 is a mixture of Al O and La O
- dielectric film (layer) Li is defined as follows according to the refractive index of the material.
- Low refractive index layer L Dielectric film Li with a refractive index of less than 1.6
- Intermediate refractive index layer M Dielectric film Li with a refractive index of 1.6 to 1.9 • High refractive index layer H: Dielectric film Li with a refractive index exceeding 1.9
- the vertical axis of the phase difference characteristic diagram indicates the difference obtained by subtracting the phase of S-polarized light from the phase of P-polarized light.
- “+” on the vertical axis indicates that the phase of S-polarized light is delayed with respect to the phase of P-polarized light
- “” on the vertical axis indicates the phase of P-polarized light.
- the transmission phase difference D that cancels out the birefringence phase difference is a value indicated by “+” in the figure.
- the dielectric multilayer film MLR of ⁇ 6 has three types of layers: a low refractive index layer L, an intermediate refractive index layer M, and a high refractive index layer H.
- the total number of layers (total number of dielectric films Li) included in the dielectric multilayer film MLR is 12 layers, 9 layers, 9 layers, 7 layers, 7 layers, respectively for the examples:! To 6 There are 5 layers.
- the dielectric multilayer films MLR of Examples;! To 6 include a repetitive structure in which the low refractive index layer L and the high refractive index layer H are alternately stacked.
- Refractive index difference (N-N) relationships are 0.73, 1.04, 0.73, 0.73, 0.73, 0.7, respectively.
- the dielectric multilayer film MLR of the comparative example has three types of layers, a low refractive index layer L, an intermediate refractive index layer M, and a high refractive index layer H, as in Examples 1 to 6. However, the total number of layers included in the dielectric multilayer MLR is three.
- the dielectric multilayer film MLR of the comparative example includes a repeating structure in which the low refractive index layers L and the high refractive index layers H are alternately stacked, as in the first to sixth embodiments.
- the number of groups is one.
- the refraction between the refractive index N of the high refractive index layer H and the refractive index N of the low refractive index layer L is refraction between the refractive index N of the high refractive index layer H and the refractive index N of the low refractive index layer L.
- the rate difference is 1.04.
- the following can be said from the reflection characteristic diagrams and phase difference characteristic diagrams of Examples 1 to 6.
- the reflectance power corresponding to the wavelengths (405, 660, 785 nm) of BD, DVD, and CD is less than 3%. Therefore, when the dielectric multilayer film MLR of Examples;! To 6 is formed on the objective lens OL, the reflected light from the coating objective lens COL is effectively suppressed.
- the transmission phase difference D [°] is specified within a certain range.
- a used wavelength of 405 nm it is as follows.
- the transmission phase difference D increases monotonously as the incident angle ⁇ increases in the range of 30 ° ⁇ ⁇ ⁇ 60 °.
- monotonic change means either monotonic increase or monotonic decrease, and an example of monotonic change is linear change.
- the incident angle ⁇ shown on the horizontal axis of the phase difference characteristic diagram is related to the radial direction of the coating objective lens COL. This is apparent from FIG. 1 showing the case where the dielectric multilayer MLR is provided on the objective lens OL!
- the objective lens OL has the first to third embodiments. It is desirable that the dielectric multilayer film MLR 6 is formed. This is because in the dielectric multilayer MLR deposited on the objective lens OL (that is, in the case of the coating objective lens COL), the transmission phase difference D is centered on the lens axis so as to correspond to the birefringence of the objective lens OL. This is because they occur radially and the amount of phase difference increases as they approach the outer edge of the objective lens OL.
- the transmission phase difference D caused by the dielectric multilayer film MLR corresponds to the birefringence phase difference caused by the objective lens OL. Therefore, in the coating objective lens COL on which the dielectric multilayer film MLR of Examples 1 to 6 is formed, when light with a wavelength of 405 nm is incident on the coating objective lens COL, the transmission phase difference caused by the dielectric multilayer film MLR D can sufficiently cancel out the birefringence phase difference caused by the objective lens OL. As a result, the astigmatism component in the wavefront aberration is reduced.
- the birefringence phase difference is inversely proportional to the wavelength used.
- the value of the transmission phase difference D was smaller than the value of the transmission phase difference D in the case of using wavelength 405 ⁇ m.
- the transmission phase difference D and the birefringence phase difference cancel each other when the wavelength used is 405 nm, the transmission phase difference D and the birefringence phase difference are obtained even when the wavelength used is 660 and 785 nm. And offset.
- the numerical apertures of the corresponding lenses are 0 ⁇ 65 and 0.5, respectively.
- the light incident on the coating objective lens COL The bundle diameter is small compared to the case where light having a wavelength of 405 nm is incident. Since light with wavelengths of 660 nm and 785 nm do not enter the outer edge of the lens, there is no problem even if a large phase difference is not generated due to the influence of birefringence.
- the reflection characteristic diagram ⁇ phase difference characteristic diagram of the comparative example the reflection skew force corresponding to the wavelengths (405, 660, 785 nm) of BD, DVD, and CD is less than 5.50 / 0 . Therefore, the case where the dielectric multilayer film MLR of the comparative example is formed on the objective lens OL is compared with the case where the dielectric multilayer film MLR of Examples;! To 6 is formed on the objective lens OL. Then, it can be seen that the coated objective lens COL corresponding to Examples 1 to 6 can more effectively suppress the reflected light than the coated objective lens COL corresponding to the comparative example.
- the dielectric multilayer film MLR of the comparative example takes into account the transmission phase difference D! /,! /. For this reason, it is difficult for the transmission phase difference D of “+” to be generated at all wavelengths used, but rather, the transmission phase difference D of “” is easily generated.
- the wavefront aberration is measured by a Twiman Green interferometer as shown in FIG.
- the Toiman Green interferometer is a laser light source 14 that emits linearly polarized light, a beam splitter 15, a spherical prototype 16, a planar prototype 17, and an image that captures interference fringe images and calculates wavefront aberration.
- a processing unit 18 The light flux from the light source is separated by the beam splitter 15, one of which is reflected by the planar master 17, and the other is collected by the lens 19, and then reflected by the spherical prototype 16.
- the reference light reflected by the planar master 17 and the measurement light transmitted through the test lens 19 again are combined by the beam splitter 15 to generate interference fringes.
- the interference fringes are input to the image processing device 18 and processed to measure the wavefront aberration of the lens 19 to be examined.
- the parallelism (divergence) of the light beam incident on the test lens 19 is appropriately adjusted according to the actual use state of the test lens 19.
- the measurement of the astigmatism component of the wavefront aberration takes the following steps.
- the test lens 19 is arranged so that the spherical center of the spherical prototype 16 and the focal position of the test lens 19 (coating objective lens COL, etc.) match, and the reflected light from the spherical prototype 16 and the planar prototype Wavefront aberration is determined from interference fringes caused by reflected light from 17 (first measurement; measurement at 0 ° lens position).
- the lens 19 is rotated 90 ° around the optical axis from the first measurement position, and then the wavefront aberration is measured in the same way as the first measurement (second measurement; lens position 90 ° Measurement).
- the astigmatism component of the wavefront aberration is obtained using the wavefront aberration (wavefront aberration at the lens position of 0 ° ⁇ 90 °) obtained as described above. Specifically, first, each wavefront aberration is expanded by a Zemike polynomial, and the coefficients of the Z4 term and the Z5 term in the polynomial are obtained. After that, the astigmatism component [m rms] of the wavefront aberration is obtained from the following equation.
- Z4 (90 °) Z4 term of Zernike's polynomial at lens position 90 °
- Z5 (90 °) Z5 term of Zernike's polynomial at lens position 90 °
- the Zernike polynomial uses a so-called Arizona-style expansion formula. Specifically, it was calculated using Metropro Zernike Application, an analysis software made by Canon Inc. Wavefront aberration is measured using linearly polarized light. In general, when the wavefront aberration is measured using an interferometer, circularly polarized light is used. However, the astigmatism component of the wavefront aberration due to birefringence is not detected by the method using circularly polarized light.
- first objective lens OL1 first objective lens OL1 'second objective lens OL2
- second objective lens OL2 The first objective lens OLl and the second objective lens OL2 are both made by glass molding, and both have a numerical aperture of 0.85.
- the astigmatism component of the wavefront aberration caused by the first objective lens OL1 was found by the above measurement method to be 20. lm rms.
- the astigmatism component of the wavefront aberration of the first objective lens OL1 formed with the dielectric multilayer MLR of the comparative example was found to be 18.8 m rms (reduction of about lm rms) .
- the value of the transmission phase difference D at a certain incident angle ⁇ is as follows.
- the astigmatism component of the wavefront aberration of the first coating objective lens COL in which the dielectric multilayer film MLR of Example 1 was formed on the first objective lens OL1 was found to be 1.7 m rms. (Reduction of about 18m rms).
- the value of the transmission phase difference D at a certain incident angle ⁇ is as follows.
- the dielectric multilayer film MLR of the comparative example cannot sufficiently reduce the astigmatism component of the wavefront aberration caused by the first objective lens OL1, but the dielectric multilayer film MLR of Example 1 It can be seen that the astigmatism component of the wavefront aberration caused by the first objective lens OL1 can be sufficiently reduced.
- the astigmatism component was 18.5 m rms.
- the astigmatism component of the wavefront aberration of the second coating objective lens COL in which the dielectric multilayer film MLR of Example 2 was formed on the second objective lens OL2 was determined as 1. lm rms. (A reduction of about 17m rms).
- the value of the transmission phase difference D at a certain incident angle ⁇ is as follows.
- the dielectric multilayer film MLR of Example 2 can sufficiently reduce the astigmatism component of the wavefront aberration caused by the second objective lens OL2.
- the objective lenses OLl and OL2 have birefringence radially around the lens axis.
- the objective lens OL was placed between the polarizing plate 12 having the transmission axis PA and the plane mirror 13 to observe interference fringes.
- Light that has passed through the polarizing plate 12 (light that vibrates in the same direction as the transmission axis PA) passes through the objective lens OL, is reflected by the plane mirror 13, passes through the objective lens OL again, and travels toward the polarizing plate 12. And proceed.
- the objective lens OL is equivalent to being arranged between parallel Nicols.
- FIG. 3B shows the objective lens OL observed through the polarizing plate 12. Specifically, white was observed in the same direction (parallel direction) and perpendicular to the transmission axis PA, while black interference fringes were observed in the direction of 45 ° (135 °) with the transmission axis PA.
- FIG. 3C shows the lens surface when the objective lens OL is rotated. The interference fringes did not rotate even when the objective lens OL was rotated.
- FIG. 3D shows the lens surface when the polarizing plate 12 is rotated. When the polarizing plate 12 was rotated, the interference fringes were rotated in the same manner as the polarizing plate 12.
- the objective lens OL has uniaxial crystal birefringence, and its optical axis is in the radial direction and the circumferential direction. That is, the objective lens OL has radial birefringence. It was also confirmed that the magnitude of the birefringence increases toward the outer edge of the objective lens OL.
- the measurement of the wavefront aberration of the coating objective lens COL was not performed by using the dielectric multilayer film MLR of Examples 1 and 2, which was formed. However, it is easy to reduce the astigmatism component of the wavefront aberration caused by the objective lens OL even with the dielectric multilayer film MLR of the other embodiments having the same phase difference as the first and second embodiments. I can guess.
- the astigmatism component of the wavefront aberration of the first objective lens OL1 exceeds 20 m rms, and the transmission phase difference D of Example 1 is 18 ° when the incident angle ⁇ force is 0 °. Since the transmission phase difference D of Examples 3 and 4 is the same as that of Example 1, it is possible to cancel birefringence similar to that of the first objective lens OL1.
- Example 5 since the transmission phase difference D of Example 5 is the same as that of Example 2, birefringence similar to that of the second objective lens OL2 can be canceled out.
- the magnitude of the astigmatism component of wavefront aberration correlates with the magnitude of birefringence, so Example 6 is effective when used for an objective lens having a smaller birefringence than the second objective lens OL 2.
- the astigmatic difference component of the wavefront aberration can be reduced.
- a dielectric multilayer film that generates a larger phase difference may be used for an objective lens having a larger birefringence than the first objective lens OL1.
- the dielectric multilayer film MLR that generates a large phase difference and realizes antireflection has a low refractive index layer L, an intermediate refractive index layer M, and a high refractive index layer H, and is preferably composed of 9 or more layers in total. (Examples correspond to! ⁇ 3).
- the dielectric multilayer film MLR includes a total of seven or more optical thin films and a repeating structure formed by alternately laminating low refractive index layers L and high refractive index layers H, and has a high refractive index.
- the difference between the refractive index N of the layer H and the refractive index N of the low refractive index layer L should be 0.5 or more (Example:!
- the number of layers of the dielectric multilayer film MLR is more preferably 20 or less. If the upper limit is exceeded, ripples occur due to variations during manufacturing, making it difficult to stably ensure antireflection characteristics.
- Dielectric multilayer MLR which generates a relatively small phase difference and realizes antireflection, has a low refractive index layer L, an intermediate refractive index layer M, and a high refractive index layer H. There should be (Examples 1 to 5 correspond).
- the dielectric multilayer film MLR includes a total of five or more dielectric films, and also includes a repetitive structure in which the low refractive index layers L and the high refractive index layers H are alternately stacked, and has a high refractive index.
- the difference between the refractive index N of the layer H and the refractive index N of the low refractive index layer L is 0.5 or more. (Examples:! To 6 correspond). Antireflection can be realized even with a smaller number of layers than the above conditions. It is difficult to generate a phase difference that can compensate for birefringence. In any case, the number of layers of the dielectric multilayer MLR is more preferably 20 or less. If the upper limit is exceeded, ripples occur due to manufacturing variations, making it difficult to stably ensure antireflection characteristics.
- the following can be said for COL. That is, birefringence occurs in the objective lens OL, which may cause a wavefront convergence in the light emitted from the objective lens OL.
- the coated objective lens COL has a dielectric multilayer MLR that reduces the astigmatism component to 5 m rms or less! / .
- D is 2 ° or more and 20 ° or less
- D is 4 ° or more and 40 ° or less
- the change of D in the range of 30 ° ⁇ ⁇ 60 ° is a monotonous change (eg linear change) and is a coated objective lens COL (example;! To 6 corresponds).
- the force and burial coated objective lens COL can effectively reduce the astigmatism component of wavefront aberration and achieve antireflection if the following conditions are satisfied (actual) Examples;! ⁇ 3 correspond).
- the astigmatism component in the wavefront aberration generated by the objective lens OL without the dielectric film Li is 20 m ⁇ rms or more.
- Low refractive index layer L Low refractive index layer L, intermediate refractive index layer M, and high refractive index layer H.
- the coated objective lens COL can effectively reduce the astigmatism component of the wavefront aberration and realize antireflection (Examples;! To 5). Is supported).
- the astigmatism component in the wavefront aberration generated by the objective lens OL without the dielectric film Li is 10 m ⁇ rms or more and less than 20 m ⁇ rms.
- the dielectric multilayer film MLR has a low refractive index layer L, an intermediate refractive index layer M, and a high refractive index layer H, and has a total of seven or more layers.
- the coated objective lens COL can effectively reduce the astigmatism component of the wavefront aberration and realize antireflection even if the following conditions are satisfied separately (Examples;! Correspondence).
- the astigmatism component in the wavefront aberration generated by the coated objective lens COL without the dielectric film Li is 20 m ⁇ rms or more.
- the dielectric multilayer film MLR includes a total of seven or more dielectric films Li, and includes a repetitive structure in which low refractive index layers L and high refractive index layers H are alternately stacked. Yes.
- the required difference in refractive index is 0.5 or more.
- the coated objective lens COL can effectively reduce the astigmatism component of the wavefront aberration and realize antireflection even if the following conditions are satisfied separately (Examples;! Correspondence).
- the astigmatism component in the wavefront aberration generated by the objective lens OL without the dielectric film Li is 10 m ⁇ rms or more and less than 20 m ⁇ rms.
- the dielectric multilayer film MLR includes a total of five or more dielectric films Li, and includes a repetitive structure in which low refractive index layers L and high refractive index layers H are alternately stacked. Yes.
- the required difference in refractive index is 0.5 or more.
- birefringence is likely to occur in the objective lens OL produced by glass molding.
- the larger the numerical aperture the more likely birefringence occurs, for example, when the numerical aperture is 0.6 or more.
- the birefringence generated as a result of the force occurs radially around the lens axis, and the amount of birefringence increases as it approaches the outer edge of the objective lens OL.
- the multi-layered dielectric MLR film formed on the objective lens OL is also transmitted radially with the lens axis as the center so as to correspond to the birefringence caused by the objective lens OL. D is generated, and the phase difference is increased as it approaches the outer edge of the objective lens OL. Therefore, if a dielectric multilayer film MLR is provided on such an objective lens OL, the dielectric multilayer film MLR cancels the birefringence phase difference with the transmission phase difference D without any problem and eliminates the astigmatism component of the wavefront aberration. Can be reduced.
- the imaging lens system may be a projection lens system or a lens used for measurement. Regardless of the lens used in any of the optical systems, it is possible to reduce performance degradation due to birefringence of the lens by generating a transmission phase difference in the dielectric multilayer film MLR.
- a force that can cancel the birefringence phase difference when the phase of S-polarized light is delayed with respect to the phase of P-polarized light is not limited to this. What is necessary is just to generate a phase difference.
- the birefringence distribution may not be axisymmetric.
- P-biased Those that reduce the birefringence of the lens by using the phase difference between the light and the S-polarized light are included in the present invention.
- the dielectric multilayer film MLR has been described as an example. However, it is not limited to this. That is, the optical thin film, and thus the optical multilayer film, may be formed of a material other than the dielectric material. Further, the dielectric multilayer film MLR is not limited to the antireflection film, and the method for forming the dielectric multilayer film MLR on the objective lens OL is not limited.
Abstract
Description
Claims
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Cited By (3)
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JP2011257677A (ja) * | 2010-06-11 | 2011-12-22 | Konica Minolta Opto Inc | 光学素子とその製造方法 |
JP2013511066A (ja) * | 2009-11-11 | 2013-03-28 | イーストマン コダック カンパニー | 位相補償型薄膜ビームコンバイナ |
JP2016197253A (ja) * | 2012-09-28 | 2016-11-24 | 株式会社ニコン・エシロール | 眼鏡レンズおよびその製造方法 |
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JP5552008B2 (ja) * | 2009-09-30 | 2014-07-16 | Hoya株式会社 | 光情報記録再生光学系及び光情報記録再生装置 |
DE102010048088A1 (de) * | 2010-10-01 | 2012-04-05 | Carl Zeiss Vision Gmbh | Optische Linse mit kratzfester Entspiegelungsschicht |
KR102135345B1 (ko) * | 2013-01-22 | 2020-07-17 | 엘지전자 주식회사 | 영상투사장치 |
CN113506598A (zh) * | 2021-07-15 | 2021-10-15 | 中节能万润股份有限公司 | 一种通过建立qsar模型预测液晶分子双折射率的方法 |
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US7986604B2 (en) | 2011-07-26 |
CN101553744B (zh) | 2012-06-27 |
JPWO2008069031A1 (ja) | 2010-03-18 |
US20080259773A1 (en) | 2008-10-23 |
JP4433086B2 (ja) | 2010-03-17 |
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