KR100439373B1 - Optical pickup - Google Patents

Abstract

The present invention provides an optical pickup apparatus including an objective lens to enable HD / DVD compatibility using a catadioptic lens.

In the optical pickup device using the HD / DVD compatible objective of the present invention, the optical incidence center of the catadioptic lens is configured in the shape of a cone lens and crosses the optical path transversely through the optical path. By processing different light reflection / transmission characteristics on the middle part, the light entrance surface of the lens and the light exit surface of the lens, in the case of HD, the incident light is transmitted to the cone lens portion and then reflected and focused inside the lens. In the case of DVD, the light incident on the cone lens part is focused onto the disc by the middle part of the lens and the reflection / transmission part of the entrance / exit surface, so that one objective lens can be used as an HD / DVD objective lens. Provides an HD / DVD compatible optical pickup device.

Description

Heterogeneous recording media compatible optical pickup device {OPTICAL PICKUP}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens of an optical pickup apparatus for optical recording and reproduction, and more particularly to an optical pickup apparatus compatible with a heterogeneous recording medium having different recording densities. The heterogeneous means includes two or more recording media having different recording densities. Say.

Due to the continuous development efforts to increase the recording capacity, optical video discs (Digital Video Disks), which have a larger recording capacity than conventional compact disks (CDs), have been developed. A high-density recording / playback disc (HD) and a drive for recording and reproducing data at a high density (more than twice the density) using CDs have also been developed. A DVD has a higher recording density (i.e. track density) than a CD and a shorter distance from the surface of the disc to the information recording surface. Because of this, it is difficult for an optical pickup device for DVD to record / reproduce information on a CD, which is spherical aberration due to a change in the distance between the surface and the information recording surface on the optical disc, and coma aberration and decoupling due to tilting of the optical disc. This is caused by astigmatism or the like caused by focus.

Spherical aberration causes the intensity of the main lobe of the light beam by the area of the information recording medium to become relatively large compared to the intensity of the side lobe by the area other than the information recording medium, thereby causing interference between information tracks. Coma aberration and astigmatism destabilize the optical system and degrade the optical characteristics. Such spherical aberration (SA), coma aberration (CA) and astigmatism (DA) are the change in the distance between the surface and the information recording surface on the optical disk, refractive index, numerical aperture (NA) of the objective lens, the amount of defocus, the degree of tilt of the optical disk Depend on

However, the optical pickup apparatus can access both the CD and the DVD when the numerical aperture NA is used to adjust the diameter of the light beam from the light source by using objective lenses.

Therefore, although different types of objective lenses having different numerical apertures can be used, an optical pickup apparatus capable of accessing both CD and DVD by coating a SWP filter on one objective lens has been proposed.

1 shows a configuration of a general CD / DVD combined optical pickup device.

Referring to Fig. 1, a first HPM (hologram pickup module) 1 for outputting DVD laser light, a second HPM 2 for outputting CD laser light, and a light beam output from the first HPM are transmitted. And a beam splitter 3 for reflecting the light output from the second HPM, a collimating lens 4 for making the light beam traveling from the beam splitter into a parallel beam, and a parallel beam passing through the collimating lens to reflect the optical path. A reflector 5 for converting?, An objective lens 6a for focusing the beam reflected by the reflector at an arbitrary point on the disk 7, and a SWP filter for adjusting the numerical aperture NA of the objective lens It comprises 6b.

The light beam output from the first HPM 1 passes through the beam splitter 3 and becomes a parallel beam by the collimation lens 4, and the light beam output from the second HPM 2 is reflected from the beam splitter 3 and collimated with the collimation lens. By (4), it becomes a parallel beam. The parallel beam made through the collimating lens 4 is changed vertically by the half mirror 5, and the light beam passing through the reflecting mirror 5 is transferred to the disk 7 by the objective lens 6a. Focused on a point on the table. At this time, the light beam incident on the objective lens 6a via the reflector 5 passes through the SWP filter 6b, thereby allowing CD / DVD sharing access by selective filtering of 650 nm (DVD) and 780 nm (CD). I would have to. As described above, a method of considering both the difference in NA, the difference in wavelength λ, the difference in disk thickness t, and the like is required for CD and DVD compatibility.

In particular, the HD objective lens for HD recording or reproduction is NA = 0.85, λ = 405 nm, and the cover glass is t = 0.1 mm, so the DVD objective lens (NA = 0.6, λ = 650 nm, t = 0.6). mm), means for overcoming the above difference in NA, λ, and t is required for compatibility with HD and DVD. That is, in the case of HD optical discs, the wavelength of the recording / reproducing laser is 405 nm, the thickness from the disc surface to the recording layer is 0.1t, the numerical aperture of the objective lens is NA = 0.85, and the laser wavelength in the case of DVD optical discs. Is 650 nm, and the thickness from the surface of the disk to the recording layer is 0.6t and the numerical aperture NA of the objective lens is 0.6, so that the difference in the thickness of the disc in order to play a DVD disc with an objective lens (optical pickup device) made for an HD disc It should be possible to compensate for spherical aberration and chromatic aberration due to the difference in laser wavelength.

An object of the present invention is to provide a heterogeneous optical recording medium compatible objective lens having a different recording density and a heterogeneous recording medium compatible optical pickup device using the same. The present invention particularly provides an optical pickup apparatus including an objective lens that enables HD / DVD compatibility using a catadioptic lens.

In the optical pickup apparatus using the HD / DVD compatible objective lens of the present invention, for the light focused / imaged on a disc through a catadioptic lens, the reflected wavelength and the transmitted wavelength are respectively corresponding to the respective HD / DVD. An optical pickup apparatus capable of HD / DVD compatibility by providing different structures and light reflection / transmission characteristic processing is provided.

In the optical pickup device using the HD / DVD compatible objective of the present invention, the optical incidence center of the catadioptic lens is configured in the shape of a cone lens and crosses the optical path transversely through the optical path. By processing different light reflection / transmission characteristics on the middle part, the light entrance surface of the lens and the light exit surface of the lens, in the case of HD, the incident light is transmitted to the cone lens portion and then reflected and focused inside the lens. In the case of DVD, the light incident on the cone lens part is focused onto the disc by the middle part of the lens and the reflection / transmission part of the entrance / exit surface, so that one objective lens can be used as an HD / DVD objective lens. Provides an HD / DVD compatible optical pickup device.

In the optical pickup device using the HD / DVD compatible objective lens of the present invention, the center of the light incident surface of the catadioptic lens is formed in the shape of a cone lens. Wavelength) is reflected (R405), DVD laser light (wavelength) is reflected (R650), and in the case of the reflection / transmission part transversely transverse to the middle of the lens, the center T405 / R650 and the edge T405 By processing the characteristics of the R650 and the center of the light exit surface of the lens with the characteristics of the T405 / T650 and the edges of the R450 / R650, an HD / DVD compatible objective is constructed so as to use an HD / Provided are an optical pickup apparatus capable of DVD compatibility.

1 is a view showing the configuration of a conventional CD / DVD combined optical pickup device

Figure 2a is a view showing the configuration of the HD / DVD compatible objective lens in the HD / DVD compatible optical pickup device of the present invention

Figure 2b is a plan view showing the characteristics of the intermediate reflection / transmission portion of the objective lens in the HD / DVD compatible optical pickup device of the present invention

Figure 2c, 2d is a view showing the light reflection and transmission path of the objective lens for HD / DVD compatible in the HD / DVD compatible optical pickup device of the present invention

2A and 2B show the configuration of the objective lens for HD / DVD compatibility according to the present invention, and are based on a catadioptic lens.

The objective lens has a structure in which the incident lens portion 21a and the exit lens portion 21b are integrated, and the cone lens portion 22 is formed in the direction in which light is incident, that is, in the direction of the light source. The cone lens unit 22 has a structure in which incident light is transmitted regardless of wavelength, and the light incident on the cone lens unit is refracted according to a predetermined refractive index and proceeds into the lens. The peripheral portion of the cone lens portion 22 is coated to reflect the incident light regardless of whether it is HD or DVD, so that the incident surface reflecting portion 23 is formed. On the other hand, in the direction in which the light incident on the objective lens is emitted, that is, in the disc direction, the exit surface transmitting portion 22a is formed at a position opposite to the cone lens portion 22, and the portion around the exit surface transmitting portion 22a is formed of light. A coating treatment for reflecting light is performed regardless of the wavelength to form the exit surface reflecting portion 24. The light reflection / transmission characteristics are also processed at the interface between the incident lens portion 21a and the exit lens portion 21b (an intermediate portion that crosses the light propagation path laterally), and the intermediate reflection / transmission portion 26a, In the case of 26b), the characteristics of the central portion and the edge portion 26b are different. In other words, the central reflection / transmission part 26a has a transmission characteristic for HD and a reflection property for a DVD, and the edge transmission part 26b has a transmission characteristic for both HD / DVD. First, in terms of the properties and characteristics of an optical thin film, a mirror having a very high reflectance generally uses a thin film to make a high refractive index and a low refractive index of a 1/4 wavelength optical thickness into a multilayer thin film. If the thickness is 1/4 wavelength or 1/2 wavelength, the characteristics of the optical coating can be expressed in a simple form, and it is very useful for understanding the characteristics of the optical thin film and can be approximated, which is widely used in the design and manufacture of the optical thin film. In an optical thin film, a thin film having a 1/4 wavelength optical thickness is denoted by a simple sign. When two thin films are used in an optical thin film design, a thinner 1/4 wavelength optical thickness having a larger refractive index (n _H ) is used. Thin films are denoted by H and thin quarter-wave optical thicknesses with small refractive index (n _L ) are denoted by L. Five-layer 1, starting with a high refractive index thin film, alternating with a low refractive index thin film and ending with a high refractive index thin film 1 / Multilayer thin films of 4 wavelength optical thickness are also expressed as (HLHLH) or [H (LH) ² ], which is a multilayer thin film obtained by further depositing H after repeating (LH) twice in pairs. Including the incidence medium and the substrate, it is expressed as [air | H (LH) ² | substrate]. Hereinafter, in a specific structural example of the optical thin film, a multilayer film using TiO ₂ and SiO ₂ as dielectrics on a glass substrate having a refractive index of n _{sub is used} . The general formula for a specific configuration where the coating transmits at 405 nm and reflects at 650 nm is: In the above description, H = TiO 2, L = SiO 2, n _H = 2.25, n _L = 1.45, refractive index n _sub = 1.51 of glass, and reference wavelength is λ o = 400 nm.

In Figs. 2A and 2C, reference numeral 25 denotes an HD disc, and 27 denotes a DVD disc.

In the case of HD, NA = 0.85, λ = 405 nm, t = 0.1 mm, and in DVD, NA = 0.6, λ = 650 nm, t = 0.6 mm. The filtering characteristic is characteristic of reflection (R405) or transmission (T405) for λ = 405 nm, reflection (R650) or transmission (T650) for λ = 650 nm. This is shown in Figs. 2a and 2b, and the beam propagation paths according to the light transmission or reflection characteristics are shown in Figs. 2c and 2d. In FIG. 2C, the solid line is HD, and the dotted line is DVD in FIG. 2D. In this case, the incident surface reflector 23 reflects both the HD and the DVD, and the cone lens unit ( Since only 22) has the property of transmission, it will pass through the objective lens with the same beam diameter regardless of the beam diameter, whether HD beam or DVD beam. This is the basis for using the same collimating lens.

The case of operating as an HD objective lens will be described. In the case of HD, the progress of light (focusing / imaging) is shown by a solid line in FIG. 2C. In the case of HD, the incident light passes only to the cone lens unit 22. That is, the cone lens portion 22 has a light transmission characteristic regardless of the wavelength, and the incident surface reflecting portion 23 at its periphery has a reflection characteristic of R405 / R650.

Therefore, the light incident on the cone lens portion 22 is refracted at the sidewall of the cone lens portion and travels inside the objective lens, and reaches the interface between the incident lens portion 21a and the exit lens portion 21b. Since the center reflection / transmission part 26a and the edge transmission part 26b of this interface have all the transmission characteristics with respect to the wavelength of the light for HD, the said HD beam is made of the entrance lens part 21a and the exit lens part 21b. Passing through the interface reaches the opposite exit face reflector 24.

Since the light for the HD that has reached the exit plane reflector 24 is R405 / T650, the characteristics of the exit plane reflector 24 are reflected and again reach the incident plane reflector 23 through the boundary surface, and the incident plane reflector ( Since the characteristic of 23 is R405 / R650, it is reflected again here and exits through the exit surface transmissive portion 22a through the interface to focus and form on the HD disk 25.

A case of operating as an objective for DVD is described. In the case of DVD, the progress of light (focusing / imaging) is shown by a dotted line in FIG. 2D.

In the case of a DVD, the incident light also passes only to the cone lens unit 22. That is, the cone lens portion 22 has a light transmission characteristic regardless of the wavelength, and the incident surface reflecting portion 23 at its periphery has a reflection characteristic of R405 / R650.

Therefore, the light incident on the cone lens portion 22 is refracted at the sidewall of the cone lens portion and travels inside the objective lens, and reaches the interface between the incident lens portion 21a and the exit lens portion 21b. The center reflection / transmission part 26a and the edge transmission part 26b of this interface have all the transmission characteristics with respect to the wavelength of the light for HD, but the reflection and the edge transmission part in the case of the central reflection / transmission part 26a with respect to the wavelength of the light for DVD. In the case of (26b), the path of light propagation is different from that of HD because it has the property of transmission.

That is, the DVD light incident on the cone lens portion 22 is refracted and travels inside the incident lens portion 22a to reach the central reflection / transmission portion 26a, and the central reflection / transmission portion 26a is formed of T405 / R650. Since it has a characteristic, it is reflected here to reach the incident surface reflecting portion 23, and the incident surface reflecting portion 23 has the characteristics of R405 / R650, so it is reflected again and proceeds inside the incident lens portion 21a to provide an edge transmitting portion ( 26b). Since the edge permeable portion 26b has the characteristics of T405 / T650, the light for DVD passes through this portion to advance the output lens portion 21b to reach the emission surface reflecting portion 24.

The light for DVD that has reached the exit plane reflector 24 is reflected and has a characteristic of the exit plane reflector 24 as R405 / R650, so it is reflected and proceeds to the exit lens part 21b again, i.e., the center reflection / transmitter 26a. To reach. Since the central reflection / transmission portion 26a has the characteristics of T405 / R650, the light for DVD is reflected back here and emitted through the emission surface transmission portion 22a to focus and form on the DVD disk 27.

Meanwhile, as another embodiment of the present invention, if the incidence lens unit 21a and the outgoing lens unit 21b are separated and an air layer is placed therebetween, the degree of refraction of the light propagating through the interface is changed and thus the focusing control is performed. Adjustment of the optical system for the tracking servo, in particular between the objective lens and the disk, can be made easily. Other embodiments of the above will be described further. First, the focus position generally changes according to the parallel plate thickness. The focal position when there is no parallel plate is closer than the focal position when there is a parallel plate having a thickness d and a refractive index n. Hereinafter, another embodiment of the present invention will be described. Incident lens portion 21a and exit lens According to the change in the air distance between the portions 21b, the angle of incidence and the position of the light beam incident on the reflecting portion of the exit lens are changed and thus the focal position is changed. The angle of incidence and the position of incidence of the light beam are changed and the focal position is changed accordingly. In addition, the focal position of the light beam reflected from the reflecting surface of the incident lens is changed. In the case of HD, the position at which the ray refracted by the cone lens unit 22 is incident on the reflecting surface of the exit lens is changed to affect the change in the focus position of the reflected light. In addition, the incident angle and position of the light beam incident on the reflective surface of the incident lens are changed to change the focus position, and the focused light beam is changed again due to the air gap change of the two lenses. The angle of incidence and the position of incidence at which the light reflected from the incident lens is incident on the reflecting portion of the exiting lens are changed to change the focus position, and then the focusing position is changed while passing through the air layer between the two lenses after reflecting at the reflecting portion of the incident lens. Between the objective lens and the disc by using the change of focus position caused by the air layer thickness change between the two lenses The focus adjustment is possible.

The present invention can implement an HD / DVD compatible optical pickup device using one objective lens. Since the present invention can implement an HD / DVD compatible optical pickup device using one objective lens, the structure of the HD / DVD combined optical system can be made light and small.

In particular, since the HD / DVD compatible objective lens of the present invention may have the same beam diameter of HD and DVD, it is possible to construct an optical system using the same collimating lens, and also to manufacture easily.

In addition, if the air layer is placed on the interface between the entrance lens portion and the exit lens portion of the HD / DVD compatible objective lens of the present invention, the degree of refraction during light propagation at the interface can be changed. The objective lens system can be easily adjusted to enable focusing or tracking servo.

Claims (6)

One or more light sources for generating light of different wavelengths; BS, which is beam separation means for performing one or more refractions, passages, and reflections on light emitted from the light source; In an optical system comprising a means for performing parallel light or reflection of the light passing through the BS and an objective lens for focusing light on a recording medium, The objective lens may include an incident lens unit, an exit lens unit, and a reflection / transmitting unit having the different types of light transmission / reflection characteristics at the interface between the incident lens unit and the exit lens unit. Optical pickup device. The method of claim 1, wherein the objective lens reflects light at a light incident surface, a light emitting surface, and an intermediate portion of an objective lens according to a wavelength for recording and / or reproducing heterogeneous optical recording media having different recording densities. An optical pickup apparatus compatible with a heterogeneous recording medium, characterized in that it is an objective lens based on a catadioptic lens having heterogeneous light reflection / transmission characteristics. 3. The objective lens according to claim 1 or 2, wherein the objective lens has a cone lens portion having a transmissive characteristic at a central portion of the light incident surface, and an incident surface reflecting portion having a light reflecting characteristic is formed at a periphery thereof. An emission surface transmissive portion is formed at the center of the emission surface to transmit light irrespective of the light wavelength, and an emission surface reflection portion having light reflection characteristics is formed around the emission surface transmission portion, and a central portion of the intermediate portion that crosses the middle of the objective lens laterally is formed. And a reflection / transmitting portion having a characteristic of selectively transmitting or reflecting light is formed. 4. The light reflection / transmission characteristic of claim 3, wherein the light reflection / transmission characteristic has characteristics of reflection (R405) or transmission (T405) for λ = 405 nm and reflection (R650) or transmission (T650) for λ = 650 nm. Heterogeneous recording media compatible optical pickup device. 4. The heterogeneous recording medium compatible optical pickup apparatus of claim 3, wherein the beam lens of the light for the heterogeneous recording medium is permitted by the cone lens unit and the incident surface reflecting unit. 4. The heterogeneous recording medium compatible optical pickup apparatus of claim 3, further comprising: an objective lens having an objective lens and another medium layer interposed at an interface between the incident lens unit and the exit lens unit.