KR19980023915A - Polarizing Beam Separator (PBS) and Optical Pickup Device for Heterogeneous Optical Discs Using the Same - Google Patents

Abstract

The present invention relates to an optical pickup device for heterogeneous optical disks, which enables recording / playback compatibility of optical disks having different substrate thicknesses. In particular, an optical beam is formed by bonding two dove-type prisms and making a PBS coated with a PBS. By injecting the beam onto the obliquely inclined surface of the PBS to cause refraction, the effective polarization angle of the incident beam is widened so that the dependence on the angle of incidence is reduced, so that accurate beam separation at the polarization beam separation surface is achieved, thereby increasing the contrast ratio and the PBS optical pickup device. When applied to, the recording / reproducing compatibility of optical discs having different thicknesses becomes modular, so that the light source and the light detector are modularized into one packet, thereby reducing the price and facilitating the assembly process.

Description

Polarizing Beam Separator (PBS) and Optical Pickup Device for Heterogeneous Optical Discs Using the Same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for heterogeneous optical disks. In particular, a polarizing beam splitter (PBS), in which each dedicated objective lens according to the type of disk is mounted on one actuator, and an incident beam is incident on an oblique inclined surface The optical pickup apparatus for heterogeneous optical disks, which transmits or reflects beams according to the polarization direction to form condensing spots at respective objective lenses, thereby enabling recording / reproducing compatibility of optical disks having different substrate thicknesses. It is about.

Recently, optical discs have a large recording capacity than conventional compact discs (hereinafter referred to as CDs) due to continuous development efforts to increase recording capacity. Has been developed.

A DVD has a higher recording density than a CD and a shorter distance from the surface of the disc to the information recording surface. In fact, a DVD has a distance of 0.6 mm from the surface of the disc to the information recording surface, while a CD has 1.2 mm.

The CD has a track pitch of 1.6 µm, a pit length of 0.834 µm, a light source of 780 nm, an objective lens of 0.45, while a DVD has a track pitch of 0.74 µm, a pit length of 0.4 µm, and a light source of 650 nm. The numerical aperture of the objective lens is 0.60.

That is, the recording capacity of a DVD is 6 to 8 times that of a CD, and video and audio data compression is used, and one film of the same image quality as that of the current TV broadcast is recorded on a disc having a diameter of 120 mm.

At this time, the data may be recorded on both sides of the disc or the recording surface may be formed in two layers to increase the recording capacity.

In addition, considering that CD format software is being used in a wide range of directions, it is necessary to make a DVD playable as well. In other words, higher regeneration compatibility must be ensured.

1 is a block diagram of such a conventional optical pickup apparatus for heterogeneous optical disks.

Referring to FIG. 1, a light source 11 generating a light beam to be irradiated to the optical disk 18, a collimator lens 12 which allows the light beam generated from the light source 11 to travel in parallel in a predetermined direction, and A polarizing beam splitter (PBS) 13 for passing or reflecting an incident light beam along the direction of polarization, and a light beam passing through the rectangular PBS 13 on the surface of the optical disc 17; An object lens 14 for condensing at one point, a reflection mirror 15 for reflecting the light beam reflected by the PBS 13 in a predetermined direction, and a light beam reflected by the reflection mirror 15 The objective lens 16 for condensing at one point on the surface of the disk 17, and the photodetector 19 for detecting the reflected light beam from the PBS 13 and converting it into an electrical signal are provided in this order.

Between the right angle PBS 13 and the photo detector 19, a sensor lens 18 for condensing the reflected light beam from the PBS 13 on the surface of the photo detector 19 is provided.

The objective lens 14 is a CD objective lens, and the objective lens 16 is a DVD objective lens.

The first information recording surface 17a is an information recording surface of a DVD, the second information recording surface 17b is an information recording surface of a CD, and the second information recording surface 17b is an optical disc 17 than the first information recording surface 17a. ) 0.6 mm away from the surface of the

Here, the right angle PBS 13 is used to separate the P wave and the S wave in the optical system or the optical pickup device of the image projection apparatus.

That is, the right angle PBS 13 is formed by bonding two pieces of glass as shown in FIG. 2, and the bonding surface 20 is coated with PBS.

Therefore, the beam is incident in the 45 ° direction with the normal line of the polarization beam splitting surface 20. The P wave is transmitted as it is, and the S wave is reflected so that the P wave and the S wave are separated.

At this time, the principle of separating the P wave and the S wave is as follows.

The polarizing beam splitting surface 20 of the PBS 13 has a P-wave / S-wave separation effect by coating a high refractive index film and a low film in multiple layers.

That is, a part of incident light is reflected at the interface of the media having different refractive indices. As the thickness and the number of the optical coatings are adjusted, the P wave components of the reflected light cancel each other, so that only the S wave is reflected. , P waves are all transmitted, resulting in separation of P waves and S waves.

In more detail with reference to Figure 3, the reflection phenomenon occurs at the interface of each medium by the reflection law

θ i = θ r, θ i 1 = θ r 1, θ i 2, θ r 2,...

Is the angle of incidence and θr is the angle of reflection.

In addition, the angle of refraction of the beam according to each refractive index is the same according to Snell's law that is refracted when passing through the same refractive index medium, so the beams that are finally reflected have the same angle.

In this case, as shown in FIG. 4, a beam is incident and the beam reflected through the n _L layer and the b beam is incident and the beam immediately reflected at the interface with the n _L layer have a constant optical path difference (l1 + l2). -13), the interference between the reflected beams is caused by this optical path difference, and the P wave component of the finally reflected beam is canceled out.

Since the optical path difference can be adjusted by the thickness of the n _L layer and θr can be adjusted by the refractive index, the refractive index, thickness, and number of the coating film of the polarization beam separation surface 20 can be properly designed and manufactured as an element that separates a desired beam. .

In FIG. 1 configured as described above, the collimating lens 12 allows the light beam generated from the light source 11 to travel in parallel to the rectangular PBS 13.

The rectangular PBS 13 reflects and transmits the incident beam according to the polarization direction of the light beam incident from the collimating lens 12.

That is, the rectangular PBS 13 passes the linearly polarized beam of P wave as it is, and the beam passing through the PBS 13 is incident to the objective lens 14.

In addition, the rectangular PBS 13 reflects a linearly polarized beam of S-waves, and the beam reflected by the PBS 13 is reflected back from the reflective mirror 15 to be incident to the objective lens 16.

At this time, the objective lens 14 condenses the light beam passing through the PBS 13 as the objective lens for the CD to the second information recording surface 17b of the optical disk 17.

That is, the objective lens 14 maintains a numerical aperture of 0.45 so that the light beam forms a condensed spot on the second information recording surface 17b of the optical disk 17, and thus the information on the second information recording surface 17b. Is recorded or the information recorded on the second information recording surface 17b is read out.

On the other hand, the light beam reflected from the second information recording surface 17b of the optical disk 17 is reflected through the objective lens 14 and the PBS 13 and is incident toward the sensor lens 18.

That is, since the beam is diffracted by the information medium on the information recording surface when reflected from the second information recording surface 17b of the optical disk 17, the polarization of the beam incident on the PBS 13 through the objective lens 14 is S It becomes a wave.

Thus, the PBS 13 reflects the incident beam, and the sensor lens 18 condenses the reflected light beam from the PBS 13 on the surface of the photo detector 19.

In this case, the collimation lens 12 and the sensor lens 18 improves the sensitivity of the reflected light beam that is degraded as the objective lens 14 moves in the horizontal and vertical directions due to the focusing and tracking servo.

On the other hand, the objective lens 16 condenses the light beam reflected from the PBS 13 as the objective lens for DVD onto the first information recording surface 17a of the optical disc 17.

That is, the objective lens 14 maintains a numerical aperture of 0.6 so that the light beam forms a condensed spot on the first information recording surface 17a of the optical disk 17, and thus the information on the first information recording surface 17a. Is recorded or the information recorded on the first information recording surface 17a is read out.

The light beam reflected from the first information recording surface 17a of the optical disk 17 is incident to the PBS 13 through the objective lens 16 and the mirror 15, and the light beam incident to the PBS 13 is Passes through the PBS 13 and is incident toward the sensor lens 18.

Similarly, when the beam is reflected from the first information recording surface 17a of the optical disk 17, it is diffracted by the information medium on the information recording surface and thus is incident on the PBS 13 through the objective lens 16 and the mirror 15. The polarization of the beam becomes a P wave.

Thus, the PBS 13 passes the incident beam, and the sensor lens 18 condenses the light beam passing through the PBS 13 on the surface of the photo detector 19.

In addition, the collimating lens 12 and the sensor lens 18 improve the sensitivity of the reflected light beam that decreases as the objective lens 16 moves in the horizontal and vertical directions due to the focusing and tracking servo.

The photodetector 19 reflects the light beam incident by the information recording surfaces 17a and 17b of the optical disk 17 and incident through the objective lens 14 or 16, the beam splitter 13 and the sensor lens 18. Convert to an electrical signal.

However, in the PBS of the conventional optical pickup apparatus described above, the multilayer coating film separating the P wave and the S wave has an angle of incidence, so even if the multilayer film coating is properly designed, if the angle of incidence shifts slightly in optical construction, Separation performance is reduced.

That is, since the angle of incidence of the rectangular PBS is configured such that the angle of incidence is 45 ° with respect to the normal of the incidence plane, even if the angle of incidence deviates slightly from 45 °, P wave / S wave separation accuracy is reduced.

In addition, since the actual light source is not 100% parallel light, it is very difficult to uniformly adjust all incident angles. The PBS has a separation performance of P wave / S wave even when only an error of ± 1 ° occurs, thereby causing a projection display. The P wave / S wave separation required by the device is not achieved.

Therefore, the contrast ratio (C.R, C.R = Pp / Ps) is considerably dropped to 200: 1 or less.

Here, Ps is the final S wave and Pp is P wave mixed in the final S wave.

In this case, as the C.R is lower, the screen becomes bluish and the sharpness is lowered.

In addition, if the P-wave / S-wave separation is not made correctly, a difference occurs in recording / reading information, and in particular, a lot of noise and errors occur during recording, which causes a problem in that information is not recorded.

In addition, since the light source and the light detector are separately configured, the price increases and the assembly process is difficult.

The present invention has been made to solve the above problems, and an object of the present invention is to bond two dove-type prisms and design the PBS so that the beam is incident on the inclined surface of the dove-type prism, thereby reducing the incident angle dependency and contrast ratio (CR). ) To provide PBS.

An object of the present invention is to provide a PBS to increase the P-wave / S-wave separation purity by applying the Brewster Angle (Brewster Angle) in addition to the polarization beam separation by the PBS coating of the polarizing beam separation surface of the PBS.

Another object of the present invention is to mount a DVD-only objective lens and a CD-only objective lens on one actuator and each objective by using a PBS that reflects or transmits the incident beam according to the polarization direction of the beam incident on the inclined plane instead of at right angles. An optical pickup apparatus for heterogeneous optical discs is provided by forming a light converging spot in a lens, thereby enabling recording / reproducing compatibility of optical discs having different thicknesses and recording densities with little contrast reduction due to changes in incident angles. .

It is still another object of the present invention to provide an optical pickup device for heterogeneous optical disks, in which the light source and the optical detector are modularized into one packet, thereby facilitating a down and assembly process of cost.

A feature of the PBS according to the present invention for achieving the above object is formed by bonding two dove-type prisms and an optical coating for polarizing beam separation on the bonding surface, the beam is an oblique inclined surface of the dove-type prism You are entering or exiting.

An optical pickup device for a heterogeneous optical disk according to the present invention is characterized in that the light source generates a light beam to be irradiated on the surface of the optical disk, and the polarization direction of the light beam positioned between the light source and the optical disk to be incident toward the optical disk. A liquid crystal shutter that selectively changes according to the type of disk and two dove-type prisms are bonded to each other, and an optical coating for polarizing beam separation is formed on the bonding surface, and the beam is incident or exited at an oblique inclined surface of the dove-type prism. And a polarization converter for converting the PBS that passes or reflects the incident beam according to the polarization direction of the incident beam, and the linearly polarized light that is reflected or passed through the PBS into circularly polarized light, and the circularly polarized light reflected from the information recording surface of the optical disk into linearly polarized light. And maintaining a different numerical aperture in accordance with the rotational direction of the circularly polarized light converted by the polarization converter. By focusing a light beam on the surface may it consists of including two different types of dedicated objective lens to record and reproduce information.

1 is a block diagram of a conventional optical pickup apparatus for heterogeneous optical disks.

Figure 2 is a detailed cross-sectional view of the PBS of Figure 1

FIG. 3 is a view illustrating a relationship between an incident angle and an exit angle when optically coating a bonding surface of the PBS of FIG. 1 in multiple layers. FIG.

FIG. 4 is a diagram for describing positions of beams incident in FIG. 3 and reflection paths at respective positions.

5 is a cross-sectional view of the PBS according to the present invention

6 is a graph for explaining the Brewster angle according to the present invention.

FIG. 7 is a graph illustrating an example in which the exit angle is controlled by adjusting the lengths of sides of the incidence and exit sides of the PBS of FIG.

8 is a block diagram showing a case where PBS according to the present invention is applied to an optical pickup device for heterogeneous optical disks;

* Description of the symbols for the main parts of the drawings *

21: light source 22: collimating lens

23: LC shutter 24: PBS

24a: polarization beam splitting surface 25: polarization transducer

26: Actuator 27: Objective lens for DVD

28: objective lens for CD 29: optical disk

29a: first information recording surface 29b: second information recording surface

30: sensor lens 31: photo detector

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

5 is a PBS according to the present invention, which is installed to be inclined at a constant angle to reduce the dependence of the angle of incidence, that is, to have an angle of incidence greater than 45 °, thereby increasing the allowable range of the angle of incidence.

At this time, the PBS 24 has a wider incidence angle error tolerance range than the rectangular PBS, so that there is almost no decrease in contrast due to the change in the incidence angle.

The PBS 24 has a polarization beam separation surface 24a formed in a horizontal direction.

That is, since the lozenge-type PBS 24 is incident on the oblique inclined plane, the incident beam is refracted by the refractive index difference between the air and the oblique inclined plane, and then is incident on the polarization beam separation plane 24a. The beam reflected or passed through the beam splitting surface 24a is also radiated once again by refraction due to the refractive index difference between the inclined surface and the air.

In this case, the PBS 24 may be configured by bonding two dove-shaped prisms having an isosceles triangle shape and applying an optical coating for polarization separation on the bonding surface.

At this time, since the dove-type prism is an internal reflection from the high glass to the air having a low refractive index at the time of emission, the incident angle and the exit angle are the same, so that dispersion is not accompanied. That is, the incident angle and the exit angle are the same.

As such, the dove-type prism has an advantage that the emission path becomes constant even when the wavelength is changed since the dopant prism has no dependency on the wavelength [lambda].

In addition, when comparing the change in the effective polarization angle of the incident beam with the conventional, the conventional angle is fixed to the incident angle (θ _O ) = 45 ° and the effective polarization angle has only ± 1 ° relative to 45 °, but the present invention because without incident at 90 ° on the incident surface of the prism is refracted at an angle incident to occur because the angle of incidence θ _O matchuge by the refraction angle of the incident beam may have a size larger than the incident angle 45 °.

That is, as shown in FIG. 5, the incident angle θ _O is designed to be 45 ° or more when designing the PBS coating film.

At this time, according to Snell's law, Sin · θin = n · Sin · θa,

Θa is determined by θ and the vertex angle r of the prism determined when the coating film is designed.

As a result, [theta] in can be determined by the refractive index of the prism and [theta] a by Snell's law.

When the light is incident on the determined θin, the beam is refracted by θa and is incident on the coating surface with a size of θ. All P waves are transmitted by the properties of the optical coating film, and all S waves are reflected to separate P waves / S waves. .

At this time, the size of θ can be designed larger than the conventional 45 ° by adjusting the refractive index when designing the optical coating has an effective polarization separation angle larger than the conventional fixed 45 °.

When the actual θin is set to 45 °, θ is obtained by about 55 ° or more, so that it has a much larger allowable range than in the prior art, and this angle can be designed to be larger if necessary.

Accordingly, if only θin is properly obtained and the angle is adjusted, polarization separation can be performed.

On the other hand, no matter how good an actual optical design is and the angle of incidence is adjusted, the incident beam may not be a complete parallel light, which may cause deviations from a given angle of incidence. Therefore, in order to solve this problem, the angle of incidence is determined as the Brewster angle.

Brewster's angle refers to a specific angle at the interface of a medium with two refractive indices, where P / S wave separation occurs naturally.

That is, a part of the beam that is always incident at both interfaces is reflected. Even in the interface without a separate coating, a phenomenon in which the P wave component is not found in the beam reflected at a specific angle naturally occurs.

The angle at this time is referred to as Brewster angle or polarization angle.

At this time, the Brewster angle θp represents the incident angle θp as tan θp = nt / ni in the case of a beam incident from ni → nt as shown in FIG. 6.

In this invention, the refractive index of each coating film is adjusted so that the angle of incidence at the interface of each medium satisfies this Brewster angle using this principle.

This can further increase the accuracy of P-wave / S-wave separation.

On the other hand, the present invention can adjust the exit angle by adjusting the length of the sides of the incident side and the exit side prism as shown in FIG.

That is, the incident angle θin and the exit angle θout are different (θin ≠ θout).

FIG. 8 is a block diagram showing a case where the dual dove prism type PBS of the present invention is applied to an optical pickup device for heterogeneous optical disks. The light source 21 generates a light beam to be irradiated onto the optical disk 29, and the light source 21 A collimating lens 22 for allowing the light beam incident from the light beam to be parallel to the predetermined direction and a liquid crystal shutter for changing the polarization direction of the light beam incident from the collimating lens 22 according to on / off of the electrode; LC shutter) 23, a double dove prism type PBS 24 which is designed so that the incident beam is incident on an oblique inclined plane and reflects or passes the incident beam in accordance with the polarization direction, and the linearly polarized beam is a circularly polarized beam or a circular The object for DVD which condenses the polarization beam 25 which converts a polarization beam into a linear polarization beam, and the circular polarization beam converted by the said polarization converter 25 to one point of the 1st information recording surface 29a of the optical disc 29. Lens 27 and the polarization edge The objective lens 28 for CD which condenses the circularly polarized beam converted by the ventilation 25 to one point of the second information recording surface 29b of the optical disk 29, and the first information recording surface of the optical disk 29 ( 29a) or a photodetector 31 which detects a light beam reflected by the second information recording surface 29b and passed or reflected by the PBS 24 and converts it into an electrical signal.

In this case, a sensor lens 30 is provided between the PBS 21 and the photodetector 31, and an actuator 26 for moving the objective lens 27 or 28 in the horizontal and vertical directions, and the light source 21 is provided. ) And the photo detector 31 are modularized into one packet.

The polarization transducer 25 uses a λ / 4 plate.

The LC shutter 23 changes the polarization direction of the light beam incident from the light source 21 in accordance with the on / off of the power source, that is, the type of the optical disk (for example, CD or DVD).

The first information recording surface 29a of the optical disc 29 is an information recording surface of a DVD, the second information recording surface 29a is an information recording surface of a CD, and the second information recording surface 29b is a first information recording surface ( Is positioned 0.6 mm further from the surface of the optical disk 29 than 29a).

In this embodiment of the present invention configured as described above, a P-wave light beam is generated from the light source 21 to be incident to the LC shutter 23, and if power is not supplied to the LC shutter 23, it is converted to S-wave and is incident to the PBS 24. When the power is supplied, the P wave is incident to the PBS 24 as it is, and the S wave reflects from the PBS 24 and the P wave passes.

The direction of polarization converted according to the polarization direction of the light beam generated from the light source 21 and whether the LC shutter 23 is supplied with power may vary according to design.

At this time, the PBS 24 is a double dove prism type PBS inclined at a predetermined angle rather than a right angle, and the incident angle error tolerance range is wider than that of the right angle PBS, so that there is almost no decrease in contrast due to the change in the incident angle.

At this time, the PBS 24 is designed by bonding two dove-shaped prisms having an isosceles triangle shape as shown in FIG. 5 and applying an optical coating for polarization separation on the bonding surface.

Since the dove-type prism is an internal reflection from the high glass to the air having a low refractive index at the time of emission, the incident angle and the exit angle are the same so that dispersion is not accompanied. That is, the incident angle and the exit angle are the same.

Therefore, the dove-type prism has an advantage that the emission path becomes constant even when the wavelength is changed because there is no wavelength dependency of the incident beam since dispersion is independent of the wavelength [lambda].

Therefore, when comparing the change in the effective polarization angle of the incident beam of the lozenge PBS 24 of the present invention using the dove-type prism, the conventional polarization angle is fixed at the incident angle θ ₀ = 45 ° and the effective polarization angle is 45 °. Although it has only about ± 1 ° relative to the present invention, the present invention obliquely enters the incidence plane of the prism to be refracted at 90 °, so that the angle of incidence θ _O is adjusted according to the size of the angle of refraction of the incident beam. It can have a large angle of incidence.

Hereinafter, the case of recording and reproducing the optical disc for DVD and the case of recording and reproducing the optical disc for CD will be described separately.

i) optical disc for DVD

That is, when a P-wave light beam is generated from the light source 21 and incident on the collimating lens 22, the collimating lens 22 causes the light beam passing through the LC shutter 23 to travel toward the PBS 24 in parallel.

At this time, when power is not supplied to the LC shutter 23, the P-wave, which is a linearly polarized beam, is converted into an S-wave and is incident on an obliquely inclined surface of the PBS 24.

The S wave is reflected by the polarization beam splitting surface 24a of the PBS 24 and is incident on the λ / 4 plate which is the polarization transducer 25. When the S wave passes through the polarization transducer 25, the S wave is converted into left circularly polarized light.

The converted left rotating circularly polarized light is incident on the objective lens 27 for DVD.

The DVD objective lens 27 condenses the left rotating circularly polarized light on the first information recording surface 29a of the optical disk 29.

That is, the objective lens 27 maintains a relatively large numerical aperture (e.g., 0.6) so that the left rotating circularly polarized beam forms a condensing spot on the first information recording surface 29a of the optical disk 29, and thus, the first Information is recorded on the information recording surface 29a or information recorded on the first information recording surface 29a is read out.

At this time, the actuator 26 moves the pickup apparatus up, down, left, and right so that the focus of the light beam is accurately formed on the first information recording surface 29a and the light beam accurately traces the information on the first information recording surface 29a.

On the other hand, when the left rotating circularly polarized light is reflected from the first information recording surface 29a of the optical disk 29, it is diffracted by the information medium on the first information recording surface 29a and converted into the right rotating circularly polarized light, and the reflected and converted right rotating When circularly polarized light passes through the objective lens 27 and the polarization converter 25, it is converted into P-wave which is a linearly polarized beam.

The P wave converted by the polarization transducer 25 is incident to the polarization beam splitting surface 24a through the inclined plane of the PBS 24, and the polarization beam splitting surface 24a of the PBS 24 is the same as the incident P wave. Pass it through.

The P wave passing through the inclined surface of the PBS 24 is incident toward the sensor lens 30.

The sensor lens 30 focuses the light beam passing through the PBS 24 on the surface of the photo detector 31.

The photo detector 31 converts the incident P-wave light beam into an electrical signal so that a high frequency signal, a focus error signal, and a tracking error signal are obtained.

In this case, the collimating lens 22 and the sensor lens 30 improves the sensitivity of the reflected light beam that decreases as the objective lens 27 moves in the horizontal and vertical directions due to the focusing and tracking servo.

ii) optical disc for CD

The information recording and reading operation of the optical disc for CD proceeds in the direction opposite to the incident path of the light beam in the optical disc for DVD.

That is, when a P-wave light beam is generated from the light source 21 and incident on the collimating lens 22, the collimating lens 22 causes the light beam passing through the LC shutter 23 to travel toward the PBS 24 in parallel.

At this time, when power is supplied to the LC shutter 23, the P wave is incident on the polarization beam separation surface 24a through the inclined surface of the PBS 24 as it is.

The P wave passes through the polarization beam separation plane 24a of the PBS 24 without reflection due to its coating property, and enters the λ / 4 plate of the polarization converter 25, and the P wave, which is a linearly polarized beam, passes through the polarization converter 25. When it passes through, it is converted to right-hand circularly polarized light.

The right-handed circularly polarized light converted by the polarization transducer 25 is incident on the objective lens 29 for the CD.

The objective lens 28 for CD condenses the right-handed circularly polarized light on the second information recording surface 29b of the optical disk 29.

That is, the objective lens 28 maintains a relatively small numerical aperture (e.g., 0.45) so that the right-turning circularly polarized beam forms a condensed spot on the second information recording surface 29b of the optical disk 29, and thus, the second Information is recorded on the information recording surface 29b or information recorded on the second information recording surface 29b is read out.

At this time, the actuator 26 moves the pick-up device up, down, left, and right so that the focus of the light beam is accurately formed on the second information recording surface 29b and the light beam accurately follows the information on the second information recording surface 29b.

On the other hand, when the right rotating circularly polarized light is reflected from the second information recording surface 29b of the optical disk 29, it is diffracted by the information carrier on the information recording surface of the second information recording surface 29b and converted into the left rotating circularly polarized light, and reflected When the converted left-rotating circularly polarized light passes through the objective lens 27 and the polarization converter 25, the converted left-rotation circularly polarized light is converted into S-wave, which is a linearly polarized beam.

The S-wave converted by the polarization transducer 25 is incident on the polarization beam splitting surface 24a through the inclined surface of the PBS 24, and the S-wave incident on the coating characteristic of the PBS 24 is incident on the polarizing beam separation surface 24a. Reflects.

The S-waves reflected by the PBS 24 are incident toward the sensor lens 30.

The sensor lens 30 focuses the light beam reflected from the PBS 24 on the surface of the photo detector 31.

The photo detector 31 converts the incident S-wave light beam into an electrical signal so that a high frequency signal, a focus error signal, and a tracking error signal are obtained.

At this time, the collimating lens 22 and the sensor lens 30 improves the sensitivity of the reflected light beam, which decreases as the CD objective lens 28 moves in horizontal and vertical directions due to focus and tracking servo.

As described above, according to the PBS according to the present invention and the optical pickup device for heterogeneous optical disks using the same, a double dove prism-type PBS is formed by bonding two dove-type prisms and PBS coating on the bonding surface, and the incident beam is refracted. Since the beam is incident on the obliquely inclined plane of the PBS, the effective polarization angle of the incident beam is widened so that the incidence angle dependency is reduced, so that accurate beam separation at the polarization beam separation surface is achieved, thereby increasing the contrast ratio.

In addition, by adjusting the refractive index of each coating film so that the angle of incidence at the interface of each medium of the PBS satisfies the Brewster angle, beam separation can be performed even at the interface without coating, so that the P-wave / S-wave separation performance is further improved. Even if the tolerance is out of tolerance, the beam separation can be performed accurately.

Therefore, since the allowable angle becomes larger for beams that are not incident at the correct angle, such as in alignment or laser diode divergence beams, beam separation is accurately performed.

In addition, by using a double dove prism type PBS in which a DVD-only objective lens and a CD-only objective lens are mounted on one actuator and the beam is incident on an oblique inclined plane, each dedicated objective lens is reflected through or reflected through a light beam incident along the polarization direction. Incidentally, recording / playback compatibility of optical discs having different thicknesses is made possible.

In addition, by applying the dove prism-type PBS to modularize the light source and the light detector into one packet, the price is reduced and the assembly process is easy.

Claims (17)

2. A polarizing beam separator, comprising: bonding two doped prisms and applying an optical coating on the bonding surface to separate a polarizing beam, wherein the beam is incident or exited on an obliquely inclined surface of the dove-shaped prism. The method of claim 1, wherein the doped prisms Polarizing beam separator characterized in that the isosceles triangle type. The method of claim 1, wherein the doped prisms A polarizing beam splitter characterized in that the incident angle and the exit angle are the same. The polarizing beam separator of claim 1, wherein the refractive index of the optical coating layer is designed to satisfy the Brewster angle. The polarizing beam splitter according to claim 1, wherein the beam is incident to the inclined plane at an angle of 45 ° to its normal. The polarizing beam separator of claim 1, wherein the incident beam incident on the optical coating layer and the interface surface is larger than 45 °. The polarizing beam splitter according to claim 1, wherein the exit angle is adjusted by adjusting the lengths of sides of the exit side and the incident side prism. A light source for generating a light beam to be irradiated on the surface of the optical disk; A liquid crystal shutter positioned between the light source and the optical disk to selectively change the polarization direction of the light beam incident on the optical disk according to the type of the optical disk; Two dove-type prisms are bonded to each other and formed by applying an optical coating for separating polarized beams on the bonding surface. Or a polarizing beam splitter for reflecting; A polarization converter for converting linearly polarized light reflected or passed by the polarization beam splitter into circularly polarized light and converting circularly polarized light reflected from the information recording surface of the optical disk into linearly polarized light; It characterized in that it comprises a different kind of dedicated objective lens to record and reproduce the information by connecting the light beam to the surface of the disk by maintaining a different numerical aperture according to the rotational direction of the circularly polarized light converted by the polarization converter Optical pickup device for heterogeneous optical discs. The method of claim 8, wherein the doped prism of the polarizing beam splitter Optical pickup device for heterogeneous optical disk, characterized in that the isosceles triangle type. The method of claim 8, wherein the doped prism of the polarizing beam splitter An optical pickup apparatus for heterogeneous optical disks, characterized in that the incident angle and the exit angle are the same. The optical pickup apparatus of claim 8, wherein the refractive index of the optical coating film of the polarizing beam separator is designed to satisfy the Brewster angle. The optical pickup apparatus of claim 8, wherein the beam incident to the polarizing beam splitter is incident on the inclined plane at an angle of 45 ° to the normal. 9. The optical pickup apparatus for heterogeneous optical disks according to claim 8, wherein the optical pickup of the polarizing beam splitter is larger than 45 [deg.] Incident on the interface. The optical pickup apparatus for heterogeneous optical disks according to claim 8, wherein the emission angle is adjusted by adjusting the lengths of the sides of the exit side and the incident side prism of the polarization beam splitter. The optical pickup apparatus of claim 8, wherein the polarizing beam splitter forms an optical coating film in a horizontal direction. The optical pickup apparatus of claim 8, wherein the polarization transducer uses a λ / 4 plate. 9. The optical pickup apparatus for heterogeneous optical disks according to claim 8, wherein the plurality of objective lenses are mounted with one actuator and used according to the type of the disk.