KR19990047817A - Beam shaping prism with chromatic aberration correction and optical pickup device - Google Patents

Abstract

An optical system for beam shaping includes a plurality of prisms having different refractive indices and dispersion values, and the plurality of prisms receives collimated light and beams the beam so that the beam cross section of the final output light is desired. Irradiation is made so that the final exit angle is always constant regardless of the change in the wavelength of light.

The conventional optical system for beam shaping has a problem that the output angle of light passing through the optical system is changed when the output of the light source is variable. According to the present invention, when the optical system of the present invention is used in an optical pickup apparatus capable of recording an optical pickup device having a constant traveling direction (emission angle) of light passing through the optical system irrespective of a wavelength change caused by a change in output of the light source, Prevents track deviation and enables stable recording.

Description

Beam shaping prism with chromatic aberration correction and optical pickup device

The present invention relates to an optical system for beam shaping and an optical pickup apparatus employing the same, and more particularly, to an optical system for beam shaping the light emitted from a light source in a desired form and an optical pickup employing the same.

Currently, optical pickups for optical storage media such as CDs, DVDs, etc. use a laser light source that emits an optical beam having an elliptical cross section. This laser light source is emitted in the form of a beam that emits light generated by the active layer of the laser diode. Referring to Figure 1 briefly described the generation of the laser light as follows.

1 shows an optical beam emitted elliptical from a laser diode. In Figure 1, we show a joint surface direction, that is, a direction parallel to the active layer of the laser diode with "∥", and displays the direction perpendicular to the bonding surface to the "⊥". Here, the direction 한다 coincides with the direction of the current flowing through the active layer of the laser diode. In the case of the laser diode of 'Model No. PS010-00' manufactured by "BLUE SKY RESEARCH", the active layer region having a size of 1 μm (direction ⊥ ) × 3 μm (direction ∥ ) centering on B of FIG. Have Laser light is generated from this active layer region. Since the starting point of the light emitted through the active layer region is two different points A and B, the emitted light has a non-point difference (ΔZ) representing the distance between the points A and B. And the divergence angle of this laser light is generally θ _⊥ = 20-40 ^o and θ _∥ = 8-20 ^o , therefore, the emitted light beam has an elliptical perpendicular cross section with respect to its optical axis, in particular its long axis. The direction in which the beam diameter is large corresponds to the direction 하며 and the direction in which the beam diameter corresponding to the short axis is small becomes an ellipse corresponding to the direction ∥ parallel to the joint surface.

However, in the optical storage medium, since the objective lens is circular, in order to increase the light utilization efficiency, a circular light beam is also required. The optical system for conventional beam shaping proposed by this request will be briefly described with reference to FIG.

2 is a beam shaping prism of the prior art. Figure 2 illustrates in plan view to match the direction ∥. As shown, light emitted in the form of a beam emanating from the laser light source described above with reference to FIG. 1 is collimated by a collimator lens (not shown) and then incident on the prism. The length of the short axis of the elliptical incident light W _i And the incident angle θ _i Two-sided expression This holds true. Therefore, when the refractive index of the prism is n for incident light of a specific wavelength W _o The acute angle of the prism so that is equal to the length of the long axis of the incident light θ _o By adjusting, the short axis of the beam passing through the prism is equal to the length of the long axis, and a perfect circular beam can be obtained.

The above is only considered for the case where the output and the wavelength of the laser light source are constant when the data recorded on the optical storage medium is reproduced using the laser light source. However, when data is recorded on the optical storage medium, the output of the laser light source is changed and the wavelength of the light source is increased by several nm. λ → λ ^′ 2 generates chromatic aberration in the prism. Thus, there is a slight angular difference in the advancing direction of the light source as compared with reproduction, which results in the formation of light spots at unwanted positions on the disc. Generally, about 0.8 μm of light spot movement occurs for a wavelength change of 10 nm of the light source, and the actuator cannot respond to the instantaneous movement of the light spot, and as a result, data is located at a position off the track on the disc. The phenomenon of recording occurs.

As described above, the conventional optical system for beam shaping has a problem that the output angle of light passing through the optical system is changed when the output of the light source is variable.

Accordingly, an object of the present invention is to provide a beam shaping prism having a chromatic aberration correction function having a constant traveling direction (emission angle) of light passing through an optical system regardless of chromatic aberration caused by a change in output of a light source.

Another object of the present invention is to provide an optical pickup apparatus employing the beam shaping prism having the above-described chromatic aberration correction function.

1 is a view for explaining a laser light source for emitting an elliptical light beam,

2 is a beam shaping prism of the prior art,

3 is an optical system for beam shaping according to the present invention;

4 is an optical pickup apparatus according to an embodiment of the present invention using the optical system of FIG.

<Description of the symbols for the main parts of the drawings>

31: laser diode 32: collimator

33: first beam shaping prism 34: second beam shaping prism

The beam shaping prism with chromatic aberration correction function for achieving the above object is a beam shaping in the optical system for beam shaping, so that the beam cross-section of the final output light to the desired shape by receiving the collimated light, It includes a plurality of prisms having optical properties that emit the final exit angle is constant regardless of the change in the wavelength of the incident light.

One preferred embodiment of the optical pickup apparatus employing a beam shaping prism with chromatic aberration correction for achieving another object of the present invention is to collimate the light emitted from the first and second laser light sources of different specifications, respectively. I) An optical pickup device for an optical storage medium having a first collimator and a second collimator, wherein the elliptical light collimated from the first collimator is beam-formed so that the beam cross section becomes circular and is constant regardless of the wavelength change of the light. And a beam shaping means that emits light at an angle, receives collimated light from the second collimator, and reflects the light collimated at right angles, and the objective lens condenses the light emitted from the beam shaping means on the optical storage medium.

Hereinafter, a preferred embodiment of a beam shaping prism having a chromatic aberration correcting function and an optical pickup device employing the same according to the present invention will be described in detail with reference to the accompanying drawings.

3 is an optical system for beam shaping according to the present invention. Figure 3 illustrates in matching the direction ∥ of the above-described laser light source plane. As shown, the optical system for beam shaping according to the present invention includes a laser diode 31 for generating an elliptical laser light source. The light emitted from the laser diode 31 is collimated by the collimator 32 connected to the rear end and incident to the first beam shaping prism 33. The first beam shaping prism 33 receives light collimated by the collimator 32 and is refracted to a predetermined refractive index and dispersion value and exits to the second beam shaping prism 34. The second beam shaping prism 34 emits the light incident from the first beam shaping prism 33 at a refractive index and dispersion value different from that of the first beam shaping prism 33.

The operation of the optical system for beam shaping according to the present invention configured as described above will be described in more detail.

The wavelength emitted from the laser diode 31 λ When the elliptical light having the incident light enters the collimator 32, the collimator 32 collimates the emitted light in parallel and exits the first beam shaping prism 33. The length of the short axis of light passing through the collimator 32 is W ₁ And the incident angle to the first beam shaping prism 33 θ ₁ to be. The acute angle of the first beam shaping prism 33 and the exit angle inside the prism are α ₁ And the wavelength λ Refractive index for incident light n ₁ The length of the short axis of the beam passing through the back surface first beam shaping prism 33 is expressed by the following equation. W ₂ Is incident on the second beam shaping prism 34.

here, Is the beam shaping ratio of the first beam shaping prism 33. The length of the short axis of light passing through the first beam shaping prism 33 is W ₂ And the incident angle to the second beam shaping prism 34 θ ₂ to be. The acute angle of the second beam shaping prism 34 and the exit angle inside the prism α ₂ And the wavelength λ Refractive index for incident light n ₂ The length of the short axis of the beam passing through the rear second beam shaping prism 34 is expressed by the following equation. W ₃ It is modeled and outputted.

here, Is the beam shaping ratio of the second beam shaping prism 34. However, the light output of the laser diode 31 λ → λ ^′ In this case, chromatic aberration occurs in the first beam shaping prism 33 and the second beam shaping prism 34, and thus the light propagation path is changed. Where the wavelength λ ^′ The advancing path of the phosphorescent light is shown by a dotted line in FIG. Wavelength λ ^′ The amount of change in the refractive index of the first beam shaping prism 33 with respect to phosphorus light Δn ₁ , The incident angle of light inside the first beam shaping prism 33 δ ₁ , The exit angle to the outside of the first beam shaping prism (33) δ ₁ ^′ , The following relation is satisfied.

here, n ₁ + Δn ₁ Silver wavelength λ ^′ It is the refractive index of the first beam shaping prism 33 with respect to phosphorus light. This light is incident on the second beam shaping prism 34, and the incident angle is θ ₂ -δ ₁ ^′ And the exit angle inside the second beam shaping prism 34 α ₂ The conditions for being equal to are as follows.

here, n ₂ + Δn ₂ Has a wavelength λ ^′ It is the refractive index of the second beam shaping prism 34 for phosphorescent light. And the wavelength λ ^′ The exit angle of the phosphor beam to the outside of the second beam shaping prism 34 δ ₂ ^′ Then, the following relationship holds.

here, δ ₁ ^′ Mute δ ₂ ^′ If you replace the expression by replacing it with '0', you get the following relation.

here, Δn ₁ And Δn ₂ Is the amount of change in the refractive index according to the change in wavelength of the first beam shaping prism 33 and the second beam shaping prism 34, respectively, α ₁ And α ₂ Are the acute angles of the first beam shaping prism 33 and the second beam shaping prism 34, respectively. And, Is the beam shaping ratio of the second beam shaping prism 34. That is, if Equation 6 is satisfied, the emission angle outside the second beam shaping prism 34 regardless of the change of the laser wavelength ( δ ₂ ^′ ) Can be set to 0˚.

The foregoing has described the operation of the beam shaping optical system with the chromatic aberration correction function of FIG. 3. 4 is a block diagram of an optical pickup apparatus according to a preferred embodiment of the present invention employing the optical system of FIG. As shown, the 650 nm laser diode 1, the first collimator 2 and the first beam shaping prism 3 have the same function and arrangement as the corresponding elements of FIG. However, the second beam shaping prism 4 is coupled with the first light splitter 5 for reflecting the laser light emitted from the 780 nm laser diode 11 toward the reflecting prism 7. Therefore, the angle of the light emitted from the first beam shaping prism 3 to the second beam shaping prism 4 is the extension of the left hypotenuse of the second beam shaping prism 4 and the first light splitter 5. It is equal to the angle formed by the extension line of the right vertical side. The refractive indices and dispersion values of the second beam shaping prism 4 and the first light splitter 5 are the same. The first light splitter 5 passes the light emitted from the second beam shaping prism 4 as it is, and the exit angle to the outside of the first light splitter 5 is always 0 ° regardless of the wavelength change of the 650 nm laser light. The light is emitted from the 780 nm laser diode 11 and incident on the collimated light from the second collimator 12 to be incident on the 45 ° inclined plane to be emitted to the second light splitter 6 at an exit angle of 0 °. The second light splitter 6 passes the light incident from the first light splitter 5 toward the reflective prism 7, and the light incident from the reflective prism 7 reflects the two 45 ° reflecting surfaces to form a photodetector lens. Exit to (13). The photodetector lens 13 condenses the light incident from the second light splitter 6 to the photodetector 14, and the photodetector 14 detects the condensed optical signal. The reflecting prism 7 reflects the light incident from the second light splitter 6 to the objective lens 8 by reflecting it vertically to the 45 ° inclined plane, and the light incident from the objective lens 8 receives the second light splitter 6. Reflect it vertically. The objective lens 8 condenses the 650 nm wavelength light incident from the reflective prism 7 to focus on the DVD disk 9 and emits the light reflected back from the DVD disk 9 surface toward the reflective prism 7. do. The objective lens 8 collects light of 780 nm wavelength incident from the reflective prism 7 while focusing on the CD-R disc 10 and reflecting light reflected back from the surface of the CD-R disc 10. Eject toward the prism (7).

As described above, the beam shaping prism having a chromatic aberration correction function according to the present invention is an elliptical or circular shape emitted from a light source by using a plurality of beam shaping prisms having different refractive indices and dispersion values in an optical system for beam shaping. It provides the effect of beam shaping at the desired rate while keeping the final emission angle constant regardless of the wavelength change.

In addition, an optical pickup apparatus employing a beam shaping optical system according to the present invention is an apparatus for recording and reproducing data on a plurality of optical storage media having different specifications, wherein the optical pickup apparatus is provided on a disk of an optical spot in response to an output change of a laser light source. It prevents track deviation and enables stable recording. By using one of the two beam shaping prisms as a light splitter, a separate optical splitter is not required, thereby providing a compact optical pickup.

Claims (17)

In an optical system for beam shaping, An optical system including a plurality of prisms having optical characteristics that emit a collimated light so that the beam cross section of the final output light becomes a desired shape, and emit the final emission angle to be constant regardless of a change in the wavelength of the incident light. . The optical system according to claim 1, wherein the plurality of prisms are beam-shaped when the beam cross section of the incident light has a circular shape, the beam being shaped so that the short axis diameter of the finally emitted light is the same as the beam diameter of the incident light. The circular beam according to claim 1, wherein the plurality of prisms are beam-shaped when the beam cross section of the incident light is elliptical, the beam diameter of which is finally beam-formed is equal to the long axis diameter of the beam cross section of the incident light. Optical system characterized in that the beam shaping to have a cross section. The optical system of claim 1, wherein the plurality of prisms include a first beam shaping prism and a second beam shaping prism having different refractive indices and dispersion values. The method of claim 4, wherein the first beam shaping prism receives the collimated light and firstly shaping the beam to exit the second beam shaping prism and has a specific wavelength. λ The refractive index of the first beam shaping prism is n ₁ An optical system characterized by satisfying the following relational expression. here, W ₁ Is the short axis diameter of the incident collimated elliptical light, W ₂ Is the short axis diameter of the beam exiting the second beam shaping prism, θ ₁ Is an incident angle to the first beam shaping prism, α ₁ Is an acute angle of the first beam shaping prism and an exit angle inside the prism. The method of claim 5, wherein the second beam shaping prism receives a beam emitted from the first beam shaping prism and exits the second beam shaping by a specific wavelength. λ The refractive index of the second beam shaping prism is n ₂ An optical system characterized by satisfying the following relational expression. here, W ₂ Is the short axis diameter of the beam emitted from the first beam shaping prism, W ₃ Is the diameter of the beam emitted from the second beam shaping prism and the long axis diameter of the elliptical light incident on the first beam shaping prism, θ ₂ Is an incident angle to the second beam shaping prism, α ₂ Is an acute angle of the second beam shaping prism and an exit angle inside the prism. The method of claim 6, wherein the first beam shaping prism and the second beam shaping prism have a wavelength of the incident light. λ → λ ^′ When the optical system characterized in that the following relationship is satisfied. here, Δn ₁ Is the amount of change in the refractive index according to the change in wavelength of the first beam shaping prism, Δn ₂ Is the change amount of the refractive index according to the change of the wavelength of the second beam shaping prism, α ₁ Is an acute angle of the first beam shaping prism, α ₂ Is an acute angle of the second beam shaping prism, θ ₂ Is an incident angle to the second beam shaping prism, Is the beam shaping ratio of the second beam shaping prism. The method of claim 1, A light source for emitting light; And a collimator which collimates the light emitted from the light source and exits the plurality of prisms. An optical pickup apparatus for an optical storage medium having first and second collimators for collimating light emitted from first and second laser light sources having different specifications, respectively. A beam beam is formed by receiving the collimated elliptical light from the first collimator so that the beam cross section becomes circular, and emits light at a constant angle regardless of the wavelength change of the light. The beam collimates the collimated light from the second collimator. Shaping means; And an objective lens for condensing light emitted from the beam shaping means onto the optical storage medium. The optical pickup apparatus of claim 9, wherein the beam shaping means includes a first beam shaping prism and a second beam shaping prism having different refractive indices and dispersion values. 12. The method of claim 10, wherein the first beam shaping prism receives light collimated from the first collimator and firstly shaping the beam to emit the second beam shaping prism and has a specific wavelength. λ The refractive index of the first beam shaping prism is n ₁ An optical system characterized by satisfying the following relational expression. here, W ₁ Is a short axis diameter of collimated elliptical light incident from the first collimator, W ₂ Is the short axis diameter of the beam exiting the second beam shaping prism, θ ₁ Is an incident angle to the first beam shaping prism, α ₁ Is an acute angle of the first beam shaping prism and an exit angle inside the prism. The method of claim 10, wherein the second beam shaping prism receives a beam emitted from the first beam shaping prism and emits the second beam shaping to emit a specific wavelength. λ The refractive index of the second beam shaping prism is n ₂ An optical system characterized by satisfying the following relational expression. here, W ₂ Is the short axis diameter of the beam emitted from the first beam shaping prism, W ₃ Is the diameter of the beam emitted from the second beam shaping prism and the long axis diameter of the elliptical light incident on the first beam shaping prism, θ ₂ Is an incident angle to the second beam shaping prism, α ₂ Is an acute angle of the second beam shaping prism and an exit angle inside the prism. 11. The method of claim 10, wherein the second beam shaping prism is composed of two prisms having the same refractive index and dispersion value to share the inclined planes with each other, both acute angles of one prism is 45 degrees around the shared boundary surface And reflecting light incident from the second collimator at right angles to the objective lens. 11. The method of claim 10, wherein the first beam shaping prism and the second beam shaping prism has a wavelength of light incident from the first collimator λ → λ ^′ When the optical system characterized in that the following relationship is satisfied. here, Δn ₁ Is the amount of change in the refractive index according to the change in wavelength of the first beam shaping prism, Δn ₂ Is the change amount of the refractive index according to the change of the wavelength of the second beam shaping prism, α ₁ Is an acute angle of the first beam shaping prism, α ₂ Is an acute angle of the second beam shaping prism, θ ₂ Is an incident angle to the second beam shaping prism, Is the beam shaping ratio of the second beam shaping prism. 10. The apparatus of claim 9, further comprising: a light splitter positioned between the beam shaping means and the objective lens to receive and transmit the light emitted from the beam shaping means and to reflect the light incident from the objective lens at right angles; A photodetector lens for condensing light reflected from the light splitter to a photodetector; And And a photodetector for detecting an optical signal from the light collected by the photodetector lens. 16. The optical pickup apparatus of claim 15, wherein the photodetector lens focuses the photodetector by multifocusing the first laser light and the second laser light having different specifications from the light splitter. 16. The optical pickup apparatus according to claim 15, wherein the photodetector detects an optical signal from the first laser light and the second laser light of different specifications condensed by the photodetector lens.