KR20030066175A - Optical pickup and assembling method thereof - Google Patents

Abstract

PURPOSE: An optical pickup and a method for assembling the same are provided to restrict aberration from generating due to manufacturing margin of optical parts and assembling margin generated in assembling the optical parts, thereby improving jitter and signal sensitivity characteristics. CONSTITUTION: A plate type beam splitter(15) converts a proceeding path of an incident beam from a semiconductor laser(11). An objective lens(17) focuses the incident beam at a spot on a recording surface of an optical disk(10). A photo detector(19) receives the beam sequentially passing the objective lens and the plate type beam splitter for detecting the beam. An optical path length adjusting device(13) made up of first and second triangular prisms(13a,13b) is arranged at a predetermined position on an optical path until the beam emitted from the semiconductor laser is received in the photo detector. A collimator lens(16) is installed on the optical path between the semiconductor layer and the objective lens for converting an emissive beam into a parallel beam.

Description

Optical pickup and assembling method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup, and more particularly, to an optical pickup and a method of assembling the optical pickup, which can suppress aberrations caused by manufacturing tolerances of the optical components constituting the optical pickup optical system and assembly errors occurring when the optical components are assembled. It is about.

Referring to FIG. 1, a conventional optical pickup includes a light source 3 for emitting light having a predetermined wavelength, a plate beam splitter 5 for changing a traveling path of light emitted from the light source 3, and an incident light. An objective lens 7 for condensing light to form light spots on the recording surface of the optical disc 1, and reflected from the recording surface of the optical disc 1, and the objective lens 7 and the plate-shaped beam splitter 5 And a photodetector 9 which receives light passing in sequence and detects an information signal and an error signal.

In the conventional optical pickup, the grating 4 splits the light incident from the light source 3 into 0th order and ± 1th order so that the track error signal can be detected by the 3-beam method, so that the light source 3 and the plate can be detected. It is provided between the beam splitters 5. The collimating lens 6 is provided between the plate-shaped beam splitter 5 and the objective lens 7 so as to convert the divergent light incident from the light source 3 into parallel light.

In FIG. 1, reference numeral 8 denotes a concave lens positioned between the plate-shaped beam splitter 5 and the photodetector 9 to enlarge the size of the light spot received by the photodetector 9.

The optical parts constituting the conventional optical pickup as described above are designed according to the required focal length and optical path length of the lens, and their installation positions are determined. However, when manufacturing the actual optical components there is always a manufacturing tolerance that differs from the design value, and when the optical components are assembled in a direction in which these manufacturing tolerances are added to each other during the optical pickup assembly, the assembly tolerance becomes relatively large.

On the other hand, in general, when light passes through the lens, the aberration increases from the center of the lens to the edge of the lens. Therefore, in view of this point, the objective lens 7 is designed in consideration of aberration, in particular spherical aberration. In a typical optical pickup, as shown in FIG. 1, the collimating lens 6 is provided, and the objective lens 7 is designed to have the smallest aberration upon incidence of parallel light.

However, in the conventional optical pickup, due to the manufacturing tolerances and the assembly tolerances of the optical components constituting the optical pickup as described above, the light passing through the collimating lens 6 toward the objective lens 7 converges or diverges. As a result, light that converges or diverges into the objective lens 7 is incident and aberration is largely generated. Due to the increased aberration in the objective lens 7, the light spot formed on the optical disc 1 becomes asymmetrical rather than a circle, and thus the light spot formed on the photodetector 9 does not become symmetrical. ) Increases. In addition, since the light is not accurately focused on the photodetector 9 side, the sensitivity of the signal is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and the structure is improved to suppress the aberration caused by the manufacturing tolerances of the optical components constituting the optical system and the assembly tolerances generated when the optical components are assembled. An object of the present invention is to provide an optical pickup and a method of assembling the same.

1 is a view schematically showing an example of a conventional optical pickup;

2 is a view schematically showing an optical configuration of an optical pickup according to an embodiment of the present invention;

3 is an enlarged view of the optical path length adjusting device of FIG. 2;

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

10 ... optical disc 11 ... light source

13 ... optical path length adjusting device 13a, 13b ... first and second triangular prisms

15 ... Plated Beam Splitter 16 ... Collimating Lens

17.Objective lens 19.Photodetector

In order to achieve the above object, the present invention provides an optical pickup that focuses light incident from a light source into an objective lens to form light spots on a recording medium, and receives and detects light reflected from the recording medium by using a photodetector. And an optical path length adjusting device provided at a predetermined position on the optical path from the light source until being received by the photodetector to adjust the optical path length.

Here, it is preferable that the adjustment device is composed of a pair of triangular prisms, and at least one of the pair of triangular prisms is movable to adjust the optical path length.

It is preferable that the said triangular prism is a right angled isosceles triangular prism.

An optical path changing device is provided on the optical path between the light source and the objective lens, and the adjusting device includes the light source and the optical path changing device, the optical path changing device and the objective lens, and the optical path changing device. It is preferably located anywhere between and the photodetector.

An optical pickup assembling method according to the present invention for achieving the above object comprises an optical path length adjusting device disposed at a predetermined position on an optical path until it is emitted from a light source and received by a photodetector to adjust the optical path length. Arranging the optical parts forming the proper position; Adjusting the adjustment device to correct optical path length errors due to fabrication tolerances and / or assembly tolerances of the optical components.

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment of the optical pickup and its assembly method according to the present invention.

2 is a view schematically showing an optical configuration of an optical pickup according to an embodiment of the present invention.

Referring to the drawings, the optical pickup according to an embodiment of the present invention, the light source 11, the optical path conversion device for converting the propagation path of the incident light, and the incident light to focus on the recording surface of the optical disc 10 An objective lens 17 for condensing into an optical spot, and a photodetector 19 for receiving and detecting light reflected from the recording surface of the optical disc 10 and sequentially passing through the objective lens 17 and the optical path changing device; And an optical path length adjusting device 13 which is disposed at a predetermined position on the optical path from the light source 11 until it is received by the photodetector 19.

The light source 11 may include a semiconductor laser that emits light of a predetermined wavelength suitable for recording / reproducing the optical disc 10. For example, when the optical disk 10 is a DVD-based optical disk, light having a wavelength of 635 nm or 650 nm, and when the optical disk 10 is a next-generation DVD-based optical disk, a 400-degree HD-DVD (High Definition-DVD) A blue light having a wavelength range of ˜480 nm and a semiconductor laser emitting light having a wavelength of 780 nm may be provided when the optical disk 10 is a CD-based optical disk.

In addition, the light source 11 may be provided with a twin LD which emits a plurality of lights having different wavelengths suitable for a plurality of optical disks having different formats. Twin LD is composed of two semiconductor lasers arranged adjacent to each other, as is well known in the art. When the light source 11 includes twin LD, the optical pickup according to the present invention further includes, for example, a hologram coupler (not shown) to match the path of the light emitted from two semiconductor lasers disposed adjacent to each other. It is preferable to provide. In this case, the plurality of optical discs having different formats may be a CD-based optical disc and a DVD-based optical disc or a DVD-based optical disc and a next-generation DVD-based (HD-DVD) optical disc.

Here, the optical pickup according to the present invention may include a light source 11 having various structures in addition to those mentioned above. For example, the light source 11 may be composed of two independent semiconductor lasers. In this case, in the optical pickup according to the present invention, the light emitted from the two semiconductor lasers may travel toward the optical disc 10 in the same optical path. A beam splitter (not shown) may be further provided.

The optical path changing device may include a plate type beam splitter 15. The plate-shaped beam splitter 15 is inclined at 45 degrees with respect to the optical axis to change the path of the light incident from the light source 11 by 90 degrees. The plate-shaped beam splitter 15 may be formed to have a transmittance of 50 ± 5% for an appropriate wavelength, for example.

As shown in FIG. 2, when the optical path changing device includes the plate-shaped beam splitter 15, a separate optical element employed for detecting a focus error signal by astigmatism in a conventional optical pickup, for example, There is an advantage that the score difference lens is unnecessary. This is because the plate-shaped beam splitter 15 is disposed at an angle of 45 ° with respect to the optical axis, so that an optical path length difference between the upper and lower sides and the left and right sides of the light transmitted through the plate-shaped beam splitter 15 is generated and the focus is increased. This is because astigmatism occurs due to different positions of formation. Therefore, by using the principle that such astigmatism occurs, it is possible to control focusing on the defocusing effect or the like caused by the wobble of the optical disc 10.

2 shows an example in which the plate-shaped beam splitter 15 is an amplitude division type provided to transmit incident light at a predetermined ratio and reflect the remaining light. The plate-shaped beam splitter 15 may be a polarization split type that transmits or reflects incident light according to polarization. In this case, a quarter-wave plate (not shown) is provided between the plate-shaped beam splitter 15 and the objective lens 17. C) is further provided.

The optical path changing device may include a cubic beam splitter instead of the plate type shown in FIG. 2.

On the other hand, the optical pickup according to the invention the collimating lens 16 for converting the divergent light emitted from the light source 11 with the emission angle on the optical path between the light source 11 and the objective lens 17 into parallel light It may be further provided. When the light source 11 is positioned at the focal position of the collimating lens 16, the light transmitted through the collimating lens 16 becomes parallel light. In the case of the structure having the collimating lens 16 as shown in FIG. 2, the objective lens 17 includes an objective lens 17 designed to be optimized for parallel incident light.

The optical pickup according to an embodiment of the present invention, when used for CD or CD and DVD compatible, can detect the tracking error signal by the 3-beam method during CD recording / playback, the light source 11 and the optical path changing device A grating 12 may be further provided to branch the incident light into the 0th order and the ± 1th order therebetween. Here, the tracking error signal at the time of DVD recording / playback uses a conventional phase detection method (DPD), as is well known in the art.

In addition, the optical pickup according to an embodiment of the present invention, coupled to the collimating lens 16 between the plate-shaped beam splitter 15 and the photodetector 19, the photodetector 19, for example, an eight-segment photodetector 19 It is preferable to further include a concave lens 18 for enlarging the size of the light spot received at the). This concave lens 18 is commonly referred to as a Yo-lens, and when the optical path changing device includes the plate-shaped beam splitter 15 as shown in Fig. 2, the plate-shaped beam splitter 15 In order to eliminate coma aberration caused by tilting, it is preferable that the plate-shaped beam splitter 15 is installed to be inclined oppositely.

The optical path length adjusting device 13 comprises, for example, first and second triangular prisms 13a and 13b of the same shape and arranged symmetrically with each other, as shown in FIG. At least one of the second triangular prisms 13a and 13b, for example, the second triangular prism 13b can be moved in a direction perpendicular to the optical axis to adjust the optical path length.

The reason for using two triangular prisms having the same shape and arranged symmetrically with the optical path length adjusting device 13 is that the transmitted light intensity second triangular prism 13b when the incident light enters the surface of the first triangular prism 13a perpendicularly. To emit light perpendicular to the plane.

The first and second triangular prisms 13a and 13b are preferably right angled isosceles triangular prisms, respectively, and are arranged to be spaced apart from each other by symmetry. The separation distance d between the first and second triangular prisms 13a and 13b is determined in consideration of the optical path length adjustment amount considering the manufacturing tolerances and the assembly tolerances of the optical components.

In general, when light passes through a medium, the optical path length is equal to the refractive index of the medium divided by the length passed through the medium. Therefore, the optical path length can be changed by the change of the refractive index and the length of light passing through the medium.

Using this principle, for example, moving the second triangular prism 13b in a direction perpendicular to the optical axis changes the length of light passing through the second triangular prism 13b to adjust the overall optical path length of the optical pickup optical system. Can be.

The optical path length adjusting device 13 as described above is disposed at a predetermined position on the optical path until it is emitted from the light source 11 and received by the photodetector 19. More specifically, the optical path length adjusting device 13 may be located between the light source 11 and the optical path changing device, as shown in FIG. 2. Alternatively, the optical path length adjusting device 13 may be disposed on the optical path between the optical path changing device and the objective lens 17 or between the optical path changing device and the photodetector 19.

The assembly of the optical pickup according to the present invention as described above arranges the optical components constituting the optical pickup at a proper position, and then the optical path length adjusting device 13, for example, the second triangular prism 13b perpendicular to the optical axis. By moving in one direction, the optical path length error caused by manufacturing tolerances and / or assembly tolerances of the optical components is corrected.

In the optical pickup according to the present invention assembled through the above process, since light traveling through the collimating lens 16 toward the objective lens 17 becomes parallel light, aberration is generated in the objective lens 17. This can be suppressed as much as possible. Accordingly, the optical pickup according to the present invention has better jitter characteristics than the conventional one, and the light is precisely focused on the photodetector 19 so that the signal sensitivity is also excellent.

Since the optical pickup according to the present invention as described above has an optical path length adjusting device that can adjust the optical path length at a predetermined position on the optical path between the light source and the photodetector, the manufacturing tolerances of the optical parts constituting the optical system and the optical parts can be assembled. It is possible to suppress the occurrence of aberration due to assembly tolerances generated at the time. Therefore, according to the optical pickup according to the present invention, the jitter characteristic and the signal sensitivity characteristic are superior to the conventional ones.

Claims (7)

In the optical pickup to focus the light incident from the light source to the objective lens to form a light spot on the recording medium, and to receive and detect the light reflected from the recording medium by using a photodetector, And an optical path length adjusting device which is provided at a predetermined position on the optical path from the light source until it is received by the photodetector and adjusts the optical path length. The optical pickup of claim 1, wherein the adjustment device is comprised of a pair of triangular prisms, and at least one of the pair of triangular prisms is movable to adjust the optical path length. The optical pickup of claim 2, wherein the triangular prism is a right angled isosceles triangular prism. The optical path changing device according to any one of claims 1 to 3, wherein an optical path changing device for converting a traveling path of light is provided on the optical path between the light source and the objective lens. And the adjustment device is located at any one of the light source and the optical path changing device, between the optical path changing device and the objective lens, and between the optical path changing device and the photodetector. According to any one of claims 1 to 3, further comprising a collimating lens for converting the divergent light emitted from the light source to parallel light, characterized in that the objective lens is optimized for parallel incident light Optical pickup. Arranging the optical components constituting the optical pickup at an appropriate position, including an optical path length adjusting device disposed at a predetermined position on the optical path from the light source until being received by the photodetector to adjust the optical path length; Adjusting the adjustment device to correct optical path length errors due to fabrication tolerances and / or assembly tolerances of the optical components. The optical pickup assembly method according to claim 6, wherein the adjustment device comprises a pair of triangular prisms that are movable so that at least one can adjust the optical path length.