Back to EveryPatent.com



United States Patent 6,188,061
Choi February 13, 2001
Optical pickup device

Abstract

A silicon substrate is disposed parallel with an optical disc. A prism for transmitting an incident beam is installed on the silicon substrate. A diffraction grating on a side surface of the prism. A beam splitter for partially reflecting and partially transmitting the laser beam is positioned inside of the prism to be slanted. The beam irradiated from the laser light source is reflected by the beam splitter after having transmitted through the diffraction grating. The reflected beam focuses onto the optical disc via a selective light-transmitting part formed on the upper surface of the prism. The beam is totally transmitted through an inner circular portion of the selective light-transmitting part and half transmitted through a peripheral portion of the selective light-transmitting part. The beam reflected from the optical disc partially is transmitted through the beam splitter, and then reflected a reflecting layer formed on the lower surface of the prism, and received a photodetector formed on an upper surface of the prism.

Inventors: Choi; Yang-Oh (Seoul, KR)
Assignee: Daewoo Electronics Co., LTD (Seoul, KR)
Appl. No.: 847476
Filed: April 25, 1997
Foreign Application Priority Data
Apr 26, 1996[KR]96-13002

Intern'l Class: G11B 007/125
Field of Search: 250/214 R,216,201.5,214.1 369/112,44.12,44.24,118

References Cited
U.S. Patent Documents
4665512May., 1987Ando369/44.
4873429Oct., 1989Kume et al.250/216.
4893296Jan., 1990Matsumoto et al.369/112.
4897828Jan., 1990Yoshitoshi et al.369/46.
5105403Apr., 1992Kando et al.369/44.
5107477Apr., 1992Fujita et al.369/44.
5231620Jul., 1993Ohuchida369/44.
5247506Sep., 1993Sugiura369/110.
5566157Oct., 1996Kojima et al.369/112.
5844879Dec., 1998Morita et al.369/118.
Foreign Patent Documents
0 258 450 A1Mar., 1988EP.
0 278 406 A2Aug., 1988EP.
0 468 612 A2Jan., 1992EP.
0 545 905 A2Jun., 1993EP.

Primary Examiner: Westin; Edward P.
Assistant Examiner: Luu; Thanh X.
Attorney, Agent or Firm: Jacobson, Price, Holman & Stern PLLC
Claims


What is claimed is:

1. An optical pickup device comprising:

a silicon substrate disposed parallel with an optical disc and provided with optical components thereon;

a prism for transmitting an incident beam disposed on the silicon substrate;

a laser light source part having a laser light source for generating laser beam, the laser light source part being spaced out from the prism on the silicon substrate;

a diffraction grating for diffracting a laser beam irradiated from the laser light source, the diffraction grating being formed on one side surface of the prism which faces the laser light source part;

a beam splitter for partially reflecting and partially transmitting the laser beam, the beam splitter being positioned inside of the prism to be slanted by a predetermined angle on the silicon substrate, so that the laser beam irradiated from the laser light source is incident on the beam splitter after having transmitted through the diffraction grating, and then the beam is partially reflected by the beam splitter toward the optical disc which is to be positioned at upper part of the silicon substrate;

a selective light-transmitting part formed on an upper surface of the prism for transmitting the laser beam proceeding to the disc after being reflected by the beam splitter, the selective light-transmitting part having an inner circular part for transmitting the laser beam with a first transmittance and a peripheral portion for transmitting the laser beam with a second transmittance;

a reflecting layer formed on a lower surface of the prism, the reflecting layer reflecting the laser beam partially transmitted through the beam splitter after being reflected from the optical disc;

a light-receiving part formed on an upper surface of the prism for receiving the laser beam reflected by the reflecting layer; and

an objective lens disposed between the prism and the optical disc for permitting the laser beam to focus on the disc via the prism,

wherein a difference between spot sizes focusing on the disc is adjustable by properly regulating an outermost angle of incidence of the laser beam which is transmitted through the inner circular portion of the selective light-transmitting part.

2. An optical pickup device as claimed in claim 1, wherein the first transmittance is higher than the second transmittance.

3. An optical pickup device as claimed in claim 1, wherein the inner circular portion is a totally transmitted one of which the transmittance is 1 and the peripheral portion is a half transmitted one of which the transmittance is 1/2.

4. An optical pickup device as claimed in claim 1, wherein the selective light-transmitting part is comprised of a circular light-transmitting plate of which peripheral portion is shaped as a ring.
Description


BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical pickup device, and more particularly to an optical pickup device of which the respective optical constituents are integrally manufactured for compaction and simplification of the device.

2. Description of the Prior Art

Information reproducing/recording systems for using optical discs such as laser discs or compact discs have been developed in recent years. Such optical information reproducing/recording systems reproduce/record a variety of information. A digital audio disc player for reproducing musical sounds and a digital video disc player for reproducing images serve as examples. It is the trend that the recording media of these optical information reproducing/recording systems has higher densities for making discs more compact and smaller, and also the disc players of these optical information reproducing/recording systems are more compacted and miniaturized. Also, the compatible systems are developed such as the recording of High Definition Television (HDTV) compatible video discs.

A construction and operation of a general optical pickup device is disclosed in U.S. Pat. No. 4,767,921 or 4,868,377.

The conventionally general optical pickup device will be described in detail with reference to FIG. 1 below.

FIG. 1 is a schematic view showing the conventionally general optical pickup device. In FIG. 1, a reference numeral 11 denotes a light source for generating laser beam, which is a laser diode 11. The laser beam emitted from laser diode 11 is diffracted while transmitting through a diffraction grating 12. The diffracted beam proceeds toward a beam splitter 13.

Here, beam splitter 13 is provided in such a manner that two right-angled prisms are installed to oppose to each other against respective inclination planes of 45.degree., and a coating layer 13a is formed along the contacting portion of the prisms, thereby transmitting some of the incident beam and reflecting the other incident beam to be perpendicular to the incident beam while securing the property of travelling straight of the incident beam.

The diffracted beam is reflected toward optical disc 15 by means of beam splitter 13. The beam reflected from beam splitter 13 focuses onto a recording plane 15a of an optical disc 15 while passing through an objective lens 14 installed in front of a recording medium such as optical disc 15. A positional accuracy, i.e., focusing error and tracking error, of the pickup device with respect to optical disc 15 is detected from an image of the beam received into a photodetector 16, and therefore, the focusing and tracking are controllable. Also, the information is read out on the basis of the amount of the reflected light determined by pits in recording plane 15a of optical disc 15.

Meantime, in the above-mentioned conventional optical pickup device, since such optical components as the beam splitter, the diffraction grating, the laser diode, and the photodetector should be individually manufactured and respectively located at their accurate positions, manufacturing and controlling of the optical pickup device are very difficult. Also, the optical pickup device and the optical disc player need to be compacted and miniaturized to act up to the recent trend relating to the optical disc player.

Furthermore, according to the conventional optical pickup device, discs of two different kinds can not be reproduced or recorded by means of a single optical pickup device. For example, if the recording capacity of the disc is to be four times like that of the digital video disc as compared with the digital audio disc, the width of pits in the disc is consequently decreased by 1/2. For this reason, a focused spot size onto the digital video disc should be half of that onto the digital audio disc with the consequence of necessarily employing different optical pickup devices in reproducing the digital video disc and digital audio disc by means of the conventional optical pickup devices. That is, in order to accurately read out data respectively recorded on the digital audio disc and digital video disc, it is required to separately apply one optical pickup device for digital audio disc of which beam spot size is approximately 1.6 .mu.m when focusing onto the digital audio disc and another optical pickup device for digital video disc of which beam spot size is approximately 0.8 .mu.m when focusing onto the digital video disc.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide an optical pickup device of which the respective optical constituents are integrally manufactured for compaction and simplification of the device.

it is another object of the present invention to provide an optical pickup device capable of reproducing discs of two kinds having different densities by forming double beam focuses of different sizes.

To achieve the above object of the present invention, an optical pickup device comprises a silicon substrate disposed parallel with an optical disc and provided with optical components thereon. A prism for transmitting an incident beam is disposed on the silicon substrate. A laser light source part has a laser light source for generating laser beam, the laser light source part being spaced out from the prism on the silicon substrate. A diffraction grating for diffracting an laser beam irradiated from the laser light source is formed on one side surface of the prism which faces the laser light source part. A beam splitter is for partially reflecting and partially transmitting the laser beam, the beam splitter being positioned inside of the prism to keep a predetermined angle with the silicon substrate, so that the laser beam irradiated from the laser light source is incident on the beam splitter after having transmitted through the diffraction grating, and then the beam is partially reflected by the beam splitter toward the optical disc which is to be positioned at upper part of the silicon substrate. A reflecting layer is formed on a lower surface of the prism to reflect the laser beam partially transmitting the beam splitter after being reflected from the optical disc. A light-receiving part is formed on an upper surface of the prism to receive the laser beam reflected by the reflecting layer. An objective lens is disposed between the prism and the optical disc for permitting the laser beam to focus on the disc via the prism.

The reflecting layer of the prism is integrally provided with a Fresnel lens for shortening the optical distance.

The side surface of the prism on which the diffracting grating is installed can be integrally provided with a Fresnel lens for shortening the optical distance.

The optical pickup device further comprises a selective light-transmitting part formed on an upper surface of the prism for transmitting the laser beam proceeding to the disc after being reflected by the beam splitter. The selective light-transmitting part has an inner circular part for transmitting the laser beam with a first transmittance and a peripheral portion for transmitting the laser beam with a second transmittance.

The first transmittance is higher than the second transmittance. Preferably, the inner circular portion is a totally transmitted one of which the transmittance is 1 and the peripheral portion is a half transmitted one of which the transmittance is 1/2.

A difference between spot sizes focusing on the disc is adjustable by properly regulating an outermost angle of incidence of the laser beam which is transmitted through the inner circular portion of the selective light-transmitting part.

According to the optical pickup device of the present invention as described above, since such optical components as the beam splitter, the diffraction grating, the laser diode, and the photodetector should be integrally manufactured, and fixed at their accurate positions in manufacturing process, manufacturing and controlling of the optical pickup device are very simple.

Also, the optical pickup device can be compacted and miniaturized by employing such a component as Fresnel lens for shortening the optical distance.

According to the optical pickup device of the present invention as described above, when the laser beam transmits through the selective light-transmitting part, the laser beam having transmitted through the inner circular portion forms the larger beam spot onto the disc and the laser beam having transmitted through the peripheral portion forms the smaller beam spot. By doing so, double beam focuses of different sizes can be formed by the use of the single optical pickup device, thereby making it possible to reproduce discs of two types with different densities by means of the single optical pickup device.

As a result, in case of the digital audio disc and digital video disc having different recording capacities from each other, both discs can be reproduced when employing the optical pickup device according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and other advantages of the present invention will become more apparent by describing in detail preferred an embodiment thereof with reference to the attached drawings in which:

FIG. 1 is a schematic view showing a conventional optical pickup device; and

FIG. 2 is a schematic view showing an optical pickup device according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An optical pickup device according to the present invention will be described in detail with reference to an accompanying drawing.

FIG. 2 is a schematic view showing the optical pickup device according to the present invention.

In this embodiment, as shown in FIG. 2, is installed a silicon substrate 110 disposed parallel with a recording plane 185 of an optical disc 180. Silicon substrate 110 is to be provided with optical components thereon. A prism 160 has a rectangular bar shape, and the opposite faces are parallel each other and the crossing faces are orthogonal.

Laser light source part 130 for transmitting an incident beam is installed at a position spaced out from prism 160 on silicon substrate 110. Laser light source part 130 has a laser diode 131 for generating laser beam and a supporting part 132 installed on silicon substrate 110 for seating laser diode 131 thereon. Supporting part 132 has a function for protecting against heat emitted from laser diode.

A diffraction grating layer 140 is formed on one side surface of prism 160 which faces the laser diode 131 for diffracting an laser beam irradiated from laser diode 131.

A beam splitter layer 161 for partially reflecting and partially transmitting the laser beam is formed inside of prism 160. Beam splitter layer 161 is slanted at an angle of 45.degree. against diffraction grating layer 140 as well as the upper surface of prism 160. Thereby, the laser beam irradiated from laser diode 131 is incident with an angle of 45.degree. on beam splitter 161 after having transmitted through diffraction grating 140, and then the beam is partially reflected with an angle of 45.degree. from the beam splitter layer 161 toward optical disc 180 parallel to the upper part of silicon substrate 110.

A reflecting layer 165 is formed on a lower surface of prism 160. Furthermore, reflecting layer 165 is integrally provided with a Fresnel lens 166 for shortening the optical distance. Fresnel lens 166 is positioned on the optical path of laser beam partially transmitting beam splitter layer 161 after being reflected from optical disc 180.

A photodetector 190 is formed on an upper surface of prism 160 to receive the laser beam reflected by reflecting layer 165.

Furthermore, the side surface of prism 160 on which diffracting grating layer 140 is installed can be integrally provided with a Fresnel lens for shortening the optical distance.

A selective light-transmitting part 150 is integrally formed on an upper surface of prism 160 for transmitting the laser beam proceeding to disc 180 after being reflected by beam splitter layer 161. Selective light-transmitting part 150 consists of an inner circular portion 151 that transmits the laser beam with the first transmittance and a peripheral portion 152 that transmits the laser beam with the second transmittance. Selective light-transmitting part 150 may be preferably formed by a circular light-transmitting plate of which peripheral portion 152 is in the form of a ring. The first transmittance is so determined as to be higher than the second transmittance. Preferably, inner circular portion 151 is a totally transmitted one, and peripheral portion 152 is a half transmitted one.

An objective lens 170 is installed between optical disc 180 and selective light-transmitting part 150 for permitting the beam transmitted through selective light-transmitting part 150 to focus onto a recording plane 185 of optical disc 180. Objective lens 170 is an unspherical lens to minimize spherical aberration. Objective lens 170 is preferably a lens for DVD so that the beam having transmitted through selective light-transmitting part 150 can reproduce digital video disc (DVD) with 0.6 mm thickness.

Hereinafter, an operation according to the foregoing embodiment will be described.

The laser beam is irradiated from laser diode 131 toward prism 160. The laser beam is divided into three beams while transmitting through diffraction grating layer 140 formed on the side surface of prism 160.

The divided beams are incident at the angle of 45.degree. on beam splitter layer 160. The laser beams are partially transmitted, and partially reflected to be bent by right angles with respect to the incident light by means of beam splitter layers 161. Then, the beams proceeds toward optical disc 180.

The beam passes through selective light-transmitting part 150 formed on the upper surface of prism 160. The beam totally transmits through inner circular portion 151 of selective light-transmitting part 150, and half transmits through peripheral portion 152 of selective light-transmitting part 150.

The transmitted beam is to focus onto recording plane 185 of optical disc 180 by means of objective lens for DVD 170 installed between optical disc 180 and prism 160.

At this time, the laser beam, which totally transmits through inner circular portion 151 of the circular light-transmitting plate 150, focuses onto optical disc 180 at an angle of .theta.1 via objective lens 170. At the same time, the laser beam, which half transmits through peripheral portion 152 of circular light-transmitting plate 150, focuses onto optical disc 180 at an angle of .theta.2 via objective lens 170.

The laser beams focusing at the angles of .theta.1 and .theta.2 on the disc transmit through circular light-transmitting plate 150 via objective lens 170 to return to beam splitter 160. The returned beams having optical information partially transmit through coating layer 161 to be received into photodetector 190 installed to the lower portion of beam splitter 160, and are thus demodulated into original signals.

At this time, two different numerical apertures (N.A.) are produced by inner circular portion 151 and peripheral portion 152 of circular light-transmitting plate 150. By these different two numerical apertures, two beam spots of different sizes are formed onto optical disc 180. Due to this fact, a difference appears in the quantities of light.

That is, N.A.1=.sup.n sin .theta.1 and N.A.2=.sup.n sin .theta.2 (where .sup.n denotes a refractive index of a medium, and .theta. is an angle formed between an optical axis and outermost incident beam).

At this time, a diameter of the beam W.sub.0 is written as:

W.sub.0 =K*.lambda./N.A. (where K is a constant), and D.sub.0 (focal depth)=R*.lambda./(N.A.).sup.2 (where R is a constant).

Thus, along with the change of the numerical aperture, the beam size and focal depth become changed.

Therefore, the beam focusing by the outermost angle of incidence .theta.2 after passing through peripheral portion 152 of circular light-transmitting plate 150 has smaller beam size and focal depth than those of the beam focusing by the outermost incident angle .theta.1 by objective lens 170 after passing through inner circular portion 151. This is because the beam size is in inverse proportion to N.A. and the focal depth is in inverse proportion to (N.A.).sup.2.

When optical disc 180 is of the digital video disc of thickness 0.6 mm, the laser beam focusing on the optical disc via objective lens 170 after transmitting through light-transmitting plate 150 forms the beam spot of 0.8 .mu.m size onto optical disc 180. Since the present objective lens is the lens for DVD, the beam can focus accurately without generation of spherical aberration on the recording surface of the digital video disc.

Meanwhile, When optical disc 180 is of the digital audio disc of thickness 1.2 mm, since the beams on and close by the optical axis totally transmit through inner circular portion 151 of circular light-transmitting plate 150, and the beams in the skirts of the optical axis half transmit through peripheral portion 152 of circular light-transmitting plate 150, the numerical aperture N.A. of the beam focusing onto the disc via objective lens 170 becomes smaller as N.A.1. Therefore, spherical aberration to be occurred due to the difference of 0.6 mm in thickness as compared with the digital video disc is sharply decreased due to the smaller numerical aperture N.A.1. Thus, digital audio disc with larger width of the pit can be reproduced.

That is, when reproducing digital audio disc, spherical aberration is to be occurred due to the difference of 0.6 mm in thickness as compared with digital video disc.

At this time, the spherical aberration is

(.DELTA.d/8)*{(.sup.n.sup..sup.2 -1).sup.n.sup..sup.3 }*(N.A.).sup.4

(where .DELTA.d is a difference of thicknesses of the discs, .sup.n is a refractive index of a medium, and N.A. is a numerical aperture)

Accordingly, the beams on and close by the optical axis which occur smaller spherical aberration totally transmit through inner circular portion 151 of circular light-transmitting plate 150. Also, the beams which pass through the skirts of the lens occur larger spherical aberration and half transmit through peripheral portion 152 of circular light-transmitting plate 150. Thereby, the numerical aperture N.A. formed by the beam becomes smaller as N.A.1=.sup.n sin .theta.1. Therefore the spherical aberration is sharply decreased in proportion to (N.A.).sup.4. Also, since the numerical aperture becomes smaller as N.A.1=.sup.n sin .theta.1, the size of beam spot formed on the disc is larger as 1.6 .mu.m in inverse proportion to (N.A.). Thus, digital audio disc with larger width of the pit can be reproduced.

According to the optical pickup device of the present invention as described above, since such optical components as the beam splitter, the diffraction grating, the laser diode, and the photodetector should be integrally manufactured, and fixed at their accurate positions in manufacturing process, manufacturing and controlling of the optical pickup device are very simple.

Also, the optical pickup device can be compacted and miniaturized by employing such a component as Fresnel lens for shortening the optical distance.

According to the optical pickup device of the present invention as described above, when the laser beam transmits through the selective light-transmitting part, the laser beam having transmitted through the inner circular portion forms the larger beam spot onto the disc and the laser beam having transmitted through the peripheral portion forms the smaller and less light beam spot. By doing so, double beam focuses of different sizes can be formed by the use of the single optical pickup device, thereby making it possible to reproduce discs of two types with different densities by means of the single optical pickup device.

As a result, in case of the digital audio disc and digital video disc having different recording capacities from each other, both discs can be reproduced when employing the optical pickup device according to the present invention.

While the present invention has been particularly shown and described with reference to particular embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be effected therein without departing from the spirit and scope of the invention as defined by the appended claims.

Top