JPS61122946A - Optical pick-up - Google Patents

Abstract

PURPOSE:To make a construction and assembling simple and to make a focusing operation easy by forming a lens composing a main optical system and a deflecting optical part composing a sub-optical system in a body with a plastic and equalizing a focus distance of both optical systems. CONSTITUTION:In a compound lens 3, a surface 3b of a sub-optical system is eccentric in one direction outside a main optical system 3 and formed in a single body. For this reason, comming-out light from the surface 3b of the sub-optical system is corrected as a sub-spot S5 at the position away from a main spot S4 on a surface D of information recording media. The sub=spot S5 is reflected from the surface D, the surface 3a of the main optical system is transmitted, and thereafter, the spot is reflected by a beam splitter 2, and converted S5 to the second light detecting device 5. The second light detects a focus error and automatically focused. Incident light from the main optical system 3a is collected as the main spot S4 on the surface D, and the reflecting light is converged S4 to the first light detecting device 4 and the information is read. The focus distance of the main optical system and the sub-optical system is equalized. Thus, the construction and assembling go to be simple and a focus operation is made easy.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical pickup that reads information from an information recording medium (hereinafter referred to as 3D) such as an optical disk. The present invention relates to an optical pickup equipped with a focus detection function that can be automatically adjusted.

2. Description of the Related Art In the above-mentioned optical pickup, a sub-beam method is known in which focus detection is performed using a sub-beam in addition to a main beam for information reading and detection.

For example, the optical pickup shown in FIG. 10 includes a semiconductor laser 1 which is a laser light source, a condensing lens 3a which is a main optical system which condenses a luminous flux emitted from the semiconductor laser 1 onto a CD surface, and a first photodetector 4 that receives the reflected light of the main spot S4 focused by the condenser lens 3a and reads information; A second lens 3b, which is a sub-optical system including a deflection optical member that focuses the light beam onto the CD surface, receives the reflected light of the sub-spot S5 focused by the second lens 3b, and detects focus. A second photodetector 5, which is a two-split photodetector, and an electromagnetic lens moving device, which moves the condensing lens 3a and the second lens 3b to focus based on the signal from the second photodetector 5. It consists of a moving device M.

The optical pickup picks up the CD by the second lens 3b.
The light reflected by the CD surface of the sub-spot focused on the surface is reflected by the second lens 31:! And CD! Focusing is detected by detecting, with the second photodetector 5, a state in which the condensing lens 3a moves in a direction intersecting the optical axis according to the distance from iiD. Also, the main spot due to the condensing lens 3a) C of S4
The information on the CD is read and detected by detecting the light reflected by the D surface with the first photodetector 4.

The optical pickup has a separate sub-optical system including a deflection optical member for focus detection and a main optical system for reading and detecting information, so that the light beam of the main optical system includes the deflection optical member. The main spot of the main optical system can be narrowed down to a minute spot without being eclipsed by the light beam of the sub-optical system, and the output of the laser light source can be used effectively. Further, since the peripheral light of the laser output is used as the light beam of the sub-optical system including the deflection optical member, the output of the laser light source can be effectively used. Furthermore, since the main optical system and the sub-optical system including the deflection optical member are provided separately, adjustment is easy and focus detection with good sensitivity and detection speed can be performed.

However, in the optical pickup, (1) the lens of the main optical system and the deflection optical member of the sub-optical system have separate structures;
Moreover, each of them has a structure that is difficult to manufacture, and requires complicated work to assemble and adjust the main optical system and the sub-optical system including the deflection optical member.
(2) Since the lens of the main optical system and the deflection optical member of the sub-optical system are made of glass and are heavy, there are problems such as difficulty in performing focusing operations smoothly.

Purpose of the Invention The present invention aims to solve the above-mentioned conventional problems.
By making the main optical system that condenses light onto a CD for bladder removal and the sub-optical system that includes a deflection optical member that produces a sub-luminous flux for focus detection, easy to manufacture, the structure and assembly are simple. It is an object of the present invention to provide an optical pickup that can eliminate focusing errors due to temperature changes in optical fibers by performing a focusing operation and making the focal lengths of the optical fibers approximately equal.

Structure of the Invention The present invention includes a laser light source, a main optical system that focuses a luminous flux emitted from the laser light source onto an information recording medium,
deflection optics that focuses the light beam emitted from the laser light source at a position on the information recording medium away from the position where the light beam is focused by the main optical system, and that passes the light beam outside the light beam that passes through the main optical system; In the optical pickup, the optical pickup includes a sub-optical system including a member, and a photodetector divided into a plurality of parts for detecting focus by receiving light guided by the sub-optical system and reflected by the information recording medium. The optical pickup is characterized in that at least one lens of the main optical system and the deflection optical member of the sub-optical system are integrally formed of plastic, and the above-mentioned structure makes it possible to I was able to achieve my goal.

Embodiments The present invention will be explained in detail below with reference to embodiments shown in FIGS. 1 to 9.

FIG. 1 shows a first embodiment, which is characterized in that a surface of a sub-optical system including a deflection optical member for focus detection is provided outside the surface of a main optical system for reading information. The optical pickup having a compound lens is a water body laser, and the 2Vi beam splitter 13 is a surface 3a of the main optical system which is a condensing lens.
and a compound lens having surfaces 3b and 7 of the sub-optical system, 4 is the main spot of the main optical system), a first photodetector that detects the information Sa r Bm, and 5 is the sub-spot of the sub-optical system. +
s5 is provided outside the surface 3a of the main optical system and eccentrically in one direction. Therefore, the sub spot Ss of the sub optical system is focused on the CD surface with a shift in the eccentric direction with respect to the main spot S4 of the main optical system. Further, the compound lens 3 is made of plastic, and a surface 3a of the main optical system and a surface 3b of the sub optical system are integrally molded. The second photodetector 5 is a two-split photodetector.

The focusing operation by the optical pickup is performed as follows. Divergent light from the semiconductor laser 1 passes through the beam splitter 2 and enters the compound lens 3. The light emitted from the surface 3b of the sub optical system is focused as a sub spot S5 at a position away from the main spot S4 on the CD surface. The light Ssld is reflected from the CD surface, passes through the surface 3a of the main optical system of the compound lens 3, is reflected by the beam splitter 2, and is focused on the second photodetector 5. The second photodetector 5 is a two-split photodetector, and detects a focusing error by comparing the amount of light in the area divided into two by the dividing line. Depending on the detected focusing error, a lens moving device (not shown) that moves the compound lens 3 toward and away from the CD surface is operated, and the object is automatically focused. Note that the light emitted from the surface 3a of the main optical system is focused on the CD surface as a main spot S4. The main spot S4 is reflected by the CD surface, passes through the compound lens 3, is reflected by the beam splitter 2, and is focused on the first photodetector 4 s4. Information on the CD is read by measuring the amount of light from the main spot s4 focused on the first photodetector 4.

Therefore, it is possible to perform tracking error detection using the far field method.

FIG. 2 shows a second embodiment, which is characterized in that the surface of the sub-optical system in the compound lens of the first embodiment is divided into two parts and is provided symmetrically and decentered with respect to the surface of the main optical system. Shows original pickup.

In Fig. 2, 3 is a compound lens, and the surface 3a of the main optical system is
It has a first surface 3b and a second surface 3b' of a sub-optical system, which are provided on the outer side of the optical system and eccentrically symmetrically with respect to the several surfaces 3a. Furthermore, each surface 31) and 3b' of the sub-optical system @ob.

As shown in FIG. 3, Ob' is set symmetrically with respect to the optical axis Oa of the surface 3a of the main optical system.

5 and 5'c, sub-spot of sub-optical system S s + 85
+35'+s 5/ to detect the focusing error.
and a third photodetector. The same reference numerals as in FIG. 1 indicate the same or corresponding members.

In the optical pickup shown in FIG. 2, the surfaces 3b and 3b' of the sub-optical system of the compound lens 3 are divided into two symmetrically with respect to the surface 3a of the main optical system as described above, so that the sub-light beam 6.
L5' has two sub-spots s5. on the CD surface. s5'
The light is focused as The sub-spot S.

85' focuses the light onto the second and @3 photodetectors 5 and 5', respectively.
5. s5', and a focusing error is detected as shown in the block diagram of the photodetecting section in FIG. Since the detected focusing error is determined by comparing the focusing errors at two points, it is possible to detect the focusing error with high precision (not affected by the inclination of the 3D plane).

Furthermore, the compound lens of this embodiment has a higher efficiency in returning the sub-luminous flux L5°L5/ than that of the first embodiment.

It should be noted that the compound lens 3 of this embodiment detects the focusing error using the sub spot S5. Since it can be performed only by S, ′, the sub spots S5 and 85′ formed by the surfaces 3b and 3b′ of the two sub optical systems are combined with the main spot S4 formed by the surface 3a of the main optical system.
The light does not need to be focused on the same plane.

FIG. 4 shows a plan view of the compound lens of the third embodiment. The surface 3b of the sub-optical system of the compound lens is a toric surface that is rotationally symmetrical with respect to the optical axis Oa of the optical system constituted by the surface 3a of the main optical system, and the optical axis of the optical system constituted by this toric surface is Indicated by ob.

In the third embodiment, the compound lens of the optical pickup shown in FIG. 2 is replaced with the compound lens shown in FIG. be illuminated. Therefore, the second photodetector 5 that detects the focusing error should be recessed concentrically with the first photodetector 4 that reads information, as shown in the block diagram of the photodetector section in FIG. I can do it. The second photodetector 5 can detect a focusing error in a wide range, so it has higher precision, higher efficiency of return of the sub-luminous flux L5, etc. than that of the second embodiment, and moreover, the focusing error is CD It is possible to detect focusing errors that are not affected by the inclination of the surface.

FIG. 7 shows an optical pickup according to a fourth embodiment, which is characterized in that a compound lens 3 is provided between a semiconductor laser 1 and a condenser lens 6. Note that the same reference numerals as in FIG. 2 indicate the same or corresponding members.

In FIG. 7, surfaces 3b, 3 of the sub-optical system of the compound lens 3
b' is the same as in FIGS. 2 and 3, and is a sub-luminous flux L5°L passing through the surfaces 3b and 3b' of the sub-optical system, and / is a sub-spot s6 on the CD surface by the condensing lens 6. ．． s,'
The light is focused as The sub spot S5+85' is C
It is reflected on the D surface, and the surface 3a of the main optical system of the compound lens 3
The light is transmitted through the beam splitter 2, reflected by the beam splitter 2, and focused on the second and third photodetectors 5, 5'. Detection of a focusing error is performed in the same manner as shown in the block diagram of the photodetector section in FIG.

In this embodiment, the focal length is mainly determined by the condensing lens 6 disposed on the CD surface side, so the compound lens 3 may have a small condensing power. Moreover, since the angle of incidence of the compound lens 3 on the condensing lens 6 is small, the efficiency of use of the luminous flux is good.

FIG. 8 shows a fifth embodiment, in which the beam splitter is removed from the second embodiment. A sub spot S5 caused by the sub light beam L5 passing through the surface 3b of the sub optical system of the compound lens 3 is returned close to the semiconductor laser 1 in a direction intersecting the optical axis of the surface 3a of the main optical system. Therefore, the second photodetector 5 for focusing and the semiconductor laser 1 can be arranged adjacent to each other facing the same direction and can be made into an integral structure, and the integral structure and the compound lens can simplify the structure. An optical pickup can be configured. Note that reading of information in this embodiment can be performed by employing a 5-coop method for detection using the self-coupling effect of the laser light source by the return light of the main optical system.

FIG. 9 shows an optical pickup according to a sixth embodiment, which is characterized in that a compound lens 3 is provided between a semiconductor laser 1 and two condensing lenses 6.7. The optical big up has the same effect as the fourth embodiment because the compound lens 3 is arranged as described above, and the same effect as the fifth embodiment because it does not have a beam splitter. It is something that plays.

In each of the above embodiments, the lens constituting the main optical system and the deflection optical member constituting the sub-optical system are integrally molded from plastic, so that the structure and assembly are simple, and each of the above-mentioned components is simple. The optical system is lightweight, and focusing operations can be performed smoothly with little force.

In each of the above embodiments, it is preferable that the main optical system and the sub optical system have the same focal length. That is, the refractive index of a composite lens made of plastic changes due to temperature changes, causing a focusing error. However, by configuring the lens as described above, the focusing error can be eliminated.

Effects of the Invention The optical pickup of the present invention is simple in structure and assembly because the lens constituting the main optical system and the deflection optical member constituting the sub optical system are integrally formed of plastic. , each of the optical systems described above is lightweight, and a focusing operation can be performed with little force.

Furthermore, in the optical pickup of the present invention, by making the focal lengths of the main optical system and the sub optical system approximately equal, it is possible to eliminate focusing errors caused by changes in the refractive index of the optical system due to temperature changes. can.

As described above, the present invention was able to provide the objective optical pickup with the above configuration.

3 is a schematic diagram of the second embodiment of the present invention, 3V is an explanatory diagram of the main part of FIG. 2, FIG. 4 is an explanatory diagram of the main part of the third embodiment of the present invention, and 5
The figure is a block diagram of the photodetector section of the second embodiment, and FIG. 6 is the SJ! Block diagram of the photodetector section of the example, FIGS. 7 to 9
The figures are schematic diagrams of fifth to seventh embodiments of the present invention, and FIG. 10 is a schematic diagram of a conventional example.

■... Semiconductor laser, 2... Beam splitter 23... Complex lens, 3a... Surface of main optical system.

31), 3b'... Surface of sub-optical system, 4... First photodetector.

5... Second photodetector, D... (3D surface.

Oa: Optical axis of the main optical system.

ob, ob'... Optical axis of the sub optical system.

S4...main spot, S5. S4...Sub spot.

Patent applicant: Konishiroku Photo Industry Co., Ltd. Di Figure 2 Figure 3 ! ! ! Figure 4

Claims (5)

[Claims] (1) A laser light source, a main optical system that focuses the light flux emitted from the laser light source onto an information recording medium, and a main optical system that focuses the light flux emitted from the laser light source on the information recording medium. a sub-optical system including a deflection optical member that condenses the light at a position away from the position where the light is emitted and transmits a light beam outside the light beam passing through the main optical system; In an optical pickup comprising a plurality of divided photodetectors that receive reflected light and detect focus, at least one lens of the main optical system and the deflection optical member of the sub optical system are made of plastic. An optical pickup characterized in that it is integrally formed. (2) The optical pickup according to claim 1, wherein one optical surface of the deflection optical member is a toric surface rotationally symmetrical with respect to the optical axis of the main optical system. (3) Claim 1 or 2, characterized in that the lens and the deflection optical member have substantially the same focal length.
Optical pickup described in section. (4) Any one of claims 1 to 3, characterized in that a laser light source and a plurality of divided photodetectors for detecting focus are arranged adjacent to each other facing the same direction. The optical pickup according to item 1. (5) Claim 1, characterized in that information is read using the self-coupling effect of a laser light source.
The optical pickup according to any one of items 1 to 4.