JPH03230326A - optical pickup device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical pickup device used in an optical device that records or reproduces information on an optical disk such as a magneto-optical disk or an optical phase change disk.

2. Description of the Related Art In general, optical devices using optical disks as a medium include, for example,
Compared to recording and reproducing devices using magnetic tape as a medium, it has advantages such as an extremely large amount of recorded information and fast access time.

The structure of an optical device is to read information by converging a parallel light beam from a light source onto the recording surface of an optical disk through various optical elements and receiving the light beam reflected from this recording surface. Focusing and tracking are performed by detecting the state of reception of the light beam reflected from the object.

In recent years, there has been a strong demand for even faster access times in such optical devices. In order to meet this demand, we have developed a fixed optical system consisting of a fixed array of optical elements including a light source, and an optical element that includes an objective lens that converges the parallel light beam from the light source on a carriage that moves in the radial direction of the optical disk. This is a separate type that is separated into a moving optical system equipped with a carriage, and the number of optical elements mounted on the carriage is minimized to reduce the weight and size of the moving optical system, thereby speeding up access time. Optical instruments are being developed. As a prior art of this separated optical device, the second
There is a recording/reproducing device shown in the figure.

That is, 1 is an optical disk, 2 is a fixed optical system, and 3 is a moving optical system. First, the fixed optical system 2 will be explained.

A coupling lens 6 that converts the laser beam 5 emitted by the semiconductor laser 4 into a parallel beam, and a shaping prism 7 that shapes the laser beam 5 are disposed on the optical axis of the semiconductor laser 4 serving as a light source. Further, a roof prism 8 is provided which reflects the laser light from the semiconductor laser 4 at right angles by a reflecting portion 9. This roof prism 8 is integrally formed with a beam splitter 10 that reflects the laser beam 5 from the reflecting section 9 toward the moving optical system 3 at right angles and transmits the laser beam that passes through the moving optical system 3. . Further, a λ/4 plate 11 is disposed near the beam splitter 10 on the moving optical system 3 side. Furthermore, on the optical path of the laser beam that passes through the beam splitter 10 from the moving optical system 3, there is a condenser lens 12 and a Knifezi prism 13 that blocks part of the laser beam converged by the condenser lens 12. , a mirror 14, and a focusing detector 15, which is a detector, are provided. This focusing detector 15 has a pair of light receiving elements 15a and 15b. Furthermore, a tracking detector 16 as a detector is disposed on the optical axis bent at right angles by the Knifezi prism 13. This tracking detector 16
has a pair of light receiving elements 16a and 16b.

Next, the structure of the moving optical system 3 will be explained.

A guide rail 17 is laid along the theta direction S along the radial direction of the optical disc l, and a carriage 18 driven by a moving means (not shown) such as a near motor is movably held on the guide rail 17. . An objective lens 19 facing the optical disc 1 and a deflection prism 20 serving as a deflection member are sequentially disposed on the carriage 18 from top to bottom.

Next, the operation will be explained. For example, when reproducing information recorded on the recording surface of an optical disk l, the laser beam 5 emitted from the semiconductor laser 4 has an optical path bent in the theta direction S by the reflection part 9 of the roof prism 8 and the beam splitter lO. Further, it is reflected upward by the deflection prism 20 of the moving optical system 3, and the reflected parallel light beam is focused onto the recording surface of the optical disc 1 by the objective lens 19. A parallel beam of light reflected according to information recorded on a specific track on this recording surface is transmitted through an objective lens 19 and bent in the theta direction S by a deflection prism 20.

The light bent in the theta direction S passes through the λ/4 plate 11 and the beam splitter 10 again, is converged on the condenser lens I2, and is further divided into a convergent beam that is bent by the Knaifezi prism 13 and a convergent beam that travels straight. It is divided into The bent and convergent light beam is transmitted to the light receiving element 16 of the tracking detector 16.
a, 16b, the tracking information of the optical disk 1 is detected, and the convergent light beam, partially blocked by the Knifezi prism 13, is reflected by the mirror 14, and is incident on the light receiving elements 15a, 15b of the focusing detector 15. , Here, the distance between the objective lens 20 and the optical disc 1 is detected.

Focusing detection is performed as follows.

The state shown in FIG. 3(a) is a case where the distance between the objective lens 19 and the optical disc 1 is appropriate, and the light receiving element 15a.

Assuming that the laser beam is focused at the center of the boundary of the light receiving element 15b, and the outputs of the light receiving elements 15a and 15b are A and B, respectively,
A-B=0. When the distance between the objective lens 19 and the optical disk l is too large, the laser beam is converged in front of the focusing detector 15, as shown in FIG. Naifetsuji Prism 13
Since the light is blocked by
The difference between the outputs of 5b is A-B>O. On the other hand, when the distance between the objective lens 19 and the optical disk l is too small, as shown in FIG.
As shown in c), the laser beam is transmitted to the focusing detector 1.
5, and a large amount of laser light is incident on the light receiving element 15b side, thereby causing the light receiving elements 15a, 1
The difference in the output of 5b is A-B(O. If A-B)>O and A-B(0(7), the objective lens 19 is vertically moved relative to the optical disc l by a focusing mechanism (not shown). be adjusted.

Further, tracking detection is performed as follows. When the optical axis of the objective lens 19 and the track T of the optical disk 1 are aligned, the laser beam is converged at the center of the boundary between the light receiving elements 16a and 16b and is received as shown in FIG. 4(a). Element 16a.

If the outputs of 16b are respectively A and B, then A-B=O. Further, when the track T is displaced, for example, to the right with respect to the objective lens 19, as shown in FIG. The difference between the outputs of 16b is A-B>O. In such a case, the position of the objective lens 19 is corrected by a tracking mechanism (not shown).

Problem to be Solved by the Invention It is difficult to completely eliminate the play between the carriage 18 and the guide rail 17 due to manufacturing errors. As a result, when moving the carriage 18 in the theta direction S,
The carriage 18 is displaced in the direction of rotation about the X-axis, which is orthogonal to the theta direction S. Therefore, as shown in FIG.
When moving the carriage 18 toward the outer circumference (to the right), the deflection surface 21 of the deflection prism 20 and the center 22 of the objective lens 19 change according to the inclination angle θ of the carriage 18.

Now, FIG. 6 shows a state in which the carriage 18 has rotated inward. In the figure, the deflection surface 21 of the deflection prism 20 indicated by the - dotted chain line forms an angle of 45 degrees with respect to the incident optical axis 23. None, the center 22 of the objective lens 19 is parallel to the incident optical axis 23,
This is a state in which the carriage 18 is not tilted. In this state, the incident light is reflected at right angles at the incident optical axis deflection point P and is converged at point Q of the optical disc l. When the carriage 18 is tilted at an angle θ toward the inner circumferential side (left side) of the optical disc l, the tilt of the deflection surface 21 of the deflection prism 20 becomes 45 degrees -0, as shown by the solid line, and the center 22 of the objective lens 19 is aligned with the incident light. It is inclined by 0 minutes with respect to a line parallel to the axis 23. In this state, the incident light enters the objective lens 19 with a 20-minute shift, and is focused by the objective lens 19 on the Q' point of the optical disc 1. At this time, the angle of incidence on the optical disc 1 is α smaller than 90 degrees, and according to the law of reflection, the optical disc l is reflected with the same reflection angle as α, and this reflected light passes through the center 22 of the objective lens 19 and enters the deflection prism 20. Although it is bent by the deflection surface 21, there is a distance Δ between this reflected optical axis 24 and the incident optical axis 23.
An offset of X occurs. Therefore, as shown in FIG. 5, when the carriage 18 is tilted toward the inner circumference or the outer circumference of the optical disc 1, the direction of offset also changes depending on the direction of inclination. Typically, tracking detection is 0.03μm
, focusing detection must be performed with an accuracy of 0.1 μm, and therefore, the offset of the reflection optical axis 24 of the deflection prism 20 with respect to the incident optical axis 23 has a large effect on tracking detection, which requires high detection accuracy. There is.

Means for Solving the Problems A fixed optical system is provided that has a light source that emits a parallel light beam in the radial direction of an optical disk and a detector that detects information from the optical disk that is disposed on an optical axis parallel to the parallel light beam. ,
A deflection member that bends the parallel light beam from the light source at a substantially right angle and an objective lens disposed between the deflection member and the recording surface of the optical disk are mounted on a carriage that moves along the parallel light beam from the light source. In the optical pickup device, the distance from the deflection point of the incident optical axis of the deflection member to the center of the objective lens is defined as n1 with respect to the optical disc.
The focal length was set to approximately twice the focal length of the objective lens described above.

The amount of offset between the optical axis of incidence on the working deflection member and the optical axis of reflection from this deflection surface is determined by the distance from the deflection point of the incident optical axis of the a1 direction member to the center of the objective lens and the focal length of the objective lens with respect to the optical disc. Although it is proportional to the distance difference, by setting the distance from the incident optical axis deflection point of the deflection member to the center of the objective lens to approximately twice the focal length of the objective lens with respect to the optical disk, the distance difference can be approximated to zero. Therefore, even if the carriage is tilted, the amount of offset can be suppressed to a minute range.

Example An embodiment of the present invention will be described based on FIG.

The parts explained in FIGS. 2 to 6 are designated by the same reference numerals, and the explanation thereof will be omitted. As mentioned above, the incident optical axis 23 from the semiconductor laser 4 is aligned with the deflection surface 21 of the deflection prism 20.
However, in the present invention, the distance from the incident optical axis deflection point P of the deflection prism 20 to the center of the objective lens 19 is Q, and the distance between the incident optical axis deflection point P of the deflection prism 20 and the objective lens 19 is The focal length of the lens 19 was set as f, and Q=2f.

In such a configuration, as described with reference to FIG. 6, when the carriage 18 rotates at an angle θ about the X axis orthogonal to the theta direction S, the deflection prism 20 rotates in accordance with the inclination direction. The offset amount ΔX between the incident optical axis 23 and the reflected optical axis 24 of the deflection prism 20 is
When calculated geometrically, it is obtained by the following formula.

Δx#2(Q-2f)θ According to the present invention, by setting Q=2 f, substituting this into the above equation results in Δx=O.

Therefore, even if the carriage 18 is tilted at an angle of θ, the incident optical axis 23 and the reflected optical axis 24 in FIGS.
The optical axes of the two are aligned, allowing accurate tracking and detection.

The objective lens 19 has a principal point 25 on the opposite side close to the deflection prism 20 side and a principal point 26 on the rear side close to the optical disk l side, but the center 22 of the objective lens 19 referred to here is the front principal point It is the center passing through 25.

Furthermore, as mentioned above, the accuracy of tracking detection is 0.
Since it is within 0.3μm, if this range is satisfied,
It goes without saying that the condition of Q x 2 f is permissible.

Effects of the Invention As described above, in the present invention, the distance from the incident optical axis deflection point of the deflection member to the center of the objective lens is set to approximately twice the focal length of the objective lens with respect to the optical disc. The amount of offset between the incident optical axis and the reflected optical axis from this deflection surface is proportional to the distance difference between the distance from the incident optical axis deflection point of the deflection member to the center of the objective lens and the focal length of the objective lens with respect to the optical disk. However, by setting the distance from the incident optical axis deflection point of the deflection member to the center of the objective lens to be approximately twice the focal length of the objective lens with respect to the optical disk, the distance difference becomes an approximate value of zero, so that the carriage Even if it is tilted, the amount of offset can be suppressed to a minute range, which has the effect of allowing accurate tracking detection to be performed.

[Brief explanation of drawings]

FIG. 1 is a side view showing the arrangement relationship between an optical disk, an objective lens, and a deflection member according to an embodiment of the present invention, and FIGS. 2 to 6 show the prior art, and FIG. 2 shows the overall configuration. FIG. 3 is an explanatory diagram showing the focusing detection operation, FIG. 4 is an explanatory diagram showing the tracking detection operation, and FIG. 5 is an explanatory diagram showing the tracking detection operation.
The figure is a side view showing the deviation between the incident optical axis and the reflected optical axis due to the inclination of the carriage, and FIG. 6 is a side view showing the details of the optical path. DESCRIPTION OF SYMBOLS 1... Optical disk, 2... Fixed optical system, 4... Light source, 15.16... Detector, 18... Carriage, 1
9...Objective lens, 20...Deflection member, P...Incoming optical axis deflection point"1", 53 (3)

Claims (1)

[Claims] A fixed optical system having a light source that emits a parallel light beam in the radial direction of the optical disk and a detector that detects information from the optical disk arranged on an optical axis parallel to the parallel light beam is provided, and the parallel light beam from the light source is emitted by a fixed optical system. an optical pickup device comprising: a deflection member for bending a parallel light beam from the light source at a substantially right angle; and an objective lens disposed between the deflection member and the recording surface of the optical disk. An optical pickup device characterized in that the distance from the incident optical axis deflection point of the deflection member to the center of the objective lens is set to approximately twice the focal length of the objective lens with respect to the optical disc.