JPH01102740A - Optical pickup - Google Patents

Abstract

PURPOSE:To obtain the miniaturization and light weight of a device and to easily shorten an access time by providing first and second light split planes opened for a light source side at a beam splitter, splitting return light beam from a recording medium, making the split light beams incident on each detecting means, and performing at least focusing and tracking on them. CONSTITUTION:The first and second light split planes 32a and 32b opened for the light source side are provided at the beam splitter 32, and the return light beam from the recording medium 35 is split, and the split light beams are made incident on the detecting means 36 and 37, and at least the focusing and the tracking are performed on them. Therefore, it is possible to make a second beam splitter or a cylindrical lens unnecessary, and also, to reduce the thickness H of the beam splitter 32. In such a way, the miniaturization and the light weight of the device can be realized, and the access time can be shortened easily.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical pickup for an optical disk device such as a compact disk, a laser disk, an image file, a text file, etc.

(Background of the Invention) The first example of a conventionally used optical pickup is
As shown in the figure.

In FIG. 10(a), 1 is a laser diode that is a light source, 2 is a first beam splitter that divides the incident light beam into two, 3 is a collimator lens that converts the light beam from the first beam splitter 2 into a parallel light beam, Reference numeral 4 designates an objective lens that moves in the direction of the arrow mark during focusing and in the direction of the arrow (■) during tracking, and forms an image of the parallel light beam from the collimator lens 5 on the recording medium 5. 6 is a second beam splitter, 7' is a cylindrical lens that functions as a lens only in a single direction (up and down in the drawing), and 8 is a focus that receives the light flux from the cylindrical lens 7 and emits an electrical signal. 4 for error detection
A split light detector 9 receives the light beam from the second beam splitter and generates an electric signal to detect a track error. To move to the reading position, the entire optical pickup (indicated by a two-dot chain line) moves in the direction of the arrow ■.

It will be done.

In such a configuration, the light beam emitted from the laser diode 1 is transmitted through the first beam splitter 2, the collimator lens 3, and the collimator lens 3. An image is formed on the recording medium 5 via the objective lens 4.

The return light from the recording medium 5 is reflected by the first beam splitter 2 and enters the second beam splitter 6. Here, the light beam is divided into two directions, and one of the light beams passes through a cylindrical lens 7 and forms an image on a four-split photodetector 8 .

The other beam forms an image on the two-split photodetector 9.

Here, (b) shows an example of the beam spot on the 4-split photodetector 8 for focus error detection, and (C) shows an example of the beam spot on the 2-split photodetector 9 for tracking error detection.
). The track error signal, focus error signal, and information reproduction signal are expressed as follows using the outputs A to F at each division plane of each photodetector 8.9.

Track error signal: A-B Focus error signal: (C+E)-(D+F) Information reproduction signal: A+8 The above track error detection method is called the push-pull method, and the focus error detection method is called the astigmatism method. .

Next, a second example of a conventionally used optical pickup is shown in FIG.

In FIG. 11(a), 11 is a laser diode that is a light source, 12 is a beam splitter that divides the incident light beam into two, and 13 is a collimator lens that converts the light beam from the beam splitter 12 into a parallel light beam.

Reference numeral 14 denotes an objective lens that moves in the direction of the arrow (■) during focusing and in the direction of the arrow (■) during tracking, and forms an image of the parallel light beam from the collimator lens 13 on the recording medium 15. Reference numeral 16 designates a roof-shaped Foucault prism provided on the side surface of the beam splitter 12, and reference numerals 17 and 18 designate two-split photodetectors that receive the light beam from the Foucault prism 16 and emit electrical signals. The movement to the reading position is performed by moving the entire optical pickup (indicated by a two-dot chain line) in the direction of the arrow (■).

In such a configuration, the light beam emitted from the laser diode 11 is transmitted through the beam splitter 12, the collimator lens 13. An image is formed on the recording medium 15 via the objective lens 14. The return light from the recording medium 15 is transmitted to the beam splitter 1
2, and is split into two directions by the two-cob prism 16, one being a two-split photodetector 17 and the other being a two-split photodetector 1.
8.

Here, an example of the beam spot on the two-split photodetector 17 and 18 is shown in (b). The track error signal, focus error signal, and information reproduction signal are expressed as follows using the output G-J at each division plane of each photodetector 17 and 18.

Track error signal @: (G+H)-(1+J) Focus error signal: (H+I)-(G+J) Information reproduction signal: G1H+l+JThe above track error detection method is the push-pull method, and the focus error detection method is the Foucault method. being called.

Next, a third example of a conventionally used optical pickup is shown in FIG.

In FIG. 12<a>, 21 is a laser diode that is a light source, 22 is a beam splitter that divides an incident light beam into two, and 23 is a beam splitter that converts the light beam from the beam splitter 22 into a parallel light beam. The collimator lens 24 is an objective lens that moves in the direction of the arrow mark during focusing and in the direction of the arrow (■) during tracking, and forms an image of the parallel light beam from the collimator lens 23 on the recording medium 15. 26 is a three-split photodetector provided on the side of the beam splitter 22. The movement to the reading position H is performed by moving the entire optical pickup (indicated by a two-dot chain line) in the direction of the arrow (■).

In such a configuration, the light beam emitted from the radar diode 21 is transmitted through the beam splitter 22, the collimator lens 23, and the beam splitter 22. An image is formed on the recording medium 25 via the objective lens 24. The return light from the recording medium 25 is sent to the beam splitter 2
2 and is imaged on a 3-split photodetector 26.

Here, an example of the beam spot on the three-split photodetector 26 is shown in (b). Track error signal.

The focus error signal and information reproduction signal are sent to each photodetector 26.
Using -M for the output, it is expressed as follows.

Track error signal: -M Focus error signal: +M-L Information reproduction signal @: +L+M The track error detection method described above is called the push-pull method, and the focus error detection method is called the beam size method.

(Problems to be Solved by the Invention) In the first example of the optical pickup shown in FIG.
A second beam splitter 6 and a cylinder lens 7 are arranged between the first beam splitter 2 and each photodetector 8.9. Therefore, there is a problem that the optical pickup becomes seriously damaged, requires more space, and the optical pickup becomes larger. Furthermore, there is also the problem that the heavy weight hinders shortening of access time.

Furthermore, since there are many parts, there are also problems in that the number of assembly steps is also increased and the cost is high.

In the second example of the optical pickup shown in FIG.
Since the two-column prism 16 is arranged on the side of the beam splitter 12, the optical beam? There is a problem that each suspension of the quad becomes heavy. In addition, in order to apply independent beam spots to the two photodetectors 17 and 18, a beam splitter 1 is used.
2 and the photodetectors 17 and 18 must be sufficiently secured. Furthermore, if the two detection i17.1s are separated and arranged so that their positions can be adjusted independently, the distance! becomes even longer. Therefore, there is a problem that the optical pickup becomes large. Furthermore, the thickness h of the beam splitter 12 is determined as follows.

As shown in FIG. 13, when the return light from the objective lens 14 enters the beam splitter 12, the diameter of the return light on the beam splitter 12 is 81, the aperture angle of the return light is θ, and the light of the beam splitter 12 is The angle of the split plane with respect to the optical axis is α
, assuming that the refractive index of the beam splitter 12 with respect to air is 1, h - a / (tan α + tan θ'>
−・・■(Here n-5inθ/sin
θ') Also, the condition that all of the returned light reflected by the light splitting surface of the beam splitter 12 is directed toward the side surface of the beam splitter 12 is as follows.

π/4-θ'/2≦α≦π/4+θ'/2...■Here, let's find an example of h.

θ=π/12. When n -1,, 5, θ'-5 in θ-1 (sin (π/12)/n)
-■ α that minimizes h is α-π/4+θ'/2 .

In this way, h is thicker than H of the present invention, which will be described later, which poses a problem that seriously affects the optical pickup and impedes shortening of access time.

Also in the third example of the optical pickup shown in FIG.
The thickness h,' of the beam splitter 22 is also +1' = a / (tan α + tan θ') as in the second example.
...■, and the optical pickup became seriously ill.
There are problems that hinder shortening of access time.

The present invention has been made in view of the above-mentioned problems, and its objectives are to provide an optical pickup that is small, lightweight, easily shortens access time, has a small number of parts, reduces assembly man-hours, and is inexpensive. Our goal is to provide the following.

(Means for Solving the Problems) The present invention, which solves the above problems, forms an image of a light beam emitted from a light source onto a recording medium via a beam stabilizer and an objective lens, and returns the light beam from the recording medium. In an optical pickup that separates a light beam by the beam splitter and makes it incident on a photodetecting means for at least focusing and tracking, the beam splitter includes a first beam splitter that is open to the source side. The present invention is characterized in that a second light component v1 plane is provided to divide the returning light beam from the recording medium and make each of them incident on the detection means to perform at least focusing and tracking.

(Function) In the optical pickup of the present invention, the returning light beam from the recording medium is transmitted to the first. The second light splitting surface splits the light beam into two directions, and each of the split light beams enters a light detection means, where at least focusing and tracking are performed.

(Example) Next, a first embodiment of the present invention will be described using the drawings.

In FIG. 1(a) showing the first embodiment, 31 is a laser diode which is a light source, and 32 is a beam splitter. The beam splitter 32 has three beam splitters as shown in FIG.
The first light splitting surface 32 is made up of two prisms having the same refractive index bonded together, and is open to the laser diode 31 side.
a and a second light splitting surface 32b. 33 is a collimator lens that converts the light beam from the beam splitter 32 into a parallel light beam; 34 moves in the direction of the arrow during focusing and in the direction of the arrow ■ during tracking; This is an objective lens that forms an image. 36 and 37 are the first . This is a second two-split photodetector. The movement to the reading position is performed by moving the entire optical pickup (indicated by the two-point tA line) in the direction of the arrow {circle around (2)}.

In such a configuration, the light beam emitted from the laser diode 31 is transmitted through a beam splitter 32, a collimator lens 33, and a collimator lens 33. An image is formed on an optical disk 35 via an objective lens 34. The return light from the optical disk 35 is transmitted to the first . By the second light splitting surfaces 32a and 32b,
It is divided into a first two-split photodetector 36 direction and a second two-split photodetector 37 direction. One beam of the divided pickpocket light is sent to the first two-split photodetector 36, and the other beam is sent to the second split light detector 36.
The image is formed on a two-split photodetector 37.

This embodiment is suitable for cases in which a convex or concave bit is provided on a recording medium such as a CD (compact disc) and an information recording signal is created using light diffraction development, or when a reversible phase change between crystal and amorphous is performed. This method is suitable for recording information recording signals by using a recording medium made of an optical recording material and providing bits with different optical reflectances on the recording medium.

Here, examples of beam spots on the two-split photodetector 36 and 37 are shown in (b) and (c). The track error signal, focus error signal, and information reproduction signal are expressed as follows using the outputs 0-R of the respective division planes of the photodetectors 37 and 38.

Track error signal: (0+P) - (Q+R) Focus error signal: (P+R) - (0+Q) Information reproduction signal: O+P+Q+R According to the above configuration, the following effects can be obtained.

(1) Comparison with the first example of the conventional optical pickup shown in FIG. 10 ■ The second beam splitter 6 is not required, making it possible to reduce the size and weight.

(2) Comparison with the second example of the conventional optical pickup shown in FIG. 11 ■ Find the thickness H of the beam splitter 32 of this real part example.

In FIG. 3, the diameter of the returning light on the beam splitter 32 is 81, the aperture angle of the returning light is θ, and the first . The angle of the second light splitting planes 32a, 32b with respect to the optical axis! If α is good and n is the refractive index of the beam splitter 32 with respect to air, then 1''=a/(2(tan a+tanθ'))−・
・Compared with the formula ■ (where n = 5 in θ7s + nθ'), the equation becomes 1-1-h/2...■, and therefore, it is possible to reduce the size and weight.

■If the image is formed on or near the side surfaces 81 and 82 of the beam splitter 32, the side surface S of the beam splitter 32! , 32 and the two-split photodetector 36, 37 can be shortened, allowing for miniaturization.

(3) Comparison with the third example of the conventional optical pickup shown in Fig. 12■ Same as the first example, H-h'/2 ... ■■ Therefore, it is possible to reduce the size and weight. .

Furthermore, if the beam splitter 32 is designed so that the angle of emission from the side surface Sz, 82 is large, the focus sensitivity will be improved.

Next, a second embodiment will be explained. This example is an optical pickup used in magneto-optical recording that utilizes the property that when a magnetic material is irradiated with linearly polarized light, the polarization plane of the transmitted light or reflected light rotates, and the direction of rotation is reversed depending on the direction of magnetization of the magnetic material. suitable for

In FIG. 4 showing the second embodiment, 41 is a laser diode which is a light source, and 42 is a beam splitter. As in the first embodiment, the beam splitter 42 is constructed by pasting together three prisms with the same refractive index, and has a first light splitting surface 42a open to the laser diode 41 side and a second light splitting surface 42a. 91 plane 42b is provided. A half-wave plate 43 is disposed between the beam splitter 42 and the laser diode 41. 44 is a beam splitter 42
A collimator lens 45 is an object that moves in the direction of the arrow during focusing and in the direction of the arrow (■) during tracking, and forms an image of the parallel light from the collimator lens 44 on an optical disk 46 which is a recording medium. It's a lens. 47 and 48 have polarization planes that are perpendicular to each other and are disposed on the side surfaces Sx and 84 of the beam splitter 42, respectively; 49 and 50 are first polarization elements disposed on the 47° and 48 sides of the polarizing elements, respectively; ．． This is a second two-split photodetector. Therefore, movement to the reading position is performed by moving the entire optical pickup (indicated by a two-dot chain line) in the direction of the arrow {circle around (2)}.

In such a configuration, the light beam emitted from the laser diode 41 has its deflection plane adjusted by the half-wave plate 43, and the beam splitter 42. Collimator lens 44. The image is formed on an optical disk 46 through an objective lens 45.

The returning light from the optical disk 46 is transmitted to the first . The second light splitting surfaces 42a and 42b allow the first two
It is divided into a split photodetector 49 direction and a second two-split photodetector 50 direction. One of the divided return beams passes through a polarizing element 47 and forms an image on a two-split photodetector 49 .

The other beam passes through the polarizing element 48 and forms an image on the two-split photodetector 50.

Here, the reproduction principle of magneto-optical recording will be briefly described using FIG. For example, binary information is written on the optical disk 46, with upward magnetization corresponding to information 11111 and downward magnetization corresponding to information P0''. In FIG. Polarized light, R, is reflected polarized light. The reflected polarized light R is a light whose azimuth angle is tilted by θK (Kerr rotation angle) than the input light. The θ angle changes to positive or negative depending on the direction of magnetization. Therefore, if the polarizing element 47 (or 48) is installed at an angle of θ from the extinction angle of the incident polarized light, the light focused on the two-split photodetector 49 (or 50) will become arrow A or arrow B in the figure. This causes a change in intensity.

Next, an example of the beam spot on the two-split photodetector 49.50 is shown in FIGS. 4(b) and 4(C).

track error signal, focus error signal,
The information reproduction signal is expressed as follows using the outputs S to {circle around (2)} at each division plane of the photodetector 49 and 50.

Track error signal: S/T-U/V focus error signal: (T+V)-(S+U) information reproduction signal
: (S+T)-(U+V) An example of a circuit in this case is shown in FIG. In this figure, 608-60d are
Photodetector/19. The first stage amplifier converts the current generated on each side of 50 into voltage, 618 to 61d are adding amplifiers, 6
28 to 62d are log amplifiers, and 63a to 63d are differential amplifiers.

Alternatively, the track error signal may be (S+T)-(U+V). In this case, the detection method is the same as that for the information reproduction signal, but since the frequency band of the track error signal is usually two or more orders of magnitude lower than that of the information reproduction signal, the two can be separated by passing the signal through a filter circuit.

According to the above configuration, 1q of effects similar to those of the first embodiment can be obtained. Also, the polarization plane of the light returning from the half-wave plate 43 is the deflection element 4.
Approximately 45° with respect to the deflection plane of 7.48 (θ→ in Fig. 5)
If adjusted so that it becomes 45°, #θ is a small angle),
The reproduced signal due to the Kerr effect can be maximized.

Also, in this second embodiment, the beam splitter 42
is used as a polarizing beam splitter, and most of the polarized components of the returned light from the optical disk 46 accompanied by Kerr rotation, and the components perpendicular to the polarization direction of the incident light, are reflected by the polarizing plane of the polarizing beam splitter. Then, C of the information reproduction signal
/N improves. (For example, if a polarizing beam splitter is
The polarized light is set to transmit 0% A, and the S polarized light 0%. In this way, only 30% of the return light from the optical disk 46 is the PI light component that is not involved in Kerr rotation.
9.8 which is not suitable for 50, but is involved in car rotation! The light component will be 100% directed. ) Next, the first. second fruit 7
The angle β formed by each light component tl of the beam splitter 32 and 42 at i1J is determined.

Although the first embodiment will be explained here, the second embodiment is also similar.

(1) The angle of the returned light near the optical axis with respect to the optical axis is always approximately O°, regardless of whether the returned light is convergent light or parallel light. Therefore, when β≧90'', the light ray near the optical axis is reflected by the light splitting surfaces 32a and 32b and then hits the surface SO of the beam splitter 32 on the objective lens 34 side, where it undergoes total reflection and the light ray becomes a light beam. Detector 36
．． There is a possibility that it will be incident on 37. Therefore, by setting β to 90°, such total reflection at the surface S can be prevented.

(2) If β<90't', light splitting plane 328.32b
The beam split by the side surface 31 of the beam splitter 32
．． Go in direction 82. Therefore, if the angle of incidence on the side surface S+, 82 is less than the critical angle, the ray will be transmitted to the side surface Ss, 82
The light is not totally reflected by the light beam and travels toward the photodetectors 36 and 37.

Note that the present invention is not limited to the above embodiments.

For example, as shown in FIG. 7, a beam splitter 72 having light splitting surfaces 72a and 72b may be provided between a collimator 73 and an objective lens 74.

In this case, the angle β between the light splitting surfaces 72a and 72b is 90
If it is less than "2", after passing through the collimator lens 73,
Almost none of the light reflected by the two light splitting surfaces 72a- and 72b returns to the laser diode 31, and there is no fear of causing resonance within the laser diode 31.

(If β-90', the reflected light returns to the laser diode 31, so a λ/4 plate or the like must be provided to prevent this.) Also, if β is made as small as possible, the side surface S1 of the beam splitter 72, The output angle in S2 becomes larger, and focus sensitivity improves.

The present invention can also be applied to an optical pickup provided with a triangular anamorphic prism 75 to correct the anisotropy of the light beam from the laser diode 31 as shown in FIG. 8, and as shown in FIG. - In order to reduce the size of the layer, a collimator lens is not used, and the objective lens 8 with a finite specification is used.
The present invention can also be applied to an optical pickup using 4.

Furthermore, although the above embodiments have been explained using an optical pickup for reproducing information, it goes without saying that the present invention can also be applied to an optical pickup for recording and erasing information.

(Effects of the Invention) As explained above, according to the present invention, one beam splitter has a first beam splitter. By providing the second light splitting surface,
It is small and lightweight, making it easy to shorten access time, have fewer parts, reduce assembly man-hours, and realize a low-cost optical pickup.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment of the present invention, and FIG. 2 is a diagram showing a first embodiment of the present invention.
3 is an explanatory diagram for determining the thickness of the beam splitter in FIG. 1, FIG. 4 is a diagram showing the second embodiment of the present invention, and FIG. 6 is a circuit diagram to which the outputs S to V in FIG. 4 are input, FIG. 7 is a diagram showing another embodiment, and FIG. 8 is a diagram showing another embodiment. 9 is a diagram showing another embodiment, FIG. 10 is a diagram showing a first example of a conventionally used optical pickup, and FIG. 11 is a diagram showing a second example of a conventionally used optical pickup. Figure showing an example, 1st
FIG. 2 is a diagram showing a third example of a conventionally used optical pickup, and FIG. 13 is an explanatory diagram for determining the thickness of the beam splitter at d5 in FIG. 11. 1.11, 21.31.41... Laser diode 2.6, 12.22, 32.42.72... Beam splitter 32a, 32b, 42a, 42b, 72a. 72b... Light splitting surface 3.13.23.44.73... Collimator lens 4.14.24.34.45, 74.84... Objective lens 5.15.25... Recording medium 35 .46...Optical disc 8...4-split photodetector 9.17.18, 36.37.49.50...2-split photodetector 26...3-split photodetector Patent applicant Roku Konishi Photographic Industry Co., Ltd. Agent Patent Attorney Fuji Ijima 1 person Figure 2 Negative tower 4 Figure 7 Figure 8 Corner 411 Figure 4-11 ÷■ Negyo 12 Figure -1-■ Figure 13

Claims (2)

[Claims] (1) A light beam emitted from a light source is imaged on a recording medium via a beam splitter and an objective lens, and a return light beam from the recording medium is separated by the beam splitter and made incident on a photodetecting means, at least for focusing. , in an optical pickup that performs tracking, the beam splitter is provided with first and second light splitting surfaces that are open to the light source side;
An optical pickup characterized in that the returning light beam from the recording medium is divided and each part is made incident on the detection means to perform at least focusing and tracking. (2) The optical pickup according to claim 1, wherein the angle formed by the first and second light splitting planes is less than 90°.