JPH0721581A - Optical pickup - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce the size, cost and thickness of an optical pickup in which an optical element is arranged on the surface of a light-transmitting block and integrated. A semiconductor laser 22, photodetectors 23 and 24, and an objective lens 25 are arranged on the surface of a light transmissive block 21, and a light propagation path of a substantially straight line is formed inside the light transmissive block 21 in the longitudinal direction. The light reflecting surfaces 28, 29 or the light branching surfaces 26, 27 are provided at positions facing the optical elements 22, 23, 24, 25 in the propagation path.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup for reading information, for example, by focusing a laser beam on a fine spot light and irradiating it onto a disk or the like, and detecting the reflected light. The present invention relates to an optical integrated pickup for a compact disc.

[0002]

2. Description of the Related Art In general, an optical pickup for reading signal information recorded on an optical disc such as a compact disc is equipped with a focus / tracking servo function. The servo function is for accurately causing the optical pickup to follow mechanical fluctuations such as surface wobbling and eccentricity due to rotation of the optical disc.

FIG. 8 is a block diagram of a conventional optical pickup. The configuration will be described below together with the operation. A semiconductor laser 2 is mounted as a light source arranged below the optical disc 1. The light beam emitted from the semiconductor laser 2 passes through a diffraction grating 3 for generating three beams, a beam splitter 4, a collimator lens 5, and an objective lens 6,
It is focused on the optical disc 1. The light beam reflected by the optical disc 1 passes through the objective lens 6 and the collimator lens 5, the light path is deflected by 90 ° by the beam splitter 4, and then passes through the concave lens 7 and the cylindrical lens 8 to the multi-segment photodetector 9. The light enters and is photo-detected by the multi-division photo detector 9. A reproduction signal, a focus error signal, and a tracking error signal are obtained from this detection signal.
Detection of these error signals is performed using the astigmatism method.

The objective lens 6 is built in the actuator and is moved at high speed in the optical axis direction and in the direction perpendicular to the track in accordance with the error signal. These are called focus / tracking servos.

[0005]

However, the conventional optical pickup shown in FIG. 8 has a large number of optical components constituting eight points and each of them is an individual component, so that the optical axes of these components can be accurately adjusted. Need to be fixed.
Therefore, a large number of man-hours are required for manufacturing, and there is a limit in achieving downsizing and cost reduction.

By the way, an optical pickup shown in FIG. 9 has been developed as an optical pickup for solving the above-mentioned drawbacks of the optical pickup. This is JP 61
The optical head device disclosed in Japanese Patent Publication No. 296540. The optical head device is called an optical waveguide type pickup and focuses a light beam emitted from a semiconductor laser 2 on an optical disc 1 through an optical waveguide formed inside a transparent substrate 10 having a plate shape. Take a schematic configuration. In the figure, 4 is a beam splitter, 11 is a photodetector, and 12 is a converging grating coupler.

However, since the optical head device has a very thin optical waveguide of less than 1 micron,
At present, there is a limit to efficiently couple the light beam from the semiconductor laser 2 to the optical waveguide.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical pickup which can be reduced in size, price, and thickness.

[0009]

In the optical pickup of the present invention, optical elements such as a light emitting element, a light receiving element and an objective lens are arranged on the surface of a light transmissive block, and the inside of the light transmissive block is elongated in the longitudinal direction. And a light-reflecting surface or a light-branching surface corresponding to each of the optical elements is provided so as to intersect the propagation path.

In the optical pickup according to claim 1,
The light transmissive block is provided with a plurality of block parts each having a light reflecting surface or a light branching surface provided on a desired surface, and the block parts are bonded to each other and integrated. .

The optical pickup according to claim 2,
The light transmissive block includes a trapezoidal first block component and a single or a plurality of diamond-shaped second block components.
At least one surface of the light-transmissive block is bonded to form the same surface, the light-branching surface is formed between adjacent block components, and the light-transmissive block is opposed to the light-branching surface. The light-reflecting surface is formed on at least one surface of the.

The optical pickup according to claim 1, 2 or 3 is characterized in that at least the light emitting element and the light receiving element are integrated on a compound semiconductor substrate.

[0013]

According to the above structure, the optical pickup according to the first aspect is a structure in which the optical elements such as the light emitting element, the light receiving element, and the objective lens are integrally mounted on the surface of the light transmitting block, so that the optical pickup is small in size. And the price can be reduced. Further, since the light emitted from the light emitting element propagates inside the light transmissive block in a substantially straight line in the longitudinal direction, the thickness can be reduced and the thickness can be reduced.

Further, in the optical pickup according to the second or third aspect, the light branching surface can be formed on the plane of the desired block component, and the light branching surface can be easily manufactured.

Further, in the optical pickup according to the fourth aspect, since at least the light emitting element and the light receiving element are integrated on the compound semiconductor substrate, the alignment accuracy and mass productivity can be improved.

[0016]

1 is a perspective view showing an embodiment of the present invention.

In the optical pickup of this embodiment, a semiconductor laser 22, two photodetectors 23 and 24, and an objective lens 25 are arranged on the same surface of a light transmissive block 21 made of resin or glass. Permeable block 2
The inside of 1 is a light propagation path (not shown) that is substantially linear in the longitudinal direction. Optical branching surfaces 26 and 27 are provided at positions corresponding to the semiconductor laser 22 and the photodetector 24 so as to cross the propagation path, and further correspond to the photodetector 23 and the objective lens 25. Light reflection surface 2 at the position
8, 29 are provided.

The light-transmitting block 21 comprises a first block part 21a having a trapezoidal shape in front view and two second block parts 21b, 21c having a rhombus shape in front view. That is, a pair of parallel planes are used as upper and lower planes and tilted in the opposite direction.
A relatively large first block part 21a having one 5 ° inclined surface facing each other and a pair of parallel planes as upper and lower surfaces, and two relatively small 45 ° inclined surfaces inclined in the same direction. The second block parts 21b and 21c are used.

These three block parts 21a, 21b,
The parts 21c are bonded to each other at their 45 ° inclined surfaces, and are integrated so that the propagation paths can be branched by the optical branching surfaces 26, 27 formed on one of the 45 ° inclined surfaces that overlap each other in advance. Light reflection surfaces 28 and 29 are formed on the remaining two 45-degree inclined surfaces so that the propagation path can be deflected by 90 degrees. The light branching surfaces 26 and 27 are formed of a light branching thin film (for example, a dielectric multi-layer film coating), and reflect a part of light and transmit the remaining light. The light reflecting surfaces 28 and 29 are formed of a light reflecting film. In this example,
The light splitting surfaces 26 and 27 are for deflecting a part of light by 90 degrees.

As shown in FIG. 1, the light-transmissive block 21 thus bonded together has a first light-reflecting surface 28, a first light-branching surface 26, and a second light-reflective surface 28 that are inclined from the left to the left. The diverging surface 27 and the second light reflecting surface 29 inclined to the upper right are arranged, and the light transmissive block 21 is a flat surface whose upper surface and lower surface are parallel to each other even after being bonded.

Further, in this embodiment, the semiconductor laser 22,
The photodetectors 23 and 24 are integrated on a substrate 30 in a hybrid or monolithic manner. As the substrate 30, a compound semiconductor substrate is used.

The semiconductor laser 22 and the first photodetector 2
3 and the second photodetector 24 respectively include a first light splitting surface 26 and a first light reflecting surface 2 in the light transmissive block 21.
8 and the second light splitting surface 27. The objective lens 25 is formed of, for example, an aspherical objective lens, and is arranged at a position facing the second light reflecting surface 29.

With the above structure, the optical system of the optical pickup is integrated into a small size. In this embodiment, since the detection method is one beam, which will be described later, a diffraction grating for generating three beams is unnecessary.

The operating principle of this optical system will be described below. The light beam from the semiconductor laser 22 enters the light transmissive block 21, hits the first light splitting surface 26, and
It is deflected by 0 degrees. After that, the light beam travels in parallel with the upper and lower surfaces of the light transmitting block 21 and passes through the second light branching surface 27 as it is, and reaches the second light reflecting surface 29, where the 90 ° optical path is deflected again. The light beam emitted from the upper surface of the light transmissive block 21 is emitted from the objective lens 25 and focused on the optical disc 31. The light beam reflected from the optical disk 31 passes through the objective lens 25, enters the light transmissive block 21, is deflected 90 degrees by the second light reflecting surface 29, and is parallel to the upper and lower surfaces of the light transmissive block 21. The light propagates and reaches the second light branching surface 27, the first light branching surface 26, and the first light reflecting surface 28 in this order. Here, the second light splitting surface 27,
The light beams branched or reflected by the first light reflecting surface 28 in the direction perpendicular to the upper and lower surfaces of the light transmissive block 21 are emitted from the upper surface of the light transmissive block 21 and then, respectively, the second light detector 24, incident on the first photodetector 23, the optical disk 3
The reproduction signal of the information on 1 and the focus / tracking error signal are detected. Since the optical system is integrated as described above, the entire optical system is moved by the actuator according to the detected focus / tracking error signal, and servo is applied.

According to the above structure, the optical pickup of the present invention has a structure in which the semiconductor laser 22, the photodetectors 23 and 24, and the objective lens 25 are integrally mounted on the surface of the light transmitting block 21. The size can be reduced and the price can be reduced.

Further, since the light emitted from the semiconductor laser 22 propagates inside the light transmissive block 21 in a substantially straight line in the longitudinal direction, the thickness of the light transmissive block 21 can be made thin and thin. Can be achieved.

The light-transmitting block 21 has a first
Block component 21a and second block components 21b, 2
Since it is configured by 1c, the light splitting surfaces 26 and 27 are arranged on the plane of a desired block component (for example, the second block component 2).
It is possible to form the optical branching surfaces 26 and 27 with ease, since it can be formed at a position which becomes a propagation path with the 45 ° inclined surface of 1b).

Further, since the semiconductor laser 22 and the photodetectors 23 and 24 are integrated on the compound semiconductor substrate 30, the positioning accuracy and mass productivity can be improved. The focus / tracking detection method adopted in the above embodiment will be described below with reference to FIGS.

FIG. 2 is a diagram for explaining the focus error signal detection, FIG. 2A is a side sectional view of the optical pickup, and FIG. 2B and FIG. It is a top view of the A part and B part of a). FIG. 3 is also a diagram for explaining the focus error signal detection, FIG. 3A is a side sectional view of the optical pickup, and FIG. 3B and FIG. 3C are respectively the same FIG. 3 is a top view of a C portion and a D portion of FIG. FIG. 4 is also a diagram for explaining the focus error signal detection, FIG. 4A is a side sectional view of the optical pickup, and FIG. 4B and FIG. FIG. 7 is a top view of an E portion and an F portion of FIG. FIG. 5 is a diagram for explaining the tracking error signal detection, FIG. 5A is a side sectional view of the optical pickup, and FIG. 5B and FIG. It is a G part and a H part top view. 6 and 7
3A and 3B are views for explaining tracking error signal detection, respectively. FIG. 4A is a top view of the photodetector 23, and FIG. 3B is a top view of the photodetector 24.

The distance between the first light reflecting surface 28 and the first light branching surface 26 in the light transmitting block 21 and the distance between the first light branching surface 26 and the second light branching surface 27 are defined as follows. At equal intervals, the light beam incident on the first photodetector 23 via the first light reflecting surface 28 and the second light branching surface 27 are branched by being reflected by the second light branching surface 27. The light beams incident on the light beams are defocused in the opposite directions by the same optical path length from the position where the reflected beam returning to the optical pickup has just focused on the disc 31. The detectors 23 and 24 are hit, and the light beam size becomes the same. As the photodetectors 23 and 24, four-divided detectors are arranged at the first photodetector position and the second photodetector position, respectively. The four-division detector has three division lines that are parallel to each other, two inner segments are small, and two outer segments are large.

Next, the principle of detecting in-focus and out-of-focus for applying focus servo will be described with reference to FIGS. 2 to 4, the light beam is reflected from the disk and is incident on the detector, and at the same time, the shapes of the light spots irradiated on the respective photodetectors are shown together for easy understanding. . First, at the in-focus position as shown in FIG. 2, as shown in FIG. 2A, the light beam reflected from the optical disk 31 has the first and second light beams as shown in FIGS. The light spots 32 and 33 having the same size are irradiated onto the photodetectors 23 and 24, and at this time, among the four segments a, b, c and d of the first photodetector 23, the inner segment b, The total light amount Vb + Vc received by c is the same as the total light amount Va + Vd received by the outer segments a and d, and the inner segment f of the four segments e, f, g, and h of the second photodetector 24 is the same. , G is the same as the total amount of light received by the outer segments e and h, that is, (Va + Vg).
Vd) + (Vf + Vg) = (Vb + Vc) + (Ve + V
h). However, as shown in FIG. 3A, as the optical disc 31 shifts from the in-focus state and moves away from the objective lens 25, the spot 32 on the first photodetector 23 increases as shown in FIG. 3B. Therefore, the total amount of light Vb + Vc incident on the two inner segments of the first photodetector 23 decreases, and the outer segments a and d decrease.
The total amount of light Va and Vd received at is reduced. Also, FIG.
As shown in (c), the light spot 33 on the second photodetector 24
On the contrary, it becomes smaller because of the
The total light amount Vf + Vg received by the inner segments f, g among the one segment e, f, g, h increases, and the total light amount Ve + Vh received by the outer segments e, h decreases. As a result, (Va + Vd) + (Vf + Vg)>
(Vb + Vc) + (Ve + Vh). On the other hand, FIG.
As shown in (a), as the optical disc 31 moves out of focus and approaches the objective lens 25, the first photodetector 2
The light spot 32 on 3 becomes smaller, so that the total amount of light incident on the two inner segments of the first photodetector 23, Vb + Vc, increases and the outer segments a, d.
The total amount of light received at, Va + Vd, decreases. Also, the second
On the contrary, the light spot 33 on the photodetector 24 becomes larger,
To this end, the four segments e of the second photodetector 24,
The total light amount Vf + Vg received by the inner segments f and g among f, g, and h decreases, and the total light amount Ve + Vh received by the outer segments e and h increases. as a result,
(Va + Vd) + (Vf + Vg) <(Vb + Vc) +
(Ve + Vh). Therefore, when the optical disk 31 is displaced from the in-focus position due to surface wobbling, the output V
= {(Va + Vd) + (Vf + Vg)}-{(Vb + V
c) + (Ve + Vh)} produces an output for focus servo having a sign corresponding to the direction of the surface wobbling.

Next, the principle of detecting the track position for applying the tracking servo will be described with reference to FIGS. When the light beam is reflected from the optical disc 31 and is incident on the photodetectors 23 and 24, at the same time as the 0th-order diffracted light which is the reflected light, the ± 1st-order diffracted light is simultaneously generated due to the unevenness of the pits on the optical disc 31. First and second photodetector 2
The light spots 32 and 33 irradiated onto the light beams 3 and 24 have an intensity of only the 0th-order diffracted light that is the reflected light and the intensity in which the 0th-order diffracted light that is the reflected light and the 1st-order or −third-order diffracted light are superimposed. There is a part. In FIGS. 4 to 7, the portions of the first and second photodetectors 23 and 24 where the diffracted light is superimposed are hatched. First, as shown in FIG. 5A, when a spot is irradiated at an accurate position on the track, the portion where the diffracted light of the light beam reflected from the optical disc 31 is superposed is symmetrically divided into four parts. It is incident on the detector. That is, as shown in FIGS. 5B and 5C, the four segments a, b, and
The total amount of light Va + Vb received by the segments a and b on one side of c and d is the same as the total amount of light Vc + Vd received by the segments c and d on the other side, and the second photodetector 24 also has four segments e. , F, g, h, the total amount of light received by the segments e, f on one side Ve + V
The total light amount V received by f and the other segments g and h
g + Vh becomes the same. As a result, (Va + Vb) + (V
g + Vh) = (Vc + Vd) + (Ve + Vf).
However, when a spot is projected off from one of the accurate positions on the track, the portion where the diffracted light of the light beam reflected from the optical disc 31 is superposed is asymmetrical and the light is reflected by one of the two portions. It is incident on the split detector. That is, like the two examples shown in FIGS. 6 and 7, the four segments a of the first photodetector 23,
Of the b, c and d, the total amount of light received by the segments a and b on one side, Va + Vb, and the total amount of light received on the segments c and d on the other side, Vc + Vd, are not equal, and FIG.
Then, (Va + Vb) <(Vc + Vd), and in FIG. 7A, (Va + Vb)> (Vc + Vd). The second photodetector 24 also has four segments e, f, g,
The total amount V of light received by the segments e and f on one side of h
e + Vf and the total amount of light received by the segments g and h on the other side Vg + Vh are not equal to each other, and in FIG.
e + Vf)> (Vg + Vh), and in FIG. 7B, (Ve +
Vf) <(Vg + Vh). As a result, in FIG. 6, (Va + Vb) + (Vg + Vh) <(Vc + Vd) +
(Ve + Vf), (Va + Vb) + (Vg + V in FIG. 7
h)> (Vc + Vd) + (Ve + Vf), and an output for tracking servo having a code corresponding to the direction of the position shift is generated according to the relationship between the track position on the optical disc 31 and the focused spot position irradiated. .

By feeding back the focus position detection signal and the track position detection signal thus obtained to each servo coil and applying each focus / tracking servo, stable information reproduction becomes possible.

The optical pickup of the present invention is not limited to the above embodiment, but an optical element is integrated on the surface of the light transmissive block 21, and the inside of the light transmissive block 21 is formed in a substantially straight line shape. Any may be used as a light propagation path, and a light branching surface or a light reflecting surface corresponding to each of the optical elements is provided so as to intersect with the light propagation path.

For example, a vertical optical pickup can be obtained by forming the light reflecting surface 29 of the above-described embodiment at a right angle without forming a 45-degree inclined surface and providing the objective lens 25 on the side surface. Further, the semiconductor laser 22 and the photodetectors 23 and 24 may be individually manufactured and attached. Further, the light-transmissive block 21 may be a single block component, and the light branching surfaces 26, 27 may be formed in a desired location by, for example, a laser beam, ultraviolet light, infrared light, or the like.

[0036]

As described above, according to the optical pickup according to the first aspect of the present invention, since the optical element is integrated with the light transmissive block, the size and cost can be reduced. Further, since the inside of the light transmissive block is configured as a substantially linear propagation path, it is possible to reduce the thickness.

According to the pickup of the second or third aspect, the light branching surface can be easily manufactured.

Further, according to the pickup of the fourth aspect, it is possible to improve the positioning accuracy and mass productivity.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention.

FIG. 2 is a diagram for explaining focus error signal detection, and FIG. 2A is a side sectional view of an optical pickup;
Figures (b) and (c) show the parts A and B in Figure (a), respectively.
FIG.

3A and 3B are diagrams for explaining focus error signal detection, FIG. 3A is a side sectional view of an optical pickup, and FIGS. 3B and 3C are each a portion C of FIG. 3A. FIG. 6 is a top view of a D part.

FIG. 4 is a diagram for explaining focus error signal detection, FIG. 4A is a side sectional view of an optical pickup, and FIGS. 4B and 4C are each a portion E of FIG. 4A. It is a F part top view.

5A and 5B are views for explaining detection of a tracking error signal, FIG. 5A is a side sectional view of an optical pickup, and FIGS. 5B and 5C are a G portion and a portion in FIG. 5A, respectively. It is a H part top view.

FIG. 6 is a diagram for explaining tracking error signal detection, and FIGS. 6A and 6B are top views of respective photodetectors.

FIG. 7 is also a diagram for explaining tracking error signal detection, and FIGS. 7A and 7B are top views of respective photodetectors.

FIG. 8 is a side view showing a conventional example.

FIG. 9 is a perspective view showing another conventional example.

[Explanation of symbols]

 21 Light Transmitting Block 22 Semiconductor Laser (Light Emitting Element) 23, 24 Photo Detector (Light Sensing Element) 25 Objective Lens 26, 27 Light Splitting Surface 28, 29 Light Reflecting Surface

Claims (4)

[Claims] 1. A light emitting device on the surface of a light transmissive block,
A light receiving element and an optical element such as an objective lens are arranged, and the inside of the light transmissive block is used as a substantially linear light propagation path in the longitudinal direction, and light reflection corresponding to each of the optical elements intersects with the carrying path. An optical pickup having a surface or an optical branching surface. 2. The light-transmissive block comprises a plurality of block parts each having a light-reflecting surface or a light-branching surface on a desired surface, and the block parts are bonded to each other and integrated. The optical pickup according to claim 1. 3. The light transmissive block has a first trapezoidal shape.
A block component and a single or a plurality of diamond-shaped second block components are adhered to each other so that at least one surface of the light-transmitting block forms the same plane, and between the adjacent block components. The optical pickup according to claim 2, wherein a light branching surface is formed, and the light reflecting surface is formed on at least one surface of the light transmitting block facing the light branching surface. 4. The optical pickup according to claim 1, wherein at least the light emitting element and the light receiving element are integrated on a compound semiconductor substrate.