JP2000021012A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup device having a light source unit, capable of preventing entry of any stray light to a signal reproducing light receiving element. SOLUTION: The light source unit 10 of an optical pickup device incorporates a semiconductor laser 2 and a signal reproducing light receiving element 3 in its package 20. A package lid plate 22 as a constituting element of the package 20 includes a light shielding projection 60 formed between the semiconductor laser 2 and the signal reproducing light receiving element 3. By this light shielding projection 60, among forward and backward laser light emitted from the semiconductor laser 2, a light (stray light) not used as effective luminous flux is cut off. Thus, entry of the stray light to the signal reproducing light receiving element 3 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device provided with a light source unit having a configuration in which a semiconductor laser and a light receiving element are incorporated in a common package.

[0002]

2. Description of the Related Art An optical pickup device used for recording / reproducing an optical disk such as a CD, DVD, MO, etc.
2. Description of the Related Art There is known a light source unit having a light source unit in which optical elements such as a semiconductor laser, a light receiving element, and a hologram element are incorporated in a package. Such an optical pickup device is disclosed, for example, in Japanese Patent Application Laid-Open No. 3-278330.

In an optical pickup device disclosed in Japanese Patent Application Laid-Open No. 3-278330, a hologram element and an objective lens are arranged in this order from a semiconductor laser toward an optical disk. Further, an objective lens, a hologram element, and a reflection mirror are arranged in this order from the optical disk toward the light receiving element (for signal reproduction).

In this optical pickup device, a semiconductor laser is mounted on a semiconductor substrate fixed to a heat sink, and these are integrated as a light source unit. In this light source unit, a sub heat sink is mounted on a semiconductor substrate, a semiconductor laser is mounted on the upper surface, and a laser beam is emitted in a direction parallel to the substrate surface of the semiconductor substrate.
A light receiving element (for signal reproduction) is formed behind the semiconductor laser on the substrate surface of the semiconductor substrate, and a reflection mirror is arranged above the light receiving element. In addition to the light receiving element for signal reproduction, a monitoring light receiving element for feedback-controlling the laser light output of the semiconductor laser is formed behind the semiconductor laser.

[0005] In this optical pickup device, laser light (forward laser light) emitted from the front emission end face of the semiconductor laser is transmitted through the hologram element and then focused on the optical disk via the objective lens. The return light from the optical disc is diffracted by the hologram element, then falls by the reflection mirror, and is guided to the light receiving element for signal reproduction.
Signal reproduction, tracking error detection and focus error detection are performed according to the detection result of the light receiving element.

In this type of optical pickup device, a part of the laser light (rearward laser light) emitted from the rear emission end face of the semiconductor laser directly irradiates a monitor light receiving element formed on the surface of the semiconductor substrate. I do. Feedback control is performed based on the detection result of the monitoring light receiving element so that the laser light output of the semiconductor laser becomes constant.

Here, the front and rear laser beams emitted from the front and rear emission end faces of the semiconductor laser are spread outside the effective spread angle. In particular, the spread in the direction perpendicular to the active layer is large. In the conventional optical pickup device, of the rear laser light, a light component (effective light flux) having an effective spread angle and a large light intensity is used as monitor light.

[0008]

A light component which is not used as monitor light and spreads outside the effective light beam is emitted in a direction deviating from the light receiving surface of the monitor light receiving element. There is a possibility that the light may directly enter the signal reproducing light-receiving element disposed behind the laser.

When unnecessary light (stray light) other than the return light from the optical disk enters the signal reproducing light receiving element, the ratio of the noise component included in the output signal of the signal reproducing light receiving element increases. As a result, adverse effects such as a significant decrease in the S / N ratio and an unstable operation of tracking and focus control of the objective lens occur.

It is conceivable to arrange the signal reproducing light receiving element beside the semiconductor laser so that the component of the rear laser light that is not used as the monitoring light does not directly enter the signal reproducing light receiving element. However, even in this case, the light may be reflected on the inner wall of the package and indirectly incident on the light-receiving element for signal reproduction. Similarly, in the forward laser light, a part of the light component spreading outside the effective light beam may enter the light-receiving element for signal reproduction.

In view of the above, an object of the present invention is to provide an optical pickup device having a light source unit capable of preventing light other than return light from an optical disk from being incident on a light receiving element for signal reproduction. Is to do.

[0012]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a semiconductor laser that emits front and rear laser beams from front and rear emission end faces, and a semiconductor laser that emits light from the front emission end face of the semiconductor laser. Focusing means for condensing the forward laser light on the optical recording medium, a signal reproducing light-receiving element for detecting return light from the optical recording medium, and the return light to the signal reproducing light-receiving element. An optical pickup device having a light guide system for guiding, and a light source unit having a configuration in which the semiconductor laser and the light-receiving element for signal reproduction are built in a common package. A light shielding means for preventing light emitted from the semiconductor laser from being incident on the signal reproducing light receiving element.

In the light source unit of the optical pickup device of the present invention, of the light (forward laser light and rear laser light) emitted from the semiconductor laser, weak light (stray light) that is not used as an effective light beam is blocked by the light shielding means. Therefore, it is possible to prevent such light from being incident on the signal reproducing light receiving element. Therefore, since the noise component caused by the stray light can be removed from the output signal of the signal reproducing light receiving element, the S / N ratio can be increased, and the tracking and focus control operations of the light collecting means can be stabilized. .

As the light shielding means, a light shielding wall arranged between the semiconductor laser and the signal reproducing light receiving element can be adopted.

Here, the light guide system includes a reflection mirror for guiding the return light to the signal reproducing light receiving element, and the signal reproducing light receiving element is arranged with respect to the front emission end face of the semiconductor laser. In the emission direction side of the forward laser light, if it is arranged at a position avoiding the optical axis of the forward laser light, the inner surface portion of the package facing the light receiving surface of the signal reproducing light receiving element, It is desirable to form a mounting portion for the reflection mirror, and extend the mounting portion in a state of protruding toward the light receiving surface to a position beyond the rear emission end face along the emission direction of the rear laser light.

With this configuration, a part (light not used as an effective light beam) of the rear laser light emitted from the rear emission end face of the semiconductor laser can be used as an inner part of the package or an optical component housed in the package. Even if the light is reflected toward the light receiving element for signal reproduction, the light can be shielded by the mounting portion. Therefore, it is possible to further effectively prevent unnecessary light (stray light) from reaching the light-receiving element for signal reproduction. In the case of such a configuration, a configuration in which the light shielding wall and the mounting portion are integrated can be adopted.

In the present invention, it is preferable that an inner surface of the package facing the rear emission end face of the semiconductor laser is inclined with respect to a direction orthogonal to an optical axis of the rear laser light. This makes it difficult for a part of the rear laser light emitted from the rear emission end face to be reflected toward the signal reproducing light receiving element on the inner surface of the package.

Here, in the optical pickup device of the present invention, the light source unit is provided with separating means for separating the forward laser light emitted from the semiconductor laser into the signal reproducing laser light and the tracking error detecting laser light. In addition, it is preferable that the focusing error detection of the focusing unit is performed using the tracking error detection laser light. According to such a configuration, a diffraction unit having only a simple optical path separation function can be adopted as a diffraction unit for diffracting and separating return light from the optical recording medium. With such a diffraction means, the diffraction pattern can be greatly simplified. For example, a linear diffraction pattern can be used. Diffraction means having such a diffraction pattern is relatively stable against factors that degrade diffraction characteristics, such as wavelength fluctuation and displacement of the mounting position of each optical element. Therefore, it is possible to realize an optical pickup device in which desired optical characteristics can be stably obtained. In addition, since a simplified diffraction pattern may be manufactured, the manufacturing error tolerance of the diffraction pattern can be increased, and the manufacturing cost of the diffraction means can be reduced.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

(Overall Configuration of Optical Pickup Device) FIG. 1 shows a schematic configuration of an optical system of the optical pickup device.
The optical pickup device 1 includes a semiconductor laser 2 and a rising mirror 1 that raises a laser beam Lf emitted from the semiconductor laser 2.
1, an objective lens (condensing means) 12 for converging the launched laser beam Lf on the optical disc 4, a signal reproducing light receiving element 3 for detecting the return light Lr from the optical disc 4, and an optical disc And a light guide system 70 for guiding the return light Lr from the light receiving element 4 to the light receiving element 3 for signal reproduction.
Further, a first diffraction element (separation means) arranged at an intermediate position in an optical path from the semiconductor laser 2 to the rising mirror 11
13. The first diffraction element 13 is an element for splitting a laser beam emitted from the semiconductor laser 2 into a laser beam for signal reproduction and a laser beam for tracking error detection.

The light guide system 70 receives the return light L from the optical disc 4.
A second diffraction element 14 for diffracting r and a reflecting mirror 15 for guiding the light diffracted by the second diffraction element 14 to the light receiving element 3 for signal reproduction are provided.

In the optical pickup device 1 of the present embodiment, the semiconductor laser 2, the signal reproducing light receiving element 3, the light guide system 70 and the first diffraction element 13 are built in a common package 20,
The light source unit 10 is integrated.

(Configuration of Light Source Unit) FIGS. 2 and 3 show a light source unit. FIG. 2A is a plan view of the light source unit, and FIGS. 2B and 2C are FIGS.
It is sectional drawing in the AA 'line of (A), and sectional drawing in the BB' line. FIG. 3 is a front view of the light source unit as viewed from the front (the direction of arrow C in FIG. 2A). In FIG. 2A, a part of the package is omitted for easy understanding of the internal configuration of the light source unit. In the following description, the width direction of the package is described as an X direction, the vertical direction of the package is defined as a Y direction, and the front-rear direction of the package is defined as a Z direction.

As shown in these figures, the light source unit 1
The package 20 has a flat rectangular parallelepiped shape. Inside the package 20, a semiconductor substrate 11, a submount 24 mounted on a substrate surface 111 of the semiconductor substrate 11, and an upper surface of the submount 24 are provided. And a light-receiving element 3 for signal reproduction formed on the substrate surface 111 of the semiconductor substrate 11. Further, the package 20 is provided with the reflection mirror 15 and the first and second diffraction elements 13 and 14.

A cylindrical projection 201 is formed on the front surface 204 of the package 20 so as to project vertically forward.
A light passage hole 203 is formed by the cylindrical projection 201, and the first and second diffraction elements 13 and 14 are attached thereto. The forward laser light Lf emitted from the semiconductor laser 2 is emitted to the outside via these elements 13 and 14, and the return light Lr from the optical disc 4 is guided to the inside of the package 20.

The package 20 comprises a substantially square package main body 21 whose upper part is open, and a package lid plate 22 closing this upper opening. A chamber 20 in which the semiconductor substrate 11 and the submount 24 are mounted by the package body 21 and the package cover plate 22.
2 are formed and the cylindrical projection 201 is formed.

FIG. 4A is a plan view of the package body, and FIGS. 4B and 4C are D- FIGS.
It is sectional drawing in the D 'line, and sectional drawing in the EE' line. As shown in these figures, the package body 21
Has a substantially rectangular bottom wall 211, a front wall 212, a rear wall 213, and left and right side walls 214 and 215 rising from four sides of the bottom wall 211. Front wall 21
2 is cut in a concave shape, and a pair of left and right protruding side walls 216 and 217 extend perpendicularly to the front wall 212 from both sides thereof. The lower ends of these protruding side walls 216, 217 are connected by a protruding bottom wall 218 extending forward from the bottom wall 211. The protruding side walls 216 and 217 and the protruding bottom wall 218 form an extension 219 protruding forward.

The width of the extension 219 is smaller than the width of the package body 21, and the extension 219 is
1 is formed at a position offset from the center in the width direction.

The surface of the bottom wall 211 of the package body 21 is flat, and the semiconductor laser 2 and the submount 24
And reference plane 3 for defining the position of semiconductor substrate 11
It is set to 0. A rectangular plate-shaped stage 231 of the lead frame 23 is fixed to the reference surface 30. The leads (12 leads in this example) 232 of the lead frame 23 have pad portions located on the reference surface 30, and portions serving as external connection terminals pass through the rear wall 213 of the package body 21. Extending to the outside.
These external connection terminal portions are arranged at regular intervals in the width direction of the package.

(Structure of Semiconductor Substrate and Its Peripheral Part)
FIG. 5 is an enlarged perspective view showing a semiconductor substrate and its peripheral portion, and FIG. 6 is a plan view showing a substrate surface of the semiconductor substrate. As shown in FIGS. 2, 5, and 6, the semiconductor substrate 11 is bonded to the stage 231 of the lead frame 23 with a silver paste. Semiconductor substrate 11
On one side of the substrate surface 111 in the width direction,
A substantially rectangular electrode portion 111a long in the front-rear direction is formed, and a signal processing circuit 26 is formed on the other side.
The submount 24 is fixed on the electrode portion 111a with a silver paste. The submount 24 is formed of a semiconductor substrate having a certain thickness, and the semiconductor laser 2 is fixed on the upper surface thereof with a silver paste.

The semiconductor laser 2 has a front emission end face 2f from which the front laser light Lf is emitted, and a rear emission end face 2b from which the rear laser light Lb is emitted. From these emission end surfaces 2f and 2b, the substrate surface 111 of the semiconductor substrate 11 is formed.
The laser beams Lf and Lb are emitted forward and backward, respectively, in a direction parallel to. The emission point of the forward laser light Lf of the semiconductor laser 2 is located at substantially the center in the vertical direction of the package 20 on the front emission end face 2f. The forward laser light Lf emitted from this point is attached to the light passage hole 203. First and second diffraction elements 13 and 14
And is emitted to the outside.

On the substrate surface 111 of the semiconductor substrate 11,
Signal processing circuit 2 formed on the side of electrode section 111a
Reference numeral 6 increases the level of the output signal of the light-receiving element 3 for signal reproduction, and generates a pit signal (RF signal), a tracking error signal (TE signal), and a focus error signal (FE signal) by an external control device. This is a circuit to make it easier. The signal reproducing light receiving element 3 is formed in front of the signal processing circuit 26. Therefore, the signal reproducing light receiving element 3
Is formed at a position in front of the front emission end face 2f of the semiconductor laser 2 and at a position laterally deviated from the optical axis Lu of the front laser beam Lf.

A monitor light receiving element 2 for feedback-controlling the laser light output of the semiconductor laser 2 is provided behind the semiconductor laser 2 on the upper surface of the submount 24.
5 are formed. Back emission end face 2 of semiconductor laser 2
A part of the rear laser beam Lb emitted from b is directly incident on the monitoring light receiving element 25.

(Configuration of Signal Reproducing Light-Receiving Element) FIG. 7 shows the signal reproducing light-receiving element 3 in an enlarged manner. As shown in this figure, the light-receiving element 3 for signal reproduction has seven light-receiving surfaces A, B1, B2, C, D1, and elongated in the width direction (X direction).
D2 and E are provided. The light receiving surface A is for detecting a pit signal (RF signal), and the remaining light receiving surfaces are a tracking error signal (TE signal) and a focus error signal (FE signal).
It is for detection. In the light-receiving element 3 for signal reproduction, the remaining light-receiving surfaces are arranged three by three in the front-rear direction with the light-receiving surface A as a center. In front of the light receiving surface A, a light receiving surface B1, a light receiving surface C, and a light receiving surface B2 are arranged in this order.
, A light receiving surface D1, a light receiving surface E and a light receiving surface D2 are arranged in this order. The amounts of light received on these light receiving surfaces are converted into electric signals and supplied to the signal processing circuit 26. The method of generating the tracking error signal (TE signal) and the focus error signal (FE signal) will be described later.

The signal processing circuit 26 amplifies the electric signal supplied from each light-receiving surface and converts the signal into a voltage corresponding to the amount of received light, and appropriately calculates a signal obtained by the I / V amplifier. It is composed of an arithmetic circuit section and the like. The output of the signal processing circuit 26 is applied to the substrate surface 11 of the semiconductor substrate 11.
Each of the electrodes 111b is taken out from each electrode 111b.

Here, the length of the connection pattern between the signal reproducing light receiving element 3 and the I / V amplifier of the signal processing circuit 26 is an important factor for speeding up signal processing. That is, if the connection pattern becomes longer, the capacity of the connection pattern itself becomes larger, so that the frequency characteristics are deteriorated and the speeding up of the signal processing is hindered. On the other hand, in the light source unit 10 of the present example, the signal processing circuit 26 formed on the substrate surface 111 of the semiconductor substrate 11 and the signal reproducing light receiving element 3 are adjacent to each other in the front-back direction. For this reason, since the connection pattern between the signal reproducing light receiving element 3 and the I / V amplifier of the signal processing circuit 26 is short, the speed of signal processing can be increased.

Each electrode 111b is electrically connected to a predetermined lead pad of the lead frame 23 by wire bonding (see FIG. 2). Further, electrodes (not shown) formed on the semiconductor laser 2 and the submount 24 are also electrically connected to pad portions of predetermined leads 232 by wire bonding. Each electrode 1
An output signal from the semiconductor laser 2b is guided to a control device (not shown) disposed outside the light source unit 10 via the lead frame 23 to generate an RF signal, a TE signal, and an FE signal. The feedback control of the laser light output is performed.

Here, when the semiconductor laser 2 and the submount 24 are located at the center of the substrate surface 111 of the semiconductor substrate 11, the electrodes formed thereon and the predetermined leads 2
If wire bonding is performed directly between the wiring wires 32 and 32, the length of the wiring wire becomes long, and the wiring wire may be bent and come into contact with another wiring wire. Therefore, when the semiconductor laser 2 and the like are arranged at the center of the substrate surface 111, the middle position of the wiring wire is
, It is necessary to reduce the length of the wiring wire between the bondings.

On the other hand, in the light source unit 10 of the present embodiment, the semiconductor laser 2 and the submount 24 are installed at positions deviated in the width direction from the center of the substrate surface 111 of the semiconductor substrate 11. If the leads 232 to be connected are arranged on the side of the semiconductor laser 2, the distance between them can be reduced, and therefore, the wiring wires connected between them can be shortened, and they do not bend.

(Reflection Mirror Mounting Structure) As shown in FIGS. 2 and 3, in the light source unit 10, the reflection mirror 15 is mounted at a predetermined position of the package 20. The reflection mirror 15 has a rectangular shape, and is attached to a package lid plate 22 that defines an inner surface portion of the package 20 facing the substrate surface 111 of the semiconductor substrate 11 of the package 20.

FIG. 8A is a plan view of the package cover plate 22, and FIGS. 8B and 8C are a left side view and a front view, respectively. FIG. 8D is a cross-sectional view taken along line FF ′ of FIG. 8A. Package lid plate 22
An upper wall portion 221 which closes an upper opening of the package body 21 and defines an upper wall of the package 20;
The upper wall portion 221 is basically composed of an extended portion 222 extending forward from the front end side. Upper wall part 221
A mirror mounting portion 50 of the reflection mirror 15 is integrally formed on the inner surface of the package.

The mirror mounting section 50 is a projection having a trapezoidal cross section formed from almost directly above the light receiving element 3 for signal reproduction toward the rear. This trapezoidal mirror mounting part 50
Front surface is a mirror mounting surface 51 inclined 45 degrees toward the front.
Here, the reflection mirror 15 is fixed with an adhesive or the like.

The return light Lr from the optical disk 4 which enters the package via the first and second diffraction elements 13 and 14 strikes the reflection mirror 15 and falls down at a right angle by this mirror 15 to receive the signal for reproducing light. Irradiate 3.

The rear surface 52 of the mirror mounting portion 50 is a vertical surface, and the semiconductor laser 2 mounted on the submount 24 is
Are located behind the rear emission end face 2b.

In the upper wall portion 221 of the package cover plate 22, the semiconductor laser 2
(A front laser beam L emitted from the front emission end face 2f of the semiconductor laser 2)
A light-blocking projection (light-blocking wall) 60 that blocks a part of f, etc.) is formed. The light-shielding projection 60 is provided on the mirror mounting portion 5.
0, and has a truncated pyramid portion 61 extending downward from the upper wall portion 221 in a tapered state, and a prism portion 62 extending vertically downward from the lower surface. The lower end surface 63 of the light-shielding projection 60 is the mirror mounting portion 5.
0 is substantially at the same height as the lower end face 53 of the semiconductor laser 2.
Is located on a line connecting the front emission end face 2f of the light-receiving element 3 and the light-receiving element 3 for signal reproduction.

FIG. 9 schematically shows the emission state of the front and rear laser beams Lf and Lb emitted from the semiconductor laser 2. The front and rear laser beams Lf, Lb emitted from the respective emission end faces 2f, 2b of the semiconductor laser 2 also spread outside the effective spread angle. For this reason, a part of the light component (stray light) Lf1 of the front laser light Lf emitted from the front emission end face 2f of the semiconductor laser 2 is directly transmitted to the signal reproducing light receiving element 3 located forward of the front emission end face 2f. There is a risk of incidence.

In the light source unit 10 of this embodiment, the light-shielding projections 6 are provided between the front emission end face 2f and the signal reproducing light-receiving element 3.
0, and the light-shielding projection 60 substantially separates the front emission end face 2f from the light-receiving element 3 for signal reproduction. Accordingly, since the light component Lf1 is blocked by the light-blocking projection 60, the light component Lf1 can be prevented from reaching the signal reproducing light-receiving element 3.

In this embodiment, the light-shielding projections 60 have a function of reliably preventing the forward laser light Lf emitted from the front emission end face 2f of the semiconductor laser 2 from reaching the signal reproducing light-receiving element 3. The amount and shape of the protrusion should be determined so that the function can be sufficiently exhibited.

On the other hand, the rear emission end face 2b of the semiconductor laser 2
Of the rear laser light Lb (effective light flux) emitted from the semiconductor laser 2 directly enters the monitoring light receiving element 25 and is used as monitor light for feedback-controlling the laser light output of the semiconductor laser 2. Light component (stray light) Lb of the rear laser light Lb that is not coupled to the monitoring light receiving element 25
1 may be reflected multiple times on the inner wall of the package 20 or the like and travel toward the signal reproducing light receiving element 3.

The mirror mounting portion 50 of the light source unit 10 of this embodiment protrudes from the package lid plate 22 toward the substrate surface 111 of the semiconductor substrate 11 and extends rearward. For this reason, the semiconductor laser 2 and the signal reproducing light-receiving element 3 are substantially partitioned by the mirror mounting portion 50. Therefore, the above-mentioned light component Lb1 is blocked by the mirror mounting part 50, so that the rear laser light Lb
Part Lb1 of b can be prevented from being incident on the signal reproducing light-receiving element 3.

The rear end face 52 of the mirror mounting portion 50 is located behind the rear emission end face 2b of the semiconductor laser 2. In this case, compared to the case where the rear end face 52 is located forward of the rear emission end face 2b,
The stray light in the package can be more reliably prevented from being incident on the light-receiving element 3 for signal reproduction. The amount of protrusion of the mirror mounting portion 50 has a property to be determined so that the light component Lb1 can be reliably shielded.

As described above, in the light source unit 10 of this embodiment, it is possible to prevent light (stray light) other than the return light Lr from the optical disk 4 from being incident on the signal reproducing light receiving element 3. Therefore, since the noise component caused by the stray light can be removed from the output signal of the signal reproducing light receiving element 3, the S / N ratio can be increased, and the tracking and focus control operation of the objective lens 12 can be stabilized. Can be.

Here, as shown in FIGS. 2 and 3, the inner wall of the package 20 facing the rear emission end face 2b of the semiconductor laser 2, that is, the rear wall 21 of the package body 21
The inner surface 65 of 3 is an inclined surface that protrudes downward. When the inner side surface 65 of the rear wall 213 is inclined as described above, in other words, when the inner side surface 65 is inclined so as to have an angle other than a right angle with respect to the optical axis of the rear laser beam Lb, the inner side surface 65 has It is possible to reduce the light amount of the backward laser light Lb that travels toward the signal reproducing light receiving element 3 after being reflected. Note that the inner side surface 65 may be inclined in a direction of retreating downward. Further, the inner side surface 65 may be an inclined surface inclined in the width direction of the package 20.

(Attaching Structure of First and Second Diffractive Elements) Both the first and second diffractive elements 13 and 14 have a rectangular shape, and are attached to the package body 21.

FIG. 10 schematically shows the mounting structure of the first diffraction element 13, and FIG.
4 is schematically shown. 4 and 1
As shown in FIG. 0, on the reference surface 30 of the package main body 21, a horizontal step surface 31 which is one step lower than the reference surface 30 is formed at the boundary with the extension 219. The step surface 31 is formed along the width direction of the package 20 and has a constant length in the front-rear direction. This step surface 3
A step surface 32 orthogonal to the step surface 31 is formed at the boundary between the reference surface 1 and the reference surface 30, and a step surface (mounting surface) 33 orthogonal to the step surface 31 is formed at the boundary between the step surface 31 and the extending portion 219. Is formed.

Therefore, the first diffraction element 13 is connected to the step surface 33.
When it is arranged so as to be in contact with, the arrangement position in the front-back direction is automatically defined. Further, the optical axis of the first diffraction element 13 is substantially parallel to the optical axis Lu of the forward laser light Lf from the semiconductor laser 2 emitted from the light passage hole 203.
The attitude of the first diffraction element 13 is automatically defined.
In this state, the first diffraction element 13 holds the package 2 in this state.
After the arrangement position in the width direction of 0 is finely adjusted, it is fixed with an adhesive or the like.

As shown in FIGS. 3, 4 and 11, the front surface 35 of the extension 219 is a vertical surface. The size of the second diffraction element 14 is slightly larger than the opening of the light passage hole 203. Therefore, when the second diffraction element 14 is disposed so as to be in contact with an edge portion (mounting surface) 36 which defines a part of the opening of the light passage hole 203 of the package 20 on the front surface 35, the arrangement in the front-rear direction is provided. The position is defined automatically. Further, the posture of the second diffraction element 14 is set such that the optical axis of the second diffraction element 14 is substantially parallel to the optical axis Lu of the forward laser light Lf from the semiconductor laser 2 emitted from the light passage hole 203. Is automatically defined. The second
In this state, the arrangement position of the package 20 in the width direction is finely adjusted in this state, and then fixed by an adhesive or the like.

(Outer Shape of Package) As shown in FIG. 3, on the outer surface of the projecting side walls 216 and 217 of the extension portion 219 in the package body 21, the forward laser light Lf emitted from the light passage hole 203 is provided. 4 centered on the optical axis Lu
Arc surfaces 40a, 40b, 40c, and 40d are formed. These arc surfaces 40a to 40d are formed at the corners of the protruding side walls 216 and 217, respectively, and have the same central angle. In addition, these arc surfaces 40a to 40d
Of these, the two arc surfaces 40a and 40c are line-symmetric with respect to the optical axis Lu, and the remaining two arc surfaces 40b and 40d also have the optical axis L
u is line symmetric. The front surfaces 41a and 41b of the front wall 212 of the package body 21 are flat reference surfaces orthogonal to the optical axis Lu.

Therefore, when the light source unit 10 is mounted on the optical pickup device 1, if the reference surfaces 41a and 41b are used, the optical axis of the objective lens 12 and the like and the forward laser beam L
The orientation of the light source unit 10 can be set so that the optical axis Lu of f coincides with the optical axis Lu. Further, if the reference surfaces 41a and 41b are used, the light source unit 10 can be easily attached to the optical pickup device 1. On the other hand, by adjusting the rotation angle of the light source unit 10 using the arc surfaces 40a to 40d, the rotation of the sub-beam (tracking error detection laser beam) for performing tracking by the three-beam method and the track of the optical disk 4 is performed. Angle adjustment can be easily performed. That is, the diffraction direction in the first diffraction element 13 can be set appropriately. Thus, the correlation between the optical axis Lu of the forward laser beam Lf emitted from the light passage hole 203 of the light source unit 10 and the optical axes of the first and second diffraction elements 13 and 14, and the first diffraction element Since the diffraction characteristics (diffraction direction) of No. 13 can be appropriately set, an optical pickup device having excellent optical characteristics can be realized. In addition, since the arc surfaces 40a to 40d centering on the optical axis Lu need only be produced, it is easy to produce an arc surface symmetrical to the optical axis Lu, and it is also possible to improve the surface accuracy of the arc surface. further,
The light source unit rotates around the optical axis Lu when the rotation angle is adjusted because the arc surfaces 40a to 40d center on the optical axis Lu. Therefore, the position of the optical axis Lu does not change with the rotation angle adjustment.

(Basic operation of optical pickup device)
The basic operation of the optical pickup device will be described with reference to FIG. In the light source unit 10, the forward laser light Lf emitted from the semiconductor laser 2 enters the first diffraction element 13 almost perpendicularly. The first diffraction element 13 has a diffraction grating surface (not shown). This diffraction grating surface has a function of dividing the forward laser light Lf that has entered substantially perpendicularly into a main beam and two sub beams.
In addition, the optical disc 4 has a function of converting the wavefronts of the two sub beams so that the two sub beams focus on the optical disc 4 before and after the optical axis. This diffraction grating surface
When the return light from the optical disk 4 is incident on the first diffraction element 13 again, it is formed at a position where it does not pass through the diffraction grating surface again.

For this reason, the forward laser beam Lf is split by the diffraction element 13 into a main beam and two sub beams. Of these beams, the main beam is used as laser light for signal reproduction (laser light for signal reproduction), and the two sub-beams are used as laser light for tracking error detection (laser light for tracking error detection).

The laser beam for signal reproduction and the two laser beams for tracking error detection reach the second diffraction element 14. The second diffraction element 14 determines the zero-order diffraction efficiency in the optical path where the three laser beams reach the optical disc 4,
Is set so that the product of the first order diffraction efficiency and the first-order diffraction efficiency in the optical path from the light-receiving element 3 to the signal reproducing light-receiving element 3 is maximized. The diffraction grating surface formed on the second diffraction element 14 is substantially parallel to the diffraction grating surface of the first diffraction element 13.

Of the three laser beams, the second diffraction element 1
The light component (0th-order diffracted light) transmitted through the light source unit 10
After being emitted from the optical disk and bent at a right angle by the rising mirror 11, the light is focused on the recording surface of the optical disk 4 via the objective lens 12. At this time, the laser beam for signal reproduction focuses on the recording surface, and the two laser beams for tracking error detection enter a front focus state and a rear focus state.

The three laser beams condensed on the recording surface of the optical disk 4 are reflected there and become return light Lr traveling from the optical disk 4 to the light-receiving element 3 for signal reproduction. These return lights Lr are again transmitted to the objective lens 12 and the rising mirror 1.
The light is incident on the second diffraction element 14 of the light source unit 10 through the light source 1.

Here, the second diffraction element 14 has only a function of diffracting each return light in a direction parallel to the substrate surface 111 of the semiconductor substrate 11, in this example, in the width direction of the package 20. There is no function of performing wavefront conversion such as focusing and diverging on each return light Lr. For this reason, the three return lights Lr incident on the second diffraction element 14 are diffracted by the diffraction action of the diffraction element 14 to change the traveling direction.

The light diffracted by the second diffraction element 14 is the first
Incident on the diffraction grating 13. As described above, the diffraction grating surface of the first diffraction grating 13 is not formed in a range where these diffracted lights enter. For this reason, each diffracted light incident on the diffraction grating 13 passes through the first diffraction grating 13 and reaches the reflection mirror 15. These diffracted lights fall vertically by the reflecting mirror 15 and irradiate the respective light receiving surfaces of the signal reproducing light receiving element 3.

As shown in FIG. 7, the diffraction light of the return light of the laser light for signal reproduction forms light spots s1 and s2 on the light receiving surface A. Further, the diffracted light of the return light of the laser light for tracking error detection forms light spots s3 and s4 on the light receiving surfaces B1, B2 and C. The diffracted light of the return light of the other laser light for tracking error detection forms light spots s5 and s6 on the light receiving surfaces D1, D2 and E.

In this example, an RF signal is detected based on the amount of light received on the light receiving surface A of the light receiving element 3 for signal reproduction. The TE signal is detected by calculating the difference between the sum S1 of the light reception amounts of the light receiving surfaces B1, B2, and C and the sum S2 of the light reception amounts of the light receiving surfaces D1, D2, and E. The FE signals are received on the light receiving surfaces B1, B2, E
Is obtained by calculating the difference between the sum S3 of the received light amounts of the light receiving surfaces and the sum S4 of the received light amounts of the light receiving surfaces D1, D2, and C. In addition,
These signals are transmitted to the lead frame 23 of the light source unit 10.
Is generated by a control device (not shown) electrically connected to the lead 232.

A part of the rear laser light Lb emitted from the rear emission end face 2 b of the semiconductor laser 2 directly enters the monitoring light receiving element 25 formed on the upper surface of the submount 24. Feedback control of the laser light output of the semiconductor laser 2 is performed based on the output signal of the monitoring light receiving element 25. The feedback control is also performed by the above-described control device.

As described above, in the optical pickup device 1 of the present embodiment, the diffraction direction of the second diffraction element 14 is set to the width direction of the package 20. For this reason, the second diffraction element 1
The light diffracted by 4 can be prevented from interfering with the wires connecting the electrodes 111b of the semiconductor substrate 11 and the pad portions of the leads 232 of the lead frame 23. Therefore, reproduction, tracking and focusing control of the optical disk 4 can be performed with high accuracy. Further, the thickness dimension of the light source unit 10 can be made smaller than when the diffraction direction of the second diffraction element 14 is set in the vertical direction of the package 20.

Here, in the optical pickup device 1 of the present embodiment, the second diffraction element 14 has a function of diffracting the return light from the optical disk 4, but does not have a function of wavefront conversion. For this reason, the second diffraction element 14
And the optical path length from the second diffraction element 14 to the light receiving element 3 for signal reproduction is equal. As a result, the optical path length of the return light can be made shorter than before, and the optical system of the optical pickup device can be made compact. As a result,
The size of the device can be reduced.

More specifically, since the second diffractive element 14 has a function of diffracting the return light and does not have a function of transforming the wavefront, the convergence point of the light diffracted by the diffractive element 14 is
It is optically conjugate with the virtual light emitting point of the semiconductor laser 2 and the two tracking error detection laser beams divided and generated by the first diffraction element 13. Therefore, the following relationship is established between the emission point of the forward laser light Lf of the semiconductor laser 2 and the center of the signal reproducing light receiving element 3.

As shown in FIGS. 12 and 13, the thickness of the submount 24, the submount 24 and the semiconductor laser 2
From the surface in contact with to the light emitting point O, the optical path separation angle at the second diffraction element 14 at the wavelength of the semiconductor laser 2, and the laser light from the semiconductor laser 2 to the diffraction grating surface of the second diffraction element 14. The optical distances of Lf along the optical axis Lu are ts, hLD, θbs, and dbs, respectively. With this definition, the XZ coordinate of the center of the signal reproducing light-receiving element 3 when the light-emitting point O in the (X, Z) plane where the signal reproducing light-receiving element 3 is formed is defined as Equation (1).
And (2).

X = dbs × sin (θbs) (1) Z = dbs × {1−cos (θbs)} + ts + hLD (2) The diffraction of the semiconductor laser 2 and the second diffraction element 14 As can be seen from FIG. 12, the optical distance of the forward laser beam Lf to the grating plane along the optical axis Lu is the second diffraction element 14.
Corresponds to the distance between the semiconductor laser 2 and a position slightly shifted from the light incident surface toward the semiconductor laser 2. FIGS. 12 and 13 show the case where the reflection angle of the reflection mirror 15 is set to 45 degrees, and the deviation of the reflection angle of the mirror 15 and the angle deviation around the optical axis are not considered.

In the optical pickup device 1 of this embodiment, the focus error signal of the objective lens 12 is generated by using the tracking error detecting laser light, and the second diffraction element 14 that diffracts and separates the return light from the optical disk 4. The one having only a simple optical path separation function is adopted. For this reason,
The diffraction pattern of the diffraction element 14 can be simplified. For example,
A linear diffraction pattern can be employed. A diffraction element having such a diffraction pattern is relatively stable against factors that degrade diffraction characteristics, such as wavelength fluctuation and displacement of the mounting position of each optical element. Therefore, the target optical characteristics can be stably obtained. In addition, since a simplified diffraction pattern may be produced, the tolerance for the production error of the diffraction pattern can be increased, and the production cost of the diffraction element can be reduced.

(Other Embodiments) In the optical pickup device 1, the light-shielding projections 60 are provided on the package cover plate 22.
Are formed integrally, but the light shielding member is
The light-shielding protrusions 60 may be formed by separately attaching the light-shielding protrusions 60 to the projections 2. Further, a configuration in which a light shielding member is attached to the substrate surface 111 of the semiconductor substrate 11 may be adopted.

The optical pickup device 1 uses the first and second diffractive elements 13 and 14 that are independent from each other. One of the surfaces has the optical characteristics of the first diffractive element 13 and the other has the optical characteristics. Of course, a single optical element having the optical characteristics of the second diffraction element on the surface may be employed.

Further, the submount 24 is mounted on the semiconductor substrate 1.
1 is mounted on the substrate surface 111, but the submount 24 is mounted on the stage 231 of the lead frame 23.
Alternatively, the configuration may be such that it is mounted on the lead 232.

Further, the optical system of the optical pickup device 1 includes not only the optical element shown in FIG.
a lens for converting f into a parallel light beam, a beam shaping prism for adjusting the light beam diameter in two orthogonal directions of the laser beam, an aperture limiting means for reading information of an optical disk of different specifications, a wavelength-selective optical element, and the like. An optical element may be included.

[0080]

As described above, according to the present invention, in the package of the light source unit, the light shielding means for preventing the light emitted from the semiconductor laser from entering the light receiving element for signal reproduction is formed. I have. For this reason, even if light other than the effective light flux in the laser light in front and behind the semiconductor laser is directed to the light-receiving element for signal reproduction, the light can be blocked by the light shielding means. Therefore, it is possible to prevent the stray light from reaching the light receiving element for signal reproduction, so that a noise component caused by the stray light can be removed from the output signal of the light receiving element for signal reproduction. As a result, the S / N ratio can be increased, and the tracking and focus control operations of the light condensing means can be stabilized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical system of an optical pickup device to which the present invention has been applied.

2A is a schematic configuration diagram of a light source unit, FIG. 2B is a cross-sectional view taken along line AA ′ of FIG. 2A, and FIG. 2C is a cross-sectional view taken along line BB ′ of FIG. .

FIG. 3 is a front view of the light source unit shown in FIG.

FIG. 4A is a plan view of a package body which is a component of the package of the light source unit, and FIG.
FIG. 4C is a cross-sectional view taken along line D ′, and FIG. 4C is a cross-sectional view taken along line EE ′ in FIG.

FIG. 5 is an enlarged perspective view showing a semiconductor substrate and its peripheral portion in a light source unit of the optical pickup device.

FIG. 6 is an enlarged plan view showing a substrate surface of a semiconductor substrate in the light source unit of the optical pickup device.

FIG. 7 is an enlarged plan view showing a light-receiving element for signal reproduction in a light source unit of the optical pickup device.

FIG. 8A is a plan view of a package cover plate which is a component of a package of the light source unit, and FIGS.
Are left and right side views, respectively, and (D) is FF ′ of (A).
It is sectional drawing in a line.

FIG. 9 is a diagram schematically showing an emission state of front and rear laser beams emitted from a semiconductor laser.

FIG. 10 is a diagram for explaining a mounting structure of a first diffraction element in a light source unit of the optical pickup device.

FIG. 11 is a diagram for explaining a mounting structure of a second diffraction element in the light source unit of the optical pickup device.

FIG. 12 is a diagram for explaining a formation position of a light-receiving element for signal reproduction in a width direction of a package in a light source unit of the optical pickup device.

FIG. 13 is a view for explaining a formation position of a light-receiving element for signal reproduction in a front-rear direction of a package in a light source unit of the optical pickup device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 optical pickup device 2 semiconductor laser 2 f front emission end surface 2 b rear emission end surface 3 light receiving element for signal reproduction 4 optical disk 10 light source unit 12 objective lens 13 first diffraction element 14 second diffraction element 15 reflection mirror 20 package 21 package body 22 Package lid plate 24 Submount 25 Monitor light receiving element 50 Mirror mounting part 60 Light shielding projection 65 Inner surface of rear wall 70 Light guide system Lf Forward laser beam Lb Rear laser beam

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tamminori Masawa 14-888 Ako, Komagane City, Nagano Prefecture Inside the Sankyo Seiki Seisakusho Komagane Plant (72) Inventor Yuichi Takei 14-888 Ako Komagane City, Nagano Prefecture Sankyo Seiki Seisakusho Komagane Plant (72) Inventor Hisahiro Ishihara 5329 Shimosuwa-cho, Suwa-gun, Nagano Pref.

Claims (7)

[Claims] 1. A semiconductor laser for emitting front and rear laser beams from front and rear emission end faces, and a collector for condensing the front laser light emitted from the front emission end face of the semiconductor laser on an optical recording medium. Optical means, a signal reproducing light receiving element for detecting return light from the optical recording medium, and a light guide system for guiding the return light to the signal reproducing light receiving element, the semiconductor laser and the In an optical pickup device including a light source unit having a configuration in which a signal reproducing light receiving element is built in a common package, light emitted from the semiconductor laser is transmitted to the signal reproducing light receiving element inside the package of the light source unit. An optical pickup device comprising a light blocking means for preventing incidence. 2. The optical pickup device according to claim 1, wherein said light shielding means is a light shielding wall disposed between said semiconductor laser and said signal reproducing light receiving element. 3. The light guide system according to claim 2, wherein the light guide system includes a reflection mirror for guiding the return light to the light receiving element for signal reproduction. An inner surface portion of the package, which is disposed on the emission direction side of the front laser light with respect to a front emission end surface and avoids an optical axis of the front laser light, and faces a light receiving surface of the signal reproducing light receiving element. A mounting portion of the reflection mirror is formed, and the mounting portion protrudes toward the light receiving surface and extends to a position beyond the rear emission end face along the emission direction of the rear laser light. An optical pickup device characterized by the above-mentioned. 4. The optical pickup device according to claim 3, wherein the mounting portion and the light shielding wall are formed integrally. 5. The package according to claim 1, wherein an inner surface of the package facing the rear emission end face of the semiconductor laser is inclined with respect to a direction orthogonal to an optical axis of the rear laser light. An optical pickup device. 6. The separation unit according to claim 1, wherein the light source unit separates the forward laser beam emitted from the semiconductor laser into a laser beam for signal reproduction and a laser beam for tracking error detection. And an optical pickup device for detecting a focus error of the focusing means using the tracking error detection laser light. 7. The light source unit according to claim 1, wherein: