JPH06111357A - Optical pickup - Google Patents

Abstract

PURPOSE:To obtain the optical pickup which detects an excellent signal by eliminating deviation of the optical axis in a plastic prism due to temperature variation in an optical pickup which uses the plastic prism. CONSTITUTION:An air layer which has low heat conductivity is formed between an optical system 1 which constitutes the optical pickup and a silicon substrate 60 provided with a laser diode 70 which emits laser light into the optical' system 1. Then a spacer 35 for heat insulation is interposed to radiate heat, conducted into the silicon substrate 60 by the laser diode 70, to the air layer.

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 recording / reproducing information using an optical recording medium, and more particularly to an optical pickup using a transparent substrate for an optical system.

[0002]

2. Description of the Related Art An optical pickup for recording / reproducing information using an optical recording medium such as an optical disk is generally assembled by using individual parts such as a laser diode, a prism and an objective lens. It is difficult to reduce the size of such a conventional optical pickup because of the position adjustment of each component and the operability during assembly.

In order to solve the above-mentioned drawback, for example, Japanese Patent Laid-Open No. 62-146444 discloses a prism type optical pickup which achieves downsizing by using a transparent substrate. The optical pickup proposed here detects a laser diode, an element that diffracts the laser light emitted from this laser diode, an element that focuses the laser light on an optical recording medium, and a return light from the optical recording medium. The photodetector and the like are integrally formed on a transparent substrate.

The operation of the optical pickup disclosed in this publication will be briefly described. The laser light emitted from the laser diode propagates while being repeatedly reflected on the upper and lower surfaces of the transparent substrate, and the laser light emitted from the laser diode is collected on the substrate. Depending on the optical element,
It is focused on an optical recording medium arranged outside the substrate.
Then, the return light from the optical recording medium is again guided into the transparent substrate, propagates while repeating reflection, and is detected by the photodetector via the diffraction element. The return light detected by this photodetector is photoelectrically converted, whereby an information signal and a servo error signal from the optical recording medium are obtained. The transparent substrate is driven by a servo coil (not shown) or the like so that the focused spot always follows the track of the optical recording medium based on the detected servo error signal.

[0005]

The prior art disclosed in the above-mentioned publication is small in size and low in size by integrating the respective components constituting the optical pickup, such as a condensing element, a beam splitter, and a photodetector. Aiming to realize a cost optical pickup.

However, when a plurality of aspherical surfaces are provided on the transparent substrate forming the optical path, the weight of the optical pickup is reduced, or the mass productivity is increased, the transparent substrate is necessarily made of plastic. There is no choice but to use a molded product. As described above, since the constituent parts of the optical pickup are integrated, the plastic molded product may be thermally deformed by the heat generated from the light source and the servo coil.

In the prior art, no measures are taken for heat generation, so that the optical axis is displaced due to thermal deformation of the plastic forming the optical path. If the optical axis shifts, the light condensing property deteriorates, and in the worst case, the signal cannot be read.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a compact integrated optical pickup in which a detected signal does not deteriorate even if a plastic prism is used. .

[0009]

In order to solve the above problems, an optical pickup according to the present invention is a substrate having a light source and a photodetector, and is fixed to this substrate to internally reflect the light emitted from the light source. And a control means for controlling the substrate so that the light emitted from the optical recording medium is focused on the track of the optical recording medium. It is characterized in that an optical axis shift preventing means for preventing the shift of the optical axis that occurs is provided.

[0010]

A heat radiating means is provided to prevent heat generated from a heat source such as a light source of an optical pickup or a servo mechanism from being transmitted to the base body and deforming the base body, thereby preventing an optical axis shift in the base body, and thus an optical recording medium. To prevent the deterioration of the light condensing characteristics.

Alternatively, even if the substrate is deformed by the heat generated by the heat source, the deviation of the optical axis in the substrate is minimized.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the basic structure of the optical system of an optical pickup according to the present invention will be described with reference to FIGS.
The optical pickup shown below is of a type using a magneto-optical disk as an optical recording medium (magneto-optical pickup).

As shown in FIG. 1, an optical system 1 of a magneto-optical pickup comprises a transparent substrate 10, a pair of microplates 5 integrally attached to the substrate, and a substrate 60 made of, for example, silicon. Have Hereinafter, the configuration of the optical system 1 will be described according to the manufacturing process.

First, a plastic transparent substrate (hereinafter referred to as a prism) 10 having a shape as shown in FIG. 1 is injection-molded. The prism 10 includes an upper surface 11, a lower surface 12 parallel to the upper surface 11, and a left side surface 1 perpendicular to these surfaces and facing each other.
3 and a right side surface 14, a condensing surface 16, a pair of concave portions 20, and an exit end surface 15 on which laser light is incident. A hologram optical element (HOE) 22 as shown in FIG. 2 is formed on the left side surface 13. The HOE 22 is a curved grating having a pitch of 2 to 3 μm and a depth of 0.3 μm, and a master is formed by a general etching process. By forming an inverted replica of this HOE in the injection mold, the HOE 22 is formed on the left side surface 13 of the transparent substrate simultaneously with the injection molding. As will be described later, the HOE 22 is divided into two parts in the vertical direction on the left and right sides so that the return light from the magneto-optical disk can be detected by the beam size method, and the left and right focal lengths have different focal lengths. (See FIG. 4).

After the prism 10 is injection-molded, metal is vacuum-deposited on the left side surface 13, the right side surface 14 and the light collecting surface 16 to form reflection mirror surfaces. After the reflection mirror surface is formed, the silicon substrate 60 is fixed to the right side surface 14.

As shown in FIG. 4, photodetectors 65 and 66 (both divided into three parts) and 67 and 68 are formed on the silicon substrate 60, and these photodetectors 65 to 68 are used. A circuit (not shown) for converting the signal of 1 to current-voltage conversion is formed.
Further, the end face of the silicon substrate 60 is obliquely cut out to form a slope 61, and the laser diode (LD) 70 is mounted on the slope 61. This LD7
0 is P-type or N-type AlG on a GaAs substrate by vapor phase epitaxy.
It has a wavelength of 790 nm in which an aAs crystal layer is laminated.
The low melting point alloy of Au is used for fusion on the slope 61.

The exit end surface 15 of the prism 10 and the slant surface 61 of the silicon substrate 60 are LDs fused on this slant surface.
The laser light emitted from 70 is aligned so as to enter the emission end face 15 vertically. Further, the angle θ of the slope 61 of the silicon substrate 60 is such that the light emitted from the LD 70 is
It is set so as to be totally reflected by the upper surface 11 and the lower surface 12 of the prism 10. The prism 10 and the silicon substrate 60, which are emitted from the LD 70, monitor the laser light focused on the outside of the prism 10 by the focusing mirror surface 16, and are fixed at the position where the aberration is the smallest.

A pair of recesses 20 formed in the prism 10.
A microplate 50 having the same refractive index as that of the prism 10 is fixed to each. These small plates 50
A dielectric multilayer film 51 for separating polarized light is applied to the lower surface of the. The dielectric multilayer film 51 has a function of transmitting the light of the polarization component that is vertically incident on this surface and reflecting the light of the polarization component that is horizontally incident. A dense lattice may be formed on the microplate 50 as a means for separating polarized light.

The path of light in the above-mentioned optical system 1 will be described below with reference to FIGS.

The laser light emitted from the LD 70 into the prism 10 is reflected by the reflection mirror surface 13 on which the HOE 22 is formed, and enters the lower surface 12. As mentioned above, L
D70 is aligned so that the emitted laser light is totally reflected by the upper and lower surfaces 11 and 12 of the prism 10, and the light incident on the lower surface 12 is totally reflected and directed to the reflection mirror surface 14. The light totally reflected by the reflection mirror surface 14 enters the condenser reflection mirror surface 16 via the upper surface 11. Then, the laser light reflected by the converging / reflecting mirror surface 16 passes through the upper surface 11 of the prism 10, enters the transparent substrate 24 of the magneto-optical disk, and focuses on the recording layer 23.

Information is recorded on the recording layer 23 by reversing the direction of the magnetic field, and the incident light is reflected by the plane of polarization of which is rotated according to the direction of the magnetic field, and the path that has passed up to that point. Return to reverse. In FIG. 2, only the path through which the laser light emitted from the LD 70 is focused on the recording layer 23 of the magneto-optical disk is shown, but the light reflected by the recording layer 23 is in the direction opposite to the arrow direction in the figure. Proceed to.

The return light from the magneto-optical disk is HOE2.
Diffracts when reflected at 2. Of these, as shown in FIGS. 3 and 4, the ± 1st-order diffracted lights are polarized separation multilayer film surfaces 51,
51, and the transmitted light is divided into three photodetectors 65,
At 66, the reflected light is received by photodetectors 67 and 68, respectively. The polarization plane of the light reflected and diffracted by the HOE 22 enters the polarization separation multilayer film surface 51 at an intermediate angle. As described above, the polarization planes of the components passing through the multilayer film surface 51 and the components reflecting the same are orthogonal to each other, and the orthogonal components of the polarized light incident at the intermediate angle are detected by the respective photodetectors. It

In this case, if the outputs of the respective photodetectors are represented by the same symbols as the respective reference symbols, the magneto-optical signal can be obtained by (65 + 68)-(66 + 67). Further, the focus error signal is detected by the beam size method and is (65a + 65c + 66b) − (65b
+ 66a + 66c). Further, the tracking error signal is detected by the push-pull method, and (65+
67)-(66 + 68).

In the optical system configured as described above (see FIG. 5), the laser beam emitted from the optical system is always focused on and follows the track of the magneto-optical disk based on the detected servo error signal. Servo function must be added as described above. An example of the servo function added to this optical system will be described with reference to FIGS. 6 to 8.

As shown in FIG. 6, the front surface 17a of the optical system 1 is
A servo coil, that is, a focusing coil 25, and a pair of tracking coils 26a and 26b arranged on both sides of the focusing coil are fixed to the servo coil. Further, servo coils in the same arrangement as these servo coils are fixed to the rear surface 17b of the optical system 1. Further, on the front surface 17a of the optical system 1, four wires 27a to 27b that support the entire optical system so as to be movable in the tracking direction and the focusing direction.
One end of 27d is fixed.

The optical system 1 to which the servo coil and the four wires are attached is supported by the chassis 30 shown in FIG. On the chassis 30, the four wires 27a-2
A wall portion 30a to which the other end of 7d is fixed is formed.
Further, on this chassis, servo magnets are provided so as to correspond to the servo coils 25 and 26a, 26b attached to the optical system. That is, a pair of focusing magnets 31 arranged in the focusing coil 25 and tracking magnets 32a, 32b arranged so as to face the openings of the tracking coils 26a, 26b, respectively, in the front and rear portions of the chassis. Is projected.

FIG. 8 shows a state in which the optical system 1 is supported by the chassis 30 (overall structure of the magneto-optical pickup). As described above, when the photodetector detects the focus error signal, a control current flows through the focusing coil 25, and the optical system 1 is driven in the focusing direction by the electromagnetic action between the coil and the magnet. Similarly, when the tracking error signal is detected by the photodetector, the tracking coil 26
A control current flows through a and 26b, and the optical system 1 is driven in the tracking direction.

As described above, when an optical pickup is constructed by using a plastic prism, the plastic is thermally deformed by heat conduction from various parts, and the optical axis is displaced. Examples of the heat source that transfers heat to the prism include a laser diode that is a light source and a servo coil. It is important to quickly release the heat generated from these to other components having a large heat capacity, such as the chassis, so as not to be transmitted to the prism as much as possible.
If a certain temperature rise is unavoidable, the effect of the temperature rise should be minimized.

In the present invention, for example, in an optical pickup configured as shown in FIG. 8, heat is not transmitted to the prism 10, or even if heat is transmitted, the occurrence of optical axis deviation is minimized. In addition, for example, various optical axis deviation preventing means described below are provided. Less than,
A specific configuration of the optical axis shift means will be described. In addition,
The same components as those described with reference to FIGS. 1 to 8 are designated by the same reference numerals, and the description thereof will be omitted.
Or simplify it.

As described above, the material of the substrate on which the laser diode and the photodetector are formed is silicon. Since silicon has good thermal conductivity, the heat emitted from the laser diode is instantaneously transferred to the entire substrate. on the other hand,
A prism to which a silicon substrate is attached has a thermal conductivity several ten times worse than that of silicon. However, if the prism does not have an effective optical axis shift prevention means, the temperature of the prism will eventually rise.

Therefore, as shown in FIG.
Between the silicon substrate 60 and the silicon substrate 60, a square-shaped heat insulating spacer 35 having a thickness of about 0.5 mm is interposed between the silicon substrate 60 and the silicon substrate 60 so that the heat of the silicon substrate is transferred to the air having a low thermal conductivity. Makes it easier to dissipate heat. A large number of notches 35 a are formed in the heat insulating spacer 35 so that the air layer convects. With such a configuration, the heat generated from the laser diode is less likely to be transmitted to the prism 10, and the temperature rise of the prism can be suppressed. Further, the insulating spacer having this shape can alleviate the distortion and deformation of the prism due to the difference in the coefficient of thermal expansion between the substrate and the prism, and has an effect of preventing the deviation of the optical axis.

The shape of the heat insulating spacer is not limited to that shown in the drawing, and various modifications are possible. In addition to air, a material having low thermal conductivity may be interposed between the prism 10 and the silicon substrate 60.

FIG. 10 is a diagram showing a second embodiment of the optical axis shift prevention means. The silicon substrate 60 on which the laser diode and the photodetector are formed always needs electric wiring for supplying electric power and transmitting signals. As shown in FIG. 8, in the case of an optical pickup in which a light source and a condensing function are integrated, the entire optical system is driven at a high frequency in order to follow the surface contact of the magneto-optical disk. For this reason,
A flexible wiring board, generally a printed wiring board in which a wiring pattern using a copper thin film is sandwiched between polyimide resins is used for the electric wiring so as not to adversely affect the drive system. Since this wiring board is directly attached to the silicon substrate 60, an effect can be expected in releasing the heat of the silicon substrate.

Therefore, in this embodiment, as shown in FIG. 10 (b), a printed wiring board of polyimide resin having a thickness of about 100 μm is laminated with a copper foil having a good thermal conductivity of about 50 μm. The wiring board 36 connects the silicon substrate 60 and the chassis 30. As a result, the heat generated from the laser diode 70 is promptly transferred to the chassis 3
It escapes to 0, and the temperature rise of the silicon substrate and the prism is suppressed.

11 and 12 are views showing a third embodiment of the optical axis deviation preventing means. As described above, the optical system is driven by utilizing the electromagnetic force using the servo coil and the ferromagnetic material. Therefore, the heat generated by the electrical loss of the coils cannot be ignored, and this heat is easily transferred to the prisms to which these coils are fixed.

On the other hand, as shown in FIG. 6, the optical system 1
Are supported by four wires 27a to 27d. These wires are generally made of a metal material and have an effect of releasing heat to the chassis side. Therefore, if the heat generated by the servo coil is transmitted to the four wires, the heat can escape to the chassis side and the temperature rise of the prism can be prevented.

The tracking coil 26 shown in FIG.
a, 26b and the focusing coil 25 are shown in FIG.
As shown in FIG. 1 (a), they are connected in series and are connected to the terminals provided on the chassis side. In this case, since the coil uses a thin conductive wire having a diameter of about 0.1 mm, connecting the four wires in this state has a small effect of releasing heat.

For this reason, as shown in FIG. 11B, the wire diameter is made thicker from the end of the coil winding (about 1 mm in diameter).
Then, the coils are connected, and the ends of the thickened coil windings are connected to the wires 27a to 27d through the terminals 27. Then, a current is supplied to each coil by four wires.

FIG. 12 shows a state in which a servo coil having a wire diameter increased from the end of the coil winding is actually connected to the wires 27a to 27d. In the winding part of the coil, multiple conductor wires are wound, and the amount of heat transfer in this part is large, but by connecting a thick conductor wire with a diameter of about 1 mm so that this part contacts with a large contact area, the heat of the coil is quickly generated. It can be released to the chassis and the temperature rise of the prism can be suppressed.

FIG. 13 is a diagram showing a fourth embodiment of the optical axis deviation preventing means. As described above, the silicon substrate 60
Has good thermal conductivity, but its surface area is small, so the amount of heat radiated to air is not so large. Therefore, by increasing the surface area of the substrate or the portion in contact with the substrate to increase the amount of heat radiation, it can be expected to prevent the temperature rise of the substrate itself.

In the structure shown in FIG. 6, the size of the silicon substrate is set to 4 mm × 5 mm in accordance with the size of the prism. In this embodiment, as shown in FIG. 13, a U-shaped heat dissipation plate 38 is attached to the silicon substrate 60 to increase the surface area of the portion in contact with the substrate. In this case, if the heat radiating plate is made too large, the weight of the optical pickup increases, and high-speed seek cannot be achieved. In this embodiment, the size of the heat dissipation plate is set so that a surface area about 5 times the surface area of the silicon substrate 60 alone can be obtained.

As a result, a large heat radiation effect can be obtained, and the temperature rise of the silicon substrate 60 can be prevented. Of course, the shape of this heat dissipation plate is not limited to that shown in the figure, and various modifications are possible.

FIG. 14 is a diagram showing a fifth embodiment of the optical axis shift preventing means. In this embodiment, the optical system 1 shown in FIG. 5 is surrounded by a square-shaped plastic cover 40. On the inner peripheral surface of the plastic cover 40, a pair of connecting pieces 40a perpendicular to the surface is formed, and the connecting pieces 40a are fixed to the front surface 17a and the rear surface 17b of the optical system 1. The outer peripheral surface of the optical system 1 and the inner peripheral surface of the cover 40 have a gap G of about 1 mm, and the upper and lower surfaces are open. Although not shown, the four wires supporting the servo coil and the optical system are bonded to the outer peripheral surface of the cover 40.

As shown in FIG. 14 (c), as the magneto-optical disk rotates, an air flow which is sucked up from the lower opening and blown out from the upper opening in the gap G between the optical system 1 and the cover 40. Occurs. Due to such convection, the amount of heat radiation to the air centering on the silicon substrate increases, and the temperature rise of the optical system is suppressed. Further, since the servo coil is not directly fixed to the prism, the heat generated by the servo coil is not transferred to the prism.

FIG. 15 is a modification of the structure of the cover shown in FIG. In this modification, the cover 41 is made of a thin aluminum plate and the cover is made of a silicon substrate 6.
By directly fixing it to 0, the same heat dissipation effect as in the fourth embodiment is provided. With this configuration, in addition to the effect obtained in the fifth embodiment, the effect obtained in the fourth embodiment can be obtained.

FIG. 16 is a diagram showing a sixth embodiment of the optical axis shift prevention means. In general, the optical pickup is used in a temperature range of a considerably wide range, so that the influence of the temperature change of the atmosphere cannot be avoided. Therefore, the prism 10
The bonding portion between the silicon substrate 60 and the silicon substrate 60 was in the state shown in FIG. 16A at room temperature due to the difference in the coefficient of thermal expansion between the prism and the silicon substrate.
As shown in FIG. As can be seen from this figure, a large deformation occurs at the joint between the prism 10 and the silicon substrate 60. The joint between the two is a light ray reflecting surface, and if a large warp occurs on this surface, the wavefront shape of the light reflected here changes, and when the light is finally focused on the disk surface, aberration will occur. It is generated and the focused spot becomes large. This aberration becomes remarkable as the magnitude of the warp increases, and the magnitude of the warp increases as the bonding length between the prism 10 and the silicon substrate 60 increases.

In order to suppress the influence of the warp to a small extent, the bonding surface may be set so that the length of the bonded portion between the silicon substrate and the plastic prism is shortened. That is, the warp of the bonding surface between the silicon substrate and the prism occurs because both are fixed on the entire surface and both do not slide at all.

Therefore, as shown in FIG. 16C, the upper half of the silicon substrate 60 is firmly fixed to the prism 10 with a hard adhesive, and the lower half is fixed with a soft adhesive. When the two are bonded together in this way, when a temperature rise occurs, the prism having a large coefficient of thermal expansion causes slippage due to the soft adhesive, and the warpage is alleviated. As a result, it is possible to suppress the deterioration of the wavefront aberration of the light ray internally reflected.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above-mentioned embodiments and can be variously modified. For example, the optical axis shift prevention means of each embodiment may be combined and configured as needed. Further, although the above-described embodiment is a pickup for a magneto-optical disk, it may be a read-only CD pickup except for the deflection separation element.

[0050]

According to the present invention, in the optical pickup in which the optical path is formed by using the prism, the prism is prevented from being deformed by thermal deformation because the optical axis deviation preventing means is provided, and the prism is emitted from the laser diode. The optical axis of the laser beam does not shift. As a result, a good detection signal can be obtained without deteriorating the light condensing property on the surface of the optical recording medium.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of an optical system of an optical pickup according to the present invention.

FIG. 2 is a side view showing a path of laser light emitted from an LD in the optical system shown in FIG.

FIG. 3 is a front view showing a path of light toward a photodetector in the optical system shown in FIG.

4 is a diagram showing a path of light detected by a photodetector formed on a silicon substrate in the optical system shown in FIG.

5 is a perspective view showing a state where the optical system shown in FIG. 1 is assembled.

6 is a perspective view showing a state in which a servo function is added to the optical system shown in FIG.

FIG. 7 is a perspective view of a chassis supporting the optical system shown in FIG.

FIG. 8 is a perspective view showing an overall configuration of an optical pickup.

FIG. 9 shows a first embodiment of an optical axis shift preventing means used in the optical pickup of the present invention, (a) is a perspective view,
(B) is a side view.

FIG. 10 shows a second embodiment of the optical axis deviation preventing means used in the optical pickup of the present invention, (a) is a perspective view,
(B) is a cross-sectional view of a flexible substrate used in this embodiment.

11A and 11B show a third embodiment of the optical axis deviation preventing means used in the optical pickup of the present invention, FIG. 11A shows a general configuration of a servo coil, and FIG. 11B shows the present embodiment. It is a figure which shows the structure of the coil for servos used.

FIG. 12 is a perspective view of an optical system to which the servo coil shown in FIG. 11 (b) is attached.

FIG. 13 is a perspective view showing a fourth embodiment of the optical axis shift prevention means used in the optical pickup of the present invention.

14A and 14B are views showing a fifth embodiment of the optical axis shift preventing means used in the optical pickup of the present invention, wherein FIG. 14A is a perspective view, FIG. 14B is a plan view, and FIG. It is sectional drawing of the A line.

FIG. 15 is a perspective view showing a modified example of the fifth embodiment.

FIG. 16 is a view showing a sixth embodiment of the optical axis shift preventing means used in the optical pickup of the present invention, FIG. 16 (a) is a side view showing a plastic prism at room temperature,
(B) is a side view showing the plastic prism at a high temperature, (c) is a side view showing a bonded state of the silicon substrate and the plastic prism in this embodiment, and (d) is a high temperature in the bonded state shown in (c). It is a side view which shows the state of the moment of time.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical system, 10 ... Plastic prism, 25 ... Focusing coil, 26a, 26b ... Tracking coil, 27a-27d ... Wire, 30 ... Chassis, 35 ...
Insulating spacers, 36 ... Wiring board, 38 ... Radiating plate.

Claims (1)

[Claims] 1. A substrate having a light source and a photodetector, a substrate fixed to the substrate, internally reflecting the light emitted from the light source, and condensing the light on an optical recording medium; and a substrate emitting from the substrate. And a control means for controlling the base so as to focus the emitted light on the track of the optical recording medium. In the optical pickup, the optical axis deviation prevention means for preventing the deviation of the optical axis caused by the thermal deformation of the base is provided. An optical pickup characterized by that.