JPH11283272A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup device equipped with a coating layer for preventing the subordinate reflection film of an optical element provided on a substrate from corroding without optical interference. SOLUTION: This device is provided with a prism element 1 for reading information from an optical information medium and forming an optical path to a light receiving element by refracting and reflecting incident light from an external light emitting element while having the laminate structure of laminating plural light transmissible substrates 3, 4, 5, 7 and 8, and the optical elements of different optical system characteristics provided on the light incident surfaces of the substrates 3-8 are uniformly coated with the light transmissible coating layer having no interference with the optical system characteristics of the respective optical elements.

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 for recording and reproducing information on and from various optical elements and optical disks, and more particularly, to maintaining a highly accurate optical system of a laminated prism in which optical elements are integrated. The present invention relates to an optical pickup device that can be used.

[0002]

2. Description of the Related Art Conventionally, an optical head for magneto-optical recording using a laser has been used as a means for recording and reproducing information on an optical disk. This optical head is composed of a fixed optical system, which is an assembly in which individual optical components such as a prism, a lens, various sensors, and a laser are assembled with high precision, and a reflection mirror and an objective lens which are lightweight so that they can be accessed at high speed. And a movable optical system including the above.

[0003] In a system having such a fixed optical system and a movable optical system, it is necessary to form a light path for light in both systems and to form an optical path between these systems. There was a limit in reducing the size and weight. On the other hand, in order to achieve the integration of the whole system, a single integrated head was used to enable the incidence from the semiconductor laser, the emission of light to the optical disk-side imaging system, and the re-incident and reproduction of reflected light. The applicant of the present application has already proposed and proposed this in Japanese Patent Application No. 7-311.
No. 43 was filed.

This integrated optical head utilizes a laminate prism structure in which a plurality of glass substrates are stacked. The laminate prism is a prism having a laminated structure in which a plurality of wafer substrates on which optical functional elements necessary for recording and reproduction of an optical disk are mounted by using a wafer process technology are bonded and processed. In such an integrated optical head using a laminated prism, reduction in size and weight is, of course,
Compared with the conventional one, the productivity is higher and the positional relationship between the optical elements in the prism is maintained with the exposure mask accuracy, so that there is an advantage that the environmental characteristics and the long-term reliability are excellent.

When a laminate prism is used, an optical path for returning a laser beam incident from the outside toward the optical disk and returning to the reproduction sensor side, an optical path for focusing and tracking, and an optical path for incident laser monitoring are formed. There is a need.

[0006] Each substrate is formed so as to have a slope of 45 ° with respect to the horizontal incidence direction of the laser. In order to form the above-mentioned optical path, each substrate has a reflection film, a hologram, a beam splitter film and the like. Formed as required. The hologram forms a light path to a servo sensor for focusing and tracking by receiving a part of the reflected light from the optical disk, for example, and receives a part of the incident beam to a laser monitor sensor. Used to form an optical path.

The production of this hologram is performed by a process of forming a hologram profile by applying a resist to a glass substrate, developing etching, exposing and the like, and then forming a reflective film on which metal is deposited. For the reflection film formed on the hologram, it is necessary to increase the reflectance, for example, in order to maintain high accuracy of the optical system, and use a metal material having a high reflectance such as Ag or Al. Has been optimized.

[0008]

The use of a laminated prism makes it possible to reduce the size and weight of the optical system as compared with the conventional optical system. Arranging a plurality of optical elements such as holograms and beam splitters on each slope of the substrate is one effective means. That is, in a laminated prism in which a plurality of glass substrates are laminated, integration is further promoted if one substrate is a multifunctional unit rather than having only one function for an optical system. As a result, the amount of information increases and the size of the optical pickup device can be further reduced. Therefore, from the viewpoint of such multi-functionality, it is effective to form an optical element on each of two slopes of one substrate or to arrange a plurality of optical elements on the same slope.

On the other hand, the metal material used as the reflection film of the hologram preferably has a high reflectance and good adhesion to a glass substrate.
1 and the like are optimal. However, a metal material having a high reflectance generally has a high corrosiveness, and in particular, corrosion often starts even in a short time due to contact with a chemical component contained in a synthetic resin or the like. Au has high reflectivity and low corrosiveness,
Since the adhesion to glass is not stable, it can be said that it is not preferable for a laminated prism.

Therefore, Ag or A is provided on one side of the substrate.
In the case where a hologram is formed using a laser beam and a beam splitter is formed in a region included in this surface, and another optical element is provided on the other surface, Ag or Al
It is necessary to prevent corrosion. In other words, in the case where the hologram is first formed on one surface side of the substrate in the process by the wafer process and then another optical element is formed on the other surface side, Ag and Al are not changed until all the processes are completed. Often starts to corrode.

In order to prevent the corrosion of Ag and Al used as a reflection film of such a hologram, if a reflection film made of such a material is formed and then covered with an appropriate protective film, it is possible to suppress the trouble caused by the corrosion. it can.

However, as described above, when not only the hologram but also the beam splitter are provided on the same inclined surface of the substrate, the hologram and the beam splitter have different optical functions. It must be covered with a separate protective film that does not impair. In order to cover the hologram and the beam splitter in this way, a step of forming a patterned protective film is performed for each of the hologram and the beam splitter, which complicates the process and greatly affects the product yield.

In order to avoid such patterning, the entire inclined surface of the substrate may be covered with a common protective film. However, even if it is suitable for preventing corrosion of Ag and Al in the reflection film of the hologram, both the hologram and the beam splitter must satisfy the conditions that do not impair their optical characteristics. Even if a protective film made of, for example, a light-transmitting resin or the like is applied, it has a large tendency to affect the optical system, and a protective film that does not interfere with the optical characteristics at all has not yet been developed.

It is an object of the present invention to provide an optical pickup device having a coating layer which prevents corrosion of a metal reflective film of an optical element provided on a substrate and does not involve optical interference.

[0015]

The present invention has a laminated structure in which a plurality of light-transmitting substrates are laminated, and reads information from an optical information medium by refracting and reflecting incident light from an external light emitting element. And an optical pickup device including a laminate prism capable of forming an optical path to a light receiving element,
Optical elements having different optical system characteristics included on the light incident surface of the substrate are uniformly coated with a coating layer that is a light transmission type and does not interfere with the optical system characteristics of each optical element. And

With such a configuration, even if a plurality of optical elements having different optical system characteristics, such as a hologram and a beam splitter film, are arranged on the light incident surface of the substrate, the covering layer can be used as the light incident surface. By uniformly coating the surface, it is possible to protect each optical element from a metal film which does not interfere with the optical system and is easily corroded, which is contained in a hologram or the like.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 has a laminated structure in which a plurality of light-transmitting substrates are laminated, and refracts and reflects incident light from an external light-emitting element to thereby transmit light from an optical information medium. An optical pickup device including a laminate prism capable of reading information and forming an optical path to a light receiving element, wherein an optical element having a different optical system characteristic included in a light incident surface of a substrate is a light transmitting type, and Optical elements with different optical system characteristics, such as holograms and beam splitter films, are uniformly coated with a coating layer that does not interfere with the optical system characteristics of each optical element. Even if a plurality of layers are arranged, it is only necessary to coat the coating layer uniformly on this light incident surface, and there is no interference in the optical system of each optical element and protection of corrosive metal film contained in hologram etc. Also possible It has the effect of that.

According to a second aspect of the present invention, in the optical pickup device according to the first aspect of the present invention, the covering layer has a single-layer or multi-layer dielectric structure and a thickness that allows light to pass therethrough. Even if a plurality of optical elements having different optical system characteristics such as a hologram and a beam splitter film are arranged on the light incident surface of the substrate,
It is only a process of uniformly coating the coating layer on the light incident surface, and has the effect that the optical system of each optical element does not interfere and it is possible to protect the corrosive metal film included in the hologram and the like. .

According to a third aspect of the present invention, the coating layer is made of Al
_3. The laminated prism structure in the optical pickup device according to claim 2, wherein the laminated prism structure has a three-layer structure including a SiO ₂ protective film that covers both surfaces in the direction of the ₂ O ₃ coating, and each has an optical structure such as a hologram or a beam splitter film. Even if a plurality of optical elements having different system characteristics are arranged on the light incident surface of the substrate, only the process of uniformly coating the coating layer on the light incident surface is sufficient, and there is no interference with the optical system of each optical element. This has the effect that it is possible to protect a corrosive metal film contained in a hologram or the like.

According to a fourth aspect of the present invention, there is provided a light source, a light receiving means for converting incident light into an electric signal, and a plurality of optical elements, for guiding light emitted from the light source to a recording medium. A light guide member for guiding the light reflected by the recording medium to the light receiving means, and by providing a coating layer covering the optical element, the optical element can be prevented from coming into contact with air or the like. Can be efficiently suppressed from deteriorating.

According to a fifth aspect of the present invention, at least two of the optical elements are covered with the same coating layer, so that optical elements having different optical system characteristics, such as a hologram and a beam splitter film, are provided. Even if a plurality of light-incident surfaces are arranged on the light-incident surface of the substrate, only the process of coating the entire coating layer is required, and the metal film which is easily corroded can be protected.

Hereinafter, specific examples of the embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic longitudinal sectional view of an optical pickup device according to an embodiment of the present invention, and FIG. 2 is an exploded perspective view showing each substrate of a laminate prism.

In FIG. 1, inside the integrated optical head,
The prism element 1 is arranged in a posture along the submount 51 and the semiconductor laser chip 52 mounted thereon.

The prism element 1 includes a photodiode 2 at the lower end in the figure, and as shown in FIG. 2, a first substrate 3, a second substrate 4, a third substrate 5, a fourth substrate 6, a It has a structure in which a fifth substrate 7 and a sixth substrate 8 are stacked in order from the top. These first to sixth substrates 3 to 8 are all made of glass, and the angle of the interface formed by the respective lamination surfaces is 45 ° with respect to the laser irradiation direction from the semiconductor laser chip 52. Eggplant

The second substrate 4 has a reflection film 4a and a beam splitter film 4b on the interface side with the third substrate 5, and has a three-beam diffraction grating 4c on the interface side with the first substrate 3.
Is provided. The third substrate 5 includes a beam splitter film 5a and a monitor hologram 5b on the interface side with the fourth substrate 6, and the astigmatism hologram 5c on the interface with the second substrate 4 side.
And a reflection film 5d on the upper end surface side. The fifth substrate 7 functions as a polarization separation substrate.
Each of the substrates 3 to 7 is provided with a reflection film 7a and a polarization separation film 7b having a twisted attitude with respect to the 45 ° light incident and reflection surfaces.

On the other hand, the photodiode 2 is provided with a servo sensor 2a, a reproduction sensor 2b for S-polarized light and P-polarized light, and a laser monitor sensor 2c.

As shown in FIG. 1, the first to sixth substrates 2 to 7 are stacked so that the angle between the respective interfaces is 45 °, and are integrally stacked on the photodiode 2. The prism element 1 is configured.

Here, when the semiconductor laser chip 52 irradiates the laser in the horizontal direction from outside the second substrate 4, the irradiation laser is turned upward at right angles by the reflection film 4 a for 3 seconds.
The beam reaches the beam diffraction grating 4. This three-beam diffraction grating 4c
Is an NA conversion hologram for converting the light diffusion angle of the irradiation laser from NA to NA, and converts the beam into three beams of 0th-order diffracted light (main beam) and ± 1st-order diffracted light (side beam). Then, these main beam and side beam are incident on the beam splitter film 4b having polarization selectivity.

Of the light incident on the beam splitter film 4b, the light transmitted through the beam splitter film and
The light is directed toward the monitor hologram 5b of the third substrate 5 and thereafter emitted from the reflection film 5d toward the laser monitor sensor 2c of the photodiode 2.

The laser monitor sensor 2c monitors the emitted light from the semiconductor laser chip 52 by detecting the emitted light.

On the other hand, the beam components of the main beam and the side beam reflected by the beam splitter film 4b pass through the upper surface of the second substrate 3. Then, the transmitted light is incident on an objective lens (not shown) arranged on the optical disk disk (not shown) side, and is imaged on the information recording surface of the optical disk disk by the condensing action of the objective lens. At this time, the imaging spots of the two side beams on the information recording surface are imaged at substantially symmetric positions about the imaging spot of the main beam. Then, information recording or reproduction signals and so-called servo signals for tracking and focusing are read out from the information recording surface by the imaging spots of the main beam and the side beams.

The return light of the main beam and the side beam reflected by the information recording surface of the optical disk drive again enters the beam splitter film 4b of the second substrate 4. This beam splitter film 4b is almost 100% responsive to light having a vibration component parallel to the plane of incidence (P-polarized component).
And has a constant reflectance with respect to a vertical vibration component (S-polarized component).

The light transmitted through the beam splitter film 4b is incident on the polarization-selective beam splitter film 5a of the third substrate 5. This beam splitter film 5a also
Like the beam splitter film 4b of the second substrate 4, it has a transmittance of 100% for the P-polarized component and a constant reflectance for the S-polarized component. Then, of the light that has reached the beam splitter film 5a, the light component that has passed through the light splitter film 5a
b and enters the reproduction sensor 2b.

The light that does not pass through the beam splitter film 5a is reflected by this portion and then travels to the astigmatism hologram 5c, where it is applied to the servo sensor 2a to perform a focus error by the astigmatism method.

As described above, the reading and reproduction of information from the optical disk are performed by causing the laser beam from the semiconductor laser chip 52 to enter the prism element 1. At the same time as the reproduction, the detection of the focus error and the tracking error is performed at the same time, and the accuracy of the reproduction output can be improved.

FIG. 3 is an exploded schematic perspective view showing a second substrate and a coating layer covering the second substrate. As described above, the third substrate 5 is formed by arranging the beam splitter film 5a and the monitor hologram 5b on the inclined surface serving as an interface between the third substrate 5 and the fourth substrate 6. An astigmatism hologram 5c is formed. When the beam splitter film 5a, the monitor hologram 5b, and the optical elements of the astigmatism hologram 5c are respectively formed on both surfaces of the inclined surface as described above, after forming these optical elements on one inclined surface in the wafer process, The process proceeds so as to form the remaining optical element on the inclined surface.

The beam splitter film 5a is formed by applying a photoresist, exposing it to light, developing it, forming a pattern thereof, forming a film by vacuum evaporation or sputtering, and removing unnecessary portions by lift overflow. Can form the beam splitter film 5a patterned.

The surface of the monitor hologram 5b and the astigmatism hologram 5c are stepped by repeating a process of applying a resist to each inclined surface of the third substrate 5, exposing, exposing, developing, etching and further washing. It can be obtained by forming and finally depositing a metal reflective film. As the metal reflection film, Ag or Al having high light reflectance is used as described in the section of the related art.

As described above, the monitor hologram 5b or the astigmatism hologram 5c containing Ag or Al as the reflection film is used.
Then, as described above, metal corrosion is likely to occur after the deposition of the reflective film. Therefore, as shown in the example of FIG.
Beam splitter film 5a and monitor hologram 5b
By covering the entirety of the inclined surface including the above with the coating layer 9 made of a dielectric material, corrosion of the metal of the reflection film is prevented.

The coating layer 9 is formed on the inclined surface of the third substrate 5 by a vapor deposition method or a sputtering method, and is made of a dielectric material of alumina and silica. In the example shown in the figure, the coating layer 9 is a three-layer laminate of the Al ₂ O ₃ layer 9a and the SiO ₂ protective films 9b and 9c stacked on and under the Al ₂ O ₃ layer 9a. Is 90
３２０320 nm, and the thickness of the protective films 9 b and 9 c is 3
It is about 50 nm.

In such a laminated body of the Al ₂ O ₃ layer 9a and the protective films 9b and 9c of SiO ₂ , since the Al ₂ O ₃ layer 9a is thick enough to transmit light, it is made of light-transmitting SiO _2. The coating layer 9 can also be made light-transmissive by combination with the protective films 9b and 9c, so that almost all of the incident light can be transmitted, that is, the reflection can be hardly observed.

FIG. 4 is a graph showing the characteristics of light transmittance between the case where the coating layer is formed and the case where the coating layer is not formed according to the present invention. The horizontal axis represents wavelength (nm), and the vertical axis represents transmittance ( %)
Is taken.

The Al ₂ O ₃ layer 9a used for the coating layer 9 has a refractive index of 1.63 and a thickness of 320.8 nm.
SiO _{2 of the} protective film 9b has a refractive index of 1.45 and a thickness of 402.9 nm. In the diagram, those indicated by broken lines indicate the case where the coating layer 9 was not formed, and those indicated by solid lines indicate the case where the coating layer 9 was formed.
Is formed, the light transmittance is close to 100%, which is almost the same as the case of not forming. That is, the coating layer 9 almost transmits the incident light and the reflection is on the order of a value close to zero. It turns out that it does not occur.

In the wafer process, the coating layer 9
After the beam splitter film 5a and the monitor hologram 5b are formed on the inclined surface of the third substrate 5, the beam splitter film 5a and the monitor hologram 5b are uniformly formed on the entire inclined surface, and the process proceeds to a later step. For example, in FIG. 3, when the beam splitter film 5a and the monitor hologram 5b are formed on one of the inclined surfaces first, and then the astigmatic hologram 5c is formed on the other inclined surface, the astigmatic hologram 5c is formed. Is a post-process, and the metal of the monitor hologram 5b is prevented from being corroded by the coating layer 9 including the period up to the post-process.

Here, the beam splitter film 5a is designed to have constant reflectance and transmittance in order to separate the return light from the disk. That is, the reflected light guides the light beam to the astigmatism hologram 5c, and generates a servo signal on the astigmatism hologram 5c. In order to keep the servo signal constant, it is effective to form the coating layer 9 to suppress a change in the reflection characteristic. Then, as shown in FIG. 4, since the light transmittance of the beam splitter film 5a hardly changes depending on the presence or absence of the coating layer 9, the suppression of the change in the reflection characteristics by the coating layer 9 has some effect on the light transmittance. Has no effect. Therefore,
Even after the formation of the beam splitter film 5a, coating with the coating layer 9 including the Al ₂ O ₃ layer 9a does not impair the function of the beam splitter film 5a as an optical element that should be originally maintained, and does not interfere with the optical system. Is not accompanied.

On the other hand, the light transmitted through the beam splitter film 5a becomes a reproduction signal of a magneto-optical signal. In order to maintain good reproduction of the magneto-optical signal, it is necessary to prevent the transmittance characteristics and the polarization characteristics from changing even when the coating layer 9 is formed. Incidentally, the polarization characteristic means that the beam splitter film 5a is formed on a plane parallel to the incident surface of the formation surface.
The relative phase difference between the polarization component and the S-polarization component perpendicular to the polarization component, and the phase difference is designed to be zero.

FIG. 5 is a diagram showing the light reflection characteristics of the case where the coating layer is formed according to the present invention and the case where the coating layer is not formed, and FIG. FIG. 3 is a diagram showing a relative phase difference of transmitted light. In FIG. 5, the broken line indicates the case where the coating layer 9 is not formed, and the case where the coating layer 9 is formed is indicated by a solid line. Even when the coating layer 9 is formed, there is almost no difference in transmittance characteristics. Not. As is clear from FIG. 6, the relative phase difference is almost the same before and after the formation of the coating layer 9, and the effect of forming the coating layer 9 can be neglected.

Further, since the monitor hologram 5b is a metal film and does not transmit light, even if the cover layer 9 is formed, its characteristics are not affected. Therefore, similarly to the case of the beam splitter film 5a, the monitor hologram 5
b does not impair the function as the optical element. The metal such as Ag or Al used as a reflection film for the monitor hologram 5b is protected by the coating layer 9 and its corrosion is prevented, so that a good reflection film is provided from the wafer process to the product production and thereafter. Optical function can be maintained.

As described above, in the present invention, it is not necessary to pattern and form a film made of an appropriate material for each of the beam splitter film 5a and the monitor hologram 5b having different optical system characteristics. Therefore, also in the process of forming the third substrate 5, a patterning step for forming a film is not required, and the manufacturing process is not complicated.

In the above example, an example in which the uniform coating layer 9 is formed on the surface of the third substrate 5 on which the beam splitter film 5a and the monitor ologram 5b are formed has been described. Of course, it is needless to say that the present invention can be applied to a surface where the reflection film 4a and the beam splitter film 4b are formed on one surface side.

In this embodiment, a prism element 1 having a laminate structure as an example of a light guide member having a plurality of optical elements and having a function of guiding light to a predetermined position while exerting a predetermined optical action on light. However, the present invention is not limited to this, and it is also possible to use one utilizing reflection or refraction on the surface, etc., as long as it has at least two or more optical elements on the surface of the substrate. The present invention can be applied to all light guide members.

[0052]

According to the present invention, even if a light incident surface includes optical elements having different optical system characteristics, disturbance or interference may occur in the optical system of each optical element only by forming the coating layer uniformly. Since a metal film such as Ag or Al contained in a hologram or the like which is easily corroded can be protected without performing the above-mentioned process, a product with improved durability can be obtained if the optical system characteristics are maintained with high accuracy.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of an optical pickup device according to an embodiment of the present invention.

FIG. 2 is a schematic perspective view showing a disassembled substrate.

FIG. 3 is an exploded schematic perspective view showing a second substrate and a coating layer covering the second substrate.

FIG. 4 is a diagram showing characteristics of light transmittance of a case where a coating layer is formed and a case where a coating layer is not formed in the present invention.

FIG. 5 is a diagram showing light reflection characteristics of a case where a coating layer is formed and a case where a coating layer is not formed in the present invention.

FIG. 6 is a diagram showing a relative phase difference of transmitted light between a case where a coating layer is formed and a case where a coating layer is not formed in the present invention.

[Explanation of symbols]

Reference Signs List 1 prism element 2 photodiode 2a servo sensor 2b reproduction sensor 2c laser monitor sensor 3 first substrate 4 second substrate 4a reflection film 4b beam splitter film 4c 3 beam diffraction grating 5 third substrate 5a beam splitter film 5b monitor hologram 5c astigmatism Aberration hologram 5d Reflective film 6 Fourth substrate 7 Fifth substrate 7a Reflective film 7b Polarization separation film 8 Sixth substrate 9 Cover layer 9a Metal layer (AL ₃ O ₃ layer) 9b, 9c Protective film 51 Submount 52 Semiconductor laser chip

Claims (5)

[Claims] An optical path has a laminated structure in which a plurality of light-transmissive substrates are laminated, and refracts and reflects incident light from an external light emitting element to read information from an optical information medium and form an optical path to a light receiving element. An optical pickup device including a laminating prism made possible, wherein an optical element having a different optical system characteristic included in a light incident surface of a substrate is subjected to light transmission and interference with the optical system characteristic of each optical element. An optical pickup device characterized by being uniformly coated with a non-covering layer. 2. The optical pickup device according to claim 1, wherein the coating layer has a single-layer or multi-layer structure of a dielectric and has a thickness allowing light to pass therethrough. 3. The optical pickup device according to claim 2, wherein the covering layer has a three-layer structure including a SiO ₂ protective film covering both surfaces in the Al ₂ O ₃ covering direction. 4. A light source, a light receiving means for converting incident light into an electric signal, and a plurality of optical elements. The light emitted from the light source is guided to a recording medium and is reflected by the recording medium. An optical guide member for guiding the light to the light receiving means, and a coating layer for covering the optical element. 5. The optical pickup device according to claim 4, wherein at least two of said optical elements are covered with the same coating layer.