JPH09198701A - Optical pickup and optical pickup for phase change type optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a satisfactory signal characteristic by forming dielectric reflection films on presribed positions of substrates constituting an optical guide member to make the absorption loss of light small and to make the resistance to an organic solvent, etc., large. SOLUTION: This pickup has plural substrates inclined with respect to the incident light irradated from a light source 1 and also has reflection films formed in the optical path of the substrates by being laminated with plural dielectric layers. Then, the light returned by being reflected form an optical medium is guided to prescribed positions by an optical guide member and the lights are received by light receiving means 13 and also light signals are transducer into electric signals. The reflection films are formed on the prescribed positions of the surfaces of the substrates constituting the optical guide member and reflect the incident light to guide it to prescribed positions. Then the reflection film is formed by alternately laminating the dielectric film having a high refractive index and the dielectric film having a low refractive index.

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 or reproducing information on or from an optical element, an optical disc or the like, and an optical pickup for a phase change type optical disc.

[0002]

2. Description of the Related Art In recent years, an integrated optical pickup device has been developed with the aim of miniaturizing an optical pickup, and is going to be put to practical use. FIG. 14 is a block diagram of a conventional optical pickup. Reference numeral 501 is a light source composed of a semiconductor laser or the like. The light emitted from the light source 501 enters the light guide member 505. Then, it is converted into light having a predetermined characteristic by an optical element provided inside the light guide member 505 and is emitted from the light guide member 505.
The emitted light then enters the objective lens 526, is then focused on the recording medium 527, and its properties are slightly changed according to the data recorded on the information recording surface 527a formed in the recording medium 527. It is reflected and becomes reflected light. The reflected light is again transmitted to the objective lens 526 and is incident on the light guide member 505. After that, the optical path is divided into a plurality of optical members such as a plurality of reflection films provided on the light guide member 505, and the light receiving element 513 is divided. To detect a predetermined signal.

At this time, a metal reflection film is often used for the plurality of reflection films provided on the light guide member 505. FIG. 15 is a cross-sectional view of a conventional reflective film. FIG.
In the above, reference numeral 400 denotes a substrate, and the substrate 400 is usually made of a material having a high light transmittance such as glass. The light 401 traveling through the substrate 400 is incident on the metal reflection film 402 formed on the end surface of the substrate 400. The light 401 incident on the metal reflection film 402 is reflected there and guided to a predetermined position.

[0004]

However, since the metal reflection film 402 used in the above-described conventional structure has a relatively large light absorption loss inside, the reflectance is extremely set to 93% or more. was difficult. Therefore, the light receiving element 5
Since the amount of light guided to the light receiving element 13 decreases, the light receiving element 513
In, it was difficult to obtain a good signal having a high signal level with respect to the noise level. In addition, the metal reflection film 402
Since the resistance to various kinds of chemicals such as organic solvents used in the photolithography process when forming the pattern is low, the metal reflection film 40 having a predetermined thickness is formed.
Even if the layer 2 is formed, the metal reflection film 402 is damaged in the subsequent step, for example, the step of removing the resist, and it is difficult to control the film thickness. Further, the metal reflection film is a substrate 4 such as glass.
Since the bonding force with the material of No. 00 is weak, a plurality of substrates are bonded together to form a substrate block, and when the substrate block is cut to obtain the light guide member 505, the bonding site between the substrates is peeled off at the time of cutting. It had problems such as being lost.

The present invention solves the above problems by providing a reflective film with a relatively small light absorption loss, a large resistance to organic solvents, etc., and an excellent bonding strength with a substrate. It is an object of the present invention to provide an optical pickup which has a high yield.

[0006]

In order to achieve this object, a dielectric reflecting film is formed at a predetermined position on a substrate which constitutes a light guide member.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION A light source and a plurality of substrates that are inclined with respect to an incident direction of light emitted from the light source, and are formed by laminating a plurality of dielectric layers on an optical path of the substrate. And a light guide member for guiding the light from the light source to the optical medium and guiding the light reflected from the optical medium to a predetermined position, and receiving the light and receiving the received optical signal as an electrical signal. By including the light receiving means for converting to, it is possible to improve the reflection efficiency of the reflection film and to improve the bondability with the substrate.

Reflection efficiency can be improved by forming at least one dielectric layer having a different refractive index in the plurality of dielectric layers.

By alternately laminating the dielectric layers having a high refractive index and the dielectric layers having a low refractive index, the reflection efficiency can be further improved.

By making the dielectric layer closest to the substrate a dielectric layer having a low refractive index, it is possible to prevent the refractive index from changing in the dielectric layer.

By setting the difference in refractive index between the dielectric layer having a high refractive index and the dielectric layer having a low refractive index to 0.5 or more, the thickness of the dielectric reflecting film can be made extremely thin.

By forming the plurality of dielectric layers in the directions in which the respective film stresses are canceled out, it is possible to prevent the warp of the substrate and the position dependence of the reflectance of the reflective film.

By providing a λ / 4 plate between the light emitting surface of the light guide member and the optical medium, and arranging the λ / 4 plate and the optical axis of the light substantially perpendicularly, the utilization efficiency of light is improved. be able to.

The packaging of the optical pickup according to the first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 and FIG. 2 are cross-sectional views each showing a configuration of packaging of an optical pickup according to an embodiment of the present invention.

Reference numeral 1 denotes a light source. As the light source 1, various lasers such as a semiconductor laser and a gas laser such as He-Ne can be considered. Here, it is preferable to use a semiconductor laser which is the smallest among these, can reduce the size of the entire device, and has an output of several mW to several tens mW which is inexpensive. Semiconductor lasers made of AlGaAs, InGaAsP, I
nGaAlP, ZnSe, GaN, and the like are conceivable. Here, AlGaAs, which is most commonly used and is inexpensive, is used. Furthermore, when performing high-density recording, the spot diameter on the recording medium can be made smaller, and
It is preferable to use a semiconductor laser such as InGaAlP or ZnSe having a shorter wavelength than s.

2 is a submount, and the submount 2 is
Has a rectangular parallelepiped shape or a plate shape, and the light source is
1 is attached. This submount 2 is a light source 1
Along with mounting, it works to release the heat generated by the light source 1.
have. Heat is required to bond the submount 2 and the light source 1.
Considering the conductivity etc., Au-Sn, Sn-Pb, Sn-
A foil (thickness of several μm to several tens of μm) such as Pb-In is pressed at high temperature.
It is preferable to use the wearing method. Also, light source 1 and sub
If the mount 2 is not installed almost horizontally, the aberration of the optical system and
This may cause a decrease in coupling efficiency. Therefore, when joining
Source 1 is sub-mount 2 at a predetermined position and at a predetermined height with substantially water.
It is preferably mounted flat. Further sub-mount
The upper surface of the light source 2 should be in electrical contact with the lower surface of the light source 1.
An electrode surface 2a is provided. This electrode surface 2a is the light source 1
And a metal film that constitutes the electrode surface 2a.
In consideration of conductivity and corrosion resistance, use Au thin film.
Is preferred. Further, the submount 2 is generated by the light source 1.
Due to problems with heat and mounting with the light source 1, high thermal conductivity,
In addition, the coefficient of linear expansion is that of the light source 1 (about 6.5 × 10 ^-6/
A material close to ℃) is preferable. Specifically, the linear expansion coefficient is 3
~ 10 x 10^-6Thermal conductivity of 100 w / mK or more at / ° C
A substance such as AlN, SiC, T-cBN, Cu
/ W, Cu / Mo, Si etc., especially for high power laser
Thermal conductivity must be very high when
Sometimes it is preferable to use diamond or the like. light source
1 and submount 2 have the same or similar linear expansion coefficient.
Distortion between the light source 1 and the submount 2
Since it is possible to suppress the occurrence of
The mounting part with the module 2 comes off or the light source 1 is cracked.
Inconveniences, such as a problem, can be prevented. However the book
If it is out of the range, between the light source 1 and the submount 2
A large amount of distortion occurs, and the light source 1 and submount 2
The mounting part of may come off, or the light source 1 may crack.
Higher efficiency. Also, the thermal conductivity of the submount 2 can be
The heat generated by the light source 1
Can be efficiently released to the outside. However heat conduction
If the rate is below this limit, the heat generated by the light source 1
The temperature of the light source 1 rises and the light source 1
The output is reduced, the life of the light source 1 is shortened,
In case of, inconvenience such as destruction of the light source 1 occurs
Easier to do. In this embodiment, it is relatively inexpensive and these two
AlN, which is very excellent in both of the two characteristics, was used. Change
In addition, the upper surface of the submount 2 has a good bonding property with the light source 1.
In order to move from the submount 2 toward the light source 1, Ti,
It is preferable to form a thin film in the order of Pt and Au.

Reference numeral 3 denotes a block. The block 3 is basically a rectangular parallelepiped and has a large projection 3a on the side surface, and a submount 2 is mounted on the upper surface. Like the submount 2, the block 3 also has a high thermal conductivity and a material having a linear expansion coefficient close to that of the submount 2, for example, due to heat generated from the light source 1 and problems such as attachment to the submount 2. It is preferable to use Mo, Cu, Fe, Kovar, 42 alloy or the like other than those shown in the material examples of the submount 2. However, the requirements for these characteristic values are not so strict as compared with the submount 2, so that it is preferable to select them with emphasis on cost. Here, the block 3 is formed of a material such as Cu or Mo which is very inexpensive as compared with AlN and has relatively excellent characteristics. Further, in consideration of thermal conductivity and the like for joining the block 3 and the submount 2, Au-Sn, Sn-Pb, S, although slightly expensive, as in the case of the submount 2 and the light source 1.
It is preferable to press-bond a foil of n-Pb-In or the like (thickness: several μm to several tens of μm) at high temperature.

Reference numeral 4 denotes a radiator plate. The radiator plate 4 has a function of releasing heat generated by the light source 1 and transmitted through the submount 2 and the block 3 by conduction to the outside.
Various members forming the optical pickup are mounted thereon, and serve as a packaging substrate. The heat radiating plate 4 is provided with a hole 4a for adjustment. Block 3 is brazed,
It is fixed to the upper surface of the heat sink 4 by solder foil or the like. Heat sink 4
Cu, Al, Fe, etc., which have high thermal conductivity, can be considered as the material of the.

Here, the submount 2 and the block 3
Are formed separately, but when the output of the light source 1 is high and a higher thermal conductivity is required for these members, these members are integrally formed in order to improve the thermal conductivity. Is preferred. In this case, it is preferable to use those having extremely high thermal conductivity such as AlN.

It is desirable that the block 3 be larger than the submount 2 so as to have a large contact area with the heat sink 4.

Since the light source 1 is required to have high precision with respect to the optical axis, it is preferable that the upper surface of the submount 2 is horizontal with high precision. Therefore, it is preferable to pay close attention to the mounting of the submount 2, the block 3, and the heat sink 4.

Reference numeral 5 denotes a light guide member. The light guide member 5 has a rectangular parallelepiped shape, and has a plurality of slopes and various films formed on the slopes inside. It has a function of emitting the returned light and guiding the returned light to a predetermined position. The light guide member 5 is adhered on its side surface to the end surface 3b of the projection 3a of the block 3. The bonding material used for this purpose must have conditions such as high adhesive strength, workability that can be fixed at any moment, small changes in volume due to changes in volume before and after curing and changes in temperature and humidity, that is, low shrinkage. It is required, and by satisfying these, workability and stability of the joint surface can be improved. Here, a UV adhesive which is instantly cured by irradiating ultraviolet rays is used as such a bonding material. Further, a moisture-absorbing and curing instant adhesive may be used. It is preferable that the contact area (S) between the block 3 and the light guide member 5 is S> 1 mm ² in order to have a sufficient mounting strength.

Reference numeral 13 denotes a light receiving element. The light receiving element 13 is composed of various electric circuits formed on a plate-shaped semiconductor wafer, and is attached to the bottom surface of the light guide member 5. At the time of attachment, the position is adjusted using the holes 4 a provided in the heat sink 4. Regarding the attachment of the light receiving element 13 and the light guide member 5, a large adhesive strength, workability that can be fixed at any moment, change in volume before and after curing, temperature and
Conditions such as a small change in volume due to humidity, that is, a low shrinkage ratio are required. By satisfying these conditions, workability and stability of the joint surface are improved. As such a bonding material, a UV adhesive having particularly good workability was used because it is instantaneously cured by irradiating ultraviolet rays. Note that a moisture-absorbing-curing instant adhesive may be used. The light receiving element 13 has a plurality of light receiving portions for receiving the light signal emitted from the light source 1 and reflected by the light guide member 5 and the recording medium and returned. The light signal detected by the light receiving unit is converted into an electric signal according to the light amount. This electric signal has the magnitude of the current value at the beginning of the conversion. However, this current has the disadvantages that it is very weak and that noise is easily picked up.
For this reason, it is preferable here to use, as the light receiving element 13, an element formed with an IV amplifier having a function of converting a current value to a correlated voltage value and amplifying it. However, it is required that the response of the output voltage be good with respect to the incident frequency of light. Further, on the surface of the light receiving element 13, there are provided a plurality of electrodes 13a made of a thin film of Al or the like for extracting the received information as a signal.

Reference numeral 14 denotes a package.
On the upper surface of the heat radiating plate 4, the above-described block 3 and the light guide member 5,
It is provided so as to surround the light receiving element 13 and the like, and a lead frame 14a used for extracting an electric signal from the light receiving element 13, supplying power to the light source 1, and the like is molded therein. The shape of the package 14 is a rectangular parallelepiped shape with a hollow central portion.
The step 14 is formed on the inner surface of the package 14 on the side where the mold 4a is molded so as to expose the legs 14b of the lead frame.
c is provided. Note that the shape of the package 14 may be a cylindrical shape or the like. Then, the legs 14b of the lead frame exposed on the steps 14c provided on the package 14 for extracting an electric signal from the light receiving element 13
And a plurality of electrodes 13 provided on the surface of the light receiving element 13
a is connected by wire bonding with a wire 14d made of Au, Al, or the like. In order to supply power to the light source 1, the upper surface of the light source 1 and the leg 14 b of the lead frame exposed on the step 14 c provided on the package 14 are bonded by wires 14 d, and
The electrode surface 2a provided on the upper surface of the light source 1 so as to be in electrical contact with the lower surface of the light source 1 and the leg 14b of the lead frame exposed on the step 14c provided on the package 14 are also wire-bonded with the wire 14d. By connecting. The material of the package 14 is required to be excellent in low water absorption, low outgassing, and the like. Here, a thermosetting resin such as an epoxy resin, which is the most common, is used as the IC mold. As the material of the lead frame 14a, a metal such as Cu, 42 alloy or Fe plated with Ag or Au is often used. Here, Cu plated with Ni and Au plated thereon was used. Further, for attachment between the package 14 and the heat radiating plate 4, a bonding material having properties such as high adhesive strength, low water absorption, and high airtightness (low leak characteristics) is used. As a result, the stability of the bonding surface and bonding position can be improved, and impurities can be prevented from entering the inside of the packaging of the optical pickup. Here, an inexpensive epoxy adhesive excellent in these characteristics was used.

Reference numeral 15 denotes a shell, and the shell 15 also has an outer shape penetrating the center of the rectangular parallelepiped similarly to the package 14, and its horizontal cross section has substantially the same shape as that of the package 14. . The material is required to have characteristics such as low water absorption and low outgassing in order to prevent impurities from being mixed into the interior of the packaging. Here, polybutylene terephthalate (hereinafter referred to as PBT) having excellent properties is used. However, in particular, when characteristics excellent in strength, dimensional accuracy, and the like are required, an LCP that is more expensive than PBT but has these characteristics may be used. And the adhesion between the shell 15 and the package 14 is
An epoxy adhesive was used for the same reason as the attachment of the package 14 and the heat sink 4 described above. This shell 1
Instead of using 5, the height of the side wall portion of the package 14 may be made higher than that of the light guide member 5 for substitution.

Reference numeral 16 denotes a cover member. The cover member 16 prevents dust and dirt from adhering to the light guide member 5, the light receiving element 13, and the like. The cover member 16 is attached to the upper surface of the shell 15 with an epoxy-based adhesive. ing. Further, as the material of the cover member 16, it is preferable to use glass such as BK-7, FK-1, and K-3, or resin having high light transmittance such as urethane, polycarbonate, and acrylic.
Further, it is preferable to form anti-reflection films 16a on both upper and lower surfaces of the cover member 16 to prevent reflection. This antireflection film 16a is preferably formed of a material such as MgF ₂ .

The positional relationship between the cover member 16 and the light guide member 5 can be considered when the two members are brought into contact with each other or when a space is provided between them. When the two are brought into contact, the light guide member 5 is attached to the bottom of the cover member 16 with an epoxy-based adhesive or a UV adhesive. At this time, the thickness (t1) of the cover member 16 is set to 0.3 ≦ t1 ≦ 3.0 (m
m) is preferable. The reason for this is that if the lower limit is made thinner than this, the cover member 16 may not be able to withstand the weight of the light guide member 5 or the like attached thereto or the tension when the adhesive is hardened, and may be damaged. Regarding the upper limit, since the cover member 16 has a larger refractive index than air, a converging action is generated on the light and the light does not spread. As a result, the cover member 16 and the collimator lens (in the case of an infinite optical system) or the objective lens (In the case of a finite optical system), you have to increase the distance from
This is because it is disadvantageous in downsizing the pickup unit. By using such a configuration, the height of the optical pickup can be further reduced, and the pickup unit can be downsized while maintaining sufficient mounting strength.

On the other hand, when a space is provided between the two, the thickness (t2) of the cover member 16 is set to 0.1 ≦ t2 ≦
3.0 (mm), and the distance (d) between the cover member 16 and the light guide member 5 is also preferably 0.1 ≦ d ≦ 3.0 (mm). The reason for this is that the lower limit of t2 is different from the previous example in that the light guide member 5 is not attached, and it is only necessary to withstand external factors such as vibration. Also, as for d, the smaller the better, the better. However, there is a possibility that the accuracy error during assembly cannot be reduced to 0.1 mm or less. In this case, the cover member 16 comes into contact with the light guide member 5 during assembly and breaks. There is a risk that it will. By using such a configuration, the block 3 or the submount 2 is brought into thermal contact with another member while improving the relative positional accuracy between the light guide member 5 and the light source 1, the submount 2, and the block 3. Therefore, the heat generated in the light source 1 can be easily released to the outside.

The inside of the optical pickup includes a light guide 1 and a cover member 1 for preventing oxidation of the light source 1 and the light receiving element 13.
6, gas such as N ₂ or Ar, N
It is preferable to fill an inert gas such as e or He. In this case, the gap 17 existing between the heat radiating plate 4 and the light receiving element 13 is filled with a bonding material having characteristics such as a small shrinkage ratio, low water absorption, and high airtightness (excellent leak characteristics), for example, an epoxy potting agent. It is necessary to fill with solder or solder. Thereby, the inside airtightness can be improved.

By using the configuration shown above,
The heat generated by the light source 1 can be easily released to the outside, and the antioxidant gas can be easily sealed by providing a total of two openings on both end surfaces of the packaging. Further, in the optical system, the relative positional relationship between the light source 1, the light guide member 5, and the light receiving element 13 can be correctly and firmly maintained. do not do.

It is preferable that the thermal resistance of the entire optical pickup is 35 ° C./w or less because the heat can be more efficiently released outside the package. Next, the operation of the optical pickup according to the first embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a conceptual diagram of the operation of the optical pickup according to the embodiment of the present invention, and FIG. 4 is a perspective view of the light guide member according to the embodiment of the present invention.

In FIGS. 3 and 4, the laser light horizontally emitted from the light source 1 horizontally mounted on the heat radiating plate 4 via the submount 2 and the block 3 is a light guide member having a plurality of parallel inclined surfaces. 5 from the surface 5f of the light guide member 5, and converts the diffusion angle of the emitted light to the diffusion angle of the incident light formed on the second inclined surface 5b of the light guide member 5 (hereinafter, NA is converted). Hologram 7 of a reflection type having a function. The light whose NA has been converted and reflected by the diffusion angle conversion hologram 7 is reflected by the reflection type diffraction grating 6 formed on the first slope 5a as a 0th-order diffracted light (hereinafter referred to as a main beam) and ± 1st-order diffracted light (hereinafter referred to as a side beam). ). The main beam and side beam generated by the diffraction grating 6 are incident on a first polarization-selective beam splitter film 9 (hereinafter simply referred to as a first beam splitter film). The first beam splitter film 9 is a light having a vibration component parallel to the incident surface (hereinafter simply referred to as a P-polarized component).
And has a constant reflectance with respect to a vertical vibration component (hereinafter simply referred to as S-polarized component). Of the light that enters the first beam splitter film 9, the light that passes through the first beam splitter film 9 is used as the monitor light of the light emitted from the light source 1. Further, the main beam and side beam linearly polarized into the S-polarized light component reflected by the first beam splitter film 9 are:
The light passes through the surface 5 e of the light guide member 5 and the cover member 16, enters the objective lens 26, and is focused on the recording medium surface 27 a of the recording medium 27 by the light condensing action of the objective lens 26. At this time, the beam spots 29a and 29c of the two side beams are imaged on the recording medium surface 27a at positions substantially symmetric about the beam spot 29b of the main beam. Beam spots 29b, 29a, and 29c of the main beam and side beams with respect to the recording medium surface 27a
To read out information recording or reproduction signals and tracking and focusing so-called servo signals.

The divergence angle conversion hologram 7 is provided for the divergence angle conversion hologram 7 of the light emitted from the light source 1 and which can enter the divergence angle conversion hologram 7.
The angle of diffusion of the light reflected from the object is converted. Further, the light can be converted into parallel light having no diffusion angle by the diffusion angle conversion hologram 7. Also, the same diffusion angle conversion hologram 7
Thus, as shown in FIG. 3, the light flux emitted from the light guide member 5 becomes an ideal spherical wave 30 from which the wavefront aberration accumulated in the midway path is removed. Therefore, the incident light on the objective lens 26 becomes an ideal spherical wave 30, and the beam spot on the recording medium 27 by the objective lens 26 is narrowed down to the diffraction limit to an ideal size, and information recording or reproduction is easily performed. be able to.

The return light of the main beam and the side beam reflected by the recording medium surface 27a of the recording medium 27 passes through the objective lens 26 and the surface 5e of the light guide member 5 again.
The light enters the first beam splitter film 9 formed on the second inclined surface 5b of the light guide member.

The light transmitted from the first beam splitter film 9 among the return light from the recording medium 27 is the light guide member 5
The second polarization-selective beam splitter film 11 formed on the third slope 5c parallel to the first slope 5a of FIG.
(Hereinafter simply referred to as a second beam splitter film). The second beam splitter film 11 is similar to the first beam splitter film 9 in that the P beam component is almost 10
It has a transmittance of 0% and a constant reflectance for the S-polarized light component.

Here, the transmitted light 117 of the light beam incident on the second beam splitter film 11 will be described. The transmitted light 117 enters the polarization plane conversion substrate 31 laminated on the third inclined surface 5c.

FIG. 5 is a perspective view of a polarization plane conversion substrate of an optical pickup according to one embodiment of the present invention, and FIG. 6 is a diagram showing a light receiving portion arrangement and signal processing of the optical pickup according to one embodiment of the present invention. . The polarization plane conversion substrate 31 includes a first other slope 31a (hereinafter, simply referred to as a first other slope) and a second other slope 31 substantially parallel to the first other slope 31a.
b (hereinafter simply referred to as a second other slope) and a first other slope 3
A reflection film 126 is formed on 1a, and a polarization separation film 12 is formed on the second other slope 31b. The transmitted light 117 enters the polarization splitting film 12 formed on the second other slope 31b.
The angle formed between the polarization plane 117a of the transmitted light 117 and the entrance plane 128 is approximately 45 × (2n + 1) ゜: (n
Is an integer). As a result, the P-polarized light component 117P and the S-polarized light component 117S of the transmitted light 117 have an intensity ratio of about 1: 1. The P-polarized light component 117P having a polarized light component parallel to the incident surface 128 is transmitted by the polarization splitting film 12 almost 100%.
The S-polarized component 117S having a polarization component perpendicular to is reflected by the polarization splitting film 12 on the second other slope 31b substantially 100%, is incident on the first other slope 31a, is reflected by the reflection film 126, and is transmitted to the light receiving element 13. Be guided. The P deflection component 117P guided to the light receiving element 13 is sent to the light receiving unit 170 and is also converted into S
The deflection component reaches the light receiving unit 171 and creates an RF signal.

Next, the reflected light 123 of the light beam incident on the second beam splitter film 11 shown in FIG. 3 will be described. The reflected light 123 is incident on the astigmatism generating hologram 10 formed by a reflection type hologram on the second inclined surface 5b. The reflected light 123 generates astigmatism by the astigmatism generation hologram 10 and is further reflected by the reflecting films 124 and 125, and the return light of the main beam is transmitted to the light receiving section 172 on the light receiving element 13 to the side beam. The returning light of the above reaches the light receiving portions 176 and 177 on the light receiving element 13.

Next, a second embodiment of the present invention will be described with reference to the drawings. The second embodiment particularly describes the configuration of an optical pickup that is compatible with a phase change optical disc. Phase-change optical discs record information by irradiating light to change the crystal structure in the recording medium, and require more light than conventional optical recording / reproducing devices to change the crystal structure. Therefore, a more efficient optical system is required. FIG. 7 is a configuration diagram of an optical pickup for a phase-change optical disk according to an embodiment of the present invention. Note that members having the same numbers as those shown in FIGS. 1, 2 and 3 have the same functions and configurations, and thus description thereof will be omitted.

The laser light emitted from the light source 1 enters the light guide member 41 from the surface 41f of the light guide member 41 having a plurality of parallel inclined surfaces, and the diffusion angle conversion hologram 7, the diffraction grating 6 and the polarization selective light. A certain beam splitter film 3
5 (hereinafter, referred to as a beam splitter film), and is emitted from the surface 41 e of the light guide member 41. Here, unlike the case of the first embodiment, the beam splitter film 35 has an S-polarized component reflectance of 95% or more and a P-polarized component reflectance of about 1%. Of the light that enters the beam splitter film 35, the light that passes through the beam splitter film 35 (P
The polarized light component (about several percent of the total light amount) is used as the monitor light of the light emitted from the light source 1. Light guide member 4
The light emitted from the first surface 41 e passes through the λ / 4 plate 33 provided on the cover member 16. FIG. 8 is a schematic view of a λ / 4 plate. The λ / 4 plate 33 has an extraordinary optical axis of π / 4 · (2m−) with respect to the plane of polarization of the incident light from the light guide member 41.
1); (where m is a natural number: the same applies below), and the phase difference between the extraordinary component and the ordinary component of the incident light is π
It has the function of generating only 2/2 (2m-1).
Generally, a uniaxial crystal material is used as a material forming the λ / 4 plate 33. Among them, it is preferable to use quartz which is low in cost and excellent in light transmittance. In uniaxial crystals have abnormal optical axis 616 and ordinary light axis 617, and has a different refractive index, called extraordinary refractive index n _e and ordinary index n _o for each of the optical axes. Since the optical distance is different between the extraordinary light and the ordinary light, a phase difference Δ is generated which is determined by the following relational expression, where QD is the substrate thickness of the λ / 4 plate 33 and λ is the wavelength of the incident light. λ /
The thickness QD of the four plates 33 has a phase difference Δ of π / 2 · (2m−
It is decided to be 1).

Δ = 2π · (n _e −n _o ) · QD / λ In this embodiment, the wavelength λ = 790 nm and the extraordinary light refractive index ne.
= 1.5477, and ordinary refractive index no = 1.5388 (however, the refractive index differs depending on the cutting angle of the substrate. Here, the refractive index is cut parallel to a plane including both the extraordinary optical axis and the ordinary optical axis). On the other hand, the substrate thickness of the λ / 4 plate 33 is 2
1.9 · (2m−1) μm. By setting such conditions, it is possible to convert linearly polarized light that is incident at an incident angle of 0 degree into circularly polarized light. That is, the linearly polarized light including only the S-polarized component emitted from the light source 1 can be converted into circularly polarized light. Here, 21.9 μm crystal was provided on the cover member 16 as the λ / 4 plate 33,
It may be provided on the surface 41 e of the light guide member or the objective lens 26.

The light that has been circularly polarized after passing through the λ / 4 plate 33 enters the objective lens 26 and is focused on the recording medium surface 27a of the recording medium 27 by the condensing action of the objective lens 26.
Is reflected. Since the direction of rotation of the circularly polarized light reflected on the recording medium surface is reversed, the return light is
When the light passes through the λ / 4 plate 33 again, the light is converted into linearly polarized light containing only the P-polarized light component. The return light thus converted passes again through the surface 41e of the light guide member 41,
The light again enters the beam splitter film 35 formed on the second inclined surface 41b of the light guide member. As described above, the beam splitter film 35 has almost 100% of the P polarization component.
And a reflectance of about 100% for the S-polarized component. Therefore, the return light having only the P-polarized component almost passes through the beam splitter film 35.

Then, the return light enters the half mirror 34 formed on the third slope 41c parallel to the first slope 41a of the light guide member 41. The half mirror 34 has a function of reflecting a predetermined amount of the incident light and transmitting the rest.

Here, of the light beam incident on the half mirror 34, the transmitted light 117 is guided to the light receiving section 37 provided on the light receiving element 36.

Next, the reflected light 123 of the light beam incident on the half mirror 34 shown in FIG. 3 will be described. FIG. 9 is a layout diagram of a light receiving portion provided in a light receiving element of an optical pickup for a phase change optical disc according to an embodiment of the present invention. The reflected light 123 is incident on the astigmatism generating hologram 10 formed of a reflection type hologram on the second inclined surface 41b. The reflected light 123 is the astigmatism generating hologram 10
While astigmatism is generated by the reflection film 124,
The light reflected by the reflection film 125 returns the main beam to the light receiving section 38 on the light receiving element 36, and returns the side beam to the light receiving sections 39 and 40 on the light receiving element 36.

In the optical pickup having the above-described configuration, the λ / 4 plate is combined with the beam splitter film 35 and the recording medium 2.
7, and converts the output light, which is linearly polarized light of the S-polarized light component, into circularly polarized light, and then converts the circularly polarized light reflected by the recording medium 27, whose rotation direction is reversed, to the P-polarized light component only. Beam splitter film 35 by converting into linearly polarized light having
, The light reflected by the recording medium 27 can be guided almost 100% onto the light receiving element 36.
The reflectance of the S-polarized light component of the beam splitter film 35 can be greatly increased, and therefore, the amount of light applied to the recording medium 27 can be increased. That is, limited light source 1
Can be efficiently applied to the recording medium 27, and the reflected light from the recording medium 27 can be efficiently guided to the light receiving element 37.

Next, the light guide member 5 and the light guide member 41.
Reflection films 124, 125, 126 formed inside the
The details (hereinafter, simply referred to as a dielectric reflection film) will be described with reference to the drawings.

FIG. 10 is a sectional view showing a structure of a dielectric reflecting film according to one embodiment of the present invention.

The dielectric reflection film 52 is formed by the light guide members 5 and 4.
Is formed at a predetermined position on the surface of the substrate 51 constituting
That reflects the incident light and guides it to a predetermined position.
It is a spider. And its structure is high as shown in FIG.
The dielectric film 53 having a high refractive index and the dielectric film 53 having a low refractive index
The electric film 54 is alternately laminated. High refraction
As a material of the dielectric film 53 having a refractive index, ZrO_Two, Ti
O_Two, CeO_Two, Ta_TwoO _Five, Materials such as ZnS are used
Is preferred. Further, the material of the dielectric film 54 having a low refractive index
As the material, MgF_Two, SiO_TwoMaterials such as
preferable. Also these low refractive index has a low refractive index
Film 54 having a high refractive index and the dielectric film 5 having a high refractive index
When the dielectric reflecting film 52 is formed by combining 3 and
Should take into account the distribution of each film stress.
New That is, dielectrics having a high refractive index that are alternately formed
The body film 53 and the dielectric film 54 having a low refractive index are
Forming the respective film stresses in directions that cancel each other out.
Is preferred. With this configuration, the membrane response
Force is applied in a certain direction, which causes the board to be distorted.
May occur, the substrate may be deformed, or the dielectric reflection film 52 may
It is possible to avoid the problem of misalignment with respect to the optical axis.
Therefore, the yield of the light guide members 5 and 41 can be improved.
And the reliability of the optical pickup
Can be improved.

Dielectric film 5 having high refractive index shown above
Among the materials of No. 3 and the material of the dielectric film 54 having a low refractive index, it is very preferable to use a combination of SiO ₂ and TiO ₂ . Because the two materials have almost the same tensile stress and compressive stress, TiO 2
_This is because by alternately stacking ₂ and SiO ₂ , it is possible to easily form a structure in which the film stress is canceled out as a whole. Furthermore, the coefficient of linear expansion of optical glass (mainly BK-7, Cobalco glass, etc.) used as a substrate is
Since the linear expansion coefficient of TiO ₂ and SiO ₂ is almost in the middle, even if the substrate expands and contracts due to temperature change, expansion and contraction occur at a constant rate as a whole, so that the substrate and the dielectric reflection film are It is possible to suppress the occurrence of divergence between
Therefore, it is possible to provide a high-performance light guide member that is resistant to temperature changes.

Further, among the dielectric layers formed on the substrate 51,
It is preferable to form a dielectric film having a low refractive index on the first layer formed directly on the substrate 51. In general, a substance having a low refractive index is more chemically stable, and even if a film is formed on the surface of a relatively dirty substrate, the refractive index at the interface hardly changes. On the other hand, when a dielectric film with a high refractive index is formed on a relatively dirty substrate surface, negative non-uniformity, that is, the refractive index near the interface becomes abnormally higher than the original refractive index of the substance Occurs, the film thickness seems to be thicker and the reflectance changes. Therefore, by forming the dielectric layer having a low refractive index first on the substrate, negative nonuniformity does not occur near the interface with the substrate, and a stable reflectance can always be realized.

The greater the difference in the refractive index, the greater the reflectance at one interface. Therefore, sufficient reflectance can be ensured even if the number of interfaces, that is, the number of dielectric layers to be laminated is small. it can. Therefore, by making the difference in refractive index as large as possible, preferably 0.5 or more, the thickness of the dielectric reflection film 52 can be made thin, so that the number of steps for film formation can be reduced. Further, since the thickness of the dielectric reflection film can be reduced, the height of the dielectric reflection film protruding from the substrate can be reduced, and the thickness of the bonding layer when bonding the substrates can be reduced.
The joint strength between the two can be improved, and peeling that occurs at the joint portion of the substrate can be reduced. In particular, the difference in refractive index is 0.
When it is 5 or more, a reflectance of 97% or more can be realized very easily, which is more preferable.

Next, the film thickness of the dielectric reflecting film will be described. The film thickness of the dielectric reflection film is such that when the refractive index of the dielectric film is n, the wavelength of light is λ, and the angle formed by the perpendicular to the incident surface of the light with respect to the dielectric film (hereinafter referred to as incident angle) is θ. In addition, it is preferable to satisfy the relationship of n × d = λ ÷ (4 cos θ). In the present embodiment, it is particularly preferable that the thickness is 1000 Å to 3000 Å because a sufficient reflectance can be obtained even with a relatively thin film. Also, a high refractive index layer and a low refractive index layer
Since the above-mentioned lamination can sufficiently cope with the fluctuation of the refractive index at the time of film formation and can further obtain a sufficient reflectance, the dielectric reflection film should have high performance and high reliability. You can Furthermore, regarding the outermost layer of the dielectric reflection film,
Deterioration of the dielectric reflection film due to humidity or mechanical deterioration can be caused by increasing the film thickness of the substance having a low refractive index to a film thickness laminated in the dielectric layer, preferably an odd multiple of the predetermined film thickness. This is a preferable configuration because the reliability can be improved from the viewpoint of process protection such as damage.

The characteristics of the dielectric reflecting film having the above structure were examined. Hereinafter, the experiment and the comparative experiment will be described with reference to the drawings.

FIG. 11 is a schematic diagram of this experiment. Reference numeral 70 denotes a triangular prism, and the triangular prism 70 has a cross-sectional shape of an isosceles right triangle as shown in the figure. A dielectric reflection film 71 as shown in 12 is formed so as to be sandwiched between the two triangular prisms 70. Regarding the dielectric reflection film 71 on the bottom surface 70a of the triangular prism 70, an SiO ₂ film 71a having a low refractive index (refractive index 1. 45) to 6
045Å formed TiO ₂ film 7 having the next highest refractive index
1b (refractive index 2.10) is formed 1092Å and SiO ₂
The film 71c is formed in 2015Å. TiO ₂ film 7 in this order
A total of 7 layers of 1b and a total of 6 layers of SiO ₂ films 71c were alternately deposited, and finally, a SiO ₂ film 71c was formed again 2015Å to form a dielectric reflection film 71.

Then, the light from the laser 72 is made incident on the triangular prism 70 from the surface 70b of the triangular prism 70. At this time, it is necessary to pay sufficient attention to their arrangement so that the optical axis of the incident light is perpendicular to the surface 70b. Then, the light that has entered the triangular prism 70 enters the bottom surface 70 a and is reflected by the dielectric reflection film 71. Also at this time, the incident angle of the light incident on the bottom surface 70a is 45 °.
Then, the light reflected by the dielectric reflecting film 71 passes through the surface 70c, is emitted from the triangular prism 70, and reaches the sensor 73. An experiment was also conducted to measure the reflectance of the back surface of the dielectric reflecting film 71. When measuring the reflectance on the back side,
As shown in FIG. 1, the light from the laser 72 is directed to the surfaces 70b and 7b.
The back surface of the dielectric reflection film 71 is irradiated with light through 0c and the reflectance of the light there is measured. The triangular prism 70
Optical glass BK-7 is used here as the material. Light having a wavelength of 790 nm was used for the experiment. Further, a Hitachi self-recording spectrophotometer U-4000 was used for measuring the reflectance.

Next, two more experiments were conducted as comparative examples of this experiment. As a first comparative example, a sample in which an Ag reflective film was formed to a thickness of 0.1 μm on a triangular prism of optical glass BK-7 using an ion beam vapor deposition apparatus, and as a second comparative example, optical glass BK was used. AN on a -7 triangular prism
Ion beam vapor deposition device EVC-150 manufactured by ERLVA
1 was used to form a Ti underlayer of 0.025 μm, and
Further, a sample in which an Ag reflective film was formed to a thickness of 0.1 μm was prepared, the same experiment as this experiment was performed, and the reflectances on the front surface and the back surface of the three samples in total were measured.

Further, in order to inspect the adhesive force between the reflective film and the substrate in each sample, the reflective film of each sample formed on the glass substrate is subjected to the cross-cut tape method defined in JIS-K-5400. It was measured using.

Further, each sample formed on the glass substrate was immersed in a chemical solution of acetone and a remover, which are typical chemicals used in film formation, and the chemical resistance of each reflective film was examined.

The results of the experiment on the total of 4 points of the reflectance of the front surface, the reflectance of the back surface, the adhesive force and the chemical resistance are shown in Table 1 below.
It was shown to. Further, FIG. 13 shows the relationship between the reflectance on the front surface and the back surface of the dielectric reflecting film and the wavelength of incident light in the present embodiment.

[0062]

[Table 1]

As is clear from (Table 1), the dielectric reflection film of the present invention has the following chemical resistance with respect to the remover.
It can be seen that it has extremely excellent chemical resistance as compared with both the first comparative example and the second comparative example, and also has the best adhesive force among the three samples in terms of adhesive force. Further, it can be seen that the reflectance has a very good reflectance with respect to the S-polarized component used in the optical pickup.

Therefore, by using the dielectric reflecting film of the present invention as the reflecting film, both the front surface and the back surface of the dielectric reflecting film of the present invention are
Since the absorption loss is much smaller than that of the metal reflection film, an extremely high reflectance can be realized. Therefore, since the loss of light in each dielectric reflection film is small, a sufficient amount of light can be guided to the light receiving element 13.

Further, since the chemical resistance to the organic solvent is very high, the film thickness of the dielectric reflection film may be changed by various organic solvents used in the manufacturing process of other thin films after forming the dielectric reflection film. There is almost no. Therefore, since the reflectance as designed can be realized, the light can be efficiently guided to the light receiving element 13.

Further, since the adhesive force to the glass substrate is very high, the manufacturing process of the light guide members 5 and 41 for forming the substrate block by laminating the substrates after forming all the optical elements and cutting the substrate block into a predetermined shape. In the above, it is possible to prevent the peeling of the substrate or the like that occurs due to the weak adhesion between the reflective film and the substrate, and thus to provide a highly reliable and highly reliable optical guide member and thus an optical pickup. .

[0067]

EFFECTS OF THE INVENTION By providing a reflective film formed by laminating a plurality of dielectric layers on the optical path of the substrate, the reflection efficiency of the reflective film can be increased and the bondability with the substrate is good. Therefore, it is possible to secure the amount of light guided to the light receiving element, and further it is possible to prevent the peeling of the substrate that has occurred during the manufacture of the light guide member.

Further, since the reflection efficiency can be improved by forming at least one dielectric layer having a different refractive index in the plurality of dielectric layers, it is possible to secure a sufficient amount of light on the light receiving element. it can.

By alternately laminating the dielectric layers having a high refractive index and the dielectric layers having a low refractive index, the reflection efficiency can be further improved, so that a sufficient amount of light on the light receiving element can be secured. Therefore, a good RF signal can be formed from the light received by the light receiving element. Therefore, the performance of the optical pickup can be improved.

Further, by making the dielectric layer closest to the substrate a dielectric layer having a low refractive index, it is possible to prevent a change in the refractive index in the dielectric layer, so that the reflectance can be stabilized. Therefore, it is possible to reduce the individual difference of the RF signal for each optical pickup.

By setting the difference in refractive index between the dielectric layer having a high refractive index and the dielectric layer having a low refractive index to 0.5 or more, the thickness of the dielectric reflecting film can be made extremely thin. ,
The work time for film formation can be reduced.
Furthermore, since the thickness of the dielectric reflection film can be made thinner, the height of the dielectric reflection film protruding from the substrate can be lowered, and the thickness of the bonding layer when bonding the respective substrates can be made thin. It is possible to reduce the peeling that occurs at the bonding portion of the substrate.

By forming the plurality of dielectric layers in the directions in which the respective film stresses are canceled out, it is possible to prevent the warp of the substrate and the position dependence of the reflectance of the reflective film, and thus the yield of the light guide member is improved. And the reliability of the optical pickup can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of packaging of an optical pickup according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the configuration of the optical pickup packaging according to the embodiment of the present invention;

FIG. 3 is a conceptual diagram of an operation of the optical pickup according to the embodiment of the present invention;

FIG. 4 is a perspective view of a light guide member according to one embodiment of the present invention.

FIG. 5 is a perspective view of a polarization plane conversion substrate of the optical pickup according to the embodiment of the present invention;

FIG. 6 is a diagram showing a light receiving unit arrangement and signal processing of the optical pickup according to one embodiment of the present invention;

FIG. 7 is a configuration diagram of an optical pickup for a phase-change optical disc according to an embodiment of the present invention.

FIG. 8 is a schematic view of a λ / 4 plate according to an embodiment of the present invention.

FIG. 9 is a layout diagram of a light receiving section provided in a light receiving element of an optical pickup for a phase change optical disk according to an embodiment of the present invention.

FIG. 10 is a sectional view showing the structure of a dielectric reflecting film according to an embodiment of the present invention.

FIG. 11 is a schematic diagram of this experiment.

FIG. 12 is a sectional view of a reflective film according to an embodiment of the present invention.

FIG. 13 is a relationship diagram between the reflectance on the front surface and the back surface of the dielectric reflecting film and the wavelength of incident light in the embodiment of the present invention.

FIG. 14 is a configuration diagram of a conventional optical pickup.

FIG. 15 is a sectional view of a conventional reflection film.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 light source 2 submount 2a electrode surface 3 block 3a protrusion 3b end surface 4 heat sink 4a hole 5 light guide member 5a first slope 5b second slope 5c third slope 5e surface 5f surface 6 diffraction grating 7 diffusion angle Conversion hologram 9 First beam splitter film 9a Protective film 10 Astigmatism generation hologram 11 Second beam splitter film 12 Polarization separation film 13 Light receiving element 13a Electrode 14 Package 14a Lead frame 14b Lead frame foot 14c Step 14d Wire 15 Shell 16 cover member 16a antireflection film 17 gap 26 objective lens 27 recording medium 27a recording medium surface 28 second beam splitter film 29a, 29b, 29c beam spot 30 ideal spherical wave 31 polarization plane conversion substrate 31a first other slope 31b second Other slope 31c One surface 31d Second surface 33 λ / 4 plate 34 Half mirror 35 Beam splitter film 36 Light receiving element 37, 38, 39, 40 Light receiving portion 41 Light guide member 41a First slope 41b Second slope 41c Third slope 41e Surface 41f surface 51 substrate 52 dielectric reflection film 53 dielectric film having high refractive index 54 dielectric film having low refractive index 70 triangular prism 70a bottom surface 70b surface 70c surface 71 dielectric reflection film 71a SiO ₂ film 71b TiO ₂ film 72 Laser 73 Sensor 117 Transmitted light 117a Polarization plane 117S S polarization component 117P P polarization component 123 Reflection light 124 Reflective film 125 Reflective film 126 Reflective film 128 Incident surface 170, 171, 172, 172a, 172b, 172
c, 172d, 176, 177 Light receiving part 616 Extraordinary optical axis 617 Ordinary optical axis

Claims (17)

[Claims] 1. A reflection having a light source and a plurality of substrates inclined with respect to an incident direction of light emitted from the light source, the reflection being formed by laminating a plurality of dielectric layers on an optical path of the substrate. An optical guide member that has a film and guides the light from the light source to the optical medium and guides the light reflected from the optical medium to a predetermined position, and receives the light and converts the received optical signal into an electrical signal. An optical pickup, comprising: 2. A dielectric layer having different refractive indexes is formed in each of a plurality of dielectric layers.
Optical pickup as described. 3. The optical pickup according to claim 1, wherein dielectric layers having a high refractive index and dielectric layers having a low refractive index are alternately laminated. 4. The optical pickup according to claim 3, wherein the dielectric layer closest to the substrate is a dielectric layer having a low refractive index. 5. The optical pickup according to claim 3, wherein a difference in refractive index between the dielectric layer having a high refractive index and the dielectric layer having a low refractive index is 0.5 or more. pick up. 6. The optical pickup according to claim 1, wherein the plurality of dielectric layers are formed in directions in which the respective film stresses are canceled out. 7. The optical pickup according to claim 3, wherein the dielectric layer having a low refractive index is thicker than the dielectric layer having a low refractive index. 8. A light source and a plurality of substrates inclined with respect to an incident direction of light emitted from the light source, wherein a plurality of dielectric layers are laminated on an optical path on the surface of the substrate. An optical guide member that has a reflection film and guides the light from the light source to the optical medium and guides the light reflected from the optical medium to a predetermined position, and receives the light and converts the received optical signal into an electrical signal. An optical pickup for a phase-change optical disc, comprising: a light receiving unit for converting. 9. A dielectric layer having at least one different refractive index is formed in each of the plurality of dielectric layers.
An optical pickup for the described phase change optical disc. 10. The light for a phase-change optical disk according to claim 8, wherein dielectric layers having a high refractive index and dielectric layers having a low refractive index are alternately laminated. pick up. 11. The optical pickup for a phase-change optical disk according to claim 10, wherein the dielectric layer facing the substrate is a dielectric layer having a low refractive index. 12. The phase-change type according to claim 10, wherein the difference in refractive index between the dielectric layer having a high refractive index and the dielectric layer having a low refractive index is 0.5 or more. Optical pickup for optical disc. 13. An optical pickup for a phase change type optical disk according to claim 8, wherein a plurality of dielectric layers are formed in directions in which respective film stresses are canceled out. 14. The phase-change optical disk according to claim 10, wherein the dielectric layer having a low refractive index is thicker than the dielectric layer having a low refractive index. Optical pickup. 15. A λ / 4 plate is provided between the light emitting surface of the light guide member and the optical medium, and the λ / 4 plate and the optical axis of the light are substantially perpendicular to each other. (14) An optical pickup for a phase change type optical disc according to any one of (1) to (14). 16. An inclined surface is provided with a light guide means for transmitting or reflecting light and at least one of the light guiding means is provided through the inclined surface.
The optical pickup for a phase-change type optical disc according to any one of claims 8 to 15, wherein the reflected light from the optical medium is guided to a light receiving means. 17. The optical pickup for a phase-change optical disk according to claim 16, wherein the light guiding means is a half mirror.